METEORIC STONES AND SHOOTING STARS. 



in the passage of areolites through the firmament. He affirmed 

 the probability of an atmosphere of electricity surrounding the 

 earth and lying above the atmosphere of air. He supposed that 

 the meteorite rushing through this electric atmosphere would 

 decompose the electric fluid exactly as the friction of an electric 

 machine decomposes it between the cushion and the glass, and 

 that by such electric decomposition light and heat would be 

 evolved. 



It may then be admitted that all of the hypotheses above 

 mentioned will equally afford an explanation of the evolution of 

 light and heat ; and that, on the other hand, so far as regards 

 these effects, all the hypotheses are subject to the same objections 

 and the same difficulties. 



Let us, however, examine them severally, and see how 

 far in other respects they will supply an explanation of the 

 phenomena. 



10. The atmospheric hypothesis is subject to objections so 

 unanswerable, that it may be considered as altogether set aside. 

 In order to suppose it probable that aerolites could be formed in 

 the atmosphere, we must show that their constituent elements 

 can exist there. We know that hail and snow can be formed in 

 the air, because it can be proved that aqueous vapour is sus- 

 pended there, and that a temperature is sometimes produced 

 there so low as to convert that vapour, first, into the liquid, and 

 then into the solid form of snow or hail. But the most rigorous 

 analysis has never detected in the atmosphere any of the con- 

 stituents of meteoric stones, nor is there any proof that the 

 constituent principles of the air could dissolve, evaporate, or 

 sublimate such substances. Nor can it be said that, although 

 the atmosphere which immediately surrounds us may not have 

 such properties, yet, that at the great elevations in which 

 meteorites are formed, the air may consist of different con- 

 stituents ; for, besides the fact that it has been ascertained by 

 direct analysis that the atmosphere, at all elevations to which 

 man has ever yet attained, consists of exactly the same con- 

 stituents, in exactly the same proportions, there is a general law, 

 which prevails among all gaseous substances, that when different 

 gases are superposed they will, notwithstanding their different 

 degrees of levity, ultimately mingle so as to form a uniform 

 mass ; thus, if we could imagine for a moment a stratum of air 

 to exist near the top of the atmosphere, having constituents 

 different from those around us, such stratum would gradually 

 intermingle with the strata below it, until the whole would 

 acquire a uniform quality. It is, therefore, physically impossible 

 that there can exist in any elevated region of the air any 

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