676 



Prof. J. Patterson on the Electrical 



The average resistance of all the films whose resistances 

 are normal is 82 ohms for a thickness of 10" 6 cm. and 1 cm. 

 square. Using the value 6 X 10 -7 for X and 82 for a the 

 relation between specific resistance and thickness given by 

 the above formulae is plotted in fig. 14, curve A, where the 

 ordinates represent specific resistance and abscissse thickness. 

 The experimental values are plotted in curve B. 



Fig. 14. 























\ \ 























^fca- 





A 



















e 













' 



9 10 A. 



A=6XICT 7 CM 



From these two curves it will be seen that the experi- 

 mental values agree very well with the calculated for films 

 whose thickness is greater than 6 x 10" 7 cm., and for those 

 below that thickness the experimental values vary more rapidly. 



Vincent*, from his experiments on silver films, concluded 

 that at the surface of a metal there exists a thin layer which 

 he called a transition-layer or the range of molecular action. 

 The thickness of a thick film thus consisted of three parts, 

 namely : — 



A transition-layer from air to metal : an intermediate layer 

 of constant specific resistance : a transition-layer from metal 

 to glass. On this theory he obtained the following empirical 

 formula for the conductivity 



- =-A + ce, 



where a is the resistance, c the specific resistance which is 

 constant, and e the thickness, A the correction to be applied 

 for the two transition-layers. He found that this relationship 

 held down to 5 x 10 — 6 cm. and below this the formula no 

 longer held, and consequently the intermediate layer was 

 absent. He concluded from this result that the upper 

 limit for the range of molecular action was half this limiting 

 value or 2'5xl0 -6 cm. Moreau f confirmed these results 

 for silver. He also made nickel films by depositing nickel 

 electrolyticaliy on the silver films. He found that the range 

 of molecular action was 2*2 x 10 -6 cm. for nickel. 



* Annates de Chimie et de Physique [7] vol. xix. p. 421 (1900). 

 t Journal de Physique [3] x. p. 478 (1901). 



