1887.] Stress and Strain on the Properties of Matter. 221) 



On the contrary the load at the second critical point increases as 

 the magnetising force diminishes. 



32. The effect of increasing the magnetising force on both the first 

 and second critical loads is therefore opposite in direction to the effect 

 in the case of iron. 



33. Similarly the effects mentioned in 3 are opposite in direction in 

 nickel and in iron. 



34. Rise of temperature from 0° C. to 300° C. increases the maxi-. 

 mum increase of temporary magnetic permeability, which can be 

 effected by loading nickel wire, and diminishes the maximum 

 decrease. 



35. With nickel as with iron the magnetic permeability is not 

 constant, but reaches a maximum. The magnetising force which 

 produces maximum permeability is greater with nickel than with 

 iron, but the magnetic intensity at the point of maximum permeability 

 is less with nickel than with iron. 



36. Nickel wire can by shaking be more effectually de-magnetised 

 than iron. 



37. Well annealed nickel is capable of retaining subpermanently 

 a very large percentage of the whole magnetisation imparted. The 

 maximum percentage retained is, however, not so great as with 

 iron. 



38. At a certain temperature the magnetic permeability of nickel 

 vanishes. The temperature at which this occurs seems to be higher 

 the higher the magnetising force. This last, however, may perhaps 

 be due to impurities in the nickel. 



39. The magnetic permeability of nickel rises with the temperature 

 to a maximum and then diminishes. The temperature at which 

 maximum permeability occurs diminishes as the magnetising force 

 increases. 



40. The temporary effects of compression on the temporary mag- 

 netic permeabilities of iron, nickel, and cobalt, are in the opposite 

 direction to the effects of extension, provided neither the mechanical 

 nor the magnetic stress exceeds a certain amount. 



41. The temporary effect of traction transverse to the line of 

 magnetisation on the magnetic permeability of iron, is opposite in 

 direction to the effect of traction in the same line as the magnetisa- 

 tion. 



42. Temporary torsion beyond a certain limit (see 44) increases 

 the temporary magnetic permeability of iron. The amount of in- 

 crease may become very large if the wire has previously suffered 

 permanent torsion or permanent magnetisation in the opposite direc- 

 tion. , 



43. Permanent torsion decreases the temporary magnetic per- 

 meability. The amount of decrease may become very large if the 



