432 Journal of the Asiat. Soc. of Bengal. [N.S., XIV, 1918.] 
Mean deflection (mean of several experi- 
t 
ments = 28°5 Divns. 
Distance of the scale from the mirror = 100 c.m. 
Distance “‘d”’ of the plane of the filament 
from the diaphragm. =73 ¢.m. 
Therefore the upper limit of the total theoretical pressure 
(without allowing for absorption or reflexion) is equal to 
,, 8°6 x 220 x 10! x (3:25)” 
4x 73x 3x 10'° 
The pressure calculated from deflections is equal to 
2:3 x 107° x 14°25 = 3°33 x 10 * dynes (B). 
2 
=4:8x 10 * dynes (A). 
reflected by the silvered surface. As a matter of fact, none of 
these assumptions is correct. If 7 is the fraction of total 
energy transmitted by thick glass, and p be the reflecting 
power of a silver glass-surface the actual pressure should be 
i 
Pog (1+) (l1—<) 
where P, is the quantity (A). 
tungsten filament, it cannot be less than 80%. oe 
sidering these facts, we are probably justified al 
asserting that the agreement between observed and theorem 
values is at least qualitatively quite good. a aoe 
occasion we hope to return to the problem of a rigor? 
quantitative determination of total incident energy- Prof 
In conclusion, we beg to record our best thanks we ege 
C. V. Raman, and the teaching staff of the University 
of Science, for the interest they have taken in the we 
Mr. N. Basu, B.Sc., for much useful help. 
rk ; and to 
: Obtained _by extrapolation from the data of Rubens wd 
on the supposition that the maximum emission of energy Resi 
sten filament is at 1 « [Kohlrausch, Praktische Physik. Tabellen). 
