US2095391A - Television system - Google Patents

Description

Oct. 12, 1937. v J. w. LEGG 2,095,39l

TELEVISION SYSTEM Filed April ll, 1927 3 SheefSwSheet 1 WITNESSES; I INVENTOR 5. MW Jase/oh VV. Legg Oct. 12, 1937. J. w. LEGG 2,095,391

v TELEvIsIoN SYSTEM Filed April 11, 1927 s sneets-shet 2 fig-3- hillll'l'lllll WHNESSES; lNvEwToR f MWM Jose/oh l/1/. Legg Oct. 12, 1937. J. w. LEGG 2,095,391

TELEVIS I ON SYSTEM Filed April ll, 1927 5 Sheets-Sheet 3 ved 804 80 gob/ MWWNWWWMWWWWWMWWM C MM A Zero Amp//fude i Max/Mum /lmp//V-Ude WITNESSES; iNvENToR 5. MWM Jose/oh Legg '/I L I 30 defined point of light.4

Patented Oct. 12, 1937 Parent ormer aosasei i TELEvrsroN SYSTEM Joseph W. Legg, Wilkinsburg, Ita., 'assgnor tom Westinghouse Electric &'Mannfactnring Company, a corporation of Pennsylvania Application April 11, Miseria! Ne. 182,651:

' as claims. (ol. its-6).

i `This invention relates to systems for the transmission of views by communication systems, such asradio`.' "It is an object o'f this invention to produce i synchronism between .the scanningv and-reproducing. `devices without requiring an additional communication channel for this purpose,

Itisa further object of this invention to combinea synchronizing means with the view to be transrnitted. i i I i 'It is a further 'object of this invention to send over the communication channel a characteristic4 impuls'e at corre'sponding phases Of eachitraverse ofV the view by the scanning device and to automatically position the reproducing device in accordance with said phases of the traverse by V means of saird'impulses..

`It is a further object of this invention to produce`` an Optical system in which the Only parts required to move rapidly shall be the mirror sys'- tem of an oscillograph.

It is a further object of this invention to provide a light source the intensity of which may be rapidly vari'ed in accordance with the illumination of successive points in the view to be Htransmitted.

` It is a further object of my invention to provide ahlinear light source which, by means of a cylindrical lens, may be made to give7 a well- It isl a further object of my invention to provide avariable source of light in which the brilliancy shall be controlled by an impressed potential. i

`,It` is a'further object ofrmy invention to pro- .duce a conductive column of vapor to47 emit light and'tocontrol the brilliancy thereof by varying the potential along it. i

` Itisa further object of invention to com- 44) bine a linear source of lightl With an Optical system,l;including a moving part, in such a manner Y that successive portions of said sourcemay be brought, in turn,`` into operative relation to the Optical system. .5 Other objects Of my invention' will be apparent from the following detailed description and the accompanying drawin'gs'in which,

Figure 1 is a diagram, partly in perspective, illustrating the scanning apparatus, to Fig. 2 is a diagram illustrating the movable mounting of the lenses shown in Fig. 1,

Fig.'3 is a diagram, partly in section, illustrating the. receiving apparatus,

* Fig. 4 is a diagram, in perspective, illustrating o.) the 7optical parts ofv the receiving apparatus,

Fig. 5 is a diagram to assist in the explanation Y of the Operation of the vtransn'litting system,

. Fig. 6 is. an illustration of a modifioation of the optical system in either the receiving apparatus or the scanning apparatus, and 5 Fig. 'Z is a diagramillustrating a means Vfor producing a slow movement of one of the Optical parts shown in Fig. 6.

As shown in Fig. 1, an object Or a view l is visible through a window 2. Although the draw- 10 ings are intended to Suggest that the view I is' out of doorsand the Optical apparatus in a house, it will be obvious that a small boxmay enclose' the Optical parts and the window 2 will then. be an Opening in one wall of the box; i 15 At one side of the window, the wall is opaque and dark, as indicated at 3. `At the opposite side of the window a portion of thewall is brightly illuminated, as indicated at 4. The illumination may, for example, be accomplished by lamps 5 f and, if desired, the surface of the wall flush with 20 the window and with'the dark surface 3m.ay be covered with ground glass or Other means for rendering the bril'liancy uniform thereover. i i xThe scene to be'soanned by the Optical system Vin Fig;v 1 includesthe bright surface 4 and the 5 dark surface 3, as'well as the view or objects beyond the Window 2.

On the side of the window opposite the object or view I, a plurality of lenses 6 are positioned, Preferably, these lenses are, as shown in Fig. 2, numerous and comprise a large circle of lenses, whereby first one lens and then another may be brought into position inn front' of the window without requiring a high rate of Vspeed for the movement of the lenses. In the specific form of mounting, indicated in Fig. 2, the lenses are secured in a disk 'l Which is driven by an electricl motor 8. suitable reduction gearing may be employed togive the proper speed to the Wheel 'l and suitable openingsin the disc 'i provide for the passage of `light through the lenses S.

