137. TESLA’S EXPERIMENTS. _Elec. Rev._, N.Y., March 11, ’96, page 131,
March 18, page 147, April 1, page 171, and April 8, page 183. KIND OF
ELECTRICAL APPARATUS FOR OPERATING DISCHARGE TUBES FOR POWERFUL X-RAYS.
§ 106, 109, 114, 131. The experiments performed by Nikola Tesla were
particularly noteworthy for the magnitude and intensity of the rays
generated by his apparatus, under his skilful manipulation of the
adjustments and circuits particularly as to resonance. The remarkable
results that he obtained are not surprising when we learn that he
employed his well-known system for producing exceedingly enormous
potential and unusually high frequency. § 51. The primary electrical
generator as he indicated and as apparent from his system referred to in
the above section, could be either a direct or alternating current
generator, or other form. If the first is employed, of course an
interrupter is necessary in order that there may be a current induced in
the secondary.
[Illustration:
SCIAGRAPH OF RAT, TAKEN BY OLIVER B. SHALLENBERGER WITH FOCUS TUBE
(CUT AT p. 81) AND TESLA SYSTEM. § 137, pp. 136 and 138.
]
Mr. Oliver B. Shallenberger, (_Mem. Amer. Inst. Elec. Eng._) whose
laboratory is in Rochester, Pa., gave some important general
instructions concerning the Tesla system § 51, that he employed in the
production of remarkably clear sciagraphs, in conjunction with the focus
tube, § 91, representing the hand at page 68, and showing a rat shown at
this § 137. (_Elec. World_, N.Y., March 17, ’96.) Even the ligaments
were clearly shown in the sciagraph of the rat, and some of them are
dimly reproduced by the half tone process. As to the apparatus and
operation, which are especially important, it may be stated that the
current was taken from an alternator, of a frequency of 133 periods per
second, and passed through a primary coil of a transformer for
increasing the E. M. F. from 100 volts to from 16 to 25 thousand. The
secondary current was then passed through Leyden jars and a double
cascade of slightly separated brass cylinders, whereby it was changed
into an oscillatory current of an extremely high frequency, which was
then conducted through the primary of a second induction coil having
very few turns of wire, and no iron core and having a ratio of 7 to 1.
By this means the E. M. F. was raised to somewhere between 160,000 volts
to 250,000, and was used to energize the discharge tube for the
generation of X-rays. Caution should be taken, because the current
coming from the first transformer, being of large quantity and very high
E. M. F. is exceedingly dangerous, but the current of the second
secondary has been passed through one’s body without danger, as reported
by Mr. Tesla several years ago, and confirmed by Mr. Shallenberger.
138. PHOSPHORESCENT SPOT MAINTAINED COOL.—In testing the power of the
X-rays in connection with the appearance of the phosphorescent spot,
Tesla noticed that they were most powerful when the cathode rays caused
the glass to appear as if it were in a fluid state. § 61. To prevent
actual puncture, he maintained the spot cool by means of jets of cold
air. It became possible thereby to use bulbs of thin glass at the
location of the generation of the X-rays. § 119. He concluded from
certain results that not only was glass a better material for discharge
tubes than aluminum, but because, by other tests, he found that thin
aluminum cast more shadow with X-rays than thicker glass. There are, of
course, many other reasons, based on mechanical construction, why glass
is preferable, and also why a tube with an aluminum window is not to be
desired. Principally, the latter will soon leak.
139. EXPULSION OF MATERIAL PARTICLES THROUGH THE WALLS OF A DISCHARGE
TUBE.—At quite a low vacuum, and after sealing off the lamp, he attached
its terminal to that of the disruptive coil. After a while, the vacuum
became enormously higher, as indicated by the following steps: First, a
turbid and whitish light existed throughout the bulb. This was the first
principal characteristic. Next, the color changed to red, and the
electrode became very hot, in that case where powerful apparatus was
employed. The precaution should be taken to regulate the E. M. F., to
prevent destruction of the electrode. Gradually, the reddish light
subsided, and white cathode rays, which had begun, grew dimmer and
dimmer until invisible. At the same time, the phosphorescent spot became
brighter and brighter and hotter and hotter, while the electrode cooled,
until the glass adjacent thereto was uncomfortably cold to the touch. At
this stage, the required degree of exhaustion was reached, and yet
without any kind of a pump. He was enabled to hasten the process by
alternate heating and cooling, and by the use of a small electrode. This
whole phenomenon was exhibited with external electrodes as well. He
acknowledged that instead of the disruptive coil, a static machine could
be used, or, in fact, any generator or combination of devices adapted to
produce a very high E. M. F.
The reduction of temperature of the electrode he attributed to its
volatilization. Without actually testing the rays with a fluorescent
screen or photographic plate, he could always know their presence by the
relative temperatures of the phosphorescent spot and the electrode, for
when the latter was at a low temperature and the former at a high
temperature, X-rays were sure to be strong.
