The Croonian lecture : in which the power that enables the eye to see distinctly at different distances is considered / by Everard Home.

  • Home, Everard, Sir, 1756-1832.
Date:
[1795]
Catalogue details

Licence: Public Domain Mark

Credit: The Croonian lecture : in which the power that enables the eye to see distinctly at different distances is considered / by Everard Home. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    motion of the cornea was uncommonly distinct. Sir Henry now became the subject of the experiment, and changed the adjustment of his eye from one distance to another in a very irregular manner, without giving the smallest information, v.'ith a view to embarrass Mr. Ramsden who was the observer, but without effect, for Mr. Ramsden was able to tell every change in distance he had made, without a single mistake ; this exceeded our expectation, and appeared to us so satisfac- tory that we required no further proofs of the truth of our former observations. Before we concluded our experiments, every mode that could be devised was put in practice to see how far there might be any deception ; the eye was moved upon its axis, and in different directions, but these motions did not give at all simi- lar appearances to those seen in the adjusting of the eye to different distances. From the different experiments which I have had the ho- nour to lay before this learned Society, I shall consider the following facts to have been ascertained. ist, That the eye has a power of adjusting itself to different distances when deprived of the crystalline lens ; and therefore the fibrous and laminated structure of that lens is not in- tended to alter its form, but to prevent reflections in the pas- sage of the rays through the surfaces of media of different densities, and to correct spherical aberration. sd. That the cornea is made up of laminae; that it is elas- tic, and when stretched, is capable of being elongated part of its diameter, contracting to its former length immediately upon being left to itself. 3d, That the tendonjs of tlie four straight muscles of the eye