THE CENTRE OF GRAVITY. 



201 



which tlie stability of loaded carriages depends. 

 When the load is placed at a considerable ele- 

 vation above the wheels, the centre of gravity is 

 elevated, and the carriage becomes proportion- 

 ally insecure. In coaches for the conveyance 

 of passengers, the luggage is therefore some- 

 times placed below the body of the coach ; light 



Fig 



parcels of large bulk may be placed on the top 

 ■with impunity. 



When the centre of gravity of a carriage is 

 much elevated, there is considerable danger of 

 overtlirow, if a comer be turned sharply and 

 with a rapid pace ; for the centrifugal force then 

 acting on the centre of gravity will easily raise 

 24. 



'--::^c 



it through the small hight which is necessary 

 to turn the carriage over the external wheels. 



The same wagon Fig. 25. 



will have greater sta- 

 bility when loaded 

 with aheavy substance 

 which occupies a 

 small space, such as 

 metal, than when it 

 carries the same 

 weight of a lighter 

 substance, such as hay; 

 because the centre of 

 gravity in the latter 

 case will be much 

 more elevated. "!E 



If a large table be .-•^ •• 

 placed upon a single " jgti 

 leg in its centre, it will 

 be impracticable to 

 make it stand firm ; 

 but if the pillar on 

 which it rests termi- 

 nate in a tripod, it will 



have the same stabili- 

 ty as if it had three legs attached to the points 

 directly over the places where the feet of the 

 tripod rest. 



When a solid body is supported by more 



points than one, it is not necessary for its sta- 

 bility that the line of direction should fall ou one 

 of those points. If there be only two points of sup- 

 port, the lino direction must fall between them. 

 The body is in this case supported as effectually 

 as if it rested on an edge coinciding with a 

 straight line drawn from one point of support to 

 the other. If there be throe points of support, 

 which are not ranged in the same straight line, 

 the body will be supported in the same manner 

 as it would be by a base coinciding with the 

 triangle formed by straight lines joining the 

 three points of support. In the same manner, 

 whatever be the number of points on ^vhich the 

 body may rest, its virtual base will be found by 

 supposing straight lines drawn, joining the sev- 

 eral points succe.ssivelJ^ When the line of di- 

 rection falls within this base, the body will al- 

 ways stand firm, and otherwise not. The de- 

 gree of stability is detenniued in the same man- 

 ner as if the base %vere a continued surface. 



Necessity and experience teach an animal to 

 adapt its postures and motions to the position of 

 the centre of gravity of his body. W hen a man 

 stands, the line of direction of his weight must 

 fall \\"ithiu the base fonned by his feet. If A B 

 C D, fig. 26, be the feet, this base is the space A 

 BCD. It is evident that the more his toes are 

 turned outward, the more contracted the base 



JD 



G 



,1: 



« 



F 



will be in the direction E F, and the more lia- | H. and the more liable he will be to fall toward 

 ble he will be to fall backward or forward. — I cither side. 



Also the closer his feet are together, the more "When a man walks, tlie legs are alternately 

 contracted the base will be m die direction G | lifted from the ground, and the centre of gravi- 



(10.-,) 



