US2441568A - Radiant energy operated positioning control - Google Patents

Description

May 18, 1948.

H. J. FINISON RADIANT ENERGY OPERATED POSITIONING CONTROL Filed March 11, 1944 ATTORNEY:

Patented May 18, 1948 ENERGYZOPERTED CQNTROL- Harvey J;..Finison,. Baytom. Qhio Application'MarchA 111,vv 1944!,` Serial' No. 526,104i

(Cl. Z50-2) (Grantedl under.' the act 0.!" March 3`, 1883', as.

amended April' 30, 1928; 370 G. 757') The invention described herein may be manufacturedand used by.. or for the Government for governmental', purposes.I without. the payment to me of any royalty thereon.

This invention relates to improvements in radiant energy operated control devices, and more 4particularly tov radio controlled apparatus having a variably shiftable, controlling element for causing an element to. be controlled, located at. a remote location, to. be correspondingly accurately shifted an equal yor proportional' amount with respect to the movement ofthe controlllng'eliement.

Radiant energy control devices have been proposed in the prior art for controlling the position, oractuation, of control' elements to' be shifted, such as the rudders, orv other controlI surfaces of anv airplane', dirigiblev craft, or other'vehi'cle. Some of these devices employ' impulse transmitting apparatus and receivers` for receiving" the impulses and controlling the setting of the elements to be controlled* in accord' with the numloer4 of impulses received; Other' of these devices employ` transmitting means for'V transmitting a prolonged radio signal; the length orduration of the'- signal determining the position of the'v element' to= be, controlled. The apparatus employed in each of these knownsystems is. usuallylarge, heavy, complicated, expensive' to manufacture, employing special types of transmitters and` receivers having relays, signalf opera-ted switches, limit switches etc;, andthe exact position of the controlled: elements. cannot usually be accurately determined unless the operators. have1 the controlled. elements in plain View., or the. positionsof the controlled elements. are transmitted back, to the operators at the radici controlling or transmitting stations.,

The present invention -diiersz from the;` aforementioned priorl constructions in; it. utilizes anA- extremely simple transmitting; and, receiving apparatus, employingl snlostantially` conventional radio transmitting means and includes. means for impressing. a plurality of. different fixedaudio frequencies. on. a carrierwave. at.. variable amplitudes. so as. to vary the intensity of one of. the transmitted frequencies. with, respect to the intensity of the other. transmitted. frequency, and utilize this variation in the intensity or amplitude of these diil'erent frequency radio WavesV to selectively position. an element to controlled at a remote radio receiving station located in. a plane, vehicle or other structure.

An object of the invention is the. provision ofa. radio remote control system having transmitting and receivingv stations including means for:l sc- 2; lectively transmitting, and receiving at leasttwo radiant energy Waves. of. diiering frequencies, varying. the, amplitude of. atleast one oi the frequencies. at the. transmitting station` andutilizing this. variation.A in. the. amplitude. of the. radio, frefluency signals received, at. the receiving station to selectively adjust an, element, tov be controlled.

Another object ot, the invention.. is. the provision ot a radio. remote. control.. system. having. a. radio transmitter adapted to send out, tvvov radio.- sig.- nals, of ydifferent iixed. frequencies includingmeans for selectively varying the amplitude. of one. of said' signal frequencieswith respect. to the other ireqnency, and arernotely located radoreceiving station having a receiver selectively tuned to receive the, dual frequency signals from the transmi'ttng station. in. which selective circuits are tuned to receive each. frequency, and means to be, selectively controlled, common to. both selec* tivev circuits, is provided'. operable by relative. variations inthe frequency. amplitudesof the signals transmitted to selectively adjust. the position. of said selectively controlled means in accord with the degree ofV the.. relative. variation between the amplitude of the signals received.v

A further object ofA the invention is. the provision of' a. radiant energy operated remote control system having atransmtter adapted to radiate, a plurality of' signals of dilerent` relatively predetermined' frequencies including controlling means for selectively varyingy the.. amplitudes of thev transmitted lsignals in an opposite sense,l and a remotely' located radio receiver for receiving said'. transmitted signals having a plurality of selective circuits each tuned toA selectively receive a different one of said' transmitted signals and reject. the other signals, and the provision of adjustable signal amplifying, means in said selective circuits for balancing the amplitude of said transmitted signals, including a differential relay devicecommon to* said selective circuits, operable by variations in the relative amplitudes of the transmitted signals. to selectively adjust a controlled device, and an operating; connection between the controlled device and the signal ainplitude balancingJ means to balance the unbalanced amplitude of' the received; signalsV upon relativeselective movement or the controlled device incident tothe unbalancedK amplitudes of said?transniitted3 signal frequencies.

