Page 516

Page 517

New York, Jan. 27th 18723^a

Dear Sir.

In the matter of your application for patent on District Alarm Apparatus, ¹ the Patent Office will declare an interference after the usual preliminary statements are filed, giving the history and date of your invention.² The time for filing these statements has been extended to March. 15 on account of Mr. Calahan’s absence.³

If you will get these facts together and give them to me some time when you are at my office, I can prepare your affidavit. Yours truly

[Newark, January 1873?]²

I have struck a new vein in duplex telegraph; “no balance” works well enough in shop to order set made.³ Think t’will be success.

Two messages can be sent in same direction. In opposite directions.⁴

Way Stations can work on it and everything be made happy. My shop is so full of non-paying work that I should like to saddle this on W.U. shop, where they are used to it.

Called to see Mr. Prescott⁵ at 4 P.M. Left.

[Newark, c. February 1, 1873]¹

Duplex² Static^a

Impvts in defence of electrical warfare.^b

The magnets in the balancing or compensating circuit are used for the purpose of generating an after current due to the demagnetization of the iron core, which current is very powerful and by regulation made equal to the static return charge many times greater than is possible to equalize by a condenser.³ magnets when properly placed are the sworn enemiesPage 521 of static currents whether dynamic or in a muscle twisting mode.^4c

New York,^a February 6, 1873.

Dear Miller:

Say to Edison that I am ready to treat for his duplex, and that he may set it up in our office at any time. ¹ Also that I shall be glad to consider his other propositions.² Very truly yours,

Newark. N.J. Feby. 15. 1873.

Mr. Serrell Patent Solicitor

Please file following testimony of invention in Duplex Telegraphy. ¹

The fundamental principle of Duplex Telegraphy² is the neautralization of the effect of the outgoing battery up^a the receiving instrument^b

The next important device is the destruction of the effect of the static charge of the line³ upon the receiving instrument.^c

The minor essentials are, simple devices for placing the battery off and on the line, and a quick and convenient compensator.^d

I shall describe a large number of modes on which I am now experimenting preparatory to obtaining Patents. ⁴

Duplex No 1⁵

Page 523Duplex No 2

An Instrument may be inserted at X with proper resistance to prevent the spark and the key made to do what the sounder now does.⁷ The spring G is so adjusted the the shunt is not disconnected until the return static charge flows through it.⁸

Duplex No 4.

Page 524Duplex No 5. ⁹

Duplex No. 6.¹⁰

Duplex No 7¹¹

Duplex No 8¹²

Page 525Duplex No 9^c

X magnets are placed in the compensating circuit so that when the main and local battery are taken off the magnts will give an inductive charge equal to the static charge of the line.¹³

Duplex No 10¹⁴

Page 526Duplex No 11 ¹⁵

Duplex No 12¹⁶

Page 527Duplex No 13 ¹⁷

Four-plex No 14

Why not.¹⁸

Page 528Duplex No 15. ¹⁹

Duplex No 16.²⁰

Page 529Duplex No 17 ²¹

[Newark, c. February 15, 1873]¹

To be tested^a

No 18.²

Page 532No 19.³

No^b 20.⁴

No 21.⁵

No^c 22⁶

No^d 22⁷

New York, 26. Feby 1873^a

Dr Sir

You will construct for this Company 100 One hundred— “Universal Private Line Printers” to be first class in workmanship and to embrace the improvements as arranged for¹ —the whole to be made like sample Machine to be deposited in this office—

We will pay you One hundred & twenty dollars for each Machine. Yours truly

[New York or Newark, February 1873]¹

Mr. M.:²

Want order go in WU. nights to feel the pulse of my patients.³

In early 1873 Edison patented a perforating mechanism that used electromagnets rather than muscle power to punch holes in the paper tape for automatic telegraph transmission. ¹ Designed to use the same keyboard as his original, large perforator,² this mechanism was intended to solve two problems that characterized the earlier machine. First, by substituting simple electrical circuits for the original complicated series of cams and levers, the new design avoided the constant mechanical problems that plagued the large perforator.³ Second, this arrangement was “less fatiguing to the hand and arm”⁴ because the operator no longer had to supply the power to punch the holes. This last consideration was particularly important if the machines were to be operated by young girls, whose lower-priced labor was considered essential to reducing the costs of automatic telegraph systems.⁵

This was the only electric perforator patented by Edison and was apparently never used, perhaps because of the difficulty of developing sufficient power in the electromagnets to punch the tape cleanly.

[Newark, March 7, 1873?²]

The following automatic telegraph receiver embodies primarily the ideas delineated in a notebook entry of 28 July 1871.¹ The chemical solution for moistening the paper tape was kept in a small reservoir, from which a siphon fed it through a pen point to the paper. As the paper absorbed the solution, it moved under two wire points between which the incoming signal passed. In the patent application accompanying the model shown in Doc. 290, Edison claimed that this receiver would minimize the use of chemicals by applying the solution in a thin line at the center of the paper tape and passing the receiving signal immediately through it. However, that idea had already been patented, so Edison then altered his application to claim for himself the placement of the wires that marked the paper.² With the two wires placed close together, just the narrow strip between them needed to be moistened. Moreover, placing the two wires on the same side of the paper, and thereby having the signal go across the surface of the paper rather than through it, avoided the intermittently high resistance that resulted when the solution failed to penetrate the paper consistently.

[Newark, March 7, 1873?²]

New York, March 14, 1873^a

Whereas Letters Patent in Great Britain under the great seal thereof were duly granted to Henry Edward Newton ¹ of London, England, as a communication from George Harrington of the City and State of New York, United States of America for “Improvements in Mechanism for perforating paper for transmitting messages” which Letters patent are dated June 10th A.D. 1872 and numbered 1,751:²

And Whereas Thomas Alva Edison of Newark in the State of New Jersey, United States of America has invented certain “Improvements in Circuits and instruments for chemical telegraphs” ³ for which he has made application for Letters Patent in Great Britain:

And Whereas the above recited Letters Patent numbered 1751 was obtained, and the application for Letters Patent for “Improvements in Circuits and instruments for chemical Telegraphs” as above set forth was made with the full understanding between the said Thomas Alva Edison and the said George Harrington parties hereto that the benefits and advantages in and to all of said inventions and Letters Patent already granted and applied for should be held and enjoyed mutually in the proportion of one undivided third part to the said Edison and two undivided third parts to the said Harrington,⁴ and the expenses in connection with the same have been duly paid pursuant to such agreement

And Whereas it has also been understood and agreed that the said George Harrington should be entrusted entirely with all negotiations and proceedings connected with the introduction of the said inventions and improvements and the sole and exclusive right and power to negotiate and effect sales in connection with such inventions and Letters Patent:

Therefore in consideration of the premises, the said George Harrington is hereby made constituted and appointed the sole, exclusive and irrevocable attorney of the said Thomas Alva Edison to act in connection with the said inventions, improvements and Letters Patent, to attend to the introduction of the same in Great Britain, to negotiate for the sale of the whole or any portion of the right or rights in or under Page 538said Letters Patent already issued or applied for, to execute any and all contracts, assignments, deeds, transfers, licenses, or other documents and to receive any and all payments, license fees, royalties, Stock, bonds or other valuable consideration for any such rights or privileges and to give full and ample receipts for the same and to execute in the name or in behalf of the said Edison any written instrument that may properly be required for carrying out the full intent and meaning of these presents:

And the said Edison does hereby release and relinquish to the said Harrington any and all right to act in the premises and agrees that the rights and powers hereby conveyed shall be held and exercised by the said Harrington, his substitute or Attorney or his heirs or Executors as fully and entirely as he the said Edison could have held or exercised the same:

And furthermore that he the said Edison his heirs or assigns is only entitled to require of the said Harrington or his legal representatives a just and true accounting for and paying over of one third part of the net profits that may be realized from and in connection with the aforesaid inventions and Letters Patent in Great Britain.

