320 /• LeConte on the Injiuence of Solar Light on Comhustion. 



equilibrium by the loss of weiglit in the burning candle, was,^ in 

 like manner, recorded. In tliis manner, the rate of combustion 

 was determined by observing the time occupied in consuming a 

 given ivdgkt of the burning matter. The arrangements described 

 above, enabled me to perform such experiments alternately in 

 the darkened room, and in the concentrated sunbeam, without 

 moving any portion of the apparatus in the room, and under 

 external conditions as nearly identical as could be desired. Many 

 preliminary experiments were made for the purpose of testing 

 the delicacy of the arrangements, which very soon convincec 

 me that no reliable results could be obtained unless the air was 

 calm, and also^ unless the candle was allowed to burn a sufficient 

 length of time to establish regularity in the process of combustion. 

 The days selected for the experiments, were perfectly cloudless. 

 The state of the barometer and thermometer were carefully 

 noted. I now regret that I neglected to record the hygrometric 

 condition of the air. The cone of sunlight was so directed, that 

 its lower margin illuminated the charred portion of the wick of 

 the candle, while the zipper boundary of the pencil traversed the 

 flame near its apex. The following Table presents the results 

 furnished by three sets of experiments performed on as many 

 separate days.* 



Date. 



May 9, 



June 6, 



« 10, 



Bar. red.i- 

 ced 10 



2992 

 29-72 

 29 62 



'I'emp. 

 of air, 

 Fah. 



750-5 



84^ 



'!• 



riuie ot cotisiuiiing 

 60 ffrains. 



UarK. 



26"* 24* 



28 



28 



39 



55 



auniigtil 



26'« 15 

 28 45 

 28 51 



Amu\int consuiiiL-d in 

 10 minufes. 



Bark. 



Svinlis^it. 



22 73 grs. 

 20 94 *• 

 20-75 " 



22-86 gr 



20-87 *' 

 20-80 " 



s, 



It will be observed, that these experiments indicate no sensthle 

 ^fference in the rate of combustion of the cnnrllf^ in the darkened 



room, and in the same apartment^ with a pencil of concentra 



diffi ^ 



ted 



sunlight directed on the flame; provided^ the comparison is re- 

 stricted to the results obtained on any given day. In two in- 

 stances there was a slight excess in the rate of burning in the 

 sunshine, and in the other, the excess was in favor of the dar\: 

 but the differences are probably within the limits of the experi- 



inaccuracies 



The 



of varia 



flame 



indncai reservoir, furnished with two wicks. The foUowing results were 



Date. 





June 3d, 

 4th, 



4th, 

 4th, 



U 



u 



u 



29-72 

 29-7S 

 29-78 I 75° « 

 29*78 I 75° « 



Arnonnt consiiaiod in 10 minnf^s. 



Dark 



H 

 U 



it 



4U-82 grains. 

 40-95 " 

 38-34 « 

 37-52 « 



u 



4000 grs. 

 39 48 ** 



■p^ — 



^e progressive decrease in the rate of combustion, as indicated by the experimei^s 

 oi the 4th of June, shows, that the variations in the Iieighl of the liquid, are suni- 



ferial, 



