426 EECENT PEOGRESS IN PHYSICS. 



magnet, unless they be brought much nearer to one another, and the 

 appearance of the phenomenon is then entirely different. The trans- 

 ported particles appear to disengage themselves with difficulty from 

 the positive electrode, sparks fly with noise in all directions, while in 

 the former case it was a vivid liglit without sparks and without noise, 

 accompanied by the transfer of a liquid mass, and this appeared to be 

 effected with the greatest ease. It is of little moment with respect to 

 the result of the experiment whether the two rods of magnetized iron 

 present to that part of their extremities between which the luminous 

 arc springs the same magnetic poles or different poles. 



''The positive electrode of iron, when it is strongly magnetized, 

 produces, the moment that the voltaic arc is formed between it and a 

 negative electrode of whatever nature, a very intense noise, analogous 

 to the sharp hissing sound of steam issuing from a locomotive engine. 

 This noise ceases simultaneously with the magnetization. 



" For the purpose of better analyzing these different phenomena, 

 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 be- 

 tween thom, 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 alike 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 vertically 

 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 be- 

 came necessary to bring the point nearer to the plate 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 influence of the electro-magnet. 



t " 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 The luminous arc no longer maintained 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. ff It was broken incessantly, each time accompa- 

 nied by a sharp and sudden noise, similar to the discharge 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 po- 

 sition 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 phenomena. 



"Copper, and still more silver, present a remarkable peculiarity. 

 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 nega- 

 tive point presents a spot in the form of a helix, as if the melted metal 

 in this locality had undergone a gyratory motion around a centre,, at the 



