as to pass through all the stages of
invisible radiation, but in its most brilliant condition it embraces,
in an intensified form, the rays of all those stages.

And thus it is with all other kinds of matter, as far as they have
hitherto been examined. Coke, whether brought to a white heat by the
electric current, or by the oxyhydrogen jet, pours out invisible rays
with augmented energy, as its light is increased. The same is true of
lime, bricks, and 'other substances. It is true of all metals which
are capable of being heated to incandescence. It also holds good for
phosphorus burning in oxygen. Every gush of dazzling light has
associated with it a gush of invisible radiant 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 vapours. In
such cases when the curve representing the radiant energy of the body
is constructed, the obscure radiation towers upwards like a mountain,
the luminous radiation resembling 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 that 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 permitted 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, whatever 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, like
air at some height above a gas-flame; or by the shock of the aether
particles when transmitting radiant heat. The result in all cases
will be inca