On Fig. 1, the direction of movement of the lenses 6 is indicated by an are having a center I ll which, in actual construction, would be the 4 center of the Wheel 1. For the sake of clearness, the Wheel is not shown in Fig. 1.

The lenses' 6 are cylindrical, their geometric axes beingl arranged radially'of the disc 'IV andV their Optical axes being perpendicular to said disc. For the short distance that any One lens 6 moves while in operative relation to the rest of the Optical system, the motion may be regarded as pure translation at right angles to both axes. I'helens 6 is between the window 2 and a mirror II which is mounted on a device that causes the mirror to oscillate rapidly.

Any suitable means for producing rapid oscillation may be employed. I prefer to support the mirror upon the movable conductors I2 of an oscillograph and to send a high-frequency current, produced in any familiar or suitable manner, through the oscillograph to oscillate the mirror. When the oscillations are produced in this way, it is preferable that the natural period of the Vibrating system shall be the same as that of the current supplied. Between the mirror I I and the lenses 6, a lens I3 is provided.

The ribbon of light which arrives at the mirror I I from the. lenses 5 from a point on view I is refiected, passing a second time through the lens I3, and reaches a photo-cell I4. A shield I5, having a small Vertical Opening I6, is provided in front of the photo-cell I4 in order to give definiteness to the point in the scene I corresponding to the instantaneous position of the optical system.

The lens I3 focuses the light from the mirror II and lens 6 upon the window I6. The quantity of light entering the photo-cell is, therefore, that from a larger area in the view I than the size of the opening I6 would command if unaffected by the lens. If desired, additional concentration may be afforded by another lens between window IG and photo-cell I4.

The light from the scene passes through the lenses 6 and l3 and is reflected by the mirror II. Only the light from a definite point in the scene will, however, pass through the window I 6. Light from other points will be stopped by the screen I5. Thus, at each moment, a definite point in the scene is correlated to the window IS. This point changes from moment to moment, one coordinate thereof being dependent on the motion of the mirror I I and another upon the motion of the lenses 6.

The photo-cell I4 is connected to any well known or desired form of transmitting system whereby the radiations sent out by the transmitter shall be modulated in accordance with the illumination of the photo-cell I4, the amplitude of the radiation corresponding at each moment to the illumination of the cell.

A conventional radio transmitting system is illustrated in the drawings for the purpose of showing how the photo-cell l4 may control the amplitude of the radiations. The actual structure of the Vacuum-tube circuits is not a feature of my invention. In the circuits illustrated, the photocell M controls, in the usual way, a modulator tube I1 which acts to divert more or less energy from the oscillator tube I8. The oscillations from the tube IB are radiated by the antenna IS.

In Fig. 3, the receiving antenna 2I is tuned to the frequency of the oscillations generated by the tube IB at the transmitter. A detector 22 is connected, in any usual or desired way, to the antenna 2I. The output circuit of the detector includes a plate battery 23 and a resistor 24. Preferably, a second battery 25 is inserted between the resistor 24 and the filament of the detector 22. A condenser so small that it is of large impedance to all except the very high frequency, may, if desired, be connected across the output of the detector to ensure that the high frequency components of the plate current shall not affect the apparatus. Between the battery 23 and the resistoi` 24, a condenser 26 is provided in parallel with an inductor 21. The inductor 21 is also the primary of a transformer, of which 28 is the secondary. The condenser 26 and the inductor 21 together constitute a network interposed in the circuit from the plate to the filament of the tube 22. The frequency, to which the network or parallel-resonant circuit is tuned, is the frequency of the movement of the mirror II in Fig. 1.

One terminal of the secondary 28 is connected to the grid of a tube 29, and a battery 3Il is connected between the other terminal of the secondary 28 and the filament of the tube 29.

The plate current of the tube 29 is supplied from a battery 3l. If desired, the battery 25 may be replaced by a portion of the battery 3I. This can be done by connecting the left-hand terminal of resistor 24 to an intermediate point of battery I. The plate circuit includes the primary 32 of a transformer, the secondary 33 of which ls connected to the moving conductors 34 of an oscillograph 35. The moving conductors 34 carry a mirror 35. If desired, a condenser may be shunted across the primary 32 for tuning, and an additional inductance, for further control of the tuning, may be inserted in series with the primary 32. A tuning condenser large enough to compensate for the inductance 33, and also for the inductance. of the receiving device 34 may, if desired, be included in the secondary circuit.

