2OO Management of Light in Illumination. 



long wick consumes more than twice as much tallow 

 in producing any given quantity of light as when the 

 same candle is kept well trimmed. I have even found 

 that a tallow candle consumes faster when it burns 

 dim and gives little light than when it burns well 

 and furnishes a great deal of very pure light. This 

 extraordinary fact was first announced in my paper on 

 the Relative Intensities of the Light emitted by Lumi- 

 nous Bodies, which was read before the Royal Society 

 the 6th February, 1794. 



Many persons will no doubt be curious to know what 

 are the relative quantities of light usually furnisJied 

 in the combustion of tallow candles and wax candles. 



After having made a considerable number of experi- 

 ments, with a view to determining that point with as 

 much precision as the nature of the subject will per- 

 mit, I have found reason to conclude that when both 

 the wax candles and the tallow candles are of the first 

 quality, and when no more than the usual attention is 

 paid to the latter in burning them, the quantity by 

 weight of the tallow consumed in producing a given 

 quantity of light is to the quantity of wax consumed in 

 producing the same quantity of light as 130 to 100. 



When a tallow candle is of such a size as to produce 

 as much light as the wax candle, and when the great- 

 est possible care is taken to keep it constantly well 

 snuffed, equal quantities of light may be produced by 

 115 parts of tallow and 100 parts of wax; but when 

 tallow candles are small and of ordinary quality, and 

 when they are burned in the careless manner in which 

 they are commonly used, we must reckon 150 parts of 

 tallow to produce as much light as is usually produced 

 in burning 100 parts of wax. 



