210 Dr. H. R. Wright on the Photometry of the 



(10) Plaster of Paris : \ = Mixed waves. 



6. 



i=0°. 



z'=20°. 



i=40°. 



; = 60°. 



f=80°. 



-50° 











9487 



-40 











0249 



^-30 









5510 





-20 









5864 



1136 



-10 





... 



8065 















8131 



6134 



1406 



+10 





9500 





i 





+20 





9296 



7861 



5864 



1136 



+30 



9375 











+40 



8842 



8409 



6939 



4977 



0249 



+ 60 



6989 



6556 



5121 



3427 



0324 



+ 80 



2396 



1963 



0528 



9138 



8935 



(10 a) Mean values of Nos. 8 and 9 for Plaster of Paris. 



e. 



i=0°. 



? = 20°. 



«=40°. 



i = W°. 



i=80°. 



-50° 











0054 



-40 











0720 



-30 









6419 





-20 









6672 



1651 



-10 







8652 















8732 



6955 



1907 



+ 10 





9469 









+20. 





9213 



8538 



6710 



1726 



+30 



9375 











+40 



8736 



8417 



7613 



5898 



0884 



+60 



6923 



6631 



5850 



4286 



0445 



+80 



2343 



1984 



1206 



0770 



9366 



(11) Mirror: \ = 612 fifi. 



e. 



i=0°. 



2=20°. 



i=40°. 



i=ffl°. 



i=80°. 



+ 10° 





1-8346 









+20 



... 





0-3495 







+ 30 



99375 



3-6i89 



20965 







+40 





1-3436 





0-5352 





+50 







2-9541 



2-2278 





+60 





9-9266 



1-3642 







+70 







1-6049 



2-7361 





The reference-point in all the above tables is, as is evident, 

 ; = 0° and e = 30°. This has been made equal to the value of 

 Lambert (9*9375) : i = e is the position of the regular re- 

 flexion, whilst by i= —e the two rays would coincide. 



Carbonate of Magnesia, MgC0 3 , which Jenko * erroneously 

 * Jenko, Wied. Ann. Ixtl p. 1182 (1898). 