The battery 3! serves to supply also the plate circuit of a tube 31. By properly proportioning the potential of the battery 23 to that of the battery 25, the average potential of the grid of the tube 31 is determined. The potential also depends on the drop across the resistor 24 and the effect of the network 26-21.

The plate circuit of the tube 31 includes a resistor 4; which, if desired, may be a heating coil for maintaining the mercury in the tube 42 at a temperature near its boiling point. A battery 43, in series with a resistor 44, is connected to the mercury by means of cups 45 and 46 which are parts of the lamp 42. The resistor 44 may also serve as a heating coil to maintain the capillarv column 41 of the lamp in a vaporized condition. The two terminals of the resistor 4I are connected to sealed-in electrodes 48 and 49 near each end of the capillary portion of the lamp.

Although I have illustrated a mercury tube having open ends, other forms of mercury lamp may be used, such as mercury-are tubes having a low pressure of mercury vapor. The portion of the capillary tube 41 between the electrodes 48 and 49: will not generally have liquid therein, but will be filled with the glowing vapor. It is not essential that, even when the lamp is cold, f

the capillary be filled with liquid. The lamp may be started by a current through the ordnary mercury vapor if preferred.

The optical portion of the receiving system includes mirror 36, a lens 50 for bringing to a focus adjacent the lens 5I, the light from the lamp 53 which is reflected by the mirror 36. The optical system also includes a plurality of lenses 5I mounted in a disc. The optical system is best illustrated in Fig. 4, wherein the screen 52 receives light from the lamp 53 through said optical system. The screen 52 may be a photographic plate for recording the transmitted view or it may be a ground glass or a projection screen or an imaginary plane on which is focused an eye piece, or ocular to be observed by the eye, or through an ocular.

In Fig. 4, for clearness, the several directions are taken perpendicular to one another, but the invention may be used with oblique directions.

The lamp- 53 is shown as'horizontal and extending away from` the reader and toward Vthe right.

l'l'he axisof movement of the mirror 36 is shown parallel/to, and below and; 'to the' right of, the lamp. For further simplicity of description, it wilil-`l be assumed that the 'center of the mirror is in the plane perpendi'cular toithe lamp at its center, although this'feature is notl essential to,

i near said plane may 'be'regardedi as. parallel to vpotential-responsive device.

the length of' the lamp and tosthe. other: pairflof edges of` the` screen.. The `refiected light is brought, by the lens -lf, to a. focus: upon the: under side of the screen 52.

In Fig. 61, a modification of the optical Vsystem is shown, two mirrors being employed'instead of a mirror and a plurality of lenses. The mirror 3% is intended' to be oscifllated atr high frequency by the conductors 34, as alreadyexplained.. The mirror tilv is intended to osciliateat a lower fre,- quency, the oscill'atiohs of the mirror BI being produced by the means illustrated in. Fig- '7. Two lensesi 62 and 63 are Vprovided for focusing the light upon the screen. The mirror 36' is mounted .upon the conductors. of the. oscillograph; 3:51. 'The mirror 61 is mounted upon the conductors 64 which, inf this mOdifiGation, are a portion of the same os'cill'ograph. In Fig. '1, the

conductors 64' andfthe mirror 6 Il are shown below the conductors 34 and; the mirror 35; It will be evi'dent that the position`` may be,l reversed if desired and that it is not necessary to: havethe mirrors horisontal.,v

In Fig' '7, a synchronous motor 66 isflsh'own which is' intended to be driven by the same power system as thelmotor 8 in Fig' 2'. Corresponding frequencies: in the mo-vement. of. the. Wheel I and the rotor` of the motor 65 are thus obtained'.: The

conductors '5.4 have; a high resistance .1.51 in'series with. them, 'whereby the mirror'l is essentially'a A battery 'II,` feedinga ci-rcularl potentiometer 1'2, Supplies the po- 4 tential'for the conductcrs 613m The moving member '13 of the potentiometer7 is connected to. one terminal of the. co-nductors; 64 and is driven by the rotor of the motor GIS;` I I v In theoperation-of the device, the movement of the mirror IfIv in Fig. 1 causes'the window Ha' of the photo-sensitive instrumentxto be associated in succession` with a' line-of pointsextending. horizontally. across the view. The' movement' of the lens' causesf the Window IG' to beflass'ociatedxin succession with pontsatr different heights in the window 2:

The movernentA of the mirror Iflv is much more rapid than that of the lens 6. During any one swing of the mirrorl II, first'one end, thenan intermediate portion;` and then theother end of the lens` i;` is operatively J related to the mirror Ili and the window- HS. VOnlry ajsmaljl portion of:

' the whole lens Eifis operative at any one' instant.

