US1789521A - Television system - Google Patents

Description

Jan. 20, 1931. s. FEINGOLD 1,789,521

TELEVI S I ON SYS TEM Filed April 10. 1928 '7 Sheets-Sheet 1 Jg? i M Ff Z i Jan. 20, 1931.

S. FEINGOLD TELEVISION SYSTEM Filed April l0. 1928 7 Sheets-Sheet 2 ATTORNEY S. FEINGOLD TELEVIS ION SYSTEM Jan. 20, 1931.

Filed April 10. 1928 7 Sheets-Sheet 3 INVENTOR.

BY mfg, am

ATTORNEY Jan. 20, 1931. s. FEINGOLD 1,789,521

TELEVISION SYSTEM Filed April 1o, 192s 'r sheets-sheet 4 F- M We* a BY Mwlly I A TTORNEY Jan. 20, 1931. 4s. FEINGOLD TELEVISION SYSTEM 7 Sheets-Sheet 5 Filed April l0, 1928 IN V EN TOR.

A TTORNEY UTOSS luwuw Jan. 20, 1931. s. FElNGoLD TELEVISION SYSTEM Filed April 10. 1928 '7 Sheets-Sheet 6 IN 1/EN TOR. W

A TTRNEY BY (MM am Jan. 20, 1931.

s. Fl-:INGOLD TELEVISION SYSTEM Filed April 1o, 192e 7 Sheets-Sheet 7 atroz eq Patented Jan. 20, 19u31 SAMUEL FEINGOLD, F BROOKLYN, NEW YORK TELEVISION SYSTEM Application led April 10, 1928. Serial No. 268,912.

My invention relates to signalling systems, mined current values and transmitted to a reand more particularly to television systems ceiving station. At the receiving station, the in which a succession of complete images are currents are translated back into light or transmitted by electrical means to a remote color in accordance with the value assigned point at such a rate as to give the impression thereto and this light is projected on cor- 55 of a continuous image movement such as obresponding positions of the reproduced imtained in motion pictures. age. This is known as scanning and is ac- Although successful picture transmitting complis'hed by scanners which move across systems have been invented and put in operathe unit areas. It will be evident from the tion in which a single image with some deabove that in order to scan equivalent units o0 tail is transmitted within a reasonably short of the two images, the scannersmust be maininterval of time, no success has been obtained tained in synchronism and in proper phase heretofore in the development of a television relation. system because of the failure to solve the The' dimensions of these units are, of

problems encountered because of the high course, variable, depending upon the degree oz speed operation necessary. of picture detail desired. For an average As is well understood in television, a seimage, however, this area is 1/100 of an inch ries of complete images are transmitted sucsquare. A picture therefore one inch by one cessively at a rate equal to that at which sucinch will be considered as divided into 10,000

cessive images are projected upon a motion areas, there being 100 horizontal divisions picturescreen which produces upon the oband 100 vertical divisions. Employing the server the impression of a continuous moving two co-ordinate scanning elements in which event. This impression of a continuous event one scanning element scans in al vertical diis made possible by the phenomena known as rection andthe other in a horizontal, it is evipcrsistencyof vision. Vi'hen light fromran dent that while the first scanning element image is impressed upon the retina of the moves across the picture once, the vertical eye, the retina will continue to be affected scanning element must move across the picthereby for about one seventeenth of a second ture one hundred times in order to scan every after the light is cut ofi' due to light inertia unit area of the picture. Since as explained of the retina. lf, therefore, in projecting a above, the entire pictures must be scanned at au series of images on a screen, the"success1ve least seventeen times per second, the vertii images are projecting within one seventeenth cal scanner makes 1700 oscillations during of a second, after the preceding one is cut off, one second or 850 cycles.

\the observer will receive the impression of a Numerous attempts have been made to continuous picture and not of two separate produce mechanically moving parts which S5 ones. This principle of motion pictures is could lbe oscillated at the desired frequency also applicable to picture transmission so that or rotating members which could be rotated by transmitting images in succession at a at the proper speed for scanning 1700 lines rate of about seventeen images per second, per second. But in all of these attempts,

an observer will receive the impression of a difficulties have been experienced with the' continuous event. moving element due to the difliculties expe- For transmitting a picture, it is conrienced in maintaining lsynchronism an'd sidered as composed of a large number of proper phase relation. At the high speeds minute unit areas, each of which is of some at which they must naturally operate as excomponent shade or color and thewhole plained above, there is increased likelihood 90 blending together to make a picture, each of these elements falling out of step. component shade or color beine assigned a Attempts have been made to correct this predetermined current value. t the transmechanical .diiicultyof rotating members by .ting station the shade or color of each sucsubstituting non-moving members, one par! cessive unit area is translated into predeterticular arrangement including the cathode *Ul ray tube in which either electromagnetic or electro-static fields placed at right angles to each other function to move a cathode beam over a fluorescent screen. While theoretically this appears to solve the problem, aetually the arrangement was found to be entirely' impractical and to create new and more serious problems.

The cathode ray itself is of very low signal light intensity. It will be recalled that it was pointed out in' the above that for a picture one inch by one inch about 10,000 points must be scanned. Since, however, the pictures must be scanned at least seventeen times per second, there are 170,000 unit areas to be scanned per second. This means that light is impinged on one unit area of a picture for 1/170,000 of one second. It becomes evident at once that unless an extremely intense point source of light is available, the lumens in 1 /17 0,000 of one second is inconsiderable anda dim image if any at all will result. Exactly this diiiiculty is experienced in the case of the cathode ray, the intensity of which is limited to a comparatively weak beam. In actual practice it has been found as would be anticipated from the discussion above, that the intensity of the image projected on the fluorescent screen is so weak as to be practically invisible. This has been in a degree overcome by increasing the voltage impressed upon the grid of the cathode ray, but this'voltage also has a practical limit within the range of which the light admitted from the cathode is still found to be considerably insuicient to distinctly illuminate the fluorescent screen. A further diiculty is experienced with the fluorescent screen in the cathode ray tube, the light inertia of which tends to maintain the effect of an image beam impingedthereon. If, as usually happens, theimage remains effective while the succeedin image is being received, the picture will oviously blur, rendering the already dim image still less visible.

To these diiculties is added the fact that it is a practical impossibility to apply the principle of the -cathode ray tube at the transmitting end so that moving parts are still necessary thereat and since the system which is limited in its operation by the weakest pointin the system, which in this case is the transmitting end, any advantage which might have been gained by the nonmoving parts of the cathode ray tube at the receiving end is lost by reason of thefact that rotating members are necessary at the transmitting end. Although attempts have been made to provide a cathode ray at the transmitting end, none of these have proved to be successful.

Other eiorts toward eliminating mechani- German patents to Skaupy, Serial Nos. 352,581 and 355,891. In these patents a chemical solution is used having a different angle of refraction for the ordinary and extraordinary ray employed. This solution is responsive to variations in the potential of condenser plates between which it is placed to vary the angle of refraction of the ordinary ray of light, thereby changing the angle of path of the beam of light.

