-------
65. LENARD’S EXPERIMENTS. CATHODE RAYS OUTSIDE OF THE DISCHARGE TUBE.
_Wied. Ann._, Jan., ’94, Vol. LVI., p. 225; _The Elect._, Lon., Mar. 23
and 30, ’94, Apr. 6, ’94; and _Elect. Rev._, Lon., Jan. 24, ’96, p.
99.—Of more importance in connection with X-rays is the consideration of
Lenard’s experiments than any others. The reader must bear in mind that
his exhaustive investigations resulted from his discovery (founded upon
a hint from Hertz) that the cathode rays might be transmitted to the
outside of the generating discharge tube. His interest, therefore, in
the discovery was so great that his researches extended to the minutest
details. Passing from these introductory remarks, the characteristics of
the tube that he employed will be explained first. Reference may now be
made to the accompanying Fig. A. He employed several different kinds of
tubes, but finally settled upon one of which the essential elements are
shown in the said figures. It was permanently connected to the pump, §
53, so that the pressure within could be varied. Opposite the cathode,
which consisted of a thin disk of aluminum, the end of the tube was
provided with a thick metal cap, having a perforation, which in turn was
closed by a thin aluminum sheet secured by marine glue in an air-tight
manner, and called a window. The anode was a heavy brass cylinder, shown
in section, within the discharge tube and surrounding the leading-in
wire of the cathode. The anode and the aluminum window were connected to
each other, electrically, and to earth, as well as two a secondary
terminal of an induction coil, whose electrodes were in shunt to those
of the discharge tube, in order that the operator might adjust the
sparking distance which rapidly increased with the exhaustion. The
induction coil had a mercury interrupter.
65. PROPERTIES OF CATHODE RAYS IN OPEN AIR.—In all directions around the
window upon the outside and in the open air, a faint bluish glow (§ 11
and 140) extended and vanished at a distance of 5 cm., as indicated by
dotted lines in Fig. B at beginning of this chapter. The degree of
luminosity may be judged by saying that it was not sufficient to admit
of investigation by the ordinary pocket spectroscope. A new window was
void of luminosity; but with use, bluish gray and green and yellow spots
occurred thereon.
66. PHOSPHORESCENCE BY CATHODE RAYS.—Substances which generally
phosphoresced by light and cathode rays in the generating bulb, § 55,
also phosphoresced under the influence of the rays in open air,
excepting eosin, gelatin, both phosphorescent in light, were not so in
cathode rays; so also with solutions of fluorescein, magdala red,
sulphate of quinine and chlorophyll. Phosphorescence was less if the
rays first passed through a tube of glass or tinfoil lengthwise. The
phosphorescent light of the phosphides of the alkaline group, uranium
glass, calcspar and some other substances, was so great that the
luminosity of the air was invisible by contrast. The maximum distance at
which phosphorescense was discernable in open air was about 8 cm. The
best phosphorescent screen consisted of paper saturated with
pentadecylparatatolylketone. In order to prepare it, he laid a sheet of
paper upon glass and applied the fused chemical with a brush. As to the
color of the phosphorescence and fluorescence of different substances,
and as to the degree of luminosity outside of the vacuum tube, they were
about the same as reported by Crookes when located within the discharge
tube. §55. Baric and potassic and other double cyanides of platinum,
common flint, glass, chalk and asaron all exhibited the same property as
when exposed to ultra-violet light, that is, fluoresced or
phosphoresced. Sulphide of quinine in the _solid_ state fluoresced, but
not in _solution_. Petroleum spread on a piece of wood fluoresced, and
also fluorescent-hydrocarbons generally.
66_a_. The cathode rays were not easily transmitted by tinfoil or glass,
because the degree of phosphorescence on the screen was greatly reduced
by interposing such sheets. The phosphorescense ceased also by
deflecting internal cathode rays from the window by a magnet. For full
treatment of the phenomena of phosphorescence, see Stokes’ experiments,
described in _Phil. Trans._, 1852, Art. “Change of Refrangibility of
Light.” In brief, Stokes’ theory assumes that such substances have the
power of reducing the refrangibility. Example: Ultra-violet light,
highly refractive, is changed to yellowish green, less refrangible, by
reflection from uranium glass.
