108 



THE CENTRE OF GRAVITY. 



of stable equilibrium is comparatively great, so that it is 

 sufficient for bringing the point of support below the 

 centre of gravity again, and thus maintaining the body 

 in its unstable position for any length of time. 



FIG. 77 (an. proj. | real size). 



The centre of gravity sometimes lies outside the 

 body, as is the case. of a ring, a horse-shoe, a triangle 

 made of wire, and generally in bodies of a bent or 

 angular form. Such bodies cannot be placed in a 

 position of neutral equilibrium, because the centre of 

 gravity cannot be supported. But it is generally very 

 easy to place such bodies in a position of stable equili- 

 brium. A compound body of this kind, having its 

 centre of gravity outside of its mass, may be con- 

 structed with a pair of forks, a cork, and a small 

 silver coin, as shown in fig. 77. If placed upon thej 

 point of a needle (fixed upon the vertical rod of the 

 retort-stand, in which a hole is made with the bradawl) 

 the body may be made to vibrate considerably, and ever 

 to rotate, by blowing laterally upon one of the fork* 

 without overturning. Many toys, such as tumblers 



