S. P. Langley—Selective Absorption of Solar Energy. 181 
Area Outside Curve above = 1“:000 47°26 
Area Outside Curve below = 1”:000 26°49 
Total 73°66 
Area High Sun Curve above = 1":000 —.26-96 
Area High Sun Curve below = 1":000 —- 20°00 
Total 46°96 
; . Area Outside Curve 73°66 
The ratio of these areas is Area ¥ligh Saw Ourve 1 4008 7 1°569 
We have, then, adopting 1°81 cal. as the solar radiation at 
Allegheny with clear sky, 1°81 cal. x 157 = 2°84 calories as 
an approximate value of the Solar Constant. 
In all these observations, the object a been to avoid the 
registering of small variations analogous to the Frauenhofer 
lines, and to give only the general eee of the energy. 
e mapping of the peg tare” of the energy caused by visi- 
ble or invisible lines or bands forms a distinct research, and 
the results are given ites in the present article. 
e find from these preliminary observations, that the maxi- 
mum energy in the normal spectrum of a high sun at the 
ok surface is near the yellow, and “that the position of the 
maximum of heat does not in fact differ widely from that of 
ole the most transmissi 
But we see here, not waly how enormous the absorption at 
the violet end really i is, bnt that the light rays have suffere 
larger absorption before they reach us “than the “heat” rays 
(i. e. than the extreme red and infra-red rays) a Bisse ot 
opposed to the present orev ee opinion, and if t f far- 
us heat enters, our view “of the heat-storing action of this 
ae and of the conditions of life on our planet must be 
changed. Within the limits of the present charts the “dark” 
heat apparently does so esca 
We can from the data now Seibel as to the rate of abso 
tion for each ray, Pamcie a the value of the heat or energy 
value indicates that the true solar constant is larger than that 
commonly given. The ratio of the dark to luminous heat has 
been so ehclhy changed by selective absorption that we must 
