MOTION, MECHANICS, 



ETC. 



. Inertia Apparatus. Inertia is that 

 property of matter by which it resists 

 any change of state, whether of rest 

 or motion. 



This interesting piece of appara- 

 tus (Fig. 144) consists of a common 

 card and a brass ball of one inch or 

 more in diameter, supported on a 

 short pillar with a suitable base. To 

 one side of the base there is fixed a 

 steel spring, and a lever for drawing it back : on drawing 

 the spring and suddenly relieving it, the card is struck and 

 driven from under the ball off the pillar, while the ball rests 

 on the pillar as firmly as though the card had not been 

 knocked from under it. Price, $1.50. 



Fig. 145. 



Adhesion Plates. These consist of two plates of glass 

 (Fig. 145), with knobs for handles, the flat surfaces ground 

 perfectly true. On pressing these together, they can be 

 separated only by the exertion of considerable force, the 



