History of the Atlantic Cable & Undersea Communications
On the Maintenance and Durability
MINUTES OF PROCEEDINGS
ABSTRACTS OF THE DISCUSSIONS.
November 27, 1860.
No. 1,030.—“On the Maintenance and Durability of Submarine Cables in Shallow Waters.”* By WILLIAM HENRY PREECE, Assoc. Inst. C.E.
|* The discussion upon this Paper extended over portions of five evenings, but an abstract of the whole is given consecutively.|
IN July, 1859, the late Mr. Robert Stephenson, at a meeting of the Electric and International Telegraph Company, over which he presided, made some remarks respecting the durability of submarine cables, which caused, at the time, much surprise and induced considerable controversy. He stated, that so far as his own experience and opinion went, no cable, over which he had any control, was sufficiently durable, to render it a satisfactory and remunerative speculation. He was supposed to apply these remarks to all submarine cables, and much valuable information was produced to controvert such a conclusion. It is not the intention of the Author to discuss the question at length. He will simply record his own practical experience in the maintenance and repair of a submarine cable; hoping, thereby, to lay a foundation, upon which a discussion can be raised, which will tend to the solution of this important point, and will prove beneficial to the profession, and serviceable to the progress of submarine telegraphy.
The cable alluded to, is that connecting the Channel Islands, Alderney, Guernsey, and Jersey, with England. These islands are situated in the Bay of Avranches, on the north-east portion of the coast of France. The nearest island, Alderney, is 57 miles from the coast of England, and 9 miles from that of France; Guernsey lies 18 miles from Alderney, and 17 miles from Jersey. These islands are accompanied by several smaller ones, and all are closely surrounded by a mass of jagged rocks. Their geographical position renders them peculiarly subject to the full force of the great westerly gales, which prevail during the winter months. The great rolling waves of the Atlantic, as they dash and break upon these wild and rocky shores, the disastrous wrecks that annually strew their coasts, the immense boulders thrown up and rolled about by the irresistible force of the disturbed waters, give some idea of the destructive action to which any submarine cable, landed on such shores, must be liable. Moreover, as these islands are situated in that portion of the Channel where the opposite coasts begin to form, as it were, a funnel for the entrance of the tidal wave, the tides and currents possess great force. The tide, which rises on the English side only 6 feet, here attains an altitude of 40 feet; the currents also, in several localities, acquire a velocity of 7 and 8 knots per hour. It will thus be seen, that the shores upon which it is landed, the bottom of the sea upon which it lies, the heavy tide- ways which it crosses, and the peculiar disturbances of nature to which it is liable, are all calculated to try, to the utmost extent, the qualifications, for permanency and durability, of any submarine cable, connecting these islands with the mainland.
This line of telegraph was projected by the islanders themselves. It is the property of a Company formed under the Limited Liability Act, with a capital of £30,000, upon which a conditional guarantee of 6 per cent. has been given by the Government. The contract for the whole undertaking was let to Messrs. Newall and Co., who submerged the cable, constructed the land lines, and handed over the whole telegraph complete, to the Company. The sample of the cable to be used was submitted to the Directors, but the selection of the route, and the manner of carrying out the work, was left entirely to the Contractors. The connection of the Author, as Engineer, only commenced after its completion by Messrs. Newall and Co.
The line starts from Weymouth, (Plate 2, Fig. 1,) crossing the Island of Portland by underground wires, and connecting that island with Alderney, by a submarine cable 57½ miles long. It crosses the Island of Alderney, and proceeds thence to Guernsey. After crossing Guernsey, underground, it is continued to Jersey, where it terminates at the town of St. Helier’s. There is a station at each of these islands. The whole length of submarine cable submerged is 93¼ miles, and the length of the underground portion is 23 miles. The latter simply consists of a gutta-percha covered wire, coated with tarred yarn, and laid in a creosoted wooden trough, buried about 20 inches in the ground.
The cable consists of two portions, the sea part, and the shore ends. The sea part is a No. 1 gutta-percha covered wire, served with tarred yarn, and protected by ten No. 6 iron wires; it weighs 2½ tons per mile. The shore ends are similar, but they are protected by ten No. 2 iron wires; they weigh 6 tons per mile. The cables were submerged by Mr. Newall, from the steamship ‘Elba,’ in August, 1858. When completed, the line tested perfectly, and being worked by an improved system of the Morse printing instrument, constructed by Messrs. Siemens and Halske, of Berlin, and slightly altered by the Author to suit the requirements of English manipulators and the English system, the circuit was admirable for rapidity and efficiency.
The line was opened to the public, on the 7th of September, 1858. On the 23rd of November following, the wire crossing the Smallmouth Sands between Portland Island and Weymouth, was broken, owing to the sand banks being washed away by a succession of severe easterly gales. This accident was speedily remedied by the submersion of a stouter cable, in a more secure position. The second accident took place on the 27th of January, 1859, on the coast of Jersey. The cable was landed upon this island, in a small sandy bay, bounded by precipitous cliffs, and strewn with jagged rocks. It was laid in a zigzag path between the rocks, and was led up the face of the cliff in split iron pipes. The gales that raged at this period, carried away a quantity of the sand upon which the cable lay; and the wash of the breakers tore the iron pipes from their fastenings. The cable being thus loosened, was beaten about upon the rocks, and it was speedily ruptured. As the fracture happened within the line of low-water spring-tide, temporary communication was soon made, by connecting the ends together with a stout chain, and attaching a gutta-percha wire along it. This gutta-percha wire had, however, to be renewed each tide, as the rocks soon wore it away.
The communication was permanently restored in the following manner. A fresh piece of stout cable, weighing 7½ tons per mile, consisting of a portion of the Atlantic cable, served with hemp, and surrounded by ten No. 1 iron wires, was manufactured by Messrs. Glass, Elliot, and Co., and spliced on to the old cable, as far out as the tide would allow. This was laid in a straight course, between the rocks, up to the foot of the cliff. In sandy bays, if a cable is not laid perfectly tight and straight, it is sure to become loosened, and be liable to motion, and if it is allowed to scrape upon a hard rock, it must, eventually, give way. The greatest care is, therefore, requisite, in fixing the ends upon rocky shores. In this instance, the cable, from the spot where it first came in contact with the rocks, to its end in the iron testing-post, upon the top of the cliff, was served with spun yarn, saturated with tar, to protect it from detrimental exposure to the spray, and the atmosphere. Where it rested upon the rocks, it was, in addition, served with thick wire, well bound down, to protect it from abrasion, and to give it greater strength.
The shore ends of the cable are thus stouter, and stronger than any hitherto made. It is scarcely possible to imagine, that any power in nature could ever exert sufficient force, to make an impression upon such a mail-clad rope; but the Author has seen it seriously injured after having been exposed, during six months, to the violent action of the waves, and constant inspection and attention are required, to prevent a second rupture. It was clamped in strong iron crutches, (Fig. 2,) leaded into the solid rock. Where it passed between two rocks, it was chained to ring bolts, leaded into the rocks, the chains being fixed to a bell-mouthed pipe constructed in two pieces, and fitting closely to the cable, as shown in Fig. 3. The crutches, though heavy, and well fixed, have, in more than one instance, become loosened, and the chains have broken, but the cable remains secure, and with careful attention, it will probably outlast the other portions.
As the landing-places on the south end of Guernsey, and on the western side of Alderney, are equally rough and precipitous, after the accident at Jersey, the shore ends at those places were also examined. At Guernsey, where the cable is landed in a bay similar to that at Jersey, it bore severe marks of attrition, and in one spot, it could not have lasted many days. The cable was straighter and tighter than at Jersey, for this was the end from which the vessel started in paying out, and consequently, a strain was placed upon the rope. It was protected, strengthened, and fixed, as at Jersey.
The most exposed landing-place is, undoubtedly, that at Alderney. The cable stretches through a series of rocks, lying about half a mile off the shore. It is landed in a small bay, having a sandy bottom, and lofty rocky sides, surrounded by perpendicular cliffs several hundred feet high, up which the cable is taken. It was a hazardous undertaking to attempt the descent of these cliffs, but the Author and two other persons succeeded in accomplishing the task, by the assistance of the cable. It was found, where it lay among the rocks, loose, bent, and injured to an alarming extent. One mass of stone had fallen upon it, and perfectly flattened the iron covering. It was protected, strengthened, and fixed, in the same way as at Jersey and Guernsey. In doing this, the cable had to be cut on the beach, and hauled up to the top of the cliff, while a temporary wire maintained the communication uninterrupted. It has not yet shown any symptoms of decay, which is so far fortunate, as the operation of repairing it would be difficult. It has, probably, fallen between the rocks, and has thus been protected instead of being destroyed by them.
The next interruption to which the line was subjected, took place off Portland Island, on the 19th of April, in the same year. In paying out this portion of the cable, Messrs. Newall started from Alderney, rather late in the day, and did not succeed in making Portland Island until night. In consequence, the landmarks were missed, or mistaken, and thus the Portland Race was crossed with the cable. The tidal current, when unobstructed, flows, generally, in the English Channel at from 8 knots to 4 knots per hour, but in Portland Race it runs at the rate of 8 knots and 9 knots. The rapid passage of waters extending to the bottom of the sea, not only affects the placidity of the surface, but scours, roughens, and ploughs up the ground below. The bottom, as far as the Race extends, is extremely rough and rocky. A cable, resting on such a surface, must, necessarily, be very insecure, and so it proved, for on the 19th of April, the cable parted at the distance of 31 miles from the shore, having been completely severed by abrasion upon the sharp edge of a rock.
All previous accidents at sea to submarine cables, which have come within the Author’s knowledge, have been the result of accidents from well-known causes. Ships have either dragged their anchors across a cable, too weak to sustain the strain suddenly placed upon it, or the cable has been brought to the surface, and then wilfully, or accidentally cut. But in this instance the cable was broken, in the short space of six months, by the operation of the great forces of nature. Fig. 4 will explain the probable cause of this accident. When a rope is stretched across a current of water, a quivering motion may be observed. The rush of the tide would give a cable, laid in the position shown, a similar vibration, which would make the rock act like a file, and the iron coating of the cable would be rapidly abraded. The outer iron wires bear distinct marks of this abrasion, and the ends have been worn down to a small diameter. The cable was, evidently, laid so tight, that the instant a few wires had been worn through, the remaining wires, together with the gutta-percha wire, were too weak to bear the strain, and were, consequently, broken.
The cable was picked up from the shore, considerably beyond the break, in the hope of removing it from the rough ground, and it was relaid further to the eastward. The original and the present course of the cable are shown upon the chart; (Fig. 1.) A new cable, of larger dimensions, was submerged across the portion of the original ground, which could not, without great expense, be avoided. In repairing this cable, several places were picked out, where this same action had commenced. The first mile from the shore, with the exception of the existence of two bad ‘kinks,’ was in excellent condition, showing no signs of decay, or wear, and lying undisturbed at the bottom of the sea. The rest of it, however, which lay through the Race, was much decayed, not only by friction upon the rocks, but by rapid oxidation. Shoals of mussels, zoophytes, and rank vegetation were found, clustering on the wire.
The communication was restored on the 18th of May. Much time was occupied in the repairs, owing to the unpropitious state of the weather. This is not of material consequence in paying out a cable, except in the operation of landing the ends, but in repairing cables, it is essential, that the weather be fine, and the sea comparatively calm. During the month occupied in these repairs, only four days occurred which were at all suitable for carrying on the operations.
In picking up the last portion of the cable, a stone, about 1 foot square, and 3 inches thick, came up attached to it. Across this stone there was a groove, bearing an exact impression of the cable, which appears to the Author to have gradually, by some chemical action, made a bed in the stone. Its substance differs from any stone found in the neighbourhood of Portland Island.
The line continued in excellent working order, during the whole of the ensuing summer, but in September, a serious fracture occurred off Jersey, and in November, another off the Island of Portland. In the latter case the cable was broken in two places, at 6¾ miles, and at nearly 12 miles from the shore; each fault was precisely similar in character to that previously described. Off Jersey, the cable became defective on the 16th of September, and the accident was also of the same nature. All the previous fractures had taken place without warning. In one instance, during the transmission of an important message, and while the line was in good working order, the communication was suddenly interrupted. In this case, however, symptoms of failing strength early displayed themselves, and for several weeks, the cable had been working indifferently. A serious defect showed itself in the cable between Guernsey and Jersey, at some spot not far from the Jersey shore, and gave intimation of rapid decay. At last, the communication ceased, and steps, were taken to repair the cable.
Three faults were discovered within a length of half a mile, two were due to ‘kinks,’ and the other to abrasion, the last being the cause of the cessation of the communication. The cases of abrasion previously explained, occurred in the smaller-sized sea portion of the cable; but this took place in the heavy shore end. The outer wires, with the exception of one, were completely worn through, the gutta percha was nearly destroyed, and the interior copper conductor had been completely abraded. The cable had, no doubt, been resting on the edge of a rock, and had been sawn through by the vibratory movement given to it by the tide.
The ‘kinks’ were made, when the cable was laid down; the gutta percha had been forced out, causing two considerable faults, which would inevitably, before long, have stopped the communication. Kinks are frequently caused in the operations of repairing, when picking up a cable, but it is very easy to distinguish a kink, made in laying down a cable, from one made in repairing. The one shows signs of oxidation and age, the tar of the serving is washed away, and the gutta percha is frequently visible; the other looks fresh, and of very recent formation. Kinks are not, as a rule, of serious consequence, unless the cable is laid on rough ground, or in a heavy tideway; but on such a line as that to Jersey, they are fatal. Only four kinks have been discovered, which must be considered as highly creditable to the Contractor; but the same praise cannot be awarded for the manner in which the end was landed in Jersey.
This is the most difficult operation connected with the submersion of cables, and that which requires the greatest care and skill. When once the cable has been started, there is little, or no difficulty in paying out. Attention and care are only required, to see that every part of the machinery works well. But when the landing-place is approached, the coast, the depth of water, the weather, and the tides, have to be consulted. If the coast is rugged, care must be taken to avoid the rocks; if the water is shallow, the ship must be kept off the ground and; if the weather is boisterous, the end must be cut, dropped, and buoyed, and the operation completed upon a more favourable occasion; and if the tides run fast, care must be taken to allow for their effect upon the ship, and to steer her course accordingly. At certain times of the tide, a sharp current runs past Cape Grosnez, near which the cable is landed, and the pilot in charge of the ‘Elba’ evidently overlooked this, for the cable, in place of taking a straight course into the bay, is laid as is shown in the chart; (Fig. 1.) It thus crosses some rocky ground, which might have been avoided, if proper allowance had been made for the current. It was upon this rocky ground, that the cable failed: it seems, moreover, to have been thrown out loosely, for it was lying zigzag in considerable bends, and a length of half a mile of cable was afterwards saved, by laying it straight; (Fig. 1.)
The cable was again broken on the 9th of January, 1860. The same kind of accidents which had occurred off Portland, were repeated off Alderney, and the cable was severed by the rocks, at a distance of 6 miles from that island. It was in precisely the same condition, abraded and decayed, so much so, that it was broken in picking up. Five miles of new cable, of a superior description, were submerged; it was a piece of the Atlantic cable, strengthened with ten No. 6 iron wires, similar to the excellent cable which the Submarine Company have laid between Jersey and the French coast. The cable subsequently failed in September last, at the same place and from the same cause. It has also been broken three times off the coast of Jersey, from having been accidentally caught by ships’ anchors. The following Table gives a list of all the accidents that have occurred up to the present time:—
1. Broken also 12 miles off the land. 2. Tested from Guernsey.
It will be seen, that since the submersion of the cable, in August, 1858, it has been ruptured in eleven different places. Two of these accidents were the result of carelessness, or negligence, in landing the end of the cable on the Jersey shore. Four were caused by ships dragging their anchors, and five were produced by the action of the rocky bottom upon the slender wire. The accidents arising from ships’ anchors all took place between Jersey and Guernsey. Those resulting from abrasion, occurred between Alderney and Portland. Between Guernsey and Alderney the cable bas never failed.
The constant interruptions of this line are attributable, the Author believes, to two causes, weakness of cable, and error of judgment in the selection of the route. The cable should never have been laid between Guernsey and Jersey, but from Jersey to Alderney. It not only crosses ground, where ships are frequently in the habit of anchoring, but also, in a portion of its route, it lies upon a rough uneven bottom, swept by strong tides. A stouter cable might lessen the liability to accidents from the first cause; while by a détour to the westward, this rocky ground would be avoided. But by carrying the wire from Jersey to Alderney, neither danger would be encountered. There is no anchorage along that route, and the ground is smooth and free from rocks, except on the immediate shores of the island.
This route was the first selected, but it was objected to by the Government, on account of its proximity to the French coast. In the event of a new cable being laid, this route will be adopted. Neither should the cable have been laid between Alderney and Portland, but from Alderney to the Isle of Wight. The bottom here, excepting immediately outside Alderney, is smooth and soft, the whole way across; the run of the tides is not so great; the shores of the Isle of Wight are devoid of rocks; and ships never anchor on any portion of the route. The distance is, certainly, greater, but the liability to accident from every cause, is considerably less.
It must, however, be stated, in justice to those who decided on the route adopted, that reliance was, perhaps, unfortunately placed on the Admiralty Charts, which the Author has never found to be correct in describing the nature of the bottom. They truly represent the depth of water, and the currents, but they as frequently show rocks where sand is found, and sand and gravel where there are rocks. This is especially the case off Portland, where ledges of rocks, of which no intimation is given on the charts, extend 15 miles, or 20 miles out to sea. A cable should never be trusted to the unseen and unknown action of the bottom of the sea, without its course having first been carefully surveyed and examined.
The Channel Islands cable is also too weak for the locality in which it is placed. It cannot resist the strain of a heavy ship, nor can it, for any length of time, withstand abrasion from a rock. The run of the tides, and the decomposing action of the water upon such a small cable will, eventually, and indeed very shortly, so weaken and corrode it, that the expense and difficulty of repairing it will be very much increased. The chief defect, however, in the system, cannot be said to be so much in the cable used, as in the route selected.
In conducting the repairs of this cable, it was curious to observe the effect of the water, in different localities, in oxidising the outside covering. In places where the cable had become slightly buried in the sand, it was as perfect as when it was first laid. On rocky ground, where it was swept by the tides, it was being rapidly corroded, and where vegetation and zoophytes adhered to the cable, patches of decay were visible. The Author is of opinion, that in localities where a cable cannot bury itself, it must speedily be destroyed by oxidation, and that the period of its durability will solely depend upon its size. In such places, some outer protection to the iron wire is necessary.
Mr. Latimer Clark, Assoc. Inst. C.E.,) has devised a method of applying hemp saturated with asphalte, on the outside of the iron wires; and it was applied to the Isle of Man cable. This plan, though promising, is liable to cause injury to the inside wires, through the necessity of applying the asphalte at a high temperature. But there should be no difficulty in discovering an equally effective material, which may be used cold. The Report of Mr. Cromwell Varley,* on the attempted repairs to the Atlantic cable, off Newfoundland, described the state of preservation in which the wire was found, wherever it was coated with hemp. No cable should ever be submerged in shallow waters, without some exterior protecting coating, to preserve it from oxidation.
* Vide “The Engineer,” July 27 1860.
The Channel Islands cable was also laid much too tight; wherever a break has occurred, through abrasion, it has been observed, that after six, or seven wires have been worn through, the rest, with the gutta-percha wire, have parted, being unequal to bear the strain. Cables in shallow water should be laid slack, and be payed out with only sufficient strain, to make them take the sinuosities of the ground, without falling into bends and kinks. Moreover, the slacker they are laid, the easier they are to repair, and repairs must be anticipated and provided for, in all submarine cables. Figs. 4 and 5 exhibit the difference between a cable laid tight and a cable laid slack.
In designing a cable, its durability and maintenance, points at present almost altogether overlooked, should be primarily considered. The present construction of heavy cables is believed by the Author to be defective. These cables depend for weight and strength, on a number of large-sized iron wires, surrounding the insulated conductors. When these outer iron wires are what is technically called ‘short,’ they break in running over the break drums. If ships accidentally catch the cable, the wires are also broken, and the surging of the anchor along the rope rapidly increases the evil by ‘rucking’ them up. The outer wires should, in the Author’s opinion, either be stranded, or the cable should be surrounded with two servings of smaller-sized wire. The Atlantic cable is, on a small scale, an example of the first, and the Jersey and France cable, of the second.*
It follows, from what has been said, that in establishing a submarine telegraph for crossing shallow waters, experience has shown, that the Engineer should, first, select a proper route, and secondly, that he should design a cable suitable for that route. He should vary the construction of the cable, according to the nature of the ground to be crossed, as it would be absurd to lay a heavy cable intended to resist anchorage, over soft ground, not frequented by ships. In regard to the route, it would, frequently, be more economical to make a détour of fifty miles, in connecting two points by a submarine telegraph, than to take the straight line.
|* The Electric and International Telegraph Company have adopted this suggestion, in their new cable to Holland.—Author. February, 1862.|
The system which the Author has adopted in conducting his repairs, is analogous to that originated by Mr. F. C. Webb, (Assoc. Inst. C.E.,) in repairing the cables in the North Sea, belonging, to the Electric and International Telegraph Company, and described by him in his Paper, read before the Institution, in 1858.* Having, by a system of careful tests, determined the position of the fault, a steamer was fitted up for the purpose of grappling the cable, as close to the fault as its position, and the nature of the ground would allow. The cable, when raised, was cut, and the end which was perfect between the ship and the shore, was carefully buoyed. The portion of the cable leading towards the fault was then picked up, and was coiled down until the fault came on board. The other end was then grappled for, and when secured, a fresh piece of cable was spliced to it, and payed out to the buoyed end, to which it was also spliced, and the communication was thus restored.
