Page:On Radiation.djvu/49

What then is the real origin of the luminous radiation? We find it appearing when the radiating body has attained a certain temperature; or, in other words, when the vibrating atoms of the body have attained a certain width of swing. In solid and molten bodies a certain amplitude cannot be surpassed without the introduction of periods of vibration, which provoke the sense of vision. If permitted to speculate, one might ask, are not these more rapid vibrations the product of the slower? Is it not really the mutual action of the atoms, when they swing through very wide spaces, and thus encroach upon each other, that causes them to tremble in quicker periods? If so, it matters not by what agency the large swinging space is obtained; we shall have light-giving vibrations associated with it. It matters not whether the large amplitudes are produced by the strokes of a hammer, or by the blows of the molecules of a non-luminous gas; such as the air at some height above a gas-flame; or by the shock of the ether particles when transmitting radiant heat. The result in all cases will be incandescence. Thus, the invisible waves of our filtered electric beam with which incandescence has been produced, may be regarded as generating synchronous vibrations in the platinum on which they impinge; but once these vibrations attain a certain amplitude, the mutual