In Witness whereof I, the said Thomas A. Edison have hereunto set my hand and affixed my seal this fourteenth day of March Anno Domini 1873, in the City of New York, State of New York, United States of America.

GThomas Alva Edison    Geo Harrington

Witnesses David G. Barnitz Gerard W. Vis.⁵

[Newark or New York, c. March 15, 1873]²

I have tried to date with make-shift instruments, seven duplex, between New York and Boston.³ Six of them worked charmingly. The seventh was a satisfactory failure. I have fifteen more to try.⁴

[Newark, Winter 1873]²

Duplex.

Repeater

Fac similes

Dot & Dash Chemical “Autos”

Magnetic Autos

Telegraph Inductive & discharge Currents.

Printing Instruments.

Transmitters for d[itt]o.

Perforating Machines.

Relays

Sounders

Morse Recording insts Movements.

Applications of Magnetism

" " Electricity

Mechanical Electric Movements

Magneto Telegraphy

Induction Coil telegraphy

Contracts

Batteries.

Novel

Connections.

Manipulations Novel.

Electromagnetic Engines^a

Duplex.³ Stearns—get copies patents =

“ Farmer " " " Extension & Reissue.

“ Siemens & Halske = Kramer,⁴ get copy teleghr giving description =

Edisons as shown in telegrapher Mention farmers Clockwork Double Trans

“ Edisons Magneticald[itt]o sameprinciple & result Boston Experiments

Page 540Have Double transmitter Article in Dub, Schellen & Blavier DuMoncel Translated =⁵

Edisons No 1 as in telegraphr

Edisons No 2 Vibratory

Edisons No 3 Mechanical Equalizer

“ No 4 Shunt with Rev battery on single relay

Reverse Current one & increase & decrease other =

Double trans Chemical

Rheos in connection

and Condenser Applications by Stearns and other means such as a Condenser of a duble Coil. No Condenser but Extra Coil on relay to take induction also to shunt Duplex relay with water Resist ance =

[Newark, Winter 1873¹]

Duplex.² wound opposite³

Page 541Mem⁴ you cannot reverse a current through an electromagnet without opening it.⁵

Principle =⁶

Reversing a Battery without much mechanism a Morse key in a circuit

[New York?,] March 31, 1873^a

Whereas by a certain Contract and agreement bearing date the first day of October A.D. 1870, between Thomas A. Edison of the City of Newark, State of New Jersey on the one part, and George Harrington of the City of Washington, District of Columbia of the other part, wherein it was stipulated and agreed on the part of the said Edison, that for and in consideration of certain valuable considerations as therein set forth, he the said Edison should invent and develope for practical use a System of Automatic or Fast Telegraphy embracing Perforators and other instruments and devices necessary thereto, and thereafter change, modify, add to and otherwise improve said System, instruments, devices, and other matters and things connected therewith as his experience and ability as an Inventor and Electrian might suggest and allow, all of said inventions, devices, instruments and System being held as provided in and covered by said contract and agreement of October 1st A.D. 1870.

And whereas it is the desire of said Harrington that the said Edison shall, if practicable and possible, invent and develope a practical System of Fast Telegraphy, whereby intelligence or despatches may be transmitted at a rapid rate in such manner as to reproduce the intelligence or despatch so transmitted at the receiving office in Roman Characters or letters in such form and in such legible and permanent manner as will permit the delivery thereof directly to the general public or parties to whom addressed or for whom intended, without the necessity for translating, copying or transcribing as is now necessary before delivery, with the power to take drop copies at will and in Roman characters permanently imprinted at intermediate or way stations—¹

And Whereas the said Edison is ready to undertake the discovery, invention and developement into practical use of a System producing the results as above set forth² Now therefore it is hereby stipulated and agreed by said Edison, that hePage 543 the said Edison shall at once proceed to invent and discover a method whereby intelligence or despatches may be transmitted over the ordinary wires now in use for telegraph purposes at a speed of Five Hundred words per minute over ordinary circuits of Three hundred miles in length, and at a rate of speed not less than Eighty words per minute over circuits of One Thousand miles in length—the intelligence or despatches so transmitted to be received at any one or more offices within the circuit, in plain, clearly defined and permanent Roman characters or letters and equally and at the same time when so desired or required at the several intermediate stations or offices as “drop Copies” all, without the necessity for further manipulation in translating, transcribing or copying, ready for delivery to the parties to whom addressed or intended.

And the said Harrington on his part or the said Harrington and J. C. Reiff his associate, of the City of New York, State of New York, stipulate and agree to advance to said Edison from time to time the aggregate sum of Three hundred dollars and to further pay to the said Edison, immediately after the satisfactory accomplishment of his undertaking³ a further sum to a whole aggregate of Fifteen Thousand dollars, to cover the extra expenses and extra labors of said Edison in producing the System and results as above set forth; but the said sum of Fifteen Thousand dollars shall cover the cost of Three sets of instruments for terminal and way offices complete for immediate use.

And the said Edison further stipulates agrees and guaranties that the inventions, devices and System as above recited shall be practical, easily learned and manipulated, and shall be original, so as to be secured by Letters Patent in the United States and in all foreign countries, for which purpose the said Edison shall cause to be made the necessary models, drawings and descriptions when required so to do, and that all of said Patents shall be held and controlled in the manner and proportions and for the purposes as set forth in the contract and agreement first hereinbefore recited;⁴ the said Harrington on his part agreeing that any of the inventions and devices of said Edison covered by Patents now held by said Harrington may under the stipulations and for the exclusive purposes herein set forth, be utilized and used as a part of said System, until the same shall be in due form assigned as herein contemplated in accordance with the contract and agreement of October first A.D. 1870 hereinbefore recited.

Page 544And the said Edison further stipulates and agrees for himself his heirs and Executors that he or they shall and will truly make and execute any and all further papers necessary or requisite in the premises, as they may be required, to complete and confirm the right, title, interest and control of said Harrington in accordance with and in fulfilment of the stipulations and purposes of the parties hereto, as hereinbefore set forth, and as pointed out in the before recited contract of October 1st A.D. 1870.