From the fact that the vacuum became higher and higher by the means
stated, he was very much inclined to believe that there was an expulsion
of material particles through the walls of the bulb. When these
particles which were passing with very great velocities struck the
sensitive photographic plate they should produce chemical action. He
referred to the great velocity of projected particles within a discharge
tube, pages 46 and 47, and to Lord Kelvin’s estimate upon the same, and
reasoned that with very high potentials, the speed might be 100 km per
second. The phenomenon indicated, he said, that the particles were
projected through the wall of the tube and he entered into an elaborate
discussion on this point. He referred to his own experiment of causing
the rays from an electrode in the open air to pass directly through a
thick glass plate. § 13. He performed an experiment also of producing a
blackening upon a photographic plate apparently by the projected
particles, an electrical screen being employed to prevent the formation
of sparks. § 35. which as well known will cause chemical action upon the
plate. No stronger proof as to the expulsion of material particles could
be desired than an operation in which the eyes can see for themselves
that such an action must have taken place. Usually he was troubled by
the streamers (cathode rays) from the electrode suddenly breaking the
glass of the discharge tube. This occurred when the spot struck was at
or near the point where the same was sealed from the pump. He arranged a
tube in which the streamers did not strike the sealing point, but rather
the side of the tube. It was extraordinary that a visible but fine hole
was made through the wall of the tube, and especially that no air rushed
into the vacuum. On the other hand, the pressure of the air was overcome
by something rushing out of the tube through the hole. The glass around
the hole was not very hot, although if care were not taken, it would
become much hotter, and soften and bulge out, also indicating a pressure
within, § 27. greater than the atmospheric pressure. He maintained the
punctured tube in this condition for some time and the rarefaction
continued to increase. As to the appearances, the streamers were not
only visible within the tube, but could be seen passing through the
hole, but as the vacuum became higher and higher, the streamers became
less and less bright. At a little higher degree of vacuum, the streamers
were still visible at the heated spot, but finally disappeared.
This electrical process of evacuating varies in its rapidity according
to the thinness of the glass. Here again he noted the application of his
theory in that an easier passage was afforded for the ions. § 47. A few
minutes of operation produced through thin glass, a vacuum from very low
to very high, whereas, to obtain the same vacuum through much thicker
glass over 1/2 hour was necessary. Again with a thick electrode the time
required was much greater. The small hole was not always visible and it
was thought that the material went through the pores. The result
obtained by the following experiment tends to uphold Mr. Tesla’s
emission theory.
139_a_. LAFAY’S EXPERIMENT. GIVING TO X-RAYS THE PROPERTY OF BEING
DEFLECTED BY A MAGNET BY PASSING THEM THROUGH A CHARGED SILVER LEAF.
_Comptes Rendus_, March 23, ’96 and April 7, 13, 27, and _L’Ind. Elec._,
April and May ’96. From trans. by Louis M. Pignolet. He placed at about
.5 cm. below a discharge tube, a lead screen pierced by a slit 2 mm.
wide; and 0.04 m. lower, a second lead screen having a slit 5 mm. wide
completely covered by an extremely thin leaf of silver. Opposite the
silver leaf and exactly in the axis of the slit, was fixed a platinum
wire 1.5 mm. diameter. Thus, the rays which passed successively through
the two slits projected a shadow of the wire on a photographic plate
below.
When the silver leaf was connected to the negative pole of the induction
coil that excited the tube, the rays, which had become electrified (§
61_b_, p. 47) bypassing through the leaf, were deflected by a magnetic
field of about 400 L. G. S. units, whose lines of force were parallel to
the slit. The direction of the deflection was determined by the same law
as that of the deflection by a magnetic field of the cathode rays in the
interior of a discharge tube. § 59. When the silver leaf was not
connected to the coil, no deflection was produced. § 79.
To double the apparent deflection, one part of the slit was covered by a
lead plate during the first half of the experiment. The lead plate was
removed and placed over the other part of the slit, and the direction of
the magnetic field reversed during the last half of the experiment. Thus
the distance on the sciagraph between the two parts of the wire, was
double the deflection produced by the magnetic field.
The deflection was in the same direction when the silver leaf was
connected to the negative pole of a static electric machine, but was in
the opposite direction when the leaf was connected to the positive pole
of the machine. The test was criticised in the scientific press, and,
therefore, in order to be certain that the deflections observed were not
due to the combined effects of the electro-magnet which produced the
magnetic field and the electric field of the charged silver leaf, the
experiments were modified. To remove this uncertainty, the electrified
rays were caused to enter a grounded Faraday cylinder (see figure at E.
F. G. H., p. 47), through a small opening, before passing between the
poles of the electro-magnet. The deviations which were recorded on a
photographic plate in the box were the same as before.
Additional experiments showed that the deflections by the magnetic field
took place as well when the rays were electrified, after their passage
through another magnetic field, as before. Lafay continued the
experiments in great detail and by many control tests, and he took
accurate measurements and followed the suggestions of others. It would
be well for those who have facilities to repeat these most interesting
and important researches, to determine for themselves some satisfaction.
It is of interest to note that an American, Paul A. N. Winand, (_Mem.
Amer. Inst. Elect. Engs._), in the absence of facilities for
experimenting, proposed (_Elect. World_, N.Y., June 6, ’96) to interpose
a hollow sphere, which had high potential, in the path of X-rays, and to
learn in what manner, if any, the rays are influenced. He argued that it
would seem natural that, inasmuch as the rays produce a discharge, there
should be a reaction of the charged surface upon the rays.
It is evident that if any one repeats these experiments, expert
manipulation is required.
139_b_. GOUY’S EXPERIMENTS. THE PENETRATION OF GASES INTO THE GLASS
WALLS OF DISCHARGE TUBES. _Comptes Rendus_, March 30, ’96. From trans.
by Louis M. Pignolet. From observations with slightly different glass
from four tubes, it seemed that the cathode rays cause the gases in the
tubes to penetrate the glass where they remain occluded until the glass
is nearly softened (after cutting off the current), by heat, whereby
they are set at liberty as minute bubbles visible by the microscope,
which finally partly combine and become visible to the naked eye.
