Management of Light in Illumination. 199 



When the greatest effect was produced by the lamp 

 No. 3, it was found that 100 parts of the oil consumed 

 gave as much light as could have been furnished by 

 160 parts of wax, as we have just seen. 



On comparing these results, we find that the maxima 

 of the effects of these three lamps, in respect to the 

 economy of the oil, were as follows : — 



That of the lamp No. i 149 



No. 2 140 



No. 3 160 



The quantity of light which the lamp No. 3 usually 

 furnished, when in good order, was seldom greater than 

 700°; and its ordinary consumption of oil, when furnish- 

 ing that quantity of light, was at the rate of 470 parts 

 per hour. This gives for the maximum of the effect 

 of the lamp, in the ordinary course of its service, 

 100 parts of oil equal in effect to 149 parts of wax; 

 and hence we might conclude that the light furnished 

 by the smallest lamp did not cost more than that fur- 

 nished by the largest. 



From the results of all these experiments, I think we 

 may safely conclude that i lb. of purified oil of colza 

 burned in a good Argand lamp, well trimmed and prop- 

 erly managed, gives as much light as \\ lb. of beeswax, 

 when good wax candles of the common size are used. 



When tallow candles are used, the quantity of light 

 produced will depend much on the attention that is 

 paid to the management of them. If they are not 

 frequently snuffed, a great deal of the tallow will be 

 dissipated in vapour and lost, filling the air with a most 

 insupportable stench. 



I have found by the results of many experiments 

 that a tallow candle which is suffered to burn with a 



