1881.] 



Molecular Magnetism. 



223 



similar but reverse action takes place as regards torsion ; for if the 

 wire is magnetised by the coil we obtain an almost complete zero of 

 sound by simply moving the torsion index 45° on either side, and as 

 this was the degree which gave silence in the previous experiments 

 for the same wire, it was no doubt due to the same rotation of its 

 polarised molecules. If we now pass a constant current through the 

 wire whilst the intermittent one is upon the coil, we hear augmented 

 sounds, not in pitch but loudness ; and if we give torsion of 45° to one 

 side we have silence, or nearly so, whilst, to the other side, it gives 

 increased tones which become silence by reversing the battery. If, 

 whilst the wire by torsion has been brought to zero, we decrease or 

 increase the mechanical longitudinal strain, then at once the polarised 

 molecules are rotated, giving loud sounds ; and we further remark 

 that when the wire is loosened, and we again tighten it, we gradually 

 approach a zero, and on increasing the strain the sounds return ; thus 

 we can rotate the molecules by a compound strain of torsion and 

 longitudinal strain. 



If we wish to notice the influence of a constant current passing 

 through the wire under the influence of the intermittent current in 

 the coil, we find, if the wire is free from torsion, that, on passing 

 the current, the tones are diminished or increased according to the 

 direction of the current. The tones then have an entirely distinctive 

 character, for whilst preserving the same musical pitch as before, 

 the tones are peculiar, metallic, and clear, similar to those given out 

 when a glass is struck, whilst the tones due to longitudinal magnetism 

 are dull and wanting in metallic timbre. If we now turn the index of 

 torsion upon one side, we have a zero of sound with or without the 

 current; but turning in the opposite direction gives increased tones 

 whilst current is passing through the wire, but zero when not. Here 

 again a peculiarity of timbre can be noticed, as although we have loud 

 tones due only to the action of the current through the wire, the timbre 

 is no longer metallic, but similar to that previously given out by the 

 influence of the coil ; evidently then the metallic ring could only be 

 due to the angular polarisation of the molecules, and when these were 

 rotated by torsion the tones were equally changed by its action upon 

 the wire. 



I have already shown that a permanent magnet brought near the 

 wire can rotate its polarisation, and it equally can produce sound or 

 silence (while the wire is at its zero of torsion, and a constant current 

 is sent through the wire as in the last experiment) : we find that 

 either pole of the natural magnet has equal effect in slightly diminish- 

 ing the sound by an equal but opposite rotation from the line of its 

 maximum effects ; but if the wire is brought nearly to zero by torsion, 

 then on approaching one pole of the natural magnet we produce a 

 complete silence, but the opposite pole at once rotates the molecules 



