ON THE EFFECTIVE TEMPERATURE OF THE SUN, 
383 
From a large number of concordant observations he finally deduces a value of the 
solar constant = 323 in the scale divisions of his thermo-pile, while in the tables on 
p, 546 he gives the deflections corresponding to values of e from IM up to 4-8. 
We plotted these values on curve paper (fig. 8), and thus found 229 as the corre¬ 
sponding deflection for the sun in the zenith, so that using the above symbols, 
X = 323, M = 229. The absorption for one thickness therefore equals 
M _ 229 
X “ ^ “ 323 
= 1 
- 71 = -29. 
So that 29 per cent, of the total outside radiation is absorbed, and 71 per cent, 
reaches the earth, with the sun in the zenith. 
The ratios corresponding to other values of e were similarly calculated, and the 
results plotted down, giving the curve (fig. 8), the abscissae of which are zenith 
distances and the ordinates percentage absorptions. 
The 29 per cent, thus deduced from Rosetti’s results, it will be seen, is consider¬ 
ably greater than the old estimate, which we know to be incorrect, and less than the 
41 per cent, of Langley, which is indeed a difference to be, a priori, expected for 
the following reason. 
We know that by far the greater proportion of the energy (as properly measured 
by its heating effect) in the solar radiation is confined within narrow limits of wave¬ 
length, and that for these wave-lengths atmospheric absorption is less than for the 
waves of higher refrangibdity. The larger transmission coefficients in Langley’s 
calculations should therefore have more weight given to them, and it would be 
possible to draw up another series with assumed coefficients, by which the 29 per cent, 
could be reproduced, with the 21 per cent., 19 per cent., &c., following. 
