252 



PROCEEDINGS OE THE AMERICAN ACADEMY. 



The Investigation of Toroid II. 



Coil II occupied the same position with respect to the circuit, (Fig- 

 ure 3,) as did coil I ; the secondary was in series with the ballistic gal- 

 vanometer and the secondary of the calibrating coil, the primary in 

 series with the amperemeter, rheostats, and storage cells. 



The method of demagnetization was that first used, the reversing 

 switch (Figure 3), and the alternating current transformer. Certain 



features of the latter are 

 important. The secondary 

 could not be drawn con- 

 tinuously away from the 

 primary without reducing 

 the demagnetizing fields 

 more rapidly than was 

 deemed advisable. Hence it 

 was moved a short distance 

 and allowed to rest a few 

 seconds. This reduced the 

 field by steps and in such a 

 manner that both the total 

 number of steps and the 

 number of reversals in each 

 step were not regulated even 

 roughly. Consequently no 

 two magnetizations were ex- 

 actly alike or approximately 

 alike. In other words, the 

 history of the iron just 

 previous to what we have 

 regarded as the initial con- 

 dition, was subject to varia- 

 tion. It would be strange 

 if the initial condition were not afiected by this variation. In that 

 case the result of the first application of the field to the iron after one 

 demagnetization might well differ from that obtained by the first 

 application after the next demagnetization. 



The work on this coil was done before that on coil I, but as the 

 results can be discussed more readily by reference to the more exten- 

 sive data on the latter it was thought best to treat them in this order. 

 The objection to any extended investigation with coil II lay in a weak 

 consequent pole discovered at one point in the ring. The difficulties 



Figure 14. Set IV: B 10,100: first mag- 

 netization; O indicates 1-step reversals; x 

 5-step reversals. 



