London Philosophical Society. 387 



logy of an organ, it is necessary to consider its anatomy: 

 the lecture, therefore, commenced by a very accurate and 

 perspicuous description of the anatomy of the Eye, and 

 its adjacent parts. As he proceeded to demonstrate the 

 various parts of this most beautiful organ, he noticed the 

 appearance and pecuharities of them in different animals, 

 showing their adaptation to the elements in which they 

 exist. 



Having explained the anatomy, Mr. P. proceeded to elu- 

 cidate the action of the eye by physical experiments, and, 

 after examining the nature of light and colours, applied it 

 to the subject of vision. Here he enlarged on the power 

 of the eye, by which it adjusts itself to the distinct per- 

 ception of objects ; and having noticed the opinions of 

 Kepler, Le Cat, Des Cartes, Young, Pemberton, and some 

 others, from the lately discovered muscle, by Mr. Campion, 

 in an eagle, which is attached to the sclerotica, capable of 

 producing; the change in the focal distance, inferred that 

 something analogous might exist in the human species, 

 which would perform the three changes suggested by Mr. 

 Ramsden and Mr. Home, viz. a motion of the crystalline 

 lens — an elongation of the axis of vision — and an increase 

 of curvature in the cornea. 



From this subject the learned author proceeded to con- 

 sider the theory of Hartley, on the manner in which the 

 rays of light in falling upon the bottom of the eye excite 

 Vibrations in the tunica retina, which he seemed much dis- 

 posed to coincide with; — the myoplic and presbyoptic 

 slates of the eye, with their remedies ; — and the manner in 

 which the optic imace is reverted. After examining the 

 different suggestions on this latter important subject, he 

 determined the theory of Mr. A. Walker, of Edinburgh, 

 to be the most rational and deserving of attention. We 

 shall close this article by submitting a few extracts from 

 3\Ir. W.'s work, selected by the lecturer*. 



Mr. W. supposes " the eye to be acted on by light pre- 

 cisely as some kinds of the reflecting telescope, which, after 

 rcceivina the image inverted upon its interior lens, reflects 

 and reverses it upon its exterior lens, and permits it to be 

 seen in its natural situation. In the same way, the interior 

 part of the retina, having received the image inverted, re- 

 flects, reverses, and presents it in its natural position upon 

 its anterior part." 



" The anatomical fact, that, at the posterior part of the 



• See Archives of Universal Science, vol.ii. April 1809, p. 162. 



retina. 



