CENTRE OF GRAVITY. 



231 



Fig. 17. 



When G is so placed that the line of direction G D shall fall on the point 

 P, the cylinder will be in equilibrium, because its weight acts upon the point 

 on which it rests. There are two cases represented in fig. 17 and fig. 18, in 

 which G takes this position. Fig. 17 represents the state of stable, and fig. 18 

 of instable equilibrium. 



Fig. 18. 



When a body is placed upon a base, its stability depends upon the position 

 of the line of direction and the height of the centre of gravity above the base. 

 If the line of direction fall within the base, the body will stand firm ; if it fall 

 on the edge of the base, it will be in a state in which the slightest force will 

 overthrow it on that side at which the line of direction falls ; and if the line of 

 direction fall without the base, the body must turn over that edge which is 

 nearest to the line of direction. 



In fig. 19 and fig. 20, the line of direction G P falls within the base, and it 



Fig. 19. 



Fig. 20. 



is obvious that the body will stand firm ; for any attempt to turn it over either 

 edge would cause the centre of gravity to ascend. But in fig. 21, the line of 



