US1863278A - System and apparatus for the electrical production of images - Google Patents

Description

June 14, 1932. C NKEOLSQN I 1,863,278

SYSTEM AND APPARATUS FOR THE ELECTRICAL PRODUCTION OF IMAGES Filed Oct. 7. 1929 4 Sheets-Sheet 1 INVENTOR NZYANDER M LEM NICOLSO ATTORNEY Jlmfl 9 A. M L. NICOLSON 8 SYSTEM AND APPARATUS FOR THE ELECTRICAL PRODUCTION OF IMAGES Filed Oct. 7, 1929 4 Sheets-Sheet 2 I //5 ALEXANDER MLEAN NICOL SON ATTORNEY June 14, 1932. .A. McL. NlCbLSON SYSTEMAND APPARATUS FOR THE ELECTRICAL PRODUCTION OF IMAGES 4 Sheets-Sheet 3 Filed Oct. 7, 1929 INVENTOR ALEXMDB! mum mean-sou 1 BY 41am:

ATTORNEY June 14, 1932.

A. M L. NICOLSON SYSTEM AND APPRATUS FOR THE ELECTRICAL PRODUCTION OF IMAGES Filed 001;. 7, 1929 4 Sheets-Sheet 4 Patented June 14, 1932 UNITED STATES PATENT OFFICE- ALEXANDER MCLEAN NIOOLSON, or new YORK, N. Y., assrenon'. '10 coinaumca'rron PATENTS, mo, on NEW YORK, N. Y., A CORPORATION or DELAWARE SYSTEM m1) APPARATUS-FOR TnnELEcTaIcAL PRODUCTION or maens Application filed october 7, 1929. Serial No. 397,826.

This invention relates to a method and appara-tus for transmitting and reproducing images electrically. It relates more particularly to a. television system. i

In the transmission of images electrically the object is first illuminated, in order that the light and shade used to produce the picture maybe present. The object is viewed in successive portions or individual unit areas,

1 and the lights and shadows or variations of light at each unit area are changed into proportional variations of electrical current. At the reproducer each electrical variation is reconverted into a light variation that corresponds in intensity and relative position to that of the corresponding unit area of the object at the transmitter.

The human eye is retentive of images originating over a range of intervals extending from a fraction of a millionth of a second where the luminosity is intense to a-fraction of a second where the duration is greater and the light contrast that of ordinary vision. For the short interval, lightning and timed electrical discharges register on the retina of the eye as continuous impressions, while for longer exposures as in motion picture projection, sixteen interruptions per second of the image fail to cause perceptible flicker.

In television wherethe images of moving objects are to be reproduced, the scene to be transmitted must be viewed in its entirety at least sixteen times per second, in order that the eye may retain a continuous image. Successive portions of the scene have to be viewed, of course, at much higher speeds. For a given sized scene to be scanned, the amount of detail which it is desired to be re- 0 produced governs the size of-the'individual unit areas which are successively viewed; the

- greater the amount of detail the smaller the individual unit area, the greater the-number of areas to be viewed and the less the time available for viewing each unit area. Suppose, for example, a rectangular scene having 100 unit areas in each dimension. is to be scanned in its entirety sixteen times per second. Thescene has a total of 10,000 unit areas, all of which must be viewed sixteen times per second, so that it IS necessary that the transmitting apparatus have a viewing or scanning speed of 160,000 units of area per second. If the scene is larger or it is necessary to reproduce more realistic pictures having greater detail, the scannin speed, of course, has to be much higher. are diflicult to obtain in practice where moving elements such as the well-known rotating scanning discs are employed, and itis difiicult where such speeds are obtained to synchronize exactly the transmitting and receiving apparatus. 7

Three factors'areessential for successful television. These are-adequate light, sufiicient detail and absolute synchrony. Three more factors are necessary to make television reliable, simple and universal. These further factors are motionless structure, reversible or simultaneous transmission and reception and the use of electricity as thesole acplish television with transmitting and receiving apparatus containing no moving parts whatsoever.

Another object of the invention is to produce a continuously moving electro-dynamic arc.

Another object of the invention is to obtain high scanning speeds through the use of a continuously moving electro-dynamic are having nophysical mass.

Another object of the invention is to obtain absolute synchrony of transmission and reception. .H'

Still another object of the invention is to combine the functions of transmitter and receiver in an electro-dynamic arc screen.

According to a feature of this invention the scanning screen at the transmitter and the reproducing screen at the receiver comprise endless rail electrodes, between which an electric spark or are in-a gas at suitable pressure is produced and moves. The screens consist of rows of parallel electrodes of alternate polarity with corresponding turning corners foreach row in succession. The scanning screen is open to direct view or is enclosed in a camera with an optical outlet. The are is initiated between the electrodes and moves uch speeds rapidly alongbetween one row of electrodes; is constrained to turn the corner into another row along which it moves and so travels back and forth across the screen and scans the ob-- ject which is to be transmitted.

