^16 Dr Fyfe on the Illuminating and Heating Power of 



a piece of wire-gauze in the flame. When held in the white 

 flame, carbon, in the form of smoke, instantly appears, but 

 when put in the blue flame there is no smoke. Or if the gauze 

 be held over the burner, and at a little distance from it, so as 

 to allow the gas before it is kindled to mix with air, and a 

 flame is then applied above the gauze, the combustion goes on 

 also without smoke, but with very little light, — the ingredients 

 at once entering into union with the oxygen of the air, without 

 the carbon being previously set free from the hydrogen. 



It is evident then, that when gas is to be used for affording 

 light, it ought to be so consumed that there will be decompo- 

 sition; that, in fact, it must not be burned as a hydro-carbon, 

 by the ingredients at once and at the same instant entering 

 into union with oxygen, but by the hydrogen first combining 

 with oxygen, and setting the carbon free, which is then to 

 unite with oxygen ; and this is to be accomplished by the due 

 admission of air. Hence it is, that not only do different bur- 

 ners afford very different light for equal consumpt of gas, but 

 the same burners will, under different circumstances, also vary 

 in their illuminating power. 



The truth of these observations has been fully and satisfac- 

 torily illustrated, in an elaborate and interesting paper pub- 

 lished by Drs Christison and Turner in the Edinburgh Philo- 

 sophical Journal, 1825. While engaged in a series of experi- 

 ments on the illuminating power of coal-gas and oil-gas, they 

 were led to examine the circumstances affecting the emission 

 of light, — such as the height of flame, the peculiar construc- 

 tion of burners, and the shape of the glass chimney ; their ex- 

 periments relating chiefly to argands. With regard to the 

 length of flame, they found that the light was' not always in 

 proportion to the consumpt, even when the same burner was 

 used. Thus taking a jet flame of three inches as the standard, 

 and considering its light and consumpt as 100, the light afford- 

 ed for equal expenditures was, for a flame of two inches, 100 ; 

 three inches, 109 ; four inches, 131 ; five inches, 150 ; six 

 inches, 150. 



In these trials, by lengthening the flame, there was of course 

 an increased consumption of gas, but then the light was in- 

 creased in a greater ratio. When of five inches in length, the 



