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



heightened : it is neither increased nor lessened when the tube 

 is of' copper, only in this case another sound is heard which 

 seems to proceed from the copper tube. This tube, however, 

 is not traversed by a current, but it is probably acted upon 

 by the currents of induction, which the interrupted currents 

 traversing the conductor placed in the axis of the helix pro- 

 duce in it. I constructed a double helix formed of two thick 

 copper wires covered with silk and coiled, each forming several 

 circumvolutions, the one exterior to the other. In making a 

 continuous current pass through the exterior wire, and an 

 interrupted current through the interior one, I heard a re- 

 markably intense sound. In the reverse case, the sound ex- 

 isted, but was much weaker. This fact is evidently connected 

 with the known property of helices traversed by electric cur- 

 rents exercising scarcely any magnetic influence exteriorly, 

 whilst in the interior this action is very energetic. 



Metals and solid bodies are not the only substances which 

 produce the phaenomena I have just described; all conducting 

 bodies, whatever may be their state or their nature, appear to 

 be capable of producing them. Thus, I have observed them 

 with pieces of charcoal of all kinds and shape. Mercury also 

 produces them in a very marked manner. I have inclosed 

 mercury in a tube of glass an inch in diameter, and ten inches 

 long : the tube was completely full and closed with care, so 

 that the mercury could have no motion. As soon as it was 

 traversed by an interrupted current, transmitted by means of 

 two platinum wires, and the electro-magnet or the helix was 

 made to act upon it, a sound- was heard remarkable for its 

 intensity. When the mercury was placed in an open trough, 

 instead of being inclosed in a tube, it likewise produced a 

 sound, and in addition there was seen on its surface an agita- 

 tion or vibratory motion, very different from the gyratory 

 motion observed by Davy, which appears under the influence 

 of the poles of a magnet when traversed by a continuous cur- 

 rent. 



Dilute sulphuric acid, and what is even better, salt water, 

 were successively put in a capsule of platinum placed on one of 

 the poles of an electro-magnet. A point of platinum immersed 

 in the liquid, served, together with the capsule, to send an 

 interrupted current through it. A sound was again heard, 

 but less distinct, on account of the noise produced by the 

 disengagement of the gas : still it was so clear that no doubt 

 could be entertained of its existence. 



It may perhaps be thought that in the experiments I have 

 just described, the sounds are produced by the mechanical 

 action of attraction or repulsion exerted by the electro-magnet 



