316 COSMOS. 



equatorial and polar regions engenders two opposite currents 

 in the upper strata ot the atmosphere and on the Earth's sur« 

 face. Owing to the difierence between the rotatory velocity 

 at the poles and at the equator, the polar current is deflected 

 eastward, and the equatorial current westward. 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 the opposition of these two currents, 

 on the place where the upper one descends, and on the dis- 

 placement of the one by the other. Thus the figures of the 

 clouds, which form an animated part of the charms of a land- 

 scape, announce the processes at work in the upper regions of 

 the atmosphere, 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 relative 

 position of large continental and oceanic surfaces, 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 decli- 

 nation,* and which were known to the Greek navigators un- 

 der the name of Hippalos. In the knowledge of the mon- 

 soons, which undoubtedly dates back thousands of years among 

 the inhabitants of Hindostan and China, of the eastern parts 

 ■)f the Arabian Gulf and of the western shores of the Malayan 



lie excellent observations of Kamtz on the descent of the west wind 

 of the upper current in high latitudes, and the general phenomena of 

 the direction of the wind, in his Vorlesungen uber Meterologie, 1840, s. 

 58-66, 196-200, 327-336, 353-364; and in Schumacher's Ja^riwc^ /Sr 

 1838, s. 291-302. A very satisfactory and vivid representation of me- 

 teorological phenomena is given by Dove, in his small work entitled 

 Wittertmgsverkdltnisse von Berlin, 1842. On the knowledge of the 

 earlier navigators of the rotation of the wind, see Churruca, Viage ai 

 Magellanes, 1793, p. 15 ; and on a remarkable expression of Columbus, 

 which his son Don Fernando Colon has presented to us in his Vida del 

 Almirante, cap. 55, see Humboldt, Examen Critique de VHist. de G€- 

 ographie, t. iv., p. 253. 



* Monsun (Malayan musim, the hippalos of the Greeks) is derived 

 from the Arabic word mausim, a set time or season of the year, the time 

 of the assemblage of pilgrims at Mecca. The word has been applied 

 to the seasons at which certain winds prevail, which are, besides, named 

 from places lying in the direction from whence they come ; thus, for 

 instance, there is the mausim of Aden, of Guzerat, Malabar, &c. (Las- 

 een, Indische Alterthumshunde, bd. i., 1843, s. 211). On the contrasts 

 between the solid or fluid substrata of the atmosphere, see Dove, in Der 

 AbhaJtdl. der Akad. der Wiss. zu Berlin aus dem Jahr 1842, s. 239 



