1891.] on the Molecular Process in Magnetic Induction. 401 



and heat is absorbed which is given out again when the reverse 

 change takes place. In cooling from a red heat, the iron actually 

 extends at tlie moment when this change takes place (as was shown 

 by Gore), and so much heat is given out that (as Barrett observed) it 

 reglows, becoming brightly red, though just before the change it had 

 cooled so far as to be quite dull. [Experiment, exhibiting retraction 

 and reglow in cooling, shown by means of a long steel wire, heated to 

 redness by the electric current.] The changes which occur in iron 

 and steel about the temperature of redness are very complex, and I 

 refer to this as only one possible direction in which a key to them 

 may be sought. 



An interesting illustration of the use of these models has reached 

 me, only this morning, from New York. In a paper just published in 

 the Electrical World * Mr. Arthur Hoopes supports the theory I have 

 laid before you by giving curves which show the connection, deter- 

 mined experimentally, between the resultant polarity of a group of 

 little pivoted magnets and the strength of the magnetic field, when 

 the field is applied, removed, reversed, and so on. I shall throw these 

 curves upon the screen, and, rough as they are, in consequence of the 

 limited number of the magnets, you see that they succeed remarkably 

 well in reproducing the features which we know the curves for solid 

 iron to possess. 



It may, perhaps, be fairly claimed that the models whose behaviour 

 we have been considering have a wider application in physics than 

 merely to elucidate magnetic processes. The molecules of bodies 

 may have polarity which is not magnetic at all — polarity, for instance 

 due to static electrification — under which they group themselves in 

 stable forms, so that energy is dissipated whenever these are broken 

 up and rearranged. When we strain a solid body beyond its limit of 

 elasticity, we expend work irrecoverably in overcoming, as it were, 

 internal friction. What is this internal friction due to but the 

 breaking and making of molecular ties ? And if internal friction 

 is to be ascribed to that, why not also the surface friction which causes 

 work to be spent when one body rubs upon another ? In a highly 

 suggestive passage of one of his writings, | Clerk Maxwell threw out 

 the hint that many of the irreversible processes of physics are due to 

 the breaking up and reconstruction of molecular groups. These models 

 help us to realise Maxwell's notion, and, in studying them to-night, 

 I think we may claim to have been going a step or two forward 

 where that great leader pointed the way. [J. A. E.] 



* Reprinted in the Electrician of May 29tli, 1891. 

 t ' Eiicyc. Bi'it.' Art. '• Constitution of Bodies." 



