FOkCE VAUYIXO AB TUB DI8TAXCB. 



ssion reduces to Virpx. Thus if g denote the attra 

 nt th top of the mountain 



a- denote the mean i'.arih, so that 



I 7 /' 



mass of the Earth 



; 

 4wor AWift 



* m -*r m 



thin 



^ 



Now the mean density of the Karth in known to be about 



v halt times that of water, and from what may be 



'tared of the <1. n.sit y of matter at the Earth's surface, we 



may suppose 



-!. And 



thus <7* * 



v far the approximations mad- le are allow- 



miglit I it an- 



pears that in taking 2wpx to represent the attraction of tnc 



. we do in fact make the mountain to consist of a 



thickness x, hut uf infinite c.v 



For investigations r factions of mountains 



nt may consult Pratt's treatise on Attractions... and 

 if the Earth. 



.. hitherto confined ourselves to simple exair. 

 of the ordinary law of . : ; we now proceed to con 



some other laws of at and also some more complex 



cases of the ordinary law. 



. If the particles of a body attract with a force varying 

 as the product of the mass into the distance, the resultant at- 



>n of the body is the same as if the whole mass of the body 

 were collected at its centre of gravity. 



