-------
118. EDISON’S EXPERIMENTS. CHARACTERISTICS OF DISCHARGE TUBE,
PHOTOGRAPHIC PLATES, ELECTRICAL APPARATUS, FLUORESCENCE, ETC. _Elec.
Eng._, N.Y., Feb. 19, ’96; Mar. 18 and 25; Apr. 1, 8, 15 and 29, ’96.
X-RAYS BEGIN BEFORE STRIAE END.—The reader may remember a former
section, § 10, pointing out that striae were usually obtainable without
very high vacua, and that phosphorescence of the glass occurs only with
high vacua. § 54. In carrying the vacuum up higher and higher, Edison
observed that feeble Roentgen rays were detected before the striae
ceased. Prof. Elihu Thomson independently performed a like experiment
and found that the Roentgen rays could be obtained even when the vacuum
was so low as to produce striae. (_Elec. Eng._, N.Y., Apr. 15, ’96.)
Victor Chabaud and D. Hurmuzescu also obtained X-rays from a vacuum .025
mm., being lower than Crookes employed, which was at a maximum .001 mm.
(_L’Industrie Elect._, Paris, May 25, ’96. From trans. by Louis M.
Pignolet.)
119. REASON WHY THIN WALLS ARE BETTER THAN THICK. X-RAYS AND
POST-PHOSPHORESCENCE.—This may be understood by explanation of the
discharge tube in Fig. 1. In one experiment, the portion struck by the
cathode rays, namely B, was made 1/8 inch thick. It became soon hot and
very luminous and melted, § 61, but the X-rays were weak. When blown
thin, (§ 83) however, the glass remained cool and the X-rays were much
stronger. What is known on the market as German glass (phosphoresces
green, § 55, at centre) was found more permeable than lead glass, the
thickness of the walls being the same in both cases. There were no
lingering X-rays from after-phosphorescence, (§ 54, at end) or, if any,
could not be detected by the sciascope. The photographic test would be
objectionable because of the brief duration. Prof. Battelli and Dr.
Garbasso, of Pisa, made a very _sensitive_ test in this connection,
proving by the discharge of an electrified body (§ § 90 and 90_a_) that
feeble X-rays were emitted after the current was cut off from the
discharge tube. (From trans. by Mr. Pignolet.)
[Illustration:
DISCHARGE TUBE, FIG. 1. § 119.
DISCHARGE TUBE, FIG. 3. § 120.
]
120. TO PREVENT PUNCTURE OF THE DISCHARGE TUBE BY SPARKS.—In the
illustration, Discharge Tube Fig. 2. shows a suitable type. It is drawn
to scale, showing the correct proportion of the length to the diameter.
The shaded ends represent tinfoil on the outside and connecting with the
leading-in wires, the same preventing puncture of the glass by the
spark. They may be caused to adhere by shellac or similar glue. In place
of the metallic coating detached supplementary electrodes may be
employed, as seen in the illustration marked “Discharge Tube Fig. 3.”
The power of the X-rays was increased, being due, it was thought, to the
fact that the construction embodied the combination of internal and
external electrodes. § 121.
121. VARIATION OF VACUUM BY DISCHARGE AND BY REST.—Prof. Pupin was among
the first to test the efficiency of external electrodes for generating
X-rays. Independently of the quality of the glass and of the kind of
pump and of the presence or absence of phosphoric anhydride, the
following peculiarities were noticed, which Edison attributed to a kind
of atomic electrolysis. § 47. 80 per cent. of the lamps exhibited the
phenomena as follows: First, such a high vacuum was obtained by the pump
that the line spectrum disappeared and pure fluorescence and generation
of X-rays at a maximum occurred. The lamp was then sealed off. After
three or four hours of rest, the vacuum deteriorated, so that striae and
other characteristics of low vacuum were obtained when connected up in
circuit, but upon continuing the current, the high vacuum gradually came
back, the line spectrum vanished, and suddenly X-rays were generated.
Again the bulb was left at rest for 24 hours, after which X-rays could
not be generated until the discharge had been continued for 4-1/2 hours.
[Illustration:
DISCHARGE TUBE, FIG. 2. § 120.
