-------
41. GASSIOT’S EXPERIMENT. STRIAE. TUBE IN PRIMARY CURRENT. CURRENT
VIBRATORY. _Phil. Trans._, ’59, p. 137. _Bakerian Lectures. Phil.
Trans._, ’58, p. 1. _Proc. R. So._, x., pp. 36, 393, 404; xii., p. 329;
xxiii., p. 356.—The form of tube in which to obtain luminous striae to
the best advantage was that of a dumbbell with the electrodes located
respectively in the balls—afterwards confirmed by Sir David Solomons,
Bart. _Proc. Royal So._, June 21, ’94. _Nature_, Lon., Sept. 13, ’94, p.
490. He obtained in the vacuum luminosity with 500 Daniell’s cells,
which he found to be the least E. M. F. that could be employed. He
omitted, and apparently overlooked, the introduction of an automatic
interrupter in the circuit and the use of a very low E. M. F. § 52. In
conjunction with Spottiswoode, 1,080 cells of chloride of silver (about
2,000 volts) were employed, first without, and then with condensers. One
of the condensers consisted of the usual tinfoil type, and the other of
a self-induction kind, namely of about 1,000 feet of wire. The results
were striae with the condensers, and no striae without the condensers. §
8_a_. The results suggested to them that there was some relation in
principle between the striae and vibration of the current. They
therefore built an ingenious apparatus to test whether this was true or
not, and they found such was the case by the following related means. If
a current passing directly from the primary battery through the
condenser and the discharge tube is undulatory or intermittent in any
sense, then it would be able to induce a current in the secondary of the
induction coil. § 8 at centre. They found that there was a current thus
induced, and they detected it by means of a small discharge tube which
became luminous. Fig. 3 p. 17. This was an independent tube near the top
of the figure, having nothing to do with the one containing striae,
which were produced by the primary current and shown at the right. Dr.
Oliver Lodge, F.R.S., in treating of the cathode and X-rays in _The
Elect._, Lon., Jan. 31, ’96, p. 438, stated the following with reference
to Gassiot’s experiments: “In the days of Gassiot and other early
workers (§ 43) on the discharge in rarefied air, it was the stream from
the anode that chiefly excited attention. It is this which developed the
well-known gorgeous effects which used to be shown at nearly every
scientific conversazione.”
42. POGGENDORFF’S EXPERIMENT. EFFECTS OF INTERRUPTING A CURRENT WITHIN
DISCHARGE TUBE. _Phil. Mag._, 4th Se., vol. x., 1855, p.
203-207.—Imagine an electric bell vibrator and magnet within the glass
receiver upon an air pump. Upon connecting the magnet and vibrator in
series with a small electric battery, it is evident that in the open
air, as usual in electric bells, there will be a minute violet spark at
the terminals of the circuit breaker. § 6. Now, let the air be exhausted
as far as possible by means of a mechanical pump as constructed in 1855.
Poggendorff performed such an experiment, and he noticed that in the
poor vacuum the ordinary violet spark became yellow, while blue light
like a small enveloping tube surrounded the hammer of the vibrator and
wire leading to the opposite contact and a little projection extending
away from the hammer. His experiment was unique, because showing for the
first time that a current from a battery, if interrupted in the vacuum,
will not only produce the usual minute spark, but that a blue tube of
light will be produced around the conductors within the vacuum.
43. DE LA RUE AND MÜLLER’S EXPERIMENT. SOURCE OF THE STRIAE AT THE
ANODE. NUMBER OF STRIAE VARIED BY CHANGE OF CURRENT. _Phil. Trans._,
1878.—By an arrangement of means for causing different pressures, they
made a discovery, namely, that as far as the eye is concerned the striae
begin to have their existence at the anode. § 46. Imagine the internal
gas pressure to become less and less. First, a violet luminosity occurs
around the anode as in § 42. As the pressure becomes less and less,
luminous striae move toward the cathode accompanied by more and more
striae, which increase either to form a column reaching a certain
distance or else extending through the whole distance between the
electrodes. § 46. They observed that when the E. M. F. was constant and
the current changed, the variation in the appearance of the striae was
very regular. § 41. With some tubes the number of striae increased with
the increase of current, while with a decrease of current the number of
striae became less and less. § 8_a_. With some tubes the number of
striae increased while the current decreased. § 8_a_. With the use of a
condenser, then as the E. M. F. decreased together with a diminution of
current, the number of striae varied. The striae nearest the anode
vanished first, as they diminished in number with the fall of the E. M.
