﻿40 Dr. Ashworth on Magnetic Temperature Coefficients 



value, when there is a sudden drop to about 5 or 6 per cent., 

 after which the magnetism diminishes more slowly. 



Fig. 1. — Relation of Fractional ^Magnetic Intensity (I/T ) to 

 Temperature (C°). 

















■9 

 •8 

 ■7 

 "6 





I ~~"^L 



Zp^- 





^^^^--^ 









N 





'T^^kv 



— -6 







\ 



\ 











A/?c/r.£ 



L ^ • 





\ 







\ 





CCBflL T 







\ 



\ 







\ 











1 









\ 



I 















• 



! 















i 





















1 

 1 



The curve for iron falls smoothly tip to about 400° C. when 

 a more rapid fall begins followed by a halt or even rise of 

 magnetic intensity between 500° and 600°, after which the 

 diminution continues in a similar way to nickel, until at 

 30 per cent, of the original intensity the abrupt drop to a 

 much lower value occurs. The irregularity at 420° to 620° 

 embraces the region where there is au evolution of heat, 

 discovered by Roberts- Austen *, which he says is not 

 sudden but covers a range of 100° to 180°. It is no doubt 

 associated with the point which has been designated ArO. 

 Changes in electrical resistance have been observed in this 

 region by Prof. H. L.' Callendar f, and peculiarities in the 

 magnetic" permeability when iron passes through this range 

 of temperature have been described by Prof. D. K« Morris J. 

 The residual magnetism of iron appears to be in a very 

 sensitive state between 400° and 600° and behaves very un- 

 certainly, but the thin line in the diagram may be taken as 

 approximately the path which the magnetism follows on 

 heating. On cooling the halt occurs at a lower temperature 

 than on heating. 



When cobalt is first heated, there is a small increase of 

 magnetic intensity and it is not until about 250° that the 



* Alloys Research Comni. otli Eeport. 

 t Phil." Trans. Boy. Soc. 1887, p. 201. 

 | Phil. Mag. vol. xliv. 1897, p. 213. 



