US1396888A - Railway signaling system - Google Patents

Description

C. F. SCOTT. RAILWAY S'IGNAUNG SYSTEM. APPLICATION FILED DEC. 29, I9l5.- RENEWED JUNE 9,1920.

Patented Nov. 15, 1921.

3d INVENTOR /e: f' Swfi' WITNESSES ATTORNEY UNITED STATES PAJENT OFFICE.

.CHARLES F. SCOT'I'QOF NEW HAVEN, CONNECTICUT, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY A CORPORATION OF PENNSYLVANIA.

RAILWAY SIGNALING SYSTEM.

Specification of Letters Patent.

Patented Nov. 15, 1921.

Application filed December 29, 1915, Serial No. 69,175. Renewed .Tune 9, 1920. Serial No. 387,801.

ductors and means for minimizing the inductive disturbances that may be imposed on adjacent electrical circuits by reason of the power currents flowing in the railway systems. t i In alternating-current railway systems, it is usual to insert insulating joints at suitable points in the rails in order to provide insulated block-sections for the signaling systems. Each of these block-sections constitutes a section of the track that is protected by an indicating device which may be a semaphore or any other convenient signaling means. The operation of this signaling device is usually effected by means of a relay excited by signaling currents that are confined to the separate block-sections and are derived from a source of power independent of that furnishing the propulsion currents.

In order that the propulsion currents may flow over the tracks of a multi-track railway system, impedance bonds are usually inserted on'each side of the insulating joints defining the block sections of each traclc and are connected between the track-sections and tracks in such manner that the propulsion currents will normally divide themselves be tween the rails of the several tracks.

Adjacent impedance bonds are intercom nected by means of taps disposed at the mldpoints of their windings so that the propuL sion current from one rail traverses one-half of each winding in one direction, and the current from the other rail traverses the other half of, the. winding in the opposite direction. Since the currents in the two halves ofthe windings neutralize each other in their magnetizing action on the core members of the impedance bonds, the propulsion currents are afforded a path of low rl ilb pedance for their flow along the track. lhe

several tracks are connected to one another the signaling relay which, in turn, controls the operation of the signaling device to indicate the conditions obtaining upon a particular block-section of the railway system.

In alternating-current railway systems, it is desirable to provide means for minimizing the inductive disturbances that may arise from the flow of the propulsion currents therein. A very effective means for accomplishing this object contemplates the inser tion of a number of series transformers at spaced intervals in a railway system, the primary windings of the transformers being connected in series-circuit relationship with thetrolley or third-rail conductor, and the secondary windings thereof being connected through impedance bonds to the track rails and in shunt to the aforementioned insulating joints positioned in the rails. By confiningthe return flow of the trolley current to the track the inductive effects arising from the current flow over the trolley conductor are substantially neutralized. This system for minimizing inductive interferences is fully described in my co-pending patent application, Serial No. 170, filed January 2, 191.5, and which matured into Patent No. 1196,5300, Aug. 29, 1916. By inductively interlinking the track and the trolley conductor, as mentioned above, electromotive forces are impressed at intervals in the track which compensate for the m1- pedance of the track and serve to confine the flow of the propulsion currents to the track in preference to the earth. If it is desired to interconnect the tracks of a multi-track railroad system at points near the middle of the block-sections, it will be necessary to confine the alternating currents adapted to op crate the signaling apparatus to the separate block-sections in order to afford the proper protection to the traffic accommodated by the railroad. Therefore, in conjunct1on with the above-mentioned means for minimizing propulsion currents.

the inductive interferences, I also provide means for permitting the signaling currents to flow substantially unimpeded in each of the block-sections of the several tracks, at the same time, insuring that the signaling currents of the separate block sections be maintained independent of one another.

, An object of my invention is to provide means, in a multi-track railway system in which the block-sections of the separate tracks are not correspondingly positioned,

for dividing each track circuit into a plurality of block sections for signalmg purposes without breaking the electrical conof the trolley currents to the tracks so as to minimize the inductive disturbances that may beimpressed upon any adjacent electrical circuit, such as an intelligence-transmission circuit.

F or a better understanding of the nature and scope of my invention, reference may be had to. the following description and the accompanying drawing in which the single figure is a diagrammatic representation of a railway system embodying a form of my invention.

