1893.] Magnetic Viscosity. 353 



Fig. 1. 



ing a resistance into the primary circuit. The resistance R 2 was 

 so adjusted that the maximum current in the primary circuit was 

 such as to give the desired maximum magnetising force on the 

 ring. 



In taking the kicks on the ballistic galvanometer the method 

 adopted was as follows : — Having closed the primary by means of Si, 

 the switch S 2 was suddenly opened, thus allowing the magnetising 

 force to drop to an amount determined by B^, and the kick observed. 

 A total reversal was then taken with S b and the kick again observed. 

 The closing of S 2 again brought up the magnetising force to its 

 maximum in the opposite direction to that at starting. 



In a letter to the editor of the ' Electrician,' September 16, 1892, 

 Mr. Evershed stated that " Had the slow cycle been obtained by the 

 method described by Mr. Vignoles,* Messrs. Hopkinson would have 

 found it in almost absolute agreement with the quick cycle curve." 



To settle this point the static curve of hysteresis was obtained by 

 the ballistic galvanometer, the connexions being made according to 

 the diagram in fig. 2. This is not the method of experiment alluded 



Fig. 2. 



AcLf-ustajb CeHeslstcuzc&s . 



to by Mr. Evershed, but it is capable of varying 1he magnetising 

 force in the same way as is described by him. R is the hard steel 

 * ' Electrician,' May 15 and 22, 1891. 

 VOL. LIU. 2 C 



