436 Prof. Challis on a Theory of Galvanic Force. 



7. Let us now consider the process of generation of setherial 

 currents, and their dynamical action, in the experiment of the 

 galvanic battery. It will suffice to take the simple case of a 

 plate of zinc and a plate of copper immersed in an acid solution. 

 The chemical action between the fluid and zinc may be such as 

 to produce analysis of the fluid anterior to any galvanic current, 

 while no such action takes place at the surface of the copper. 

 This difference between the relations of the metals to the fluid is 

 an essential condition of the generation of a current. The che- 

 mical affinity between the acid solution and the zinc, causes a 

 change of position of the superficial atoms of the latter, and 

 puts it into an electric state, the action of the fluid taking the 

 place of friction in the phenomena of ordinary electricity. If 

 the zinc plate were alone immersed in the fluid, all the points of 

 its surface would be in the same electric state ; but being in 

 the presence of the copper, the latter is electrified inductively, 

 and reacts upon the zinc. Thus both metals are put into a 

 state in which a gradation of interior density exists, and conse- 

 quently, according to our theory, each tends to generate second- 

 ary currents. Also the tendency is in the same direction for 

 both, because the adjacent parts are oppositely electrified. No 

 current, however, flows unless a continuous route is provided by- 

 means of a metallic connexion between the zinc and the copper. 

 Till this is done the current is driven back by the insulation of 

 the battery and the non-conductiveness of the air. But when 

 the circuit is complete, the internal atomic conditions of the 

 zinc and copper, which originate the secondary current, main- 

 tain its dynamic action. So far as relates to the action of the 

 current, the case is exactly analogous to that of electrical attrac- 

 tion, considered in the "Theory of Electricity." As the attraction 

 towards each other of the electrified bodies was due to a steady 

 current, having a position of maximum velocity, and therefore of 

 minimum density between them, so in this instance there will, 

 for like reasons, be a position of minimum density of the sether 

 between the zinc and the copper. Consequently there will be a 

 decrement of density more or less rapid from the zinc towards 

 this position ; and if it be assumed that the current flows in 

 that direction, from what is argued in the preceding paragraph, 

 its dynamic action, being more energetic on the atoms of hydro- 

 gen than on the larger atoms of oxygen, will urge the former 

 towards the copper. After accumulating on the surface of the 

 copper, the hydrogen will rise in the fluid in the form of bub- 

 bles. In the mean time the oxygen set free obeys the law of 

 its affinity for zinc, and combines with it more copiously than it 

 did before the flow of the current. In this way the theory 

 accounts for electrolysis by the dynamic action of an setherial 



