THE INTERFERENCE OF LIGHT. 
223 
(39.) Glass and Water, r='0]5 inch. 
Ray. 
rr—r-m 
X 
i^y- 
Diff. = n. 
Remarks. 
B. 
D. 
F. 
G. 
H. 
1-526 
1-529 
1-536 
1-542 
1-546 
1-331 
1-333 
1-337 
1-341 
1-344 
+ 195 
+ 19^ 
+ 199 
+ 201 
+ 202 
+ 7672 
+ 9009 
+ 11092 
+ 12663 
+ 13796 
+ 115 
+ 135 
+ 166 
+ 190 
+ 207 
+ 20 
+ 31 
+ 24 
+ 17 
Hence arrangement 
II. will give bands. 
+ 92 
(40.) Calc-spar and Oil of Cassia, ordinary ray. Rudberg’s indices. 
Ray. 
f‘m- 
r'p — 
X 
DifF. 
Remarks. 
B. 
D. 
F. 
G. 
H. 
1-6531 
1-6585 
1-6680 
1-6762 
1-6833 
1-5945 
1-6073 
1-6358 
1-6671 
1-7025 
+ -0586 
+ -0512 
+ •0322 
+ •0091 
— •0192 
+ 2306 
+ 2353 
+ 1794 
+ 573 
+ 1311 
+ 92 
+ 94 
+ 71 
+ 23 
-52 
+ 2 
Hence with arrange- 
ment I. there will 
be no bands from 
B to D, but bands 
from D to H. 
- 23 
- 48 
- 75 
146 
(41.) For the extraordinary ray, in a plate bounded by the planes of cleavage, 
Mr. Stokes has calculated the results as follows;— 
‘^The incidence is supposed to be perpendicular; that is, strictly, the rays B, D, 
&c. are supposed to be received in succession at a perpendicular incidence : but the 
results may be applied with very little error to the case in which rays of mean refran- 
gibility are incident perpendicularly. 
“ The dihedral angle of the rhombohedron of calc-spar is 105° 5'*. 
“ If i be the inclination of the axis to the normal of the plate, we get by a spherical 
triangle, 
sin i— cos 52° 32''5 cosec 60° 
whence i=44° 36'‘6. 
Now'l' we have 
v=\/ cd- cos^ sin^ i—a cos i sec 6 
C fjJ • 
where tan 6 =- tan i=^ tan i, 
and if 
fA'=y/'oSecicos 
Also 
Hence 
log tan ?'=9’99409, and log sec 10 14758. 
log tan logjO-'o— log|«/'g-|-9‘99409 
logjW/'= logcos^-{-10‘14758 — 20. 
* Phillips’s Mineralo^-. 
-f Airy’s Tract, Art. 151. 
