ON CLIMATES AND WINDS. 549 



him. Nor can any sufficient cause be found in the attractions of the celes- 

 tial bodies, either for the general easterly trade winds, or for the current of 

 the sea in a similar direction, which appears to be the immediate effect of 

 their friction on the surface of the water. 



The second circumstance is easily explained by the greater heat of the 

 northern than of the southern hemisphere ; so that instead of coinciding 

 with the equator, the neutral portion of the atmosphere lies between 3 

 and 5 of north latitude ; the north east wind not reaching the equator, 

 and the south east continuing about 3 beyond it. But the situation of the 

 neutral portion varies with the sun's decimation, accordingly as different 

 parallels of latitude become in succession somewhat hotter than the neigh- 

 bouring parts. Where the northern and southern currents meet, their 

 joint effect must naturally be to produce a due east wind ; but in some 

 parts of the ocean, temporary calms and irregular squalls have been ob- 

 served to take place of this easterly wind, which generally prevails in the 

 neutral parts near the equator. 



The third fact, that is, the frequency of westerly winds between the 

 latitudes 30 and 40, has not yet been sufficiently explained. The most 

 probable cause of this circumstance is, that the current of heated air, 

 which we have hitherto neglected, and which passes, in the upper parts of 

 the atmosphere, from the equator each way towards the poles, and which, 

 being the converse of the trade wind, must be a south west and north 

 west wind, in the different hemispheres, becomes here sufficiently cool to 

 descend and mix with the lower parts of the atmosphere, or to carry them 

 along by its lateral friction : and while it descends to complete the circle, 

 necessary for supplying the current to the equator, its motion with respect 

 to the horizon must become at a certain time due west, since the cause 

 which stops its progress northwards, has no tendency to impede its motion 

 eastwards. The outward bound East India ships generally make their 

 easting in about 36 south latitude. It is probably also on account of the 

 rotatory motion of the earth, that south west winds are more common in 

 our latitudes than south east, and north east than north west. 



Among the local modifications to be considered in the fourth place, we 

 may reckon the greater indistinctness of the third effect in the northern 

 than in the southern hemisphere, a circumstance which is explained 

 from the more irregular distribution of sea and land : for between 30 

 and 40 south latitude the ocean is scarcely any where interrupted. In 

 lower latitudes also, near the west coast of Africa, the winds are so much 

 deflected towards the land, as to become in general westerly instead of 

 easterly. 



The monsoons, which constitute the fifth remarkable circumstance, are 

 so called from a Malay word, denoting season. They are occasioned by 

 the peculiar situation of the continent of Asia, on the north side of the 

 equator. From April to September, the sun having north decimation, the 

 heat on this continent, a little north of the tropic, is very intense, and the 

 genera -^current is consequently towards the north. The air, therefore, 

 coming from south latitudes towards the equator, becomes, on account of the 

 deficiency of rotatory motion, a south east wind, as usual, which is found 

 to prevail between Madagascar and New Holland, as far as the equator. 



