IN THE PRESSURE OF THE ATMOSPHERE, 483 
it advances and recedes with the sun, though in a much smaller 
proportion. Lach locality in the trade-zone approaches there- 
fore in the year to the exterior and to the interior limits of the 
trade-winds, or barometrically speaking, to the region of high 
and diminished barometrical pressure. It must therefore ex- 
hibit within the annual period a periodical change of the atmo- 
spheric pressure. The greater this displacement, the greater the 
bend of the barometrical curve of the place. The greatest dis- 
placement obtains in the district of the monsoons; for here the 
south-east trade-wind, in the form of the south-west’ monsoon, 
follows the sun into the latitude of 30°. The barometrical oscil- 
lation will consequently be the greatest at this spot, as exhibited 
by the curves of Table III. 
But whence this considerable advance ? 
From the western extremity of the Sahara to the eastern of 
the Gobi, in an extent of 132° of longitude, a wide, uninterrupted 
waste belt, as Von Humboldt observes, extends through the 
centre of Africa, Arabia, Persia, Candahar and the Mongoley. 
But there the sand by insulation acquires a temperature under 
the influence of a more or less vertical sun, which is found nei- 
ther in the prairies of the Mississippi nor in the primitive forests 
of the Orinoco and Amazon river. With the increasing northern 
declination of the sun therefore we meet in Hindostan with tem- 
peratures such as are not known at any other place of the globe, 
Nagpoor, Benares, Mozufferpur, Nasirabad, Seharunpur, 25° to 
29° R. in the middle of May and June. The power of the north- 
east monsoon is completely broken by this, and a vast ascend- 
ing current is formed over the compact mass of land of Asia, 
which, on the one hand, draws the south-east trade-wind, in 
the form of a south-west monsoon, as far as the base of the 
Himalaya, and, on the other hand, may cause in Europe, during 
the summer, that constant western direction of the wind from 
the Atlantic, which does not participate in this rise of tempera- 
ture, and which in the summer extends the character of the sea- 
climate further into the continent than would otherwise be the 
case. If we consider that in Iakutzk, over a soil which is during 
the whole year frozen to a depth of 400 English feet, the tem- 
perature of the air rises to above 16° Reaumur; that there, 
where the mean temperature of January falls below the freezing- 
point of mercury, this soil bears larch forests on its surface, that 
spring-wheat, rye, potatoes, cabbage and turnips are cultivated 
