220 COSMICAL ARRANGEMENTS. 



always at the same points of the orbit. There is 

 indeed a slight alteration in these points, arising 

 from disturbing forces, but this is hardly sensible 

 in the course of several ages. Now if the force 

 had followed any other law, we should have had 

 the earth running perpetually on a new track. 

 The greatest and least distances would have 

 occurred at different parts in every successive 

 revolution. The orbit would have perpetually 

 intersected and been interlaced with the path 

 described in former revolutions; and the sim- 

 plicity and regularity which characterises the 

 present motion would have been quite wanting. 



3. Another peculiar point of simplicity in the 

 present law of mutual attraction is this : that it 

 makes the law of attraction for spherical masses 

 the same as for single particles. If particles 

 attract with forces which are inversely as the 

 square of the distance, spheres composed of such 

 particles will exert a force which follows the same 

 law. In this character the present law is singular, 

 among all possible laws, excepting that of the 

 direct distance which we have already discussed. 

 If the law of the gravitation of particles had been 

 that of the inverse simple distance, the attraction 

 of a sphere would have been expressed by a 

 complex series of mathematical expressions, each 

 representing a simple law. It is truly remarkable 

 that the law of the inverse square of the distance, 

 which appears to be selected as that of the 