A. stillf further object or the invention is the provision of aradio remote control. system having a transmitter adapted to: .radiateY at least two predetermiiiedL different signal frequencies, inciuclingv controllingl means for selectively increaspredetermined movement of the element to be controlled due to a predetermined variation in the signal intensities between the two received signal frequencies.

A further object is the utilization of a single radio frequency channel to operate a number of independent control devices.

A still further object is the provision of apparatus which is simple in construction, compact, light in weight and economical to manufacture, utilizing as much as possible conventional elements in the construction and assembly of the apparatus in which the reception of signal Waves of two different selected radio frequencies and 'amplitudes are employed to selectively predetermine the position of an adjustable servomotor operated element to be controlled, located at a,l

radio receiving station.

Other objects and advantages of the invention will appear in the following description taken in connection with the accompanying drawings in which like reference characters refer to like parts in the several figures.

Figure 1 is a schematic wiring diagram of a control station employed in my invention for sending out a plurality of radio signals of different predetermined frequencies, and control means for selectively varying the amplitude of one signal frequency with respect to the amplitude of the other signal frequency.

Figure 2 is a schematic wiring diagram illustrating a remote receiving station having radio receiving means tuned to receive the signals from the sending station and having an element to be controlled which is selectively adjustably responsive to variations in the signal strength of the signals received from the sending or controlling station shown in Figure 1,

Referring to Figure 1 0f the drawing, the numeral I indicates a conventional radio telephone transmitter having the usual suitable antenna and ground connections 2 and 3 and carrier wave transmitting means, the radio transmitter being connected to a plurality of audio frequency signal generators 4v and 5 by the conductors 6 and l. The signal generators 4 and 5 produce signals of different predetermined frequencies, preferably in the audio range.

Adjusting means are provided intermediate the generators 4 and 5 and the conductors 6 and I for relatively varying the amplitude or intensity of one of the signal frequencies with respect to the intensity of the other signal frequency. The generator 4 is provided with output conductors 8 and 9 bridged by a variable resistor element I0, having adjusting means such as a sliding contact element II engageable with-the said resistor I0, the contact element II being preferably connected by a pigtail I2 to the conductor 6 of the transmitter I. The generator 5 has similar output conductors I3 and I4, bridged by a variable resistance element or resistor I5, having an ad-v justable contact member I 1, as seen in Figure 1 of the drawings. The adjustable contact member Il is suitably connected by a conductor I8 and pigtail I9 to the output conductor 8 of the gener ator 4, while the other transmitter lead I is connected directly to the conductor I4 leading from the generator 5.

Relative movement of either of the contact elements II or I'I with respect to the resistors ID or I5 will not effect the respective frequencies of the signals delivered to the transmitter I, but the respective amplitudes or voltage intensities of the signals impressed on the radio transmitter carrier wave will be materially affected. Movement of the contact element II along the resistor IE) in one direction intensifies the ampli- -tude of the frequency output of one of the signal generators while movement of th'e other element I'I with respect to the resistor I5 in the same direction effects a corresponding reduction in the amplitude of the voltage output of the other frequency signal generator.

Simultaneous movement of the two resistor contact elements II and I'I in the opposite direction from that noted above produces a converse variation in the relative intensity of the signal frequency output of the two frequency generators 4 and 5, these variations in output frequencies being delivered to the transmitter I, causing the signal strength of the signals at one frequency to be reduced, while the signal strength of the signals at the other frequency are correspondingly increased.

I provide an adjustable controlling element at the control station in the form of a control stick ZI simulating a control stick in an airplane and pivoted at 22 to a rock shaft 20, The end of the rock shaft 2l] has fixed thereto a crank arm 23, to the free end of which' is pivoted a longitudinally shiftable actuating rod 24 having the two contact elements II and Il fixed thereto and secured against relative movement with respect to each other. It is however preferable to insulate the contacts II and Il from each other and from the rod 24, this being accomplished in any well-known manner such as by insulating bushings 25 and 2S, fixed on the rod 24 and secured to the resistor contact elements II and II.