It is further stipulated and agreed by and between the parties hereto, that if the said Edison shall fail in developing practically as herein set forth, a rate of speed of Five Hundred and not less than Eighty words over circuits of the lengths hereinbefore set forth, but shall succeed at a lesser rate of speed over circuits of Three Hundred miles, then and in that case, the compensation herein provided shall be reduced as the rate of transmission falls short of the speed above set forth of Five Hundred words for circuits of Three Hundred miles, and the payment shall be as follows: If the rate of speed for circuits of Three Hundred miles shall be, but not exceed Four Hundred words per minute the compensation shall be ($12000) Twelve Thousand dollars— If the rate of speed shall be, but not exceed Three hundred words per minute, the compensation shall be^b ($10,000) Ten Thousand dollars— If the rate of speed shall be, but not exceed Two hundred words per minute the compensation shall be ($7,000.) Seven Thousand dollars. If the rate of speed shall be, but not exceed one hundred and fifty words per minute, then the compensation shall be ($5000.) Five Thousand dollars. But if the rate of speed shall not attain this latter recited speed of One hundred and fifty words per minute, then no compensation shall be claimed or allowed for extra services and labor—provided That for circuits of One Thousand miles, the minimum rate of speed shall not be less than Eighty words per minute.

It is further stipulated and agreed that the foregoing contract and agreement shall be held confidentially, that is to say, the proceedings of Edison and his purposes shall not be communicated to any one whatsoever and that neither the said Harrington, nor the said Reiff shall offer for sale the said inventions until all others now completed and in practical use are fully disposed of.

In Witness whereof the said Thomas A. Edison and said George Harrington and the said Associate of said Harrington J. C. Reiff have hereunto set their hands, and affixed their Page 545seals this Thirty First day of March Anno Domini eighteen hundred and seventy three.

Thomas Alva Edison^c

[Newark or New York, March 1873]¹

Mr Miller

You get me a Phelps Relay 125 Ohms & Phelps key I will fix rest”

The devices and arrangements in Doc. 297 reveal aspects of Edison’s work on duplex and related telegraph designs during the months after he began testing some of his apparatus on Western Union’s lines and before selected designs were specified in patent application drawings and models. ¹ In these Page 546drawings, Edison was refining or modifying some prior designs, such as the current-reversal mechanisms sketched late in 1872, while continuing to envisage and analyze additional possibilities, such as the last two drawings in Doc. 297. His considerations were related to his proposed book as well as to his inventive work for Western Union.²

[Newark, March 1873?²]

[A]³

[B]

[C]

[D]

[E]⁴

[F]⁵

[G]

Page 547[H]⁶

[I]

[J]⁷

[K]⁸

[L]

[Newark, March 1873?²]

Try this³

Duplex Static Current.⁴

no g[u]es[s] not

Try this⁵

[Newark, March 1873?]¹

Cables

Edisons system of Cables working by Centers of resistances and static accumulation²

Page 550This system gives perfect work between NYork and Washington at 1600 words per minute³

Experiments to be tried to lessen The resistance of the artificial line—

Still later 3180 words per minute areadable =

In the unfinished circuit designs in Doc. 300 Edison sought an arrangement of devices that would increase and decrease current strength and reverse current direction. Such a design would permit diplex and quadruplex telegraphy, rather than just the duplex system.¹ Drawing A is similar to the type of design with which Edison later achieved success in this field.² However, the problem of current reversals breaking up the other signals was not dealt with here, and Edison knew that without a solution for that problem the system remained impractical.³ In sketches B and C he apparently considered alternative arrangements for the terminals, but their unfinished character leaves their intended operation unknown.

[Newark, March 1873?²]

[A]³

[B]

[C]

[Newark, March 1873?²]

Telegraphing.

The object of this invention is to transmit two^a despatches in toposite and the same direction over one wire at the same time^b

The invention consists in mthe maode of rendering nil the effect of the outgoing current upon the receiving magnet³

A is the relay B is the sounder E the key D a local battery R & K resistances J a neutralizing battery H the main battery When the Key E is worked the sounder works with it so when it is closed the Lever C is brought down thro Page 553putting the battery on the line ethrough the point G a portion of the current from the battery going to the ground through R at^e the instant the [1]ever^f C closes on the point G the points N & F close and Shunt the throw an opposing Battery J on the relay, which in its effects is equal to the battery H. but in opposite character.^g Consequently the effect is neutralized any variation between the two batters being Compensated for by adjusting the Rheostat .K. to make the effect of the battery J weak or strong.⁵

[Fig? 3?]^h Showsⁱ

[Newark, March 1873?¹]

Munn & Co²

Please mention in case no. 1. a slight alteration³ Thus.^a

The compensating magnet .X. is split a local current constantly circulating in one helix, the other coil is inserted into an artificial line, the circuit of which is opposed to the local G.—

Also^b mention that an extra front point may be used instead of back point and when the main circuit was closed the local spe magnet would be cut off also that

[Newark?,] April 4, 1873.

Mr. Miller:

Please inform Mr. Orton that I have accomplished all I agreed to with one exception, and am now ready to exhibit and close the thing up.¹

duplex.

I experimented twenty-two nights; tried twenty-three duplex systems; ² nine were failures, four partial success, and ten were all right; one or two of the latter worked rather bad, but the principle is good, and if they were to be used could be improved in detail; eight were good, one of which requires no special instruments; a single wire run in a peculiar manner in a Morse set of instruments transforms them into a duplex. Ten models for ten different duplex have been delivered to Munn & Co., patent solicitors.³

“working played out wires.”

Several experiments made on Washington wires after heavy rain. With the ordinary relay the signals came hard; with attachment to ordinary relay the signals came strong, sharp and clear; two models of this have been delivered to L. M. Serrell, patent solicitor.⁴ One attachment is being made for exhibition. I will be ready in five days or sooner.

“working long circuits.”

Twenty-four hundred miles were worked by me at different times without repeater, but so far I do not think the devices I have are of any practical value. I shall not give it up. ⁵ The patents will be allowed in about three months. ⁶ In the meantime if I run across another duplex I will take steps to confine it in the Patent Office immediately, so that duplex shall be a patent intricacy, and the intricacy owned by the WU.⁷

Please ask Mr. Orton what I shall do next. Yours,

During the fourteen days preceding Edison’s April 1873 departure for England, he executed through Munn & Co. a series of eight patent applications for systems of duplex telegraphy.¹ These applications came to be known as Cases A-H owing to the designations apparently assigned to them by Munn & Co. They constitute a further development of Edison’s ideas on duplex telegraphy derived both from his many tests on Western Union lines and from further thought about still other designs or variations. All are variations of earlier designs; some are elaborations or refinements, and others are major modifications.² The last of this series—Case H (Doc. 315)—became the focus of much further work.