This arrangement, however, is only of theoretical interest inasmuch as the angle through which the light beam can be shifted by the voltage wave is so slight as to be .egligible In actual practice the shift of the angle is so slight as to have little practical value. No attempt has been made to put it ou a commercial basis and the arrangement, therefore as pointed out above, is entirely of theoretical interestand not of practical value.

Although for a number of years considerable interest has been expressed in television systems and skilled engineers in the art hav been, and are actively engaged in providing an operative and iracticai system, the general tendency has een to attempt to accomplish this not by any such theoretical and impracticable arrangements as that shown in the cathode ray, but in the more practical rotating members butthesc. as pointed out above, have certain inherent difficulties which make their use undesirable.

Not only have difficulties been experienced with the scanning at both the transmitting and receiving ends, but problems have been met in translating the received current into light of the proper comparative intensity. T'Vhile the transmitter itself has been worked out fairly satisfactorily and the photo electric cell has been developed to a point where it is extremely 'sensitive to light and will respond accurately to lightvariations occuring at the rate of 170,000 per second, the same curacy has not been obtained at the receiving end. This component of the system has also been the 'sub'ect of considerable but unsuccessful development. One commonlyY proposed device at the receiving end to overcome this diii'eulty is the neon tube, the characteristic light of which is pink. Besides numerous other drawbacks, however, the intensity of the beam of light in the neon tube is limited to a comparativey low value andV is, therefore, impracticable.

In order to provide the maximum intensity of light necessary at the receiving end, it has been proposed to employ a local source of light of any intensity desired and operating a shutter in frontof the light in accordance with the picture current varial tions so as to permit a varying amount of light to pass through to a light sensitlve defvice or screen. This, however, has limitalf cal scanners in a television system are illusi tions because of mechanical difficulties snm- .55 trated by they-arrangement, shown in the lar to those experienced in connection with scanning te a greater degree. Since the picture current variations are recei\ ed at a rate ot about 170,000 per second it is obvio'L that diiiculties will be experienced with t1; shutter which must operate this speed. Such operation is practically impossible to obtain. @ther receiving devices ot a similar character all have been tried, none of which, however, have proved effective.

lt accordingly an object et' my invention to provide a televisie-n system in which scanning is accomplished without the use of rotating members, the scanning element being maintained in synchronism and in phase automatically by the inherent characteristics of the scanning element itself to reproduce a picture at the receiving station which is distinct and easily visible, and to provide an inertialess member for varyng a local source ot light. which may be ot any intensity in accordance with received picture currents.

More specifically it is a further object of 'my invention to emploj,v the piezo electric qualities of certain crystals in a television system for scanning and operating a receiver in accordance with current variations.

further object ot my invention is to pro-A- vide scanning elements which have natural anh'the pictu ceiving elementsv i'clighaykernatr al inherent irequenles ci o tic itl@llieursatf haran-aar In systems -heretofore, neon tubes have been employed at the receiving stations to vary light in accordance with current variations. Other arrangements have been used including disks of varying thickness, that is, varying from pure transparency to opacity, so that different intensities of light are permitted to travel therethrough. In the case of the Nicols prism, light is polarized and the intensity of the light passing through is proportional to the eiiect on the analyzer of the picture currents. In all ot these systems, however, only a varying shade of light is transmitted and nocolors. A

It is a further object of my invention to provide a system in which colors as well as varying shades of white, such as trom black to white, may be transmitted.

Another object of my invention is to employ the principles of expansion and contraction of crystals or what is linown as piezo electric qualities for transmitting pictures in color.

There are other objects of my invention which together with the foregoing will appear in the specification which follows.

It is well known that if a crystal of Rochelle salt, made and cut in a predetermined manner described in the art is subjected to pressure on certain sides or along certain axes, the crystal will contract along lf impressed thereon.

these ailes and expand along axes at the right angles and will as a result produce an electromotive torce, and co versely, it an electromotive force is impressed along certain axes or upon certain sides of the crystal the crystal will either expand or contract depending upon the natural reaction of the crystal to the polarity ot the electro-motive Jforce. Similarly, it an alternating currentis iinpressed on certain sides or along a certain axis of the crystal the crystal will expand and contract in accordance therewith at a frequency depending upon the frequency of the alternating electro-motive force.

Not only, however, does the crystal showing piezo electric eii'ects vibrate when subjected to varying electro-motive forces but it has also been found that the Rochelle piezo crystal and quartz piezo crystal have a natural or resonant period of vibration and that it', the cijjsaflisubjected to a frequency'gi alternating current, which is within'the lim-, is .of .this naturel' tr'quicy of the .clystah the icrystalvwillmcontractY or expand atiits... grriftesthamplitude and if subjectedtimfi'c v1 quencies 'other` than "this natural frequency will expand and contract at a considerably less amplitude, but that always the crystal will vibrate at its natural frequencies when subjected to an alternating current, the amplitude thereof merely changing in accordance with the variation in frequency This important factx namely that the crystal has a natural frequency at which it vibrates together with the relation it shows in connection with alternating current, has been taken advantage of in my proposed system, not only in the scanning but also in translating light into electricity, the transmission of the current over the line, and the translation of the electric current into light.

Referring to the drawings,-

Figure l shows a. natural crystal of Rochelle salts, in perspective.

Figure 2 is a similar View of the same crystal cut and ready :tor mounting.

Figure 3 is a perspective View disclosing the crystal mounted as a scanning element.

Figure 4 is a similar View disclosing the same element mounted in a manner to permit freedom of oscillation so as to provide a.

maximum amplitude of movement unaffected by its own weight.

Figure 5 is a side view showing a special mounting of the reflecting mirror on the piezo crystal.

Figure 6 is an end View of the apparatus shown in Figure 5 showing the crystal of quartz.

Figure crystal.

Figure 8 is a perspective view disclosing the natural crystal ot quartz.

Figure 9 is a similar view disclosing the 7 is a form of housing for a quartz manner of mounting the crystal shown in Figure 8. A

Figure is a side view disclosing the arrangement of mounting mirrors in relation i 5 to the crystal.

Figure 11 is the top view of Figure 1() showing the slots for the admission and departure of the ray of light.

Figure 12 is a diagrammatic showing of the crystal arranged to respond to received picture currents.

Figures 13 and 14 are perspective views showing wedges of quartz cut perpendicular to their axes.

Figure l5 is a diagrammatic view disclosing a system for receiving a picture either in black and white or in color.

Figure 16 similarly discloses a receiving system for the projection of color images in accordance with the colors transmitted.

Figure 17 is a sectional View showing the manner of mounting the mirror on the scanner.

Figure 18 is a top plan view of any well known form of colo;` spectrum.

Figures 19 and 20 are diagrammatic views of the circuits and apparatus employed in one embodiment of my invention.

Figure 21 is a perspective View of the quartz slab for varying the light ray at the receiving station.

Figure 22 is an oscillograph showing of a complicated picture current wave.

Figure 23is a View of a light gradient.

Figures 24 to 28 inclusive are views of various modifications of piezo electric crystal arranged to respond to picture currents.

Figure 29 is a diagrammatic view of a modified scanner for transmitting pictures in l0 colors.

