42 
M. DE LA RIVE’S RESEARCHES ON THE VOLTAIC ARC. 
current through the interior one, I heard a remarkably intense sound. In the 
reverse case, the sound existed, but was much weaker. This fact is evidently con- 
nected with the known property of helices traversed by electric currents 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 phenomena 
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, trans- 
mitted 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 like- 
wise produced a sound, and in addition there was seen on its surface an agitation 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 conti- 
nuous current. 
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 inter- 
rupted 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 on the substance traversed by an interrupted current, and that, 
consequently, magnetism has no more share in the phenomenon than a finger might 
be supposed to have, when pressing on a sonorous cord. The simple description of 
the experiments shows this interpretation to be inadmissible. In the first place, the 
sound is the same with the wires in a helix, whether these wires be stretched or 
not, or whether they be of lead, platinum, or brass. Besides, how could this account 
for the sound produced in large masses, especially in liquids, such as mercury, and for 
the fact, that the position of the conductor traversed by the interrupted current with 
regard to the poles of the electro-magnet does not exert any influence on the pheno- 
menon ? Farther, it must be remarked that the sound in question is not a musical 
sound, such as would be produced by a string or mass made to vibrate by a cause 
acting exteriorly at its surface; it is a series of sounds corresponding exactly to the 
alternations of the passage of the current ; like a species of collision of the particles 
amongst themselves. Thus, the phenomenon is molecular; and it leads to the de- 
monstration of two important principles. 
