Tlio extreme N. W. point of tlie hot district under Purvey, has a moan winter heat of 35'^ 

 for the Isothere of 830, and the Isochcim of 35°, nearly touch each other at Lake Humboldt, 

 in Utah. It is only, therefore, in the southeastern ])art of this district that the cultivation 

 of the intertroiiical fruit-trees can be successful. 



It is true that there may be spots found in the interior protected from the cold winter 

 winds, and from frosts, where the hardier trees of the tropics, especially of the hills and 

 table-lands, such as the cinchonas, may bo introduced. 



If the winter and summer climates of the district round Uumboldt's Lake be thus strongly 

 contrasted, the summer climates of the coast, and of the mountain valleys of California, 

 are equally so. The Isothere of Fort Miller, on the San Joaquim, is 85^, and that of Mon- 

 terey, 150 miles to the west, is 57° 1 



The summer mean of the Pacific coast does not vary from 57^, between Monterey and 

 Sitka, a space of 22° of latitude, and near two thousand miles of coast. 



This extraordinary fact is no doubt caused by the cold waters of the Pacific Ocean. 

 Although there is no steady superficial polar current to be traced near the shore, it would 

 seem tliat such a current prevails in the deep sea beyond, and that the cold waters, as they 

 approach the land, are forced upwards by the shelving of the bottom. 



There is at all times a belt of cold sea-water, of the temperature of 57° to 60°, along the 

 northwestern coast of America, extending many hundred miles out to sea, which controls 

 the climate of the coast, and almost equalizes the temperature of the four seasons ! 



A similar but narrow belt of cold water borders the Atlantic coast, inside of the Gulf 

 Stream, which, tliough it does not influence the summer climate, is distinctly felt in the cool 

 northeast winds which sometimes prevail with a clear sky for weeks during spring and 

 early summer. 



The Isothere of 750 passes through the Bermuda Islands in latitude 32^, and strikes our 

 coast in latitude 39^°. It is bent to the S. W., by the Virginia Mountains, to the parallel 

 of 340, along the northern line of North Carolina and Tennessee. West of the AUeghanies 

 it again bends to the N., and then to the W., crosses the Mississippi in latitude 390, near 

 the mouth of the Illinois, and continues west to longitude 103°. It is then deflected to the 

 S., by the Rocky Mountains, to latitude 32°, in the valley of the Piio Grande. It then bends 

 again to the K. W., strikes the Great Salt Lake — the Lake Timpinagos of Humboldt — passes 

 W. in latitude 41 -^-O, till it is again bent S. by the cold atmosphere of the Pacific coast, and 

 strikes that coast in latitude 26^. 



The Isothere of 70^ crosses the Hudson at "West Point, touches the parallel of 40° in 

 Western Pennsylvania, passes through Sandusky and Chicago, thence N. W. to Fort Snelling, 

 crosses the Missouri near Fort Union, reaches the parallel of 49°, and is then bent to the 

 E. of S., by the Rocky Mountains, till it reaches latitude 35°, in the valley of the Rio Grande. 

 West of the Rocky Mountains it bends to the north, and reaches the parallel of 47^° in 

 longitude II80. It then bends suddenly to the south, and strikes the coast in latitude 34°. 



" There is a great identity," says the report, " of the temperatures of this large area, em- 

 braced by the Isothermals (Isotheres) of 70^ and 75° east of the plain, including Iowa, Illi- 

 nois, Indiana, Ohio, Kentucky, Upper Tennessee, Virginia, Maryland, Delaware, Lower Penn- 

 sylvania, and New Jersey, excepting from these some points of coast exposure, ajid of the 

 mountainous districts, the summer temperatures are more nearly uniform than almost any 

 continental area of like magnitude." 



