Diseases of the eye : a hand-book of ophthalmic practice, for students and practioners / By G. E. De Schweinitz.

  • George Edmund de Schweinitz
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of the eye : a hand-book of ophthalmic practice, for students and practioners / By G. E. De Schweinitz. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    The following table from Landolt contains the index of refraction of some of the principal substances. The index of refraction of the glass used in spectacles is about 1.53. ♦ Table of absolute indices of refraction from Landolt. I. SOLIDS Crown glass . Flint glass Ice .... Rock crystal . Quartz (ordinary index) Diamond Cornea .... Crystalline lens, cortical layer intermediate layer nucleus 1.5 1.57 to 1.58 1.310 1.562 1.547 2.48 to 2.75 1.3365 1.393 1.419 1.431 II. LIQUIDS. Water 1.336 White of egg 1.351 Human blood ....... 1.354 Sulphuric ether ....... 1.358 Rectified alcohol 1.372 Canada balsam ....... 1.532 Saturated solution of sea salt .... 1.575 Bisulphide of carbon ...... 1.678 III. GASES. Air 1.000294 Oxygen 1.000272 Nitrogen . 1.000:50(1 Carbonic acid 1.000439 Prisms.—In order to be refracted a ray of light must form an angle with the perpendicular to the surface of the medium of different density. Rays which strike the surface perpendicularly pass through without deviation. This is best understood by considering prisms. A prism is a portion of glass, or other transparent substance, included between two plane surfaces which are inclined to each other. The angle formed by the two surfaces is called the refracting <ni(/le of the prism, and is expressed in degrees. For- merly prisms were designated by the number of degrees in the refracting; angle.