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RADIANT HEAT AND ITS RELATIONS. 223

Placing a concave silvered mirror behind the electric
light I converge its rays to a focus of dazzling brilliancy.
I place in the path of the rays, between the light and the
focus, a vessel of water, and now introduce at the focus a
piece of ice. The ice is not melted by the concentrated
beam which has passed through the water, though matches
are ignited at the focus and wood is set on fire. The pow-
erful heat, then, of this luminous beam is incompetent to
melt the ice. I withdraw the cell of water; the ice imme-
diately liquefies, and you see the water trickling from it
in drops. I reintroduce the cell of water; the fusion is
arrested and the drops cease to fall. The transparent water
of the cell exerts no sensible absorption on the luminous
rays, still it withdraws something from the beam, which,
when permitted to act, is competent to melt the ice. This
something is the dark radiation of the electric light. Again,
I place a slab of pure ice in front of the electric lamp ; send
a luminous beam first through our cell of water and then
through the ice. By means of a lens an image of the slab
is cast upon a white screen. The beam, sifted by the water,
has no power upon the ice. But observe what occurs when
the water is removed; we have here a star and there a star,
each star resembling a flower of six petals, and growing
visibly larger before our eyes. As the leaves enlarge their
edges become serrated, but there is no deviation from the
six-rayed type. We have here, in fact, the crystallization
of the ice inverted by the invisible rays of the electric beam.
They take the molecules down in this wonderful way, and
reveal to us the exquisite atomic structure of the substance
with which Nature every winter roofs our ponds and lakes.

N umberless effects, apparently anomalous, might be ad-
duced in illustration of the action of these lightless rays.
Here, for example, are two powders, both white, and undis-
tinguishable from each other by the eye. The luminous
rays of the lamp are unabsorbed by both powderswfrom

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