The are is initiated at a. fore-shortened gap between the electrodes and is caused. to move through the action of a magnetic field, across the lines of flux of which, the arc acts as: an armature conductor. The screen is placed in the field of an electromagnet in a position such that the lines of magnetic flux are perwith the upper one of the top row positive.

and the lower one of the top row negative, are

' placed on this page parallel to these lines and that this page is placed on the face of the south pole of a magnet, then the lines of force of the magnet would be pointed perpendicularly into this page. When a spark or are occurs, the current flow from plus to minus is downwards, and the arc will travel to the right. As it turns the corner, the top electrode is now minus, and the bottom one is plus, so that the current flow is upwards and the arc will travel to the left. Thus the' closed lines of a zigzag, double spiral or any other mazed path forming an electrode rail and a third intermediate line within the closed lines of the pattern-forming the other electrode rail bridged across a uniform field and impressed with the proper potentials will discharge an are which is self-propagational as a scanning illuminant.

The scanning arc is initiated at a fore: shortened arrester gapfby a high frequency piloting potential difference supplied by a thermionic oscillator in conjunction with a steady electrol-motive force which is supplied by a; direct current genelgator or by a high frequency rectifier. The high frequency pilot ing potential difference ionizes the gas molecules in the gap, and this ionized space offers a low empedance to the electro-motive force supplied by the direct current generator so that this electro-motive force can produce an arc discharge. The frequency piloting discharge current is transmitted also to the receiver, and, in conjunction with a direct current generator at the receiver, initiates the moving are at a fore-shortened arrestor gap in the receiver screen positioned similarly to the gap in the transmitter screen. In this way the transmitter and receiver screens are scenery.

roughly synchronized. More exact and continuous synchrony is established by the arc itself at-frequent intervals in its travel.

At spaced intervals within the screens are provided electrode shunts which momentarily shunt a portion of the are current energy. As the arc passes the shunts, the energy at each shunt path in the transmitter screen is transmitted to a thermionic synchronizer at the receiver. The energy at each shunt at the receiver screen is fed also to the thermionic synchronizer. The master shunt signals from the transmitter screen, and the local shunt signals from the receiver screen arrive invariably similar spacial coordinates. .The

transmitter arc scanner of uniform illumination functions to measure brightness in rela tion to the coordinates of space through a pinhole or lens camera in terms of transmitted or reflected light. The light variations on I the surface of the gbject are converted into current variations-by a photo-electric cell and such variations are transmitted to the receiver by modulation of a carrier wave and at the receiver are demodulated, amplified and superposed upon the traveling are where they produce light. and shade contrasts at an alternating frequency dependent upon the degree of detail represented in the scanned The transmitter when used also as a receiver comprises the-.itraveling arc screen and an invisible anterior pinhole screen (or camera) which is opaque to the uniform scan- 'ning light, except at the pinhole or lens substitute, and a system of peripheral photo-' sensitive cells detecting reflected or transmitted light from a near object whose photoelectric currents upon amplification are sent to the receivers, one of which maybe the transmitter itself. The functions of transmitter and receiver can be combined-either by alternating the functions rapidly or by differentiating their respective spectralran'gesthat of the transmitter being mono-chromatic,-short 'or long wave length. The latter method provides'true simultaneous scanning and reproduction images by using constant non-visible light rays such as infra-red rays in the same are with the visible rays,- which are varied in intensity by the incoming picture currents. A photocell sensitive to infrasred rays is then employed for dethrough the pinhole screen; as a receiver, the

subject sees the object through the translucent screen, which is opaque, as before said, to

the transmitting rays.

The transmitter comprises also a master clock, such as a piezo-electric crystal oscillator. This, in conjunction with the thermionic synchronizer keeps the master transmitter in uniform arc scanning condition; not only framing the scanning period but may also at frequent scanning intervals corresponding to convenient positions on the transmitting screen cause the moving arc to accelerate or retard by control of the speed factors. This master oscillator may also synchronize transmitter-receiver functions by thermionic facilitation and suppression of respective operations. A local ultra-high frequency oscillator synchronized or non-synchronized at each station may occomplish the same object.

This signifies that the same scanning screen serves as transmitter-receiver by high frequency inter-change of such functions, so as to simultaneously function as transmitter and as receiver. For example, the screen may be transmitting and receiving alternately during period ot orm second per screen or element, respectively. That is to say: the alternation may be as to the entire screen in of a second or as to the individual unit rail electrodes and into the rail electrodes,

as the illuminating currents increase or de crease. This anterior-posterior translation of the arc causes expansion and contraction thereof; the expanding are giving brighter illumination. Thus, the reproducing arc moves in two directions simultaneouslyalong between the rail electrodes to successively illuminate individual unit areas'and out from the rail-electrodes variably to give the light contrasts atv each individual unit area.