67. THE ALUMINUM WINDOW, A DIFFUSER OF CATHODE RAYS. § 63_b_. The
conclusion arrived at by mounting the phosphorescent screen in different
positions and at different angles as well as by observance of the
gaseous luminosity, was that the aluminum window scattered the
rectilinear parallel cathode rays in all directions, § 57.
68. TRANSMISSION OF EXTERNAL CATHODE RAYS THROUGH METALS.—The
phosphorescence was not diminished apparently by an intervening
gold-leaf or silver or aluminum foil, while it was extinguished by
quartz .5 mm. thick which also cut off the atmospheric glow beyond
itself. The leaves and foil did not so act. The difference of thickness
should be borne in mind, as metal, as thick as the quartz did not
transmit. As to other substances, tissue paper cast a slight shadow,
which was darker with an additional sheet; but the shadow was
independent of color and blackness, § 154. Ordinary writing paper was
roughly, proportionally opaque, while the shadow was black with
cardboard .3 mm. thick. Glass films as made by blowing glass, cast faint
shadows when .01 mm. thick. He proved that there was little difference
as to the transmitting power of conductors and dielectrics when thin.
Mica and collodion sheets .01 mm. thick cast scarcely any shadow. The
reader may bear in mind the striking differences between these
properties of cathode rays, and X-rays, § 135, it being assumed always
that the generating devices are the same; for example, water permitted
the cathode rays (were these simply feeble X-rays?) to be transmitted
only when in very thin layers. Even soap water films which were only
.0012 mm. thick cast shadows, although very faintly. The shadows of
drops of water were black, while water several feet thick has been
traversed by X-rays from a small set of apparatus. By careful
measurements he found that the law of transmission must be different
from that of light, for in the latter, many substances are opaque
although exceedingly thin, while with cathode rays, the same will
traverse all films. Goldstein and Crookes reported that thin mica, glass
and collodion films made very dark shadows, § 58, within the discharge
tube, whereas Lenard found that outside of the vacuum tube, in open air,
the transparency was greater than according to the earlier
experimenters, but he acknowledged that Crookes and Goldstein were
inconvenienced and limited in the number of observations because it is
so difficult to carry on such experiments within an hermetically sealed
tube. Again, he acknowledged that perhaps the cathode rays of those
experimenters were of a different kind. The construction shown in the
above figures was modified by using a very thin glass window instead of
aluminum, and the results were the same allowing for the different
opacity, to ordinary light, of aluminum and glass.
The cathode rays acted upon the sense of smell and taste as the nose and
mouth could detect ozone, § 84, at end.
69. PROPAGATION. TURBIDITY OF AIR. Upon studying the shadows on the
phosphorescent screen, it was noticed that the rays were bent around the
edges of the object. Again, when the object had a slit, diffusion could
be noticed by the shape (as in Crookes Ex., Fig. 15, p. 17,) of the
luminous portion of the phosphorescent screen. In Fig. B, at beginning
of this chapter, the spatter work represents the shape of the luminous
portion, the darker part representing the most luminous surface of the
screen, the latter being held at right angles to the thick plate, having
the slit and opposite the aluminum window. By varying these experiments,
especially by changing the angle of the screen he found that not the all
rays were diffused, but as in the passage of light through milk, some
were transmitted in rectilinear lines.
