The Providence news. (Providence [R.I.]) 1891-1906, 1896-02-20
THE CATHODE RAYS.
Public Lecture on the Subject
by Prof. TrOwbridge.
Harvard Students Listened TO Accounts of
Results Reached.

Students sat on the floor in their eager
ness to hear the eminent scientist. lie
gave a very clear and elementary talk.
"The public,n said Professor Trow-
bridge "is not generally interested In
scientific experiments, but there is some
thing so mysterious about the invisible
rays that IL is no wonder that interest has
been aroused.
"rhe rays pass through boards, ebo-
rite, thin metals, and penetrate the in
most parts OF the body, yet they do not
pass through window pane"
Professor 1rowbridge confined his lec-
ure TO the practical application OF Roent-
gems discovery more especially to surgery.
lie called attention to the methods by
which use vas made OF the rays and the
apparatus, and dwelt especially upon the
fact that photograph can be taken with
simple means in reach OF all.
Cathode means the way down or the
way out as distinguished from the annode
the way in. Taking an ordinary Le-
clanche cell, such as Is used in connection
with the house bells, Professor Trow-
bridge showed how the carbon pole would
be the annode and the zinc pole the
cathode
1t would take 80 or go OF such cells ar
ranged in series of tandems to produce
one incandescent light
"Now il you break the loop of ire in
the middle the lamp will go out. Then
If more cells are added until the number
is 10000 pate, luminous glow will come
from the lamp.
zone terminal of the lamp is called the
cathode, and from this stream these in
visible rays
In the accounts OF experiments men
tion is often made of Crcoke's tube. AS
the lecturer showed, Ii Is nothing more
than a large receiver of air from which
the air can be exhausted.
'ln order to get the rays, however, you
must push the exhaustion only to GER
tain point. Now, instead of using the
10000 cells already mentioned. to produce
the pale blue flame, Ruhmkor1 coil is
introduced, which makes II possible to
get a high electro-motive force.
"The Ruhmkorn coil consists Of two
colts, one inside called the primary.
which is a piece OF wire only few feet
long, another on the outside, called the
secondary, about a mile long.
"By passing n strong current through
the shorter wire and breaking the current
a great electric stress and high force Is
obtained. Approximately the 10,000 cells
would produce 10, 600 volts, but the three
Ruhmkorn coils used IN these expert
ments produce approximately 30, 600 volts.
"By transformation Of the Ruhmkorf
coils in series and connecting the coil
with the tube, and then exhaustiDg the
air, you get the cathode rays"
At this point the experiment was per-
formed. Inc lHt tTOohc > luDt
was pale blue on the two poles and light
pink in the center. A huorescence YVES
given of which was of a light blueish
green color.
This, Professor Trowbridge explained,
was thought by some to be the cathode
rays, but the point is still in doubt. No
one knows TO certainty what the rays
are.
in connection with this tho lecturer
took up large slim besker filled with
Kerosene, which is generally colorless, but
when held near the lighted tube the kero-
Gene was of a light blue color.
After the experiment was finished Pro-
f5ssor Irow bridge explained that the same
light can be produced with common
electric machine, but the plate must be
exposed an hour when this machine Is
used. This shows how simple the process
really is.
The chief advantage of the large aprar-
atus is that when it is used only min
ute's exposure Is necessary. The disting-
uishing cha ter Of the cathode rays il
that they as not go between the two
poles, They can be thrown any way. For
instance q small piece of aluminium can
be used to throw them in any direction.
Coming TO the method of taking photo
graphs the lecturer showed the difference
i'll the process. In taking photograph
with cathode rays plain dry plate Is
used.
holder but there Is no central Opaque par
tition. The hand or object TO be photo
graphed is put in the slide and you get q
photograph of the shade. AS glass absorbs
the rays lens would be of no use and
would prevent the taking of photographs.
Thus the common process of photo
graphing is exactly reversed with the ca
thode rays. This was illustrated by a
picture thrown on the screen where a
camera was shown with the large end to-
ward the cathode and the lens pointed
away uselessly.
athode photographs have been called
shadow pictures, but this Is not an ex-
actly correct name for them. This is be-
cause a piece of glass as thick as a piece
of paper absorbs large number OF rays
and throws a very thick shadow on the
plate, while even thick piece of wood
throws hardly any shadow.
The shadow photograph. however, is
very exact in other respects. In the
| photograph OF the human hand il shows
the gradations of the ABSORPTION OF the
rays with the thickness OF the bones.
he rays will go through sheets of
aluminium one-tenth of an inch thick,
greater thickness OF the aluminium " III
absorb only porticn of the rays. ! he
glass OF the Croolle's tube Is only one-siX-
teenth of an inch thick, but even glass
as thin as this absorbs so many rays
that 1t presents great obstacles. IL has
Deen suggested tnHt an aluminium VIII
dow be put in the tube and that the
| photographs be taken with the rays that
come through the aluminium, for the Tea
son already shown that the aluminium abb
serbs hardly any rays, while the thinnest
glass absorbs an enormous number of
them.
The objection to the aluminium win
dows is that the atmospheric pressure OF
- pounds to the square inch would break
the tube.
Celluloid tubes and tubes of wood soak
ed I'm some substance making IL airtight
have also been suggested. The objection
TO these aie that the wires entering
through these substances get heated aud
heat everything we know Of except glass.
Doubtless the rays exist I'm common
electric lights and in sunlight, but as yet
scientists nave proved their existence only
In vessel such as CrooSe's tube With
these invisible rays photographs can be
taken at any time, even in the sunlight.
In connection with the cathode photo
graph 1t is interesting TO note the length
! ot the exposure that has been necessary 10
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