Mountains mi Temperature, 89^ 



tropical or upper current, not being met by a polar current along this 

 line, flows towards the obstruction, from whence it returns partially 

 cooled as an under current. The consequence is, that along such a 

 stripe, the great atmospherical currents, instead of proceeding from the 

 equator to the pole and back again, go on the north side from the pole 

 to the obstruction, and back to the pole ; while on the south side, the 

 flow is from the equator towards the obstruction, and back again to- 

 wards the equator, leaving the obstruction a dividing line marking great 

 difterence of climate in the winter season. 



In the New World a ridge of mountains extends from Mexico by the 

 Rocky Mountains, some of which are stated to be 25,000 feet high, to the 

 Frozen Ocean. This ridge crosses the diagonal line of the great atmo- 

 spherical currents, and constitutes such an obstruction as that described. 

 In the Old World, a number of similar ridges extend from the southern 

 point of the Himalaya Mountains to the Swiss Alps, including the range 

 of the Himalaya, Hindoo Koosh, Central Asia, Armenia, Circassia, the 

 Carpathian Mountains, and the Illyrian and Swiss Alps ; and the cli- 

 mates found to the north-east of these chains are materially different 

 from those which exist to the south-west. The greatest difference in 

 climate in those parts is found iu the beginning of winter, and is, it is 

 presumed, caused by the different quantities of atmospheric steam con- 

 densed in the respective parts. In the tropical seas, a quantity of steam 

 exists in the atmosphere sufficient to give a dew point of 80°, making the 

 steam l-4Uth j^art of the whole atmosphere. This steam, if all condensed 

 into water, would give a depth of about nine inches. The steam is re- 

 gularly carried, in the autumn and the beginning of the winter, when the 

 northern hemisphere is cooled down, from the tropical regions in a north- 

 east direction towards the polar regions, or towards some obstructing 

 elevation of the land, and is to a great extent condensed ; and it is to the 

 condensation of this steam that wc are to look for the great difference of 

 winter climate in the same latitudes of the northern hemisphere. The 

 steam in the tropical regions of tlie Pacilic Ocean that flows towards the 

 north-east, with the south and south-west winds that prevail in those 

 parts, is carried to the American ridge, and is there condensed. The re- 

 sult is, that the south-west side of this chain of mountains is wet and 

 warm in the winter, from the tropics to Xootka Sound, and still farther 

 north. Captain Cook, Lewis and Clarke, Captain B. Hall, and Hum- 

 boldt, describe the climate of this part in such way as can leave no 

 doubt of the fact. But beyond this ridge, to the north-east, we have a 

 different climate in the winter, it being as remarkable for being cold and 

 dry, as the other side is for being wet and warm. Captain Parry, Captain 

 Back, and Lewis and Clarke, represent the country in the winter, from 

 the shores of the Frozen Sea to the Missouri, as very cold, and generally 

 dry. Here we trace the off*ect of the condensation of steam, and of its 

 absence, on the climates of the different parts. In the Old ^^'orld the 

 same causes produce the same effects. On the south-west sides of the 



