4 act Sala hk 
pee. 
192 J, E. Keeler—Absorption of Radiant Heat 
ment on the absorption of air containing aqueous vapor or other 
ases ‘ 
ses. 
Further, the character of the absorption of CO, must agree 
with that of the air if this gas is the seat of the absorptive 
ower of the latter, and this gives us an independent means of 
decision. The absorption of a substance which permits the 
passage of radiant energy will exhibit peculiarities of which 
the following constitute the most marked cases. It may be 
strongly selective, i. e. confined to certain definite wave-lengths, 
by which lines would be produced in the continuous spectrum 
of a luminous source whose rays had passed through the sub- 
stance; it may affect strongly rays differing but little in wave- 
length, producing broad bands in the spectrum; or it may ex- 
tend over many wave-lengths, affecting each but little more or 
Jess than the next in succession, by which no perceptible lines 
or bands would be produced, although the intensity of the _ 
spectrum would be weakened within wide and indefinite limits. 
greatly. 
The apparatus which I made for investigating the absorption 
of CO, was originally intended to be used in connection with a 
Rowland grating, so as to test the absorption of nearly homo- 
geneous rays; but, owing to the limited amount of time at my 
disposal after it was completed, I was obliged to content myself 
with the use of artificial sources of heat, which, although far» 
from furnishing homogeneous rays, differed so widely in char- 
acter that the results obtained seem to’ me to be sufficiently 
* This Journal, xxv, March, 1883. 
