58 



MECHANICS. 



Fig. 36. a bag of grain as shown in Fig. 

 36. Ths line falling outside his 

 feet, he is compelled to draw 

 downward with great force on 

 the other end of the bag. A man 

 who carries a heavy pole on his 

 shoulder should see that the centre is directly over his 

 shoulder, otherwise he will be compelled to bear down 

 upon the Ughter end, and thus add in an equal degree 

 to the weight upon his body. 



If an elliptical or oval body, 

 Fig. 37, rest upon its side a, roll- 

 ing it in either direction elevates 

 the centre, c, because it is nearest 

 the side on wliich the body rests. 

 If, when raised, it be suffered to 

 fall, its momentum carries it be- 

 yond the point of rest, and thus it 

 contmues rocking until the force is 

 spent. The course of the centre 

 dming these motions is shown 

 by the curved dotted line, c. If 

 it be placed upon end, as in Fig. 

 38, then any motion toward ei- 

 ther side brings the centre of 

 gravity nearer the touching-point, 

 that is, causes it to descend, and the body consequently 

 falls over on its side. This may be easily illustrated 



falls when set on either end. 



The rockers of chairs, cradles, and cribs are formed 

 on the principle just explained. If so made that the 



