He led the way to the other square room mentioned, and indicated
the induction coil with which his researches were made, an ordinary
Rhumkorff coil, with a spark of from four to six inches, charged by
a current of twenty amperes. Two wires led from the coil, through an
open door, into a smaller room on the right. In this room was a
small table carrying a Crookes tube connected with the coil. The most
striking object in the room, however, was a huge and mysterious tin
box about seven feet high and four feet square. It stood on end,
like a huge packing-case, its side being perhaps five inches from the
Crookes tube.

The professor explained the mystery of the tin box, to the effect that
it was a device of his own for obtaining a portable dark-room. When he
began his investigations he used the whole room, as was shown by the
heavy blinds and curtains so arranged as to exclude the entrance of
all interfering light from the windows. In the side of the tin box,
at the point immediately against the tube, was a circular sheet of
aluminium one millimetre in thickness, and perhaps eighteen inches
in diameter, soldered to the surrounding tin. To study his rays the
professor had only to turn on the current, enter the box, close the
door, and in perfect darkness inspect only such light or light effects
as he had a right to consider his own, hiding his light, in fact, not
under the Biblical bushel, but in a more commodious box.

"Step inside," said he, opening the door, which was on the side of
the box farthest from the tube. I immediately did so, not altogether
certain whether my skeleton was to be photographed for general
inspection, or my secret thoughts held up to light on a glass plate.
"You will find a sheet of barium paper on the shelf," he added, and