so with great ease, the circular window in the glass plate allowing
them passage there.

[Illustration: DR. WILLIAM J. MORTON PHOTOGRAPHING HIS OWN HAND UNDER
RÖNTGEN RAYS.

In this case the vacuum bulb is charged from Leyden jars which, in
their turn, are excited by an induction coil.]

The current being turned on, it was found that the powerful electric
sparks visible to the eye, unable to follow a straight course on
account of the intervening rubber plate, jumped around the two plates
in jagged, lightning-like lines, and thus reached the other pole of
the machine. But it was noticed that at the same time a faint spray of
purplish light was streaming straight through the rubber between the
two holes, as if its passage was not interfered with by the rubber
plate. It was in company with this stream of violet rays, known as the
brush discharge, that the doctor conceived the invisible Röntgen
rays to be projected at each spark discharge around the plate; and
presently, when the photographic plate was developed, it was found
that his conception was based on fact. For there, dim in outline, but
unmistakable, were shadow pictures of the ten letters which stand as
historic, since they were probably the first shadow pictures in the
world taken without any bulb or vacuum tube whatever. These shadow
pictures Dr. Morton carefully distinguished from the ordinary
blackening effects on the film produced by electrified objects.

Pursuing his experiments with static electricity, Dr. Morton soon
found that better results could be obtained by the use of Leyden jars
influenced by the Holtz machine, and discharging into a vacuum bulb,