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LX. On the Duration of the Combustion of Fuses under different 

 Atmospheric Pressures. By Captain J. Mitchell. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, Madras, March 11, 1864. 



I HAVE only lately seen a paper which appeared at p. 156 

 of No. 166 of this Journal. This paper contains one or two 

 errors which M. Dufour, I have no doubt, will be glad to have 

 corrected. 



The contribution to which he refers was made by Troop 

 Quarter-Master J. Mitchell, of the Madras Horse Artillery; and 

 the fuses were not burned at the Himalayas, but at the Artillery 

 Depot at St. Thomas's Mount near Madras, at Bungalore on 

 the tableland of Mysore, and at Kotagherry and Ootacamund 

 on the Neilgherries, at the respective altitudes of about 180, 

 3000, 6500, and 7300 feet above the level of the sea. 



The experiment made here was on too limited a scale to do 

 more than show that the combustion of fuses is retarded at con- 

 siderable elevations; but that was all that was sought. Our 

 fuses had burned too loDgatthe annual practice at Bungalore on 

 two following years, and 1 pointed out the difference of altitude 

 betweenBungalore and St. Thomas's Mount as the probable cause. 



It has given me great pleasure to see that M. Dufour's expe- 

 riments, which seem to have been conducted with very great 

 care, have proved what mine only indicated, viz. that the in- 

 creased time of burning is in a constant ratio to the increased 

 altitude of the place, which is a fact that should be remembered 

 by artillerymen when employed in elevated regions. 



M. Dufour considers diminished pressure the sole cause of the 

 retardation of combustion, or, in other words, of the increased 

 time a certain length of fuse will burn at considerable altitudes. 

 It is quite true, as remarked by him, that fuse composition is 

 rich in oxygen ; but it is also true that the amount of oxygen in 

 the fuse is constant, while that in the atmosphere becomes less 

 and less as we leave the level of the sea ; and it does therefore 

 seem probable that a diminished supply of oxygen, if not the 

 sole, is at least partly the cause of combustion becoming less 

 active as we ascend above the level of the sea. His plan of burn- 

 ing fuses in carbonic acid gas appears to prove the contrary ; 

 whether it does not prove too much is a question I can only put, 

 as I have no means of conducting the experiments that would 

 enable me to confirm, or otherwise, those of M. Dufour. 

 I am, Gentlemen, 



Your most obedient Servant, 



J. Mitchell, Captain, 

 Superintendent Madras Museum. 



