60 POPULAR LECTURES AND ADDRESSES. 



the inverse square of the distance, when the dis- 

 tance is diminished below some very small limit. 

 This view might, indeed, seem inevitable, unless 

 the idea of " attraction " is to be discarded alto- 

 gether ; because the law of attraction at sensible 

 distances the Newtonian law demonstrated by 

 its discoverer for distances not incomparably 

 smaller than the earth's dimensions, and verified 

 by Maskelyne and Cavendish in a manner ren- 

 dering it impossible for any naturalist to reason- 

 ably doubt its applicability to the mutual action 

 between particles a few hundred yards or a few 

 inches asunder, seems to give only very small, 

 scarcely appreciable, forces between bodies of 

 such masses as those we experiment on in our 

 laboratories, everywhere placed as close as possi- 

 ble to one another that is to say, in contact ; and 

 does not seem to provide for any considerable 

 increase of attraction when the area of contact 

 is increased, whether by pressing the bodies toge- 

 ther, or by shaping them to fit over a large 

 area. 



But if we take into account the heterogeneous 

 distribution of density essential to any molecular 

 theory of matter, we readily see that it alone is 

 sufficient to intensify the force of gravitation 

 between two bodies placed extremely close to 

 one another, or between two parts of one body, 

 and therefore that cohesion may be accounted for 

 without assuming any other force than that o 1 



