/. LeConte on the Injluence of Solar Light on Coinhustton, 323 



i 



^ 



» 



\ 



years ago, by the engineers of the Wilmington and Manchester 

 railway, who employed analogous apparatus for securing tlie 

 foundations for the piers of the railroad bridge across the Great 

 Pee Dee river in South Carolina. So far as I have been able to 

 ascertain, the results manifested in this case, were identical with 

 those recorded by M. Triger, and afford a most striking confirm- 

 ation of the influence of condensed air in accelerating the process 



of combustion. 



On the other hand, facts are not wanting to prove, that com- 

 bustion is retarded at considerable elevations above the ocean, 

 where the air is rarefied bv diminished pressure. In a letter re- 

 cently communicated to the Eoyal Society of London, from J. 

 Mitchell, Esq., Quartermaster of artillery at Bangalore, India, 

 ^^ On the Influence of Local Altitude on the Burning of the 



ihis 



combustion 



6500, 

 burning 



3000, 6500, and 7300 feet, as contrasted with the rapidity of 



at the Artillery Depot yard. This difierence, Mr. 

 Mitchell, very rationally, attributes, '* to the rarity of the atmos- 

 pheric air^ and of its constituent oxygen, at the higher stations,"* 

 The following table, — in which I have reduced the barometric 



periments- 



the /ti 



•exhibits the mean residts of his ex- 



Heifflu in 

 Feet. 



Bar. 

 at 32° P. 



Temp. Fahr. 



Depot. 

 8000 feet 

 6500 " 

 T300 •* 



29-610 

 26-756 

 23-951 



22979 



89^ 

 82^ 

 61*^-8 

 54:^-2 



Arcrage Time of Darning 

 3 inches of Fuse. 



No. of Expts 



14'25 seconds. 

 15-78 " 

 17-10 

 18125' 



M 



U 



6 

 6 



witE great 



all in the presence of artillery officers, who were furnished with 

 the most accurate methods of measuring time. They amply 

 prove the fact, that combustion is retarded at considerable ele- 

 vations. 



Thus, a variety of well-established facts, concur in fortifying 

 tbe conclusions to which we ai'e led by a priori reasoning; 

 namely^ that the process of combustion is retarded by diminution 

 of the density of the air,- while it is accelerated b^ its condensation: 

 It has long been a matter of common observation, that ordinaiy 

 Wood-fires burn more freely when the barometer is high ; but, 

 ^fr. Marcus Bull and others maintain,! that this result is not 



lowing are the -words oi M. Triger, " A la pression de troU atiBOspMres, eette accel- 

 eration devient telle que nous avons 6t6 obligfe de renoncer aux chandelles a nieches 

 <3e coton pour lea reniplacer par de^t chandelles 4 meches de tiL Les premieres 

 brulaient avec une teUc rapidite, qu'elles duraient X peine uo quart dlieure, et elles 

 ^^pandaient en outre uue funiee intoItTable." 



* Philosophical Magazine, 4th Serie.s voL 10, p. «. July, 1855. Fuses bum mthr 

 out air; but the rate of burning is influenced by atmospheric oxygen. 



J f Vide, Trans, of Am. Philosophical Society. 2d Series, vol 3, p. 55-56.— Phila- 

 delphia, 1880. 



i\ 