* Vide Minutes of Proceedings Inst. C.E., vol. xvii., page 262.
The operation of grappling, picking up, buoying, and paying out, having been already described in the Paper alluded to, the Author will confine himself to a description of the system adopted by him, in testing cables.
There is no operation connected with the submersion and repair of submarine cables, which requires greater skill, more experience, and a more intimate knowledge of the laws that regulate that subtle force, electricity, than testing. It qualifies the Engineer to become thoroughly acquainted with the electrical condition of the wire from end to end, permitting him to glance, as it were, along the rope, however deep it may be submerged, to learn its imperfections, and to know its condition. It enables him to direct his ship with almost unerring accuracy, to the spot where any failure exists. It gives him a confidence in his operations, which astonishes the uninitiated, and pleases the men employed under him, and it considerably reduces the expense of repairing cables.
To give an idea of the accuracy with which testing can be conducted, it may be mentioned, that on one occasion, the Author pronounced a fault, (No. 6 of Table I., page 33,) to be at 6 miles from Alderney, and that 2¼ inches of copper were exposed to the action of the salt water. The fault was ascertained to be exactly 6 miles off, and 2 inches of copper were found to be exposed. He has never been more than one mile wrong in his calculations, although the tests have been made at 5 miles, at 20 miles, and sometimes, at 30 miles from the broken end. Messrs. C.F. Varley and G. Preece, have been equally accurate in the North Sea. On one occasion, Mr. Varley pronounced a defect in the Zandvoort cable of the Electric and International Telegraph Company, to be 61 miles from the English shore, and it proved to be at the exact spot indicated. Mr. G. Preece, in testing on board ship, 13 miles from land, while repairing a break at that spot, found the cable again severed at a distance, according to his tests, of 50 miles towards Holland, and the break was found at 50¼ miles.
Mr. Webb, in his Paper, has referred to and described his system of testing, but considerable improvement in the instruments used, and the manipulation required has been effected since that period. The study of testing has been generally neglected, in the education of telegraphists, and little care bas been taken by the companies, to keep a careful register of the electrical condition of their cables and lines.
The principles employed in testing may be divided into those dependent upon the laws of resistance, and those dependent upon the laws of induction. Resistance is the obstruction which materials offer to the free passage of electricity, and it may be said to represent both conduction and insulation. A perfect conductor is one which offers no resistance to the transmission of an electric current; a perfect insulator is one whose resistance to the passage of the same current is infinite. No absolutely perfect conductors and perfect insulators, however, are as yet known; and thus the perfection of an insulator, or a conductor, depends, at present, upon its amount of resistance. If a wire conducts badly, its resistance is great, and if an insulator conducts well, its resistance is slight. It is, therefore, easy to express the degree of insulation, or conduction of a substance, in units of resistance; and this is frequently done in practice.
It has been usual, hitherto, in describing the condition of a wire, or cable, to say, that it gives a° of earth, with n number of cells; that is, that a current being applied to one end of a wire, and the other end being disconnected, its imperfect insulation, or faulty places, allowed a° of current to flow to the earth, through a galvanometer. This a° is supposed to represent the insulation of the wire. It gives an approximate idea of the condition of the wire to the electrician who manipulates his own instrument, but to convey to others the state that a° represents, it is necessary to describe the instrument employed, the power used, and various other complicated details of construction and design. Every electrician must reduce this quantity to the standard of his own instrument. It will be subsequently seen, that it is easy to reduce to one universal standard, the insulation and condition of every wire and cable, in existence, or under construction.
The basis of all resistance tests, is the fundamental law of Ohm, which is expressed by the formula
The specific resistance of different metallic bodies (C), varies considerably, as will be seen from the following relative conducting powers of different metals, according to Becquerel:—
The relative conducting powers of iron and copper, which are the materials usually employed for telegraphic purposes, are, consequently, as 15.5 to 100, or as 1 to 6.45 nearly.
The resistance of a wire is directly as its length (L), and inversely as its sectional area (S). If A B represents a copper wire 1 mile in length, and C D one 10 miles in length, both being of the same dimensions and material, the resistance of C D will be exactly ten times that of A B; but if the sectional area of A B is reduced to one-tenth, then the resistance of A B will exactly equal that of C D.
Again, if the wire A B is made of iron instead of copper, the same dimensions being retained, the resistance of A B will be six and a half times greater than that of C D. If now, A B is reduced to six and a half times its length, its resistance will again equal that of C D. Thus a short length of fine iron wire, will offer the same resistance to the passage of an electric current, as a long length of ordinary-sized copper wire, and will produce the same phenomena. One mile of No. 40 iron wire offers the same resistance as about five hundred miles of No. 16 copper wire.
Short lengths of this iron wire, are cut to represent any separate lengths of copper wire of the usual dimensions, and are wound round bobbins, forming a series of what are called, ‘resistance coils.’ They can be made to represent any length of cable, but the series usually constructed consists of two hundred and twenty-one miles of No. 16 copper wire. By these means, the resistance of any cable can be ascertained, it being only necessary to compare the resistance of the material of which it is made, with that of No. 16 copper wire.
Thus the resistance of the Channel Islands cable is to that of No. 16 copper wire, as 36 to 17; consequently, 17 miles on the Author’s resistance coils are equal to 36 miles of the Channel Islands cable. In the case of the Gibraltar cable, 1 mile on these coils would represent 8 miles of that cable.
The coils, used by the Author, are constructed by Mr. Cromwell Varley, and the standard employed is one mile of the No. 16 copper wire, which was in use four, or five years ago. The quality of copper, however, owing to the presence of alloys and other imperfections, varies considerably, and its resistance differs accordingly. The best selected copper varies as much as 20 per cent. in its conductivity, and the purer it is the better it conducts. Even annealing makes a difference; annealed copper wire conducts 2.5 per cent. better than that which is hand-drawn.
This subject has been carefully investigated by Dr. Matthiessen, and the results were communicated to the Royal Society in a Paper, “On the Electric Conducting Power of Alloys.”* In the copper wire supplied to the Atlantic Telegraph Company, some lengths varied as much as 40 per cent. The attention of the Gutta Percha Company having been called to this fact, a considerable improvement in the quality of copper supplied, has been the result; every mile of copper as it enters the works, is now carefully tested by the Company. The No. 16 copper wire of the present day, conducts better than that of the standard used, in the proportion of 3 to 2. The old standard is, however, adhered to, and it is only necessary to obtain the ratio between it, and the wire under examination, to obtain the relative resistance.
Messrs. Siemens, Halske, and Co., of Berlin, employ a different standard. Their unit of resistance is a column of mercury, one mètre in length, and one square millimètre in sectional area, taken at the freezing point of water. Professor Wheatstone’s standard of resistance is one English foot of copper wire, 0.071 inch in diameter, and intermediate to Nos. 15 and 16. But these standards can easily be applied to that used by the Author, by employing the proper ratio to reduce one to the other. The Author’s resistance coils can only directly represent 221 miles of No. 16 copper wire, or 1,768 miles of the Gibraltar cable, but by the instruments employed, and the systems adopted in comparing the relative resistance of the coils and cable, they can be made to represent any resistance from unity to infinity.
* Vide Phil. Trans. 1860, p. 161.
The instrument usually employed, in comparing the resistance of two wires, is the common differential galvanometer of Becquerel, shown, at G, in Fig. 7. Two wires of equal length, and equal resistance, are wound round a magnet in the usual manner. One current passes along one wire, round the needle in one direction; the other current proceeds round the needle, through the other wire, in the opposite direction. When the two currents are exactly equal, or when the resistance of one wire is equal to that of the other, the needle is neutralised, and it remains at zero.
Another arrangement is that generally known as Wheatstone’s parallelogram, shown in Fig. 6. A simple galvanometer is placed in circuit between B and C. When the resistance of A B is equal to that of A C, the needle remains at zero, but any inequality in the resistance affects the galvanometer.
The Author has modified the common differential galvanometer, by which many useful and practical results can be obtained. It is a simple differential galvanometer, G, (Fig. 7,) and if connected up as represented, without W and P, it will show, that the resistance of R R' will exactly represent that of D D'; but if a coil P, called a ‘derived circuit,’ is inserted between A and A', so that its resistance is to that of half the coil, as 1 to 10, it will be obvious, that when the current divides itself between the two wires of the galvanometer, the whole of one-half will go through B B', but only one-tenth of the other half through A A'; consequently, the current passing through the first half, will be ten times greater than that passing through the other half.
Now, if the resistance of R R' is reduced in the same proportion, it follows, that 1 mile of resistance in R R', will exactly balance 10 miles of resistance in D D'; consequently, the ordinary coils can be made to represent any resistance from 1/10 mile to 2,210 miles. By reversing the position of the coils and the cable under examination, tests of short distances can be obtained to decimals of units. Thus the coils can be made to represent any length from h of a mile to 2,210 miles.
By making the resistance of the coil P, so that its resistance to G bears the same proportion as the relative resistance of the standard coils to the cable under examination, the length of cable being tested, can be read off, at once, on the coils, without the necessity of any calculation. With a coil, whose resistance is to that of half the coil of the differential galvanometer, as 36 to 17, the Author is able to read off his own standard coils, the length of the Channel Islands wire under test. The resistance of his galvanometer is 20 miles, consequently, the resistance of half is 10.
Now with a set of coils, giving a resistance up to 10 miles, and a Wheatstone’s rheostat, whose total resistance is equal to 1 mile, he can obtain any ratio from equality to infinity. In practice, however, it is found, that the effects of temperature, and the heating properties of currents, traversing short lengths of wire, produce such variable results, that a greater proportion between the two coils than 1 to 10, is scarcely admissible.
The proportions named are not strictly those employed in practice, nor are they correct in theory, because some allowance must be made for the reduced resistance of the galvanometer. To render them correct, additional resistance must be inserted at W, to make the combined resistance of the derived circuit, and the differential half, equal to that of the other half. But the Author has found it more convenient to obtain experimentally, that proportionate resistance between the two coils which will give the requisite multiplying power, without the necessity of employing additional compensating resistance coils. This instrument he calls the ‘multiplying differential galvanometer.’
It is not, however, advisable to attempt very high resistances with the multiplying differential, as the heavy power required might damage the coils. When the resistance exceeds 1,500 miles, the Author prefers reading off the resistance from the deflection of a delicate galvanometer. The plan he adopts is the following. He observes, on a delicate galvanometer, (Fig. 8,) the deflection of the needle, reducing, or increasing the power until the deflection amounts to 30°. He then inserts a known resistance, say 500 miles, at A B, and by the use of the derived circuit, D, reduces the deflection of the needle, until it reads the same as before; the power remaining the same. The ratio between the resistance of the derived circuit, and that of the coil, will give the ratio between the known and the unknown resistance. The same effect can be produced, by altering the battery powers to obtain the same reading on the coils and the wire. Thus, if with one cell, the galvanometer shows a° through 10 miles of resistance, and the same with one hundred and twenty cells through the wire, then:‑
It will now be seen how simple it is to express, in units of resistance, the state of the insulation and condition of a wire. If a wire, when submerged, represents upon the coils the exact resistance of its length, it insulates, and conducts well, and it is very perfect. If it gives a resistance less than its proper standard, there is a leakage, or fault, and if it gives a greater resistance than its proper standard, there is a bad joint, or imperfect continuity. If the end is disconnected, the leakage, or loss of insulation can be measured,—by the coils direct, if the loss is great,—and by the multiplying differential, or simple galvanometer, if the loss is slight. If the cable is broken at any spot, say at D', (Fig. 7,) the resistance of D D', or in other words, the distance of D' from D, is shown upon the coils R R'.
Thus in testing, from the office in Jersey, for the break marked No. 8 in Table I., the coils R R' showed the resistance of D D' to be 10⅔ miles, which placed the fault 2⅔ miles from the Jersey shore, at which spot it was found. Cables should be carefully tested by such processes, not only when laid down, and at work, but also during their construction and submersion. The Engineer in charge, would thus always possess a complete knowledge of the electrical qualifications of the cable. Had the Atlantic and Red Sea cables been so treated, the present condition and prospects of submarine telegraphy would have been considerably better.
The laws of induction are much more intricate than those of resistance. Electricity develops itself in two forms, dynamic and static. A dynamic current is a very different phenomenon from a static charge. A flash of lightning cannot be compared to the gentle current, generated by the tongue, between a shilling and a penny-piece; but they are one and the same thing under different forms. A thunder cloud can be dissipated as a dynamic current, and a dynamic current can be developed into a thunder cloud. Conduction performs the first, induction the last operation.
The insulated conductor of a submarine cable is a Leyden jar, of which the wire is the inside, and the outer iron wire, the earth, or the sea, the outside coating. Before this Leyden jar can conduct a current, its whole surface must be charged statically, by induction. When a current is thrown into a wire, its first influence is absorbed, as it were, in raising the surface of the conductor to a certain static tension, where it remains latent as long as a current flows through the conductor. But immediately the current ceases, and the end of the wire is placed to earth, the static charge flows out of the conductor at both ends, as a dynamic current. It matters not whether the end be to earth, or be disconnected, the phenomenon is the same in effect, though different in degree. If only one end is placed to earth, the other being disconnected, the whole charge flows out at that end. If both ends are to earth, the discharge is divided between the two. It is for this reason, that, in passing a current through a long submarine cable, it takes an appreciable period before it appears at the distant end, and when the current is stopped, it continues to flow out at that end, for some time after contact has been broken, while at the same time, another current of the same duration flows out at the near end; hence the speed of signalling through long cables is reduced.
The first rush of electricity into an open wire, is called the ‘charge.’ Its return, when the end is disconnected, is termed the ‘discharge’ The current flowing out at the near end, when the distant end is to earth, is the ‘return current’ The delay of the appearance of the current at the distant end, is its ‘retardation.’ The drawing out, or lengthening, of the current as it appears at the distant end, is its ‘prolongation’. These different properties have, each, their own independent laws, and have recently received full examination and development; but as the testing, and not the working of submarine cables is now under consideration, the Author will abandon the inquiry into those laws affecting retardation and prolongation, and apply himself strictly to the charge, the discharge, and the return current.
The charge and discharge obey the same laws; the one is only a reflection of the other. Whatever, therefore, is said respecting the charge, is strictly applicable to the discharge. The return current is simply a modification of the discharge.
Now the charge of a wire depends:‑
The law which regulates it may be expressed by the formula:—
C = (n S R s)/d.
But as all induction tests in submarine cables are, simply, comparative effects between certain phenomena, upon known and unknown lengths of the same wire, the consideration of the thickness and inductive capacity of the insulating medium may be discarded, and attention be alone directed to the surface exposed, the length of wire under examination, and the power of the battery used. The formula therefore becomes:—
C = n S R = n l,
when S and R remain equal, l being the length of wire.
Thus if it is desired to compare the charges of two separate wires:—
C : C' :: n l : n' l'
or, when the same power is used in each case:—
C : C' :: l : l'
and, if the lengths of the cable are the same:—
C : C' :: n : n'
From these proportions it follows, that, if a wire 10 miles long, gives a discharge of 10°, with one hundred cells, it will give 20° with two hundred cells, or 5° with fifty cells; and, if the power remains the same, it will give 5° with 5 miles, and 20° with 20 miles. Hence, if the discharge of any unit length of wire is known, the length of wire under manipulation can easily be calculated, by the above proportion. An example may be interesting, and more explicit. The cable between Guernsey andJersey was recently broken, the ends being completely disconnected, and it was tested from Guernsey. Between Guernsey and Alderney, 23½ miles, thirty-six cells gave 28°; from Guernsey to the fault, the same power gave 20°
∴ 28 : 20 :: 23½ : 16 11/14.
The actual fault was 17½ miles off, being an error of scarcely half a mile in the test.
The return current differs from the discharge, in name only. The term ‘discharge,’ is simply applied to the return current, when the distant end of the wire is disconnected. The term ‘return current,’ is applied to the discharge when the end is to earth, or when resistance is interposed between the end and the earth. The discharge formula becomes:—
C = (n l r)/a.
a being a co-efficient depending upon the length of wire, and the time that elapses between the breaking and making contact, whence it follows that, as the resistance of the end r is increased, the return current is also increased, until r is infinite, when the return current equals the discharge. The converse of this would occur, when the resistance lies between the submerged wire and the testing place, but as in practice it is always possible, and indeed essential, before commencing operations, to make the tests at one end of the cable, this question need scarcely be examined.
The instrument, which the Author employs for the purpose of measuring and registering the discharge, is either a vertical galvanometer of great delicacy, or a peculiar arrangement of his own design, called a ‘reduction inductometer.’ With short lengths of wire, and low power, the simple galvanometer gives very true results up to 30°, when applied to the formula:—
C : C' :: n l : n' l'
the discharge being registered by the swing of the needle. But for longer lengths, the following plan is used. A, (Fig. 9,) is a simple galvanometer, through which the discharge flows to earth. Now if a unit length, say 1 mile, of submerged wire, gives 30° of deflection with n cells, 10 miles could not be registered with the same power. But if, between C and D, a derived circuit, or resistance coil, B, is inserted, whose resistance is to that of the galvanometer coil, as 1 to 10, nine-tenths of the discharge current will traverse the derived circuit B, and one-tenth the galvanometer. Thus, the deflection of the needle will be the same for 10 miles as for 1 mile. By varying the distance of the derived circuit by a set of resistance coils and rheostat, as in Fig. 8, and altering the power and unit of deflection, as may be necessary, it is possible to measure the discharge of any length of cable, for one mile and upwards. This is a valuable instrument for measuring the discharge of wires up to lengths of two hundred miles, or three hundred miles, but beyond that distance, the time of the discharge and the absorption of the charge would materially interfere with any measurement upon the needle. The thin line produced on a Bain’s instrument, by the action of prussiate of potash on a steel wire, is a valuable test for the discharge of longer lengths of cable.
It will thus be seen that, by comparing the resistance with the discharge, it is easy to calculate the position of a fault, however distant from the testing place; the one is a check upon the other. But the experiments are liable to many errors, which, if not duly allowed for, produce serious mistakes. The most important relates to the resistance of the end, or fault. When the wire is completely severed, which is almost always the cause of the interruption to the working of submarine cables in shallow waters, the resistance of the end can easily be determined, as it depends entirely upon the surface of copper exposed in the water. By a series of careful experiments, detailed in the following Table, the Author is able to give the exact value of the resistance of the end, to any break in the cable under his charge.
TABLE II RESISTANCE OF ENDS.—CHANNEL ISLANDS CABLE.
No great variation. Duration, about one minute; declining rapidly in the first and mood, then gradually. Power, forty-eight cells.
A similar tabular statement could easily be obtained for any cable.
When the resistance of the end of a cable is small, and the break is not very distant, it is impossible to place any reliance upon the discharge of the wire, to verify its resistance, because a very peculiar effect is produced. When a negative current is sent through the wire, it is well known, that its end is covered with hydrogen gas, by the electrolytic action of the current upon the water, and, by the same means, the end becomes coated with oxygen, when a positive current is used. Now these two gases, acting upon the exposed end, themselves generate weak currents, which are often mistaken for discharge.
The Author designates them ‘gas currents,’ to distinguish them from the ‘water current,’ which is always generated by the voltaic arrangement of the exposed copper end, the sea water, and the outside iron covering. A positive primary current generates a negative gas current, and vice vend. The duration of this current is but momentary, and it varies little with the surface of the copper exposed. Its electro-motive force is slight, but it renders perfectly nugatory any attempt to verify the resistance tests of short lengths, by those of induction. These gas currents are identical with ‘currents of polarisation.’ When the copper wire is in contact with the outer iron wire, a case of very rare occurrence, these currents are not observed, nor does the end give any resistance, a fact which is also corroborated by the resistance given to the positive and negative currents being equal. This was the case in No. 8, Table I.; (page 33).
The occurrence of partial faults is another cause of error, and great care is requisite to maintain a thorough knowledge of the condition of the wire, and the position of these partial faults. A partial fault is a leakage, or imperfection, in the insulating medium, which does not interrupt the working of the wire, but which reduces the efficiency of the working currents. In practice, daily observations should be made, at each end of a submarine cable, to detect and determine the position of these faults, as the errors they produce are very serious. In testing from Weymouth, the Author calculated the fault No. 10, Table I., to be at 15 miles from Alderney. This arose from the existence of a partial fault near Weymouth; on testing from the other end, he found the result shown on the Table.
If A B (Fig. 10) represents the wire to be tested, and A C a fault near at hand, then the resistance of the two together will be, by Ohm’s law, calling the one x and the other y:—
Now if y = B
and xy/x+y = A
then x = (A B)/A - B
From this, it is evident, that the less the resistance y is made, the greater it will make the difference between A and x, and consequently, the greater the error produced in the test.