Referring now to the drawings, Fig. 1 is a projected view of an endless. rail screen placed along the face of the north pole of a magnet and illustrates howthe electro-dynamic arc according to this invention is made to move and to be self-propagational.

Fig. 2 is a view of another type of arc screen in which the .arc is returned to its starting point along a path external to the screen.

end and is then blown out at the instant that a new arc is initiated at the fore-shortened I gap.

Fig. 5 is a front view'of an arc screen placed in 'the field of a spherical, coreless solenoid.

Fig. 6 is a sectionalviewalong the lines 5-5 of Fig. 5 and illustrates the arrangement of the field windings of the electro- -magnet around the arc screen.

Fig. 7 shows schematic circuit arrangements of a combined master transmitter-re ceiver and a subscriber transmitter-receiver.

F ig. 8 shows a synchronizer circuit which functions to cause the arcs on the transmitter and receiver screens to travel in exact synchronism.

Fig. 9 shows schematic circuit arrangements of a combined master transmitter-re-- ceiver and a subscriber transmitter-receiver, which is. similar to those shown by Fig. 7, except that the illuminating components of current instead of being super-imposed upon the traveling arc act to energize a solenoid, the field of which is placed normal to the arc screen to cause anterior-posterior movement of the traveling arc and so accentuate the light and shadow contrasts.

In Fig. 1 the magnet 12 has arranged near and parallel to the face 13 of its south seeking pole the arc screen 14:, the electrode rails 15 and 16 of which, are arranged in parallel rows with turning corners at the end of each row. The electrode rails are marked and to indicate their polarity. The lines of magnetic flux entering the face of the magnet perpendicular thereto are represented by the arrow marked Flux. On the screen the small arrows perpendicular to the electrode rails indicate direction of current flow. The

small arrows parallel to the electrode rails indicate the direction of movement of the arc.

As an arcing potential is applied to the arrestor gap 17 across which the rail elec trodes 15 and 16 are bridged, the are being unconstrained will move, according to Flemings motor rule, between the top row of electrodes to the right. At the end of the row the arc is constrained to turn in a clockwise direction by the curved negative electrode.

and, on its entering into the second row, is 7 travelsacross and down the screen and is returned to its starting point along the external return path 19.

In the arc screen shownby Fig. 3, the electrode rails instead of being placed in parallel rows as in Figs. 1 and 2 are placed spirally. Of course, any suitable number of spiral convolutions may be used. The rails may be intermeshed, zigzagged back and forth or may take various other paths without departing from the spirit of the invention.

The screen housing 20 shown by Figs. 5 and 6 comprises the arc screen made up of the parallel rows of rail electrodes 22' and the spherical solenoid 23, the conductor windings of which are shown in section in Fig. 6. The turning corners of the rows of electrodes shown in Fig. 5 are hidden from view by the inturned portion of the member 21, which member also serves to support the screen. It is not necessary that the turning corners be hidden from view, but, for the purpose of il .port the screen housing 20. The spherical solenoid 23 is shown coreless, but it may contain a nickel iron alloy or other magnetic metal as a core on one side'of the electrodes 22, the other side being open to view, or the open sidemav be composed of hollow metallic tubing, the screen being visible there,- through. I

, In Fig. 7 the left hand circuit shows a schematic arrangement of a master transmitter-receiver station, according to this invention. The scanning screen 44 has the endless rail electrodes 24 supported in the magnetic field of a spherical solenoid, the. windings of which are represented schematicallyby the sin le turn 25, the energizing current for the solenoid being supplied by the generator 26. The master oscillator 39 contains a thermionic oscillator with its operating circuits. The oscillator oscillates at a frequency the constancy of which is controlled in the well-lmown manner by the piezo-eleotric clock 38. The master oscillator 39 serves to frame the arc screens and supplies at high frequency, voltage impulses, or what may be called piloting impulses to the fore-shortened arrestor gap 27 of the electrodes 24, through the leads 64 to the transformer input winding 29,-through the output winding 30, through the tuning condenser-31, transformer winding 32 and leads 33 and 34. Simultaneously, the generator 35 supplies an electro-motive force, or what may be called the driving component of the arc, current, through the leads 33 and 34 to the gap 27, this electro-motive force having a value sufficient to produce at the gap 27, at theinstant a piloting potential difierence supplied by the master oscillator ionizesthe gas between the electrodes 24, an are which travels in the magnetic field, as has previously ,avs

been explained, at a speed 'depending upon" photo-cells 37, which cause current changes proportional to the lights and shadows of the object. These current changes are amplified through the amplifier 40, then impressed upon the circuits of the transmitter modulator oscillator 41 in the well-known manner and then transmitted into space as modulations super-imposed upon a radio carrier wave.

