340 COSMOS. 



sphere being the controlling causes on which depend the 

 agricultural or pastoral pursuits of the inhabitants of exten- 

 sive tracts of continents. 



As the quantity of moisture in the atmosphere increases 

 with the temperature, this element, which is so important for 

 the whole organic creation, must vary with the hours of the 

 day, the seasons of the year, and the differences in latitude 

 and elevation. Our knowledge of the hygrometric relations 

 of the Earth's surface, has been very materially augmented 

 of late years, by the general application of August's psychro- 

 meter, framed in accordance with the views of Dalton and 

 Daniell, for determining the relative quantity of vapour, or 

 the condition of moisture of the atmosphere, by means of the 

 difference of the dew point and of the temperature of the air. 

 Temperature, atmospheric pressure, and the direction of the 

 wind, are all intimately connected with the vivifying action of 

 atmospheric moisture. This influence is not, however, so 

 much a consequence of the quantity of moisture held in solu- 

 tion in different zones, as of the nature and frequency of the 

 precipitation which moistens the ground, whether in the form 

 of dew, mist, rain, or snow. According to the exposition made 

 by Dove of the law of rotation, and to the general views of 

 this distinguished physicist,* it would appear, that in our 

 northern zone, " the elastic force of the vapour is greatest with 

 a south-west, and least with a north-east wind. On the west- 

 ern side of the windrose this elasticity diminishes, whilst it 

 increases on the eastern side ; on the former side, for instance, 



and Mussooree, and other mountain sites, are out of place in this ques- 

 tion, or else he fights against a shadow, or an objection of his own 

 creation. In no part of his paper does he quote accurately the dictum 

 which he wishes to oppose." 



If the mean altitude of the Thibetian highlands be 11,510 feet, they 

 admit of comparison with the lovely and fruitful plateau of Caxamarca 

 in Peru. But at this estimate they would still be 1300 feet lower 

 than the plateau of Bolivia at the lake of Titicaca, and the causeway of 

 the town of Potosi. Ladak, as appears from Vigne's measurement, by 

 determining the boiling-point, is 9994 feet high. This is probably also 

 the altitude of H'Lassa (Yul-sung), a monastic city, which Chinese 

 writers describe as the realm of pleasure, and which is surrounded by 

 vineyards. Must not these lie in deep valleys ? 



* See Dove, Meteorologische Vergleichung von Nordamerilca und 

 Europa, in Schumacher's Jahrbuch fur 1841, s. 311 j and his Meteor- 

 clogisclie Untersuchungen, s. 140. 



