266 THOMAS YOUNG. 



fessor of Natural Philosophy was offered to Young, and 

 he accepted it. The salary was to be 300. a year. On 

 August 3, 1801, the following resolution was passed : 

 'Kesolved, that the Managers approve of the measures 

 taken by Count Rumford, and that the appointment of 

 Dr. Young be confirmed.' Young, it is said, was not 

 successful as a lecturer in the Institution, and this 

 Dr. Peacock ascribes to his early education, which gave 

 him no opportunity of entering into the intellectual 

 habits of other men. More probably the defect was 

 due to a mental constitution, not plastic, like that of 

 Davy or Faraday, in regard to exposition. Young now 

 fairly fronted the undulatory theory of light. Before 

 you is some of the apparatus he employed. I hold in 

 my hand an ancient tract upon this subject by the 

 illustrious Huyghens. It was picked up on a book- 

 stall, and presented to me some years ago by Professor 

 Dewar. In this tract Huyghens deals with refraction 

 and reflection, giving a complete explanation of both ; 

 and here, also, he enunciated a principle which now 

 bears his name, and which forms one of the foundation- 

 stones of the undulatory theory. 



The most formidable obstacle encountered by Young, 

 and one which he never entirely surmounted, was an 

 objection raised by Newton to the assumption of a fluid 

 medium as the vehicle of light. Looking at the waves 

 of water impinging on an isolated rock, Newton ob- 

 served that the rock did not intercept the wave motion. 

 The waves, on the contrary, bent round the rock, and 

 set in motion the water at the back of it. Baring 

 himself on this and similar observations, he says, 'Are 

 not all hypotheses erroneous in which light is supposed 

 to consist of a pre.^sion or motion propagated through 

 a fli id medium ? If it consisted in pression or motion, 

 it would bend into the shadow.' He instances the case 



