The ophthalmoscope : a manual for students / by Gustavus Hartridge.

  • Gustavus Hartridge
Date:
1907
Catalogue details

Licence: In copyright

Credit: The ophthalmoscope : a manual for students / by Gustavus Hartridge. Source: Wellcome Collection.

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

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    ami Avill therefore never meet ; if, liowever, avc con- tinue these diverging- rays backwards, tliey will unite at a point (ii) behind the mirror; this point is called Fig. 4. the virtual focus, and an observer situated in 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 be placed nearer than its principal focus, then one sees an enlarged erect virtual image, which increases slightly in size as the mirror is made to recede; this image becomes confused and disappears as the principal focus of the mirror is reached; on moving the mirror still further away (that is, beyond its focus) one obtains an enlarged inverted image, which diminishes as the mirror is still further withdi'awn.
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