Winds mid theh' Causes, 1 75 



neers, and the proprietor, Mr. Masterton, as natural curio- 

 sities. I am, Sir, &c. 



Archd. GorrieJ 

 Annat Gardens, near Eyrol^ Perth, March 10. 1828. 



Art. XII. Of Winds, and the Causes of their different Kinds. 

 By Mr. Main. 



It has been stated by Dr. Birkbeck as his opinion, that not 

 only the causes of wind will be better understood, but also 

 the time of its happening in any particular place be predicted 

 with certainty. This would be a wonderful, as well as useful, 

 portion of human knowledge. Such foresight would regulate 

 much of the open-air business of life ; in assisting to preserve 

 the fruits of the earth ; and, in an infinite degree, to influence 

 the movements of the mariner. 



Considerable advances have been made in this science in 

 intertropical climates, where the sun exerts so much power. 

 There the prevailing winds are generally, or partially, period- 

 ical. In the central parts of the Atlantic, Pacific, and Indian 

 oceans, where the currents of the atmosphere are not dis- 

 turbed by the influences of land, the winds, if any at all, 

 blow constantly from east to west, or from the collateral 

 points. This is caused by the cooler air of evening pressing 

 westward upon the heated air of mid-day ; in other words, 

 the lower temperature of the air in the place to the eastward 

 of the sun, causes it to press westward upon the rarefied air 

 at the place over which he i^ vertical. 



This general breeze, in that part of the Indian ocean which 

 washes the southern shores of Asia, is broken into varying, 

 though nearly periodical currents, called monsoons. These 

 winds, and their changes, have been rationally accounted for, 

 by attributing their deviations from the general current met 

 with ten degrees to the southward of Ceylon, to the influences 

 of the more rarefied state of the air, over the peninsulas 

 of hither and farther India ; and also to the sun's motion in 

 the ecliptic, which, in some measure, causes those seasonal 

 influences. 



It is now a well established fact, that the exciting cause of 

 all currents of air is before, and not behind, the blast. This 

 is daily exemplified in warm countries on the sea-shore ; for 

 when the unclouded sun has risen about four hours, and has 

 heated the land to a higher temperature than the sea, imme^ 



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