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.

    24/314 (page 4)
    If the luminous point be situated at f, then the diverging rays would be reflected as parallel to each other and to the axis. If the luminous point is at the centre of the con- cavity of the mirror (c), the rays return along the same lines^ so that the point is its own image. If the luminous point be at A the focus will be at a, Fig. 3. and it is obvious that if the luminous point be moved to a, its focus will be at A; these two points therefore, A and a, bear a reciprocal relation to each other, and are called conjugate foci. If the luminous point is beyond the centre, its conjugate focus is between the principal focus and the centre. If the luminous point is between the principal focus and the centre, then its conjugate is beyond the centre; so that the nearer the luminous point ap- proaches the principal focus, the greater is the dis- tance at which the reflected rays meet. If the luminous point be nearer the mirror than p