

Effect caused hi) Incident and Emergent Liglit. 335 



of tlie experiments on very thin films o£ platinum. The 

 maximum deviation from the mean is about 1*5 per cent. 



By changing the thickness of the films the following values 

 were obtained: — 



Platinum. 





R B 



n a 









fll 1 











(1) 



B 







< — i 







^ , 



Ratio ,.^ - 



Log t Position (1). 



No. 



u 

















»-£■ 



A 





Equal to log -? . 



a 



•590 



•398 



•674 



1-399 



b 



•652 



•726 



109 



•138 



c 



•651 



•739 



1-13 



•131 



d 



•587 



■617 



1-05 



•209 



e 



•617 



•708 



1-09 



•149 



f 



•573 



•656 



1-14 



•183 



9 



•531 



•552 



104 



•257 



h 



•534 



•536 



1-00 



•270 



i 



•624 



•694 



111 



•158 



J 



•632 



•657 



104 



•182 



h 



•632 



•708 



1-12 



•148 



I 



•644 



•730 



1-12 



•136 



1 



•534 



•536 



TOO 



•271 



2 



•628 



•696 



M0 



•156 



3 



•635 



•679 



107 



•168 



4 



•639 



•719 



112 



•143 



5 



•622 



•677 



MO 



•169 



6 



•549 



•578 



1-05 



•237 



7 



•550 



•475 



•863 



•323 



8 



•536 



•566 



105 



•247 



9 



•545 



•496 



•910 



•304 



10 



•611 



•397 



•649 



•400 



11 



•660 



•394 



•600 



•404 



13 



•561 



•590 



1-05 



•228 



16 



•582 



•685 



1-17 



•164 



20 



•615 



•694 



1-13 



•158 



22 



•866 



•966 



1-11 



•015 



24 



•666 



•754 



113 



•122 



From the above data we see that the effect is a function of 

 the thickness. It was found impossible to determine the 

 thickness of these very thin films directly. From the ratio 

 of A/B in Position (1) it is possible, however, to compare 

 their relative thicknesses with accuracy. For it is known 

 that when light traverses an absorbing medium the logarithm 

 of the intensity varies as the thickness of the medium traversed. 

 Hence from the preceding arguments it will be seen that values 

 of log B/A Position (1) (equal to log i ji) will be proportional 

 to the thickness of the film plus that of the quartz plate used. 



