Shorter Wirelength Research Articles

(1) The Theory of the Submarine Telegraph and Telephone Cable (2) Alternating-current Electricity and its Applications to Industry Second Caurse

(1) IN the summer of 1850 a smali party of engineers arrived at Dover in order to lay a cable across the Channel. One of them-Willoughby Smith, who was afterwards president of the Institution of Electrical Engineers has left an interesting record of their adventures. At that period it was considered absolutely unnecessary to test copper wire. All copper wires were supposed to have the same conductivity. The cable was twenty-five miles long, made up of short lengths of wire which purported to be No. 12. Birmingham Wire Gauge, but wbich varied in diameter. It was covered with gutta-percha, so that the outside diameter was about balf an inch. No armouring of any kind was used. The cable was coiled on board the tug Goliath, and the party had to wait some weeks for a calm day. The project excited much good-natured ridicule amongst the town folk. A man was found cutting the cable with his knife 40 show his friends that there was a wire inside. A spectator was. beard explaining to interested listeners. tbat it was impossible to puli a cable of this ldnd 25 yds. long resting at the hottom of the sea. It was, therefore, absolutely impossible to puli one twenty-five miles long. He evidently thought that the function of a cable was similar to that of a beli-puli. On an ideal calm day the pioneers laid the cable from Dover to Grisnez, but they were destined to bitter disappointment. The letters printed by the typewriting instrument at Grisnez were so mixed that the few messages reccived were quite undecipberable. To make their discomfiture complete, the anchor or the trawl a llsbing-smack cut the cable in two not many hours after it was laid. They were thus prevented from carrying out experiments which would probably bave enligbtened tbem considerably on the laws governing the transmission of submarine signals. As it was, tbev had no conception tbat their failure was mainly due to i˜norance of the laws of electricai capacity and induction. (1) The Theory of the Submarine Telegraph and Telephone Cable. By Dr. H. W. Malcolm. Pp. xi + 565. (London: The Electrician Printing and Publishing Co., Ltd., n.d.) Price 18s. net. (2) Alternating-current Electricity and its Applications to Industry. Second Caurse. By W. H. Timbie Prof. H. H. Higbie. Pp. ix + 729. (New York: John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1916.) Price 13s. 6d. net.

3. Note on a New Form of Galvanometer

This instrument consists of a close spiral of insulated copper wire bent into the form of an anchor ring, so as to form an endless solenoid. The spiral is placed in a rectangular groove turned on the edge of a wooden or brass ring of suitable thickness and diameter. Short lengths of wire at both ends of the copper spiral are left straight. These, after being well insulated, are twisted together and led to two terminals, which serve as electrodes. The ring containing the spiral is fixed on a base board with its plane vertical, and at right angles to the magnetic meridian, when the instrument is in use. A short magnet, rigidly attached at right angles to the lower end of a stiff wire, is suspended from a silk fibre, so that its centre is in the circular centre line of the anchor ring.

VII. On the measurement of electric resistance

In measuring the resistances of short lengths of wire by Wheatstone’s Balance , I have often experienced considerable difficulty in consequence of the resistances presented by the contacts between the ends of the several connected branches or arcs.