XXIII -J _ THE USE OF HYPOTHESIS. 517 



Almost every problem in science thus takes the form of 

 a balance of probabilities. It is only when difficulty 

 after difficulty has been successfully explained away and 

 decisive experimenta erucis have, time after time resulted 



a35 that we ca -* to ^ 32 



The sole real test of an hypothesis is its accordance 



S ? ?' ?t CarteS celebrated Astern of vortices is 

 exploded, not because it was intrinsically absurd and 

 inconceivable, but because it could not give results in 

 accordance with the actual motions of the heavenly bodieT 

 The difficulties of conception involved in the apparatus 

 of vortices are child's play compared with those of gravi- 

 tation and the undulatory theory already descS 

 Vortices are on the whole plausible suppositions; for 

 planets and satellites bear at first sight much resemblance 

 to objects carried round in whirlpools, an analogy which 

 doubtless suggested the theory. The failure wafin he 

 first and third requisites; for, as already remarked, the 

 theory did not allow of precise calculation of planetary 

 motions and was thus incapable of rigorous verification 

 tfutso far as we can institute a comparison, facts are en- 

 toely against the vortices. Newton did not ridicule the 

 theory as absurd, but showed 1 that it was "pressed with 

 many difficulties." He carefully pointed ouT that the 

 Cartesian theory was inconsistent with the laws of Kepler 

 and would represent the planets as moving more rapidly 

 at their aphelia than at their perihelia^ The rotatory 

 motion of the sun and planets on their own axes is in 

 striking conflict with the revolutions of the satellites 

 carried round them ; and comets, the most flimsy of bodies 

 calmly pursue their courses in elliptic paths, irrespective 

 of the vortices which they pass through. We may now 

 also point to the interlacing orbits of "the minor planets 



ln ^ ^" f the 



Newton though he established the best of theories, was 



!0 capable of proposing one of the worst; and if we 



rant an instance of a theory decisively contradicted by 



iii '. Pro P- 43- General Scholium. 



2 '-' '. ro P- 43- 



n. Sect. ix. Prop. 53. 