This portion is of small enough axial.` length1to: cause the difference between it and a spherical i lens to be without substantial effect; The illumination of the window IS by .the light from the spot in the scene correspondingto the instantaneous position, of the Optical system is substantially the same as it would be if the7 portioneof lens 6 corresponding to the position of the mirror 'II. at that moment were spherical instead' of with the. brightly lighted left-hand. margin of i the scene, the mirror is moving slowly. Again, at the right-hand end of its, swing, when lt is associatng; some. point? in: the darkr surface.. 3 with the window IG, the mirror is moving. slowly., The rate of change in the mirror's motion is greatest at the points in. the swing where it is moving slowly; Overthemid-portionsiof the Swing, the mirror isl moving nearly, although. not

absolutely, at a uniform velocity. Consequently, there will be, in the reproduction, but little distortiorr of theV illumination resulting 'from the fact 7that the mirror II 'sweeps more rapidly over some parts of the view I than over other parts. In the extreme positions of f the mirror I I, either the brightly illuminated space II or the dark spacea3 is associated with the. Window IG. Since each of these two spaces is of extreme and comparatively uniform illumination, the change in. rate of movement: of the mirror in these parts of the swing is unimportant.

As the mirrowV I I swings,v the illumination; of the cell M is; atV first veryfgreat, then varies in accordance with thel illuminationof the several pointsl of the view and finally becomes zero. Both the zero illumination and the very great illumination differ greatly from the illumination of any point in the view I seen through the window 2. Thus, atthe extreme left-hand position.` and at` the extreme. right-hand position of the mirror II, the cell' I4 is subjected toa very different` degree of' illumination from that'dur-v ing therest of the traverse. When the mirror II is in such position, that 'the window IIis optically associated with a point inthe dark surface 3, the photo-electric cell I4- tion of the mirror VII is such that light from a spot in the illuminated area 4 reaches the photocell IA, the cell is highly illuminated, and, 'therefore;` sufiiciently conductiveto cause -the potential'fof the grid of the tube I'I 7 to beV more nearly positive. Czonsequently, a considerable;

amount 'of'ene'rgy is diverted from the Vacuum?- tube P8, and the oscillations either ceaselentirelyor become very small. Practcallynno i energy is radiatedby the antenna I9. under these circumstances. i

fIn any other position'of the mirrorv II, the illumination of. the photo-cell Ill' corresponds to 7the brilliance of some point in the view I.. Consequently, thephoto-cell I4 is illuminated toan intermediate degree. Some energy is, therefore, diverted from the tube I8 but not sufiicientto cause the amplitude of the radiations to become zero.

Preferably, the constants of the apparatus are so chosen that the change in the conductivity of the photo-cell I 4 will occur on the straight-line part of the characteristic curve of this cell. Likewise, the changes in the current, through the tube I1 and in the amplitude of the radiations, preferably have a straight-line relation to the changes in the illumination of the cell I4 as the mirror sweeps over the portion of the scene constituting the View I. The darkness of. the surface 3 and the brightness of the surface 4 are intended to greatly exceed the changes in the view, whereby the. changes in the amplitude of the radiation at each end of the swing of the mirror I I greatly exceed the changes during the middle portion of said swing.

It is permssible for these extremes to extend beyond the straight-line part of the characteristic, but no advantage results from having them extend very far beyond it.

Fig. 5 is a'n attempt to indicate the changes in amplitude of the radiations with changing positions of the optical system. The left-hand portion 8I of Fig. 5 corresponds to the brightly illuminated surface The right-hand portion 83 corresponds to the dark surface 3, and the middle portion 82 corresponds to the window 2.

The combined action of the mirror I I and the lens G'will cause the point in the scene optically associated with the Opening IG to explore the scene by a path which crosses the scene rapidly from side to side, entering the illuminated surface 4 at one side and the dark surface 3 at the other side. The curve 88 in Fig. 5 is intended to illustrate how the point corresponding to the window IB moves, and the accompanying changes in radiation. The serpentine character of the curve, causing it to extend across the figure many times between the right and left edges and only once between the top and bottom edges, corresponds to the progress of the point.

The sinuosities of the curve are intended to represent the oscillations constituting the radiation. It will be recognized that the wave length of these oscillations is very much shorter than illustrated by Fig. 5. A drawing to' scale would show these oscillations of, so short a wave length that they could not be recognized.

The distance which these sinuosities extend away from the mean position of the serpentine curve corresponds to the amplitude of the oscillations.

In the portion 8I of Fig. 5, the curve has no sinuosities. This is illustrated at 800,. In the portion 82 of Fig. 5, the ourve has sinuosities of changing amplitude. This is illustrated at 8019. In the portion 83, the amplitude'is a maximum, as illustrated at 800.

