Cyclopedia
of
Telephony and Telegraphy
A General Reference Work on
TELEPHONY, SUBSTATIONS, PARTY-LINE SYSTEMS, PROTECTION, MANUAL
SWITCHBOARDS, AUTOMATIC SYSTEMS, POWER PLANTS, SPECIAL SERVICE FEATURES, CONSTRUCTION, ENGINEERING, OPERATION, MAINTENANCE, TELEGRAPHY, WIRELESS TELEGRAPHY AND TELEPHONY, ETC.
Prepared by a Corps of
TELEPHONE AND TELEGRAPH EXPERTS, AND ELECTRICAL ENGINEERS OF
THE HIGHEST PROFESSIONAL STANDING
Illustrated with over Two Thousand Engravings
F O U R V O L U M E S
CHICAGO
AMERICAN SCHOOL OF CORRESPONDENCE
1919
Authors and Collaborators
KEMPSTER B. MILLER. M.E.
Consulting Engineer and Telephone Expert
Of the Firm of McMeen and Miller, Electrical Engineers and Patent Experts, Chicago
American Institute of Electrical Engineers
Western Society of Engineers
GEORGE W. PATTERSON, S.B., Ph.D.
Head, Department of Electrical Engineering, University of Michigan
CHARLES THOM
Chief of Quadruplex Department, Western Union Main Office, New York City
ROBERT ANDREWS MILLIKAN, Ph.D.
Associate Professor of Physics, University of Chicago
Member, Executive Council, American Physical Society
SAMUEL G. McMEEN
Consulting Engineer and Telephone Expert
Of the Firm of McMeen and Miller, Electrical Engineers and Patent Experts, Chicago
American Institute of Electrical Engineers
Western Society of Engineers
LAWRENCE K. SAGER, S.B., M.P.L.
Patent Attorney and Electrical Expert
Formerly Assistant Examiner, U.S. Patent Office
GLENN M. HOBBS, Ph.D.
Secretary, American School of Correspondence
Formerly Instructor in Physics, University of Chicago
American Physical Society
CHARLES G. ASHLEY
Electrical Engineer and Expert in Wireless Telegraphy and Telephony
A. FREDERICK COLLINS
Editor, Collins Wireless Bulletin
Author of "Wireless Telegraphy, Its History, Theory, and Practice"
FRANCIS B. CROCKER, E.M., Ph.D.
Head, Department of Electrical Engineering, Columbia University
Past-President, American Institute of Electrical Engineers
MORTON ARENDT, E.E.
Instructor in Electrical Engineering, Columbia University, New York
EDWARD B. WAITE
Head, Instruction Department, American School of Correspondence
American Society of Mechanical Engineers
Western Society of Engineers
DAVID P. MORETON, B.S., E.E.
Associate Professor of Electrical Engineering, Armour Institute of Technology
American Institute of Electrical Engineers
LEIGH S. KEITH, B.S.
Managing Engineer with McMeen and Miller, Electrical Engineers and Patent Experts Chicago
Associate Member, American Institute of Electrical Engineers
JESSIE M. SHEPHERD, A.B.
Associate Editor, Textbook Department, American School of Correspondence
ERNEST L. WALLACE, B.S.
Assistant Examiner, United States Patent Office, Washington, D. C.
GEORGE R. METCALFE, M.E.
Editor, American Institute of Electrical Engineers
Formerly Head of Publication Department, Westinghouse Elec. & Mfg. Co.
J.P. SCHROETER
Graduate, Munich Technical School
Instructor in Electrical Engineering, American School of Correspondence
JAMES DIXON, E.E.
American Institute of Electrical Engineers
HARRIS C. TROW, S.B., Managing Editor
Editor-in-Chief, Textbook Department, American School of Correspondence
Authorities Consulted
The editors have freely consulted the standard technical literature of America and Europe in the preparation of these volumes. They desire to express their indebtedness particularly to the following eminent authorities, whose well-known works should be in the library of every telephone and telegraph engineer.
Grateful acknowledgment is here made also for the invaluable co-operation of the foremost engineering firms and manufacturers in making these volumes thoroughly representative of the very best and latest practice in the transmission of intelligence, also for the valuable drawings, data, suggestions, criticisms, and other courtesies.
ARTHUR E. KENNELY, D.Sc.
Professor of Electrical Engineering, Harvard University.
