THE WAVE-THEORY OF LIGHT.
(1) NATURAL bodies may be divided into two classes in relation to Light. Some possess, in themselves, the power of exciting the sense of vision, and of producing the sensation of light; while others are devoid of that property. Bodies of the former class are said to be luminous; those of the latter, non-luminous. The Sun and the fixed stars are all luminous bodies; terrestrial bodies are luminous, in the states of incandescence, combustion, or phosphorescence.
Non-luminous bodies acquire the power of exciting the sensation of light in the presence of a luminous body. Thus,
p or candle illuminates all the objects in a room, and ers them visible; and the light of the Sun illuminates the Earth and the planets. This property of bodies is due to their capacity of reflecting light, and belongs to them in different degrees.
(2) The foregoing distinction of bodies, obvious as it seems, was not fully comprehended by the ancients. According to