440 THE PHYSICAL GEOGRAPHY OF THE SEA. 



drawn out each to occupy its period separately, would be equal 

 to 373 years. They exhibit several curious and suggestive facts 

 concerning the difference of the atmospherical stability in the two 

 hemispheres. 



823. If we would discover the seat of those forces which pro- 

 The propeiiins power ^^^6 this difference in the dynamical status of the 

 of the winds. ^^^ great acrial oceans that envelop our planet, 

 we should search for them in the unequal distribution of land and 

 water over the two hemispheres. In one the wind is interrupted 

 in its circuits by the continental masses, with their wooded plains, 

 their snowy mantles in winter, their sandy deserts in summer, and 

 their mountain ranges always. In the other there is but little 

 land and less snow. On the polar side of 40° S. especially, if we 

 except the small remnant of this continent that protrudes beyond 

 that parallel in the direction of Cape Horn, there is scarcely an 

 island. All is sea. There the air is never dry ; it is always in 

 contact with a vapor-giving surface ; consequently, the winds there 

 are loaded with moisture, which, with every change of tempera- 

 ture, is either increased by farther evaporation or diminished by 

 temporary condensation. The propelling poiver of the luinds in the 

 southern hemisphere resides chiefly in the latent heat of the vapor which 

 they such up from the engirdling sea on the polar side of Capri- 

 corn. 



824. The Storm and Eain Charts show that within the trade- 

 Lt. Van Go-h's storm wiud rcgions of botli hemisphcrcs the calm and rain 

 and Ram Charts. curvcs arc Symmetrical; that in the extra-tropical 

 regions the symmetry is between the calm and fog curves ; and 

 also, especially in the southern hemisphere, between the gale and 

 rain curves. Lieutenant Van Gogh, of the Dutch ISTav}^, in an in- 

 teresting paper on the connection between storms near the Cape 

 of Good Hope and the temperature of the sea,* presents a storm 

 and rain chart for that region. It is founded on 17,810 observa- 

 tions, made by 500 ships, upon wind and weather, between 14° 

 and 32° E., and' 33° and 37° S. By that chart the gale and rain 

 curves are so symmetrical that the phenomena of rains and gales 

 in the extra-tropical seas present themselves suggestively as cause 

 and effect. The general storm and rain charts of the Atlantic 



* De Stormen nabij de Kaap de Goede Hoop in verband beschouwd met de Tem- 

 peratuur dcr Zee. 



