Page:Proceedings of the Royal Society of London Vol 60.djvu/463

Rh zero. Hence at this last temperature it should be converted into a non-conductor by a sufficiently strong transverse magnetisation. This result will have to be taken into consideration in framing any theory of electrical conduction.

In this respect bismuth is a remarkable exception to other metals. We have tried the effect of transverse magnetisation at low temperatures on zinc, iron, and nickel, but find no effect sensibly greater at low than at ordinary temperatures, although these metals have their resistance affected by magnetisation to a small degree.

Bismuth has an exceptional position amongst other metals, bath in respect of its large coefficient of the Hall effect, and also in the degree to which its resistance is thus affected by transverse magnetisation, and in addition, as above shown, in the degree to which cooling to low temperatures affects this ability to be so changed by magnetisation.

Very small amounts of impurity in the metal reduce these remarkable qualities considerably.

We may mention here that we have repeated the experiments we made some time ago* on certain specimens of chemically prepared bismuth, and for which we found the electrical resistance had a minimum value for a certain temperature. We have again verified this fact, both for the same and for a similar specimen. In the former experiments the bismuth wire used was embedded in paraffin wax during the cooling, and the suspicion had arisen that strains might thus have been produced which had affected the I’esults. In the repetition of the experiments, we suspended the bismuth wire freely in liquid air, so that no strains could be produced; and, in addition, we tried the effect of mechanical stress on the resistance directly. We satisfied ourselves that the cause of the anomaly in the behaviour of the chemically prepared bismuth in respect of electrical resistance at low temperatures was not to be found in any effect due to strain.

In fig. 3 a series of curves have been drawn showing the variation in resistivity of the electrolytic bismuth for certain constant transverse magnetic fields and varying temperatures. These curves were obtained by taking sections of the curves in figs. 1 and 2. The curves in fig. 3 are practically the continuation from 19° 0. down to —186° C. of curves which have been given by Mr. J. B. Henderson,"j" for a range of temperature lying above 0° C. They show that if a wire of electrolytic bismuth is placed transversely in a certain magnetic field, there is, for a wide range of field,

Variation in the Electrical Resistance of Bismuth when cooled to the Temperature of Solid Air.” t See ‘ Phil. Mag.,’ 1894, vol. 38, p. 488.
 * See ‘ Phil. Mag.,’ September, 1895, p. 303. Dewar and Fleming “ On the