An elementary treatise on the function of vision and its anomalies / by Dr. Giraud-Teulon ; translated from the second French edition by Lloyd Owen.

  • Owen Lloyd.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: An elementary treatise on the function of vision and its anomalies / by Dr. Giraud-Teulon ; translated from the second French edition by Lloyd Owen. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    the screen is set precisely at the focal distance of the objective. This is called the emmetropic eye. § 12. ]¥ece8i8ity for a modificatioii in tlie Org-aii for vigion of near ol»jects.—It is known that if an object be presented more or less near to the objective of a camera obscura in which the screen is set at the focus of parallel rays, the image of that object upon the screen is indistinct. In order to restore its distinctness, it is necessary to remove the screen backwards in proportion to the degree of approach of the object, or, if preferred, to replace the first ob- jective by a second stronger lens, leaving the screen in its former position. § 13. Accommodation or tlie Adaptation of tlie Eye for Distances.—When man sees a near object clearly, what occurs 1 Is the retina removed from the lens, like the screen of the photographer, or does the lens undergo some change which increases its power } Both observation and experiment have learned that the latter expedient is the one adopted by nature. To meet the necessities of near vision, the refractive power of the lens-apparatus of the eye increases proportionately with the approach of the object; the screen (retina) remains in its place. § 14. Seat and Meclianism of tlie Accommo-