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+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
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+the "Copyright How-To" at https://www.gutenberg.org.
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #64592 (https://www.gutenberg.org/ebooks/64592)
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-The Project Gutenberg eBook of Harper's Electricity Book for Boys, by
-Joseph H. (Henry) Adams
-
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org. If you are not located in the United States, you
-will have to check the laws of the country where you are located before
-using this eBook.
-
-Title: Harper's Electricity Book for Boys
-
-Author: Joseph H. (Henry) Adams
-
-Contributor: Joseph B. Baker
-
-Release Date: February 18, 2021 [eBook #64592]
-
-Language: English
-
-Character set encoding: UTF-8
-
-Produced by: Richard Hulse, Harry Lamé and the Online Distributed
-             Proofreading Team at https://www.pgdp.net (This file was
-             produced from images generously made available by The Internet
-             Archive/American Libraries.)
-
-*** START OF THE PROJECT GUTENBERG EBOOK HARPER'S ELECTRICITY BOOK FOR
-BOYS ***
-
-
-  Transcriber’s Notes
-
-  Text printed in italics has been transcribed _between underscores_,
-  bold face text has been transcribed =between equal signs=. Small
-  capitals have been replaced with all capitals.
-
-  Single letters in square brackets, such as [T] and [V], represent
-  shapes rather than letters.
-
-  More Transcriber’s Notes may be found at the end of this text.
-
-
-
-
-  Harper’s Practical Books for Boys
-
-  A SERIES OF NEW HANDY-BOOKS FOR AMERICAN BOYS
-
-  _Each Crown 8vo, with many Illustrations._
-
-
-  I
-
-  HARPER’S OUTDOOR BOOK FOR BOYS
-
-  By Joseph H. Adams. With Additional Contributions by Kirk Munroe,
-  Tappan Adney, Capt. Howard Patterson, L. M. Yale, and others. Cloth,
-  $1.75.
-
-
-  II
-
-  HARPER’S ELECTRICITY BOOK FOR BOYS
-
-  Written and Illustrated by Joseph H. Adams. With a Dictionary of
-  Electrical Terms. Cloth, $1.75.
-
-  _IN PRESS_
-
-
-  III
-
-  HARPER’S HOW TO UNDERSTAND ELECTRICAL WORK
-
-  A Simple Explanation of Electric Light, Heat, Power, and Traction in
-  Daily Life. By Joseph B. Baker, Technical Editor, U. S. Geological
-  Survey, formerly of the General Electric Company.
-
-
-  IV
-
-  HARPER’S INDOOR BOOK FOR BOYS
-
-  By Joseph H. Adams and others. Cloth, $1.75.
-
-
-  V
-
-  HARPER’S MACHINERY BOOK FOR BOYS
-
-  The Boy’s Own Book of Engines and Machinery. Cloth, $1.75.
-
-
-  HARPER & BROTHERS, PUBLISHERS, NEW YORK
-
-
-[Illustration: Copyright, 1907, by Joseph H. Adams, N. Y.
-
-THOMAS A. EDISON DICTATING TO HIS GRAPHOPHONE]
-
-
-
-
-  HARPER’S
-  ELECTRICITY BOOK
-  FOR BOYS
-
-  WRITTEN AND ILLUSTRATED BY
-  =JOSEPH H. ADAMS=
-
-  AUTHOR OF
-  “HARPER’S OUTDOOR BOOK FOR BOYS”
-
-  WITH AN EXPLANATION OF ELECTRIC LIGHT, HEAT
-  POWER, AND TRACTION BY JOSEPH B. BAKER
-  TECHNICAL EDITOR, U. S. GEOLOGICAL SURVEY
-
-  AND
-
-  =A DICTIONARY OF ELECTRICAL TERMS=
-
-  [Illustration]
-
-  HARPER & BROTHERS PUBLISHERS
-  NEW YORK AND LONDON
-  MCMVII
-
-
-  Copyright, 1907, by HARPER & BROTHERS.
-
-  _All rights reserved._
-
-  Published November, 1907.
-
-
-
-
-CONTENTS
-
-
-                                                                    PAGE
-
-  INTRODUCTION                                                        xi
-
-
-  Part I
-
-
-  CHAPTER I.--SOME GENERAL EXPLANATIONS                                3
-
-  AN INVISIBLE WORLD-POWER -- GENERATING ELECTRICITY -- WHAT A BOY
-  CAN DO -- INEXPENSIVE TOOLS -- SOME PRACTICAL ADVICE
-
-
-  CHAPTER II.--CELLS AND BATTERIES                                    12
-
-  SIMPLE AND INEXPENSIVE CELLS -- HOW TO MAKE CELLS AND BATTERIES
-  -- A PLUNGE-BATTERY -- A STORAGE-BATTERY -- DRY-CELLS AND
-  BATTERIES
-
-
-  CHAPTER III.--PUSH-BUTTONS AND SWITCHES                             33
-
-  HOW TO MAKE PUSH-BUTTONS -- SWITCHES AND CUT-OUTS -- TABLE-JACK
-  SWITCHES -- BINDING-POSTS AND CONNECTORS -- LIGHTNING-ARRESTERS
-  AND FUSE-BLOCKS -- SOME PRACTICAL PRECAUTIONS
-
-
-  CHAPTER IV.--MAGNETS AND INDUCTION-COILS                            54
-
-  SIMPLE AND HORSESHOE MAGNETS -- INDUCTION-COILS -- AN ELECTRIC
-  BUZZER -- ELECTRIC BELLS -- A LARGE INDUCTION-COIL --
-  CIRCUIT-INTERRUPTERS
-
-
-  CHAPTER V.--ANNUNCIATORS AND BELLS                                  78
-
-  A DRUM-SOUNDER -- A SIMPLE ANNUNCIATOR -- A DOUBLE ELECTRIC BELL
-  -- AN ELECTRIC HORN -- HOW TO MAKE A BURGLAR-ALARM -- ELECTRIC
-  CALL-SIGNALS -- CLOCK-ALARMS -- A DINING-TABLE CALL
-
-
-  CHAPTER VI.--CURRENT-DETECTORS AND GALVANOMETERS                   102
-
-  HOW TO MAKE DETECTORS -- AN ASTATIC CURRENT-DETECTOR -- AN
-  ASTATIC GALVANOMETER -- A TANGENT GALVANOMETER
-
-
-  Part II
-
-
-  CHAPTER VII.--ELECTRICAL RESISTANCE                                125
-
-  GOVERNING THE ELECTRIC CURRENT -- OHM’S LAW -- RESISTANCE-COILS
-  AND RHEOSTATS -- HOW TO MAKE SIMPLE APPARATUS -- LIQUID
-  RESISTANCE -- IMPORTANCE OF SWITCHES -- USES OF A HOUSE-CURRENT
-  -- RUNNING A SEWING-MACHINE, FAN, OR TOYS -- AN EASY METHOD FOR A
-  BOY’S USE
-
-
-  CHAPTER VIII.--THE TELEPHONE                                       156
-
-  VIBRATORY WAVES -- A BLADDER TELEPHONE -- A SINGLE (RECEIVER)
-  LINE -- PLAN OF INSTALLATION -- A DOUBLE-POLE RECEIVER -- THE
-  TRANSMITTER -- ANOTHER FORM OF TRANSMITTER -- THE WIRING SYSTEM
-  -- A TELEPHONE INDUCTION-COIL -- AN INSTALLATION PLAN -- A
-  PORTABLE APPARATUS
-
-
-  CHAPTER IX.--LINE AND WIRELESS TELEGRAPHS                          190
-
-  A GROUND TELEGRAPH -- HOW TO TALK FROM HOUSE TO HOUSE -- THE
-  MORSE TELEGRAPH CODE -- A STORY OF EDISON -- HOW DETECTIVES USED
-  THE CODE -- WIRELESS TELEGRAPHY -- ITS TRUE CHARACTER -- HOW A
-  BOY CAN MAKE A PRACTICAL APPARATUS -- RECEIVING AND SENDING POLES
-  -- INDUCTION-COILS, BATTERIES, COHERERS AND DE-COHERERS, ETC. --
-  WORKING PLANS IN DETAIL -- AËROGRAMS ACROSS THE ATLANTIC AND,
-  PERHAPS, AROUND THE WORLD
-
-
-  CHAPTER X.--DYNAMOS AND MOTORS                                     229
-
-  DEPENDENCE OF MODERN ELECTRICITY UPON THE DYNAMO -- A FIELD OF
-  FORCE CUTTING ANOTHER FIELD OF FORCE -- VARIETIES OF DYNAMOS --
-  SIMPLER FORMS OF GENERATORS AND MOTORS -- HOW TO MAKE A
-  UNI-DIRECTION CURRENT MACHINE -- PERMANENT MAGNET, ARMATURE,
-  SHAFTS, WHEELS, ETC. -- A SMALL DYNAMO -- MACHINES TO LIGHT
-  LAMPS, RUN MOTORS, ETC. -- A SPLIT-RING DYNAMO -- A SMALL MOTOR
-  -- THE FLAT-BED MOTOR -- MOTORS OF OTHER TYPES
-
-
-  CHAPTER XI.--GALVANISM AND ELECTRO-PLATING                         266
-
-  A FASCINATING USE OF ELECTRICITY -- A SIMPLE ELECTRO-PLATING
-  OUTFIT -- THE SULPHATE OF COPPER BATH -- HOW TO MAKE THE TANK AND
-  OTHER APPARATUS -- A VARIETY OF BEAUTIFUL AND USEFUL RESULTS --
-  EXPLANATIONS OF VARIOUS BATTERIES -- THE CLEANSING PROCESS -- THE
-  PLATING-BATH -- SILVER-PLATING -- GOLD-PLATING -- NICKEL-PLATING
-  -- FINISHING -- ELECTROTYPING -- PRACTICAL DETAILS OF INTERESTING
-  WORK
-
-
-  CHAPTER XII.--MISCELLANEOUS APPARATUS                              294
-
-  MAKING A ROTARY GLASS-CUTTER -- TO SMOOTH GLASS EDGES -- CUTTING
-  HOLES IN GLASS -- ANTI-HUM DEVICE FOR METALLIC LINES -- A
-  REEL-CAR FOR WIRE -- INSULATORS -- JOINTS AND SPLICES --
-  “GROUNDS” -- THE EDISON ROACH-KILLER -- AN ELECTRIC MOUSE-KILLER
-
-
-  CHAPTER XIII.--FRICTIONAL ELECTRICITY                              312
-
-  ITS NATURE -- LIMITED USES -- SIMPLICITY OF APPARATUS -- A
-  “WIMSHURST INFLUENCE MACHINE” -- MATERIALS REQUIRED -- GLASS,
-  TIN-FOIL, SPINDLES, UPRIGHTS, WHEELS, ETC. -- A LARGE LEYDEN-JAR
-  -- APPARATUS FOR INTERESTING EXPERIMENTS -- NECESSITY OF CAUTION
-
-
-  CHAPTER XIV.--FORMULÆ                                              327
-
-  ACID-PROOF CEMENTS -- HARD CEMENT -- SOFT CEMENT -- VERY HARD
-  CEMENT -- CLARK’S COMPOUND -- BATTERY FLUID -- GLASS RUBBING --
-  ACETIC GLUE -- INSULATORS -- NON-CONDUCTORS -- INSULATING VARNISH
-  -- BATTERY WAX
-
-
-  CHAPTER XV.--ELECTRIC LIGHT, HEAT AND POWER                        334
-  (By Joseph B. Baker)
-
-  THE WORK OF THE DYNAMO -- THE ELECTRIC LIGHT -- USES OF THE
-  ARC-LIGHT -- INCANDESCENT AND OTHER LAMPS -- ELECTRIC HEAT --
-  ELECTRIC FURNACES -- WELDING METALS -- ELECTRIC CAR-HEATERS --
-  HOUSEHOLD USES -- ELECTRIC POWER -- POWER FROM WATER-WHEELS --
-  TRANSFORMERS -- ROTARY CONVERTERS -- OIL-SWITCHES -- ELECTRIC
-  TRACTION -- THE TROLLEY-CAR -- THE CONTINUOUS-CURRENT MOTOR --
-  THE CONTROLLER -- ELECTRIC LOCOMOTIVES -- OTHER FORMS OF ELECTRIC
-  TRACTION
-
-
-  A DICTIONARY OF ELECTRICAL TERMS                                   359
-
-
-
-
-INTRODUCTION
-
-
-If a handy-book of electricity like this had fallen into the hands of
-Thomas A. Edison when he was a newsboy on the Grand Trunk Railway, or
-when he was a telegraph operator, he would have devoured it with the
-utmost eagerness. To be sure, at that time, in the early sixties, all
-that we knew of electricity and its applications could have been told in
-a very brief compass. It was an almost unknown field, and the crude form
-of the telegraph then in use represented its most important application.
-There were no electric lights; there was no telephone or phonograph;
-there were no electric motors. Telegraphing, itself, was a slow and
-difficult process. All the conditions were as far removed as possible
-from the broad field of applied electricity indicated in this book.
-
-But this does not mean that we have now accomplished all that there is
-to be done. On the contrary, the next half-century will be full of
-wonderful advances. This makes it more than ever essential that we
-should become acquainted with the principles and present conditions of a
-science which is being applied more and more closely to the work of
-every-day life. It is necessary to know this from the inside, not simply
-from general descriptions. Theory is all very well, but there is nothing
-like mastering principles, and then applying them and working out
-results for one’s self. Any active and intelligent boy with an
-inquiring mind will find a new world opened to him in the satisfaction
-of making electrical devices for himself according to the suggestions
-given in this book. This will show him the reasons for things in
-concrete form, will familiarize him with principles, and will develop
-his mechanical ingenuity. He may be laying the foundation for inventions
-of his own or for professional success in some of the many fields which
-electricity now offers. Work of this kind brings out what is in one, and
-there is no satisfaction greater than that of winning success by one’s
-own efforts.
-
-The boy who makes a push-button for his own home, or builds his own
-telephone line or wireless telegraph plant, or by his own ingenuity
-makes electricity run his mother’s sewing-machine and do other home
-work, has learned applications of theory which he will never forget. The
-new world which he will enter is a modern fairyland of science, for in
-the use of electricity he has added to himself the control of a powerful
-genie, a willing and most useful servant, who will do his errands or
-provide new playthings, who will give him manual training and a vast
-increase in general knowledge. The contents of this book, ranging from
-the preparation of simple cells to the making of dynamos and motors, and
-the delightful possibilities of electro-plating, shows the richness of
-the field which is made accessible by Mr. Adams’ practical explanations,
-his carefully tested working plans, and his numerous and admirable
-drawings--all of which have been made for this book.
-
-It is in keeping with the practical character of the _Electricity Book_
-that pains are taken throughout to show the simplest and most
-inexpensive way of choosing materials and securing results. The actual
-working out of these directions can be done at very small expense.
-Furthermore, there need be no concern whatever as to possible danger if
-the book is read with reasonable intelligence. Mr. Adams has taken pains
-to place danger-signals wherever special precautions are advisable, and,
-as a father of boys who are constantly working with electricity in his
-laboratory, he may be relied upon as a safe and sure counsellor and
-guide.
-
-While this book shows boys what they can do themselves, its scope has
-been enlarged by Mr. Baker’s chapter explaining briefly the working of
-electricity all about us, in light and heat, in the trolley-car, and
-other daily applications. In addition, Mr. Adams has prepared a
-Dictionary of Electrical Terms, and these brief definitions will be
-found peculiarly helpful in the first reading of the book. It is
-believed that there is no book in this particular field comparable to
-Harper’s _Electricity Book_ in its comprehensiveness, practical
-character, and the number and usefulness of its illustrations. It
-follows the successful _Out-door Book for Boys_ in Harper’s series of
-_Practical Books for Boys_, and it will be followed by _How to
-Understand Electrical Work_, a book, not of instructions in making
-electrical apparatus, but of explanations of the commercial uses of
-electricity all about us.
-
-
-
-
-Part I
-
-
-ELECTRICITY BOOK FOR BOYS
-
-
-Chapter I
-
-SOME GENERAL EXPLANATIONS
-
-We are living in the age of electricity, just as our fathers lived in
-the age of steam. Electricity is the world-power, the most powerful and
-terrible of nature’s hidden forces. Yet, when man has learned how to
-harness its fiery energies, electricity becomes the most docile and
-useful of his servants. Unquestionably, electricity is to-day the most
-fascinating and the most profitable field for the investigator and the
-inventor. The best brains of the country are at work upon its problems.
-New discoveries are constantly being recorded, and no labor is thought
-too great if it but add its mite to the sum total of our knowledge. And
-yet, ridiculous as the statement may seem, we do not know what
-electricity is. We only know certain of its manifestations--what it can
-do. All we can say is that it does our bidding; it propels our trains,
-lights our houses and streets, warms us, cooks for us, and performs a
-thousand and one other tasks at the turn of a button or at the thrust of
-a switch. But _what_ it is, we do not know. Electricity has no weight,
-no bulk, no color. No one has seen it; it cannot be classified, nor
-analyzed, nor resolved into its ultimate elements by any known process
-of science. We must content ourselves with describing it as one
-manifestation of the energy which fills the universe and appears in a
-variety of forms--such as heat, light, magnetism, chemical affinity, and
-mechanical motion. In all probability it is one of those phenomena of
-nature that are destined to remain forever secret. Thus it stands in
-line with gravitation, magnetism, the active principle of radium, and
-the perpetual motion of the solar system.
-
-Electricity was known to the early Greeks; indeed, it derives its name
-from the Greek word for amber (electron). For many centuries amber was
-credited with certain special or magical powers. When it was rubbed with
-a flannel cloth, “the hidden spirit” came out and laid hold of small
-detached objects, such as bits of paper, thread, chips, or pith-balls.
-No one could explain this phenomenon. It was looked upon with
-superstitious awe and the amber itself was regarded as possessing the
-special attributes of divinity. But as time went on, it was discovered
-that in various other substances this mysterious attractive power could
-be excited, at will, through the agency of friction. Rubbing a piece of
-glass rod with silk or leather generated an “electricity” identical with
-that of the amber; or the same result could be obtained by exciting hard
-rubber with catskin. The conclusion followed that electricity was not a
-property of the special materials employed to generate it, but that it
-came from without, from that great reservoir of energy, the atmosphere.
-Then came Franklin with his experiment of the kite, and the invention
-of the Leyden-jar and the chemical production of the electric fluid by
-means of batteries. It was shown that the properties of the new and
-strange force were the same, whether it was produced by the static
-(frictional) process or by the galvanic (chemical) method. Electrical
-science as a science, had begun.
-
-And yet, for many years, electricity was hardly more than a scientific
-toy. It was not supposed to possess any practical usefulness. The
-entertaining experiments with the static machine and the Leyden-jar
-(chapter xiii.) were confined to the laboratory and the lecture hall.
-Electricity was an amusing display of unknown energy, but no one ever
-dreamed that it could ever be made to serve the practical ends of life.
-It was not until about 1850 that electrical science became anything more
-than a name. The galvanic and voltaic batteries (chapter ii.) opened the
-way for “current” electricity, which flowed continuously, instead of
-jumping and disappearing like the spark from a Leyden-jar. When the
-continuous current became an established fact, the telegraph and
-telephone headed the line of a long series of developments. Finally, the
-generation of electricity in greater volume, and cheaply, made possible
-the application of its power for heating, light, traction, and the other
-forms of activity in which it now does so large a share of the world’s
-work.
-
-How electricity works is a question often asked, but not easily
-answered. There are certain so-called laws, but we shall best arrive at
-a conclusion by simply stating a few of the facts that have been
-established through the observation and investigation of scientists and
-electrical engineers.[1]
-
-  [1] Explanations of any technical names or phrases used in the text
-  will be found in the simple dictionary of electrical terms which
-  appears as an appendix.
-
-For example, electricity is always alert, ready to move, and continually
-on the lookout for a chance to obtain its freedom. It will never go the
-longest way round if there is a short cut; and it will heat, light, or
-fuse anything in its path that is too weak to carry or resist it. For
-this reason, it must be generated in small volume--that is, just
-sufficient to do the work required of it. If produced in larger volume,
-it must be held in check by resistance, and only so much allowed to
-escape as may be needed for the specified work.
-
-Again, when electricity is generated this must be done in one of two
-ways--by friction or chemically. But in both processes there must be air
-surrounding the generators, and the fluid must be of a nature through
-which oxygen and hydrogen can circulate freely. Water fluids are
-suitable for this purpose, but oils cannot be used, as they contain
-hydro-carbon in large quantities and are non-conductors.
-
-Batteries are chemical generators, dynamos are magneto-electric, and
-static machines are frictional. Now the theory is that electricity is
-drawn from the ether and, in its normal state, is quiet. If it be
-disturbed and collected by mechanical or chemical means, it is always on
-the alert to escape and again take its place in the atmosphere. As its
-volume is increased, so its energy to get away is multiplied, and this
-energy may be transformed, at will, into power, heat, or light. To
-express the idea in the simplest language, it wants to go home, and in
-its effort to do so it expresses itself in the form of stored-up power,
-precisely like water behind a dam. It is for man’s cunning brain to
-devise all sorts of tasks that this power must perform before it can
-gain its release. It can’t go home until its work is done.
-
-Nearly every boy has experimented, at one time or another, with
-electricity and electrical apparatus, and whether it was with some of
-the simple frictional or galvanic toys, or with the more complicated
-induction-coils and motors, he has undoubtedly found it a most
-interesting amusement and an ever new and widening field for study. Then
-again, many boys would like to know something about simple electrical
-apparatus and how to make and use it. But his school-books relating to
-the general subject of electricity are hardly definite enough to serve
-as a practical manual. And yet there are many things in the way of
-electrical machinery and equipment that a boy can easily construct and
-use. In this book it is my purpose to show him just what can be done
-with the aid of the tools that are usually in his possession. While some
-things may have to be purchased from an electrical supply-house or other
-sources, there is still much material to be found about the house that
-may be put to good use by the amateur electrician.
-
-It is not possible or desirable to describe every variety of electrical
-equipment. We must confine ourselves to apparatus which can be readily
-understood and operated. The “practical” idea is the one to be borne in
-mind. This book shows a boy how to use his brains and the simple tools
-and material that may be at his command. Care and thought in the
-construction of the apparatus are the important qualifications for
-success. The instructions are given in the clearest possible language;
-the diagrams and drawings are intelligible to any one who will take the
-trouble to study them. If your finished apparatus does not work
-properly, read the description again and see if you have not made some
-error. A misplaced or broken wire, a wrong connection, or a short
-circuit will mean all the difference between success and failure.
-
-Save in one short chapter, static or frictional electricity (see
-Appendix) is not considered; for outside of laboratory experimenting and
-electro-medical apparatus, frictional electricity is but a
-toy--interesting and useful when generated in small volume, but very
-dangerous and difficult of control when in great volume. For example,
-the bolt of lightning is but the many times multiplied spark stored in
-the Leyden-jar by the static machine. For all practical purposes,
-galvanic electricity, in its various phases of direct and alternating
-current, meets the requirements of man. With the improved apparatus and
-the rapid advancement along the line of invention, electricity is as
-easily controlled to-day as steam--in fact, its economical use is even
-more fully under control and its adaptability more practical.
-
-In the following pages there are probably illustrations and descriptions
-of many things that will seem strange to the boy who has not heard of
-them; but if a book were written each year on the subject of
-electricity, every new one would include principles and facts not known
-before. The field of electrical research is so broad and so many are
-working in it that new discoveries are being made continually.
-
-To those familiar with the application of electricity, it is clearly
-evident that, as yet, we are only beginning to deal with this unknown
-force. For generations to come, developments will take place and
-invention follow invention until electricity assumes its rightful place
-as the motive force of the world. To the boy interested in this subject
-a wide field is open, and the youth of to-day, who are taking up this
-study, are destined to become the successful electrical engineers and
-inventors of the future. There is no better education for any boy, in
-the application and principles of electricity, than to begin at the very
-bottom of the ladder and climb up, constructing and studying as he
-progresses. When he attempts to design more technical and difficult
-apparatus the lessons learned in a practical way will be of inestimable
-value, greater by far than any theoretical principles deduced from
-books; he knows his subject from the ground up; he understands his
-machine because he has constructed it with his own hands.
-
-As I have said already, the necessary tools are few in number and not
-expensive. They may include a hammer, a plane, awls, pliers,
-wire-cutters, and tin-shears. The raw material is also cheap--lead, tin,
-wire, wood, and simple chemicals. The laboratory may be a corner in the
-attic, or even in a boy’s bedroom, so far as the finer work is
-concerned, while the hammering and sawing may be done in the cellar. The
-other best plan, of course, is to get the use of a spare room which may
-be fitted with shelves, drawers, and appliances for serious work. To
-enthusiastic beginners, as well as to those who have had some experience
-in electricity, a needed warning may be given in three words: “Take no
-chances.” Electricity, the subtle, stealthy, and ever-alert force, will
-often deal a blow when least expected. For that reason, a boy should
-never meddle with a high-tension current or with the mains from dynamos.
-The current in the house, used for lighting, cooking, or heating
-purposes, is always an attractive point for the young electrician, but
-the wires should never be touched in any way. Too many accidents have
-happened, and the conductors, lamp-sockets, and plugs should be
-carefully avoided.
-
-The boy should keep strictly to his batteries, or small dynamos run by
-water-power from a faucet; in no case should the wire from power-houses
-be tampered with. One little knows what a current it may be carrying and
-what a death-dealing force it possesses. Always bear in mind that a
-naked wire falling from a trolley equipment carries enough force to kill
-anything it strikes.
-
-Special attention is called to the dictionary of electrical terms given
-in the Appendix. The young student should never pass over a word or a
-term that he does not thoroughly understand. Always look it up at once
-and _every time_ it occurs, until you are sure that its meaning is fixed
-in your mind. This is an education in itself, at least so far as the
-theoretical knowledge of our subject is concerned.
-
-As a final word, I should like every boy interested in electricity to
-hear what Thomas A. Edison once said to me when I was a boy working in
-his laboratories. I often recall it when things do not go just right at
-first.
-
-I asked the great inventor one day if invention was not made up largely
-of inspiration. He looked at me quizzically for a moment, and then
-replied: “My boy, I have little use for a man who works on inspiration.
-Invention is two parts inspiration and ninety-eight per cent.
-perspiration.”
-
-You will never get what you are after unless you work hard for it. You
-must stick to it until you produce results. If the history of the
-world’s most valuable inventions could be fully known, the fact would be
-clearly established that the vital spark of inspiration is but the
-starting-point. Then follow the days, weeks, and sometimes years of
-industrious toil, failures, and disappointments, until finally the
-desired end is attained. One must work for success; there is no other
-means of winning it.
-
-As the table of contents shows, Part I. of this book explains principles
-and the simpler forms of electrical appliances. From this we advance to
-Part II., which deals with more complex forms of electrical work, most
-of which, however, are within the reach of intelligent boys who have
-followed the chapters carefully from the first. In a final chapter we
-have simple explanations of the great commercial uses of electricity,
-which we see all about us, although very few of us have a clear idea as
-to their operation.
-
-
-Chapter II
-
-CELLS AND BATTERIES
-
-
-Simple Cells
-
-In order to generate electricity it is necessary to employ cells,
-batteries, or dynamos. Since the construction and operation of a dynamo
-is somewhat intricate, it will be better to start with the simpler
-methods of electric generation, and so work up to the more complicated
-forms. For small apparatus, such as electric bells and light magnets and
-motors, the zinc-carbon-sal-ammoniac cell will answer very well; but for
-larger machinery, where more current is required, the bluestone and the
-bi-chromate batteries will be found necessary.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 5
-
-SIMPLE BATTERY ELEMENTS]
-
-A simple and inexpensive cell may be made from electric-light carbons,
-with the copper coating removed, and pencils of zinc, such as are used
-for electric-bell batteries and which can be purchased for five cents
-each. Copper wire is to be bound around the top of each pencil of carbon
-and zinc, and firmly fastened with the pliers, so that it will not pull
-off or become detached. It will be well to cut a groove with a file
-around the top of both the carbon and zinc, into which the wire will
-fit. The elements should then be clamped between two pieces of wood
-and held with screws, as shown in Fig. 1. A more efficient carbon pole
-is made by strapping six or more short carbon pencils around one long
-one, as shown in Fig. 3. The short pieces of electric-light carbons are
-bound to the longest carbon with heavy elastic bands, or cotton string
-dipped in paraffine or wax, to make the cotton impervious to water and
-the sal-ammoniac solution.
