124 ■ Facts in Meteorology. 



It has been found, however, that the above rule is subject to great 

 variations, owing probably to the physical character and temperature 

 of the atmospheric currents which prevail in different regions and at 

 different altitudes. Warmer strata or currents are often found rest- 

 ing upon, or interposed between, those of a lower temperature. On 

 the Himalaya mountains between the latitudes of 28° and 34° north, 

 the region of vegetation has been found to extend many thousand feet 

 above the supposed line of perpetual congelation assigned to those 

 latitudes. It is also remarkable that the line of perpetual snow is 

 found at a much greater altitude On the northern side of these moun- 

 tains than on the southern side in a lower latitude. These facts, 

 with others which are obtaining notice, will cause a revision of the 

 hitherto prevailing theories in meteorology. 



Of Trade tvinds and Monsoons,, and their circuitous character. 



The trade winds, in both hemispheres, on approaching ihe western 

 borders of the great oceans, become deflected in their course, and 

 passing into higher latitudes in the form of south-west and north-west 

 winds, they become identified with the prevailing westerly winds in 

 these latitudes. On the eastern borders of these oceans the air re- 

 turns towards the equator in the form of northerly or southerly winds, 

 which on crossing their respective parallels of 30°, become merged 

 in the easterly trades, on both sides the equator ; the locality, as well 

 as activity, of these aerial circuits, being affected more or less with 

 the change of seasons. This appears to be the great law of circula- 

 tion in our atmosphere; and it is chiefly to the physical character and 

 course of the winds in different portions of these great circuits, that 

 the peculiarities of temperature and climate which pertain to certain 

 countries lying in the same latitudes, but on opposite sides of the same 

 ocean, are to be referred ; as also the remarkable absence or predom- 

 inance of rain in certain countries and latitudes. The Monsoons of 

 the Indian seas are but a modification of the same system of circula- 

 tion. Counter circuits are sometimes formed in subordinate basins, 

 and in high latitudes ; the irregularities usually becoming greater in 

 proportion as we recede from the equatorial regions. 



The north-west and south-west Monsoons, which have been erro- 

 neously ascribed to the effects of local or continental rarefaction, are 

 found to extend themselves far to the eastward of the Asiatic conti- 

 nent and islands, and even to the central portions of the great Pacific 

 ocean. 