Figure 30 is a diagrammatic showing of a modulator and oscillator for picture currents.

Figures 31 and 32 are diagrammatic showings of the circuits and apparatus in a sys- ;5 tem for transmitting pictures in colors.

Figures 33 and 34 are showings of modified circuits and apparatus for transmitting pictures in colors.

Figures 35 and 36 are diagrammatic showings of a modified system for transmitting pictures in color.

In Fi ure 1, 1 is a natural crystal of Ro- 0..-. ....o Ul C 4 and 5. If an electro-motive force is impressed across sides 2 and 5, the crystal will either expand o r contract depending upon the polarity at either side. If an electro-motive force is impressed across sides 3 and 4 in such a direction that the potential at side, 3 with respect to side 2, the crystal will react thereto in the same manner, that is, either expand or contract depending upon the polarity. If the crystal expands with potential in one direction, it will contract with potential in the (ioppositedirection. From this, it is apparent chelle sa t, comprising sides 2 and 3, and sides across either sides 3 and 4 or 2 and 5, thecrystal will expand and contract with the reversals of the alternating current.

Notonly do these crystals oscillate when an alternating current is applied thereto, but they have been found to have a natural period of oscillation or frequency. The crystal will, therefore, oscillate at its maximum amplitude when an alternating current of the frequency to which the crystal is resonant is impressed thereacross.

This phenomena of quartz crystal is well known and has been applied to radio to maintain the carrier frequency thereof substantiall;T constant.

ln Figure 2 the crystal 1 is shown out and read;7 for mounting. It will be assumed thati the side 6 has been found by experiment to be one point of a polarity. As has already been explained in detail above, if an electro-motive force is applied to this crystal, it will expand and contractas the polarity of the electromotive force is reversed remaining at all times in step with the reversals of the alternating current.

In Figure 3 the crystal 1 is shown mounted on a base 7, which may be made of wood, rubber or any other suitable substance, the characteristic of which is such as to permit the greatest amount of freedom of the crystal in its vibration. rfhe crvstal is secured to the base 7 by a metallic pla'te 8 to which it is soldered although it will be understood that any convenient method of fastening may be employed.

Coatings 10 and 11 are soldered or cemented to the sides of the crystal 1 for providing the necessary connections for the leads 12 and 13 connected to the source of electro-motive force which is impressed across the crystal. These coatings 10 and 11 are the electrodes to which the electro-motive force is applied. Cemented to the end facing of the crystal 1 is a metal mounting 14 for supportin a mirror 15. Mounting 14 is soldered to t e crystal by means of lVoods metal as shown in the drawing although in this case also any type of soldering may be used. Although as shown, the vibrations due to the electro-motive force impressed across faces 10 and 11 is such as to impart that motion to mirror 15, it will be understood that vibrations could be obtained at other faces by impressing the electro-motive forces at other faces as, for example, at terminal 16. In any event motion to face 14 could be brought about by connections to 12, 13 or 16.

In the arrangement shown, a beam of light 17 impinged from any light source will be reiiected along the line 18. Them however, the crystal has expanded, the mirror moves forward and reiiects the beam 17 at an advanced position, thus shifting or displacing the beam to 19 as shown. By arranging the angle ofl the beam 17 with respect to the mirror 15 any extent of displacement of beam desired can be obtained.

In Figure 4 the crystal 1 is shown mounted in a housing 22 comprising wood, hard rubber, or any other suitable material. A tin foil coating 23 and 24 is cemented to the crystal 1 and to which in turn are soldered the leads 25 and 26. The housing 22 is filled with wax 27, in which the crystal l is securely imbedded. To the facingI 28 of the crystal 1 is mounted a mirror holder 29 to which is soldered the mirror 32. A mounting lug 33 is provided to facilitate mounting of the crystal. In this arrangement, it is obvious that as the crystal is held so to speak suspended in the wax, it is free to move in this elastic medium and its amplitude is accordingly greater than could ordinarilyT be obtained in the mounting shown in Figure 3.

It will be seen that in Figures 3 and 4 a simple arrangement is provided for shifting or displacing a beam of light in accordancewith the vibrations of the crystal. It is, however, possible as is well known in the leverage principles, to obtain a considerably greater movement of the mirrors and accordingly greater displacement of the beam of light for the same small movement of the crystal. To this end I have shown the arrangement in Figures 5 and 6. The crystal 1 is here shown encased by a rubber' tape 35 wrapped therearound. Connections to the crystal are made as shown in Figures 3 and 4 with a girdle of tin foil 36 at the center of which is soldered the lead 37. As shown in Figure 6, the crystal 1 is placed in a receptacle or housing 38 and rigidly held so that it fits snugly between the walls 39 and 42. Metal straps 43 and 44, Figure 5, hold the crystal 1 rigidly in position against the base. The crystal 1 is also urged into rigid connection against the metallic plate 45 to which is attached the lead 46. Metal plate 45 and the tin foil 36 around the girdle are the electrodes of the crystal' and are so chosen that the crystal will expand or contract in the direction of its length. Secured to the extension 47 of housing 38, mounted upon `the side 48 is a metal rod 49 pivoted at 50 carrying a mirror 52. At the end of the crystal 1 is mounted a hard rubber cap 53 which bears against the rod 49 through the bearing member 54. A spring 55, the tension of which can be adjusted by turning the thumb screw 56 urges the lever 49 to maintain engagement with pivot 54.

Asv will be clearly seen, when the crystal vibrates, the lever arm 49 is moved on its ivot 50 and in turn oscillates the mirror 52.

ecause of the leverage obtained, the movement of the mirror and accordingly the beam displaced thereby, Twill be considerably greater than in the case where the mirror is directly attached to the crystal.

\This4 same principle can be applied to'two iieiereuce x lcrystals arranged adjacent to each other, the one arranged to expand at the instantthe second contracts, the arm 49 being pivotally mounted on both crystals resulting in a movement thereof which is the function of the sum of the contraction of one crystal and the expansion of the other.

The crystal 1 with a mirror 15, 32 or 52 secured thereto is adapted for scanning at both the transmitting and receiving stations. I' Then so employed, a crystal having a natural period equivalent to 2,000 cycles and another having a natural period equivalent to 20 cycles have connected across their electrodes currents of 2,000 and 20 cycle frequency. The mirrors secured to the crystals are then positioned relative to each other in such a manner that a beam of light playing on one of them from a fixed source is reected to the other and moved along one co-ordinate as the first crystal oscillates, the beam being reflected by the second mirror and moved along a path at right angles to the movement by the iirst mirror. As a result of these two component movements an entire image is scanned once while for example the iirst mirror moves the beam up and down 100 times and the second mirror moves the beam across once. It will be understood, however', that the figures assumed in the above, that is the 2,000 and 20 cycle crystals are arbitrary and any values may be chosen depending upon the accuracy and detail of picture desired. It must be borne' in mind that a complete cycle applied to a crystal will cause expansion in a certain direction, then a contraction to Zero and a further contraction in the opposite direction, then back to zero. In other words, a single linear displacement will result.

