THE DEDUCTIVE METHOD. 517 



what the method has done for us, from the case of the celestial 

 motions ; one of the simplest among the greater instances of 

 the Composition of Causes, since (except in a few cases not 

 of primary importance) each of the heavenly bodies may he 

 considered, without material inaccuracy, to be never at one time 

 influenced by the attraction of more than two bodies, the sun 

 and one other planet or satellite ; making, with the reaction of 

 the body itself, and the force generated by the body's own 

 motion and acting in the direction of the tangent, only four 

 different agents on the concurrence of which the motions of that 

 body depend ; a much smaller number, no doubt, than that by 

 which any other of the great phenomena of nature is determined 

 or modified. Yet how could we ever have ascertained the 

 combination of forces on which the motions of the earth and 

 planets are dependent, by merely comparing the orbits or velo- 

 cities of different planets, or the different velocities or positions 

 of the same planet ? Notwithstanding the regularity which 

 manifests itself in those motions, in a degree so rare among 

 the effects of a concurrence of causes ; and although the 

 periodical recurrence of exactly the same effect, affords positive 

 proof that all the combinations of causes which occur at all, 

 recur periodically; we should not have known what the 

 causes were, if the existence of agencies precisely similar on 

 our own earth had not, fortunately, brought the causes them- 

 selves within the reach of experimentation under simple 

 circumstances. As we shall have occasion to analyse, further 

 on, this great example of the Method of Deduction, we shall 

 not occupy any time with it here, but shall proceed to that 

 secondary application of the Deductive Method, the result of 

 which is not to prove laws of phenomena, but to explain 

 them. 



