10 THE EXTERIOR OF THE HORSE. 



2.-ELEVATION OF THE HEIGHT AT THE CROUP. 



Let us see now what is understood by the terms equilibrium and base of 

 support. 



Equilibrium in mechanics is the state of a body induced by the forces 



which destroy one another or which are 

 annulled by a resistance (Littre). 



In animals the body seldom rests upon 

 the ground by a continued surface (decubitus). 

 It is supported by four broken columns ar- 

 ticulated from distance to distance and desig- 

 nated by the name of members. The polygon 

 formed by the lines joining the four points 

 which touch the ground at rest represents 

 what is called the base of support. This 

 polygon is sometimes a triangle; at other 

 times the base of support is reduced to a 

 line ; finally it may -be only a point. What- 

 ever may be the form and extent of the base 

 of support, it is necessary, in order to obtain 

 equilibrium, that the line of gravitation does 

 not meet the ground outside of this base. 



The equilibrium will be so much more 

 stable as the base of support becomes larger, 

 the centre of gravity placed lower, and the 

 line of gravitation nearer the centre of the 

 base. It will be unstable in the contrary con- 

 ditions. In fact, in the solid here represented 

 (Fig. 3) it will be seen that if the centre of 



gravity is displaced from A to (7, having reached to the point (7, the slightest 

 oscillation of one side or the other, (7(7 for example, will cause the line of 



