124 



THE PENDULUM. 



manifest properties which are best studied by means of 

 a simple pendulum, that is, a pendulum consisting of a 

 small heavy body suspended by a fine thread, the weight 

 of which may be neglected, as being exceedingly small 

 compared with that of the body. Such a pendulum 

 was employed in art. 12, fig. 53, but it is difficult to 



FIG. 91 (an. proj. ^ real size). 



make it swing long together in the same vertical plane; 

 the best way of confining the vibrations to one plane is 

 to hang a leaden bullet by two threads of equal length, 

 which are fastened to points a little distance apart. 

 Two such pendulums, of equal length, are suspended 

 as shown in fig. 91 ; the threads should be of very fine 

 silk, one of the pendulums consisting of a bullet of lead, 

 the other of a bullet of gypsum (plaster of Paris), both 

 being provided with small hooks. Both pendulums after 