The piloting impulses from the master oscillator 39 are also super-imposed upon the transmitted carrier wave. The carrier wave with its super-imposed currents is picked up byv the receiver 43 of the-subscriber station represented by the schematic'circuit connections shown to the right of Fig. 7. The currents pass from the receiver 43, through the pair of leads 46, and into the wave filter 47. This filter 47 has such electrical characteristics that the illuminating components of the current which occur at much higher frequencies than the synchronizing or piloting components cannot pass through. characteristics are such that frequencies above the value of the synchronizing frequencies are eliminated. Such a filter is described in the U. S. Patent No. 1,227,113 granted May 22, 1917 to Campbell. Piloting currents are amplified by the amplifier 45, then/pass into the transformer input winding 48, by inductive transfer to the transformer output winding .49, through condenser 50 and winding 51, through the leads The ionize the gas molecules in the gap. The

electrodes 55 of the receiving screen 56 are placed in the field of a spherical solenoid represented schematically by the single coil 57 to which is connected the energizing generator 58. The generator 59 supplies through the inductance 60 and leads 52 and 53 the driving component of the arc current in the same manner as the generator 35 of the mas-.

ter transmitter receiver, the operation'of which has been explained. The piloting components ,of the arc current in both the transmitterscanning screen 44 and the receiver screen 56 are thus supplied by the same master oscillator. The arcs at both the transmitter and receiver arrestor gaps are initiated by the combined actioh of the piloting and driving components ofthe are currents and are thus produced in exact synehrony at the arrestor gaps. The arcs once initiated in the screens continue to travel along the rail electrodes as long as the magnetic field and the. driving components are maintained. Only the first piloting impulse is required to initiate the arc. Since the rail electrodes are in shunt to the fore-shortened arrestor gap. the arc in motion acts effectively to short-circuit its arrestor gap. The potential, therefore, in each successive piloting impulse, instead of initiating a new are at the fore-shortened gap, takes the path of lowest impedance and flows across the arc. The speed of motion of the arc and the frequency of the piloting impulses originating at the master oscillator 39 are so chosen that the arc should make one complete circuit of the screen and arrive back at the fore-shortened gap at the very same instant that the piloting impulse arrives there. It may be that the are at either the master screen 44 or the subscriber screen 56 has its speed advanced or retarded due to some undesired influence, so that were no provision made to control the spped of are movement, the arc might arrive at the arrestor gap in advance of or'behind the piloting impulse. It is necessary that the piloting impulses continue to be sent out from the master oscillator 39 and that the arc in.the master screen arrive at the fore-shortened gap 27 s'imuh taneously therewith, in order that a subscriber station may be started up at any time and its are initiated in synchronism with the master arc. The piloting impulses from themaster-oscillator 39 serve to initiate arcs in the arc screens when the screens are put into service. Once an arc is initiated in a particular arc screen, the succeeding piloting impulses are obviously not required in their arc initiating functions. These succeeding piloting impulses are employed to advance or retard the arcs as required to cause them to pass the fore-shortened gaps at the correct instant. This is accomplished at the master station through the medium of the local synchronizer 42 and at the subscriber station through the medium'of the local synchronizer 65.. These synchronizers not only act to synchronize the arcs as they pass the fore shortened gaps 27 at the master station and 54 at the subscriber station but also act tosynchronize the arcs at numerous points throughout their path as will now be explained.

The master oscillator 39, as has previously been explained, sends out periodically, piloting or ionizing impulses, the frequency of these. impulses being controlled, for example, in the well-known manner, by the fundamental of the iezo-crystal 38. These piloting impulses siiould preferably have a wave form sharply peaked, although impulses having the familiar sine-wave form, would perform satisfactorily. The master oscillater 39 also sends out at spaced intervals.

between the piloting impulses intermediate synchronizing impulses which may be controlled by one of the higher harmonics of the piezo-crystal 38. These intermediate synchronizing impulses have a peak voltage very much lower than the peak voltage of the piloting impulses and cannot act to completely ionize the gas between the fore-shortened arrestor gaps 27 and 54 and so initiate an arc. The oscillations sent out from the master oscillator 39 thus have a wave form in which the piloting impulse peaks are separated and followed by a plurality of intermediate synchronizer peaks, the latter peaks having amplitude much less than the piloting impulse pea-ks. In the master are screen 44 the intermediate shunt paths 61 and in the subscriber are screen 56 the intermediate shunt paths 66 are'positioned and spaced in the are paths with respect to the fore-shortened gaps 27 and 54 respectively in the exact space relation that the intermediate synchronizer impulse peaks from the master oscillator 39 are positioned and timed with respect to the piloting impulse peaks.

