ATMOSPHERIC CURRENTS. 367 



the cause of many important i)rocesses in the aerial chaffer 

 ocean. The difference of temperature between tlie equa- -^^^^^^ 

 torial and polar regions en£;enders two opposite currents Effects of 

 in the upper strata of the atmosphere, and on the earth's '^™^®'^ "^"^ 

 surface. Owing to the difference between the rotatory ve- 

 locity at the poles and at the equator, the polar current 

 is deflected eastward, and the equatorial current west- 

 ward. The great phenomena of atmospheric pressure, 

 the warming and cooling of the strata of air, the aqueous 

 deposits, and even, as Dove has correctly represented, 

 the formation and appearance of clouds, alike depend on Formation 

 the opposition of these two currents, on the place where 

 the upper one descends, and on the displacement of the 

 one by the other. Thus the figures of the clouds, which 

 form an animated part of the landscape, announce the 

 processes at work in the upper regions of the atmos- 

 phere, and, when the air is calm, the clouds will often 

 present, on a bright summer sky, the ' projected image' 

 of the radiating soil below. 



Where this influence of radiation is modified by the Continent.^ 



1 ,. .^. J. , i.' J. 1 J • and oceanic 



relative position ot large continental and oceanic sur- jnfluencea. 

 faces, as between the eastern shore of Africa and the 

 western part of the Indian peninsula, its effects are 

 manifested in the Indian monsoons, which change with 

 the periodic variations in the sun's declination, and 

 which were known to the Greek navigators under the 

 name of Bippalos. In the knowledge of the monsoons, Monsoons. 

 which undoubtedly dates back thousands of years 

 amongst the inhabitants of Hindostan and China, of 

 the eastern parts of the Arabian Gulf and of the west- 

 ern shores of the Malayan Sea, and in the still more 

 ancient and more general acquaintance with land and 

 sea winds, lies concealed, as it were, the germ of that 

 meteorological science, which is now making such rapid 

 progress." 



Not the least remarkable of the indications afforded, Obsena- 

 in late years, of the peaceful, but sure triumphs of sci- *°""- 

 ence, is to be found in the great chain of observatories, — 



