-------
100. THOMSON’S EXPERIMENTS. _Elect. Eng._, N.Y., Mar. 11, Apr. 8 and
Apr. 22, ’96. _Elect. Rev._, N.Y., Apr. 8, ’96, p. 183. STEREOSCOPIC
SCIAGRAPHS. _Elect. World_, N.Y., Mar. 14, ’96.—Prof. Elihu Thomson, of
the Thomson-Houston Electric Company, described experiments to determine
the practicability of making stereoscopic pictures by X-rays. A solid
object may be considered as composed of points which are at different
distances from the eye. By monocular vision, the solidity of an object
is not assured. However, by the use of both eyes, the objects appear
less flat. The experimenter used, as the different objects, a mouse,
also metal wires twisted together, and, again, a block of wood having
projecting nails. In order to produce a stereoscopic picture with
X-rays, he took a sciagraph in the ordinary way. He then caused the
relative displacement of the discharge-tube and the object, and took
another sciagraph. By mounting the two sciagraphs in a stereoscope, he
found that the effect was as expected, and in the case especially of the
skeleton of the mouse, it was very curious,—less like a shadow picture
and more like the real object. The picture was more realistic, as in the
well-known stereoscope for viewing photographs.
[Illustration:
MULTIPLE SCIAGRAPHS. FIG. 1, § 101, p. 95.
]
[Illustration:
MULTIPLE SCIAGRAPHS. FIG. 2, § 101, p. 95.
]
101. THOMSON’S EXPERIMENT. MANIFOLDING BY X-RAYS.—If one desires to take
a print of a negative, for example by means of sun-light, it is evident
that, on account of the opacity of the photographic paper, only one
sheet would be placed under the negative for receiving a print. However,
the X-rays are so penetrating in their power that it is possible for
them to produce sciagraphs through several sheets, and thereby to result
in the production of several pictures of the same object with one
exposure. Without an experiment to prove this, one might argue that the
chemical action of one sheet would absorb all the energy. The experiment
of Prof. Thomson shows that this is not so. The elements were arranged
as follows: First a discharge tube; then an object, namely, a key
escutcheon of iron; then yellow paper; then paste board; then black
paper; then two layers of albumen or sensitized paper; then two célérité
printing papers; then two platinum printing papers; then one célérité;
then six layers of sensitive bromide paper; then four layers of heavy
sensitive bromide paper (heavier); then three layers of black paper, and
finally, at the maximum distance from the discharge-tube, a sensitive
glass plate of dry gelatine, with its face up, thereby making
twenty-five layers in the aggregate. It is interesting to notice that an
induction coil was not employed, but a small Wimshurst machine, having
connected to each pole a small Leyden jar. § 106. 1,200 discharges
occurred during exposure. The results were as follows: No sciagraphs
developed upon the albumen, célérité nor platinum, which, it should be
noticed, were merely printing papers. § 128. The impressions on the ten
bromide papers were weak. See Multiple Sciagraphs, Fig. 2, p. 94. He
attributed the reason of this to the thinness of the film. Although the
glass plate was furthest away from the discharge tube, yet the
impression was greater than on any of the papers, the result being shown
in Multiple Sciagraphs, Fig. 1, p. 94. He suggested that the plates for
use with X-rays should have unusually thick films. Incidentally he found
that the intensifying process could be employed with profit to bring out
the small details distinctly. Dr. Lodge also recommended thick films.
See _The Elect._, Lon., Apr. 24, ’96., p. 865.
101_a_. LUMIÈRE’S EXPERIMENT. ENORMOUS TRANSPARENCY OF SENSITIVE
PHOTOGRAPHIC PAPER. _Comptes Rendus_, Feb. 17, ’96. Translated by Mr.
Louis M. Pignolet.—With a ten-minutes exposure, objects were sciagraphed
through 250 super-imposed sheets of gelatino-bromide of silver paper, to
observe the absorption of the X-rays by the sensitive films. The one
hundred and fiftieth sheet was found to have an impression.
102. PROPOSED DOUBLE CATHODE TUBE. See also _Elect. Rev._, N.Y., Apr.
15, p. 191.—The nature of this will be apparent immediately from the cut
which is herewith presented and entitled “Standard X-Ray Tube.” With
unidirectional currents the concave electrodes in the opposite ends may
each be a permanent cathode, while the upper terminal connected to the
angular sheet of platinum may be the anode. Cathode rays, therefore,
will be sent out from each concave disk, and striking upon the platinum
will be converted into X-rays, assuming that the platinum is the surface
upon which the transformation from one kind of ray to another takes
place. § 63, at end. This is called a standard tube, because it may be
employed with efficiency with any kind of generator. § 8_a_, 26_a_, 115,
116 and 145. It is interesting to notice a confirmation of the
efficiency of such a tube, for Mr. Swinton, in a communication to the
_Wurz Phys. Med. So._ (see _The Elect._, Lon., and _Elect. Eng._, N.Y.,
June 3,) showed and described a picture of an exactly similar tube. By
an experiment, the tube operated as expected. First proposed by Prof.
Elihu Thomson, who is an author also of the following experiment:
[Illustration:
STANDARD X-RAY TUBE.
