Resistivity of Bismuth at the Temperature of Liquid Air. 75 



It will thus be seen that whereas the immersion of the electrolytic 

 bismuth wire, at ordinary temperatures, 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 mag- 

 netic 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 that 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. We are engaged in extending these observa- 

 tions to stronger fields. 



The behaviour of electrolytic bismuth in fields of various strengths 

 and at various temperatures, from C. to 100 C., has been studied 

 by Mr. J. B. Henderson (see ' 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 tempera- 

 tures are 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 mag- 

 netic fields. 



G t> 



