

96 Dr. W. E. Sumpner on the Diffusion of Light. 



Table VI. — Keflective Powers. 





Begular. 



per cent. 

 



4-8 „ 

 2'7 „ 

 2-2 „ 



Diffused. 



Total. 





82 per cent. 



so 



30-9 „ 

 31-6 „ 



19-8 „ 



82 per cent. 

 80 



357 „ 

 343 „ 

 220 „ 



Cartridge-paper 



Tracing-cloth (shiny side) ... 



„ „ (rough side)... 



Tracing- j »appr 







Table VII. — Transmissive Powers 







Direct. 



Diffused. 



T. 2 . 



Total. 

 r. 





27 per cent. 

 25 „ 

 13-4 „ 



29-8 „ 



6 - 5 per cent. 



8'7 „ 

 41-0 „ 

 46-2 



9"2 per cent. 

 11-2 



544 „ 

 76-0 „ 







s 





We may now collect the coefficients y, a, t, determined by 

 the foregoing independent methods, and. compare their sum 

 with unity. Table vnL 





17. 



a 





T. 



T]-\-a-\-T. 



Bl-jttiug-paper 



82 per cent. 



13*8 per cent. 



9 - 2 per cent. 



105-0 per cent. 



Oartridge-paper ... 



80 „ 



12-2 



i> 



11-2 „ 



1034 



Tracing-cloth 



35 „ 



15 



» 



54-4 „ 



104-4 „ 



Tracing-paper 





7-0 



» 



76-0 „ 



1050 



The numbers in the last column differ from the true value 

 of 100 per cent, to a greater extent than can fairly be accounted 

 for by the limits of experimental error. They are all over 100 ; 

 and this was the case, not only for the tests here given, but 

 also for every one of many sets of tests taken. The small dis- 

 crepancy would be accounted for by assuming that the law of 

 cosines is not exactly fulfilled. A very slight departure from 

 this law would be amply sufficient to explain the results. 



Suppose the candle-power of a unit area of a diffusing 

 surface in the direction of the normal is B, and in any 



