Clifton College Scientific Society. 57 



them into itself. Thus when a fire is lit, we, according to this 

 hypothesis, bring into contact with the coals a portion of the 

 element fire, which begins immediately to consume them by 

 converting them into that element, and what is unfit food is 

 left behind in the form of ashes. Dr Hooke, in 1665, proposed 

 an ingenious theory : he assumed that there exis-ted in common 

 air a certain substance similar, if not identical, with that fixed in 

 saltpetre, and which gave to it its combustible character. This 

 theory, first set forth in his MicrogrcipMa, was about ten years 

 afterwards further elaborated by Mayow. To this solvent, the prin- 

 ciple of combustion, he gives the name of spiritus nitro-aereus. 

 It consists, he surmised, of minute particles constantly at variance 

 with the particles of combustibles, and " from their quarrels all 

 changes of things proceed ; " fire consists in their rapid motion, 

 heat in their less rapid motion. From these theories philosophers 

 were soon directed to a theory df Beccher, which before it had 

 become generally known, was remodelled by Stahl, and that in 

 such an able and elegant form as soon to become universally re- 

 ceived. He supposed that the molecules of the elementary fire or 

 phlogiston were lodged in those of the body, as in so many little 

 covers or wrappers, where they experienced a compression similar 

 to that of a bent spring ; in combustion the fire escaping in conse- 

 quence of its expansive force, the particles by which the deflagation 

 is commenced impress 011 the neighbouring particles a blow, which 

 occasions their rupture by the unbending or expansion of the fire 

 which they conceal, and the commotion thus produced would 

 propagate the conflagration from one particle to another tlirough- 

 out the whole mass. So far these theories were purely physical, 

 and took no cognisance of any change of identity in either the 

 burning body, or in the air in which it is burnt. 



Lavoisier shortly, however, pointed out that combustion was at- 

 tended by an essential cliange in composition of the substances 

 involved — in fact, that it was due to a combination of the particles 

 of the burning body with those of the oxj^gen in the surrounding 

 air, with an evolution of light and heat. This discovery, which was 

 first made public in 1778, brought about a complete revolution in 

 the scientific world ; and the question may now be considered 

 as entirely settled. 



The subject of the present paper is the light attendant upon 

 combustion. This may be of two kinds, incandescence smdfiame. 

 The actual nature of flame, as the general phenomenon of com- 

 bustion, was for long ages unknown. By the earlier philosophers 

 it was regarded as " a simple substance reared from a combination 

 of primordial atoms." This was the tenet of the Epicureans, but 

 was controverted by Aristotle and the Peripatetics, who, denyiniy 