-
-Another arrangement of elements is shown in Fig. 2, where a zinc rod is
-suspended between two carbons, the carbons being connected by a wire
-that must not touch the zinc.
-
-A fruit-jar, or a wide-necked pickle-bottle, may be employed for a cell,
-but before the solution is poured in, the upper edge of the glass should
-be coated with paraffine. This should be melted and applied with a
-brush, or the edge of the glass dipped in the paraffine.
-
-The solution is made by dissolving four ounces of sal-ammoniac in a pint
-of water, and the jar should be filled three-fourths full. In this
-solution the carbons and zinc may be suspended, as shown in the
-illustration (Fig. 4) of the sal-ammoniac cell. The wood clamps keep the
-carbon and zinc together, and the extending ends rest on the top of the
-jar and hold the poles in suspension. Plates of zinc and carbon may be
-clamped on either side of a square stick and suspended in the
-sal-ammoniac solution, as shown in Fig. 5, taking care, however, that
-the screws used for clamping do not touch each other.
-
-If one cell is not sufficiently powerful, several of them may be made
-and coupled up in series--that is, by carrying the wire from the zinc
-of one to the carbon of the next cell, and so on to the end, taking care
-that the wire from the carbon in the first cell and that from the zinc
-of the last cell will be the ones in hand, as shown in Fig. 6. This
-constitutes a battery. Be sure and keep the ends of the wire apart, to
-prevent galvanic action and to save the power of the batteries.
-
-This battery is an excellent one for bells and small experimental work,
-and when inactive the zincs are not eaten away (as they would be if
-suspended in a bi-chromate solution), for corrosion takes place only as
-the electricity is required, or when the circuit is closed. A series of
-batteries of this description will last about twelve months, if used for
-a bell, and at the end of that time will only require a new zinc and
-fresh solution.
-
-The cell in which the plates shown in Fig. 5 are used may contain a
-bi-chromate solution; and for experimental work, where electricity is
-required for a short time only, this will produce a stronger current.
-But remember that the solution eats the zinc rapidly, and the plates
-must be removed as soon as you have finished using them.
-
-The bi-chromate solution is made by slowly pouring four ounces of
-commercial sulphuric acid into a quart of cold water. This should be
-done in an earthen jar, since the heat generated by adding acid to water
-is enough to crack a glass bottle. Never pour the water into the acid.
-When the solution is about cold, add four ounces of bi-chromate of
-potash, and shake or mix it occasionally until dissolved; then place it
-in a bottle and label it:
-
-  BI-CHROMATE BATTERY FLUID
-
-  POISON
-
-Before the zincs are immersed in the bi-chromate solution they should be
-well amalgamated to prevent the acid from eating them too rapidly.
-
-The amalgamating is done by immersing the zincs in a diluted solution of
-sulphuric acid for a few seconds, and then rubbing mercury (quicksilver)
-on the surfaces. The mercury will adhere to the chemically cleaned
-surfaces of any metal except iron and steel, and so prevent the
-corroding action of the acid. Do not get on too much mercury, but only
-enough to give the zinc a thin coat, so that it will present a silvery
-or shiny surface.
-
-A two-fluid cell is made with an outer glass or porcelain jar and an
-inner porous cup through which the current can pass when the cup is wet.
-Fig. 7.
-
-[Illustration: FIG. 4]
-
-[Illustration: FIG. 7]
-
-[Illustration: FIG. 8]
-
-[Illustration: FIG. 6]
-
-A porous cup is an unglazed earthen receptacle, similar to a flower-pot,
-through which moisture will pass slowly. The porous cup contains an
-amalgamated plate of zinc immersed in a solution of diluted sulphuric
-acid--one ounce to one pint of water. The outer cell contains a
-saturated solution of sulphate of copper in which a cylindrical piece of
-thin sheet-copper is held by a thin copper strap, bent over the edge of
-the outer cell. A few lumps or crystals of the copper sulphate, or
-bluestone, should be dropped to the bottom of the jar to keep the copper
-solution saturated at all times. When not in use, the zinc should be
-removed from the inner cell and washed off; and if the battery is not to
-be employed for several days, it would be well to pour the solutions
-back into bottles and wash the several parts of the battery, so that it
-may be fresh and strong when next required. When in action, the
-solutions in both cups should be at the same level, and be careful never
-to allow the solutions to get mixed or the copper solution to touch the
-zinc. Coat the top of the porous cell with paraffine to prevent
-crystallization, and also to keep it clean. Take great care, in handling
-the acid solutions, to wear old clothes, and do not let the liquids
-spatter, for they are strong enough to eat holes in almost anything, and
-even to char wood. The two-fluid cells are much stronger than the
-one-solution cells, and connected up in series they will develop
-considerable power.
-
-For telegraph-sounders, large electric bells, and as accumulators for
-charging storage-batteries, the gravity-cell will give the most
-satisfactory results. The one shown in Fig. 8 consists of a deep glass
-jar, three strips of thin copper riveted together, and a zinc crow-foot
-that is caught on the upper edge of the glass jar. These parts will have
-to be purchased at a supply-house, together with a pound or two of
-sulphate of copper (bluestone).
-
-To set up the cell, place the copper at the bottom and drop in enough of
-the crystals to generously cover the bottom, but do not try to imbed the
-metallic copper in the crystals; then fill the jar half full of clear
-water. In another jar dissolve two ounces of sulphate of zinc in enough
-water to complete the filling of the jar to within two inches of the
-top; then hang the zinc crow-foot on the edge of the jar so that it is
-immersed in the liquid and is suspended about three inches above the top
-of the copper strip. The wire that leads up from the copper should be
-insulated with a water-proof coating and well covered with paraffine. A
-number of these cells may be connected in series to increase the power
-of the current, and for a working-battery this will show a high
-efficiency. Note that at first the solutions will mingle. To separate
-them, join the two wires and start the action; then, in a few hours, a
-dividing line will be seen between the white, or clear, and the blue
-solutions, and the action of the cell will be stronger. After
-long-continued use it may be necessary to draw off some of the clear
-zinc sulphate, or top solution, and replace it with pure water. The
-action of the acids reduces the metallic zinc to zinc sulphate and
-deposits metallic copper on the thin copper strips, and in this process
-an electrical current is generated.
-
-
-A Plunge-battery
-
-When two or more cells (in which sulphuric acid, bi-chromate of potash,
-or other strong electropoions are employed) are coupled in series, it
-would be well to arrange the copper and zinc, or the zinc and carbon,
-poles on a board, so that all of them may be lowered together into the
-solutions contained in the several jars. A simple arrangement of this
-kind is shown in Fig. 9, where a rack is built for the jars and at the
-top of the end boards a projecting piece of wood, supported by a
-bracket, is made fast. A narrow piece of board nearly the length of the
-jar-rack is fitted with the battery-poles, as shown at Fig. 9 A. The
-carbon and zinc, or copper and zinc, poles are attached to small blocks
-of wood (as described for Fig. 5), and this block in turn is fastened to
-the under side of the board with brass screws. The poles of the cells
-are to be connected (as explained in Fig. 6), and when the battery is in
-use the poles are immersed in the solution contained in the jars. When
-the battery is at rest the narrow board should be lifted up and placed
-on the projecting arms of the rack, so that the liquid on the poles may
-drain into the jars directly underneath. One or more of these
-battery-racks may be constructed, but they cannot be made to hold
-conveniently more than four or six cells each; if more cells are
-required, those contained in each rack must be coupled up in series.
-
-[Illustration: FIG. 9]
-
-[Illustration: FIG. 10]
-
-A simpler plunge-battery is shown in Fig. 10. A cell-rack is made of
-wood and given two or three coats of shellac. The narrow board (to the
-under side of which the battery-poles are attached, as explained in Fig.
-9) is hung on chains or flexible wires, which in turn are made fast to
-an iron shaft running the entire length of the cell-rack. This shaft is
-of half-inch round iron, and is held in place, at one end, by a pin and
-washer; while at the other the end is filed with a square shoulder, and
-a handle and crank is fitted to it, so that the shaft may be turned. A
-small hole, made at the side of the crank when it is hanging down, will
-receive a hard-wood peg, or a steel nail, and this will prevent the
-crank from slipping when the board holding the poles is raised. If a
-gear-wheel and tongue can be had to fit on the shaft, it will then be
-possible to check the shaft securely at any part of a turn of the crank.
-The battery-poles are to be connected in series along the top of the
-portable board, as explained for Fig. 6. When two or more of these
-plunge-batteries are used at one time, the wire from the carbon of one
-is to be connected with the zinc pole of the next, and so on. The wire
-from the zinc of the first battery, and the wire from the carbon of the
-last battery, will be the ones available for use.
-
-
-A Storage-battery
-
-When more current is desired than the simple batteries will give, a
-storage-battery should be employed as an accumulator. This result can be
-secured by coupling primary cells in series, so that they will be
-constantly generating and feeding the battery. Storage-batteries are too
-heavy to be shifted about, like single cells or small plunge-batteries;
-they should be placed in a cellar, where the charging or primary cells
-can be located close by, and, unless positively necessary, the battery
-of cells and the accumulator should not be moved.
-
-With sufficiently large insulated wires (Nos. 12, 14, or 16 copper), the
-current may be carried to any part of the house for use in various
-ways--such as running a light motor or a fan, lighting a lamp-circuit,
-or fusing metals and chemicals for experimental purposes. While the
-battery to be described is not a light one in weight, nor as economical
-as the improved new Edison storage-battery, it is a good and constant
-one, and, if not overcharged or abused, will last for several years.
-
-The component parts of a storage-battery are lead in metallic and
-chemical form, the electrolyte, or fluid, in which the plates are
-immersed, and the water-tight and chemical-proof cell or container. From
-a plumber, a supply-house, or a lead-works, obtain a quantity of
-three-eighth by one-quarter-inch strip-lead of the kind called chemical,
-or desilverized; also a larger quantity of lead-tape, one-sixty-fourth
-of an inch thick and three-eighths of an inch wide. This last is also
-known as torpedo-lead, and is kept by electrical supply-houses.
-
-If the three-eighths by quarter-inch strip-lead cannot be had, then
-purchase eight or ten pounds of heavy sheet-lead, and, with a
-tin-shears, divide it into strips three-eighths of an inch wide and
-twenty-nine inches long, taking care to cut it of uniform width and with
-true edges. From hard-wood three-eighths or half an inch thick, cut a
-block six by seven inches and make four countersunk holes in it, so that
-it may be screwed fast to a table or bench, as shown in Fig. 11 A.
-Around this the lead strips should be shaped and beaten at the corners
-to make the angles sharp.
-
-From the three-eighths by quarter-inch, or sheet-lead strips, make seven
-frames as shown in Fig. 12. This is done by binding a strip of the lead
-around the block, as shown at Fig. 11 B. Where the ends come together
-insert a short piece of lead, three-eighths or half-inch, as shown at
-Fig. 12 A, and solder it fast. A soldering-iron may be heated with a
-Bunsen-burner gas-flame or in a charcoal fire. However, if gas is
-available, it would be better to use the blue flame from a Bunsen
-burner and direct the hot blast directly on the work with a blow-pipe,
-and so fuse the lead points together. After a little practice with the
-blow-pipe it will be used for many pieces of work in preference to the
-soldering-iron. If the sheet-lead is used for the frames in place of the
-three-eighths by quarter-inch strips, two or three strips will have to
-be taken, so as to build up the band of the frame to about a quarter of
-an inch in thickness. When soldered together, or fused at the edges,
-these built-up frames will be as rigid as the solid metal.
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 12]
-
-[Illustration: FIG. 13]
-
-Now cut a number of strips of the thin lead-tape six inches and a half
-long, and others that will necessarily be somewhat longer, for each
-frame is to be filled with straight and crimped pieces, as shown in Fig.
-13. If there is a fluting-iron in the house, the crimping may be done in
-the brass gears at one end of the machine. Or two wheels may be cut from
-hard-wood with a fret-saw, and made fast to a block with screws, as
-shown in Fig. 14. A handle, attached to one wheel, will make it possible
-to turn the gears; and they should be placed just far enough apart to
-allow the tape to pass through without tearing or squeezing. Put a
-washer between the wheel and the block to prevent friction.
-
-When a frame is in the position shown in Fig. 13, and lying on a piece
-of slate or flat stone, you will first put in a crimped piece of tape,
-as shown at Fig. 13 A, and under this arrange a straight piece (Fig. 13
-B); then, with the blow-pipe and flame, fuse fast to the frame and catch
-the flutes of the crimped piece to the straight one every inch or two.
-Add alternate crimped and straight strips until the frame is filled and
-presents the appearance of Fig. 13. When the seven frames are ready, lay
-three of them aside for the positives and four for the negatives. Note
-that the positives are red and the negatives a dark yellow when they are
-filled with the active material.
-
-There are several methods of depositing the active material in the mesh
-or net-work of the plates, but some of them are too technical, others
-too complicated, and still others require charging machinery. The
-following plan will be the simplest and easiest for the amateur:
-
-At a paint-store, or from a wholesale druggist, obtain several pounds of
-oxide of lead (red-lead) and a similar quantity of litharge
-(yellow-lead). In an earthen vessel, or large jar, make a solution
-composed of water, twenty ounces, and commercial sulphuric acid, two
-ounces. This is the mixture commonly known as “one to ten.” Place some
-red-lead (dry) in an old saucepan or soup-plate, and add a little of the
-acid solution: then, with an old table-knife or small trowel, mix the
-lead into a stiff paste, like soft putty. Do not get it too thin or it
-will run; nor too thick, as then it will not properly adhere to the
-lead-mesh of the frames. With the frame lying on its side, plaster in
-the red composition between the flutes and fill up the frame solid with
-it. Treat all three of the positive frames in the same manner, taking
-care that the exposed surfaces of the composition-filling is smooth and
-flush with the edges of the lead frame and mesh. Do not disturb these
-plates for a while, but let them remain in position, so as to set and
-partially dry. Add acid solution to the yellow-lead in a similar manner,
-and fill the four negative plates. When partially dry, the plates will
-be ready to combine in a pile.
-
-[Illustration: FIG. 14]
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-[Illustration: FIG. 17]
-
-At a supply-house obtain some sheets of cellulous fibre,
-three-sixteenths of an inch thick, or some asbestos cloth. If neither
-can be had, then soak some pieces of ordinary brown card-board in a
-solution of silicate of soda and let them dry. Lay a negative (yellow)
-plate on the table with the lug at the left (Fig. 13 C). On this place a
-square of the fibre, asbestos, or card-board; and on top of it lay a
-positive (red) plate with the lug at the right side. Continue in this
-manner until the seven plates are stacked, the four negative lugs being
-at the left and the three positives at the right. Tie the plates
-securely together with cotton string bound about them in both
-directions; then stand the pile up so that the lugs are at the top, as
-shown at Fig. 15, with every alternate lug in an opposite direction.
-Obtain two lead bars three-eighths of an inch square, or cut strips from
-the sheet-lead and solder them together, turning the ends as shown at
-Fig. 13 D. Drop one of these bars into the lugs of the positive plates,
-as shown in Fig. 15 H, and solder it fast at the three unions. Repeat
-this with the other bar in the lugs of the negative plates, and the pile
-will then be ready for immersion in the electrolyte. To both ends of
-each plate-bar solder binding-posts, so that the conductor-wires can be
-attached at one end and the feed-wires at the other. If a hard rubber or
-glass cell can be had for the battery so much the better; if not, a
-stout box may be made from pine, white-wood, or cypress, and thoroughly
-coated with asphaltum varnish or asphaltick. At an electrical
-supply-house you can purchase some “P and B” compound, which is acid and
-water proof. This is excellent for the inside coating as well as for the
-outside of the box.
-
-The box should be made of wood not less than three-quarters of an inch
-thick, and the sides, ends, and bottom should be in one piece, free from
-knots, sappy places, or cracks. Brass screws should be used to hold the
-boards together, and before the joints are made the butt-ends of wood
-and the sides, against which they impinge, must be thoroughly coated
-with the asphaltum or compound. Put together the four sides first and
-then make the bottom fast, placing the screws two inches apart and
-countersinking the wood, so that the screw-heads will lie flush, as
-shown in Fig. 16. The box should be large enough to allow about one inch
-of space all around the pile, and deep enough for the solution to cover
-the plates and two inches of space above it to the top edge of the cell.
-The complete storage-battery will then appear as shown in Fig. 17.
-
-The electrolyte is composed of sulphuric acid and water in the
-proportion of one ounce of acid to four of water, making a five-part
-solution. This should be mixed in an earthen or glass jar, and the acid
-poured slowly into the water, the latter being stirred while the acid is
-added. When the solution cools (for adding acid to water creates heat),
-add about two ounces of bicarbonate of soda, and mix the solution
-thoroughly.
-
-When the pile is in place within the box (having first removed the
-string which bound the plates together) pour the electrolyte slowly
-into the cell, taking care that none of it spatters, for it will eat
-clothing or anything else that it touches. Before placing the pile, or
-electrolyte, in the box, it should be thoroughly tested for leaks by
-allowing water to stand in it for several days. Indeed, you should be
-very generous with the asphaltum, or compound, when coating the angles
-and points inside the box; for if the acid solution gets at the screws
-it will corrode them and the box will soon leak and fall apart. As a
-precaution against the acid working over the top of the box, the upper
-edge, for an inch or two, should be coated with paraffine over the
-asphaltum or acid-proof coating.
-
-A cell constructed in this way should accumulate about two volts and one
-hundred ampere-hours, and will run a one-sixteenth horse-power motor.
-The expense of making these plates is about twenty-five cents each, and,
-including the cell and coating materials, each storage-battery will cost
-approximately two dollars. The lasting qualities of the battery depend
-on the use or abuse it is put to; but with ordinary care it should last
-from three to five years.
-
-When the battery ceases to accumulate properly the pile should be
-removed, and, after washing it thoroughly, the bars should be cut away
-and new positive plates made and installed. The positive plates are the
-ones that deteriorate and need replacing; the negatives are almost
-everlasting, and with proper usage will live for fifteen or twenty
-years.
-
-Directly the electrolyte is in the cell, connect the poles of your
-primary cells so as to begin the accumulation of current. Never exhaust
-the charge of electricity from your storage-cell, and never leave it
-uncharged when the electrolyte is in, or the plates will be ruined. A
-battery consisting of from five to twenty bluestone cells will be the
-best with which to charge this accumulator; and if more than one cell is
-desired, any number of them can be made and coupled up in series. Take
-care, when connecting the wires from the primary cells, to see that the
-positive wire is connected with the positive plates and the negative
-with the lead bar joining the yellow plates. If by accident you should
-make a misconnection, bubbles will rise from the electrolyte. This is
-not right, so reverse the wires and the accumulation of current will
-then take place without agitation in the cell.
-
-
-Dry-cells and Batteries
-
-Dry-cells are extensively used nowadays, since their cleanliness, high
-efficiency, and low internal resistance make them preferable to the
-Leclanché and other open-circuit batteries for bells, annunciators, and
-other light work. In the dry-cell, the electrolyte, instead of being a
-liquid, is a gelatinous or semi-solid mass, which will not run nor slop
-over. When the capping of pitch or tar is in place, the cell may be
-placed in any position, with full assurance that the electrolyte will
-not become displaced nor run out. Dry-cells may be made of almost any
-size for convenience of handling, but those commonly used vary from one
-to four inches in diameter, and from four to fifteen inches high. For
-bells and general electric work, a cell two inches and a half in
-diameter and seven inches high will be found a convenient size to make
-and handle.
-
-The component parts of a dry-cell are the cell itself (which is made of
-zinc and acts as the positive pole), the carbon, the electrolyte or
-active excitant element, and the pitch or tar cap to hold the
-electrolyte and carbon in place.
-
-From a tinsmith obtain some pieces of sheet zinc, and roll them into
-cylindrical form as shown in Fig. 18 A. The sheets should measure seven
-by eight inches, and when formed the edges are to be lapped and
-soldered.
-
-[Illustration: FIG. 18]
-
-From a smaller piece of zinc cut round bottoms, fit them in the
-cylinders and solder securely in place, taking care to close up all
-seams or joints to prevent the escape of the electrolyte.
-
-From a supply-house obtain battery-carbons, one inch and a half wide by
-half or three-eighths of an inch thick and eight inches long. These
-should be provided with a thumb-screw or small bolt and nut at the top
-so as to make wire connections with the carbon. A strip of zinc should
-be soldered to the outside upper edge of the zinc cup to which wire
-attachments may be made with thumb-screws or small bolts and nuts. When
-the parts are ready to assemble, make a wooden mould or form a trifle
-larger than the carbon. This is intended to act as a temporary plunger,
-and is inserted, at first, in place of the carbon plate. This wooden
-plunger should be smooth, and given a coat of shellac to prevent it
-from absorbing any moisture.
-
-Insert the plunger in the zinc cup and support it so that it will be at
-least half an inch above the bottom and centred at the middle of the
-cup. The electrolyte is then placed in the cup, and, when it has set a
-little, the wooden plunger is removed and the carbon inserted in its
-place.
-
-The electrolyte is composed as follows:
-
-  Ammonium chloride    1 part
-  Zinc chloride        1 part
-  Plaster of Paris     3 parts
-  Flour                ¾ part
-  Water                2 parts
-
-Mix these together and place the compound within the zinc cups, so that
-the mass settles down and packs closely about the plunger. The space
-left unfilled about the carbon should be filled with a mixture composed
-as follows:
-
-  Ammonium chloride    1 part
-  Zinc chloride        1 part
-  Manganese binoxide   1 part
-  Granulated carbon    1 part
-  Flour                1 part
-  Plaster of Paris     3 parts
-  Water                2 parts
-
-These proportions may be measured in a tin cup, a table-spoon, or any
-other small receptacle. Note that the measurement by parts is always by
-bulk and not by weight.
-
-Do not fill the zinc cup to the top, but leave an inch of space, so that
-half an inch of sealing material may be added. See that the inside top
-edge of the zinc cup is clean; then melt some tar or pitch and pour it
-over the top of the electrolyte, so that it binds the zinc cup and
-carbon into a solid form. Drive an awl down through the capping material
-when it is nearly dry, and leave the holes open for the escapement of
-gases.
-
-Give the outer surface of the zinc cells a coat of asphaltum varnish,
-and wrap several thicknesses of heavy paper about them to prevent
-contact and short-circuiting. Protect the bottoms in a similar manner,
-and as a result you will have a cell that will appear as shown in Fig.
-18 B. A battery of cells powerful enough for any light work can be made
-by connecting the cells in series, each having an electro-motive force
-of one and a half volts, with an internal resistance of less than
-one-third of an ohm.
-
-
-Chapter III
-
-PUSH-BUTTONS AND SWITCHES
-
-
-Push-buttons
-
-Push-buttons and switches are a necessity in every home where electric
-bells, lights, or fans are used, for with them connections are made or
-broken. The telegraph-key and the commutators on a motor and dynamo are
-only improved forms of the push-button, and this simple little device is
-really an indispensable part of any electrical equipment.
-
-The simplest form of push-button is a bent piece of tin or thin
-sheet-metal screwed fast to a small block of wood, as shown in Fig. 1.
-Under the screw-head one end of a wire is caught, and the other wire end
-is secured by a washer and a screw driven into the block directly under
-the projecting end of the strip of metal. By pressing a finger on the
-tin it is brought into contact with the screw-head under it, and the
-circuit is closed; on releasing it, the tin flies up and the circuit is
-opened again.
-
-An enclosed push-button is shown in Fig. 2. It is made of the cover or
-body of a wooden box, a spool-end, and several other small parts. A
-round piece of thin wood is cut to fit inside the box and so form the
-base for the button. On this the spring strip is attached with screws,
-and the wire ends are made fast, as shown in Fig. 3. The wires are
-carried through the bottom of the base and along grooves to the edge,
-and thence to their final destination. The end of a spool is cut off and
-glued to the top of the box, as shown in Fig. 2, and a hole is made in
-the box to correspond in size with that in the spool. Through this
-aperture the button (cut from a wooden dowel or shaped out with a knife)
-passes, so that the end projects about a quarter of an inch beyond the
-spool. To prevent the button from falling out, a small steel nail should
-be driven across the inner end, or a washer may be tacked to the end of
-the stick, as shown in Fig. 4.
-
-[Illustration: FIG. 1]
-
-[Illustration: FIG. 2]
-
-[Illustration: FIG. 3]
-
-[Illustration: FIG. 4]
-
-The button is mounted by screwing the base fast to the door or window
-casing, it being understood that the wires have been first arranged in
-place. The button is then set in the hole and the cap is placed over
-the base, covering it completely. By means of small screws, passed
-through the rim of the box and into the edge of the base, the cap is
-held in place. A coat of paint or varnish will finish the wood-work
-nicely, and this home-made button should then answer every requirement.
-
-
-Switches and Cut-outs
-
-In electrical equipment and experimental work, switches and cut-outs
-will be found necessary, particularly so for telegraph and telephone
-lines. Care should be taken to construct them in a strong and durable
-fashion, for they will probably be subjected to considerable wear and
-tear.
-
-A simple switch (Fig. 5) is made from a base-block of wood three inches
-long, two wide, and half an inch in thickness, together with some small
-metal parts. It has but one contact-point, and that is the brass-headed
-tack (T in Fig. 5) driven through the binding-post, the latter being a
-small plate of brass, copper, or even tin screwed to the base-block. The
-end of a wire is caught under the screw-head before it is driven down. A
-similar binding-post is arranged at the lower side of the block, and the
-movable arm is attached to it with a screw. Between the arm and the
-post-plate there should be a small copper washer, to make it work more
-easily. The arm is cut from a thin piece of hard sheet brass or copper
-(tin or zinc will also answer very well), and at the loose end the half
-of a small spool is attached, with a brass screw and washer, to serve as
-a handle. The end of the screw that passes through a hole in the arm is
-riveted to the under side to hold it securely in place. This
-arrangement is shown in Fig. 6.
-
-[Illustration: FIG. 5]
-
-[Illustration: FIG. 6]
-
-[Illustration: FIG. 7]
-
-[Illustration: FIG. 8]
-
-[Illustration: FIG. 9]
-
-The under edges of the arm may be slightly bevelled with a file, so that
-it will slip up easily on the oval head of the brass tack. The drawing
-shows an open switch; when the circuit is closed the arm rests on the
-tack-head. By means of small screws this switch-board may be fastened to
-a table or to any part of the wood-work in a house.
-
-In Fig. 7 a complex switch is shown. This is the principle of the
-shunt-box switch, of the resistance-coil, and also of the commutators of
-a motor. A motorman’s controller on a trolley-car is a good example of
-the shunt, and, with it and the resistance-coils, the car can be
-started, stopped, or run at any speed, according to the current that is
-admitted to the motor.
-
-The complex switch is made in the same manner as described for the
-single switch, except that any number of binding-posts may be employed,
-arranged on a radial plan, so that the end of the arm will rest on any
-tack-head at will. Bells in various parts of the house may be rung by
-this switch, or it may be coupled with a series of resistance-coils to
-control any amount of current.
-
-The simple cut-out (Fig. 8) is constructed in the same manner as the
-simple switch, except that there are two points of contact instead of
-one. This is the principle of the telephone and telegraph instrument
-wiring, so that a bell or sounder may be rung from a distance. The arm
-is then thrown over and the bell cut out, allowing the “phone” or key to
-be brought into use. In lifting the transmitter from the hook on a
-telephone, a cut-out is operated and the bell circuit is thrown out of
-action. It is in operation again directly the transmitter is returned to
-the hook. The switch cut-out (Fig. 9) is inactive when the arm is in the
-position shown in the illustration; but when it is thrown over (as shown
-by the dotted line) it connects the poles at opposite ends of the board.
-It may be thrown over in both directions, and is a useful switch for
-many purposes.
-
-For strong currents the lever-switch, that rests on a brass tack-head,
-will not be suitable, as the switch-bar must be held firmly in place to
-make a perfect connection. Strong currents throw weak switches open,
-causing an open or broken circuit.
-
-A single pole-switch, to carry a current up to one hundred and
-twenty-five volts and twenty-five amperes, is shown in Fig. 10. This
-consists of a base-block, a bar which is attached to the vertical ears
-of a binding-post, and a clutch that will hold the bar when it is
-pressed down between the ears.
