164 S. P. Langley—Atmospheric Absorption. 
heat gives about 21 percent. In fact, many thousands of obser- 
vations by scores of observers, during the past and present cen- 
tury, seem to have determined this proportion with all the 
exactness of which it is capable. 
I have arrived at a result so wholly different, that, in the face 
of such authority, I almost hesitate to announce it; for I have 
been forced to the conclusion, that all these determinations are 
in error; and not in some small degree, but by a quantity 
probably at least equal to the total amount in question. 
I hasten to say, that I do not dispute the general accuracy of 
the numerous skillful investigators of known repute who have 
made these determinations, but that I dissent from the method 
in almost universal use for reducing them, for since it is certain 
that none of these observers have been outside the atmosphere 
to see what the radiation really is; all of them, however skilled, 
must depend on inference to determine what it would be, if they 
could thus observe it. It is certain that nearly all have used a 
formula of which it seems capable of absolute demonstration 
that it is not only erroneous, but that its error always lies in — 
one direction, so as to invariably make the calculated absorption 
too small, and it may be further shown with an evidence which 
seems little less than demonstrative, that the numerical value of 
the error is very large in relation to the quantities involved. 
I have been led however, not by theoretical considerations — 
alone, but by experimental investigation, (during the-course 
which I have observed both near the sea-level and at great alti- 
tudes), to the conclusion that the laws under which solar and 
stellar light and heat are absorbed by the atmosphere, are 80 
i Pe ena aoe 
2 Se ces igi 30a eget 
SIRES tee eal toe eae i ae yt eae Se, Pfr ee Se ge se ae ee 
dark room, the light is partly interrapted by the particles of a 
dust or mist in the air, the apartment is visibly illuminated by 