Edison signed these applications, but he later said they were poorly done and that he found them confusing and partly unintelligible.³ He had provided models and drawings of the designs, as well as some notes, drafts, and comments about them, but he left the actual wording of the applications to the firm of patent agents.⁴ All of these applications were initially rejected; only for Case H did Edison eventually receive a patent,Page 557 and that only after considerable amendment of the description.⁵

New York, April 9, 1873^a

Specification—describing a new and Improved Duplex Telegraph Apparatus: invented by Thomas A. Edison of Newark, in the County of Essex, and State of New Jersey—

My invention relates to apparatus for simultaneous transmission of two dispatches or signals from opposite ends over the same line wire; and consists in combination with opposing relay and local magnets, of a device which by mechanical means, prevents the lever vibrating between said magnets from responding to the signals transmitted from the home station, but does not prevent the same from responding to the signals from the distant station—²

In the accompanying drawing,—

Figure 1, represents a plan view of my apparatus for double transmission and

Figure 2. a modification of the same, showing the arrangement of an opposing & local battery for neutralizing each other, whereby it is not necessary to break the circuit.

Similar letters of reference indicate corresponding parts,— Case A^b

Inventor:^c T. A. Edison Per^c Munn & Co. Attorneys.^c Witnesses:^c Chas. Nida.³ [P.?]^d Sedgwick^4e

In the drawing A, is the receiving magnet. B. is an opposing magnet, operated by a local battery, L.B. placed in circuit with the sounder lever SL, by spring extension a, and contact b .

L. is the armature lever of the receiving magnet A, and local magnet B, pivoted so as to vibrate between them.

S, is its spring, the tension of which is greater than the power of each magnet singly, but of less tension than the combination of either magnet with the current of the line.—

SM is the sounder Magnet, operated by the sounder battery SB, and key R, ⁵ d, the contact stop connecting main battery MB, by sounder lever SL, and wire m, to the line wire, R, A⁶ rheostat, placed between relay A, and the earth—plate E, and transmitting part of the force of the main battery to the earth, sending the other part of the current to the distant station without overcoming the tension of spring S—

Page 559The local circuit is closed, when the home station is not transmitting, the local magnet being not strong enough to attract the lever L, on account of the resistance of spring S. If however the distant station is sending, the combined power of the line current and local current overcomes the resistance of the spring S. and the relay responds to the signals of the distant station.

When, however, the local circuit is opened, by the depression of key R, and attraction of the sounder lever SL, to its magnet, the sounder lever breaks contact with b, and closes the circuit with the main battery at contact d, the current passes through the relay A, to the line without moving the lever L, not being strong enough to overcome the resistance of spring S—Thus the signals of the home station are transmitted through the receiving magnet, which is always in circuit with the distant station, without responding to them—If however, a current be transmitted from the distant station simultaneously with the closing of the main circuit at the home station, the power of the electro magnet A, is increased, a greater power is exerted on the vibrating lever L, namely: the combination of the power of both main batteries and the resistance of the spring S, is overcome, so that lever I⁷ moves, transmitting the signals of the distant station:

The relay at the other end of the line responds in similar manner to the signals of the home station, transmitting thereby simultaneously the signals from either station at the same time.

By connecting the local battery LB, with an opposing battery OB, in the same circuit they will neutralize each other, but preserve at the same time the continuity of the circuit.—

The magnet B, discharges itself within its own circuit for the purpose of being rendered more sluggish, avoiding thereby the danger of attracting lever L, and creating a confusion of signals.—

Having thus described my invention—

I claim as new and desire to secure by Letters Patent.

1st The armature lever L, placed between the receiving and local magnets A and B, having strong spring S, to be vibrated by the joint action of either with the line current, when singly they are too weak to change its position substantially as described.—

2d The sounder lever S,L, having spring extension a or equivalent, in combination with the contact stops b, d, to constitute a joint conductor for the current of the main or local battery, as described.—

Page 5603rd The combination of the receiving magnet A, with the main battery MB, sounder lever SL, and rheostat R, to regulate outgoing current of main battery and establishing earth circuit, substantially as and for the purpose described.—

New York, April 9, 1873^a

Specification^b describing a new and Improved Duplex Telegraph Apparatus invented by Thomas A. Edison of Newark, in the County of Essex, and State of New Jersey.

My invention has for its object the simultaneous transmission of two signals over the same wire, but in opposite directions and consists of the combination of two relays with their armature lever, pivoted between them and placed at different distances from the same, so as to prevent the relays to respond to the signals transmitted from the home station without being prevented from receiving the signals of the distant station. ²

Page 561Case B^c

The accompanying drawing represents a plan view of my improved apparatus for double transmission, in which A. and B. are the receiving magnets. L. their armature lever, pivoted between them and adjusted at greater distance from magnet A. than from magnet B. requiring therefor an increased amount of power to attract the same to A. instead to magnet B. The magnet B. is connected by wire m, with contact stop a, and by spring contact z, ⁵ to the earth. An insulated extension a’ , of contact, a, serves also as back stop for sounder lever SL. which acts, on closing to the sounder magnet S. on a second contact z’ of spring contact z, disconnecting the stops a b, and throwing relay B, out of circuit. Magnet A, is connected by wire m’ with the line and over the main batter M.B. to sounder lever S.L. operated by means of key k, sounder battery S.B. and magnet S.

By closing the sounder lever S.L. the same acts on contact z’ separating contacts a.z. and throwing magnet B. out of circuit. The current of the main battery MB. passes through magnet A. to the line. Magnet A. is placed at such a distance from lever L. that the power of the main batter M.B. is insufficient to attract the same, the signals are therefore transmitted to the distant station without being responded to by the home station. If however the sounder lever SL. be open, the Page 562main battery M.B. and magnet A, are thrown out of circuit and magnet B. being adjusted much closer to lever L. and placed by contacts a.z. in circuit, attracts lever L. and responds to the signals of the distant station. The line current is then conducted by contacts a.z to the earth B. ⁶ When both stations are transmitting, so that sounder lever S.L. is closed at each station, the combined strength of the main batteries both of the home and distant station is passed through magnet A. attracting the armature lever L. and responding thereby to the signals from the distant station.

Having thus described my invention—

I claim as new and desire to secure by Letters Patent.

1st. The pivoted armature lever L. in construction⁷ with the magnets A. and B. adjusted between them as set forth and operated as described.

2d The sounder lever SL. in connection with spring contacts z.z’. and contacts a.a’. to throw either magnet A.B out ol circuit, substantially as set forth.

Edison drew several closely related duplex designs that employed adjustable resistance coils to make a relay insensitive to outgoing signals but responsive to incoming ones, which was the fundamental goal of a duplex circuit.¹ Edison applied for a patent on such an adjustable relay at the same time that he was applying for many duplex patents in April 1873; the relay patent was granted as U.S. Patent 160,405. He also appears to have used a similar design in his work on automatic telegraphy (see Docs. 324 and 336).Page 563

[Newark or New York, c. April 15, 1873]

[Newark or New York, c. April 15, 1873² ]

New York, April 16, 1873^a

Specification^b describing a new and Improved Duplex Telegraph Apparatus invented by Thomas A. Edison of Newark in the County of Essex and State of New Jersey.

This invention relates to apparatus for simultaneous transmission of two dispatches or signals over the same line wire in opposite directions and consists in the neutralizing of the effect of the out going current on the receiving instrument by an adjustable opposing magnet, operated by a local battery so that the relay is prevented from responding to the signals of the home station. It also consists in the arrangement of an induction magnet in connection with the local battery and the main line, for neutralizing the static current of the line.² In the accompanying drawing

Figure 1—represents a plan view of my improved apparatus for double transmission, and

Figure 2—is a side elevation partly in section, of the relay and the opposing local magnet.