-
-The base-block should be made from some non-conducting material, such as
-soapstone, marble, or slate. If a piece of soapstone can be procured,
-that will be just the thing, since it is easily worked into the proper
-shape and size. Soapstone may be sawed and smoothed with a file; it is
-easily bored into with a gimlet-bit, and it is one of the best
-non-conducting substances. The base for this switch is six inches long,
-two inches wide, and as thick as the soapstone happens to be--say
-three-quarters of an inch. The top edge may be bevelled for the sake of
-appearance or left square.
-
-Two pieces of heavy sheet copper or brass are to be cut as shown at A in
-Fig. 11. The ears are half an inch wide, and the total height of the
-strip is two inches and a half, while the part with two holes in it side
-by side is one inch and a quarter long, including the half-inch width of
-the vertical strip. With round and flat-nosed pliers bend the long ears
-into shape, so as to form a keeper for the bar which is then to be
-riveted in place. Omit the holes at the ends of the long ears in the
-other plate; then bend it into shape to form a clutch that will hold the
-bar when it is pressed down between the ears. These binding-posts should
-be made fast to the base-block with brass machine-screws and nuts, which
-will fit in countersunk holes in the bottom of the soapstone. If
-hard-wood is used for the base, ordinary brass wood-screws will answer
-very well.
-
-The connection-bar is cut from metal the same thickness as that employed
-for the binding-posts and clutches; it should be shaped so as to appear
-as shown at B in Fig. 11. A handle should be driven on the slim end, and
-where the lower edge enters between the ears of the clutch, the corners
-of the bar should be rounded with a file. Countersunk screw-holes are
-bored in the base, so that it can be made fast to the wood-work.
-
-[Illustration: FIG. 10]
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 12]
-
-A double pole-switch is shown in Fig. 12, and in general construction it
-is similar to the single pole-switch described above. The binding posts
-and bars are cut and bent from the patterns A and B in Fig. 11; but in
-this case the long, slim ends of the bars are omitted. A short turn is
-made at the handle end of each bar and a hard-wood block is placed
-between the bar-ends and held in position with screws driven through
-holes made in the bars and into the ends of the block. A handle is made
-fast to the middle of the block with a long and slim wood-screw; or a
-steel-wire nail may be passed through the handle and block, a burr
-slipped over the end opposite the head, and the small end riveted fast.
-When the binding-posts (to which the ends of the bars are attached) are
-screwed onto the base, be sure and see that the bars are parallel and
-the same distance apart at both ends. In like manner, when the cleat
-binding-posts are made fast, see that they are directly in line with the
-bars, so that the yoke will drop into the spaces between the ears
-without having to be pulled to one side or the other. This is a very
-useful switch for strong currents, and may be placed close to a dynamo,
-so that the current in both wires may be cut out at once.
-
-
-Table-jack Switches
-
-A table-jack switch is a most convenient piece of apparatus where
-several lines of bells, alarms, or telephone circuits are to be switched
-on and off.
-
-The single table-jack switch, shown in Fig. 13, is made of a hard-wood
-block three-quarters of an inch thick, five inches wide, and seven
-inches long. It is to be smoothed and varnished, or given several coats
-of shellac. At the four corners small holes are made to receive slim
-screws, and at one end of the block five short metal plates are screwed
-fast, with the heads of the screws countersunk, so that they will be
-flush with the top of the plates. These small plates should be half an
-inch wide and one inch long, and may be of brass, copper, or tin. But if
-they are of tin the plates are made of a longer strip tacked to the
-board and then bent over, as shown at A in Fig. 14. They will therefore
-form short springs, the upper parts of which will rest against the long
-spring-arms. From spring brass or copper five arms are to be cut and
-shaped, as shown in Fig. 13. Holes are made at one end of each, and
-others again two inches from these, through which to pass screws.
-
-Screw-eyes are passed through copper washers and the end holes in the
-strips, and then screwed into the wood plate. These will act as
-binding-posts, while the second line of screws will hold the plates down
-to the base. The arms should be bent, so that when the screws are driven
-down the lower edge will press on the small plates under them.
-
-The outlet wires are attached to the binding-posts at the head of the
-block, and the plug (A in Fig. 13) is inserted between the arm and plate
-at the foot, so that contact and connection are made. This plug is a
-small plate of metal to which the end of a flexible wire is made fast.
-It should be of copper or brass, but for light work a strip of tin may
-be bent over with the wire caught between the plates and a copper tack
-passed through the sides and riveted, as shown at B in Fig. 14.
-
-A double jack-switch (Fig. 15) is made on the same general plan as the
-single, but it has no binding-posts. A block of the same size is used,
-and two rows of short plates are made fast at each end. The arms are
-made with two screw-holes near the middle, as shown in Fig. 15, and
-through these holes screws are driven to hold the arms down to the base.
-Several plugs are used for each end, so that the in and out lines can be
-shifted, and from one to four lines used at a time.
-
-[Illustration: FIG. 13
-
-FIG. 14
-
-FIG. 15
-
-FIG. 16
-
-TABLE-JACK SWITCHES]
-
-A convenient slip-switch for single or double line work is shown in Fig.
-16. This consists of a small wooden base, on which a brass arm and
-handle are screwed fast and connected with a binding-post (A in Fig.
-16). A slip-plate is made from a piece of sheet-brass and bent so as to
-form a pocket into which the arm will fit. This pocket piece is
-connected with the binding-post B. When the switch is thrown out the
-circuit is broken, unless a contact-point, C, is provided, from the
-under side of which a wire leads out to a second circuit. When the
-switch is in place, as shown in Fig. 16, the circuit is closed through A
-and B; but when the arm is thrown out the circuit through A and B is
-broken and that through A and C is closed.
-
-
-Binding-posts and Connectors
-
-To make quick connections between wires and other parts of electrical
-apparatus, binding-posts are the most convenient device, since the turn
-of a screw binds or releases a wire instantly. Binding-posts may be made
-in many forms, but the simple ones that a boy will need can be made from
-screw-eyes, burrs, stove-bolts, and nuts, together with thin strips of
-metal and nails.
-
-Five simple posts are shown in Fig. 17. A is made from a screw and two
-burrs, B from a screw-eye and two burrs, and C from a thin plate of
-metal and two screws, with oval or round heads. This last, however is
-more of a connector than a binding-post. The ends of the wires to be
-connected should be caught under the screw-heads or between the burrs
-before the screws are driven down.
-
-In D a simple arrangement of a stove-bolt and two nuts is shown. The
-under bolt is screwed down tightly against the wood, and under the head
-a wire is made fast, so that another wire may be caught under the upper
-nut. If a small thumb-nut can be had in place of the plain nut, it will
-be easier to bind the upper wire. In Fig. 17 E a thin strip of metal may
-be folded over, and at the loose ends a hole should be punched through
-which a screw-eye will pass. The metal is held to a wood base with a
-screw, under the head of which a wire is caught. The second wire end is
-slipped between the metal plates, and a turn of the screw-eye will bind
-and hold it securely.
-
-[Illustration: FIG. 17]
-
-[Illustration: FIG. 18]
-
-Connectors are employed to unite the ends of wires temporarily, and are
-made in many forms. A simple and useful one is made from a piece of
-spiral spring fastened to a block of wood by two staples, as shown at
-Fig. 18 A. The ends of the wires are pressed down into the coils of the
-spring and are held with sufficient security for temporary use. Another
-connector is made from a block of wood, a strip of thin metal, and two
-screw-eyes (Fig. 18 B). The metal is bent around the ends of the block,
-and through holes made in the ends of the strip screw-eyes are driven
-into the block. When the ends of wires are slipped under the metal, a
-turn of the eyes will hold them fast, as shown at Fig. 18 B.
-
-A short bolt threaded at each end and provided with four nuts will also
-act as a connector. The inner nuts are screwed on tightly and the outer
-ones are loose, so that when wires are placed between them they may be
-tightened with the fingers, as shown at C in Fig. 18. These are a few
-simple forms of connectors; the ingenious boy can devise many others to
-suit his needs and ideas.
-
-
-Lightning-arresters and Fuse-blocks
-
-All lines of exposed wire that run from out-doors into the house should
-be provided at both ends with lightning-arresters, particularly if they
-are telephone or telegraph lines, burglar alarms, or messenger
-call-boxes. In many instances where unprotected telephone lines have
-been the plaything of lightning, painful accidents have happened, and it
-is only the part of prudence to provide against them. It is better to
-have an arrester at both ends of a line, and as the cost is
-insignificant it is hardly worth considering as against its feature of
-safety.
-
-Lightning-arresters may be constructed in many ways and of different
-materials; the ones here shown and described are easily made and
-efficient. The principle of all arresters is simply a fuse which burns
-out whenever the wire is carrying a greater amount of current than is
-required for the proper working of the apparatus, thereby arresting the
-current and protecting the instruments from destruction.
-Induction-coils, relays, fine windings on armatures, or a magnet helix
-are quickly destroyed if a too powerful current is permitted to pass
-through them, and it is therefore advisable to protect them. When a fuse
-burns out under a trolley-car, or in the shunt-box of a motor-car or
-engine, it is because a greater amount of current is trying to pass in
-than the motor will safely stand. When a fuse “blows out,” the apparatus
-or motor is put out of commission until the fuse is replaced, but the
-delicate mechanism and the fine wiring on the field-magnets or armatures
-are saved.
-
-The simplest form of single pole-fuse is a fine piece of lead wire held
-between two binding-posts, as shown at A in Fig. 19. The lead wire may
-be of any length; but for small instruments, where a moderate current is
-employed and where there is a possibility of lightning travelling on the
-wire, the fuse should be from two to three inches long. For inside work,
-however, where it is to be used simply as a safety, the wire may be
-shorter and finer.
-
-To make the lightning-arrester shown in Fig. 19, cut out a hard-wood
-block five inches long, an inch wide, and half an inch thick. Give this
-several coats of shellac; then place a piece of mica, or asbestos paper,
-over the top of the block, and make it fast with thick shellac to act as
-a glue. From small pieces of copper or brass cut two plates one-half by
-one inch, and drill holes in them to take screws and screw-eyes. Place
-copper burrs under the screw-eyes for connectors, and drive two brass
-screws half-way down in the block through the holes at the inner ends of
-the binding-post plates. See that these screws fit snugly in the holes
-in the plates so that contact is perfect. If the holes are too large and
-the screws fit loosely, two copper burrs will have to be used and the
-screws driven in, so that the heads bind the burrs on the ends of the
-fuse-wire. From an electrician, or supply-house, purchase a few inches
-of fine lead fuse-wire--say Nos. 20, 22, or 24--and twist the ends of a
-length around the screws, as shown in the drawing. Perfect contact
-should be had between the lead wire and the screws; by way of
-precaution, a bit of solder will dispel all doubt. Just touch the point
-with a little soldering solution; then apply a soldering-iron having a
-drop or two of solder on the end.
-
-Perfect connection is absolutely necessary for telephone, telegraph, or
-annunciator work, and where there is a lightning-arrester and the line
-is not working well, the trouble may often lie in the poor contact of
-lead and brass or copper, or possibly in using wire that is too fine.
-Lead is a very poor conductor, and a fine wire would act as a check. For
-a test, first insert a piece of copper wire to see that the line is
-working properly; then use lead wire of sufficient size to carry the
-current as well as the copper did. The action of metals and wire, as
-current retarders, will be explained in the chapter on resistance and
-resistance-coils.
-
-For general commercial use the base-blocks of all lightning-arresters
-should be made of porcelain, slate, or some of the composition
-non-conductors, such as moulded mica, silex and shellac, or fibre. As
-these are not always available, wood, with a covering of mica, will
-answer every purpose and can be readily adapted for use.
-
-The apparatus pictured in Fig. 19 is known as a single-pole
-lightning-arrester, and is the simplest form of this kind of electrical
-paraphernalia. In Fig. 20 a double-pole arrester is shown. This is
-constructed in the same manner as described for the single one. The
-block is five inches long, two inches wide, and half or five-eighths of
-an inch thick. A countersunk hole is made in the middle of all the
-lightning-arrester blocks through which a screw can be passed to hold
-the apparatus fast in any desired location.
-
-In Fig. 21 another form of fuse is shown. It is made from a piece of
-mica three-quarters of an inch wide and four inches long, two pieces of
-thin sheet-copper, and a piece of lead fuse-wire. The copper is
-three-quarters of an inch wide, and one piece of it is bent in the form
-of a [V], as shown at A in Fig. 21. One end of the mica strip is dropped
-in the [V], and with a pair of pliers the [V] is closed up by pinching
-it at the bottom. To further insure its staying in place, the top and
-end, or open edges, should be soldered. Punch a small hole through the
-copper ends, at the inside edge, slip the ends of the fuse-wire in them,
-and touch the union with a drop of solder to insure perfect contact.
-With shears and file cut a [U] from the side of one copper band and from
-the end of the other; these will allow the copper ends to pass under the
-heads of screws, thus avoiding the necessity of removing the entire
-screw from the block in order to set the fuse in place.
-
-[Illustration: FIG. 19
-
-FIG. 20
-
-FIG. 21
-
-FIG. 22
-
-FIG. 23
-
-FIG. 24
-
-FIG. 25
-
-FIG. 26
-
-LIGHTNING-ARRESTERS AND FUSE-BLOCKS]
-
-The block on which this fuse is held is shown in Fig. 22, and is made in
-a similar manner to the one shown in Fig. 19, except that the metal
-plates are a trifle longer and are bent up, as shown in the drawing.
-Thus the mica fuse-plate will be elevated above the block. If the brass
-or copper used for the binding-post plates is too thin to stand the
-pressure of the screws when the fuse ends are screwed fast, put a few
-burrs on the screws below the plates; then the pressure of the screws
-cannot bend down the extending ears of the plates and make an imperfect
-contact.
-
-Another form of fuse-block is shown in Fig. 23. The same sort of a fuse
-is employed as shown in Fig. 21, but without the [U] cuts at the ends.
-The clutches are made by binding brass or copper plates, as shown in the
-drawing; they should then be screwed fast to a base-block five inches
-long, one inch and a half wide, and five-eighths of an inch thick. The
-opening between them should just admit the copper ends of the fuse, and
-pressure should be used to force the fuse in place so that the contact
-will be perfect.
-
-Still another form of fuse is shown in Fig. 24. This last may more
-properly be called a non-sparking fuse, for the lead wire is encased in
-a glass tube, and when it fuses no sparks fly and no small pieces of
-melted metal can get away from the inside of the tube. The plug is made
-from a piece of glass tube half an inch in diameter, two metal caps, and
-a short piece of lead wire. The metal caps are of thin sheet-copper, and
-are caught at the edges with solder. One end of the lead fuse-wire is
-passed through a hole in the end of a cap and soldered, as shown at A in
-Fig. 24. The wire is then passed through the tube and the cap placed
-over one end of it. This is repeated at the other end and the wire
-soldered fast. As a result, you will have a glass tube with metal caps
-held on the ends of the tube, by means of the thin lead wire which runs
-through the middle of the tube. The base-block to which this fuse-plug
-is attached is of wood one inch and a half wide, five or six inches
-long, and five-eighths of an inch thick. Two metal straps are made and
-screwed fast to the block, and the circuit wires are attached under the
-copper burrs and held down by the screw-eyes.
-
-To place or replace a fuse-plug, unscrew the eyes and raise each strap
-slightly, so that the copper cap ends will pass under them. A turn or
-two of the eyes will clamp the plug in position and at the same time
-bind the circuit wires.
-
-A spring lightning-arrester is shown in Fig. 25; it is simply a modified
-form of that shown and described in Fig. 19. The base-block is five by
-one-and-a-quarter by five-eighths of an inch, and is properly protected
-by a sheet of mica or asbestos. The two metal plates are cut for the
-binding-posts and screwed in place with screws, burrs, and screw-eyes.
-From spring-brass wire bend a hook and slip one end of it under the
-screw-head at the left side of the block. From a longer piece of wire
-make two or three turns around a piece of wood half an inch in diameter;
-then form a hook at one end and a turn at the other, so that it can be
-made fast under the screw-head of the binding-post. When at rest, the
-spring-hook should stand in an upright position, but when sprung and
-tied it occupies the position shown in the drawing. The spring-hook is
-to be bent down so that the two hooks are brought within an inch of each
-other. They are held in this position with a piece of lead fuse-wire.
-This last is given a turn about the hooks and one or two turns about
-itself, close to each hook, to prevent the spring from tearing itself
-away. When the wire is fused by a current the spring-hook flies up and
-away from possible contact with the short hook attached to the opposite
-binding-post. This is the construction for a single-pole-spring
-lightning-arrester; a double one is made in a similar manner, and the
-parts mounted on a wider block, as shown in Fig. 20.
-
-For doubtful currents, where there is no means of knowing how strong
-they are, a combined fuse and single-pole switch is shown in Fig. 26.
-This is nothing more than a combination of the apparatus shown in Fig.
-21, and the single-pole switch (Fig. 10). The base block is seven inches
-long and two inches wide. Or it may be made half an inch wider if it is
-to be bevelled at the top, as shown in the drawing. It should be
-three-quarters of an inch thick and provided with two countersunk holes
-for screws that will hold it in place on a ledge or against a casement.
-The little angles to hold the copper-ended mica fuse-plate are described
-for the apparatus pictured in Fig. 21. If it is desired that one of the
-ends should be provided with burrs and a screw-eye, the little plate of
-brass should be an inch long and an inch wide, with a half-inch-square
-piece snipped from one corner, as shown at A in Fig. 26. It is provided
-with two holes, and then bent on the dotted line, so that the part with
-the holes will lie on the block and the ear will stand in a vertical
-position. A reverse-plate made on this pattern will act as one side of
-the switch-bar clutch at the opposite end of the block. For the metal
-clutch and keeper at the middle of the block the metal plate (before it
-is bent) will appear as shown at B in Fig. 26. The long plate with two
-holes lies on the base, while the first ear (or the one without the
-hole) forms part of the clutch for the fuse end, the ear with the hole
-acting as one side of the bar-lever strap. An opposite plate to this
-forms the other side of the clutch and strap, and the two plates are
-screwed side by side, so that the fuse-plate will be held securely when
-pushed into place.
-
-For the switch-bar use a piece of hard copper or brass four inches long,
-half an inch wide, and about one-eighth of an inch thick, or the same
-thickness as the copper straps at the ends of the mica fuse-plate. Bore
-a hole at one end of this bar, and with a copper rivet attach it between
-the two upright ears at the middle of the block. With a file cut away
-the two edges at the other end of the bar for a distance of an inch, so
-that the bar will have an end as shown at C in Fig. 26. Drive a small
-file-handle on this end and give it a coat or two of shellac; then bevel
-the lower edges of the bar with a file where it enters between the
-blades of the clutch. The circuit wires are made fast at both ends of
-the block, and the current travels through the binding-posts, the lead
-fuse-wire on the mica plate D, and the switch-bar. If the current is too
-strong, then when the switch-bar is pushed into the clutch the
-safety-fuse will burn out and save the apparatus; or it will arrest a
-flash of lightning.
-
-
-Chapter IV
-
-MAGNETS AND INDUCTION-COILS
-
-
-Simple and Horseshoe Magnets
-
-Every boy has a horseshoe magnet among his collection of useful odds and
-ends, and whether it is a large or small one its working principle is
-the same. If large enough it will lift a jack-knife, nails, or solid
-weights, such as a small flat-iron or an iron padlock. A horseshoe
-magnet is made of highly tempered steel and magnetized so that one end
-is a north pole and the other a south pole. In more scientific language
-these poles are known as, respectively, positive and negative. Once
-magnetized the instrument retains that property indefinitely, unless the
-power is drawn from it by exposure to intense heat, and even then, by
-successive heating and cooling, the magnetism may be partially restored.
-
-An electro-magnet may be made of any scrap of soft iron, from a piece of
-ordinary telegraph-wire to a gigantic iron shaft. When a current of
-electricity passes through a wire a magnetic “field” is produced around
-the wire, and if the latter is insulated with a covering and coiled
-about a soft iron object, such as a nail, a bolt, or a rod, that object
-becomes a magnet so long as a current of electricity is passing through
-the coils of wire or helix. A coil of wire in the form of a spiral
-spring has a stronger field than a straight wire carrying the same
-current, for each turn or convolution adds its magnetic field to that of
-the other turns.
-
-A simple form of electro-magnet is made by winding several layers of No.
-20 insulated copper wire around a stout nail or a carriage-bolt; by
-connecting the ends to a battery of sufficient power, some very heavy
-objects may be lifted. A single magnet, like the one shown in Fig. 1, is
-made with a piece of soft iron rod six inches long and half an inch in
-diameter, the ends of a large spool sawed off and worked on the rod, and
-half a pound of No. 20 insulated copper wire. The spool-ends are
-arranged as shown in Fig. 2. An end of the wire is passed through a hole
-in one flange when you begin to wind the coils, and when finished, the
-other end is passed through a hole at the outer rim of the same flange.
-This magnet may be held in the hands when in use; or a hand-magnet may
-be constructed of a longer piece of iron on one end of which a handle is
-driven and held in place with a nut and washer, as shown in Fig. 3. The
-wires from the coil pass through holes made in the handle and come out
-at the butt end, where they may be attached by connectors to the
-pole-wires of a battery. To protect the outer insulated coil of wire
-from chafing and a possible short-circuit, it would be well to wrap
-several thicknesses of stout paper around the coil and glue it fast; or
-a leather cover will answer as well.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-FIG. 7
-
-SIMPLE AND HORSESHOE MAGNETS]
-
-A more powerful magnet may be made from a stout bolt, two nuts, and a
-wooden base, with about three-quarters of a pound of No. 18 insulated
-copper wire to wind about the body of the bolt. A block of wood an inch
-thick, four inches wide, and six inches long is provided with a hole at
-the middle for the bolt to pass through. A larger hole is made at the
-under side of the block so that a nut can be easily turned in it. A
-three-quarter-inch machine-bolt, with a square head, and seven inches
-long, is set in the block, head up, as shown in Fig. 4; and composition
-or thin wooden disks or washers are placed on the bolt to hold the coils
-of wire in place. The ends of the wire pass out through the bottom
-washer and are made fast to binding-posts on the block, and to these
-latter the battery-poles are made fast when the magnet is in use. Coils
-of wire may be wound on an ordinary spool, and the hole in the middle
-may be filled with lengths of soft iron wire. When a current is passing
-around the spool the wires become highly magnetic, but lose the
-magnetism directly the current ceases.
-
-Horseshoe electro-magnets are made by winding coils on the ends of
-[U]-shaped pieces of soft iron, but the winding must be done so that the
-current will pass around them in opposite directions, otherwise you
-would have two negatives instead of a negative and positive. For a small
-horseshoe magnet a stout iron staple may be used, but for the larger
-magnets it would be best to have a blacksmith bend a piece of round iron
-in the desired shape.
-
-A powerful horseshoe magnet may be made from a piece of tire-iron bent
-as shown in Fig. 5 A; when wound with No. 18 wire it will appear like
-Fig. 5 B. A volt or two of current passing through the coils will render
-this magnet powerful enough to lift several pounds.
-
-For bells, telegraph-sounders, and other electrical equipment requiring
-the horseshoe or double magnet, several kinds may be used, but the
-simplest is constructed from two carriage or machine bolts and a yoke of
-soft iron, as shown in Fig. 6. The yoke is five-eighths of an inch in
-width, two inches and a half long, and provided with two
-three-eighths-inch holes, one inch and a half apart from centre to
-centre. Two-inch carriage or machine bolts are used, and they should be
-three-eighths of an inch in diameter. The nuts are turned on the thread
-far enough to admit the yoke, and then another nut is applied to hold it
-in place and bind the three pieces into one compact mass. Wooden
-spool-ends or composition washers are placed on the bolts to hold the
-ends of the wire coils in place, and the winding may be done on each
-bolt separately and locked to the yoke after the winding is completed.
-Double cotton-insulated No. 20 or 22 copper wire should be used for the
-coils.
-
-It is a tedious and bothersome job to wind a coil by hand, and if
-possible a winder should be employed for this purpose. Several varieties
-of winders are on the market, but a simple one for ordinary spools may
-be made from a stick held in an upright piece of wood with staples. This
-idea is pictured in Fig. 7, where the round stick is shown cut with two
-grooves into which the staples fit. One end of the stick is made with a
-square shoulder, so that a handle and crank can be fitted to it. A few
-wraps of wire are taken around the crank to prevent it from splitting,
-and it is held to the round stick with a slim steel nail. The opposite
-end of the round stick is shaved off so that it will fit snugly in the
-hole of a spool; if it should be too small for some spools, a few turns
-of cord around the small end will make it bind. The block to which the
-shaft and crank is attached may be held in a vise or screwed to the edge
-of a table.
-
-
-Induction-coils
-
-A simple induction or shocking coil may be made of a two-and-one-half by
-five-sixteenths-inch bolt, a thin wooden spool, and two sizes of
-insulated copper wire. An induction-coil is a peculiar and wonderful
-apparatus; it figures largely in electrical experimenting and is a part
-of every complete equipment.
-
-A piece of curtain-pole may be used for the spool. First bore a
-five-sixteenths-inch hole through the wood to receive the bolt; then in
-a lathe turn it down into a spool with less than one-eighth of an inch
-of wood about the hole and with flanges about one-eighth of an inch in
-thickness. Smooth the spool with sand-paper, while it is still in the
-lathe, and give it a thin coat or two of shellac.
-
-Slip the spool on the winder (Fig. 7) and wind on three layers of No. 24
-cotton-insulated copper wire, taking care to wrap the coils evenly and
-close. Bring six inches of the ends out at either end of the spool
-through small holes pierced in the flanges; then wrap several
-thicknesses of brown paper around the coil. A current passing around
-this three-layer coil will magnetize the bolt. This is the primary coil
-and the one through which the battery current will pass.
-
-A secondary coil is now made over the primary one with eleven or
-thirteen layers of No. 30 insulated copper wire. It will take some time
-to carefully put on these layers, and when doing so mark down each layer
-so as to keep an accurate count, for there must be the right number of
-layers to make the coil act properly. No. 30 wire is quite fine, and if
-the layers are not inclined to lie smooth, make a wrap or two of brown
-paper between each three layers. Bring six inches of each end of the
-wire out from the flanges of the spool, and to protect the outer coil
-wrap paper about the coils and attach it fast with thread or paraffine.
-Slip the bolt through the hole and screw the nut on the threaded end.
-Cut out a wooden block four inches long, three inches wide, and
-three-quarters of an inch thick, and with two thin metal straps and
-screws attach the coil to the middle of the block, as shown in Fig. 8.
-Make four binding-posts and screw them fast at the corners, and to A and
-B of Fig. 8 attach the ends of the heavy wire from the primary coil, and
-to C and D of Fig. 8 the ends of the fine wire from the secondary coils.
-The induction-coil is now ready for any use to which it may be put, and
-by mounting it on the block with the delicate wire ends attached to the
-binding-posts, it is in less danger of damage than if the wire ends were
-left loose for rough-and-ready connections.
-
-In order to get a shock from this coil it will be necessary to have a
-pair of handles and a current interrupter. The handles may be made from
-two pieces of tin rolled into the form of cylinders to which wires are
-soldered. Or, better yet, use pieces of thin brass tubing an inch in
-diameter. The buzzer shown in Fig. 9 may be employed for a current
-interrupter, and a bichromate battery will furnish the current.
-
-In order to make the connections, the wires from the handles are
-attached to the binding-posts C and D in Fig. 8--that is, to the wires
-of the secondary coil. One spool of the battery is connected with A of
-Fig. 8 and the other with A of Fig. 9. A wire connects C of Fig. 9 with
-B of Fig. 8, and the circuit is closed. The buzzer now begins to
-vibrate, and any one holding the handles will receive a shock the
-intensity of which depends on the strength of the batteries. A switch
-should be introduced somewhere in the circuit, so that it may be opened
-or closed at will; a good place for it is between a battery-pole and the
-binding-post A in Fig. 8.
-
-If the shock is too intense it may be weakened by drawing the carbon and
-zinc poles partly out of the bichromate solution; or a regulator may be
-made of a large glass tube and a glass preserving-jar filled with water.
-If the tube cannot be had, an Argand gas-burner chimney will answer as
-well.
-
-Solder a wire to the edge of a small tin or copper disk, as shown in
-Fig. 10, on which the chimney rests at the bottom of the jar, and
-another wire to a tin box-cover with some small holes punched in its
-top, this latter being suspended within the chimney. This second wire is
-passed out through a cork at the top of the chimney made of a disk of
-cardboard and a piece of wood. One wire is connected with A of Fig. 8
-and the other with a battery-pole. This apparatus acts the same as a
-resistance-coil, and by raising or lowering the box-cover the current is
-increased or diminished. The closer the cover comes to the disk the
-stronger the current, as there is less water for the electricity to pass
-through and therefore less resistance; while if the cover touches the
-disk the current flows as freely as if there were no regulator and the
-wires ran directly to the cell.
