If 



265 



air, seeking to expand itself, as that would swell and escape equally 

 in all directions. But upon the supposition of a vortex rolling- over 

 the surface of the ocean, the explanation is simple and easy. 



The following statement, quoted by Daniel], from the " Account 

 of the Arctic Regions," of a fact, apparently of common occurrence 

 in those latitudes, places in a clear and strong light the unsatisfactory 

 character of the views of the nature of the movement of the air dur- 

 ing a wind, that are commonly taken. " Ships, within the circle of 

 the horizon, may be seen enduring every variety of wind and weath- 

 er 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 wit- 

 nessed near the equator, in that part of the Atlantic called the Rains. 

 See the passage heretofore quoted from Halley. Two vortices, re- 

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

 neighborhood of each other, and of a portion of air that is perfectly 

 calm and motionless, but except upon the supposition of such vorti- 

 ces, these facts 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 resting 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 opposite direction. 

 But the fact is not commonly adverted to, that these horizontal breez- 

 es 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 die 

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

 offshore, in other places not so many miles, and in some places they 



scarce peep without the rocks." " These land winds are 



eold, and though the sea-breezes are always much stronger, yet 

 these are colder by far."* 



very 



Dnmpier's Voyage* 