Referring to the drawing, a source of alternating current (not shown) supplies propulsion currents to trolley conductors 1 and 2 and to their associated tracks 3 and 1, respectively, the latter, in combination, constituting a path for the return flow of the Spaced insulating joints 5 are inserted at intervals in the trolley conductor 1, and correspondingly positioned insulating joints (S' are inserted in the trolley conductor 2. His presumed that the block sections comprising the insulated track-sections are not correspondingly placed in the tracks 3 and at, and, for convenlence, I

. assume, in this instance, that the ends of the block sections of the track 3 are substantiallypositioued at the mid-points of the block sections of the track 1. Insulating joints 7 are inserted in each of the rails of the track 3 at spaced intervals to define the block sections thereof, and other insulating joints 7 of the track 4 are arranged in staggered relationship to the insulating joints 7 of the track 3 to define the block sections of the track 1. Insulating joints 8 are inserted in each of the rails of the track 3 at points corresponding to the location of the insulating joints 7 of the track 4: and, similarly, insulating joints 8 of the track 4: are inserted at points corresponding to the location of the insulating joints 7 of the track I). It is apparent, therefore. that the block sections of the tracks 3 and 4 are disposed in staggered relationship with respect to one another. I propose, however, to interconnect the tracks to each other both at the ends and the mid points of the block sections aiuh at the same time, to inductively intcrlink the trolley conductors and the tracks to each other in order that the return flow of the propulsion currents may be confined coujointly to the tracks.

Each of the track sections intermediate the insulating joints 7 and 7 of the tracks 3 and at respectively, constitutes a block-section of the signaling system, each block section being provided with a signaling device 9 and a track transformer 10, a primary winding 11 of which is connected to mains 12 of the signaling supply circuit, and a secondary winding 13 of which is connected across the rails of a track section. As this is a usual arrangement for the signaling system. further explanation thereof is not deemed necessary.

Adjacent to each other and on both sides of the insulating joints '7 and 7, impedance bonds let and 14, respectively are inserted, which comprise currcnt-carrying windings provided with taps 15 and 15, respectively, at their mid-points.

An intelligence transmission conductor 16, shown as a telegraph circuit, is disposed in proximity to the trolley conductors 1 and 2 and the tracks 3 and at and is, therefore, under the inductive influences arising from the power currents flowing in the railway system. It is important, therefore, to minimize the inductive disturbances that may be impressed upon the conductor 16 in order to insure satisfactory operation of the tele graph circuit. At the same time, the tracks are interconnected with each other in order to provide a return conductor of low impedance for the propulsion currents. In addition, it is to be understood that the signaling devices 9 must operate independently of one another in order to amply protect the railway trafiic accommodated upon the railway system. To this end, transformers 17 and 18 are provided, each of which comprises a plurality of windings that are connected to the railway circuits, as will be here inafter described.

Since the railway circuit comprising the trolley conductor 1 and the track is similar in all respects to the other railway circuit, my description will be confined to the operation of the former.

Referring particularly to a block section 19 formed in the track 3, it will be noted that the insulating joints 8 are inserted substantially midway in the block section. Since the signaling currents for operating the signaling device 9 mustbe shunted across the 1nsulating joints 8, mutually inductivelyrelated windings 20 and 21 are connected :be substantially unimpeded. A winding 26,

wound on the same core member as the windings 20 and 21, is connected across the insulating joint inserted in the trolley conductor 1, and asecond winding 26 is a connected to the trolley conductor 2 in shunt rated with the track 4, and vice versa.

to the insulating joint 6 which corresponds to the insulating joint 5 of the trolleyconductor ,1. A secondary winding 27 is connected, in a usual manner, through impedance bonds 14: to the track 4. The windings 26 and 27 constitute primary and secondary windings, respectively, of a series transformer that inductively interlinks the trolley conductor 2 with the track 4. y This series transformer may be considered as being embodied in the transformer 18 which, for convenience, comprises a single core member (not shown) having the windings --21, 26-26 and 27 wound thereuponin proper relationship, as hereinbefore explained.