-
-An apparatus comprising a coil, an interrupter, or armature, and a
-switch may be set on one block, and the arrangement of the several parts
-is clearly shown in the drawing of the complete galvano-faradic
-apparatus (Fig. 11). The block should be six inches long, four inches
-wide, and seven-eighths of an inch in thickness.
-
-[Illustration: FIG. 8]
-
-[Illustration: FIG. 9]
-
-[Illustration: FIG. 10]
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 12]
-
-The coil is made as described for Fig. 8, the spool being three inches
-long and one inch and a quarter in diameter. A carriage-bolt three
-inches and a half long and five-sixteenths of an inch in diameter, with
-a bevelled head, is made fast in the spool, and this coil is strapped to
-the block with two metal bands and screws. Two binding-posts (A and B of
-Fig. 11) are arranged at the upper corners, and to these the ends of the
-secondary coil wires are attached. Two more binding-posts (C and D of
-Fig. 11) are arranged at the lower side and provided with a switch to
-open and close the circuit. One of the primary coil wires is made fast
-to C, and the other one to a block which contains the set-screw that
-bears against the vibrating armature. Its arrangement and the wire
-connection is explained in Fig. 9 B.
-
-An armature of thin brass or tin is made and attached to a block (E in
-Fig. 11). At the loose end that is opposite the bolt-head several wraps
-of tin are made and soldered fast, or a small block of soft iron may be
-riveted to the armature. It must be of iron or tin, however, so as to be
-attracted by the electro-magnetized bolt-head. This arrangement may be
-seen in Fig. 12. Attach a thick piece of paper over the bolt-head, so
-that the lug at the end of the armature will not adhere to it through
-residual magnetism.
-
-In regular galvano-faradic machines the current regulator is formed of a
-hollow cylinder which is drawn from the core of the coil; but in this
-simple machine the water-jar regulator may be connected between a pole
-of the battery and the binding-posts (D or E of Fig. 11). The wires of
-the handles are attached to posts (A and B of Fig. 11), and when all the
-wires are in place and the current turned on by means of the switch, the
-vibrator begins to work and the shocking-current is felt through the
-handles. By means of the regulating-screw that bears on the armature,
-the number of vibrations may be increased or diminished, but for faradic
-purposes the vibrations should be as quick as possible. Much amusement
-may be had with this apparatus, and a large number of people may be
-given a shock by getting them to join hands when standing or sitting in
-a circle.
-
-
-An Electric Buzzer
-
-This piece of apparatus is, in theory, nothing more than the electric
-bell, and might properly be included in Chapter V., on Annunciators and
-Bells. But since it is the logical development of principles just laid
-down, it has been thought best to give it its present position.
-
-The electric buzzer is constructed on the principle of the
-telegraph-sounder, but instead of making a single click or stroke the
-current is made to act on the armature and keep up a continuous motion
-so long as the electricity passes through the helix of the cores, the
-armature, and the contact-points of the apparatus.
-
-A buzzer has the same movement as an electric bell with the ringing
-apparatus removed. For offices, houses, and quiet calls it is often
-preferred to the loud ringing of a bell.
-
-The electric buzzer shown in Fig. 13 is easy to make; it is operated by
-the aid of a cell and a push-button. Cut a base-block three inches and a
-half wide, five inches long, and three-quarters of an inch thick, and
-mount a horseshoe magnet made of bolts and a yoke and coils about at the
-middle of it, as shown in Fig. 9. The magnet is held to the base by a
-flat wooden cleat and a screw passed down through a hole in the cleat
-and into the base, between the coils. An armature of soft iron, two
-inches long and half an inch wide, is riveted to a piece of
-spring-brass, as shown in Fig. 14 A, and the end is bent so that it will
-fit around the corner of a block to which it is held fast with two
-screws. This armature is mounted so that there is a space one-sixteenth
-of an inch wide between it and the bolt-heads, as you can see in Fig. 9.
-The brass is bent out slightly and runs parallel with the armature for
-one inch and a quarter. Against this the end of the screw mounted in
-block B Fig. 9 rests.
-
-[Illustration: FIG. 13]
-
-[Illustration: FIG. 14]
-
-The block B is a small piece of hard-wood screwed fast to the side of
-the base to hold the set-screw and also the wire that comes from the
-outside of the upper coil. A small hole is made in the edge of the block
-and the wire passed in, so that the end rests in the screw-hole as shown
-by the dotted line. When the screw is placed in the hole and turned, it
-comes into contact with the wire and makes a connection. This block and
-its attachment is shown in Fig. 14 B.
-
-On the base, near the armature-block, a binding-post is made fast, and
-the current, passing in through the wire A in Fig. 9, goes through the
-coils and around to the screw B, then through the armature to the block,
-and out through the wire C. In its circuit the bolts are magnetized, and
-they draw the armature, but the instant they do so the loose
-spring-brass end is pulled away from the screw-point B and the circuit
-is broken, the bolts cease to be magnetized, and the armature flies back
-under the influence of the spring-brass neck at D. The loose brass end,
-on touching the screw-point, conducts the current through the coils
-again, with a continual vibrating action, so long as the electric
-current is passing in at A and out at C. The greater the volume of
-current the greater the number of vibrations, and to properly regulate
-the contact the set-screw B must be adjusted at the right point. Paste
-pieces of heavy paper over the heads of the bolts to overcome residual
-magnetism.
-
-A single electric bell is made the same as a buzzer, but continuing on
-from the end of the armature a wire or rod is mounted with a ball at the
-end which strikes the bell as the current causes the armature to
-vibrate. The bell-block may be made longer, and a bell from an old clock
-or a bicycle should be mounted at the proper place on a wooden dowel
-driven into the base. A screw passes through the hole at the middle of
-the bell and into the top of the dowel. The ball at the end of the rod
-may be made of brass with a hole in it, and a drop of solder will hold
-it in place. Or it may be made of wire wound round the end and soldered
-into a compact mass.
-
-
-A Large Induction-coil
-
-As has been said, the induction-coil is one of the mysterious phenomena
-of electrical science. While its practical value is known and recognized
-in all branches of voltaic electricity for use in transforming currents,
-its actual workings have never been clearly explained.
-
-The construction of a small induction-coil was explained in the
-description of a shocker or medical battery. For bigger equipments,
-wireless telegraphy and other uses, a large induction-coil will be
-necessary, and the following illustrations and descriptions should
-enable the young electrician to construct an apparatus that will be both
-simple and efficient in its working.
-
-For the tube (in which to wind the primary coils) obtain a piece of red
-fibre-tubing, one inch inside diameter and not more than one-eighth of
-an inch in thickness. The length should be ten inches. If fibre cannot
-be had use a paste-board tube.
-
-From white-wood, half an inch in thickness, saw two blocks four inches
-square and in the centre of each cut a hole so that the tube will pass
-through it and fit snugly. Some shellac and a few slim brass escutcheon
-pins will hold the blocks in place, as shown at Fig. 15. The wood blocks
-and fibre or paper tube should be treated to several successive coats of
-shellac to give them a good finish and prevent the absorption of
-moisture. Four binding-posts, with wood screw-ends, are to be made fast
-at the top edges of the end-blocks, as shown at Fig. 15. Holes bored in
-the blocks near the foot of the binding-posts will admit the ends of
-the coil-wires so that contact can be made. The ends of the
-conductor-wires should then be placed in the holes in the binding-posts
-and held in place with the thumb-screws.
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-The primary coil is made by winding four layers of No. 20 insulated
-copper wire on the tube and between the end-blocks, as shown at Fig. 16.
-Each layer must be wound evenly, and the strands should lie close to
-each other. When the first layer is on give it a coat of shellac; then
-wrap a piece of thin paper about it and give that also a coat of
-shellac. When the second layer is on repeat the operation of shellacking
-and paper-coating, and continue with the third layer. When the fourth
-layer is on give the coil a double wrap of paper and two or three coats
-of shellac to thoroughly insulate it and keep out all moisture. The
-winding may be done by hand, but it is much easier to do it on a winder
-or reel, which can be operated to revolve the core, the wire unwinding
-from its original spool as it is wound on the tube.
-
-A convenient winder may be made on a base-board which can be clamped to
-a table or bench. The board is twelve inches long, eight or ten inches
-wide, and seven-eighths of an inch thick. Two uprights, three inches
-wide, ten inches long, and three-quarters of an inch thick, are screwed
-and glued to the ends of the base-board. A notch is cut in the top of
-the end-boards, into which the spindle or shaft can rest; and at the top
-of the end-pieces two small plates of wood or metal are screwed down to
-hold the spindle in place when the tube and ends are being revolved. A
-small hole, bored in each upright end two inches above the top of the
-base-board, will admit a rod on which a spool of wire can revolve, as
-shown at Fig. 17.
-
-Two plugs of wood, shaped like corks, are made to fit in the ends of the
-fibre-tube. A hole is bored through each one so that a wire or rod
-spindle will pass through them and fit tightly. One end of the rod is
-bent and provided with a small wooden handle, by means of which the core
-may be revolved.
-
-This winding-rack makes it easy to handle the core-tube while putting on
-the layers of wire, and it holds the tube securely while the wraps of
-paper and shellac are applied.
-
-The secondary coil is laid over the primary, and should be of Nos. 30 to
-36 insulated copper wire. The finer the wire the higher the resistance
-and the longer the spark, but nothing heavier than No. 30 should be
-used.
-
-Begin by making one end of the wire fast to a binding-post; then turn
-the core-tube with one hand, holding the wire in the other. Take care
-not to bind the wire nor stretch it, but wind it on smoothly and evenly,
-like the coils of thread on a new spool of cotton or silk. Be very
-careful to avoid kinks, breaks, or uninsulated places in the wire.
-Should the wire become broken, give the coil a coat of shellac to bind
-the wound strands; then make a fine twisted point and cover it with the
-silk or cotton covering, with a coat of shellac to hold it in place, and
-proceed with the winding. Between each layer of wire place a thin sheet
-of paper and coat it with paraffine, or shellac, to make a perfect
-insulation; then proceed with the next layer.
-
-With a battery and small bell test the wire layers occasionally to see
-that everything is all right, and that there are no breaks or short
-circuits. This is very necessary to avoid making mistakes, and,
-considering the time and care spent in winding the coils, it would be a
-great disappointment if the coil were defective.
-
-[Illustration: FIG. 17]
-
-[Illustration: FIG. 18]
-
-About one pound and a half of wire should constitute the secondary coil,
-and, if possible, it is best to have it in one continuous strand,
-without splices.
-
-Over the last coil, after the winding is completed, several thicknesses
-of paper should be laid and well coated with shellac between each wrap.
-This is a protector to insure the fine wire strands from damage. To
-improve the appearance of the coil a wrap of thin black or colored
-leather may be glued fast, with the seam or point at the under side.
-
-The ends of the wires forming the primary coil should be made fast to
-the binding-posts at one end, while those of the secondary coil should
-be attached to the posts at the other end.
-
-For the core, obtain some soft iron wire, about No. 18, and cut a number
-of lengths. Straighten these short wires and fill the tube with them,
-packing it closely, so that the wires will remain in place under a
-mutual pressure. It is better to make a core of a number of rods or
-wires rather than to have it of one solid piece of soft iron.
-
-Now, from hard-wood, cut a base three-quarters of an inch thick, five or
-six inches wide, and twelve inches long. Attach the coil to the base by
-means of screws passed up through the board and into the lower edges of
-the end-blocks. The wood is to be stained and given several successive
-coats of shellac.
-
-Now connect the wires of a battery to the binding-posts in contact with
-the primary coil, and attach two separate wires to the secondary coil
-binding-posts. Bring these ends near to each other, and a spark will
-leap across from one end to the other, its size or “fatness” depending
-on the strength of the battery. The completed apparatus is shown at Fig.
-18.
-
-In producing a long spark a condenser is an important factor; it is used
-in series with an induction-coil. There are several forms of
-condensers, but perhaps the simplest and most efficient is the Fizeau
-condenser, which is made up of layers of tin-foil with paraffined paper
-as separators.
-
-From a florist’s supply-house purchase one hundred and fifty sheets of
-tin-foil seven by nine inches, or sheets that will cut to that size
-without waste; also ten or twelve extra sheets for strips. At a paper
-supply-house obtain some clear, thin, tough paper about the thickness of
-good writing-paper. Be careful to reject any sheets that are perforated
-or have any fine holes in them. The sheets should be eight by ten
-inches, or half an inch larger all around than those of the tin-foil.
-The paper must be thoroughly soaked in hot paraffine to make it
-moisture-proof and a perfect non-conductor. This is done by placing
-about two hundred sheets on the bottom of a clean tin tray, or
-photographic developing-dish of porcelain. Don’t use glass or rubber.
-After placing some lumps of paraffine on the paper, put the tray in an
-oven so as to dissolve the paraffine and thoroughly soak the paper.
-
-Open the oven door and, with a pin, raise up the sheets one at a time,
-and draw them out of the liquid paraffine. As soon as it comes in
-contact with cool air the paraffine solidifies and the sheet of paper
-becomes stiffened. Select each sheet with care, so that those employed
-for the condenser are free from holes or imperfect places.
-
-From pine or white-wood, a quarter of an inch in thickness, cut two
-boards, eight by ten inches, and give them several good coats of
-shellac.
-
-To build up the condenser, lay one board on a table and on it place two
-sheets of paraffined paper. On this lay a sheet of tin-foil, arranging
-it so that half an inch of paper will be visible around the margin. From
-the odd sheets of tin-foil cut some strips, one inch in width and three
-inches long. Place one of these strips at the left end of the first
-sheet of foil, as shown at Fig. 19. Over this lay a sheet of the
-paraffined paper, then another sheet of the foil. Now on this second
-sheet of foil lay the short strip to the right end, and so proceed until
-all the foil and paper is in place, arranging each alternate short strip
-at the opposite end. Care must be taken to observe this order if the
-condenser is to be of any use.
-
-[Illustration: FIG. 19]
-
-[Illustration: FIG. 20]
-
-When the last piece of foil is laid on, with its short strip above it,
-add two or three thicknesses of paper, and then the other board. With
-four screw-clamps, one at each corner, press together the mass of foil,
-paper, and boards as closely as possible, then bind the boards about
-with adhesive tape, or stout twine, and release the clamps. Attach all
-the projecting ends of foil at one side by means of a binding-post, and
-those at the other end with another binding-post. The complete condenser
-will then appear as shown in Fig. 20.
-
-When in operation one wire leading from the secondary coil should be
-connected with a binding-post of the condenser, so that it is in
-series.
-
-The object of the condenser is to increase the efficiency of induction,
-and it should be made in proportion to the size of the induction-coil
-with which it is to be employed.
-
-
-Circuit-Interrupters
-
-When an induction-coil is to be employed as a shocker (and there is no
-vibrating armature arranged in connection with the core), a
-circuit-interrupter must be employed to get the effect of the
-pulsations, as given out by the secondary coil when a current is passing
-through the primary.
-
-There are various forms of circuit-breakers that may be made for this
-purpose, but for really efficient service the type shown in Fig. 21 is
-perhaps the best that can be devised.
-
-This interrupter consists of a metal cog-wheel with saw-teeth, a pinion
-or axle, and a handle. Also a base-block, with uprights to support it,
-and a piece of spring-brass wire, arranged so as to bear against the
-wheel. When the wheel is revolved the spring-wire will be driven out by
-each tooth; and when released it flies back to the wheel, striking the
-bevelled edge of a tooth at each trip.
-
-Two binding-posts, arranged on the block, will provide means of
-connecting in-and-out wires. With a coat or two of shellac on the
-wood-work and black asphaltum varnish on all surfaces of the metal that
-are not used for contact, this circuit-interrupter will be ready for any
-use in connection with an induction-coil.
-
-The base-block is of pine, white-wood, or cypress, seven-eighths of an
-inch thick, three inches wide, and five inches long. The uprights, which
-support the wheel, are half an inch thick and one inch wide. The wheel
-is three inches in diameter and is made of brass one-sixteenth of an
-inch thick. The design of the wheel should be laid out with a compass
-and marked with lead-pencil or a sharp-pointed awl, which will leave a
-mark clear enough to be seen when sawing and filing the teeth and open
-places.
-
-[Illustration: FIG. 21]
-
-[Illustration: FIG. 22]
-
-A true plan is shown at Fig. 21 A. Through the middle of the wheel a
-small hole is bored to receive the axle of brass which is to be soldered
-in place. When the wheel is set up, a metal crank and wooden handle
-should be soldered fast to one end of the axle. A piece of spring-brass
-wire is fastened to the block, with a staple, and the lower end bent so
-that the screw in one binding-post will hold it in place. The upper end
-of the wire is bent in the form of an [L]. From the other binding-post,
-through the block and up one support, a wire is passed, the end of which
-comes into contact with the axle. The current, passing in through one
-binding-post, is carried through this wire to the axle, then to the
-wheel, and so on out through the spring-wire and remaining binding-post.
-When in action the circuit is constantly being broken, as the
-spring-wire jumps from the end of one tooth back to the face of the next
-tooth. The pulsations are increased or diminished by the fast or slow
-speed of the wheel, as regulated by the hand motion. The strength of the
-current is regulated by the force of the battery and should be
-controlled by a water resistance, as described for the medical battery,
-or shocking-coil.
-
-The interrupter, shown in Fig. 22, is built up on a block six inches
-square and seven-eighths of an inch thick.
-
-A circle is cut from sheet-lead and laid on the face of the block,
-through which pins, or steel-wire nails, are driven. The lead circle is
-five inches in diameter and half an inch in width, making the inside
-diameter four inches.
-
-The pins or nails are driven a quarter of an inch apart, and should be
-properly and accurately separated, so that an even make-and-break will
-be the result.
-
-It is not necessary to bore holes in the lead, but the pins or nails
-should be driven clear through it, so that perfect contact can be had by
-the metal parts coming together. Otherwise the apparatus would be
-useless.
-
-Over the circle of pins a brass bridge is erected, so that the
-cross-strips will clear the heads of the pins. A hole is bored at the
-middle of the bridge so that the revolving axle will pass through it.
-
-The axle is made from a piece of stout wire, or light rod, and near the
-foot of it, and about half an inch above the base-board, a disk of metal
-is soldered fast. A piece of spring-brass wire is attached to this disk,
-so that when the axle is turned the end of the wire trips from pin to
-pin, thus making and breaking the circuit. The upper part of the axle
-is bent and provided with a small wooden or porcelain knob.
-
-One wire from the secondary coil is caught under a screw that holds one
-end of the brass bridge to the base; and the other to a screw, which may
-be placed at one corner of the block, and from which a short wire leads
-to the lead ring. Binding-posts may be arranged to serve the same
-purpose, and, of course, they are much better than the screws, because
-they can be easily operated by the fingers and do not require a
-screw-driver every time the interrupter is placed in series with an
-induction-coil. An interrupter on this same order may be made from a
-straight strip of lead with the pins driven through the middle of it.
-One wire from the secondary coil is made fast to the lead plate, and the
-end of the other wire is passed along the pins, thus making and breaking
-the circuit in a primitive manner.
-
-
-Chapter V
-
-ANNUNCIATORS AND BELLS
-
-
-A Drum Sounder
-
-A unique electric sounder that is sure to attract attention is in the
-shape of an electric-bell apparatus, with a drum sounder in place of a
-bell, or knockerless buzzer. Fig. 1.
-
-The outfit is mounted on a block four inches and a half wide and seven
-inches long. The cores and yoke are made as described for the electric
-buzzer (chapter iv.) and are wound with No. 22 cotton-insulated wire.
-The magnet is then strapped fast to the block by means of a hard-wood
-plate having a screw passed down through it; and between the coils and
-into the block an armature is made and mounted on a metal plate, which
-in turn is screwed to the block. Another block, with a contact-point, is
-arranged to interrupt the armature, and the series is connected as shown
-in the drawing Fig. 1.
-
-The end of the wire projecting above the armature is provided with a
-hard-wood knocker which operates upon the head of the drum. The drum is
-made from a small tin can, having one or two small holes punched in the
-bottom. Over the top a thin membrane, such as a bladder or a piece of
-sheep-skin or cat-skin, is drawn and lashed fast with several wraps of
-wire, having the ends twisted together securely. The membrane must be
-wet when drawn over the can end, and great care should be taken to get
-it tight and even. Then, when it dries, it will stretch and draw, like a
-drumhead, and hold its elastic, resonant surface so long as it does not
-become moistened or wet.
-
-This drum is arranged in the proper position and lashed fast with wires
-passed over the box and down through holes in the block; where, after
-several turns, the ends may be securely twisted together. In place of
-the drum a small wooden box may be lashed fast with its open end against
-the block, so as to form a hollow enclosure. The raps of the knocker
-against its sides will give forth a resonant xylophone tone.
-
-
-An Annunciator
-
-A simple annunciator may be made from a core, a helix, and some brass
-strips. A soft iron core, made of a piece of three-eighth-inch round
-iron and threaded at one end, is converted into a magnet by having a
-spool and wire coil arranged to enclose it. This in turn is screwed into
-a strip of brass bored and threaded to receive it. Fig. 2.
-
-This brass strip is shaped as shown at Fig. 3 A, and the ears are bent
-to serve their several purposes. The lowest ears are turned out and the
-lower part of the plate is bent forward so as to form the hinge on which
-the drop-bar turns. The drop-bar is only a strip of metal turned up at
-one end, on which a numeral or letter can be attached; while at the
-other the metal should be bent over so as to form a core into which a
-pin or wire may be passed and the extending ends bent down, after being
-caught through the holes in the ears. Above the magnet the strip is bent
-forward and the top or end ears bent up, so as to form the hinge on
-which the armature swings. Holes are made in the long ears, through
-which screws pass to hold the annunciator fast to the box or wood-work.
-
-The armature is made from a strip of brass and is shaped like B in Fig.
-3. The two ears at the top are bent down and fit within those at the top
-of the first strip. A screw or wire passed through the holes in the ears
-will complete the hinge. The strip is bent down so as to fall in front
-of the magnet, and to its inner side a button or disk of sheet-iron is
-riveted fast, so as to form an attraction-plate to be drawn against the
-magnet when the current is passing around it. The lower part of the
-armature is bent in hook fashion so as to hold up the drop-bar.
-
-A slot is cut in the drop-bar through which the hooked end will project.
-A short spring is arranged at the top of the annunciator so as to keep
-the bar and the hook in place when not in action. The current passing
-around the soft iron core magnetizes it and draws the iron button on the
-armature towards it. This action immediately releases the hook from
-under the edge of the metal at the forward end of the slot, and the bar
-drops, bringing the figure down and into plain sight. It is necessary,
-of course, to mount this annunciator so that the bar will not drop down
-too far. This may be done by having a platform or wire run along under a
-series of the drops, so that they will rest on it.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-ANNUNCIATORS AND BELLS]
-
-
-A Double Electric Bell
-
-For loud ringing, and to get the benefit of both the forward and
-backward stroke of the knocker, a double bell, similar to the one shown
-in Fig. 4, may be constructed upon the general principle of the
-single-stroke buzzer already described (chapter iv.).
-
-Two soft iron cores are made, as described for the other bells, but
-instead of being yoked together with iron, so that the three parts will
-form a horseshoe magnet, the yoke is of brass or copper. Each core will
-then be an independent magnet.
-
-The spools are wound with No. 22 insulated wire and the ends left free,
-so that the coils are not connected together. If the drawing is examined
-closely you will see that the armature swings on a pivot at the base of
-the knocker-bar. When the bell is not in action the knocker might rest
-naturally against one bell or the other; or it might stand in the centre
-and not touch a contact-point, were it not for the small spring which
-draws it to the left. Directly the current is run through the coils it
-alternately magnetizes first one and then the other. This action is due
-to the making and breaking of the circuit by the spring on the armature.
-It first comes into contact with one point, and then is drawn away from
-it to come into contact with the other. Fig. 4 shows the knocker-bar at
-rest between both bells and the armature unattracted by either magnet.
-This position is purposely given so as to indicate the balance of the
-armature and the spaces between it and the cores and also the
-contact-points above it.
-
-The small, light wire spring shown in the drawing draws the knocker to
-one side; therefore, when at rest, one circuit is closed. Otherwise the
-bell would not act when the current is run through the parts--in fact,
-the current could not run through at all, if one or the other contact
-were not made.
-
-The magnets are held fast to a base with a long screw and a small plate
-of wood laid across them as shown in Fig. 4. The armature is a piece of
-soft iron one-eighth of an inch thick, half an inch wide, and three
-inches long. This has a spring-brass piece attached to it as shown at A
-A in Fig. 5. Small holes are bored through the strip and the iron, and
-escutcheon pins are passed through and riveted. A small hole is made
-down through the middle of the iron plate and a pin is driven into it,
-so that a quarter of an inch projects at both sides.
-
-Another hole is made through the side of the plate for the knocker-bar.
-Then the armature is set in place so that there is a space of one-eighth
-of an inch between it and the magnet ends. The armature is held in place
-at the top by a bent metal strip (B B in Fig. 5). This is screwed fast
-to the base and the bottom is countersunk into the wood.
-
-Two contact-points (C C in Fig. 5) are arranged so that when a magnet
-draws the armature down it brings the opposite end of the armature
-spring into contact with a point.
-
-The wiring is at the under side of the base and is shown in Fig. 6. The
-current enters binding-post A, and passes around coil and magnet No. 1
-by entering at B and leaving at C; from thence to D, entering the
-armature spring at E, when the small spring has drawn the knocker-bar
-over to the left. The current passes along the armature and out at F;
-then along to binding-post G, and so on around through battery K and
-push-button L, thus completing the circuit. Directly that this is done
-the magnet draws the spring end of the armature away from contact-point
-D and up against contact-point J, so that the circuit is broken through
-coil No. 1 and is sent through coil No. 2. This immediately magnetizes
-core No. 2 and draws the armature down to it, breaking its contact with
-J and re-establishing it with D. The rapid alternate making and breaking
-of the circuit, and the rapid and strong motion of the armature in its
-seesaw action, causes the knocker to rap the bells soundly each time it
-travels from right to left and back again.
-
-Two bells of similar size, or two drums or wooden boxes, may be employed
-for this double striker, and the more current that is run through the
-coils the more power and a corresponding increase of noise.
-
-
-An Electric Horn
-
-One of the most useful pieces of apparatus where a loud noise is
-required (such as in a motor-boat or an automobile) is the electric
-horn.
-
-It is a rearranged principle of the telephone, for instead of sound
-entering or striking against the membrane or tympanum to be transmitted
-elsewhere, the disturbance takes place within the horn and the sound is
-emitted.
-
-Everybody has been close to a telephone when others have been using it,
-and has heard noises, rasping sounds, and even the voice of the speaker
-at the other end of the line. If a cornet were played at the other end
-of the line it could be distinctly heard through the receiver by many
-persons in the room, since its vibrations are loud enough to set up a
-forcible succession of sound-waves.
-
-The same principle operates in the electric horn, but instead of being
-agitated at a long distance it is done within the enclosure, and a very
-much louder vibration is consequently produced.
-
-It is quite as easy to make an electric horn as to construct a bell, but
-care must be exercised to have the parts fit accurately and the wiring
-properly done. If the drawings are studied and the description closely
-followed, there is no reason why a horn cannot be made that will demand
-any one’s attention from some distance away.
-
-The complete horn is shown in the illustration Fig. 7, and as it is made
-of wood it is easily attached with screws to a boat or a motor-car.
-
-From white-wood, half an inch thick, cut two blocks three inches and a
-quarter square. In one of them (the rear one) bore a hole at the centre,
-of such size that a piece of three-eighth-inch gas-pipe can be screwed
-into it. In the other one make a hole two inches in diameter, so that
-the cover of a small tin can will fit into it. Outside this hole, and on
-one side of the block, cut the wood away and down for one-eighth of an
-inch, forming a rabbet, as shown at A in Fig. 7. This will be the back
-of the front block.
-
-[Illustration: FIG. 7
-
-AN ELECTRIC HORN]
-
-Have a gas or steam fitter cut a piece of two-inch iron pipe one inch
-and three-quarters long. This will measure a trifle over two inches and
-a quarter, outside diameter, and will form the cylinder or cover for the
-mechanism. The piece of pipe should fit snugly in the front board, and
-at the rear one the wood should be cut away so as to let it in an eighth
-of an inch, as shown in the sectional plan of Fig. 7.
