432 Prof. De la Rive on the Vibratory Movements 



circumference to the centre. As soon as a continuous current 

 was transmitted through the wire of the ambient helix, a well- 

 marked succession of metallic sounds was heard in the disc. 



Even mercury can produce sounds, as I have already re- 

 marked. To render them perceptible, it is only requisite to 

 introduce the mercury into a tube a few millimetres in diameter, 

 and shaped so as nearly to envelope the pole of the electro- 

 magnet. As soon as the latter is magnetized, and the discon- 

 tinuous current traverses the mercury, a series of sounds is 

 heard similar to those which would result from a regular suc- 

 cession of sparks produced by a strong current between the 

 mercury and a metallic wire. There is not, however, any 

 trace of this, as may be easily ascertained ; and, moreover, a 

 current too feeble to produce sparks passed through the mer- 

 cury is capable of producing the phaenomenon. A remarkable 

 fact is, that if, instead of being a little below the polar surface 

 of the electro-magnet, the tube which contains the mercury 

 is upon that surface itself, the sound is not heard. All these 

 effects are very distinct from the movement which the mercury 

 acquires under the influence of magnets, when it is traversed 

 by either discontinuous or continuous currents. 



I shall not for the present recur to the remarkable sounds 

 which the voltaic arc occasions under the influence of the 

 electro-magnet, — sounds which I have carefully described in 

 a previous memoir*. They are evidently of the same nature 

 as those of which I have just spoken ; for in the voltaic arc 

 the current is, so to say, intermittent from the very nature of 

 the arc which conducts it. 



The following, therefore, is the general phaenomenon. When 

 any solid conductor, liquid or gaseous (at least very much 

 divided, as in the voltaic arc), is traversed by an electric cur- 

 rent, — a magnet, or an assemblage of electric currents closed, 

 and having consequently magnetic properties, acts upon the 

 particles of this conductor so as to give them a relative position 

 different from that which they have naturally. Hence it re- 

 sults that, if the transmitted current is discontinuous, the par- 

 ticles oscillate between their normal position and the forced 

 position which the magnetic influence tends to impart to them ; 

 this gives rise to the sounds, and explains the modifications 

 which it presents. 



Does the action of the magnetism alone suffice to alter 

 the relative position of the particles of all the bodies, or is the 

 combined action of the magnetism and the electric currents 

 requisite? Faraday's experiments seem to favour the first 

 hypothesis; for the action exerted on light by transparent 

 * Phil. Mag. vol.xxxi. p. 321. 