]
122. EXTERNAL ELECTRODES DISCHARGE THROUGH HIGHER VACUUM THAN
INTERNAL.—A vacuum that was so high that no discharge took place with
internal electrodes was made luminous by the use of electrodes on the
outside of the glass bulb. Then he made the vacuum so high that even
with a 12-inch spark from Leyden jars, no discharge took place with
external electrodes, and the tube was dark, this part of the experiment
indicating another limit at which an extremely high vacuum is not a
conductor and appearing to overthrow, as Edison intimated, Edlund’s
theory that a vacuum is a perfect conductor. § 25.
123. DEPOSIT ON GLASS FROM ALUMINUM ELECTRODE.—It has always been common
to employ aluminum for electrodes in vacuum tubes, on the ground that no
deposit took place, and therefore no blackening, nor whitening of the
glass wall. § 40. Edison observed also that no blackening was visible,
but stated that his glass blower, Mr. Dally, upon breaking the bulb and
submitting the interior surface of the glass to an oxydizing process,
the oxide of aluminum was so thick as to be opaque to light. With
magnesium, also, a mirror was produced, of a lavender color, by
transmitted light. In the case of aluminum, he was able to obtain a
visible spot at the phosphorescent portion, but only after a great many
hours of use. See cut from a photograph of a discharge tube used for
several months by Prof. Dayton C. Miller, and having a heavy aluminum
deposit opposite the aluminum cathode. With the increase of the deposit,
the power of the X-rays diminished, but, he thought, not on account of
the absorption, but because, “through lack of elasticity at the
surface.”
[Illustration:
DISCHARGE TUBE, § 123.
]
124. FLUORESCENT LAMP. In an English patent of ’82, granted to Rankin
Kennedy, there is described a vacuum bulb in which the electrodes are
covered with fluorescent or phosphorescent substances, intended for the
purpose of obtaining greater candle power by impact of cathode rays upon
anode of platinum, covered with alumina or magnesia. Edison coated the
inner wall of the discharge tube, for generating X-rays, with calcic
tungstate in the crystalline form. The luminosity, when measured,
amounted to about 2-1/2 C. P. As to the efficiency, he stated that this
was accomplished “with an extremely small amount of energy.” Such a
coating was found to weaken the X-rays radiated therefrom, which, of
course, was natural, because they had been converted into phosphorescent
light. The spectrum showed strongly at the red line, thereby suggesting
the reason why the light was of a pleasant character.
124_a_. PILTCHIKOFF’S EXPERIMENT. Greater emission of X-rays by a tube
containing an easily fluorescent substance. _Comptes Rendus_, Feb., 24,
’96. From trans. by Mr. Louis M. Pignolet. As the X-rays emanate from
the fluorescent spots on the glass of the discharge tube, he reasoned
that more powerful effects would be obtained by replacing the glass by a
more fluorescent material. He therefore tried a Puluj tube and found
that it shortened the time necessary for taking a photograph in a
“singular” degree. Experiments of others have certainly shown that as
phosphorescence decreases with increase of vacuum, the X-rays increase
to a certain maximum, § 105. Let it be noticed however, that this does
not prove that with the same vacuum, an increase of phosphorescence by a
superior phosphorescent material of equal thickness would not increase
the power of the X-rays. The best way to determine such points, is to go
to extremes. Edison applied so much easily phosphorescent material
(calcic tungstate) to the inside of the discharge tube, that much light
was radiated, but only feeble X-rays. On the other hand, without any of
the tungstate, the rays were strong, § 124. Experiments generally tend
to prove that it depends upon the chemical nature of the material rather
than its phosphorescing power, in other words upon the permeability. §
119, near end.
125. ELECTRODES OF SILICON CARBIDE. (Carborundum.) Edison called
attention to Tesla’s discovery that this substance is a good conductor
for high tension currents. Its advantages for electrodes in the
discharge tube are its high conductivity, no absorbed nor released gas
bubbles, and its infusibility and non-blackening power of glass even
when the voltage was increased to a point where the glass melted.
[Illustration:
EDISON (AT RIGHT) AND T. COMMERFORD MARTIN USING THE SCIASCOPE. § 97,
p. 84.
Cut also shows Sprengel vacuum-pump. Discharge-tube is in the box.