At the master station the oscillations made up of the piloting impulses and the intermediate synchronizing impulses, travel through the pair of leads 64 into the synehronizer 42. The intermediate shunt paths I 61 and theforeshortened gap shunt are con-,

nected in shunt and are connectedto the synchronizer 42 by the pair of leads 63. With the arc in motion, as it passes each of the shunt paths 61 and. the foreshortened gap shunt, a portion of the are energy is absorbed and is fed into the synchronizer 42. If the piloting impulses from the master oscillator and the energy impulses from the fore-shortened gap shunt arrive at the synchronizer 42 at the same time, they balance each other out, the are being in its correct position at the gap .27. In the same way, if the intermediate synchronizer. impulses from the master oscillator 39 and the energy impulses from the shunt paths 61 arrive at the synchronizer 42 at the same time, they balance each other out, the are being in its correct position at each shunt path. It the energy impulses from the master oscillator 39 do not arrive at the synchronizer 42 at the same time as the impulses from the shunt paths, the arc speed is obviously too slow or too fast. The synchronizing impulses from the master oscillator or the shunt path impulses aetuate a work circuit within the synchronizer 42 in the order of their arrival to change the current flow in the field winding 25 of the spherical solenoid through energy transfer from the synchronizer to speed up or slow down the are as required to maintain it in its correct position throughout its travel. V

The details of the synchronizer circuits are shown by Fig. 8, where between the electrode rails 55 are shown a plurality of receiver electrode shunts 114 and a fore-shortened gap 115. The shunts areconnected to a common circuit separate from the electrode rails, the common circuit being connected in turn to the input of the thermionic amplifier 70. Therefore, as the arc passes a shunt or probe in its path, a voltage impulse will be im- Qpressed upon the grid of tube 70. The en'- a value as to equalizethe actuating voltages on the tubes when the arc is travelling at its proper speed. It is also possible to connect the shunts or probes directly to the rails, thus permitting the impulses from the master oscillator to arrive at both tubes of the synchronizer at the same instant, the energy at the shunt then decreasin the voltage on the synchronizer tube 7 0. y the proper value of the resistances 116 and 117, the absolute value of the voltages on tubes 70 "and 7.1 may be made equal, the synchronizer circuit operating in the same manner in either case. Common to the plate circuits ofthe amplifiers 70 and 71 is the triangular bridge 72 which is made up of resistances 73, 74 and 75.

The current in resistance 75 depends in direction on whether amplifier 70 and 71 operates. The thermionic amplifier 76 has the resistance 75 shunted'across its input circuit. Across this output circuit is placed the power amplifier 77. The triangular bridge circuit 78 is connected to the output circuit of the power amplifier 77 and is made up of the resistances 79, 80 and 81 Since the current in resistance 75 depends in direction on whether amplifier 7 O or amplifier 71 operates, the input potential in the amplifier 7 6 varies accordingly, and the amplified power in the power amplifier 77 varies its output current proportionately, feeding into the bridge 78. Accordingly the grid of amplifier 82 becomes positive or negative, depending on which signal, that is from the arc impulse amplifier 70 or the master synchronizer impulse amplifierv 71, arrives at the synchronizer The amplifier 82 feeds increased or decreased currents, as the case may be, into the spherical solenoid which supplies the'magnetic field to drive the are screen. If the localsignal impulse appears first, owing to the arcaccelerating by reason of a changed field or a strengthened arc, then the space current in the thermionic ampli fier will rise, generating a drop of potential across resistance 75, making the grid electrode 84 in the thermionic amplifier 76 positive. This results in a change-0f potential across 79 which produces a difierent bias upon the grid of amplifier 82. There is a potential drop across the resistances and 81, making the grid in the amplifier 70 positive and the grid in the amplifier 71 negative with respect to ground or the neutral lead 85. Thus, while the amplifier 70 with positive grid is maintained functioning throughout the signal impulse, the amplifier 71 with negative id is suppressed for the same duration. imilarly, if the master oscillator initiates the time signal, in which case the traveling. arc is in retardation, the local station is suppressed, while the amplifier 82 acts to accelerate the moving arc between the elec trode shunts. V

