The San Francisco call., 1896-04-02

distance of the plate from the axis of the tube
was four inches and the time of exposure was
forty minutes Besides the thin boards filled
with nails, keys and coins were also placed on
the plate, with the hope that if they cast
double shadows the two sources of the rays
might be better indicated by them than the
nails
The print clearly shows that the side of the
anode which was facing the cathode was the
source of the Roentgen rays in greatest num-
Der and intensity, while the reverse side was
also the source of some OF the rays, but not to
the same extent as the side facing the cathode.
The line dividing the two is blurred, as the
cross was not exactly plane. Double shadows
of the coins and keys, as well as the nails, were
cast from the forescent glass at the ends OF the
tube, which can be seen in the negative, but
which cannot be made out from the print.
The forescent glass then was source OF the
Roentgen rays, but the number and intensity
coming therefrom are small as compared with
the metal anode. The glass, which was flores
cent was directly in the path Of the cathode
rays.
At the same time that this radiograph was
made plate was exposed at the large end OF
the tube upon which the shadow of the alumni
mum cross was cast A lead plate with hole
three-eighths of an inch in diameter was
placed between the end of the tube and the
Photographic plate, to cut off if possible any
effect from the forescent glass. The only por-
ton of the glass of the tube which could affect
the plate in the region OF the hole was that
shaded by the cross. The plate indicated that
the Roentgen rays came from the reverse side
of the anode, the negative being very dark in
the center where the plate exposed
through the hole in the lead plate. The for
escent glass, however, which was beyond the
shading action of the aluminium cross, and /,
therefore, received the cathode discharge di-
rect, did have an effect on the plate, Ithe
shadow of the nails near the edges of the plate
showing clearly.
Finally, to show that the anode is not neces-
sarily the source of the Roentgen rays unless
it receives the cathode rays on its surface, the
experiment was tried of making the anode a
tinfoil plate pasted on the exterior of the glass
tube. Accordingly the anode was put on the
tube ordinarily shaded by the cross. The
cathode was as before the small disk electrode
in the painted end of the tube The aluminium
cross was disconnected entirely, SO that it was
neither enode nor cathode, but was placed in
such a position that it received directly
the cathode rays. Another large plate was
then exposed parallel to the axis of the
tube as in the previous experiment when the
aluminium cross was the anode. The resulting
radiograph was a negative that shows that the
Sluc VI LHe HluInluuIn Cross lHclilR tne catnO0e
the principal source of the rays just as it
had been in the previous experiment. The
side of the aluminium cross facing the anode
was also source of the rays, but the number
and intensity were less from the cathode side
The horescent glass cast the double shadows as
before, and perhaps to little greater extent
than in the former care when the aluminium
cross was the anode.
plate was then exposed to the end of the
tube, upon which had been pasted the tinfoil
on the outside as the anode. The result indi.
Gates that some Roentgen rays came from the
aluminium cross, and in the central portion
passed through the tinfoil anodc ana the glass
OF the TUBE affecting the plate.
The negative secured thus shows the radio
graph taken when the aluminium cross was
neither anode nor cathode but q1as connected
TO the ground through a water pipe. The
anode was, as before, the tinfoil plate and the
cathode was the circular disk electrode in the
small end of the tube. The whole appearance
OF the tube was changed, the shadow of the
cross on the end of the tube being much en-
larged. The cross was hinged on the top and
swung freely back and forth as the current was
turned on and off. When the connection was
permanently made the cross swung over
toward the cathode as If attracted toward il.
The sources of the rays when the cross was
connected to the earth seemed to be many, al
though still the cross gave out the greater
number. The torescent glass. however. seems