of certain Winds and Storms. 295 



unsatisfactory character of the views of the nature of the move- 

 ment of the air during a wind that are commonly taken. - " Ships 

 within the circle of the horizon may be seen enduring every va- 

 riety of wind and weather at the same moment ; some under 

 close-reefed topsails laboring under the force of a storm, some 

 becalmed and tossing about by the violence of the waves, and 

 others plying under gentle breezes, from quarters as diverse as 

 the cardinal points." The same thing is witnessed near the 

 equator in part of the Atlantic called the Rains. See the pas- 

 sage heretofore quoted from Halley. Two vortices, revolving 

 either in the same or in different directions, may exist in the 

 neighbourhood of each other, and of a portion of air that is per- 

 fectly calm and motionless, but except upon the supposition of 

 such vortices, these do not appear to admit of any explanation. 



The phenomena of the common land and sea breezes are well 

 known, and easily accounted for. The land is more heated by 

 the sun's rays during the day than the water ; the air restino" 

 upon it is rarefied and ascends, whilst that overhanging the sea 

 comes in to supply its place : during the night the land is more 

 cooled than the water by radiation, and the movement is in the op- 

 posite direction. But the fact is not commonly adverted to, that 

 these horizontal breezes must owe their existence to vortices of 

 very moderate dimensions, which establish themselves around 

 the shores where these breezes prevail, and revolve in opposite 

 directions in different parts of the twenty-four hours. " These 

 winds," (the land breezes) " blow off to sea a greater or less 

 distance, according as the coast lies more or less exposed to the 

 sea winds, for in some places we find them brisk three or four 

 leagues off shore, in other places not so many miles, and in some 

 places they scarce peep without the rocks." — " These land winds 

 are very cold, and though the sea breezes are always much 

 stronger, yet these are colder by far *."" 



Now, it is well known, that even within the limits of the trade 

 winds, and in tlie seas where they blow with great violence, an 

 alteration of land and sea breezes is experienced in islands of 

 very moderate extent, — in the Sandwich Islands for example, 

 where does the land wind come from ? The atmosphere over- 

 hanging the island would soon be exhausted. It must evidently 



* Daminer's Voyages. . 



