392 Sir David Brewster on the Lines of the Solar Spectrum. 
the least refrangible side of it. It develops a beautiful Jine in 
the middle of the double line D, and by enlarging a group of 
small lines on the red side of D, it creates a band almost as 
dark as the triple line D itself. It widens generally all the 
lines, but especially the darkest one which I call m between 
Cand D._ It develops a band on‘the least refrangible side of 
m, and it acts especially upon several lines, and develops a se- 
parate band on the most refrangible side of C. The lines A, 
B, and C are greatly widened, and lines and bands are parti- 
cularly developed between A and B, and generally through- 
out all the red space. 
Most of the lines thus widened by the atmosphere are faint 
lines previously existing in the spectrum, and I have no doubt 
that they would be seen in the spectrum of the lime ball light 
condensed by a polyzonal lens, and acted upon by thirty miles 
of atmosphere. . 
The absorptive action of the atmosphere shows itself in a 
less precise manner in the production of dark bands, whose 
limits are not distinctly defined. A very remarkable narrow 
one, corresponding to one produced by the nitrous acid gas, 
is situated on the most refrangible side of C. Another very 
broad one lies on the most refrangible side of D, close to a 
sharp and broad band of yellow light, displayed by the general 
absorption of the corresponding part of the superimposed blue 
spectrum. There is also an imperfectly defined atmospheric 
action, corresponding to a group of lines where Dr. Wollas- 
ton placed his line C. 
This general description of the atmospheric lines, while it 
indicates the remarkable fact, that the same absorptive ele- 
ments which exist in nitrous acid gas exist also in the atmo- 
spheres of the sun and of the earth, leads us to anticipate 
very interesting results from the examination of the spectra of 
the planets. Fraunhofer had observed in the spectra of Venus 
and Mars, some of the principal lines of the solar spectrum. 
This, indeed, is a necessary consequence of their being illu- 
minated by the sun, for no change which the light of that 
luminary can undergo, is capable of replacing the rays which 
it has lost. But while we must find in the spectra of the pla- 
nets and their satellites, all the defective lines in the solar 
spectrum, we may confidently look for others arising from the 
double transit of the sun’s light through the atmospheres 
which surround them. 
Allerly, April 12, 1833. 
