e reversed 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.

Numberless effects, apparently anomalous, might be adduced in
illustration of the action of these lightless rays. These two
powders, for example, are both white, and undistinguishable from each
other by the eye. The luminous rays of the sun are unabsorbed by
both--from such rays these powders acquire no heat; still one of them,
sugar, is heated so highly by the concentrated beam of the electric
lamp, that it first smokes and then violently inflames, while the
other substance, salt, is barely warmed at the focus. Placing two
perfectly transparent liquids in test-tubes 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 78 deg.C,
which is speedily reached; that of the second liquid is only 48 deg.C,
which is never reached at all. These anomalies 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.

A substance, as many of you know, has been discovered, by which these
dark rays may be detached from the total emission of the electric
lamp. This ray-filter is a liquid, 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. When these invisible rays are brought to a focus, at a
distance of several feet from the electric lamp, the dark rays form an
invisible image of their source. By proper means, this image may be
transformed into a visible one of dazzling brightness. It might,
moreover, be shown, if time permitted, how, out of those perfectly
dark rays, could be extracted, by a process of transmutation, all the
colours of the solar spectrum. It might also be proved that those
rays, powerful as they are, and sufficient to fuse many metals, can be
permitted to enter the eye, and to break upon the retina, without
producing the least luminous impression.

The dark rays being thus collected, you see nothing at their place of
convergence. With a proper thermometer it could be proved that even
the air at the focus is just as cold as the surrounding air. And mark
the conclus