II. The Bakerian Lecture. On the mechanism of the eye

Abstract

I. In the year 1793, I had the honour of laying before the Royal Society, some observations on the faculty by which the eye accommodates itself to the perception of objects at different distances. The opinion which I then entertained, although it had never been placed exactly in the same light, was neither so new, nor so much forgotten, as was supposed by myself, and by most of those with whom I had any intercourse on the subject. Mr. Hunter, who had long before formed a similar opinion, was still less aware of having been anticipated in it, and was engaged, at the time of his death, in an investigation of the facts relative to it ; an investigation for which, as far as physiology was concerned, he was undoubtedly well qualified. Mr. Home, with the assistance of Mr. Ramsden, whose recent loss this Society cannot but lament, continued the inquiry which Mr. Hunter had begun ; and the results of his experiments appeared very satisfactorily to confute the hypothesis of the muscularity of the crystalline lens. I therefore thought it incumbent on me, to take the earliest opportunity of testifying my persuasion of the justice of Mr. Home’s conclusions, which I accordingly mentioned in a Dissertation published at Gottingen in 1796, and also in an Essay presented last year to this Society. About three months ago, I was induced to resume the subject, by perusing Dr. Porter field’s paper on the internal motions of the eye ; and I have very unexpectedly made some observations, which I think I may venture to appear to be finally conclusive in favour of my former opinion, as far as that opinion attributed to the lens a power of changing its figure. At the same time, I must remark, that every person who has been engaged in experiments of this nature, will be aware of the extreme delicacy and precaution requisite, both in conducting them, and in drawing inferences from them ; and will also readily allow, that no apology is necessary for the fallacies which have misled many others, as well as myself, in the application of those experiments to optical and physiological determinations.