Similar letters of reference indicate corresponding parts.

Page 565Case D^c

Inventor:^d T. A. Edison Per^d Munn & Co. Attorneys.^d Witnesses:^d Chas. Nida.³ [P.?]^e Sedgwick^4f

A represents the receiving magnet, the cores a of which are provided with projecting pieces a’ placed sideways of the axis of the cores towards each other, requiring a smaller armature, of lever L. The local magnet B having projecting cores b, is placed against the magnet A, with opposing poles, the N and S poles of the local magnet respectively. The lever L, with its armature is working between the forward projecting cores of the magnet B. The local magnet B is connected by guide rods d and d’ with pillar e and made adjustable towards magnet A by means of spiral spring f and thumb screw g. The magnet B may thereby be adjusted so as to exactly neutralize the effect of the out going current of the main battery on lever L. The local magnet B is operated by the local battery L.B. placed by Page 566contact h in connection with spring contact h’ of sounder lever SL which is again operated in the usual manner by sounder battery LB, Key K and magnet S. The local battery may be dispensed with and a secondary current sent from the main battery be made in the usual manner. The main battery connects by wire m to the relay A and the line and by wire n to the sounder lever which is placed by contact stop i through rheostat R in a shunt circuit with the carbon poles of the main and neutralizing batteries MB and MB’, the latter being connected to the earth E. C is an induction magnet, having one coil D in the same local circuit, the other coil F in circuit with the main line.

On operating the apparatus, the out going current of the main battery MB, on closing sounder lever SL, is divided, one portion passing through relay A to the line, the other through contacts i and rheostat R to battery MB and the earth. Rheostat R is of slight resistance, to prevent too much spark on contact, point i. The local circuit is connected at the same time by contacts h h’ and thereby the effect of the outgoing current upon the cores a, of the relay neutralized by the opposite polarities of the cores b of the local magnet B. The current passes therefore to the distant station, without effecting the lever L, as the sounder lever closes the local circuit, at the moment the main battery is thrown on the line.

When the sounder lever SL is open the armature lever L responds to the current of the distant station, as no opposing polarity of the local magnet prevents its attraction.

When the sounder levers are closed at both stations, the current of the main battery at the home station is neutralized by the local magnet, but the current of the distant station, being of equal polarity with it, attracts the lever L and responds thereby to the signals of the distant station.

The static current of the line is neutralized at the moment of closing and opening the sounder lever SL. When the sounder lever is closed the induction coil D of the local battery is acting upon the iron core C, which induces a momentary current into F and upon the line opposite to and of equal duration with the static current thereby neutralizing each other. At the moment of opening the sounder lever, the static current is at opposite polarity and is then neutralized by the induction current of coil F, which is also in opposite direction. The amount of induction electricity can be regulated by means of a rheostat shunt around the magnet D.

Page 567Having thus described my Invention—what I claim as new and desire to secure by Letters Patent is

First—In apparatus for double transmission, the receiving instrument A, having inside projecting cores a in combination with the opposing magnet B having projecting cores b, adjustable towards the former and operated substantially as for the purpose described.

Second—The induction magnet C, having coils D and F placed in the local battery LB and the main line, to neutralize the static current on the same, substantially as and for the purpose described.

New York, April 16, 1873^a

Specification^b—describing a new and Improved Duplex Telegraph Apparatus: invented by Thomas A. Edison of Newark, in the County of Essex, and State of New Jersey.—

My invention relates to apparatus for transmitting dispatches or signals simultaneously over the same line wire in opposite directions and consists of the neutralization of the effect of the out going current by the main batteries themselves, which are connected with same poles to both sides of the relay, the other poles being connected to the sounder lever and thence to the earth.²

Page 568Case E^c

The accompanying drawing represents a plan view of my improved apparatus for double transmission in which

A, represents the receiving instrument or relay, L, its armature lever and M,B, two main batteries of equal strength, arranged at both sides of the relay in such a manner that the zink pole of one main battery is connected to one side of the relay, and the zink pole of the other main battery to the other side of the same. The carbon poles of both main batteries M,B, are connected to the sounder lever SL, which is operated in the usual manner, by its key K, sounder battery S,B, and magnet S, Both zink poles of the main batteries are connected to the relay A, through rheostats R, and R’⁵ adjusted with slight resistance to prevent shunting or short circuiting of the relay A. A third rheostat R ², is placed between the relay A, and the earth plate E—The contact stop a, of the sounder lever SL, is also connected with the earth.

On closing the sounder lever S,L by the depression of key K, the carbon current is rounded through contact a, to the earth, the zink currents of both main batteries, pass through the relay A, to the line, but acting against each other, neutralizePage 569 their effect on the relay A. The circuit with the main battery at the distant station is thereby closed, and the signals are transmitted over the line, without affecting the armature of the relay. When the sounder lever is open, the signals from the distant station pass through the relay A, and the rheostat R², to the earth. The lever L, responds to them as the two main batteries being in a shunt around the relay and opposing each other, produce no effect on the same.—

When, however, both sounder levers are simultaneously closed at the home and distant station, the relay R, ⁶ responds in similar manner to the current from the distant station, and the relay of the distant station to the outgoing zink current of the home batteries so that thereby two signals are transmitted at the same time, one from either station.—

Having thus described my invention.

I claim as new and desire to secure by Letters Patent—

1st The receiving relay, in duplex telegraph apparatus, combined with the same poles of two main batteries, to neutralize effect of outgoing current on the relay, substantially as set forth.—

2nd The rheostats RR’, placed within the circuits of the opposing main batteries for the purpose described.—

New York, April 16, 1873^a

Specification^b describing a new and Improved Duplex Telegraph Apparatus invented by Thomas A. Edison, of Newark, in the County of Essex and State of New Jersey.

This invention relates to apparatus for the simultaneous transmission of two dispatches or signals from opposite ends over the same line wire and consists in the working of the receiving instrument by induction currents, generated in a secondary helix by the incoming current, when the outgoing current is neutralized by helices wound in opposite directions on the same magnet, so that the receiving instrument responds to the signals of the distant station without responding to the signals of the home station.— By means of an electro magnet placed between the battery and the induction coils the effect of the discharge of a static current is neutralized by the charge and discharge upon its iron core.² In the accompanying drawing—

Figure 1. represents a plan view of my improved apparatus for duplex transmission worked by induction currents and

Figure 2. a detail side elevation of the secondary helix placed at right angles to the primary coils.³

Similar letters of reference indicate corresponding partsPage 571

Case F^c

Inventor:^d T. A. Edison Per^d Munn & Co. Attorneys.^d Witnesses:^d Chas. Nida.” [P.?]’ Sedgwick^{5 f}

A, in the drawing represents the receiving instrument, being a polarized relay or other electro-magnet of the usual form. It is connected by wires m. with the secondary helix H, supported by a standard a and placed in a plane, vertical to the axis of the magnet B. Two coils I, and I’ are wound upon the magnet B in opposite directions, helix I connecting with the line and the battery MB, helix I’ with the battery M,B, and a rheostat R to the earth E.— These helices may also be wound in opposite directions in one coil instead of being separated. The secondary helix H embraces vertically the helix I, the core B of which is supported by standards a’.— C is an electro-magnet placed between battery M,B, and the magnet B and connected by wire n to contact stop b of the sounder lever S,L, which is again connected to the zinc poles of the two opposing batteries M,B and M,B’ and the latter with the earth plate E′.

