daneieaunt 
4 
; 
j 
: 
; 
C. S. Hastings—Optical Constants of Glass. 273 
amount determined from the formula given above. The prisms 
were as follows 
I, Of Feil’s flint glass, No. 1237, sp. 
-» D554, 
of prism, 60° 4' 56"-210"'18, 
ng 
III, Of Feil’s crown glass, No. 1219, sp. gt, 2°482. 
Angle of prism, 60° 10’ 9”°04+-0"°23. 
IV, Flint glass, sp. gr., 3°497. 
Angle of prism, 50° 7’ 53”°01-0"-20. 
V, Crown glass, sp. gr., 2°510. 
Angle of prism, 59° 48’ 127-404-0"-08. 
The materials of IV and V have been in my possession a 
long time, and there is no way to determine what they are 
except from their optical properties, and the statement of the 
optician from whom I procured them, that the first is of French 
and the second of English manufacture. I suppose IV to be a 
flint glass of Feil’s making, while V is doubtless of the so-called 
‘soft crown” of Chance Brothers. 
he temperature affecting the observations ranges from 
14°-9 ©. to 29° C., though most of the lines were measured 
with a maximum difference of 10° C. 
The reduction of the observations on the first three prisms 
to a temperature of 20° C. and barometric height of thirty 
inches gave the following indices of refraction : 
Temperature, 20° C. Barometric height, 30 inches. 
i IL. TL 
Line. n e n e n ée 
A 1°615258 +3 1572464 | +6 1512456 | +3 
B 1-618706 3 1575332 7 1514369 3 
CG 1620482 3 1576815 6 1515334 3 
2 1°62542 3 1°580905 6 [517965 3 
5614 1°628001 2 17583024 6 1519292 3 
1°631893 2 1586214 ' 521274 3 
1637756 2 1°590989 5 524182 3 
4548 1°643524 3 1595660 , 526981 3 
1°649086 3 1°600129 Y 1°529597 3 
h 1°654848 3 1604749 y 1°532251 3 
3951 1°659757 2 | 1608658 V4 1°534458 3 
which the indices of refraction, in columns hea n, reter. 
The last line is beautifully defined and lies nearly midwa 
between H, and H,. The columns under e give the probable 
errors of each determination in units of the sixth place decimal. 
It should be remarked here that the larger probable errors 10 
the determinations of prism II arise from the greater probable 
error in the determination of its refracting angle, hence the 
