US2428007A - Telephone call-indicating facilities - Google Patents

Description

Sept. 30, 1947.

, E..M. BOARDMAN I TELEPHONE CALL-INDICATING FACILITIES I 2 Sheets-Sheet 1 MACH/NE File d Dec. 1, 1944 MACH/NE RING/N6 I MACH/NE RING/N6 MACH/NE RING/NC T0 LOCAL POWER MACH/IVE RING/MG sxrlwslow .nsr

NORMAL SE T MA CHINE RING/N6 lNVE/VTOR BY E M BOARD/VAN aamAg A TTORNL v Patented Sept. 30, 1947 U NIT ED STATES PAT 01 GB 2,428,007 TELEPHONE; CALL-IN DICAT-IN G FACHiI-"HES;

Edward M; Boardinan, Mountain Lakes; N; J1, as

signer to Bell" Telephone Laboratories; In'co'r porated; New York, N. Y'., ac'orporation-of' New York Application December 1, 1944, Serial No. 566,053

9 Claims.

1 This invention relates to signaling facilities for use at telephone subscribers stations and particularly to call-indicating facilities which. function' to indicate at a subscribers station or at an extension set associated therewith, the arrival. of a telephone call by time spaced signals of distinctive characters.

The signaling equipment'commonly used at tel ephonesubscribers stations comprises an electromagnetic device; generally characterized as. a

ringer, which respondsto each application of ringing current to the subscriber's line to produce sound signals of uniform intensity. While such signals function satisfactorilv t has been found desirable in some instance' tt'o furnish a.

having a relatively low sound output; Such a" solution of theproblem, however, introduces the possibility that the tone signalswould be ofsuch asubdue'd character as to. be useles in arresting'theattention of the subscriber when'loc'atedat any appreciable distance from the telephone with the inevitable result that numerous calls incoming to'the' statio'nwould go unanswered and wouldbe lost.

It is. the object of this invention to provide eall indicating equipment for use with a telephone subscrihers'telephone set or as an. extension set associated therewith, which responds. to the'application' of signaling current to thesu'bscribers line so as to indicate the'arrival of a call first'by a signal, at the'telephone set, oflo-W attention-arresting quality, and subsequently, either atithe telephone set or at an extension set by'a signal of higher attention-arrestingquality.

This object is attained in accordance with a feature of the invention by the provision of signaling facilities which render it possible for a single audible signalingdevice to operate and emit sound signals of different characters at time spacedintervals at. a telephone subscribers station, or to supplement the regular audible signal atla subscribers station with either visual or audible signals at ail-extension set, the latter signals having a higher attention-arresting quality than the regular signal associated with the subscriber telephone set.

The signaling-facilities contemplated by-this invention are desirable not only at subscribers premises whichare equipped with a single-telephone, but also find particular utility:- in many 2 locationsat wh'icli there are'located-a pluralityof independent" telephones; in that the" supplementary signal of higher" attention-arresting quality affords a; Iiibslt'il/(i identification 0f the" line" on which a call'has arrived. m tlie'Iatterca'se-the supplementary signaling equipment may" be rurnished as" an extension set and" located either in close proxiinitwwithtlie" telephone setor at a distance therefrom so that "positive identification of' the called line may; be given the" subscriber when he isiloc'ated at a point remote from" his telephone. I

Theinvention. will be readily uriders'tood from the" following detailed description madewitlt reference" to the accompanying drawings in* which:

Figs. 11,2 13; 4, 5and6*illi1sti'ate"diagrammatically several embodiments of the invention which provide 'twouistincti types ofealrsignels' at timesp'ace'd intervals;

Fig. '7. is a circuit diagram showing a number of signaling facilities? arranged" for" mounting in an" extension set, and" indicates a; plurality; of possible connections which may be effected to produce diiferent signaling)- arrang'ements';'

Fig. 8*is' a schematic"representation"ofa slow-- to op'erate switching device which is particularly suitable for use in the circuits shown in Figs. 1, 4-, 5an'cl 6; v

Fig; 9 shows" the switch of Fig. '7" fully" operated; and v Fig. 10 illustrates a; ringer. design which is particularlysuitable forus'e-as the audible" signal in'the 'circuit'shown' in Fig, 3

It 'is' to 'be understoodthat the signaling" facilities' illustrated'in Figs: 1, 2; 3; 4, 5- andfdmay be used not only as" replacements for the regular ringer equipment located at a subscribers. station, but also maybehousediin'a'separate'container as an extension set' and" located at a point remote from thesubscribers' telephone, if conditions warrant it.

