Chap. 8] 



MAGNETIC METHOD 



307 



shown in Fig. 8-10, a transformer with 

 secondary in series opposition with the 

 induction coil was used to compensate 

 for current fluctuations in the magnetiz- 

 ing circuit. The quantity of electricity^ 

 Q induced in the coil by pulling a speci- 

 men of the magnetic moment M through 

 it is given by 



Q = 



47rA^oKHy.lO" 



R 



coulombs, (8-13) 



where No is the number of turns per unit 

 length on the ballistic coil, R the resist- 

 ance of the ballistic circuit, v the volume, 

 and H the reduced magnetizing field in 

 the specimen. A number of hj'^steresis 



curves taken in this manner are illustrated in Figs. 8-11 to 8-14. 



Remanent magnetism and coercive force may be determined qualitatively 



in the earth's field and quantitatively from hysteresis loops. The first 



Fig. 8-10. Arrangement for bal- 

 listic susceptibility determination 

 (after Puzicha). A, ammeter; B, 

 ballistic galvanometer; T, trans- 

 former; S, magnetizing coil. 



*■// 



Fic. 8-11. Hysteresis curve of magnetite, Striberg, Sweden (after Puzicha). 



method consists of a determination of the difference in the attraction of a 

 specimen when reversed 180° (see page 300). If dr is the remanent mag- 

 netization and if Si and S2 , respectively, are deflections obtained in the two 

 positions of the specimen, the intensity of remanent magnetization 

 (assuming that the two magnetizations can be added algebraically) 

 Br = (si — S2)/2. dr is oftcn expressed in percentages of Bi. Coercive 

 force and remanent magnetism may be determined directly from the 



