INDUCTIVE AFFINITY. 



FIG. 3. 



the copper, does not occur at all unless that plate be in me- 

 tallic connexion with the zinc, by means of a wire as in the 

 figure, or by the plates themselves touching without or within 

 the acid fluid. This would seem to indicate that while the 

 decomposition travels from the zinc to the copper through the 

 acid, some force or influence is propagated at the same time 

 through the wire, from the copper back again to the zinc. 

 That something does pass through the wire in these circum- 

 stances is proved by its being heated, and by its temporary as- 

 sumption of certain electrical and magnetic properties. Whether 

 anything material does pass, or it is merely a vibration or 

 vibratory impulse, or a certain induced condition that is pro- 

 pagated through the molecules of the wire, of which the elec- 

 trical appearances are the effects, cannot be determined with 

 certainty. But a power to effect decomposition, the same in 

 kind as that occurring in the acid jar, and which acts in the 

 same sense or direction, is propagated through the wire, and 

 appears to be fundamental to all the other phenomena. 



Let the wire, supposed to be 

 of platinum, connecting the zinc 

 and copper plates, be divided in 

 the middle, and the extremities A 

 and B of the portions attached to 

 the copper and zinc plates respec- 

 tively be flattened into small plates, 

 and then dipped at a little distance 

 from each other in a second vessel 

 containing hydriodic acid. Iodine 

 will soon appear at A, although 

 that element is incapable of com- 

 bining with the substance of the platinum, and hydrogen gas will 

 appear at B. If the connecting wire and the small plates A and 

 B were of zinc or of copper, the hydriodic acid would be decom- 

 posed precisely in the same manner, but the iodine as it reached A 

 would unite with the metal and form an iodide. Supposing a de- 

 composing force to have originated in the zinc plate, and to have 

 circulated through the hydrochloric acid in the jar to the copper 

 plate, and onwards through the wires and the hydriodic acid 

 back to the zinc, as indicated by the direction of the arrows, 

 then the hydrogen of the hydriodic acid has followed the same 

 course, and been discharged against the metallic surface to 

 which the arrow points. 



