S. P. Langley—Selective Absorption of Solar Energy. 177 
where ¢ is the coefficient of vertical transmission by air at a 
barometric pressure of one decimeter. A tabular statement of 
these coefficients has been seam but the average or adopted 
value only is here given 
TABLE IIT. 
A= “400 *450 “500 “600 “700 “800 -900 1°000: 
Adopted 7 “884 "892 “909 923 “942 "955 "965 -970 “9T1 
fi-6 “392. 420... AS had P6Re WOR S tes. od “799: 
It is important to notice that (contrary to a generally received 
opinion), the yp eneer ote of the atmosphere is here found to be 
greatest for the infra-red rays. 
All good noon observations have been reduced to a uniform 
battery current of 0-25 webers, and the results, arranged in two. 
sets, the first for winter and the second for spring measures. 
ee tables are not here given but the average results are 
as fo 
TABLE IV. 
ae 375 400 450 -500 ‘600 -700 *800 ee 1-000: 
inter d, (mean of 7 ser ‘aay SL 88° 190. 294 328 259 142 91 
Wi 
Spring d, “(mean of 9 series) 18 57 139 218 281 271 188 131 94 
The average noon deflections for winter and spring, given in 
the previous table, require further correction; first, for the 
se p ich is 
tensity one-thirtieth that of the first. Second, for the selective 
absorption by silver surfaces. Third, for the selective absorp- 
ion by one surface of speculum metal. Fourth, for the diminu- 
tion of heat in the diffraction spectrum with increase of the 
angle of diffraction, which is here oe taken as pro- 
portional to secant r. The selective absorption by the material 
of the bolometer is here treated as negligable. 
orrections are expressed as factors by which the 
by special researches on setae absorption, which will form 
the subject of a separate me 
The researches here on she saloon absorption of lampblack, 
it should be added, are incomplete and the value given may be 
yet subject to a farther correction due to this error. 
TABLE V. 
Ass 3175 -400 -450 °500 600 -700 +800 -900 1:000 
Correct’n 
I (subir.) 0 se xdso dex das dex dso 
IT a aeto ; ood 206% lL se ‘si? 1: si ae i oa 1166 1145 
-923 1-802 1°695 1550 1-460 1:408 1:389 @ 1°370 
iv _ : an aks 1°051 1:064 1-096 teat 1193 1266 0 ©=-:1°366 
‘ 
