THE ELECTRICAL PROPERTIES OF CON- 

 DUCTORS AT VERY LOW TEMPERA- 

 TURES 



By FRANCIS HYNDMAN, B.Sc. 



Some of the properties of matter which are of special interest, 

 in that they help to form an idea of its constitution, are only 

 capable of exact measurement under very difficult experimental 

 conditions. Great interest attaches just now to the electrical 

 properties, owing to the new developments in the theory of 

 the electric current which have been advanced in quite recent 

 years, and which are indicating relations between widely 

 different properties of matter. The most interesting and 

 instructive field for investigations on these properties of matter 

 is at very low temperatures, because there phenomena are found 

 which are either non-existent or unmeasurable at higher tempera- 

 tures, and which throw important light on electric theory. 



In the number of July 191 3, vol. viii. p. 26, I gave an 

 account of some of the new investigations in the low tempera- 

 ture region, which had been rendered possible by the discovery 

 of the means of liquefying helium, a gas which boils normally 

 at the extremely low temperature of 4*25° K. (— 268-84° C). 

 Since July 10, 1908, when Kamerlingh Onnes first liquefied 

 helium at Leiden, the technics of the subject have been advanced 

 in the most active way. Measurements of all kinds are 

 now undertaken in a systematic manner in liquid helium, 

 which has been transferred to the special vessel required for 

 them. Here it can then be held under reduced pressures, 

 which allow of a reduction of temperature to i^K, 1 and the 

 maintenance of a constant temperature from this up to 4-25° K. 



Before passing to the particular subject of this paper it will 

 be useful to consider briefly the exact present position with 

 regard to the thermodynamic properties of helium as related 

 to those of an ideal monatomic gas, or to the perfect gas where 



1 See Communications from the Physical Laboratory of the University of 

 Leiden, by Prof. H. Kamerlingh Onnes, Director of the Laboratory. 



586 



