698 Proceedings of the Royal Society 
(5.) Bunsen, Zollner. — Explosive Power of G-ases. 
(6.) Newton, Waterston, Ericsson, Secchi. — Badiation. 
(7.) Thomson, Helmholtz. — Mechanical Equivalent of Heat. 
(8.) Deville, Debray. — Dissociation. 
After treating of the great disparity of opinion regarding the 
temperature of the sun, the author proceeds to detail how it is pos- 
sible, from the known luminous intensity of the sun, to derive a 
new estimate of solar temperature. This calculation is based on a 
definite law relating temperature and luminosity in the case of 
solids, viz., the total luminous intensity is a parabolic function of 
the temperature, above that temperature where all kinds of luminous 
rays occur. So that if T is a certain initial temperature, and I its 
luminous intensity, a a certain increment of temperature, then we 
have the following relation : — 
T + n (a) = n 2 1 . 
The temperature T is so high as to include all kinds of luminous 
rays, viz., 990° C., and the increment a is 46° C. This formula 
expresses well the results of Draper, and I have used his numbers 
as a first approximation. It results from the above equation, 
that at a temperature of 2400° 0., the total luminous intensity will 
be 900 times that which it was at 1037° O. Now, the temperature 
of the oxyhydrogen flame does not exceed 2400° C, and we know 
from Eiseau and Eoucalt’s experiments that sunlight has 150 
times the luminous intensity of the lime light ; so that we only 
require to calculate at what temperature this intensity is reached 
in order to get the solar temperature. This temperature is 
16,000° C.,in round numbers. Enormously high temperatures are 
not required, therefore, to produce great luminous intensities, and 
the temperature of the sun need not, at least, exceed the above 
number. Sir William Thomson, in his celebrated article, “ On the 
Age of the Sun’s Heat,” says, “ It is almost certain that the sun’s 
mean temperature is even now as high as 14,000° C.,” and this is 
the estimate with which the luminous intensity calculation agrees 
well. 