]
103. X-RAYS. OPALESCENCE AND DIFFUSION. _Elect. World_, Apr. 25, ’96.—He
alluded to opal glass and milk to illustrate that light is reflected not
only at the surface of a body, but from points, or molecules, or
particles, located underneath the surface. By some experiments with
X-rays, he found that they had a similar property only not to such a
large per cent., but on the other hand by the way of contrast, there are
many more substances opalescent to X-rays than there are to light, for
the reason that the former will penetrate more substances and to greater
distances. He made many observations with a modified sciascope, § 105,
by pointing it away from the discharge tube and towards different
substances struck by X-rays. To all appearances, such substances became
the sources of the X-rays. He alluded to Mr. Tesla’s experiments on
reflection, § 146, but noticed that there was a slight difference
between reflection and diffusion and he was satisfied that reflection
took place from the interior of the substances as well as from the
surface. Metal plates, he said, gave apparently little diffusive effect,
appearing to reflect feebly at angles equal to the incident angles. He
alluded to Edison’s experiment also, § 133, with a large thick plate
cutting off the X-rays and attributed the luminosity of his modified
sciascope to rays both reflected and diffused from surrounding objects,
which generally as a matter of course, are more of non-metallic objects
than metallic, such as floor, ceiling, walls, tables, chairs and so on.
Evidently, the interior of one’s hand causes diffusion; very little,
however, for a sciagraph by means of a focus tube gives wonderfully
clear outlines, and yet the rays do not come from a mathematical point.
§ 88. Prof. Thomson acknowledged that independently of himself, Dr. M.
I. Pupin, of Columbia College, had reported in _Science_, Apr. 10, ’96,
see also _Electricity_, Apr. 15, ’96, p. 208, upon investigations on the
same general subject, namely diffusion, and also referred to experiments
of Lenard, § 69, and Roentgen on diffusion. Agrees also with experiments
of A. Imbert and H. Bertin-Sans in _Comptes Rendus_, Mar. 2, ’96. He
suggested that this property of diffusion acted as an explanation why
sciagraphs can never have absolutely clearly cut shadows of the bones or
other objects imbedded in a considerable depth of flesh.
103_a_. A. IMBERT AND H. BERTIN-SANS’ DIFFUSION AND REFLECTION IN
RELATION TO POLISH. X-RAYS. _Comptes Rendus_, Mar. 2, ’96. Translated by
Louis M. Pignolet.—They concluded, under the conditions of their
experiments, that if X-rays were capable of reflection it was only in a
very small proportion; on the other hand, the rays can be diffused _en
assez grande quantité_, the intensity of the diffusion appearing to
depend much more upon the nature of the diffusing body than upon its
degree of polish. From this they attributed to the rays a very small
wave length, such that it would be impossible to get in the degree of
polish necessary to obtain their regular deflection. Perrin attempted
unsuccessfully to reflect the rays from a polished steel mirror and a
plate of “flint,” but with exposures of one hour and seven hours
respectively, nothing was obtained. From trans. by L. M. Pignolet,
_Comptes Rendus_, Jan., 96. By exposing a metal plate to the rays and
suitably inclining it in front of the opening, Lafay also proved
reflection, for it was possible to discharge the electrified screen;
hence, as he called it, diffused reflection. _Comptes Rendus_, Apr. 27,
’96; from trans. by L. M. Pignolet.
104. FLUOROMETER.—He constructed an instrument for comparing the merits
of different discharge tubes, and for indicating the comparative
luminosity of different screens subjected to the action of the same
discharge tube. The instrument served also to act as an indicator of the
diffusing power of different materials. “By placing two exactly similar
fluorescent screens at opposite ends of a dark tube, and employing a
Bunsen photometer screen, movable as usual between the screens, a
comparison of the diffusing power of different materials might be made
by subjecting the pieces placed near the ends of the photometer tube
outside, to equal radiation from the Crookes’ tube.” From Prof.
Thomson’s description.
The author performed some experiments (_Elect. Eng._, N.Y., Apr. 15,
’96, p. 379) in relation to candle-power of X-rays by looking into a
sciascope and moving it away until the luminosity just disappeared. He
then detached the black paper cover from the phosphorescent screen and
pointed the sciascope toward a candle flame and receded away until the
fluorescence also disappeared. The distances, with different candles,
would, of course, somewhat vary, but it would in the rough be a constant
quantity, while different discharge tubes would cause the vanishing
fluorescence at different distances. Now, assuming that the X-rays vary
inversely as the square of the distance, as believed by Röntgen, their
power to fluoresce could, therefore, always be named as so much of a
candle-power.
105. SIMPLE DEVICE FOR COMPARING AND LOCATING THE SOURCE AND DIRECTION
OF X-RAYS. PHOSPHORESCENCE NOT ESSENTIAL.—In the ordinary sciascope, the
fluorescent screen is located at one end, and the eyehole at the other.