[Illustration:
HALOS 1 FT. DIAM., IN CLEAR AIR, AROUND INCANDESCENT ELECTRIC LAMPS
OF USUAL SIZE. CROSS AT CENTER OF EACH HALO. § 140, p. 143.
Observed by means of a photograph, in 1882, by William J. Hammer.
]
[Illustration:
MORTIFICATION OF THE ULNA. § 204.
From sciagraph by Prof Miller.
]
Under the same conditions, tubes which have been used for a long time
exhibit numerous wrinkles, indicating a superficial modification of the
glass. These may exist with or without the bubbles.
140. DISCHARGE TUBE SURROUNDED BY A VIOLET HALO. By means of enormous
potential and high frequency, the tube was surrounded, Tesla stated, by
violet luminosity or halo. § 6. and 74. From the fact that Lenard
obtained a similar appearance in front of the aluminum window, it might
be reasonable to conclude that there is some close relationship between
the two phenomena.
As an illustration of halo by light, may be mentioned the well known
appearance so often occurring in the atmosphere concentrically with the
moon, and sometimes surrounding the sun. Under favorable circumstances,
(in a mist or dust in the air), a halo, at some distance from a flame or
other light is faintly visible. It has generally been assumed that the
reason of a halo by light is based upon the laws of reflection, or
refraction or both, the bending of the rays taking place, through, or
upon the surface of the particles of moisture. Others have held that
particles of ice in the upper atmosphere, are the reflectors or
refractors, or both. More puzzling has been the attempt to explain the
novel appearance reproduced fairly well in the cut, page 140. It is here
represented in print for the first time, but the photograph from which
it was taken, was at various times, shown to different physicists, some
of whom attributed the beautiful effect to the property of interference
of light, and naming Newton’s rings as an analogous production. Prof.
Anthony in an interview expressed himself as well satisfied that
interference could not occur under the circumstances named. He
recognized that there was a curved surface of glass which might be
considered as made up of an infinite number of layers. The author
introduces the matter for the purpose of consideration by others, and
especially because it is so intimately connected with the subject of the
vacuum tube and electricity. The details must be understood for the
purpose of proper appreciation. Mr. William J. Hammer, of New York, had
a photograph taken of the large Concert Hall at the Crystal Palace,
Sydenham, Eng., by the light of the Edison incandescent lamps with which
the Hall was illuminated. This photograph was made in 1882 during the
International Electrical Exhibition held at the Crystal Palace. The
picture shows a small section of the whole photograph and represents
(although probably no one would judge so by looking at the picture) a
festoon of _pear_-shaped incandescent electric lamps, each one hanging
downward, and separated from its neighbor by between _three and four_
feet. They were so far away from the camera that a picture of the lamps
unlighted, would have represented them as mere specks. The bright
circles with the bright central crosses in the centre of the dark spaces
were, therefore, fully one foot in diameter, while the lamp bulbs
themselves were only about two or three inches thick, as usual. Why then
should there be the halos? Why should the crosses appear? And why should
the black area be so large? If the electricity and vacuum have nothing
to do with it, why should not the halos appear when photographs are
taken of flames and other sources of light in the absence of mist and
dust? In order to answer questions which will perhaps be proposed, let
it be stated that there was no visible dust nor moisture in the room,
the photograph being taken early in the evening and at a time when the
Hall was not in use. The halos were not apparent except when reproduced
by a photograph. The lamps had the usual carbon filaments hanging so
that the several filaments were in different planes, and they were of 16
candle power and were connected in parallel circuit, the average E. M.
F. being about 110 volts. The lamps were fed by the Edison direct
current dynamos. The festoon shown, is one of a dozen or more which were
suspended between the columns rising from the gallery and supporting the
roof and were hung about forty feet from the floor. The hall was further
illuminated by a huge electrolier pendant from the centre of the
ceiling. These details were obtained from Mr. Hammer, who planned the
installation.
141. ANÆSTHETIC PROPERTIES OF X-RAYS.—Tesla reported that he and his
assistants tested the action of the rays upon the human system, and
found that upon continued impact and penetration of the head by very
powerful radiations, strange effects were noticed. He was sure that from
this cause a tendency to sleep occurred (§ 84, at end), and the
faculties were benumbed. He said that time seemed to pass quickly. The
general effect was of a soothing nature, and the top of the head seemed
to feel warm under the influence of the rays. Incidentally, he noticed,
as he stated, “When working with highly strained bulbs, I frequently
experienced a sudden and sometimes even painful shock in the eye. Such
shocks may occur so often that the eye gets inflamed, and one cannot be
considered cautious if he abstains from watching the bulb too closely.”
The author calls to mind the reports in the daily press that Edison also
noticed that the eyes were in some way sensitive to the rays. The eye,
it was reported, became fatigued at the time, and yet later, objects
could be more easily distinguished.
In this connection, it should be remembered that there are not only
cathode rays, X-rays, etc., but the electric force that Lenard spoke of
in the neighborhood of the discharge tube, and in testing the effects
upon the eyes, of course, the precaution should be taken to determine
whether cathode rays, X-rays or the electric sparks are answerable for
the peculiar effects. Roentgen reasoned, § 84, that the eyes were not
sensitive, but the rays, in his case, were not strong enough to travel
40 to 60 feet, as in Tesla’s experiments, but only 2 m. (about 7 ft.).
