1895 word came out of Germany of a scientific discovery
that startled the world. It came first as a rumor, little credited; then
as a pronounced report; at last as a demonstration. It told of a new
manifestation of energy, in virtue of which the interior of opaque
objects is made visible to human eyes. One had only to look into a tube
containing a screen of a certain composition, and directed towards
a peculiar electrical apparatus, to acquire clairvoyant vision more
wonderful than the discredited second-sight of the medium. Coins within
a purse, nails driven into wood, spectacles within a leather case,
became clearly visible when subjected to the influence of this magic
tube; and when a human hand was held before the tube, its bones stood
revealed in weird simplicity, as if the living, palpitating flesh about
them were but the shadowy substance of a ghost.

Not only could the human eye see these astounding revelations, but the
impartial evidence of inanimate chemicals could be brought forward to
prove that the mind harbored no illusion. The photographic film recorded
the things that the eye might see, and ghostly pictures galore soon gave
a quietus to the doubts of the most sceptical. Within a month of the
announcement of Professor Roentgen's experiments comment upon the
"X-ray" and the "new photography" had become a part of the current
gossip of all Christendom.

It is hardly necessary to say that such a revolutionary thing as the
discovery of a process whereby opaque objects became transparent, or
translucent, was not achieved at a single bound with no intermediate
discoveries. In 1859 the German physicist Julius Plucker (1801-1868)
noticed that when there was an electrical discharge through an exhausted
tube at a low pressure, on the surrounding walls of the tube near the
negative pole, or cathode, appeared a greenish phosphorescence. This
discovery was soon being investigated by a number of other scientists,
among others Hittorf, Goldstein, and Professor (now Sir William)
Crookes. The explanations given of this phenomenon by Professor Crookes
concern us here more particularly, inasmuch as his views did not
accord exactly with those held by the other two scientists, and as his
researches were more directly concerned in the discovery of the
Roentgen rays. He held that the heat and phosphorescence produced in a
low-pressure tube were caused by streams of particles, projected from
the cathode with great velocity, stri