He modified this construction by employing a long straight tube, made of
thick metal, so that X-rays could not enter through the wall. About at
the centre of the tube was a diaphragm of a fluorescent material. Now,
it is evident that if this is directed toward the phosphorescent spot
and placed very close to the same, and the other end be looked into, the
screen will become fluorescent, if X-rays are emitted from the area
expected. Such a result occurred. With this instrument, he was able to
show, in a similar way, that X-rays did not come from the anode, nor
from the cathode directly. In one case, he provided a piece of platinum
within the discharge tube, in such a position as to be struck by the
cathode rays. § § 91 and 116. The instrument showed that X-rays radiated
from the platinum, although the latter was not luminous nor
phosphorescent,—illustrating again that phosphorescence is not a
necessary accompaniment of X-rays, and assisting in upholding the
principle that as the phosphorescence diminishes by increase of vacuum
and increase of E. M. F., the X-rays increase. It should be noticed that
Prof. Thomson emphasizes that the tube should be made of thick metal.
106. RICE’S EXPERIMENT. APPARATUS FOR OBTAINING X-RAYS. § 109, 114, 131,
137. TUBE ENERGIZED BY A WIMSHURST MACHINE. _Elect. Eng._, N.Y., Apr.
22, p. 410.—Roentgen had always employed the induction coil. As to those
who first excited the discharge tube by the Holtz or Wimshurst machine
or generators of like nature, it is not certain; but, according to
public records, they were independently Prof. M. I. Pupin, of Columbia
College, and Dr. William J. Morton, of New York. See _Electricity_,
N.Y., Feb. 19, ’96. The accompanying cut marked “Rice’s Experiment, Fig.
1,” is a diagram representing the several elements of the apparatus,
while “Rice’s Experiment, Fig. 2,” shows what kind of a sciagraph can be
obtained by means of a Wimshurst machine. § 101, at centre. The details
of the apparatus as employed by Mr. E. Wilbur Rice, Jr., Technical
Director of the General Electric Co., were as follows: A Wimshurst
machine, having a glass plate 16 inches diameter, coupled up with the
usual small Leyden jars, spark under best conditions of atmosphere,
etc., 4 inches. “The usual method of taking pictures with such a machine
is to connect the interior coatings of the two jars, respectively, to
the positive and negative conductors of the machine, the terminals of
the discharge tube being connected between the external coatings of the
Leyden jars. In this condition, the disruptive discharge of the Leyden
jars passes through the tube and across the balls upon the terminals of
the conductors of the machine, the length of spark being regulated by
separating the balls in the usual way.” Later, he found that by omitting
the Leyden jars, the generation of the X-rays was practically
non-intermittent. He therefore connected the terminals of the discharge
tube directly to those of the Wimshurst machine as indicated in “Rice’s
Experiment, Fig. 1,” which also illustrates the details in the carrying
out of the experiment for obtaining the picture, Fig. 2, of the purse
containing the coins and a key. The principal feature was the
introduction of a lead diaphragm containing a small central opening 7-8
inch diameter opposite the fluorescent spot. Sciagraphs taken thus
required a little more time, about 60 minutes, while without the
diaphragm, the time could be shortened to about 30 minutes, but the
shadows were not so clear in the latter case. The figures are on p. 100.
[Illustration:
RICE’S EXPERIMENT. FIG. 1, § 106, p. 99.
Diagram.
]
[Illustration:
RICE’S EXPERIMENT. FIG. 2, § 106, p. 99.
Taken with the above apparatus.
]
107. SOURCE OF X-RAYS TESTED BY PROPAGATION THROUGH A SMALL HOLE.—This
would illustrate not only that the fluorescent spot is the source of
X-rays, but also that a very small portion comes from other parts that
are probably bombarded by stray cathode rays (due to irregular surface
of cathode § 57, or by reflected X-rays or cathode rays.
He tested the source of the X-rays by means of the following arrangement
of the apparatus: It will be noticed that the lead diaphragm is quite
close to the fluorescent spot. Upon holding the sciascope on the
opposite side, and pointing it toward the spot, the luminous area of the
fluorescent screen was about the same as that of the opening in the
diaphragm, but the size grew rapidly upon receding from the diaphragm.
If the rays had come from the cathode, however, the fluorescent spot on
the screen would not have increased in size so rapidly during recession,
and, therefore, the rays must have come from the spot on the glass
struck by the cathode rays. § 113, 116, 117.
107_a_. LEEDS’ AND STOKES’ EXPERIMENT. USE OF STOPS IN SCIAGRAPHY.
_Western Electrician_, Mar. 14, ’96.—In order to obtain clear
definitions of the shadows, Messrs. M. E. Leeds and J. B. Stokes
provided lead plates with holes, varying in size from 1/4 inch to an
inch between the discharge tube on one side and the object and
photographic plate on the other. In this manner they obtained excellent
sciagraphs of animals having very fine skeletons. See the picture of the
rattlesnake at § 135 and of a fish on page 63. See also the frog taken
abroad page 90.
107_b_. MACFARLANE, MORTON, KLINK, WEBB AND CLARK’S EXPERIMENT. X-RAYS
FROM TWO PHOSPHORESCENT SPOTS. _Elect. World_, Mar. 14, ’96.—By means of
nails projecting vertically from a board (similar to the process carried
out by Dr. William J. Morton, _Elect. Eng._, N.Y., Mar. 5, ’96), they
proved, undoubtedly, that the source of the X-rays was at the surface of
the glass directly opposite the cathode. By modification, which acted as
further proof, a tube was provided with a cathode at the centre. There
was a phosphorescent spot at each end. One board was placed laterally to
the tube, and two shadows of each of certain nails were cast, which were
caused as proved by measurement, by a double source of X-rays. This
experiment illustrates the importance of preventing double shadows. The
plate should be perpendicular to the line joining the two sources of the
X-rays when there are two such sources. Even with the focus tube Dr.
