ILLUMINATION 



883 



same candles, four in tho pound, are ^ths of an inch in diameter, and 13 inches long. 

 Each gives very nearly the same quantity of light as the corresponding wax candles : 

 viz. ith of the light of the above mechanical lamp, and consumes 142 grains per hour. 

 Multiplying the last number by 11, the product, 1,562 grains = 0-223 of a pound, would 

 be the consumption of spermaceti requisite to give 100 of illumination. Multiplying 

 the last number by 24c?., the price of the candles per pound, the product, 5'352^. is the 

 relative cost of 100 of this illumination. 



9. Stearic acid candles, commonly called German wax, consume 168'5 grains, or 

 0'024 of a pound per hour, when emitting the same light as the standard wax candle. 

 Multiplying the latter number by 11, and by 16d. (the price of the candles per lb.), the 

 product 4'224c?. will represent the relative cost of 100 of this illumination. 



10. Tallow candles : moulds, short threes, 1 inch in diameter, and 12 in length ; 

 ditto long threes, ^ths of an inch in diameter, and 15 in length ; ditto, long fours, 

 ^ O ths of an inch in diameter, and 13f in length. Each of these candles burns with a 

 most uncertain light, which varies from -~th to ^th of the light of the mechanical 

 lamp the average may be taken at ^th. The three consume each 144 grains, or 

 0"2 of a pound, per hour; which number, multiplied by 14, and by 9d. (the price per 

 pound), gives the product 2'52c?. for the relative cost of 100 of this illumination. 



11. Palmer's spreading wick candles. Distance from the screen 3 feet 4 inches, 

 with a shadow equal to the standard. Consumption of tallow per hour 232*5 grains, 

 or 0-0332 of a pound. The square of 3 feet 4 inches = 1T09 is the relative illumination 

 of this candle = 11-09 : 0-0332 :: 100 : 0-3 x 10^. = 3d. is the relative cost of this 

 illumination. 



12. Cocoa-nut stearine candles consumed each 168 grains per hour, and emitted a 

 light equal to ^th of the standard flame. Multiplying 168 by 16, the product 30'88 

 grains, or 0'441 of a lb., is the quantity which would be consumed per hour to afford 

 a light equal to 100. And 0'441 multiplied by IQd., the price per lb., gives the pro- 

 duct 4'441d. as the cost of 100 of this illumination per hour. 



13. A gas Argand London lamp, of 12 holes in a circle of | of an inch in diameter, 

 with a flame 3 inches long, afforded a light =78^ compared to the mechanical lamp: 

 and estimating the light of the said mechanical lamp as before at 100, that of the hot- 

 oil lamp is 121, and that of the above gas-flame 78-57, or in round numbers 80, and 

 the common French lamp in general use 50. 



Collecting the preceding results, we shall have the following tabular view of the 

 cost per hour of an illumination equal to that of the mechanical lamp, reckoned 100, 

 or that of eleven wax candles, three to the pound. 



Table of Cost per Hour of One Hundred of Illumination. 



Pence Pence 



The following Table contains, according to Peclet, the illuminating powers of differ- 

 ent candles, and their consumption of material in an hour ; the light emitted by a 

 Carcel Argand lamp, consuming 42 grammes ( = 42 x 15| grains) in an hour, being 

 called 100: 



3L2 



