14 Stress and Strain and the Properties of Matter. [Dec. 5, 



the dissipation of energy, arising from statical friction among the 

 molecules, in the performance of the cycle. 



4. The internal friction of iron, nickel, and cobalt in any complete 

 cycle may be decreased by repetition of the cycle ; the molecules are 

 said to be " accommodated " by this process. 



5. The molecular " accommodation " of freshly-annealed iron can 

 be largely aided by repeatedly raising the metal to 100° C. and then 

 allowing it to cool. 



6. The "accommodation" of the molecules of iron, nickel, and 

 cobalt is disturbed by very slight mechanical shocks, by small change 

 of temperature, or by magnetisation beyond certain limits ; under 

 such influences the internal friction may for a time, or even per- 

 manently, be considerably increased. 



7. The values of A and B for iron, nickel, and cobalt can be very 

 largely decreased by permanent mechanical strain. They may also 

 be largely decreased in the case of steel by sudden cooling from a 

 high temperature. No amount of strain, however, whether produced 

 by mechanical or thermal agency, can reduce either the magnetic 

 permeability or the internal friction below certain limits. 



8. The values of A and B for iron are temporarily increased by 

 loading not carried beyond a certain limit ; beyond this limit both A 

 and B decrease with increase of load. 



9. The values of A and B for iron, nickel, and cobalt are temporarily 

 increased when the temperature is raised from 0° C. to 100° C. 



The amount of increase is much greater in freshly-annealed iron 

 wire than in the same wire after it has been repeatedly raised to 

 100° 0. and then cooled. 



10. In both torsional and magnetic cycles of sufficiently minute 

 range, the dissipation of energy from internal friction is independent 

 of the rate at which the cycle is performed. 



11. In both torsional and magnetic cycles of given range of force 

 the average dissipation of energy per cubic centimetre does not 

 depend upon the dimensions, provided that in magnetic cycles the 

 length is sufficiently great to permit of neglecting the effect of the ends. 



12. It follows from 3 that the dissipation of energy in a magnetic 

 cycle is proportional to the cube of the maximum magnetising force 

 in the cycle. On the contrary, the dissipation of energy in a torsional 

 cycle is proportional to the square of the maximum torsional force 

 provided the force does not exceed certain limits. 



13. As regards "accommodating" influences and also as regards 

 those influences which disturb " accommodation," the dissipation of 

 energy in a magnetic cycle seems to be strictly analogous to the 

 dissipation of energy in a torsional cycle. But the temporary and 

 permanent effects of mechanical stress and the temporary effects of 

 change of temperature are very different in the two kinds of cycles. 



