BOOK III. CHAP. VII. 607 



clufive of their greater elevation, muft ever be tlie mofl: temperate; 

 for the flat lands near the coaft are feldom fhaded in this manner, 

 but lie expofed wliole days to the uninterrupted torrefaftion of the 

 fun. The clouds, being driven on upon the Eadern extremity of 

 the ifland by the fea-breeze, are accumulated over the mountains, 

 or middle region, and there detained, fometimes by the reverbe- 

 ration of wind from different angles of high ridges ; at other 

 times by the confliiSliog currents o:cafioned by vallies, gullies, and 

 other in-draughts, till they are either condenfed into rain, or at 

 length forced onwards along the range to the Weftvvard by the 

 ftrenuous impulfeofthe breeze. The lands therefore, which lie 

 under this track, have few days without a fhower, and none with- 

 out fhade ; whilft the lowlands remain parched, for want of thefe 

 feafonable irrigations ; and, being rarely overfliadowed by vapours, 

 the fun's impreflion is more intenfely felt there. The like remark 

 occurs in the places lituated under the Equator, where the air is in- 

 variably mod: cool when the fun is vertical ; at which time their 

 periodical rains come on, and the thick Ikreen of vapours, inter- 

 cepting the folar rays, brings the atmofphere below into a very 

 pleafant temperature. The uneafy fenfations, felt in Jamaica 

 about the time of the periodical leafons, when the days are calm, 

 and only a few fhowers fall now and then, as a prelude to the 

 heavy fall, may be thus accounted for. 



It has been experimentally found, that fixty-three degrees of liear, 

 in a damp, hot atmofphere, is much more incommodious to remain 

 in for a time, than feventy degrees of heat in a dry, hot fun-fliine; 

 the great irkioraenefs arifing from a damp heat being'occafioned not 

 only by obftruding the refpiration, but by relaxing the fuiface of 

 the body: and the like difference is obferved between a damp, or 

 a dry, cold air ; the former, with a lefs degree of cold, in- 

 commoding much more, than the latter, with a greater degree. 

 The reafon of which is, that dry air attra^ls moifture ftrongly, 

 and, by carrying off the frouzy vapours which exhale inceflantly 

 from the body, promotes a freer perfpiration, which refrelhes and 

 exhilarates; when infpired into the lungs, it dihues their imall 

 veficles more than a damp air will, and caufes a freer circulation ot 

 the blood. In a ftagnation of the air, thcfe fleams remain ho- 



vering 



