426 Prof. De la Rive on the Vibratory Movements 



It seems to me to result from what precedes, that the effect 

 of the transmitted current is to give to the molecules of the 

 iron a transversal direction, as the effect of the magnetization 

 "WSLS to give them a longitudinal one. If the arrangement of 

 the particles of the iron-filings around an iron or any other 

 metallic wire, traversed by an electric current, be examined 

 with attention, these filings are seen to arrange themselves 

 in parallel transversal lines. This is very evident on fixing 

 the conducting wire into a groove made in a wooden board. 

 The filings, being unable to go round the wire, assume a 

 transverse position above it, forming small threads of 3 to 4 

 millimetres in length, which present opposite poles at their two 

 extremities. When the wire is free, these threads, instead of 

 remaining rectilinear, unite at their two ends, and envelope 

 the surface of the wire, forming around it a closed curve. 

 Now the arrangement which the iron-filings assume around 

 any conducting wire transmitting a current, should be equally 

 assumed by the molecules of the surface of a soft iron wire 

 itself traversed by a current, owing to the effect of this cur- 

 rent transmitted through the whole mass of the wire. This 

 is moreover proved by the experiments of Mr. Joule, which 

 show that a soft iron wire or rod experiences a shortening from 

 the effect of a transmitted current. It results, therefore, that 

 when the transmitted current is intermittent, the particles of 

 the surface oscillate between that transversal position and their 

 natural one, and that consequently there is a production of 

 vibrations. These oscillations are the more easy, and conse- 

 quently the vibrations are the stronger, in proportion to the 

 softness of the iron ; with hardened iron, and especially with 

 hard steel, there is a greater resistance to overcome, and the 

 effect is consequently less perceptible. In the first case, the 

 transmission of a continuous current, by impressing on the 

 particles in a permanent manner the position which the dis- 

 continuous current tends to give them, must annul or at least 

 materially diminish the oscillatory movement ; this in fact takes 

 place. In the case of the hardened iron or steel, the conti- 

 nuous current must, on the contrary, by disturbing the par- 

 ticles from the normal position, without however being able 

 completely to impress on them the transversal direction, on 

 account of the too great resistance which they offer to a dis- 

 placement, facilitate the oscillatory action of the discontinuous 



nuous currents without external current ; but they acquire numerous poles. 

 Is this magnetization attributable to the effect of the terrestrial magnetism 

 which the molecular vibrations experienced b)' the steel would favour, or 

 is it a direct effect of the current transmitted intermittently? New re- 

 searches would be necessary to solve this question. 



