322 COSMOS. 



temperature between the equatorial and polar regiont 

 engenders two opposite currents in the upper strata of the 

 atmosphere, and on the Earth's surface. Owing to the dif- 

 ference 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 atmo- 

 spheric 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 displacement 

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

 which form an animated part of the charms of a landscape, 

 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 



the 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 Vorlesunyen tiber Meterologie, 1840, 

 s. 58-66, 196-200, 327-336, 353-364 ; and in Schumacher's Jahrbuch 

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

 of meteorological phenomena is given by Dove, in his small work 

 entitled Witterungsverhdltnisse von Berlin, 1842. On the knowledge 

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

 Viage al 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 

 rjiist. de Geographic, 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. 

 (Lassen, Indische Alter thurmkunde, bd. i. 1843, g. 211). On the con- 

 trasts between the solid or fluid substrata of the atmosphere, see Dove. 

 in Der AbkandL der Akad. der Wiss. zu Berlin aus dcm J. 1842, a. 239, 



