APPARATUS FOR DEMONSTRATING LAWS OF MOTION. 49 



98^ each, two of l gr each, and one of 4 gr , having the 

 form shown at u, are required. A perpendicular scale, 

 l m *5 long, is divided into half- decimetres, and the brass 

 plate J3. which is suspended by three threads, and 



FIG. 43 (an. proj. i real size). 



has a hole in the middle, may be moved along the scale 

 and held in front of it at any required height by means 

 of a counterpoise. 



An apparatus is also required for measuring time. 

 If no clock is at hand which audibly beats seconds, a 

 pendulum, fig. 44, may be used, consisting of a leaden 



