the Theory of Luminous Flames. 371 



was obtained crowded with little glowing particles which as- 

 cended with a spiral motion, escaping from each horn of the 

 half-moon (fig. 2). The separation of solid carbon within a 

 coal-gas flame is thus rendered visible to the eye. The experi- 

 ment further shows that in an ordinary coal-gas flame the 

 solid particles are very small but numerous, and that, when a 

 number of these are gathered together in a special part of the 

 flame, that part becomes continuously luminous. 



Frankland looks upon the fact of the transparency of lumi- 

 nous flames as militating against the view that they contain 

 solid particles. We know, however, that many substances 

 containing solid matter (for instance, paper soaked in oil) are 

 more or less transparent. Stein has also shown that it is very 

 difficult to distinguish ordinary letters placed behind a gas- 

 flame consisting of several layers, or behind the flame of a pe- 

 troleum lamp. My own experiments confirm those of Stein, 

 and prove that the lower non-luminous portion of a gas-flame 

 is much more transparent than the upper luminous portion, 

 and that it is almost impossible to distinguish an object when 

 viewed through several layers of such flame, the same object 

 being seen when viewed through a single layer. The eye 

 becomes dazzled by the light of the flame, and so incapable of 

 sharply distinguishing objects which emit lesser degrees of 

 light. Tested in the sunlight, all non-luminous or slightly 

 luminous flames appear exceedingly transparent, luminous 

 flames appear transparent only when viewed in thin layers, 

 and smoky flames only when viewed in small masses. 



Frankland asks how a luminous flame can be so transparent 

 as it is if it contain particles of sol-id carbon. A simple ex- 

 periment suffices to show that the smoky portion of the flame 

 of turpentine, which Frankland must admit contains solid 

 particles, is as transparent as the flame itself. The pre- 

 sence of solid particles but very slightly decreases the trans- 

 parency of a thick layer of flame. The spaces between the 

 solid particles are comparatively large, and the particles are 

 also in a state of rapid motion : a continuous image of any 

 body placed behind the flame is therefore communicated to 

 the eye, as is the case when one looks at an object behind a 

 swiftly rotating spoked wheel. 



In examining some of these luminous flames in sunlight, it 

 occurred to me that if they really contain solid matter, they 

 should throw a shadow on a white screen placed behind them. 

 The flame of a candle I found experimentally does cast such a 

 shadow as is depicted in fig. 3 ; the shadow extends as far as 

 the luminous flame-mantle. The blue portion of the flame 

 close to the wick, as also the upper blue portion, casts no 



2B 2 



