16 SCIENTIFIC THOUGHT. 



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 



10. labours of Biot in France and Brewster in this country ; 



Biot, 



Brewster, whilst no doubt Laplace's great predilection for atomic 



and Laplace 



tmdniatory an( ^ 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 



11. the subject of detailed study by Huygens, Newton's 



Euler the 



successor 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 vibrations ; but 

 the first great step in advance, based upon experiment 



12. and calculation alike, was taken by Dr Young, who 



Young. 



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, 1 a province where 



1 In his ' Reply to the Edinburgh 

 Reviewers ' (published as a pam- 

 phlet in 1804, see Works, ed. 

 Peacock, vol. i. pp. 192-215), Young 

 gives the following history of his 

 speculations : " When I took a 



degree in physic at Gottingen, it 

 was necessary, besides publishing a 

 medical dissertation, to deliver a 

 lecture upon some subject connected 

 with medical studies, and I chose 

 for this the Formation of the Human 