142. SCIAGRAPHS OF HAIR, FUR, HEART, ETC., BY X-RAYS.—Tesla was probably
the first to be at all successful in the representation in sciagraphs of
such objects as hair and cloth and similar easily permeable objects. In
the case of a rabbit, not only was the skeleton visible, but also the
fur. Sciagraphs of birds exhibited the feathers fairly distinctly. The
picture of a foot in a shoe not only represented the bones of the foot,
and nails of the shoe, but every fold of the leather, trowsers,
stockings, etc. His opinion as to the useful application of the rays was
that any metal object, or bony or chalky deposit could be “infallibly
detected in any part of the body.” In obtaining a sciagraph of a skull,
vertebral column, and arm, even the shadows of the hair were clearly
apparent. It was during such an experiment that the anæsthetic qualities
were noticed. The author saw several of the above named sciagraphs.
Furthermore, on the screen he believed he detected the pulsations of the
heart. _Elect. Rev._, N.Y., May, 20, ’96.
Although we do not doubt this report concerning what Mr. Tesla saw, yet
some scientific men are exceedingly dubious concerning the results
obtained by other scientists, unless the same are confirmed by
additional witnesses. It will certainly be of interest to such skeptics
to have corroboratory evidence. In company with Prof. Anthony, Mr. Wm.
J. Hammer and Mr. Price, editor of the _Elect. Rev._, N.Y., the author
visited a laboratory at 31 West 55th street, New York City, for the
purpose of beholding the pulsations of the human heart by means of an
experiment performed by Mr. H. D. Hawkes, of Tarrytown, N.Y. There was
nothing new about his apparatus, the admirable results being due merely
to accurately proportioned electrical and mechanical details and
skillful manipulation. The Tesla system was not used, but merely a large
induction coil and rotary interrupter, and a direct current from the
incandescent lamp circuit of 110 volts, all substantially as Roentgen
himself employed. The sciascope was provided with the Edison calcic
tungstate screen. In order to overcome the sparking between the
terminals on the outside of the tube after a few minutes of use, he
heated the cathode end by means of a Bunsen burner flame. § 139, near
beginning. The utility consisted in the evaporation of condensed
moisture upon the cool end of the discharge tube. The temporary heating
always prevented, for several minutes, any sparking on the outside.
After some preliminary experiments, each person, in turn, pressed the
sciascope upon the breast of another, at the location of the heart,
while the discharge tube was directly at the back of a young man. The
ribs and spinal column were visible, and, projecting from the spine,
appeared a semi-circular area, which expanded and contracted. Any one
viewing such an operation, and knowing that he is looking at the
movements of the heart, cannot but be impressed with weird wonder, and
cannot but credit great honor, not only to Roentgen and Lenard, but to
all those early workers who have gradually but surely, successfully made
discovery after discovery in the department of the science of
discharges, finally culminating in the most wonderful discovery of all.
The author remembers seeing in some medical paper that William J.
Morton, M.D., of New York, had also witnessed the beating of the heart
with the sciascope at an early date. Similar reports are occurring
weekly.
§ 142_a_. Mr. Norton, of Boston (_Elect. World._, N.Y., May 23, ’96)
also stated that the heart could be seen in faint outline, and also its
pulsations. The lungs were very transparent. The liver being quite
opaque, its rise and fall with the diaphragm was plainly followed.
Others have suggested drinking an opaque (to X-rays) liquid, like salt
water, and tracing its path.
143. PROPAGATION OF X-RAYS THROUGH AIR TO DISTANCES OF 60 FT.—In
Roentgen’s first experiments, the maximum distances at which the
fluorescent screen was excited was about 7 ft. Tesla obtained similar
action at a distance of over 40 ft. Photographic plates were found
clouded if left at a distance of 60 ft. for any length of time. This
trouble occurred when some plates were in the floor above and 60 ft.
distant from the discharge tube. He attributed the wonderful increase
largely to the employment of a single electrode discharge tube, because
the same permitted the highest obtainable E. M. F. that could be
desired.
[Illustration:
SCIAGRAPH OF FOOT IN LACE SHOE. § 204.
By Prof. Miller.
]
144. X-RAYS WITH POOR VACUUM AND HIGH POTENTIAL.—In the course of
Tesla’s experiments, he observed that the Crookes’ phenomena and X-rays
could be produced without the high degree of vacuum usually considered
necessary, § 118. but by way of compensation, the E. M. F. must be
exceedingly high, and, of course, the tube and electrical apparatus
substantially of those dimensions involved in Tesla’s work. One must be
careful not to over-heat the discharge tube, which is likely to occur by
increase of potential. He gave definite instructions for preventing the
destruction of the tube by heating, by stating that it is only necessary
to reduce the number of impulses, or to lengthen their duration, while
at the same time raising their potential. For this purpose, it is best
to have a rotary circuit interrupter in the primary instead of a
vibrating make and break, for then it becomes convenient to vary the
speed of the interrupter, which may be, evidently, so constructed that
the duration of the impulses may also be varied, for example, by
different sets of contact points arranged on the rotary interrupter, and
made of different widths.
