132 THE PHYSICAL GEOGRAPHY OF THE SEA. 



the tropical regions was higher in the northern than in the southern 

 hemisphere ; for they show that the difference is such as to draw 

 the equatorial edge of the southeast trades far over on this side 

 of the equator, and to give them force enough to keep the north- 

 east trade-winds out of the southern hemisphere almost entirely. 



328. Consequently, as before stated, the southeast trade-winds 

 being in contact with a more extended evaporating surface, and 

 continuing in contact witli it for a longer time or through a greater 

 distance, they would probably arrive at the trade-wind place of 

 meeting more heavily laden with moisture than the others. 



329. Taking the laws and rates of evaporation into considera- 

 tion, I could find no part of the ocean of the northern hemisphere 

 from which the sources of the Mississippi, the St. Lawrence, and 

 the other great rivers of our hemisphere could be supplied. 



330. A reo;ular series of meteorolo2;ical observations has been 

 carried on at the military posts of the United States since 1819. 

 Rain maps of the whole country* have been prepared from these 

 observations by Mr. Lorin Blodget at the surgeon general's office, 

 and under the direction of Dr. Cooledge, U. S. A. These maps, 

 as far as they go, sustain these views in a remarkable manner ; for 

 they bring out facts in a most striking way to show that the dry 

 season in California and Oregon is the w^et season in the Missis- 

 sippi Valley. 



331. The w^nds coming from the southwest, and striking upon 

 the coasts of California and Oregon in winter, precipitate there 

 copiously. They then pass over the mountains robbed in part 

 of their moisture. Of course, after watering the Pacific shores, 

 they have not as much vapor to make rains of, especially for the 

 upper Mississippi Yalley, as they had in the summer time, when 

 they dispensed their moisture, in the shape of rains, most sparingly 

 upon the Pacific coasts. 



332. According to these views, the dry season on the Pacific 

 slopes should be the wet, especially in the upper Mississippi Val- 

 ley, and vice versa. Blodget's maps show that such is actually 

 the case. 



333. Meteorological observations in the " Ecd Piver country" 



* See Army Meteorological Observations, published 1855. 



