256 THE POPULAR SCIENCE MONTHLY 



THE FLAME OF A CANDLE. 



By C. FIEVEZ, 

 astronomer at the royal observatory at brussels. 



THE little yellow candle-flame, which, is gradually disappear- 

 ing from our households to give place to brilliant gas and 

 electric lights, still plays a considerable part in the labors and 

 researches of physicists, chemists, and astronomers. The former 

 find in it a source of heat capable of melting and oxidizing or 

 reducing the most refractory metals. The last employ it as a 

 photometric unit, both to measure the most considerable lights 

 and to determine the luminosity of stars so faint that they can 

 hardly be seen in the great telescopes. But the most curious 

 and interesting thing about this little flame is the fact that the 

 optical study of it has contributed very largely to our knowledge 

 of the elementary composition of the celestial bodies. 



Carefully examined with the naked eye, the flame of a candle 

 is composed of three distinct layers or envelopes, viz., a dark 

 central part, the dark cone around the wick, formed of gaseous 

 products of low temperature, and holding in suspension carbon 

 in a state of fine division, but not yet incandescent ; a luminous 

 part, surrounding the dark part, and composed of carbon raised 

 to a bright incandescence; and a thin external envelope, only 

 faintly luminous and faintly colored, yellow toward the top, 

 where the carbon is completely burned, and bluish toward the 

 base, where the primary products of the decomposition of the 

 matter of the candle are burning in contact with the air. 



Analyzed by the aid of the spectroscope, the luminous cone 

 gives a brilliant and continuous spectrum — that is, one having 

 the appearance of a ribbon exhibiting all the colors of the rain- 

 bow, while the exterior, faintly luminous envelope gives a dis- 

 continuous si^ectrum formed of three bright bands — one yellow, 

 one green, and one blue. 



As only solid incandescent bodies are capable of giving a con- 

 tinuous spectrum, we conclude that carbon in the solid state is 

 incandescent in the luminous envelope of the flame. But, the 

 spectrum of the exterior envelope being discontinuous, we con- 

 clude that it is composed entirely of gaseous products. 



The flame of illuminating gas presents, both to the naked eye 

 and in the spectroscope, the same aspect as the flame of the can- 

 dle, whence it is concluded that its lighting and heating powers 

 are derived from the same cause — the more or less complete com- 

 bustion of carbon. 



By blowing air or injecting oxygen through the blow-pipe 

 into a candle-flame or a gas-light, its aspect is greatly changed. 



