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 color with the color 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
aluminium, wood, and other substances and produce photographic results
beyond. It was left, however, for Professor Röntgen to discover that
during the discharge another kind of rays are set free, which differ
greatly from those described by Lenard as cathode rays The most marked
difference between the two is the fact that Röntgen rays are not
deflected by a magnet, indicating a very essential difference, while
their range and penetrative power are incomparably greater. In fact,
all those qualities which have lent a sensational character to the
discovery of Röntgen's rays were mainly absent from these of Lenard,
to the end that, although Röntgen has not been working in an entirely
new field, he has by common accord been freely granted all the honors
of a great discovery.

[Illustration: SKELETON OF A FROG, PHOTOGRAPHED
THROUGH THE FLESH. THE SHADINGS INDICATE, IN ADDITION TO THE BONES,
ALSO THE LUNGS AND THE CEREBRAL LOBES.