62 CANDLES AND LAMPS. 



that is necessary to enable the reader to understand what 

 I am going to say about light is, that combustion is a pro- 

 cess that develops great heat, and that the intensity of the 

 heat depends in a great measure on the rapidity and abun- 

 dance of the supply of oxygen. 



The intensity of the light which is developed by the heat 

 depends, in a great measure, on the substance heated con- 

 sisting of solid particles, for, at the same temperature, the 

 particles of a solid substance are found generally to emit 

 a stronger light than those of a gaseous one. But then, on 

 the other hand, certain gaseous substances emit a greater 

 degree of heat in combustion than most solid ones. 



It results from this that, in order to have an intense 

 light, one way, at least, would be to have a gaseous sub- 

 stance to burn in order to produce the heat, and some 

 solid particles, or solid substance, to be heated by it, to af- 

 ford the light. 



This is very simple, and yet this is the philosophy of the 

 modes generally adopted to produce artificial light and to 

 increase the intensity of it. 



Take a common lamp or candle, for example, burning 

 with a naked flame that is, without any glass chimney. 

 The tallow, or wax, or spermaceti, or paraifine, or oil, or 

 kerosene, or whatever other similar combustible is used, is 

 composed chiefly of carbon and hydrogen, and all these 

 substances are called, accordingly, hydrocarbons. When 

 they are burned in the wick of the candle or lamp, the hy- 

 drogen, which is the gas, burns and produces a great heat, 

 and the floating particles of carbon, which, though exceed- 

 ingly minute too minute altogether to be seen by the 

 naked eye are yet solid, become intensely heated, and it 

 is they that emit the bright light. 



Hydrogen, burning alone, emits a very feeble light. We 

 sometimes see, in a wood fire, faint blue flames here and 



