Of THE 



-'i* IVERSITT 

 51 



GRAVITATION. 



support. This fact affords a ready means of determining 

 the centre of gravity experimentally. 



Let any irregularly shaped body, as a stone or chair, be 

 suspended so as to move freely. Drop a plumb-line from 

 the point of suspension, and make it fast or mark its direc- 

 tion. The centre of gravity will lie in this line. From a 

 second point, not in the line already determined, suspend 

 the body ; let fall a plumb-line as before. The centre of 

 gravity will lie in this line also. But to lie in both lines, the 

 centre of gravity must lie at their intersection. (Fig. 19.) 



1O9. May be Outside of the Body. The cen- 

 tre of gravity may be outside of the matter of which, a 

 body consists, as in the case of a ring, hollow sphere, box, 

 or cask. The same fact is illustrated by the " balancer," 

 represented in the figure. The centre 

 of gravity is in the line joining the 

 two heavy balls, and thus under the 

 foot of the waltzing figure. But the 

 point wherever found will have the 

 same properties as if it lay in the mass 

 of the body. In a freely falling body, 

 no matter how irregular its form, or 

 how indescribable the curves made by 

 any of its projecting parts, the line of 

 direction in which the centre of grav- 

 ity or point of application moves will 

 be a vertical line ( 65 [2] ). 



FIG. 20. 11O. Equilibrium. Inasmuch 



as the centre of gravity is the point at 



which the weight of a body is concentrated, when the 



centre of gravity is supported, the whole body will 