In Fig. lthereis shown at llla'sourcje'of'machine ringing currentwhich is generally l'ocated at'a, central office. The telephoneline extending from the central'offioe' to a" subscribers"station comprises the tip and'ring'conductors H and" [2, respectively. The equipment shown'to theright of the source l-Ui ashereinbeforeindicatedmay replace the regularringer equipment at the subscribers 'stationcr may be housed in aseparate container and located elsewhere' on the premises as an'extension' set. For descriptive purposes-only, itwill be assumed-that this;ec1uipn'ient replaces the usual ringer 'equipmen-ta. As. the station a ringer tarot well-known design is: connected =acro'ss" two branch circuits each of which is bridged across the tip and ring conductors l l and I2 of the subscribers line. One circuit includes a dry rectifier M, a resistance l and a condenser H5. The other circuit includes a dry rectifier I! and a condenser IB. One ringer terminal is connected to a point between the resistance l5 and the condenser-I6, while the other terminal of the ringer is connected to a point between the rectifier IT and the condenser IS. The rectifiers l4 and I! are poled oppositely. A slow-to-operate switch is is connected across the tip and ring conductors l l and ii of the subscribers line in series with a condenser 20 and a current limiting resistance 2 l. The armature and contact of the switch or relay [9 are so connected in the circuit that they effectively short-circuit the rectifier I! when the relay is fully operated.

The rectifiers l4 and l! and the condensers l6 and I8 are so interconnected with respect to the ringer l3 that they function as a voltage doubling arrangement. In accordance with the theory of operation of the voltage doubling arrangement, the condensers l6 and I8 are alternately charged from the alternating current from source Ill to the same polarity through the rectifiers H and. I4, so that voltages approximately equal to the peak value of the alternating current source are maintained across each condenser. Since the condensers I6 and I8 are in series with respect to the ringer i3, the ringer is subjected to an operating direct current voltage substantially equal to twice the voltage of the alternating current source and this voltage is maintained as long as the alternating current is applied. Since, by design, the ringer is the well-known polarized type of device, it operates upon the application of the machine ringing source to the line to cause its clapper to strike one of its associated gongs. When the signaling current is interrupted, the ringer is deenergized and the biasing spring of the ringer restores the clapper to its normal position against the other gong causing the said other gong to be actuated. Thus, if the ringing current is connected to the line for two (2) seconds and disconnected therefrom for four (4) seconds in accordance with usual practice, each gong of the ringer will be struck once every six (6) seconds. This operation of the ringer produces an audible signal of low attention-arresting quality.

Before proceeding further with the description of the operation of the circuit shown in Fig. 1, it may be well to refer to Figs. 8 and 9 which illustrate a preferred form of slow-to-operate switch which may be used as the slow-to-operate switch conventionally illustrated at IS in Fig. 1.

The switch shown in Figs. 8 and 9 functions to effect a circuit closure in response to a predetermined number of spaced impulses impressed on its winding.

The structure of this switch includes a sealed vertical tube 80 having a pool 8| of mercury in the bottom and a hollow cylindrical armature 82 open at the top and closed at the bottom except for a small orifice 83. In its normal position, as shown in Fig. 8 the bottom of the armature is forced down against the surface of the mercury pool 8| by mean of a limiting stop 84 so that a small portion of the mercury rests within the armature 82 and in physical communication, through the small opening 83 in the bottom, with the remainder of the mercury mass in the tube below. One terminal 85 of the switch projects down from the top of the tube into the interior of the armature while the other switch terminal 86 projects up from the bottom of the tube into the mercury mass 8|. When the operating coil 81 of the switch is energized for an interval by a pulse of current from the machine ringing source the armature 82 is forced down against the mercury pool 8|, causing a corresponding amount of the mercury to flow up through the orifice 83 into the armature. On the next open period of the coil, the forces of surface tension in the mercury cause it to flow back through the orifice, moving the armature upward toward its normal position. By choosing the length of the current impulses and the length of the spacing between them, the level of the mercury within the armature may be made to rise and fall successively, each rise exceeding somewhat the succeeding fall, thus causing the surface of the mercury within the armature to approach stationary terminal 85. After the desired number of impulses have been received, the surface of the mercury engages the end of the contact 85 and clings thereto by adhesion. On the succeeding fall of the mercury level, the force of adhesion causes the mercury body to become displaced so as not to break the contact that has been established. On the next few succeeding interruptions in the operating current the level within the armature may fall somewhat below the stationary terminal, but the adhesion of the mercury to the terminal serves to maintain constant engagement until the general level of the mercury rises above the end of the terminal and the armature reaches its full downward position. Thus the circuit once established is safeguarded against opening. Obviously, when the energizing source is disconnected for any appreciable time the armature restores to its normal position and the circuit is opened.

