NATURAL PHILOSOPHY. 201 



results are considered more significant, from the fact that if light exercised 

 the decided retarding influence on the rate of combustion which Dr. M'Kee- 

 ver's experiments seemed to indicate, we might reasonably anticipate a 

 much more striking effect, when its intensity was increased tenfold by the 

 action of a lens. Prof. Le Conte thinks that the results obtained by Dr. 

 M'Keever were not produced by the influence of solar light, but by want of 

 identity in the external conditions, and particularly by the higher tempera- 

 tura of the air which supplied the combustion in the sunshine, and the irreg- 

 ular agitations to which it was subjected in his mode of experimenting. 

 JV'jf. LG Conte's own experiments afford striking illustration of the effects 

 produced by comparatively slight alterations in the external conditions, on 

 the rate of combustion. For, although he found the rate of burning to be the 

 same in the dark and in the sunshine, on any given day, yet it varied from 

 day to day, according to the barometric pressure and temperature of the air. 

 This fact led him to investigate the probable effects of the three external 

 conditions which may be supposed to influence the process of combustion. 

 These are, first, barometric pressure ; second, temperature of the air ; and 

 third, amount of aqueous vapor present. 



1. Inasmuch as an increase or diminution of barometric pressure, cceteris 

 paribus, necessarily augments or lessens the density of the air, and conse- 

 quently influences the amount of oxygen contained in a given volume, we 

 should a priori expect that it must exercise a corresponding effect on the 

 rate of combustion. But we are not left to mere conjecture on this point. 

 The experiments of Sir Humphry Davy prove that combustion is ac eel era-ted 

 in condensed, while it is retarded in rarefied air. But the most striking and 

 satisfactory experiment on the effects of condensed air in accelerating the 

 process of burning, were those furnished incidentally, by M. Trigcr, a 

 French Oivil Engineer, in the year 1841, during the operations necessary 

 for working a bed of coal underlying the alluvium bordering the river Loire, 

 in the Department of Main-et-Loire. In traversing an overlying stratum 

 of quicksand from fifty-nine to sixty-five and a half feet thick, he found it 

 requisite to devise some means of excluding the semifluid quicksand and 

 water, which found their way under every arrangement analogous to ordin- 

 ary cofferdams, in such quantity as to defy all pumping operations intend- 

 ed to keep them dry. For this purpose, M. Triger employed large sheet- 

 iron cylinders, about 3 '39 feet in interior diameter, securely closed at the 

 top, in which, by mea-ns of a condensing pump incessantly worked by a 

 steam-engine, air was condensed to an amount sufficient to counteract 



o * 



the external hydrostatic pressure. The ingenious contrivance fully justified 

 the expectations of the engineer ; but the workmen were thus compelled to 

 labor in air condensed under a pressure of about three atmospheres. Among 

 other curious results of this state of tilings noticed by M. Trigcr, were the 

 remarkable effects of condensed air on combustion. Much annoyance was 

 at first experienced from the rapid combustion of the candles ; which was 

 only obviated by substituting flax for cotton threads in the wicks. 



On the contrary, the observations of Mr. J. Mitchell, quartermaster of 

 aitillery of the English army, at Bangalore, in India, prove conclusively 



