1881.] Molecular Electro- Magnetic Induction. 



535 



or recomposition of its magnetism. For this purpose, using no 

 battery, I join the rheotome and telephone to the coil, the wire having 

 no exterior circuit. If I strongly magnetise the two ends of the wire, I 

 find by rapidly moving the coil, that there is a Faradaic induction of 

 50° at both poles, but very little or none at the centre of the wire ; now 

 fixing the coil at the centre or neutral point of the wire, and listening 

 intently, no sounds are heard, but the instant I give a slight elastic tor- 

 sion to the free pole, a rush of electric tertiary induction is heard, whose 

 value is 40°. Again, testing this wire by moving the coil, I find only 

 a remaining magnetism of 10, and upon repeating the experiment of 

 elastic torsion, I find a tertiary of 5 ; thus we can go on gradually dis- 

 charging the wire, but it will be found that its discharge is a recom- 

 position, and that it first passed through the stage I have mentioned. 



Heat has a very great effect upon molecular magnetic effects. On 

 iron it increases the current, but in steel the current is diminished. 

 For experimenting on iron wire, which gave a tertiary current of 50° 

 positive (with a torsion of 20°), upon the application of the flame of 

 a spirit-lamp, the force rapidly increases (care being taken not to ap- 

 proach red heat), until the force is doubled, or 100 positive. The same 

 effects were obtained in either direction, and were not due to a molar 

 twist or thermo-current, as if care had been taken to put on not more 

 than 10° of torsion, the wire came back to zero at once on removal of 

 the torsion. Hard tempered steel, whose value was 10° whilst cold, 

 with a torsion of 45°, became only 1° when heated, but returned (if 

 not too much heated) to 8° when cold. I very much doubted this 

 experiment at first, but on repeating the experiment with steel several 

 times, I found that on heating it, I had softened the extreme hard 

 (yellow) temper to that of the well-known blue temper. Now, at 

 blue temper, hot, the value of steel was but 1° to 2°, whilst soft iron of 

 a similar size gave 50° of force cold, and 100° at red heat. Now, as 

 I have already shown that the effects I have described depend on 

 molecular elasticity, it proves at least, as far as iron and steel are 

 concerned, that a comparatively perfect elastic body, such as tempered 

 steel, has but slight molecular elasticity, and that heat reduces it, but 

 that soft iron, having but little molar elasticity, has a molecular 

 elasticity of a very high degree, which is increased by heat. 



The objects of the present paper being to bring the experimental facts 

 before the notice of the Royal Society, and not to give a theoretical 

 solution of the phenomena, I will simply add, that if we assume with 

 Poisson, that the paths of the molecules of iron are circles, and that 

 they become ellipses by compression or strain, and also that they are 

 capable of being polarised, it would sufficiently explain the new effects. 



Joule has shown that an iron bar is longer and narrower during 

 magnetisation than before, and in the case of the transverse strain, the 

 exterior portions of the wire are under a far greater strain than those 



2 p 2 