70. PHOTOGRAPHIC ACTION.—He performed with sensitive silver compound
papers, an experiment somewhat similar to those with phosphorescent
bodies and also others. Behind a rather thick opaque plate the chemical
film was not acted upon, but the rate of blackening near the aluminum
window without obstruction of intermediate bodies was about the same as
that with befogged sunlight. The former, moreover, was acted upon at a
much greater distance than that at which phosphorescence was exhibited
and beyond the atmospheric luminosity. By means of shadow pictures or
sciagraphs, he compared the shadows produced by the external cathode
rays with those which would have been obtained by light. Referring to
Fig. C, beginning of this chapter, the sensitive plate was half covered
with a plate of quartz, Q, and half with a plate of aluminum, A´
overlapping the quartz. With light, the shadows would have appeared as
in said figure, that is, one-half black as produced by aluminum, a
quarter rather light as produced by quartz, and the other quarter
bright, or a similar arrangement, according to whether the negative or
the positive photograph is considered; but with the cathode rays, the
appearance of the developed plate was as in Fig. D., beginning of this
chapter. The quartz cast the black shadow, while the aluminum, the
lighter one. Furthermore, the luminosity of the air produced a variable
light on the other quarters. A similar appearance was produced by
casting shadows of such plates upon the phosphorescent screen; but, of
course, the picture was not a permanent one. The photographic plate
served to accumulate the power, for the cardboard which cast a faint
shadow upon the phosphorescent screen, showed a black shadow upon the
photographic paper by sufficiently long exposure. At the same time,
strips of thin metal were placed side by side between the chemical paper
and the cardboard, and they showed different degrees of shading. The
cardboard was quite thick, being .3 mm. Prof. Slaby (see _Elect. Rev._,
Lon., Feb. 7, ’96), _after_ Röntgen’s discovery, produced sciagraphs of
the bones of the hand at the window of the Lenard tube. Lenard doubted
whether the cathode rays produced direct chemical action. Iodine paper
became bluish, but he could not obtain other chemical effects usually
produced by light, and other agencies, for example, oxygen and hydrogen
mixed together in the proportion to form water, and which were in their
nascent state, and which were located in a soap-bubble, did not explode
or ignite. No effect was produced upon carbon bi-sulphide nor
hydrogen-sulphide, although the exposure was very long. Ammonia was not
formed when the rays acted upon a mixture of three parts hydrogen and
one part nitrogen, as to volume. He thought that he noticed a small
expansion of air, hydrogen and carbonic acid separately located in a
vessel having a capillary tube and water to indicate the expansion. He
attributed the slight expansion to an indirect action, although very
slight, caused by heat produced by the cathode rays, § 27, and yet
neither the thermopile nor the thermometer showed any calorific effects
although the thermopile responded to the flame of a candle 50 cm.
distant.
71. CATHODE RAYS AND ELECTRIC FORCES DISTINGUISHED. The earth connection
heretofore mentioned with the aluminum window was for the purpose of
dispensing with sparking, but even then the approach of another
conductor connected to earth would cause some sparking. Sparks could be
drawn when the cathode rays were deflected from the aluminum window by a
magnet. Fig. E, at beginning of chapter. He argued that the rays and the
electric forces of the spark are non-identical. He was not satisfied
with this as an absolute proof, and he instituted others. He enclosed
the whole generator in a large metal box. In the observation space, that
is, around and near the window, he located another box, having an
aluminum front facing the window. See Fig. E, at beginning of chapter.
It was within this second box that he took the sciagraph shown in Fig.
D, at beginning of chapter. It is important to notice that sparks could
not be drawn at points within the said second box, shown at the left,
even by a metallic point shown projecting thereinto. No spark occurred
whatever, not even from the aluminum front. Sparking occurred when the
pointed wire was extended to a considerable distance outside of the back
of the small box, but it was remarked that the electric force did not
enter through the front wall but was introduced “from behind into the
box, by the insulation of the wire.” No one can, therefore, enter the
objection that the cathode rays experimented with, were generated from
the aluminum window as a cathode. They came from the cathode referred to
entirely within the vacuum tube. Prof. J. J. Thomson, F. R. S., had at
an early date conjectured that cathode rays did not pass through thin
films of metal, but that these films acted as intermediate cathodes
themselves. See his book on “_Recent Researches_,” p. 26, also _The
Elect._, Lon. March 23, ’94, p. 573, in an article by Prof. Fitzgerald,
who names that citation.
72. CATHODE RAYS PROPAGATED, BUT NOT GENERATED IN A HIGH VACUUM.—The
proposition was proved by having two tubes, one called the generating
tube and one the observation tube, the former being like that shown in
Fig. A, at beginning of chapter, which is partly repeated in Fig. F, at
beginning of chapter, combined with the observation tube, which contains
the two electrodes for casual use; but the one on the right is a disk
extending nearly throughout the cross sectional area, and having a small
central opening. Although both tubes were connected to the air pump,
yet, by means of stop-cocks, the vacuum in one tube could be maintained
at a maximum degree for hours, while the other was at a minimum. The
first experiment was performed with a vacuum, about as high as that
employed in Crookes’ phosphorescent experiments, § 53. There was a patch
of green light, § 57, at the extreme left end of the observation tube
and the glass was green at the right, § 54, and a little to the left of
the perforated disk electrode _a_. The other electrode of this tube was
located at the upper left and lettered _k_.