Reference may now be had to the transformer 17 whichresembles the transformer 18 in all-respects, with the exception that those transformer windings of the transformer 18 which are associated with the track 3 are, in the transformers 17, associ I For instance, windings 20 and 21 are connected across the insulating joints 8 of the track 4., the winding 20 being provided with a tap 22 disposed at its mid-point and connected through a conductor 23 to one ter minal of an impedance coil The winding 21 is similarly provided with a tap 22 which is connected a conductor 24 to the other terminal of the impedance coil 25. A primary winding 26 is connected in shunt to the insulating joint 5 of the trolley conductor 1, and a secondarywinding 27* is connected to the mid-points of impedance bonds 14' which are disposed 011 both sides of'the insulating joints 7 in the track 3. Another winding 26 corresponding to the winding 26 of the transformer 18, is connected in shunt to the insulating joints 6 of thetrolley conductor 2. From the foregoing description, it will be noted that the trolley conductors 1 and 2 are inductively interlinked at alternate points with the track 3 and with the track 4.

It will be understood that, when the return propulsion currents are allowed to flow through the ground, a very large inductive loop is thereby formed and that the inductive interference with any nearby intelligence-transmission conductor therefore tends to become excessive. By dividing the propulsion currents, in the manner hereinafter to be described, among the various tracks of the railway system, I, am able to materially reduce the size of the inductive loop formed and subsequently decrease the amount of inductive interference.

As-mentioned above, the two tracks 3 and 4- areelectrically interconnected to pro vide a return conductor of low impedance for the propulsion currents, and this is effected through the impedance coils 25 and 25. To illustrate: The winding of the impedance coil 25 is provided with a tap 28 at its mid'point which, in turn, is connected by a conductor 29 to a mid-point tap on the winding 27, the latter being connected throughithe impedance bonds 14k and 14 to the track 4;. Similarly, the winding of the impedance bond 25 is provided with a tap 28* at its mid-point which is connected, by

a conductor 29, to a mid-point tap 30 of the winding 27, the latter being connected through impedance bonds 14: to the track 3. Assume that alternating propulsion current is traversing the track 3. By reason of the discontinuity of the rails of track 3, be-

causeof the insertion of the insulating joints 8, a portion of this current will traverse the entire length of windings 20 and 21 and the other portion will traverse simulta-neously portions only of the windings 20 and 21 in its endeavor to bridge the insulating joints 8. The mid-points of the windings 20 and '21, as explained above, are connected to the terminals of the impedance coil 25, the mid-point 28 of which is connected, through the conductor 29, to the mid-point 30 of the winding 27.

By reason ofthe relatively high impedance offered by the windings 20 and 21 to the flow therethrough of alternating currents traversing the two rails of the track 3 in the same direction, a portion of these currents will take the path afforded by the conductors 23 and 24, extending respectively from the mid-points of the windings 20 and 21, the winding 25, which offers substan tially zero impedance, and the conductor 29 to the mid-point 30 of the winding 27.

The terminals of the winding 27 are connected to mid-points 15 and 15 of the impedance bonds 14 and 1 1 that are connected across the rails of the track 1. By introducing propulsion currents from the track 3, as explained above, through the conductor 29, the mid-point 30 of the winding 27 and either the mid-points 15 or 15 of the impedance bonds 14 and i i, respectively, the currents are permitted to flow to the track el, which is desired, since the two tracks 8 and 4 are thus electrically connected to each other to furnish conjointly a return path of low impedance for the propulsion currents. The impedance coils 25 and 25, therefore, furnish means for interconnecting the mutually inductively related windings Q0 and 21 of the track 3 and the mutually inductively related windings 20 and 21 of the track 4 to the secondary windings 2? and 27 respective y, of the tracks 3 and i. As a consequence, the tracks 3 and i are electrically connected to each other, as regards the propulsion currents, but the separate block-sections of the tracks are maintained electrically independent of one another, as regards the signaling currents.