It can be similarly shown, that the further the fault is from A, and the greater its resistance, the less will be the error introduced. Hence, before the correct resistance of a wire can be definitely proved, the value of y must always be known. To show, practically, the serious error a partial fault may produce:—
Suppose y = 100,—by no means a very serious fault,—
and xy/x+y = 48
then x = 92 4/13:
reducing the distance of the fault by nearly one-half.
There are several methods of testing for partial faults. The following are those usually adopted:—
Fast, When the two ends are at hand;—by inserting resistance at A, (Fig. 11,) until the differential galvanometer marks zero;
then x+y = R
and x = y+r
∴ 2y = R—r
y = (R — r)/2
Secondly, When only one end is obtainable:—
Let x + y = R, resistance of the cable, when perfect;
x + Z = A, the resistance, when the end is disconnected;
then x + (y z)/(y + z) = B, the resistance, when the end is to earth;
from which x, y, and z can easily be resolved; x and y being the distances of the fault from the ends, and z, the resistance of the fault. This method requires great care, and is liable to serious errors through the variability of the resistance of the fault. The test should be verified by repetition at the other end, but the Author prefers to obtain simultaneous tests, at both ends, by two manipulators, who possess instruments precisely similar in every respect, by which method great accuracy is obtained, and the variation of the resistance of the fault is of little, or no, consequence.
The methods of testing by resistance and induction, which have now been detailed, will enable the Engineer to possess a thorough knowledge of the condition of the wire under his charge, and to detect, at once, the existence and position of any fault, however distant, which may occur to interfere with the proper working of the cable.
* This ratio (d) is expressed by Professor Thomson [a] thus: 2 log. D'/D; where D is the diameter of the wire; D', the diameter of the insulating medium; and log. the Napierian logarithm. Professor Wheatstone’s ratio [b], is sqrt (r/t); where r is the radios of the wire; and t the thickness of the coating.
Faults are of various kinds, and result from various causes. There are faults arising to the insulating material, from adulteration in its composition, and imperfections in its manufacture. There are mechanical injuries sustained by the gutta percha in its transport from the manufactory to the machine, or in the process of making it into a submarine cable. The cable is liable to injury in every stage of its existence; and when submerged, it is in the greatest danger. In shallow waters, rocks destroy it, and ships damage it with their anchors. Atmospheric electricity plays an important part in its existence, in deep as well as in shallow water; one flash of lightning, entering the wire, would speedily destroy its utility. The immoderate use of battery power would irretrievably destroy a damaged wire.
But there is no imperfection which cannot be detected, and no accident which cannot be provided against. If the cable is thoroughly examined and tested before it enters the machine; if it is completely supervised, and tested under water, before being coiled in the ship; if it is payed out, with due regard to the course taken, and the nature of the bottom; if in shallow waters it is made so strong, that no ship can injure it, and it is laid along such a route, that no rocks can damage it; if it is properly protected against lightning and other natural causes; and if it is constructed, and worked, upon true principles, then submarine telegraphy may hope to flourish. But when experience is ignored, and the true principles of the science neglected; when a red line is drawn across a chart, and a cable is laid along that route, without any reference to the currents, and the bottom; when cables, which, in their design, are scarcely made for unfrequented rivers, are laid in rough channels; and when no regard whatever is paid to their durability and maintenance; then no surprise need be felt, that opinions should be expressed unfavourable to the permanence and efficiency of submarine telegraphy.*
The Paper is illustrated by a series of diagrams, from which Plate 2, (Figs. 1 to 11,) has been compiled. [not presently available.]
Mr. HAWKSHAW, V.P., observed, that during the last two generations, there had been three great movements in the engineering world; one, when Watt invented the steam engine, which supplied power; another, when railways were introduced, which supplied locomotion, and the third was the invention of the electric telegraph, which, as an agent for transmitting thought, he considered to be as important as either of the others. Those who had paid attention to the subject, knew the great progress which had already been made in the science of electricity; yet he believed it to be still in its infancy. The Paper before the Institution was one of the most important which had been presented, and it afforded a convincing proof of the rapid advances now taking place in one of the most valuable fields of scientific research.
Mr. W.H. PREECE remarked, that, in condensing the Paper within reasonable limits, he had, necessarily, been obliged to omit many particulars deserving of notice; he had, however, carried out as well as he was able, his intention of forming a framework, upon which a discussion might be raised. He had scarcely alluded to the effect of temperature upon wires, which was a frequent cause of serious error, nor to the defects of stranded wire. He felt, that it would have been desirable to have given greater extension to his remarks upon testing under water, upon working damaged wires with single currents, and upon the comparative advantages of screw and of paddle-wheel steamers in repairing cables; and he should, more particularly, have referred to the improvements in testing, of Messrs. Siemens, Halske, & Co., of Berlin, whose instruments, exhibited before the British Association, accomplished, although in a different manner, the objects he had pointed out. On reference to No. 4 of the Table of Fractures, it appeared, that the actual fault was only ¾ths of a mile from Jersey; while the testing gave 1½ mile, an apparent error of 100 per cent, But the error was not a per-centage error, it was simply an error due to the resistance of the end; and had the test been made at a distance of 100 miles, the difference of ¾ths of a mile would have still been the same.
The chief points for discussion were the importance of thoroughly surveying the route before laying the cable; the choice of a proper insulating medium; and the necessity of applying some exterior protecting coating to all cables, not only in shallow water, but also in deep seas. The want of coating to retain unimpaired the strength of the cable, was exemplified in the case of some of the recent failures in deep-sea cables, and particularly, in that of the Atlantic cable. Had the latter been protected against the action of the sea water upon the outer wires, its repair would have been easy, and the transmission of messages across the Atlantic, would now be in full operation. The Report of Mr. Varley showed, that the wires had become so decayed, as to be incapable of repair, whilst those parts which had been coated with hemp, were as good as when the cable was first laid.
Again, in the case of the Red Sea cable, he had heard, that those who undertook the repairs, found the cable, when brought to the surface, similarly decayed. Some cables, however, had been made, which partially carried out the ideas he advocated; the one most recently laid was the Toulon and Algiers cable, which had a covering of hemp. The Red Sea cable was the best specimen that had been brought forward, at the time it was laid, and if it was combined with the principle of the Algiers cable, the former acting as a cone for the outer wires of the latter, he thought that the proper form for a deep-sea cable would be attained; the former giving strength, and the latter, durability. In cables similar to the Algiers cable, a ‘kink’ would occasionally occur, and cause serious damage, but he believed that was a defect which would easily be overcome, by the cable he suggested.
The important question of insulating media had occupied the attention of the Government; and the Commission which had been appointed had, he understood, collected some interesting facts relating to it. That Commission, however, had not yet published its Report. He quite agreed with the remark, that submarine telegraphy was still in its infancy, but the knowledge of the correct form and construction of cables could never be ascertained, except by the accumulated experience of all those who were engaged upon the subject. His own experience had been freely placed before the Institution, and if others would, in like manner, contribute their quota of information, Engineers would, ere long, arrive at the true form of submarine cable, both for efficiency and durability.
Mr. CROMWELL F. VARLEY called attention to what he considered were errors in the calculations of the reduced resistances, in the instruments described in the Paper.
Mr. W. H. PREECE observed, that he had pointed out in the Paper, the means of compensating the irregularity alluded to. He had, generally, in making these instruments, taken the amounts of resistance experimentally, which gave the result required.
Mr. VARLEY continued. With regard to the mode of measuring and using a derived circuit, the first idea was suggested to him by Professor Thomson; and he described an instrument for effecting a similar object to that proposed by Mr. Preece, but based upon a different principle. It did not appear to him, that the induction formula correctly expressed the discharge from different cables, because it did not show, that the ratios between the diameters of the interior conductor and the outer covering, remained constant, and because it omitted the specific inductive capacity of the material employed.
Some remarks had been made as to the insulating powers of different materials, on which he would offer a few observations; and as gutta percha had, hitherto, been exclusively used, he would speak of that material first. The manufacture and preparation of gutta percha had, recently, been much improved by the Gutta Percha Company. They had produced specimens more compact to the eye, with as low an inductive capacity as india rubber, whilst the insulating power had, be believed, been increased forty times. The gutta percha, as now prepared, possessed insulating power enough for all practical purposes, in working cables; but in testing, the higher insulating power would be of great service. If this new preparation of gutta percha could be sold at a reasonable price, a material would be obtained, which would test more perfectly than common gutta percha, and it would also have the advantage of allowing a higher rate of transmission; for whilst with the ordinary gutta percha, only 7.45 words per minute could be sent, with this new substance, 12 words per minute might be transmitted.
Pure india rubber seemed to give the greatest resistance to induction, of any substance that had been examined. The next material, which was on a par with this special gutta percha, had been introduced by Mr. Wray, and was a composition of India rubber, shellac, and ground glass. Some specimens charged over-night, were not found to have sustained any appreciable loss, when tested the following morning; and one specimen, a yard in length, retained its charge with a very trifling loss, for a fortnight. Vulcanised indict rubber, as applied by Mr. Daft, (Assoc. Inst. C.E.,) was also a promising substance. Although considerable improvements had been made in insulating materials, none had yet been adopted, to any great extent, except india rubber and gutta percha. It was very desirable that telegraph companies should institute a series of experiments on a large scale, to test the merits of different insulating materials.
As an illustration of the importance of ascertaining, with some degree of accuracy, the nature of the bottom on which the cable was to rest, Mr. Varley stated, that he and Captain Kelk had found the Atlantic cable lying upon a reef of rocks across Trinity Bay, Newfoundland, which was the continuation of a range striking out from the shore, at about 15 fathoms below the surface of the water, in a position where the charts indicated a depth of 50 fathoms, and upon these rocks, the cable had suffered severely. He had seen parts of the iron wire of this cable, where it was covered with hemp saturated with Stockholm tar, which had retained its brightness, after having been immersed in the sea for a long time, a result attributable, he believed, to the preservative properties of the tar, rather than to those of the hemp. The portions not so protected, were found to be corroded to such an extent, that it was not possible to raise the cable, without constantly breaking the thin wires, of which the outer covering was composed. There were evidences of metallic copper on the outside of the iron wire, and as the gutta percha was quite sound, it could not have resulted from the decomposition of the copper wire of the cable. He imagined, that it must have arisen from the cable resting upon some copper ore, at the bottom of the sea.
In the first cable which was laid from Hurst Castle to the Isle of Wight, some of the wires were found to be eaten through, whilst others were sound. On that coast, there were large quantities of stone, which was used for the manufacture of cement, and which was known to contain red oxide of iron. This ironstone, when tested against copper, was found to be highly negative, and where iron rested upon it, the iron was certain to be corroded. The only method of preventing that action, and of preserving the wires, was to insulate them by a covering of yarn and of some pitchy compound. He thought, that zinc only afforded a partial protection, owing to its impurity, but that tinning would be more effective, and not more expensive than galvanising.
As regarded the Atlantic cable, an observation had been made, that if it had been covered with a protecting coating, it might still have been in good working order. He entertained a different opinion; because, as shown by the tests to which it was subjected by Professor Thomson, it was, undoubtedly, defective, before it was submerged. It was never tested before being laid, and that had been the case with almost all the other cables that had failed. He believed the failure of the Atlantic cable was not due to any imperfection in the gutta percha, but to gross carelessness and want of knowledge.
Mr. BIDDER,—President,—said, that an approach was gradually being made to a correct appreciation of electrical phenomena and the proper condition of telegraph cables; and within a short period, the science of the transmission of electric currents, through wires insulated in various substances, would, probably, be brought within the range of formula:, as accurate as those which determined the flow of water, through pipes of various diameters. But in order to utilise that knowledge, it was also necessary to ascertain the proper method of laying down electric cables, both in deep and in shallow water, and of maintaining them in a state of efficiency, after their submersion. The progress in this respect, had been, hitherto, extremely unsatisfactory; there had been a disastrous failure in the Atlantic cable, and if possible, a still more signal failure in the Red Sea telegraph.
He hoped, therefore, that the discussion would not be confined to the theory of electricity, but that it would also be directed to the practical point of rendering the knowledge and information available, as a great commercial and national object. He should take an opportunity, at the close of the discussion, of making some remarks upon the subject, and he should not shrink, through any fear of giving offence, from frankly expressing his own opinions upon a question of such vast national importance. The Commission, appointed by the Government, was now sitting, and had collected a considerable amount of information but all the evidence was of a purely voluntary character, and could not, therefore, be subjected to a searching cross-examination. For that reason, he thought that a discussion at the Institution, fairly analysing all that had been hitherto done, and bringing forward accurate facts, would be of assistance to the Commission, and that it would also have a great effect in relieving the profession from the cloud that was, at present, hanging over that particular department of engineering science.
Mr. C.W. SIEMENS felt more than usual difficulty in approaching the subject, because the Paper, although dealing only with the phenomena which presented themselves in the treatment and management of some short lines of telegraph cables, opened for discussion a branch of science which embraced many others, from chemistry to naval architecture.
He had engaged, on the part of the Contractors, to superintend the electrical condition of the Channel Islands cable, during its submersion, and also to arrange the instruments of the line. At the time the cable was laid, nothing could be more satisfactory than the results it afforded. The electrical condition was, considering the state of perfection then arrived at, very satisfactory; the instruments acted with the greatest facility, and with very low battery power; and he took this opportunity of stating, that he considered it an essential point, to save a cable as much as possible from the strain of great battery power. The Paper dealt, more particularly, with the mechanical accidents that occurred to the cable, upon which, he would, in passing, make a few remarks. The route, as was justly stated, was not well chosen; it would have been better, no doubt, had it passed direct from the Isle of Wight to Guernsey; but he was under the impression, that the choice of the route was not left to the Contractors, but that it was, as had generally been the case, determined by the Company, in concert with the Government. He also agreed with the Author, that the shore ends had, generally, been made too light, and that the specimens he exhibited presented far greater power of resistance to wear and tear. But Mr. Siemens had adopted the plan, when laying electric wires across rivers, or bays, of enclosing them in a succession of tubes, connected together by universal joints. This plan was more advantageous than using a strong cable, for each tube took a firm position upon broken ground, allowing the cable inside to make its own permanent serpentine curve; whereas a strong cable would, owing to its elasticity, always be moving between its supports, and be thus exposed to continual abrasion.
Passing to the larger work of the Red Sea cable, he would, first, explain the position in which he had stood with regard to that undertaking, or rather the position of the firm of Messrs. Siemens, Halske, and Co., of which he was a partner. They were employed to superintend the electrical condition of the cable during submersion. Unfortunately, they had not had an opportunity of examining the cable regularly, until it was on board ship; and it was one of the most prolific causes of failure, that cables were not thoroughly tested under water, before they were deposited in the ocean. In laying the Red Sea cable, faults occasionally occurred, which, by the system of testing adopted, were instantly detected and rectified; but none of these would have happened, if the cable had been previously immerged.
When the operation was completed, it proved, like most lines when just laid, very successful. The telegraph was worked from Alexandria to Aden, a distance of 1,200 miles, with double relay stations at Kosseir, and Suakin, at the rate of ten words per minute; and the general condition of the line was such as must be pronounced to have satisfied the terms of the contracts. There were, no doubt, a few embryo faults, which, by their system of testing every five minutes during submersion, they were enabled to trace, and to map by means of diagrams, representing the copper and gutta-percha resistances. The times of observation were not left to the discretion of those on land, and on board the ship, from which the cable was payed out, but they were prescribed by a peculiar clockwork arrangement, which reduced the work of the observer to a simple registration, and obviated much uncertainty and delay in these operations.
The line was in a satisfactory electrical condition when laid, and he believed it might have been worked successfully, for a considerable space of time, if a permanent system of daily tests and of timely repairs had been, at once, established. The Author had mentioned some of the difficulties with which cables had to contend, and the injuries to which they were exposed, but probably, he had not had an opportunity of watching the effects of tropical heat, or of metallic veins at the bottom of the sea, which also tended to destroy them. He could refer to several cables, which had remained perfectly sound for a certain distance, but had been, in certain places, so completely corroded, that in attempting to repair them, they, literally, fell to pieces. Such had been the case, as had been already mentioned, with the Atlantic cable. It was too much the fashion to regard a cable, when once laid, as of indefinite durability, and, in most cases, no sufficient means were adopted to test it at regular intervals. No means, for instance, were provided for effecting repairs in the Red Sea cable, as the necessity might arise, and under those circumstances, it was surprising, that it should have lasted for nine months before the first fault occurred, it having given way only the day before the extension was completed to India.
Upon the return of the expedition engaged in laying the cable, it was the general opinion, that energetic measures should be adopted for its maintenance. The neglect of this might, in a great measure, be attributed to the diverse interests of the several parties concerned. There was the Government, who had given an absolute guarantee to the Company, which had the management of the line, without being sufficiently interested in maintaining it in good working condition; there was the Contractor, who had fulfilled his engagement, when once the line was successfully laid; there was the Pioneer, who had laid down the direction it should take, but who had not had sufficient opportunity of testing the nature of the bottom; there was the Engineer, who superintended the making and submerging of the cable on behalf of the Company; and finally, there was the Electrician, who had, probably, the most anxious and trying work of all, but the importance of whose office had not, he thought, been sufficiently considered, in making the general arrangements. The necessity of adopting a better system, was, however, beginning to be acknowledged; in proof of which, he would instance the Government cable, about to be laid between Rangoon and Singapore, where an opportunity had been afforded, for the first time, of carrying out a complete system of testing, before the cable was shipped.
|* It is gratifying to the Author to find, that the conclusions he had arrived at and the opinions he had expressed in this Paper, were corroborated and confirmed by the Joint Committee in their Report to the Government, issued in 1861. Several accidents of a similar nature to those described, have occurred to the Channel Islands cable, and the undertaking is now being abandoned.—AUTHOR, February, 1862.|
The method of testing employed by Messrs. Siemens, differed essentially from those hitherto adopted. He would not, at present, enter upon the mathematical part of this subject, which was very intricate, but would confine himself to giving an outline, which would sufficiently show the relative advantages of the system, referring those who might feel more interested in the subject, to a Paper by his Brother and himself, read, in 1860, before the British Association at Oxford.* The old system was to test the insulation by the galvanometer, and to judge the condition of the line by the angle of deflection, and the battery power employed. This was unsatisfactory, for the angle of deflection of an instrument was never the same for two consecutive days, nor could an instrument be constructed with a constant amount of deflection for the same current; there was, therefore, no means of comparing results. If a mile of cable was measured by one instrument, and several miles by another, or by the same instrument the next day, no useful comparison could be made.
But Messrs. Siemens adopted the method of expressing the conductivity of the insulating coating, as well as of the conductor, by certain units of resistance. The unit adopted by the Author, and which might suffice for the particular case mentioned in the Paper, was the mile of No.16 copper wire. It resulted, however, from the investigations of Dr. Matthiessen, that the copper of commerce varied in its conductivity, between the limits of 100 and 7; in speaking, therefore, of the resistance of a mile of copper wire, no distinct estimate of its value could be formed. The unit developed by his Brother, and which had since been adopted by them in all their operations, was the resistance of a column of pure mercury of one metre in length, and one millimètre in sectional area; this unit, over others, the advantages of being invariable, and of being easily reproduced.
Coils of resistance were next formed of German silver wire, representing, respectively, units, tens, hundreds, thousands, and tens of thousands of units of resistance, By introducing these variable resistances into the three sides of a Wheatstone’s bridge, or electric balance, the resistance of the fourth side, which was the gutta-percha, or copper conductor of the cable under examination, could be ascertained with the utmost certainty, the limit of error not exceeding, practically, one in one thousand. It was desirable, sometimes, to determine fractions of units, in measuring copper conductors; and at others, millions of units, in measuring the gutta- percha resistance of a short piece of cable, to accomplish which the apparatus could be modified in different ways.
Another feature of this method of testing consisted in the close observance of the time during which the electric current was allowed to act, before the observation was taken. This was of the utmost importance, in order to obtain results that could be relied upon, for the conductivity of gutta percha was changed, even for days, by the application of electric currents. Their method of ascertaining the inductive capacity of cables was also peculiar, being based upon their discovery, that inductive tension, in passing from the conductor through the insulating covering, followed owed the simple law of Ohm, regarding electric condition, and admitted, therefore, of being subjected to the same precise methods of measurement. Although this system of testing cables had not been long in use, resistance coils had been employed by them, since the year 1849, for determining the position of faults in subterranean lines.
In the case of the Rangoon cable, each mile of core was tested at the works, after submersion during twenty-four hours in water, at a temperature of 75°. Comparative testing would be useless, unless made at the same temperature, because the conductivity of gutta percha increased in a very unequal ratio, with the increase of temperature. After submersion, the cable was placed in Reid’s pressure tank, in order to discover the existence of any cavities in the covering, but the pressure that could be applied was insufficient to force the water into the cavities of the lower coatings. The results of the electrical tests were then noted in tables, reduced to units of resistance per nautical mile.
