396 MESSRS. W. E, WJLSON AND P. L. GRAY, TEMPERATURE OF THE SUN. 
everywhere equal to that at the centre, the radiation would be increased by 4/3, and 
the temperature would become approximately 
7370 X ^(4/3) = 7370 X 1-074 7900°. 
Secondly, assuming Wilson and Rambaut’s result for the total loss due to absorp¬ 
tion in the solar atmosphere—viz., that about one-third of the radiation is cut off— 
the radiation would be multiplied by 3/2 if the sun’s atmosphere were removed, and 
our estimate of the temperature would have to be multiplied by >^(3/2), so that (again 
taking the highest value given above as being probably nearest the truth) we get 
finally 
7900 X ^(3/2) = 7900 X 1-107 = 8740° 
AVe may therefore summarize as follows ;— 
Effective temperature of the sun, taking 
(1) llosETTi’s estimate of loss in the earth’s atmosphere . = 6200° C. 
(2) Langley’s estimate.= 6500° C. 
(3) Angstrom’s estimate.= 7400° C. 
And finally, considering the probable effect of the sun’s own atmosphere, allowing for 
it by the figures given in Wilson and PtAMBAUx’s paper already quoted, and using 
the highest value just obtained, the effective temperature comes out as approximately 
8700° C. 
Note, added July 24tei, 1894. 
Some investigations by the authors in connection with the temperature of the 
carbon of the electric arc, which are now in progress, lead to the conclusion that the 
simple fourth-power law of radiation used above is only an approximation to the 
truth, closer in the case of bare platinum than in that of blackened, so that the 
assumption made in the paper that both follow the same law is not strictly correct. 
The new work will shortly be published, and wdll probably result in raising by a few 
hundred degrees the value obtained above. It may be noticed, meanv\diile, that the 
experimental figures given in this paper are sufficient to serve as a basis-—whate\'er 
law^ of radiation may be used—from which the solar temperature may be calculated 
with an accuracy increasing with a growth of more accurate knowledge as to the law 
of radiation, and the amount of the atmospheric absorption. 
