GRAVITATION 



tions to the remark that all bodies on or near the surface 

 of the earth, tend to move towards it. Smoke ascends ; 

 vapors rise ; clouds float gently in the sky ; and bal- 

 loons, filled with peculiar gases, soar into the air, bear- 

 ing with them heavy burdens. These, however, far from 

 being exceptions to the rule, are only instances of its 

 perfect operation. A block of wood, though it has in 

 itself a tendency to fall, will rise to the surface of the 

 water, into which it is plunged. The water having a 

 stronger tendency to move towards the earth, presses 

 down under it, and it rises by the very power of gravita- 

 tion itself. The gravitating air, in the same manner, 

 forces up the vapor, the smoke and the balloon, all of 

 which would fall with the rapidity of a stone, if nothing 

 resisted their motion. 



4. GRAVITATION BETWEEN SMALL BODIES AND PARTS 

 OP THE EARTH. 



The facts which have been mentioned under the pre- 

 ceding heads, show the existence and the power of grav- 

 itation in cases so numerous and diversified as to render 

 it highly probable that this force is a universal property 

 of matter. There remains, however, much to be added 

 to the evidence ; and one very interesting class of exper- 

 iments are those which show the attracting power of 

 mountains. It was suggested by Newton, that if the 

 law which he discovered were a universal law, a plumb 

 line suspended by the side of a mountain, would deviate 

 from a perpendicular by the attraction of the mountain. 

 The experiment has since been made in two instances, 

 and with complete success. It was first tried in South 

 America, by the side of the celebrated Mountain, Chim- 

 borazo, by some French Mathematicians. It was ascer- 

 tained by very accurate experiments that a plumb line 

 suspended near the mountain was drawn out of its per- 

 pendicular towards the mountain eight seconds. This, it 

 will be perceived, is a very small angle, and the deviation 

 would be expected to be small, if we consider how small 

 is the mountain compared with the whole bulk of the 

 earth. There is every reason to place confidence in the 

 correctness of the result. 