72_a_. The magnet deflected the rays _in the observing tube_ as
indicated by the partial extinction of the phosphorescent patch. He
noticed that with the rarefied atmosphere the amount of turbidity was
enormously reduced, or in other words, that the rays were propagated
more nearly in rectilinear lines. All the experiments on the cathode
rays, in this observing tube, were of about the same nature as those
which could be produced in the discharge tube.
[Illustration:
FROM SCIAGRAPH OF CAT’S LEG, BY PROF. WILLIAM F. MAGIE.
Copyright, 1896, by William Beverly Harison, pub. of X-ray pictures,
59 Fifth Ave., New York City.
]
72_b_. The principal experiment consisted in exhausting the observing
tube to such a degree that cathode rays could not be generated therein.
The vacuum was so perfect that when used as a discharge tube all
phosphorescence gradually died away until it disappeared, and no current
passed (§ 25) except on the outside surface of the glass. The coil was
so large, electrically, that the length of the spark between spheres was
15 cm. Upon charging the right hand tube and generating cathode rays, it
was determined by means of magnetic deflection, phosphorescence and
other effects, that the cathode rays traversed the highest possible
vacuum (§ 19, near end, where energy must have passed through the high
vacuum to produce luminosity in the inner bulb). The external and
internal rays were certainly different forms of energy. Inasmuch as he
noticed that rarefied air was less turbid and less absorptive than air
at ordinary pressures, it occurred to him to make a very long tube,
namely, 1 m, or a little over 3 feet. He employed very severe steps for
obtaining an exceedingly high vacuum, the operation occupying several
days. The pump used was a Toepler-Hagen, while a Geissler pump was
employed separately for the discharge tube. The pencil of cathode rays
traversed the whole length of the long tube. See a portion of the
apparatus in Fig. G, at beginning of this chapter. One disk was of metal
and perforated with a pin hole and the other was a phosphorescent
screen, so that when the cathode pencil passed through the hole in the
plate a patch was seen upon the phosphorescent screen. The
phosphorescent spot was always, no matter what the relative distances of
the disks were from each other, and from the end of the tube,
substantially the same as it would have been by calculation assuming
that there was no turbidity effect. The patches, in each instance, were
a little smaller in diameter than the calculated ones. For example with
one measurement, at certain distances, the actual diameter of the patch
was 2.5 mm., while the calculated diameter was 2.9 mm. In his
experiments with light under the same conditions, the luminous spots
were also a little smaller than the calculated or geometrical. The disks
had iron shoes and were moved to different positions by a magnet. He
concluded, therefore, that in what may be called a perfect vacuum, light
and cathode rays have a common medium of propagation, namely, the
assumed ether. Prof. Fitzgerald, in _The Elect._, Lon. Mar. 23, ’94,
does not agree broadly with him in this; neither does he contradict him.
He argues rather on the point that the cathode rays and light rays are
not identical, but Lenard does not affirm this, because the magnet will
attract the former and not the other. Prof. Fitzgerald admits this and
calls to mind that even in a vacuum, as obtained by Lenard, there were
still ten thousand million molecules per cu. mm. and therefore he thinks
it is better to look to matter rather than ether as the medium of
propagation of cathode rays. § 61_b_. On the other hand, Lenard agrees
with certain other predecessors, Wiedemann, Hertz and Goldstein, in
favor of cathode rays being etheric phenomena. See _Wied. Ann._, IX., p.
159, ’80; X., p. 251, ’80, XII., p. 264, ’81; XIX., p. 816, ’83; XX., p.
781, ’83. The vacuum with which Lenard operated, was .00002 mm.
pressure, obtained by cooling down the mercury to minus 21° C. This
vacuum was so high that all attempts to prove the presence of matter
failed. Neither did the exceedingly high vacuum deaden the cathode rays.