145. DETAIL CONSTRUCTION AND USE OF SINGLE ELECTRODE DISCHARGE TUBES FOR
X-RAYS. He pointed out that with two electrodes in a bulb as previously
employed by nearly all experimenters, or an internal one in combination
with an adjacent external one the E. M. F. applicable was necessarily
greatly limited for the reason that the presence of both, or the
nearness of any conducting object “had the effect of producing the
practicable potential on the cathode.” Consequently he was driven, as he
said, to a discharge tube having a single internal electrode, the other
one being as far away as required. § 9. In view of his ingenious
arrangements of the disruptive coil, and circuits, condensers and static
screens for the bulb, he found it immaterial to pay attention to some
other details followed by experimenters. For example, it made
comparatively little difference in his results whether the electrode was
a flat disk or had a concave surface.
[Illustration:
TESLA’S FIGS. 1 AND 2, REFLECTION AND TRANSMISSION OF X-RAYS BY
DIFFERENT SUBSTANCES. § 145 and § 146_a_.
]
The form of tube described by Tesla in full, will hereinafter be alluded
to as exhibited in the several figures accompanying this description,
and it consisted, therefore, of the long tube “_b_” made of very thick
glass except at the end opposite the electrode “_e_”, where it was blown
thin, p. 149. The electrode was an aluminum disk having a diameter only
slightly less than that of the tube and located about one inch beyond
the rather long narrow neck _n_, into which the leading-in wire _c_
entered. It is important that a wrapping _w_ be provided around this
wire, both inside and outside of the tube. The sealing point was on the
side of the neck. An electric screen has been referred to heretofore. It
is lettered _s_, and was formed of a coating of bronze paint applied on
the glass between the electrode and neck _n_. The screen could be made
in other ways, for example, as shown at _s_, Fig. 2, where it consists
of an annular disk behind and parallel to the electrode disk. This ring
_s_ in Fig. 2. must be placed at the right distance back of the
electrode _e_, but just how far can only be determined by experience.
The unique service of the screen was that of an automatic system for
preventing the vacuum from becoming too high by use. The peculiar action
was as follows, namely from time to time, a spark jumped through the
wrapping _w_ within the tube to the screen and liberated just about
enough gas to maintain the vacuum at an approximately constant degree.
Another way in which he was able to guard against too high a vacuum,
consisted in extending the wrapping _w_ to such a distance inside of the
tube, that the same became heated sufficiently to liberate occluded
gases. As to the long length of the leading-in wire within a long neck
behind the cathode, Lenard found the same to be valuable in conjunction
with a wrapping around the wire. With high potential, a spark, at a
certain high degree of vacuum, formed behind the electrode, and
prevented the use of very high potential, but by having the wire extend
far into the tube and providing wrappers, the sparking was much less
likely to occur. By proper adjustment as before intimated, Tesla could
produce just about enough to compensate for the electrical increase of
the vacuum. Another difficulty that presented itself in connection with
high E. M. F. was the undue formation of streamers heretofore referred
to, apparently issuing from the glass, and so often disabling it. He
therefore immersed the discharge tube in oil as pointed out in detail
hereinafter. The walls of the tube served to throw forward to the thin
glass many of those rays that otherwise would have been scattered
laterally. Upon comparing a long thick tube of this kind with a
spherical one, the sensitive plate was acted upon by the rays in 1/4 the
time with the tube. A modification consisted in surrounding a lower
portion of the tube, with an outside terminal _e_, indicated in dotted
lines in Fig. 1. In this way the discharge tube had two terminals. The
greatest advantage probably in using a long tube, was that the longer it
was, within the proper limits, the greater the potential which could be
applied with advantages. As to the aluminum electrode, he noticed that
it was superior, in comparison with one made of platinum which gave
inferior results, and caused the bulb to become disabled in an
inconveniently short period of time.
146. PERCENTAGE OF REFLECTED X-RAYS. He performed some preliminary
experiments, testing roughly as to whether any appreciable amount of
radiation could be reflected or not from any given surface. Within 45
minutes he was enabled to obtain clear and sharp sciagraphs of metal
objects, and the same could have been obtained only by the reflected
rays, because he screened the direct rays by means of very thick copper.
By a rough calculation he found that the percentage of the total amount
of rays reflected was somewhere in the neighborhood of 2 per cent.
Prof. Rood, of Columbia University, N.Y., (_Sci._, Mar. 27, ’96.) by
means of an experiment with platinum foil, § 80, concluded that the per
centage was about .005, the incident angle being 45 degrees. He regarded
this figure as the mere first approximation. Judging from Roentgen, §
85, Tesla, Rood and others, therefore, it seems to be established that
the percentage of X-rays reflected is very small.
Prof. Mayer, of Stevens Institute, (_Science_, May 8, ’96,) is of the
opinion that there is a regular or specular reflection, having witnessed
some experiments obtained by Prof. Rood, of Columbia Univ., N.Y. Prof.
Mayer reported that the original negatives were taken in such a way as
to substantiate regular reflection, and were carefully examined by six
eminent physicists at the _National Acad. of Sci._ at Washington, April
23, ’96, and none had the slightest doubt concerning the completeness of
the demonstration. The material employed for reflecting was platinum
foil. § 103_a_.
