SCIENTIFIC INVESTIGATION 39 



lar delusion that the scientific inquirer is under a sort 

 of moral obligation to abstain from going beyond that 

 generalisation of observed facts which is absurdly called 

 "Baconian" induction. 3 But any one who is practically 

 acquainted with scientific work is aware that those who 

 refuse to go beyond fact, rarely get as far as fact; and 

 any one who has studied the history of science knows 

 that almost every great step therein has been made by the 

 " anticipation of Nature," that is, by the invention of 

 hypotheses, which, though verifiable, often had very 

 little foundation to start with; and, not unfrequently, 

 in spite of a long career of usefulness, turned out to 

 be wholly erroneous in the long run. 



The geocentric system of astronomy, with its ec- 

 centrics and its epicycles, was an hypothesis utterly at 

 variance with fact, which nevertheless did great things 

 for the advancement of astronomical knowledge. 

 Kepler 4 was the wildest of guessers. Newton's corpus- 

 cular theory of light was of much temporary use in 

 optics, though nobody now believes in it; and the un- 

 dulatory theory, which has superseded the corpuscular 

 theory and has proved one of the most fertile of in- 

 struments of research, is based on the hypothesis of 

 the existence of an "ether," the properties of which are 

 defined in propositions, some of which, to ordinary ap- 

 prehension, seem physical antinomies. 



It sounds paradoxical to say that the attainment of 

 scientific truth has been effected, to a great extent, by 

 the help of scientific errors. But the subject-matter of 

 physical science is furnished by observation, which can- 



3 See p. 19, n. 



4 Johan Kepler (1571-1630), a German astronomer, devoted 

 years to the observation of the orbit of Mars, with the result that 

 he announced in his Astronomia, 1609, the laws of elliptical 

 orbits, "one of the cardinal principles of modern astronomy," and 

 other important discoveries. 



