272 REASONING. 



(he might have added) were unable to conceive the reverse of. 

 He cannot intend to justify this mode of thought : he cannot 

 mean to say, that we can be right in regarding as inconceivable 

 what others have conceived, and as self-evident what to others 

 did not appear evident at all. After so complete an admission 

 that inconceivableness is an accidental thing, not inherent in 

 the phenomenon itself, but dependent on the mental history of 

 the person who tries to conceive it, how can he ever call upon 

 us to reject a proposition as impossible on no other ground 

 than its inconceivableness ? Yet he not only does so, but has 

 unintentionally afforded some of the most remarkable examples 

 which can be cited of the very illusion which he has himself 

 so clearly pointed out. I select as specimens, his remarks on the 

 evidence of the three laws of motion, and of the atomic theory. 

 With respect to the laws of motion, Dr. Whewell says : 

 " No one can doubt that, in historical fact, these laws were 

 collected from experience. That such is the case, is no 

 matter of conjecture. We know the time, the persons, the 

 circumstances, belonging to each step of each discovery."* 

 After this testimony, to adduce evidence of the fact would be 

 superfluous. And not only were these laws by no means 

 intuitively evident, but some of them were originally para- 

 doxes. The first law was especially so. That a body, once 

 in motion, would continue for ever to move in the same direc- 

 tion with undiminished velocity unless acted upon by some 

 new force, was a proposition which mankind found lor a long 

 time the greatest difficulty in crediting. It stood opposed to 

 apparent experience of the most familiar kind, which taught 

 that it was the nature of motion to abate gradually, and at last 

 terminate of itself. Yet when once the contrary doctrine was 

 firmly established, mathematicians, as Dr. Whewell observes, 

 speedily began to believe that laws, thus contradictory to first 

 appearances, and which, even after full proof had been ob- 

 tained, it had required generations to render familiar to the 

 minds of the scientific world, were under " a demonstrable 

 necessity, compelling them to be such as they are and no 



. * History of Scientific Ideas, i. 264. 



