424 Prof. A. de la Rive's Memoir of 



chemical theory. This theory, foreseen by Wollaston and Fa- 

 broni, but opposed by most of the physicists of the early part of 

 the present century, had found a powerful argument in its favour 

 in the beautiful experiments of the elder Becquerel upon the 

 electricity developed by chemical actions. It was then (fron 

 1825 to 1835) that, profiting by these experiments, and seeking, 

 on my own part, to make others of the same kind although in a 

 slightly different direction, I published several memoirs to sup- 

 port and render more precise the chemical theory of the voltaic 

 pile. But I cannot but admit that we are indebted to Faraday 

 for having based this theory upon irrefutable proofs, not only by 

 the great number and variety of his researches, but especially by 

 his beautiful discovery of the definite decomposing action of the. 

 electric current — a discovery which established between the ex- 

 ternal chemical action of the voltaic pile and the chemical action 

 which takes place in the interior of this apparatus, a relation so 

 intimate that it is impossible not to see in the latter the cause of 

 the former. 



III. 



In 1831 Faraday discovered electrical induction ; it is the 

 most important, although perhaps not the most brilliant of his 

 discoveries. Ten years before (in 1821) he had observed a per- 

 fectly new phenomenon in the science of electrodynamics, — that 

 science which issued complete, as we may say, from the brain of 

 Ampere, after (Ersted's discovery. Struck by the experiments 

 of the great French physicist upon the mutual attractions and 

 repulsions of electrical currents and magnets, Faraday was led, 

 by theoretical ideas which were rather disputable and not very 

 conformable to the principles of mechanics, to assume that an 

 electric current must turn round the pole of a magnet with a 

 continuous movement, and reciprocally that the pole of a magnet 

 must in like manner turn round an electric current. He verified 

 this double result by experiment ; and Ampere soon showed its 

 accordance with his theory, adding to it other facts of the same 

 nature. It is not the less true that the discovery of a continuous 

 movement of rotation due to the combined action of a magnet 

 and an electric current was quite unforeseen, and at the same 

 time very important ; for up to that time there was no example 

 of any such action in physics. It was a first step in the course 

 which was to lead to the finding of a relation between mecha- 

 nical movement and the molecular forces. . 



Arago (in 1824) was the first who directly established this re- 

 lation, by his beautiful discovery of magnetism by rotation ; for 

 he showed that simple mechanical movement could render a 

 body, in itself non-magnetic, capable of acting upon the magnet. 