Reverting back to Fig. 1, the slow-to-operate switch just described responds in a step-by-step manner to the successive applications of signaling current to the line and after a predetermined number of such applications, the switch contacts are closed to effectively short-circuit the rectifier I1. Thus, the ringer is subjected to periodic impulses of one polarity which traverse the rectifier l4, resistance l5, ringer l3 and condenser 18, whereupon each gong of the ringer is struck once for each half-cycle of current passed by the rectifier l4. One gong is struck upon the application of each half-cycle of current to the line and the other gong is struck between successive half -cycles of the same polarity by virtue of the clapper restoring action of the ringer biasing spring.

Thus the ringer I3 is operated to emit a preliminary audible signal of low attention-arresting quality and, after a predetermined interval of time, that is, when relay I9 operates, it is operated to emit a secondary audible signal of greater intensity. When the subscriber responds to the signal, the ringing current is tripped in the wellknown manner whereupon the ringer I3 is silenced and the switch l9 restores to normal.

The condenser 20 in series with the winding of the switch [9 is used for direct current blocking purposes. The resistance I 5 is provided to reduce the over-all shunting eflect of the condenser 16 when the switch I!) operates to short-circuit the rectifier H.

For purposes of simplicity, the telephone sets at the subscribers stations of Figs. 1, 2, 3, 4, 5 and 6 have not been illustrated.

The circuit of Fig. 2 is substantially identical to that of Fig. 1, except that the slow-to-operate relay '29 is provided with a transfer contact arrangement so that when the relay operates, the circuit to rectifier 24 is opened, the rectifier 21 is shortcircuited and the ringer 23 is connected directly across the line by way of the front contact and armature of relay 29.

The preliminary signal emitted by the ringer 23 is identical to the preliminary signal emitted by ringer !3 (Fig. 1), but the secondary signal is produced by both half cycles of applied current since both rectifiers 24 and 21 are rendered ineffective by the operation of switch 29.

While the switch illustrated in Figs. 8 and 9 is not shown equipped with a transfer contact and therefore would not function in Fig. 2, it is to be understood that any slow-to-operate switch having armature controlled front and back contacts will serve in its place. The particular design of slow-to-operate switch does not, of itself, constitute a part of thepresent invention and the design illustrated in Figs. 8 and 9 has been described merely as an example of one type of switch particularly suitable for use in the circuits of Figs. 1, 4, 5 and 6.

Fig, 3 illustrates an arrangement whereby the preliminary ring is at a twenty-cycle rate on only one gong of the ringer, twenty cycles being the frequency of the alternating current source included in the machine ringing supply in. For

'this purpose a ringer of the design illustrated in Fig. may be used. This ringer is similar in design to the ringer illustrated in United States Patent 2,269,108 to J. D. Hubbell and C. F. Wiebusch and diifers therefrom in that the leaf spring 9!] is placed on the stop side of the armature air-gap; in other words the spring 90 is positioned on the ringer structure to oppose the normal bias spring 9| and to leave a small space at 92 available on the stop side.

A gas-filled tube 3| is connected in series with the ringer33 by way of a current limiting resistance 32 and is poled to pass pulses through the ringer in such a direction as to pull the armature up on the stop side, that is, so as to cause the clapper to strike gong 93 (Fig. 10). This produces a low volume ring on this gong as a preliminary signal of low attention-arresting quality. The relay, or switch 34, functions after a predetermined interval of time to effectively short-circuit the rectifying tube 3| and to connect the ringer 33 directly to the line by way of the condenser 35. The ringer then functions in a manner such that both gongs are struck by the ringer clapper. The tube 3|, when activated also acts as a preliminary visual signal.