Joint Author of "The Electric Telephone." "The Electric Telegraph," "Alternating
Currents," "Arc Lighting," "Electric Heating," "Electric Motors," "Electric Railways,"
"Incandescent Lighting," etc.
HENRY SMITH CARHART, A.M., LL.D.
Professor of Physics and Director of the Physical Laboratory, University of Michigan.
Author of "Primary Batteries," "Elements of Physics," "University Physics," "Electrical
Measurements," "High School Physics," etc.
FRANCIS B. CROCKER, M.E., Ph.D.
Head of Department of Electrical Engineering, Columbia University, New York; Past-President,
American Institute of Electrical Engineers.
Author of "Electric Lighting;" Joint Author of "Management of Electrical Machinery."
HORATIO A. FOSTER
Consulting Engineer; Member of American Institute of Electrical Engineers; Member
of American Society of Mechanical Engineers.
Author of "Electrical Engineer's Pocket-Book."
WILLIAM S. FRANKLIN, M.S., D.Sc.
Professor of Physics, Lehigh University.
Joint Author of "The Elements of Electrical Engineering," "The Elements of Alternating Currents."
LAMAR LYNDON, B.E., M.E.
Consulting Electrical Engineer; Associate Member of American Institute of Electrical
Engineers; Member, American Electro-Chemical Society.
Author of "Storage Battery Engineering."
ROBERT ANDREWS MILLIKAN, Ph.D.
Professor of Physics, University of Chicago.
Joint Author of "A First Course in Physics," "Electricity, Sound and Light," etc.
KEMPSTER B. MILLER, M.E.
Consulting Engineer and Telephone Expert; of the Firm of McMeen and Miller,
Electrical Engineers and Patent Experts, Chicago.
Author of "American Telephone Practice."
WILLIAM H. PREECE
Chief of the British Postal Telegraph.
Joint Author of "Telegraphy," "A Manual of Telephony," etc.—
LOUIS BELL, Ph.D.
Consulting Electrical Engineer; Lecturer on Power Transmission, Massachusetts Institute of Technology.
Author of "Electric Power Transmission," "Power Distribution for Electric Railways,"
"The Art of Illumination," "Wireless Telephony," etc.
OLIVER HEAVISIDE, F.R.S.
Author of "Electro-Magnetic Theory," "Electrical Papers," etc.
SILVANUS P. THOMPSON, D.Sc, B.A., F.R.S., F.R.A.S.
Principal and Professor of Physics in the City and Guilds of London Technical College.
Author of "Electricity and Magnetism," "Dynamo-Electric Machinery,"
"Polyphase Electric Currents and Alternate-Current Motors," "The Electromagnet," etc.
ANDREW GRAY, M.A., F.R.S.E.
Author of "Absolute Measurements in Electricity and Magnetism."
ALBERT CUSHING CREHORE, A.B., Ph.D.
Electrical Engineer; Assistant Professor of Physics, Dartmouth College; Formerly instructor in Physics, Cornell University.
Author of "Synchronous and Other Multiple Telegraphs;" Joint Author of "Alternating Currents."
J. J. THOMSON, D.Sc, LL.D., Ph.D., F.R.S.
Fellow of Trinity College, Cambridge University; Cavendish Professor of Experimental Physics, Cambridge University.
Author of "The Conduction of Electricity through Gases," "Electricity and Matter."
FREDERICK BEDELL, Ph. D.
Professor of Applied Electricity, Cornell University.
Author of "The Principles of the Transformer;" Joint Author of "Alternating Currents."
DUGALD C. JACKSON, C.E.
Head of Department of Electrical Engineering, Massachusetts Institute of Technology;
Member, American Institute of Electrical Engineers, etc.
Author of "A Textbook on Electromagnetism and the Construction of Dynamos;"
Joint Author of "Alternating Currents and Alternating-Current Machinery."
MICHAEL IDVORSKY PUPIN, A.B., Sc.D., Ph.D.
Professor of Electro-Mechanics, Columbia University, New York.
Author of "Propagation of Long Electric Waves," and "Wave-Transmission over Non-Uniform Cables and Long-Distance Air Lines."
FRANK BALDWIN JEWETT, A.B., Ph.D.
Transmission and Protection Engineer, with American Telephone & Telegraph Co.
Author of "Modern Telephone Cable," "Effect of Pressure on Insulation Resistance."
ARTHUR CROTCH
Formerly Lecturer on Telegraphy and Telephony at the Municipal Technical Schools, Norwich, Eng.
Author of "Telegraphy and Telephony."