-
-Obtain a piece of three-eighth-inch gas-pipe, threaded at one end. Cut
-it with a hack-saw, and file the blunt end so that it will measure one
-inch and seven-eighths long, as shown at C in Fig. 7. This is to be
-screwed into the front of the rear block so that it will project one
-inch and a half.
-
-Make a spool to fit the pipe, as shown at B in Fig. 7, or use two wooden
-button-moulds attached to the pipe with shellac or glue. Between them
-wind on the coils of No. 22 wire to form the helix.
-
-Cut a hole in the tin-can cover, as shown at D in Fig. 7, and have a
-tinsmith solder a small funnel to it (for the horn, or bell, as it is
-called), cutting away the lower part of the funnel so that the hole in
-it will correspond in size with that in the can cover.
-
-This joint can be made at home by fitting the funnel in the hole and
-then turning back the edge, as shown in the sectional drawing at E in
-Fig. 7. Then, with a spirit-lamp, some soldering solution, and solder,
-make a good joint.
-
-Small holes are to be made at the corners of the blocks, through which
-stove-bolts two inches and a half long will fit to bind the front, back,
-and cylinder together.
-
-Select a good, clean, and flat piece of tin and cut a disk two inches
-and a quarter in diameter, and through the middle make a small hole. Cut
-two pieces of iron about the size and thickness of a cent, and bore a
-small hole through the centre of each. Obtain a piece of stout brass
-wire, or thin rod, and file one end of it as shown at G in Fig. 7, so
-that the small end will fit in the holes made in the iron buttons. Place
-one button on either side of the tin disk, and pass the wire through;
-then clamp it in a vise and rivet the top of the rod so that you will
-have a disk with a button at each side of the centre and all attached
-firmly to a brass rod, as shown at F in Fig. 7. The total length of this
-rod should be two inches and a half, and the lower end is to be threaded
-and provided with two small brass nuts. A piece of spring-brass
-three-eighths or half an inch wide is made fast to a small block at the
-back of the horn, as shown at H in Fig. 7, and at its opposite end a
-contact-piece of metal, bent at an angle, is screwed fast. Around the
-back of the back block a wooden frame is attached to protect the rear
-mechanism of the horn.
-
-The parts are now ready to assemble. First see that the metal angle
-contact-point is in place with the long brass strip resting on it, and
-that this in turn is properly fastened to the block on the side opposite
-the contact-point, as shown at H in Fig. 7. There should be a small hole
-through the middle of the brass strip directly in line with the middle
-of the hole in the gas-pipe. Place this back-board down on the table so
-that it will lie in a position as indicated in the sectional plan of
-Fig. 7. The gas-pipe is then to be screwed onto the plate. Over this the
-spool with its layers of wire is to be slipped and made fast, and the
-cylinder of iron is then placed in position. Over this the disk F is
-laid, so that the brass rod extends down through the pipe and brass
-strip; then the nut is screwed on to hold it in place. Next comes the
-front block, with its horn or bell, and the entire mass is locked
-together by means of the four bolts at the corners.
-
-The wiring is simple. One inlet being through block I, the current
-passes through strip J to contact-point K; then through the coil and out
-at wire L. The inlet and outlet wires are connected to a battery and to
-a push-button or switch, so that the horn can be operated. The proper
-adjustment of this horn depends on the nuts at the foot of the brass
-rod. They must be screwed on tight enough to draw the strip J so that it
-rests on the contact-point K.
-
-The current, passing in at I, through J, K, the coil, and out at L,
-magnetizes the piece of pipe and draws the iron buttons or disks
-attached to the tin disk. But so soon as it does so it breaks the
-contact between J and K, and the buttons fly back into place, having
-been drawn there by the rigidity of the tin disk to which they are
-attached. Again the current is closed and the magnet draws the iron
-buttons. The brass rod moves but a very slight distance up and
-down--enough, however, to make and break the contact between J and K. As
-a result of this rapid movement and the consequent snapping of the tin
-disk, a loud noise is emitted through the bell, which can be heard a
-long distance and closely resembles a long blast blown on a fish-horn.
-
-
-Burglar-alarms
-
-A unique burglar-alarm trap may be made from a plate of wood, five by
-six inches and half an inch thick, a movable lever, and a brass strip
-having the ends turned out. These are arranged as shown in Fig. 8. The
-brass strip is fastened to the plate with screws, and the ends extend
-out for half an inch from the board. The lever is made from a strip of
-brass, and the upper part is bent out so as to clear the strip and
-screws that are under it. A hole is made at the lower end of the lever,
-through which a brass ring and the end of a spring may be fastened. The
-opposite end of the spring is attached to a screw, and a wire carried
-from it to a binding-post, A. Another wire connects the back plate with
-binding-post B. A string or piece of fine picture-wire is made fast to
-the ring and carried to any part of a room.
-
-To set the trap, make the block fast in any convenient place, such as
-the door-casing or the surbase, and carry the string out from the trap
-and fasten the end of it. Any one running against it in the dark will
-draw the lever over to the right side and connect the circuit.
-
-[Illustration: FIG. 8]
-
-[Illustration: FIG. 9]
-
-[Illustration: FIG. 10]
-
-When setting the trap, have the string adjusted so that the lever is in
-a vertical position, as shown in the drawing of Fig. 8. When the string
-is disturbed it will pull the top of the lever over to the right side;
-but if the string is broken by the person running against it, the spring
-attached to the bottom of the lever draws it over to the right side with
-a snap, and the top of the lever goes to the left side, when the circuit
-is closed and the alarm given.
-
-This trap is connected the same as a push-button, one wire leading to
-the bell, the other to the battery; then the battery and bell are
-connected together so that when the circuit is closed the bell will ring
-until some one throws a switch open to break it.
-
-Another form of circuit-closer is shown in the door-trap (Fig. 9). This
-is a wooden block that rests on the floor close to the bottom of a door,
-and is held in place by means of four sharp-pointed nails driven down
-through the corners of the block. The points should project a quarter of
-an inch or more, according to whether the block is on a hard floor or on
-a carpet. The front edge of the block is bevelled so that the bottom of
-a door that fits closely to the floor will pass over it.
-
-The block is five by seven inches, and three-quarters of an inch thick.
-At the left side a strip of metal (A) is held close to the block with
-straps or wide staples driven over it, but not so close but that it can
-move freely back and forth. To the front end a round piece of wood is
-made fast. This is the bumper against which the door will strike when
-opened. At the middle of the strip a screw is riveted fast; or it may be
-a machine-screw let into a threaded hole in the metal. At the right side
-of the block another strip of metal (B) is attached, but this is held
-fast with a screw at the middle and a screw-eye and washer at the rear
-end to act as a binding-post. The front end of this strip is turned up
-so as to form a stop; then a movable lever (C) mounted over both strips,
-with one end bent up, is attached to the block with a screw. A slot is
-cut at one end so that the screw in the movable strip (A) will move
-freely in it, and near the other end a small hole is made to receive the
-end of a spiral spring (D). To set the trap, the block is placed on the
-floor and the wires from battery and bell are made fast to the
-binding-posts. The spring D keeps the lever C away from the strip-end B,
-while at the same time it throws the strip A forward. When the door is
-opened it shoves the bumper and strip A back through the staples, while
-the screw operates lever C and causes its loose end to come into contact
-with the end B, thereby closing the circuit and ringing the bell or
-buzzer. When the door is closed again the spring draws lever C away from
-B, and the circuit is opened.
-
-The block acts as an obstruction as well as an alarm, for the pins will
-hold in the floor and the little block will stand its ground. A simple
-form of contact for doors is shown at Fig. 10. This is simply two strips
-of spring-brass bent as shown, and screwed fast on either side the crack
-of a door, at the hinge side, so that when the door is opened one piece
-of metal bears on the other and the circuit is closed. This is to be
-operated in connection with a switch, so that the circuit may be opened
-in the daytime when the door is in use.
-
-
-Signals and Alarms
-
-There are many different kinds of electric call-signals used in and
-about the house; among these are some that a boy can readily make--for
-example, the ordinary call-buttons and the signals between house and
-stable or other out-buildings.
-
-A portable call-bell, or alarm, is one of the most convenient things in
-any home. It may be temporarily rigged up from one room to another, or
-from one floor to the next, the small, flexible wire being run over the
-tops of door-casings, where it is held by slim nails or pins driven into
-the wood-work.
-
-The main terminal of this portable outfit consists of a wooden box that
-will hold a large dry-cell, and to the side of which an electric bell or
-buzzer may be attached. Binding-posts are arranged at another side, to
-which the ends of the flexible wire-cord can be made fast, and a cover
-fitted to the box to hide the battery and wiring. The complete outfit,
-except the flexible wire-cord and push-button, will appear as shown in
-Fig. 11. No definite size can be laid down for the construction of this
-box, as dry-cells vary in size and shape, some being long and thin,
-while others are short and fat. By removing the cover and looking into
-the box, it will appear as shown in Fig. 12. The carbon is connected
-with one binding-post and the zinc to one of the poles of the bell. The
-other bell-pole is connected with the remaining binding-post, and it
-requires but a switch or push-button to close the circuit between the
-two binding-posts. This is done by the long line of flexible wire-cord,
-which may be of the silk or cotton covered kind, having the two strands
-twisted together as is customary with flexible electric-light wire. A
-pear-shaped push-button may be connected at the end of the line, and
-this may be arranged at the head of a bed or on a chair placed
-conveniently near an invalid’s couch.
-
-This same apparatus is a very convenient thing for a lecturer where a
-stereopticon is used. A buzzer takes the place of the bell, which would
-be too loud in a hall or lecture-room, and the cord, passing from the
-apparatus close to the operator, is hung over the lecturer’s stand, or
-the button held by him in the hand, to be pressed whenever he desires
-the pictures changed.
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 12]
-
-[Illustration: FIG. 13]
-
-This apparatus can be used also in connection with an alarm-clock, where
-the winding-key is exposed at the back, as it is in most of the
-nickel-cased clocks that are operated by a spring and which have to be
-wound each day. For this purpose obtain a piece of hard rubber or fibre,
-one-sixteenth of an inch thick, an inch long, and half an inch wide. A
-piece of stout card-board or a thin piece of hard-wood soaked in hot
-paraffine will answer just as well, if the fibre or rubber cannot be
-had. Bore a small hole at the two upper corners and one at the middle
-near the lower edge. Obtain three garter-clips, with springs, and rivet
-one of them fast to the little plate of non-conducting material. Cut two
-lengths of old brass watch-chain, four inches long, or obtain eight
-inches of chain at a hardware-store, and divide it in half. Attach a
-garter-clip to one end of each piece, and make the other end fast in the
-holes at the corners of the small plate as shown in Fig. 13. This will
-be the connector and will close the circuit when the alarm goes off.
-
-When the clock is wound and the alarm-spring is tight, catch one
-binding-post with a clip at the end of a chain and the other post with
-the remaining clip. Place the clock near the box and grasp the alarm-key
-with the clip on the plate. When the alarm goes off the bell on the
-clock will begin to ring, and when the key has made one revolution it
-twists the two pieces of chain together, closes the circuit, and the
-electric bell rings until some one unfastens one of the clips on the
-binding-posts and breaks the circuit. The great advantage in this
-double-alarm outfit is that it keeps the bell ringing until the
-attention of the sleeper is attracted. The bell on the clock will stop
-ringing directly the spring is unwound or run down; but in so doing it
-twists the chain and sets the electric mechanism in motion, to run until
-it is stopped, or until the battery polarizes or is exhausted.
-
-
-A Dining-table Call
-
-One of the most convenient of house electric-calls is that between the
-dining-room and the butler’s pantry or the kitchen, its purpose being to
-summon the waitress without the necessity of ringing a bell at the
-table, or calling.
-
-There are various forms of push-buttons for this purpose--some embedded
-in the floor, others hanging from the centre light, and others again
-where the wire runs up from under the table, and the pear-shaped push
-rests on the cloth within easy reach. These last are good enough in
-their way, but are inconvenient, unsightly, and quite liable to get out
-of order.
-
-In order to use the floor-push the table must stand in exactly the right
-place; with the drop-string from a chandelier the cord is continually
-getting in the way; and as for the portable push that comes from under
-the table, one must be forever hunting for the button every time the
-table is set. And yet it is quite possible to avoid all these troubles
-and construct an apparatus that is always in order and always available,
-wherever the table may be placed. A visitor at a certain house noticed
-that the number of the family present at a meal was apt to vary largely,
-necessitating frequent lengthenings and shortenings of the table. And
-yet the waitress invariably appeared just at the right time, and whether
-one end or the other of the table was to be served, she was always on
-the spot where she was needed. The visitor tried to study it out, but
-was finally obliged to ask for an explanation of the mystery. The boy of
-the house smiled and intimated that he was responsible for this
-domestic miracle; later on, when dinner was over, he removed the centre
-leaves from the table and displayed the simple apparatus that he had
-constructed and which had worked for several years without adjustment or
-repairs.
-
-The illustration (Fig. 14) represents the frame of a dining-table with
-the middle cross-bar made fast to the side-rails, so as to support the
-mechanism. At both ends, and inside the rail, push-buttons are arranged
-and wires carried from them to binding-posts close at hand, as may be
-seen at the left side. The cross-bar at the middle of the table supports
-a large spool on which the flexible cord is wound, and kept taut by
-means of a clock-spring. This spool takes up the slack between the ends
-of the table when it is lengthened or shortened, while the smaller one
-opposite it keeps taut the feed-wires that come up through the floor. A
-short distance from the floor the wire is provided with a connector, so
-that when the rug is removed the feed-wires may be disconnected and
-slipped down.
-
-The large spool can be had at any dry-goods store where braids or fancy
-cords are kept. It should be about four inches long, three inches in
-diameter, and with sides thick enough to enable screws to be driven into
-it without fear of splitting the wood. An old clock-spring is attached
-at one side of the spool, while at the other two circular bands of brass
-are made fast, one within the other. An axle of stout wire should be
-driven through the spool; but if the hole is too large, wooden plugs may
-be glued in at each end so that a front view of the spool will appear as
-shown at A. The metal bands are cut with shears from sheet-brass, and
-are attached with fine steel nails, the heads of which are driven in
-flush with the wood. A hole is made in the side of the spool, close
-beside each band, so that the ends of wires may be brought through them
-and attached to the bands. This arrangement is illustrated at B, and at
-C the opposite end is shown, with its clock-spring, one end of which is
-made fast to the side of the spool and the other to the cross-rail. A
-small round piece of wood is slipped over the axle, at the spring side,
-and projects a quarter of an inch beyond the spring. This is to keep the
-spring away from the arm that stands out on that side to hold the spool
-in place.
-
-[Illustration: FIG. 14
-
-A DINING-TABLE CALL]
-
-About half an inch of space is left between the spool and the arm at the
-opposite side, so that the spring contact-strips may be made fast to the
-arm and still have room to act. A view looking down on the spool and
-springs is shown at D, and E illustrates the arrangement of the circular
-strips and the spring contact-strips. If the table is to remain
-permanently in the same position, only one spool will be required, for
-the floor wires can come up and connect directly with the
-contact-strips. But if the table is to be moved about, a tension-spool,
-independent of the push-button wires, is necessary so that the position
-of the table may be changed without unwinding the large spool and
-dropping the cords down to the floor. The smaller spool is made and
-mounted in the same manner, and should be placed close to the large one.
-But a lighter spring will operate it. One end of a double wire-cord is
-made fast to binding-posts, mounted on a yoke of hard rubber or fibre,
-so that the terminals will be kept apart, as shown at F. The other ends
-are passed through the holes at one side of the small spool and soldered
-fast to the circular strips, or a small screw may be passed down
-through the hole, binding the wire and touching the edge of one strip.
-Take care that it does not touch the other strip. The cord is then wound
-on the spool, and it is slipped in place so that the loose end of the
-spring is caught and held over a nail or screw-head. Turn the spool over
-several times to partially wind the spring; then attach the terminals to
-the wires that come up from the floor and the tension of the spring will
-draw the wires taut. The two contact-strips of brass, that rest against
-the brass circles, have insulated wires leading out from them in order
-to connect them with the corresponding wires leading from the strips of
-the larger spool.
-
-A simple way to mount the spools is shown at A in Fig. 15. A notch is
-cut in the face of the blocks large enough to admit the axle; then a
-face-plate is screwed over the end of the block to hold the axle in
-place. This arrangement makes it easy to remove the spool, in case of
-necessity, without detaching the arms from the cross-rail.
-
-[Illustration: FIG. 15]
-
-Two sets of wires are wound on the large spool, one leading to the
-right-hand and the other to the left-hand push-button on the
-table-rails. The ends of the wires are arranged so that one leading from
-both directions is made fast to one circular strip on the spool, the
-other two being attached to the remaining band. This is more clearly
-shown at B in Fig. 15, where the ends are visible as they are twisted
-together and pass through their respective holes. The spool is then
-turned over, and six or eight feet of wire wound on from each side. The
-spring is coiled up and caught on the nail or screw, and the ends of the
-wires are made fast to the binding-posts near the push-buttons. The
-wires from both push-buttons are then in connection with the circular
-bands, which in turn are connected to the bands on the smaller spool,
-and lead the current down through the floor wires. By pushing the button
-at either end the circuit is closed and the buzzer or bell is rung in
-the kitchen or pantry.
-
-Arranged in this manner, the wires are kept off the floor, no matter
-where the table is moved, and it can be drawn open as wide as may be
-found necessary to put in leaves. When closed again, the spring causes
-the large spool to revolve and wind up the wire.
-
-
-Chapter VI
-
-CURRENT-DETECTORS AND GALVANOMETERS
-
-A current-detector is a necessary part of the amateur electrician’s
-equipment; technically, this piece of apparatus is called a
-galvanoscope.
-
-When a wire or a number of them are brought near a magnetic needle or a
-small compass, the needle will be deflected from its north and south
-line and will point east and west, or west and east, according to the
-direction in which the current is passing through the wires. All wires
-that are conducting electricity have a magnetic field, and when brought
-near the magnetized needle of a compass they have the power to act on it
-the same as another and stronger magnet would.
-
-The action of detectors depends upon two things--first, the magnetized
-needle that, when properly balanced, will point north and south; and,
-secondly, a current of electricity passing through a wire or wires held
-above the needle, or both above and below it. This is more clearly shown
-in Fig. 1, where a compass is resting on a wire connected to a battery.
-The wire also passes over the top of the compass, which doubles the
-electro-magnetic field.
-
-When the compass (with the needle pointing north) is resting on the
-wire that is attached to the zinc pole of a battery, and when the end of
-the wire that passes back over the top of the compass is attached to the
-carbon pole, the needle will fly around and point to the east. When the
-wires are reversed, the needle will point to the west. Thus the
-combination of a battery or other source of electric current, a magnetic
-needle, and a coil of wire properly arranged, make an instrument that
-will detect electric currents and may be correctly called a
-current-detector. The pressure of more or less current is determined by
-instruments wound with wire of different sizes; the finer the wire the
-more sensitive the instrument, and consequently the more delicate. A
-very weak current can only be detected with a delicate and sensitive
-instrument. The coarser the wire and the larger the instrument, the
-better it will be for testing strong currents that would perhaps burn
-out the fine wire of the more delicate apparatus.
-
-This instrument, when placed between a source of electricity and a piece
-of apparatus, such as a bell, a motor, or lamp, does not weaken the
-current, for it requires no waste of electricity to operate the magnetic
-needle. Consequently, when a very weak current is being used for any
-tests, it is well to place a detector between the battery and the
-apparatus to show that the current is actually passing through the wire.
-
-A simple detector is made by winding fifteen or twenty feet of
-cotton-insulated copper wire No. 26 or 28 around the lower end of a
-drinking-glass. Leave six inches of each end loose; then after slipping
-the coil from the glass, tie the wires with thread at least four times
-around the circle, so as to bind the wires together. Press two sides of
-the hoop together so as to flatten it; then with paraffine attach the
-coil to a square block of wood, as shown in Fig. 2.
-
-[Illustration: FIG. 1]
-
-[Illustration: FIG. 2]
-
-[Illustration: FIG. 3]
-
-[Illustration: FIG. 4]
-
-[Illustration: FIG. 5]
-
-From a thin clock-spring, not more than three-eighths of an inch wide,
-cut a piece two inches and a half long, and with a stout pair of
-tin-shears cut the ends so as to point them, as shown in Fig. 3 A. With
-two pair of pliers bend a hump at the middle of the strip on the dotted
-lines shown in A, so that a side-view will appear like B in Fig. 3. Turn
-this strip over on a hard-wood block or a piece of lead, and with a
-stout steel-wire nail and a hammer dent the inverted [V] at the middle
-so that it will rest on the top of a needle-point without falling off.
-
-With three little pieces of wood make a bridge and attach it to the
-wooden base over the paraffine that holds the wire-coil, and drive a
-needle down in the middle of it, taking care that it does not go through
-the back and touch the wires underneath. On this needle hang the strip
-of steel spring, and, if it does not properly balance, trim it with the
-shears or a hard file until it is adjusted properly. Rub this piece of
-steel over the pole ends of a large horseshoe magnet, or place it within
-the helix of a large coil and turn a powerful current through the coil.
-This will magnetize the strip of steel, which will then become a
-magnetic needle and hold the magnetism. Attach two binding-posts to
-corners of the block, and make the loose ends of the coil-wires fast to
-them. You now have a current-detector, or galvanoscope, as shown in Fig.
-4. Turn the block so that the needle points to north and south and
-parallel to the strands of wire.
-
-When the conductors from the poles of a battery or dynamo are made fast
-to the binding-posts, the needle will fly around to a position at right
-angles to that which it first occupied, as shown by the dotted line A A
-in Fig. 4. When the connection is broken the needle will turn around
-again and point to north and south, since the magnetic field about the
-wire ceases and disappears the instant the circuit is broken.
-
-This is one of the strange and unknown phenomena of electricity, for
-while the current exerts a force that deflects the needle, it does not
-destroy its magnetism. On the breaking of the contact, no matter how
-long it may have held the needle away from its true course, it again
-points to north, and its magnetism is not affected.
-
-Another simple current-detector is shown in Fig. 5. A piece of
-broomstick is sawed in half and both pieces are made fast to a block
-which is mounted on a base of wood three-quarters of an inch in
-thickness. The vertical block should measure five inches long, three
-inches high, and five-eighths of an inch thick. The half-circular pieces
-of wood are mounted so that the flat surfaces are three inches apart and
-the lower edges are one inch above the base-block. These may be held in
-place with glue and screws driven through the back of the vertical block
-and into the ends of the projecting half-circular pieces. The base-block
-is six inches long and four inches wide, and the vertical block is
-mounted on it one inch from an edge. The pieces of broomstick are two
-inches long, and at the front ends a thin bar of brass or copper is
-screwed fast to hold them apart and in proper position, as shown at A in
-Fig. 5. To improve the appearance of this mounting, all the wood-work
-may be stained and shellacked before the metal parts are attached.
-
-With No. 26, 28, or 30 cotton-insulated wire make from fifteen to twenty
-wraps about the middle of the half-circular pieces of wood and carry the
-ends down through small holes in the base-block and thence through
-grooves cut at the under side of the block to the front corners, where
-they are to be made fast to binding-posts. A needle is to be set in the
-base-block midway between the two pieces of half-circular wood and
-through the strands of wire. Great care must be taken that the needle
-does not touch any bare wires, and as a precautionary measure it would
-be well to wrap the needle with a piece of insulating-tape where it
-passes through the strands of wire. Now place on the top of it a
-magnetized piece of steel, as described for the detector shown in Fig.
-4. As it may not always be convenient to turn the instrument so that the
-needle points north, a small bar of magnetized steel or a stout needle
-that has been magnetized with a horseshoe magnet or a helix, may be laid
-across the half-circular wood pieces, so that it is parallel with the
-top layer of wires--in fact, it should rest on top of them.
-
-By means of this needle, or bar, the magnetic piece of steel balanced on
-the vertical needle between the upper and lower strands of insulated
-wire may be held in one position no matter which way the block is
-turned. When the current passes in through one binding-post and out
-through the other (having thus travelled through the coil on the
-half-circular blocks) the needle is deflected and points out at the
-brass bar and back at the upright block.
-
-When making any of these pieces of apparatus, where delicately balanced
-magnetic needles are employed, all parts of the mounting blocks or other
-sections must be put together with glue and brass nails or screws. It
-will not do to use steel or iron nails, screw-eyes, or washers, nor
-pieces of sheet-iron, tin, or steel, for they will exert their influence
-on the vital parts of the apparatus and so destroy their usefulness.
-This is not so important when making buzzers, bells, motor-induction
-coils, or similar things, but in delicate instruments, where magnetic
-needles or electro-magnets are used for recording, measuring, or
-detecting, iron and steel parts should be carefully avoided, except
-where their use is expressly indicated.
-
-
-An Astatic Current-detector
-
-Astatic current-detectors and galvanometers are those having two
-magnetic needles arranged with the poles in opposed directions.
-
-The ordinary magnetic or compass needle points to the North, and in
-order to deflect it a strong magnetic field must be created near it. For
-strong electric currents the ordinary single-needle current-detector
-meets all requirements, but for weak currents it will be necessary to
-arrange a pair of needles, one above the other, with their poles in
-opposite directions, and placed within or near one or two coils of fine
-wire. This apparatus will be affected by the weakest of currents, and
-will indicate their presence unerringly.
-
-The word “astatic” means having no magnetic directive tendency. If the
-needles of this astatic pair are separated and pivoted each will point
-to North and South, after the ordinary fashion. For all astatic
-instruments we must employ two magnetic needles in parallel, either side
-by side or one above another, as shown in Fig. 6, with the N and S poles
-arranged as indicated. This combination is usually called Nobili’s pair.
-If both needles are of equal length and magnetic strength, they will be
-astatic, for the power of one counterbalances that of the other. As a
-consequent neither points to North.
-
-A compound needle of this form requires but a very feeble current to
-turn it one way or the other, and this is the theory upon which all
-astatic instruments are constructed.
-
-A simple astatic current-detector may be made from a single coil of
-fine insulated wire, a pair of magnetic needles, and a support from
-which to suspend them, together with a base-block.
-
-For the base-block obtain a piece of white-wood, pine, or cypress, four
-inches square and three-quarters of an inch thick. Sand-paper it smooth,
-and then give it two or three coats of shellac. From a strip of copper
-or brass (do not use tin or iron) make a bridge, in the form of an
-inverted [V], seven inches high, using metal one-sixteenth of an inch
-thick and half an inch wide. This bridge is to be screwed to the outside
-of the block, as shown at Fig. 7, so that it will be rigid and firm. A
-small hole is drilled through the top of the bridge to admit a screw-eye
-for the tension.
-
-Make a coil of No. 30 insulated wire, using ten or fifteen feet, and
-wind it about the base of a drinking-glass to shape it; then remove it
-and tie the coil, in several places, with cotton or silk thread, so as
-to hold the strands together. Shape it in the form of an ellipse and
-make it fast to the middle of the base-board with small brass or copper
-straps, and copper tacks or brass screws. Be very careful not to use
-iron, steel, or tin about this instrument, as the presence of these
-metals would deflect the needles and make them useless.
-
-Separate the strands at the top of the coil so that one of the needles
-may be slipped through to occupy a position in the middle of the coil.
-Ordinary large compass needles may be employed for this apparatus, or
-magnetized pieces of highly tempered steel piano-wire will answer just
-as well.
-
-[Illustration: FIG. 6]
-
-[Illustration: FIG. 7]
-
-[Illustration: FIG. 8]
-
-A short piece of brass, copper, or wood will act as the carrier-bar for
-the needles. These should be pushed through holes made in the bar, and
-held in place with a drop of shellac or melted paraffine. A small hole
-is drilled at the top of the bar, or a small eye can be attached,
-through which to pass the end of a thread. The upper end of the thread
-is tied in a screw-eye, the screw part of which passes up through the
-hole in the bridge and into a wooden button or knob, which can be turned
-to shorten or lengthen the thread, and so raise or lower the needles.
-The lower needle must be pivoted at an equal distance between the upper
-and lower parts of the coil.
-
-Two binding-posts are arranged at the corners of the base, and the ends
-of the coil wires are attached under the screw-heads. The in-and-out
-wires are to be made fast under the copper washers on the screw-eyes.
-
-Owing to the astatic qualities of the needles, the base-block does not
-have to be turned so that the coil may face North and South, as in the
-current-detector. When the slightest current of electricity passes
-through the coil it instantly affects the needles, turning them to the
-right or left according to the way in which the current is running
-through the coil.