]
126. CHEMICAL DECOMPOSITION OF THE GLASS BULB. During the generation of
the X-rays the sodium line of the spectrum appeared in the spectroscope,
thereby indicating decomposition of the glass. With combustion tubes the
glass gave the weakest soda line, while lime soda glass gave the
strongest, and was most permeable to the X-rays. “The continuous
decomposition of the glass makes it almost impossible to maintain a
vacuum except when connected to the pump and even then the effect of the
current is greater in producing gas than the capacity of the pump to
exhaust, but the ray is very powerful.” It is supposed that for this
reason, as well as for others easily apparent that Edison as well as
other experimenters have always carried on their investigations with the
discharge tube permanently connected to the pump. The next best thing is
to let the tube contain a stick of caustic potash for maintaining an
exceedingly high vacuum. By gradually heating this, the desired degree
of vacuum can be obtained. § 54.
127. SCIAGRAPHS. DURATION OF EXPOSURE DEPENDENT UPON DISTANCES. With the
given discharge tube, he obtained sciagraphs at a distance of 3/8 inch
from the phosphorescent spot in one second, a vulcanized cover being
between; at two ft. distant the time was 150 sec.; at three ft., 450
sec.; the opaque plate being interposed each time. Consequently
“Roughly, the duration of exposure may be reckoned as proportional to
the square of the distance.”
128. DIFFERENCE BETWEEN X-RAYS AND LIGHT ILLUSTRATED BY DIFFERENT
PHOTOGRAPHIC PLATES. TIME OF EXPOSURE. The rapid plate for light gave
not the deepest images by X-rays. Several different kinds of small
sensitive plates were laid side by side. A sciagraph of a metal bar was
taken upon them all simultaneously. In this way, he obtained the result,
whereby it would appear preferable to employ the mean rapid plate for
the purpose of obtaining sciagraphs. On account of the opacity of
platinum, it occured to E. B. Frost, (_Sci._, N.Y., Mar. 27, ’96,) to
try platinum photographic paper of the kind used for portraits, but such
paper (intended for long exposures in printing in sunlight) was far too
lacking in sensitiveness to produce any effect.
128_a_. GEORGES MESLINS INSURED A REDUCTION OF TIME FOR TAKING
SCIAGRAPHS BY THE DEFLECTION OF THE CATHODE RAYS BY MEANS OF A MAGNETIC
FIELD. _Comptes Rendus_, March 23 and 30, 1896. From trans. by Louis M.
Pignolet. The method consists in using a permanent or electro-magnet to
create a magnetic field perpendicular to the cathode rays in the tube.
By this means, the active fluorescent spot on the tube is condensed, and
the intensity of the X-rays generated there is increased. Another
advantage is that, when the active part of the tube becomes inactive
owing to the formation of a light brown deposit upon it, another part
can be used by very slightly altering the position of the magnets. Thus,
each time a new part of the tube can be used. The magnetic field must
not be uniform but must have a suitable variation to produce the desired
concentration of the cathode rays.
A. IMBERT AND H. BERTIN-SANS’ EXPERIMENT. (_Comptes Rendus_, March 23,
’96. (From trans. by L. M. P.) They shortened the time by use of a
magnet.
JAMES CHAPPIN’S EXPERIMENT. (_Comptes Rendus_, Mar. 30,’96. (From trans.
by L. M. P.)—Claimed priority in having shown publicly, on Feb. 19, a
sciagraph of a hand, marked “Photograph obtained by concentration of the
cathode rays, by means of a magnetic field.” The increase of the
intensity of the X-rays obtained by this means was in the proportion of
8 to 5, as measured by the time of fall of the leaves of a Hurmuzescu
electroscope.
Prof. Trowbridge, of Harvard University, in a lecture, gave an
interesting review (_Western Elect._, Feb. 29, ’96) of the length of
time required in the early days of photography. Improvements are being
made whereby the duration required in sciagraphy becomes less and less.
In 1827, by heliography, 6 hours’ exposure was necessary; in 1839, by
daguerreotype, 30 minutes; in 1841, by calotype, 3 minutes; in 1851, by
collodion, 10 seconds; in 1864, by collodion, 5 seconds; in 1878, by
gelatine, 1 second. The author remembers the photographs for use in the
Edison kinetoscope were taken at the rate of 20 per second. The focus
tube brings the time of exposure in behalf of X-rays down to a matter of
seconds instead of minutes. For an admirable review of authorities,
facts and theories relating to the causes of the darkening of
photographic plates by light, see Cottier, in _Elect. World_, N.Y., May
23, ’96.
