562 



Professor Dewar 



[Jan. 22, 



being greater tlian unity, a deflection of the ballistic galvanometer 

 was observed on reversing the same primary current. The induction 

 through the primary circuit of the small transformer is increased in 

 the same proportion that the permeability of the transformer core 

 is increased by the substitution of liquid oxygen for gaseous oxygen, 

 and hence the ballistic deflection measures at once the amount by 

 which the magnetic permeability of the liquid oxygen is in excess 

 over that of the air or gaseous oxygen forming the core of the trans- 

 former when the transformer is lifted out of the liquid. As a matter 

 of fact, it was never necessary to obtain the inductive balance pre- 



WWW 

 r\AAAA/\ 



Vwvw 



r 



Fig. 2. — Arrangement of the Circuits of the Transformer and Induction Coil. 



cisely. All that was necessary was to observe the throw of the bal- 

 listic galvanometer, first when the transformer was wholly immersed 

 under the surface of liquid oxygen, and, secondly, when it was lifted 

 out into the gaseous oxygen lying on the surface of the liquid, the 

 strength of the primary current reversed being in each case the same. 

 In order to standardise the galvanometer and to interpret the mean- 

 ing of the ballistic throw, it was necessary to cut out of circuit 

 the primary coil of the balancing induction coil, and to reverse 

 through the primary circuit of the small transformer a known small 

 primary current, noting at the same time the ballistic throw pro- 

 duced on the ballistic galvanometer, this being done when the 

 transformer was underneath the surface of liquid oxygen. It will 

 be seen, therefore, that this method requires no calculation of any 



