of Light on Combustion. 219 



I have lately had a good opportunity of testing this action at 

 the works of Price's Patent-Candle Company at Battersea. Under 

 the direction of Mr. Hatcher, the accomplished chemist of the 

 Company, the greatest possible care is taken to ensure identity 

 of composition and illuminating-power in candles of the same 

 name. There has lately been an extensive series of experiments 

 on the photo-metrical value of sperm candles, during which, at 

 my request, Mr. Hatcher was good enough to note the rate of 

 combustion of such candles in a darkened room, and also in broad 

 daylight and even in sunshine. 



In the first observation, three hard and three soft candles 

 were burned each for four hours in a dark closet. A similar 

 set of candles taken from one and the same filling were burned 

 during the same time in open daylight, partly in sunlight. The 

 average consumption per hour of each candle was as follows : — 



Sperm in the dark . . . . 134 grains. 

 Sperm in the light .... 141 „ 



No. 2 Composites in the dark. 133 ,, 

 „ Composites in the light. 140 „ 



It must be noticed that the temperature in the light was 72°, 

 and in the dark 71°. Moreover in the light there was a much 

 greater motion of the air than in the dark closet. Both these 

 circumstances would operate in producing a larger consumption 

 of candle. 



In a second trial with No. 2 composites the results were : — 



In the dark . . . 140 grains each candle. 

 In the light . . . 134 „ „ 



In a third, also with No. 2 composites, the results w T ere :— 



In the dark . . . 131 grains. 

 In the light ... 129 „ 



In these two trials the flames were protected as far as possible 

 from currents of air, and in the third trial the temperature both 

 in the light and in the dark was nearly equal. 



The fourth trial was made on a bright sunshiny day with hard 

 sperm candles, which are less affected by variations of tempera- 

 ture than the composites. The results were — 



In the dark (temp. 81°) . . 544 grains, 

 or 13G grains per hour. 



In the light (temp. 84°) . . 567 grains, 

 or 142 grains per hour nearly. 



It is evident that in this case the increase of temperature 

 caused by the bright sunshine led to an increased consumption 

 of material. 



Q2 