The synchronizing impulses consisting of the piloting impulses and the intermediate impulses of lower value are transmitted from the master oscillator 39 (Fig. 7) to the transmitter modulator oscillator 41 where they are superimposed as modulations upon the locally generated radio carrier wave. At the subscriber station the receiver 43 demodulates the signals from the carrier wave. The demodulated signals pass along the pair of leads 46, into the filter 47 where, as has previously been explained, the illuminating components are eliminated, into the amplifier 45 and then into the receiver synchronizer 65. The receiver synchronizer 65 as well'as the transmitter synchronizer 42 consists of the bridge circuit and the auxiliary field circuit shown in detail by Fig. 8. The arcvenerg'y impulses from the receiver are shunt paths 66 and the receiver fore-shortened gap shunt are fed into the receiver synchronize! 65 along with the received synchronizing impulses from the master station. The two trains of impulses in the order of their arrival at the bridge circuit of the synchronizer actuates the synchronizer work circuit to feed increased or decreased currents into the solenoid field winding 57 and thus control the speed of the subscriber are in exactly the same manner as, as has previously been explained, the speed of the master arc is controlled.

In Fig. -8 the shunt paths. are designated 114. These correspond to shunt paths 61 in the master screen and to shunt paths 66 in ii i the subscriber screen. The fore-shortened gap 115 in Fig. 8 corresponds to gaps 27 and 54 of the master and subscriber screens respectively.

By the above described method the arcs in the master and subscriber screens are int ated in exact synchrony and are maintained 1n exact synchrony throughout their travel under the contol of the master oscillator 39 in which not only the. piloting or initiating impulses but also the synchronizing impulses I are originated. I

Another satisfactory method of maintaining the master and subscriber arcs in exact synchrony throughout their travel isto have impulses from the shunt paths 61 in the master screen transmitted to the synchronizer 65 at the subscriber screen where they act to speed up or slow down the receiver are in'case it is not travelling in synchronism with the master are. When this method is employed the synchronizer 42 at the master screen 44 is. connected to the gap 27 and is not connected to the shunt paths 61. The energy impulses from the shunt paths 61 are carried by leads 33 and 34 into the transform-- awinding 30, by inductive transfer into the transformer winding 29, through leadsr64= into the master oscillator 39 where they are super-imposed upon the piloting impulses. The piloting impulses have a much greater amplitude than the shunt path impulses, and, at the receiver, the combined synchrony impulses now made up of piloting impulses and shunt path impulses actuate the synchronizer 65 in exactly the same way as if the shunt path impulses orginated at the master oscillator 39. i

' Although only two shunt paths have been shown in the master and'subscriber screens, it should be understood that any desired number within the limitations of the apparatus could be used.

For the purpose of illustration, the synchronizing of the arcs at frequent points in the arc paths has been described with the speed control accomplished through the weakening or strengthening of the magnetic field. The arcs may also be speeded up or slowed down as required by control of the electro-motive force of the generator supplying the driving component of the arc current.

Instead of using shunt electrodes atfrequently spaced intervals along the arc path, one or the other of the rail electrodes between which the arc travels may be perforated at each synchronizer station, and a photo-electric cell may be so placed that the light from the traveling arc illuminates it as it passes before the perforation. The current impulses from the photo-electric cells at the transmitter and at the receiver screens may be fed into the synchronizer, as has been previously described in connection with the arc shunt impulses. 7 I

The portion of the electrodes-24 (Fig. 7) at the master station which contain the electrode shunts 61 and the fore-shortened gap 27 is placed without the border of the master arc screen 44. Similarly the electrode shunts 66' and the fore-shortened gap 54 of.

the subscriber electrodes are placed outside the border of'the subscriber are screen 56. This arrangement ismade in order that the I current in the piloting and synchronizing impulses which are fed into the arc path may be superimposed upon the travelling are only when it is out of the scanning or reproducing range. These impulses thus do not interfere in the least with the scanning or reproducing functions of the arc.

The illuminating components of the transmitted arc current are demodulated from the transmitter carrier wave by the receiver, 43 (Fig. 7) and are passed into the receiver amplifier 87 into the transformer input winding 88; then by inductive transfer to the transformer winding 51; then through condenser 50, transformer winding 49; leads vary the brightness of the arc inaccordance with the modulation of the carrier.-

It has been previously explained that the functions of the transmitter-receiver screens may be rapidly alternated. The high frequency function oscillator 90, thefrequency of which may be controlled by a piezo-electrio crystal, serves to interchange at the subscriber station the transmitterreceiver function. At the master station the high frequency function oscillator 120 serves to interchange the transmitter receiver functions of the master station.