JAMES ERSKINE-MURRAY, D.Sc.
Fellow of the Royal Society of Edinburgh; Member of the Institution of Electrical Engineers.
Author of "A Handbook of Wireless Telegraphy."
A.H. MCMILLAN, A.B., LL.B.
Author of "Telephone Law, A Manual on the Organization and Operation of Telephone Companies."
WILLIAM ESTY, S.B., M.A.
Head of Department of Electrical Engineering, Lehigh University.
Joint Author of "The Elements of Electrical Engineering."
GEORGE W. WILDER, Ph.D.
Formerly Professor of Telephone Engineering, Armour Institute of Technology.
Author of "Telephone Principles and Practice," "Simultaneous Telegraphy and Telephony," etc.
WILLIAM L. HOOPER, Ph.D.
Head of Department of Electrical Engineering, Tufts College.
Joint Author of "Electrical Problems for Engineering Students."
DAVID S. HULFISH
Technical Editor, The Nickelodeon; Telephone and Motion-Picture Expert; Solicitor of Patents.
Author of "How to Read Telephone Circuit Diagrams."
J.A. FLEMING, M.A., D.Sc. (Lond.), F.R.S.
Professor of Electrical Engineering in University College, London;
Late Fellow and Scholar of St. John's College, Cambridge; Fellow of University College, London.
Author of "The Alternate-Current Transformer," "Radiotelegraphy and Radiotelephony,"
"Principles of Electric Wave Telegraphy," "Cantor Lectures on Electrical Oscillations and Electric Waves," "Hertzian Wave Wireless Telegraphy," etc.
F.A.C. PERRINE, A.M., D.Sc.
Consulting Engineer: Formerly President, Stanley Electric Manufacturing Company;
Formerly Professor of Electrical Engineering, Leland Stanford, Jr. University.
Author of "Conductors for Electrical Distribution."
A. FREDERICK COLLINS
Editor, Collins Wireless Bulletin.
Author of "Wireless Telegraphy, Its History, Theory and Practice," "Manual of Wireless Telegraphy," "Design and Construction of Induction Coils," etc.
SCHUYLER S. WHEELER, D.Sc.
President, Crocker-Wheeler Co.; Past-President, American Institute of Electrical Engineers.
Joint Author of "Management of Electrical Machinery."
CHARLES PROTEUS STEINMETZ
Consulting Engineer, with the General Electric Co.; Professor of Electrical Engineering, Union College.
Author of "The Theory and Calculation of Alternating-Current Phenomena," "Theoretical Elements of Electrical Engineering", etc.
GEORGE W. PATTERSON, S.B., Ph.D.
Head of Department of Electrical Engineering, University of Michigan.
Joint Author of "Electrical Measurements."
WILLIAM MAVER, JR.
Ex-Electrician Baltimore and Ohio Telegraph Company; Member of the American Institute of Electrical Engineers.
Author of "American Telegraphy and Encyclopedia of the Telegraph," "Wireless Telegraphy."
JOHN PRICE JACKSON, M.E.
Professor of Electrical Engineering, Pennsylvania State College.
Joint Author of "Alternating Currents and Alternating-Current Machinery."
AUGUSTUS TREADWELL, JR., E.E.
Associate Member, American Institute of Electrical Engineers.
Author of "The Storage Battery, A Practical Treatise on Secondary Batteries."
EDWIN J. HOUSTON, Ph.D.
Professor of Physics, Franklin Institute, Pennsylvania; Joint Inventor of Thomson-Houston System of Arc Lighting; Electrical Expert and Consulting Engineer.
Joint Author of "The Electric Telephone," "The Electric Telegraph," "Alternating Currents," "Arc Lighting," "Electric Heating," "Electric Motors," "Electric Railways," "Incandescent Lighting," etc.
WILLIAM J. HOPKINS
Professor of Physics in the Drexel Institute of Art, Science, and Industry, Philadelphia.
Author of "Telephone Lines and their Properties."
Foreword
The present day development of the "talking wire" has annihilated both time and space, and has enabled men thousands of miles apart to get into almost instant communication. The user of the telephone and the telegraph forgets the tremendousness of the feat in the simplicity of its accomplishment; but the man who has made the feat possible knows that its very simplicity is due to the complexity of the principles and appliances involved; and he realizes his need of a practical, working understanding of each principle and its application. The Cyclopedia of Telephony and Telegraphy presents a comprehensive and authoritative treatment of the whole art of the electrical transmission of intelligence.
