Constants of Pure Ice, fyc, at Low Temperatures. 317 



constants afc very low temperatures,* and there is, therefore, no need 

 to repeat these descriptions. 



In the present paper we give the results we have obtained for the 

 variation of dielectric constants at low temperatures when using 

 certain carefully purified bodies as dielectrics. 



As pure water is a standard substance the electrical constants of 

 which have been very carefully studied, we desired in the first place 

 to repeat our former experiments on the dielectric constant of ice, 

 using, however, very pure distilled water as the means of pro- 

 curing it. 



Dr. Scott very kindly prepared for us in the Davy- Faraday labo- 

 ratory a sample of pure water distilled in a silver still, and the gilt 

 cone condenser used was carefully washed out with this water. The 

 condenser was then kept full of this water for ten days, the water 

 being changed twice a day. During the day-time the condenser full 

 of water was kept at a temperature of 90° C. Having thus very 

 carefully purified the condenser it was again filled with the pure dis- 

 tilled water, and this water frozen into ice by the aid of liquid air. 

 The whole mass of the condenser and the ice being reduced to 

 — 185° C. by immersing the cones in a large vacuum vessel full of 

 two litres of liquid air, the condenser was then raised out of the 

 liquid air into the equally cold gaseous air lying above it in the 

 vacuum vessel, and was allowed to warm up very slowly, taking 

 four hours thirty minutes to rise in temperature from — 185° C. to 

 5° C. 



During this rise of temperature the dielectric constant of the ice 

 was measured at various temperatures by the arrangements already 

 described, and also the resistance of the ice condenser. 



The corrected galvanometer scale deflection, when the condenser as 

 used was filled with gaseous air at the ordinary temperature of 

 15° C, was 3*73 centimetres, using a charging voltage of 100 volts. 

 This value is corrected for the capacity of the leads and for that of 

 the vibrator. In the following table the temperature of the ice is 

 given in platinum degrees in terms of our standard platinum thermo- 

 meter Pi. 



* See Fleming and Dewar, " On the Dielectric Constants of some Frozen Electro- 

 lytes at and above the Temperature of Liquid Air," ' Roy. Soc. Proc.,' vol. 61, p. 299, 

 1897; also Dewar and Fleming, "Note on the Dielectric Constant of Ice and 

 Ethylic Alcohol at very Low Temperatures," ' Roy. Soc. Proc.,' vol. 61, p. 2, 1897. 



