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EXPERIMENTAL GENERAL SCIENCE 



set up which may be limited to a portion of a township, a 

 county, or extend over one or more States. The currents 

 which flow along the ground from one region to another are 

 familiarly known as winds. Since changes in the position of 

 the air are due to differences in its density, it is easy to realize 

 that the greater the difference between two regions the greater 

 will be the speed of the winds produced. Most interesting 

 illustrations of this may be observed near large bodies of water. 

 During the hours of sunshine, the land warms more rapidly 



FIG. 33. Convection currents in a room. (Tower, Smith and Turton.} 



than the water, and early in the day the breeze begins to blow 

 inland. At night the land loses heat much more rapidly than 

 the water and soon is cooler. Then the breeze from the land 

 to the water sets in. In regions where the land slopes rapidly 

 toward the water and also receives the direct rays of the sun, 

 the effects are especially noticeable. The winds which blow 

 toward the great storms or cyclones that move across the 

 country from west to east at intervals of a few days during 

 most of the year do not blow straight toward the center of 

 the storm area. Owing to the rotation of the earth they 



