194 L. 3f. Cheesman — Mechanical Hardening. 



The same holds for the permanent specific magnetism of 

 iron,* as for steel where (^) is less than a . These results are 

 in entire accordance, qualitatively, with the results obtained 

 by Buthsf and others with heat hardened magnets. 



Differences between the mechanical and heat hardening. — We 

 have thus seen that both mechanical and heat hardening bring 

 about changes in steel and iron, which, for the most part, affect 

 their magnetic properties similarly, and the question naturally 

 arises whether there is any reason for believing the conditions 

 caused by each to differ, other than in degree. 



A comparison of their effects on some of the physical prop- 

 erties of steel would seem to require an affirmative answer. 



Thus the specific resistance of steel has been shown to be 

 very materially altered by the heat hardening, a change of 200 

 per cent taking place at times,;}; while the specific resistance 

 of steel wires hardened by " pulling" is thereby altered, at the 



Thus also, if we consider the change of specific gravity by 

 hardening and that of the corresponding specific magnetism, 

 we are led to believe the two conditions to be different ; steel, 

 if heat hardened, has the smallest specific gravity! when hard- 

 est and the largest specific magnetism [pre-supposing y- small], 



hammering, on the other hand, the specific magnetism [^ sma11 ] 



and specific gravity increase together, as I have repeatedly 

 found by experiment 



It would seem also to follow from the foregoing that the 

 — -~h moment is not dependent on the specific gravity, as 