It is'one of the features of this invention not only to take advantage of this expansion and contraction characteristic of quartz when subjected to an alternating electro-motive force for varying a beam of light at the receiving station in accordance with the received picture currents. As is well known, quartz isa triagonal trapezohedral crystal with double refracting uni-axial positive characteristics. The refractive index for the extraordinary ray is 1.5533 while for the ordinary ray it is 1.5442 and it is evident, therefore, that the degree of separation between the ordinary and extraordinary ray is negligibly small.

Such a crystal in its natural state is disclosed in Figure 8. In its normal state, the ends 57 and 58 of the crystal 59 are in the form of a six sided pyramid, although for purposes of illustration, fiat end portions are here shown.

The crystal 59 comprises an optical axis 62 and electric axis 63 and axis 64. The

opt-ical axis 62, it will be noted, coincides in' this case with the crystallographic axis. From a crystal ofthis character in its nat-- ural state, a slab is cut including the cross hatched portion 65. This rectangular slab portion is so cutthat its edges are perpen- "dicular to each other and the top and bottom lfaces 66 and 67, Figure 9, are made parallel as are the endand side faces 68 and 69. r[his is the shape of the crystal as ordinarily .em-

ployed for maintaining constant frequencies in radio telegraphy. .If to a crystal of this character` an electro-motive force is applied along the electric axis 63, the crystal will expand and contract in the direction of this axis. Here again the expansion or contraction depends upon the polarity at any one electrode. When the crystal is in a state .of contraction along the axis 63 it is in a state of expansion along the axis 64 and vice versa. It vWill be noted 4that under these conditions no changes take place along the axis-62. If

rnow an alternating current is applied along the elect-ric aX-is 63, the crystal -Wilfl expand and contract along this axis with the alternations of the curnen-gt.

The crystal 59 is mounted upon a metal plate 72, Figure .9, which serves as one electrode. Suspended a minute Adistance above the crystal 59 in -order that the ,electrostatic field may be as large as possible, is another plate 73. A. slot 74 is cut in a plate 73 in order to adm-it a beam of light for -the puriose to be described in detail hereinafter. A similar slot is cut in .the plate 7 2 for the same purpose.

In Figure 10, will be noted that mirrors f 75 and 76 are located above and below the crystal slab 69. Electrical circuit connections are made 'to the plate 72 and 73 by conductors 74 and 75 respectively. In Figure 11, I have disclosed a top View illustrating the slots 77 and 78 cut in the container 79.

Referring to Figure 12, the path taken by a beam light as i-t passes through a quartz crystal and is reflected by the mirror is disclosed in accordance with received picture currents. A beam of light 80 from any source is admittedv through a slot and impinges on` the quaitz sla-b a-t 8l when the quartz is in its normal state, that is, neither expanded nor contracted. This bea-m is retracted due to the change in velocity of the light in the quartz slab as shown by the full line `82 and after passing through the .quarta slab, passes through the air medium until it is reflected by the mirror at 83. The reflected. beam 80 now again is impinged on the quart-z slab at 8l and is aga-in refiected by the mirror at 85. In t'his manner, it is seen that a series of refractions and refiections take place until the beam 80 ultimately emerges through an opening and is impinged on the screen at 86. This condition, as pointed out above, exists with the crystal in its normal sta-te. Assum ing now that the crystal is under the' infin.- ence of an electro-motive force, which is varying in ascendance with' the variations of Vstantaneous picture currents being Areceived due to an incurrent value received, the crystal is contracted as shown by the dotted line 87. The same ray of light 8O non' impinges on the crystal at 88 before being refracted by the crystal and is accordingly displaced a distance equal to the perpendicular distance from the point S8 to the first described path ofthe beam before contraction of the crystal took place. Thereafter. as will be noted, the beam follows a path parallel to the original path maintaining, however, a displacement equal to the distance noted above until the beam emerges from the crystal at point 89. At this point., refraction ceases for this second beam although the original beam at an equivalent position, continues to be retracted and the second 'beam is therefore displaced still further from the first beam so that when novv the second beam is again reflected by 'the mirror at 90, the displacement is greater than that of the distance at point 88. It will now be levident that each time the beam is reflected and retracted, through the crystal the distance of displacementof the second beam with respectl to the first when the crystal is contracted or expanded increases until at the point of emergence from the crystal the second beam is at a dista-nce 91 from the original beam. This distance for any fixed length of crystal will, it is obvious, be proportional to the exten-t of ex ansion and contraction of the crystal, w' ich can be made greater or smaller for any fixed expansion or contraction of the crystal by varying the length of the crystal and accordingly the number of refiections and refractions which occur 'before the beam emerges therefrom.

It will now be understood that the vibrations of the crystal or its expansions and contractions' have had the effect of moving the ray of light from 86 to 92 and the distance that the beam of light will undergo between the entrance and exit points is dependent upon the distance of the mirrors.

It will also be obvious from the a'bove description, that a quartz crystal can be employed to vary a beam of light in accordance with the picture currents received. Since the gpartz slab can be made to vibrate at high equencies, it vvillt follow substantially all vari-ations of the picture currents irrespective of the rate at which they are received.

lIt is an important object of my invention to provide an arrangement for transmitting pictures in color and, I have accordingly shown the apparatus and arrangement for such a system in Figures 13 to 1'7.

Referring to Figure 13, a wedge of quartz 95 is shown eut perpendicular to its axis and designed to vary in thickness uniformly. The quartz slab isalso provided with opaque portions 96 which as wiil be described here- Ul Uuu inafter corresponds to small current values from a photo electric cell and represents a dark spot on the picture being transmit-ted. As. shown in Figure 16, a quartz slab is positioned in the path of a beam of light from a source of intense white light 96 located in a housing 97. The beam passes through a lens 98 and through a slot 99 to the receiver crystal 102. The crystal 102 is similar to that disclosed and described in connection with Figures 12 and 10 with the addition of a mirror 103 which, it will be observed, reflects the beam to start it back over` a continued path thus doubling the number of refiections and refractions for the same length of quartz slab. An electro-motive force varying in accordance with picture currents is impressed across the quartz slab 102 which is therefore vibrated in accordance with the received picture currents. The beam of light passes through the slot 103 after having been shifted or displaced from its normal path by the contraction or expansion of the crystal in accordance with the received picturecurrents and then passes through the lens 104 to the polarizing Nicols prism 105 thence through lens 106, quartz slab 107, lens 108, to the analyzing prism 109 and is thereafter focused on the scanner 112. The beam is reiiected from the scanner 112 through lens 113 and focused on the scanner 114 from where it is reflected to the screen 115.

