EASTIXG OF THE TEADE-AYINrDS, ETC. 161 



have not as mucli vapour to make rains of, specially for tlie npper 

 Mississippi Valley, as they had in the summer-time, when they 

 dispensed then- moistm-e, in the shape of rains, most sparingly upon 

 the Pacific coasts. According to these views, the diy season on 

 the Pacific slopes should be the wet, especially in the upper Mis- 

 sissippi Yalley, and vice versa. Blodget's maps show that such is 

 actually the case. Meteorological observations in the " Eed Eiver 

 countrv " and other parts of British America would throw farther 

 light and give farther confirmation, I doubt not, both to these 

 ^dews and to this interesting question. These army observations, 

 as exj^ressed in Blodget's maps, reveal other interesting featm-es, 

 also, touching the physical geography of the country. I allude 

 to the two isothermal lines 45° and 65° (Plate YIII.), which in- 

 clude between them all places that have a mean annual tempera- 

 tm-e between 45° and 65°. I have di-awn, for the sake of com- 

 parison, similar hues on the authority of Dove and Johnston (A. K., 

 of Edinbm-gh), across Europe and Asia. The isothenn of 65° 

 skirts the northern limits of the sugar-cane, and separates the in- 

 tertropical from the extra-tropical plants and productions. I have 

 di'a^^Tx these two lines across America in order to give a practical 

 exemplication of the nature of the advantages which the indus- 

 trial pm'suits and the pohtical economy of the country would de- 

 rive by the systematic extension of our meteorological observa- 

 tions from the sea to the land. These lines show how much we 

 err when we reckon chmates according to parallels of latitude. 

 The space that these two isotherms of 45° and 65° comprehend 

 between the Mississippi and the Piocky Mountains, o^ving to the 

 singular effect of those mountains upon the climate, is larger than 

 the space they comprehend between the Mississippi and the At- 

 lantic. Hyetographically it is also different, being dryer, and pos- 

 sessing a pm-er atmosphere. In this grand range of climate be- 

 tween the meridians of 100° and 110° W-., the amount of precipi- 

 tation is just al)out one half of what it is between those two iso 

 therms east of the Mississippi. In this new country west of it, 

 winter is the day, and spring the rainy season. It includes the 

 climates of the Caspian Sea, which Humboldt regards as the most 

 salubrious in the world, and where he fomid the most dehcious 

 fruits that he saw dming his travels. Such was the pm'ity of the 

 air there, that pohshed steel would not tarnish even by night ex- 

 posiu'e. These two isotherms, mth the remarkable loop which 

 they make to the north-west, beyond the Mississippi, embrace the 



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