Philip M. Jones, of San Francisco, determined that there were two
phosphorescent spots. These should be taken into account in all cases
and attempts made to produce but one strong focus upon the platinum.
_Elect. World_, N.Y., May 23, ’96.
[Illustration:
STINE’S EXPERIMENT. FIG. 1, § 108, p. 104.
]
[Illustration:
STINE’S EXPERIMENT. FIG. 2, § 108, p. 104.
]
108. STINE’S EXPERIMENTS. SOURCE OF X-RAYS DETERMINED BY SCIAGRAPHS OF
SHORT TUBES. _Elect. World_, N.Y., Apr. 11, ’96, pp. 392, 393.—Prof.
Stine, of the _Armour. Inst. of Tech._, by means of the diagram shown in
Fig. 1, p. 102, clearly proved that the X-rays have their source at the
area struck by the cathode rays located directly opposite the disk
marked “cathode.” If the reader will investigate the diagram and the
sciagraphs, he will obtain a clearer knowledge of the evidence than by
any verbal description, further than to explain how the elements are
related to one another. In Fig. 1, therefore, will be noticed covered
photographic plates, located as indicated with reference to the extreme
left-hand end of the discharge tube, where the cathode rays strike. The
surface of Plate 5 is parallel to that of the cathode, and the
phosphorescent spot is in line between the two above named elements. The
result is shown in Fig. 2, p. 102, the objects sciagraphed being several
short sections of tubes with diameters varying from 1/2 to 3 inches.
A, in Figs. 3, 4, p. 104 and in Figs. 5, 6, p. 112, identifies the ends
lettered A in Fig. 1. The sciagraph in Fig. 3 was obtained on the plate
shown at the top in Fig. 1; that in Fig. 4, on Plate 2; that in Fig. 5,
on Plate 3; and that in Fig. 6, on Plate 4. Not only were direct shadows
visible, but also secondary shadows, indicating, therefore, that,
although the source of practically all the rays was at the
phosphorescent spot, yet a portion of the rays came slightly from other
directions, either by reflection or by actual production of rays, upon
other portions of the tube. Look now especially at Fig. 3, p. 104. If
the rays came from the anode, then would this appearance necessarily be
the same as that in Fig. 2. Similarly, the other sciagraphs may be
considered to show that the rays do not come from the anode. In the case
of the sciagraphs in Figs. 4, 5 and 6, only a single tube acted as the
body for casting a shadow. Prof. Stine stated that the experiments were
repeated over and over again, thereby establishing the phenomena as
uniform.
109. STINE’S ELECTRICAL APPARATUS EMPLOYED. § § 106, 112, 114, 131,
137.—Prof. Stine gave the following suggestive points:
“Among the first points investigated was the influence of the
interrupter. The coil was provided, first with the familiar mercury make
and break, and then an ordinary vibrator. The mercurial device gave very
good results.
[Illustration:
STINE’S EXPERIMENT. FIG. 3, § 108, p. 104.
]
[Illustration:
STINE’S EXPERIMENT. FIG. 4, § 108, p. 104.
]
The small interrupter was found the more reliable, and seemed to shorten
the needed time of exposure. A rotary contact-maker, giving two
interruptions of the current per revolution, was also tested. This was
driven by a motor with a condenser capacity of fourteen microfarads
connected across the brushes. Owing to the large capacity of the
condenser, a heavy current could be broken without marked sparking. The
circuit breaker was tested at speeds ranging from 500 to 4,000 per
minute, to note the influence on the time of exposure. The best results
were obtained at the lower speed.... As no especial advantage could be
noted when using the mercury breaker, it was abandoned for the vibrating
interrupter.” This point is noted in detail, since so many experimenters
seem to prefer such cumbersome devices, but they are, in reality,
unnecessary.
[Illustration:
STINE’S EXPERIMENT, FIG. A. § 110.
]
110. APPARENT DIFFRACTION OF X-RAYS REALLY DUE TO PENUMBRAL SHADOWS.
_Elec. Eng._, Apr. 22, ’96, p. 408.—By referring to the diagram marked
“Stine’s Experiment, Fig. A,” the arrangement of the elements may be
seen, while the photographic print is shown in “Stine’s Experiment, Fig.
B.” p. 106. Prof. Stine described the investigation as follows:
Diffraction is naturally one of the first kinematical points to be
investigated in the Roentgen experiments. It was noticed that when the
opaque object was some distance from the plate, pronounced penumbral
shadows resulted. These were of such width as to indicate diffraction.
However, when such shadows are plotted back to the tube they are found
to be purely penumbral, and not caused by diffraction. To completely
demonstrate this point the experiment illustrated in Fig. A was
undertaken. Here A_{1} to A_{4} are brass plates one inch wide and 1/8
inch thick, and of the length of the dry plate employed. They were first
fastened together, so as to leave two parallel slots 1/8 of an inch
wide. These plates are placed within 3/8 of an inch of the bulb, were
one inch apart, and rested 1-1/8 inches above the dry plate. The
resulting sciagraph is shown in Fig. B. In the diagram S_{1} S_{2}, the
edges of the penumbral shadow are very sharp and distinct. The direction
of the rays is indicated, showing that there was absolutely no
diffraction. This experiment has been modified in a variety of tests,
with always the same result.”
