194 



Prof. D. E. Hughes. 



[May 10, 



can, however, perceive the result of a supposed cause, and, as De la 

 Hive has done, base a theory upon molecular rotation ; but if we have 

 previously analysed these movements by the aid of the induction 

 balance, the following experiments will render visible effects due to 

 molecular rotation. 



The apparatus needed is simply a good compound horseshoe 

 permanent magnet, 15 centims. long, having six or more plates, 

 giving it a total thickness of at least 3 centims. We need a suffi- 

 ciently powerful magnet, as I find that I obtain a more equal 

 distribution of magnetism upon a rod or strip of iron by drawing it 

 lengthwise over a single pole, in a direction from that pole as shown in 

 fig. 5, as we can then obtain saturation by repeated drawings, keeping 

 the same molecular symmetry in each experiment. A few well 

 suspended magnetic needles of different powers are required, and as 

 the needle itself induces magnetism, all observations should be made 

 as far as possible by means of repulsion, repulsion being the only 

 certain test (whenever the magnetism is feeble) that the iron or 

 steel possesses independent polarity from that induced by the 

 needle. 



We should have also several flat strips of hoop-iron or thin band- 

 iron, varying in width from 1 to 3 centims., and at least 30 centims. 

 long, in order to observe one polarity free from the disturbance 

 caused by the other. I find rods § millim. in thickness are the most 

 easily magnetised to saturation, and this is the size of ordinary 

 common hoop or band iron sufficing for the following experiments. 



If we magnetise one of these rods by drawing it over one of the 

 poles of the permanent magnet, we find that it is strongly magnetic ; 

 bat if we apply a few slight elastic torsions the magnetism rapidly 

 disappears. This effect has been observed and numerous researches 

 have been made on this subject since Gilbert, 1600. Wertheim, 1857, 

 in the " Ann ales de Chimie," has given a detailed account of his 

 experiments upon the diminution of magnetism by torsion. 



The diminution depends entirely upon the freedom of its molecules, 

 for if we take a pure Swedish charcoal iron well annealed, a single 

 slight torsion completely renders the rod free from magnetism, the 

 molecules at once rotate to neutrality. I have in my possession, and 

 will demonstrate with it at the reading of this paper, a solid bar of 

 iron, 2 centims. diameter, 40 centims. in length, which, when strongly 

 magnetised, and acting strongly upon the magnetic direction needle, 

 loses instantly all its apparent residual magnetism by the simple 

 torsion produced by the fingers upon its surface. Hard tempered 

 steel loses but 2 per cent, by continuous and violent torsion, its 

 molecular rigidity is so great that we cannot rotate the molecules by 

 any mechanical strains. We may thus roughly estimate the degree of 

 molecular freedom by the number of torsions required to render it 



