t
Dr. Roentgen himself called the phenomena the X, or unknown, rays.

In the experimentation referred to, Roentgen had covered the glass tube
at the end with a shield of black cardboard. This rendered the glow at
the cathode pole completely invisible. It chanced that a piece of
paper treated with platino-barium cyanide for photographic uses was on
a bench near by. Notwithstanding the fact that the tube was covered
with an opaque shield, so that no _light_ could be transmitted,
Professor Roentgen noticed that changes in the barium paper were taking
place, _as though_ it were exposed to the action of light! Black lines
appeared on the paper, showing that the surface was undergoing
chemical change from the action of some invisible and hitherto unknown
force!

This was the moment of discovery. The philosopher began experimenting.
He repeated what had been accidentally done and was immediately
convinced that a force, or, as it were, invisible rays were streaming
from the cathode pole of the tube through the glass, and through a
substance absolutely opaque, and that these rays were performing their
work at a distance on the surface of paper that was ordinarily
sensitive only to the action of light.

Certain it was that _something_ was doing this work. Certain it was
that it was _not light_. Highly probable it was that it was not any
form of _electricity_, for glass is impermeable to the electrical
current. Certain it was that it was _not sound_, for there was no
noise or atmospheric agitation to produce such a result. In a word, it
was demonstrated then and there that a hitherto unknown, subtle and
powerful agent had been discovered, the applications of which might be
of almost infinite range and interest.

Professor Roentgen soon announced his discovery to the Physico-Medical
Society of Wuerzburg. It was at the December meeting of this body that
the new stage in human progress was declared. The news was soon
flashed all over the world, and scientific men in every civilized
country began at once to experiment with the cathode light--if light
that might be called that lighted nothing.

In Roentgen's announcement he stated that there had been by the
scientists Hertz and Lenard, in 1894, certain antecedent discoveries
from which his own might in some sense be deduced. There was, however,
a great difference between the discovery made by Roentgen and anything
that had preceded it. His stage of progress in knowledge was this,