If instead of a candle we place our head before a concave mirror, we shall see ourselves magnified as in [fig. 21].
Fig. 21.—Concave Mirror.
We shall easily see how this happens by tracing the paths of the rays in [fig. 22].
Fig. 22.—Magnifying effect of Concave Mirrors.
Fig. 23.—The Reversal of real Images.
The rays, for instance, which proceed from the forehead at the point a are reflected from the point o to the eye in such a way as to appear to proceed from a point beyond the mirror, A. In the same manner the rays reflected from the chin appear to take their origin from the point B. If, on the other hand, we place ourselves at a distance from the principal focus, we shall produce a reversed and diminished image of our face. This image is not illusory, like the preceding ones, but is real, and may be received upon a screen, as shown in [fig. 23].
We may easily follow the path of the rays as shown in the figure, and we shall see that the rays forming the images of the church-tower and the terrace below, cross at a certain point.