36 MECHANICS. 



quently this is the centre sought. If the mass or body, 

 instead of being flat like a board, be shapeless like a stone 

 or lump of chalk, holes bored from diflferent suspending 

 points directly downward will all cross each other exactly 

 at the centre of gravity. 



LINE OF DIRECTION. 



An imaginary line from the centre of gravity perpendic- 

 ularly downward to where the body rests is called the 

 line of direction. 



Now in any solid body whatever, whether it be a wall, 

 a stack of grain, or a loaded Avagon, the line of direction 

 must fall within the base or part resting upon the ground, 



Fig. 28. Fig. 23. ^^ ^^ ^^'^^^ immediately be 



thrown over by its own 

 weight. A heavily and even- 

 ly loaded wngon on a level 

 road will be perfectly safe, be- 

 cause the line of direction falls 



Centre'of gravity on lelsTa^ inclined equally bctWCCn the wliecls, 



^'^'- 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 outside the wheels, as in fig. 23, 

 it must be instantly overturned. If, however, instead of 

 the higli 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 5, and thus, the line falling within the wheels, the 

 load wiU be safe from upsetting, unless the upper wheel 

 pass over a stone, or the lower wheel sink into a rut. 

 The centre of gravity of a large load may be nearly ascer- 

 tained by measuring with a rod ; and it may sometimes 

 happen that by measuring the sideling slope of a road, all 

 of which may be done in a few minutes, a teamster may 

 save himself from a comfortless upsetting, and perhaps 



