74 



lioped soon to be able to lay the final results before tbe 

 Society. 



On the Cause of the LuMtNOsiTr of Flame. 

 Professor Lamb called attention to a very interesting 

 discussion which had recently taken place on the above subject 

 in Germany. Luminous flames are of two kinds. In the first 

 kind — for example the upper part of the flame of a candle or 

 of an ordinary gas flame — we have an intense white light, 

 caused, as is generally held, by particles of solid carbon shining 

 in virtue of their high temperature, just as an iron bar becomes 

 white hot if its temperature be sufficiently raised. It is fair to 

 mention, however, that this explanation has been called in 

 question, but the balance of evidence seems on the whole 

 decidedly in its favour. The discussion to which Prof. Lamb 

 wished to call attention had reference to the second class of 

 flames, where we have a gas shining with a light (generally 

 faint) of its own, and containing no solid particles. An 

 instance is the flame of a Bunsen's burner well supplied with 

 air. It is generally supposed that this light is simply due to 

 the fact that the gas is at a high temperature ; that in the 

 chemical processes of combustion a certain amount of heat is 

 set free, which has the effect of raising the temperature of the 

 gas ; and that the luminosity is a secondary effect due to the 

 rise of temperature. This view has been recently called in 

 question by W. Siemens, of Berlin, who finds that air and some 

 other gases may be raised to a temperature considerably above 

 that of the Bunsen flame without becoming in any degree 

 luminous. The observations were made at night on the air,. 

 &c., contained in an oven, used in the manufacture of hard 

 glass, the walls of which could be raised to a temperature 

 above that of melting steel. The line of vision passed through 

 two opposite apertures in the walls, and care was taken, by 

 arranging suitable screens, that no light from the walls them- 

 selves should reach the eye. Siemens suggests that the light 

 of the Bunsen flame is a direct result of the chemical changes 

 which are going on, and has nothing to do with the temperature 

 of the gas. It is, in fact, conceivable that the violent tearing 

 asunder of the molecules and the rearrangement of their 

 constituents in other combinations may give rise to distur- 

 bances in the luminiferous ether. This explanation i is 

 supported by the fact that if care be taken to secure a more 

 intimate mixture of the air and other gases before combustion 

 the flame becomes shorter, although much hotter, the chemical 

 processes being completed within a shorter distance from the 

 nozzle. If the light were the result of the temperature, then 

 the flame ought to become longer instead of shorter, for the 



