scovered 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 before the necessary time elapses for this article to
attain publication in America, it is in all ways probable that the
laboratories and lecture-rooms of the United States will also be giving
full evidence of this contagious arousal of interest over a discovery so
strange that its importance cannot yet be measured, its utility be even
prophesied, or its ultimate effect upon long established scientific
beliefs be even vaguely foretold.

The Roentgen rays are certain invisible rays resembling, in many
respects, rays of light, which are set free when a high-pressure
electric current is discharged through a vacuum tube. A vacuum tube is a
glass tube from which all the air, down to one-millionth of an
atmosphere, has been exhausted after the insertion of a platinum wire in
either end of the tube for connection with the two poles of a battery or
induction coil. When the discharge is sent through the tube, there
proceeds from the anode--that is, the wire which is connected with the
positive pole of the battery--certain bands of light, varying in colour
with the colour of the glass. But these are insignificant in comparison
with the brilliant glow which shoots from the cathode, or negative wire.
This glow excites brilliant phosphorescence in glass and many
substances, and these "cathode rays," as they are called, were observed
and studied by Hertz; and more deeply by his assistant, Professor
Lenard, Lenard having, in 1894, reported that the cathode rays would
penetrate thin films of aluminum, wood, and other substances, and
produce