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 temperature of the object and the character of the su 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.