It is now well known that quartz has in addition to the property of expansion and contraction described above, the characteristic of producing rotary polarization of light. This property7 may be described as follows:

Assuming that a ray of homogeneous light is polarized and the analyzer say of a Nicols prism is turned until the light does not pass therethrough, if a thin section of a quartz crystal cut at right angles to the aXes is placed between the polarizer and analyzer with its plane at right angles to the ray, it

. will be found that light will now again pass through the analyzer. If now the analyzer is turned, it will be found that the light passing through the analyzer is plane polarized but in a plane inclined to a certain ano-le to the plane of primitive polarization. ff the beam of light which passes through the slab is red and the slab is one millimeter thick this angle is about 17 degrees. Investigation of the above phenomena has disclosed the fact that for a given color the angle through which the plane of polarization is turned is proportional to the thickness of the quartz, the rotation for a fixed thickness of quartz being different for different colors. f

It will be evident from the above that with a plate of a fixed thickness, a beam of red light will be rotated a fixed angle and a beam of voilet light rotated a different angle while all other beams of light intermediate these two Will be rotated at angles intermediate the limits set by the red and violet beams. Accordingly, with a beam of white light, for any one position of an analyzing Nicols prism, a greater or smaller quantit of each color will be passed through, depen ing upon the direction of rotation of the Nicols prism. Conversely if a quartz slab of varying thickness is employed and a beam of light passed therethrough the analyzing prism in one position will permit varying colors to pass hrough depending upon the thickness of the plate and the points through which the beam passes.

It will now be evident from the above description that the receiving arrangement disclosed in Figure 16 will operate in accordance with varying light. source 96 normally passes through the quartz 102 and the Nicols prism 105 and analyzer 109 to the scanning elements 112 and 114, the

two scanners oscillating under control oi alternating currents impressed thereacross at different frequencies in the manner described above for scanning the entire picture. The scanner 112 may shift the beam in a horizontal line while 114 moves the beam vertically and the resultant as is well known in the television art is to cover the entire picture ai the screen 115. Although in this particualr modification the form of scanning disclosed in Figure 3 is shown for purposes of convenience, it will be evident that a scanner such as disclosed in Figure 5 may more preferably be employed as providing a greater deviation of the beam of light and accordingly permitting a greater area to be scanned. In this system it will be assumed that the photo electric cell varies in sensitivity in accordance with the beam of light impinged thereon from the image to be transmitted. Accordingly the picture current of the beam will be in accordance with the color of the image being transmitted and the quartz slab 102 will contract or expand in accordancewith the received currents to displace the beam of light from the source 96. Current due to a white the beam from source 96 follows.v This beam, it will be noted, passes around the Nicols prism 105 and passes through the end portion of the quartz disk 107 so that white light isA transmitted without being polarized through the analyzer 1.09 tothe scanning elements 112 and 114 and is thencey projected upon the screen115. If, however, a colored picture is received, a current in accordance with a colored point of a picture is received. the quartz slab 102 is expanded or contracted, as the case may be to such an extent that the beam passes through the ANicols prism 105. The extent of the expansion or contraction of the slab 102 which itself is cont-rolled by the picture current will determine through which portion of the quartz slab 107 the beam passes and since as shown in Figure 13 the slab is The beam from the' pas.

of varying thickness, the beam will pass through a more or less thick portion thereof and will accordingly he rotated a varying amount. )is pointed out above, the extent ot' rotation ot the polarized beam is dependent upon the color, a greater rotation producing a greater color. Accordingly, the beam which reachesA the scanners will bc of a color similar to that of the point on the image to the light of which the photo electric cell at that instant responded.

It will be evident. of course, that the eye may take the placa` of the screen 115 and Will receive the impression, of an image, similar to that which would have been projected upon the screen 115.

In Figure 14, I have shown a modified form of quartz slab which may be employed, the shape of which is determined by the characteristics of the photo electric cell. The photo electric cell to be employed in connection with the quartz wedge shown in Figure 13 has the characteristic of uniformly varying sensitivity throughout the entire spectrum. In Figure 14, on the other hand, the extended portion 116, the light passing through which will not strike the first Nicols prism as described in connection with Figure 13, is made of varying thickness and will, therefore, give white light of varying intensity in accordance with the intensity of the picture being transmitted. One end 117 is opaque as illustrated, to correspond to small picture currents due to a dark spot on the image.

Figure 17 shows the mounting for a scanning mirror 118 on member 119. It Willbe noted that the mirror 118 is made small. due to the fact that since the beam of light is brought to a focus on the mirror it need not be very large, although of course, it will be understood that any size mirror may be employed.

In Figure 15, I disclose a modification of the receiving apparatus for operation in accordance with the colors transmitted and also black and White images.

In the case of transmission of black and white, the slab 122 is graduated from clear transparency atwoevend to opacity 't the other end. Inasmuch as the. intensity of light leaving the slab will depend upon the portion thereof through which the light passes and the displacement of the lightrays is a function ofthe picture current, the intensity of light thrown on the screen 115 will be proportional to the picture currents. The graduated slab 122 shown in Figure 18 is graduated in the dii'erent colors of the spectrum starting'with black for an area of no light and ending with violet for an area of violet light and thereafter continuing with diffused and pure White. The slab 122 may be made of glass and dyed the proper color although it will-be understood that any spectrum arrangement maybe employed. Preferably, the spectrum is arranged so that the colors will start from deep red and go to light red, then deep orange to light orange, deep yellow to lightyellow and so on, rather than uniformly dyed although it will be understood that such an arrangementmay be employed. The slab 122 is placed in the path of the ray in the system shown in Figure 15 comprising the same source of light and receiving apparatus as shown in Figure 16. In this system, as described in detail hereinabove, the displacement of the beam is a function of the amplitude of the received picture current which in turn is proportional to the color of the point image being transmitted. It is evident that the beam of light which passes through the focusing lens 1 08 to the scanning elements 112 and 114 will be of a color depending upon the portion of slab 122 through which the light passes which in turn is proportional to the expansion or contraction of the picture current responsive crystal 102. From the arrangements thus far described, it should be clear now that a simple arrangement for transmitting pictures in color is disclosed.

Referring now to Figures 19 and 20, the circuit arrangements and apparatus at both the transmitting and receiving ends'of one embodiment of my invention is disclosed. rhe transmitting apparatus is shown in Figure 19 and the receiving apparatus in Figure 20. The circuit arrangements are such that a single carrier current generated at the transmitting end is modulated by an oscillating current which is composed of the frequencies of the currents which operate the scanning elements at the transmitting end and the frequencies of the picture currents from the photo electric cell. This modulated carrier current in turn operates the associated scanners at the receiving station in synchronism and proper phase with the scanner at the transmitting end since by this arrangement the same frequency operates the scanners at the transmitter and receiving stations. The equivalent scanners at each station are operated by piezo crystals having substantially the same natural frequencies.

