328 /. LeConte on the Injlitence of Solar Light on Comhustion, 



S. The results of Mr. Mitcheirs experiments at different alti- 

 tudes, majj in like manner, be subjected to a similar numerical 

 test. The subjoined table is constructed from the data contained 

 in that which is given on a previous page. 



Ratio of Rate of Burning. 



In exp'ts 1 (fe 2 



« « 2 it 3 



" « 8 & 4 



« « 1 <fe3 

 « « 2 A4 



« « 1 &4 



I 

 1 

 1 

 1 

 1 

 1 



1-1074 

 10836 

 1-0599 

 1-2000 

 1-1486 

 12119 



Katie of Density of Air. ] 



Difr. 



1 

 1 



1 



1 

 1 



1 



10926 

 r0755 

 10270 

 1'1751 

 ri045 

 1-2068 



J 



in one 



This comparison places in a still stronger light the fact that 

 the augmentation in the rate of burning, increases in a somewhat 

 higher ratio than the density of the air ; while at the same time, it 

 clear] J demonstrates the controlling influence of atmospheric density 

 on the phenomenon of combustion. The extreme rates of burn- 

 ing are as the numbers 100 to 127, while the corresponding den- 

 sities of the air are as 100 to 121, nearly; in the other cases the 

 approximation to identity in the ratios is still closer. "Would the 

 variations in the hygrometric state of the atmosphere, which we 

 have left out of consideration, explain this discrepancy? In^the 

 absence of the experiments necessary for testing this question, 

 it would be premature to hazard any conjecture. I may remark, 

 however, that in the case of Mr. Mitchell's experiments, the cor- 

 rection for the effects of aqueous vapor would, probablj 

 point of view^ operate in the wrong direction^ and thus tend to in- 

 crease the discrepancy in the ratios. For as the temperature 

 was decidedly higher at the lower stations, it is more than prob- 

 able that the tension of vapor was greater there than at the upper 

 ones ; and, consequently, that its influence in retarding combus- 

 tion should be relatively greater at the points nearer the sca-leveL 

 This, of course, would tend to equalize the rates of burning at 

 lower and higher altitudes, when no correction is made for this 

 cause. On the contrary, it is obvious that the influence of vapor 

 having a given tension in altering the relative amount of air in a 

 given volume^ must be greater when the barometer is low. From 

 this cause the aqueous vapor at the upper stations might have 

 had a greater effect in retarding combustion, and thus tended to 

 exaggerate the difference in the rates of burning. 



The comparatively large rate of consumption indicated by my 

 first experiment of the 9th of May, (being more than nine per 

 cent above the others,) was most probably attributable to a com- 

 bination of causes. All of the three external conditions concurred 

 m accelerating the process. The barometer was high, the tem- 

 perature low, and the atmosphere excessively dry. The last-men- 

 tioned condition was accidentally forced upon my attention from 



