of Magnetic and Non-magnetic Bodies, 429 



in the form of a tube, or of a large wire turned into a helix. I 

 likewise convinced myself, by employing rods of large dimen- 

 sions, that the production of the sound could not be attributed 

 either to a calorific effect of the current, nor to a mechanical 

 action exerted by the electro-magnet or by the helix upon the 

 conductors traversed by the discontinuous current. I have 

 since made some new observations which sufficiently show 

 that this kind of action is of a particular nature, probably 

 molecular, like that which takes place in magnetic bodies. 



Let us first remark, that with a single discontinuous current 

 the phaenomenon may be produced without having need in 

 addition of a continuous current or of an electro-magnet. It 

 suffices, for this, to twist the wire which conducts the discon- 

 tinuous current into the form of a helix. A magnet is thus 

 created ; for every time that the current traverses the helix, 

 the latter acquires magnetic properties, and at the same time 

 the wire of the helix is itself a conductor traversed by the dis- 

 continuous current upon which the whole of the helix con- 

 sidered as a magnet acts. Moreover, every helix constructed 

 of any metallic wire, the coils of which, whether covered or 

 not with silk, are more or less pressed together, emits a very 

 distinct sound when it is traversed by a discontinuous current. 

 A continuous current, transmitted in the same direction as the 

 discontinuous one, causes the sound to cease entirely, or di- 

 minishes its intensity materially, although a notable increase 

 results from it in the electro-magnetic intensity of the helix. 

 This neutralizing effisct is probably owing to the fact, that the 

 continuous current impressing permanently on the particles 

 of the wire the position which they should take under the 

 magnetic influence which the helix itself exerts, the disconti- 

 nuous current no longer causes, at the instant when it is trans- 

 mitted, new displacements. This effect is perfectly similar to 

 that which is exerted by a continuous current when it passes 

 through an iron wire traversed by a discontinuous current; 

 it causes a cessation of the sound which this wire made under 

 the action of the last current. 



But if the continuous current, instead of traversing the wire 

 of the same helix which conducts the discontinuous current, 

 circulates through the wire of another helix which surrounds 

 the first, the effect is totally different. In this case the sound 

 is perceptibly increased, and becomes in general more metallic; 

 this increase is more perceptible in proportion to the weakness 

 of the discontinuous current, and the energy of the ambient 

 continuous current. In this experiment the two currents pass 

 in the same direction ; so that the two helices, considered as 

 magnets^ present each the same magnetic pole at their same 



