M. DE LA RIVE’S RESEARCHES ON THE VOLTAIC ARC. 
41 
substance submitted to its action ? This question I am unable to decide. I incline, 
however, rather to the latter of these explanations, seeing that the effect is not equally 
perceptible in all bodies, and that it is, for example, more sensible in a bar of bismuth 
than in one of copper. 
It is needless to remark that the calorific action of the current could not have any 
influence on the production of the phenomenon, since there could have been no 
development of heat, on account of the dimension of the bars compared with the force 
of the current. Besides, if the expansion arising from the heating of the body 
traversed by interrupted currents had caused the sound, the effect would have 
been produced equally, whether the bar had been under the influence of the magnet 
or not. This last remark applies equally to the following experiments, as to the 
preceding. 
The intensity of the sound appears to depend much less on the nature of the sub- 
stance submitted to the experiment, than on its form, its volume, and its mass. 
Tubes of platinum, of copper and of zinc, emitted more marked sounds than massive 
cylinders of the same metals. I wound a leaden wire in the form of a helix round a 
cylinder of wood; I did the same with a very fine platinum wire, and also with copper, 
zinc, and tin wires, taking care to place the coils of the helices so far apart that each 
should be isolated. Placed like bars and tubes, whether in the direction of, or across 
the poles of the electro-magnet, these helices emitted very powerful sounds when, the 
electro-magnet being charged, they were traversed by the interrupted current. It 
was particularly surprising to hear the lead wire emit so strong a sound. A helix 
constructed with copper wire, covered with silk, and composed of several coils wound 
round each other, emitted a very intense sound ; it also emitted one, but much feebler, 
under the action of the electro-magnet. 
It is almost needless to remark, that in all these experiments an ordinary magnet 
produces the same effect as an electro-magnet. But what is more interesting, is to 
replace the action of the electro-magnet by that of a helix traversed by a strong con- 
tinuous current, in the axis of which helix is placed the bar, the tube or the coiled 
wire, through which the interrupted current is transmitted. Experiments have shown 
me that in this case the results are the same ; the intensity of the sounds is not very 
different, especially when tubes and wires coiled as helices are used. 
If, between the exterior helix and the metal submitted to the action, a tube of soft 
iron is placed, the effect is a little 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 produce 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 
MDCCCXLVII. G 
