l£2 Dr. S. W. Richardson on the Magnetic 



The experiments made extend over temperatures ranging 

 from -83° C. to +900° C. 



To obtain the low temperatures, the specimen, wound with 

 primary and secondary coils, was immersed in an ether bath 

 surrounded by a cooling medium of either ice and salt or 

 carbon-dioxide snow. The ether bath was connected with a 

 water-pump, by means of which rapid evaporation could be 

 set up, and the ether thus cooled below the temperature of 

 the surrounding medium. 



The carbon-dioxide snow was obtained from Guinnesses 

 brewery, Dublin, and was sent over in a barrel packed with 

 cowhair. Although the journey took three days, the loss due 

 to evaporation was comparatively small, being not more than 

 one quarter of the whole amount. While working with the 

 carbon-dioxide snow the experiments were continued through- 

 out the night, and on one occasion the author conducted an 

 experiment for 36 consecutive hours. 



The high temperatures were obtained by means of Fletcher's 

 improved muffle-furnace, furnished with a governor to re- 

 gulate the supply of gas to the furnace. In later experiments, 

 however, the alloys have been heated electrically by an ar- 

 rangement similar to that used by Morris* in his experiments 

 on the magnetic properties of iron. This method has been 

 found to be in every respect superior to the furnace method. 



The temperatures were deduced from the resistance of the 

 secondary coil, which was of platinum wire, and was wound 

 next to the ring. 



The chief results obtained from the experiments recorded 

 in this paper may be summed up generally as follows : — 



(1) The alloys behave magnetically as though they con- 

 sisted of two distinct media superposed. 



(2) The general roundness of the curves and their lack of 

 abruptness near the critical point seem to indicate that the 

 alloys are heterogeneous in structure. A similar lack of 

 abruptness near the critical point will be seen in the curves 

 obtained by Hopkinson for nickel-iron alloys. 



(3) The permeability decreases with rise of temperature 

 near the critical point until a minimum value is reached, when 

 further rise of temperature produces very slight diminution, 

 if any, in the permeability. 



Morris f has shown that in the case of iron we have a 

 remanent permeability after passing the critical point (which 

 result has since been corroborated by Hopkinson J). 



(4) The experiments suggest that the maximum value of 



* Phil. Mag. Sept. 1897. t Loc. cit. 



% l Proceedings of the Royal Society/ 1898. 