The communication engineer—if so he may be called—requires a knowledge both of the mechanism of his instruments and of the vagaries of the current that makes them talk. He requires as well a knowledge of plants and buildings, of office equipment, of poles and wires and conduits, of office system and time-saving methods, for the transmission of intelligence is a business as well as an art. And to each of these subjects, and to all others pertinent, the Cyclopedia gives proper space and treatment.
The sections on Telephony cover the installation, maintenance, and operation of all standard types of telephone systems; they present without prejudice the respective merits of manual and automatic exchanges; and they give special attention to the prevention and handling of operating "troubles." The sections on Telegraphy cover both commercial service and train dispatching. Practical methods of wireless communication—both by telephone and by telegraph—are thoroughly treated.
The drawings, diagrams, and photographs incorporated into the Cyclopedia have been prepared especially for this work; and their instructive value is as great as that of the text itself. They have been used to illustrate and illuminate the text, and not as a medium around which to build the text. Both drawings and diagrams have been simplified so far as is compatible with their correctness, with the result that they tell their own story and always in the same language.
The Cyclopedia is a compilation of many of the most valuable Instruction Papers of the American School of Correspondence, and the method adopted in its preparation is that which this School has developed and employed so successfully for many years. This method is not an experiment, but has stood the severest of all tests—that of practical use—which has demonstrated it to be the best yet devised for the education of the busy, practical man.
In conclusion, grateful acknowledgment is due to the staff of authors and collaborators, without whose hearty co-operation this work would have been impossible.
Table of Contents
VOLUME I
Fundamental Principles By K. B. Miller and S. G. McMeen [[A]] Page 11
[CHAPTER I]—Acoustics—Characteristics of Sound—Loudness—Pitch—Vibration of Diaphragms—Timbre—Human Voice—Human Ear
[CHAPTER II]—Speech—Magneto Telephones—Loose-Contact Principle—Induction Coils
[CHAPTER III]—Simple Telephone Circuit—Capacity—Telephone Currents—Audible and Visible Signals
[CHAPTER IV]—Telephone Lines—Conductors—Inductance—Insulation
Substation Equipment By K. B. Miller and S. G. McMeen Page 63
[CHAPTER V]—Transmitters—Variable Resistance—Materials—Single and Multiple Electrodes—Solid-Back Transmitter—Types of Transmitters—Electrodes—Packing—Acousticon Transmitter—Switchboard Transmitter
[CHAPTER VI]—Receivers—Types of Receivers—Operator's Receiver
[CHAPTER VII]—Primary Cells—Series and Multiple Connections—Types of Primary Cells
[CHAPTER VIII]—Magneto Signaling Apparatus—Battery Bell—Magneto Bell—Magneto Generator—Armature—Automatic Shunt—Polarized Ringer
[CHAPTER IX]—Hook Switch
[CHAPTER X]—Electromagnets—Impedance, Induction, and Repeating Coils
[CHAPTER XI]—Non-Inductive Resistance Devices—Differentially-Wound Unit
[CHAPTER XII]—Condensers—Materials
[CHAPTER XIII]—Current Supply to Transmitters—Local Battery—Common Battery—Diagrams of Common-Battery Systems
[CHAPTER XIV]—Telephone Sets: Magneto, Series and Bridging, Common-Battery
Party-Line Systems By K. B. Miller and S. G. McMeen Page 227
[CHAPTER XV]—Non-Selective Party-Line Systems—Series and Bridging—Signal Code
[CHAPTER XVI]—Selective Party-Line Systems: Polarity, Harmonic, Step-by-Step, and Broken-Line
[CHAPTER XVII]—Lock-Out Party-Line Systems: Poole, Step-by-Step, and Broken-Line
Protection By K. B. Miller and S. G. McMeen Page 287
[CHAPTER XVII]—Electrical Hazards
[CHAPTER XIX]—High Potentials—Air-Gap Arrester—Discharge across Gaps—Types of Arrester—Vacuum Arrester—Strong Currents—Fuses—Sneak Currents—Line Protection—Central-Office and Subscribers' Station Protectors—City Exchange Requirements—Electrolysis
Manual Switchboards By K. B. Miller and S. G. McMeen Page 317
[CHAPTER XX]—The Telephone Exchange—Subscribers', Trunk, and Toll Lines—Districts—Switchboards
[CHAPTER XXI]—Simple Magneto Switchboard—Operation—Commercial Types of Drops and Jacks—Manual vs. Automatic Restoration—Switchboard Plugs and Cords—Ringing and Listening Keys—Operator's Telephone Equipment—Circuits of Complete Switchboard—Night-Alarm Circuits—Grounded and Metallic Circuit Line—Cord Circuit—Switchboard Assembly
[Review Questions] Page 387
[Index] Page 401
[A] For professional standing of authors, see list of Authors and Collaborators at front of volume.