Similarly, the carrier current generated at the transmitting end is modulated by picture currents which are arranged to operate a receiver piezo crystal. A single carrier is thus employed for the scanning and picture currents. The oscillating circuit 132, Figure 19, comprises a three element tube 133 of the standard well known type comprising a plate grid and filament connected in a tuned radio frequency circuit including the condenser 134 and the primar windings 135 and 136 of the transformer 13 the secondary winding 138 of which is connected to the antennae 139 for radiation of the carrier current enerated in the oscillating circuit 132. Thet reeelelnent tube 142 with i1 ipedance 143 and a condenser 144 with the oscillator described above comprise a modulator and oscillator of the Heising type or of tl e absorption type., Although for purposes of illustration a specifi-2 form of modul. r is disclosed. it vfill be understood t. c of the numerous vfell lcnoivn l or ost.. laters may bel employed in prl ct ig my invention.

lie oscillator 145. comprises a three element tube 146 connected in the oscillating circuit in lua-i the primar windings 146 and 147 of transformers 148 and 149 respectively. A variable condenser 152, the capacityvv of yhich may be changed, alters the constants of the circuit until it is tuned to oscillate at a frequency for example of cycles per second. rl`he secondary 153 of the transformer 141) is connected to the input of the l modulator 142 through which it modulates the oscillations of the. radio frequency generator 132. The saine oscillations generate in the circuit 145 are transmitted through the secondary Winding 153 of the transformer 148 to the scanner 154 which is vibrated at 20 cycles per second. The scanning element 154 h re disclosed is of the Rochelle salt type deibed in connection With TJifrures. 1 to Although the scanner is here shown as that disclosed in the modified form of Figure 3, it will be understood that this is merely for piuposes of illustration as the arrangement shown in Figure 5 is more preferably employed because of the greater amplitude which can be obtained although `for certain specific purposes the arrangement shown in Figure 3 may be preferable. A similar oscillating circuit 155 comprises a three element tuto, primary vindings 156 of the transformc-rs 157 and 158 and a variable condenser 159, the adjustment of which is such that the circu is tuned to oscillate at 2,000 cycles and accordingiv generates oscillations of 2,000 cycles per second. T he secondary Winding of the transformer 156 is connected to the input of the modulator 142 and thence to the oscillating circuit 132. The same oscillations are transmitted through the vsecondary of the transformer 158 to the second scanningy element 162 which is accordingly oscillated at a frequency of 2,000 cycles per second. The scanning element 162 as in the case of the scanning element 154 is of the type shown in the Figures 1 to 5, although it will be understood that any of the modifiedfforms iliustrated in the specilication heretofore may be employed. .Y A source of light 163 is projected upon the image 164 from which it is reflected throu h the focusing lens 165 upon the scanning e ement 162. This scanner as it oscillates, picks up light rays from successive points. along one co-ordinate of the image and refiects .the rays therethrough focusing lens 166 upon the scanning element 154Aand thence through the ltllilouco slot 167 and diverging lens 168 to the photo electric cell 169. As the scanner 154 makes `one oscillation, the scanner 162 will have completed 100 oscillations and will have, therefore, scanned the entire image. This will be repeated for each oscillation of the secoue. scanner 154. The photo electric cell 169 is thereby successively subjected to the succession of points comprising the limage 164. Photo electric cell 1.69, as it is Well understood com arises a light sensitive -substance such as potassium hydride or any other Well known element of similar characteristics, and a second electrode 170 is connected in circuit with the tvfo rectifier units 171 and 172 each comprising the standard tvvo elements Well understood by those skilled in the art. The Jlate circuits of rectifier units 171 and 172 are connected to the secondary Winding of the transformer 173, the mid-terminal of which is connected to the primary Winding of the transformer 174, and thence to one electrode of the photo electric cell.

An oscillating circuit 175 comprises a standard three element tube 176 and the primary Winding of the transformer 173 and the .variable adjustable condenser 177. By proper adjustment of condenser 177, the circuit 175 is tuned to oscillate at 100,000 cycles. The circuit including tubes 171 and 172 acts as a full wave rectifier for the oscillation produced in circuit 175 whi ch flows in the secondary of transformer 173 through the primary thereof. rlhe amplitude of this rectified current is then varied in accordance with the variations of light intensity impinged on photo electric cell 169 from the image 164.

In order to operate the crystal at the receiviner station properly in accordance with the picture currents, it is essential that a current of a single frequency, the amplitude of which varies, be transmitted in order that the crystal in the receiving station should operate at its resonant frequency. It is evident.l however, that if a darli spot of a picture is being scanned, the cell will be of such re- `sistance that no current Will flow in the circuit. Accordingly there Would be a momentary change inthe frequency of the picture current, which would not conform with the resonant frequency of the receiving crystal. To overcome this difficulty a resistance 168a is connected across the photo electric cell to insure a minimum flow of current through the circuit at all times. With this arrangement, when a dark spot on the image is reached, a flow of current of very small magnitudewill result and the current variations will increase in accordance with the intensity of light to which the photo electric cell is subjected, although at no time of zero value.

The character of the transmitted picture fre-v quency is thus kept constant, the amplitude being the sole varying factor. v

The picture currents in the output of the photo electric cell flow through the primary winding of the transformer 174 and are impressed across the input of the amplifying tube 175 of the standard three element type, the output of which is connected through the transformer 176 to a second stage amplifier tube 177 The output of the amplifier tube 1.77 in turn is connected to the transformer 178, the secondary of which is connected in circuit with the modulator and oscillator 132. By this circuit arrangement the carrier oscillator current 132 is modulated in accordance with the two synchronizing or scanning frequency and the picture currents. A single carrier current modulated in accordance with variations of three different faequencies is radiated over the antennae 139, or impressed upon a line which is not shown in the drawings.

At the receiving station, Figure 20, the signals are received over the antennae 182 and are transmitted through the radio frequency transformer 183 to the tuned circuit 184. The tuned circuit 184 in addition to the secondary of the transformer 183, com-- prise a variable condenser 185 and vacuum tube 186. By properadjustment of the capacity of condenser 185 this circuit can be tuned to the carrier current frequency for maximum reception. The received carrier current is then impressed across the detector and amplifier tube 186. Althou h no radio frequency amplifying stages are s iown,it will be understood that radio frequency amplication employing any well known circuit therefor properly neutralized may be employed.

The amplified and detected wave is then transmitted through transformer 187 'to the tuned circuit 188. The capacity of a variable condenser 189 connected in the tuned circuit is varied until the circuit is tuned' to a frequency of the received picture currents. The picture currents are thus selected from the detected modulated carrier current in the output circuit of tube 186. These picture currents are now transmitted through amplifying and detecting tube 192, transformer 193, the second stage amplifier 194, trans-A former 195, and impressed across the trodes ofthe crystal 196. y

The ray of light emanating from the source of intense white light 197e and made parallel by the lens 208 passes through the crystal 196 to be refracted and reflected from mirrors 209 and 212 as described in detail hereinabove. The ray is then passed through a slot to lenses 213 and 214 which will amplify the distance that the beam transverses through the Nicols prism 197. Nicols prism 197' plane polarizes the light 'which has been elliptically polarized by the receiver crystal 196. I-f a Nicols prism is rotated in the path of a ray of light which is elliptically polarized, no partof the ray is cut off although its intensity is varied. Since the phenomenon of color, due to double rotation depends upon a ray of plane polarized light the Nicols prism 19T must polarize the ray of light at its maximum intensity. This beam then passes through lens 215 to the quartz wedge 198 so adjusted that when the crystal 196 is oscillating at its maximum am litude for an elementary area of no color, 1. e. black, the ray of light falls in the black ledge of the slot. The ray then passes through converging lenses 199 and 205, and through the analyzing Nicols prism 205 upon the mirror 202 of the scanner 226. From thence it is reflected through the converging lens 206 upon the mirror 203 of the scanner 233. Thence through the converging lens 207 upon the screen 204. As has been described in detail hereinabove, the wedge slot in conjunction with the Nicols prisms now passes through light of varying color in accordance with the extent of displacement of the beam of light and focuses 1t upon the screen 204.

