assumed the radiant form. But it cannot
be doubted that the same effect would be produced by radiant heat of
the same periods, provided the motion of the aether could be rendered
sufficiently intense. [Footnote: This was soon afterwards
accomplished. See the section on 'Transmutation of Rays'.] The
effect in principle is the same, whether we consider the lime to be
struck by a particle of aqueous vapour oscillating at a certain rate,
or by a particle of aether oscillating at the same rate.

By plunging a platinum wire into a hydrogen flame we cause it to glow,
and thus introduce shorter periods into the radiation. These, as
already stated, are in discord with the atomic vibrations of water;
hence we may infer that the transmission through water will be
rendered more copious by the introduction of the wire into the flame.
Experiment proves this conclusion to be true. Water, from being
opaque, opens a passage to 6 per cent. of the radiation from the
spiral. A thin plate of colourless glass, moreover, transmits 68 per
cent. of the radiation from the hydrogen flame; but when the flame
and spiral are employed, 78 per cent. of the heat is transmitted.

For an alcohol flame Knoblauch and Melloni found glass to be less
transparent than for the same flame with a platinum spiral immersed in
it; but Melloni afterwards showed that the result was not
general--that black glass and black mica were decidedly more
diathermic to the radiation from the pure alcohol flame. Melloni did
not explain this, but the reason is now obvious. The mica and glass
owe their blackness to the carbon diffused through them. This carbon,
as first proved by Melloni, is in some measure transparent to the
ultra-red rays, and I have myself succeeded in transmitting between 40
and 50 per cent. of the radiation from a hydrogen flame through a
layer of carbon which intercepted the light of an intensely brilliant
flame. The products of combustion of alcohol are carbonic acid and
aqueous vapour, the heat of which is almost wholly ultra-red. For
this radiation, then, the carbon is in a considerable degree
transparent, while for the radiation from the platinum spiral, it is
in a great measure opaque. The platinum wire, therefore, which
augmented the radiation through the pure glass, augmented the
absorption of the black glass and mica.

No more striking or instructive illustration of the influence of
coincidence could be adduced than that furnished by t