of A chromatic Object- Glasses . 
From D = 84° 13' 
Take \ a =. 12 24 
E = 71 49 
9*6989700 
From cos Q = 120°, or i 
60 J 9 ' ( 
Take cos E = 71 49' - 9*4942861 
Nat N° ~ 1.6019 = Index 0*2046389 
8. Operation. Flint Prism . 
To P = 108° 45' 
Add d - 8 7 
Second Observation. 
To J a = 12° 24' 
Add d = 8 7 
From sum 116 52 
Sum B = 20 31 
Subtract | a 
12 24J 
A = 104 27 
Cot § a = 12° 24' 
Tan A = 104 27 or 
75 31 
Tan B = 20 31 
10*6578454 
j- 10-5889079 
9-5731227 
30-8198760 
Subtract 20-0000000 
Tan 81° 23' = D - - 
From D = 81° 23' 
Take § a = 12 24 
10-8198760 
E = 68 59 
From cos Q = 125° O' or t 
55 0 1 9-7585913 
Take cos E = 68 59 
9*5546581 
Nat. N° = 1-5993 Index . 0-2039332 
