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



affords a good criterion of the extent to which the principles 

 and the formulae, referred to in this paper, can be relied 

 upon. 



The following Tables III., IV., and V. contain the results 

 of three sets of tests on the transmitting-} lower of blotting- 

 paper and tracing-cloth, and on the reflecting-power of 

 tracing-cloth. The values of Y obg are calculated with the 

 aid of (12) and (16) from the observed values of as and#. All 

 the dimensions are given in centimetre-units. In the accom- 

 panying sheet of curves the values of Y obs are plotted as 

 ordinates, with the corresponding values of X as abscissas. 

 From the straight line most nearly representing the connexion 

 between the points the values of Y calc have been obtained, 

 and are given in the tables. From this straight line also the 

 true value of the transmitting (or reflective) power can be 

 found by finding the value of the ordinate when X = 4. The 

 intercept on the axis of Y shows the portion of the light which 

 is diffused. 



Table 111. — Transmitting-Power of Blotting-paper. 

 A=9S0. K = 26. &=2. r=92. Y cale/ =Cv50-|-2-7X/4. 



GO 



50 



40 



45 



55 



60 



154 



120 



88-4 



1046 



137 



154 



136 



9-8 



70 



8-25 



11-40 



136 



155 



13-2 



112 



12-0 



14-4 



15-5 



15 7 



131 



11-2 



121 



14-2 



15-7 



Table IV. — Transmitting-Power of Tracino-cloth. 



K=231. k=2. r = 54-4. 



calc. 



:410 + 13-4X/4. 



X 



40 



50 



60 



70 



80 



75 



65 



55 



45 





39-2 



G-98 



53 5 

 9-80 



701 

 13 6 



89-4 

 174 



105-6 

 22-30 



958 

 19-4 



77*7 

 15 4 



61 

 11-2 



46-1 



8-25 



X 



Y obs. ••• 



63-5 



7-1-3 



861 



970 



116 



107 



91-8 



81-7 



69-3 



^calc. -- ' 



64-4 



737 



85-6 



99-2 



115-8 



106 



940 



78-5 



68-7 



