190 THE PHENOMENA OF MOTION 



the senses when the stone, for example, rests upon a 

 table, the particles of which oppose a resistance to the 

 manifestation of its gravitation. The force of gravity, 

 however, is constantly present, and manifests itself as a 

 pressure on the supporting body ; but the stone remains 

 at rest ; it has no motion. The manifestation of its 

 gravity in the state of rest, we call its weight. 



That which prevents the stone from falling is a re- 

 sistance produced by the force of attraction, by which 

 the particles of the wood cohere together ; a mass of 

 water would not prevent the fall of the stone. 



If the force which impelled the mass of the stone 

 towards the centre of the earth were greater than the 

 force of cohesion in the particles of the wood, the latter 

 would be overcome ; it would be unable to prevent the 

 fall of the stone. 



When we remove the support, and with it the force 

 which has prevented the manifestation of the force 

 of gravity, the latter at once appears as the cause of 

 change of place in the stone, which acquires motion, or 

 falls. Resistance is invariably the result of a force in 

 action. 



According as the stone is allowed to fall during a 

 longer or shorter time, it acquires properties which it had 

 not while at rest ; it acquires, for example, the power 

 of overcoming more feeble or more powerful obstacles, 

 or that of communicating motion to bodies in a state 

 of rest. 



If it fall from a certain height it makes a permanent 

 impression on the spot on which it falls ; if it fall from a 



