Page:Proceedings of the Royal Society of London Vol 60.djvu/89

74 there is no tendency of the resistivity carve to a minimum value. Down to the lowest temperatures reached in these experiments, the resistivity of bismuth continues to decrease in a perfectly regular manner, and in such a way as to show that it would be no exception, in all probability, to the ordinary law, that resistivity of pure metals vanishes at the absolute zero of temperature. On comparing the results of these measurements with those in the former experiments made with chemically prepared bismuth, it is seen th at the electrolytic bismuth used by us has a very much lower resistivity at 0° C., viz., 108,000 units, and it has a lower value than that given by Matthiessen for pure bismuth, which is 129,700. We have, then, an additional indication that the bismuth used by us in the experiments in 1895 must have contained sufficient, though slight, impurity to markedly alter its resistivity, and to change entirely the character of the resistivity curve. W ith this electrolytic bismuth we have repeated the experiments which wTe made last year, on the variation of the electrical resistance of bismuth when placed transversely to the direction of the force in a magnetic field, and when cooled to the temperature of liquid air. For this purpose we constructed a flat spiral of the electrolytic bismuth, so arranged that its resistances could be measured at ordinary temperatures, and at the temperature of liquid air, by immersing it in a flat vacuum-jacketed test-tube, both when in a powerful magnetic field, and when merely in the terrestrial field. W ith this electrolytic bismuth we have confirmed the observation which we made last year, with a small sample of electrolytic bismuth, viz., that the effect of a given transverse magnetic field in increasing the resistivity of bismuth is immensely increased by cooling the bismuth to the temperature of liquid air. The figures in the following table will show the actual results obtained in these last experiments:—

74 Profs. J. Dewar and J. A. Fleming. On Electrical Variation of Electrical Resistance of Electrolytic Bismuth in Magnetic Fields of different Strengths. Temperature in platinum degrees. Magnetic field strengths in C.Q-.S. units. Zero. 1400 units. 2750 units. Remarks. Resistance of bismuth coil. + 20° ohms. 1-679 ohms. 1-700 ohms. 1-792 A t ordinary tem perature. -2 0 2 ° 0-5723 1-4435 2 -6801 In liquid air.