438 Prof. Challis on a Theory of Galvanic Force. 



of lateral action. The velocity within the wire is also increased 

 by the contraction of the channel by the occupation of space by 

 the atoms. Now as the axis of the electrode thus becomes a 

 line of maximum velocity, and therefore of minimum density, 

 there must be a tendency of the contiguous fluid to flow towards 

 this axis. But if this motion actually took place, the stream 

 would immediately be stopped. Hence this tendency must be 

 counteracted by a uniform circular movement kept up by the 

 accelerative force due to the decrement of density towards the 

 axis. Thus the resulting motion will be in spiral lines about the 

 electrode. This conclusion will be put to a severe test when we 

 come to consider the mutual action of galvanic currents and 

 magnets. 



11. It is readily seen from this theory why the current flows 

 as soon as two wires connected with the poles of a battery are 

 put in contact ; for by the action of the battery the fluid is im- 

 pelled along one w T ire, and draiun along the other, and the circu- 

 lation of the stream results from the junction. Simple contact 

 suffices to produce the effect, apparently because it provides an 

 axis for the spiral movement, which, as explained above> is ne- 

 cessary for maintaining the current. It is not so easily seen 

 why there is no current unless the poles are brought into con- 

 nexion. "When the ends of the wires are in air, it is sufficient 

 to say that the air, being a non-conductor, stops the flow of the 

 current, the explanation of the non-conductive property being 

 not at present under consideration. But the experiments of 

 Mr. Gassiot have proved (Phil. Trans, vol. cxlix. part 1. p. 150) 

 that a perfect vacuum is a non-conductor. The explanation of 

 this fact must be drawn from the laws of movement of the rcthc- 

 rial fluid. On this point I have the following considerations to 

 offer. Assuming that galvanic currents are identical with a? i he- 

 rial currents, experience shows that the conductive property of 

 a substance allows an setherial stream to permeate freely through 

 its whole interior, and, supposing it to be insulated, that its 

 bounding surface contains the stream w T ithin limits, just as a 

 closed channel of any shape contains a stream of water. In this 

 manner a metallic wire is a channel for the setherial current ; but 

 in this case, if the insulation be not perfect, on account of the 

 narrowness of the channel, the surrounding sether is perceptibly 

 acted upon, so as to make a spiral movement necessary, as above 

 stated, for the maintenance of the current. The spiral motion 

 may be conceived to originate where the stream issues from a 

 wider space into the electrode, just as the same phenomenon 

 occurs when water issues from a vessel through an orifice ; also, 

 where the stream issues from the electrode into a wider space, a 

 like movement may be produced. In both cases, a rapid change 



