LOCAL CLIMATOLOGY. 93 



Latitude. Coldest month. Hottest month. 



Fort Himiboldt, Cal 40.4(3 43.1 5«.G 



Geneva, N. Y.... 42.53 25.29 70.25 



Marseilles, France _. .43.17 44.42 74.66 



Montpelier, " 43.36 42.08 78.08 



Eonie, Italy 41.53 42.26 77.00 



The cause of this diiference I think is easily- found in the fact 

 that the return current is in i)art at least the surface current, 

 bringing with it the heat of the tropics much farther north than 

 latitude 45 deg. in the summer, and therefore the i)()siti()n and 

 direction of these great mountain ranges does not exert so per- 

 ceptible an intluence upon the temperature of places in this lati- 

 tude in the sunmier as in the winter ; but in the winter the return 

 curi-ent is not much felt north of latitude 40 deg., and that por- 

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

 replaced by the polar current which must lind 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 mountains, shutting ofi* the polar current from the Indian 

 ocean, there are no trade winds perceptible there ; but on the 

 contrary, we find the Monsoons — winds which blow from the 

 southwest to the northeast in our summer, when South Africa is 

 cold and Southern Asia is hot ; and on the other hand, they l)low 

 from the northeast to the southwest in our winter, when Southern 

 Asia, being in the northern hemisphere, is cold, and South Africa, 

 being on the other side of the Equator, is hot. But across the 

 Atlantic, where there is the same conformation and distribution 

 of lands as between the north of Africa and the south of South 

 America, there are not only no Monsoons, but the trade winds are 

 most marked of any place on the surface of the globe ; and these 

 trade winds of course are but the polar current become the sur- 

 face current within the tropics. 



3. In the third place, the extremes of heat in sunnncr and of cold 

 in winter are not so great as indicated by the line of real tempe- 

 rature as the computation would lead us to expect. This remark 

 applies, of course, not to individual and peculiar days, but rather 

 to general average for the hottest and the coldest days. The 

 hottest day by the general average is August 1st, 73.29 deg., and 

 the hottest week is that ending August 5th, 71.82 deg. ; whereas 

 computation gives for that week 75.28 deg., a diHereucc of 3.46 



