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Dr. Holyokl's Esiimaie of the Excess of Heat ami Cold. 75 



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pose they ab'ound most at present, I imagine they must be 



very much thinned by this time. But what will all these a- 

 raount tOj TV^hen brought into a comparison Avith the ever- 

 greens of America ? 



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From these considerations I think it must appear highly 

 probable; that America is furnished with sources of dephlo- 



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gisticated air, which are now exhausted in Europe ; and 

 that therefore, most probably, its atmosphere is really more 

 pure and dephlogisticjited. 



Whether this be in reality the fact, may be determined 

 most satisfactorily from meteorological observations. For 



the sensible qualities of the atmosphere, which are the objects 

 of meteorology, may, if properly attended to, and noted down 

 for a course of years, determine not only which country cii- 

 joys the dryest and purest air ; but also the quantity of the 

 difference (if any there be) may as easily and as precisely be 

 known, as the difference of their heat and cold. 



To such observations then w^e must recur j and, if we are 



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enabled to determine — the quantity of evaporation — the 

 quantity of rain — the number of clear fair days — the num- 

 ber of cloudy days — of rainy day?! — and of foggy days, in 

 each continent, for a competent course of years, there is no 

 doubt but the poiiit may be satisfactorily determined. This 

 I shall next attempt; after premising that we have not yet, 

 perhaps, observations enough to settle the matter witliout all 

 doubt ; yet enough, I imagine, to shew that it is in the 

 highest degree probable, that the climate of America is much 

 drier in general, than that of Europe."'' • The 



♦ Perhaps the most direct way of determining tlie dryness of the atmosphere is by 



the hygrometer; but till this instrument is more improved than at present, and ob- 

 servations 



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