1895.] 



in the Magnetic Permeability of Iron. 



241 



Table IV. 



(Without application of heat ; magnetised only for a few minutes 

 occasionally for purpose of measuring loss.) 



Watts. 

 Before applying pressure ...... 59'8 



-^ . f 72*5 on application. 



r^?! " - Pr J 70 ' 2 ^ 9 day- 

 of 1500 Ibs. per sq. m. (10'57< . * 



-i-i \ ! '* - 44 



kilos, per sq. cm,) [ 7Q . 2 ^ 8Q 



Without pressure ............ 59 ! 4 on 30th day. 



The author has a test in hand to find the effect of heat combined 

 with considerable pressure, but cannot yet give any results. 



APPENDIX II. 

 The results obtained in this way, so far as the investigation has 



gone, 



are as follows : 



A ring was made up of iron ribbon, wound in a close volute, the 

 convolutions separated from each other by paper. This was then 

 wound with a magnetising winding of copper wire covering the 

 whole ring. A test was taken on January 15, 1895, of the resistance 

 of the iron, and of the energy spent in magnetising it to 2500 B at 

 100 /^/. It was then kept in an oven at a temperature ranging 

 between 60 and 75 C. It was taken out, cooled, and the tests 

 repeated on January 25 and February 8 as below : 



Thus the hysteresis loss has gone up considerably, as a result of 

 continued heating, and the resistance has also risen. This result is 

 in accordance with what is known as to the connection between the 

 magnetic permeability and the electrical resistance of iron. Pro- 

 fessor Hughes showed many years ago* that the lower the resistance 

 of iron the better its magnetic qualities. 



As bearing on this point, the author has measured the resistance of 

 some soft annealed iron strips, which were then hardened by being 



* Eoy. Soc. Proc.,' December, 1883. 



