1877.] 



Refractive Indices of Glass. 



297 



Extra Dense Flint. — Determinations from only one angle, 

 density =3-88947. 

 a=0-664226. 6=2-4446. c=l-87. 





A. 



B. 



C. 



D. 



E. 



b. 



Most probable value of \i 

 and n from formula . . . 



I 



1-642874 



1-644866 



1-650388 



1-657653 



1-659122 





1-639143 



1-642894 



1-644871 



1-650374 



1-657631 



1-659108 







F. 



(G.) 



G. 



h. 



H x . 





Most probable value of 1 

 H and ju from formula J 



1-664226 



1-676111 



1-677019 



1-683577 



1-688569 





1-664246 



1-676090 



1-677020 



1-683575 



1-688590 



Double Extra Dense Flint. — Determinations from two angles, 

 density=4-42162. 

 ce=0-727237. 6=2-7690. c=2-70. 





A. 



B. 



0. 



D. 



E. 



b. 



Most probable value of \ 

 y and /x from formula J 





1-701060 



1-703478 



1-710201 



1-719114 



1-720924 



Mean of observations . . . 



1-696531 



1-701080 



1-703485 



1-710224 



1-719081 



1-720908 







F. 



(G.) 



G. 



h. 



H x . 





Most probable value of 1 

 H and fx from formula J 



1-727237 



1-742063 



1-743204 



1-751464 



1-757785 



Mean of observations ... 



1-727257 



1-742058 



1-743210 



1-751485 





The following Table gives the value of ^L(c-c') for each glass 



when combined with the standard. It serves to show how little there is 

 to choose between the glasses ordinarily used. 



Hard 

 Crown. 



Soft 

 Crown. 



Titanic 

 Crown. 



Extra 

 Light 

 Flint. 



Light 

 Flint. 



Dense 

 Flint. 



Extra 

 Dense 

 Flint. 



Double 

 Extra 

 Dense 

 Flint. 



-11-7 



-107 



-9-4 



-9-9 



-9-4 



-11-8 



— 11-9 



-13-2 