129. SIZE OF DISCHARGE TUBE TO EMPLOY FOR GIVEN APPARATUS.—A small tube
required but a small E. M. F., and therefore should be employed with a
small induction coil. The greater the distance of the sensitive plate
and the object, considered together, from the discharge tube, the
sharper the shadow. In short exposures, the tube should be small and at
a short distance.
130. PREVENTING PUNCTURE AT THE PHOSPHORESCENT SPOT.—In experiments
where he employed a flat cathode, a very thin pencil of rays of
increased power came from the exact centre, and in two or three seconds
made the glass red hot at the centre of the phosphorescent spot.
Immediately, the atmospheric pressure perforated the bulb. This occurred
several times. He stated that “the best remedy is to permit the central
ray to strike the glass at a low angle; this greatly increases the area
and prevents the trouble.” EDISON.
Mr. Ludwig Gutmann furnished a translation of a note by Prof. Walter
König, found in _Eleck. Zeit._ of May 14, ’96, relating to this same
subject matter. Recognizing that the sharpness of the outlines is the
most important requirement in connection with sciagraphy, and that if
the rays start from a large surface the impressed shadows will be
uncertain in configuration, and noticing, as Edison and Tesla did, §
130, the frequent destruction of the tube at the place where the rays
were concentrated to a focus, he placed over the inner surface of the
glass, aluminum foil for distributing the heat over a larger area, at
the same time causing radiation of X-rays from a single point. The focus
tube outweighs this in importance. § 91.
131. ELECTRICAL DIMENSIONS OF APPARATUS. The best kind of instruction
for the student in reference to equipping a plant is to follow the
construction employed by those who have been successful. § § 106, 109,
114, 137. Edison used the usual incandescent-lamp current, voltage at
110 to 120 volts, current being continuous, but not connected directly
to the induction coil, there being a bank of eight to twenty 16 candle
power incandescent lamps arranged in parallel. The interrupter for the
primary consisted of a rotating wheel in appearance like a commutator of
a dynamo, and was rotated rapidly by a small electric motor, making
about 400 interruptions per second, and so constructed that the circuit
was closed twice as long as it was open. A sudden interruption was
caused by an air blast playing at the point of make and break, the use
of which made that of a condenser needless. § 3. The discharge tube
terminals were connected respectively and directly to those of the
secondary. Prof. Pupin, Columbia Univ. N.Y. (_Lect. N.Y., Acad. Sci._,
April 6, ’96, and _Science_, N.Y., April 10, ’96) gave valuable and
practical instruction concerning the apparatus, which the author
witnessed. “A powerful coil was found indispensable for strong effects
and satisfactory work. The vibrating interrupter is too slow and
otherwise unsatisfactory, and it was replaced by a rotary interrupter,
consisting of a brass pulley, 6 inches in diameter and 1-1/4 inches in
thickness. A slab of slate 3/4 inch thick was inserted and the
circumference was kept carefully polished. This pulley was mounted on
the shaft of a Crocker-Wheeler 1/8 H. P. motor giving 30 revolutions,
and, therefore, 60 breaks per second. Two adjustable Marshall condensers
of three microfarads each were connected in shunt with the break, and
the capacity adjusted carefully until the break-spark was a minimum and
gave a sharp cracking sound. Too much capacity will not necessarily
increase the sparking, but it will diminish the inductive effect which
is noticed immediately in the diminished intensity of the discharge. A
powerful coil with a smoothly working rotary interrupter will be found a
most satisfactory apparatus in experiments with Röntgen radiance.” §
106, 109, 114, 131, 137.
132. SALTS FLUORESCENCE BY X-RAYS. See also, _Elect. Rev._, N.Y., April
19, ’96, p. 165. Edison examined over 1800 chemicals to detect and
compare their fluorescent powers if any, under the action of X-rays
first transmitted through some opaque material such as thick cardboard.
