MEMOIR II.] SPECTRUM ANALYSIS OF FLAMES. 53 



light and heat as material bodies which can be incor- 

 porated or united with ponderable substances, supposed 

 that they are disengaged as chemical changes go on. In 

 this confusion of opinions a multitude of interesting and 

 hitherto unanswered questions present themselves. It 

 is known that different substances, when burning, emit 

 rays of different colors. Thus sulphur and carbonic 

 oxide burn blue, wax yellow, and cyanogen lilac. What 

 are the chemical conditions that determine these singular 

 differences? How is it that, by changing the conditions 

 of combustion, we can vary the nature of the light? 

 We turn aside the flame of a candle by means of a 

 blow-pipe, and a neat blue cone appears. Why does it 

 shine with a blue light? 



Such inquiries might be multiplied without end ; but 

 a little consideration shows that their various answers 

 depend on the determination of a much more general 

 problem, viz., Can any connection be traced between the 

 chemical nature of a substance, or the conditions under 

 which it burns, and the nature of the light it emits ? It 

 is to the discussion of that problem that this memoir is 

 devoted. 



Sir H. Davy has already furnished us with two im- 

 portant facts in relation to the nature of flame : 1st, All 

 common flames are incandescent shells, the interior of 

 which is dark ; 2d, the relative quantity of light emitted 

 depends upon the temporary disengagement of solid par- 

 ticles of carbon. 



It is only by a very general examination of the light 

 arising from various solids, vapors, and gases, when 

 burning, that we can expect to obtain data for a true 

 theory of combustion. This is what I shall endeavor 

 to furnish on the present occasion. 



As was foreseen by all the older chemists, the true 

 theory of combustion, whatever it may prove to be, 