Movement of the stick 2I forward or back, as indicated by the arrow 2'I, rotates the shaft 20, actuating the crank 23, which in turn shifts the rod 24 longitudinally, moving the two resistor contact elements I I and I'I with respect to the resistors IG and I 5, effecting a relative decrease or increase in the signal output amplitude at one frequency with a corresponding relative lncrease or decrease in the relative signal strength of the other frequency signal depending upon which direction the stick 2I is moved.

Additional pairs of radio signal frequency gen- .erators similar to generators 4 and 5 may also be provided having frequencies differing from each other and from the just described radio signal frequency outputs, and signal intensity control meansvlike that just described may be provided for each additional pair of signal frequency generators connected for operation by the control stick 2l when the same is moved back and forth in planes at different angular relations to the plane of movement of the stick, as indicated by the arrow 21 in Figure l. These additional different radio signal frequencies may also be introduced into the radio transmitter I by the conductors 6 and I for selectively causing actuation arri-,see

of another element to. be controlled by the said vconductons 3i and 32 to two selective circuits or networks generally indicated at 35i and se, each consisting of parallel and series resonant circuits tuned to selectively receive the frequency signals of one of the signal generators ci or Si.

My radio control system is based on the use selective circuits r tuned receiving networks, each consisting of a combination oi series and parallel resonant circuits in which the values of inductance and capacitance are such as to give resonance lor both circuits the same frequency in audio or near audio range. For any frequency other than the resonant frequency, the low impedance cf each parallel circuit forms practically a short circuit across the input of the tube, and the signal does not appear in the pla-te circuit. The actual short circuit-ing or the non-resonant frequency is prevented by the series circuit which has a high impedance at all iieciucncies other the resonant frequency,

If a voltage of the resonant frequency is in1- pressed across the input ci the selective circuit, the impedance oi the parallel circuit is high that of the series circutl is low, and the signal then appears in the plate circuit of the tube.

High Q circuit components are employed which maintain the .selectivity of these circuits fairly sharp so the combination of such selective circuits will effectively sort out a combination of input frequencies .so that each frequency will appear only in its proper plate circuit.

Referring again to Figure 2, the signal amplifier is operated class A to give as little harmonic distortion possible and to preserve a linear relationship between the input and output voltages. The parallel circuit for the selective circuit or network 33 is indicated at series circuit is indicated at The output from the receiver i8 at the resonant frequency is imposed on the plate circuit or the radio tube it in the usual manner.

yThe parallel circuit of the other selective cir-`- cuit or network 34 is indicated at 3l', while the series circuit is indicated at signals resonant to this circuit S4 are imposed on the plate circuit of the radio tube 3d in the usual manner. Load resistors tu and iii are connected to the common conductor t2 at The other end ci the resistor lil is connected to the plate circuit of the tube 35 while the resistor il has its other end connected to the plate circuit oi tire tube 3%, as indicated at lie. The resistors are of the variable type, each having a movable part for variably controlling the resistance such as the sliding contact members t5 and 11S, respectively, arranged to contact the resistor elements t and The output voltages of the tube. and in` the respective selectivo circuits or networks and are each a function of si nal strengtl of the resonant signals selectively received by on orthe other of the respective circuits 33 an M and the signal strength or voltage intensity of the signals is introduced in the respective amplitying circuits il and 48 over the aforesaid corn- 'mon conductor member ft2 and the conductor leads 49 and 5G bridged by the variable load resisters 5l and 52 having cooperating adjustable 3i while the vices and contacts 53 and 54, respectively, connected-to the grids of the amplifying or triode radio tubes 55 and 56. The plate circuit or voltage output from the tubes 55 and 55 may be further ampliiied if desired inany convention-al manner, these plate voltage output -circuits from the amplifying tubes being connected as indicated at 5i and 58 to one terminal of each of the magnet devices 59 and 6o and to the other or common terminal for both of the magnet devices 59 and 60 through the common conductor 42a. 'The magnet devices 59 and @il constitute a part of a differential relay control device. A, B and C batteries for the respective tubes tt, 35i, 55 and 5t are provided in the usual manner indicated at El, B2 and 63 in the drawings.

