.104 Prof. Draper on the Production of Light 



lations were disappointed ; for instead of the combustion being 

 increased, the coal was actually extinguished by the jet play- 

 ing on it. I therefore replaced the anthracite with a flat piece 

 of well-burnt charcoal, kindled at the part opposite the slit, 

 and throwing a stream of oxygen on this part, the combustion 

 was greatly increased ; and through the telescope I saw a spec- 

 trum rivalling that of the sunbeams in brilliancy, all the co- 

 lours, from the extreme red to the extreme violet, being present. 



Now on shutting off the supply of oxygen the combustion 

 of course declined ; and whilst this was going on, I looked 

 through the telescope and saw the violet, the indigo, the blue, 

 the green, &c. fade away in succession. By merely turning 

 the stopcock, through which the oxygen came, I could re- 

 establish the original colours or witness their decline. And 

 it was very interesting to see with what unerring regularity, 

 as the chemical action became more intense, the more refran- 

 gible colours were developed ; and how, as it declined, they 

 disappeared in due succession; the final tint being red, and 

 that ash-gray in the position of the yellow, which I have de- 

 scribed in my former memoir. (Phil. Mag. May 1847, p. 34'9.) 



In the form of experiment here made the combustion is of 

 course merely superficial ; and the rays come from the char- 

 coal, not as an incandescent, but as a burning body. 



III. Of the co7istitution of flames ; ■proving that they consist of 

 a scries of concentric and differently coloured shells. 



I regard the foregoing experiments as affording the means 

 of explanation of the much more complicated phaenomena of 

 flames; and proceed to inquire whether the principle I have just 

 brought forward, of the co-ordinate increase of refrangibility 

 and chemical action, will hold good, premising the experiments 

 now to be detailed with the following considerations. 



All common flames, as is well-known, consist of a thin 

 shell of ignited matter, the interior being dark, the combustion 

 taking effect on those points only which are in contact with 

 the air. From the circumstances under which the air is usu- 

 ally supplied, this ignited shell cannot be a mere mathematical 

 superficies, but must have a sensible thickness, Ifwe imagine 

 it to consist of a series of strata, it is obvious that the phaeno- 

 mena of combustion are different for each. The outer stratum 

 is in absolute contact with the air, and there the combustion 

 is most perfect; but by reason of the rapid diffusion of gases 

 into one another, currents, and other such causes, the atmo- 

 spheric air must necessarily pervade the burning shell to a 

 certain depth ; and in the successive strata, as we advance 

 inwards, the activity of the burning must decline. On the 



