558 



Mr. G. C. Simpson on the Electrical 



In the space between the two, water from a thermostat 

 circulated, so keeping the bismuth (placed in oil) at the 

 required temperature. 



For temperatures below atmospheric a similar vessel was 

 used, except that the space between the two walls was evacuated, 

 and different freezing-mixtures placed in the inner vessel. 



Low temperatures were obtained as follows : — Liquid air 

 gave a constant temperature of —185°, a mixture of solid 

 C0 2 and acetone gave —70°, while —95° was obtained by 

 bubbling air through this mixture; solid C0 2 in alcohol 

 produced —40°. 



The bismuth wire having a very low resistance (about 2 ohms 

 at 17°) and the field being comparatively weak, owing to 

 the large separation of the pole-pieces necessitated by the 

 glass vessel, the whole effect to be measured was extremely 

 small, so that it was found convenient to work only with 

 the strongest field to be obtained under the conditions (about 

 7000 lines) and with a frequency of 30 per sec. With this 

 field and frequency complete experiments were made at 

 -185°, -70°, -40 b , 0°, 17°, 43°, 68°, and 100°, the results of 

 which are given in fig. 7. In this figure it will be seen 























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that the lines all cross the abscissa in the same point, hence 

 the angle of lag is independent of temperature. 



