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 anything. The discharge was in
full force, and the rays were flying through my head, and, for all I
knew, through the side of the box behind me. But they were invisible
and impalpable. They gave no sensation whatever. Whatever the
mysterious rays may be, they are not to be seen, and are to be judged
only by their works.

I was loath to leave this historical tin box, but time pressed. I
thanked the professor, who was happy in the reality of his discovery
and the music of his sparks. Then I said: "Where did you first
photograph living bones?"

"Here," he said, leading the way into the room where the coil stood.
He pointed to a table on which was another--the latter a small