148 ANNUAL OF SCIENTIFIC DISCOVEEY. 



hitherto been called electro-dynamic, or electro-magnetic induction, but which, 

 for the future, it will be convenient to designate exclusively by the term 

 electro-magnetic. The new phenomena 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 more 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 pass- 

 ages parallel to its length, 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 then- lengths, or the velocity of the fluid so great, that 

 the motions are not sensibly affected by inertia, and are consequently depend- 

 ent altogether on hydrostatic pressure and fluid friction. Hence the author 

 considers himself justified in calling the kind of electric action now alluded 

 to, peristaltic induction, to distinguish it from the electro-magnetic kind of 

 electro-dynamic induction. Among the results noticed, he mentioned, as 

 being of practical importance, that the experiments which have been made 

 on the transmission of currents backward and forward 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 6 times the 

 length of the Varna and Balaklava wire, if of the same lateral dimensions, 

 would give 36 times the retardation, and 36 tunes the slowness of action. 

 If the distinctness of utterance and rapidity of action, practicable with the 

 Varna and Balaklava wire, are only such as to be not inconvenient, it would 

 be necessary to have a wire of 6 times the diameter ; or better, 36 wires of 

 the same dimensions ; or a larger number of still smaller wires twisted to- 

 gether under a gutta percha covering, to give tolerably convenient action by 

 a submarine cable of 6 times the length. The theory shows how, from care- 

 ful observations on such a wire as that between Varna and Balaklava^ an 

 exact estimate of the lateral dimensions required for greater distances, or 

 sufficient for smaller distances, may be made. Immense economy may be 

 practiced in attending to these indications of theory in all submarine cables 

 constructed in future for short distances ; and the non-failure of great under- 

 takings can alone be insured by using them in a preliminary estimate." 



