Resistance of Tliin Metallic Films. 



483 



are quite independent of any assumptions with regard to the 

 relation between u 2 and the time of deposit. Before leaving 

 the question of the temperature variations of the films we 

 must, however, look carefully into one point further. 



Referring to Table III., we see that film 3, which shows a 

 reversal of the temperature coefficient in the neighbourhood 

 of the room temperature, has a resistance about 20 times 

 the normal value, i. e. the value for the thickest films. Thus 

 Sj is about 20. Now if we knew \/l as a function of it 

 would be possible to calculate the value of s x corresponding 

 to a reversal at any temperature, by substituting in the 

 expression for S\ the value of u 2 obtained by differentiating 

 ,9 with respect to and equating to zero. Suppose, for 

 example, \\l were independent of the temperature and equal 

 to 1/J0. We find for this case 4a#/3mw 2 =0'52 and s 1 = l m 75, 

 i. e. the value is far less than 20, and a consideration of the 

 reasons which have been responsible for this small value of 

 s l will show that they are not such as would be modified in 

 such a direction as to give a larger value of s l by a modifi- 

 cation of the above assumption as to the constancy of X/l. 



In fig. 5, curve A represents s x plotte I against 4a0/3mw 2 , 



A 





B 



/ 











1 1 



/ 









h r^ 7 











M i / 











\ 



/ 











p 



/ 







^ 





r\ 



/ 









C\ 













/ 





\ 



/ 











\/ 













































O'V o-b 



Values of (Uuf = &*. 



0-8 



. being independent of 0, and B represents s plotted against 



(thescaleof the ordinates being arbitrary). Xow B is obtained 



2 12 