The resistance 36 and condenser 31 in circuit with the winding of switch 34, serve the same purposes as do resistance 2| and condenser 20, respectively, of Fig. 1.

While Fig. 4 is substantially identical to Fig. 3, it is intended to illustrate the use of a glow lamp 4| which is non-rectifying in its operating function, whereas the tube 3| of Fig. 3 functions as a rectifier to control the sound signal emitted by the ringer 33. In Fig. 4 the tube 4| is connected in series with ringer 43 and functions as a visual signal when the ringing source In is connected to the subscriber line. After a predetermined time interval the delay switch 44 operates to short-circuit the visual signal 4| and to connect the ringer 43 directly to the line whereupon the ringer operates in a normal manner to give forth a secondary audible signal. It will be noted that the current which traverses the visual signal 4| alsopasses through the ringer so that the ringer may function as a preliminary audible signal if the magnitude of the current is sufiicient to cause the operation of the ringer clapper. However, the ringer under this condition will operate only in a subdued manner. By adjusting the value of the tube current the operation of the ringer as a preliminary audible signal may be prevented, if desired. 7

Fig. 5 distinguishes from Fig. 4 essentially only in the substitution of a resistor 54, having a negative temperature coefiicient of resistance, for the slow-to-operate switch 44 of Fig. 4. The resistor 55 is connected in parallel with the lamp 5| and in series with the ringer 53. The characteristics of this resistor are such that when it is cold its resistance is so high as to prevent sufiicient current to pass through the ringer 53, but with the passage of time, its resistance drops to a negligible value and the ringer operates at full intensity. When the resistance of resistor 54 reduces to a negligible value the lamp 5| is effectively short-circuited. The same types of signals are obtained from the circuit arrangement of Fig. 5 as are obtained from th circuit arrangement of Fig. 4.

In some cases it may be desirable to provide a preliminary visual signal of greater intensity than can be obtained with the visual signal devices mentioned hereinbefore. The circuit of Fig. 6 provides such a service. In this showing the subscribers line is bridged by two ringing current responsive circuits each including a condenser '|0| or I92, a slow-to-operate relay M3 or 'IM, and a current limiting resistance I05 or I06. Relay )3, when operated, connects the ringer it] in series with condenser Hi3 across the line. Relay Hi4, when operated, connects the lamp signal N39 to a local source of power. The relays H13 and W4 may be of the type shown in Figs. 8 and 9 and adjusted so as to have different time operate characteristics. With the relay H14 adjusted to operate quicker than relay m3 it is obvious that upon the application of ringing current to the line for a brief interval of time the lamp I09 will be lighted as a visual signal of relatively high intensity. Subsequently, relay I03 operates .to connect the ringer to the line causing it to give a secondary audible signal. When the call indicated by the operated signals is answered the ringing current is tripped in the well-known manner and the signals are rendered inoperative.

The signaling arrangement shown in Fig, 6 may be modified in accordance with the requirements of th subscriber to provide, for example, the usual ringer signal followed by a visual signal.

'In this case the extension set would supplement the normal set and would include the condenser Iii-l, slow-to-operate relay I33, current limiting resistance I05, all connected across the line, a lamp signal I09 and a power circuit control relay. The normal ringer would respond to the incoming signaling current to give th usual audible signal and the slow-to-operate relay me would, after a predetermined interval of time, operate to connect the power circuit control relay to the line so as to subject it to the incoming signaling current. This relay responds to the incomin ignaling current to complete a local power circuit which includes the lamp signal [09. Thus, if the normal ringer signal is not answered within the predetermined interval of time, the lamp signal would be actuated to provide a secondary visual signal. Such a lamp signal could be located at some distance from the telephone with which the normal ringer is associated, if desirable;

Obviously, the signaling arrangement of Fig. 6,

agaspov as well as those of the preceding figures maybe used as substitutes for the regular signaling device at a telephone station or may be housed in separate containers as extension sets for location elsewhere on the subscribers premises and to supplement the regular ringer at the subscribers station. In the latter case, the regular ringer would respond immediately to the ringing current applied to the line and if the call is unanswered, the ringer signal would be followed by the operation of the visual signal 109 and of ringer 101 in that order at the locality of the extension set. It is to be understood that the extension sets may be located anywhere in the subscribers premises and need not be closely associated with the subscribers telephone.