On the other hand, as noted, they were assisted rather than hindered. §
135.
73. CATHODE RAYS. PHENOMENA IN DIFFERENT GASES.—The apparatus consisted
of an observing tube having a tubular gas inlet and outlet both in one
end and arranged in line with the cathode of the discharge tube. See
construction in Fig. H, at beginning of this chapter, the tube being
about 40 cm. long and 3 cm. in diameter. He was very careful in every
case to chemically purify and dry the particular gas. He omitted the
perforated disk and provided an opaque strip of the phosphorescent
screen on the side toward the window and made his observations from the
other side, the object of the experiment being particularly to test the
transmission of cathode rays in different gases. With any particular
gas, he moved the phosphorescent screen along by means of a magnet until
the shadow on the screen became invisible. It is evident that the
distances of the screen from the window for different gases would
indicate the relative transmitting powers. He also modified the
experiment by varying the density of the gases, hydrogen being taken as
1 as usual, nitrogen 14, and so on. The transmitting power of hydrogen
was nearly five times as great as that of nitrogen, air, oxygen and
carbonic acid gas, which did not much differ. § 10 and 18. Sulphurous
acid was a very weak transmitter. All the gases became luminous near the
window as in air. § 65. The colors were all about the same as far as
distinguishable, § 11, which was difficult in view of the brightness of
the phosphorescence on the glass. It was a universal rule, that when the
density decreased, the transmitting power increased. In high vacua, in
all gases, the rays went through the space in rectilinear lines in all
directions from the window, and generally it made no difference what gas
was employed provided the vacuum was as high as hundredths of a
millimetre. At this pressure all gases acted the same. To be sure, the
phosphorescence did not occur at this high vacuum at a great distance as
might be expected, but it should be remembered that the intensity of the
rays varied as the square of the distance, and, therefore, at very great
distances, the action was very weak.
74. CAUSE OF LUMINOSITY OF GAS OUTSIDE THE DISCHARGE TUBE.—At ordinary
pressures, in the cases of hydrogen and air, as has been noted, the gas
became luminous in the observing tube, the effect being, of course, the
same as entering open air, represented in Fig. A, beginning of this
chapter. In order to determine the luminosity at less pressures, the
gas, of whichever kind, was enclosed in a rather long observing tube and
only at rather high vacua did the bluish and sometimes reddish gaseous
luminosity disappear. Upon grasping the tube with the hand or
approaching any conductor connected to earth, of large capacity, the
column stopped at that point so that the remainder of the tube, beyond
the hand, measured from the discharge, was dark. The phosphorescence on
the glass wall of the tube produced by the cathode rays was not
influenced in any way by outside conductors, such as the hand. Cathode
rays themselves were not stopped apparently by the hand, because the
phosphorescent screen and glass, located beyond the hand, became
luminous. He concluded, therefore, that the glowing of the gas had no
close connection with the cathode rays. He proved this also by
deflecting the cathode rays in the discharge tube from a certain space,
and yet the gaseous luminosity remained. As an exception, the cathode
rays sometimes appeared to be closely associated with the light column.
He attributed the luminosity of the gas in general, at low pressures,
not to the cathode rays, but directly to the electric current or some
kind of electric force, § 11 and 14, which, as already remarked,
permitted sparks to be drawn from the aluminum window and surrounding
points.
The negative glow light in Geissler tubes, § 30, is also to be regarded
as gas illuminated by cathode rays. (Compare Hertz, _Wied. Ann._, XIX.,
p. 807, ’83.) Between that phenomenon and the glow observed here and
attributed to irradiation, there exists a correspondence, inasmuch as in
both cases the light disappears at high exhaustions, § 53, appears
fainter and larger when the pressure increases, § 54, and then becomes
brighter and smaller, § 54. But, whereas, the glow in the Geissler tube
has become very bright and small at 0.5 mm. pressure, the gas in our
experiment remains much darker up to 760 mm. pressure, and yet the
illuminated spot is much larger. This difference cannot, therefore, be
attributed to an inferior intensity of the rays here used. But it will
be explained, § 76, as soon as we can show that at higher pressures
cathode rays of a different kind are produced, which are much more
strongly absorbed by gases than the rays investigated hitherto and
produced at very low pressures.
