=Influence of Lakes and Rivers.= With the exception of contributing to the formation of occasional fogs over their surfaces and the adjacent low lands, through the rising of warm water vapor into the cold air that often collects at the bottom of valleys during nighttime, rivers exercise little influence on climate. Lakes exert a modifying influence on the temperature of places near their shores but only for a few miles therefrom, and they are too small to exert any appreciable influence on rainfall. If one examine charts showing the average rainfall for the United States by seasons, he will observe that the amount gradually shades off as the distance from the Gulf or Ocean increases, without any relation whatever to the five Great Lakes. Deserts exist on either side of the Caspian Sea, although it slightly increases the rain of the Elburz Mountains to the south. If these great bodies of water do not influence the rainfall, how ridiculous to assume that the changing of forest areas to other forms of vegetation possibly can affect precipitation or influence droughts. Stress is laid on the fact that some land is left bare and then is eroded into deep gullies. This is true, but the fault is one that may be corrected by a proper system of plowing and cultivation. And at most the area so eroded is so infinitesimal in comparison to the vast regions changed from forests to growing crops as to be negligible. [Illustration: CHART 14.—MEAN ANNUAL ISOTHERMS (Buchan).] =Influence of Ocean Currents on Climate.= Climates are markedly influenced by the currents of oceans. Charts 15 and 16 show the normal wind circulations of the globe; note that the centers of the great swirls are coincident with the location of the High and the Low centers of action located on Charts 1 and 2. Next observe Chart 13, showing the ocean currents, and it will be seen at once how closely the circulation of the great ocean currents follows that of the winds, due to the friction of the air upon the water, and to the interposition of bodies of land that turn about or deflect the currents. [Illustration: CHART 15.—NORMAL WIND DIRECTION AND VELOCITY FOR JANUARY AND FEBRUARY (Köppen).] [Illustration: CHART 16.—NORMAL WIND DIRECTION AND VELOCITY FOR JULY AND AUGUST (Köppen).]