Assuming that the frequency generators 4 and 5, as illustrated in Figure 1, are in operation, and the dual frequency signals are introduced into the radio-telephone transmitter l, these signals will be transmitted or radiated in the usual way by the antenna and ground connections 2 and 3. If the control stick 2! is in neutral position the variable resistors i0, li, and it', Il will be adjusted so that the intensity or amplitude of the transmitted signal strengths will be equal. Shifting the control stick 2l one wayin the direction of the arrow 2l, however, simultaneously moves the two variable resistor controlling elements ll and il in the same direction, intensifying the signal strength of one of the signal frequencies and reducing the intensity of the other signal frequency.

The dual frequency signals received at the restation, such as disclosed in Fig. from transmitting station, are picked up by the and ground connections and and s through the radio receiver 2S, alter which i y will be at or near audio range. According to the resonant `irecuiencies or" the transmitted "ie other i the selective circuits and 34 and their relaiv ntensitieswill be aniplied. Assuming that e v .ia-ble resistors ill, and 5E, ha been are equal in intensity, the magnetic devices will be equally energized and the will be centralised. Uponl an inin the signal strength of one of the incoming resonant l frequencies the voltage delivered to one of the magnetic devices til or @il will be creased, depending upon which selective to the other magnetic device will be correspond- .ingly reduced since the other signal frequency output at the control ete-tion is correspondingly reduced, The signals received by one ci the selective circuits is reduced in intensity as the signl-,l received by the other selective circuit is correspondingly increased, producing an unbalrelaticn between the respective magnet de- 'lhe two magnet devices 5e and preferably in the form ci solenoid coils orrning a part of the diierential relay, having a roel armature Sii provided with a contact arm 'ce carrying a central contact movable by the armature arm ell to engage either one of a oi spaced electrical contacts and connected respectively to a pair oi conductors tti and connecting the ends of two field coils of a conventional split iield reversible electric motor il. A battery l2 supplies current by means ci the conductor 'i3 to the central contact arm t5 and contact e6 of the armature 64I, the

't affected, and the voltage delivered battery being connected by a conductor 'I4 connected in series with a conventional electromagnetic clutch device 'l5 of any well-known type which, upon the passage of current therethrough, energizes the motor 'll to selectively rotate the same in either direction, and will automatically connect the armature of the motor 'ii to a shaft lo and rotate the same in the same direction las the rotation of the motor, and upon de-energizing, the motor will cause an uncoupling of the shaft l5. This arrangement provides means for uncoupling of the shaft 16 from the motor ll immediately on the breaking of the operating circuit and stopping of the shaft so as to prevent cverrunning of the motor and the elimination of any hunting movement of the shaft due to the overrunning action. The shaft l has fixed thereon a Worm drive member 1l meshing with a worm gear segment 18, pivoted at 'J9 to a stationary part of the frame 30, the segment having an operating lever arm 8| fixed thereon and connected by a link member 82 to an element to be controlled, such as a rudder or other control surface i3 of an airplane, vehicle or other movable structure. Rotation of the shaft in either direction will correspondingly shift the control element 83 in either direction.

In order to provide a follow up mechanism to again equalize or balance the voltage output or amplitude of the two selective circuits after the controlled elements 83 has been shifted to a selected position corresponding to the relative difference in the intensities of the transmitted signal frequencies ya gear 84 is provided fixed on the shaft l5 meshing with a large gear 85 on a shaft 86. The shaft 86 carries a small gear 81 fixed thereon, forming part of a reduction gear train. The gear el meshes with a large gear 88, secured on the shaft 89 at one end, this shaft having crank arm 9G ilXed thereto to the end of which is pivoted an actuating rod 9|, having the contact control members 45 and 45 of the adjustable load resistor elements 4B and 4! xed thereon. The arms 45 and 4B are insulated from the shaft 9! and from each other.

As the motor 'Il is put into operation, when the armature 54 is shifted by the magneticl devices 59 and 6), due to a variation in the signal strength of the two incoming radio frequencies with a corresponding variation between the output voltages of the two selective circuits 33-34, the controlled member 83 is shifted at a different angular position, and the arm 9i] on the EQ is, through the reduction gear train Stv-8B, shifted to simultaneously vary the position of the adjustable load resistor members 45 and 4.6. Depending upon the relative intensity of the incoming signal frequencies, the output voltages of the selective circuits 33 and 34 are again brought into balance as the motor 1| moves the controlled element 83 to some predetermined position at which said controlled element will remain xed until the relative signal strength between the incoming signals is again changed.