Throughout the region 8I and the region 83, the rate of movement of the mirror I I is changing rapidly, but, since the brightness of the surface 3 is always zero and that of the surface 4 is uniform, the amplitude is uniform (and minimum) in the region 8I and also uniform (and maximum) in the region 83. The change in rapidity of movement of the mirror II is, therefore, without effect upon the outgoing radiations. Over the region 82, the rate of movement of the mirror II changes only slowly. Very little distortion will, therefore, be produced by the circumstance that the mirror passes more quickly over certain portions of the scene than over other portions.

The radiations are received upon the antenna 2I, represented in Fig. 3, which is so tuned that other frequencies are of little effect upon the grid circuit of the tube 22 which acts to detect the signals.

The plate current of the detector 22 will vary in accordance with the amplitude of the radiations. Consequently, the plate current will vary irregularly while radiations corresponding to the region 82 in Fig. 5 are being received, and will show a large and abrupt change when the exploring point enters the region 3, and a large and abrupt change in the opposite direction when the window I6 is correlated to a point in the region 4.

The tuned circuit 26-21 is thus subjected, at the instants of each end of the traverse, to impulses due to the sudden change in the character of the plate current. The impulses are of one character when the mirror II is at one end of its swing and of the opposite character when it is at the opposite end of its swing. They, therefore, set the circuit 26-21 into oscillation at its natural period. This period is adjusted to correspond to the period at which the mirror II is oscillated. The impulses caused by the bright surface 4 and the dark surface 3 thus insure that the phase of the current circulating in the network 26-21 will always agree with the phase of the movement of the mirror II.

The tube 29- delivers to the primary 32 a current which is controlled by the secondary 28, and which, therefore, agrees in phase with the movements of the mirror I I. To add still greater certainty to the synchronizing effect, the plate circuit of tube 29 may be tuned by a condenser in parallel with the primary 32. Preferably, the lnductance in the tuned circuit is not all included in the primary, but a portion, in series with the primary, is added for Convenience in adjusting the tuning.

The secondary 33 is energized from the primary 32 to deliver current to conductors 34, which causes the mirror 36 in the oscillograph 35 to move. The provisions just described for insuring the synchronism cause the movements of the f mirror 38 to agree accurately with those of the mirror II. The position of a selected point in the view I corresponds accurately, so far as its right and left co-ordinate is concerned, with the position of the corresponding point of screen 58 determined by the mirror 36.

The Vertical coordinate of the point in the view I optically associated with the photo-cell I4 depends upon the position of the lens 6. This position ls changed by the rotation of the disc 1, which, being driven by the motor 8, may be made very regular, depending only upon the frequency of a Commercial power supply. Similarly, the movement of the lens 5I in the receiving apparatus shown in Fig. 4 may be produced by a motor similar to the motor 8 and fed from the same power supply. The center of the wheel or disc carrying the lenses 5I is indicated at 15 in Fig. 4.

The movement of the lenses is slow, as compared with the movements of the mirrors |2 and 36. It is, therefore, feasible for an operator to adjust the position of one set of lenses 6 or 5I relative to the otherjif the appearance of the reproduced picture shows that such an adjustment is needed.

The light for the receiving apparatus is supplied from a linear light source 53. In one extreme position of the mirror` 36, light from this source is refiected to a point near one end off a lens SI. As the mirror,36 swings,l the light is directed to successive lportons of Vthe lens:I until, at the other end, of the Swing, it is` refiected to a point near the other end of said lens.` Y -11 1 As the lens 5I passes across the screen 52, successive portions of the linear light source 53;are concentrated toa point onithe screen 52..

When the lens 5I passes, out of operative position and.- the-next lens 5I enters operativeposition, the illuminated point on the screen 58 changes abruptly from one sidefof the screenVV .to thejother. -f i 7`The movementV of the mirror 36 causes the spot of light to travellengthwise of the screen 52;

rthat,.is,V between the two edges shown in Fig. 4 asshort edges. 4Themovement of'the lenses 5I i causes the illuminated 7point to travel. between the edges shown .as longf'edgesin said figure.

The movement of .the illuminatedpointfin re-`` sponse, to the motion of; the mirror 36, is (prefer-i ably greater than the l'ength of the screen 52. Consequently, the bright surface 4 and the dark surface 3Y are: not, represented 'upon the screen 52.

The changes in the intensity Vof the lightflreceived from the several. pointsthroughout the. 'V

scene I, 33.; and 4, Fig. 1, cause. changes in the magnitude of the current in the 'plate circuit of thetube 22,.iFig. 3. The potential drop across the; resistor 24 .isjthereby varied, with the result that variations occur in the plate circuit of the tubeir'i'lfand causencorresponding variations i in*` the` potenti'a'l'fdrfopl across the resistor My' 'The potential7 acrossfthexresi'stor 4I isimpreSSed' between. the electrodes 48 and 49; Thisis added to the;- potential across this portion of the arc in thefmercuryt vapor orother -vaporalready established by .the source 43 andy controlled by the stabilizing'resistor 44.