Having thus obtained a complete record of the copper and gutta-percha resistances of each mile of cable, it was sent to the wire works to be covered with hemp and iron. By this complete record, or table, it would he possible to detect the slightest fault, where lengths of the core, equal to, say one hundred miles, had been joined together; the copper resistance should not, in that case, exceed the sum of all the resistances contained in the table, due allowance being made for change of temperature, whilst the resistance of the gutta percha should not be less than the sum of the resistances, divided by 100. If it varied, it was a sure indication, that there was some defect which, after the cable was laid, would, probably, develop itself into a fault. But the value of these tests extended much further; if either during the laying of the cable, or afterwards, any slight decrease of insulation occurred, it would, at once, show the existence of a slight fault, although the line, if measured by others unacquainted with the previous tests, might appear perfect. The position of that fault should be immediately determined, and be carefully watched from day to day. In fact, complete records of the condition of the cable ought to be telegraphed each day, or each second day, to the chief superintendent of the line, in order that he might be able to direct timely operations of repairs. So long as there was a single fault in the line, they could, by their methods of testing, find out its position with the greatest certainty.
It had been, originally, intended that the Rangoon cable should be immersed in water during its entire progress. After having been tested at the Gutta-Percha Works, it was to have been placed at the Contractor’s works in tanks, leaving them only for the short apace of time necessary for passing the cable through the machine. From these tanks it was eventually to have been coiled into others on board the ships, in order that it might be payed out from water, into the sea. But the tanks of the Contractor were unable to support the great pressure of water, and thus the cable became exposed to atmospheric influences. It was soon observed, that there was a loss of insulation, indicating an increase of temperature, which, subsequently, became so great, that mist was seen to arise from one portion of the cable, and it became necessary to pour water over it. Thereupon, the Government requested Professor Miller to investigate the subject chemically, and they called upon Mr. Siemens to make a report on the electro-thermal phenomena.
It was requisite, for this purpose, to test the temperature of every part of the coil, for which Mr. Siemens devised a peculiar thermometer, constructed upon the principle of the resistance of copper wire to the electric current, varying, in a fixed ratio, with the changes of temperature. It consisted of a rod, or tube of metal, round which were wound several layers of fine wire, covered with silk; and the whole was hermetically sealed with india rubber, and gutta percha, to prevent the access of the water. The two ends of the wire were then brought in contact with the instrument for measuring resistances. Supposing the coil to have been adjusted to represent, at zero, 100 units of resistance, then for every 1° Fahrenheit, the resistance would increase by 0.4 of a unit. The advantages of this thermometer were, that while it could be placed at almost inaccessible points, it could be read, at all times, with great accuracy.
In coiling the cable on board, he inserted several of these thermometers, at different layers of the coil. The coil remained nearly a week on board, without his being able to test it; at the end of that time, it was at once apparent, that there had been a spontaneous generation of heat. On the 10th of November, 1859, the tests of the cable had given 553 millions of units per nautical mile, at the temperature of 49° Fahrenheit. On the 21st of the same month, when the cable was first tested on board, the gutta-percha resistance per nautical mile, had diminished to 199 millions, showing a considerable increase of heat, unless, indeed, the decrease was due to a fault. On the 1st of December, it was only 61 millions, showing a still further rise of temperature. At the Gutta-Percha Works the standard resistance per nautical mile, was 100 millions of units, at the temperature of 75° Fahrenheit. The different resistance thermometers inserted in the cable gave the following temperatures: 84°, 75°, and 62°; thus proving that the heat was unequally developing itself throughout the mass, the highest temperature being about 3 feet below the upper surface of the coil.
On the 2nd of December, the insulation, or gutta-percha resistance, had decreased to 54 millions of units, and the temperature had increased about 3° Fahrenheit in every part. Water was then applied to the cable, and after some hours, the temperature was sensibly diminished. The cable had, till then, given no external signs of heat; the temperature of the hold itself was not greater than 60°, nor would a mercury thermometer, placed in any part of the hold, indicate a higher temperature; yet, when large quantities of water at 42° Fahrenheit, were poured on, it issued from the bottom of the hold at 72°, corroborating the results of the electrical observations. This occurrence proved, that it had been most injudicious not to have carried out the original plan, of having the cable placed in water-tight tanks on board the ships. It also led to the supposition, that the destruction of several previous cables, more particularly the Atlantic cable, which had been coiled wet on board, might, very probably, have been owing to the same cause.
If the Rangoon cable, while in its heated condition, had been tested on board the ‘Queen Victoria,’ with the most accurate galvanometer, it would have been pronounced more perfect than any cable hitherto sent out, because the Red Sea cable gave, at ordinary temperatures, only 22 millions of units, and the Atlantic cable, when reduced to the same sectional area, only 7, or 8 millions of units; whereas the Rangoon cable did not fall below 61 millions. Yet if the heating had been allowed to continue only a few days longer, it was absolutely certain, that the gutta percha would have been softened, and the copper conductor would have sunk in the insulating medium.
A great desire was generally manifested, for some improvement upon the present construction of cables: and he believed there was great room for amelioration. An iron cable, without an external covering to protect it against the action of the water, should never be adopted. So far from the iron being an element of strength, it became an element of absolute weakness, when the cable required to be raised for repairs. It had frequently been observed, that the iron was oxidised, and in certain parts, rapidly destroyed; and if the ground was uneven, the cable would then even break by its own weight, between the points of support. But the outer covering should not be of hemp, for there had been cases of hemp-covered cables having been completely destroyed by marine animals. As to the cause of the generation of heat in the Rangoon cable, his own impression had been, that it was due to the fermentation of the hemp covering; he was bound, however, to add, that, in Professor Miller’s opinion, it arose simply from the rusting of the iron. His own view was founded upon his observation, that the resistance thermometers between the coils in contact with the iron, exhibited a less temperature than would follow from the resistance of the copper of the cable itself; showing that the core of the cable was 5° hotter than the spaces between the iron covering. It might be, that both causes had been active in producing the rapid increase of heat, which had been observed.
The most important part, perhaps, of the cable was the insulating medium, for which many new substances had been proposed, each possessing some degree of merit. The great disadvantages attending the use of gutta percha were, that it was readily softened by heat, that it was affected chemically by every current that passed into it, and that it frequently contained cavities. The passage of electricity through gutta percha was due, not to its conductivity, but to a slight decomposition of the water which it contained. The consequence was, that in places where the thickness of the covering was much reduced by any accidental cause, a fault would gradually be produced, by the electrolytic action of the currents employed. He was, therefore, a strong advocate of low battery power, so long as gutta percha was employed for the insulating medium; and his instructions to the electrical staff proceeding to Rangoon were, that not more than twenty-two Daniell’s cells should ever be used. India rubber possesses a much higher power of resistance to electricity than gutta percha. Wray’s mixture, composed of India rubber, shellac, and powdered flint, and other compounds of india rubber possessed valuable properties as insulating materials. He had made some attempts to combine them in a cable, but he should refrain from entering further into this question, for his present object was rather to inquire into the causes of failure of the cables hitherto laid, than to consider the comparative merits of new projects.
In answer to a question from the President, Mr. Siemens stated, that the Red Sea telegraph was worked between Aden and Suez, from the summer of 1859 till February 1860.
* Vide “Outline of the Principles and Practice involved in dealing with the Electrical Conditions of Submarine Electric Telegraphs.” by M. Werner and C. W. Siemens, in the “ Report of the Joint Committee appointed to Inquire into the Construction of Submarine Telegraph Cables.” Folio. London, 1861. Page 155.
Admiral FITZROY, as a practical seaman, would offer some remarks, bearing upon professional points, which might be of assistance to the younger Members of the Institution, who had not had experience in similar technical matters. He would first, however, advert to and corroborate a remark of the Author of the Paper, as to the little dependence that could be placed on marine surveys made previously to the last few years, with regard to the configuration, the description, and the nature of the bed of the sea, beyond 6 fathoms, or 7 fathoms of vertical depth. This was not owing to negligence on the part of the surveyors of former years, but because submarine telegraphy being so new a subject, it was only recently, that accurate and minute surveys of the bottom of the sea, had been considered indispensably necessary.
The Surveyor of the Channel Islands, between 1820 and 1830, was Captain Martin White, one of the best practical marine surveyors ever employed, whose accuracy in detailing all that was then required, was most exemplary; he proved all his work by true bearings and horizontal angles, either by the theodolite, or the sextant, and not by a fallacious compass. It was exceedingly difficult, when on board a vessel paying out a submarine wire, or even in an ordinary sounding survey, to compare the position of a moving body in a tideway, with an exact spot on the chart, unless methods as exact as those employed by the scientific surveyor who prepared the charts, were used by those engaged in this department of nautical engineering. The compass was always a fallible guide, on which little reliance ought to be placed. The only depths considered of primary consequence in the early surveys, were those under 7 fathoms, the depth at which a large line-of-battle ship might strike the bottom. In the harbour of Alderney, not many months ago, a frigate struck upon a rock, which was not laid down on any chart* and even at the entrance of Milford Haven, a rock had lately been discovered in the fairway channel, upon which it was possible for a large ship to strike.
With regard to the manner in which submarine wires had been, hitherto, supposed to be protected, when at the bottom of the sea, he maintained, that iron should, on no occasion whatever, be employed as a covering, or armour. Such a defence should be composed of copper, or some metal, or other substance, that would not oxidise, and would be capable of receiving a gradual calcareous deposit, which would become a permanent protection against damage, or decay. However expensive in the first instance, it would be much more economical, than to use a covering which would not last more than a few years. He had been told by Mr. Park, formerly Master Attendant of Portsmouth Dockyard, that they were obliged to lift the chain moorings throughout the harbour, at least once in about four years, because in certain places, the cables became so corroded, that they could no longer be trusted. In some South American ports, there were copper veins cropping out at the bottom.
In the Bay of St. Blas, 40 deg South latitude, between the Rivers Plata and Negro, a ship lay two months moored by chain cables, one of which was found to be so corroded in that short time from lying across copper ore, cropping out, and exposed as rocky patches, or ridges, that the cable was condemned, even in a merchant ship. Several instances of a similar nature to the galvanic action of copper and saline moisture on iron, had been mentioned, as having occurred near St. John’s, on the other side of the Atlantic, where the copper appeared to have very seriously affected the iron sheathing of the cable, at the places in contact with it. That iron and copper with saline moisture in contiguity, were rapidly antagonistic, had long been known. Many years ago, when Mr. Peake, now Master Shipwright, was an assistant in Woolwich Dockyard, a vessel which had been fitted with Sir Humphry Davy’s iron ‘protectors’ came into dock to be examined. The object of placing these bars of iron on the bottom, was to keep the copper clean, and the plan perfectly succeeded in this respect, but the iron became decomposed in less than a year, and was reduced to a condition resembling plumbago. Mr. Peake put some of this decomposed iron, wrapped in brown paper, into his coat-pocket, for future examination, but soon afterwards, smoke was observed to issue from his pocket, and the iron was found to be quite hot. This fact tended to corroborate Dr. Miller’s view of spontaneous combustion, consequent on the decomposition of iron under certain circumstances.
Admiral Fitzroy thought, that a sufficiently pliable, durable, and protective, as well as insulating composition might be devised, partly vitreous, or siliceous, and partly calcareous, with a mixture of lead, or other metallic substance. In his opinion, the insulator should not be a vegetable substance, such as gutta percha, or India rubber, (which was the better of the two,) but it should be such a composition as he had already mentioned. That such a composition would be discovered and applied to this important purpose, could hardly be doubted, when every year attested the progress made in chemical science and in its practical application. He would not further encroach on the Electrician’s province than to state, that the result of his own efforts in that direction was, that wires of the purest copper, and of the largest diameter, when durably insulated, were much superior to combinations of small wires, used on the erroneous notion, that electricity required superficies for its transit, rather than sectional area.
He would now advert to some purely nautical points. In paying out a cable from the extreme end of the stern of a vessel, it would greatly moderate the suddenness and the degree of vertical motion in pitching, if one, or two rafts were placed astern of the ship, to break and divide the vertical action; this would allow the wire to run out smoothly, without being subject to sudden jerks. Yielding floats, or buoys, should also be used. It was well known to those who had been engaged in sounding voyages, that it was only at a comparatively short distance from the shore, that the bottom was rocky and irregular; consequently, it was only at such places, or ‘on soundings,’ as it was termed by sailors, that protection of any kind was required for the wire, in the deep ocean. As far as experience had shown, scarcely more than the insulating covering was generally required, in great depths.
Mr. LATIMER CLARK would confine his remarks to a statement of his own experience, which might be more useful than theoretical opinions. Submarine cables for shallow waters might be comprised under four classes. First, the hempen cable: secondly, the galvanised iron cable: thirdly, the unprotected iron cable: and fourthly, the iron cable with some protecting covering. With respect to the hempen cables, there were mechanical defects sufficient to condemn their use, as in the few attempts that had been made to lay them in shallow waters, they had soon been destroyed by the continual action of the tide and of the rocks. Galvanised iron cables, of which many hundred miles had been laid from the English coast, had proved, wherever they had been embedded in mud, or sand, to be very durable; so much so, that some specimens which had been under water during four, or five years, looked so bright and new, that it was scarcely possible to believe they hadbeen submerged at all.
He considered galvanised iron cables buried in mud, or sand, might last for fifty years, or sixty years, or perhaps more; but wherever they were exposed to the free action of the tide, corrosion was certain to occur. Judging from his experience, galvanised cables had, in all cases, a durability of at least three years beyond that of unprotected iron cables, but after that time, the zinc generally disappeared, and all cables whether originally galvanised, or not, were alike. acted upon by the sea water. This corrosion was conjectured to result from the cable lying upon copper ore, or some other material which was electro-negative with respect to iron. Sulphuret of copper would cause a galvanic action, and the iron would soon be corroded. Cables were often quite perfect for a great length, and then suddenly, there was a spot where a piece had been, as it were, carved out of the cable by some local corrosion; in some places the iron had disappeared altogether, and nothing was left but the hemp and gutta percha. If there was copper in the sea water, it would be deposited on the iron in the metallic form, and galvanic action would immediately commence.
The first cable between Hurst Castle and the Isle of Wight, which was laid only five, or six years ago, became, in eighteen months, so deeply corroded at places, from the action of the copper, or of some other material, that it was broken by a ship’s anchor. This was replaced by a smaller cable, which did not last a year, and subsequently, by a third of stronger construction, which was now being superseded by a fourth cable. Three cables, therefore, had been already destroyed, partly by ships’ anchors, and partly by corrosion. Pure sea water, he believed, was not sufficient alone to produce this destructive action upon iron; it was, probably, occasioned by copper, sulphuret of copper, iodine, or ozone held in solution. A cable buried in mud, or sand, was, of course, continually exposed to the action of the water, but as the same portion of water always remained in contact with the cable, he apprehended, that it gave off at first its corrosive element to the iron, and became incapable of further mischief. This would account for the greater durability of cables, under such circumstances. In 1859, he had attempted to imitate this action in a cable from Whitehaven to the Isle of Man, which he coated with asphalte, or rather with a serving of jute saturated with common asphalte; this process was inexpensive, and he thought the cable would last for a long period of time.
The failures of the Atlantic and the Red Sea cables demanded serious consideration. That some mischance should occur to the Atlantic cable was not surprising, when the limited experience then obtained, of submarine telegraphy in deep water, was taken into account. The cable was elegant in form and construction, but every seaman knew, that it would very soon rust away. But in the case of the Red Sea cable, there was no excuse for using unprotected iron, scarcely thicker than bell wire, for the covering, as there had then been abundant evidence to prove, that after being only a few months in the sea, it would become so rusted, that should any repairs be necessary, it would not be possible to lift the cable to the surface. In a conversation with the Secretary of that Company, he had intimated to him, that the outer covering could e y be expected to last more than two years, an opinion which the Secretary did not dispute. However, he certainly had not expected, that it would have failed so quickly as it had done. He believed, that in some cases, failure arose from the formation of black sulphuret of iron, arising from the decomposition of animal matter in contact with the cable.
Similarly, the cable about to be sent to Rangoon, would not be fit for use for more than three, or four years, under the most favourable circumstances; and if repairs were required, it would be found to be so much decayed, that it would be impossible to raise it. It was much to be regretted, that such a costly cable, electrically perfect, and designed for deep water, should have been laid with the certainty, that in a short time, it would have to be replaced. It was also to be regretted, that a cable designed to be laid from Falmouth to Gibraltar, should have had its destination changed to a much warmer climate, because the electrical conductivity of gutta percha was greatly increased, or its insulation was impaired by heat. For warm latitudes, a less fusible material than gutta percha was preferable for the insulator.
He believed he might claim some credit to himself for the testing instrument described by the Author. The ultimate principle of the instrument was by no means new, but the adaptation of it was his own; the Author, however, had paid more attention to the subject than himself; and had produced a useful and valuable instrument.
With respect to the paying out of cables, he would allude to a circumstance that repeatedly came under his notice. The captains of the vessels so employed, often steered direct from one point to another, being merely desirous of making the quickest passage, without reference to the position in which the cable should be laid. A vessel sailing direct from east to west, and encountering several tides, would deposit the cable in a number of zigzags. Such, for example, was the case between Dunwich and Zandvoort, on the coast of Holland; more cable being used, than was fairly required for the distance. Captains were, generally, so well satisfied with their own practical knowledge, that they often regarded the suggestions of landsmen, as an ignorant interference. But it was important to draw their attention to this fact, for by such steering, they not only wasted the cable, but they rendered it difficult, afterwards, to ascertain its position when repairs were required.
Mr. BIDDER,—President,—said, that the discussion had taken a wide, a general, and a very important bearing. At the present moment, telegraphic communication with India was entirely an open question; all attempts to maintain it effectually having, hitherto, failed. It had also been announced, during the discussion, that the cable designed to be laid down from Rangoon to Singapore had exhibited evidences of spontaneous heating, as to the cause of which, discrepant opinions were entertained by scientific men. Mr. Siemens, (M. Inst. C.E.,) to whose energy and research into this subject it was difficult to do justice, had given one theory upon the subject, whilst Dr. Miller had propounded another. It had been ascertained, however, that the core of that cable was at a much higher temperature than the external covering.
When such new and unexpected phenomena were presenting themselves, it became a most serious question, whether the country ought to continue to make such large sacrifices, in attempting to establish telegraphic communication with the extreme points of the empire, in the present state of information and experience upon the subject of submarine telegraphy, of which the importance could scarcely be over-rated. Money should not be spared in establishing telegraphic communications, if they could be thoroughly depended upon; but when £500,000 had been uselessly spent in one case, and £800,000 in another, in laying down a cable which had never carried a single message, and when a large additional sum was expended in unavailing attempts to render these cables useful, the greatest disappointment was, no doubt, occasioned to the public, and indeed, to the whole world. He would suggest, therefore, that the discussion should be directed to the consideration of what was best to be done under existing circumstances; and whether it was advisable to send to a distant part of the empire, a cable in such a condition as that which had been alluded to.
An undertaking of this kind should be regarded in the same light, as the initiation of a railway between the Land’s End and the Metropolis. In his opinion, preliminary steps should be taken to establish telegraphic communication between London and Alexandria, or some point on the Asiatic coast, and at the same time to examine whether it could not be also effected onwards by land, and to what extent it was possible to subsidise the Arab Sheikhs, so as to insure communication with India by two routes; the land route would, no doubt, be more economical in first cost, and still more so, in maintenance. Another important question to be considered, was the manner in which these telegraphic communications could be best established; whether by subsidising an intermediate company, like the Red Sea Company; or whether the Government itself should enter into a direct contract with men of character and responsibility, and if so, what should be the proper conditions, which would render the interests of the Contractors, coincident with those of the Government.
|* Mr. May, the Resident Engineer of the Harbour Works at Alderney, writes under date of August, 1860, that the position of the rock “is laid down on the chart published by the Admiralty, and is one of the shoals drawn on the contract plan for the works for the purpose of being blown up.” This contract plan was signed 3rd February, 1860, and the vessel did not touch on the rock until August of that year.|
It would, however, appear, that submarine telegraphs were not only liable to accidents from physical causes, but to others arising from moral causes. In a cable lately submersed by the Electric and International Telegraph Company, one wire out of four, was entirely lost, and £4,000 or £5,000 had been expended in attempting to rectify the fault. On examination, it was found, that a nail had been skilfully inserted into the cable connecting the external covering with the conducting wires in the core. The Directors of the Company had come to the determination of paying half the expenses of a prosecution; but he had suggested, that a reward of £1,000, would more effectually lead to the discovery of the perpetrator of such an infamous act, and, no doubt, legal proceedings could be adopted.*
* Vide “Guildhall, February 20th and 21st, 1861. Before Chief Justice Erie and a special jury. Glass v. Boswell. Transcript of Messrs. Cooks’ short-hand notes.” 8vo. London: Waterlow and Sons.
Mr. MARSHMAN said, the inference which would naturally be drawn from the observations of Mr. Latimer Clark was, that a public company had expended a large sum of money, intrusted to them by the Government, in the construction and laying down of a cable, which they themselves, through their Secretary, acknowledged would not last more than about two years. Such an impression must be very injurious to the character of any public body, and it was his present object to remove that imputation. In a letter addressed to him, by Mr. Peel, the Secretary of the Red Sea Company, he stated, that his observations must have been entirely misunderstood, on the occasion referred to, and that they were never intended to bear the interpretation which had been put upon them. He “certainly was, at that time, under the impression, that if a cable had been once successfully laid in deep water, it was a matter of secondary importance, whether the outer covering lasted, or not, but he should never have presumed to offer an opinion, as to the probable durability of any form of submarine cable.”
