Chemical Science. 337 



phenomenon to-day, before the Academy, was the inverse of the 

 preceding. As a needle in motion is retarded by a plate at rest, 

 M. Arago thought it would follow, that a needle at rest would be 

 affected and drawn by a plate in motion ; and, in fact, if a plate 

 of copper, for instance, be made to revolve with a certain velo- 

 city under a magnetic needle perfectly enclosed, the needle no 

 longer takes its usual position, but one out of the magnetic me- 

 ridian, and the more removed as the rotation is more rapid. If 

 the motion is sufficiently quick, the needle itself, at any distance 

 from the plate, will turn constantly in the same direction round 

 the thread by which it is suspended. — Ann. de Chim.^ xxviii. 325. 



3. On the Voltaic Pile and Current, by M. A. de la Rive. — 

 M. A. de la Rive, whilst experimenting on the decomposing action 

 of the voltaic pile on solutions, or on water, was led to observe 

 the effect produced by the introduction of metallic plates into the 

 solution, in such direction as to cross, as it were, or intersect the 

 current. The following are the conclusions he has drawn : 



1. That one or more metallic plates, placed perpendicularly in 

 a liquid conductor on a line extending from pole to pole, dimi- 

 nishes the intensity of the current which is obliged to traverse 

 them. 



2. That this diminution is almost nothing when the current 

 which traverses the plates is very energetic, and produced by a 

 pile of many pairs of plates ; but that the intensity of the cur- 

 rent traversing the same number of plates diminishes the more 

 rapidly, according as its original intensity is less considerable ; 

 and that therefore a very energetic current must be employed to 

 obtain at each pole the same quantity of gas by decomposition 

 when the liquid is continuous, or interrupted by the introduction 

 of plates. 



3. That having two currents of the same intensity, the one 

 originally, the other after having traversed one or more metallic 

 plates, the first will diminish much more by the introduction of one 

 plate, than the latter by the introduction of a plate in addition 

 to those it already has passed. 



These results were obtained with the use of plates of platina. 



At the end of the same memoir, the author has the following 

 further conclusions : — 1. That in the present state of science the 

 least improbable explanation that may be given of electrochemical 

 decompositions, is to consider them dependant on the electric 

 currents diffused throughout the liquid conductor. 



2. That these currents, of which the existence is demonstrated 

 throughout all the liquid serving to complete the voltaic circuit, 

 are susceptible of certain modifications relative to their intensity, 

 when one or more metallic plates, or imperfect fluid conductors, 

 are placed in their course. ^j 



Vol. XIX. Z 



