The errors of accommodation and refraction of the eye and their treatment : a handbook for students / by Ernest Clarke.

  • Clarke, Ernest, 1857-1932.
Date:
1911
Catalogue details

Licence: In copyright

Credit: The errors of accommodation and refraction of the eye and their treatment : a handbook for students / by Ernest Clarke. 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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    ERRORS OF ACCOMMODATION AND REFRACTION OF THE EYE CHAPTER I REFRACTION—PRISMS- LENSES Light is propagated in straight lines which diverge from any luminous point in all directions, and these lines of direction are called luminous rays. The propagation is produced by ether waves which are across the path of light. The velocity of light is, in round numbers, 186,000 miles per second, and is appreciably retarded in passing through a denser medium. Rays of light entering the eye coming from any luminous point at a greater distance than 6 metres may be assumed, for all practical purposes, to be parallel. Light is absorbed, refracted, or reflected. Refraction of Li^ht.—A ray of light passing from a rarer into a denser transparent medium, if it be perpen- dicular to the surface, and the boundaries of the medium be parallel, will pass out of the denser medium in the same straight line (Fig. i, l), the only effect upon it being a retardation. If the ray enter the denser medium other than perpendicularly, or if the boundaries of the medium be not parallel, the ray is bent or refracted. A simple illustration will explain this. Explanation of Refraction.—As ether waves are at right angles to the path of light, if a beam of light enter