CENTRIFUGAL FORCE. 5 



rectly opposed to that of gravity, "which is however 

 far greater than the former ; otherwise the bodies 

 would be thrown off from the earth. It has been 

 calculated, that if the earth turned round seven- 

 teen times as quickly as it does, the centrifugal 

 force at the equator would become exactly equal 

 to the force of gravity. Bodies, in that part of 

 the earth would then seem to have no weight ; and 

 anything that might be thrown up to a height, 

 would not return to the earth, but would travel 

 round it, like the moon. 



In fact, the moon is in the condition of a body 

 whose centrifugal force is just balanced by its 

 weight. Since the distance of the moon from the 

 earth is known, the strength of the attraction be- 

 tween the two planets is easily calculated. It is 

 found to be three thousand six hundred times less 

 than the force of gravity at the surface of the earth. 

 The centrifugal force of the moon, due to its revolv- 

 ing round the earth, is just equal to this ; so that the 

 one of these forces always balances the other, and 

 thus the moon is hindered from ever straying 

 from its path around the earth. The earth and 

 the other planets are in exactly the same condition 

 as regards the sun. 



Since the centrifugal force of bodies on the 

 earth acts perpendicularly to the earth's axis, this 

 force cannot act in the direction of gravitation 

 anywhere except at the equator. 



