658 JAMAICA. 



even three, placed fide by fide, would enable the obferver to be as 

 exa£l as poffibk, by noting their deviations, and taking the medium 

 of all. Fahrenheit's conflrudion, from its fimplicity, is more ge- 

 nerally approved of, and perhaps more ufeful, than the other fcales. 

 But, whatever inftrument is thought mofl eligible, the graduation 

 ought always to be noticed and prefixed to the diary. A want of this has 

 made many regifters unferviceable, in refpeft to the advantage that might 

 be hoped from a comparifon of climates ; and dependent on this, the ana- 

 logy of fymptoms and difeafes correfpondent to the various changes of 

 the atmofphere in different countries. There are no lefs than 1 6 or more 

 of thefe inftruments of various inventions; fo ttiat a perfon, ignorant of 

 their graduation, or the method of comparing them one with another^ 

 would find himfelf greatly puzzled in the attempt. In 1740, Dr. 

 George Martine publiflied fome very intelligent eflays on the fubjecl of 

 Thermometers, and added a plate, exhibiting the graduation of 1 5 of thefe 

 inftruments in a comparative view ; this Defogul'iers has given {p. 364) 

 vol. II.) and it will be found extremely ufeful to experimentors. 



SECT XL 

 BAROMETER. 



According to four years obfervations at Spanijh Towtu 



In one Day One Year Jamaica. In England, 



Inch.-ioths. Inch.-ioths. Inch.-ioths. Inch.-ioths. 



GiCiitell fall on the approach of a gull or "1 „ 



galeof v/iiid from S.W'. attended u-ith rain, J 



General fubfidence before 1 /i- u. ,1, » 

 , ^ r t ibsjhr Ihowers, o ? 



Afcent attcr J . 



The fame before and after violent rains, c 6 



Whole range, 3 £ 



General flation, 



Greatell afcent, 



Lowell fall, 



Doftor Halley obferves, that near the Equinoftial there is little or no 

 variation in the height of the barometer. He accounts for it thus ; " that 

 " in thefe places there is is always an caly gale of wind blowing nearly 

 *' from the fame point ; fo that, there being no contrary current of air 

 ** to exhauft or accumulate it, the atmofphere continues much in the fame 

 ♦' ftatc. However, upon hurricanes, the mercury has fubfided very low; 

 '•' but this happens only once in two or three years, and it foon recovers 

 *' its fettled flate of about 29 i inches, as at Barbadocs." At this ifland 



(laft 