Of all these, calcic tungstate by measurement, fluoresced with six times
the luminosity of barium platino cyanide, which was referred to in
connection with Roentgen’s experiment. Other authorities agree as to its
great sensitiveness. In making this comparison, it was assumed that the
power of the X-rays varied inversely as the square of the distance from
the discharge tube. Between the two above chemicals came strontic
tungstate. Baric and plumbic tungstate scarcely fluoresced. Salicylate
of ammonium crystals equalled the double cyanide of platinum and barium,
and differed therefrom in that the fluorescence increased with the
thickness of the layer of crystals up to 1/4 of an inch, showing great
fluorescing power and low absorptivity. This experiment showed that the
best fluorescent materials were not necessarily the salts of the
heaviest metals, like platinum. It is assumed that the reader knows the
difference between phosphorescence and fluorescence, but the dividing
line is so difficult in some cases and the one not being distinguished
from the other by experimenters, that the author has used the same words
as the experimenters, although he admits that fluorescence is often
meant where phosphorescence is stated, and _vice versa_. An anomaly
presented itself as to rock salt, which although transparent to light
yet powerfully absorbed X-rays and was strongly fluoresced thereby.
Again, fluorite which is transparent to light, fluoresced strongly with
the X-rays, and under their action became brighter and brighter and
continued after cutting off the X-rays, the material therefore, being
highly phosphorescent, the light enduring for several minutes. Upon
watching the phosphorescence of fluorite, the same penetrated the plate
very slowly to the depth of one-sixteenth of an inch, but beyond that
depth there was complete darkness. The only other truly phosphorescent
substance noticed was calcic tungstate, especially in thick layers, so
that the shadow of the bones of the hand remained thereon for a minute
or two upon cutting out the discharge tube from the circuit. Some
chemicals, within a dark box and _very close_ to the discharge tube,
phosphoresced by giving spots here and there, but they did not
phosphoresce at a greater distance, and the light was probably not due
to the X-rays. Edison attributed the result directly to the “electrical
discharge.” The list is as follows: ammonium sulphur cyanide, calcic
formate, and nitrate, ferric citrate, argentic nitrate, calcic and iron
citrate, soda, lime, “zinc, cyanide” (perhaps this means cyanide of
zinc), zinc hypermanganate, and zinc valeriate. The salts of the
following metals did not fluoresce under the influence of the X-rays.
Aluminum, antimony, arsenic, boron, beryllium, bismuth, barium,
chromium, cobalt, copper, gold, iridium, magnesium, manganese, nickel,
tin, and titanium.
[Illustration:
ROENTGEN RAYS AT THE UNIVERSITY OF MINNESOTA.
1. Watch and chain.
2. College badges in mahogany box.
3. Copper coin.
4. Weights in heavy velvet-lined mahogany box; blank space contains
aluminum.
5. Coins in inner pocket of heavy seal purse.
6 and 7. Colored glass.
8. Key
9. Lead-pencil.
_West. Elect._, Mar. ’96.
]
Edison stated that the following substances were among those which
fluoresced more or less under the action of the X-rays. Mercurous
chloride, mercury diphenyl, cadmic iodide, calcic sulphide, potassic
bromide, plumbic tetrametaphosphate, potassic iodide, plumbic bromide,
plumbic sulphate, fluorite, powdered lead glass, pectolite, sodic
cressotinate, ammonic salicylate, and salicylic acid. Compared with the
above, the following fluoresced less. Powdered German glass, baric,
calcic and sodic fluorides, sodic, mercuric, cadmic, argentic and
plumbic chlorides, plumbic iodide, sodic bromide, cadmic and “cadmium,
lithia bromide, mercury, cadmium sulphate,” uranic sulphate, phosphate,
nitrate, and acetate, molybdic acid, dry potassic silicate, sodic
bromide, wulfenite, orthoclase, andalucite, herdinite, pyromorphite,
apatite, calcite, danburnite, calcic carbonate, strontic acetate, sodic
tartrate, baric sulphobenzoic, calcic iodide, and natural and artificial
ammonium benzoic. Not one of all the 1800 crystals and precipitates
fluoresced through a thick cardboard under the influence of the arc
light, 16 inch spark in air, a vacuum tube so highly exhausted that a 10
inch spark left it dark, nor the direct rays of the sun at noon time. As
calcic tungstate was phosphorescent by friction, he theorized that the
X-ray is a wave due to concussion.
Flame sensitive to X-rays. Edison stated that his assistants submitted
the sensitive flame and the phonographic listening tube to the action of
the X-rays, and found that they were responsive thereto.
133. X-RAYS APPARENTLY PASSED AROUND A CORNER. Referring to the figure
“X-ray Diffusion Fig. 1”, p. 129, it will be noticed that there were
three principal elements. First a discharge tube, then a thick steel
plate and then a sciascope, all arranged in the proportion indicated in
the figure, where the sciascope was within six inches of the edge of the
plate, “well within the shadow” thereof. § 69. Fluorescence was seen
under these conditions. When the sciascope was directly behind the
middle of the plate and opposite the discharge tube, there was no
fluorescence, showing that the plate was thick enough to cut off all the
rays and therefore the energy must have traveled in two directions for
some reason or other.
