232 



CENTRE OF GRAVITY. 



direction falls upon the edge, and if the body be turned over, the centre of 

 gravity immediately commences to descend. Until it be turned over, however, 

 the centre of gravity is supported by the edge. 



In fig. 22, the line of direction falls outside the base, the centre of gravity 



Tig. 21. 



Fig. 22. 



has a tendency to descend from G toward A, and the body will accordingly 

 fall in that direction. 



When the line of direction falls within the base, bodies will always stand 

 firm, but not with the same degree of stability. In general, the stability de- 

 pends on the height through which the cebtre of gravity must be elevated be- 

 fore the body can be overthrown. The greater this height is, the greater in 

 the same proportion will be the stability. 



Let BAG, fig. 23, be a pyramid, the centre of gravity being at G. To 



Fig. 23. 



turn this over the edge B, the centre of gravity must be carried over the arch 

 G E, and must therefore be raised through the height HE. If, however, the 

 pyramid were taller relatively to its base, as in fig. 24, the height H E would 

 be proportionally less ; and if the base were very small in reference to the 

 height, as in fig. 25, the height H E would be very small, and a slight force 

 would throw it over the edge B. 



> It is obvious that the same observations may be applied to all figures what- 

 ever, the conclusions just deduced depending only on the distance of the line 

 of direction from the edge of the base, and the height of the centre of gravity 

 above it. 



Hence we may perceive the principle on which the stability of loaded car- 

 riages depends. When the load is placed at a considerable elevation above 

 the wheels, the centre of gravity is elevated, and the carriage becomes pro- 

 portionally insecure. In coaches for the conveyance of passengers, the lug- 



