254 THOMAS YOUNO. 



printed in the 'Transactions of the Eoyal Society'; 

 and in the year following, at the age of twenty-one, he 

 was elected a Fellow of the Society. 



Young's memoir evoked sharp discussion, both as 

 regards the priority and the truth of the discovery. It 

 was claimed by John Hunter, while its accuracy was 

 denied by Hunter's brother-in-law, Sir Everard Home, 

 who, jointly with Mr. Kamsden, affirmed that the 

 adjustment of the eye depended on the changed 

 curvature of the cornea. A couched eye that is to say, 

 an eye from which the crystalline lens had been re- 

 moved they affirmed to be capable of adjustment. In 

 the face of such authorities Young, with the candour 

 of a true man of science, abandoned the views he had 

 enunciated. But it was only for a time. He soon 

 resumed his inquiries, and proved to demonstration 

 that couched eyes had no trace of the power ascribed 

 to them. Before the time of Young, moreover, weighty 

 authorities leaned to the view that the adjustment of 

 the eye depended on the variation of the distance 

 between the cornea and the retina. When near objects 

 were viewed, it was thought that the axis was length- 

 ened, the retina or screen being thereby thrown farther 

 back. In distant vision the reverse took place. But 

 Young proved beyond a doubt that no such variation in 

 the length of the axis of the eye occurs ; and this has 

 been verified in our own day by Helmholtz. The change 

 in the curvature of the crystalline lens has been also 

 verified by the most exact experiments. When we pass, 

 for instance, from distant to near vision, the image of a 

 candle-flame reflected from the front surface of the lens 

 becomes smaller, proving the lens to be then more 

 sharply curved. When we pass from near to distant 

 vrsion, the image becomes larger, proving the curvature 

 of the lens to have diminished. The radius of curvature 



