Page:Proceedings of the Royal Society of London Vol 60.djvu/90

Rh It will thus be seen th at whereas the immersion of the electrolytic bismuth wire, at ordinary tem peratures, transversely in a magnetic field of strength 2,750 C.G.S. units, only increased its resistance by about 6 per cent., the immersion of the same wire in the same m agnetic field increased its resistance to more than four and a half times when it was cooled to the temperature of liquid air, and the effect of the cooling with liquid air is more than nullified by the field, so th at the bismuth cooled in liquid air and at the same time placed in the field has a resistance of 50 per cent, greater than it was when not cooled and not in the field. W e are engaged in extending these observations to stronger fields.

The behaviour of electrolytic bismuth in fields of various strengths and at various temperatures, from 0° C. to 100° C., has been studied by Mr. J. B. Henderson (see 4 Phil. Mag.,’ vol. 38, ]894, p. 488), and he has given a series of curves showing the variation of resistance of bismuth between these temperatures for fields of strength varying from zero to 22,700 C.G.S. units. Our observations at low temperatures arh quite consistent with Mr. Henderson’s curves. His curves indicate that at lower temperatures the effect of any given field in increasing the resistance of the bismuth becomes more marked.

Pressed to its limit it would appear that pure bismuth, which would in all probability be made a perfect conductor by reducing to the absolute zero of temperature, would be then converted into a non-conductor if at the same time immersed in a magnetic field of sufficient strength. Both M. van Aubel and Mr. Henderson have pointed out that the temperature coefficient of bismuth at any given temperature is quite altered by placing it in a magnetic field, and it will therefore be a matter of great interest to examine the effect of an exceedingly strong magnetic field as bismuth when cooled to the temperature of solid air.

By enclosing a bismuth wire and a platinum thermometer wire in the same mass of paraffin wax we have been able to measure the variation of resistance of the bismuth from the temperature of liquid air up to ordinary temperatures at a number of intermediate points, and to determine the resistance both in a zero magnetic field and in one of known strength, but the results we wish to reserve until we have had the opportunity of repeating them with stronger magnetic fields.