CENTER OF GRAVITY, 



49 



What is the 

 Line of Direc- 

 tion? 



because ■svben a solid body falls, its center of 

 gravity moves along tbis line until it reacbes 



tbe ground. Wben bodies are supported upon a basis, 



their stability depends on the position of their Line of 



Direction. 



96. If the line of direction falls within the 

 base upon which the body stands, the body 

 remains supported ; but if it falls without the 



base, the body overturns. 



When will a 

 body stand, 

 »nd when will 

 It faU ? 



Fig. 16. 



Fig. 17. 



Thus, in Fig. 16, the line directed Terticallv from the center of gravity, G, 

 falls within the base of the body, and it remains standing; but in Fig. 17 a 

 similar line falls Ts-ithout the base, and the body, consequently, can not bo 

 maintained in an upright position, and must faU. 



A wall, or tower stands securely, so long as the perpendicular line drawn 



through its center of gravity falls 

 within its base. The celebrated 

 leaning-tower of Pisa, 315 feet high, 

 wliich inclines 12 feet from a per- 

 fectly upright jwsition, is an example 

 of this principle. For instance, the 

 line in Fig. 18, falling from the top 

 of the tower to the ground, and 

 passing through the center of gravity, ' 

 falls within the base, and the tower 

 stands securely. If) however, an 

 attempt had been made to build tho 

 tower a little higher, so that the per- 

 pendicular hne passing through the 

 center of gravity, would have fallen 

 beyond the base, the structure cc -dd 

 no longer have supported itselfl 



97. The broader, or larger 