The sounder lever S,L, is operated in the usual manner by sounder battery L,B, Key R and sounder magnet S.

The working of this apparatus for double transmission is based on the principle of galvanic induction, according to which by each closing and opening of the battery momentaryPage 572 induction currents of opposite directions are produced. When therefore, a current from the distant station passes over the main line into helix I of core B, a momentary current in opposite direction to the same is induced in helix H, which throws the lever or tongue L of the polarized relay A over to one side.—

When the battery at the distant station is disconnected, the induction current in the secondary helix, though of equal direction with it, is in opposite direction to the first induction current and throws therefore tongue L back to its former place. The relay A responds in this manner to the signals from the distant station by the opposite induction currents of helix H.

On transmitting signals from the home station to the distant station, the current divides, before entering into coils I and I’.— They being wound in opposite directions on magnet B, exercise no influence upon it and induce consequently no currents in the secondary helix H. One part of the main current passes therefore to the distant station, the other part through rheostat R to the earth. The outgoing current exercises no effect on relay A, the relay at the distant station responding to the same.—

When both stations are transmitting at the same time, the current from the distant station produces induction currents in the secondary helix H so that the relay A responds to the signals of the distant station. The outgoing current being neutralized in the manner described, operating the relay at the distant station.— The conditions of double transmission are therefore fulfilled and the respective relays responding simultaneaously to the currents from the other stations.—

The object of the electro magnet C is to neutralize the static current and to prevent a spark at contact b. The magnet C could also be placed on the compensating circuit, but would not be so effective.—

The disturbing effects of a discharge of a steady current on the magnet B and its helices I, amd I’ are neutralized by the charge and discharge of the current upon its iron core.—

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is

First. In apparatus for double transmission, a polarized relay A, placed in a secondary circuit to be worked by induction currents, generated by primary and secondary helices I, and H, as described.

Second.— The secondary helix H in connection with magnetPage 573 B, having opposite helices I and I’ to neutralize effect of outgoing current, substantially as described.—

Third.— The electro magnet C, arranged as set forth, to destroy the static discharge, as described.—

New York, April 16, 1873^a

Specification^d describing a new and Improved Duplex Telegraph Apparatus by Thomas A. Edison, of Newark, in the County of Essex, and State of New Jersey.

This invention relates to apparatus for simultaneous transmission of dispatches or signals over the same line wire in opposite directions and consists in encircling the armature of the receiving instrument by a double coil and sending an equal current in opposite direction to the outgoing current through the same, so that the effect of this current is rendered nugatory on the receiving instrument. It consists further in placingPage 574 an electro-magnet in the circuit of the main battery, for generating induction currents, and neutralizing the effect of the static current on the receiving instrument. By spring connection of the sounder lever, the main battery is inserted on closing, and the continuity of the circuit preserved, on opening the same.²

In the accompanying drawing.—

Figure 1, represents a plan view of my apparatus for double transmission, and—

Figure 2, a detail side elevation of the receiving instrument with the double helix, encircling its armature.

Similar letters of reference indicate corresponding parts

Case G^c

Inventor:^d T. A. Edison Per^d Munn & Co. Attorneys.^d Witnesses:^d Chas. Nida.³ [P.?]^e Sedgwick^4f

A, in the drawing is the receiving relay, L its armature lever. B the double helix encircling horizontally the armature above and below the lever L and between the extended cores a, of Page 575the relay A. A vertical standard b, supports the helix B.

The current of the main battery is divided, passing equally but in opposite directions through relay, A and helix B. A regulating rheostat R connects the helix B to the earth at E. A third circuit branches off by wire m, from the main current and passes through the coils of the magnets C and C to the earth. M,B, is the main battery connecting with both poles to a wedge shaped double contact d , e, of sounder lever S,L. Contacts d, and e, are insulated from each other, but act, on closing the sounder lever to its magnet S, respectively on two spring contacts f, g, also of wedge shape, which are supported by standard h,. When the sounder lever S,L is open, the edges of spring contacts f, g, touch each other, and being connected to the earth at E′, preserve the continuity of the circuit. The wedge contacts d, e, by separating contacts f, g, insert thereby main battery M,B, into the circuits.

Wire m′ conducts the current of the main battery from spring contact f , to the relay A, helix B and magnets C, C’, on the closing of sounder lever S,L. The latter is operated in the usual manner by sounder battery S,B, key R and magnet S.

When the distant station is sending, the armature of the receiving relay A, responds to the signals, the current passing over wire m’ and spring contacts f, g, to the earth. When however the home station is transmitting the sounder lever S,L, separates by its wedge contacts d, e., the spring contacts f, g, throwing thereby the main battery M,B, into the circuit. The current passes equally through the relay A to the line, and through helix B, in opposite direction to the earth, preventing the action of the armature, by balancing the magnetic current of relay A. The relay at the distant station responds therefore to the signals of the home station, the effect of the outgoing current on the relay of home station being neutralized. By placing the coil B in this manner around the armature the generation of induction currents may be prevented in the relay itself, when one helix is enclosed within the other.

When both stations are transmitting at the same time, relay A responds to the signals of the distant station, as the outgoing current is neutralized in the manner described. The relay of the distant station responds to the signals of the home station, transmitting the dispatches simultaneously over the line.

The magnets C, C’, form a third circuit of the main battery M,B, and generate by their charge and discharge induction currents equal to the static currents of the line.

These induction currents act on the double helix B in opposite directions as the static currents on the relay A, and neutralizePage 576 therefore their effect on the same. The regularity of the working of the relay and helix are thereby secured and confusion of signals effectively prevented.

Having thus described my invention.

What I claim as new and desire to secure by Letters Patent, is—

First. The armature of the receiving instrument A encircled by double helix B, placed between the extended cores a, of the relay A, substantially as set forth.

Second.— The sounder lever S,L, having insulated wedge contacts d, e , in combination with spring contacts e, f to insert main battery and preserve continuity of circuit, substantially as described.

Third. The induction coil or magnets placed within, a compensating circuit for neutralizing the effect of the static current, substantially as shown and described, and for the purpose set forth.

[Newark,] April 17 1873¹

[A]²

[B]³

Page 577[C]⁴

[D]⁵

[E]

[F]

Duplex Same direction⁷

Edison⁶

[G]

[Newark,] April 21, 1873

General

Mr Bergman¹ was contracted with² to build a Universal Model for 125 This model will be finished and delivered to you probably by Wednesday P.M. I put the price low and out by peice work so as to prevent shirking work Bergman has altered this model several times at my suggestion some of the alterations were very sweeping, and were made on account of a doubt

If he only receives 125 he will have lost money and as he has worked concientiously and hard I think that 200 is but fair and at that it is a very cheap model which on the old plan of day work would cost double I think you will find that This machine is about perfect It is very convenient.