When the receiver screen 56 is functioning as a transmitter, the reflected light from the object being scanned through the pinhole or lens 121 strikes the photo-cells 91 arranged around the periphery of the screen 56, which cause current variations through the ampli- .-iier 92 which are transmitted to the transmitter modulator oscillator 93 where the illuminating current components are superimposed illuminating currents are demodulated in the well-known manner and pass into the receiw er amplifier 95, along the pair of leads 96, into the transformer input winding 97, by inductive transfer into the transformer winding "32, then through condenser 31, tra'ns former winding 30 and leads 33 and 34 to the electrodes 24 at the arrestor gap 27 where they are super-imposed uponthe traveling are at the transmitter screen at the instant the transmitter screen is serving as receiver screen.

When the functions of the arc screens are rapidly alternated, the eye, owing to 'the brightness of the. arc-discharge, retains the pictured image during the period that the screen is scanning the local object.

rangements are identical with those of Fig.

7, except that the illuminating currents instead of being super-imposed upon the traveling are are made to actuate a coreless solenoid which supplies a magnetic field transverse to the field of the are driving solenoid. This transverse magnetic field is normal to the rows of rail electrodes, and as it is-made' stronger 'or weaker by the flow of illuminating currents, it causes anterior and posterior movements of the are without interfering with its advance movement. As has previously been explained, the arc bows variably out from the rail electrodes in a direction at right angles to its normal movementto give variable light contrasts; the illumination be ing brighter the more pronounced the bowing. At the subscriber station the illuminating currents flow from the amplifier 87 into the transverse field winding 108. At the master station the illuminating currents flow from the amplifier 95 into the transverse field winding 109.

The illuminating screen may have its rail electrodes exposed to the air or they may be supported in an evacuated container. It is preferred that the electrodes be contained within a glass or other suitable container conreason for thisis that a tainingheliumor other suitable gases at a pressure slightly below' atmospheric. The I gas such as helium slightly below atmospheric pressure between the rail electrodes iomzes more easily and also offers less resistance tothe movement of the are.

' The type of rail electrodes shown by Fig. 4 may be used satisfactorily in the place of the endless .rail electrodes which have been used to illustrate this invention. With this type of electrodes the travelling arc is blown out at the horn gaps 141 at one end of the screen, at the same instant that another are is initiated at the fore-shortened'gap 140. The

tween closely spaced electrodes or it may be a larger are travelling between more .widely spaced electrodes. To give the effect of continuous vision to the eye, the arc may travel at very highspeeds with extreme brightness or it may travel at slower speeds with less brightness. The various factors of arc speed,

screen herein described may be employed in other apparatus than that used for television, and it should be understood that the various elements of the invention are not to be limited to use in television.

What is claimed is:

1. In an illuminating screen comprising an.

arc path, means for obtaining a magnetic field in which said path is located,- and means for initiating an arc in said path, said path having stationary electrodes directing said are along adjacent paths.

2. In an illuminating screen comprising stationary rail electrodes, means for obtaining a magnetic field in which said electrodes are located, and means for initiating an are on said electrodes, said electrodes directing said are along adjacent paths.

3. An illuminating screen comprisin a plurality of rows of interconnected e cotrodes, electromagnetic means for creating a ma etic field in which said electrodes are positioned, and means for creating an are between said electrodes.

4. An illuminating screen comprising a plurality of rows of electrodes of alternate polarity, electromagnetic means for creating a local magnetic field around said electrodes, and means for creating an are between said electrodes.

5. The method of producing a moving illuminating discharge for scanning an object in unit areas, which comprises creating an arc in a magnetic field of sufiicient strength to move said arc, and causing said are to transverse a particularized stationary path for completely scanning said object in unit areas.

6. The method of synchronizing electrodynamic arcs in a plurality of similar arc screens, which comprises simultaneously transmitting piloting impulses to said screens to ionize the arc path whereby locally applied potentials across the arc path pro.- duce discharges.

7. The method of synchronizing a moving electro-dynamic are at a transmitter with a similar are at a receiver, which comprises transmitting from the transmitter a train of synchronizing impulses, transmitting a train of electrical impulses from the receiver are path to denote the passage of the receiver are and employing said trains of impulses in the order of their arrival to advance or retard image to be viewed y the subject and scanning another object for transmission with said are.

9. A luminous screen comprising a .gas filled envelope containing stationary .rail electrodes, means for creating an arc between said electrodes, and means for obtaining a magnetic field in which said electrodes are positioned for creating a driving force on said arc, said electrodes directing said are along adjacent paths.

10. In a luminous screen of stationary electrode rails, an arc path formed by said rails having a particularized configuration, means form-eating an arc on said rails, means for creating a magnetic field surrounding said are for driving it along said electrode rails, and means controlled by said are for regulating its speed of movement.

'11. A two-way television system comprising at each end a luminous screen having stationary electrode rails forming adjacent paths, means for creating magnetic fields around said electrode rails having comparable strengths, means connecting said screens, means for scanning an object by one past said point.

of said screens, means for receiving a picture of said scanned object on the other of said screens, and means for changing the function of each screen simultaneously.

