From whatever surface light is reflected, it always takes place in obedience to two fixed laws.
First. The incident and reflected rays always lie in the same plane.
Second. The angle of incidence is equal to the angle of reflection.
With a single jointed two-foot rule, both of these laws are easily illustrated. The rule may be held in the hand, and one end being marked with a piece of white paper may be called the incident ray, i.e., the ray that falls upon the surface; and the other is the reflected ray, the one cast off or thrown back. A perpendicular is raised by holding a stick upright at the joint. (Fig. 260.)
Fig. 260.
a d. A two foot rule; the end a may be termed the incident ray, and the end d the reflected ray. s. The stick held perpendicularly. The angle a b c is equal to the angle d e f, and the whole may be moved in any direction or plane, either horizontal or perpendicular, g g. The reflecting surface.
One of the most simple and pleasing delusions produced by the reflection of light, is that afforded by cutting through the outline of a vase, or statuette, or flower, drawn on cardboard, and if certain points are left attached, so that the design may not fall out, all the effect of solidity is given by bending back the edges of the cardboard, so that the light from a candle placed behind it, may be reflected from the back edge of one cardboard on to the design, which is bent back. The light reflected from one surface on to the other, imparts a peculiarly soft and marble-like appearance, and when the design is well drawn and cut, and placed in a good position, the illusion is very perfect, and it appears like a solid form instead of a mere design cut out of cardboard. (Fig. 261.)
Fig. 261.
Cardboard design in frame, cut and bent back. The lighted candle is behind.