'102 &1S&N SCIENCE READER 



ments it was found that if the flame temperature were high 

 enough the luminosity was directly proportional to the 

 amount of acetylene in the flame at the point where lum- 

 inosity generally begins. Acetylene was introduced at the 

 corresponding place in a non-luminous flame through very 

 fine holes in a small capillary platinum tube, and the rate 

 of its flow, as well as that of the illuminating gas, was 

 measured and controlled so as to have present the amount 

 of acetylene, which analysis showed to exist in a similar 

 luminous flame. At the holes there was an intense light, 

 and dull red streams of carbon passed upward in the flame. 



Lewes sums up his conclusions, drawn from all his work, 

 about as follows : When the hydrocarbon gas leaves the jet 

 at which it is burned, those portions which come in con- 

 tact with the air are consumed and form a wall of flame, 

 which surrounds the issuing gases. The unburnt gas in its 

 passage through the lower heated area undergoes a number 

 of chemical changes, brought about by the heat radiated 

 from the flame walls; the principal change being the con- 

 version of hydrocarbons into acetylene, hydrogen and 

 methane. The temperature of the flame rapidly increases 

 with the distance .from the jet and reaches a point at which 

 it is high enough to decompose acetylene into carbon and 

 hydrogen with a rapidity almost that of an explosion. The 

 latent heat so suddenly set free is localized by the proximity 

 of carbon particles, which by absorbing it become incandes- 

 cent and emit the larger part of the light given out by the 

 flame ; although the heat of combustion causes them to glow 

 somewhat until they come into contact with oxygen and 

 are consumed. This external heating gives rise to little of 

 the light. 



There have been opponents to this theory of the cause 

 of luminosity as there are, fortunately, of all theories 

 but the evidence is so strong and covers so many points, 

 and so many investigators have confirmed one part or 

 another of the work, that it has been generally accepted as 

 a true statement of the facts with which it deals. 