In addition to these remarks of the Secretary, he would observe, that the question of the proper form of submarine telegraph cable to be adopted for this line, was a subject of long and intense solicitude to the Directors of the Company; that, in accordance with the request of the Treasury, the Board sought the opinions of some of the most eminent scientific authorities in London, to whom a specimen of the proposed cable was submitted, and who generally concurred in the propriety of adopting it; and further, that on no occasion, did these gentlemen dissuade the Directors from using a cable covered with iron wire.
The advice of the late Mr. Robert Stephenson was also desired by the Board; but he declined to give a written opinion, on the ground, that the question did not exactly lie within his sphere of practice. At a personal interview, however, not of a business, or professional character, Mr. Stephenson said, that a light cable simply covered with hemp, was, probably, the form which would, ultimately, be generally adopted, and that wire-covered cables would only, hereafter, be found in the British Museum as antique curiosities; but as sufficient experience had not been gained as to the durability of the hempen cable, he could not recommend its adoption either to the Board, or to the Government, for this telegraph line; that the wire cable which had been recommended to the Board, and which was submitted to his inspection, was as good as any manufactured, at the present early stage of submarine telegraphy. He believed, that Mr. Robert Stephenson had also expressed himself in similar terms to the ex-officio Director of the Company, Mr. Stephenson, of the Treasury. Fortified by this and other opinions, the Board no longer hesitated to adopt that form of cable, covered with wire, which had been laid down in the Red Sea.
Mr. Marshman, in reply to a question from the President, as to whether any messages had been transmitted through the whole length of the cable, said, that pending the action which had been brought by the Contractors against the Company, he must abstain from discussing that point.
Mr. F.C. WEBB, before addressing himself to the subject of the Paper, would refer to the so-called ‘unknown’ rock, in Alderney Harbour. Whether that rock was shown in the surveys published by the Admiralty, he could not say; but he could state that, thirteen years ago, be surveyed that harbour himself, and the rock on which the frigate struck, was shown upon the chart, which he now exhibited, on a scale of 3 chains to the inch. The rock, he was informed, was perfectly well known to all who were acquainted with the harbour, and it was laid down upon some of the oldest charts. It might be argued, that such a rock ought not to exist in a large harbour, but it would be difficult to construct a harbour at Alderney, without some rocks in it; all that could be done, was to lay them down in the survey as accurately as possible.
With regard to submarine cables, he thought their maintenance had been greatly neglected, in most of the later and larger undertakings. The theory, that a submarine cable once laid successfully, would last indefinitely, had been, in general, acted upon too blindly. From his own experience, he considered, that this was a most dangerous principle upon which to act, in designing and constructing cables, and that, on the contrary, the more the Engineer regarded the probability of early failure, the greater would be the durability of the cable, because precautions would be taken to enable it to be easily repaired. On many lines, it had been the practice to select a small description of cable, and then a contract was entered into for making it, laying it down, and working it for a week, or a month. Upon the failure of the cable, difficulties were started about the depth at which it was laid, the size of the cable, the tightness with which it was payed out, and many other points which should have been considered beforehand.
In selecting the route, the facility for repairing should be the first consideration, and although in deep water, a well-chosen cable might last for a long time, if perfectly laid, yet he thought, that deep water should be avoided where possible, even if a considerable détour had to be made. In a depth of 100 fathoms, a cable was, in most localities, beyond the reach of attrition, and it was as little likely to be injured, as when laid at a depth of 200 fathoms, or 300 fathoms; whilst it could be repaired almost as easily, as if it lay in water only 30 fathoms, or 40 fathoms deep. The nature of the bottom should also be considered, as where rough ground and rocks existed, the cable could not be easily grappled. To ascertain this correctly, the mere arming of the lead was not sufficient, as it only brought up a small portion of the surface material, which could give no information as to the presence of rocks, mud, or sand at the bottom; a mushroom anchor, which would bring up a bucketful of the surface material, and occasionally, deep-pronged grapnels, ought to be employed.
The line should be divided into short sections, of about 100 miles in length; for although it might be possible to ‘work’ through 500 miles, or 1,000 miles, yet when one section was damaged, the consequences were more serious. Considerable portions of the Red Sea and Indian telegraph cables might have been laid, where they could easily have been grappled, and lifted for repairs; and in the line from Suez to India, there would not have been any difficulty in dividing it into sections of 50 miles each, throughout nearly the whole distance, except in crossing the Gulf of Oman, where a section of 120 miles would be required. He thought that, in the later lines, the strength of the cable had been much neglected. In the earlier cables, the aim was to make each stronger than its predecessor, but of late, the object appeared to be to construct them lighter, the question of maintenance being altogether disregarded. As long as a cable could be laid down, and a few messages transmitted, that was considered sufficient to meet the interests of all who had a voice in the management. In some cases it had happened, that the company owning the line, did not actually know where their cable was laid, having no plan of its course. In crossing the Atlantic, it was impossible to choose a Rue that could be maintained by yearly repairs; but between England and India, a line could and should be chosen, on which a cable of suitable proportions and construction might be properly maintained, at a moderate yearly outlay.
MR. LATIMER CLARK would be extremely sorry, if he had been the means of conveying an impression, that the Red Sea and India Telegraph Company had manufactured and laid down a cable, which they believed, at the time, would not last. His object, in alluding to the conversation in question, was not to give the opinions of the Secretary, but to show what his own opinions were at that period. He was fully satisfied, that the Directors believed in the excellence of the cable they had selected, but so many instances had already occurred at that time, of the oxidation of the iron covering of cables, and their decay was so much a matter of notoriety, that provision ought to have been made to protect the iron from the destructive action of the sea water. With respect to the other cable alluded to, that must, eventually, be also destroyed, for it was not galvanised, and being covered with light wires, it was not calculated to last in salt water. He had forgotten to mention one point of interest connected with the cable between England and Holland. At one part, near the English shore, and at another on the opposite coast, seven of the small cables were found twisted together into one mass, which did not exhibit any symptoms of rust; whereas the single cables, lying under precisely the same conditions, rapidly oxidised. He might also state, that the thicker wire of the larger cables generally oxidized much less quickly, than the wires of the smaller and lighter cables.
Sir CHARLES BRIGHT was not able to follow the course of discussion suggested by the President, with respect to the Rangoon cable, and the way in which, under the present unfortunate circumstances, it could be best turned to account, because he was not in possession of any official information as to the details of the case, and he could speak only from rumour. He would, therefore, deal with the original subject of the Paper, the maintenance and durability of shoal-water cables. This question, in so far as it concerned the relative proportions of submarine cables for different depths of water, had already been brought under the notice of the Institution, in 1858, by the Paper of Messrs. Longridge, (M. Inst. C.E.,) and Brooks,* which was principally devoted to a mathematical consideration of the requirements and conditions of deep-sea cables, and recommended the lightest possible form of cable for such lines.
After a long discussion upon the subject, he retained the same opinion he had held before, that although, as a matter of theory, the lightest possible form of cable might appear most desirable for deep water, yet in practice, unless a certain amount of weight was put into the cable, so as to cause it to reach the hollow before the paying-out ship was too far distant, and to accommodate itself to the irregularities of the bed on which it was laid, no deep sea-cable could be durable. A hemp-covered cable had been suggested, but even supposing the objection which he had mentioned to be disposed of, he did not yet see his way to the manufacture of a good cable of this class, which would get rid of the difficulty of the pressure of the water causing the fibres of the material to contract, and thereby, to influence the gutta-percha core, which would not be affected in the same manner. The cable which he had recommended to Government for the Falmouth and Gibraltar line, possessed many advantageous features. He did not, however, wish to be understood as expressing his approval of the Rangoon and Singapore cable, which had the core of the proposed Falmouth line, but which he did not consider well adapted to the depth and bottom of the route, over which it was to be laid.
* Vide Minutes of Proceedings Inst, C.E., vol. xvii., p. 221.
The immediate question before the Meeting was the durability and maintenance of cables in shoal water. As was also the case in deep-sea lines, there were two schools, as it were, of Engineers, holding opposite opinions in regard to shoal-water cables, one advocating and adopting comparatively light cables, the other making them as heavy as possible. On considering the numerous calamities which had befallen the lines of the Channel Islands Company, as shown in Table I., which presented records of eleven fractures within a very short period of time, it required no lengthy argument from him to prove which was right, and that cables of that class could not be suitable for shoal water.
It might be useful to refer very briefly to the early history of submarine telegraphy. The first submarine cable of any length, was the Dover and Calais line, which was laid in 1851, by Mr.Crampton, (M. Inst. C.E.,) for the Submarine Telegraph Company. This was followed by the Dover and Ostend, and the Magnetic Company’s lines to Ireland, and other strong cables, all of which contained several conducting wires covered with a thick serving of hemp, and protected by massive iron wires of large gauge. Those cables had been singularly fortunate. It was true, that some of them had been injured by ships’ anchors, but such occurrences were rare, their great strength protecting them from harm from any but large vessels; but they had never suffered from some of the causes enumerated in Table I., such as ‘abrasion,’ or being ‘washed away by the sea.’
The new system of laying light cables in shoal water, from which the Channel Islands Company was suffering so grievously, was first adopted by the Electric Company in their lines from Orfordness to the Hague, where, instead of laying one strong and heavy iron cable, four comparatively light cables, each with one conductor only, were laid across the North Sea, on the principle, that the chances were against all the four being broken down at the same time. That system which had also been adopted between Dublin and Holyhead, had been, however, far from satisfactory, the annual cost for repairs having amounted, during several years, to from £10,000 to £12,000, and the Company had been, finally, compelled to lay a heavy cable from Dunwich to Zandvoort, in Holland, the working of which had been very successful. The same error which had proved so fatal to the Channel Islands line, had been pursued on the Red Sea line, where the cable was laid, to a great extent, in shoal water. With these exceptions, however, all the shoal-water lines which he then remembered, had been laid with strong cables, and there were many in existence in different parts of the world, which had only required the most trifling expenditure for repairs, since the date of their submersion.
He had himself had very little experience in repairing submarine cables, for although he had several important cables for some years under his charge, they had cost nothing whatever for repairs up to that date. In two cases, they were necessarily laid on a rocky bottom, and were subject to the action of strong currents, but they were heavy cables of great strength, laid with sufficient slack to meet any irregularities in the bed of the sea He might also instance the heavy cables laid in 1854, between Spezia and Corsica, and across the Straits of Bonifacio, passing over depths of between 700 fathoms and 800 fathoms of water, crossing several reefs, and being also laid in shoal water for some distance; yet these cables had worked well and continuously.
The line laid by Messrs. Glass and Elliott for the Submarine Company, from St. Catherine’s in Jersey, to Pirhou on the coast of Normandy, (Fig. 1,) although not very much larger in dimensions, than the Channel Islands Company’s cable, had from some cause, or other, been more successful, for it had never given any trouble since it was laid; while during the same period, the other line had suffered no less than six of the interruptions recorded in the Paper. Whether this was owing to the manner in which the two lines were laid, he was unable to say, but he was on board during the laying of the Normandy line, and the operation was effected with great care. He did not, of course, mean it to be inferred, that any of the cables of which be had spoken, would have given satisfactory results, had they been improperly laid; but he thought there was sufficient reason for concluding, that the casualties which had occurred, could not be considered as inherent, of necessity, in shoal-water cables. It was evident, that the cables themselves were not suited to the work, and he thought, that a continual recurrence of the disastrous fractures, could be easily prevented by proper means.
The Paper had treated, principally, of the various arrangements devised for testing, from the shore, the position of faults in submarine cables, and he thought it would be interesting to those who, from want of experience in telegraphic experiments, were unable to follow the technicalities of the formula which had been given, to explain, in simple language, the principles involved in the first plan proposed for the purpose, by his Brother and himself, in 1852, shortly after the laying of the first cable. An electric current having the choice of two routes, would pass by that which was shortest, or which offered the least resistance, being divided proportionately, according to the conditions of the circuits. The power of artificially representing, by coils of fine wire, the resistance of a much greater length of wire of the larger section used for telegraphic purposes, was also well understood. A submarine, or underground conductor, which was fractured, or defective in its insulating covering, would be connected to the earth at the point of defect, by the sea in the one case, and by the humidity of the ground in the other.
If now, a battery was connected by one pole to earth, and by the other to one side of a galvanometer, the other side of which was connected to the defective conductor, and also to another galvanometer, (or to the other coil of a differential galvanometer), the other side of which was connected to a coil, or series of coils, of fine wire, the end of which was connected to earth; then by adding coils of fine wire to the series, until the current divided itself equally through the two galvanometer coils, the length of the conductor between the testing place and the fault might be calculated, by allowing for the resistance offered by the fault itself to the full and perfect passage of the current, which was determined by a different process. The connection to earth was an important feature of the arrangement, and with this and some other modifications, Professor Wheatstone’s ingenious instruments for determining the resistance of various bodies might be turned to similar account In fact, all the processes which had been mentioned in the Paper and in the discussion, had been modifications of the system of using resistance coils in connection with the earth, with more, or less of Professor Wheatstone’s appliances engrafted upon it. He was, therefore, somewhat at a loss to understand the many claims put forward for the first invention of various parts of the system, which had been an established fact before the claimants had much experience in telegraphy, and certainly, none in submarine telegraphs.
Sir Charles Bright, in reply to a question from the President, said, that for the Rangoon and Singapore line, he should have recommended a cable well protected from oxidation, and stronger than the one about to be laid down.
Mr. C.W. SIEMENS, in answer to a question from the President, replied, that the testing of the cable had been continued on board the Queen Victoria, with results confirming his previous statements. Unless the cable was effectually cooled by pumping cold water over it daily, the heat increased at the rate of about 3° Farenheit per day. Considering that the weight of cable on board that vessel amounted to more than 1,000 tons, it was evident, that the amount of heat generated daily was considerable, and that very effective measures would have to be adopted, if it was to reach its destination in safety.
Mr. FORDE said, that although the Chairman of the Red Sea Telegraph Company had stated reasons, for not discussing certain points connected with that enterprise, there were some facts relative to which no concealment need be observed. The fine was divided into six sections, three of which were in the Red Sea. The first was from Suez to Cossire, 255 knots; the second was from Cossire to Suakin, 474 knots; and the third was from Suakin to Aden, 630 knots; in all, 1,359 knots of direct distance, between Suez and Aden. From Aden to the Kooria Mooria Islands the distance was 717 knots; from the Kooria Mooria Islands to Muscat, 486 knots; and from Muscat to Kurrachee, 481 knots: in all 1,684 knots between Aden and Kurrachee. The whole length of the Red Sea and Indian line was thus 3,043 knots. Messages had been transmitted between Aden and Suez, during a period of about nine months, and separate sections of this portion of the line had been worked during eighteen months.
He was precluded from discussing the causes of the failure of the line, but considering the number of stoppages that had occurred in the cables crossing the Channel, from breakage, or imperfect insulation, he thought the Red Sea cable presented a favourable comparison. He was bound to say, that before the Company adopted the cable recommended by Mr. Lionel Gisborne, (Assoc. Inst. C.E.,) and himself, the Directors consulted Mr. Edwin Clark, (M. Inst. C.E.,) Mr. Cromwell Varley, and Mr. Henley, none of whom, at that time, condemned the iron cable. Some, indeed, proposed a thicker outside wire, whilst others, on the contrary, considered it ample, or even more than sufficient. This cable had been under- run and examined for many hundred miles; and it was not found to be corroded to the extent which had been imagined. The report stated, that after one year’s submersion, the strength of the cable had not, as a general rule, been diminished from that cause, more than one-tenth. The Directors of the Company, whose officers superintended the manufacture and the laying of the cables, were now endeavouring to throw the entire risk upon the Contractors.
With regard to the Rangoon cable, he, in conjunction with Mr. Lionel Gisborne, was intrusted by the Government with that undertaking. The cable was originally intended to have been laid from Falmouth to Gibraltar, and was, therefore, essentially designed for deep water. After mature deliberation and a series of teats, an outer covering of hemp and steel, was recommended for the deepest portion of the sea. This form he had found to possess greater tensile strength, in proportion to its weight in water, than any other cables he had tested, and it also had, in his opinion, sufficient weight to sink and to accommodate itself to the inequalities of the bottom. That class of cable had received the approval of Sir Charles Bright and of the late Mr. Robert Stephenson. The destination of this cable was afterwards changed to Rangoon and Singapore, but the iron-covered portion of it, which had been designed for depths not exceeding 600 fathoms, had then been in part manufactured, and could not be altered; however, as the whole cable was iron-covered, and the main portion of the line was removed from any anchorage ground, he thought that, upon the whole, it was well suited for its destination.
The shore ends were thick and heavy, and the precaution was always taken to lay them at a great distance from land, in two instances as much as 50 knots, and when the line approached a spot in which ships were likely to anchor, a thick cable was inserted. The tensile strength of the cable was great, and the iron was not so thin as had been represented. For great distances, however, a comparatively light cable must, necessarily, be employed, for it would be too expensive, in order to avoid occasional injuries, to lay down a cable weighing from 6 tons to 8 tons per knot, through the whole distance of 3,500 miles. Had that system been adopted with the Red Sea cable, it would have increased the cost to four times the amount.
The line from Toulon to Algiers, had also been intrusted to them by the French Government, and the cable was made exactly upon the same principle as that already described, for the deep-sea portion of the original Gibraltar line. He was not present when it was laid, but he understood, that it payed out with great ease and with little strain; and on one occasion, when a ‘kink’ occurred, the cable was hauled back for three miles, out of water 1,600 fathoms deep. He ventured to say, that such an operation. could not be effected upon any other cable, hitherto laid, with as much facility, or without great risk of fracture.
Of all the systems adopted for testing cables, he thought that of Messrs. Siemens was the best, and was the only one which gave a true description of the cable, for all the figures, when reduced to a certain standard, represented the state of every portion of the cable. It would, probably, save the Rangoon cable from arriving at its destination, in a condition unfit to be laid, and it was to be feared, that other cables had materially suffered by not having been properly tested. There was no reason, however, to believe, that the Rangoon cable had suffered the slightest injury.
In answer to questions from the President, Mr. Forde said, be was present during the laying of the cable between Aden and Kurrachee, but, he must decline stating how far he and his agents were allowed to interfere, or whether the cable was loosely, or tightly laid, and under what strain. He had worked the line, by means of translation, from Aden to Kurrachee, at very good speed, but the whole distance from Suez to Kurrachee had not, to his knowledge, been worked throughout.
Mr. FREDERICK BRAITHWAITE said, having been engaged in the inspection of a cable, 240 miles in length, for the Government of Tasmania, he had come to the conclusion, that so long as the cable was covered with wire, whether light, or heavy, its durability was only a question of time. It would be in the recollection of many, that the portions of the Atlantic cable which had been protected from the action of the sea water, came up as bright and as perfect as when they were laid down, whilst iron cables of large dimensions, had been totally destroyed by the action of the salt water. He was sorry so little attention had been paid to the testing of cables under water, previously to laying them.
In the case of the Tasmanian cable, Mr. Latimer Clark directed, that it should be submerged as soon as possible after it left the reel, and a tank was provided for that purpose. One day, a fault was detected, and on tracing back, it was discovered to be in a portion of the cable which had been made four days previously; showing the great probability, that the fault would not have been detected, without submersion. He ordered diagrams, with accompanying tables, to be made, showing the temperature of the water, night and day, and also the effect of the working of the cable so submersed. But with all these precautions, he was afraid, from its having been covered with unprotected iron wire, that it had already shared the fate of other cables similarly constructed. So long as Engineers were not agreed upon any one single point relative to the construction of cables, little progress could be hoped for in submarine telegraphy.
Dr. WALLICH believed, that there were no obstacles in laying down cables, which could not be overcome by the engineering science of the age; but he would draw attention to the very imperfect manner, in which surveys of the bottom of the sea had, been conducted. In no single instance, had there been a survey of a character sufficiently complete to render the submerging of a cable a safe operation, or to afford data whereby it was possible to ascertain, with any degree of accuracy, the nature of the bottom, throughout any given line. It was almost needless to state, that in these undertakings, instead of determining by survey the most eligible route, its selection had often been made the preliminary measure. In one instance, the Engineer had actually arrived with the cable, at the scene of operations, before he was made acquainted with the nature of the bottom on which it was to be laid.
It was customary, in surveying shallow portions of the sea, to take soundings at moderate intervals, and as deep water was approached, those intervals were extended. In an examination of the records of surveys, he found, that in deep water, the mean interval of the soundings was twenty miles, and, therefore, the elevations and depressions by which the contour line of the bottom was estimated, depended upon observations, taken at those intervals. Now on the Valentia side of the Atlantic, a dip of 7,200 feet had been ascertained to exist in ten miles, or at the rate of 720 feet per mile, and near the east coast of Greenland there was another dip of 3,468 feet in three miles and a half, which was at the rate of 1,000 feet per mile. It was evident, that in these instances, unless soundings were closely continued in one, or both directions, very inaccurate estimates of the true extent of the dips might be arrived at.
Thus in the proposed line from England to Labrador, there would be no certainty, that the excess of depth,—400 fathoms,—asserted as occurring in the mid-Atlantic route, might not be surpassed. He did not believe, that great depth alone would endanger the safety of a cable: for the greater the depth, the less would be the amount of animal life and the changes of level. The recent examination of the North Atlantic line showed that, near Iceland, there was a series of abrupt elevations and depressions at short intervals, producing a saw-like disposition of the surface, which was composed of volcanic rock that never lost its abrasive character, or the angularity of its particles. In the operation of sounding, much depended upon the apparatus; in the survey of the ‘Bull-dog,’ some new forms of sounding apparatus had been employed which surpassed in efficacy those previously in use.
