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S. P. Langley—Selective Absorption of Solar Energy. 195: 
Our white light, then, is not the sum of all radiations, but 
only of a DAC even of the visible ones. 
4t e can, by measuring the area of the curve veg our 
atmosphere and comparing it with the area of the ve 
within, obtain by a method never before pursued, Nits Sa in 
close accord with theory, a value for the Solar Constan 
exactness of that in the first decimal place is Story open to 
doubt. The conclusion which we are entitled to draw from 
Sth. These Mom ang show heat in extreme ultra violet 
ays and the change of temperature (hitherto unobserved), in 
the Frauenhofer lines. They lend increased probability to the 
belief that all the energy in any ray can HE ited as heat, if 
there be a proper medium to receive this energy. Their evidence, 
So far as it goes, then, favors the conception of one solar 
energy which is interpreted in terms of heat, or of light, or of 
chemical action, sera to the medium by means of which 
we choose to observe it. 
th. The ratio of pee ee to dark heat has bcc eal been 
wholly changed by the selective absorption. The ratio at the 
sea-level may be found with close approximation by ee 
the two areas, (1st) above ee pou where we assume the lu- 
minous spectrum to end, and (2d) below it. This point each 
one may define diff fferently, for the extent of the luminous. 
Spectrum depends much upon our precautions for observing it. 
we assume it to end near B, then three-quarters of the 
energy must be termed invisible : if at the actual visual ex- 
tremity (far below A), then less than half. To fix our ideas, let 
us suppose it to terminate at Frauenhofer’s A. We then find 
luminous and ultra-violet energy (within the 
smooth curve) 0°368 
infreréd onetwy (isi oucdns does cide es 0°632 
1°000 
The ratio of the invisible (infra-red), to the whole then is 
0°632, and there is reason to believe this value rather too small 
than too large. If, however, we deduct the space occupied by 
the gaps in the lower spectrum the ratio becomes 0562. The 
