On the aqueous lines of the solar spectrum / by Josiah P. Cooke.

  • Josiah P. Cooke
Date:
[1866?]
Catalogue details

Licence: Public Domain Mark

Credit: On the aqueous lines of the solar spectrum / by Josiah P. Cooke. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    7/8 (page 7)
    t 7 Some time since, iMr. Gassiot, of London, gave in the Chemical News a representation of the D line as seen with his instrument, showing several lines in addition to those seen by myself and other observers. On visiting the Kew observatory, in_the summer of 18G4, I was sur- prised to find that this instrument was less powerful than the one I was then using; and I also learned that^se lines were only seen on a single occLion. The moist clitnate of England is the evident expla- nation of the additional lines. As I stated at the first of this paper, the D line has been selected simply to illustrate a general truth. The development of aqueous lines in contiguous portions of the spectrum is even more marked than in the exceedingly limited portion here represented. Indeed, as has been already intimated, the number of these lines seen in the yellow region of the spectrum, on the 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 during dry weather only a comparatively few lines can be distinguished, was then as thickly crowded with lines as the blue or the violet, but the lines were of course far less intense. Professor Tyndal, 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 elemen- tary gases of the atmosphere exert little or 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 intercepted by the earth are absorbed in passing through the at- mosphere; and it now appears that aqueous vapor is a most important, if not the chief, agent in producing this result. It is impossible, however, from any data we yet possess, to determine how great a power of absorp- tion is exerted by the oxygen and nitrogen gases, which constitute the great mass of our atmosphere. I have shown that a very great many, and I have no doubt that almost all, the lines hitherto distinguished as air lines are simply aqueous lines ; but it is very difficult to distinguish atmospheric lines from the true solar lines, and our knowledge of the first is as yet very incomplete. It still remains to make careful comparisons throughout the whole extent of the spectrum, before we can absolutely determine the lelative absorbing power of the ditferent constituents of our alinos[)here.