188 



Prof. D. E. Hughes. 



[May 10 ; 



induced force as before, and with the same clear zero. Thus the 

 molecules are not only rotated by torsion as already shown, but they 

 have an inherent polarity which cannot be augmented nor destroyed. 



We may, however, increase the molecular rotation and consequent 

 force obtained by the application of heat, thus allowing greater 

 molecular freedom. Annealing increases the effect in iron in a 

 marked degree, and alloying has a marked influence in rendering the 

 molecules of iron more rigid. The induction balance allows us to 

 appreciate this differential freedom in different varieties of iron and 

 steel, and in a future paper I shall show how this phenomenon of 

 rotation can be applied to important practical results by investigations 

 into the chemical nature of different varieties of iron and steel, 'and 

 show distinctly the separating line of iron and steel. 



Molecular Inertia. 



A phenomenon of inertia is observed in these experiments, which I 

 regard as not only being a proof of rotation, but of possession by the 

 molecules of true inertia. For when a slight torsion of 20° has been 

 applied to the strip or rod of iron, and we return it slowly to its zero 

 of torsion, we have a remaining rotation of the character of residual 

 magnetism ; this is generally about a quarter of the maximum effects 

 and of the same polarity, the rod then requiring a momentary 

 mechanical vibration in order to allow the molecules freedom to 

 return, which they at once do to an absolute zero ; we have here a 

 lagging behind which is characteristic of inertia. We have, however,, 

 more evident proofs, for if instead of freeing the rod gradually from 

 torsion, we allow it to spring back suddenly, then the molecules 

 continue their rotation by their acquired velocity far beyond zero, 

 producing in most cases (where the rod of iron is very soft) a 

 contrary polarity of fully one-half of its previous value, and although 

 the rod is perfectly free from torsion, we must apply a slight torsion 

 in the previous direction before obtaining a zero ; we have here a zero 

 under torsion evidently due to molecular inertia, for the instant- we 

 give the slightest mechanical vibration to the rod, the molecules 

 return to their true zero, and now the slightest torsion produces its 

 true polarity as before. 



This inertia is far greater in soft iron than in hard iron or steel, 

 be ing directly proportional to its softness, the consequence of this 

 being that the time of rotation or discharge of soft iron is very slow 

 compared with that of steel, and requires a compensation for time of 

 discharge for each species of iron. I have already mentioned this as a 

 difficulty in obtaining true zero observations, and I now make use of 

 this very troublesome inertia to determine at once the degree of 

 softness of any wire or rod. 



We can understand this phenomenon when we know that while the 