Prof. Elihu Thomson remarked concerning this experiment that he
considered, in view of some experiments of his own, on diffusion and
opalescence (§ 103), that the sciascope was luminous in view of
reflection (§ 146) of the X-rays from various objects in the room, as
from the walls and floor of the room, tables, metal objects, electrical
apparatus and so on. Theory admits the property of diffraction, which
would cause the rays to turn around the edge of the plate, according to
the principles of diffraction of light, provided the X-rays were due to
transverse or longitudinal or any vibrations. See _Elect. Eng._, N.Y.,
April 15, p. 378.
While Edison generally devotes his energy to actual experiments and
dealings with facts and principles, rather than with theories, yet, in
this instance, he merely suggested that the fluorescence under the
conditions named might indicate that the propagation of X-rays was
similar to that of sound in air, the wave being of exceedingly short
length. He referred to Le Conte’s experiment of ’82 (see _Phil. Mag._,
Feb. ’82), where an experiment of a somewhat similar nature was
performed in connection with the propagation of sound.
[Illustration:
X-RAY DIFFUSION, FIG. 1, § 133.
]
Prof. William A. Anthony (see _Elect. Eng._, Apr. 3, ’96, p. 378) held
that the Le Conte experiment did not warrant Edison’s conclusion, for
the experiment of Le Conte showed comparatively sharp sound shadows; for
even at a distance of twelve feet there was no apparent penetration
within the geometrical boundary. He referred to Stine’s, § 110. Scribner
and M’Berty’s, § 111, as upholding rectilinear propagation. While he did
not explain what the Edison result was due to, yet he argued that the
cause was other than that ascribed by Edison. In this connection, the
author performed an experiment (_Elect. Eng._, Apr. 22, ’96, p. 409) to
substantiate that X-rays were propagated through such a high vacuum that
it was necessary to have electrodes within 1/8 of an inch of each other,
in order to obtain a discharge with a coil that gave 15 in. spark in
open air. The experiment consisted in casting the shadow of an
_uncharged_ tube upon the screen of a sciascope. The shadows of the wire
forming the electrodes within the vacuum were produced very sharply,
while the glass tube was faintly outlined. Inasmuch as the shadows of
objects _within_ the vacuum tube were obtained, therefore the X-rays
must have passed through the evacuated space. Sound and X-rays are
therefore dissimilar. The shadows were as sharp and as dark as those
made by similar wires in open air. In this connection, see also Lenard’s
experiment, § 72, showing that external cathode rays were also
transmitted by a vacuum in a “dead” tube. Roentgen’s experiment showed
that X-rays from a mass located entirely within the vacuum in the
discharge tube radiated X-rays into the outside atmosphere. § 91. This
experiment would hardly prove, however, that X-rays, after having been
liberated in open air, would pass through a second vacuum space, because
there may have been some X-rays, generated at the surface of the glass
in Roentgen’s experiment, struck by those rays which radiated from the
mass at the centre of the vacuum space. Did not Lenard and Roentgen
experiment with the same radiant energy? The author answers, yes. § 77.
134. PERMEABILITY OF DIFFERENT SUBSTANCES. Lenard § 68. determined the
permeability of several substances to cathode rays. Roentgen also the
same in regard to X-rays. § 82 and 83. Others have made comparisons.
From the sciagraph made by Edison, the following classification is made,
each sheet of material being about 1/32 inch thick. The most opaque were
coin silver, antimony, lead, platinum, bismuth, copper, brass, and iron,
which were about the same as one another. Slate, ivory, glacial
phosphoric acid shellacked, and gutta percha, were about the same as one
another and less than the above. Aluminum, tin, celluloid, hard rubber,
soft rubber, vulcanized fibre, paper, shellac, gelatine, phonographic
cylinder composition, asphalt, stearic acid, rosin, and albumen, were
about the same as one another and less than the above group, as to
permeability.
