366 Dr. J. R. Ashworth on the Anhysteretic 



The principal characteristics of these curves are the same 

 for iron and nickel, but as the effects in nickel are more 

 pronounced, and as this metal is not apparently affected try 

 anomalous thermal disturbances as iron is, attention may be 

 directed more particularly to the nickel curves. 



A prominent feature to note is the concavity of the curves 

 to the axis of temperature until the critical temperature is 

 reached, when an inflexion takes place, and the curve after- 

 wards passes outwards asymptotically. All the curves as 

 far as the critical temperature exhibit the features which are 

 associated with forces strongly orientating the molecular 

 magnets. The concavity of these curves, however, always 

 grows less as the external field diminishes, and in the curve 

 for H = 0'65, in nickel, it has nearly disappeared and the 

 curve is almost linear for the greater part of its course. 



There is one feature of interest and importance which is 

 strongly marked in this curve and is observable in the others;, 

 the convexity of the curve, which is its characteristic above 

 the critical point, expands under low fields, and one is led to 

 think that for a still lower field with an appropriate alter- 

 nating current it might pervade the whole curve. The 

 entire group of curves would then exhibit a gradual change 

 from ferro-magnetic to para-magnetic properties*. 



(8) To test this view another set of experiments was. 

 arranged with this minor difference, that in this set the 

 alternating current, instead of being led through the wire, 

 was sent through the solenoid surrounding it, and the- 

 magnetic force acting on the nickel wire was the vertical 

 component of the Earth's magnetism. Alternating currents, 

 of l'O, 1*7, and 2*0 amperes were . successively used, and 

 the results which are graphed in Diagram VII. show the 

 increasing expansion of the convex part of the curve. The 

 curve obtained when the alternating current was 2*0 amperes 

 is particularly interesting, as it would be difficult to fix for it 

 a definite critical temperature. Observations (omitted from 

 the diagram) which were taken when the alternating current 

 was 3*0 amperes yielded a curve of similar shape to the one 

 at 2*0 amperes. 



In Diagram VI. the most prominent feature is the fact that 

 the critical temperature can be lowered nearly 100 9 C. by 

 the application of an alternating current, and it is now clear 

 from Diagram VII. that it may be made almost indefinite. 



* A purely para-magnetic material is such that I is directly propor- 

 tional to H and inversely proportional to T. 