A second circuit for the detected and ainplified received modulated carrier current in the output of the tube 187 is completed through the transformer 217 the secondary winding of which together with the variable condenser 218 are of such values that the circuit is tunedto a frequency of the 20 cycles.

Accordingly this circuit will select from the received modulated carrier wave the 20 cycles impressed thereon by the oscillating circuit at the transmitting station. This selected frequency will be amplified by the three element tube 219 and transmitted through the transformer 222 to the second stage amplifying tube 223. Before this stage, however, an impedance coil 224 is connected in the circuit for choking or keeping out any higher frequencies than the 20 cycle wave current.

From tube 223 current which is transmitted through transformer 225 to the scanning element 226 which comprises a Rochelle salt piezo electric crystal having a natural frequency equal to 20 cycles and accordingly it f will be oscillated in synchronism therewith.v

A similar tuned circuit including the secondary of transformer 227 and the condenser 228 is resonant to 2,000 cycles generated at the transmitting station by the tuned circuit l.

period of 2,000 cycles .Y ca

modulate a carrier current. Simultaneously picture currents obtained as a result of subj ectin g a. photo electric cell to light from successive points on an image modulate the carrier current and accordingly a single carrier is radiated, modulated in accordance with the two scanning frequencies and the picture current. At the receiving station a tuned circuit tuned to the frequency of the picture currents picks out these currents from the carrier and impresses .them across a quartz receiver device in a manner described in detail above. A second and third circuit each tuned to a particular scanning frequency select them from the oscillating circuit and impress them across piezo -crystals having natural periods equal to the particular frequency impressed tliereacross. i

It will be evident that by using crystals at the transmitting and receiving stations having a natural period equal to the scanning frequency and impressing currents of the same frequency thereacrcss that the crystals will oscillate at maximum amplitudes in synchronism. These crystals are known to be substantially inertialess and therefore provide no mechanical problem even at the high rate of operation to which they are subjected. Similarly, the receiving quartz crystal will respond to any frequency of picture currents without distortion, inasmuch as it also is substantially inertialess. Since no limitation beyond practical difficulties is placed upon the intensity of light at each station, a maximum intensity of light can be obtained to provide the necessary7 lumens of light for operation at the high speed and short light period available in television.

Although it will be evident from this description that only7 the simplest forms of circuit are disclosed, any forni of improved radio system maybe applied to my invention. rlChe particular circuits shown are of the simplest type, inasmuch as this does not form a part of my invention. Although tubed circuits are used for separating the various frequencies, it will be evident that similar results can be obtained by means of electrical lters in which the various frequencies are filtered out rather than by employing tuned circuits.

Summarizing, the system employs a quartz crystal having a natural period of v2,000 cycles, a scanner oscillating at 2O cycles and f', a second scanner oscillating at 2,000 cycles.

The relation between the scanners at the transmitting stations and the scanners at the receiving stations are so adjusted that they are in phase and will-maintain synchronism. This is easily done becauseV of the natural characteristics of the crystal itself. As has been mentioned before, it willbe like apolarized relay and merely by determining faces of different polarity it is lpossible to make a phase difference, between -the scanners zero.

Since the constants of the electrical circuits are so chosen that a value similar to the natural period of the crystals frequencies are transmitted, and since the crystals have a. natural period they must keep in step and evident therefore that this properly tales care of the matter of synchronizing. Y

In Figure 22 I have shown a form of the wave which the picture current received may take. It will be noted from this form that the wave is complicated with values above and below zero, and accordingly a quartz slab cut as the quarts 198 would allow only onehalf of the wave, either the upper half or the lower half to be utilized. The efficiency therefore of the type of wedge would be only fifty per cent. In order to obtain the maximum value a double wedge such as shown in Figure 21 may be employed. In this arrangement it will be noted that the dark-portions 236 of the wedge 237 is at the center of the wedge to provide for proper operation at the receiver for an area of no color value, as for example black. The Wedge consists of two crystals 238 and 239 which may be secured to each other. One of these crystals is a. right handed quartz crystal and the other a left hand d quartz crystal. The portion in the center may be a foreign substance to which is cemented the two quartz wedges. The width of this dark portion should of course, be suiiicient to completely oblitcrate the light which would result from the transmission of a black area. In transmitting a complexwa-ve such as shown in Figure 52, in which the upper and lower halves are not symmetrical, the first two cycles, the amplitude of which being symmetrical, would cause light to shine on the dark area. The upper half of the curve would cause light to be impinged on the right hand side of the double wedge while the lower half of the curve would cause light to be impinged on the left hand side of the double wedge. In this manner, it is at once seen that if the curve is not symmetrical, as

it probably would not be, the correct color valuation could be obtained by means of this arrangement. The double wedge could be so cut as to give the exact color valuation ifl the curve were symmetrical: in other words, the amplitude of one half of the'cycle of a wave would be exactly the same as the amplitude of the other half. It will be understood, however, that the present invention is not limited by any particular form of wedge as there are many similar modifications thereof which come within the scope of this invention.

The scanner shown in the above system, although shown as of the type disclosed in Figure 3, may be of any of the modified forms illustrated and it will be understood that the invention is not limited to any particular. form of scanner employed..

. cannot vary even by a small amount. yIt is In the systems thus far described, the pictures are transmitted in either black or white or in colors by a. specific circuit arrangement. In the systems non7 to be described, colored pictures are transmitted by the three color system. rl`he principle of the three color process as is Well known is based upon the factthat any colors in the visible spectrum can be matched by the combination of three of the so-called primary colors, namely; orange-red, green and blueviolet, popularly called red, green, and blue. It is vrell known that if a red screen is placed in the path of white light to act as a filter, it Will permit only red light to be passed through. Similarly, a blue screen vvili act as a lter permitting only blue light to be transmitted therethrough and green screens will act as a filter to permit only green light to pass through. In each case, all the other light will be prevented from passing through the filter. In cases Where combinations of light colors are passed throu h a lter, these lights may be further ltere out from each other. Conversely, it is known that by combining the above mentioned primary lights in combinations and proportions, a resultant color comprising any part of the entire spectrum may be obtained.

It is manifest from the above that if a multicolored object be viewed through the three-colored filters, namely; red, green and blue, the complementary colors only will be seen. If the complementary colors are again recombined, the original color will again be transmitted. By the use of different amounts of these colors or by the use of colors of different intensity any color in its correct value can be reproduced. A system for transmitting a picture in colors by means of the three colors scheme is disclosed in Figures 31 and 32. Figure 31 discloses the transmitting apparatus and Figure 32 the receiving apparatus. Y

In Figure 31 an oscillating circuit 242 similar to that disclosed in Figure 19 gencrates a carrier current which is radiated over the antenna 243 or over a pair of Wires,-

not shown. A modulator 244 similar to that shown in Figure 19 modulates the carrier current in accordance with the oscillations impressed thereon. An oscillator 245 which produces currents of 20 cycles frequency and oscillator 246 producing currents of 2,000 cycles frequency as described in Figure 19, operate through circuit 244 to modulate the carrier current generated in circuit 242. A circuit 247 producing oscillations of 100,000 cycles, is provided with a double Wave rectifier 248 in circuit with which are connected photo electric cells 249, 250, and 251.

