650 JAMAICA. 



wife thofe vaft rivers, which burrt: forth at a prodigious elevation 

 among them, could not be fo plentifully fupplied at thofe times 

 when the lowlands are parched with drought. Not that they owe 

 the whole of their waters to the rain that falls here, for they un- 

 doubtedly derive the grcateft portion from the ocean, by percolation, 

 or fome other fubterraneous procefs of nature. But they receive a 

 large increafe from rains and dews. If thefe woody parts were cleared, 

 the rains that might fall there would be more moderate, and the 

 rivers would lofe a part of their bulk. This vifibly has been the 

 cafe with refpedl to fome others, which antiently ran much higher 

 than they do at prefent ; for being laid open to the fun and wind, 

 the quantity loft by evaporation, together with what is diminifhed for 

 want of the ufual fupply from dews and rains, their ftreams muft: 

 neceflarily decreafe to a certain degree. Yet as the condenfations 

 proceeding from the height of ridges would ftill continue, therefore 

 thefe midland parts would ftill have rains futhcient, though probably 

 but feldom fo exceflive as at prefent ; and thus they may be faid to 

 inherit a permanent fertility, which will infure fuccefs to their cul- 

 tivators in the drieft years ever likely to happen here. 



Extraordinary falls may fometimes happen, which may unufually 

 augment the annual calculation, for no two years are or can be exadl; 

 but an average of fix or icven may turn out nearly fo. One or two 

 dry years are almoft uniformly fucceeded by one or two wet ones, fo 

 that what fails in one part of the average number, is perhaps made 

 up pretty regularly in the other. 



The rain which fell in this ifland during the hurricane (Odl. 20, 

 1744) was meafured by an ingenious gentleman, and found to equal 

 the general quantity that falls in England in a whole year. 



So in the year 1754, the fall at Barbadoes was 87 _^^ cubic inches, 

 equal to 7 feet 3 -^J^-^ inches perpendicular. Whereas the medium of 

 five years amounted there to no more than 64 -rW> equal to 5 feet 

 4 iVo inches, far too little for its necell'ary fupply. 



Seven inches are allowed in mnft parts of Europe for evaporation ; 

 what remains is fuppofed to re[)lenilh the earth and vegetables with 

 moifture, and fupply the wafte of fprings and rivers. But as the 

 evaporation muft be in a far larger quantity in the W'eft-Indies than 

 in Europe, fo we muft ufe fome proportion in applying the rule to 

 both places. The evaporation in Jamaica is conftant all the year 

 liirough j indeed, from fome late difcoveries, there are grounds to 

 fufpedt that it never ceafes in the coldeft countries, proofs having been 

 given of an evaporation even from ice. However, in Jamaica it fuffers 

 no interruption from a dcfedl of heat in the earth or atmofphere. 



Now 



