VOL. LXXXIV.] PHILOSOPHICAL TRANSACTIONS. 371 



when the Argand's being placed at the distance of 134 inches, the common 

 lamp was placed at the distance of 95.2 inches, from the field of the photometer. 

 Both lamps having been very exactly weighed when they were lighted, they were 

 now, without being removed from their places before the photometer, caused to 

 burn with the same brilliancy just 30 minutes ; when they were extinguished 

 and weighed again, and were found to have consumed of oil, the Argand's lamp 

 ■jV-gV, and the common lamp VtVt of a Bavarian pound. 



Now as the quantity of light produced by the Argand's lamp, in this experi- 

 ment, is to the quantity produced by the common lamp, as 17Q56 to go63, 

 or as 187 to 100; while the quantity of oil consumed by the former is to 

 that consumed by the latter only in the ratio of 253 to l63, or as 155 to 100, 

 it is evident that the quantity of light produced by the combustion of a given 

 quantity of oil in an Argand's lamp is greater than that produced by burning the 

 same quantity in a common lamp, in the ratio of 187 to 155, or as 100 to 85. 

 The saving therefore of oil which arises from making use of an Argand's lamp, 

 instead of a common lamp, in the production of light, is evident ; and it ap- 

 pears from this experiment that that saving cannot amount to less than 15 per 

 cent. How far the advantage of this saving may, under certain circumstances, 

 be counterbalanced by inconveniences that may attend the making use of this 

 improved lamp, he will not pretend to determine. 



5th. On the relative Quantities of Light emitted by an Argand's Lamp, and by a 



Common IVax Candle. 



After making a considerable number of experiments to determine this point, 

 the general result of them is, that a common Argand's lamp, burning with its 

 usual brightness, gives about as much light as 9 good wax candles ; but the sizes 

 and qualities of candles are so various, and the light produced by the same can- 

 dle so fluctuating, that it is very difficult to ascertain, with any kind of preci- 

 sion, what a common wax candle is, or how much light it ought to give. He 

 once found that the Argand's lamp, when it was burning with its greatest brilliancy, 

 gave 12 times as much light as a good wax candle \ of an inch in diameter, but 

 never more. 



6i/j. On the Fluctuations of the Light emitted by Candles. 



To determine to what the ordinary variations in the quantity of light emitted 

 by a common wax candle might amount, he took such a candle, and lighting it, 

 placed it before the photometer, and over against it an Argand's lamp, which was 

 burning with a very steady flame ; 3nd measuring the intensity of the light emit- 

 ted by the candle from time to time, during an hour, the candle being occasion- 

 ally snuffed when it appeared to stand in need of it, its light was found to vary 

 from 100 to about 60. The light of a wax candle of an inferior quality was 

 still more unequal, but even this was but trifling compared to the inequalities of 



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