List of Photographs
[A TYPICAL SMALL MAGNETO SWITCHBOARD INSTALLATION]
![[A TYPICAL SMALL MAGNETO SWITCHBOARD INSTALLATION]](#1895676483475499077_pic_p011.jpg.id-6444820749136667165.wrap-0.html.html){kind=link}
[A TYPICAL CENTRAL OFFICE FOR RURAL EXCHANGE
Line Protectors on Wall at Left.]
![[A TYPICAL CENTRAL OFFICE FOR RURAL EXCHANGELine Protectors on Wall at Left.]](#1895676483475499077_pic_p012.jpg.id-1872692328416818122.wrap-0.html.html){kind=link}
[OLD BRANCH-TERMINAL MULTIPLE BOARD, PARIS, FRANCE]
![[OLD BRANCH-TERMINAL MULTIPLE BOARD, PARIS, FRANCE]](#1895676483475499077_pic_p016.jpg.id-1855789591768456136.wrap-0.html.html){kind=link}
[No. 10 SERIES MULTIPLE SWITCHBOARD
Monarch Telephone Mfg. Co.]
![[No. 10 SERIES MULTIPLE SWITCHBOARDMonarch Telephone Mfg. Co.]](#1895676483475499077_pic_p033.jpg.id-5724145375452417146.wrap-0.html.html){kind=link}
[OPERATOR'S EQUIPMENT
Clement Automanual System]
![[OPERATOR'S EQUIPMENTClement Automanual System]](#1895676483475499077_pic_p052.jpg.id-5755545488062396365.wrap-0.html.html){kind=link}
![[MAIN ENTRANCE AND PUBLIC OFFICE, SAN FRANCISCO HOME TELEPHONE COMPANYContract Department on Left. Accounting Department on Right.]](#1895676483475499077_pic_p069.jpg.id-6118060623084531092.wrap-0.html.html){kind=link}
![[MAIN OFFICE BUILDING, BERKELEY, CALIFORNIAContaining Automatic Equipment, Forming Part of Larger System Operating in San Francisco and Vicinity. Bay Cities Home Telephone Company.]](#1895676483475499077_pic_p086.jpg.id-2581453719184007863.wrap-0.html.html){kind=link}
![[GRANT AVENUE OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCO, CAL.A Type of Central-Office Buildings in Down-Town Districts of Large Cities.]](#1895676483475499077_pic_p103.jpg.id-4577621121205326369.wrap-0.html.html){kind=link}
[INTERIOR OF WAREHOUSE FOR TELEPHONE CONSTRUCTION MATERIAL]
![[INTERIOR OF WAREHOUSE FOR TELEPHONE CONSTRUCTION MATERIAL]](#1895676483475499077_pic_p122.jpg.id-6113298507104411762.wrap-0.html.html){kind=link}
![[HOWARD OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCOAn All-Concrete Building Serving the District South of Market Street.]](#1895676483475499077_pic_p139.jpg.id-4128302608157994716.wrap-0.html.html){kind=link}
![[WEST OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCOServing the General Western Business and Residence Districts.]](#1895676483475499077_pic_p157.jpg.id-6791321618949926625.wrap-0.html.html){kind=link}
[COMPRESSED AIR WAGON FOR PNEUMATIC DRILLING AND CHIPPING IN MANHOLES]
![[COMPRESSED AIR WAGON FOR PNEUMATIC DRILLING AND CHIPPING IN MANHOLES]](#1895676483475499077_pic_p161.jpg.id-2659056289467788632.wrap-0.html.html){kind=link}
[SOUTH OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCO]
![[SOUTH OFFICE OF HOME TELEPHONE COMPANY, SAN FRANCISCO]](#1895676483475499077_pic_p175.jpg.id-7997176993608668038.wrap-0.html.html){kind=link}
[THE OPERATING ROOM OF THE EXCHANGE AT WEBB CITY, MISSOURI]
![[THE OPERATING ROOM OF THE EXCHANGE AT WEBB CITY, MISSOURI]](#1895676483475499077_pic_p194.jpg.id-5581060156056695144.wrap-0.html.html){kind=link}
[A TYPICAL MEDIUM-SIZED MULTIPLE SWITCHBOARD EQUIPMENT]
![[A TYPICAL MEDIUM-SIZED MULTIPLE SWITCHBOARD EQUIPMENT]](#1895676483475499077_pic_p211.jpg.id-6439668232916948826.wrap-0.html.html){kind=link}
[MAIN OFFICE, KEYSTONE TELEPHONE COMPANY, PHILADELPHIA, PA.]
