Eyesight, good & bad : a treatise on the exercise and preservation of vision.

  • Carter, Robert Brudenell, 1828-1918.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: Eyesight, good & bad : a treatise on the exercise and preservation of vision. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    CHAPTER II. ON LIGHT, AND THE FORMATION OF IMAGES BY LENSES. It has been stated In the foregoing chapter that vision is dependent upon the formation of images upon the retina, by h'ght reflected from the objects which are seen; and, before considering how these images are produced within the eye, it is necessary to explain the formation of analogous images by artificial means. We mean by light a mode of force which is resolvable into molecular wave movements, and which is well known to us in many of its manifestations. Disregarding the wave movements, an account of which is not necessary for the purpose now before us, we may speak of light as a force which emanates from luminous bodies, and which travels in straight lines in all directions. If we hght a candle, and place it in the middle of an otherwise dark room, all parts of the room equidistant from the flame will be equally illuminated ; and the amount of light falling upon equal surfaces will be inversely as the squares of their distances from the source of illumination.