10. Crown glass, 1 millimetre thick, covered with a very thin layer of
gold.

11. Red crown glass, 2 millimetres thick.

12. Block of Iceland spar (very transparent to ordinary light, but
very opaque to Roentgen rays).

13. A bit of tinfoil.

14. Aluminium medal, showing faint traces of the design and lettering
on both sides, as if it were translucent.

15. Metallic mirror, shows no effect of regular reflection.

16. Bit of sheet-lead, 1 millimetre thick.

17. Quarter-of-a-dollar coin, silver.

18. Piece of thin ebonite, such as is used for photographic
plate-holder.]

[Illustration: DR. WILLIAM KONRAD ROeNTGEN, DISCOVERER OF THE X RAYS.

From a photograph by Hanfstaenge, Frankfort-on-the-Main.]

THE NEW MARVEL IN PHOTOGRAPHY.

A VISIT TO PROFESSOR ROeNTGEN AT HIS LABORATORY IN WUeRZBURG.--HIS OWN
ACCOUNT OF HIS GREAT DISCOVERY.--INTERESTING EXPERIMENTS WITH THE
CATHODE RAYS.--PRACTICAL USES OF THE NEW PHOTOGRAPHY.

BY H.J.W. DAM.

In all the history of scientific discovery there has never been,
perhaps, so general, rapid, and dramatic an effect wrought on the
scientific centres of Europe as has followed, in the past four weeks,
upon an announcement made to the Wuerzburg Physico-Medical Society, at
their December meeting, by Professor William Konrad Roentgen, professor
of physics at the Royal University of Wuerzburg. The first news which
reached London was by telegraph from Vienna to the effect that a
Professor Roentgen, until then the possessor of only a local fame
in the town mentioned, had discovered a new kind of light, which
penetrated and photographed through everything. This news was received
with a mild interest, some amusement, and much incredulity; and a week
passed. Then, by mail and telegraph, came daily clear indications
of the stir which the discovery was making in all the great line of
universities between Vienna and Berlin. Then Roentgen's own report
arrived, so cool, so business-like, and so truly scientific in
character, that it left no doubt either of the truth or of the great
importance of the preceding reports. To-day, four weeks after the
announcement, Roentgen's name is apparently in every scientific
publication issued this week in Europe; and accounts of his
experiments, of the experiments of others following his method, and
of theories as to the strange new force which he has been the first
to observe, fill pages of every scientific journal that comes to
hand. And