LOCAL CLIMATOLOGY. 



77 



the polar and the retiuri currents usually change position. The conse- 

 quence is that the polar current is seldom if ever felt south of this 

 mountain range, while an undue share of the return current is retained 

 to raise the temperature of all the places that are thus sheltered from 

 the polar current. 



On our own continent we have, in like manner, the Hocky mountains 

 stretching across the continent from southeast to northwest. If now 

 we select for comparison some places in the same latitude, one on the 

 Pacific coast, another on the plain east of the mountains, and another 

 still farther east and east of the Mississippi, we shall see the effects of 

 this mountain range. Thus : 



Latitude. 



Locality. 



Summer. 



Winter. 



Year. 



Latitude 40° 



Fort Humboldt, Cal 



Fort Kearnej', Neb 



57°. 4 

 71 .5 

 78 .4 

 62 .9 

 64 .8 



■45°. 2 

 23 .0 

 29 .7 

 39 .5 

 14 .0 



52°. 1 

 47 .7 

 52 .2 

 50 .8 

 89 .9 



do 



do 



Latitude 47° 



Fort Steilacoom, W.T 



Sandv" Lake Min 



do 







Farther south, the difference is of course much less. But in latitude 

 40'^, with the summer 14°. 1 warmer than on the Pacific coast, the 

 winters are 22^.2 colder, and the average for the year is in conse- 

 quence 4°.4 colder on the western side of the Rocky mountains; 

 while in Indiana, beyond the more immediate effects of this obstruc- 

 tion to the polar and return current, the summers are 6°.9 and the 

 winters 6°.7 warmer, with a difference in the general average 4°.5 for 

 the year. Farther north, as latitude 47°, the contrast becomes still more 

 remarkable; with summers 2°.l warmer than on the Pacific coast, the 

 winters 25°.5 colder, and a difference in the general average for the year 

 of 10°.9. 



Or, to compare the effects in another way: The isothermal for winter 

 that passes through the places of western New York that lie along the 

 borders of Lake Ontario, and from ten to twenty miles south, starts on 

 the Pacific coast far north of Sitka, 57° north latitude, and reaches in 

 New Mexico, just east of the mountains, the low latitude of 36°, 

 then reaches ours, about 43°, in Michigan; while the isothermal for our 

 summer, 67°, starts from latitude 30° on the Pacific coast, and passes the 

 plains just east of the Rocky mountains in latitude 35°. Thus the cool 

 winds from the pole which pass along down by the side of the mountains, 



