Volume 3

The anatomy and physiology of the human body.

  • Bell, John, 1763-1820.
Date:
1826
Catalogue details

Licence: Public Domain Mark

Credit: The anatomy and physiology of the human body. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    When a ray of light passes from a rarer to a denser medium, or from a denser into a rarer (as A into B), it alters its course, if there be any obliquity in the original direction ; but if it strikes from one medium into another perpendicularly to the surfaces (as C), its original direction is not changed. If the ray passing from the air enter obliquely into glass or water, or any denser medium, it turns more towards the perpendicular; but if it pass through the glass and emerges again into the air, it resumes its original direction, diverging from the perpendicular. This effect of different mediums upon the ray of light, is called refraction: when a ray of light impinging upon a surface does not enter, it rises again ac- cording to the angle of its incidence; and this is reflection. A The prism is a piece of glass of a triangular form, of which we have here a section at A; the inclined surfaces of which, when placed in the course of the A