of Electric Induction and Conduction. 369 



if it be correct, viz. 



her * 

 a<r 



This velocity v is not the rate of propagation of potential ; it 

 is the actual velocity of the electricity itself (on the hypothesis 

 that it travels with the ions) when passing through that par- 

 ticular cell and liberating ho- grammes of hydrogen gas every 

 second. I see no way, however, of ascertaining the unknown 

 density a 1 ', except through a determination of v by an experi- 

 ment founded on equation (4). 



I have hitherto supposed water to be the electrolyte ; but 

 practically, of course, dilute sulphuric acid would be used, 

 and it would be the group of atoms S0 4 which would travel 

 against the current, and not oxygen. This group being forty- 

 eight times as heavy as hydrogen, we must read 47 for 7 in 

 the above formula. It therefore seems reasonable to expect 

 that if the method succeeded and gave measurable results, in- 

 formation might be obtained by means of it concerning the 

 actual chemical action caused directly by the electric current, 

 independent of any secondary chemical action to which the 

 products ultimately liberated at the electrodes may be due. 



Besides the sudden kick mentioned above, a continuous mo- 

 tion of the vessel seems possible, because fresh matter is con- 

 tinually being set in motion, while the matter already in motion 

 is being ejected. The momentum generated per second from 

 this cause should be equal to 4:1 ha v. But then the impact of 

 the matter liberated at the electrodes might exert force on 

 them, which would be almost exactly equal and opposite to 

 that exerted on the ions. Various ways, however, suggest 

 themselves of looking for the two forces separately, or of 

 making them assist instead of oppose each other ; and it is easy 

 to arrange so that there shall be no evolution of gas. The 

 impact of the cathion would be advantageously observed by 

 depositing silver on a flat electrode, varnished on one side, 

 and hung to the end of a torsion-arm — remembering that ro- 

 tation due to the earth's magnetism, and probably other dis- 

 turbing causes, such as " migration of the ions," will have to 

 be eliminated. 



Different Electromotors. 



§ 17. We have hitherto supposed the electromotive force to 

 be applied to the cord in the shape of a weight hung to it. 

 This may be said to represent roughly a battery or thermopile 



* Jt would be more correct to write a' ( 1 — — ] instead of a' in this and 



equation (2). The whole of § 16, however, is very questionable at present. 

 Phil. Mag. S. 5. Vol. 2. No. 12. Nov. 1876. 2 B 



