204 Management of Light in Illumination. 



I shall now endeavour to estimate the cost of light 

 which is produced in the combustion of purified oil of 

 colza ; and in doing this it will be indispensably neces- 

 sary to have regard to the intensity of the light which 

 is furnished, as also to the size of the lamp which is 

 used in producing it. But the first thing to be ascer- 

 tained is the price of the oil. 



The best purified oil of colza is now selling at Paris 

 for 20 sous the kilogramme, which is at the rate of two 

 shillings and tenpence half penny sterling, the English 

 wine gallon. 



By an experiment made with my smallest Argand 

 lamp (No. i) I found that when it was arranged and 

 managed in such a manner as to furnish constantly 

 just 100° of light during one hour, the lamp consumed 

 just 9.4 grammes of oil. 



Now as 1000 grammes of this oil cost tenpence 

 sterling, or 40 farthings, these 9.4 grammes must cost 

 0.3759 ^^ ^ farthing, which is less than half what the 

 same quantity of light costs when furnished by tallow 

 candles. 



But this lamp being so constructed as to produce its 

 best effect when it furnishes 300° of light, the saving 

 which will result from the use of it will be still greater 

 when that quantity of light is produced. 



In an experiment several times repeated, in which 

 this lamp was made to furnish constantly 300° of light 

 during one hour, it was found to consume, at a me- 

 dium, 14.4 grammes of oil during that time. 



Farthings. 



This quantity of oil, at the price it is now sold in 



Paris, would cost 0.57600 



The same quantity of light furnished by the best 



tallow candles well managed would cost . . . 1.8 1362 



Furnished by wax candles, it would cost . . . 5.59980 



