132 STEPPES AND DESERTS. 



and the Maritime Alps of New California through which 

 the Oregon or Columbia River finds a passage. Since the 

 highly honourable establishment, by John Calhoun, of unin- 

 terrupted observations of temperature, made on an uniform 

 plan at 35 military posts, and reduced to daily, monthly, 

 and annual means, we have arrived at more just climatic 

 views than those which were so generally received in the 

 time of Jefferson, Barton, and Yolney. These meteorolo- 

 gical stations or observatories extend from the point of 

 Florida and Thompson's Island, (Key West), lat. 24 33', 

 to the Council Bluffs on the Missouri ; and if we reckon 

 amongst them Port Vancouver, lat. 45 37', they include 

 differences of longitude of 40. 



It cannot be affirmed that, on the whole, the mean annual 

 temperature of the second or middle region is higher than 

 that of the first or Atlantic region. The further advance of 

 certain plants towards the north, on the west of the Alle- 

 ghany mountains, depends partly on the nature of those 

 plants, and partly on the different distribution of the same 

 annual quantity of heat. The wide valley of the Mississipi 

 enjoys at its northern and southern extremities the warming 

 influence of the Canadian Lakes, and of the Mexican Gulf 

 stream. The five lakes, (Superior, Michigan, Huron, Erie, 

 and Ontario), occupy a space of 92,000 English square miles. 

 The climate is much milder and more equable in the neigh- 

 bourhood of the lakes; for example, at Niagara, (lat. 

 43 15'), the mean winter temperature is only half a degree 

 of Reaumur (1.2 Fahrenheit) below the freezing point, 

 while at a distance from the lakes, in lat 44 53 f , at the 



