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diant heat, which far transcends the light in energy. This
condition of things applies to all bodies capable of being
raised to a white heat, either in the solid or the molten
condition. It would doubtless also apply to the luminous
fogs formed by the condensation of incandescent vapors.
In such cases when the curve representing the radiant en-
ergy of the body is constructed, the obscure radiation tow-
ers upward like a mountain, the luminous radiation resem-
bling a mere spur at its base. From the very brightness
of the light of some of the fixed stars we may infer the
intensity of the dark radiation, which is the precursor and
inseparable associate of their luminous rays.

We thus find the luminous radiation appearing when
the radiant 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. How are we to figure this? If per-
mitted to speculate, we might ask, Are not these more
rapid vibrations the progeny 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, what-
ever be the agency by which the large swinging space is
obtained, we shall have light-giving vibrations associated
with it. It matters not whether the large amplitudes be
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 may be regarded as generating
synchronous vibrations among the atoms of the platinum
on which they impinge; but once these vibrations have at-

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