110_a_. JEAN PERRIN’S NON-DIFFRACTION. _Comptes Rendus_, Jan. 27, ’96.
From trans. by Louis M. Pignolet.—The active part of a tube was placed
before a very narrow slit; 5 cm. further, there was a slit 1 mm. wide;
10 cm. further, there was the photographic plate. An exposure of nine
hours gave an image with sharply defined borders, upon which there was
no diffraction fringe.
[Illustration:
STINE’S EXPERIMENT. FIG. B. § 110.
]
159a. NON-REFRACTION.—Refraction was attempted with prisms of paraffine
and of wax, but no refraction was noticed.
111. SCRIBNER AND M’BERTY’S EXPERIMENT. SOURCE OF X-RAYS DETERMINED BY
INTERCEPTION OF ASSUMED RECTILINEAR RAYS FROM THE CATHODE. _Elect.
Eng._, N.Y., Apr. 8, ’96, p. 358; _Amer. Inst. Elec. Eng._, Mar. 25,
’96. _West. Branch._—Refer now solely to Fig. 1, S. and M.’s experiment.
Notice the relative arrangement of the elements. First, the discharge
tube with the cathode at the upper part and the phosphorescent spot
opposite thereto; then below a thick lead plate with a single opening;
then a second lead plate with two small openings placed laterally at
such a distance that if there were rectilinear rays from the cathode
they could not strike (by passing through the small hole), the covered
photographic plate which was the next element in order. The description
did not state that the photographic plate was covered, but the
experimenters must have had the usual opaque cover upon it or else the
luminous rays could have produced images. The developed plate showed two
spots strongly acted upon and surrounded by portions which were less
acted upon, the same as would be produced by light radiating from a
surface as distinguished from a point. From the fact that they stated
that the exposures were very long, it may be concluded also that the
plates were covered by a material opaque to ordinary light. Measurement
showed that the rays which produced the images came from the
phosphorescent spot (§ 106, 109, 114, 131, 139) and not from the cathode
directly by rectilinear propagation.
[Illustration:
S. & M.’S EXPERIMENT, FIG. 1. & 2.
]
112. SOURCE ON INNER SURFACE OF THE DISCHARGE TUBE DETERMINED BY
PIN-HOLE IMAGES. Reference may now be made to S. and M.’s Experiment,
Fig. 2.—The discharge tube has, as before, a cathode on one side, and
the phosphorescent spot during operation on the opposite side. Lead
plates were provided in positions indicated by the heavy black straight
lines, there being a pin hole in each one. Behind these lead plates,
measured from the discharge tube, were the covered photographic plates,
as indicated. By measurement, it was afterwards determined that
practically all the X-rays started from the phosphorescent spot. The
electrode was put in an oblique position, as indicated, so that the same
would not obstruct any X-rays trying to pass through the pin hole in the
uppermost plate. The experiment served specifically to show that the
X-rays started from the inner surface of the glass, because images
produced on the upper and lower plates were equally strong. Perrin also
found that the X-rays are developed at the interior sides of the tubes.
(_Comptes Rendus_, Mar. 23, ’96. From trans. by L. M. P.) The rays, in
producing each image, had to pass through an equal thickness of glass.
If the rays had come from the outer surface, for example, two
thicknesses would have been traversed by the rays striking the upper
plate, and no thickness by those impinging upon the lower plate. That no
rays came from any other portion or element of the discharge tube was
evident, because a picture of the phosphorescent spot was the only one
produced, and this picture was inverted, as usual, with pin hole
cameras. (A pin-hole camera is the same as any other, with the lens
replaced by a very small hole, which acts as a lens.)
In the way of further evidence, if not enough already, Meslans early
determined that the phosphorescent spot on the glass is the source of
X-rays (_Comptes Rendus_, Feb. 24, ’96. From Trans. by Mr. Louis M.
Pignolet).
JEAN PERRIN’S EXPERIMENTS. THE ORIGIN OF X-RAYS. _Comptes Rendus_, Mar
23, ’96. From Trans. by Louis M. Pignolet.—He also confirmed that X-rays
radiate from the phosphorescent spot.
112_a_. DE HEEN’S EXPERIMENT. THE ANODE BELIEVED TO BE THE SOURCE OF
X-RAYS. _Comptes Rendus_, Feb. 17, ’96. From trans. by Louis M.
Pignolet.—A lead screen, pierced by several holes, was placed between
the discharge tube and the photographic plate. The shadows of the holes
on the plate indicated that the rays emanate from the positive pole of
the tube.
As both Thomson (E.) and Rowland, as well as De Heen, at first concluded
likewise, is it not probable that the anode was struck by the cathode
rays (see § § 113, 116)? For it was fully admitted that the anode,
otherwise, does not emit X-rays.
