THE EARTH. 



less and less as we approach the poles. Since, then, the centrifugal force 

 depends conjointly on the magnitude of the circle of revolution and the velocity 

 of the motion, it fellows that it will be less and less as we approach the poles, 

 and greater and greater as we approach the equator. 



This force, however, exists at all latitudes, in a greater or less degree of 

 energy, and it is everywhere directed from the centre of the circle of di- 

 urnal rotation. Let N S, figure 12, be the earth, and E Q the equator. 



Fig. 12 



Let P be a point on the surface of the earth anywhere between the equator 

 and poles. Since P is carried by the diurnal motion round the centre C, it 

 will have a tendency to fly from the centre in the direction P R. This ten- 

 dency will be partially counteracted by its gravity, which acts in the direc- 

 tion P O. But since P O is not directed immediately against P R, the result 

 will be that a particle of matter P thus acted on will move toward Q. To coun- 

 teract this tendency, there must be such a protuberance at Q as will place an 

 acclivity before P so steep as to prevent its ascent. Without such a protuber- 

 ance, all the fluid and loose matter on the globe would run toward the line. 



It appears, then, that the effect of the earth's revolution would be to cause 

 all loose matter placed on the surface of the earth in either hemisphere to 

 move toward the equator ; and that if the earth were a perfect globe, there 

 would be no power to resist this tendency, and the effect would consequently 

 be actually produced. 



Let us, then, suppose an exact globe, partially covered with land and water, 



revolving on an axis in twenty-four hours ; the land or solid matter composing 



it would be affected by the centrifugal force, like all other matter, but the 



cohesive principle which gives it solidity would prevent a derangement of its 



structure or change of position by such a cause, and the effect of the centrim- 



! gal force would therefore be confined to the fluid matter, which, in obedience 



J to the tendency above described, would flow from either hemisphere toward 



i the regions about the equator, where it would be gradually heaped up so as to 



' form a convex protuberance around the line between the tropics, and to give to 



I the earth, so far as the fluid matter upon it is concerned, the form of an oblate 



I spheroid. But this movement of the fluid would cease as soon as the equato- 



) rial protuberance should attain a certain limit ; for we may regard such a pro- 



? tubenmce as a sort of mountain piled round the equator, down the sides of which 



( there would be a tendency to fall, in obedience to gravitation, as would be the 



f case down any other declivity. 



5 The particles of fluid placed upon the side of this protuberance would be 

 I affected by two opposite forces : that which would result from the rotation 



