42i Prof. De la Rive on the Vibrator^/ Mmements 



the researches which I have just made, to the investigation 

 of the cause of the fundamental fact, that is to say, of the 

 oscillations which the particles of bodies experience around 

 their position of equilibrium by the action of either external 

 or transmitted currents. With this view, I first submitted to 

 experiment bodies, like iron, susceptible of magnetism, and 

 then other conducting bodies which are not magnetic. 



§ I. Examination of the Vibrations produced in magnetic bodies 

 by either external or transmitted currents. 



On placing very fine iron-filings in the interior of a helix 

 with the axis vertical, these filings are seen to form themselves, 

 under the influence of the current traversing the helix, into 

 small pyramids, elongated in the direction of the axis, which 

 are destroyed and re-formed rapidly when the current is in- 

 termittent. The action of the current of the helix on these 

 filings consists, therefore, in distributing them under the form 

 of an elongated thread parallel to the axis, — a thread which 

 the weight alone prevents being as long as the helix itself. 



This experiment, which I have ali^eady described, and which 

 succeeds as well with very fine iron powder as with iron- 

 filings, proves that the particles of iron under the influence of 

 external magnetization tend to approach each other in the 

 transversal direction, and to extend in the longitudinal direc- 

 tion. It is probable that this phaenomenon is due to the form 

 of the elementary particles of the iron, and to the manner in 

 which they are polarized. One thing is certain, that it ac- 

 counts for what passes in an iron bar or wire submitted to the 

 influence of the intermittent current of the helix. The particles 

 of the iron contending with the cohesion arranjje themselves 

 In the longitudinal direction when the current acts, and return 

 to their primitive position as soon as it ceases; from this re- 

 sults a series of oscillations which are isochronous with the 

 interruptions of the current. This manner of viewing the 

 phaenomenon entirely agrees with the contraction in the trans- 

 versal direction accompanied by an extension in the longitu- 

 dinal direction, which Mr. Joule observed in iron wires and 

 bars submitted to magnetization*. 



The same physicist has also remarked that when the wire 

 is much stretched, the magnetization occasions a shortening 

 instead of a lengthening, — an effect which agrees with the 

 cessation of the sounds I have observed when the tension 

 becomes too strong. 



Ail these effects are much more decided in soft iron than 



* Phil. Mag. Feb. 1847 and April 1847. 



