424 PROF. PIAZZI SMYTH ON THE CONSTITUTION OF THE LINES 
absorption, it produces dark, in all the spectrum places where, when in a state 
of incandescence, it produced bright, lines. 
Now we know by laboratory experiments what bright lines are given out 
by both oxygen and nitrogen in various states of incandescence ; and not one of 
those lines is in the place, and at the same time endowed with the physiognomy, 
of great A or great B, or of the a (alpha) band of the sunset solar spectrum. 
To get over this astonishing difficulty, ANcsTRéM, who held that all these 
three bands are of a similar visible constitution, viz., a thick line and then a 
band of thin lines stretching out towards the red end of the spectrum—sug- 
gested that they might be produced by “carbonic acid.” But over and above 
the difficulty that carbonic acid is an almost insensible impurity in the open 
air, and could hardly be expected to extinguish every sign of the existence of 
the atmosphere’s two great constituents,—we do know the spectrum given by 
incandescent carbonic acid in the laboratory, and it cannot claim to having a 
band in the place of either A or B or a (alpha), besides its series being turned 
in the opposite direction, or every band vanishing towards the violet, in place 
of the red, end of the spectrum. 
Evidently then, in despair, this sorely tried and now departed philosopher 
of Upsala, but who is still our chief authority in this line, on page 41 of his 
Memoir already cited, after acknowledging that he had, in another place, sug- 
gested “carbonic acid,” says further, perhaps it is ozone which produces these 
bands. No reason is given, but the prudent caution is inserted,—if there is free 
ozone in the earth’s atmosphere. Or, again, he adds as a third supposition, 
perhaps they are produced by “ fluorescence of oxygen,” a gas which he there 
states gives forth “a faint phosphorescence in a Geissler gas-vacuum tube 
when an electric current is caused to pass through it.” But this is just as far 
from presenting us with the very definite lines constituting the bands of 
ereat A, great B, and a (alpha) of the sun-set telluric solar spectrum, as before. 
Now I have not, any more than all the rest of the world at this moment, 
any positive and proved means of raising Professor ANGSTROM out of the diffi- 
culties he eventually sunk under. But the minute triplicity of the greater part 
of the low temperature lines of the oxygen spectrum described in the beginning 
of this paper, may perhaps let in a chink of light upon the difficulty, when com- 
bined with the true constituent features of these grand telluric lines A, B, and 
a (alpha) as set forth in my Lisbon solar spectrum, so recently honoured by 
the Royal Society, Edinburgh, with their Makdougall-Brisbane Prize. 
ANGSTROM, observing these three bands when they were thick and clumsy 
at sunset, pronounced their constitution as being exactly similar in every case. 
I, on the contrary, observing them in a high sun, when they were divested of 
the rotundity of flesh, and only their thin, lmear, bones appeared, found the 
O_O 
