382 
MESSRS. W. E. WILSON A.ND P. L. GRAY 
method of his work,” he divides the radiant energy before absorption into ten parts 
A, B, C, . , . J, each having its own coefficient of transmission, a, h, c, . . .j, so that 
the total radiation outside our atmosphere being 
A + B + C + D + &c_= X, 
the intensity after passing through unit thickness of air (i.e., e = 1, a zenith 
observation) will be 
Aa + B?> + Cc + T)d + &c. . . . = M, 
after passing through two thicknesses (e = 2) will be 
Aa^ + + Cc^ + DcP + &c_= N, 
and so on, assuming that a, h, &c., remain constants for more than one integral value 
of e, which is not exactly true. 
Of course X is unknown from experiment, but M, N, 0, &c., can be measured. 
Then the ratio N/M will give the transmission of the second thickness compared 
with the first, and 1 — N/Ad the absorption, and similarly with the other series, and 
these may all agree within close limits. The great mistake lay in assuming that if 
aiyproximately, then the same ratio held for the 
first thickness. 
By giving values of a, 6, c . . . &c. = ’01, ’1, '2, '6, '7, '7, *8, '9, ’9, and I'O, 
while A = B = C = &c. = 1, Langley shows that this equality of the ratios is at 
once destro 3 md, and holds that this rough division of the whole radiation into parts 
with varying coefficients of absorption, must give an approximation to the truth. 
Taking A = B = C = &c. = J = 1, the total outside radiation =10, while 
Then 
while 
Aa + B6 + . . . JJ = 5-9 = AI 
Aa2 + B63 + . . . Sf = 4-65 = N 
Ard + BP . Jf := 3-88 = 0, &c. 
= - 21 , 1 - 
= -19, 1 - 
•18, &c.. 
1 — 
M 
X 
_^9 
10-0 
= -4 
so that instead of 21 per cent, being absorbed in one thickness of atmosphere, it may 
very well be double that absorption taking place. 
We now come to an examination of Rosetti’s careful investigation on this point. 
He does not give the value of the absorption explicitly, but it may be deduced from 
the figures given by him on p. 546* of his paper already quoted. 