The accompanying picture, p. 6, marked Terry’s Sciagraph, Fig. 1, is a
sciagraph of pieces of different materials named as in the following
list, taken by Prof. N. M. Terry of the U.S.N.A., see also p. 127. “1,
rock salt, 0.6 inch thick; 2, cork, 0.4 inch thick; 3, quartz, 0.45 inch
thick, cut parallel to optic axis; 4, verre trempe, 0.4 inch thick; 5,
glass, 0.7 inch thick; 6, chalk; 7, Iceland spar; 8, mica, very thin; 9,
quartz, over a square piece of glass; 10, aluminum foil, [_a_] four
thicknesses, [_b_] two thicknesses, [_c_] one thickness; 11, platinum
foil; 12, tourmaline; 13, aragonite; 14, paraffine, 0.4 inch thick. 15,
tin foil, [_a_] one thickness, [_b_] two thicknesses, [_c_] three
thicknesses; 16, rubber insulated wire; 17, electric light carbon; 18,
glass, 0.32 inch thick; 19, alum., 1.4 inch thick; 20, tourmaline; 21,
gas coal; 22, bee’s wax; 23, pocket-book, 10 thicknesses of leather; 24
coin in pocket-book; 25, key in pocket-book; 26, machine oil in ebonite
cup; 27, ebonite, 0.25 inch thick; other samples have given very faint
shadows like wood and leather; this was polished; 28, wood, 0.2 inch
thick; 29, steel key.” _Elect. Eng._, N.Y.
134_a_. HODGES’ EXPERIMENT. ILLUSTRATION OF PENETRATING POWER OF LIGHT.
_Elec. Eng._, N.Y., March 4, ’96. Attention has been invited in the
scientific press to the penetrating power of heat rays and of light rays
of low refrangibility. In conjunction with this, let it be remembered
that the photographic plate has the property of being impressed
practically, only by rays having a higher refrangibility than red. It
would be natural, therefore, to conclude that if the spectrum could be
turned around, the photographic impression might be produced through
opaque bodies. This perhaps, was the kind of reasoning which prompted
Mr. N. D. C. Hodges, formerly editor of _Science_, to perform an
experiment, the gist of which consisted in attesting the permeability of
rays of light which had been passed through fuchsine. Christiansen,
Soret and Kundt performed experiments with an alcoholic solution of this
material and found that the order of the colors in the spectrum was
somewhat reversed, namely, violet was the least refracted, then red, and
then yellow, which was the most refracted. Mr. Hodges used a pocket
kodak, carrying a strip for twelve exposures. This camera was placed in
a closely fitting pasteboard box. Thus protected, some portions of the
film were exposed to sunlight, so far as it could penetrate the end of
the pasteboard box, while other exposures were made with a prism, on the
end of the box, containing an alcoholic solution of fuchsine. The
portions of film exposed to the anomalous rays produced by the fuchsine
solution were fogged, while the control experiments with ordinary light
showed none. The anomalous rays must have penetrated the pasteboard, and
probably the wood and leather of which the camera was made.
135. PENETRATING POWER OF X-RAYS INCREASED BY REDUCTION OF TEMPERATURE.
§ 23 and 72_b_ at end. Among the hundreds of ideas that occured to
Edison in connection with Roentgen ray tests was that concerning what
might happen by cooling the discharge tube to a very low temperature. As
before, he maintained the tube in connection with the air pump so as to
be able to vary the vacuum. The reduction of temperature was obtained by
means of ice water. Of course the bulb could not be placed in the water
itself on account of trouble which would occur from electrolysis,
therefore, the discharge tube was immersed in a vessel of oil, § 13,
which in turn was surrounded by a freezing mixture. The vessel was a
stout battery jar 14 inches high, eight inches in diameter with glass
walls 5/10 of an inch thick. The oil employed was paraffine. The
refrigerating jar was 12 inches high and 12 inches in diameter and the
glass wall thereof, 3/8 inch thick. He tested the difference in the
power of the rays by first noticing the thickness of steel that was not
penetrated by the rays generated from the tube while in air. Crucible
steel 1/16 of an inch thick did not transmit rays sufficiently to
illuminate the sciascope, and yet with the use of oil and reduction of
temperature, and after the rays had passed through two thicknesses of
glass as well as through the oil and ice water, the sciascope was made
luminous by rays after passing through a plate of steel of double the
thickness, __i.e.__ 1/8 in. thick. See in this connection, Tesla’s
experiment, § 135, where powerful rays were obtained by immersing the
discharge tube in oil. Accounts of these two experiments were published
simultaneously. Tesla attributed the idea of this use of oil to Prof.