In answer to questions by the President, Dr. Wallich stated, that he was present at the survey between England and Labrador, which happened to have been made during an exceptional season, in which no cable could have been laid off Greenland; otherwise, he had not observed any difficulties, which might not be surmounted by engineering skill. The possibility of laying a cable by that route, entirely depended on the accident of weather. The survey which had been made, indicated the necessity for a more perfect and close series of soundings, especially near the coast of Iceland, than those taken from on board the ‘Bull-dog.’ However efficient the old system might be for navigation, it was almost useless for the purposes of submarine telegraphy.
Mr. WEST observed, that gutta percha had, hitherto, been considered the sole material for insulation; but recent experiments undertaken by the Government had shown, that india rubber possessed high insulating power with extraordinary low specific inductive capacity, great flexibility, and elasticity. There was, however, one point which the Government experiments could not, and which time only could test its durability. As a proof of its qualifications in this respect, Mr. West exhibited a specimen of wire insulated with india rubber, which had been used, experimentally, between H.M.S. ‘Pique’ and ‘Blake,’ in the year 1845, and across Portsmouth Harbour, in the following year; also, a large coil of wire so insulated. In these cases, the India rubber had remained perfectly durable and hard, while the rope yarn, which had been well saturated with tar, over which these insulated wires had been laid, had become decomposed; the tar had disappeared, and the rope yarn had lost its tenacity and had become rotten.
He was of opinion, that the failures of the Atlantic, of the Red Sea, and of the Rangoon cables, were attributable to their want of proper insulation. It was well known, that from the porosity of gutta percha, which admitted a slow transudation of fluids through its mass, chemists could not use it, when made into bottles, or other vessels, for the purposes of holding their chemical fluids. It became, therefore, a question for serious consideration, whether more caution ought not to have been used, before this material was selected by those who were intrusted with the management of these cables, at an expenditure of more than £1,000,000 of the public money.
Mr. SAWARD remarked, that the discussion appeared to have diverged from the original question of the causes of failure in submarine telegraph cables. It would seem to have escaped notice, that there already existed no less than about thirty separate undertakings in submarine telegraphy, owning, in the aggregate, about three thousand miles of cable, a large proportion of which had been completed and at work during many years; and some of which, though more recent, had been successfully laid in deep water. These cables had, hitherto, remained in almost perfect working order, having cost an inconsiderable percentage in maintenance, since submersion; and it was remarkable, that all of them, except about one hundred miles, had been made and laid by one manufacturer. Some of these cables appeared to him to afford a fair basis for reasoning upon the causes of failure, at least in shallow water, and he would afterwards glance, separately, at the failures which had taken place in deep-sea cables.-
The first successful cable was that between Dover and Calais, which was laid in 1851. It was strongly constructed, and it was protected with thick iron wires of the best quality; and, having been so successful, it might have been taken as a model for future cables in shallow waters. It was so considered by some Electrical Engineers, and the cables they had designed had also been successful, as for instance, those between Portpatrick and Donaghadee, between Portpatrick and Carrickfergus, and between Dover and Ostend. But a desire of originality and of innovation upon established practice was soon evinced, in the first cable laid between Holyhead and Dublin. That cable was made on his own private account, by an eminent Contractor, who, moreover, was at the very time, under contract to a public company, to make and lay a large cable between Portpatrick and Donaghadee, to which, if successful, his own would have proved a serious rival. This cable, however, which was very slender, lasted only about twenty-four hours after submersion.
Then followed the Irish lines of the International Telegraph Company, and the galvanised iron cable from Orfordness to the Hague, all cables of small dimensions and of limited strength, the failures of which seemed to establish the fact, that these changes in the character of cables had been made, without due regard to the risks of breakage, from anchorage and other causes. He was glad to find, that in the last cable of the Electric Telegraph Company, they had returned to the old model; and he was convinced, that if that were adopted for the Irish, and for the Channel Islands cables, the failures would become exceedingly rare. He considered, that in shallow waters, the thickness and strength of the cable ought to be limited only by the power of the machinery to lay it, and the ability of the projectors to pay for it. He would further observe, that for cables in the seas around Great Britain, additional security might be obtained, by careful surveys of the bottom, with the view of selecting the most suitable places for depositing them. He would also suggest, that the best iron only should be used for the exterior covering, as wire varied considerably, according to its quality, in the time required for its oxidation. This became an important consideration in shallow waters, where the cables had, occasionally, to be lifted on account of damage.
In deep-sea cables, there had, unfortunately, been little else than failures, the causes of which were apparent, and which fell, perhaps, rather within the scope of the moralist and the man of the world, than of the man of science. The details of the Atlantic cable were arranged before anything was practically known about deep-sea cables; the route was sounded and examined, even more than, in those days, was thought necessary, or had been the practice; the cable itself, was designed upon the last and most enlightened principles of that time; and if such a cable were constructed under proper supervision, he believed it could be laid, even at the present day, with facility, and with a probability of lasting success, although the conductor, owing to its small size, would never have worked with the rapidity that could now be easily attained.
But a great mistake was made from the first, in the mode of organising the undertaking; there was a Provisional Committee, consisting chiefly of the promoters and expectants of office under the Company, and these not only decided upon the form of cable, but they entered into and completed the conditions of the contracts for making it. The contracts were given to two rival manufacturers, at the very time in litigation with each other, one-half of the cable being made in London, and the other half in Birkenhead. The result had been, jealousy, carelessness, shifting of responsibility, want of supervision, and impossibility of properly testing the cable; and the final catastrophe might easily have been predicted from such a commencement. The abnormal forms under which portions of the cable, examined since the cessation of working, had been found, afforded sufficient proof of the correctness of his assertions. The radical fault, no doubt, was the precipitate manner in which the contracts were let, whereby the Board of Directors, subsequently appointed, were precluded from appropriating any portion of the funds of the Company towards preliminary practical experiments, or from exercising that control over the proceedings, which would, otherwise, necessarily have occurred to them. Nor could they even postpone the laying of the cable, without breaking faith with the shareholders and the public; for the promoters were also the persons who had raised the capital, and they had pledged themselves to make the attempt in 1857.
The Red Sea cable was another instance in which a disastrous waste of money had its origin, in other causes than scientific difficulties. After the concession had been purchased, and a liberal arrangement had been made with the Company by the British Government, which should have rendered the property very valuable, it was found that, owing to certain complications, the Directors had also acquired an Engineer and a Contractor, who had secured all the concessions that could be obtained in Constantinople; that, practically, the form of the cable was already decided upon, and that little remained for the Board but to furnish the money. Although, at the instance of Lord Stanley, a specimen of the proposed cable was shown to several scientific authorities, this was not done, until its form had become a foregone conclusion, as the contract for its manufacture had already been entered into.
The Blue Book showed, that there had been previous dealings between the Engineer and the Contractor; the concession for an important of the route, that between Constantinople and Alexandria had been already sold to the Contractor for the Red Sea cable, and thus it was considered imperative to give the latter contract to Messrs. Newall and Co., at a higher price, as they alone could promise a direct through communication with England, by a stated time. The contract was wrong in principle, as it was taken for a certain fixed sum, limiting the length of the cable to 3,800 miles, thereby offering a premium upon the chances of saving some part of the slack, or surplus, cable. That fact, probably, more than the, unsuitable nature of the cable itself, had caused the failure, as there was reason to believe, that the fractures were occasioned by the tightness with which the cable was laid; and he had understood, that several attempts to repair it had been frustrated, from the same cause.
Having touched upon the chief points relative to the two principal deep-sea cables, he thought it unnecessary to examine into the causes of the failures in the Mediterranean and elsewhere. He hoped, that these observations would have the effect of leading men of eminence in scientific and mercantile pursuits, to the latter of whom these cables were of great consequence, to consider carefully the whole subject, and in so doing, they would satisfy themselves, that submarine telegraphy was not an enterprise involving so much risk as had been supposed, and that by careful and continued supervision, success might, in most cases, be obtained.
With regard to the Rangoon cable, he thought the core was the most perfect which had yet been made, and it was to be regretted, that a perilous experiment had been made upon so valuable a property. If the surrounding wires had been saturated with tar, as had always been the practice with former cables, he apprehended the heating could not have taken place. In the case of the Rangoon cable, however, every particle of tar was pressed out of the hemp, before it was wound round the core. When it had received its iron armour, it was placed in water, out of which it was subsequently taken, without passing the bright iron wires through tar, or any other mixture to prevent oxidation, and it was coiled up wet in the hold of the ship.
It might, possibly, have been imagined, that the dry yarn would prevent the tar from forming an insulator round the core, to such an extent as to conceal, temporarily, a fault in the gutta percha. If such was the case, the arrangement was, in that sense, to be approved of, proper precaution being used in other respects. He thought great and useful changes in the intervening covering between the core and the outer wires of cables, were likely to result from the experiments recently carried on by Mr. Willoughby Smith, at the Gutta-Percha Works. But if it had been deemed proper to leave the yarn dry, for testing purposes, this ought not to have prevented proper precautions being taken, for preserving the outside wires from oxidation; for to this oxidation and the consequent recall and detention of the ships, the subsequent disasters to the Rangoon cable were mainly to be traced.
In order to be able to compare the respective merits of india rubber and gutta percha, as insulating media, it would be necessary, that the qualifications of the former should first be tested, by laying down short lengths in the sea, and allowing them to remain there for two, or three years. The capabilities, as well as the defects of gutta percha, were fully known; portions of the original Dover and Calais cable had been brought to the surface, after nine years’ submersion, and they were found as perfect as when first laid down; indeed, the texture was closer than that of new material. On the other hand, the very imperfect trials that had, as yet, been made with india rubber, had not proved favourable; those, therefore, on whom rested the responsibility of advising the expenditure of large sums of money, could have no hesitation in giving the weight of their recommendation to the tried, rather than to the untried material, especially in carrying out a long line of cable.
Mr. FLEEMING JENKIN was present when the cable was laid between Alderney and Portland. The route, he was told by Mr. Newall, had been selected by the Government. He wished to be informed, whether the first fracture of the cable, described as due to the sand having been washed away, was supposed to have resulted from a strain upon the cable, or from the motion caused by the tide and waves; whether in the fourth fracture, (Table I.,) in the shore end, where the cable was much thicker and stronger, any signs of corrosion were visible; also what evidence there was, that after some of the wires had been worn through by abrasion, sufficient elasticity had remained in the cable to sever it. He believed the cable had been payed out with a strain of about 15 cwt.
The cable between the Island of Sardinia and the coast of Africa, belonging to the Mediterranean Company, was laid down in the year 1857. In 1858, it became necessary to repair it, and he accompanied Mr. Liddell, one of the partners of the firm of Messrs. Newall & Co., to the spot, for that purpose. A length of about 30 miles was picked up, from the Sardinian end, and it was again successfully replaced. Within the last few months, the cable having completely failed, he was employed by the Mediterranean Telegraph Company to repair it. Testing showed the existence of faults, about 40 miles from Sardinia, and also, that the cable was broken at about 5 miles off the African coast. On picking up the cable at the African shore, he found that the shore end was uninjured by corrosion, but as soon as the smaller portion of the cable was reached, it broke in the same depth of water, during the attempt to lift it. He then grappled beyond, and at last, he came to the original fracture, which he believed to have been caused by the trawls of the coral fishers, after the outer wires had been corroded. An extensive coral fishery existed on that part of the coast, and its grounds were crossed by the cable, showing the little care that was formerly taken in the selection of a route. Beyond this fracture, the cable was discovered to be again broken, at the distance of 2 miles. The whole of the smaller cable, near Africa, was corroded; it was covered with marine animals, and much coral was found deposited on it.*
The second fracture was due to corrosion and to the coral fishers, as in the previous instance. Beyond that point, the cable was so much corroded, that it broke during the operation of lifting, in 70 fathoms of water. The sea end, however, was found, and he ascertained from testing, that some of the wires were good, up to about 40 miles from Sardinia, but not the faintest signal was received. Sound cable was then laid to the African shore. He afterwards picked up the cable from the Sardinian end, and the first 39 miles were as sound as when it was first laid down; in some specimens, no rust whatever was apparent, and the section of the wire was not, in the least degree, altered. At this distance from the shore, there was a change in the nature of the bottom, evidenced by the different colour of the mud; and the wires were much corroded.
Shortly afterwards, the cable broke in a depth of 1,200 fathoms, at a distance of one mile from the spot, where the electrical tests showed, that the cable had previously broken. Thus the previous fracture, which had stopped the working of the cable, had occurred at the above depth, as the cable lay, apparently, undisturbed, but with the wires greatly corroded. This did not amount to a positive proof, that in deep water a cable must, necessarily, break, if the outer covering was corroded, but he thought it would be dangerous, after such a precedent, to lay down an unprotected iron- covered cable in deep water.
With those 40 miles of cable, much coral and many marine animals were brought up, but it did not appear, that their presence had injured the cable, for they were attached to the sound as well as to the corroded portions. Specimens of the rust from the cable had been submitted to analysis, which did not afford any evidence that the decomposition of the animal matter had led to the corrosion. There was corrosion near the African Boast, but none near the Sardinian coast, although rocks and animals were found near both. The cable, where it was uncorroded, had not been buried in mud, as was proved by the short, fine seaweed upon it.
The cable was covered with eighteen wires of No. 11 gauge, similar to that adopted for the Rangoon cable, but it appeared, that wire of that gauge was not a sufficient protection. The was ignorant of the cause of the fracture, in deep water, of the Bona cable, but he imagined it was due to the elasticity of the cable, which, having been laid too tight, severed the core after the decay of the outer covering. He had inquired what evidence there was of this having occurred in the Channel Islands cable, because he wished to apply to failures in deep water, the explanation which had been given by the Author, of the failures in shallow water.
The first remedy for these disasters appeared to be the employment, in shallow waters, of wire of a larger gauge. The evidence, that the thinner portion of the cables corroded, whilst the shore ends remained perfect, was in favour of that plan. An instance of the kind was afforded by the Spezia and Corsica cable, but perhaps, the ground crossed was favourable. The difficulty of paying out a cable of large wires from small drums, had been exaggerated, for be had payed out, with facility, a cable 11 inch in diameter, from a drum 6 feet in diameter. But for a long deep-sea cable, it was impossible to adopt heavy wire coverings, on account of the number of ships which would be required coverings, its conveyance.
A second remedy was to coat the external wires with some bituminous composition, which would not injure the gutta percha by heat when applied, and was not too expensive in its application. A third remedy which had been proposed, was to make careful soundings of the bottom, along the route where the cable was to be laid, but until the particular character of bottom which caused corrosion was better known, this remedy could not be relied on. A fourth possible remedy might be, the adoption of a light cable not covered with iron wire; because, although at the present time, the general feeling was in favour of heavy cables, in consequence of the failure of small iron-covered cables, there was no evidence to show, that cables quite unprotected by iron wire, would also fail. An unprotected cable would be free from the dangers arising from being laid too tight; for the weight and elasticity of the iron covering had been found to add to the insecurity, when, from any cause, some particular part was weakened. He would also remark, that there were no marks of abrasion on any portion of the cable between Africa and Sardinia, and that, therefore, to all appearance, an unprotected cable might have lasted uninjured in deep water.
* The following is a list (1-15,) of the marine animals attached to the cable:-
1. Salicornaria, one of the Polyzoa.
The failure of the Atlantic cable was due to defective supervision and imperfect construction, and even if it had succeeded in the first instance, it would, probably, have failed, after a short time, from corrosion; but possible failure from this cause, was not generally suspected at that period. The Malta and Corfu cable, of somewhat similar construction, lasted for eighteen months, and during the time it was in operation, the Red Sea cable was designed. The discussion upon the Paper by Messrs. Longridge and Brooks, in 1858, chiefly turned on the comparative merits of light and heavy cables: but corrosion, he believed, was not once mentioned, on that occasion, as a source of danger to cables. As a further proof, that men of experience did not, at that time, foresee the danger of corrosion, Messrs. Newall & Co., in the same year, 1858, made a cable for their own line in the Levant, of very similar construction to that used for the Red Sea. As the Levant lines belonged, principally, to Messrs. Newall & Co., and were worked by them, they, at least, must have believed that form of construction to be durable. It was, however, singular, that the Levant cable should have proved an exception to the general law of destruction. All the sections of that cable which were laid, still remained in working order; that is to say, the sections between the Dardanelles and Scio, between Scio and Candia, between Scio and Syra, between Scio and Smyrna, and between Syra and Athens; in all, about 600 miles.*
On the other hand, since 1858, many instances of corrosion had occurred in the Atlantic, in the Black Sea, in the Mediterranean, and in the Red Sea, and also near the English coasts. For these reasons, he believed, that it would be unwise to send a light iron-covered cable, such as the Rangoon cable, to a distant part of the world, without further protection. It had been shown, that cables of a somewhat similar description, had failed in deep water, after the corrosion of the outer wires; and in shallow water, there was still greater risk of failure, for it was difficult even to avoid the danger of laying it too tight. To lay it slack in 30 fathoms, or 50 fathoms of water, the tension required was so small, that it was scarcely sufficient to draw the cable out of the hold of the vessel; at all events, with the machinery to which he had been accustomed.
Passing to the electrical part of the Paper, Mr. Jenkin observed, that he preferred Wheatstone’s bridge, especially as arranged by Messrs. Siemens, Halske, & Co., to the instrument described by the Author. It was stated, that the charge was inversely proportional to the ratio of the external and internal diameters of the gutta-percha coating, but Mr. Jenkin believed the charge was inversely proportional to the logarithm of that ratio; neither did he consider, that the charge was proportional to the surface of the copper conductor. The reduction galvanometer of the Author assumed the battery power, and the magnetism of the needle, to be both constant; an hypothesis which could not be granted. Having observed the water current described in the Paper, he did not think, that where the resistance of the cable formed a large part of the circuit, the deflections given by the water current could be of much use in determining the distance of a fault, or the amount of copper exposed; the deflection produced, depended on two unknown quantities, the resistance of the circuit, and the electromotive force of the copper and iron voltaic couple at the fault.
* Several of these cables have since required repair.—F.J. March 1862.
He had frequently remarked the so-termed ‘gas currents,’ caused by what was commonly called polarisation, and he had also found. that these currents interfered with observations of the discharge, or return currents in short cables, and in longer cables when small battery power was used. Messrs. Siemens had pursued an independent investigation of the electrical phenomena connected with submarine cables, but having obtained their valuable results unaided, seemed not to be aware of what had already been done by others.
The practice of expressing the resistance of gutta percha by units of resistance, was introduced, in 1857, by Professor W. Thomson, at the British Association in Dublin, when he gave the specific resistance of gutta percha, with considerable. accuracy. At the suggestion of Professor Thomson, Mr. Jenkin tested the Red Sea cable in such a manner as to express its insulation, in terms of the resistance of the gutta percha, and in 1859, he communicated the result to the British Association, at Aberdeen,(1) giving a value to the specific resistance of gutta percha, which corresponded to a resistance per knot, of 94 millions of Messrs. Siemens’ units, at 60° Fahrenheit. He had published, at the same time, temperature curves derived from actual experiment upon various lengths of gutta percha, and he also mentioned the great influence of continued electrification which, he thought, had not been attended to in the system of Messrs. Siemens. Complete details of his experiments had been read at the Royal Society in 1860,(2) and the specific resistance of the gutta percha at 75°, then given, was equivalent to a resistance per knot, of 46 millions, after one minute’s electrification.
His measurements were not made with Wheatstone’s parallelogram, but by angular deflections. It had been asserted, that angular deflections would not give correct results; but if instruments of precision were employed, such as tangent, or sine galvanometers, and care was taken to measure the battery resistance and electro-motive force in each instance, then angular deflections might be used to determine the resistance of gutta percha, in units; and they formed, in some cases, the most convenient method of obtaining that resistance.
1. Vide “On Gutta Percha as an Insulator, at various Temperatures,” by Fleeming Jenkin; in the “ Report of the British Association,” 1859. Transactions of Sections, p. 248.
2. Vide “Proceedings of the Royal Society of London,” vol. x., p. 409.
It might be asked, if the Red Sea cable was so well tested, and if its insulation had been so accurately measured, attention being paid to variations in temperature and all other disturbing causes, why should faults have occurred in the cable, when it was laid down. The reason was simple: the cable had not been immersed in water during the tests. He had long been aware, that unless the cable was immersed, a fault could not be detected; but so far as the resistance of gutta percha, and the investigation of the qualities of that material were concerned, he had not found, that immersion was of consequence. If the cable was sound, and the temperature remained the same, the test of the gutta percha would be the same, before and after immersion. The reason the cable had not been immersed, was the fear of oxidation of the outer wires; but that was not a sufficient excuse for the omission, because the cable should have been so constructed, as not to be liable to injury from that cause; and to send abroad a cable which Electricians dared not properly test, seemed an act of folly.