[Illustration]
113. LODGE’S EXPERIMENT. X-RAYS MOST POWERFUL WHEN THE ANODE IS THE PART
STRUCK BY THE CATHODE RAYS. PIN-HOLE PICTURES BY X-RAYS TO DETERMINE
SOURCE OF X-RAYS, AND PIN-HOLE IMAGES UPON GLASS COMPARED. _The Elect._,
Lon. Apr. 10, ’96, p. 784.—The object of the experiment was to confirm,
if possible, by a modified construction, the source of the X-rays, as
being the surface struck by cathode rays, whether the surface is that of
glass or any other substance. He had constructed, for this purpose, a
discharge tube, as illustrated in the diagram, which may be seen, at a
glance, to contain a concave electrode at one end, and a flat electrode
at the other. Between them, and connected to the concave electrode, is
an inclined sheet of aluminum, shading both electrodes. The wires
leading to the aluminum sheet are well protected by glass. He arranged
matters so that either the concave or the flat electrode could be made
positive or negative. The operation consisted first in taking through a
pin hole, 1/4 of an inch in diameter, X-ray pictures on photographic
plates, from different points, at measured distances. After these were
taken, glass plates received the luminous images at the positions of the
sensitive plate. Pencil drawings were then made, and compared with the
X-ray pictures. The experiment involved also the repetition of this
operation, except that the polarity of the terminals was changed.
“When the small flat disk was cathode, every part of the complicated
anode appeared strongly and quickly on the plate, especially the tilted
and first bombarded portion on a photographic plate placed above the
tube. The cathode disk itself did not show at all. On a plate placed
below the bulb, the anode cup appeared strong, but the tilted disk did
not appear. On the other hand, … its focus spot acted as a feeble point
source, by reason of a few rays reflected back on to it from the cup.
“When the current was _reversed_, the small disk anode showed faintly,
being excited by rays which had penetrated the interposed tilted disk,
but again the cathode hardly showed at all, not even the tilted portion
on a plate placed below the bulb. This is confirmed by J. Perrin. In no
case could an image of the cathode be obtained. (_Comptes Rendus_) Mar.
23, ’96. From trans. by L. M. P.) By giving a very long exposure (two
hours), some impression was obtained by Dr. Lodge about equal to that
from the shaded anode disk; but, of course, if the tilted plate had been
under these circumstances an anode, it is well known that a few minutes
would have sufficed to show it strong upon the plate beneath.
“Hence, undoubtedly, the X-rays do not start from the cathode _or from
anything attached to the cathode_ but do start from a surface upon which
the cathode rays strike, whether it be an actual anode or only an
‘anti-cathodic’ surface. Best, however, if it be an actual anode.
(Independently discovered by Rowland, § 116. and Roentgen, § 91.”)
“When the glass walls, instead of receiving cathode rays, are pierced
only by the true Roentgen rays from the disk in the middle, no evidence
is afforded by my photograph that the glass under these circumstances
acts as a source. It is well that it does not, for its only effect would
be a blurring one. § 91. With focus tubes, the glass phosphoresces under
the action of the X-rays as anything else would phosphoresce, but its
phosphorescence is not of the least use. It is a sign that a tube is
working well, and that the rays are powerful; but if by reason of
fatigue (§ 58) the glass ceases to phosphoresce strongly, the fact
constitutes not the slightest detriment.”
[Illustration]
X-RAY UNINFLUENCED BY A MAGNET. SEVERE TEST.—His first experiment on
magnetic deflection, the sciagraph of a magnet with a background of wire
gauze, only showed that if there were any shift by reason of passage of
rays between the poles it was very small; but he definitely asserted, as
in accompanying diagram, that a further experiment has been made which
effectually removes the idea of deflectibility from his mind, and
confirms the statement of Professor Roentgen. § 79. A strong though
small electro-magnet, with concentrated field, had a photograph of its
pole-pieces taken with a couple of wires, A and C, stretched across them
on the further side from the plate—nearer the source—and a third wire,
B, also stretched across them, but on the side close to the plate. These
three wires left shadows on the plate, of which B was sharp and
definite, while A and C were blurred. Two sciagraphs were taken by Mr.
Robinson, one with the magnet on, and one with the magnet reversed. On
subsequently superposing the two plates, with the sharp shadows of B
coincident, the very slightest displacement of shadows A and C could
have been observed, although those shadows were not sharp. But there was
absolutely no perceptible displacement, the fit was perfect.
Consequently the hypothesis of a stream of electrified particles is
definitely disproved as no doubt had already been effectively done in
reality by Professor Roentgen himself. But it must be noted, he stated,
that the hypothesis of a simple molecular stream—not an electrified
one—remains a possibility. The only question is whether such an
unelectrified bombardment would be able to produce the observed effects.
It must be remembered, Dr. Lodge stated, that Dr. Lenard found among his
rays two classes as regards deflectibility—some much deflected, others
less deflected; and it must be clearly understood that his deflections
were observed, not in the originating discharge tube, where the fact of
deflection is a commonplace, but outside, after the rays had been, as it
were, “filtered” through an aluminum window. He did not, indeed, observe
the deflection in air of ordinary density; it was in moderately rarefied
air that he observed it, § 72_a_, but he showed that the variation of
air density did not affect the amount, but only the clearness of the
minimum magnetic deflection. The circumstance that affected the amount
of the deflection was a variation in the contents of the originating or
high-vacuum tube.
