THE LITERARY 



OF THE LINN^AN ASSOCIATION OF PENNSYLVANIA COLLEGE. 



Vol. II. OCTOBER, 1846. No. 12. 



PHILOSOPHY OF STORMS. NO. III. 



BY PROF. WASHINGTON L. ATLEE, M. D. PHILADELPHIA, PA. 



Although the earth is enveloped in a gaseous atmosphere, we are 

 constantly surrounded by an ocean of steam. This steam, better 

 known by the term aqueous vapor, is thrown into the atmosphere by 

 various means, though principally by evaporation, its quantity varying 

 yet not corresponding with the temperature of the air. The tempera- 

 ture may be the same, and the quantity of vapor may vary, for the air 

 is not always in a state of saturation : sometimes, it is excessively dry, 

 at others fully saturated, and again varies between these extremes. This 

 variation in the hygrometrical condition of tlie atmosphere is intimately 

 connected with the productions of storms. 



I mentioned in my last number that as the air ascends it comes un- 

 der less pressure and expands. Expansion in itself is a cooling process, 

 and of course such an ascending current must continue to diminish in 

 temperature. Apart from this, however, the temperature of the atmos- 

 phere varies with its elevation. The atmosphere, receiving its heal solely 

 from the earth, its temperature becomes progressively lower, as the dis- 

 tance from the eailh increases. Another circumstance, contributing to 

 the same effect, is the increasing tenuity of the atmosphere ; for the tem- 

 perature of rarefied air is less raised by a given quantity of heat, than 

 that of the same portion of air when compressed, owing to its specific 

 heat being greater in the former state than in the latter. From the joint 

 influence of both these causes it has been ascertained, by the researches 

 of Gay Lussac, Humboldt, and others, that, in ascending into the atmos- 

 phere, the temperature diminishes at the rate of one degree for about 

 every three hundred and fifty-two leet. The rate of decrease is proba- 

 bly much slower at considerable distances from the earth; but still there 

 is no reason to doubt that the temperature continues to decrease with 

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