186 



Prof. J. Le Conte on the Influence of 



the darkened room and in the concentrated sunbeam, without 

 moviny 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 convinced 

 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 regularitij 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 hygronietric 

 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 upper 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*. 



It will be observed that these experiments indicate no sensible 

 difference in the rate of combustion of the candle in the darkened 

 room and (in the same apartment) with a pencil of concentrated 

 sunlight directed on the flame, provided the comparison is I'e- 

 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 



* The difficultj' of keeping the pencil of solar light properly directed on 

 a flame of variable altitude, induced me to try a " burning fluid " lamp, 

 having a shoit cylindrical reservoir, fiu-nished with two wicks. The fol- 

 lowing results were obtained : — 



The progressive decrease in the rate of combustion, as indicated by the 

 experiments of the 4th of June, shows that the variations in the height of 

 the liquid arc sufficient to vitiate the results obtained from burning any _^Mirf 

 material. 



