Book 16
18
Optics effect many surprising things, such as the appearance in one mirror of several images of the same thing; also that a mirror placed in a certain position shows no image, but when moved to another spot gives reflections; also that if you look straight into a mirror, your reflection is such that your head appears below and your feet uppermost. The first effect is produced when the surface of a mirror is divided into numerous smaller mirrors. Pliny, N. H. xxxiii. 129, describes cups, the interior of which was so fashioned as to give numerous reflections. The second is described (e.g.) in Pausanias viii. 37. 7. The third is produced when one looks into a concave mirror from a certain distance. Magic mirrors of various kinds and properties were known in antiquity, as well as divination by means of mirrors. See Trans. Numais. and Ant. Soc. of Phila., 1910, pp. 187 ff. This science also gives the reasons for optical illusions, such as the magnifying of objects seen in the water, and the small size of those that are remote from the eye.