Assuming that the block section 19 is open to traiiic, the signaling device 9 indicates an open block since the signaling currents traverse freely the mutually inductively related windings 20 and 21 of the transformer 18 by being oli'ered negligible impedance only. The signaling currents flowing simultaneously and in opposite directions through the said windings neutralize the inductive effects that would necessarily be occasioned by a uni-directional current flow therethrough. The impedance coil 25, while connectel. across the windings 20 and 21, precludes the flow therethrough of the signaling currents, inasmuch as it acts in the same manner as the impedance bonds 14. The signaling currents, therefore are forced to flow through the associated relay of the signaling device 9. l'ZVhen a railway train, such as indicated at 31, bridges the block section 19, the signaling currents are shunted through the trucks oi the train, thereby short-circuiting the signaling device 9 which operates to indicate that a train occupies the block 19. it will be noted that the impedance bonc s i l" cenfine the signaling currents to the insulated blocir section 19, thereby pemitting each block section to be operated independently of the others The propulsion currents supplied to the train 31 will traverse the primary winding 26* of the transformer 17', and the primary winding 26 or" the transformer 18, wiich windings are connected across the insulating joints 5 inserted in the trolley corductor 1. The flow of the trolley currents through the primary windings of the trans formers l7 and 18 will induce compensating electromotive "forces-in the secondary windings whereby the return flow of the propulsion currents may be confined to the tracks 3 and 4. The secondary winding 2'? directly connected to the track 3 through the impedance bonds 14- {LHCh consequently, the return flow of a portion of the propulsion currents may be directed theretlnough in the 1 graph circuit 16.

usual manner. The propulsion currents flowing from the train ill will return through each of the rails ot the block section 19 and through at least a portion ol? the windings 20 and Eli which, as before mentioned, are connected across the insulating joints 8. Under the particular conditions assumed, substantially one-half of the propulsion currents may ilow through the whole of the windings 20 and El and return through. the track 2. The other hall of the propulsion currents may flow simultaneously from the taps 2 and 522 along the conductors Q3 and 24: and oppositely thrmrgh the winding of the in'ipedance coil 25 lo the mid-point tap 28. From the tap 28 they may iiow through the conductor 29 to the tap of the secondary winding 27 and then traverse one-halt oi the secondary winding 2'? to the impedance bond i l by means of which they are directed into the rails ot the track 4. The portion of the pl'Ol'llllsion current flowing through the impedance coils 25 and 25 will be oll'erod negligible impedance since the induction resulting from the oppositely-directed current flow therethrough is substantially neutralized. It will be noted that the t'ans'liormers 1'? and is provide means itCl interchanging the current flow in the tracks 3 and 41-, inasmuch as the transformers l7 and 18 are similar, in all respects, the corresponding windings thereof, however being connected to the di llcreut railway circuits, as liQI'OllllIlQfOlO explained It may be desimhlc, under certain operating conditions, to design the several circuits so as to have a uniform impedance pe' unit length of track. In this manner the return how of the propulsion currents will he suhstal'itially equally divided between the tracks and a which results in providing a return conductor 05 very low impedance. This apparent by considering that the trolley or primary currentsupplicd to the train 31 will flow through the primary winding 9.6 of the transformer 18, necessiorting that a portion of the return current llow through the coils 20 and 21. (hie-hall" ol the return current will. in this instance, return through the track 3, and the other hal t of the propulsion current will llow through portions only of the coils Q0 and 21 to the mid-point taps 22 and 22 by means of which it is conducted to the track From the foregoing description, it will he observed that the return flow ol the propulsion current is confined to the tracks, thereby minimizing the inductive disturbances that may be impressed upon the telei\ t the same time. each block .l'eii lOll is electrically continuous to the signaling currents and provides a path ol low impedan .:e therefor. Moreover, the tracks 3 and -l are electrically intercmmectml in order that tl'iepropulsion currents may arranged in staggered relationship in the tracks, and insulating joints inserted at corresponding points in both tracks, of means for-inductively interlinking each trolley conductor to its associated track, mutually inductivelyrelated windings for bridging the insulating joints positioned at intermediate points in the block-sections, andequal ining means for equalizing the return flow of the propulsion currentsin the twotracks,

said equalizing means comprising inductively related coils: connected" between said tracks and, in turn, inductively interlinked with said means whichwserve to interlink said trolley conductor and said track;

In an electric railway system, the combination with two tracks each having an associated trolley conductor and comprising a plurality of insulated block sect1ons, and insulatin joints which are arranged in stag:

gered re ationship with respect to one an other in thetracks inserted in the rails intermediatethe ends ofthe block sections,of current-carrying windings connected in shunt to said insulating joints and being mutually inductivelyfrelated to one another, and impedance coils having theirterminals connected to the mid-pointsof said currentcarrying windings of one track and their midpoints connected to the other track. i

