eet of barium paper on the shelf," he added, and
then went away to the coil. The door was closed, and the interior of
the box became black darkness. The first thing I found was a wooden
stool, on which I resolved to sit. Then I found the shelf on the
side next the tube, and then the sheet of paper prepared with barium
platino-cyanide. I was thus being shown the first phenomenon which
attracted the discoverer's attention and led to the discovery, namely,
the passage of rays, themselves wholly invisible, whose presence was
only indicated by the effect they produced on a piece of sensitized
photographic paper.

A moment later, the black darkness was penetrated by the rapid
snapping sound of the high-pressure current in action, and I knew
that the tube outside was glowing. I held the sheet vertically on
the shelf, perhaps four inches from the plate. There was no change,
however, and nothing was visible.

"Do you see anything?" he called.

"No."

"The tension is not high enough;" and he proceeded to increase the
pressure by operating an apparatus of mercury in long vertical tubes
acted upon automatically by a weight lever which stood near the coil.
In a few moments the sound of the discharge again began, and then I
made my first acquaintance with the Roentgen rays.

The moment the current passed, the paper began to glow. A
yellowish-green light spread all over its surface in clouds, waves,
and flashes. The yellow-green luminescence, all the stranger and
stronger in the darkness, trembled, wavered, and floated over the
paper, in rhythm with the snapping of the discharge. Through the metal
plate, the paper, myself, and the tin box, the invisible rays were
flying, with an effect strange, interesting, and uncanny. The metal
plate seemed to offer no appreciable resistance to the flying force,
and the light was as rich and full as if nothing lay between the paper
and the tube.

"Put the book up," said the professor.

I felt upon the shelf, in the darkness, a heavy book, two inches in
thickness, and placed this against the plate. It made no difference.
The rays flew through the metal and the book as if neither had been
there, and the waves of light, rolling cloud-like over the paper,
showed no change in brightness. It was a clear, material illustration
of the ease with which paper and wood are penetrated. And then I
laid book and paper down, and put my eyes against the rays. All was
blackness, and I neither saw nor felt a