It will be noted that the oscillator 245 is connected in multiple to three scanning elements 252, 253 and 254. 'The oscillator 246 is similarly connected in multiple to three scanning elements 255, 256 and 25T.

Light from source 258 is impinged on an image 259 which is to be reproduced at a remote station. Any one beam from a point, as for example 262, is refiected through a focusing lens 263 to the scanner 257. The same beam is then refiected through focusing lens 264 to the scanner 254 from Where it is again reflected through a red lter 265 to photo electric cell 249. Photo electric cell 249 is, therefore, affected only by red light emanating from the image 259. From the same point 262 on an image a beam is refiected through lens 266, scanner 256, lens 268, scanner 253 and through the blue filter 269 and photo electric cell 250 will be affected only by the blue rays emitted from the image 259. A third beam from point 262 passes through focusing lens a, scanner 255, lens 27 3, scanner 252 and through the green filter 274 to photo electric cell 251. Similarly, therefore, photo electric cell 251 will be affected only by green rays emitted from the image.

From the above description, it is now clear that the rays from image 259 can be divided into their component primary colors and a separate photo electric cell is afi'ectedby the intensity of these rays. There are, therefore, produced three separate picture currents, one in accordance with the intensity of the red light from the image, al second in accordance with the intensity of blue light from the image, and a third in accordance with the intensity of green light from the image.

The currents of 100,000 cycles from oscillator 247 are rectified by the double wave rectifier 24S and this rectified current is varied in amplitude in circuits 275, 276, and 277 in accordance with the variations of the light intensity playing on the photo electric cells 249 to 251 respectively. The picture current from the photo electric cell 249 is transmitted through the transformer 255 to the repeating and amplifying circuit 252 including tubes 253 and 254 to the transformer 244 and thence to modulator 244 and gcillator 242 and radiated over the antennae The picture currents generated by the photo electric cell 250 are transmitted through the amplifier tubes 256 and 257 to the modulator 258 and oscillator 259 of a type similar to that disclosed at 244 and 242. It will be understood, of course, that the oscillations produced in oscillator 259 are sufficiently separated in frequencies from that produced by the oscillator 242 to enable separation thereof at the receiving stations.

Similarly, the picture currents fiowing from the photo electric cell 251 are transmitted through the repeating and amplifying tubes 262 and 263 to modulator 264 and oscillator 265 from thence they are radiated over the antennae 266. oscillations generated by the oscillator 265 are, of course, of sufficiently different frequency from that generated in the oscillators 259 and 242 to permit proper separation at the receiving stations. y

It will be evident from this description that three picture currents are now transmitted, the value of each being in accordance with the amount of red, blue, or green in an image. f t the receiving station shown in Figure 32, the modulated carrier currents are received over the antenn 267 and circuit 268 tuned to the frequency of the carrier current generated by the oscillator` 242. This current is then amplified and detected by the tube 269. A circuit 272 tuned to the frequency of 20 cycles will separate the oscillations from generator 245 from the carrier and these currents are then transmitted through the'am-4 fgliier tubes 273 and 27 4 to the scanner 275. Similarly, a circuit 276 tuned to 2,000 cycles selects currents of this frequency from the carrier. These currents flow through the repeaters and amplifier tubes 277 and 278 to ille scanner 279. Accordingly the scanner 27 5 Will oscillate at 20 cycles and in synchronis-m and in proper phase relation with the scanne-rs 252 to 254 While the scanner 279 will oscillate in synchronism and in proper phase relation with the scanners 255 to 257. A circuit 280 tuned to 200,000 cycles Will select the received picture currents from the carrier and will transmit these currents through amplifier 281. These currents will hen be impressed across the quartz crystal 282 which will vibrate in accordance with amplitude of these received currents in the manner hereinbefore described. Inasmuch as the picture currents which modulated the oscillator 242 Were those generated by the photo electric cell 249 which is subjected to the red light in the image 259, the quartz crystal 282 will be operated in accordance with the intensity of the red light emitted from the particular point of picture at that time being scanned. A

Similarly the circuit 283 is tuned to the frequency of the carrier current generated by.

cell 259. These currents will, therefore, flow in this circuit and through the detector and amplifier tubes 284 and 285 and will then be impressed across the quartz crystal receiver 286. It will be recalled that the currents generated by the oscillator 259 were modulated by picture currents from the photo electric cell 250 which in turn Was operated in response to the blue portions of the image and accordingly the crystal 286 operates in accordance' with the intensity of the blue light emitted from the image the particular point thereof being scanned at that instant. Similarly, the oscillating circuit 287 is tuned to the frequency of the oscillator 265 modulated by picture currents. yThese currents, will therefore, be picked up, amplified and detected by the tubes 288 and 289 and then impressed across the quartz crystal receiver 290 which in turn will operate in response to the green light emitted from that point of the picture at the instant being scanned due to the fact that the currents generated by the oscillating circuit 265 are n'iedulated by currents from the photo electric cell 251 responding to the green light rays ofthe picture. J

A beam of light from a sour-ce 292 passes through the proper lens arrangement 293 and thence through a red filter 294 so that only red light is retracted by the quartz crystal receiver 282. The red light then passes through the lens in front and back of the light gradient 295, and impinges upon the mirror 296 from whence -it is reflected to the scanners 279 and 275 from where they are impinged to produce an image upon the screen 296. Since the intensity ofthis light will depend upon the extent of displacement of the beam through gradient 295, it is evident that the amount of light which Will be impinged upon the scanner 179 will be of the same intensity as the red light Which is impinged upon the photo electric cell 249. Similarly, light from a source 297 passing through the proper lens arrangement 298 and thence through the green ilter'299 is shifted in accordance with the expansion or contraction of the quartz crystal receiver 290, pas-ses through the proper lens system 301 and light gradient 302 to the scanners 279 and 275 and screen 296. Since the intensity of the green light thus emitted depends upon the operation of the quartz crystal 290 which in turn is operated in ac coi-dance with the amount of light impressed upon the photo electric cell 251 which in turn is a function of the green light emitted from the image' 259, it Will be evident that the amount of green light impinged lupon the screen 296 is proportional in this instance to the amount of green light emitted from the image at the transmitting station. In a similar manner the beam from the source 303 passes through the lens arrangement 304, the blue filter 305, the crystal 306, the vlens arrangement 307, light gradient 308 to the scanning elements 279 and 275. y From the above, it Will now be evident that at any instant the amount of light impinged upon the screen 296 at the receiving end comprises red, blue and green light in proportions equal to the amount of red, green and blue light in the image 259 being transmitted from the transmitting station, at that point and at that instant.

When at the receiif'ing end, the proportions of red, green and blue are infproper amounts, the resultant picture produced will be of the same color as that emitted from the image at the transmitting station.

It 'will be noted from the above descrip-

Images