320 



Seientific Proceedings^ Royal Dublin Society. 



during a period of six months. In every ease, as will be seen from Table IV., 

 the magnetic moment is increased after the month's rest, due no doubt to the 

 material coming back to its state of molecular equilibrium after the heat 

 treatment ; there is then a gradual decrease in the moment till each of the 

 four magnets becomes practically permanent. 



It is well known that the value of the dimension ratio of a magnet makes 

 a great difference in its permanent magnetism.' The B-H cyclic curves of 

 the four specimens in fig. 3 were determined some ten years ago,' tlieir 

 dimension ratio being about 200 ; and by taking the residual induction tlien 

 obtained, and dividing by 47r times the density of the material, we get the 

 specific magnetization or magnetic moment per gramme as shown here in 

 Table V. 



Table V. 



There is no evident relation between tlie numbers in the last column of 

 this table and the corresponding numbers in the tenth column of Table IV. 

 The values in Table V., however, are of the same order as those obtained by 

 Hopkinson for chrome and tungsten steels,* whose method of testing was a 

 closed circuit one. The values of the specific magnetizations are 97 for the 

 specimen containing W = 4-65 ; C = 1'36, and 68 for that containing W = 2-35 ; 

 C = 0-86. 



1 The Electromagnet, S. P. Thompson, p. 383. 



2 Scient. Trans. Royal Dublin Soc, vol. vii., 1900, p. 67. 



3 Scient. Trans. Royal Dublin Soc, vol. ix., 1907, p. 59. 



^ Phil. Trans. Roy. Soc, vol. clxxvi., part 2, p. 463, 1885. 



