112 BODIES SUPPORTED IN TWO POINTS. 



A remarkable behaviour is shown by a double con< 

 placed upon two inclined rails which meet at a propei 

 angle. The arrangement is represented in fig. 80, at 

 in an isometric projection, at B when viewed from tl 

 side, and at C when viewed from above. 



The inclined rails are formed by the upper edges 

 two equal small boards, joined at their lower ends, while 

 their upper ends are about as far apart as the distant 

 between the two points of the double cone. Th< 

 difference in the height of both ends of the rails 

 less than half the width of the double cone at its widest 

 part ; in the figure the heights are 7 and 4 cm> 5, the 

 difference therefore 2 cm *5, while the double cone is 

 28 cm long, and 10 cm wide in the middle, the half- 

 width therefore 5 cm . If the double cone be placed 

 upon the rails in such a manner that the line joining 

 its points is parallel to the line joining the upper ends 

 of the rails, it will run up the inclined plane, ap- 

 parently in opposition to the direction in which it 

 is acted upon by gravity. Close observation shows, 

 however, that the cone really descends, although 

 it moves towards the higher end of the rails. Tim 

 is still more distinctly seen from fig. 80, B. At the 

 lower end the cone rests upon the rails at its middle 

 the distance of the centre of gravity from the horizonta 

 plane is there 4*5 + 5 = 9 cm *5. At the upper end tin 

 cone rests at its extremities: the distance of the centr* 

 of gravity from the same horizontal plane is there onb 

 7 cm . Again, the centre of gravity of the homogeneou 

 and regular double cone is its centre, s, the vertica 

 through 5, sa in B, is the line of gravitation, but th 

 line of support, bb in (7, lies somewhat to the right o 



