Prof. Challis on a Theory of Galvanic Force, 437 



current. I have assumed the atoms of hydrogen to be smaller 

 than those of oxygen in accordance with a theoretical result 

 obtained in the Philosophical Magazine for February 1860. If 

 this be a true explanation, the theory decides that the flow of 

 the galvanic current is from the zinc to the copper, that is, from 

 the positive to the negative pole of the battery. 



8. In the usual experiment for decomposing water, the ter- 

 minals being of platinum wire, there is no direct action between 

 the metal and the fluid ; but as one wire is connected with the 

 positive pole of the battery, and the other with the negative, 

 they must have opposite electricities, and will also act upon 

 each other inductively. Hence, by the same reasoning as be- 

 fore, an setherial current is generated, which may be capable of 

 separating the hydrogen from the oxygen by impelling the 

 atoms of hydrogen more energetically than those of oxygen. In 

 this case the oxygen, not having an affinity for platinum, rises 

 in bubbles at the positive terminal, while the hydrogen is driven 

 off to the negative terminal. As there must be a decrement of 

 density at the negative terminal towards the position of mini- 

 mum density between the two, it is possible there may be a 

 decomposition of the water at this terminal also, but in less 

 degree than at the positive, because the decrement of density is 

 in the direction contrary to that of the stream. If there be 

 such decomposition, all the oxygen liberated may unite with 

 hydrogen sent from the other terminal, and thus hydrogen alone 

 will rise from the negative terminal, as is known to be the fact from 

 experience. This last remark applies also to the case considered 

 in the preceding paragraph, if there should be any decomposi- 

 tion, by the agency of the current, at the surface of the copper. 



9. It will be seen from the above explanations, that the gene- 

 ration of a galvanic current without actual analysis of the fluid, 

 the possibility of which appears to be proved by the water-bat' 

 tery, is consistent with the theory. 



10. The investigation of the motion of the setherial current 

 along an electrode of fine wire is a very difficult hydrodynamical 

 problem, the solution of which I shall not attempt to give at 

 present ab initio. But admitting the existence of such currents, 

 and that they are steady, it is not difficult to state what must be 

 their chief characteristics. In the first place, if not confined 

 within limits by non-conducting substances, they must exert 

 an influence at considerable distances from the electrode. Hydro- 

 dynamically it would be impossible for an unconfined stream to 

 flow along the electrode without producing motion in the sur- 

 rounding fluid. The velocity of the sether is greater within the 

 wire than without, because the wire is the effective channel of 

 the stream, and the motion of the surrounding fluid is the result 



