M. De la Rive's Researches on the Voltaic Arc. 333 



molecular state not taking place instantaneously in the sub- 

 stance submitted to its action ? This question 1 am unable to 

 decide. I incline, however, rather to the latter of these ex- 

 planations, 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 cur- 

 rent could not have any influence on the production of the 

 phaenomenon, 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 fol- 

 lowing experiments, as to the preceding. 



The intensity of the sound appears to depend much lesson 

 the nature of the substance 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 in- 

 terrupted 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 

 continuous 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 



