556 Professor Tyndall [Jan. 22, 



the whole career of life in the midst of labours of the body and efforts 

 of the mind ; whom neither tranquillity nor relaxation, nor the flat- 

 tering attentions of his equals in age and station, nor public games 

 nor banquets would delight; who would regard nothing in life as 

 desirable which was not united with dignity and virtue ; — such a man 

 I regard as being, in my judgment, furnished and adorned with some 

 special gifts of the gods." 



His medical studies were pursued with the same thoroughness 

 which marked everything Young took in hand. He was an assiduous 

 attendant at the best lectures. His delight in optics naturally drew 

 him to investigate the anatomical structure of the eye. In regard to 

 this structure most of you will remember that in front is the cornea, 

 holding behind it the aqueous humour ; then comes the iris, surround- 

 ing the aperture called the pupil, at the back of which we have the 

 beautiful crystalline lens. Behind this, again, is the vitreous humour 

 which constitutes the great mass of the eye. Thus, optically con- 

 sidered, the eye is a compound lens of great complexity and beauty. 

 Behind the vitreous humour is spread the screen of the retina, woven 

 of fine nerve-fibres. On this screen, when any object looked at is 

 distinctly seen, a sharply defined image of the object is formed. 

 Definition of the image is necessary to the distinctness of the vision. 

 Were the optical arrangements of the eye rigid, distinct vision would 

 be possible only at one definite distance. But the eye can see dis- 

 tinctly at different distances. It has what the Germans call an 

 Accommodations Vermogen — a power of adjustment — which liberates 

 it from the thrall of rigidity. By what mechanical arrangement is 

 the eye enabled to adjust itself both for near and distant objects ? 

 Young replied, " By the alteration of the curvature of the crystalline 

 lens." His memoir on this subject was considered so meritorious, 

 that it was printed in the ' Transactions of the Royal 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. Ramsden, 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 crystal- 

 line lens had been removed, they affirmed to be capable of adjust- 

 ment. 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 lengthened, 

 the retina or screen being thereby thrown further back. In distant 



