COLOR, the visual impression derived from the hue of any object. The color of any source of light, or of any object which we see, is solely dependent upon the wave-lengths of the vibrations of the light which come to our eyes from the object. In the case of self-luminous objects these wave-lengths are principally dependent on the temperature of the object and the character of the surrounding absorbing atmosphere, if it has any such; or, in the case of gaseous masses, likewise upon their electrical condition and the pressure to which the gas is subjected. In the case of the non-luminous bodies the wave-lengths are dependent upon the reflecting nature of their surfaces, and are also modified by surrounding atmospheres if they have such.