Light is distributed in rays. These rays are straight in all directions. The velocity of light is almost inconceivable. It travels at a rate of 186,500 miles a second. The latest computation with electric light has given a rate of 187,200 miles a second; but the blue rays in the light experimented on probably account for the difference, for blue rays travel quicker by one per cent. than red rays. Römer first found out the velocity of light, which comes to us from the sun—ninety millions of miles—in eight minutes. Fizeau calculated the velocity by means of a wheel, which was set moving with tremendous speed by making the light pass between the teeth of the wheel and back again. When rays of light meet substances they are deflected, and the phenomena under these circumstances are somewhat similar to the phenomena of heat and sound. There are three particular conditions of rays of light: (1) they are absorbed; (2) they are reflected; (3) they are refracted. Firstly. Let us see what we mean by light being absorbed; and this is not difficult to understand, for any “black” substance shows us at once that all the sunlight is taken in by the black object, and does not come out again. It does not take in the light and radiate it, as it might heat. The rose is red, because the rays of light pass through it, and certain of them are reflected from within. So colour may be stated to be the rays thrown out by the objects themselves—those they reject or reflect being the “colour” of the object. [Illustration: Fig. 85.—Angle of reflection, etc.] Secondly. Bodies which reflect light very perfectly are known as mirrors, and they are termed plane, concave, or convex mirrors, according to form. A plane mirror reflects so that the reflected ray _d i_ forms the same angle with the perpendicular as the incident ray _r i_; in other words, the angle of incidence is always equal to the angle of reflection, and these rays are perpendicular to the plane from which they are reflected. The rays diverge, so that they appear to come from a point as far behind the mirror as the luminous point is in front, and the images reflected have the same appearance, but reversed. There is another law, which is that “the angular velocity of a beam reflected from a mirror is twice that of the mirror.” The Kaleidoscope, with which we are all familiar, is based upon the fact of the multiplication of images by two mirrors inclining towards each other. [Illustration: Fig. 86.—Concave mirror.]