If the control stick 2| is moved to again equalize the intensity of the transmitted signal frequencies from the generators 4 and 5, these ignals, although being now of equal amplitude.

the contact l66 into engagement with one or the other of the contacts 61 or 68, depending upon the relative difference in the intensity of the voltage output between the plate circuits of the tubes 55 and 56. Depending upon which tube output is greater, the motor 'H is put into operation until the follow up means simultaneously shifts the variable resistors 45 and 46 to positions where the voltage output to the magnet devices or coils 59 and 60 of the differential relay is again balanced with the controlled member 83 in its central position corresponding to the position of the controlling member 2| at the control station.

Means are provided for initially balancing the output voltage intensity of the resonant circuits 33 and 34 or networks so that any slight voltage variation due to tube variations or other causes may be compensated for. With the incoming signal frequencies at equal amplitudes the variable resistors 5I, 53 and 52, 54 are initially adjusted so as to position the armature 64 in its mid position, as shown in Fig. 2 of the drawings. Once the resistors just mentioned have been adjusted to effect this balance in the output voltage between the selective circuits 33-34 the resistors 5|, 53 and 52, 54 are not further adjusted or disturbed.

It is preferable to provide light equallzing springs 92 and 93 to hold the contact arm 65 and contact 66 of the armature 64 in a mid position out of contact at all times with the contacts 6l and 68 while the control apparatus is not in operation, such as when the incoming signals are interrupted for any reason, and to assist in moving the armature 64 to mid position when the output voltages from the tubes 55 and 5B are equalized.

While the construction and arrangement of the device as herein described and illustrated is that of a generally preferred form, obviously modifications and changes may be made Within the scope of what is claimed without departing from the spirit of the invention.

I claim:

l. In a remote control system, a transmitter adapted to radiate at least two distinct predetermined radio signal frequencies, control means for selectively Varying the relative intensities of said radiated signal frequencies, a radio receiver for receiving said radiated radio signal frequencies comprising at least two signal frequency receiving networks each tuned to selectively receive one of said radiated signal frequencies and having a voltage output, a differential relay device common to said networks and operable by a variation in the output voltage between the said networks due to a variation in the signal strength between the radio signal frequencies received by each of said radio networks, a member to be controlled selectively operable by said differential relay device, follow up means including voltage controlling means common to both networks interposed between the networks and said differential relay device and connected for simultaneous operation with said element to be controlled to selectively restore a balance between the voltage outputs of said networks upon a predetermined movement oi said member to be controlled relatively corresponding to the amount of said signal intensity variation in the radiated frequency signals received by said networks.

2. In a radiant energy operated remote control system, a transmitter for radiating at least two distinct radiant energy signal frequencies, adinstable control means for selectively varying the said radiated signal balancing means common to both networks for balancing the voltage output between the networks, differential relay means selectively operable by the voltage output of said networksdua to a variationin the voltage output betweerlthe networks,ga reversible motor device selectively operable by said differential relay device, axshiftable element to bel controlledmovable by: said.

motor device, follow up means operatively connected between said motor device and said adjustable voltage balancing means for adjusting said voltage balancing means in proportion to the out-of-balance relation of the signal frequency simplifications received by said networks to balance the voltage output of said networks upon predetermined movements of said element to be controlled incident to the operation of said relay device due to predetermined variations between the relative amplitudes of the radiant energy Vsignal frequencies received by said networks.

In. a remote control system, a radiant energy transmitter for transmitting at least two radio signal frequencies, control means for varying the amplitude of one of said transmitted frequencies with respect to said other transmitted frequency, a radio receiver having parallel selective circuits each tuned to receive one only of said transmitted signal frequencies, and to reject the other transmitted frequency and having a voltage output circuit for delivering a voltage proportional to the amplitude of the received radio signal frequency, adjustable voltage balancing means common to said parallel', circuits for balancing the amplitude of the output voltages of said selective circuits, a differential relay device selectively operable by variations in the said voltage outputs of said selective circuits, reversible servomotor means operable in one direction by said relay device upon a relative increase in voltage output of one of said selective circuits with respect to the voltage output of the other selective circuit, said servomotcr means being operable in the reverse direction by said relay device upon a relative decrease in the voltage outputs between the Iiust mentioned selective circuits, means for rendering said relay device inoperative with respect to said motor device when the selective circuit voltage outputs are equalized, and shiftalole mea-ns simultaneously operable by said motor device including an element to be controlled and voltage regulating means common to both selective circuits for variably shifting said element to be controlled in ratio to the difference in amplitudes between the voltage outputs and adjusting said voltage regulating means to balance said selective circuit voitage outputs when said element to be controlled is so shifted.

