£2 REPULSION. 



base; but it will tumble or roll down, when that 

 line falls without the base. Thus the body E 

 (fig. 5.) will only slide down the inclined plane C D, 

 whilst the body B rolls down upon it. 



When the line of direction falls within the base 

 of our feet, we stand, and most firmly, when it is 

 in the middle; but when it is out of the base, we 

 immediately fall. And it is amusing to reflect 

 upon the various methods and postures which we 

 use, to retain this position, or to recover it when 

 lost, without our being sensible of it. Thus we 

 bend our body forward when we rise from a chair, 

 or when we go up stairs; and for this purpose a 

 man leans forward when he carries a burden upon 

 his back, and backward when he carries it on his 

 breast; and to the right or left side, as he carries 

 it on the opposite side. 



Many of the feats of balancing depend solely 

 upon this principle. 



REPULSION. 



As observation has shewn us, that there are 

 powers in nature, by which not only the larger 

 masses, but also the smaller portions of matter have 

 a general tendency to approach each other, so the 

 same experience convinces us that matter is, in 

 some cases, endowed with a repulsive power, by 

 which the parts recede or fly off from each 

 other. Striking instances of this may be seen in 

 the magnet, when the disagreeing poles are pre- 

 sented to each other ; and also in electricity. It 

 would appear that all, or most bodies, are sur- 

 rounded by a power of repulsion, by which they 

 are prevented from being in actual contact, even 

 when they appear to the sight to touch : and it 

 may be calculated, that it requires a considerable 



