52 MECHANICS. 



Then hang it by the hook c, and it wUl be somewhere 

 in the line c d. Now the point e, where they cross 

 each other, is the only point in both, consequently this 

 is the centre sought. If the mass or body, instead of 

 being flat like a board, be shapeless Uke a stone or lump 

 of chalk, holes bored from different suspending points 

 directly downward wOl all cross each other exactly at 

 the centre of gravity. 



LINE OP DIRECTION. 



An imaginary line from the centre of gravity perpen- 

 dicularly downward to where the body rests is called 

 the line of direction. 



Now in any sohd body whatever, whether it be a 

 wall, a stack of grain, or a loaded wagon, the line of 

 direction must fall within the base or part resting upon 

 the ground, or it will immediately be thrown over by 

 its own weight. A heavily and evenly loaded wagon 

 on a level road will be perfectly safe, because the line 

 of direction falls equally between the wheels, as shown 

 in Fig. 22, by the dotted 

 line, c being the centre. But 

 if it pass a steep side-hill 

 road, throwing this line out- 

 side the wheels, as in Fig. 

 r, , ^ , , , ^ , ^ 23, it must be instantly 



Centre of gravity on level and inclined ' J 



^""^^ overturned. If, however, 



instead of the high load represented in the figure, it be 

 some very heavy material, as brick or sand, so as not 

 to be higher than the square box, the centre will be 

 much lower down, or at b, and thus, the line falling 

 within the wheels, the load will be safe from danger, 



