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yOL. XUX.] PHILOSOPHICAL TRANSACTIONS. SQl 



erratic winds. To account for all the irregular winds within the tropics, he 

 says, that where such happen, it must be by means of some tracts of land, which 

 rise to a greater height above the horizontal level, than vapours generally do; by 

 which the motion of the vapours is stopped, and the vapour accumulated by 

 succeeding vapour, and the air, on which they float, is of consequence pressed 

 into a new direction. And from hence may also be explained the cause of the 

 rains, particularly so called in the sea language. 



He next considers what becomes of the vapour, &c. floating from over the 

 tropics toward the poles; which being less affected by the heat of the sun, re- 

 flected from the surface of the globe, the surrounding electrical fire begins to 

 condense more and more as it moves toward the poles, and the vapours of course 

 to descend; and that part most, which is most remote from, or is farthest left 

 behind by the sun; and of consequence the higher column of air must tend 

 that way to restore the equilibrium ; which motion, at this side the equator, must 

 be to the north-east; and as the vapour, &c, fall again to the earth, the motion 

 must be more to the east. Hence our south-west and westerly winds, which 

 blow a considerable part of the year. 



But as this system is too regular to account for the phenomena of the erratic 

 winds, he considers whence they arise. He had before observed, that tracts of 

 land rising into the atmosphere will stop the regular motion of the vapour, &c. 

 and that the vapour being accumulated by succeeding vapour, the subjacent air 

 must be pressed into new directions Now this cause, added to the daily dilata- 

 tion of the electrical fire, and the contraction at night, and the coalition of the 

 vapours, to occasion their total descent, will be sufficient to produce a very great 

 variety of winds on this side the tropic. 



It now remains to show, how the general phenomena of the weather and baro- 

 meter arise from this system. First, Why it generally rains in winter, while 

 the wind is south, south-west, and westerly. Secondly, Why north-west winds 

 are generally attended by showers in the beginning, and become more dry, as 

 they are of longer continuance. Thirdly, Why north and north-east winds are 

 generally dry. Fourthly, Why the east wind continues dry and dark for a con- 

 siderable time together. Fifthly, Why squalls precede heavy and distinct 

 showers; and why a calm ensues for some little time after they are passed. 

 Sixthly, Why storms and high winds seldom happen in a serene sky without 

 clouds. Seventhly, Why the vapours, in warm seasons, coalesce to form those 

 distinct dense clouds, which produce thunder and heavy showers. Eighthly, 

 Why the barometer falls lowest in long continued rains, attended by winds; ana 

 why it rises highest in long continued fair weather; and why the intermaliate 

 changes happen. Ninthly, Of land-breezes and sea-breezes, and water-spouts. 



First, the vapours passing the tropics into colder regions, have their sur- 