[Illustration:
USE OF STOPS IN SCIAGRAPHY. (PERCH.) § 107., p. 101.
By Leeds and Stokes.
]
Fig. I, p. 52, illustrates the apparatus by which he studied the
rectilinear propagation and whereby he found that it was rectilinear
only in a very high vacuum. In the figure, the gas is at ordinary
pressure, and it will be noticed that the turbidity of the same is
indicated by the curved lines while the dotted lines show the volume
that would be occupied by light or other rectilinear rays, unaccompanied
by any kind of diffusion. In the observing tube, there was a disc having
a central hole at _a_. Beyond this disc, measured from the aluminum
window, was a fluorescent screen which, as well as the perforated disc,
could be moved to different distances by means of a magnet acting on a
little iron base. It is evident that upon moving the fluorescent screen
to different distances, the diameter of the luminous patch would be a
measure of the amount of turbidity. The curved lines intersecting the
peripheries of the luminous spots indicate, therefore, the field of the
cathode rays, so that said field would appear like a kind of curved cone
if the same were visible. Although hydrogen is the least turbid gas, yet
the phosphorescent patches were all larger except with a high vacuum
than they could have been with rectilinear propagation. An additional
characteristic of the phosphorescent spot, was its being made up of a
central bright spot and a halo less luminous, appearing like some of the
pictures of a nebula, see Fig. I´, p. 52, the darker or centre
indicating the brighter portion. In a perfect vacuum the halo did not
exist. He performed a similar experiment with ordinary light. No halo
occurred on a paper screen which was used instead of the phosphorescent
screen, but upon introducing a glass trough of dilute milk between the
window and the perforated disc, or between the disc and the paper
screen, nuclei and halos were obtained, illustrating a case of the
effect of a turbid fluid upon light, and assisting in proving that gases
act as a turbid medium to cathode rays as milk and similar substances do
to light; also in other gases than hydrogen, and by the use of cathode
rays, nuclei and halos were not obtained at high exhaustion, all the
gases becoming limpid. Taking into account pressure and density, all
gases behaved the same as to the power of transmission when they were of
the same density, without any regard whatever to their chemical nature.
Density alone determined the matter, according to Lenard.
75. CATHODE RAYS OF DIFFERENT KINDS ARE VARIABLY DIFFUSED.—He discovered
the remarkable property, contrary to his expectation, that if the rays
are generated at high pressures, they are capable of more diffusion than
when generated at lower pressures. This can be easily proved by any one,
for it will be noticed that upon increasing the pressure in the
discharge tubes the spots on the phosphorescent screen will not only
grow darker but larger and more indefinite as to the nucleus and halo.
He called attention to the agreement with Hertz, who also found that
there were two different kinds of rays, see _Wied. Ann._, XIX, p. 816,
’83, also see Hertz’s experiment. Lenard also pointed out the analogue
in respect to light, which, when of short wave length, is more diffused
in certain turbid media than that of greater wave length. Although
Lenard held that his experiment proved that cathode rays were phenomena
in some way connected with the ether, yet he pointed out an important
difference in connection with the property of deflection of the rays by
the molecules even of elementary gases like hydrogen, producing
diffusion of the rays, which accordingly may be considered as behaving
like light in passing through, not gases, but vapors, liquids and dust.
In the case of the cathode rays the molecules of a gas acted as a turbid
medium, but in the case of light, turbidity is only exhibited by vapors
or certain liquids, as so eloquently explained by Tyndall, in “Fragments
of Science,” 1871, where it is shown that _aggregation_ of molecules,
like vapors or dust in the presence of light, make themselves known by
color and diffusion, whereas the substances in a molecular or atomic
state do not serve to show the presence of rays of light.
