272 



Prof. J. A. Ewing. 



[June 20, 



Adding to these the equivalent of the compensating coil, we see 

 that just after the immediate magnetising force was suddenly applied, 

 the value of the magnetism was 25, which increased after 5 seconds 

 to 33, and after 1 minute to 38 ; and that when the magnetising force 

 was suddenly withdrawn, there was at first a residual magnetism 

 of 13, which fell to 5 in 5 seconds, and disappeared altogether in less 

 than 1 minute. 



Next a current 41 (producing a magnetising force of 0*084 c.g.s.) 

 was made and broken in the same way. The compensating coil 

 scarcely required to be moved from its former position, and its equi- 

 valent on the magnetometer was now 48. The column headed " to f tal " 

 gives the sum of the magnetometer reading and the part balanced by 

 the compensating coil. 



Magnetometer. 



Time after 

 " make." 







5" 

 60" 



Observed. 





 20 

 31 



Total. 

 48 

 68 

 79 



Time after 

 < 'break." 







5" 

 60' 7 



Magnetometer. 



31 

 13 

 4 



Here out of the whole original residue of 31, a small part refused 

 to disappear after the lapse of a minute, and it is probable that with 

 this magnetising force some of the residual magnetism is permanent. 



Fig. 1. 



The above results are shown in fig. 1 where the arrows indicate the 

 sequence of magnetic changes. One scale division of the magneto- 

 meter is here equivalent to 0'01 7 7 c.g.s. units of | (intensity of 



