66o JAMAICA. 



three feet longer than the laft. If, therefore, for an height of 1,035 feet, 

 the mercury falls one inch, the different ftages of its fall, in proceeding 

 upTOcirds towards the mountain top, will be marked as follows : 



N°. of feet afcent. Fall of the Mercury, tenths •f i inch. 



90 I 



93 I 



^6 I 



99 I 



I02 I 



105 I 



108 I 



III I 



I 14 I 



117 I 



1035 4-2^ths or I inch 



It is from fuch kind of obfervations that doftor Halley, and others, 

 framed tables, to fhew what would be the heights of the mercury in the 

 tube, and the denfity of the air, at different heights from the earth. 



The following two are abridged from Dr. Halley 's, as it would be 

 unneceffary, for the purpofe of meafuring mountains, to carry the cal- 

 culation further than their greateft known height. 



AtabJefhewingihealtitudpsofn moun- A table, fliewing the height of the mercury at giving 



will to given heights ot the mercury. altitudes ot a mountain. 



Inches. Feet. 



• Thefe tables, it is faid, do not perfedly agree with phaenomena, yet 

 they are thought to be tolerably acurate ; at leail lufficieiitly fo for fiicli 

 menfurations where exacftnefs to a few fathoms is not required ; and, un- 

 til better tables are conftrufted, thefe may ferve to render the work prac- 

 ticable with lefs trouble and difficulty [cl. 



The 



[//} ChiiTiho-raso, one of the Coi-dilleras, is nearly four miles above the level of the fea. 

 [c] The ingenious Mr. Hryilanc, who has lately favoured ihc public iviih a Mty entertaining ac« 

 «PHiit of mount .£"/««, obfervcs; that PUart (the mofl cxad ol all the Frejich academicians) al-. 



lows. 