![[MAIN OFFICE, KEYSTONE TELEPHONE COMPANY, PHILADELPHIA, PA.]](#1895676483475499077_pic_p230.jpg.id-6516904846686282202.wrap-0.html.html){kind=link}
[MAIN OFFICE, KANSAS CITY HOME TELEPHONE CO., KANSAS CITY, MO.]
![[MAIN OFFICE, KANSAS CITY HOME TELEPHONE CO., KANSAS CITY, MO.]](#1895676483475499077_pic_p247.jpg.id-3711337650768984250.wrap-0.html.html){kind=link}
[VENTILATING PLANT FOR LARGE TELEPHONE OFFICE BUILDING]
![[VENTILATING PLANT FOR LARGE TELEPHONE OFFICE BUILDING]](#1895676483475499077_pic_p254.jpg.id-5575416443380298772.wrap-0.html.html){kind=link}
![[ONE WING OF OPERATING ROOM, BERLIN, GERMANYUltimate Capacity 24,000 Subscribers' Lines and 2,100 Trunk Lines. Siemens-Halske Equipment. Note Horizontal Disposal of Multiple]](#1895676483475499077_pic_p262.jpg.id-2389909423153406152.wrap-0.html.html){kind=link}
[OPERATING ROOM AT TOKYO, JAPAN]
![[OPERATING ROOM AT TOKYO, JAPAN]](#1895676483475499077_pic_p285.jpg.id-6257139579383650853.wrap-0.html.html){kind=link}
![[ONE WING OF OPERATING ROOM, BERLIN, GERMANYUltimate Capacity 24,000 Subscribers' Lines and 2,100 Trunk Lines. Siemens-Halske Equipment. Note Horizontal Disposal of Multiple Jack Field.]](#1895676483475499077_pic_p298.jpg.id-5711623849244049638.wrap-0.html.html){kind=link}
[VIEW OF A LARGE FOREIGN MULTIPLE SWITCHBOARD]
![[VIEW OF A LARGE FOREIGN MULTIPLE SWITCHBOARD]](#1895676483475499077_pic_p315.jpg.id-3028924183836835431.wrap-0.html.html){kind=link}
[OLD SWITCHBOARD OF BELL EXCHANGE SERVING CHINATOWN, SAN FRANCISCO, CALIFORNIA]
![[OLD SWITCHBOARD OF BELL EXCHANGE SERVING CHINATOWN, SAN FRANCISCO, CALIFORNIA]](#1895676483475499077_pic_p334.jpg.id-6368823593477009122.wrap-0.html.html){kind=link}
![[ONE OF THE FOUR WINGS OF THE OLD KELLOGG DIVIDED MULTIPLE BOARD OF THE CUYAHOGA TELEPHONE COMPANY, CLEVELAND, OHIOUltimate Capacity, 24,000 Lines. One of the Two Examples in the United States of a Multiple Switchboard Having an Ultimate Capacity over 18,000 Lines. Replaced Recently by a Kellogg Straight Multiple Board Having an Ultimate Capacity of 18,000 Lines and a Present Capacity of 10,000 Lines.]](#1895676483475499077_pic_p351.jpg.id-8144627237818682095.wrap-0.html.html){kind=link}
![[MAIN EXCHANGE, CLEVELAND, OHIO.Largest Four-Party Selective Ringing Switchboard in the World. Kellogg Switchboard and Supply Co.]](#1895676483475499077_pic_p354.jpg.id-5879680147732713623.wrap-0.html.html){kind=link}
[A SPECIALLY FORMED CABLE FOR KEY SHELF OF MONARCH SWITCHBOARD]
![[A SPECIALLY FORMED CABLE FOR KEY SHELF OF MONARCH SWITCHBOARD]](#1895676483475499077_pic_p370.jpg.id-8029202691329062428.wrap-0.html.html){kind=link}
TELEPHONY
INTRODUCTION
The telephone was invented in 1875 by Alexander Graham Bell, a resident of the United States, a native of Scotland, and by profession a teacher of deaf mutes in the art of vocal speech. In that year, Professor Bell was engaged in the experimental development of a system of multiplex telegraphy, based on the use of rapidly varying currents. During those experiments, he observed an iron reed to vibrate before an electromagnet as a result of another iron reed vibrating before a distant electromagnet connected to the nearer one by wires.