-
-
-An Astatic Galvanometer
-
-The sensitiveness of an astatic detector may be increased by the added
-strength of the coil-field for a given current.
-
-There are two ways of accomplishing this result. The number of turns of
-wire may be increased in the coil, or two coils may be used, placed side
-by side. The latter method is the more satisfactory, since then the coil
-does not have to be opened at the top to admit the lower needle, the
-latter being dropped down between the coils. This apparatus is shown in
-the illustration of an astatic galvanometer, Fig. 8. The general
-arrangement of needles, bridge, and coils, is the same as described for
-the astatic current-detector.
-
-Each coil is made separately of ten feet of No. 30 insulated copper
-wire, wound about the base of a drinking-glass to shape it; then
-pressed into elliptical shape, and fastened to a base-block with a brass
-or copper strip, and held down with small brass screws.
-
-The base-block should be four inches square, with the corners sawed off.
-Smooth the block with sand-paper, and then give it several good coats of
-shellac.
-
-The bridge is made from brass one-sixteenth of an inch thick and half an
-inch wide. The coils of wire are arranged about half an inch apart, and
-at both ends a small separator-block is placed between the coils, and
-then bound with silk or cotton thread. A circular indicator disk of
-bristol-board should be cut out and marked and attached to the top of
-the coils with a few drops of sealing-wax or paraffine; then the needles
-are suspended so as to hang properly, one above the card, the other
-between the coils.
-
-Three binding-posts are placed at one end of the block, and to them the
-end wires of the coils are led and attached. To the first binding-post
-(at the left) the strand of wire leading to the first coil is attached.
-It leads in and is coiled as the hands move on a clock, from left to
-right. The leading-out wire from the coil is made fast to the middle
-post. The leading-in wire to the second coil is also made fast to the
-middle post. The coil wires should have the turns in the same direction
-as the first coil; then the last wire is attached to the right-hand
-post.
-
-When making connections for a strong current, use an end and middle
-post. This arrangement will operate but one coil. For very weak currents
-make the leading in and out wires fast to the end-posts. This latter
-plan is more clearly shown in the diagram, Fig. 9. A and B represent
-the coils, C, D, and E the binding-posts. The current, entering at C,
-passes through the coil A (as the hands move about the dial of a clock)
-and out at D, where connection is made with the wire leading in to coil
-B. The current passes through this coil in the same direction as the
-clock hands move, and out to post E. Be careful to arrange the wiring
-and connections after this exact manner, otherwise the instrument will
-not be of any use.
-
-The adjustment at the top of the bridge may be made with an inverted
-screw-eye and a small cork into which the eye can be screwed, thus
-raising or lowering the needles to the proper position. Be sure to have
-the needles in parallel when at rest.
-
-As the needles and coils are very sensitive it would be well to cover
-the instrument with an inverted glass jar. A bluestone or gravity
-battery jar will answer very well, and after the wires are connected to
-the binding-posts the glass may be placed over the entire apparatus.
-
-
-A Tangent Galvanometer
-
-For testing the various degrees of intensity of a current a tangent
-galvanometer is usually employed. In this apparatus the increased
-strength is indicated by the index-pointer as it plays over a scale or
-graduated circle.
-
-A simple tangent galvanometer may be made from a flat hoop of wood-fibre
-or brass, mounted on a base by means of two uprights, together with the
-necessary compass needle, an index-card, insulated wire, and
-binding-posts for the electrical connections. This piece of apparatus
-is shown in Fig. 10. It is built on a base-block six by seven inches
-and three-quarters of an inch thick. The block should be of selected
-wood, and after it is made smooth it should be given several coats of
-shellac.
-
-Two upright pieces of wood, five inches long, half an inch thick, and
-one inch in width, are screwed fast to the rear edges of the base-block
-to support the hoop on which the insulated wire is wound. Be careful not
-to use any iron or steel in the construction of this or any other
-recording instrument, except where it is expressly stated. Screws,
-nails, staples, or any bits of anchoring wire should be of copper or
-brass. String, thread, or silk may be used, especially where coils of
-wire are to be bound or fastened to hoops or base-blocks. The balance of
-the indicating needle is so delicate, and the sensitiveness of the coils
-is so easily affected, that nothing about or near the instruments should
-be of iron or steel.
-
-The hoop may be made of very thin hickory wood, steamed and bent so as
-to form a ring six inches outside diameter and one inch wide. It is even
-possible to construct a satisfactory hoop from a ribbon of brown paper,
-rolled and lapped, the several thicknesses being glued as the turns are
-made.
-
-If a metal hoop is to be used, solder the ends of a thin, hard ribbon of
-brass, copper, or zinc. This strip should be provided with holes, set in
-pairs about four inches apart, all around the hoop, and where the hoop
-is to be attached to the uprights two holes should be made close to the
-margins through which brass screws may pass.
-
-Across the middle of the hoop a strip of wood six inches long, an inch
-wide, and a quarter of an inch thick is made fast. On this the graduated
-card is placed, and at the centre the balanced magnetic needle is
-arranged on a pivot.
-
-After the cross-stick is in place, wind five turns of No. 24 insulated
-copper wire about the hoop, keeping it as nearly in the centre as
-possible. One end of the wire (the beginning) is to be attached to the
-first binding-post on the front of the base, and the other end to the
-second post. The wire should be wound round the hoop in the same
-direction as the clock hands travel about a dial.
-
-Another coil, composed of ten turns of wire, is made over the first one,
-the beginning end being attached to the middle binding-post and the last
-end to the third post. This arrangement is shown in Fig. 11, D and E
-representing the coils, while A, B, and C are the binding-posts. The
-current enters at A, passes through coil D, and out at post B. The next
-passage is in at B, through E, and out at C. A current passing in at A
-will travel to B, thence through E, and out at C. If the leading-in wire
-is made fast to A, and the out wire to C, the current will travel
-through the entire coil.
-
-Under this plan one or both coils may be used (the short or long one as
-desired) by making connections with the first and second binding-posts,
-the second and third, or the first and third, as the strength of the
-current will warrant.
-
-Strong currents will deflect the needle when travelling through a short
-coil, but the weaker the current the more coils it will have to pass
-through to properly deflect the needle and indicating pointer.
-
-[Illustration: FIG. 10
-
-FIG. 11
-
-FIG. 12
-
-FIG. 13
-
-FIG. 14
-
-FIG. 15
-
-TANGENT GALVANOMETERS]
-
-When the coils are all on, the hoop should be attached to the uprights
-with small brass screws driven through holes in the hoop and into the
-wood. The wire is bound to the hoop by means of threads or silk passed
-through each pair of holes in the hoop, and then tied fast. Fine
-insulated wire may be used in place of the thread, but care should be
-taken that the insulation is in perfect shape on both the binding and
-coil wires; otherwise a short-circuit will quickly destroy the value of
-the coils.
-
-The hoop should not touch the base-block, but should clear it by a
-quarter or half an inch. Make the coil ends fast (as described for the
-astatic galvanometer and illustrated at Fig. 9) by means of
-binding-posts. The wires need not be carried over the top of the block,
-but may run through holes under the hoop and along grooves cut in the
-under side of the block and leading to the foot of the binding-posts.
-
-The graduated card should be made from a piece of stout bristol-board or
-heavy card-board having a smooth, hard surface. It is laid out with a
-pencil or pen compass, as shown at Fig. 12, and should be three inches
-in diameter. The card is placed on the wood strip or ledge, so that the
-zero marks will be at the front and rear, or at right angles to the hoop
-and coils of wire. The compass needle, when at rest, should lie parallel
-with the coils, so that the current will deflect the needle and send the
-indicator around to one side or the other of zero, according to the
-direction in which the current is passing through the coils.
-
-This is more clearly shown at Fig. 13. The circle represents the outside
-diameter of the card; the dark cross-piece, the magnetic needle; and the
-pointed indicator, a stiff paper, or very thin brass or copper strip,
-cut and attached to the needle with shellac or paraffine.
-
-When at rest the magnetic needle should be parallel to the coils. To
-insure this the instrument must be moved so that the lines of wire
-forming the coil will run North and South. Otherwise the N-seeking end
-of the magnetic shaft will point to North, irrespective of the position
-occupied by the wire coil.
-
-The magnetic needle may be made as described for the compass (see
-chapter iv., Magnets and Induction Coils). It should be arranged to rest
-on a brass pivot pressed down into the cross-piece of wood.
-
-The indicator-needle may be cut from stiff paper, thin sheet-fibre, or
-very thin cold-rolled brass or copper, the latter being commonly known
-as hard or spring-brass. Only one pointer is really necessary--that
-pointing to the front. But the weight of the material would have a
-tendency to upset the magnetic needle, and therefore it is better to
-carry an equally long tail or end, on the opposite side, to properly
-balance the needle.
-
-A very weak current, passing in through the first post and out at the
-third, will cause the indicator to be deflected considerably, or so that
-it will point from 40° to 60° on either side of the zero point,
-according to the direction in which the current is running through the
-coils.
-
-When not in use the magnetic needle should be removed from the pivot,
-and placed in a box or other safe place, where it will not become
-damaged.
-
-A differently arranged tangent galvanometer is shown at Fig. 14. As the
-line of binding-posts would indicate, there are several coils of wire
-about the circle or hoop.
-
-This galvanometer can be used for either strong or weak currents, since
-it is wound with both coarse and fine insulated wire. An upright plate
-of wood, seven inches wide and eight inches high, supports the hoop and
-compass. The top corners are sawed off, and four inches above the bottom
-a straight cut is made across the plate, five inches wide and arched in
-a half-circle five inches in diameter. A shelf of wood a quarter of an
-inch thick, three inches wide, and five inches long is made, and
-attached as a ledge in this arched opening, so that a compass three
-inches in diameter may rest upon it.
-
-The shelf should be arranged so that it will hold the compass in the
-middle of the circle instead of at one side. The turns of wire will then
-be in line with the magnetic needle when the latter is at rest. A
-base-block seven inches long, three inches wide, and seven-eighths of an
-inch thick is cut and attached to the upright plate by driving screws
-through the bottom of the plate and into the rear edge of the base. The
-corners are to be cut from the front of the base, and ten small holes
-are to be bored half an inch out from the upright and about a quarter of
-an inch apart. These are for the end wires that will extend down from
-the coils, and from thence to the binding-post holes. Grooves may be cut
-in the under side of the base-block for the wires to rest, in, as shown
-at Fig. 15, which is a view of the inverted base.
-
-A hoop is made of brass, six inches in diameter and an inch wide. It is
-held to the upright plate with copper wire passed through a small hole,
-bored at the inner edge of the band, and back through two small holes
-bored in the plate, the ends being twisted together at the back of the
-plate. A wire at the top, bottom, and both sides will be sufficient to
-hold it securely in place.
-
-The first coil of wire is made of No. 18 insulated, and the beginning
-end is made fast to the binding-post at the left. The wire is carried up
-through the first hole under the hoop, and after three turns have been
-made the end is carried down through the second hole and made fast to
-the foot of the second binding-post.
-
-The second coil is of No. 24 insulated copper wire. The beginning end is
-made fast to the second binding-post, carried up through the third hole,
-given five turns about the hoop, drawn down through the fourth hole, and
-attached to the third binding-post.
-
-The third coil is of the same size wire but has ten turns. The fourth
-coil has twenty turns, and the fifth, of No. 30 insulated wire, has
-thirty turns, the last end being attached to the post at the right. In
-all the coils there should be a total of sixty-eight turns, or about one
-hundred and five feet of wire.
-
-For strong currents the in-and-out wires may be attached to posts Nos. 1
-and 2 at the left, and for weaker currents to Nos. 2 and 3. For still
-weaker currents, use Nos. 3 and 4, and so on. To detect the very weakest
-currents, attach the in-and-out wires to the first and last post, and
-let the current travel through all the coils or the entire length of the
-wire wound about the hoop.
-
-The magnetic needle is made in the same manner as described for Fig. 10,
-and the pointer is attached in a similar fashion. But instead of being
-mounted on a pivot over a card, and so exposed to the open air and
-possible draughts, the delicate mechanism is arranged within a brass
-hoop, which is made fast to the ledge. The graduated card is at the
-bottom of the hoop, or box formed by it, and to protect the needle and
-prevent it from being displaced it should be covered with glass. This
-can be done by making a split ring of spring-brass wire and pressing it
-down inside the hoop. Over this a round piece of glass is placed, and
-another hoop is pressed in above it to hold the glass in position. If
-the rings are carefully made and of stout wire they will stay in place;
-otherwise a drop of melted sealing-wax or paraffine will be necessary to
-keep them where they are wanted.
-
-The glass should be arranged close enough to the needle to prevent it
-from jumping or being shaken off the supporting pin, but not so close as
-to prevent its moving easily.
-
-
-
-
-Part II
-
-
-Chapter VII
-
-ELECTRICAL RESISTANCE
-
-The science of controlling forces is so well understood and figured out
-that it becomes a simple mechanical proposition to adapt the various
-types of controllers to any form of power that may be employed. The
-tremendous force stored within the mechanism of a great transatlantic
-liner is governed by the twist of a man’s wrist. The locomotive that
-will pull a hundred cars loaded with coal, representing a weight of
-thousands of tons, is started and stopped by a short lever that is drawn
-in one direction or the other by a man’s hand. Great forces of all kinds
-are quite as easily controlled as the supply of gas through a jet--by
-simply turning the key that lets out so much as may be required, no
-matter what the pressure is back of the flow.
-
-This same principle applies to electricity, but the means of governing
-it is vastly different from the methods employed for other forces.
-Electricity is an unknown and unseen force, coming from apparently
-nowhere and returning to its undiscovered country immediately upon the
-completion of its work. The flow of steam, water, liquid air, gas, and
-compressed air through pipes is governed by a throttle or cock, which
-allows as much or as little to pass as may be required; and if the
-joints, unions, and couplings in the pipes are not absolutely tight
-there will be a leakage. Electricity is controlled by resistance in its
-passage through solid wires, rods, or bars, and cannot be confined
-within a given space like water, nor held in tanks or pipes as a vapor
-or gas. It is invisible, colorless, odorless, and occupies no apparent
-space that can be measured; it is the most powerful and terrible and yet
-docile force known to man, doing his bidding at all times when properly
-governed and regulated. In some respects, electricity can be compared to
-water stored in a tank--for instance, if you have a tank of water
-containing fifty gallons at an elevation of twenty-five feet, and a pipe
-leading down from it, the pressure of the water at the outlet of the
-pipe will be a given number of pounds. Now if the tank were double the
-size the pressure at the outlet of the pipe would be proportionately
-greater. Now if you have a battery made up of a number of cells they
-will develop a given number of volts, and if the number of the cells be
-doubled the voltage will be correspondingly increased. Or if you have a
-dynamo giving a certain number of volts, that number may be increased by
-doubling the size.
-
-The water contained within the tank represents its pressure at the
-outlet of the pipe. The current in volts, generated in a battery or
-dynamo, represents its pressure on an outlet or conductor wire; and both
-represent the force behind their respective conductors. The valve, or
-faucet, at the end of the pipe plus the friction in the pipe would
-represent the resistance to the flow of water, while the
-resistance-coils or other mediums plus the size of the wire, or
-conductor and switch, would regulate the flow of electric current. The
-flow of water in a pipe under certain pressure would represent its
-gallons per minute or hour, while with electricity its flow in a wire or
-other conductor would represent its amperage. It is to govern the flow
-of current that resisting mediums are employed.
-
-The resistance of electric current is measured in ohms, and it is with
-this phase that we are interested in this chapter. If there is only a
-small resistance put in the path of a current, then it requires but a
-small pressure or voltage to send it through the wires or circuit. This
-is easily understood by the boy who has experimented with small
-incandescent lamps in which short pieces of carbon-filament are
-contained. It requires the pressure of a few volts only to send the
-current through the carbon; but for the large carbon-filaments,
-measuring ten or twelve inches in length, from one hundred to five
-hundred volts may be necessary. The ordinary house lamps require one
-hundred and ten volts and half an ampere to give sixteen candle-power.
-
-It is easily understood, then, that it requires a high pressure or
-voltage to force the current through the resisting carbon-filament, or
-across the space from one carbon to the other in the arc-lamps used for
-street lighting. The shorter and larger the conducting wires the less
-the resistance, and consequently the lower the voltage or pressure
-necessary to force it. Contrariwise the longer and finer the conducting
-wares, the greater the resistance. As copper is the best commercial
-conductor of electric currents, it is in universal use, and in it the
-minimum of resistance is offered to the current. Iron wire is a poorer
-conductor, and is not used for high voltage (such as trolleys or
-transmission of power), but is confined to telegraph and telephone lines
-and low-pressure work. German-silver wire, one of the poorest
-conductors, is not used for lines at all, but is employed solely as a
-resisting medium for controlling current.
-
-
-Ohm’s Law
-
-This is the fundamental formula expressing the relations between
-current, electro-motive force, and resistance in an active electric
-circuit. It may be expressed in several ways with the same result, as
-follows:
-
-1. The current strength is equal to the E. M. F. (electro-motive force)
-divided by the resistance.
-
-2. The E. M. F. (electro-motive force) is equal to the current strength
-multiplied by the resistance.
-
-3. The resistance is equal to the E. M. F. (electro-motive force)
-divided by the current strength.
-
-All these are different forms of the same statement; and when figuring
-electrical data, C stands for current, E for electro-motive force, and R
-for resistance.
-
-
-Resistance-coils and Rheostats
-
-The method by which electricity is controlled is resistance. No matter
-how great the voltage of a current, nor its volume in amperes, it can be
-brought down from the deadly force of the electric trolley-current to
-the mild degree needed to run a small fan-motor, an electric bell, or a
-miniature lamp. This is accomplished by means of resisting mediums,
-such as fluids or wires, which hold back the current, and allow only
-the small quantity to pass that may be required to operate the
-apparatus.
-
-The jump from the high voltage of the trolley-current to the low one
-required for the electric bell, a lamp, or a small motor, is frequently
-made in traction-work, but in this case regular transformers are used.
-For the small apparatus, that may have its current supplied from a
-battery, or a small dynamo driven by a water-motor, the forms of
-resistance-coils and rheostats described on the following pages should
-meet every requirement.
-
-The standard unit of resistance is called an ohm, so named after Dr. G.
-S. Ohm, a German electrician, whose theory on the subject is accepted as
-the basis on which to calculate all electrical resistance. The legal ohm
-is the resistance of a mercury column one square millimetre in
-cross-sectional area and one hundred and six centimetres in length, and
-at a temperature of 0° Centigrade or 32° Fahrenheit, or the
-freezing-point for water. The conductivity of metals is dependent
-greatly on their temperature, a hot wire being a much better conductor
-than a cold one. Since counter-electro-motive force sometimes gives a
-spurious resistance, the ohmic resistance is the true standard by which
-all current is gauged.
-
-In technical mechanism and close readings the ohmic resistance counts
-for a great deal, but in the simple apparatus that a boy can make the
-German-silver resistance coils and the liquid resistance will answer
-every purpose.
-
-To give a clearer idea of the principle of the rheostats, a short
-description of the mercurial column will first be presented. During the
-early part of the last century wires were not used as a resisting medium
-for electric currents. In their place, glass tubes, filled with mercury
-sealed at one end and corked at the other, were arranged in rows and
-supported in a wooden rack.
-
-[Illustration: _=Fig. 1=_]
-
-Wires led out from the top and bottom of each tube, and were brought
-down to metal buttons arranged in a row along the front edge of the
-base-plate, as shown in the illustration of a mercurial rheostat (Fig.
-1). Each tube represented a certain resistance--one or more ohms, as
-required. The outlet wire was attached to the button at one end of the
-row, and the inlet could be moved along from button to button, until the
-required amount of current was obtained.
-
-The mercurial rheostat was an expensive, cumbersome, and treacherous
-thing to handle; it was liable to break, and its weight often prohibited
-its use in places where the more convenient and easily handled
-German-silver rheostats are now in universal employment. Overheating the
-mercury in the columns caused it to expand, and sometimes, before the
-switch could be thrown open, an end would be forced out and the mercury
-would climb over the edge of the glass columns.
-
-All metals have a certain amount of resistance for electric currents,
-and some have more than others. German-silver, for instance--a metal
-made of a mixture of other metals with about eighteen per cent. of
-nickel (see Appendix)--is considered to be the best commercial
-resistance medium, while pure copper is regarded as the best commercial
-conductor. Unalloyed copper is universally employed for electric
-conductors of high voltage; but for telegraph and telephone work,
-galvanized iron wire is still used extensively.
-
-The finer the wire, the higher is its resistance, and the more resistant
-the metal, the greater are the number of ohms to a given length. To nine
-feet and nine inches of No. 30 copper wire there is one ohm resistance,
-while to No. 24--which is six sizes coarser--there is one ohm to
-thirty-nine feet and one inch. In many cases it is necessary to use the
-coarser wire and greater length, as the current would superheat or burn
-the fine wire, while the coarser would conduct it safely.
-
-For very high voltage and amperage--such as used in traction cars, in
-power stations, and in manufacturing plants--castings of German-silver
-are employed and linked in series. They are more easily handled than the
-coils of wire, and a greater number of them can be accommodated in a
-small space.
-
-[Illustration: _=Fig. 2=_]
-
-For light currents in experimental work, where batteries are employed,
-obtain a pound or two of bare German-silver wire, from Nos. 24 to 30,
-and wind the strands on a round piece of stick attached to a winder (see
-Magnets and Induction-Coils, chapter iv.). Make several of these coils,
-two or three inches long, with the wire wound closely and evenly. When
-pulled apart the coils will appear as shown in Fig. 2 A, and will
-resemble a spiral spring. This can be made fast over a porcelain knob
-and the ends caught down, as shown at B in Fig. 2, or it may be drawn
-over a round stick, a porcelain tube, or a lug made of plaster of Paris
-and dextrine (three parts of the former to one of the latter), as shown
-at C in Fig. 2, and the ends securely bound with a strand or two of
-wire, twisted tight to keep the ends from slipping.
-
-The lugs may be made in a mold, using as a pattern a piece of
-broom-handle--shellacked and oiled to prevent the plaster from adhering
-to it. Obtain a small square and deep box, and drop some of the wet
-mixture down in the bottom; on this place the broomstick, small end down
-(it should be slightly tapered), and around it pour in the wet plaster
-mixture. While it is setting, turn the stick with the thumb and fingers,
-so as to shape the hole perfectly then draw it out, and a true mold will
-be the result. When dry enough, pour some shellac down into the mold and
-revolve it, so that the shellac will be evenly distributed, and let it
-harden for a day. Then saw off the end of the mold, so that it will be
-open at both ends.
-
-In order to make the lugs, pour in the plaster mixture, taking care to
-oil the mold before each pouring, so that the lug can be drawn out when
-the mixture has set. If it sticks, tap the small end gently to start it.
-For coils where there is little or no heat, ordinary pieces of
-broom-handle, or round sticks having a coat or two of shellac, will
-answer very well; but where the current heats the core, it must be of
-some material that will not char.
-
-Another method of making resistance-coils is to measure off a length of
-wire; then double it, and with a small staple attach the loop end at one
-end of the (wooden) core. Pay out the two strands of wire an equal
-distance apart with the thumb and fingers, and with the other hand
-twist the core. At the other end of the spool catch the loose ends of
-the wire under small staples, taking great care not to let the staples
-touch or even be driven close together. This arrangement is shown at D
-in Fig. 2, and for a field resistance-board any number of these coils
-may be made.
-
-[Illustration: _=Fig. 3=_]
-
-In Fig. 3 the mode of connecting coils is shown. The dots represent
-contact-points to which the movable arm can be shifted. The wires at the
-bottom of coil, Nos. 1 and 2, are connected together, while those at the
-top of No. 2 and 3 are joined, and so on to the end. The leading-in
-current is connected at pole H and so on to J, while the leading-out
-wire is made fast to pole I. The switch-arm is moved on the first dot,
-or contact-point, and the current passes up wire A, down coil No. 1, up
-coil No. 2, down No. 3, up No. 4, and so on to No. 6, and down wire G
-and out at I. Supposing that this offers too much resistance, the
-switch-arm is moved up one point. This cuts out coil No. 1, as the
-current passes up wire B, through coil No. 2, down No. 3, and so on, and
-out through G and pole I. Another move of the switch and coil No. 2 is
-cut out, the current passing up wire C, down coil No. 3, up No. 4, and
-so on, and out at I. Each move of the switch cuts out one coil,
-lessening the resistance; but when moved to the last contact-point the
-current flows without resistance--in at H, through the switch-arm, and
-out at I.
-
-The plan of arranging the coils suggested at Fig. 2 B is shown in Fig.
-4, where four of the coils are arranged in series over porcelain knobs,
-and the lower ends made fast to the base-board with small staples. Small
-pieces of brass are used for the switch contact-plates; those are
-provided with one plain and one countersunk hole for a flat and round
-headed screw.
-
-The screw-heads are arranged in a semicircular fashion, so that the
-switch-arm, attached at one end to the screw J, will touch each plate as
-it is moved forward or backward.
-
-[Illustration: _=Fig. 4=_
-
-_=Fig. 5=_
-
-TWO SIMPLE FORMS OF RHEOSTATS]
-
-The current passing in at binding-post A travels to J and B, the latter
-being the resting-plate for the switch-arm. A move of the arm to C sends
-the current up over the first coil and down; then over the second,
-third, and fourth coils, and out at G; through plate H (which is the
-rest at the right side), and out at I.
-
-A move of the switch-arm to D cuts out the first coil; a move to E, the
-first and second coils; and so on until the last plate is reached, when
-the current will pass without resistance in at A, through J, and out at
-I.
-
-A simple arrangement for a resistance-coil is shown in Fig. 5. This
-consists of a set of small metal plates in which two holes are made, one
-for a screw, the other for a screw-eye (see Binding-posts, chapter
-iii.). Two lines of steel-wire nails are driven along a board, and
-German-silver wire is drawn around them in zig-zag fashion, beginning at
-the left and going towards the right side of the board. One end of wire
-is made fast under the screw-head on plate A. The strand is carried out
-around the first nail on the lower row and over the first one on the
-upper row, then down, up, down until six nails have been turned. The
-wire is then carried down to the screw in plate B, given two turns, and
-carried up again and over the nail on the top row, repeating the
-direction of zigzag No. 1, until six of them are made. The end of the
-wire is then made fast to plate G, and all the screws are driven in to
-hold the plates and wire securely.
-
-The inlet wire is attached to A, the outlet to G, and any degree of
-resistance can be had by moving the inlet wire to the various plates
-along the line, cutting out sections Nos. 1 to 6 as desired.
-
-For heavier wire the arrangement as shown in Fig. 6 should be
-satisfactory.
-
-[Illustration: _=Fig. 6=_]
-
-[Illustration: _=Fig. 7=_]
-
-A frame twelve by fifteen inches is constructed of wood three-quarters
-of an inch thick and one inch and a quarter wide, having the ends
-securely fastened with glue and screws. Spirals are wound of
-German-silver wire (any size from No. 16 to 22), and drawn apart. The
-ends are caught to the frame with small staples, and each alternate
-coil-end is joined, as shown in Fig. 6. The leading-out wires to the
-contact-points on the switch should be of insulated copper, and are to
-run down the sides of the frame, and so to the switch-board. To clearly
-illustrate, however, the plan of wiring, the drawing is made so as to
-show the leads from the coil-ends to the switch. Care should be taken to
-study this drawing well, so as not to make an error in connecting a
-wrong end to a contact-point, thereby causing a short circuit. When
-properly connected the current passes in at A and out at I; but if wires
-are improperly connected, the current will jump when the switch-arm
-reaches the misconnected contact.
-
-The switch is an important part of every rheostat, and should be
-carefully and accurately made. One of the simplest and most practical
-switches is constructed from a short, flat bar of brass or copper having
-a knob attached at one end and a hole provided at the other through
-which a screw may pass (see Switches, chapter iii.). The contact-points
-are made from one or two copper washers, with the holes countersunk so
-that a machine screw of brass, with a flat head, will fit the hole
-snugly. The top of the head will then be flush with the top of the
-washer, as shown at Fig. 7 A. The bolt is passed down through a piece of
-board, then slate or soapstone, and caught with a washer and nut, as
-shown at Fig. 7 B. A loop of wire is passed about the bolt end, then
-another nut is screwed tightly over it to hold it in place, as well as
-to lock the first nut. The binding-posts that hold the inlet and outlet
-wires may be made of bolts and nuts also, as shown at Fig. 7 B; but the
-bolt must be passed through the switchboard so that the head is at the
-rear and the ends project out to receive the nuts.
