Solar Light on Combustion. 



189 



remarkable effects of condensed air on combustion. Much annoy- 

 ance was at first experienced from the rapid combustion of the 

 candles, which was only obviated by substituting flax for cotton 

 threads in the wicks*. Similar phsenomena were observed a few 

 years ago by the engineers of the Wilmington and Manchester 

 Railway, who employed analogous apparatus for securing the 

 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 wei'e 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, 

 whei-e the air is rarefied by diminished pressure. In a letter 

 recently communicated to the Royal Society of London, from 

 J. Mitchell, Esq., Quartermaster of Artillery at Bangalore, India, 

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

 Fuses of Shells," this officer shows that there was a progressive 

 retardation of the rate of combustion of the fuses at altitudes of 

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

 burning at the Artillery Depot yard. This difference Mr. 

 Mitchell very rationally attributes " to the rai'ity of the atmo- 

 spheric air, and of its constituent oxygen, at the higher sta- 

 tions f-" The following Table, in which I have reduced the 

 barometric heights to the freezing-point, exhibits the mean results 

 of his experiments : — 



These experiments seem to have been made with great care. 



* Vide Comptes Rendus, vol. xiii. p. 884 et seq. Paris, 1841. Also 

 Annates de Chimie et de Physique, 3 ser. vol. iii.^p. 234 et seq. Paris, 1841. 

 The following are the words of M. Triger : — "A la pression de trois atmo- 

 spheres cette acceleration devient telle que nous avons ete obliges de renoncer 

 aux chandelles a meches de coton pour les remplacer par des chandelles k 

 meches de fil. Les premieres brilaient avec une telle rapidite, qu'elles 

 duraient a peine un quart d'heurc, et ellcs repandaient en outre une fumee 

 intolerable." 



t Philosophical Magazine, S. 4. vol. x. p. 48, July 1855. Fuses 

 burn without air ; but the rate of burning is influenced by atmospheric 

 oxygen. 