If 'the changes in radiation andvin thev``4 plate circuit,l from. the tube 22: are in such 7direction thatv theapotential difference across the resistor 4I increases for brightv portions offthei picture,

thjebattery 43 will be arranged to give a poten- `tial* along the capillary-itube in the same direction as the potential. across the resistor 4I, but, if-.thewchanges in the potential acrossv the Vresistorr4=I arein` the opposite direction. to'the changes im illumination of. cell Iz4', the battery '43' will be .connected -in= the opposite direction. Consequentlmwhether. the .electrodes 48 and IIIladdtoV the' potential across the portion of the capillary between themnorldiminishc it; the result, in either case; is that the instantaneousfpotential across? this part ofpthe `capillary `isV greater when the point `in the scene I' which, at the moment;l is

correlated` to the window Hi; is lbrighter. The

potential along. the capillary determines the brightness of` the light emitted by the vapor therein. Consequently, the light source is more brilliant when the corresponding point in the scene I is bright. i i

Another way of enablingfthe changes in illumination om. the screen 52lt'o .certainly be always :inithelsame direction astthe changes in the scene isV teureplace the grid: leak and condenser at' the tube 22 in: Fig; 3: by an adjustable C battery. The tube` can then be adjusted to either the lower curved part or' the upper curved part of the; characteristic.. VThis will cause'7 the sense of thetchanges: in the.. output current tox depend upon the adjustment.. i

`.Themovernent' of, the mirror Bli-and of l.the lenses 5I always associate some portion of. the

.lightsource 53-.withV apoint in 7thescreen 52 corthan the mirror I I or the mirror (iii.

by a rotating potentiometer.

responding to that point in the scene I deter-' i mined b-y the position of the mirror II and the lenses 6. Since the mirrors II and' 36 always move in. synchronism, and theV lenses 6 and 5I always move atthe same' speed and are readily adjusted to synchronism, the illuminated point on the screen 52 always corresponds to the point in the scene I optically associated at that moment with the window IG. reproduction of the scene screen 58.

Ther speed of .thelenses 6 and 5I is so chosen that the Vertical co-ordinates of the corresponding points on the Screen and'in the scene are varied throughout their amplitude rapidly enough to Vcause persistence of vision to make the picture on the screen 52 appear to represent the actual movements of the moving' objects-in Vthe'view I. r

The rate of movement ofthe mirrors II and 36 is great enough Vto cause the horizontal co- Vordinate of the corresponding points to vary` Vthroughout their amplitude many times during one cycle of the variation of the Vertical coor-` dnate; as many times as there should be lines in the picture to give a satis'factory "grain".

Thus, if the picture isto have 60 lines to the inch, the` mirror I I must make complete vibrations for each movement of the 7lens 6 over one inch, and the'lens ti must move at such a speed that the. complete Vertical height of the picture is traversed byxfit in at least a tenth of a second.. 7In the `Operation of7 the Optical system illustrated in Figs. 6 and 7, the moving lenses 5I are replaced by a mirror which movesmore slowly The movement of the slowly moving mirror is'controlled The arm of this potentiometer, being drven'by a synchronous motor, moves at a Constant speed. Motors for driving the potentiometer arms maybe used at rboth the sending and -the receiving station, or a wheel carrying lenses may be used at one station and af potentiometer at another. In either case, equality of speed is insured by Connecting the motor to a common power supply. I

As the arm 13 traversesthe potentiometer 12, the Vpotential impressed upon the oscillograph conductors 54 gradually increases, causing the mirror GI to swing farther and farther. As the arm 13 passesV from one end of the potentiometerv 12 to the other across the adjacent ends of the resistor, the potentialv impressed upon the conductors 64 changesabruptly. The movement of the mirror GI, therefore, will closely simulate The resultI is'that a` I is obtained upon the the action of the lenses, comprising'a gradual to be scanned for i'mpressing on the scanning device an intensity effect differing from that of substantially any found in said subject, means controlled by said differing-intensity producing means, for producing a characteristic impulse at each traverse of said subject by the scanning device and oscillatory means controlled by said impulses for producing a corresponding position of the reproducing device.

2. In a television system, a sending instrument including means for delivering carrier energy, a scanning device adapted to make traverses of a subject to be scanned and means adjoining said subject for producing a characteristic modulation of said carrier energy during portions of each traverse by the scanner where subject elements are absent and a receiving instrument including an oscillatory member adapted to move in accordance to said modulation, whereby the traverses in the receiving instrument will be maintained in fixed relation to those in the scanning device.

