M. De la Rive's Researches on the Voltaic Arc. 329 



ized, produces, the moment that the voUaic arc is formed be- 

 tween it and a negative electrode of whatever nature, a very 

 intense noise, analogous to the sharp hissing sound of steam 

 issuinjif from a locomotive engine. This noise ceases simul- 

 taneously with the magnetization. 



For the purpose of better analysing these different phaenc 

 mena, I placed an electro-magnet of large dimensions and great 

 power in such a manner as to enable me to place on each of 

 its poles, or between them, different metals destined to form 

 one of the electrodes of the pile, while one point of the same 

 metal, or another substance, acted as the other electrode. I 

 have aUke employed as electrodes, placing them in the same 

 circumstances, two points of the same metal or of different 

 metals. The following are the results which I have obtained. 

 A plate of platinum was placed on one of the poles of the 

 electro-magnet, and a point of the same metal was placed ver- 

 tically above it; the voltaic arc was produced between the 

 plate and the point, the plate being positive and the point 

 negative. As soon as the electro- magnet was charged, a sharp 

 hissing was heard ; it became necessary to bring the point of 

 the plate nearer to enable the arc to continue, and the bluish 

 circular spot which the platinum plate presented, became 

 larger than when the experiment was made beyond the influ- 

 ence of the electro-magnet. The plate was made negative, 

 and the point positive; the effect was then totally different; 

 the luminous arc no longer maintained its vertical direction 

 when the electro-magnet was charged, but took an oblique 

 direction, as if it had been projected outwards towards the 

 margin of the plate; it was broken incessantly, each time ac- 

 companied by a sharp and sudden noise, similar to the dis- 

 charge of a Leyden jar. The direction in which the luminous 

 arc is projected, depends upon the direction of the current 

 producing it, as likewise on the position of the plate on one 

 or other of the two poles, or between the poles of the electro- 

 magnet. A plate and a point of silver, a plate and a point of 

 copper, and generally a plate and a point of any other metal, 

 provided it be not metal too easily fused, present the same 

 phaenomena. 



Copper, and still more silver, present a remarkable pecu- 

 liarity. Plates of these two metals retain on their surfaces the 

 impression of the action that took place in the experiments 

 just described. Thus, when the plate is positive, that portion 

 of its surface lying beneath the negative point presents a spot 

 in the form of a helix; as if the metal melted in this locality 

 had undergone a gyratory motion around a centre, at the same 

 time that it was uplifted in the shape of a cone towards the 