DIFFERENCE BETWEEN DIFFUSION AND REFLECTION. Judging from the
experiments above related, as well as those considered in § 103_a_,
there might at first appear to be contradictory results, reported by
different authorities. Experts, it is thought will, without argument,
discover the harmonious agreement, and will commend the work of
scientists, who, in different parts of the world, and at about the same
time, made similar experiments, which now being considered jointly, are
found to agree so wonderfully closely. Upon reading the above sections
and those referred to, there can be no doubt whatever but that X-rays,
upon striking a body are, to a certain per cent. scattered, or thrown
back, or bent from their straight course, and sent in a backward and
different direction, at one angle or another. The only apparent absolute
contradiction to this is that of Perrin, § 103_a_, _near the end_. But
his is a case of one witness against scores, and, therefore, evidence
based upon his experiments, must be counted out. The error was either
due to some oversight of his own, or more probably the mistake is merely
a typographical one, for often a mistake creeps in between a man’s
dictation and the printed work. It is difficult to accuse Perrin of a
mistake, for he is a great French authority in such matters. Assuming
that no error has occured, let it be noticed that he does not pronounce
non-reflection from all substances, but only from steel p. 154, l. 9,
and flint, which have been so polished as to form a mirror-like surface,
whereas all other experimenters, with scarcely an exception, have not
employed such surfaces. The difficult point to believe is that, after
six hours, no energy from the mirror could be collected. If we accept
Perrin’s results it must be only in regard to those two particular
materials, polished steel and flint. Another feature which is on the
edge of conjecture, is that of true or specular reflection, referred to
by Prof. Mayer, § 146. Many attempts have been undertaken to prove
whether the rays were thrown backward on the principle of reflection as
light from a mirror, or of diffusion as light from chalk. Let the
student notice that the evidence is overwhelming in favor of the turning
back of the rays to a very small per cent. upon striking any object. As
to specular reflection, which means similar to the reflection of light
from a polished mirror, it is practically the same as diffusion, the
difference being substantially of a technical nature. This allegation is
based upon the detail distinction between reflection and diffusion given
by P. G. Tait, professor of natural philosophy, Univ. of Edinburgh, who
states, in _Encyclo. Brit._, vol. 141, p. 586:—
“It is by scattered light that non-luminous objects are, in general,
made visible. Contrast, for instance, the effect when a ray of sunlight
in a dark room falls upon a piece of polished silver, and when it falls
on a piece of chalk. Unless there be dust or scratches on the silver,
you cannot see it, because no light is given from it from surrounding
bodies except in one definite direction, into which (practically) the
whole ray of sunlight is diverted. But the chalk sends light to all
surrounding bodies, from which any part of its illuminated sides can be
seen; and there is no special direction in which it sends a more
powerful ray than in others. It is probable that if we could, with
sufficient closeness, examine the surface of the chalk, we should find
its behavior to be in the nature of reflection, but reflection due to
_little mirrors_ inclined to all conceivable aspects, and to all
conceivable angles to the incident light. _Thus scattering may be looked
upon as ultimately due to reflection._ When the sea is perfectly calm,
we see it in one intolerably bright image of the sun only. But when it
is continuously covered with slight ripples, the definite image is
broken up, and we have a large surface of the water shining by what is
virtually scattered light, though it is really made up of parts each of
which is as truly reflected as it was when the surface was flat.”
146_a_. REFLECTED AND TRANSMITTED X-RAYS COMPARED.—In order to carry on
a series of investigations, Mr. Tesla constructed a complete special
apparatus represented in Fig. 2, p. 149, and embodied in it also an idea
which he attributed to Prof. William A. Anthony, which consisted in
arranging for sciagraphs to be produced by the rays transmitted through
the reflecting substance as well as by the reflected rays themselves.
The figure serves to show at a glance the construction and, therefore,
the explanation need be but brief. It consisted of a _T_ tube, having
three openings, those at the base and side being closed by photographic
plates in their opaque holders, which carried on the outside the objects
_o_ and _o´_ to be sciagraphed. At an angle to both plates, and
centrally located, was a reflecting plate, _r_, which could be replaced
by plates of different materials. At the upper opening of the plate _B_
was a discharge tube, _b_, placed in a heavy Bohemian glass tube, _t_,
to direct the scattered rays downward as much as possible from the
electrode, _e_, to and through the thin end of the discharge tube. The
objects to be sciagraphed, namely _o_ and _o´_, were exact duplicates of
each other. No statement could be found as to the thickness of the
tested plates, _r_, except that they were all of equal size. The
distance from the bottom of the discharge tube to the reflecting plate,
_r_, was 13 inches, and from the latter to each photographic plate about
7 inches, so that both pencils of rays had to travel 20 inches in each
instance. One hour was taken as the time of exposure. After a series of
experiments with a great many different kinds of metals, they arranged
themselves as to their reflecting power, in an order corresponding to
Volta’s electric contact series in air. § 153. The most electro-positive
metal was the best reflector, and so on. For exhaustive investigations
upon the discovery of Volta, see _“Experimental Researches” of
Kohlrausch, Pogg. Ann., ’53_, and Gerland, _Pogg. Ann., ’68_. The metals
Tesla tested were zinc, lead, tin, copper and silver, which were, in
their order, less and less reflecting, and the order is the same in the
electro-positive series, zinc being the most positive, and the others
less and less so, in the order named. For a complete list of the metals
arranged by the Volta series, see any standard electrical text-book. He
could not notice much difference between the reflecting powers of tin
and lead, but he attributed this to an error in the observation.
He tried other metals, but they were either alloys or impure. Those
named in the list above were the pure metals. However, he carried on
experiments with sheets of many different substances, and arrived at the
following table, which shows particularly the relative transmitting and
reflecting powers of the various substances in the rough.
Impression by Impression by
Reflecting Transmitted Rays. Reflected Rays.
