ATTRACTION OF GRAVITATION. 81 



of the distance, we mean, that if one body, or substance, attracts another body 

 with a certain force at the distance of a mile, it will attract with four times 

 that forc^ at half a mile, nine times the force at one third of a mile, and so 

 on, in like proportion. On the contrary, it will attract with but one fourth of 

 the force at two miles, one ninth of the force at three miles, one sixteenth of 

 ttLQ force at four miles, and so on, as the distance increases. 



Pj(j 3 This law may be further 



illustrated by reference to 



9 Fig. 3. Let C be the center 



^~~*~;^"— / of attraction, and let the four 



/ . -f^-~r:::r.v ~.. dotted lines diverging from 



/j __ ..n ■::Z'-~^''^'^^'^^*^ represent lines of attraction. 



— y " „_ — -t^-' ^t a certain distance from C 



^-J^-"""" they will comprehend the 



small square A ; at twice that 

 distance they will include the large square B, four times the size of A ; and 

 since there is only a certain definite amount of attraction included within 

 these lines, it is clear that as B is four times as great as A, the attraction ex- 

 erted upon a portion of B equal to A, will be only one fourth that which it 

 would experience when in the position marked 1, just half as far from C. 



As gravitative attraction is the common property of all 

 alUwdfes up- bodies, it may be asked, why all bodies not fastened to the 

 on the earth's earth's surface do not come in contact? They would do. so, 

 in contect'?™^ were it not for the overpowering influence of the earth's at- 

 traction, which in a great measure neutralizes, or overcomes, 

 the mutual attraction of smaller bodies on its surface. 



Does a feather ^® throw up a feather into the air, and it falls through the 



attract the influence of the earth's attraction ; but as all bodies attract 



^^ each other, the feather must also attract, or draw up, the 



earth, in some degree, toward itself This it really does, with a force pro- 

 portioned to its mass ; but as the mass of the earth is infinitely greater than 

 the mass of the feather, the influence of the feather is infinitely small, and we 

 are unable to perceive it. 



In some instances, where bodies are free to move, the mu- 

 lustrations of tual attraction of all matter exhibits itself. If we place upon 

 fa^^K'^' ? '^'^ water, in a smooth pond, two floating bodies at certain dis- 

 tances from each other, they will eventually approach, the con- 

 ditions affecting the experiment being alike for each. Two leaden balls sus- 

 pended by a string near each other, are found, by delicate tests, to attract 

 each other, and therefore not to hang quite perpendicular. A leaden weight 

 suspended near the side of a mountain, inclines toward it to an extent pro- 

 portionate to the magnitude of the mountain. 



What is the '^^^ earth attracts the moon, and this in turn attracts the 



cause of earth. The solid particles of matter upon the earth's surface, 



' ®* ■ not being free to move, do not sensibly show the influe«ce of 



the moon's attraction ; but the particles of water composing the ocean, being 



