1886.] on Thomas Young. 557 



vision the reverse took place. But Young proved beyond a doubt that 

 no sucli 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 vision, the 

 image becomes larger, proving the curvature of the lens to have 

 diminished. The radius of curvature of the lens under these cir- 

 cumstances has been shown to vary from six to ten millimetres. 

 The theory of Young, therefore, with regard to the adjustment of 

 the eye, has been completely vei-ified. But it is still a moot point as 

 to what the mechanism is by which the change of curvature is pro- 

 duced. Young thought that it was effected by the muscularity of 

 the lens itself. The muscles, however, would require nerves to 

 excite them, and it would be hardly possible, in the transparent 

 humours of the eye, for such nerves to escape detection. They, 

 however, have never been detected. 



While passing through Bath in 1794, Young, at the instance of 

 Dr. Brocklesby, called upon the Duke of Eichmond. The impression 

 made by Young at this time may be gathered from a note addressed 

 by the Duke to the Doctor, in these terms : — " But I must tell you how 

 pleased we all are with Mr. Young. I really never saw a young man 

 more pleasing and engaging. He seems to have already acquired 

 much knowledge in most branches, and to be studious of obtaining 

 more. It comes out without affectation on all subjects he talks upon. 

 He is very cheerful and easy, without assuming anything ; and even 

 on the peculiarity of his dress and Quakerism, he talked so reasonably, 

 that one cannot wish him to alter himself in any one particular. In 

 short, I end, as I began, by assuring you that the Duchess and I are 

 quite charmed with him." The Duke, then Master of the Ordnance, 

 was a very competent man. He was well acquainted with the 

 instruments used in the great Trigonometrical Survey under his 

 control. He offered to Young the post of private secretary. Young's 

 acceptance would have brought within his reach both honour and 

 emolument. But, to his credit be it recorded, he refused the post, 

 because its acceptance would have rendered necessary the abandon- 

 ment of his costume as a member of the Society of Friends. Soon 

 afterwards, he paid a visit to a celebrated cattle-breeder near Ash- 

 bourne, and describes with vivid interest what Mr. Bickwell had 

 accomplished by the process of artificial selection. Facts like these 

 it was which, presented afterwards to the pondering mind of Darwin, 

 caused the great naturalist to pass from artificial to natural selection. 

 Young visited Darwin's grandfather, and criticized his ' Zoonomia.' 

 The inspection of Dr. Darwin's cameos, minerals, and plants, gave 

 him great delight, the supreme pleasure being derived from the 



