Profs. J. A. Fleming and J. Dewar. On the 



to know the number. The coil so constructed constituted a small 

 induction coil or transformer, with a closed air-core circuit, but which 

 when immersed in a liquid, by the penetration of the liquid into the 

 interior of the primary coil, became changed into a closed circuit 

 transformer, with a liquid core. The transformer so designed was 

 capable of being placed underneath liquid oxygen contained in a 

 large vacuum vessel, and when so placed formed a transformer of the 

 closed circuit type, with a core of liquid oxygen. The coefficient of 

 mutual induction of these two circuits, primary and secondary, is 

 therefore altered by immersing the transformer in liquid oxygen > 

 but the whole of the induction produced in the interior of the 

 primary coil is always linked with the whole of the turns of the 

 secondary coil, and the only form-change that can be made is a small 

 change in the mean perimeter of the primary turns due to the con- 

 traction of the coil as a whole. In experiments with this transformer 

 the transformer was always lifted out of the liquid oxygen into the 

 cold gaseous oxygen lying on the surface of the liquid oxygen, and 

 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 

 turns 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 



