16 



SCIENTIFIC THOUGHT. 



10. 

 Biot, 

 Brewster, 

 and Laplace 



against the 

 undulatory 

 theory. 



11. 

 Euler the 

 successor 

 of Huygens. 



12. 

 Young. 



far as the mathematical side was concerned — was 

 studied later. The former theory has been furthered 

 more by the ingenuity of physical observers, the 

 latter more by mathematical reasoning applied to the 

 invention of crucial experiments which pure observa- 

 tion would probably never have suggested. Since the 

 time of Newton, whose name has been used in a one- 

 sided way to discredit the vibratory theory, although, 

 as already stated, his discoveries contributed equally to 

 the formation of both views, the development of the 

 corpuscular theory owes most to the experimental 

 labours of Biot in France and Brewster in this country ; 

 whilst no doubt Laplace's great predilection for atomic 

 and astronomical explanation of all natural phenomena 

 gave it great support in the eyes of his many followers 

 and admirers. The vibratory theory was first made 

 the subject of detailed study by Huygens, Newton's 

 contemporary ; it was accepted on purely mathematical 

 grounds by Euler : the lines of reasoning on which its 

 ultimate success depended were elaborated by Lagrange's 

 and d'Alembert's mathematical study of \dbrations ; but 

 the first great step in advance, based upon experiment 

 and calculation alike, was taken by Dr Young, who 

 from 1793 onward studied the subject, and who in 

 1801 published his 'Principle of Interferences.' Young 

 was led to his reflections on the phenomena of light by 

 an inquiry into the nature of sound,^ a province where 



^ In his ' Reply to the Edinburgh degree in physic at Gottiugen, it 



Reviewers ' (published as a pam- was necessary, besides publishing a 



phlet in 1804, see Works, ed. medical dissertation, to deliver a 



Peacock, vol. i. pp. 192-215), Young lecture upon some subject connected 



gives the following history of his with medical studies, and I chose 



speculations: "When I took a for this the Formation of the Human 



