BODIES SUPPORTED IN TWO POINTS. 



113 



sa, as will be best seen when the cone is carefully 

 observed while on the rails, hence the cone moves 

 towards the left. 



The rails are formed by two boards of the shape of A in fig. 81, 

 40 cm long ; the lower ends are joined by a piece of linen glued over 



P 



FIG. 81 (I real size}. 



the edges, the upper ends are kept apart by a board of the shape of J5 

 in fig. 81, 28 cm long, or by a piece of cord of the proper length. 

 Stout pasteboard may be used for the rails, if thin wooden boards 

 cannot be obtained. The double cone is best made of wood by a 

 turner, but it may also be made hollow of pasteboard. This may be 

 done in the following manner. With a radius of 15 cm describe the arc 

 aid, fig. 82 ; measure off 

 ab and Id, each equal to the 

 radius ; join a and d to c by 

 straight lines. Cut the ob- 

 tained figure twice of card- 

 board, and apply glue along 

 etc and cd, after having bent 

 each figure in the shape of 

 a cone. Unless the card- 

 board is very stout, little 

 iaps may be left, as shown FlG - 82 (I real si * e ) 



the figure, for joining ac and cd. Small triangular flaps should 

 be left along the arc of one of the figures : they serve for 

 -ttaching both cones at their bases. The flaps are slightly bent 

 awards, so as to fit into the interior of the other cone, along the 

 >ase of which, inside, a layer of glue has been spread. The joints 

 f the two cones should be on opposite sides, or otherwise the 

 'litre of gravity will not be in the centre. 



If a body is supported in three or more points, or 



