LOCAL CLIMATOLOGY. 



93 



ference, and by consequence each place within this region has about 

 three times as much of the cold polar winds as it ought, and is, more- 

 over, deprived by the same cause of a portion of the amount of the warm 

 return current to which it is entitled. 



Nor is this all. From the direction of the polar current from northeast 

 to southwest, in a rhomb or loxodromic curve, the influence of this con- 

 formation of the surface is felt much more severely on the westerly side 

 of this gap thaia on the easterly side ; that is, in the United States, than 

 on the Atlantic ocean. This we see in the direction of the isothermals. 

 The isothermal of 50° for the year, for example, leaves Santa Fe, in New 

 Mexico, latitude 3o°.41, and passes so much to the north of east on its 

 way across the American continent and the Atlantic ocean, that it meets 

 Great Britain in latitude 52° or 53°. So also of the other isothermals. 



This difference, however, between our average for the year and that 

 which is due to our latitude, is felt rather in the winter than in the 

 summer, as will be seen from the following comparison of places in nearly 

 the same latitude, selected on both continents : 



LOCALITT. 



Fort Humboldt, Cal 



Geneva, N. Y 



Marseilles, France . . 

 Moutpelier, do 

 Rome, Italy 



Latitude. 



40.46 

 42.54 

 43.17 

 43.36 

 41.53 



Coldest 

 month. 



43.10 

 25.29 

 44.42 

 42.08 

 42.26 



Hottest 

 month. 



58.60 

 70.25 

 74.66 

 78.08 

 77.00 



The cause of this difference, I think, is easily found in the fact that 

 the return current is in part, at least, the surface current, bringing with 

 it the heat of the tropics much farther north than latitude 45° in the 

 summer, and therefore the position and direction of these great mountain 

 ranges do not exert so perceptible an influence upon the temperatm-e 

 of places in this latitude in the summer as in the winter ; but in the 

 winter the return current is not much felt north of latitude 40°, and that 

 portion to which we are entitled is shut off by the mountains and replaced 

 by the polar current, which must find its way through this gap to the 

 tropics. 



I will notice but one other effect of this peculiar conformation of the 

 mountain ranges. In consequence of the situation of the Asiatic moun- 

 tains, shutting off the polar current from the Indian ocean, there are no 

 trade winds perceptible there ; but on the contrary, we find the monsoons. 