4. In a remote control system, a transmitter for transmitting a plurality of different radio frequency signals. interconnected means for simultaneously varying the relative amplitude of the transmitted frequency signals and a shiftable control member operatively connected to :frequency signal amplitude varying means selectively movable to vary the relative amplitude between the transmitted frequency signals in a predetermined ratio to the relative movement of said control member, a remote signal frequency 10j' receiving station having dual signal frequency receiving networks each tuned to selectively receive one of said transmitted frequencies and having a voltagefoutput proportional to the amplitude of the received signal frequency, adjustable voltage balancing means common to said dual frequency networks for restoring a balanced relationvin the voltage output of` tbe dual fre- Cluency networks, a shiftablemember to be selectively controlled. in a predetermined ratio to the relative, difference in the transmitted signal-frequency amplitudes operable by variations in the voltage output between the dual signalfrequency receiving networks including follow 'up means voperably connected between'said shiftable member to be controlled and said adjustable voltage balancing means for causing said voltage balancing means to balance said output voltages upon predetermined movement of said shftable member to be controlled incident to the said initial voltage variation between said voltage output of the networks due to the variation between the transmitted signal frequency amplications.

5. In a remote control system, a radio transmitter, an associated control member variably shiftable to similarly shift a member to be controlled located at a remote radio receiving station, means for transmitting a plurality of different radio frequency signals, means for selectively varying the degree of intensity of said transmitted frequency signals, operable by variable shifting movement of said variably shiftable control member, a radio receiver at said remote receiving station for selectively receiving said radio frequency signals including a plurality of frequency signal receiving networks each tuned to receive one of said transmitted signal frequencies and having a voltage output proportional tc the amplitude of the received signal frequency, adjustable voltage output balancing means common to said networks, to balance the volt-age output from said networks, reversible servomotor means selectively operable by variations in said voltage output between the networks and having an operating connection with the member to be controlled and an operating connectio-n with said output voltage balancing means for restoring a balance in the voltage output of the networks upon predetermined shifting movement of said member to be controlled incident to a predetermined amplitude variation in the transmitted frequency signals, and separate means in each network for independently regulating the voltage output thereof in proportion to the transmitted signal frequency received by said network.

y 6. In a remote control system, a transmitter for transmitting radio frequency signals having a plurality of different audio frequency modulations, interconnected means for simultaneously varying the relative amplitude of the transmitted audio frequency modulations and a shiftable control member operatvely connected to said audio frequency modulation amplitude varying means selectively movable to vary the relative amplitude between the transmitted audio frequency modulations in a predetermined ratio to the relative movement of said control member, a remote signal frequency receiving station having dual signal frequency receiving networks each tuned to selectively receive one of said transmitted audio frequency modulations and havin@ a voltage output proportional to the amplitude of the received modulation, `adjustable voltage balancing means common to said fuel frequency networks for restoring a balanced relation in the voltage output of the dual frequency networks, a shiitable member to be selectively 4controlled in a predetermined ratio to the relative difference in the transmitted audio frequency modulation amplitudes operable by variations in the voltage output between the dual signal frequency receiving networks including follow up means operably connected between said shiftable member to be controlled and said adjustable voltage balancing means for causing said voltage balancing means to balance said output voltages upon predetermined movement of said shiftable member to be controlled incident to the said initial voltage variation between said voltage output of the netl5 2,264,056

works due to the variation between the transmitted audio frequency modulation amplifications,

HARVEY J. FINISON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,600,204 Alexanderson Sept. 14, 1926 1,822,868 Grimes Sept. 8, 1931 2,247,294 Goble et al June 24, 1941 Thacker et al. Nov. 25. 1941

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