3. In a television system, a sending instrument including means for delivering carrier energy, a scanning device adapted to make traverses of a subject to be scanned and means for modulating the carrier energy in accordance with the intensity of the elemental areas of said subject covered by the scanning device during said traverses, means for presenting to said scanning device at the extremity of each traverse an intensity differing from that of substantially all the elemental areas in said subject, whereby a corresponding difference in the modulation is produced and a receiving instrument including an oscillatory member responsive to said different modulation..

4. In a television system, a sending instrument including means for delivering carrier energy, a scanning device adapted to make traverses of a subject to be scanned and means for modulating the carrier energy in accordance With the intensity of the elemental areas of said subject met by the scanning device during said traverses, means for impressing upon the scanning device between traverses of said subject an intensity differing from that of any of the elemental areas in the subjectywhereby a corresponding difference in the modulation is produced and a receiving instrum ent including an oscillatory member responsive to said different modulation and means for preventing response of said member to the modulation corresponding to brightness of the scene.

5. In a picture reproducing device, a linear source of light, a screen and means for projecting the light from successive portions of said source upon the screen, said portions being in a line corresponding to change of one coordinate in the picture to be reproduced and means for deflecting the light in a direction at an angle to said line.

6. In a picture reproducing device, a linear source of light, a cylindrical focusing device, means for directing the light from successive portions of said source progressively upon successive portions of said focusing device and means for moving said focusing device at an angle to its length.

7. In a television system, a scanning device, means for producing radiation comprising a carrier Wave mcdulated in accordance with the intensity of the elemental areas of a subject selected by the scanning device, means independent of said subject and scanned by said scanning device for producing a characteristic modulation of said carrier Wave upon each traverse by said scanning device, a reproducing device including means for producing a scanning medium of an intensity corresponding to said elemental area modulation and means controlled by said characteristic modulation for directing said scanning medium in accordance with the movement of the scanning medium at the transmitting end.

8. In an optical system for view-transmission,v

a lens having a cylindrical surface, means for moving said lens at an angle to the axis of said surface, Whereby successive positions of said axis lie in a plane, a mirror and means for oscillating said mirror about an axis forming an angle with the normal to said plane.

9. In an Optical system for view-transmission, a lens having a cylindrical surface, means for moving said lens at an angle to the axis of said surface, whereby successive positions-of said axis lie in a plane, a mirror and means for oscillating said mirror about an axis parallel to said plane.

10. In an Optical system for transmission of views, a plurality of cylindrical lenses, a carrier therefor, means for moving the carrier to bring` said lenses successively into the same position, a mirror, and means for causing said mirror to oscillate about an axis substantially parallel to the plane of rotation of said lenses.

11. In an Optical system for transmission of views, a plurality of cylindrical lenses, a carrier therefor, the lenses being mounted thereon in a circle with their several axes radial thereof, means for rotating the carrier about the center Of said circle, a mirror, and means for causing said mirror to oscillate about an axis substantially parallel to the plane of rotation of f said lenses.

12. In .an optical system for transmission of views, a plurality of cylindrical lenses, a carrier therefor, the lenses being mounted thereon in a circle with their several axes radial thereof, means for rotating the carrier about the center of said circle and a mirror mounted to oscillate in such direction that it will sweep lengthwise over one of said lenses.

13. In a picture-reproducing system, a linear source of light, a screen, a vibratory mirror, a plurality of cylindrical lenses and means for causing said lenses to successively pass intermediate' said vibratory mirror and said screen, whereby the light from successive portions of said source is caused to fall upon said screen.

14. In a view-transmission system, means for transversely scanning a subject, means adjacent to said subject cooperating With said scanning means for the production of periodic electrical impulses representative of the rate of scanning, oscillatory scanning means at a receiving station, and means whereby said oscillatory scanning means is constrained to vibrate in synchronism` with said periodic electrical impulses.

15. In a television system, a transmitter comprising scanning means including a ray of energy, a reproducing device comprising similar scanning means, means exclusive of a subject to be scanned and disposed within the range of Operation of said ray for producing, in combination With the scanning means, a characteristic impulse at a denite frequency in the energy output of said transmitter and means for utilizing said characteristic impulses for producing corresponding momentary positions of the scanning means of said reproducing device.

16. In a system of the television type, means for scanning a subject, means adjacent to said subject and adapted to be scanned by said scanning means throughout the scanning period for the production of a continuous train of periodic electrical impulses representative of the rate of scanning.

17. In a system of the television type, means aooasci;

the energy output of said systemnmay be-pro`-;

duced for synchroni'zing purposes.