The arrangements thus fardescribed illustrate various means for obtaining time-spaced telephone call signals of diiferent attention-arresting qualities. It is apparent that the various signals may be combined in manners other than those described. It is also apparent that the facilities described are particularly suitable for installation as extension sets and also as substitutes for the regular signaling equipment located at a subscribers station.

In Fig. 7 several of the ringing facilities previously described are illustrated as housed in a separate housing constituting an extension set with switching means for connecting the various elements to the subscribers line in different combinations. The arrangement illustrated serves primarily as a means for conveniently demonstrating to a prospective subscriber several different types of signals which are available to him and which embody the idea of providing a preliminary signal of low attention-arresting quality followed by a signal of greater intensity. The manual switching devices are represented by broken lines terminated by an arrow-head.

To the left of the broken line box shown in Fig. 7 there is indicated the regular machine ringing source 69 which is located at a central office and which, in a well-known manner, is connected to the line conductors El and 62 extending to a subscribers station. The manually operable switching devices are designated 1, 2, 3', 4, 5, 6, l and 8. If it is desirable that the subscribers station be furnished with the regular audible type of signal only, the switch 8' would be closed to the point 8 on the line conductor 61 and all other switches illustrated would be opened. Under this condition the ringer 53 would respond to the application of signaling current from the source 51! to the subscribers line {ii-52, inthe well-known manner, and its operation would cease when the ringing current was tripped in the usual manner when the subscriber answered the call.

Should it be desired that a visual signal be provided which responds to the incoming ring at the same time that the ringer 63 operates, then the switch 6 would be closed to the point 5 on the line conductor 6! to effectively connect the gas tube 5 2 in parallel with the ringer 63 across the line. Obviously, both the ringer 63 and the tube 64 respond simultaneously to the signaling current from the source 633 to provide both audible and visual indications of an incoming call.

To provide a subdued audible signal only, switch 8 is operated to the-point 2, switch 3 to the point 3 and switch 4 to the point 5, and all other switches are opened. Under these conditions the rectifiers 65 and 58, condensers 61 and 6B and the ringer 59 are connected across the.

line 61-62, as a voltage doubling arrangement similar to that shown in Fig. 1, except that the slow-to-operate switch '19 is not connected to alter the signal after the elapse of a predetermined interval of time. This circuit arrangement results in the operation of the ringer 69 in a manner such that each ringer gong is struck once every six seconds, assuming the ringing current to be connected to the line for two seconds, and disconnected therefrom for four seconds, as described in connection with Fig. 1. V

The subdued signal described in the preceding paragraph may be followed by a sound signal of greater attention-arresting quality by operating switch 7' to the point I and switch 2 to the point 2. Thus with switches l, 2', 3', 4 and I operated, the circuit arrangement shown in Fig. 1 is effected, and as described in connection with Fig. 1, the ringer functions first, to emit a sound signal of low attention-arresting quality as a preliminary signal and then, after a predetermined time interval, it functions to give forth a signal of greater intensity.

With switch 6, switch I, and switch 2 closed to their respective contact points 6, l and 2 and all other switches open, the tube 64 would function as a preliminary visual signal and after a predetermined time interval, switch 10 would function to connect the ringer t9 and condenser 68 across the line to cause the ringer to emit an audible signal.

By operating switch 8' in place of switch 6 in the previous paragraph, the ringer 63, which may be adjusted to produce a signal of reduced sound intensity would operate as a preliminary audible signal of low attention-arresting quality and after a predetermined time interval the switch 10 would function to connect the ringer B9 in circuit.

The ringer 63 is illustrated in Fig. 7 as being connectable to the line through the medium of a switch 8"merely for purposes of simplification of the description of the various combinations of signals obtainable. Actually this ringer would be permanently connected to the line at a subscribers station in the well-known manner,

' and in demonstrating the possibilities of the extension set and of the signal combinations obtainable thereby the normal connection of the ringer at the telephone set would be opened, or closed as desired.

