75 
Sir H. Davy’s researches on flame. 
Journal of Science and the Arts, explain the nature of the 
light of flames and their form. When in flames pure gaseous 
matter is burnt, the light is extremely feeble : the density of 
a common flame is proportional to the quantity of solid char- 
coal first deposited and afterwards burnt. The form of the 
flame is conical, because the greatest heat is in the centre of 
the explosive mixture. In looking steadfastly at flame, the 
part where the combustible matter is volatilized is seen, and 
it appears dark, contrasted with the part in which it begins to 
burn, that is where it is so mixed with air as to become 
explosive. The heat diminishes towards the top of the flame, 
because in this part the quantity of oxygene is least. When 
the wick increases to a considerable size from collecting 
charcoal, it cools the flame by radiation, and prevents a 
proper quantity of air from mixing with its central part ; in 
consequence, the charcoal thrown off from the top of the 
flame is only red hot, and the greater part of it escapes un- 
consumed. 
The intensity of the light of flames in the atmosphere is 
increased by condensation, and diminished by rarefaction, 
apparently in a higher ratio than their heat, more particles 
capable of emitting light exist in the denser atmospheres, 
and yet most of these particles in becoming capable of emit- 
ting light, absorb heat ; which could not be the case in the 
condensation of a pure supporting medium. 
The facts stated in Section I. show that the luminous 
appearances of shooting stars and meteors cannot be owing 
to any inflammation of elastic fluids, but must depend upon 
the ignition of solid bodies. Dr. Halley calculated the height 
of a meteor at ninety miles, and the great American meteor 
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