18. In a system for the transmission trical impulses to produce pictures, an area of varying light reactivevalue arranged in effective position to bescannediwith the object to be pictured, and means for scanning said area coordinately with said object, for producing electrical impulses of scanning frequency. I

19. In a system for the transmission of elec- 'trical impulses to produce pictures, an area arrangeol in effective position to be scanned with the object to be pictured, andmeans for scanning said area coordinately withV said object for producing electrical impulses of scanning fre'- quency, the elementary units of said area having a light reactive value whichV is a function of their position in said area.

20. In a system for the transmission of electrical impulses to produce pictures, an area arranged in effective position to be scanned with the object to be pictured, and means for scanning said area coordinately with said object for producing electrical impulses of scanning frequency, the elementary units of said area having a light reactive Value which is a function of the effective position of said area with respect to said object.v Y 21. Ina system for the transmission of electrical impulses toproduce pictures, an area arranged in effective position to be scanned with the-object to be pictured, and means for scanning said area coordinately with said object for producing electrical impulses ofv scanning 'freduency, said area 'having a light reactive value varying in accordance with a system 'different from the picture. i

22. In a system for the transmission of electrical impulses to produce pictures, a shaded border arranged to be effective as if bounding the object to be pictured, and means for scanning said border coordinately with said object for producing electrical impulses of scanning frequency.

23. The step in the method of synchronizing a transmitter and receiver of electric impulses for the production of pictures which comprises scanning an area of varying light reactive Vva-lue co-V and a receiverof electrical impulses for the pro- Y duction of pictures which comprises bounding the object to be pictured with a shaded border, producing a current corresponding to the illumination from successive elementary units of said object and border, and utilizing the current corresponding to said border to control the frequency i of a receiving scanning system.

26. In a system for the transmission of electrical impulses to produce pictures, a shaded border arrangedas if bounding the object to be transmitted, means-for scanning said object and said border toproduce a current varying with the illumination from successive elementary units of said object and border, means for transmitting eler;

Vimpulses alternately of picture and scanning frequencies, .means for' detecting a low. frequency component of 'the transmittedfimpulses, meansf for filtering out substantially all but the fundamental frequency of said Component, and means for utilizing said fundamental frequency to actuate a receiving scanning means.

' '28. In asystem of the television type, a subject to `rbe scanned, a scanning ray, means for Vcausing said ray to scan said subject for causing energy to be modulated according to the light 'intensity of the elemental areas of said subject,

and means disposed beyond the boundaries of said sub-ject but within theioperating range of said scanning ray for impressing upon said energy a pieriodic characteristic impulse for synchronizing purposes.

29. In apparatus of the television type, a subject tobe scanned, a scanning ray, means; for causing said ray to sweep= across said subject and beyond at least one of its edges and means disposed beyond the area of said subject but within the operating range of said ray for producing a periodic characteristic impulse in the output energy of said apparatus.

30. A television synchronizing system including a photoelectric cell, screening means of varying optical density for optically modulating the same so as: to produce a sinusoidal electric'wave form, alternately with the signals produced by scanning each line of the picture, means for transmitting this wave form, means for receiving this wave form,rmeans for separating it from other wave forms due to signals present on the same transmission channels, and rmeans for applying it to eifect the synchronization of said television system;

31. In television transmitting app-aratus electro-Optical apparatus means for the production o-f synchronizing signals, between groups of picture signals, each of said vgroups representing a single line scanning, including screening members whose degree of opacityrvaries according to a sinusoidal law, in respect to distances measurable upon said screening members, cooperating with the vbalance of the transmitting system to cause the said synchronizing signals to Vbe of a sinusoidal form.

32. A television transmitter including op-tical reactive means effective between thescanning of each line and that of the line next scanned, said means o-ptically producing synchronizing signals `of a predetermined rate of amplitude change and of a predetermined range of amplitude Values, an image to be scanned having a range of light Values at least as great as has said Optical reactive means, piortions o-f said image which have said light Values being so positionedl relative to one another as to produce image signals at least Vsome of which have a rate of amplitude change greater than` Vthat of said synchronizing signals and the amplitude range of which isnever greater than the amplitude range of said synchronizing signals, and means for alternately transmitting said image signals and said synchronizing signals whereby said synchronizing signalsV may be effectively separated and selected from said image signals and from extraneous signals at a television receiver.

33. Means for transmittng television and synchronzing signals eifectively separable from one another including Optical means for scanning in turn each line of an image, means optically discrete from said scanning means for modifying the light falling upon said Optical scanning means after the scanning of each line, said modifying means being provided with a substantially continuous gradation from s'uostant'ially maximum light' reactive value to substantially minimum light reactive value, and means for alternately transmitting said image signals and said synchronizing signals Whereby said synchronizing signals may be efiectively tuned and distinguished from extraneous signals at a television receiver.

JOSEPH W. LEGG.

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