F. The striae on the other hand originated at the anode, when the charge
of the condenser was gradually increased from a minimum, and then the
striae continued to increase from the anode as the source. As to the
color of the striae, the same was changed by an alteration of the
current.
44. SOLOMONS’ EXPERIMENT. DARK BANDS BY SMALL DISCHARGES. _Nature_,
Lon., Sept. 13, ’94. _Proc. R. So._, June 21, ’94.—Solomons found that
in a very dark room, striae (alternate light and darkness) appeared with
very _minute_ discharges, and as the current was increased, they
vanished, appearing again when the discharge was strong. He could not
obtain them until the luminous column extended to the glass forming the
large glass tube. § 40.
45. SPOTTISWOODE’S EXPERIMENT. GOVERNING THE MOTION OF STRIAE. EFFECT
UPON MOTION BY DIAMETER OF DISCHARGE TUBE. MOTION STOPPED BY MAGNET.
_Proc. R. So._, vol. 33, p. 455.—Spottiswoode found that he could obtain
motion when he desired. He introduced some constant resistances and also
a rheostat of fine adjustment. The least change of resistance caused
some effect upon the striae. The general principle that he established
was that letting it be assumed that the striae are stationary then; “An
increase of resistance produces a forward flow, and a decrease of the
resistance a backward flow,” differences of as little as 1 ohm in the
primary current caused the effect. Sometimes the velocity of the flow is
fast and sometimes slow, being so rapid in certain instances that the
unaided eye cannot distinguish them, but they are known to exist by the
use of the revolving mirror. § 46. With tubes of small diameter,
compared with their length, he noticed the fact that the striae in one
portion of the tube moved faster than those in another portion. § 46.
Sometimes one group moved while the other one was stationary. Sometimes
they moved in opposite directions. This last named phenomenon occurred
also in very wide tubes. The points at which the charge took place he
called nodes. He discovered external means for stopping this action. He
did it by means of a magnet located opposite one end of the tube. § 31.
When the magnet was energized, all motion ceased. § 31.
[Illustration:
FROM SCIAGRAPH OF FOOT DEFORMED BY POINTED SHOES. § 204.
By Prof. Miller.
]
[Illustration:
FROM HAMMER’S MOLECULAR SCIAGRAPH. § 117., p. 114.
]
46. THOMSON’S EXPERIMENT. VELOCITY OF STRIAE CHECKED AT THE CATHODE.
_Nature_, Lon. Jan. 31, ’96, p. 330.—A tube 50 ft. long was exhausted, §
8_a_., as to striking distance. In this particular experiment, he caused
a single interruption in the primary of the induction coil, and observed
the motion of the striae from the anode to the cathode by means of a
rotating mirror. § 43. The luminosity began at the anode and travelled
toward the negative with a high velocity, but upon its arrival at the
negative pole its velocity was checked. He said that the striae did not
disappear at the cathode like a rabbit would in entering a hole, but
they lingered around the electrode for some time. As a consequence of
this delay, he found as expected, an accumulation of positive
electricity, § 4, in the neighborhood of the cathode. It is a general
principle, therefore, that when a discharge passes between a gas and
metal, there is an accumulation, illustrating that the discharge
experiences a difficulty or resistance. § 32 and 33. The experimenter,
Prof. J. J. Thomson, acknowledged that Profs. Liveing and Davy had
noticed similar effects.
