194 Management of Light in Illumination. 



I provided three lamps, all constructed on Argand's 

 principles (with circular wicks), but which varied con- 

 siderably in size. 



The first, which I shall call No. i, is a portable lamp 

 with an Argand burner, which is so small that the cir- 

 cular wick of the lamp is only 0.28 of an inch in diam- 

 eter, measured internally. 



No. 2 is likewise a portable lamp with an Argand 

 burner, but its burner is much larger. The diameter 

 of the circular wick of this lamp is just 0.5 of an inch 

 internally (half an inch). 



No. 3 is an Argand lamp of the largest size com- 

 monly sold at Paris. The diameter of the wick of this 

 lamp is 0.65 of an inch, measured internally. 



These lamps being all in perfect order, each of them 

 in their turns was exactly weighed, and was made to 

 burn before the photometer just one hour, and was so 

 managed as to be made to furnish constantly during 

 that time the same given quantity of light; and on 

 being removed from before the photometer was imme- 

 diately extinguished and again weighed, in order to 

 ascertain how much oil had been consumed in the 

 experiment. 



The results of these important experiments were as 

 follows : — 



When the lamps were made to furnish just 100° of 

 light, which is the quantity furnished by a good wax 

 candle, of such a size as to consume regularly 108 grains 

 Troy of wax per hour (which quantity, for greater con- 

 venience, I shall call 100 parts of wax), the quantities 

 of the best purified oil of colza consumed were found 

 to be as follows : — 