Trowbridge of Harvard University, who showed that a discharge tube
immersed in oil is adapted to the generation of X-rays of increased
penetrating power. See cut at p. 135.
[Illustration:
SCIAGRAPH OF RATTLESNAKE BY USE OF STOPS. § 107., p. 101.
By Leeds and Stokes.
]
NON-REFLECTION OF X-RAYS. (_Elect. Eng._, Feb. 19, ’96, p. 190.
Apparently extracted from the daily press.)—That the X-rays were only
slightly reflected (Roentgen, § 81., and even when very powerful (Tesla,
§ 146., was determined in a severe manner by Edison. The first
experiment consisted in employing a funnel 8 inches long and 3/4 inch at
the smaller end. The discharge tube was in the larger end, and the
photographic plate across the smaller end. After experiment and
development, the plate showed overlapping circular images, which would
indicate reflection from the inner surface of the funnel. This may have
been due to a jarring vibration of the funnel. Therefore, he carried the
experiment further by using a funnel 9 feet long. The plate did not
indicate any signs of reflection, as it merely became generally fogged.
The material of the tube is not named, but if of brass or other
impermeable metal, it is thought that his experiment would have shown a
result agreeing with that of others herein. Again, the reporter may have
been in error. Also, the rays may have been very weak, as the experiment
was performed when Edison first started to investigate the subject.
136. X-RAYS NOT YET OBTAINABLE FROM OTHER SOURCES THAN DISCHARGE
TUBES.—Edison exposed covered plates to the direct sun-light at noon for
three or four hours; no photographic impression; also to electric sparks
in open air, of twelve or more inches in length; no clouding even of the
photographic plate.
Profs. Rowland et. al., of the Johns Hopkins University, in a
contribution to _Electricity_, Apr. 22, ’96, p. 219, confirmed this
point by stating: “As to other sources of Roentgen rays, we have tried a
torrent of electric sparks in air from a large battery, and have
obtained none. Of course, coins laid on or near the plate, under these
circumstances, produce impressions, but these are, of course, induction
phenomena.” (See Sandford and McKay’s Fig. p. 20). “As to sun-light,
Tyndall, Abney, Graham, Bell and others have shown that some of the rays
penetrate vulcanite and other opaque objects.” Poincaré, at an early
date, advanced the hypothesis that X-rays are due to phosphorescence,
whether produced by electrical or other means. _Elect. World_, Digest.,
Mar. 28, ’96, p. 343, where it is also stated that Chas. Henry thought a
certain experiment of his own was in favor of the hypothesis. The
experiment was performed with a phosphorescent material which had been
exposed to the light and then brought into darkness. Niewengloswski
inferred, from an experiment, that phosphorescent bodies increase the
penetrating power of sun-light. Tesla admitted the possibility of the
radiation of X-rays from the sun. In an article describing important
experiments in the _Elect. Rev._, N.Y., Apr. 22, ’96, p. 207, he stated:
“I infer, therefore, that the sun-light and other sources of radiant
energy must, in a less degree, emit radiations or streamers of matter
similar to those thrown off by an electrode in a highly exhausted
enclosure. This seems to be at this moment still a matter of
controversy.” Roentgen, in his first announcement, showed that the
phosphorescent spot was the source of the X-rays. § § 79 and 80. All the
different opinions and theories, therefore, indicated that
phosphorescence by sun-light might possibly emit X-rays. Probably few
had sufficient belief in the matter, one way or the other, to try the
experiment in an extreme manner. The author was curious to prove the
question, but he only obtained negative results. It cannot be conceived
how the matter could have been more severely tested, for he concentrated
the light of the sun nearly to a focus by a large lens, namely 5 in. in
diameter, together with a reflecting funnel. The maximum phosphorescence
was therefore obtained by placing suitable chemicals at the opening in
the funnel. The sciascope showed absolutely no X-rays present.
Photographic plates were not in the least acted upon, even after hours
of exposure, the same having opaque covers of aluminum. See _Elect.
Eng._, N.Y., Apr. 8, ’96, p. 356. If X-rays are emitted from the sun,
they are all absorbed by the atmosphere of the earth, or are overcome by
some other force.
[Illustration:
COOLING DISCHARGE TUBE. EDISON. § 135.
]
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