114. LODGE’S EXPERIMENT. APPARATUS EMPLOYED. _The Elect._, Lon., April
10, ’96, p. 783.—With his apparatus, he was able to obtain rays
sufficiently powerful to illuminate the usual fluorescent screen after
passing through one’s skull. It is of interest to note about the details
of the electrical apparatus (§ § 106, 109, 131, 137) used by those who
experimented. The best results were obtained by a make and break of a
direct primary current at a point under alcohol, the primary battery
consisting of three storage cells, and the current of the primary acting
on a large secondary coil. Leyden jars he considered entirely
unnecessary, and he preferred direct currents to alternating currents
for the primary. He did not give the exact dimensions of the primary and
secondary coils, but, judging from reports of others and the author’s
own experience, it is highly preferable to have what is called a very
large inductorium, 15 in. spark in open air, or else the Tesla system (§
§ 51, 137). There is little satisfaction in trying to perform the
experiments with induction coils adapted to give only a 2 or 3 in. spark
in open air.
[Illustration:
STINE’S EXPERIMENT. FIG. 5, § 108, p. 103.
]
[Illustration:
STINE’S EXPERIMENT. FIG. 6, § 108, p. 103.
]
115. LODGE’S EXPERIMENT. X-RAYS EQUALLY STRONG DURING FATIGUE OF GLASS
BY PHOSPHORESCENCE. _The Elect._, Lon., Apr. 10, ’96.—In order to
explain in what way the rays were propagated, he says that it is not as
if the glass surface were a wave front from every point of which rays
proceed normally, but that the glass radiates X-rays just as a red-hot
surface radiates light, namely, a cone of rays starts from each point,
and all the rays of each cone start in a different direction. Every
point of the glass radiates the rays independently of all other points.
Crookes’ Experiment (§ 58) may now be called to mind in reference to the
fatiguing of the glass after phosphorescing for a while. Lodge tested
the fatiguing as to the power to emit X-rays, but found that there was
no such property whatever. The glass which became fatigued as to
luminous phosphorescence (§ 105) was not fatigued as to the power of
X-rays. He noticed that the phosphorescent spot became less and less
bright, and yet the X-rays remained of the same power.
116. ROWLAND, CARMICHAEL AND BRIGGS’ EXPERIMENT. AREA STRUCK BY CATHODE
RAYS ONLY AN EFFICIENT SOURCE WHEN POSITIVELY ELECTRIFIED.
_Electricity_, N.Y., Apr. 22, ’96, p. 219.—Experiments carried on at the
Johns Hopkins University led the above named investigators to think at
first that the source of the X-rays was at the anode. _Amer. Jour.
Sci._, March, ’96. Prof. Elihu Thomson was led to give the same opinion
during his first experiments. _Elect. Rev._, N.Y., Mar. 25, ’96. See
also § 112_a_. Many other experiments certify to the allegation that
X-rays are certainly generated at the phosphorescent spot on the glass.
§ 79, 105, 107, 108, 111, 112, 113. From the experiments of Prof.
Rowland, _et al._, the confusion is accounted for by the fact that they
overlooked the electrical condition of the spot struck by the cathode
rays. Prof. Rowland, _et al._, constructed a tube having a platinum
sheet located at the focus of the concave electrode, and _not_ connected
to the anode. Although the platinum became red hot, it emitted no
X-rays, but when the platinum was made the anode, there was profuse
radiation of X-rays in all directions from that side of the platinum
struck by the cathode rays, and no radiation from the other side. § 91.
(See also Roentgen and Tesla, concerning 1/2 platinum and 1/2 aluminum
and radiation therefrom.) They inferred as a final conclusion in
connection with this point, “That the necessary condition for the
production of X-rays is an anode bombardment by the cathode discharge.”
§ 113. They recognized apparently that it had been conclusively proved
that X-rays radiated from the phosphorescent spot on the glass. They
held that such a spot is “The induced anode formed on the glass.” § 49,
at end. They did not prove this by an experiment according to the
article referred to, but based it upon “The fact that the bombarding
cathode rays coming in periodical electrified showers alternately raise
and lower the potential of the glass, thus making it alternately an
anode and a cathode. In the case of the platinum, this could not occur
to the same extent.”
117. SALVIONI’S EXPERIMENT. TRANSPOSITION OF PHOSPHORESCENT SPOT.
_Elect. Rev._, Lon., Apr. 24, ’96, p. 550; _Med. Sur. Acad._, of
Perugia, Italy, Feb. 22, ’96. Personal interview with Prof. Salvioni in
_Elect. Rev._, N.Y., Apr. 8, ’96, p. 181.—In order to change the
location of the phosphorescent spot when desired, without a magnet, and
at the same time to concentrate or intensify the source of X-rays, he
placed near the same, on the outside of the tube, the hand or a metal
mass connected to earth. The spot immediately jumped to the other side
of the tube, § 49, near centre, and to all appearances was smaller and
brighter. Elster and Geitel had performed similar experiments at an
earlier date. (See _Wied. Ann._, LVI., 12, p. 733, also _Elect. Eng._,
about April, ’96.) They carried on the most minute investigations as to
the deflection of the cathode rays by an outside conductor. Tesla had
also noticed a similar deviation. See Martin’s _Tesla’s Researches_. He
used alternating currents as described in his system in § 51. Elster and
Geitel used the Tuma Alternating system. (See _Wied. Ann._, Ber. 102,
part 2A, p. 1352, ’94.) The source from which Salvioni’s description was
taken had no sketch, therefore the diagram made by Elster and Geitel is
reproduced. See Fig. 1. The cathode was aluminum and was connected to
one terminal of the transformer. The anode was connected to earth, and
also was the other terminal. Upon bringing the hand or other conductor
connected to earth to the phosphorescent spot, the cathode rays deviated
and the spot jumped over to the other side. § 50. The anode was a ring
surrounding the leading-in wires of the cathode, and the two leading-in
wires were surrounded by glass. It may be asked why the cathode rays
bent downward in the first place? Elster and Geitel found that they were
thrown thus in view of the nearness of some neighboring object connected
to earth. To overcome the action of surrounding objects, the tube was
surrounded by a ring as shown in Fig. 2. However, the rays were still
sensitive to objects well connected to earth, and when brought quite
close to the tube.
