The refraction of the eye : a manual for students / by Gustavus Hartridge.

  • Hartridge, Gustavus, 1849-1923.
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: The refraction of the eye : a manual for students / by Gustavus Hartridge. Source: Wellcome Collection.

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    the principal focus, tlie rays will be reflected as diver- gent, and will therefore never meet: if, however, we continue these diverging rays backwards, they will unite at a point (h) behind the mirror; this point is called the virtual focus, and an observer situated in Fig. 4. the path of reflected rays will receive them as if they came from this point. Thus it follows that— Concave mirrors produce two kinds of images or none at all, according to the distance of the object, as may be seen by looking at oneself in a concave mirror. If the mirror is placed nearer than its principal focus, then one sees an enlarged virtual image, which in- creases slightly in size as the concave mirror is made to recede; this image becomes confused and disap- pears as the principal focus of the mirror is reached; on moving the mirror still further away (that is be- yond its focus) one obtains an enlarged inverted image, which diminishes as the mirror is still further withdrawn.