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XXIV. On the Finite Extent of the Atmosphere. 5j/ Thomas 

 Graham, M.A. * 



Edinburgh, Dec. 14, 1826. 



TO Dr. Wollaston we owe a satisfactory reason for a limit 

 to the atmosphere, even upon mechanical principles. The 

 idea, that the mere weight of the matter of gaseous substances 

 might afford, at a certain degree of rarefaction, a balancing re- 

 sistance to further expansion, is certainly beautiful, — a con- 

 ception worthy of that sagacious philosopher. Mr. Faraday, 

 with his usual felicity in experimental research, has endea- 

 voured to adduce instances of this equilibrium between the ex- 

 pansive power of gaseous matter and its clogging gravity — to 

 give an experimental demonstration of the hypothesis. 



Admitting, as we do without hesitation, that the cause as- 

 signed would be fully adequate to produce the effect, the 

 question still remains, — but is it really the cause which does 

 produce the effect ? The atmosphei'e may possess some well- 

 known property, which necessarily renders it limited, and the 

 proposal of any supposititious cause may be therefore unne- 

 cessary. 



Such a property we believe the atmosphere does possess, 

 although we are not aware of its having been noticed with this 

 view previously. The law of the expansion of gaseous bodies 

 by heat and their contraction by cold involves a curious conse- 

 quence, which has attracted the attention of several philoso- 

 phers. Bodies cannot exist in that state below a certain tem- 

 perature. Let us direct our attention to a volume of air at 

 32° Fahr. It is a well-established law, that for every degree 

 Fahrenheit which the volume of air is heated above that tem- 

 perature, it increases l-4-80th part; and also for every degree 

 which it is cooled below 32° it is reduced 1 -4.80th part of 

 what it was at that temperature. Hence if it should be cooled 

 down 480°, and reduced by so many parts, it would be re- 

 duced into a volume infinitely small : — it would really be an- 

 niliilated. To avoid this absurdity, we are constrained to be- 

 lieve, that all gases would be reduced into the liquid or solid 

 state, by a fall of temperature which does not amount to 480° 

 below the freezing point of water. The proposition, therefore, 

 that the earth's atmosphere cannot exist in the gaseous state 

 at a temperature below —480° + 32° = —448° Fahrenheit, 

 is susceptible of demonstration ad abstirdum. 



Now meteorologists have discovered a law in the atmospheric 

 temperature, which makes this fact available in elucidation 

 of our subject. It has been found that the temperature of the 



* (,'oniiiiunicatcd by the Author. 



P 2 atmosphere 



