Incandescence.

Incandescence. The hotter a body the greater the disturbance which its particles, always oscillating, set up in the surrounding ether, and the greater is the proportion of ether-waves of short length which are set up. Thus, as a body becomes progressively hotter it first becomes visible in the dark as a fog-gray object (platinum at 390° C., gold at 417° C., and iron, not quite free from rust, at 377° C.—H. F. Weber), then ash-gray, then yellowish-gray, then faintly red, then red hot, orange, yellowish-white, white hot, and lastly, when there is at very high temperatures a preponderance of the more refrangible rays, it becomes bluish or even distinctly blue, as it seems the sun would appear were it not for our atmosphere (Langley). Incandescence is usually witnessed in solids; in liquids it is not known by sight; in gases we have examples in the hydrogen flame and in the condition of the air traversed by lightning or the electric arc. For Incandescent Electric Lamps, see ELECTRIC LIGHT; and for the incandescent gas-light, see GAS-LIGHTING, Vol. V. p. 103.