432 THE rilYSICAL GEOGRAPHY OF THE SEA. 



be the time when the fiends of the storm are most busily at work 

 in the West Indies. During the remainder of the year, these ex- 

 tra-tropical gales, for the most part, come from the northwest. 

 But the winter is the most famous season for these gales. That 

 is the time when the Gulf Stream has brought the heat of summer 

 and placed it (§ 172) in closest proximity to the extremest cold of 

 the north. And there would, therefore, it would seem, be a con- 

 flict between these extremes; consequently, great disturbances in 

 the air, and a violent rush from the cold to the warm. In like 

 manner, the gales that most prevail in the extra-tropics of the 

 southern hemisphere come from the pole and the west, i. e., south- 

 west. 



808. Storm and Kain Charts for the Atlantic Ocean have al- 

 stoi-m and Rain Charts, ready bccu published by the Observatory, and 

 others for the other oceans are in process of construction. The ob- 

 ject of such charts is to show the directions and relative fre- 

 quency of calms, fogs, rain, thunder, and lightning. These charts 

 are very instructive. They show that that half of the atmos- 

 pherical coating of the earth which covers the northern hemi- 

 sphere — if we may take as a type of the whole what occurs on 

 either side of the equator in the Atlantic Ocean — is in a much 

 less stable condition than that which covers the southern. 



