1897.] on Properties of Liquid Oxygen, 561 



which is at the same temperature. On lifting out the transformer, 

 the liquid oxygen drains away from the interior of the primary coil, 

 and is replaced by gaseous oxygen of very nearly the same tem- 

 perature. 



The vacuum vessel used had a depth of 60 cm. outside and 53 cm. 

 inside, and an internal diameter of 7 cm. It held 2 litres of liquid 

 oxygen when full ; but, as a matter of fact, 4 or 5 litres of liquid 

 oxygen were poured into it in the course of the experiment. 



Another induction coil was then constructed, consisting of a long 

 cylindrical coil wound over the four layers of wire, and a secondary 

 circuit was constructed to this coil, consisting of a certain number of 

 iurns wound round the outside of the primary coil, and a small 

 adjusting secondary coil, consisting of a thin rod of wood wound over 

 with very open spirals of wire. The secondary turns on the outside 

 of the primary coil were placed in series with the turns of the thin 

 adjusting coil, and the whole formed a secondary circuit, partly out- 

 side and partly inside the long primary cylindrical coil, the coefficient 

 of mutual induction of this primary and secondary coil being capable 

 of being altered by very small amounts by sliding into or out of the 

 primary coil the small secondary coil. This last induction coil, which 

 will be spoken of as the balancing coil, was connected up to the small 

 transformer, as just described, as follows : — 



The primary coil of the small transformer was connected in series 

 with the primary coil of the balancing induction coil, and the two 

 terminals of the series were connected through a reversing switch 

 and ammeter with an electric supply circuit, so that a current of 

 known strength could be reversed through the circuit, consisting of 

 the two primary coils in series. The two secondary coils, the one on 

 the transformer and the one on the balancing induction coil, were con- 

 nected in opposition to one another through a sensitive ballistic 

 galvanometer in such a manner that on reversing the primary 

 current the galvanometer was affected by the difference between the 

 electromotive forces set up in the two secondary coils, and a very fine 

 adjustment could be made by moving in or out the adjusting coil of 

 the balancing induction coil. 



The arrangement of circuits is shown in Fig. 2. 



For the purpose of standardising the ballistic galvanometer 

 employed, the primary coil of the balancing induction coil could 

 be cut out of circuit, so that the inductive effect in the ballistic 

 galvanometer circuit was due to the primary current of the closed 

 circuit transformer alone. A resistance box was also included in the 

 circuit of the ballistic galvanometer. The resistance of the ballistic 

 galvanometer was about 18 ohms, and the resistance of the whole 

 secondary circuit 80 '36 ohms. The experiment then consisted in 

 first balancing the secondary electromotive forces in the two coils 

 exactly against one another, then immersing the transformer in liquid 

 oxygen, the result of which was to disturb the inductive balance, and 

 in consequence of the magnetic permeability of the liquid oxygen core 