With regard to the heating of the Rangoon cable, he had tested many cables which had been, alternately, in and out of water, some which had been picked up from the sea, and others which had been immersed at Messrs. Newall & Co.’s works, but, hitherto, he had never discovered any heating. He generally placed in the centre of the coils, thermometers in tubes, which would not have failed to detect heating, if it had occurred; and in cases where thermometers had not been used, the change in insulation, consequent on the change of temperature, would, certainly, have drawn his attention to this fact. He attributed the absence of heating in the cases alluded to, to the hemp having been saturated with tar, and each coil of cable having been well coated with it.
The insulation of the Rangoon cable, being 100 millions of Messrs. Siemens’ units per knot, was very high: the resistance of the Red Sea cable gave only 46 millions of units, at the same temperature. Now the ratio of the internal and external diameters of the gutta-percha covering was nearly the same in the Rangoon, and in the Red Sea cables; the Rangoon cable, therefore, tested, at the temperature of 75°, better than the Red Sea cable, by more than double. It would be desirable to know whether any portion of the Rangoon cable which had been overheated, had returned to its original condition, and whether the resistance, when it cooled down, was as high as it had been before the heating; because he had found, that gutta percha deteriorated, although not so much as to make it useless, within the limits of 1 and 10.
The gutta percha of the 40 miles of the Bona cable which he had lately picked up, was all sound, and there was no difference between the portions in deep and in shallow water. The specific resistance was not, however, so high as in cables, when recently made, although he had found that some cables, shortly after they were manufactured, would fall lower than others which had been three years under water. This variation rendered the testing of a cable a very delicate matter, unless the electrician had been well acquainted with the cable when it was first made.
With regard to the question of units, it was desirable to introduce a system which should be invariably adopted; but it was not a matter of indifference which units were chosen. Messrs. Siemens had taken an arbitrary length and a section of an arbitrary material; owing, however, to the judicious choice of the latter, this unit could easily be reproduced. But now that the relation between electricity and mechanical effect was understood, it was possible to express electrical values in units, depending directly upon the absolute units of force. Not only could electrical resistance be so expressed, but also the strength of a current, the electro-motive force of a battery, and the quantity of electricity. Units so chosen, did not depend upon an arbitrary assumption of some one quantity for unit, of the same nature as the thing to be measured, but upon the relation between the mechanical effect and the different forces. This system of units was first proposed in 1851, by Weber, in Germany, and shortly afterwards, Professor W. Thomson proposed its adoption in England. The absolute unit of resistance which he gave was such, that about 30 millions were equal to one of Messrs. Siemens’ units.
In answer to a question, Mr. Jenkin said, that in the large number of cables he had raised, he had never observed any electrical action between the copper wires and the gutta percha, to which the destruction of the cable might be attributed.
Mr. WILLOUGHBY SMITH said, that being anxious to elucidate the causes of failure in submarine cables, he had tried many experiments, from which he thought he should be able partly to account for several of the failures that had taken place.
In the first experiment, a length of core, having the conductor exposed in four different places, which were afterwards covered with hemp, saturated with Stockholm tar and tallow, so as to represent, as nearly as possible, the core of a cable after it had passed through the serving machine, was immersed in water, and the insulation remained perfect for three ’days, the test being frequently applied from a battery of 504 pairs of plates. This length was then joined to a line eight miles long, and again immersed. The line was kept charged from a battery of 504 elements, (the current being reversed 400 times each minute,) for a period of 468 hours, during which time the line was frequently tested for insulation, and some curious results were obtained, owing to the varying amount of resistance offered by the tarred yarn. The line had now been 172 hours uncharged, and when again tested, the defects offered so little resistance, that only 108 elements could be used.
In the second experiment, five nails, passing through the strand conductor, were forced through the gutta percha, in a length of core, which was then served with hemp, saturated with tar and tallow. This was immersed and remained perfect in insulation, for 168 hours, the same battery power and instrument being used as in the first experiment. At the expiration of 192 hours, the fault had become so bad, that were it to be charged with reversals for 24 hours from a strong battery, continuity would be destroyed.
In the third experiment, another length of core was prepared in the same manner, but the nails were withdrawn, previously to being served. This length had been immersed during 676 hours, yet the insulation was still perfect. These results clearly proved, that the failures of submarine cables, after working successfully for various periods, had not been caused by any deterioration of the gutta percha, but by the injuries to the core, which had been temporarily concealed by the tarred serving.
It had already been stated, that a fault was discovered in the Tasmanian cable, at a part which had only been manufactured four days previously; and he recollected an instance of a cable having been submerged, during six weeks, on the manufacturer’s premises, yet the fault was not detected till a few days before its final submersion. This danger might be obviated by saturating the serving with a conducting, instead of an insulating fluid, thus keeping the core constantly under an electrical test.
Serious apprehensions having been entertained, that the core of the Rangoon cable might be damaged by the heat generated on ship-board, he had made the following experiments, with a view to ascertain the degree of heat which would affect the core. A length of the same sized core as that of the Rangoon cable, was wound on an iron cylinder, 12 inches in diameter, and was immersed in water at 100° Fahrenheit, during two months; at the expiration of which time, it presented no signs of alteration. One nautical mile of the same sized core had also been immersed, at the same temperature, for 676 hours, and it was now as perfect in every respect as at first. Two lengths of a smaller-sized core had already been immersed at the same temperature, during 1,102 hours, the insulation tests being taken with a battery of 504 pairs of plates, and a very sensitive galvanometer. These lengths had not, as yet, shown any deterioration, but a gradual improvement in insulation no doubt need, therefore, be entertained of the Rangoon cable, so long as the temperature did not exceed 100° Fahrenheit. The increased resistance of gutta percha by long immersion, was also very remarkable at low temperatures.
Mr. EDWIN CLARK would not assert, that a heavier cable between England and Holland might not have possessed some advantages but the cables alluded to by Mr. Saward were, really, the first long cables that were attempted, and when they were laid down, there was little experience to guide the Engineer. The only cable previously in use was that between Dover and Calais: and it was then almost impossible to have laid down a cable of that weight, over a distance of 100 miles, even had it been thought desirable. He might state, that great difficulty was experienced in finding a steamer capable of carrying a cable weighing only 1¼ ton per mile, for it was not every vessel that was available for such purposes: this was not, however, the only motive for adopting four light cables, instead of one heavy one. It was considered, that as some risk attended the paying out of the cable, the loss of a single wire would not be so serious as the loss of the whole. It was also considered, that in a shallow sea where so many vessels were constantly passing, these cables would, in spite of every precaution, be liable to damage from anchors, while there were many chances against the whole of the four cables being simultaneously injured. These light cables were not only advantageous from the facility with which they could be laid down, but also from the ease with which they could be taken up, if required to be repaired, or renewed. The necessity of constant repair and renewal was always calculated upon, as an element in the first estimate of cost.
With respect to the electrical part of the subject, no difficulty existed with regard to the core; a good cable might be made either with gutta percha, or india rubber, as both might be relied upon. But laying down a cable was attended with many difficulties, which had great weight at the early period of their history. The repair and renewal, however, were the salient points which determined the size adopted, and it was still a question, whether any more economical method of insuring a constant communication, could be adopted. These cables had not failed from metallic corrosion: the wire was, even now, but little corroded. The only interruption to which they had been subject was caused, as had been foreseen, by damage from anchors, the cables being laid in a sea traversed by so many ships, and from their lightness, being frequently lifted out of the water. In some cases, the cable received no injury, but in others, it was either wilfully, or accidentally, much damaged, or broken.
The Hague cables, he believed, had never failed from any other cause; they had been as successful as any that had been laid down, and even now, they were working well. Although a larger cable had since been laid along- aide, it also had already been several times broken from the same cause, and the repair and renewal became a much more costly operation, while, at the same time, the whole communication was stopped, as all the wires were broken. On this account, especially, the maintenance of several small cables was cheaper than that of a single heavy cable; and a stock of small cable was always kept ready at either end. ’With a single line, the repair, or renewal, required but little time, and only simple apparatus; and no instance had occurred of the four cables being all simultaneously broken.
Mr. C. W. SIEMENS, in answer to the President, said that recently, the ‘Queen Victoria,’ which carried the Rangoon cable, had been wrecked, and the hold being filled with water, the cable was now cool. It was about to be transferred to other vessels, and he should again carefully watch it The temperature, at present, had descended to below 60°, and the insulation was very perfect His experience had not been the same as that of a previous speaker, for he had invariably found, that after a cable had been once heated, it never returned to the same perfect state of insulation as before; implying that some slight change had taken place in the constitution of the gutta percha, which had not, hitherto, been well ascertained. He would also observe, that less tar than usual had not been used in the Rangoon cable, for the sake of facility in testing; if it was made dryer than other cables, it was for a reason entirely unconnected with the department of the Electrician.
Mr. DAFT,—through the Secretary,—said, that during practical experience of many years, he had invariably found india rubber to decompose, when in its natural state, and in contact with brass, or copper, even when a coating of shellac had been interposed, and pressure added to exclude the air.
On the introduction of the process of vulcanising, about 1844, it was applied to washers for steam joints, and he had found it less disposed to decomposition than common, or pure India rubber; still, whenever it came in contact with copper, or brass, it was prejudicially acted upon. In 1848, he discovered the means of making vulcanised india rubber adhere to brass, and the process was applied with success. India rubber was not injuriously acted upon by a temperature under 300° Fahrenheit; it would withstand a great amount of rough usage, and as copper wire could easily be coated with brass, he believed there was no difficulty in making a cable with the conductor and insulating material, for which india rubber was so well calculated, in perfect unity.
He considered, that some improvement was necessary in the construction of vessels, charged with paying out extensive deep-sea cables. He thought the best form to adopt, would be what he had designated a ’twin ship,’ with great length and beam, and with the same angle at the bottom, at stem and stern, which would insure a high rate of speed. A part of the deck between-ships, could be made moveable, to fall from one end and hang aft, at an angle suitable for running out the cable, and if hung on centres at the forward end, the stern end could be lowered by suitable machinery to the water’s edge, or even below it, thus forming a gangway for the entrance, or paying out of the cable. Such a vessel could take in cables, or other cargo from the shore, or be beeched in places, to approach which, would be fatal to other vessels, and it would allow of the cable being payed out with steadiness and safety in any weather.
Mr. W. H. PREECE remarked, that many facts yet remained to be elicited, before the causes of the failures of submarine cables could be fully ascertained; the main object, however, of the Paper, had been accomplished. It was divided into three parts; the first was devoted to the Channel Islands cable, its construction and route, a detailed account of all the accidents that had happened, and the means taken to repair them. In the second portion, he had stated the conclusions at which he had arrived, from his own experience, respecting the failures, and the defects in the construction of submarine cables for shallow waters. The third part contained a description of the methods that had been adopted, for testing the point at which a fault in a cable existed.
The first portion of the Paper, being restricted to a narrative of facts, had excited little criticism. It was, indeed, stated, that the route of the cable, which was admitted to have been the chief cause of the failure of the Channel Islands cable, was not selected by the Contractors, but by the Government. For him, however, it was not a question of persons; his only object had been to draw attention to the want of proper precaution in surveying routes, before cables were submerged, and he hoped, that the corroborative observations which had been made during the discussion, would have the effect of inducing the Admiralty authorities to give instructions to their hydrographers, that, in future surveys, the bottom of the seas surrounding these islands, should be as carefully depicted, as the surface of the land on geological maps.
In reply to the questions which had been asked, relating to the fractures in Table I, Mr. Preece stated, that in No. 1, the cable rested upon a bottom of sand, which had been washed from beneath it by the tide; the cable, therefore, became loose, and being swayed backwards and forwards by the tides and waves, was gradually worn, and eventually, broken. Fracture No. 4 was not the result of corrosion, but simply of abrasion, caused by the sharp edge of a rock upon which the cable had rested. The fracture which had occurred in the Bona cable, at a depth of 1,200 fathoms, was not exactly similar, although approaching, to that which he had described. The Channel Islands cable was laid at the bottom, with such an amount of tension that it broke, as soon as its strength was reduced by abrasion. This tension was proved by the ends of the fracture, where every separate wire had been drawn out and broken in a different manner. This fact seemed to show that, in shallow waters, cables should be laid as slack as it was possible, consistent with avoiding kinks. With regard to the causes tending to affect the steering of a ship across tideways, when paying out submarine cables, that subject had been so fully investigated in the Paper by Mr. Webb,* that it would be unnecessary to make any further allusion to it.
In arriving at the conclusions he had given in the second part of his Paper, he was not only guided by his experience in the Channel Islands, but also by his long connection with the cables in the North Sea and in the Irish Channel, and more particularly, with that connecting the Isle of Wight with the mainland. The failures of submarine cables in shallow waters, did not appear to be due so much to inherent defects in the cables themselves, as to the localities in which they were placed. In support of the contrary opinion, it had been urged, that the Portpatrick and Donaghadee cable, which had been submerged eight years, had never been damaged; but on the other hand, the Dover and Calais, the Dover and Ostend, and other cables equally as strong, had been broken. It was, certainly, very remarkable, that a cable in one locality should break, while a cable of precisely the same construction in another locality, should continue in working order.
So again, with regard to the cable connecting Jersey with Pirhou, on the coast of France, which was laid in the latter part of 1859, and which had remained in good working order, while the Channel Islands cable had been broken in five, or six places during the same time; yet a similar cable, 5 miles, or 6 miles in length, obtained from the Submarine Telegraph Company, and laid off Alderney, was found, when taken up a short time ago, to be in a very bad condition. Now if the former, lying between Jersey and France, upon a soft sandy bottom, with no rocks, remained in good order, whilst the latter, which lay upon a rough rocky bottom, very rapidly deteriorated, the only conclusion was, that the cause of the failure must be sought, not in the cable itself, but in the locality in which it was placed.
Again, although the Hague cables, which were of the same construction as the Channel Islands cable, had given great trouble, yet a similar cable laid in 1857, on the coast of Norway, had remained in good working order. The Danish commissioner, Mr. Neilson, stated, that the cable was now in as good condition as when it was first laid. The cable between Cumberland and the Isle of Man, which was laid about the same time, and was similar to that used for the Channel Islands, gave way soon afterwards, on account of having been laid upon enormous masses of seaweed, which, by their motion, broke the cable; but after being repaired, it had remained in working order for two years. These facts corroborated his view of the cause of failure, and those who adopted the Portpatrick cable as their model, would find, that if it was laid upon the point of a rock, or was brought to the surface by the anchor of a large ship, it would not last longer than the Hague, or the Channel Islands cables. The duration of that cable was mainly owing to its having been deposited upon a sandy bottom, devoid of rocks, where no ships’ anchors could touch it.
It had been stated, that there were two schools in telegraphy, one which advocated the use of heavy cables, of the type of the Dover and Calais and the Dover and Ostend lines, and another which advocated the use of light cables, of the description used in the North Sea. It had also been said, that whereas all those stout and heavy cables that were first submerged, had continued in working order to the present day, the small cables of the International Telegraph Company only had failed, and that these cables had been reduced in weight, merely for the sake of change. Now it was a curious fact, that the former advocates of light cables were, at present, using the heaviest cables that could be made, for the Electric and International Telegraph Company’s last cable was the heaviest ever laid; whereas those who started with heavy cables, were now adopting light ones, for the last which had been laid in shallow water, viz., those to Denmark and Hanover, were essentially light cables. Under these conflicting circumstances, he mast adhere to the opinion he had expressed, that cables must be made to suit the varying circumstances of the ground, and that a careful and accurate survey could alone furnish proper data for designing them. A heavy cable should be used for anchorage and for rocky ground, and a lighter cable for sandy bottoms; not one long length of heavy, or one long length of light cable, but a varying cable in weight to suit the requirements of the route to be crossed.
|* Vide Minutes of Proceedings Inst. C.E., vol. xvii., p. 276.|
The next point to be considered, was the decay of cables from corrosion, which, according to his experience, was owing to three causes. First, to simple oxidation from water running over the cable; secondly, to the cable lying upon a metallic surface; and thirdly, to a cause which had not been much observed, the formation of vegetation upon the cable. With regard to the last cause, it was a curious fact, that off Portland, the animalcule and zoophytes which formed upon the cable, rapidly corroded it; whereas between Guernsey and Jersey, a different deposit was formed, which contributed to keep it in perfect condition. From the evidence already obtained, it would seem to be essential, that in the submersion of future cables, some means should be adopted to prevent that rapid deterioration and decay, to which they were, at present, subject. There were objections to the plan proposed by Mr. Latimer Clark, but he thought, that such difficulties could easily be overcome.
He recollected, that in a previous discussion, one of the projectors of the Atlantic cable had exhibited an old pistol and the shank of an anchor, deeply encrusted with lime, and expressed an opinion, that such would be the condition in which the Atlantic cable would be found, after submersion;* but he must have been grievously disappointed, on reading Mr. Varley’s report of the state of that cable off the coast of Newfoundland, where it was so much decayed, as to be useless. The composition recommended by Mr. Preece for covering cables, was that known as Peacock and Buchan’s; it had been applied to the bottoms of large steamers, which were found to be, after long voyages, as clean as when the vessels started. He had been surprised, that in the course of the discussion, so little notice should have been taken of the faulty construction of the present heavy cables. He had pointed out in the Paper, that although a cable protected with heavy wires was, when complete, strong enough to bear the strain which the anchor of a ship would be likely to occasion, yet owing to the quality of iron generally used, the wires would, probably, break singly, and thus, eventually, cause the fracture of the whole; such had been the case in the North Sea. The only way to obviate this danger in heavy cables, was to cover them with stranded wires, or two servings of smaller-sized iron wire.
* Vide Minutes of Proceedings Inst. C.E., vol. xvii., p. 322.
The third part of the Paper was devoted to an explanation of the different systems of testing, from which, as he had purposely omitted all names, it had been erroneously concluded, that he had taken credit to himself for everything he had described. His claim was limited to two instruments only, the ‘multiplying differential galvanometer,’ and the ‘inductometer.’ He was not aware, that Mr. Latimer Clark had previously proposed an instrument, similar in principle to the ‘inductometer.’ No claim, however, had been advanced for the galvanometer, which was the more important of the two. He did not claim the invention of resistance coils, the credit for which should be attributed to Professor Wheatstone, who, in 1843, described them in a Paper read before the Royal Society.* They were used by the Electric Telegraph Company before 1852, for the same purposes to which they were applied at the present moment. Their introduction and useful application in England was due, he believed, to Mr. Cromwell Varley; he could not, therefore, accord any credit to Sir Charles Bright, for the invention. He agreed in the opinion, that it was very desirable to adopt some fixed standard for expressing the electrical condition of the wires, and he hoped all Electricians would combine to accomplish that object.
* Vide Phil. Trans. 1843, p. 312.
The imperfections in gutta percha considerably affected the durability of submarine cables. It frequently happened in repairing a cable, that on the surface of the gutta percha, there was found a small lump, or a little hole, presenting, sometimes, the appearance of having been produced by a flash of lightning, or the burning of a fusee. These defects were generally, but, in his opinion, erroneously, attributed to lightning. The great enemy to be contended with, in working a cable, he believed to be ozone. When the smallest puncture admitted the least atom of water, the decomposition which took place generated ozone, which was known to attack, in a very rapid manner, all inorganic substances like India rubber, or gutta percha.
With regard to the comparative superiority of India rubber and gutta percha, as insulating materials, the electrical qualities of the former had been proved to be far superior to the other, and the only thing wanting, in order to justify its use for long deep-sea cables, was positive proof of its durability. Now he had under his charge, during several years, an india-rubber submarine cable, connecting Hampshire with Hurst Castle; and also crossing the Yarmouth River, in the Isle of Wight. That cable was made in 1852, for the Submarine Telegraph Company, and was afterwards purchased by the Electric Telegraph Company, who submerged it m its present position: and it was, at present, as durable and as good as when it was first laid down. It fortunately happened, that pure india rubber was employed in making the cable; spurious material had, of late, been introduced into the country, and he believed it was mainly owing to that cause, that india rubber had not, hitherto, gained the position which it deserved.
He thought that, in the construction of deep-sea cables, the greatest care should be taken to insure their retaining their original strength unimpaired; there would be then, no greater difficulty in repairing them at depths of 1,000 fathoms, or 1,500 fathoms, than in shallow water. There was no reason why submarine cables should not be taken up for examination periodically, and, where necessary, be repaired, in a similar manner to the wires of an overground line, or the permanent way of railroads. In such routes as the Channel, or the North Sea, lengths of ten miles, or twenty miles, should be examined, picked up, and relaid, every two, or three years.
He believed, that submarine telegraphy would shortly arrive at sufficient perfection, to preserve the communication unimpaired, for an almost indefinite period. The discussion which his Paper had elicited had not solved the question of the durability of submarine cables; but he felt assured, that it would have the effect of assisting the progress of submarine telegraphy.
Mr. BIDDER,—President,—said, that if the Paper and the discussion had exhibited the subject as one of national importance, it had also shown it to be a branch of the profession, the practice of which, up to the present time, had been signally unsuccessful. Upwards of 9,000 miles of submarine telegraph cable had been laid down, of which not more than 3,000 miles could be said to be in working order; so that there were 6,000 miles which were almost useless. This result showed conclusively, that there was either a lamentable want of knowledge on the subject, or some radical practical error, which should be carefully inquired into, with the view of applying a remedy. The present deplorable state of submarine telegraphy, was endeavoured to be accounted for, in Blue Books and other published documents, by reference to causes which practical men could not admit; and the conviction which forced itself upon the minds of unprejudiced persons, was, that the obstacles to success had been more of a moral than of a mechanical nature.
