On the Meteors of 13th November, 1S33. 153 



and if that body had been analogous to this meteor, we should have 

 seen it by reflected light at least, for the same reason that we see the 

 moon, except at places where the sun was so far below the horizon, 

 that it might fall within the shadow of the earth, and this could not 

 have been the case, when the sun was at a less depression below 

 the horizon, than 50° 41'. Or had it been a mere cloud made up 

 of a congeries of the small bodies, such a cloud though less favorable 

 for reflecting light than a solid sphere, would nevertheless have reflect- 

 ed enough of the sun's light to have been visible. Hence, we infer 

 that neither the falling bodies themselves, nor the source from which 

 they emanated, could have had a constitution analogous to known 

 aerolites. 



The immediate consequence of the prodigious velocity with which 

 the meteors fell into the atmosphere, must as already suggested, be a 

 powerful condensation of the air before them, retarding their progress, 

 and producing, by such a sudden compression of the air, a great evo- 

 lution of heat. If by forcing down a solid piston in a small barrel, we 

 can elicit heat sufficient to set tinder on fire, an effect which takes 

 place when the air is suddenly compressed into one fifth of its former 

 volume,* what must be the heat evolved by the moiion of a large body 

 in the atmosphere with a velocity so immense. According to Dalton, 

 when the rarefied air of the receiver of an air-pump is suddenly con- 

 densed to half its bulk, its temperature is raised fifly degrees. f We 

 must remember, also, that as air expands, or enlarges its volume, its 

 specific heat increases ; and hence that the rarefied air of the upper 

 regions will as truly afford heat on condensation, as the denser air near- 

 er the surface, though less favorable to the support of combustion. 



On account of the increase of capacity for heat which air under- 

 goes by rarefaction, the absolute quantity of heat contained in a giv- 

 en volume of atmospheric air is, according to Leslie, the same at all 

 elevations above the earth, more being in the combined, and less in the 

 sensible state, as the rarefaction is greater; consequently, when a por- 

 tion of air which had been rendered cold by expansion is powerfully 

 condensed, a vast amount of sensible heat is suddenly liberated. J Jn 

 accordance with this principle, Professor Leslie has given a formula, 



* Library of Useful Knowledge, Heat, p. 38. 



t Thomson's Chem. 1. 135, Pictet, Phil. Mag., xiv. 364. 



\ Leslie, Encyc. Brit., Sup. Art. Climats. Thomson on Heat and Electricity, 



p, 121 



Vol. XXVL— No. 1. 20 



