THE USE OF HYPOTHESIS. 135 



expression experimentum crucis in his ' Opticks/ but 

 this is the only expression, so far as I am aware, which 

 could indicate on the part of Newton direct or indirect 

 acquaintance with Bacon's writings b . 



Other great physicists of the same age were equally 

 prone to the use of hypotheses rather than the blind 

 accumulation of facts in the Baconian manner. Hooke 

 emphatically asserts in his posthumous work on Philo- 

 sophical Method, that the first requisite of the Natural 

 Philosopher is readiness at guessing the solution of many 

 phenomena and making queries. * He ought to be very 

 well skilled in those several kinds of philosophy already 

 known, to understand their several hypotheses, sup- 

 positions, collections, observations, &c., their various ways 

 of ratiocinations and proceedings, the several failings and 

 defects, both in their way of raising, and in their way of 

 managing their several theories : for by this means the 

 mind will be somewhat more ready at guessing at the 

 solution of many phenomena almost at first sight, and 

 thereby be much more prompt at making queries, and at 

 tracing the subtlety of Nature, and in discovering and 

 searching into the true reason of things.' 



We find Horrocks, again, than whom no one was more 

 filled with the scientific spirit, telling us how he tried 

 theory after theory in order to discover one which was in 

 accordance with the motions of Mars c . It might readily 

 be shown again that Huyghens, who possessed one of the 

 most perfect philosophical intellects, followed the deductive 

 process combined with continual appeal to experiment, 

 with a skill closely analogous to that of Newton. As to 

 Descartes and Leibnitz, their investigations were too much 

 opposed to the Baconian rules, since they too often 



b See ' Philosophical Transactions/ abridged by Lowthorp. 4th edit, 

 vol. i. p. 130. 



c Horrocks, ' Opera Posthuma' (1673), p. 276. 



