J. P. Cooke on Aqueous Lines of the Solar Spectrum. 188 
sions. With a more powerful instrument a larger number of 
aqueous lines would be seen under the same atmospheric condi- 
pear as in fig. 2. , 
_ The facts stated in this paper fully account for the discrepan- 
cies in the representations which different observers have given 
oceasion. The moist climate of England is the evident expla- 
nation of the additional lines. 
17th of November was at least ten times as great as that of the 
true solar lines. That part of the yellow of the spectrum which 
lies on the more refrangible side of the D line, and in which 
luring dry weather only a comparatively few lines can be dis- 
tinguished, was then as thickly crowded with lines as the blue 
or the violet, but the lines were of course far less intense. 
Professor Tyndall of London has shown by a remarkable 
Series of experiments with the thermo-multiplier not only that 
aqueous vapor powerfully absorbs the obscure thermal rays; 
but also that the elementary gases of the atmosphere exert little 
Tf no action upon them. I have endeavored to establish in this 
Paper, from direct observations with the spectroscope, a similar 
truth in regard to the luminous rays. It has been estimated by 
Pouillet and others that about one-third of the solar rays inter- 
cepted by the earth are absorbed in passing through the atmos- 
ni Ss 
phere. T have shown that otf great many, 
40ubt that almost all the lines, hit! 