The telephone resulted from this observation with great promptness. In the instrument first made, sound vibrated a membrane diaphragm supporting a bit of iron near an electromagnet; a line joined this simple device of three elements to another like it; a battery in the line magnetized both electromagnet cores; the vibration of the iron in the sending device caused the current in the line to undulate and to vary the magnetism of the receiving device. The diaphragm of the latter was vibrated in consequence of the varying pull upon its bit of iron, and these vibrations reproduced the sound that vibrated the sending diaphragm.
The first public use of the electric telephone was at the Centennial Exposition in Philadelphia in 1876. It was there tested by many interested observers, among them Sir William Thomson, later Lord Kelvin, the eminent Scotch authority on matters of electrical communication. It was he who contributed so largely to the success of the early telegraph cable system between England and America. Two of his comments which are characteristic are as follows:
To-day I have seen that which yesterday I should have deemed impossible. Soon lovers will whisper their secrets over an electric wire.
Who can but admire the hardihood of invention which devised such slight means to realize the mathematical conception that if electricity is to convey all the delicacies of sound which distinguish articulate speech, the strength of its current must vary continuously as nearly as may be in simple proportion to the velocity of a particle of the air engaged in constituting the sound.
Contrary to usual methods of improving a new art, the earliest improvement of the telephone simplified it. The diaphragms became thin iron disks, instead of membranes carrying iron; the electromagnet cores were made of permanently magnetized steel instead of temporarily magnetized soft iron, and the battery was omitted from the line. The undulatory current in a system of two such telephones joined by a line is produced in the sending telephone by the vibration of the iron diaphragm. The vibration of the diaphragm in the receiving telephone is produced by the undulatory current. Sound is produced by the vibration of the diaphragm of the receiving telephone.
Such a telephone is at once the simplest known form of electric generator or motor for alternating currents. It is capable of translating motion into current or current into motion through a wide range of frequencies. It is not known that there is any frequency of alternating current which it is not capable of producing and translating. It can produce and translate currents of greater complexity than any other existing electrical machine.
Though possessing these admirable qualities as an electrical machine, the simple electromagnetic telephone had not the ability to transmit speech loudly enough for all practical uses. Transmitters producing stronger telephonic currents were developed soon after the fundamental invention. Some forms of these were invented by Professor Bell himself. Other inventors contributed devices embodying the use of carbon as a resistance to be varied by the motions of the diaphragm. This general form of transmitting telephone has prevailed and at present is the standard type.
It is interesting to note that the earliest incandescent lamps, as invented by Mr. Edison, had a resistance material composed of carbon, and that such a lamp retained its position as the most efficient small electric illuminant until the recent introduction of metal filament lamps. It is possible that some form of metal may be introduced as the resistance medium for telephone transmitters, and that such a change as has taken place in incandescent lamps may increase the efficiency of telephone transmitting devices.
At the time of the invention of the telephone, there were in existence two distinct types of telegraph, working in regular commercial service. In the more general type, many telegraph stations were connected to a line and whatever was telegraphed between two stations could be read by all the stations of that line. In the other and less general type, many lines, each having a single telegraph station, were centered in an office or "exchange," and at the desire of a user his line could be connected to another and later disconnected from it.
Both of these types of telegraph service were imitated at once in telephone practice. Lines carrying many telephones each, were established with great rapidity. Telephones actually displaced telegraphic apparatus in the exchange method of working in America. The fundamental principle on which telegraph or telephone exchanges operate, being that of placing any line in communication with any other in the system, gave to each line an ultimate scope so great as to make this form of communication more popular than any arrangement of telephones on a single line. Beginning in 1877, telephone exchanges were developed with great rapidity in all of the larger communities of the United States. Telegraph switching devices were utilized at the outset or were modified in such minor particulars as were necessary to fit them to the new task.
In its simplest form, a telephone system is, of course, a single line permanently joining two telephones. In its next simplest form, it is a line permanently joining more than two telephones. In its most useful form, it is a line joining a telephone to some means of connecting it at will to another.
