220 PHYSICAL SCIENCE 



At this point we reach for the first time in 

 our inquiry the idea of an all-pervading medium 

 • — an idea which has played such a large part in 

 the development of physical science, that a con- 

 siderable digression will be necessary. Newton 

 explained the phenomena of light by a corpuscular 

 theory. He supposed that streams of corpuscles 

 were projected from luminous objects, and pro- 

 duced the sensation of sight by impinging on the 

 nerves of the eye. Ultimately Newton's theory 

 was abandoned, mainly for two reasons. The 

 phenomena of refraction could only be explained by 

 it on the assumption that the corpuscles travelled 

 more quickly in dense media than in air, and this, 

 always improbable, was eventually disproved. On 

 the other hand, the theory failed to explain the 

 phenomena of interference and diffraction of 

 light, except by the addition of so many 

 arbitrary supplementary hypotheses, that, in the 

 end, it was borne down by the weight of its 

 own superstructure. 



This illustrates a case, oft recurring, not only 

 in the realm of science, where men have been 

 deceived and led to form opinions wide of the 

 truth through the agency of certain resemblances 

 to that truth. The corpuscular theory of light 

 was put aside, but not before it had appreciably 

 retarded the progress of science. The master- 

 mind, the originator of the theory, had been 

 withdrawn before altered circumstances and in- 

 creased knowledge reversed the weight of evidence. 

 He who would have been the first to detect 

 the want of harmony, the first to move on to 

 new conceptions in the search for truth, by the 

 irony of fate, became for a time, in virtue of his 