Body
Brass Strong Fairly good
Toolsteel Barely perceptible Very feeble
Zinc None Very strong
Aluminum Very strong None
Copper None Fairly strong but much
less than zinc
Lead None Very strong but a little
weaker than zinc
Silver Strong, a thin plate Weaker than copper
being used
Tin None Very strong about like
lead
Nickel None About like copper
Lead-glass Very strong Feeble
Mica Very strong Very strong about like
lead
Ebonite Strong About like copper.
By comparing, as in previous experiments, the intensity of the
photographic impression by reflected rays with an equivalent impression
due to a direct exposure of the same bulb and at the same distance, that
is, by calculations from the times of exposure under assumption that the
action upon the plate was proportionate to the time, the following
approximate results were obtained:
Impression
Reflecting by Impression
Body Direct by
Action Reflected
Rays.
Brass 100 2
Tool steel 100 0.5
Zinc 100 3
Aluminum 100 0
Copper 100 2
Lead 100 2.5
Silver 100 1.75
Tin 100 2.5
Nickel 100 2
Lead-glass 100 1
Mica 100 2.5
Ebonite 100 2
He stated that while these figures can be but rough approximations,
there is, nevertheless a fair probability that they are correct, in so
far as the relative values of the sciagraphic impressions of the various
objects by reflected rays are concerned.
In order to devise means for testing the comparative reflecting power in
a more decided manner, he laid pieces of different metals side by side
upon a lead plate. Consequently the reflecting surface was formed of two
parts corresponding to the two metals. § 80. The vertically
perpendicular partition of lead served to prevent the mingling of the
rays from the two metals. Ingenious precautions were taken; as for
example, so arranging matters that upon equal areas of the two plates,
equal amounts of X-rays impinged. § 80. He undertook to determine the
position of iron in the series by thus comparing it with copper. It was
impossible to be sure which metal reflected better. The same regarding
tin and lead and also in reference to magnesium and zinc. Here, a
difference was noticed, namely that the magnesium was a better
reflector.
He has made practical application of the power of the substances to
reflect a certain per cent. of the rays by employing reflectors for the
purpose of reducing the time required for exposure of the photographic
plates. It admits, he stated, of the use of reflectors in combination
with a whole set of discharge tubes, whereby rays which would be
otherwise scattered in all directions are brought more nearly to a
single direction of propagation.
[Illustration:
FROM SCIAGRAPH OF KNEE-JOINT. STRAIGHT, FRONT VIEW.
By Prof. Goodspeed. _Photo. Times_, July, ’96.
]
It might be argued, that in as much as zinc would reflect only about
three per cent. of the incident rays, no practical gain would ensue in
sciagraphy by the use of a reflector. He pointed out the falsity of such
an argument. In the first place, the angle employed in these tests was
45°. With greater angles, the proportion of reflected rays would be
greater assuming that the law of reflection is the same as that of
light. By mathematical calculation and tests, he showed that there was
no doubt whatever about the advantage of using reflectors. He obtained a
sciagraph, on a single plate, of the ribs, arms and shoulder, clearly
represented. He stated the details as follows. “A funnel shaped zinc
reflector two feet high, with an opening of five inches at the bottom
and 23 inches at the top, was used in the experiment. A tube similar in
every respect to those previously described, was suspended in the
funnel, so that only the static screen of the tube was above the former.
The exact distance from the electrode to the sensitive plate was four
and one-half feet.”
147. DISCHARGE TUBE PLACED IN OIL.—When the E. M. F. was increased, by
having the discharge tube, as usual, in open air, sparks formed behind
the electrode, and within the vacuum, and endangered the life of the
discharge tube. He obviated this difficulty partly by having the
electrode located well within the evacuated space, so that the wire
leading to it was unusually long. By excessive E. M. F., also, streamers
broke out at the end of the tube. To overcome all difficulties in
connection with sparking and breaking of the tube, he followed the
proposition of Prof. Trowbridge, and submerged the discharge tube in
oil, § 11, at end, and § 13, which was continually renewed by flowing
into and out of the vessel in which the discharge tube was contained,
all as shown in the accompanying figure, p. 157, “Discharge Tube
Immersed in Oil.” The discharge tube, _t_, may be recognized by its
shape, and it is located horizontally in a cylindrical tube lying
sidewise upon a table. To regulate the flow of the oil, the reservoir
may be raised and lowered by a bracket, s. The X-rays enter the outside
atmosphere by passing first through glass, then oil, and then through a
diaphragm of “pergament” forming the right hand end of the oil vessel.
When the results were compared with those obtained by Roentgen in his
first experiments, the rays were found so powerful that it is not
surprising that Tesla was able to obtain more definitely a closer
knowledge of the properties of the rays. Roentgen obtained, with his
tube and a screen of barium platino cyanide, a shadow picture of the
bones of the hand at a distance of less than 7 ft., while Tesla obtained
a similar picture with a screen of calcic tungstate, and with his tube
immersed in oil at a distance of 45 ft. Tesla also made sciagraphs with
but a few minutes’ exposure at a distance of 40 ft., by the help of
Prof. Henry’s method, __i.e.__, with the assistance of a fluorescent
powder. § 151. He referred also to Salvioni’s suggestion of a
fluorescent emulsion. He attributed to Mr. E. R. Hewitt the conjecture
that the sharpness of the sciagraphs might be increased by a thin
aluminum sheet having parallel groves. Several experiments were made,
therefore, with wire gauze, as well as with a screen formed of a mixture
of fluorescent and iron-fluorescent powders. With the strong power of
the rays as obtained by Tesla in combination with such adjuncts, the
shadows were sharper, although the radiation, of course, was weakened by
the obstruction. § 107_b_.
