Crook — Yoke with iritercepted Magnetic Circuit, etc. 365 



Art. XXX. — On a Yoke with intercepted Magnetic Circuit 

 for measuring Hysteresis ; by Zeno Crook, A.M., Fellow 

 in Physics, University of Nebraska. 



Hopkinson's bar and yoke method of studying the mag- 

 netic hysteresis in iron necessitates either breaking the con- 

 tinuity of the magnetic circuit in the specimen to be examined 

 or using the " step up " method. In many instances it is 

 impossible to break the magnetic circuit as in the first method, 

 while the " step up " method cannot be used when it is desir- 

 able to determine the magnetic flux without varying the same. 

 For example, if we wish to study the effect on the magnetic 







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flux of an electric current it is impossible to break the mag- 

 netic circuit or vary the same during the observations. These 

 difficulties may, however, be overcome by measuring the flux 

 in the yoke itself. This method has been resorted to by 

 Koepsel and others in direct-reading permeameters. In all 

 these instruments, however, the air gap is so large that the 

 reluctance of the circuit is very much increased. 



' These difficulties are overcome in a yoke designed by 

 Professor D. B. Brace and constructed for him by Messrs. 

 Siemens and Halske of Berlin. This yoke was forged from 

 the best Norway iron and carefully annealed. Its cross-sec- 

 tion is 100 □ cm. and the mean length of its magnetic circuit 

 is 54 cm . It is divided into two like parts. The two halves, 

 fig. 1, are mounted on a solid base and so arranged that the 



A.M. Jour. Sci.— Fourth Series, Vol. XI, No. 65.— May, 1901. 

 24 



