EMPIRICAL KNOWLEDGE, EXPLANATION, &c. 173 



1759, and though Halley did not live to enjoy the sight, 

 it was actually detected on the night of Christmas-day, 

 1758. A second return of the comet was witnessed in 

 1835 nearly at the time anticipated. 



In recent times the discovery of Neptune has been the 

 most remarkable instance of prevision in astronomical 

 science. A full account of this discovery may be found 

 in several works, as for instance Herschel's ' Outlines of 

 Astronomy' and 'Grant's History of Physical Astronomy/ 

 Chapters xn and xin. 



Predictions in the Science of Light. 



Next after astronomy the science of physical optics has 

 furnished the most beautiful and early instances of the 

 prophetic power of correct theory. These cases are the 

 more striking because they proceed from the profound 

 application of mathematical analysis, and show an insight 

 into the mysterious workings of matter which is sur- 

 prising to all, but especially to the great majority of men 

 who are unable to comprehend the methods of research 

 employed. By its power of prevision the truth of the 

 undulatory theory of light has been conspicuously proved, 

 and it is especially to be remarked that even Newton 

 received no assistance from his Corpuscular theory in the 

 detection of new experiments. To his followers who 

 embraced that theory we owe little or nothing in the 

 science of light, and even the lofty genius of Laplace did 

 not derive from it a single discovery. As Fresnel himself 

 remarks : 



' The assistance to be derived from a good theory is 

 not to be confined to the calculation of the forces when 

 the laws of the phenomena are known. There are certain 

 laws so complicated and so singular, that observation 



Taylor's < Scientific Memoirs,' vol. v. p. 241. 



