OP THE PROPERTIES OF MATTER. 



15 



center of gravity as that center ascends or descends, LECT. 

 we must look upon the whole body to do so too.' But 

 as it is contrary to the nature of heavy bodies to ascend 

 of their own accord, or not to descend when they are 

 permitted ; we may be sure, that unless the center of 

 gravity be supported, the whole body will tumble or fall. 11 

 Hence it is, that bodies stand upon their bases when the 

 line of direction falls within the base ; for in this case 

 the body cannot be made to fall without first raising the 

 center of gravity higher than it was before. 



Thus, the inclining 

 body A D, whose cen- 

 ter of gravity is E, 

 stands firmly on its 

 base D K, because the 

 line of direction E F 

 falls within the base. 

 But if a weight, as 

 A G H, be laid upon 

 the top of the body, 

 the center of gravity of 

 the whole body and 

 weight together is rais- 

 ed up to /; and then, 

 as the line of direc- 

 tion / D falls with- 

 out the base at D, the 

 center of gravity, / is 

 not supported and the 

 whole body and weight tumble down together. 



Note 11. There are two apparent eiceptions to the general law o. 



gravitation, which it may be proper to notice on the present occasion. 



f these is well known, and is called the hanging tower of Pisa 



he other is a nearly similar building at Caerphilly in Glamorganshire. 



:hese two towers, the one leans twelve feet from the perpendicular 



=md the other nearly fifteen, but as in both cases the center of gravity 



is within the base, no danger of their falling need be apprehended. 



whilst the materials retain their cohesive power. 