12. Electrical apparatus comprising rail electrodes means for creating a magnetic field surrounding said electrodes, means for producinga moving are between said electrodes, and means controlled by said arc'for transmitting a signal from a point in its path between said electrodes to denote its passage 13. In a television system, a transmitter scanning screen employing an electrodynamic arc in a magnetic field, means for initiating a continuous arc in said screen at a defin'ite position, means for propagating said arc over continuous electrodes in said screen,

means for impressing periodic impulses on said screenin a time-space relationship with respect to said are on said electrodes, and means for controlling-the space relationship of said are in said screen to conform with the time of impression of said impulses thereon,

14. In a television system, a transmitting screenhaving a plurality of electrodes means for initiatingan are on said electrodes. and propagating said are thereover at a rate to cause said screen to appear as a solid-illuminated field, means for absorbing energy from I said arc at spaced intervals along said electrodes, and means for utilizing said energy to control the speed of propagatlon of said are over said electrodes.

15. In a television system, a transmittin screen and a receiving screen, both'of sai screens comprising stationary electrode rails, means for propagating arcs along the rails of both of said screens at a rate sufiicient to cause said screens to appear as solid illuminated fields, means for projecting light from one of said arcs successively over unit areasof an ob ect to be scanned, a photoelectric cell for obtaining current variations characterized bythe varying densities of light and shade in said object, means for transmitting said current variations to said second screen, and means in said second screen for varying the illumination thereof proportionally to the variation in currents from said photoelectric cell.

16. In a television system, a plurality oi illumination screens comprising stationary electrode rails located in magnetic fields, and an oscillator circuit for generating an are producing voltages on said rails in each of said screens, said oscillators also producing impulses for controlling the speed ofsaid are along said rails.

'17. In a television system, a transmitter scanning screen having stationary electrodes and employing an electrodynamic arcin a magnetic field, means for detecting varying intensities of light and shade of an object, a

receiving screen employing a similar electromagnetic arc in a magnetic field, means for transmitting said photocell currents to said receiving screen, and means at'said receiving screen for modulating said are in accordance with said photoelectric currents.

18. A television system in accordance With claim 17 in which said modulating means include a quadrature magnetic field for moving said are anteriorly and posteriorly with respect to a plane parallel to said screen.

19 In a television system, a transmitting screen having a plurality of alternately polarized electrodes, means for initiating an are between said electrodes and for propagating said are thereover, means associated with said screen for detecting varying intensities of light and shade of an object, and a similar receiving screen including a quadrature field for bowing said are perpendicularly to its line of travel, said quadrature field being controlled by currents characterized by the light ing said energy to synchronize the speed of propagationof the arcs over both of said sets of electrodes.

21. In a television system,-a transmitting screen comprising a plurality of electrodes, a similar receivng screen, means for initiating an arc on both of said screens and propagating said are thereover, means for synchroniz- 10 I 1,ses,27s

ing said arcs, means for producing arcs having invisible light of a constant intensity for scanning objects at both of said screens, said arcs also projectin visible light, and meansassociated with eac of said arcs for varying said visible light in accordance with the li ht and shade intensities of objects at the ot er of said arcs. 4

22. In a television system, a set of electrodes, means for creating a magnetic field around said electrodes, a source of potential for initiating an are between saidelectrodes, said are being propagated along said electrodes by said'field, a plurality of photocells 15 adapted to receive light from said are at certain intervals during its propagation along said electrodes, and means connected to the outputs of said photocells to operate a work circuit in accordance with the speed of propm agation of said are.

' 23. In a television system, a set of electrodes, means for obtaining a magnetic field surrounding said electrodes, a potential supply for polarizing said electrodes and in 15 itiating an arc therebetween, said are being driven along said electrodes by said magnetic field, a plurality of openings at intervals along said electrodes, a corresponding plurality of photoelectric cells positioned op- '9 posite said openings adapted to be activated by light from said are, and means connected to the output of said photoelectric cells for operating a work circuit in accordance with the speed of said are along said electrodes.

85 24. In. a television system, a set of elec trodes, means for obtaining a magnetic field surrounding said electrodes, a'potential supply for polarizing said electrodes and .in'itiating an arc therebetween, said are being driven along said electrodes by said magnetic field, a plurality of. openings at intervals along said electrodes ,a plurality of photoelectric cells positioned to receive light from said are, and meansfior utilizing the impulses from said photoelectric cells to control the speed of said are along said electrodes.

In testimony whereof, I have signed my name to this specification this 25th day of September, 1929.

5. ALEXANDER MOLEAN NICOLSON.

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