398 



Mr. L. Schwendler on a 



accuracy of the photometer-readings, and other influences to 

 be named further on (see fig. 8). 



d + d'=T) = 250 millims. (constant). 



Light i produced by P. L. S. (III.) ; light i' produced by 

 P. L. S. (II.), — the balance between the two lights being ob- 

 tained by moving the prisms within that fixed distance. A 

 piece of red glass was used for taking the readings. 



In the following Table the results are given : — 



"S 



P. L. S. 



il 







<c 







-£= 2 







g 







d 9 









II. 



III. 



° s 



.9 fc* 



i' 



Kemarks and Particulars. 



© 



producing i' 



producing i 



O °3 



i 





km 



O 



d' millims. 



d millims. 



5g ^ 







o" 



from prism. 



from prism. 



ft s 







ft 







tuo 







1. 



100 



150 



o 

 18-8 





Both lights having glass 





100 



150 



18-8 





covers ; but glasses were 





100 



150 



18-8 





quite clear, 





100 



150 



18-8 









100 



150 



18-8 









99 



151 











100 



150 







A clear glass cover on No. 



99-86 



15014 



18-8 



0-44 



2. 



103 



147 



18-8 







102 



148 



18-8 





III. ; no glass cover on 





102 



148 







No. II. 





103 



147 











102 



148 







A clear glass cover on No. 



102-4 



147-6 



18-8 



0-48 



3. 



98 



152 



18.8 







97 



153 



18-8 





II. ; no glass cover on 





98 



152 



18-8 





No. ni. 





98 



152 











98 



152 











99 



151 











98 



152 







A glass cover on No. III., 



98 



152 



18-8 



0-42 



4. 



98 



152 



18-8 







98 



152 



18-8 





the back of it covered 





99 



151 



18-8 





inside with black paper ; 





100 



150 



18-8 





a clear glass cover on 





100 



150 







No. II. 





98 



152 





0-43 





98-83 



151-17 



18-8 



