The herald., 1896-12-06

that the discharge produces fuores-
cence, which is the property inherent in
certain substances of appearing lumin-
GUS In the dark. after having been ex-
posed to sunlight; like some of the cal
cium salts or luminous paint. In this
experiment the tube contains some ru-
bies at one end, and the discharge
thrown upon them will show you that
the rubies fiuoresce. You Will also see
the bombardment of the radiant matter
produces light when it is thrown on TINS
rhomb of Iceland spar which is at the
bottom of the tube.
In the fifth. most beautiful expert
ment, you will notice that these rays
pass through in straight lines. In the
path Of the discharge is a Maltese cross
of metal, which intercepts the rays.
The shadow of the cross is seen on one
end of the tube, as only the nylng IIoie-
cules that are not intercepted by the
cross. strike the glass which huoresce
So again we see these rays pass IN
straight lines only. On dropping the
cross, and again turning on the current
what before was the shadow. or the
cross now becomes luminous; from
which we infer that the part which is
first acted on is tired and needs rest to
restore it. Again, / will put the cross
into position and you will see the SHADOW
once more; and when i move magnets
about the tube you will observe that tha
| shadow changes position, that l am NOV
| ing the shadow showing the rays are ue-
, hected by magnets.
| All these rays, so far as we have seen
| them, as well as the electric current or
| discharge, can be DETECTED by magnet
| and turned aside from their path; show
! ing you they produce motiH, heat, light
, and are acted on by magnets.
| Some years after these experiments
. first took place it was discovered that
| "Crookes' tubes" which l have just
| shown you, emitted light that was found
/ to pass through thin layers of many
! substances supposed to be Opaque.
| These were called cathode rays, and are
considered now to be the parent of the
X-rays. Crookes showed us the effect Of
! cathode rays inside of the tube, but ii is
| only lately their effect outside of the
| tube has been known. 1t seems to be Il
| question of degree, as to how little air
| there is left in the tube. When the tube
| is so much exhausted, and the dark neg
atlve space which I have shown you
| expands and fills the tube, the glass be-
| comes huorescent alone and begins to
produce X-rays. Prof. Roentgen expert
| menting with one Of these highly eX-
| hausted "Crookes' tubes" which was
| covered with card board, accidentally
| discovered that some sensitive photo
| graphic paper that he had left on bench
| near by was acted upon, and as is often
| the case, this started a new train of
| thought. the result being that he found
rays were produced which acted on sem
sitive plates through solid bodies. and
| that were more powerful than cathode
rays, of which he had full knowledge.
| DIR. Seton will now take photograph
| of his own hand, and will have the plate
| developed, that you may see the mega
tive before the close of the lecture. He
! will use one of the tubes that produce the
| X-rays.
You will observe that the luminosity
| of the tube Is entirely due to the fiuores-
cence of the glass, and that the mega
! tive dark space has so increased that 1t
1 fills the whole tube.
| The glass only fluoresces. The lamp
: has two electrodes, one a concave me-
talic mirror, the negative which con-
| centrates the rays and throws them on
| the other electrode, the positive. plat.
| mum plate set at an angle of forty-five
| degrees DETECTING the rays in the desired
| direction. AS the vacuum is so nearly
! perfect it Is hard to start the current,
so we have something to reduce it a lit
| tie by heat driving out the residual
/ molecules of air which have gone into
! the pores of the glass.
| The sensitive Photographic plate is
| enclosed in the paper bag with the film
| side up; it takes something like three
minutes to photograph the hand, fifteen
! minutes for the elbow, twenty minutes
/ for the knee. I have photographed the
| ribs in forty minutes. OF course it all
| depends on the power of the lamp. I'm
like ordinary negatives taken by sun