EXPLANATION OF LAWS. 555 



motion is resolved, namely, the law of the permanence 

 of rectilineal motion, and the law of an uniform cen- 

 tripetal force. If, therefore, in the course of ages, 

 some circumstance were to manifest itself which, 

 without* defeating the law of either of those forces, 

 should merely alter their proportion to one another, 

 (such as the shock of a comet, or even the accumu- 

 lating effect of the resistance of the medium in which 

 astronomers have been led to surmise that the motions 

 of the heavenly bodies take place) ; the elliptical 

 motion might be changed into a motion in some other 

 curve ; and the complex law of the heavenly motions, 

 as at present understood, would be deprived of its 

 universality, although the discovery would not at all 

 detract from the universality of the simpler laws into 

 which that complex law is resolved. The law, in 

 short, of each of the concurrent causes remains the 

 same, however their collocations may vary ; but the 

 law of their joint effect varies with every difference in 

 the collocations. There needs no more to show how 

 much more general the elementary laws must be, than 

 any of the complex laws which are derived from them. 



5. Besides the two modes which have been 

 treated of, there is a third mode in which laws are 

 resolved into one another; and in this it is self- 

 evident that they are resolved into laws more general 

 than themselves. This third mode is the subsumption 

 (as it has been called) of one law under another; 

 or (what comes to the same thing) the gathering up 

 of several laws into one more general law which 

 includes them all. The most splendid example of this 

 operation was, when terrestrial gravity and the central 

 force of the solar system were brought together 