The results are quick with the machinery working slow I can do no better I consider it the private line machine and my experience covers over 63 different printing telegraphs of my own and a constant work of 5 years 17 hours a day = in a diversity of mechanisms as complicated as 40 bushels of spiders webs

Page 579I believe it would be to the interest of the Co³ to give the order to me to build more than 100, but I do not know if it would be to my interest Yours Resp.

New York, April 22, 1873^a

Specification^d describing a new and improved “Duplex Telegraph Apps” invented by Thomas A Edison of Newark, in the County of Essex and State of New Jersey

This invention relates to apparatus for simultaneous transmission of two dispatches or signals from opposite ends over the same line wire and consists in placing a shunt circuit around the relay, which in connection with an equating battery and adjustable rheostat neutralizes the effect of the main battery on the receiving instrument, preventing it thereby, to respond to the signals transmitted from the home station without preventing it to respond to the signals from the distant station.— ²

Page 580Case C^c

The accompanying drawing represents a plan view of my improved apparatus for double transmission in which, A is the receiving relay L its armature lever, M,B , and MB’ two main batteries of equal strength, but with opposing poles, the latter being connected to the earth at E. The equating Battery E,B , is placed in a shunt around the relay A with its current in opposite direction to that of the main battery MB, neutralizing thereby the effect of the same in relay A at the same moment, when the battery MB is put on the line. The resistance of the shunt and the consequent increase and decrease of the equating battery EB is obtained by the adjustable Rheostat R, placed between the battery EB and the relay A. The other pole of the equating battery EB is connected to the spring contact a of sounder lever SL, which is operated in the usual manner in duplex instruments by sounder battery SB, key R and sounder magnet S. The sounder lever SL is placed by means of wires m m′ and contact stop d in circuit with the opposing battery MB’, its insulated spring contact a, connecting the shunt circuit over contact stop b and wire n.

When the home station is not sending, so that the sounding lever is open, the line current passes through the relay, attracting lever L and thence to the earth at E. When however the sounder lever SL is closed, three different circuits are formedPage 581 by spring contacts a, b , and contact d, viz: the circuit of the opposing main battery M,B’, over wire M, sounder lever SL , contact d and wire m, the shunt circuit through rheostat R and relay A and the main circuit from battery M,B, through relay A and line to the distant station. In the circuit of the main battery MB’ a slight resistance may be thrown in to prevent spark at contact d. The outgoing main current is rendered nugatory in its effect on the relay, by the neutralizing influence of the opposing current of the shunt battery. One part of the main current passes around the relay over the shunt to the line, and transmits thereby the signals to the distant station, the relay A being prevented to respond to them.

When, however, both stations are transmitting signals at the same time, the current from the distant station operates the relay A, the outgoing current, being neutralized in its effect thereon, working in similar manner the receiving instrument at the distant station.

Having thus described my invention

I claim as new and desire to secure by Letters Patent

First, In apparatus for double transmission, the combination of the receiving instrument with a shunt circuit and equating battery, to neutralize effect of outgoing current substantially as described.

Second, the sounder lever SL having spring contact a in connection with contacts d and b, to close circuit of opposing main battery MB’ and shunt circuit, substantially as and for the purpose described

New York, April 22, 1873^a

Specification^b describing a new and useful improvement in Duplex Telegraph App’s—invented by Thomas. A. Edison of the City of Newark in the County of Essex and State of New Jersey.

The invention has for its object the simultaneous transmission of two dispatches or signals over the same line wire from opposite directions and consists in working the relays at the distant stations by means of reversals of the current at the home station, while transmitting the signals from the distant station by the increase and decrease of the strength of the current of the line. ²

The accompanying drawing^d represents a plan view of my improved apparatus for double transmission, showing connection of home station with distant station.

A and B are electro magnets of equal strength and placed at equal distances from the armature lever L pivoted between them. Both magnets are arranged with seperate batteries battery MB being connected with magnet A and with its positivePage 583 pole to the line, battery .M,B’, with magnet B, being negative to the line.

Batteries MB and M,B’, are alternately placed into circuit by the action of sounder lever S.L on double spring contact a and then conducted to the earth.

The sounder key^f lever S,L is operated as usual by its battery S,B, key R ⁵ and magnet S.

Magnets A and B communicate over wire mm′ and the line wire with the distant station, where C is a polarized relay, to be operated by positive and negative currents, K′ a Morse key and R a Rheostat connected to key R′ and the earth at E’. The object of the key at K′ and rheostat R is, to increase and decrease the current upon the line, so as to affect the lever of the relays A,B . This increase and decrease of the current does not affect the polarized relay C , so that signals may be transmitted by the positive and negative currents of the batteries at the home station, which operate the polarized relay, while at the same time signals may be sent to the home station which are caused by the depression of key K′ and consequent effect on the relays A,B .

On the closing the sounder lever S,L, relay B and its battery M,B’, are thrown out of circuit and relay A and battery M,B with its positive polaritye to the line⁸ placed into the circuit. In like manner when the sounder key^f lever SL is open, relay magnet^f A is thrown out of circuit, and relay magnet^f B with its negative polaritye to line,^h thrown into the circuit. The armature lever remains thereby constantly attracted to the electro-magnets A,B , as the instantaneous transfer of polarity permits no seperation of the same. If both positive and negative currents were passed through one magnet only, a charge and discharge would be produced with the change of polarities, and the armature would be attracted and repulsed. ⁶

The effect on the line is the same, whether a current of one polarity or the other is sent, but as each magnet receives a current, of the same polarity, reversal of the current takes place on the line without affecting the relays A,B. The polarized relay is self adjustable and follows the positive and negative currents, whether the tension of the batteries is suddenly increased or decreased.

The polarized relay can be placed at a number of stations on the line and each will be able to receive the signal from the transmitting station.

The simultaneous depression of the keys RKⁱ and R’K′ⁱ at both stations produces the responding of the polarized relay,Page 584 at the distant station to the signals of the home station by reversal of the current, while the relays at the home station respond to the signals of the distant station by the decrease and increase of the strength of the current on armature lever L

Having thus described my invention

I claim as new and desire to secure by Letters Patent.

First. The armature lever L, pivoted between relays A,B to b[e]^j operated by key R′ and rheo[stat]^j R from the distant station [by]^j the increase and decrease [of]^j the current, substantially as described.

Second. The sounder lever SL in combination^k with double spring contact a, to throw alternately the battersies MB and MB’ with reversed polarities on the line for working polarized relays at distant stations, substantially as described.

