CONSTITUTION OF THE GLOBE. 19 



the centre and circumference, which, under the cir- 

 cumstances of a greater centrifugal force in the equa- 

 torial parts, and the consequent diminution of gravity 

 in these regions, must balance each other. 



Now as, on the surface of the earth, there is a 

 diminution of gravity as we proceed from the poles to 

 the equator, depending partly on the greater distance 

 of the equatorial surface from the centre, and partly on 

 the greater quantity of its centrifugal motion, we can 

 determine what this force ought to be at different 

 points ; and if the Newtonian hypothesis be admitted, 

 the force of gravity at the poles will exceed that at the 

 equator by a similar quantity. 



But the actual force of gravity on the different parts 

 of the surface may be measured by the pendulum, as 

 the tabular view just given indicates: a greater number 

 of vibrations being performed in a given time, in pro- 

 portion as that force increases at any particular point. 

 Thus astronomy furnishes both calculations and expe- 

 riments from which geology may derive information 

 relating to the interior parts of the earth, and may 

 learn whether the whole globe is of homogeneous 

 density or not. For if we assume the Newtonian 

 hypothesis, the force of gravity should increase from 

 the equator to the pole, so that the latter should ex- 

 ceed the former by ^ part ; or if the force of gravity 

 at the equator be expressed by 1, its increase at the 

 pole should be 0,00435. But observations on the 

 oscillations of the pendulum in different latitudes gave 

 reason to suppose that this increase is 0,00567 ; and 

 hence it would be inferred that the earth is not homo- 

 geneous. It has been truly said, in observing on this 

 conclusion, that the earth needs not therefore be stra- 

 tified throughout : nor is there indeed any geologist 

 who now believes this: but when it is said that the 



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