CARBOX IX THE FLAME. 139 



they serve as solid particles, to emit light by their incan- 

 descence. 



It is from these solid particles individually solid, though 

 inconceivably minute that the chief portion of the light 

 of such a flame comes. The combustion of the hydrogen 

 alone, or of any other gaseous substance, though it would 

 produce great heat, would afford very little light. For 

 some mysterious reason, it is necessary that there should 

 be solid particles present to transform, as it were, a portion 

 of the heat into light, and emit it in that form. 



These solid particles of carbon in the flame are not di- 

 rectly visible, but, as in the case of vapor of water, we can 

 easily, by the use of proper means, bring them into view. 

 If, instead of holding the cold iron in the air above the 

 flame, we hold it, or any other solid substance, actually in 

 the flame, the black particles are suddenly cooled by it, and 

 deposited upon its surface as soot is upon the back of the 

 chimney. This black substance, on account of its being 

 produced in this way, is called lamp-black. 



The process Avhich thus takes place in the burning of 

 a candle is quite a complicated, and a very curious one, 

 and if, in watching it, our powers of vision were sufficiently 

 acute to enable us to distinguish the several steps, we 

 should be greatly interested in observing it. In the first 

 place, we should distinguish in the oil, slowly coming up 

 the wick, particles of carbon and hydrogen conjoined. We 

 must not, however, conceive of the particles of carbon as 

 black ; they are black when separated from their combina- 

 tions and existing in a certain form by themselves, but 

 they may be of any other color. Color, as will be ex- 

 plained more fully in a future chapter, depends altogether 

 upon the manner in which any substance absorbs or re- 

 fiects the light, and this does not depend upon its intrinsic 

 character at all, but apparently upon the mechanical ar- 



