336 On the Low-Temperature Spectrum of Oxygen. 



Evidently, then, in despair, this sorely tried and now de- 

 parted 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, suggested 

 " carbonic acid," says further, perhaps it is ozone which pro- 

 duces these bands. No reason is given; but the prudent 

 caution is inserted — if there is free ozone in the earth's atmo- 

 sphere. 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 

 (xeissler 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 great 

 A, great B, and a (alpha) of the sunset 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 Pro- 

 fessor Angstrom out of the difficulties 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 combined 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 of Edinburgh with their Makdougall- 

 Brisbane Prize. 



Angstrom, observing these three bands when they were 

 thick and clumsy at sunset, pronounced their constitution to 

 be exactly similar in every case. I, on the contrary, obser- 

 ving them in a high sun, when they were divested of the 

 rotundity of flesh, and only their thin, linear bones appeared, 

 found the ultimate constitution of the a (alpha) to be per- 

 fectly different from that of A and B ; for in place of many 

 regular and symmetrically arranged powerful lines, it was 

 made up of little doublets and triplets of both inconceivable 

 minuteness and very irregular occurrence (see the said 

 Lisbon spectrum as printed in vol. xxix. of the Society's 

 Transactions). These Lilliputian foundation-stones of the 

 a (alpha) band appeared to me at the time almost ridiculous 

 in their smallness; but now I recognize them as having a 

 close family resemblance to the triplicity of the low-tempera- 

 ture oxygen-lines which I have been trying hereinbefore to 

 describe. They are not indeed the very same; for they are in 

 different spectrum places ; but they do give the idea (sug- 

 gested also by some points in both the aurora-spectrum and 

 cometary spectra not yet reproduced in any laboratory elec- 



