90 MODERN SCIENCE READER 



answer to these two questions the origin of carbon parti- 

 cles and the source of heat is given in the "acetylene 

 theory," first advanced in 1892 by Professor Vivian B. 

 Lewes, of England. 



This theory expressed briefly is that a portion of the 

 hydrocarbon gas, by the heat of combustion of another por- 

 tion, is converted into acetylene, and that this on being 

 decomposed by heat furnishes the carbon particles, which 

 particles are rendered incandescent mainly by the heat 

 liberated when the gas is decomposed; acetylene being a 

 substance which absorbs heat during its formation and 

 hence liberates heat when it breaks down. Whatever is 

 burned, whether a solid candle or liquid oil, must pass 

 through the gaseous state, and hence this applies to all 

 flames used for lighting purposes. 



But before explaining this theory more fully and seeing 

 upon what experimental evidence it is based, it would be 

 well to consider its genesis and briefly recall the ancient 

 notions regarding "artificial" light. 



Light was first confused with seeing, and it is said that 

 up to the time of Aristotle men commonly thought they 

 saw by reason of something shooting out from the eyes and 

 coming in contact with objects; the converse of the Carte- 

 sian conception of many centuries later, that certain move- 

 ments in bodies cause them to shoot out minute particles in 

 all directions, which, striking the eye or causing "glob- 

 ules" of air to strike it, excite vision. 



The fluid nature of fire and the corporeal nature of light, 

 which were believed in throughout the early and middle 

 ages, seem to have been first doubted by Sir Francis Bacon 

 about the end of the sixteenth century, although he was by 

 no means sure that these conceptions were wrong. Bacon 

 classed together the light from flames, decayed wood, glow- 

 worms, silks, polished surfaces, etc., and said that inas- 

 much as some animals can see in the dark, air has some 

 light of itself. Boerhaave, somewhat later, also expressed 

 doubts as to the substantive nature of fire. 