-
-A very compact and simple rheostat and switch is shown in Fig. 8. It is
-composed of a base-board, eight blocks of hard-wood, and a top strip
-used as a binder to lock the upper ends of the blocks together. The
-hard-wood blocks are three-quarters of an inch thick, one inch and a
-half wide, and four inches long. A small hole is made near each end of
-the block and through one of them an end of the wire is passed. The wire
-is then wound round the block, taking care to lay it on evenly, and with
-about one-eighth of an inch of space between each strand. When the
-opposite hole is reached, pass the end of the wire through it and clip
-it. The block will then resemble Fig. 7 C. There should be three or four
-inches of wire at each end for convenience in connection, and when the
-eight blocks are wound they are to be mounted on end at the rear side of
-a base-board measuring ten inches long, three inches wide at the ends,
-and nine at the middle (or across the face of the switchboard to the
-rear edge behind the blocks). Use slim steel-wire nails and glue to
-attach the blocks to the base; or slender screws may be employed. Across
-the top lay a piece of wood a quarter of an inch in thickness, and drive
-small nails or screws down through it and into the blocks.
-
-[Illustration: _=Fig. 8=_
-
-_=Fig. 10=_
-
-_=Fig. 9=_
-
-COMPACT FORMS OF RHEOSTATS]
-
-Connect the ends of the coils together in series, as already described,
-and carry the wires under the base-plate in grooves cut with a
-[V]-shaped chisel. If the sunken wires are bothersome, the work may be
-avoided by running the wires direct to the foot of the contact-points
-and elevating the rheostat on four small blocks that may be screwed, or
-nailed and glued, under the corners, as shown in Fig. 8. These will
-raise the base half an inch or more above the table on which the
-rheostat will rest so as to allow room for the under wires.
-
-A rheostat of round blocks standing on end is shown at Fig. 9 A. These
-are pieces of curtain-pole, four inches long and wound with loops of No.
-16 or 18 wire, as shown at Fig. 9 B. The loop and loose ends are caught
-with staples, and when arranged on a base-board they are to be connected
-in series as before described. One long, slim screw passed up through
-the base-board and into the lower end of the block will hold each block
-securely in place. To keep it from twisting, a little glue may be placed
-under the blocks so that when the screw draws the block down to the base
-it will stay there permanently upon the hardening of the glue. The
-leading wires should be slipped under the washers forming the
-contact-points of the switch; or they may be carried under the board to
-the nuts that hold the lower ends of the bolts.
-
-Another form of rheostat (Fig. 10 A) is made by sawing a one-inch
-curtain-pole into four-inch lengths and cross-cutting each piece with
-eight or ten notches, as shown at Fig. 10 B. These pieces are screwed
-and glued fast along each side of a base-board eight inches wide and
-fourteen inches long, so that the notches face the outer edges of the
-board. The strand of wire passes round these upright blocks and fits
-into the notches so as to prevent them from falling down.
-
-The top end of wire at each pair of blocks is made fast by a turn or two
-of another piece of wire and a twist to hold it securely; then the
-loose end is carried down through a hole and along under the board to
-the foot of a contact-point.
-
-Any number of these upright coils may be made, and on a long board the
-switch may be arranged at one side instead of at the end, as shown in
-Fig. 10 A. When making ten or more coils it is best to use three or four
-sizes of wire, beginning with fine and ending with coarse. For instance,
-in a twelve-coil rheostat make three coils of No. 26, three of No. 22,
-and three of No. 18; or if coarser wire is required use Nos. 20, 16, and
-12.
-
-German-silver comes bare and insulated. It is preferable to have the
-fine wire insulated, but the heavier sizes may be bare, as it is
-cheaper; moreover, if heated too much the insulation will burn or char
-off. When cutting out the coils always begin at the end where the finer
-wire is wound; then as the current is admitted more freely the heavier
-wires will conduct it without becoming overheated.
-
-For running a sewing-machine, fan, or other small direct-current motor
-wound for low voltage, the house current (if electric lights are used in
-the house) may be brought down to the required voltage with
-German-silver rheostats similar to these already described. Another and
-very simple method is to arrange sixteen-candle-power lamps in series,
-as shown in Fig. 11. Six porcelain lamp-sockets are screwed fast to a
-wood base and the leading in and out wires brought to binding-posts or
-the contact-points of a switch. The leading-in wire to the series is
-made fast at binding-post A, which in turn is connected with screw B,
-under the head of which the switch-arm is held. When the switch is
-thrown over to contact-point C the current passes through lamp No. 1
-back to point D; through lamp No. 2 back to E; then through lamps Nos.
-3, 4, 5, and 6, and out through point I to post J. A turn of the switch
-to D cuts out lamp No. 1, to E cuts out No. 2, and so on. The filaments
-of incandescent lamps in their vacuum are among the very best mediums of
-resistance, and with a short series of lamps a current of 220 volts can
-quickly be cut down to a few volts for light experimental work or to run
-some small piece of apparatus.
-
-[Illustration: _=Fig. 11=_]
-
-[Illustration: _=Fig. 12=_]
-
-[Illustration: _=Fig. 14=_]
-
-Lamps in series are often used to cut down the current for operating
-electric toys and trains. The adjustment of the current should never be
-left to children, however, but should be attended to by some one
-qualified to look after the apparatus. Otherwise an unpleasant or even
-dangerous shock may be received. Another simple form of resistance
-apparatus is made from the carbon pencils used for arc lights. Short
-pieces will answer very well, but if the long bare ones can be had they
-will be found preferable. Do not use the copper-plated ones as they
-would conduct the current too freely; they should be bare and black. Now
-around the ends of each piece take several turns of copper wire for the
-terminals and cut-out wires. Fasten those pencils down on a board (as
-shown at Fig. 12) by boring small holes through the board, passing a
-loop of copper wire down through the holes, and giving the ends a twist
-underneath. The leading wires to and from the contact-points should be
-insulated and may be above or below the board. From the descriptions
-already given, the connections of this rheostat can readily be
-understood.
-
-The rheostat shown in Fig. 13 is perhaps the most complete and practical
-apparatus that a boy could make or would need. It is composed of a
-frame, six porcelain tubes, a switchboard, and the necessary
-German-silver and copper wire.
-
-From an electrical supply-house obtain six porcelain tubes fourteen by
-three-quarter inch. Porcelain tubes and rods warp in the firing and are
-seldom straight; in purchasing these select them as nearly perfect as
-possible in shape, size, and length.
-
-[Illustration: _=Fig. 13=_
-
-A PANEL RHEOSTAT]
-
-Buy, also, twelve small porcelain knobs that are the right size to fit
-inside the large tubes. These should have holes bored through them to
-admit screws. Construct a frame of hard-wood to accommodate the tubes,
-as shown in the drawing, and leave one end loose. With slim screws make
-the porcelain knobs fast to the top and bottom strips of the frame, as
-shown in Fig. 14. The porcelain rods will fit over these and will thus
-be held securely in the frame, one small knob entering the tube at each
-end, as indicated by the dotted lines in Fig. 14.
-
-The first porcelain tube to the left is wound with No. 22 German-silver
-wire, the next with No. 20, the third with No. 18, then Nos. 16, 14, and
-12; so that in this field a broad range can be had for a current of 110
-volts.
-
-The coils are connected in series, as explained for the other rheostats,
-and the leading wires brought down to the back of a switchboard of which
-Fig. 13 A is the front and Fig. 13 B the rear view. The switchboard is
-made of thin slate or soapstone; or a fibre-board may be employed.
-Fibre-board is especially made for electrical work, and can be had from
-a large supply-house in pieces of various thickness, three-eighths of an
-inch being about right for this board. Brass bolts and nuts and copper
-washers are used for the contact-poles, and when the ends of the leading
-wires are looped around the bolts the nuts are to be screwed down
-tightly so as to make good contacts. This rheostat may be used when
-lying on a table, or it can be hung up by means of two screw-eyes driven
-in the top of the frame, as shown in Fig. 13 A.
-
-A convenient form of rheostat for fine wire and high resistance is shown
-in Fig. 15. This is on the plan of the well-known Wheatstone rheostat
-and does not require a switchboard nor a series of coils. Two rollers,
-one of wood the other of metal or brass-covered wood, are set in a
-frame, and by means of a handle and projecting ends with square
-shoulders, one or the other of the rollers may be turned so that the
-wire on one winds up while on the other it unwinds.
-
-The wooden roller may be made from a piece of curtain-rod one inch in
-diameter, and it should have a thread cut on it. This will have to be
-done on a screw-cutting lathe, and any machinist will do it for a few
-cents. There should be from twelve to sixteen threads to the inch--no
-more--although there may be as few as eight. Twelve will be found a good
-number, as that does not crowd the coils and the risk of their touching
-is minimized. The ends of the roller should have bearings that will fit
-in holes made in the end-pieces of the frame, and at one end of each
-roller a square shoulder is to be cut, as shown at A in Fig. 16. A short
-handle may be made from two small pieces of wood, as shown at B in Fig.
-16. It must be provided with a square hole so that it will fit on the
-roller ends. The metal roller may be made from a piece of light brass
-tubing one inch in diameter through which a wooden core is slipped; or
-it can be a piece of brass-covered curtain-pole with the ends shaped the
-same as the wooden one. The wood roller should have a collar of thin
-brass or copper (or other soft metal except lead) attached to the front
-end; or several turns of wire may be made about the roller so as to form
-a contact-point. A piece of spring brass, copper, or tin rests on this
-collar and is held fast under a binding-post, which in turn is screwed
-to the wooden frame. A similar strip of spring metal is held under
-another post on the opposite side of the frame and bears on the metal
-roller.
-
-[Illustration: _=Fig. 15=_]
-
-[Illustration: _=Fig. 16=_]
-
-German-silver wire is wound on the wooden roller, one end having been
-made fast to the metal collar; and when all the thread grooves on the
-wood roller are filled the opposite end of the wire is attached to the
-rear end of the metal roller. The current entering at binding-post No. 1
-crosses on the strip of spring metal to the collar, travels along the
-coil of wire, and crosses to the metal roller and is conducted out at
-binding-post No. 2 (see Fig. 15). If the resistance is too great slip
-the handle over the end of the metal roller and give it several turns.
-The current will then pass with greater freedom as the wire on the
-wooden roller becomes shorter. This may be readily seen by connecting a
-small lamp in series with a battery and this rheostat. As the metal
-cylinder is turned the current flows more freely and the filament
-becomes red, then white, and finally burns to its full capacity. Take
-care, however, not to admit too much current as it will burn out the
-lamp. Some sort of adjustment should be made to prevent the rollers
-turning of themselves and thus allowing the wire coils to slacken. This
-may be done by boring the two holes for the rollers to fit in and then,
-with a key-hole saw, cutting the stick as shown at C in Fig. 16, taking
-care not to split it at the ends. The result will be a long slot which,
-however, has nothing to do with the bearings. Down through the middle of
-the stick make a hole with an awl, so that the screw-eye will move
-easily in the upper half but will hold in the lower half. Under the head
-of the eye place a small copper washer; then with the thumb and finger
-drive the screw-eye down until the head rests on the washer.
-
-A slight turn of the eye when it is in the right place will draw the
-upper and lower parts of the stick together and bind the wood about the
-bearing ends of the rollers. The rollers should not be held too tightly
-as that would strain the wire when winding it from one to the other. It
-should be just tight enough to keep the wire taut.
-
-Two or more of these roller resistance-frames may be made and connected
-in series so that a close adjustment can be had when using battery
-currents for experimenting.
-
-
-Liquid Resistance
-
-Apart from metallic, mercurial, or carbon resistance a form of liquid
-apparatus is frequently used in laboratory and light experimental work.
-
-[Illustration: _=Fig. 17=_]
-
-[Illustration: _=Fig. 19=_]
-
-This style of resistance equipment is the least expensive to make, and
-will give excellent satisfaction to the boy who is using light currents
-for induction-coils, lamps, galvanometers, and testing in general. The
-simplest form of liquid resistance is made by using a glass bottle with
-the upper part cut away. The cutting may be done with a steel-wheel
-glass-cutter. The bottle should then be tapped on the cut line until the
-top part falls away. Go over the sharp edges with an old file to chafe
-the edge and round it; then solder a tin, copper, or brass disk to a
-piece of well-insulated wire and drop it down in the bottom of the
-receptacle, as shown at Fig. 17. Cut a smaller disk of metal, or use a
-brass button, and suspend it on a copper wire which passes through a
-small hole in a piece of wood at the top of the jar. Notches should be
-cut at the under side of this wood cross-piece so that it will fit on
-top of the jar and stay in place. The jar is to be nearly filled with
-water, having a teaspoonful of sulphate of copper dissolved in it. This
-will turn the water a bluish color and make it a slightly better
-conductor, particularly when the button is lowered close to the round
-disk. If a high resistance is desired the copper may be omitted leaving
-the water in its pure state. The wires leading in and out of the jar
-should be connected between the apparatus and the battery so that the
-proper amperage can be had by raising or lowering the button. A series
-of these liquid resistance-jars may be made of glass tubes an inch in
-diameter and twelve inches long. One end of them may be stopped with a
-cement made of plaster of Paris six parts, ground silex or fine white
-sand two parts, and dextrine two parts. Mix the ingredients together
-when dry, taking care to break all small lumps in the dextrine; then add
-water until it is of a thick consistency like soft putty. Solder the
-ends of some copper wires to disks of copper or brass and set them on
-the middle of bone-buttons; these in turn are to be imbedded in the
-mixture after the wire has been passed through a hole in the bottom.
-
-Their location can be seen in the bottom of the tubes Fig. 18, and Fig.
-19 A is an enlarged figure drawing of the plate, button, and wire. The
-wires are brought out under the lower edge of the tubes, and enough of
-the composition is floated about the bottom and outer edge of the tube
-to form a base, as shown in the drawing. A base-board is made six inches
-wide and long enough to accommodate the desired number of tubes. Two
-pieces of wood one inch wide and three-quarters of an inch thick have
-hollow notches cut from them at one side, as shown at Fig. 19 B. In
-these notches the tubes are gripped. Screws are passed through one stick
-and into the other so as to clamp the wood and tubes securely together.
-The rear stick is supported on two uprights which are made fast to the
-rear edge of the base-plate with screws and glue.
-
-Along the front of the base-board small metal contact plates, or
-binding-posts, are arranged (see Binding-posts, chapter iii.) and the
-wires led to them from the tubes, as shown in the drawing. The top or
-drop wires in the tubes are provided with metal buttons at the ends; or
-the end of the wire may be rolled up so as to form a little knob. The
-manner of connecting the wires was freely explained in the
-resistance-coil descriptions and may be studied out by examining the
-drawing closely. In this resistance-apparatus there are two ways of
-cutting out a medium--first, by lowering the wire in the tube so that
-both contact-points meet; and second, by cutting out the first tube
-altogether by connecting the incoming wire with the second binding-post.
-Then again the resistance may be regulated quite accurately by raising
-or lowering the wires in the liquid.
-
-For example, there is too much resistance if the current has to travel
-through all the tubes. If it is too strong when one tube is cut out, the
-wire in tube No. 1 is lowered so that the contacts are an inch apart.
-Then the more accurate adjustment is made by dropping the wire in the
-second tube, as shown in Fig. 18. The wires leading out at the top of
-the tubes are pinched over the edge to hold them in place. They should
-be cotton insulated and the part that is in the liquid should be coated
-with hot paraffine.
-
-The water may be made a slightly better conductor if a small portion of
-sulphate of zinc, or sulphate of copper, is added to each tubeful.
-
-[Illustration: _=Fig. 18=_]
-
-Hittorf’s resistance-tube is one of the oldest on these lines, and two
-or more of them are coupled in series, as described for this water-tube
-resistance; glass tubes are employed that have one end sealed with a
-permanent composition, as described for Fig. 18. A metallic cadmium
-electrode is placed at the bottom of the tube, and the tube is then
-filled with a solution of cadmium iodide one part and amylic alcohol
-nine parts, and then corked. A wire passing down through or at the side
-of the cork is attached to another small piece of metallic cadmium,
-which touches the top of or is suspended a short distance in the liquid.
-
-As the alcohol is volatile the cork cannot be left out of the tube, and
-the wire must be drawn through the cork with a needle so that no opening
-is left for evaporation. A number of these tubes may be made and coupled
-in series and the wires led down to the contact-points of a switch.
-
-
-Chapter VIII
-
-THE TELEPHONE
-
-For direct communication over short or moderately long distances,
-nothing has been invented as yet that will take the place of the
-telephone. A few years ago, when this instrument was first brought out,
-it was the wonder of the times, just as wireless telegraphy is to-day.
-Starting with the simple form of the two cups with membranes across the
-ends, and a string or a wire connecting them, we have to-day the complex
-and wonderful electric telephone, giving perfect service up to a
-distance of two thousand miles. Some day inventors in the science of
-telephony will make it possible to communicate across or under the
-oceans, and when the boys of to-day grow to manhood they should be able
-to transact business by ’phone from San Francisco to the Far East, or
-from the cities near the Atlantic coast to London, Paris, or Berlin.
-
-It is hardly necessary to enter into the history of telephones, as this
-information may be readily found in any modern encyclopædia or reference
-work. But the boy who is interested in electricity wants to know how to
-make a telephone, and how to do it in the up-to-date way, with the wire
-and ground lines, switches, cut-outs, bell connections, and other vital
-parts, properly constructed and assembled. In this laudable ambition we
-will endeavor to help him.
-
-The general principle of the telephone may be explained in the statement
-that it is an apparatus for the conveyance of the human voice, or indeed
-any sounds which are the direct result of vibration.
-
-Sound is due to the vibrations of matter. A piano string produces sound
-because of its vibration when struck, or pulled to one side and then
-released. This vibration sets the air in rapid motion, and the result is
-the recording of the sound on our ear-drums, the latter corresponding to
-the film of sheepskin or bladder drawn over the hollow cup or cylinder
-of a toy telephone. When the head of a drum is struck with a small stick
-it vibrates. In this case the vibrations are set in motion by the blow,
-while in the telephone a similar phenomenon is the result of vibratory
-waves falling from the voice on the thin membrane, or disk of metal, in
-the transmitter. When these vibrations reach the ear-drum the nervous
-system, corresponding to electricity in the mechanical telephone,
-carries this sound to our brains, where it is recorded and understood.
-In the telephone the wire, charged with electricity, carries the sound
-from one place to another, through the agencies of magnetism and
-vibration.
-
-Over short distances, however, magnetism and electricity need not be
-employed for the transmission of sound. A short-line telephone may be
-built on purely vibratory principles. Almost every boy has made a
-“phone” with two tomato-cans over which a membrane is drawn at one end
-and tied. The middle of the membrane is punctured, and a button, or
-other small, flat object, is arranged in connection with the wires that
-lead from can to can.
-
-
-A Bladder Telephone
-
-A really practical talking apparatus of this simple nature may be made
-from two fresh beef bladders obtained from a slaughter-house or from the
-butcher. You will also need two boards with holes cut in them, two
-buttons, some tacks, and a length of fine, hard, brass, copper, or
-tinned iron wire. The size should be No. 22 or No. 24. The boards should
-be ten by fourteen inches and half an inch in thickness. Cut holes in
-them eight inches in diameter, having first struck a circle with a
-compass. This may be done with a keyhole saw and the edges sand-papered
-to remove rough places. Prepare the bladders by blowing them up and
-tieing them. Leave them inflated for a day or two until they have
-stretched, but do not let them get hard or dry.
-
-When the bladders are ready, cut off the necks, and also remove about
-one-third of the material, measuring from end to end. Soak the bladders
-in warm water until they become soft and white. Stretch them, loosely
-but evenly, over the opening in the boards, letting the inside of the
-bladder be on top, and tack them temporarily all around, one inch from
-the edge of the opening. Test for evenness by pushing down the bladder
-at the middle. If it stretches smoothly and without wrinkles it will do;
-otherwise the position and tacks must be changed until it sets perfectly
-smooth.
-
-[Illustration: _=Fig. 1=_]
-
-[Illustration: _=Fig. 2=_]
-
-[Illustration: _=Fig. 3=_]
-
-[Illustration: _=Fig. 4=_]
-
-The bladder must now be permanently fastened to the board by means of a
-leather band half an inch wide and tacks driven closely, as shown in
-Fig. 1. With a sharp knife trim away the rough edges of the bladder that
-extend beyond the circle of leather. Attach a piece of the fine wire to
-a button, as shown in Fig. 2, and pass the free end through the centre
-of the bladder until the button rests on its surface. Then fasten an
-eight-pound weight to the end of the wire and set in the sun for a few
-hours, until thoroughly dry, as shown at Fig. 3.
-
-When both drums are complete, place one at each end of a line, and
-connect the short wires with the long wire, drawing the latter quite
-taut. The course of the main wire should be as straight as possible, and
-should it be too long it may be supported by string loops fastened to
-the limbs of trees, or suspended from the cross-piece of supports made
-in the form of a gallows-tree or letter F. To communicate it will be
-necessary to tap on the button with a lead-pencil or small hard-wood
-stick. The vibration will be heard at the other end of the line and will
-attract attention.
-
-By speaking close to the bladder in a clear, distinct tone, the sound
-will carry for at least a quarter of a mile, and the return vibrations
-of the voice at the other end of the line can be clearly recognized.
-
-
-A Single (Receiver) Line
-
-The principal parts of the modern telephone apparatus are the
-transmitter, receiver, induction-coil, signal-bell, push-button,
-batteries, and switch. The boxes, wall-plates, etc., etc., are but
-accessories to which the active parts are attached.
-
-The first telephone that came into general use was the invention of
-Graham Bell, and the principle of his receiver has not been materially
-changed from that day to this, except that now a double-pole magnet and
-two fine wire coils are employed in place of the single magnet and one
-coil. A practical form of single magnet receiver that any boy can
-easily construct is shown in Fig. 4, and Fig. 5 is a sectional drawing
-of the receiver drawn as though it had been sliced or sawed in two, from
-front to rear.
-
-It is made from a piece of curtain-pole one inch and an eighth in
-diameter and three inches and a half long. A hole three-eighths of an
-inch in diameter is bored its entire length at the middle, and through
-this the magnet passes. At one end of this tube a wooden pill-box (E) is
-made fast with glue, or a wooden cup may be turned out on a lathe and
-attached to the magnet tube. If the pill-box is employed it should be
-two inches and a half in diameter, and at four equidistant places inside
-the box small lugs of wood are to be glued fast. Into these lugs the
-screws employed to hold the cap are driven. The walls of pill-boxes are
-so thin that without these lugs the cap could not be fastened over the
-thin disk of metal (D) unless it were tied or wired on, and that would
-not look well. If the cup is turned the walls should be left thick
-enough to pass the screws into, and the inside diameter should then be
-one inch and three-quarters.
-
-[Illustration: _=Fig. 5=_]
-
-[Illustration: _=Fig. 6=_]
-
-The cap (B) is made from thin wood, fibre, or hard rubber. It is
-provided with a thin rim or collar to separate its inner side from the
-face of the disk (D). Four small holes are bored near the edge of this
-cap, so that the screws which hold it fast to the cup (E) may pass
-through them. The magnet (M) is a piece of hard steel three-eighths of
-an inch in diameter and four inches and a quarter long. This may be
-purchased at a supply-house, and if it is not hard enough a blacksmith
-can make it so by heating and plunging it in cold water several times.
-It may be magnetized by rubbing it over the surface of a large horseshoe
-magnet, or if you live near a power station you can get one of the
-workmen to magnetize it for you at a trifling cost. Should you happen to
-possess a bar magnet of soft iron with a number of coils of wire, and
-also a storage-battery, the steel bar may be substituted for the soft
-iron core and the current turned on. After five minutes the steel can
-be withdrawn. It is now a magnet, and will hold its magnetism
-indefinitely.
-
-Now have a thin, flat spool turned from maple or boxwood to fit over one
-end of the rod, and wind it with a number of layers of No. 36 copper
-wire insulated with silk. This is known in the electrical supply-houses
-as “phone”-receiver insulated wire, and will cost about fifty cents an
-ounce. One ounce will be enough for two receivers. It should be wound
-evenly and smoothly, like the strands of thread on a spool, and this may
-be done with the aid of the winder described on page 58.
-
-When the wire is in place a drop of hot paraffine will hold the end so
-that the wire will not unwind. The ends of this spool-winding should be
-made fast to heavier wires, which are run through small holes in the
-tube (A) and project out at the end, as shown at F F. The magnet, with
-its wire-wound spool on the end, is then pushed through the hole in A
-until the top end of the rod is slightly below the edges of the cup (E),
-so that when the metal disk (D) is laid over the cup (E) the space
-between the magnet and disk, or diaphragm (D), is one-sixteenth of an
-inch (see Fig. 5). Put some shellac on the magnet, so that when it is in
-the right place the shellac will dry and hold it fast.
-
-The cap (B) holds the disk (D) in place, and protects the spool and its
-fine wire from being damaged and from collecting dust. After giving the
-exterior a coat of black paint and a finishing coat or two of shellac,
-the receiver will be ready for use.
-
-The original telephone apparatus was made up of these receivers
-only--one at each of a line in connection with a battery, bell,
-push-button, and switch. On a window-casing, or the wall through which
-the wires passed, a lightning-arrester was arranged and made fast. Using
-receivers only, it was necessary to speak through the same instrument
-that one heard through, and for a few years this unhandy method of
-communication was the only one possible. Then the transmitter was
-invented.
-
-
-Plan of Installation
-
-Many of these single-receiver lines are still in use, and as they
-require but a small amount of constructive skill a diagram of the wiring
-and the plan of arrangement is shown in Fig. 6.
-
-At the left side, R is the receiver at one end of the line and R 2 that
-at the other, line No. 1 being a continuous wire between the two
-receivers. When the boy at R wishes to call his friend at R 2 he uses
-his push-button (P B), and the battery (B B) operates the electric bell
-(E B 2) at the other end. In order to have the bell connections
-operative, the switch (S 2) must be thrown over to the left when the
-line is “quiet,” while the switch (S) should be thrown to the right.
-With the switches in this position the boy at either end may call his
-friend at the opposite end.
-
-With the switch (S 2) thrown to the left (the position it should be in,
-except when talking over the line), the boy at the other end pushes his
-button (P B), first throwing switch S to the left. This makes connection
-for the battery (B B), and the circuit is closed through wires that join
-line No. 1 and line No. 2 at 1 and 2. The branch lines to the bell (E B
-2) join the main lines at 3 and 4, through switch S 2, when the bar is
-thrown to the left. The circuit being complete, the batteries (B B) at
-one end of the line ring the bell (E B 2) at the other end of the line.
-
-In the reverse manner, when the switch (S) is thrown to the right, the
-boy at the opposite end rings the bell (E B) by pressing on the button
-(P B 2), first throwing switch S 2 over to the right. If the boy at the
-left is calling up the boy at the right, the switch (S) should be thrown
-to the left, and he keeps ringing until the other operator throws switch
-S 2 over to the right. If now he has the receiver (R) up to his ear he
-can hear the vibration of the bell (E B 2) ringing through the receiver
-(R) at his end of the line. But when the boy summoned to R 2 takes up
-the receiver and places it to his ear, he throws switch S 2 over to the
-right side, and the boy at R leaves switch S over on the left side. This
-brings the lines into direct connection with the receivers in series. Be
-careful, when setting up this line, to have the batteries (B B) in
-series with B 2 B 2; otherwise there would be counter-action. The carbon
-of one cell should be connected with the zinc of the next cell, and so
-on.
-
-Another receiver is shown at Fig. 7. The tube (A) and the cup are turned
-from one piece of wood, and the cap (B) from another piece. The length
-of the receiver is five inches, and the cap is two inches and a half
-across. The shank, or handle, through which the magnet is passed
-measures one inch and a quarter in diameter.
-
-These wood parts will have to be made by a wood-turner; and before the
-long piece is put in a lathe the hole, three-eighths of an inch in
-diameter, should be bored. It must be done carefully, so that the wood
-shell will be of even thickness all around the hole. Also two small
-holes should be made the entire length of the handle, through which the
-wires leading from the coil to the binding-posts may pass.