47. THOMSON’S EXPERIMENT. DISRUPTIVE DISCHARGE AND ELECTROLYSIS.
_Nature_, Lon. Jan. 31, ’95. _Lect. S. Inst. The Electr._, Lon. vol. 31,
p. 291, 316, and vol. 35, p. 578. _Trans. R. So._, ’95.—The discharge of
electricity through conducting liquids is, with scarcely an exception,
(example, mercury) accompanied by a chemical action. Faraday and Davy
both performed early experiments in this direction. Prof. J. J. Thomson
has set forth some instructive facts and which act as evidence that
there is a close relation between the disruptive discharge and chemical
action between the dielectric and electrodes. § 6 and 7. He made this
experiment in connection with his investigations relating to the
difficulty the positive electricity experiences in passing from a gas to
the negative electrode. § 46. He carried this experiment further, by
testing gases of different chemical natures. The apparatus he employed
consisted first of an alternating current generator, a high tension
converter, a bulb for containing first one gas and then another, whose
metal electrodes were connected with the secondary of the transformer,
and an electrometer connected to a third electrode which could be moved
about within the bulb. The operation was as follows: when the bulb
contained oxygen which is an electro-negative gas, the third movable
electrode received a positive charge in whatever part of the bulb it was
moved to, but with hydrogen instead of oxygen at atmospheric pressure,
the third electrode received a positive charge far away from the arc
between the other electrodes, but very near the arc it received a
negative charge. He then rarefied the atmosphere of hydrogen and he
noticed that the space where the third electrode became negative,
contracted, and at about 1/3 of an atmosphere became practically
nothing, so that the said third electrode connected to the electrometer
became slightly positive at all points within the hydrogen. § 4. The
next step consisted in using a bulb, having oxydized copper electrodes
and a hydrogen atmosphere at the pressure where there was only positive
electricity, that is about 1/3 of an atmosphere. This remarkable
phenomenon occurred; there was no positive electricity, but only
negative. When the copper oxide was reduced, the positive electricity
only, existed in all parts of the bulb. In brief, bright copper
electrodes left a positive charge in the gas, while oxydized electrodes
left a negative charge. He argued upon the results of this experiment to
account for the delay in the passage of the electricity from the gas to
the metal, § 46. In later experiments, he used the spectroscope to
detect decomposition. § 6, at end.
48. DE LA RUE AND MÜLLER’S EXPERIMENT. HEAT STRIAE. _Phil. Trans._, vol.
159, 1878—They arranged for the best conditions, that is, when a small
number of striae occurred in conjunction with a wide, dark interval. §
44. They found that the heat was greatest at the position of maximum
luminosity, but they also found that heat was generated at the dark
spaces. A novel feature was the discovery of the development of heat in
the middle of the tube even when there was no luminosity, § 9_a_, near
end, so that they thought it probable there may be what might be termed
heat striae, independently of luminous striae.
49. SPOTTISWOODE AND MOULTON’S EXPERIMENT. SENSITIVE STATE. AIR-GAP IN
CIRCUIT FORMS BEST METHOD OF OBTAINING. BRANCH CURRENT TO EARTH VERIFIED
BY A TELEPHONE. SENSITIVE STATE BY A SINGLE QUICK DISCHARGE. _Phil.
Trans._, 1879, p. 165, and April 8, 1880.—By sensitive state of luminous
effects in a Geissler tube is meant the susceptibility of the light (§
28) to an outside conductor connected to earth. Fig. 5, p. 17. When
one’s hand is brought near a Geissler tube the change near the hand
sometimes occurs and sometimes it does not. § 8. In the first place, the
effect is more easily noticeable if the vacuum tube is comparatively
wide or thick in diameter. With the electric egg, for example, the
luminous effect, instead of extending more or less across the space
between the electrodes, reaches from one of the poles to a conductor on
the outside of the egg, provided said conductor has an earth connection
or large capacity. Some of the light continues to exist nevertheless
between the two poles. The general principle is that the division exists
because of the re-distribution or branching of the disruptive discharge.
It was not known why the luminosity should be affected by such an
outside conductor sometimes, and remain the same at other times but the
above named experimenters discovered causes which could be depended upon
to produce the sensitive state. The apparatus will be described. They
had the usual Geissler tube with the platinum wire electrodes, and a
Holtz machine as the generator. They were led to believe that
intermissions of the current had a great deal to do with the production
of the sensitive state, and accordingly they arranged for an air-gap in
circuit with the machine and with the vacuum tube. § 51. They not only
observed that such a gap caused the sensitive state, but that an
increase in the length of the gap made the luminous column more
sensitive. They increased the gap so much that the ramifications of the
light could be seen. If an induction coil is employed as the secondary
generator, a condenser should be coupled up in connection with it. The
two in combination thereby produce the sensitive state, but upon cutting
out the coil and charging the tubes from the condenser the sensitiveness
can not be detected. Instead of the permanent air-gap, may be employed a
rapid circuit interrupter, coupled up between a Holtz machine and a
vacuum tube. The manner of coupling up is to place the interrupter in a
shunt to the vacuum tube. Difficulty had been found in early experiments
to obtain the sensitive state with those vacua which give striae. With a
rapid circuit interrupter and an induction coil, the breaks occurring
240 per second, the luminous column was not only broken up into striae,
but were acted upon by the approach of an outside conductor connected to
earth. The sensitive state is not always made apparent by the appearance
of attraction of the luminous light to the outside conductor. Sometimes
the light seems to be repelled. These two phenomena may be caused in the
same tube. This feature of the sensitive state constitutes the beginning
of radiations of energy through the walls of a vacuum bulb, like X-rays.
