1887.] Stress and Strain on the Properties of Matter* 227 



When the above-mentioned limit is exceeded the effect of the per- 

 manent strain is reversed. 



15. The effects mentioned in 12, 13, and 14 are for the most part 

 really the results of subpermanent molecular strain, and can be in great 

 measure removed by severely shaking the wire. 



16. The permanent molecular strain which is left on the removal of 

 any load, produces, both for low and high magnetising forces, a per- 

 manent diminution of magnetic permeability increasing with the 

 strain up to a certain amount of the latter. When, however, the 

 strain is such that the wire is sensibly increased in length, the tem- 

 porary permeability increases considerably, and the permanent permea- 

 bility diminishes considerably up to a second limit of permanent 

 strain, when once more decrease of temporary permeability sets in. 



17. The first maximum of the decrease of permeability mentioned 

 in 16 at first decreases with increase of the magnetising force to 

 nearly zero ; it increases again, however, if we exceed a. certain limit 

 of magnetising force. 



On the contrary, the maximum increase of temporary permeability 

 at first rises with the magnetising force until the permeability is more 

 than doubled, when it begins to fall as the magnetising force is pushed 

 further. 



18. Mere rest after permanent extension has little or no effect on 

 the alteration of the temporary permeability which is produced by 

 loading, whereas it very perceptibly increases the longitudinal elasti- 

 city of iron. 



19. For magnetising forces not exceeding a certain limit there are, 

 for all temperatures between 0° C. and 300° C, two critical values of 

 loading for which no alteration in the temporary permeability is pro- 

 duced by the load (see 1). 



The value of the load at the first critical point diminishes, and that 

 at the second critical point increases, as the temperature is raised from 

 0° C. to 100° C. but as the temperature is raised still further the 

 first critical load becomes greater and the second becomes less, until 

 at some temperature between 250° C. and 300° C. the two critical 

 points coincide. 



20. For magnetising forces exceeding a certain limit the two critical 

 points of loading approach each other, at first slowly and then rapidly, 

 with increase of temperature from 0° C. to 300° C. Both critical 

 loads diminish with rise of temperature, but the second more rapidly 

 than the first. 



21. The effect of loading on the permanent permeability diminishes 

 with rise of temperature from 0° C. to 300° C. 



22. As the magnetising force increases, the total magnetic permea- 

 bility of annealed iron which has not been previously magnetised rises 

 to a maximum and then begins to decline. The maximum permeabi- 



r 2 