[Illustration:
DISCHARGE TUBE IMMERSED IN OIL, § 147, PAGE 156.
]
With the apparatus involving the discharge tube in oil, and with
tremendously high potential, he obtained what may be called wonderful
results; for with the sciascope he obtained shadow pictures of the
vertebral column, outline of the hip bones, the location of the heart
(and later detected its pulsations), ribs and shorter bones, and,
without the least difficulty, the bones of all the limbs. More than
this, a sciagraph of the skeleton of the hand was perceived through
copper, iron or brass very nearly 1/4 inch thick, while glass 1/2 inch
thick scarcely dimmed the fluorescence. The skull of the head of an
assistant acted likewise, while at a distance of three feet from the
discharge tube. The motion of the hand was detected upon the screen
although the rays first passed through one’s body. In making
observations with the screen, he advised that experimenters should
surround the oil box closely, except at the end, with thick metal
plates, to prevent X-rays from coming in undesired directions by
reflection from different objects in the room. Obviously the shadows
will be sharper.
148. BODIES NOT MADE CONDUCTORS BY X-RAYS. Tesla referred to Prof. J. J.
Thomson as having announced some time ago “that all bodies traversed by
Roentgen radiations become conductors of electricity.” The author has
witnessed other similar expressions giving credit to Thomson in this
respect, but he understands that Prof. Thomson, having discovered that
X-rays discharge both negatively and positively charged bodies,
conjectured or drew a corallary as to the probability of the bodies
therefore becoming conductors. Tesla, nevertheless, seems to have proved
that the corallary does not hold. In the first place he employed the
very powerful rays, and next, he let the oil be the substance traversed
by the rays. Besides this, he applied a sensitive resonance test. See
detail treatment of his experiments on this subject in _Elect. Rev._,
N.Y., June 24, ’93, p. 228. In brief “a secondary not in very close
inductive relation to the primary circuit, was connected to the latter
and to the ground, and the vibration through the primary was so adjusted
that true resonance took place. As the secondary had a considerable
number of turns, very small bodies attached to the free terminal
produced considerable variations of potential of the latter. Placing a
tube in a box of wood filled with oil and attaching it to the terminal,
I adjusted the vibration through the primary so that resonance took
place without the bulb radiating Roentgen rays to any appreciable
extent. I then changed the conditions so that the bulb became very
active in the production of the rays.”
According to the corallary above referred to, the oil should be, with
such an environment and under such subjection, a conductor of
electricity, but it was not. He emphasized his satisfaction in the
results by saying “the method I followed is so delicate that a mistake
is almost an impossibility.”
Prof. W. C. Peckham, _Elect. World_, N.Y., May 30, ’96, reasoned that
the oscillating electro-static action upon the outside of the tube, is
concerned in the production of fluorescence, and other properties of
X-rays. “These oscillations are certainly synchronous with the
vibrations of the cathode rays in the tube, which in turn synchronize
with the oscillation in the induction coil. If the vibrations of the
tube cannot keep time with those of its coil, few or no X-rays will be
given out. The cause seems to be similar to that of sympathetic
vibrations in sound. In a word, the discharge tube is a resonator for
its coil, and when the coil and tube are properly attuned, the maximum
effect is obtained.
149. APPLEYARD’S EXPERIMENT. NON-CONDUCTORS MADE CONDUCTORS BY CURRENT.
_Proc. Phil. So._, May 11, _Nature_, Lon., May 24, ’64, p. 93. A piece
of celluloid was pressed between two metal plates serving as terminals.
A galvanometer was employed to indicate the diminution of resistance by
time, and it also showed that the electrification was negative. When
mercury was one of the metals, the abnormal results did not occur,
except to a very small extent. When the celluloid was replaced by gutta
percha tissue, the electrification was normal. Many non-metals were
employed, and several were lowered in resistance.
149_a_. RESISTANCE SOMEWHAT INDEPENDENT OF METAL PARTICLES.—Through a
mixture of conducting and non-conducting materials, like a sheet of
gutta percha, having brass filings imbedded therein,—with 750 volts, no
current passed, and this held true until the proportion in weight of the
metal to the gutta percha was 2 to 1. Let it be remembered, also, that
selenium is reduced as to resistance under the influence of light.
150. MINCHIN’S EXPERIMENT. RESISTANCE LOWERED BY ELECTRO-MAGNETIC WAVES.
_Nature_, Lon., May 24, ’94, p. 93.—Referring to Appleyard’s experiment,
it will be noticed that he found that mixtures of certain limited per
cents. of metallic particles and insulators were exceedingly high in
resistance. Prof. G. M. Minchin found that such materials became
conductors under the influence of powerful electro-magnetic
disturbances, and that after the current was conducted, its resistance
remained greatly lowered in behalf of very weak impulses, although,
before the experiment, the resistance was so high. § 14_a_. But after
the current was interrupted by moving the terminal away from the
mixture, the high resisting power returned slowly, at a rate somewhat in
proportion to the hardness of the mixture. The film employed consisted
of shellac or gelatine or sealing wax, while among the metals was
pulverized tin. In the latter case, the resistance was reduced by the
electro-magnetic waves from apparent infinity to 130 ohms, the
electrodes being displaced by 1 cm.
------------------------------------------------------------------------