3. In an electric railway system, the combination with two tracks each having an associated trolley conductonsaid tracks comprisinginsulated block sections whichare arrangedin staggered relationship in the tracks a and insulating joints inserted at correspondingpoints in both tracks, of trans formers located at the insulating joints in a the tracks, said transformers COIDPI'lSIIl w ndings for inductively interlinkingbot trolleyconductors alternately to said tracks,

a and mutually inductively related windings for bridging the insulating joints positioned inthe rails intermediate the ends of the a block sections, and impedance coils having theirterininals connectedto the mid-points of alternate groups of said mutually inductively related windings and their mid-points connected alternately to the mid-points of the aforementioned windings associated with the tracks wherebythe return flow of the propulsioncurrents in the tracks may beequal 4:. In an electric railway system, the combination with two tracks each having an associated trolley conductor, said tracks comprising blocksections which are arranged in staggered relationship with respect to one another in the tracks, and insulating joints in serted at corresponding points in both tracks and both trolley conductors, of transformers for inductively interlinking the trolleys and tracks to one another comprising means for bridging the insulating joints at intermediate points in the block-sections, and equalizing means for equalizing the return flow of transformers located at the insulating joints for inductively interlinking both trolley conductors with the tracks, said transformers comprising mutually inductively related windings for bridging the insulating joints intermediate the ends of the blocksections, and equalizing means for electrically interconnecting said tracks to each other whereby the return flow of the propulsion currents may be divided between both tracks, said equalizing means comprising inductively related coils connected between said tracks and, in turn, inductively interlinked withsaid means which serve to interlink said trolley conductor and said track.

6. In an electric railway system, the combination with two tracksez-ich having an associated trolley conductor, spaced insulating joints insertedat corresponding points in the tracks and the trolley conductors,"and impedance bonds connected to each track on both sides of alternate insulating joints and staggered in position with respect to one another in the two tracks, of transformers for inductively interlinking the tracks andtrolley conductors with one another, each offsaid transformers comprisinga common core member, primary windings connected in shunt to the insulating joints inserted in the trolley conductors, a secondary winding which is connected through said impedance bonds to one track and mutually inductively related windings which are connected across insulating joints in the other track, and impedance coils havingtheir terminals connected to mid-points ofsaid mutually inductively related windings and their mid points connected to mid-points of saidsecondarywindings. s a

. and also as the two sides of the signaling current circuits, the combination of a pair of tracks, eachcomprising a pair of rails, an insulating joint in each of said rails, a transformer having three windings, each of said windings havin a midtan two of said g; 1

windings being connected respectively across the insulating joints of the rails of'one of said. tracks, an induction device connected between the mid-taps of said two windings, said inductance device havinga mid-ta p connected to the mid-tap of the third winding of said transformer, and a pairo'f additional inductance devices, one of said additional inductance devices connecting the rails of the other of said tracks on each side of said insulating joints, said additional inductance devices having mid-taps connected respectively to the ends of said third transformer winding.

8. A system as specified in clainr'l', includingtwo additional windings on the transformer, a trolley conductor for each track, and an insulatingjoint in each of said trolley conductors, said additional transformer windings being connected across the insulating joints of the respective trolley conductors.

7 one of said tracks oneach side of said insulating joints, whereby the signaling currents onopposite sides of said insulating joints are rendered independent of each other, each of said inductance devices having a mid-tap, an additional inductance device connecting said mid-taps, said additional inductance device also having a midtap, bridging means for bridging the insulating joints of the other track, and means associated with the last-mentioned mid-tap and said bridging means for equalizing the propulsion currents flowing across said insulating joints'in the same direction in all of said rails.

10; A system as specified in claim 9, including a trolley-conductor for each track, an insulating joint in each of said trolley conductors, and means bridging said trolley conductor joints for confining the flow of return-current to said rails.

11. In an alternating-current railway signaling system of thetype wherein the two rails of each track serve as parallel paths for the return flow of propulsion currents and also as to the two sides of the signaling current circuits, the combination of a pair of tracks, each comprising a pair of rails, an insulating joint in each of said rails, and means comprising windings bridging the insulating joints in the respective tracks for forming a continuous path for propulsion currents and inductively related windings associated with the two tracks whereby the return flow of propulsion currents across said insulating joints is equalized in all four rails, and whereby the signaling currents in the two tracks are kept independent of one another.

12. A system as specified in claim 1.1, including a trolley conductor for each track, an insulating joint in each of said trolley conductors, and means bridging said trolley-conductor joints for confining the flow of return-current to said rails.

