INTRODUCTION. 2.5 



or atmosphere receive a greater degree of cold or heat than it had 

 before, its parts will be put in motion, and expanded or compressed. 

 But when air is put in motion, we call it wind in general, and a 

 breeze, gale, or storm, according to the quickness or velocity of that 

 motion. Winds, therefore, which are commonly considered as 

 hings extremely variable and uncertain depend on a general cause, 

 and act with more or less uniformity in proportion as the action of 

 this cause is more or less constant. It is found, by observations 

 made at sea, that, from thirty degrees north latitude to thirty de- 

 grees south, there is a constant east wind throughout the year blow- 

 ing on the Atlantic and Pacific oceans, and called the Trade Wind. 

 This is occasioned by the action of the sun, which, in moving front 

 east to west, heats, and consequently expands, the air immediately 



. under him ; by which means a stream or tide of air always accompa- 

 nies him in his course, and occasions a perpetual east-wind within 

 these limits This general cause, however, is modified by a num- 

 ber of particulars, the explication of which would be too tedious and 

 complicated for our present plan. 



The winds called the Tropical Winds, which blow from some 

 particular point of the compass without much variation, are of three 

 kinds ; 1. The General Trade Winds, which extend to nearly thirty 

 degrees of latitude on each side of the equator in the Atlantic, Ethio-. 

 pic, and Pacific seas. 2. The Monsoons, or shifting trade winds, 

 which blow six months in one direction, and the other six months 

 in the opposite. These are mostly in the Indian or Eastern Ocean, 

 and do not extend above two hundred leagues from the land. Their 

 change is at the vernal and autumnal equinoxes, and is accompanied 

 with terrible storms of thunder, lightning, and rain. 3. The Sea 

 and Land Breezes, which are another kind of periodical winds, that 

 blow from the land from midnight to midday, and from the sea from 

 about noon till midnight; these, however, do not extend above two 

 or three leagues from shore. Near the coast of Guinea in Africa, 



' the wind blows nearly always from the west, south-west, or south. 

 On the coast of Peru in south America, the wind blows constantly 

 from the south-west. Beyond the latitude of thirty north and south, 

 the winds, as we daily perceive in Great Britain, are more variable, 

 though they blow oftner from the west than any other point. Be- 

 ;ween the fourth and tenth degrees of north latitude, and between 

 the longitude of Cape Verd and that of the easternmost of the Cape 

 Verd Islands, there is a tract of sea condemned to perpetual calms, 

 attended with terrible thunder and lightning, and such rains, "that 

 this sea has acquired the name of the Rains. 



Tides.. ..By the Tides is meant that regular motion of the sea ac- 

 cording to which it ebbs and flows twice in twenty-four hours. The 

 immortal sir Isaac Newton was the first who satisfactorily explain- 

 ed the cause and nature of the tides by his great principle of attrac- 

 tion, in consequence of which all bodies mutually draw or attract 

 each other, in proportion to their masses and distance. By the ac- 

 tion of this power, those parts of the sea which are immediately 

 below the moon must be drawn towards it ; and, consequently, 

 wherever the moon is nearly vertical the sea will be raised, which 

 occasions the flowing of the tide there. A similar cause produces 

 the flowing of the tide likewise in those places where the moon is 

 in the nadir, and which must be diametrically opposite to the former; 

 for, in the hemisphere farthest from the moon, the parts in the nadir. 

 Vol. I. E 



