122 Prof. Thomson, On the theory of Electric Conduction, etc. 



where X is the mean free path. Thus when the film becomes so 

 thin that the mean free path is diminished, not merely is the 

 specific resistance increased, but the effect of a magnet on the re- 

 sistance is very materially diminished. This is strikingly shown by 

 Patterson's experiments 1 , which prove that in thin films of bismuth 

 the effect of the magnetic field on the resistance is very small. 

 The electrical properties of thin metallic films as investigated by 

 Longden and Patterson are qualitatively at any rate in accordance 

 with the results of the theory discussed in this paper ; further 

 experiments are however needed on films of the various metals 

 and with as wide as possible range in thickness to see if the 

 numerical results obtained by experiment are in agreement 

 with those predicted by theory. 



1 Proc. Camb. Phil. Soc. Vol. xi. p. 118. 