13; In an alternating-current railway signalingsystem of the type wherein the two rails of each track serve as parallel, paths for the return flow of propulsion currents and also as the two sides of the signaling current circuits, the combination of a pair of: tracks, each comprising a pair of rails, an insulating joint in each of said rails, a pair of inductively related windings bridging' the insulating joints of the respective rails of one of said tracks, each of said windings having a mid-tap, bridging means bridging the insulating joints of the other track, and means associated with said mid-taps and with said bridging means for equalizing the propulsion currents flowing across said insulating joints in the same direction in all of said rails.

14:. A system as specified in claim ltl. incl uding a trolley conductor for each track. an insulating joint in each of said trolley conductors, and means bridging said trolleyconductor joints for confining the flow of re turncurrent to said rails.

15. In an electrical transmission system. the combination, of two pairs of conductors adapted for the sinniltancous transmission of two separate component alternating urrents, the two conductors of each pair scrially constituting the circuit of one of said component currents and in parallel one side of the circuit of the other of said component currents, an insulating joint inserted in ouch of said conductors. a; transformer having three windings, each of said windings ha ving a mid-tap, two of saidwindings being connected respectively across the insulating joints of the conductors of one of aid. pairs, an inductance device connected between the mid-taps of said two windings, said inductive device having a mid-tap connected. to the mid-tap of the third winding of said transformer, and a pair of additional inductance devices, one of said additional inllll ductance devices connecting the conductors of the other of said pairs on each side of said insulating joints, said additional in ducta-nce devices havingmid-taps connected tional transformer windings being coni so nectedgacross the insulating joints of the res eetive third conductors.

1 In an electrical transmission system, the combination of two pairs of conductors adapted for the simultaneous transmission sorted in each of said conductors, an in duetance devlce'eonnectmg the conductors of one of said pairs on each side of the insulating joints, whereby the first mentioned component currents onopposite sides of said insulating joints are rendered independent of each other, each of said inductance devices having a mid-tap, an additional inductance device connecting, said mid-taps,

said additional inductance device also having a mid-tap, bridging means for bridging the insulating joints of the other pair of I conductors, and means associated with the last mentioned mid-tap and. said bridging means for equalizing the second mentioned component currents flowing across said insulating joints in the same direction in all j, of said conductors.

18. A system as specified in claim 17, in-

eluding a third conductor for each pair, an

insulating joint in each of said third condnctors, and means bridgingsaid third conductor joints, whereby the sum of the currents in said third conductors and the sum of the currents in said pairs of conductors 1 may be substantially equalized.

component currents and in arallel one side of the circuit of the other 0 said component currents, an insulating joint inserted in each of said conductors, and means comprising windings bridging the insulating jolnts in the respective pairs for forming a continuous path for the second mentioned component currents and inductively related windings associated with the two pairs of conductors whereby the flow of said second component currents across said insulating joints is equalized in all four conductors, and whereby the first mentioned component currents in the two pairs of conductors are kept independent of one another.

20. A system as specified in claim 19, ineluding a third conductor for each pair of conductors, an insulating joint in each of said third conductors, and means bridging said third conductor joints, whereby the sum of the currents in said third conductors and the sum of the currents in said pairs of conductors may be substantially equalized.

21. In an electrical transmission system, the combination of two pairs of conductors adapted for the simultaneous transmission of two separate component alternating currents, the two conductors of each pair serially constituting the circuit of one of said component currents and in parallel one side of the circuit of the other of said component currents, an insulating joint inserted in each of said conductors, a pair of inductively related windin s brid in the insulatinfl C C) if) C joints of the respective conductors of one of said pairs, each of said windings having a a mid-tap, bridging means bridging the insulating joints of the other pa r, and means associated with said mid-taps and with said bridging means for equalizing the second mentioned component currents flowing across said insulating joints in the same direction in all of said conductors.

22. A system as specified in claim 21, in-

cluding a third conductor for each pair of conductors, an insulating joint in each of said third conductors, and means bridging said third conductor joints, whereby the sum of the currents in said third conductors and the sum of the currents in said pairs of conductors may be substantially equalized.

In testimony whereof, I have hereunto subscribed my name this 22nd day of Dec.

CHARLES r. soorr.

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