Some action or other in these cases takes place through the glass. They
tried an experiment in which one of the electrodes of the vacuum tube
was entirely on the outside. The electrical discharge was found to be
sensitive, for the discharge was changed in its appearances by the
presence of an outside conductor connected to earth. Another cause of
the sensitive state was observed, namely, the brevity of the charge.
This may be illustrated with a Leyden jar, which is known to give an
almost practically instantaneous discharge. A single discharge from such
a jar produced a flash of light which was in the sensitive state. The
nomenclature by which the experimenters defined the cause of the
phenomena is made up of the words: Re-distribution of electricity, and a
relief of the external strain.
49_a._ No re-distribution took place unless the outside conductor was
connected to earth or to a conductor of large capacity, nor would an
outside conductor, which was already charged, serve to exhibit the
sensitive state. The re-distribution effect was proved by means of a
telephone connected in circuit between the outside conductor and the
earth Fig. 5, p. 17. When the state was sensitive, that is, during the
use of the air-gap, the telephone produced a sound in unison with the
intermissions occurring at the air-gap. § 9 and 9_a_.
50. REITLINGER AND URBANITZKY’S EXPERIMENT. SENSITIVE STATE ILLUSTRATED
BY A FLEXIBLE CONDUCTOR WITHIN THE DISCHARGE TUBE. _Proc. Vienna Acad._,
1879. _Nature_, Nov. 20, 1879.—The discharge tube was 20 cm. long. It
had the usual platinum electrodes, and it stood upright. From the upper
electrode, was suspended a strip of tinfoil in the middle of the tube,
which was connected to a pump so that the density of the gas could be
varied. At atmospheric pressure, the secondary current of a Ruhmkorff
coil connected to the electrodes caused the strip to be attracted to the
glass tube. The attraction was less and less as the process of
exhaustion was carried on, and when a pressure indicated by 7 mm. was
reached, the strip was neither attracted nor repelled, but hung downward
the same as without any electricity whatever, but it was _attracted_ by
a neighboring shell-lac rod which had been rubbed with cloth, and it was
_repelled_ by a glass rod which had been rubbed with amalgam, it being
assumed that the strip was connected to the anode. § 36. The opposite
action took place when it was connected to the cathode. As the
exhaustion continued and became greater and greater, these actions died
away also up to a rarefaction of about 4 mm. Independently of the degree
of rarefaction, the flexible strip of tinfoil was always deflected by an
outside conductor connected to earth. § 49.
51. TESLA’S EXPERIMENT. INCANDESCENT ELECTRODE BY HIGH POTENTIAL AND
ENORMOUS FREQUENCY. SYSTEM REFERRED TO BY ROENTGEN FOR GENERATING
POWERFUL X-RAYS. _U. S. Letters Pat._, No. 454, 622, June 23, ’91.
_Martin’s Researches of Tesla_; _Trans. Amer. Inst. Elec. Engineers_,
May 20, ’91; _Elec. Review_, N.Y., June 24, ’93, p. 226; _Lect. Franklin
Inst._, Feb. 24, ’93, and _Nat. Elec. Light Asso._, Mar. 1, ’93; also
_Lect. in Europe_. Later he again experimented in this direction, see
_Elec. Review_, N.Y., May 20, ’96, p. 263.—By the U. S. Patent Office he
was granted, among other claims, the following: “The improvement in the
art of electric lighting herein described, which consists in generating
and producing for the operation of lighting devices, currents of
enormous frequency and excessively high potential, substantially as
herein described.” A simple combination of circuits together with great
skill in the construction of apparatus involving high powers of
insulation, resulted in the production, within a vacuum, of an electrode
radiating intensely white light. The circuit may be easily traced in the
diagram Fig. 17 p. 17. Briefly described, there may be noticed an
alternating current generator of comparatively low E. M. F. The current
from this generates a secondary current by means of an induction coil.
