11 6 BAROMETRICAL MEASUREMENT or 



K°. XXIV. 



Darcmctrical Meafurement of the Blue-Ridge, JFarm- 

 Sprbig, and Alleghany Mountains, in Virginia y taken 

 in the Summer of the year 1791. 



Mount Pleafaiu on Schuylkill, Nov. 13, 1795* 



Dear Sir, 



Read Nov. HT^HE cnclofed Journal would have been long 

 20, 1795- J_ fince prefented to the Philofophical Society 

 if I had been fatisfied as to the accuracy of barometrical 

 calculations, when applied to the meafuring of heights in 

 this climate ; but finding much variation in repeated ex- 

 periments made at a known height,* in winter, fpring and 

 fummer, I grew difcouraged, and my labours would have 

 pafTed into oblivion if the advice of our wort! y Prefident 

 and yourfelf had not induced me to prefent my Journal as 

 it is, difregarding the errors incident to local circumftan- 

 ces and fmall elevations, which may not affedl the prin- 

 ciple of barometrical meafurement on a more extended 

 fcale. 



1 have ufed the table you favoured me with, making 

 proportionate calculations for every deviation from 30 

 inches of the mercury ; this I have compared with the 

 calculated height of the Andes, in Don L Ilea's Voyages, 

 and the afcent of Mr. Charles in the balloon at I'aris, 

 defcribed by M. Faujas de St. Fond ; the refult of thefe 

 comparifons has fo well confirmed the accuracy of the 

 table, that I have no doubt of my calculations being pro- 

 portionate to thofe of Europe and South-America. 



* The higheft acceffible part of Chrift's Church Steeple, infide, is i66 fees 

 from the ground. By barcmetrical meafurement it varied from 105, to 

 243 feet. 



4 I beg^ 