A telephone exchange central office contains means for connecting lines at will in that useful way. The least complicated machine for that purpose is a switchboard to be operated by hand, having some way of letting the operator know that a connection is wished and a way of making it. The customary way of connecting the lines always has been by means of flexible conductors fitted with plugs to be inserted in sockets. If the switchboard be small enough so that all the lines are within arm's reach of the operator, the whole process is individual, and may be said to be at its best and simplest. There are but few communities, however, in which the number of lines to be served and calls to be answered is small enough so that the entire traffic of the exchange can be handled by a single person. An obvious way, therefore, is to provide as many operators in a central office as may be required by the number of calls to be answered, and to terminate before each of the operators enough of the lines to bring enough work to keep that operator economically occupied. This presents the additional problem, how to connect a line terminating before one operator to a line normally terminating before another operator. The obvious answer is to provide lines from each operator's place of work to each other operator's place, connecting a calling line to some one of these lines which are local within the central office, and, in turn, connecting that chosen local line to the line which is called.
Such lines between operators have come to be known as trunk lines, because of the obvious analogy to trunk lines of railways between common centers, and such a system of telephone lines may be called a trunking system. Very good service has been given and can be given by such an arrangement of local trunks, but the growth in lines and in traffic has developed in most instances certain weaknesses which make it advisable to find speedier, more accurate, and more reliable means.
For the serving of a large traffic from a large number of lines, as is required in practically every city of the world, a very great contribution to the practical art was made by the development of the multiple switchboard. Such a switchboard is merely such a device as has been described for the simpler cases, with the further refinement that within reach of each operator in the central office appears every line which enters that office, and this without regard to what point in the switchboard the lines may terminate for the answering of calls. In other words, while each operator answers a certain subordinate group of the total number of lines, each operator may reach, for calling purposes, every line which enters that office. It is probable that the invention and development of the multiple switchboard was the first great impetus toward the wide-spread use of telephone service.
Coincident with the development of the multiple switchboard for manually operated, central-office mechanisms was the beginning of the development of automatic apparatus under the control of the calling subscriber for finding and connecting with a called line. It is interesting to note the general trend of the early development of automatic apparatus in comparison with the development, to that time, of manual telephone apparatus.
While the manual apparatus on the one hand attempted to meet its problem by providing local trunks between the various operators of a central office, and failing of success in that, finally developed a means which placed all the lines of a central office within connecting reach of each operator, automatic telephony, beginning at that point, failed of success in attempting to bring each line in the central office within connecting reach of each connecting mechanism.
In other terms, the first automatic switching equipment consisted of a machine for each line, which machine was so organized as to be able to find and connect its calling line with any called line of the entire central-office group. It may be said that an attempt to develop this plan was the fundamental reason for the repeated failure of automatic apparatus to solve the problem it attacked. All that the earlier automatic system did was to prove more or less successfully that automatic apparatus had a right to exist, and that to demand of the subscriber that he manipulate from his station a distant machine to make the connection without human aid was not fallacious. When it had been recognized that the entire multiple switchboard idea could not be carried into automatic telephony with success, the first dawn of hope in that art may be said to have come.
Success in automatic telephony did come by the re-adoption of the trunking method. As adopted for automatic telephony, the method contemplates that the calling line shall be extended, link by link, until it finds itself lengthened and directed so as to be able to seize the called line in a very much smaller multiple than the total group of one office of the exchange.
A similar curious reversion has taken place in the development of telephone lines. The earliest telephone lines were merely telegraph lines equipped with telephone instruments, and the earliest telegraph lines were planned by Professor Morse to be insulated wires laid in the earth. A lack of skill in preparing the wires for putting in the earth caused these early underground lines to be failures. At the urging of one of his associates, Professor Morse consented to place his earliest telegraph lines on poles in the air. Each such line originally consisted of two wires, one for the going and one for the returning current, as was then considered the action. Upon its being discovered that a single wire, using the earth as a return, would serve as a satisfactory telegraph line, such practice became universal. Upon the arrival of the telephone, all lines obviously were built in the same way, and until force of newer circumstances compelled it, the present metallic circuit without an earth connection did not come into general use.
The extraordinary growth of the number of telephone lines in a community and the development of other methods of electrical utilization, as well as the growth in the knowledge of telephony itself, ultimately forced the wires underground again. At the same time and for the same causes, a telephone line became one of two wires, so that it becomes again the counterpart of the earliest telegraph line of Professor Morse.