This secondary current generates a tertiary current by a second
induction coil. An air-gap for automatic and intermittent disruptive
discharges, § 49 near end, is in the circuit of the secondary coil of
the first named induction coil, which is directly charged by the
alternating current generator. The gap may be noticed between the two
balls. In shunt to the air-gap is a condenser (see Fizeau, chapter I.)
represented by several parallel lines. The lamp consists merely of an
evacuated bulb having an electrode of carbon or other refractory
material, which is connected to one pole of the last secondary coil
while the other pole may be outside, and may consist, for example, of
the walls of a room, which in such a case should be of some electric
conducting material. The higher the vacuum the more intense the light;
he found no limit to this rule. Fig. 16_a_ p. 17 illustrates his ideal
method of lighting a room. He found that with two plates at a distance
apart as indicated and connected to the poles of the coil, and with
electrodeless vacuum bulbs, the latter became bright in space—no
mechanical or electrical connection other than air and the assumed
ether.
52. MOORE’S EXPERIMENT. LUMINOSITY IN DISCHARGE TUBE BY SELF-INDUCED
CURRENTS. _Trans. Amer. Inst. Elect. Eng._, Sept. 20, ’93 and April 22,
’96. _Several U. S. Letters Patent._ Invented 1892.—During or about
1831, Prof. Henry discovered that when the circuit of a primary battery
was interrupted, a self-induced current, which he called an extra
current, was produced. When the circuit was closed, there was also a
self-induced current, but very much feebler than that obtained on
interruption. The self-induced current occurred only at or about the
instant of interruption or completion. He found also that the
self-induced current produced by interruption was enormously increased
in E. M. F. if the circuit included a helix of very long and fine wire.
It was further increased by the presence of an iron core. With one or
two cells, the spark upon interruption was scarcely visible, but with a
fine wire 30 or 40 feet long, an appreciable spark was obtained during
interruption. With but a comparatively few cells, and with a magnet for
example like a telegraph relay, the E. M. F. arose to several thousand
volts at the instant of interruption. D. McFarland Moore introduced into
such a circuit a Geissler tube and provided a rapid automatic
interrupter. Page, Ruhmkorff and others had, at an early date, noticed
the desirability, in operating Geissler tubes by secondary currents, to
obtain quick interruption in the primary circuit in order to produce the
best effects in the Geissler tube. Moore caused the interruptions to
take place in a vacuum, so high that a disruptive electrical discharge
could not pass. The break was therefore, absolutely instantaneous and
complete. By this system, illustrated in diagram in Fig. 18, p. 17, he
obtained all the luminous effects, actions by magnets, the sensitive
state, striae and all the other phenomena heretofore noticed in Geissler
tubes and some of those obtained by Tesla with his apparatus as just
described. In greater detail, it will be noticed that he had a dynamo of
rather low E. M. F., generally 100 volts, and a high vacuum containing a
circuit interrupter operated automatically by a magnet outside like a
vibrator in an electric bell. The magnet served also as the self
inductive device. The magnet and interrupter were in series with each
other, therefore, while the Geissler tube was in series with the magnet,
and the electrodes extended either inside of the Geissler tube or
remained on the outside. He performed numerous experiments on similar
lines and developed the system on a large scale, whereby rooms (e.g. the
hall of the _Amer. So. Mech. Eng._, N.Y.) have been illuminated as if by
other artificial illuminants, by employing long and numerous vacuum
tubes. Among several discoveries was that of the production of a bright
pencil of light along the axis of a long open helix, which formed one of
the internal electrodes. The Patent Office made strenuous efforts to
determine the degree of novelty, assuming that some one else must have
conceived the idea of employing a self-induced current to operate
Geissler tubes; but nothing nearer than Poggendorff’s experiment § 42
could be found, and therefore the following claim (in patent 548576,
Oct. 22, ’95,) was granted among a hundred or so relating to
developments and details and particularly covering the vacuum
interrupter. “The method of producing luminous effects, consisting in
converting a current of low potential into one of high potential, by
rapidly and repeatedly interrupting the low potential current in its
passage through a self-inductive resistance, and passing the former
current through a Geissler tube, thereby producing light within the
tube.”
[Illustration:
EDISON’S BENEFICENT X-RAY EXHIBIT, § 82, p. 71, and § 132, p. 126.
Calcic tungstate screen at center, sciascope near right.
]
------------------------------------------------------------------------