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by Carbon Dioxide. 197 
under the two different circumstances as the proportion of the 
total radiation transmitte ‘4 meters of gas. 
The first source of heat employed was a kerosene lamp with 
large argand burner and glass chimney, and was more constant 
than any of the sources tried later, the irregularities in a series 
of observations being only about one-half per cent of the aver- 
age value of a deflection. Three experiments gave an absorp- 
tion of 7:1, 7:2 and 7-9 per cent, the mean of which is 7-4 per 
cent. 
The next source was a copper plate heated from behind toa 
point just below redness by a Bunsen flame, so that all of the 
radiations consisted of invisible rays. Of these 11 per cent 
were absorbed. 
Next was tried the feebly luminous flame of the Bunsen 
burner itself. This indicated a greater absorption than any of 
the other sources, three experiments giving a mean of 35°8 
per cent. 
was repeated under various conditions of the apparatus. The 
water cell completely cut off the rays from the Bunsen burner. 
Finally, although the apparatus did not admit of experiments 
with aqueous vapor, the enormous absorbing power of water 
was strikingly shown by a soap-bubble film stretched on a 
wire loop, which cut off 38 per cent of the rays from the 
Bunsen burner, or. more than the 8°4 meters of CO, The soap 
solution from which the film was obtained, when placed in the 
water cell, indicated an absorption of the rays from the lamp 
20 per cent greater than that of water. 
In these results we may especially note the following facts: 
1. That the luminous rays of the spectrum are not appreciably 
absorbed by a column of CO, 3°4 meters in length, whereas it 
has been shown that thesé rays are strongly absorbed by an 
atmospheric column containing the same quantity of CO,. The 
evidence afforded by the eye, inasmuch as the gas appears 
perfectly transparent, is confirmed by direct measurement of 
the energy of transmitted luminous rays. 2. That as the range 
_ of the wave-lengths given out by the radiant source is narrowe 
_ down toward a certain invisible limit, the absorption of the 
mes greater and greater, corresponding to the production 
