Management of Light in Illumination. 193 



account was given in a paper read before the Royal 

 Society the 23d of January, 1812, that the quantity of 

 light thus produced is not in an invariable proportion 

 to the quantity of inflammable matter consumed, but 

 that it depends much on the form and dimensions of 

 the flame, and that when the volume of the flame is 

 given the quantity of light will be greatest when the 

 form of the flame is such that the red-hot particles of 

 which it is composed can retain their heat the longest 

 time, I was led by this discovery to conclude that the 

 great quantity of light which is emitted by an Ar- 

 gand lamp depends principally on the peculiar form 

 of its flame, which is that of a hollow cylinder, and 

 which is extremely well adapted for preserving its heat 

 against the cooling influence of the surrounding cold 

 bodies. 



I saw likewise that lamps of different sizes, con- 

 structed on the same principles, must necessarily con- 

 sume very different quantities of oil in producing equal 

 quantities of light; for their flames being of different 

 dimensions, and also of forms that are not exactly 

 similar, they must necessarily be cooled with different 

 degrees of celerity on being projected into a cold 

 atmosphere. 



As soon as the particles of which flame is composed 

 have been so cooled as to be no longer red-hot, they 

 cease to be luminous, and consequently to be visible ; 

 and they disappear entirely. 



These facts appeared to me to be much too impor- 

 tant to be neglected in establishing the principles of 

 the art of illumination ; and I contrived and executed 

 a set of experiments for the sole purpose of giving them 

 a thorough investigation. 



O O 



VOL. IV. 13 



