of Edinburgh, Session 1881 - 82 . 
817 
Ray. 
Scale Readings. 
Mean. 
Corresp. 
Rotation. 
Total 
Rotation. | 
| 
D 
85° 20' 
85° 40' 
85° 12' 
85° 36' 
85° 30' 
85° 42' 
85° 12' 
85° 20' 
85° 28' 
85° 12' 
85° 25' 
14° 35' 
194° 35' 
E 
35° 52' 
35° 52' 
35° 8' 
35° 48' 
34° 52' 
35° 18' 
35° 16' 
35° 14' 
35° 32' 
35° 26' 
64° -34' 
244° 34' 
b 
26° O' 
26° 56' 
26’ 20' 
26° 30' 
25° 16' 
25° 56' 
25° 54' 
25° 16' 
25’ 10' 
25’ 55' 
74’ 5' 
254° 5' 
F 
10° 32' 
10° 44' 
10° 30' 
10° 36' 
10° 52' 
10’ 24' 
10° 36' 
110° 36' 
290’ 36' 
The angles recorded under the heading “ Corresponding Rotation ” 
are explained by the fact that the scale-reading 100° is taken as 
the standard of reckoning. The multiple of tt to be added is easily 
A 2 
obtained from the approximate formula i-1 = -§ . 
P2 A. 1 
Hence, to the sixth power of the wave-length (rotations being 
expressed in minutes, and wave-lengths in fractions of an inch), 
P (D)= 11675 = ^ 
B 
( 5381) 24 
p(E) = 14674 
A 
B 
4303 (4303) ; 
+ 
p(F) =17436 
A B 
3662 + (3662) 2 
C 
(5381) 3 ’ 
C 
(4303) 3 * 
C 
(3662) 3 ' 
These equations give 
A = 6661(10) 4 , B = - 4233(10) 7 , C = 1180(10)“ . 
Applying the formula 
6661(10) 4 4233(10) 7 1180(10)“ 
p ~ A 2 A 4 + A« 
to calculate the rotation for the ray b, where A = 0-00020367, we get 
P = 16069-6 - 2463-3 + 1656*9 = 15263 . 
The value obtained by direct observation, as given in the table 
above, is 15245. 
With another specimen of quartz 70 mm. in length, the follow- 
ing results were got : — 
