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TRANSACTIONS OF THE SECTIONS. 43 



Atlantic coast, and though, only from 2000 to 4000 feet in elevation, exercised a 

 marked influence in giving peculiar development to certain atmospheric disturbances 

 •which took place in the Atlantic States. To the west of this chain lies the vast 

 valley of the Mississippi; its surface forms an easy ascent towards the Lakes of 

 about one foot in a mile. This great basin is thus exposed to the free course of the 

 south winds from the Gulf of Mexico. But the Rocky Mountains on the west, 

 stretching from the Arctic Circle, appear to be the grand physical feature which in 

 a great measure determines the peculiarities of the meteorology of North America. 

 This range has an average elevation of 10,000 to 12,000 feet, which is almost 

 unbroken to the Isthmus of Panama. This vast natural wall forms a barrier to the 

 trade-winds of the Caribbean Sea, as they cannot cross this ridge and flow into the 

 Pacific. By means of this elevated land, which forms the isthmus connecting the 

 two continents, the trade-wind is gradually directed northwards until it reaches 

 Texas as a south wind, which is the prevailing one in that State throughout the year, 

 but more especially in summer. The great fertility of the climate of the United 

 States and Canada is to be chiefly ascribed to this physical feature of the country. 

 The flow of the south wind in winter brings moisture and mild weather — in summer 

 intense heat, with thunder-storms. The wind, which is entirely opposite in its cha- 

 racter to the south, is the west. In winter, a due west wind is intensely cold over 

 the whole territory of Canada and the United States, and it often blows with great 

 violence : there is no relaxing of the cold weather so long as it continues. In sum- 

 mer it is dry, and the sky assumes that bright azure tint which is so striking to one 

 from our island. It is a singular fact, that a west upper current flowing across the 

 Rocky Mountains seems to prevail almost constantly during the whole year. This 

 must never be lost sight of in discussing the atmospheric phanomena of North 

 America. The upper current is nearly due west at Washington and the States to 

 the south; it is a point or two north of west in the New England States and Canada. 

 The west and north-west wind of the United States must be regarded as the descent 

 of this upper current. In fact, the winds of the United States, especially during 

 great atmospheric disturbances, may all be considered to become modifications of the 

 south and the west wind. The indications of the thermometer and hygrometer are 

 entirely in favour of this arrangement. The N. and N.W. winds must be regarded 

 as modifications of the upper westerly current descending to the surface of the 

 ground, and the S.W., S.E., E., and even N.E., as modifications of the south wind. 

 The difference betwixt the temperature of the Arctic current and the Gulf-stream, as 

 they meet beyond the Newfoundland coast, is not nearly so great as the difi"erence 

 of the temperature, in winter, between the west current which descends along the 

 eastern slopes of the Rocky Mountains, and the south wind from the warm waters 

 of the Gulf of Mexico. The vast territories of the United States to the east of the 

 Rocky Mountains are subjected alternately to these two currents so opposite in their 

 characters, and hence the great changeableness of the climate, to which we have 

 nothing that can be compared in Europe. The exceeding coldness of the west wind 

 arises from its being robbed of its moisture as it crosses the Rocky Mountains. It 

 is especially worthy of being kept in mind, that the west wind, or its modifications, 

 is light and pleasant in the warm season, but intensely cold in winter, and blows 

 with great vehemence when it succeeds the south wind. After the west wind has 

 blown for some time in winter, the whole area over which it has extended is subjected 

 to a great depression of temperature. As a general rule, the temperature rises in the 

 far west in winter for some time before it rises in the Atlantic States. The weather 

 first moderates in the territory east of the Rocky Mountains and west of the Missis- 

 sippi, by a south wind, 500 to 700 miles in breadth, setting in and blowing along 

 the eastern slopes of the Rocky Mountains, and probably extending into the Arctic 

 Circle. The rise of temperature thus takes place over all the regions swept by the 

 south wind. The rising of temperature is apparently propagated from west to east 

 in the United States, by the south wind flowing in succession over those States which 

 are more easterly. This is the cause of the winter storms of the United States tra- 

 veUing from west to east, as has been maintained by Prof. Espy, who was the first 

 that made the discovery, and which has since been corroborated by Profs. Hare and 

 Loomis. The distance between the ridge of the Rocky Mountains arid the east coast of 

 Florida is about 1400 miles, but in the latitude of Newfoundland the Rocky Mountains 



