Electrical Resistivity of Electrolytic Bismuth. 431 



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 tem- 

 peratures 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, both 

 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 remark* 

 able 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 results. 

 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 trans- 

 verse 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 C. down to 

 186 C. of curves which have been given by Mr. J. B. Heiiderson,f 

 for a range of temperature lying above C. 



They show that if a wire of electrolytic bismuth is placed trans- 

 versely in a certain magnetic field, there is, for a wide range of field, 



* See ' Phil. Mag.,' September, 1895, p. 303. Dewar and Fleming " On the 

 Variation in the Electrical [Resistance of Bismuth when cooled to the Temperature 

 of Solid Air." 



t See ' Phil. Mag.,' 1894, vol. 38, p. 488. 



