MKMOIR II.] SPECTRUM ANALYSIS OF FLAMES. 59 



consist of a series of concentric and differently colored 

 shells. 



I regard the foregoing experiments as affording the 

 means of explanation of the much more complicated 

 phenomena of flames, and proceed to inquire whether 

 the principle I have just brought forward of the co-or- 

 dinate increase of refrangibility and of 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 com- 

 bustion taking effect on those points only which are in 

 contact with the air. From the circumstances under 

 which the air is usually supplied, this ignited shell can- 

 not be a mere mathematical superficies, but must have a 

 sensible thickness. If we imagine it to consist of a series 

 of cone-like strata, it is obvious that the phenomena of 

 combustion are different in each. The outer stratum is 

 in 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 at- 

 mospheric air must necessarily pervade the burning shell 

 to a certain depth, and in the successive strata, as we ad- 

 vance inward, the activity of the burning must decline. 

 On the exterior stratum oxygen is in excess, at the in- 

 terior the combustible vapor, and between these limits 

 there must be an admixture of the two, which differs 

 at different depths. Admitting the results of the fore- 

 going experiments with anthracite coal and charcoal to 

 be true, viz., that as the combustion is more active, rays 

 of a higher degree of refrangibility are evolved, it fol- 

 lows that each point of the superficies of such a flame 

 must yield all the colors of the spectrum, the violet coming 

 from the outer strata, the yellow from the intermediate, 

 the red from those within. If we could isolate an ele- 



