GRAVITATION. 35 



CHAPTER III. 



ATTRACTION. 



SECTION I. 

 GRAVITATION. 



The earth, as is well known, is a mass of matter in 

 the form of a globe, the diameter being upward of 

 7900 miles. From its enormous size and the small 

 portion seen from one point, the surface appears flat, 

 except where broken into mountains and valleys. 



The tendency which all bodies possess of faUing to- 

 ward the earth is owing to the attractive force which 

 this great mass of matter exerts upon them. This kind 

 of attraction is called gravitation. The force with 

 which a body is thus drawn is the weight of that body. 



When a stone is dropped from the hand, its velocity 

 is at first slow, but continues to increase till it strikes 

 the earth ; hence, the further it falls, the harder it will 

 strike. This accelerated motion is precisely similar to 

 that of a steam-boat when it first leaves the wharf; the 

 force of gravity may be compared to the driving power 

 of the engine, and the quickened velocity of the falhng 

 stone to the increased headway of the boat. 



All bodies, whether large or small, fall equally fast, 

 unless they are so light as to be borne up in part by 

 the resistance of the air. In the first second of time 

 they fall 16 feet ; in the next second, 3 times 16, or 

 48 feet ; in the third second, 5 times 16, or 80 feet, and 

 so on. Or, if the whole distance fallen be taken togeth- 