New Yowk, April 23,1873.¹

I hereby appoint Norman C. Miller my attorney, sole and exclusive, to arrange, sell, bargain, transfer, convey for any sum he may see fit all my right, title and interest of every conceivable description in eight duplex telgh. patents, obtained by Munn & Co.,² and three duplex telgh. and two compensating relay patents, obtained by L. Serrell,³ to any corporation which shall go by the name of the Western Union Telegraph Co.⁴

Witness: J. C. Masea.⁵

New York, April 23, 1873^a

case 82.

1^b Specification describing an Improvement in Electric Telegraphs, invented by Thomas A. Edison of Newark in the County of Essex and State of New Jersey.

2 In cables and long telegraph lines, there is a limit to the speed with which perfect signals can be transmitted and received, whether the receiving instrument consists of an electromagnet, a galvanometer, a relay or a chemical telegraph instrument; this limit in speed arises from the fact that the moment the line or cable is charged by the battery being connected, a static charge is instantly set up which is in an opposite direction to the dynamic charge, and the tendency is to defer the reception of the signal at the distant station,¹ and at the moment of breaking the battery connection, the static charge disperses by dividing at the center of resistance and going in both directions one part going to the ground at the transmitting station in a direction opposed to the battery, and the other part going towards the receiving instrument in the same direction as the previous current from the battery.

3 This electrical condition is of sufficient duration to render the signals unintelligable at the receiving instrument after a certain speed is attained.

4 The time of discharge is directly proportioned to the resistance at the points of discharge at the ends of the line, and the result is, that the speed of the instruments is limited to the speed with which the line will free itself through the channels aforesaid.

5 My invention relates to the discovery of a method of neutralizing the effects of the static charge in any length of line or cable by balancing the electric forces and the discovery of a point of no electric tension or zero, as regards the static charge, so that the receiving instrument when located at that point will be operated by the rise of tension produced by a pulsation that is connected at such receiving instrument and made as instantly and definitely operative as the pulsation given at the transmitting station.²

6 I obtain this point of no tension by forming at the receiving end an artificial line having an equal or nearly equal resistance and electro static capacity, or capacity for producing static charges, as that of the cable or land line, and connect this with the line or cable, and place between the cable and the artificial line the receiving instrument, which hence is in the center of resistance and static accumulation. When this Page 587 balance is obtained the signals are received perfect and the rapidity is governed only by the strength of the battery.

7 The artificial line is made with an adjustable rheostat: liquid in a tube is preferable.

8 I connect, between the receiving instrument and the earth, one or more condensers or other accumulators of static electricity, which are made adjustable by having them in sections and bringing one or more sections in or out by a switch so as to increase or decrease the static charge from the artificial cable: it may also be done by placing a very high adjustable resistance coil between one leaf of the condenser and the artificial line.

9 I maintain a very low resistance between the line and the ground at the transmitting station so as to discharge the static current at this end as rapidly as possible.

10 The mode which I prefer, is to keep my transmitting battery in circuit at all times and include in the same circuit another battery of equal power with opposite poles so that when both are in there is no current generated and the resistance of the wire to earth is no more than the resistance of the battery.

11 The transmission of a pulsation is made when the circuit is closed through the perforation in the paper or otherwise, so as to short circuit or shunt the neutralizing battery and send a current upon the line.

12 The current at the receiving paper is shunted through a resistance so as to preserve a constant and equal resistance, which the chemical receiving paper does not give, owing to being more damp in one place than another.

13 In balancing the resistance and static current, the resistance of the instrument is to be added to the line and the resistance of the two equalized by the same amount of resistance in the artificial cable or line.

14 If the receiving instrument is out of the center of resistance towards the line, the pulsations will be weakened by the static charge acting against the pulsation, but if the instrument is towards the artificial cable on the other side of the zero point, the signals or characters will be slightly prolonged owing to the static charge discharging in the same direction as the current. It is at this point that I prefer to place the instrument because by placing an electro magnet in the shunt of the receiving instrument I obtain enough counter discharge from that magnet to cut off this prolongation locally and this discharge from the magnet will not interfere with the line butPage 588 has only a local effect on the receiving instrument to prevent tailing on the chemical paper.

Inventor Thos A. Edison, per Lemuel W. Serrell atty. Witnesses Chas H Smith, Harold Serrell

15 In the drawing, Figure 1 . illustrates my invention in the form that I find most generally available. The batteries a , and b, are connected in opposite positions, the positive poles being towards each other and the negative poles connected to the ground g, and line 1. respectively.

16 The transmitting instrument c, is in a circuit d, to the Page 589 battery b, in which circuit d, is a resistance e. When the circuit d, is broken the two batteries a, b, neutralize each other and there is no charge sent on the line, but when the circuit d, is closed through a perforation in the paper, or by a key, or otherwise, the battery b, is short circuited and the battery a, being unbalanced sends a pulsation on the line. The artificial line between the receiving instrument f, and the earth g’, is made by introducing a resistance or rheostat at r , preferably a tube containing liquid with adjustable points: this rheostat is made to balance or equal, or nearly so the resistance of the line 1, and the instrument f, and the condenser s, or other accumulator of static electricity is of a capacity to about equal that of the line, hence the receiving instrument will occupy a zero or neutral point in regard to the static charge from which the static charges will discharge both ways to g, and g′.

17 The condenser or accumulator s, should be in sections to bring in a greater or less number of sections by switches.

18 When the receiving instrument is chemical, the paper is^d preferably prepared by dipping it in a solution of at least one pound of iodide of potassium in one gallon of water, to which is added a small quantity of flour: this paper cannot be maintained at uniform moisture hence its resistance to the passage of electricity varies; this is compensated for by the shunt circuit t, in which is a resistance u, sufficient to direct the necessary amount of electricity to the paper to make the mark and allow the remainder to pass to the artificial line, thus the varying condition of the paper does not change the resistance of the line.

19 I have discovered that when an electro magnet is energized and the circuit broken, a pulsation is set up in the opposite direction to that passing into such magnets;³ I avail of this to prevent tailing upon the chemical paper and at v, I have shown an electro magnet for this purpose. It will be seen that this electro magnet will discharge itself within a short local circuit containing the receiving instrument, and that the reactionary current therefrom moving in the opposite direction to the main current frees the receiving instrument from the tailing caused by the discharge of static electricity, and this magnet v, may be employed in many places to effect the object before named, even when there is not an artificial line.

20 In some instances with very long lines, there may be intermediate artificial lines arranged as aforesaid or reactionary magnets with branch circuits to the earth, to either receive drop copies in such branch circuits or to free the line of static Page 590electricity and aid in obtaining the signals perfectly at the last receiving station with the greatest rapidity.

21 Figures 2 , and 3 , represent the same parts as before described but in Figure 2 , only a single battery is shown and the resistance e, is between the line and the earth to regulate the proportion of electricity sent over the line, by adjusting such rheostat to prevent too great return to the battery through such rheostat.⁴

22 In Figure 3 , a condenser h, is introduced in addition to this rheostat that it may react between the pulsations of electricity on the main line to aid in clearing such line of the static charge.^e

I claim as my invention,—

An artificial line between the receiving instrument and the earth to balance the resistance and static charge or nearly so at both sides of the receiving instrument substantially as set forth—

Signed by me this 23rd day of April a.d. 1873.