[Illustration:
Figs. 1 and 2.
]
117_a_. HAMMER AND FLEMING’S MOLECULAR SCIAGRAPH, WITHIN A VACUUM TUBE.
(_Citations below._)—In view of the overwhelming evidence concerning the
generation of X-rays by the impact of cathode rays, within a high vacuum
upon the glass or material which preferably forms the anode, it becomes
appropriate, it is thought, to review the state of this department of
science, in order to arrive a little more closely at the relations which
exist between phenomena of low and high vacua. With the former, in that
condition in which striae are formed, permanent black bands or deposits
are produced upon the surface of the glass; the motion of the particles,
therefore, appearing to be in planes at right angles to the line joining
the anode and cathode. § 40. That the striae should touch the walls of
the tube seems to be necessary for the production of the deposit. § 44.
With a high vacuum, the direction of the cathode rays may be any that
one desires, it being only necessary to shape the cathode properly, on
the principle that the rays radiate normally from the surface. It is
known that the radiation is normal as much from the position of the
deposit as from that of the phosphorescent spot. It is certain that they
are rectilinear. § § 57 and 58. The phosphorescent spot becomes always,
sooner or later, when occurring upon the same part of the glass, the
location of a deposit from the cathode (§ 123), even when the cathode is
aluminum. § 123. The deposit is not the cause of the fatigue of the
glass. § 58. Puluj verified this. A wheel was made to rotate by the
radiations from the cathode, and therefore it is highly probable that
the motion of the molecules, which caused the deposit, is the force that
made the wheel rotate. § 58_a_. Why does it not follow that with
increase of E. M. F. the particles are thrown with such rapidity that
upon striking the proper surface (§ 80), X-rays are generated, but that
they are not generated when the velocity of the molecules is
insufficient. § 61_b_, p. 46. Attention is now invited to a phenomenon
which illustrates that a permanent sciagraph of objects may be impressed
upon the inner surface of a vacuum tube, by the deposit of molecules of
one of the electrodes. Refer, therefore, to the figure on page 30,
“Hammer and Fleming’s Molecular Sciagraph.” As will be seen from further
explanation and from the picture itself, the sciagraph _a b_ is made
because of the projection, in rectilinear lines, of molecules of carbon
or metal, from one of the electrodes, or at least from one more than the
other. One leg of the carbon, being in the way of the other, causes a
less deposit to be produced upon the glass at the intersection of the
plane of the horse-shoe filament and the wall of the vacuum tube.
Electrodes exist because the filament is of such a high resistance as to
produce a difference of potential between the two straight lower
portions of the filament. Mr. William J. Hammer possesses a remarkable
faculty for observing phenomena often overlooked by others. He first
observed a molecular shadow in 1880 and made records of his observations
in the Edison Laboratory note book. Since that time he has examined over
600 lamps, which were made at various periods during thirteen or
fourteen years, by twelve different manufacturers. (_Trans. Amer. Inst.
Electrical Eng._, Mar. 21, p. 161.) Every one, more or less, exhibited
the molecular shadow. It is a principle, therefore, that if the carbon
filament has both legs in the same plane, a sciagraph of one of them
will be produced. As the shadow is on one side of the bulb only, the
molecules fly off from only one electrode, viz., the cathode. By means
of photography, the effect is increased because of certain well-known
principles. The figure heretofore referred to is taken from a
photograph, but, of course, does not represent the sciagraph as well as
the original photograph, in view of the loss of effect by re-production
by the half-tone process. For further theoretical considerations, see
the Institute paper referred to, where the matter was discussed by
Profs. Elihu Thomson, Anthony and others. Independently of Mr. Hammer’s
discovery, Prof. J. A. Fleming, professor of electrical engineering in
the University College, London, England, discovered and studied the
matter, and presented it before the _Phys. Soc._ of London, appearing
about 1885 (_from memory_). The name “molecular sciagraph” is given by
the author because it is an accepted explanation that the deposit is due
to either molecules or atoms of the electrode, given off by evaporation
(page 46, lines 5 to 10), or electrical repulsion (§ 61_a_, lines 22 to
25), or, as some hold, by mere volatilization by the intense heat of
incandescence, or one or more combined; but electrical repulsion
certainly has something to do with the rectilinear propagation, for the
molecules are charged according to § 4.
[Illustration]
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