

in a Magnetic Field at Different Temperatures. 699 



law. The above expression therefore indicates that \ increases 

 somewhat with rise o£ temperature. 



As far then as the variation of mean free path with tem- 

 perature is concerned, these experiments may be satisfactorily 

 explained on the older electron theory. 



Sir J. J. Thomson * accounts for this change of \ by 

 supposing that collision occurs in metals between the cor- 

 puscles and clusters of atoms, these clusters undergoing a 

 process of disintegration at higher temperatures. 



The same hypothesis would enable an explanation to be 

 given of the relatively large values of \ which experiments 

 on change of resistance in a magnetic field require on this 

 theory. g 



The values of — obtained at the temperature of liquid air 



in the case of the metals cadmium and zinc might be taken 

 to indicate that at very low temperatures X tends to become 

 constant, but any further speculation should rather be 

 reserved until more complete data are obtained. 



The results obtained in this paper may be summarized 

 as follows : — 



(i.) In the case of the substances examined — cadmium, 



zinc, and graphite — the change of resistance, - , in a mag- 

 netic field H, is proportional to H 2 for the range of fields 

 used. 



(ii.) This change of resistance in all cases increases at 



1 £s 



lower temperatures; for the metals cadmium and zinc jn — 



at the temperature of liquid air is about 20 times as large as 



1 oY 



at atmospheric temperatures, while for graphite yjr, shows 



only a threefold change over this range of temperature. 



(iii.) The increase of resistance, — , in the case of graphite 



is about 1 per cent, in a field of 11,000 c.G.s. units at atmo- 

 spheric temperatures ; this is about equal to the decrease of 

 resistance of nickel in the same field, and is many times 

 larger than the change of resistance occurring in any of the 

 non-magnetic metals hitherto examined except bismuth. 



The above experiments were carried out in the Physios 

 Laboratory of the Blackburn Municipal Technical School. 



Technical Institute, Loughborough, 

 January 31, 1'JIU. 



* ' Corpuscular Theory of Matter," p. 72. 



