Western Territories Valley oj Ohio Alleghanies Atlantic

CLIMATE OF NORTH AMERICA.

which the southerly current, supplying thecopious rains and snows that fall during winter,is propagated, is somewhat similar to thatwhich takes place along the Gulf of Mexico.Indeed, west of the Alleghanies, the actionappears to be quite similar. Owing to thecircumstance, however, of the southerly cur-rent often being a middle one (which is againoverlaid by the west upper current), the sur-face wind is often from the north-east, forreasons already given when illustrating PlateVI. The following figure, representing a sec-tion of the storm of 10th November 1854, iuthe Northern States, will exhibit more clearlythe veering of the wind as storms progressfrom west to east:—

A B represents the cold wind which hadjust crossed the Mississippi on the morningof the 10th November. The cold air therecauses the barometer to rise, because it isheavier. B C the space occupied by thesoutherly winds, at that time about 700 milesin breadth, which being warm, are light, andcause the barometer to stand low.

The cold and heavy air A B is forcedtowards the lighter and warmer air B C, forthe same reason, that the colder and heavierair, resting on the sea, is forced towards theland in the sea breeze. The difference in thetemperature and weight of the westerly andof the southerly winds, forms the propellingpower of the westerly winds.

The gradual manner in which the temper-ature decreases from the western to the easternedge of aerial Gulf Stream B C is remarkable.On the Atlantic coast the southerly windshave just set in, and the air is still cold anddry; whereas, in the eastern parts of Illinois,the temperature and moisture have attained