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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    Making these experiments fatigued the eye considerably, and repeating them after very short intervals made the eye water, and gave a slight degree of pain ; this, however, soon went olf. In looking at objects through this glass, the image was free from any tinge of colour, unless he directed his eye towards the circumference of the glass, and then it had a considerable tinge, which evidently arose from the prismatic figure of that part of the glass. A comparative experiment was made upon the perfect eye, with a glass of 15 inches focus. Objects were found in one ex- periment to appear most distinct at 83- inches, the extremes 3 inches and 11 inches ; in another, most distinct at 7 inches, the extremes as before, 3 and 11 inches. On the 29th of December, 34 days after the operation, the following experiments were made by candle-light, about six o'clock in the evening. The experiment with the double convex glass was repeated, the aperture being diminished to -^^ of an inch ; objects ap- peared most distinct at 5 inches, the extremes 3 inches and 7^ inches. The aperture was diminished to -^-^ of an inch, and vision appeared most distinct at 5 inches, the extremes 3^- inches and 7 inches. When the aperture was reduced to ~ of an inch, the inflexion of the rays produced tbe appearance of a speck, which obscured his vision. By diminishing the aperture, spherical aberration was in a great measure corrected, and vision rendered more distinct. A plano-convex glass of inches focus, with the plane towards the eye, was now applied, and the objects were most