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IV. " On Peristaltic Induction of Electric Currents." By Pro- 

 fessor WILLIAM THOMSON, F.R.S. Received May 10, 1856. 



Recent observations on the propagation of electricity through wires 

 in subaqueous and subterranean telegraphic cables have brought to 

 light phenomena of induced electric currents, which, while they are 

 essentially different from the phenomena of what has hitherto been 

 called electro-dynamic induction, are exactly such as might have been 

 anticipated from the well-established theory of electrical equilibrium, 

 had experiment afforded the data of relation between electrostatical 

 and electro-dynamic units wanted for determining what dimensions 

 of wire would be required to render these phenomena sensible to 

 ordinary observation. They present a very perfect analogy with the 

 mutual influences of a number of elastic tubes bound together late- 

 rally 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 (uninsulated), or stopped (insulated), or 

 subjected to any other particular conditions. The hydrostatic press- 

 ure 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 an incompressible elastic solid*, bored out symmetrically 

 in four, six, or more circular passages parallel to its length, will cor- 

 respond to an ordinary telegraph 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 liquid 

 so great, that the motions are not sensibly affected by inertia, and 

 are consequently dependent altogether on hydrostatic pressure and 

 fluid friction. The electrical induction now alluded to depends on 

 the electrostatic forces determined by Coulomb ; hut it would be in 



* Such as india-rubber very approximately is in reality. 



