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Published online by Cambridge University Press: 06 July 2012
Of all the various spectra which the progress of experimental science has enabled man to observe in the present day, none are so rich, varied, and important, as those of gases. And no wonder! for it is only when matter has been reduced to the gaseous condition, that it is able to specialise itself and write its character with much of its history in any otherwise smooth, undefined, continuous spectrum; while, if in former times, men would have found it an impossibility to drive many of the more refractory substances into the state of incandescent vapour, what is there now anywhere on the surface of this earth which, in small quantity, can resist the action of a powerful and condensed induction spark of electricity; and what application of that spark is so neat, elegant, convenient, and economical, as when it is employed in conjunction with so-called gas-vacuum tubes.
page 152 note * Dull and band-like; probably double lines (?)
page 152 note † Nova Acta Reg. Soc. Sc. Upsal., Ser. iii. vol. ix.
page 153 note * Salet, as well as Plücker and Hittorff, struck by the identity of this spectrum in all the nitrogen-bearing tubes, was led to the opinion from its constancy that the real source of the fluted spectrum is nitrogen itself.
page 153 note † A different view of this spectrum is, however, taken by Mr Lookyer, in whose opinion it is one form of the spectrum of elemental carbon. The smooth-shaded tube-carbon bands, in fact, resolve themselves into the line-bearing gas-flame ones on simply strengthening the induction discharge with a condenser, and especially on introducing at the same time an air-break also in its course. The experiment was tried after the present paper was read, with the above described carbonic acid and cyanogen vacuum-tubes, on July 23, 1880, on its prescription by Mr Lockyer to the writer of the paper, and to Professor Piazzi Smyth, and it succeeded in the presence of its suggester, literally as he expected!
page 154 note * Professors Liveing and Dewak's, and Dr Huggins' simultaneous recognitions of the remarkable ultra-violet spectrum of aqueous vapour in the light of all hydrogen-bearing flames (‘Proceedings of the Royal Society of London,’ June 1880), although announced just previously to the presentation of the above reflections, had not yet been received. But they afford as yet no certain evidence that the same spectrum, indicative of aqueous vapour, is also producible by electrical discharges in gas-vacuum tubes.
page 154 note † (a, c, See the accompanying sketch, p. 157).
page 158 note * In a careful search for low-temperature lines in an oxygen gas vacuum tube, Professor Piazzi Smyth has met with an extreme-red line at W. No. 32,600 (circa), which may perhaps be identical with that above noticed as mapped in an “air-spectrum” at about W. No. 32,670. The latter line, in that case may perhaps be an oxygen-line, and not a nitrogen-line as here supposed.