What is claimed is:

1. The combination, in a signaling system, of

a line, a source of current, a signal device, means connecting said signal device to said line by way of a branch circuit having electric characteristics such that said signal device is caused to operate in a particular manner as a preliminary signal when said source of current. is connected to said line, and electromagnetic time delay means responsive to current from said source for altering the electric characteristics of said connecting means, whereby said signal device is caused to operate in a different manner by current from said source, as a secondary signal,

2. In a telephone signaling system, a line circuit, a station thereon, a signal device at said station, a source of signaling current, a circuit normally connecting said signaling device to said lineand in which said signaling device operates in a particular attention arresting manner upon the application of current from said source to said line, and electromagnetic switching means responsive to the application of current from said source to said line and efiective a predetermined interval of time after the said application for altering the electric characteristics of said normally connected circuit, whereby said signaling device is operated in a different attention arresting manner by current from said source.

3. In combination, a station, an audible signal device at said station, a line on which said station is located, a source of Signaling current, a current rectifying device, a circuit bridged across said line including said signal device and said current rectifying device, and time delay means responsive to current from said source when applied to said line, for efiectively excluding said current rectifying device from said bridged circuit.

4. In combination, a station, an audible signal device at said station, a line on which said station is located, a source of signaling current, a circuit connecting said signal device to said line comprising a pair of parallel arms connected across said line, each arm including a half-wave rectifier and a condenser and each having a point intermediate its respective rectifier and condenser to which opposite terminals of said signal device are connected, a time delay device responsive to current from said source when applied to said line, and means controlled :by said time delay device for efiectively connecting said signal device to said line independent of said rectifiers.

5. In combination, a line, an audible signal having an operating winding, a source of signaling current, means connecting said audible signal to said line comprising a voltage doubler of the rectifier type consisting of two series circuits each including a unidirectional current conducting device and a condenser connected across said line with the winding of said signal device connected between said circuits to a point in each circuit between its respective unidirectional current conducting device and condenser, and means responsive to the application of current from said source to said line for a predetermined interval of time for short-circuiting one of said unidirectional current conducting devices.

6. The combination, in a signaling system, of a line, a ringer comprising a pair of gongs, a striker, a restoring spring for said striker and an operating winding, a source of alternating signaling current adapted to be connected to said line at repeated time intervals, circuit means connecting the operating winding of said ringer to said line and including rectifying means which function to cause the operating winding of said ringer to be energized once for each application of current from said source to said line, whereby said striker actuates one of said gongs for each application of current to said line and actuates the other gong, under the restoring action of said spring, for each disconnection of said source of current from said line, and means operating in response to a predetermined number of applications of current from said source to said line to disable the rectifying means of said circuit connecting means whereby said striker functions to repeatedly actuate both said gongs during each application of current from said source to said line.

7. The combination, in a telephone signaling system, of a telephone line, an electromagnetically operated ringer connected to said line, a source of signaling current, rectifier means connected in circuit with said ringer for causing said ringer to operate in a particular attention arresting manner in response to the application of current from said source to said line, and other means responsive to current from said source for altering the connection of said rectifier means to said ringer whereby said ringer is caused to operate in a difierent attention arresting manner in response to an application of current from said source to said line of a predetermined time duration.

8. In combination, a line, a source of machine ringing current connected to said line for intermittently applying signaling current therefrom to said line, a signal on said line, circuit means connecting said signal to said line and having. characteristics such that said signal operates in a characteristic attention arresting manner on each application of signaling current to said line, and electromagnetic switching means responsive to a predetermined number of applications of current from said source to said line for altering the characteristics of said circuit connecting means whereby said signal operates in a different characteristic attention arresting manner on applications of current from said source to said line in excess of the said predetermined number.

9. The combination, in a signaling system, of a line, an audible signal device associated with said line, a source of signaling current, a circuit connecting said audible signal device to said line and including an element normally electrically in circuit with said audible signal de vice to cause said signal device to operate in a distinctive manner as a preliminary signal upon the application of current from said source to said line, a slow operating electromagnetic switching device connected to said line so as to be subject to current from said source, and means controlled by said switching device when operated for abruptly altering the normal connection of said element with said signal device whereby said signal device is caused to operate in a different distinctive manner as a secondary signal.

EDWARD M. BOARDMAN.

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

UNITED STATES PATENTS Number Name Date 2,332,448 Inglis Oct. 19, 1943 2,151,726 Allen Mar. 28, 1938 2,180,334 Bredehoft Nov. 21, 1938 2,291,615 Ferrell Aug. 4, 1942 2,302,544 Halligan Nov. 17, 1942

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