76. LAW OF PROPAGATION.—Lenard recognized continually that there were
two kinds of cathode rays. One of them may have been X-rays without his
knowing it. In the latter part of ’95, he made some experiments
especially of a quantitative nature as to the principle of absorption of
the rays by gases. By mathematical analysis, based upon experiments, he
arrived at the principle that the absorptivity of a gas is proportional
to its pressure, or what is the same thing, to its density, or as to
another way of stating the law, “the same mass of gas absorbs at all
pressures the same quantity of cathode rays.” See _Elect. Rev._, Lon.,
as cited, p. 100.
77. CHARGED BODIES DISCHARGED BY CATHODE RAYS.—An insulated metallic
plate was charged first with positive electricity and in another
experiment with negative electricity. In each instance, the plate was
discharged rapidly by the cathode rays as indicated by the electroscope,
and the same held true when a wire cage in contact with the aluminum
window, surrounded the electroscope and the metallic plate. The effect
was stopped by cutting off the cathode rays by quartz .5 mm. thick. The
discharge took place, however, through aluminum foil. A magnet was made
to deflect the internal cathode rays, whereupon the discharge did not
take place, all showing that the discharge of the insulated plate was
directly due to those rays. A remarkable occurrence was the
accomplishment of _the discharge at a much greater distance than that at
which phosphorescence was exhibited_. See also Roentgen’s experiment—who
suggested that Lenard had to do with X-rays in this experiment, but
thought they were cathode rays. The maximum distance for the discharge
was about 30 cm. measured normally to the aluminum window. He caused a
discharge of a plate also in rarefied air. He admitted that the
experiments were not carried far enough to know whether the effect was
due to the action of the cathode rays upon the surface of the window, or
upon the surrounding air, or upon the plate. The author could not find
in Lenard’s paper any positive or negative proof that he had actually
deflected the external cathode rays by a magnet while passing through
air or gas at ordinary pressure. He had deflected them while passing
through a very high vacuum in the observing tube. Dr. Lodge, who briefly
reviewed Lenard’s experiments, expressed the same opinion. See _The
Elect._, Lon., Jan. 31, ’96, p. 439. For theoretical considerations of
the electric nature of light, the discharge law in the photo-electric
phenomena, the simple validity of the discharge law, the occurrence of
interference surfaces in the blue cathode light, the cathode rays in the
axis of symmetry, the necessary degrees of longitudinal electric waves,
the frequency of the cathode rays, and proof of longitudinal character
of cathode rays, see Jaumann in _The Elect._, Lon., Mar. 6, ’96;
translated from _Wied. Ann._, 571, pp. 147 to 184, ’96, and succeeding
numbers of _The Elect._, Lon., which were freely discussed in foreign
literature contemporaneously.
78. DE KOWALSKIE’S EXPERIMENT. SOURCE, PROPAGATION AND DIRECTION OF
CATHODE RAYS. _Acad. Sci._, Paris, Jan. 14, ’95; _So. Fran. Phys._ Jan.
’95; _Nature_, Lon. Jan. 24, ’95; Feb. 21, ’95.—The conclusions he
arrived at are, 1. The production of the cathode rays does not depend on
the discharge from metallic electrodes across a rarefied gas, nor is
their production connected with the disintegration of metallic
electrodes. 2. They are produced chiefly where the primary illumination
attains suitable intensity, that is, where the density of the current
lines is very considerable. 3. Their direction of propagation is that of
the current lines at the place where the rays are produced, from the
negative to the positive poles. They are propagated in the opposite
direction to that in which the positive luminosity is supposed to flow.
§ 43. He employed a Goldstein tube reduced at the centre. § 41. It was
found that the cathode rays are formed not only at the negative
electrode, but also at the constriction, directly opposite the cathode.
De Kowalskie carried on further experiments in this line in order to be
satisfied with the principles named above, which he formulated. In one
tube, he was able to produce cathode rays at either end of the capillary
tube forming the constricted part of a long vacuum tube. No electrodes
were employed. The tube was merely placed near a discharger through
which “Tesla currents” were passed? He seems to have been working with
X-rays without knowing it; for his results agree with those of Roentgen
and later experimenters that the source of X-rays is the surface of a
substance where it is struck by cathode rays. The statements were about
as definite as could be expected at that date.
[Illustration:
HAND, BY OLIVER B. SHALLENBERGER, TAKEN WITH FOCUS TUBE.
§ 137, p. 136.
]
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