GASEOUS SPECTRA UNDER HIGH DISPERSION. 427 



reviewed a number of them before any night of final observation for the 

 present paper, in order to find out if any changes with time and use were 

 going on amongst them, and to ascertain more particularly for the service of 

 the great spectroscope, which tube of them all, whatever its original label, was 

 just then capable of showing a particular part of the spectrum of some specially 

 required gas, with the greatest purity and the utmost vigour. 



If this is still to be held up to public reprobation by London central and 

 immovable scientific authority, as my " trusting to a label put on by a glass- 

 blower," — and because I did not fill my own tubes, — there is nothing left for 

 me but to request the Royal Society, Edinburgh, to judge between us, — if I 

 shall venture to set forth, before the close of this paper, how much more of the 

 undoubted phenomena, of at least one particular gas I have succeeded in 

 discovering, identifying, and micrometrically recording on an extended scale, 

 than have any of those London and British Association gentlemen ever been 

 able to observe in their tubes, although they filled them for themselves. 



Resuming then, by this Society's leave, we come next to 



PART II. 



Citron, and Green, Bands of CH, in Vacuum Tubes. 



After preliminary experiments with Alcohol, Marsh gas, Turpentine, Coal 

 gas and defiant gas — I settled clown to working chiefly the two last of these 

 Carbo-hydrogen vapours or gases. 



Of these gases much desired, pure CH spectrum, by electric light, but 

 under atmospheric pressure, — MM. Angstrom and Thalen have given the two 

 brightest bands, viz., the Citron and the Green, in their Mesures Micrometriques. 



Those well-known bands make therein a very brilliant picture, especially 

 as they are engraved in ne plus ultra style of both refinement and force; 

 in the positive manner too, or with the lights white, on a field of black for 

 darkness, and with an effect that Rembrandt might have envied. 



The Swedish scientists do also there give a considerable indication of hazy, 

 fluted linelets, continually getting closer, and brighter as they approach the 

 least refrangible side of each band. But, strange to say, they have wholly 

 omitted the vastly superior brilliancy of the leading lines in each band ! 



These strong leading lines are the first exact features which a beginner in 

 spectroscopy makes out, to his great delight, when studying each CH Blow- 

 pipe band ; though at first sight, and with a too broad slit, said bands had 

 probably appeared to him as only composed of smooth haze. And I can now 

 further vouch, that those CH bands' leading lines, whether in blow-pipe or 

 vacuum tube, remain equally conspicuous over the linelets, in all my subsequent 



