Properties of Thin Metal Films. 



659 



bands were obtained from the arrangement shown in fig. 7, 

 the phase of the light was changed so that, instead of dark 

 bands on a bright background, there were bright bands on a 

 dark background. This gave greater distinctness to the 

 spectrum, and enabled one to measure the thickness with 

 greater accuracy. An example is given in Table I. of a set 



Table I. — Determination of the Thickness of a Film. 



Vernier 



readings. 







1 







Fraction of 

 wave-length 



Wave- 

 length 



Thickness 

 of film 







First set of 



Displaced 



displaced. 



in /ijU. 



in cm. 



bands. 



position. 









31° 53 



31° 48 









31 17 



31 12 



5/72 



4960 



3 44 10-6 



30 48 



30 44 



5/58 



5220 



450 



30 23 



30 19 



4/50 



5490 



4-39 



29 57 



29 54 



4/52 



5800 



446 



29 36 



29 33 



3/42 



6090 



435 



29 12 





3/48 



6520 



4-08 



32 12 



32 06 









31 38 



31 32-5 



6/68 



4800 



422 



31 10 



31 06 



5-5/56 



5020 



493 



30 44 



30 40 



4 52 



5260 



405 



30 19 



30 15-5 



4 50 



5540 



443 



29 56 



29 53 



3 5/46 



5820 



443 



29 36 5 





3/39 



6080 



467 



Mean of 12 readings 4-33 10-6. 



of readings taken to determine the thickness of a film. Not 

 all the measurements of the thickness of the films were as 

 good as this. The greatest error occurred in the very thin 

 films as the displacement was so small that it was exceedingly 

 difficult to measure it. It was impossible to measure less 

 than 2 x 10~ 6 cm. by this method. 



Measurement of Resistance. 



The resistance was measured with a standard Wheatstone 

 bridge. The resistance of the silvered ends was neglected as it 

 was negligible compared with the resistance of the film itself. 

 The length of the film between the silvered ends was measured 

 with a cathetomet< j r. Several methods of fastening electrodes 

 to the silvered ends were tried. One method was to wind 

 fine copper wire around the silvered end and then deposit 



2X2 



