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224 FRAGMEN TS OF SCIENCE.

those rays they acquire no heat; still one of the substances,
sugar, is heated so highly by the concentrated beam of the
electric lamp that it first smokes violently and then inflames,
while the other substance, salt, is barely warmed at the
focus. Here, again, are two perfectly transparent liquids
placed in a test-tube at the focus; one of them boils in a
couple of seconds, while the other in a similar position is
hardly warmed. The boiling-point of the first liquid is 7 8°
0., which is Speedin reached; that of the second liquid is
only 48° C., which is never reached at all. These anoma-
lies are entirely due to the unseen element which mingles
with the luminous rays of the electric beam, and, indeed,
constitutes 90 per cent. of its calorific power.

I have here a substance by which these dark rays may
be detached from the total emission of the electric lamp.
This ray-filter is a black liquid—that is to say, black as
pitch to the luminous, but bright as a diamond to the non-
luminous radiation. It mercilessly cuts off the former, but
allows the latter free transmission. I bring these invisible
rays to a focus at a distance of several feet from the electric
lamp; the dark rays form there an invisible image of the
source from which they issue. By proper means this in-
visible image may be transformed into a visible one of daz-
zling brightness. I could, moreover, show you, if time per-
mitted, how out of those perfectly dark rays we might ex-
tract, by a process of transmutation, all the colors of the
solar spectrum. I could also prove to you that those rays,
powerful as they are, and sufficient to fuse many metals,
may be permitted to enter the eye and to break upon the
retina without producing the least luminous impression.

The dark rays are now collected before you; you see
nothing at their place of convergence ; with a proper ther-
mometer it could be proved that even the air at the focus
is just as cold as the surrounding air. And mark the con-
clusion to which this leads. It proves the ether at the focus

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