J. LeCoiite on the hijiuence of Solar Light on Comhustion. 327 



of combustion in the sunshine. A remarkable difference is ob- 

 served in the rate of consumption in experiments 1 and 2. Num- 

 ber 1 was made with a "green wax taper," and No. 2 with a 



taper;" but, as from the context, the second experiment appears 

 to be a repetition of the/r^ the presumption is, that the same 

 kind of taper was used in both cases. The rate of burning in 

 experiments Nos. 3 and 4, was determined bj the time required 

 to consume a given length ; and as one of them was made with a 

 mould-candle and the other with a taper, no comparison can be 

 extended to them, so far as the rates of consumption in these 

 two cases are concerned. The irregularities exhibited in these 

 results, probably arose from the agitations of the atmosphere, 

 which were incident to the method of exposing the burning 

 body to the sunshine in the open air. As the excess of the 

 consumption in the dark, varied from 5 to 11 per cent, whereas 

 the excess in the density of the air was only 2 '3 per cent, it is 

 evident, that some other cause than temperature must be evoked 

 to explain the difterence. 



2. In my experiments, the conditions were such as to elimin- 

 ate the effects of temperature on the results obtained in the dark 

 and in the sunshine, on any given day; and it has been shown, 

 that for each pair of experiments thus conducted, the variations 

 la rate of combustion do not exceed the probable limits of ex- 



perimental error. 



ofl 



be 



served on different days^ can be explained by the va . . _ , 



barometer and thermometer? For this purpose, I shall take the 

 G^^era^^e of each _pmr of experiments, as a nearer approximation to 

 the correct rate of burning on each of the three days. The fol- 

 ■lowing table, in which the relative densities of the air have been 

 calculated, by combining the effects of barometric and thermo- 



icillations 



Italic of Consumption. 



In exp't 1 & 2=1 : 1-0904 



2 <fe 8=1:1-0063 

 1 & a=l: 1-0967 



(t 



(( 



Ratio of Density of Air. 





1 : 10230 

 1:10193 

 1:10428 



DifT. 



f 



-4-6-74 per cent 

 -1-30 •* 

 +5-39 •* 



It will be seen, that the rate of combustion increases in a de- 

 cidedly higher ratio than the density of the air. If, therefore, we 

 a^ume that the rapidity of burning is, cceteris paribus^ in the di- 

 rect ratio of the density of the air, it follows, that some other 

 agency must have cooperated in these cases. 



* In making these calculations. I used the following formula, based upon the two 

 ^ell-known phybical laws, that the densiti/ of any permanent gas, varies direcily as 

 the compressing force, and inversely as the volume : 



d:d^ 



6 



« « 



1+0-002036(^-32) •l4-0002036(i:'-32)* 



iQ 'Which d and d' represent the densities ; h and i 

 to the freezing point; and t and t' the iemperatur 



h and h' the baromelric heighlt reduced 



ei on Fahrenheit's scale. 



