}(H> Mr. 0. J. Lodoe on a Mechanical Illustration 



r> 



supposed to have weak springs; for the hydrogen clings tightly 

 to it, and the reverse current, occasioned by the expansion of 

 the compressed springs, lasts a considerable time. 



I have supposed the buttons rigidly stuck to the cord ; but 

 if any electrolyte allows a trace of electricity to pass through 

 it by ordinary conduction without equivalent electrolysis, then 

 the cord must be allowed to slip through the buttons a little*. 



§ 14. But the model is as yet only half a one ; it does not 

 represent the oxygen proceeding up stream to the anode. To 

 show this we require another set of buttons, ranged alongside 

 the first set, on a cord which is driven in the reverse direction 

 by the same weight W, and which represents a simultaneous 

 equal opposite current of negative electricity. These buttons 

 are also attached to rings sliding on rods a! and V \ and these 

 rods o! and V must lie close to a and b respectively, so that 

 the H buttons and the buttons may rub against one another 

 as they travel in opposite directions. Indeed I imagine that 

 the rods themselves are to be infinitely smooth (and might 

 really be dispensed with, rings and all), so that there is 

 no real metallic resistance in an electrolyte, but only the 

 resistance (which, however, has been found to follow Ohm's 

 law) due to the clinging of the atoms. This clinging of the 

 atoms is not great — it does not represent chemical combina- 

 tion ; for, according to the theory of Clausius, it is not the 

 chemically combined atoms which are undergoing electrolysis, 

 but some comparatively free ones knocking about among them. 

 Our model then only represents the Clausian atoms. 



The electrode at which the oxygen atoms are liberated must 

 not be supposed to impede their progress, but on the con- 

 trary to assist it, especially if made of zinc or some metal oc- 

 cupying a similar position in the voltaic series. It may be 

 conceived of as attracting each button, as it comes near, 

 against its knife-edge and cutting it off the cord ; it is thus 

 generating electromotive force in the same direction as W, 

 and rendering any external electromotive force unneces- 

 sary for the propulsion of the cord, provided that the opposi- 

 tion at the cathode does not overpower it. We have here 

 imagined a voltaic cell carrying on electrolysis and genera- 

 ting a current on its own account. The buttons cut off at the 

 anode stick to it by reason of its attraction, and may be con- 

 sidered as combining with a portion of it. They will then 

 tend to block up the circuit unless washed off; and so the pole 

 gets eaten away. 



Seeing that the smallest force is sufficient to make the move- 



* Faraday is said to have found this to occur in certain cases. (See 

 Thomson on Electrolysis in the Phil. Mag. for December 1851, p. 431.) 



