THE IRISH TELEPHONE CABLE.
On the 4th inst. Her Majesty’s Post Office telegraph ship “Monarch” successfully laid a new cable, containing four conductors of special size, designed for telephonic use between Great Britain and Ireland. The cable was laid between Port Kail on the Scotch Coast and Donaghadee on the Irish coast. The engineering staff of the Post Office has been busily engaged during the last eight months in erecting the land wires, and the cable connections having been completed on Thursday last week, the wires were tested by Mr. J.C. Lamb and Mr. W.H. Preece. Conversation was carried on with perfect ease and freedom between Belfast and Glasgow. Amongst the first to speak between Glasgow and Belfast were: Lord Kelvin, Sir John Purvis, the Lord Provost of Glasgow, and Sir Daniel Dixon, Lord Mayor of Belfast, all of whom expressed their gratification with the great success of the new communication.
To ensure that the go and return land wires shall preserve the same mean distance from disturbing causes, they are made to exchange their positions, as in the case of the London-Dover section of the London-Paris line, by revolving round each other like the strands of a rope over the whole distance, about seven complete twists being made in every mile. The cable wires are twisted in a similar manner.
At present only the Belfast-Glasgow circuit is completed, but a second pair of wires is erected as far as Stranraer on the way to Manchester, Liverpool, Leeds, and eventually London; whilst a pair is also just being commenced to Dublin, and will ultimately be extended to Cork. The Belfast-Glasgow line will be opened very shortly to the public. The charge for a conversation of three minutes will be 5s. The tariff for the London-Paris line is, it will be remembered, 8s. for a similar period.
The Belfast-Glasgow line is 150 miles long, and the cable 23½ nautical miles. The London-Paris line is 303 miles long, and its cable 21 nautical miles. Both cables are made to practically the same specification. The conductors are of 160lb. copper, and the dielectric 300lb. gutta percha; the electrical resistance at 75°F. is 7½ ohms, and the electrostatic capacity .3 micofarad per nautical mile of 2,029 yards. Both cables have been made by Messrs. Siemens Bros. and Co.
There is one point alone in which they differ. Surrounding the core of the Irish cable there is, as will be seen by our illustration, a sheathing of brass tape, intended to protect the conductors from the ravages of the teredo. This has not been considered necessary in cables laid heretofore in British waters, but the teredo has now made its appearance here and must be guarded against.