The promised Report of the Government Commission on Submarine Cables, would soon appear, and he hoped it would give facts, which would either confirm this opinion, or dispel such an impression. It was understood, that the Report would go fully into the questions of the methods of insulation and of testing cables. These had been already brought within the province of mathematical certainty, yet the application of the results had not been satisfactory; and patents were even recently taken out, as if for the purpose of adding difficulties to processes which were, already, sufficiently complex. He was not perhaps, himself without blame in this respect, having been one of those who contributed £160,000, to secure the original patents for electric telegraphy. But patents had proved the curse of telegraphy, for scarcely was the ink of the agreement for the purchase of one patent dry, before another was offered, which was warranted to supersede all that had been previously accomplished; and he had little doubt, that if it were possible to obtain exact statistical returns, it would be found, that the law officers of the Crown had derived more benefit from those patents, than the public, or those to whom they had been granted. He should have considered testing as the last subject on which a patent could be justified, yet some parties had proceeded by injunction, to restrict others from applying such different modes of testing as had been suggested by daily experience; thus endeavouring to retard the progress of scientific knowledge.
The first considerable failure of a submarine cable, was that of the Atlantic Telegraph Company. It would be remembered, that in a discussion at this Institution, several months before the cable was laid, it had been strongly urged, that the cable should be tested during its manufacture, and subsequently, that it should not be laid until it had been tested under water, as nearly as possible under the conditions to which it would be subjected, when it was deposited in the sea. In violation of all these precautions, the cable was laid, with a strong suspicion of its not being in a perfect date; a capital of upwards of £300,000 was sunk, and the cause of electric telegraphy was seriously jeopardised. It must he admitted, that even if the cable had been perfect when it was submerged, there were natural causes in operation which would, probably, have destroyed its conductibility in little more than twelve months; this, however, could not excuse the recklessness with which so large a capital was risked, without adequate precautions. It had been urged, in extenuation, that the expectations of England and America had been so highly raised by the original promoters, that the Directors of the Company found themselves trammelled by engagements and contracts which left them no alternative; but in such case, it was their duty to have pursued the straightforward course of abandoning their responsibility, until the undertaking was placed in such a shape, as to offer every reasonable probability of success.
The last great failure which had excited public attention, was that of the Red Sea Telegraph. It was not for him to judge of the personal considerations, or the moral ingenuity which had been alleged to be at the root of this undertaking; yet he could not help remarking, that if such causes had been at work, they could not have been more adroitly, or more skilfully applied. Before, however, proceeding further, he felt he had a duty to perform to one whose memory would ever be revered in this Institution. It had been stated, that the sanction of the late Mr. Robert Stephenson had been obtained as to the form of the Red Sea cable. This was probable, as he was always ready to give advice, whenever it was asked; but when responsibility was attempted to be fixed upon him, it became necessary to ascertain to what extent his sanction had been given. Did the gentlemen who consulted Mr. Stephenson as to the construction of the cable, inform him who was to be the Contractor? Did they communicate to him the conditions of the contract, or the restrictions under which it was to be carried out ? If they did not do so, his opinion as to the mere form of a piece of cable, given probably in the free communication of one gentleman to another, and not as a professional opinion, with all the circumstances of the case before him, should not be made use of, to shift the onus of failure from the living to the dead.
The Red Sea line assumed more than ordinary importance, because the country was under engagement to pay to the Company, about £36,000 per annum, as guaranteed interest upon an outlay which, up to the present time, was utterly useless, and which did not appear to afford much hope of ever being otherwise. The history of this undertaking, as far as it had been made public, was given in the Parliamentary Papers, on “Telegraphic Communications in the Mediterranean and with India.” (1859 and 1860). He would quote from these published documents only; and, without entering into all the minute details, it would suffice to lay before the Meeting the broad facts, whence it would be seen, that moral causes had entered largely into the fate of this unfortunate undertaking.
On the 26th of June, 1858, the following letter was addressed, by Messrs. Glass and Elliot, to the Lords Commissioners of the Treasury “We beg most respectfully to address your Lordships on the subject of the proposed line of telegraph to India, by way of the Red Sea, which project is now under the consideration of your Lordships, at the instance of the Red Sea Telegraph Company.
“That your Lordships may be fully informed of the circumstances which have led to this communication, it becomes necessary to lay before you the following brief history, in connection with the progress of the undertaking, and our connection with the same.
“In the year 1855, application was made to us by Mr. Lionel Gisborne, who represented himself as acting for, and under the authority of Her Majesty’s Government, for information to enable him to prepare estimates for the carrying out of a telegraphic line to the East; and on his assurance, that we should be placed in a position to tender for the execution of the work, upon his completing certain arrangements with the Turkish Government, we provided the necessary information, accompanied with many specimens of submarine cables, best suited for the contemplated line, with estimates, &c.; upon which Mr. Gisborne proceeded to Constantinople, and obtained the necessary firman from the Sultan, to lay down the line now under consideration. Shortly after his return to this country, these concessions were placed at the disposal of a body’ of gentlemen, who formed themselves into a company, (the Red Sea Telegraph Company,) for the purpose of carrying out the lines, under the concessions obtained by Mr. Gisborne. In the month of August last, the Directors called upon us to assist them with information, and afterwards, to tender, for the execution of the whole, or one-half the line; which we did, and a prospectus was issued, founded on this estimate, but an insufficient amount of capital was subscribed, caused by certain statements appearing in the public newspapers, to the effect, that it was impossible to lay a cable in the Red Sea, from its great depth, and other causes.
“In this state of things, we suggested the propriety of an application to Her Majesty’s Government, to cause a survey to be made, with a view of testing the truth of these statements: this course was adopted, and the ‘Cyclops’ was ordered on the expedition, and instructions, forwarded, on our suggestion, to the Admiralty through the Hydrographer, were sent out to the officer m command of the ’Cyclops,’ and the result having been highly satisfactory, a further attempt was then made by the Directors to carry out the line; hence the proposal now under the consideration of your Lordships. The undertaking having thus far proceeded, it was found, that the agreement between Mr. Gisborne and the Directors of the Red Sea Telegraph Company had, in the meantime, lapsed by a few days; and on being called upon by the Company to renew the same, he consented, but insisted, as we have been informed, that in addition to the sum of £15,000, agreed to be paid to him in consideration for the concessions, that he should be appointed Engineer to the Company, and that the whole of the work should be given to Messrs. Newall and Company, without tender, Messrs. Newall and Company having become interested with him in the concessions; and he was bound to them accordingly.
“The Directors have felt themselves constrained, under the peculiar circumstances of the case, to submit to the terms imposed by Mr. Gisborne, and a conditional contract has been entered into with Messrs. Newall and Company, approved by Mr. Gisborne, to carry out the work for the sum of £650,000, or thereabouts. The Directors having given us an opportunity of seeing these estimates, we are in a position to inform your Lordships, that we are prepared to execute similar work for £100,000 less than that amount.
“Should your Lordships find, on inquiry, that our statements are correct, we feel sure, that your Lordships will not, under such circumstances, sanction the application of public money to this purpose for the private gains of individuals to the prejudice of the public.”
Upon this there followed a Treasury Minute, dated August 4, 1858:—
“Inform Messrs. Glass, Elliot and Company, that my Lords have made an arrangement with the Red Sea Telegraph Company, by which, on certain conditions, a guarantee on the part of Her Majesty’s Government is granted to that Company.
“It is one of the conditions in the arrangement, that the line of telegraph shall be laid down on the responsibility of the Company; my Lords do not propose to interfere in the selection of the parties who are to execute the work, further than to see, that its proper execution is sufficiently secured. My Lords have no doubt, that the Company will adopt the proper means of procuring contracts for the execution of the work on the best terms, and can only refer Messrs. Glass, Elliot, and Company, to the Directors of the Company. The first of these documents proceeded from rival manufacturers, who might have been impelled by hostile feelings; but no public contradiction, or explanation had ever been offered of the facts alleged.
On the 27th of August, 1858, the Chairman of the Board of the Red Sea Telegraph Company, in a letter to the Treasury, said:—"As regards the selection of Contractors, they [the Directors] beg to state, that the choice lay between two firms, and that, in a matter of so much importance, and with so limited a number of competitors, it appeared to them, that the early and satisfactory completion of the enterprise would be most effectually promoted, by the selection of the Contractors who combined the highest reputation, with the largest experience in laying submarine cables. The reputation of Messrs. Newall and Co. stood preeminent, and they had already succeeded in laying several telegraphic lines.”
Inclosed in this letter, was “A Memorandum of Agreement made and entered into between the Red Sea and India Telegraph Company, of the one part, and Robert Stirling Newall, Charles Liddell, and Lewis Dunbar Brodie Gordon, all of Abingdon Street, Westminster, trading under the firm of Newall and Co., of the other part,” covenanting, that “the said Messrs. Newall and Co. shall manufacture and lay down ‘the cable’ from Suez to Aden, and, if the Board should require it, and announce their desire to that effect, within four weeks from the date hereof [left blank in the Blue Book], from Aden to Kurrachee, at their own risk and responsibility, and deliver ‘the cable’ complete, and in full working order and condition, for the sum following, viz.:‑
“From Suez to Aden, for the sum of £225,000;
“From Aden to Kurrachee, for the additional sum of £246,425.
“The Board are to have the right of inspecting the cable and materials, during manufacture and while laying, by their own members, and by their officers and persons appointed by them, in such manner and at such times as they may think fit.”
On the 23rd of September, 1858, Mr. J. Cosmo Melvill wrote:‑
“With regard to the proposed arrangements for executing the work, Lord Stanley is not aware of the reasons which induced the Directors of the [Red Sea] Telegraph Company, to enter into a contract for the cable, without resorting to the system of competition; and he does not perceive why that principle could not have been advantageously applied in this case, or why both the firms engaged in the manufacture of the cable, which the Directors appear to have taken for their model, should not have had the opportunity of making a tender.
“With regard to the description of cable which has been fixed upon, Lord Stanley is inclined to urge, that every precaution should be taken to secure the best that can be devised for the purpose. It is well known, that grave doubts are entertained by some authorities, as to whether the Atlantic cable meets all the requirements of a submarine telegraph work, and he would suggest, therefore, the desirableness of obtaining the concurrent opinion of two, or more eminent authorities upon the subject, before making final arrangements.
“Having perused the proposed Agreement with the Contractors, the only observations with regard to its terms which I am desired to make, are, that it would be desirable to modify the first clause, to as to oblige the Contractors to keep ‘the cable’ in working order for one month, at least, from the date of the first message passing through it; and that Clause IV. should be made quite clear upon the power of the Telegraph Company to test, as well as inspect the cable and its component parts, in all stages of its manufacture.”
This letter must be borne in mind, as it related to the important points of the contract being given without competition,—the form of the cable, referring to the “grave doubts” entertained with respect to the Atlantic cable, which, at that period, had virtually failed,—and the obligation to be imposed on the Contractor to keep ‘the cable’ in working order for one month at least, from the date of the first message passing through it, the original proposed period of maintenance being only ten days.
It should be observed that, up to this point, no mention was made of the testing, or of the reception of ‘sections’ of the cable; but ‘the cable,’ meaning the whole extent of the cable from Suez to Kurrachee, was, evidently, intended by the Government, and by the Red Sea Telegraph Company.
In the letter of the 28th of September, 1858, from the Chairman of the Red Sea Telegraph Company to the Treasury, after repeating the former reasons for giving the contract to Messrs. Newall and Co., it was stated:—"But it was also supported by the consideration, that the firman from the Turkish authorities, which was the basis of their operations, would lapse, unless the telegraph was established between Constantinople and Alexandria, before the end of the present year (1858); and that Messrs. Newall and Co. engaged, on receiving the Red Sea contract, to complete that telegraphic communication from their own resources, in time to save the Turkish concession.”
Now it must be observed, that up to the present time (1861), no communication between Constantinople and Alexandria had ever been made; yet that was one of the chief reasons for not submitting the contract to public competition.
In that same letter it was said:—” The Board have communicated to the Contractors the desire of Lord Stanley, that the period for which they should be bound to maintain ‘the cable ‘in working order, be extended from ten to thirty days, and they hope to be able to effect the arrangement.”
In the contract with Messrs. R. S. Newall and Co., dated October 23, 1858, it was stipulated, that they “shall manufacture and lay down ‘the cable’ from Suez to Kurrachee, at their own risk and responsibility, and deliver over the same to the Company, complete, in full working order, and in condition to transmit ten words per minute.”
In Clause V. of this contract, which stipulated for certain payments being made to the Contractors as the work proceeded, it was said: “And no part of the money is to be considered as due until the cable, ‘for each section,’ shall have been efficiently at work, as hereinbefore specified, for one clear calendar month,” &c.
“Any surplus cable remaining, after the final completion of the contract, is to belong to the parties of the second part [the Contractors].”
These documents exhibited, prominently, the duty of an Engineer, to exercise great care in drawing up a contract, as well as to see all the provisions scrupulously carried out.
It would be observed, that whereas the tender of Messrs. Glass, Elliot and Co., was £460,000, that of Messrs. Newall and Co., was £471,425; yet the general result involved in the tender of the former firm, was evaded. It must be borne in mind also, that Messrs. Glass, Elliot and Co. had stated in their first letter to the Treasury, that they had examined the estimates, and were prepared to execute the same work for £100,000 less. This, however, was entirely overlooked by the Directors, who only said they considered the question of £10,000 was immaterial, because they had received an undertaking from Messrs. Newall and Co., to complete the cable from Constantinople to Alexandria, and thus to connect India with Europe; which, however, was not even yet accomplished. It was to be remarked, however, that no formal undertaking, on the part of Messrs. Newall and Co., to complete this communication, appeared in the official papers.
These details might appear prolix, but it was impossible, otherwise, to lay clearly before the Meeting, even an outline of the case, and still less, to give a notion of the causes which had led to that lamentable failure.
In the contract, Clause IV., it was provided, that the Board itself, or by its officers, were to have the right of inspecting and testing the cable as well as all the materials, during manufacture, and whilst being laid, but not so as to interfere with the process of manufacture. But as regarded the laying, the Meeting had been told by one of the Engineers of the Company, that they never had any responsibility, as they never were permitted to interfere in the laying of the cable.
Another condition of the contract was, that the estimates allowed 20 per cent. of extra length, in order that the cable might be laid sufficiently slack. Another clause, however, gave to the Contractors ail such portions of the extra length as were not actually laid; thus actually offering a premium for laying the cable as ‘taut’ as possible. The obvious result was, that in consequence of the Engineers not having any authority to interfere with the mode of submerging, the cable was laid with so little slack, that failures declared themselves almost immediately; and eventually, a vessel was engaged, during one hundred and eighty-two days, in abortive attempts to repair one hundred and eighty-four miles of cable.
It was evident, that a contract had been made, which absolved all parties from responsibility. The Engineers had no power of interference, and the liability of the Contractors was restricted to thirty days. Even here, however, there was an ambiguity; the Government demanded that ‘the cable,’ meaning the entire cable, should be kept in perfect working order, during thirty days, at least: but in dealing with the Contractors, the Company apparently omitted to insist upon this condition, as although it was admitted, that each of the subdivisions of the cable, when laid, had conveyed messages during the minimum period, yet no messages had ever travelled throughout the line, (beyond one, or two days,) according to the evident intention and provision of the Government, and on the faith of which a guarantee had been granted. It had recently been stated, that Messrs. Newall and Co. declined to enter into the contract, if they were held to the maintenance of the entire line for thirty days. The question appeared to have been settled by a compromise between the Company and the Contractors, and the public was saddled with the payment of nearly £36,000 per annum; whilst, probably, all the work would have to be done over again, as the present cable, now lodged on the bottom of the Red Sea, was of no earthly utility, save to the zoophytes, which, no doubt, were closely attached to it.
Now as to the Rangoon cable. The Government requested the opinion of the late Mr. Robert Stephenson, upon the form of a cable to be laid between England and Gibraltar, and the suitable construction was pointed out. This recommendation was reported upon by the Engineer, who was appointed to the project. It was however imagined, that the line might be interfered with, in case of hostilities, and this cable, which was originally designed for a deep-sea line, was now ordered to be transferred to Rangoon, to be laid between that place and Singapore, a considerable portion of which route was through comparatively shallow water. The next that was heard of this unhappy cable was, that it was in a state of fermentation; whether from the hemp covering, or from the oxidation of the iron, was not stated. But its destination had been again changed, and it was now, apparently, to be transferred to the station between Malta and Alexandria, to supersede the cable for establishing a communication between Constantinople and Alexandria, which Messrs Newall and Co. had undertaken to lay, but which had not yet been completed. The statements of the Blue Books on this subject were curious, and deserved careful attention. As to the construction of the cable, it appeared to be of superior character, and it was a matter of regret, that it had not been laid in the place for which it was originally designed.
It was evident, that there were in electric telegraphy, other considerations beyond scientific knowledge and mechanical skill, and those who had to deal with the subject, must be prepared to cope with difficulties arising from other and far different causes. An instance in point, was the accident which had recently happened to a line laid between England and the Continent, for the International Telegraph Company. The cable contained four conducting wires, and whilst it was coiled, the whole acted perfectly, but when it was laid, only three of the wires were found to be capable of performing their duty. The Directors, unlike the Government, had bound die Contractors to lay a perfect cable; they refused, therefore, to receive it in that condition. The Contractors expended a large sum in ineffectual attempts to raise the cable, and to discover the cause of the failure, during a stormy season. On the return of propitious weather, they were more successful, and they then discovered, that a nail had been skilfully inserted into the cable, in such a manner as to destroy the action of one wire. A person who had been on board during the submersion of the cable, at length confessed, that he had been in the pay of other parties; that at their instigation, he had sought for employment under the Contractors, and had, under instruction, inserted the nail. As the case would very shortly be brought before a court of justice, it would be improper to enter into further particulars, but the occurrence justified the severe remarks as to ‘moral causes,’ that had been made during the discussion.*
The most important part of this question, was the necessity of taking the proper steps for insuring a satisfactory submarine telegraphic communication. Several of the deep-sea Mediterranean lines had failed from mechanical causes, some of which had been foretold, before the submersion of the cables had been attempted. This demonstrated the necessity for more careful and accurate surveys of the bottom of the ocean, to the depth of 500 fathoms, or 600 fathoms on the lines where cables were to be laid.
Although it was essential, that a proper route should be selected, it was not requisite to have the entire bottom of the sea mapped out, with the great accuracy which had sometimes been contended for, as it would involve too great an expense. Experience had shown, that the destruction from mechanical abrasion only took place within limited depths; the more elaborate survey might, therefore, be restricted to practical depths, and in shallow waters it should be minute. Within soundings, the cable should be strong, and heavy, but a smaller section might be used beyond. At all events, if that plan was adopted for the cable between England and Gibraltar, there would be little fear of damage from hostile disturbance. He suggested, that an instrument might be devised which would indicate, with sufficient accuracy, the general character of the bed of the ocean, upon a plan similar to that adopted for measuring the rise and fall of tides, the record being made by the passage of a pencil over a sheet of paper moved by clockwork.
Corrosion, could not be prevented, especially where the cable reposed upon sand; but, commercially, that difficulty could be met, by making a provision for renewal, at intervals, say of seven, or eight years. So serious an element in the cost of submarine cables, was their liability to corrosion, that in the cables of the uric Telegraph Company, the depreciation arising from this cause alone, was estimated at £8,000 per annum.
A main point was the form of contract which the Government should enter into with parties offering to lay down cables. It appeared, that at present few, if any, of the submarine telegraphs were remunerative ‘per se’; and with the failures of the Atlantic and the Red Sea cables as precedents, companies would scarcely be found to embark in such undertakings, without some Government assistance. Then came the question of the terms upon which the Government might safely enter into such engagements. After considering all that had been done up to the present time, as described in the Blue Books, it appeared, that the safe course would be to negotiate only with such Contractors as were known to be responsible and trustworthy, to pay them a sum not exceeding the actual cost of the cable, and then to covenant to pay a liberal per centage for the use of the cable, for the period during which It actually remained in working order. The amount paid for effective service was a minor consideration, when compared with the arrangement, by which the country had been saddled with an annual payment of nearly £36,000, without the chance of deriving any practical benefit.
He believed, that the free discussions of the subject in this Institution, would materially aid the progress of submarine telegraphy, and would, eventually, enable Engineers to proceed with the same certainty as to the result, which was attached to the other branches of Civil Engineering. He also hoped, that the expression of opinion which had been elicited, would lead, elsewhere, to a more practical consideration of the question, than it had, hitherto, received.
December 4 and 11, 1860.
GEORGE PARKER BIDDER, President, in the Chair.
The discussion upon the Paper, No. 1,030, “On the Maintenance and Durability of Submarine Cables in Shallow Waters,” by Mr. W. H. Preece, was continued throughout these evenings, to the exclusion of any other subject.
Preece's paper was well received; at a later date this note appeared in the minutes of the Institution:
THE Council have awarded the following premiums for the
|* Vide “Guildhall, February 20th and 21st, 1861. Before Chief Justice Erie and a special jury. Glass v. Boswell. Transcript of Messrs. Cocks’ short-hand notes.” 8vo. London: Waterlow and Sons.|
Last revised: 9 December, 2016