The principles of refraction in the human eye : based on the laws of conjugate foci / by Swan M. Burnett ; illustrated with 25 original diagrams by Chas F. Prentice.

  • Burnett, Swan M. (Swan Moses), 1847-1906.
Date:
1904
Catalogue details

Licence: In copyright

Credit: The principles of refraction in the human eye : based on the laws of conjugate foci / by Swan M. Burnett ; illustrated with 25 original diagrams by Chas F. Prentice. 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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    The Essential Functions of Optical Systems. a. The prime function of all optical apparatus is to change the course of rays of light from their original to some other definite direction. b. In ophthalmic optics we have principally to deal with those apparatus which act upon rays of light in such a manner that those emanating from each single point of an illuminated object shall be directed, after being acted upon, towards another corresponding point, or assume a direction as if they had come from such a corresponding point. This corresponding point is called the image of the point in the object. The inherent properties of these optical apparatus are such that rays of light follow the same path going and coming, so that if the object should occupy the position of the image, the image would occupy the position of the object. c. The points to be considered in any study of the activities of such apparatus are: the essential properties of the apparatus itself, including the curvature of the surfaces and, in the case of refracting apparatus, the index of refraction of the medium, and the positions of the object and image in relation to the apparatus—which positions are called the foci of the apparatus. d. When any one of the essential properties of the appa- ratus undergoes a modification, the relation of one or both foci to the apparatus is changed. So long, however, as the essential properties of the apparatus remain fixed, any change in the position of one focus is accompanied by a corresponding change in the position of the other focus, and in accordance with certain definite laws. On account of this intimate,