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other compounds are decomposed ; but it occurred to me that the 

 oxyhydrogen flame must consist partly, if not entirely, of glowing 

 steam, since it is only when the two elements combine that the heat 

 is evolved ; and that similarly the flame of carbonic oxide burning in 

 air must contain the light emitted from glowing carbonic acid. I 

 therefore subjected these two flames to prismatic examination. 



The result of the comparison has been that not one of these obser- 

 vations shows any accordance between the luminous bands due to 

 the gas, and the dark lines that make their appearance in the solar 

 spectrum when the sun is shining through a great depth of air. 

 Hydrogen alone is inconclusive. Neither is there any accordance 

 between these luminous bands and the more prominent lines of the 

 ordinary solar spectrum. 



This shows that oxygen and nitrogen, and perhaps other gases, 

 though in enormous quantity, do not absorb at the ordinary tempe- 

 rature rays of the same refrangibility as those they emit when heated 

 by the means specified. 



It would not be legitimate to infer from this that the atmospheric 

 lines have not their origin in the absorbent power of one or more of 

 the common constituents of the atmosphere. It is well known that 

 some gases when placed before a continuous spectrum produce lines 

 of absorption ; among these are bromine and iodine vapour ; yet the 

 dark lines caused by these two halogens * do not coincide with the 

 bright lines into which Pliicker found the light of Geissler's tubes 

 containing bromine and iodine to be resolved by the prism ; nor 

 have I succeeded in reversing them by bringing these substances into 

 a very hot but little luminous flame. Bright lines were discerned, 

 but in other positions. In connexion with this subject, it may be 

 worth noting that a prismatic examination of the sun's rays passing 

 through three inches of mercury vapour at above 300 C., did not 

 afford the least indication of the reversal of the bright rays that 

 appear when that metal is rendered incandescent. 



From the fact that the atmospheric lines do not always present 

 the same appearance when the sun is on the horizon, and that the 



* See " Experiments and Observations on some cases of lines in the prismatic 

 spectrum produced by the passage of light through coloured vapours and gases, 

 and from certain coloured flames," by Prof. W. A. Miller. Phil. Mag. August 

 1845. 



