GASEOUS SPECTEA UNDER HIGH DISPERSION. 419 



it would seem that I ought to begin with the simple, elementary gases ; and 

 afterwards touch on their compounds if desired. 



But the practical methods of inductive inquiry into Nature, oblige me to 

 proceed in exactly the opposite manner, and begin, as did also the great Upsala 

 leaders, with the manufactured compound gas most immediately at hand in 

 any and every situation in life, viz., illuminating gas, whether of coal, oil, wax, 

 or tallow. 



There may be, as we shall see presently, some difficulty in deciding on the 

 chemical interpretation to be put on the spectrum thence obtained, but there 

 is none in procuring a view of it ; for whether we observe the blue flame of a 

 blow-pipe of coal-gas and air, or the blue base of an upright flame of either 

 those or any other of the ordinary illuminants of night employed by man, 

 burning in the open air, — there appears to be always the same identical 

 spectrum present, differing in no one case from another, except in degree of 

 brilliancy. 



Were we to burn the illuminant in a current of pure oxygen, something 

 additional might be seen. But I have purposely refrained from doing that, and 

 confined myself, in this part of the inquiry, to the grand aerial constant for all 

 men, compound though it be, of the earth's atmosphere, for the sole elementary 

 aid to combustion, as a mode of obtaining incandescent temperature. 



To make the effects of that, however, more visible than usual, I have em- 

 ployed a blow-pipe nearly a foot long ; with coal-gas in quantity from the 

 service pipes of the house, but urged in intensity by air from a bag under 

 pressure equivalent to 6 or 8 inches of water : and have further always 

 placed the flame thence procured " end-on " to the spectroscope's slit, in the 

 manner described to, and approved by, the Eoyal Scottish Society of Arts 

 several years ago. Thence results what the Brittish Association calls, 



The Candle-Spectrum, in Air, 



or, as named here, for reasons presently to appear, CH, i.e., Carbo-Hydrogen, 

 in Blow-Pipe Flame. 



Having been introduced to this Society nearly thirty years ago, by our 

 respected Fellow, Professor Swan, this particular spectrum will doubtless be 

 well known to every one present, as offering a charmingly simple arrangement 

 of five bands, most aptly to be compared to the human hand. For the first of 

 them, orange coloured, and therefore in the orange region of the spectrum, is 

 comparatively thin and weak, say like the little finger. The second, citron 

 coloured, much stronger like the next finger. The third in the green, the 

 brightest and strongest of the whole, like the middle finger. The fourth, in 

 the blue, intermediate for strength between the first and second, like the index 



