gh the receiver, still possessing sufficient power to
ignite the charcoal, and thus initiate the attack of the oxygen. If,
instead of being plunged in oxygen, the charcoal be suspended in
vacuo, it immediately glows at the place where the focus falls.

********************

8. Transmutation of Rays: Calorescence.

[Footnote: I borrow this term from Professor Challis, 'Philosophical
Magazine,' vol. xii. P. 521]

Eminent experimenters were long occupied in demonstrating the
substantial identity of light and radiant heat, and we have now the
means of offering a new and striking proof of this identity. A
concave mirror produces, beyond the object which it reflects, an
inverted and magnified image of the object. Withdrawing, for example,
our iodine solution, an intensely luminous inverted image of the
carbon points of the electric light is formed at the focus of the
mirror employed in the foregoing experiments. When the solution is
interposed, and the light is cut away, what becomes of this image? It
disappears from sight; but an invisible thermograph remains, and it is
only the peculiar constitution of our eyes that disqualifies us from
seeing the picture formed by the calorific rays. Falling on white
paper, the image chars itself out: falling on black paper, two holes
are pierced in it, corresponding to the images of the two coke points:
but falling on a thin plate of carbon in vacuo, or upon a thin sheet
of platinised platinum, either in vacuo or in air, radiant heat is
converted into light, and the image stamps itself in vivid
incandescence upon both the carbon and the metal. Results similar to
those obtained with the electric light have also been obtained with
the invisible rays of the lime-light and of the sun.

Before a Cambridge audience it is hardly necessary to refer to the
excellent researches of Professor Stokes at the opposite end of the
spectrum. The above results constitute a kind of complement to his
discoveries. Professor Stokes named the phenomena which he has
discovered and investigated _Fluorescence_; for the new phenomena here
described I have proposed the term _Calorescence_. He, by the
interposition of a proper medium, so lowered the refrangibility of the
ultraviolet rays of the spectrum as to render them visible. Here, by
the interposition of the platinum foil, the refrangibility of the
ultra-red rays is so exalted as to render them visible. Looking
through a prism at the incandesce