TRANSACTIONS OP THE SECTIONS. 21 



metal in each case, whether the whole bar was heated so much by a spirit-lamp 

 that it could scarcely be held in the liand, or no part of it was heated above the 

 temperature of the air, and one end cooled by being covered with cotton kept 

 moistened with aether. Taking into account the results of previous experiments 

 which the author had made on a number of different metals, including three speci- 

 mens of platinum wire (Pj, Pj, Pg), probably differing from one another as to 

 chemical purity, which he used as thermo-electric standards, he concluded that at 

 temperatures of from 10° to 32° Cent., the following order subsists unchanged 

 as regards the thermo-electric properties of the metals mentioned :— Bismuth, P3, 

 Aluminium, Tin, Lead, Pg, Copper, P„ Zinc, Silver. Cadmium, Iron. As he had 

 found that a brass wire, on which he experimented, is neutral to P3 at —10° Cent., 

 and to P2 at 38°, he infers that at some temperature between —10° and 38° Alumi- 

 nium must be neutral either to the brass or to P3. He intends, as soon as he can 

 procure a few inches of aluminium wire to experiment with, to determine this 

 neutral point, and others which he infers from the experiments already made, will 

 probably be found at some temperature not very low, between Aluminium and Tin, 

 and Aluminium and Lead ; and to look for neutral points which may possibly be 

 found between Aluminium and P3 and Aluminium and Pa, at either high or low- 

 temperatures. 



On Peristaltic Induction of Electric Currents in Submarine Telegraph 

 Wires. By Professor W. Thomson, M.A., F.R.S. 



Recent examinations of the propagation of electricity through wires in subaqueous 

 and subterranean telegraphic cables, have led to the observation of phenomena of 

 induced electric currents, which are essentially different from the phaenomena (dis- 

 covered by Faraday many years ago) of what has hitherto been called electro- 

 dynamic, or electro-magnetic induction, but which, for the future, it will be con- 

 venient to designate exclusively by the term electro-magnetic. The new phsenomena 

 present a very perfect analogy with the mutual influences of a number of elastic 

 tubes bound together laterally throughout their lengths, and surrounded and filled 

 with a liquid which is forced through one or ^ore of them, while the others are left 

 with their ends open or closed. The hydrostatic pressure applied to force the 

 liquid through any of the tubes will cause them to swell, and to press against the 

 others, which will thus, by peristaltic action, compel the liquid contained in them 

 to move in different parts of them in one direction or the other. A long solid 

 cylinder of India-rubber, bored symmetrically in four, six, or more circular passages 

 parallel to its lengrh, will correspond to an ordinary telegraphic cable containing 

 the same number of copper wires, separated from one another only by gutta percha ; 

 and the hydraulic motion will follow rigorously the same laws as the electrical 

 conduction, and will be expressed by identical language in mathematics, provided 

 the lateral dimensions of the bores are so small, in comparison with their lengths, 

 or the viscosity of the fluid so great, that the motions are not sensibly affected by 

 inertia, and are consequently dependent altogether on hydrostatic pressure and fluid 

 friction. Hence the author considers himself justified in calling the kind of elec- 

 tric action now alluded to, peristaltic induction, to distinguish it from the electro- 

 magnetic kind of electro-dynamic induction. The mathematical treatment of the 

 problem of mutual peristaltic induction is contained in the paper brought before the 

 Section ; but the author confined himself in the meeting to mentioning some of the 

 results. Among others, he mentioned, as being of practical importance, that the 

 experiments which have been made on the transmission of currents backwards 

 and forwards by the different wires of a multiple cable, do not indicate correctly the 

 degree of retardation that is to be expected when signals are to be transmitted 

 through the same amount of wire laid out in a cable of the full length. It follows, 

 that expectations as to the working of a submarine telegraph between Britain and 

 America, founded on such experiments, may prove fallacious ; and to avoid the chance 

 of prodigious losses in such an undertaking, the author suggested that the working 

 of the Varna and Balaklava wire should be examined. He remarked that a part 

 of the theory communicated by himself to the Royal Society last May, and published in 

 the Proceedings, shows that a wire of six times the length of the Varna and Bala- 