-
-[Illustration: _=Fig. 7=_]
-
-The spool for the fine insulated wire coil is turned from box-wood or
-maple, and wound as described in chapter iv., on Magnets and
-Induction-coils. Small binding-posts (F F) with screw ends should be
-driven down into the holes at the end of the handle and over the bare
-ends of the wires that project out of the holes. The magnet (M) is
-three-eighths of an inch in diameter, and is provided with the spool and
-coil (C) at the large end of the receiver.
-
-The disk (D) is of very thin iron, and is held in place by the cap (B)
-and four small brass screws driven through the edge of B and into the
-cup end of A. A screw-eye should be driven into the small end of the
-receiver from which it may hang from a hook. If a double hook and bar is
-employed the receiver will hang in the fork, being held there by the
-rim of wood turned at the small end of A.
-
-
-A Double-pole Receiver
-
-[Illustration: _=Fig. 8=_]
-
-Another form of receiver is shown at Fig. 8. This is a double-pole
-receiver, with the coils of fine wire arranged on the ends of a bent
-band of steel and located in the cup (A), so that the ends of the magnet
-are close to the diaphragm (D). Fig. 8 is a sectional view of an
-assembled receiver, but a good idea can be had from the drawings of the
-separate parts. The magnet (M) is of steel one-eighth of an inch thick
-and five-eighths of an inch wide. A blacksmith will make this at a small
-cost. It should measure two and one-half inches wide, two and one-half
-inches long, the ends being five-eighths of an inch apart.
-
-Thin wooden spools are made from wood or fibre to fit over the steel
-ends, and are wound with No. 36 silk-insulated wire. A wooden cup, or
-shell (A), is turned from cherry, maple, or other close-grained wood,
-and at the back a hole is cut just large enough for the magnet ends to
-slip through exclusive of the coils wound on them. A plug of wood (A A)
-is driven between the ends of the magnet to hold them in place. Some
-shellac on the edges of the hole and the plug will harden and keep the
-parts in place.
-
-The coils (C C) are placed on the magnet ends, and the fine wires are
-made fast to the binding-posts (E E), the latter being screwed fast to
-the shell (A). The diaphragm (D) is then arranged in place and held with
-the cap (B) and the small screws which pass through it and into the
-shell (A).
-
-
-The Transmitter
-
-With any one of these receivers a more complete and convenient telephone
-can be made by the addition of a transmitter and an induction-coil.
-
-Following the invention of the receiver, several transmitters were
-designed and patented, among them being the Edison, Blake, Clamond,
-Western Union, and Hunning. The Edison and Hunning are the ones in
-general use, and as either of them can easily be made by a boy a
-simplified type of both is shown in Figs. 9 and 11.
-
-[Illustration: FIG. 9
-
-FIG. 10
-
-FIG. 11
-
-FIG. 12
-
-SIMPLIFIED TYPE OF TRANSMITTER]
-
-Some small blocks of wood, tin funnels, small screws, granulated or
-powdered carbon, some thin pieces of flat carbon, and a piece of very
-thin ferrotype plate will be the principal things needed in making a
-transmitter similar to the one shown in Fig. 9. All that is visible from
-the outside is a plate of wood screwed to a block of wood, and a
-mouth-piece made fast to the thin board.
-
-In Fig. 10 an interior section is shown, which when once understood will
-be found extremely simple. The block (A) is of pine, white-wood, birch,
-or cherry, and is two inches and three-quarters square and five-eighths
-or three-quarters of an inch thick. A hole seven-eighths of an inch in
-diameter is bored in the centre of this block, half an inch deep, and a
-path is cut at the face of the block one inch and a half in diameter and
-one-eighth of an inch deep. Be careful to cut these holes accurately and
-smoothly, and if it is not possible to do so, it would be well to have
-them put in a lathe and turned out.
-
-The face-plate (B) is two inches square, with a three-quarter-inch hole
-in it, and the under-side is cut away for one-eighth of an inch in depth
-and one inch and a half in diameter. The object of these depressions in
-block A and face-plate B is to give space for the diaphragm (D) to
-vibrate when the voice falls on it through the mouth-piece (C).
-
-From carbon one-eighth of an inch in thickness two round buttons are cut
-measuring three-quarters of an inch across. A small hole is bored in the
-centre of each button, and one of them is provided with a very small
-brass screw and nut, as shown at F F. One side of the button-hole is
-countersunk, so that the head of the screw will fit down into it and be
-flush with the face of the carbon. With a small three-cornered or square
-file cut the surface of the buttons with criss-cross lines, as shown at
-F F. When the buttons are mounted in the receiver these surfaces will
-face each other. Cut a small washer from felt or flannel, and place it
-in the bottom of the hole in block A. Line the side of the hole with a
-narrow strip of the same goods; then place the button (F F) in the hole,
-pass the screw through the hole and through the block (A), and make it
-fast with the nut, as shown at F. Place a thin, flat washer under the
-nut, and twist a fine piece of insulated copper wire between washer and
-nut for terminal connections, taking care that the end of the wire under
-the nut is bare and bright, so that perfect contact is assured. Since
-the practice of telephony involves such delicate and sensitive vibratory
-and electrical phenomena, it is best to solder all joints and unions
-wherever practicable, and so avoid the possibility of loose connections
-or corrosion of united wires.
-
-From very thin ferrotype plate cut a piece two inches square, and at the
-middle of it attach the other carbon button by means of a small rivet
-which you can make from a piece of copper wire. Or a very small brass
-machine screw may be passed through the button and plate; then gently
-tapped at the face of the plate to rivet it fast, as shown at E. Lay the
-block down flat and partly fill the cavity with carbon granules until
-the button is covered. Do not fill up to the top of the hole. Over this
-lay the disk (D), so that the carbon button at the under side of it will
-fit in the top part of the hole between the sides of felt or flannel.
-Make the disk fast to the block (A) with small pins made by clipping
-ordinary pins in half and filing the ends.
-
-A slim bolt (G) is passed through the block (A), and a wire terminal is
-caught under a nut and between a washer at the back of the block, as
-described for F. The japan or lacquer must be scraped away from the disk
-(D) where the bolt-head touches it, so that perfect electrical contact
-will be the result.
-
-A small tin funnel is cut and made fast to the face-plate (B), or if an
-electrical supply-house is at hand a mouth-piece of hard rubber or
-composition may be had for a few cents. The block (B) is then screwed
-fast to A, forming the transmitter shown at Fig. 9. When this
-transmitter stands in a vertical position the granules, or small
-particles of carbon, drop down between the buttons of carbon, packing
-closely at the bottom of the cavity. At the middle they are loosely
-placed, and at the top there are none. As the high or low vibrations of
-the voice fall on the disk (D) they act accordingly on the carbon
-granules, which in turn conduct the vibrations to the rear carbon
-button, and, by the aid of electricity reproduce the same sound, in high
-or low tone, through the receiver at the other end of a line.
-
-This improved transmitter makes it possible to talk in a moderate tone
-of voice over distances up to one thousand miles, while with the old
-form of the instrument it was necessary to talk very loud in order to be
-heard only a few miles away. Where a portable apparatus is desired, this
-block may be attached to a box or an upright staff.
-
-This transmitter will not work when on its back or so that the funnel is
-on top, because the particles of carbon would settle on the rear button
-and not touch the front one. It is essential that the carbon grains
-should touch both buttons at the same time, and at the lower part of the
-cavity they should lie quite solid. It is not necessary, however, to
-pack it in, for the vibratory action of the voice, or other sounds, will
-cause the particles to adjust themselves and settle in a compact mass.
-
-
-Another Form of Transmitter
-
-In Fig. 11 another style of transmitter is shown. It is assembled on the
-front of a box. This front or cover swings on hinges, and can be opened
-so that the mechanism in the interior of the box may be gotten at
-easily.
-
-A sectional view of this transmitter is shown in Fig. 12. A hole one
-inch and a half in diameter is cut in the cover (A). A round or square
-block (B) two inches and a quarter across and half an inch thick is made
-fast to the rear of the cover, and in this a hole is bored seven-eighths
-of an inch in diameter and one-quarter of an inch deep.
-
-The sides and bottom of this hole are lined with flannel or felt, and a
-carbon button with roughened surface, as shown at F F, is made fast in
-it by a small machine screw and nut (F). A diaphragm (D) is cut from
-thin ferrotype plate, and a carbon button is made fast to the middle of
-it by a small machine screw or a rivet made from soft copper or brass.
-When the block (B) has been screwed fast to A, place some granules of
-carbon in the space (H); then lay the diaphragm over the opening, and
-make it fast with small screws or pins driven around the edge.
-
-From a small tin funnel and a tin-can cap make a mouth-piece (C) by
-cutting a hole in the cap and slipping the funnel through it, then
-cutting the end of the funnel that projects through the hole and bending
-back the ears so that they lap on the inner side of the cap. These small
-ears may be soldered to the cap so as to hold the mouth-piece securely
-in place. From felt or flannel cut a washer the size of the can top and
-about three-eighths of an inch in width. Lay this over the diaphragm;
-then place the mouth-piece on it and fasten it to the door (A) with
-small screws. The use of this washer is to prevent any false vibrations
-in the mouth-piece affecting the sensitive diaphragm. Make a small hole
-through A and B and pass a bolt (E) through this hole, taking care to
-lap a thin piece of sheet-brass on the diaphragm (D), bending it over so
-that it will lie under the head of the bolt (E). The diaphragm must be
-scraped where the metal touches it, so as to make perfect electrical
-connection between D and E. At the rear end of E arrange a washer and
-nut (G), so that the current passing in at G travels through E and D,
-then through the carbon buttons and granules, and out at F.
-
-From pine or white-wood one-quarter or three-eighths of an inch thick
-make a box four inches wide, six inches high, and two inches and a half
-deep. To the front of this attach a cover, which should measure a
-quarter of an inch larger all around than the width and height of the
-box. Use brass hinges for this work so that the cover may be opened.
-Fasten a transmitter to the front of the cover, or make one on the
-cover, as shown in Fig. 11, and attach the box to a back-board or
-wall-plate five inches wide and seven inches high made of pine or
-white-wood half an inch in thickness (see Fig. 13).
-
-[Illustration: FIG. 13]
-
-[Illustration: FIG. 14]
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-At the left side of the box cut a slot through the wood, so that a lever
-and hook may project and work up and down. The end of this lever is
-provided with a hook on which a receiver may be hung, as shown in Fig.
-13, and the inside mechanism is arranged as shown at Fig. 14. A is an
-angle-piece of brass or copper, which acts as a bracket and which is
-screwed fast to the inside of the box. B is the lever and hook, which is
-cut from a strip of brass. The attached end is made wider, and an ear
-(C), to which a wire is soldered, projects down beyond the screw.
-
-A view looking down on this lever and bracket is shown at Fig. 15. A is
-the bracket, B the lever, and E the screw or bolt holding the two parts
-together, with a thin copper washer between them to prevent friction.
-When the lever and bracket are made fast to the box, a spring (D) should
-be arranged, so that when the receiver is removed from the hook the
-lever will be drawn up to the top of the slot. A small contact-plate (F)
-is made of brass, and fastened at the lower end of the slot. On this the
-lever should rest when the receiver is on the hook. A contact-wire is
-soldered to this plate, which in turn is screwed fast to the inside of
-the box. This mechanism is part of a make-and-break switch to cut out
-and cut in the bells or telephone, and will be more clearly understood
-by referring to the diagram in Fig. 17. At the right side of the box a
-small push-button is made fast, and this, with two binding-posts at the
-top and four at the underside of the box, will complete the exterior
-equipment of one end of a line.
-
-The construction of the push-button is shown in Fig. 16, A being the box
-and B the button which passes through a small hole made in the side of
-the box. C is a strip of spring-brass screwed fast to the box. It must
-be strong enough to press the small bone or hard rubber button towards
-the outside of the box. A wire is caught under one screw-head, and
-another one is passed under the screw-head which holds the other spring
-(D) to the box. When the button (B) is pushed in, it brings spring C
-into contact with D, and the circuit is closed. Directly the finger is
-removed from B the spring (C) pushes it out and breaks the circuit. This
-button is used only in connection with the call-bells, and has nothing
-to do with the telephone. The wires leading from the interior of the box
-pass through the wall-plate and along in grooves to the foot of the
-binding-posts, which are arranged below the box on the back-board, as
-shown in Fig. 13.
-
-A buzzer or bell is made fast to the inside of the box, unless it is too
-large to fit conveniently, in which case it may be attached to the wall
-above or below the box.
-
-
-The Wiring System
-
-Fig. 17 shows the wiring system for this outfit, which, when properly
-set up and connected, should operate on a circuit or line several miles
-in length, provided that the batteries are strong enough.
-
-This system may be installed in the box shown in Fig. 13, the flexible
-cord containing two wires being attached to the binding-posts at the top
-of the box and to the posts at the end of the receiver. This system
-differs from the one shown in Fig. 6 only in the addition of receivers T
-and T 2, and in the substitution of the automatic lever-switches (L S
-and L S 2) for the plain switches (S and S 2) in Fig. 6. When the line
-is “quiet” the receiver (R) should be hanging on the lever-switch (L S),
-which rests on the contact-plate (A). At the opposite side of the line
-the receiver (R 2) hangs on the lever-switch (L S 2), which in turn
-rests on the contact-plate (A A). This puts the bell circuit in
-service.
-
-[Illustration: FIG. 17
-
-PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTER, ELECTRIC
-BUZZERS OR BELLS, LEVER-SWITCHES, PUSH-BUTTONS AND BATTERIES FOR
-STATIONS NOT OVER FIVE MILES APART.]
-
-If the boy at the left wishes to call up the boy at the right he removes
-the receiver (R) from the hook (L S) and presses on the button (P B).
-This closes the circuit through the battery (C C C), and operates the
-electric buzzer or bell (E B 2) at the other end of the system, through
-line No. 1 and line No. 2. The operation may be clearly understood by
-following the lines in the drawing with a pointer. The boy at the left
-may keep on calling the boy at the right so long as the receiver (R 2)
-hangs on the lever (L S 2) and holds it down against the plate (A A).
-But directly the receiver (R 2) is removed, the lever (L S 2) flies
-up--being drawn upward by the spring (D) shown in Fig. 14--and closes
-the telephone circuit through the spring-contact (B B), at the same time
-cutting out the bell circuit. The boy at the left having already removed
-his receiver, the telephone circuit is then complete through lines Nos.
-1 and 2 and batteries C C C and C 2 C 2 C 2, the boys at both ends
-speaking into the transmitters and hearing through the receivers. The
-contacts B and B B are made from spring-brass or copper, and are
-attached inside the boxes at the back, so that when the levers are up
-contact is made, but when down the circuit is broken or opened. In Fig.
-18 an interior view of a box is shown, the door being thrown open and
-the receiver left hanging on the hook.
-
-[Illustration: FIG. 18
-
-FIG. 19
-
-FIG. 20
-
-TELEPHONE INSTALLATION. INTERIOR VIEW OF BOX]
-
-The arrangement of the several parts will be found convenient and easy
-of access. E B is the electric buzzer, L S the lever-switch, P B the
-push-button, T the transmitter, and R the receiver. Nos. 1, 2, 3, 4, 5,
-6, 7, 8 are binding-posts or terminals, and B is the spring-contact
-against which the lever-switch (L S) strikes when drawn up by the spring
-(D).
-
-The wires that pass from 6 to 7 and from 4 to 8 should be soldered fast
-to one side of the hinge, and those running from the terminals or nuts
-at the back of the transmitter (T) to 7 and 8 should be similarly
-secured. Small brass hinges are not liable to become corroded at the
-joints, but to insure against any such possibility the ends of several
-fine wires may be soldered to each leaf of the hinge, so that when the
-door is closed the wires will be compressed between the hinge-plates.
-For long-distance communication it will be necessary to install an
-induction-coil, so that the direct current furnished by the batteries,
-in series with the transmitter, can by induction be transformed into
-alternating current over the lines connecting the two sets of apparatus.
-This system is somewhat more complicated and requires more care in
-making the connections, but once in operation it will be found far
-superior to either of the systems hitherto described.
-
-
-A Telephone Induction-coil
-
-It will be necessary to make two induction-coils, as described in
-chapter iv., page 62, Fig. 8. A telephone coil for moderately
-long-distance circuits is made on a wooden spool turned from a piece of
-wood three inches and a half long and one inch square, as shown at Fig.
-19. The core-sheath is turned down so that it is about one-sixteenth of
-an inch thick. This spool is given a coat or two of shellac, and two
-holes are made at each end, as shown in the drawing. The first winding
-or primary coil is made up of two layers of No. 20 double-insulated
-copper wire, one end projecting from a hole at one end of the spool, the
-other from a hole at the other end. This coil is given two or three thin
-coats of shellac to bind the strands of wire and thoroughly insulate
-them, and over the layer a piece of paper is to be wrapped and
-shellacked. The secondary coil is made up of twelve layers of No. 34
-silk-insulated copper wire, and between each layer a sheet of paper
-should be wound so that it will make two complete wraps. Each paper
-separator should be given a coat of shellac or hot paraffine; then the
-turns of wire should be continued just as thread is wound upon a spool,
-smoothly, closely, and evenly, until the last wrap is on. Three or four
-wraps of paper should be fastened on the coil to protect it, and it may
-then be screwed fast inside a box. The core-hole within the coil should
-be packed with lengths of No. 24 soft Swedes iron wire three inches and
-a half long. In Fig. 19 the wires are shown projecting from the end of a
-spool, and Fig. 20 depicts a completed telephone induction-coil. The
-installation of the induction-coils is shown in Fig. 21.
-
-[Illustration: FIG. 21
-
-PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTERS, ELECTRIC
-BUZZERS OR BELLS, LEVER-SWITCHES, INDUCTION-COILS, PUSH-BUTTONS, AND
-BATTERIES FOR STATIONS UP TO FIVE HUNDRED MILES APART.]
-
-The wiring is comparatively simple, and may be easily followed if the
-description and plan are constantly consulted when setting up the line.
-R and R 2 are the receivers, T and T 2 the transmitters, C 1 and C 2 the
-batteries, E B and E B 2 the buzzers or bells, P B and P B 2 the
-push-buttons, and L S and L S 2 the lever-switches. For convenience of
-illustration the induction-coils are separated. The primary coil (P C)
-is indicated by the heavy spring line and the secondary coil (S C) by
-the fine spring line. When the line is “dead” both receivers are hanging
-from the hooks of the lever-switches. If the boy at the left wishes to
-call the boy at the right he lifts the receiver (R) from the hook (L S)
-and presses the button (P B). This throws the battery (C 1 C 1 C 1) in
-circuit with lines Nos. 1 and 2, and operates the buzzer (E B 2). When
-the boy at the right lifts his receiver (R 2) from the hook (L S 2), the
-bell circuit is cut out and the ’phone circuit is cut in. When the
-lever-switches are drawn up against the contact-springs (A, B, and C and
-A A, B B, and C C), both batteries are thrown into circuit with the
-transmitters at their respective ends through the primary coils (P C and
-P C 2). By inductance through the secondary coils (S C and S C 2), lines
-Nos. 1 and 2 are electrified, and when the voice strikes the disks in
-the transmitters the same tone and vibration is heard through the
-receivers at the other end of the line. While conversation is going on
-the batteries at either end are being drawn upon or depleted; but as
-soon as the receivers are hung on the hooks and the lever-switches are
-drawn away from the contact-springs, the flow of current is stopped. The
-buzzers or bells consume but a small amount of current when operated,
-and in dry cells the active parts recuperate quickly and depolarize. The
-greatest drain on a battery, therefore, is when the line is closed for
-conversation.
-
-
-An Installation Plan
-
-A simple manner in which to install this apparatus in boxes is shown in
-Fig. 22. The box is depicted with the front opened and with the receiver
-hanging on the hook. When the lever-switch (L S) is down it rests on
-the contact-spring (A), thus throwing in the bell circuit. When the boy
-at the other end of the line pushes the button on his box it operates
-the buzzer (E B). This can be understood by following with a pointer the
-wires from the buzzer to the outlet-posts (Nos. 1 and 3) at the bottom
-of the wall-plate.
-
-[Illustration: _=Fig. 22=_]
-
-When the receiver (R) is lifted from the hook (L S), it cuts out the
-bell circuit and cuts in the telephone circuit, through the
-spring-contacts (B and C). This circuit may easily be followed through
-the wires connecting transmitter, receiver, induction-coil, and
-batteries. The heavy lines leading out from the induction-coil are the
-primary coil wires, and the fine hair lines are those forming the
-secondary coil. The medium lines are those that connect the
-binding-posts, batteries, and lines.
-
-When the bell circuit is connected the impulse coming from the other end
-of the line enters through wire No. 10 to post No. 3, thence to strip E
-and plate G, and so on to E B, which it operates. The current then
-passes from E B to contact A, through L S to post No. 1, and out on wire
-No. 11.
-
-To operate the buzzer at other end of the line the button (P B) is
-pushed in. This moves the spring (E) away from the plate (G), and brings
-it into contact with F. This connects the circuit through the battery
-wire (No. 8) to post No. 1 to line No. 11 without going into the box,
-and from wire No. 9 to post No. 2; thence to hinge No. 7 to plate F,
-through E, down to post No. 3, and out through wire No. 10. In this
-manner the current is taken from the batteries at the foot of wires Nos.
-8 and 9, and used to ring the buzzer at the other end of the line.
-
-When the hook (L S) is up the circuit is closed through T, I C, and
-battery. The current runs from the battery through wire No. 8 to post
-No. 1, to L S, through C and primary coil out to hinge No. 6, through
-transmitter to hinge No. 7, to post No. 2, and back to battery through
-wire No. 9.
-
-By inductance the sound is carried over the line, in at wire No. 10, to
-post No. 3, through secondary coil to post No. 4, through receiver R to
-post No. 5, through B and L S to post No. 1, and out through wire No.
-11. At the other end of the line it goes through the same parts of the
-apparatus.
-
-
-A Portable Apparatus
-
-For convenience it is often desirable to have a portable transmitter,
-and so avoid the inconvenience of having to stand while speaking. A neat
-portable apparatus that will stand on a ledge or table, and which may be
-moved about within the radius of the connecting lines, is shown in Fig.
-23.
-
-The wooden base is four inches square and the upright one inch and a
-half square. The stand is twelve inches high over all, and on the bottom
-a plate of iron or lead must be screwed fast to make it bottom-heavy, so
-that it will not topple over.
-
-The lever-switch may be arranged at the back of the upright and the
-push-button at the front near the base, as shown at A. The wall-box
-contains the buzzer and induction-coil, and within it the wiring is
-arranged from the portable stand to the batteries and line as shown at
-C. This illustration is too small, however, to show the complete wiring,
-and the young electrician is therefore referred to Fig. 22. The battery
-(B) is composed of as many dry or wet cells as may be required to
-operate the line. These must be connected in series at both ends. At D a
-rear view of the upright and transmitter is shown to illustrate the
-manner in which the wiring can be done. If a hollow upright is made of
-four thin pieces of wood a much neater appearance may be secured by
-enclosing the wires.
-
-[Illustration: FIG. 23
-
-A PORTABLE APPARATUS]
-
-In all of these telephone systems one wire must lead to the ground, or
-be connected with a water-pipe, taking care, however, to solder the wire
-to a galvanized pipe so that perfect contact will be the result. If the
-wire is carried directly to the ground it must be attached to a plate,
-which in turn is buried deep enough to reach moist earth, as described
-in the chapter on Line and Wireless Telegraphs, page 215.
-
-Care and accuracy will lead to success in telephony, but one slip or
-error will throw the best system out of order and render it useless.
-This, indeed, applies to all electrical apparatus; there can be no
-half-way; it will either work or it won’t.
-
-
-Chapter IX
-
-LINE AND WIRELESS TELEGRAPHS
-
-
-A Ground Telegraph
-
-Nearly every boy is interested in telegraphy, and it is a fascinating
-field for study and experimental work, to say nothing of the amusement
-to be gotten out of it. The instruments are not difficult to make, and
-two boys can easily have a line between their houses.
-
-The key is a modified form of the push-button, and is simply a contact
-maker and breaker for opening and closing an electrical circuit. A
-practical telegraph-key is shown in Fig. 1, and in Fig. 2 is given the
-side elevation.
-
-The base-board is four inches wide, six inches long, and half an inch in
-thickness. At the front end a small metal connector-plate is screwed
-fast, and through a hole in the middle of it a brass-headed
-upholsterer’s tack is driven for the underside of the key to strike
-against. Two [L] pieces of metal are bent and attached to the middle of
-the board to support the key-bar, and at the rear of the board another
-upholsterer’s tack is driven in the wood for the end of the bar to
-strike on and make a click. The bar is of brass or iron, measuring
-three-eighths by half an inch, and is provided with a hole bored at an
-equal distance from each end for a small bolt to pass through, in order
-to pivot it between the [L] plates. A hole made at the forward end will
-admit a brass screw that in turn will hold a spool-end to act as a
-finger-piece. The screw should be cut off and riveted at the underside.
-A short, strong spring is to be attached to the back of the base-block
-and to the end of the key-bar by means of a hook, which may be made
-from a steel-wire nail flattened. It is bound to the top of the bar
-with wire, as shown in Figs. 2 and 3.
-
-[Illustration: FIG. 1]
-
-[Illustration: FIG. 4]
-
-The incoming and outgoing wires are made fast to one end of the
-connector-plate and to one of the [L] pieces that support the key. When
-the key is at rest the circuit is open, but when pressed down against
-the brass tack it is closed, and whether pressed down or released it
-clicks at both movements. A simple switch may be connected with the
-[L]-plate and the connection-post at the opposite side of the key-base,
-so that, if necessary, the circuit may be closed. Or an arm may be
-caught under the screw at the [L]-plate, and brought forward so that it
-can be thrown in against a screw-head on the connector-plate, as shown
-in Fig. 3. The screw-head may be flattened with a file, and the
-underside of the switch bevelled at the edges, so that it will mount
-easily on the screw.
-
-In Fig. 4 (page 191) a simple telegraph-sounder is shown. A base-board,
-four inches wide, six inches long, and seven-eighths of an inch in
-thickness, is made of hard-wood, and two holes are bored, with the
-centres two inches from one end, so that the lower nuts of the horseshoe
-magnet will fit in them, as shown in Fig. 5. This allows the yoke to
-rest flat on the top of the base, and with a stout screw passed down
-through a hole in the middle of the yoke and into the wood the magnets
-are held in an upright position.
-
-From the base-block to the top of the bolt the magnets are two inches
-and a quarter high. The bar of brass or iron to which the armature (A in
-Fig. 5) is attached is four inches and a half in length and
-three-eighths by half an inch thick. At the middle of the bar and
-through the side a hole is bored, through which a small bolt may be
-passed to hold it between the upright blocks of wood. At the front end
-two small holes are to be bored, so that its armature may be riveted to
-it with brass escutcheon-pins or slim round-headed screws. The heads are
-at the top and the riveting is underneath. A small block of wood is cut,
-as shown in Fig. 6, against which the two upright pieces of wood are
-made fast. This block is two inches and a half long, one inch and a
-quarter high, and seven-eighths of an inch wide. The laps cut from each
-side are an inch wide and a quarter of an inch deep, to receive the
-uprights of the same dimensions.
-
-At the top of this block a brass-headed nail is driven for the underside
-of the bar to strike on. A hook and spring are to be attached to the
-rear of the sounder-bar, as described for the key, and at the front of
-the base two binding-posts are arranged, to which the loose ends of the
-coil-wires are attached.
-
-Just behind the yoke, and directly under the armature-bar, a long screw
-is driven into the base-block, as shown at B in Fig. 5. It must not
-touch the yoke, and the head should be less than one-eighth of an inch
-below the bar when at rest. On this the armature-bar strikes and clicks
-when drawn to the magnets. The armature must not touch the magnets;
-otherwise the residual magnetism would hold it down. The screw must be
-nicely adjusted, so that a loud, clear click will result.
-
-[Illustration: FIG. 2
-
-FIG. 3
-
-FIG. 5
-
-FIG. 6
-
-FIG. 8
-
-TELEGRAPH KEY AND SOUNDER]
-
-When the sounder is at rest the rear end lies on the brass tack in the
-block, and the armature is about a quarter of an inch above the top of
-the magnets. The armature is of soft iron, two inches and a half long,
-seven-eighths of an inch wide, and an eighth of an inch thick. These
-small scraps of metal may be procured at a blacksmith’s shop, and, for a
-few cents, he will bore the holes in the required places; or if you have
-a breast or hand drill the metal may be held in a vise and properly
-perforated.
-
-By connecting one wire from the key directly with one of the
-binding-posts of the sounder, and the other with the poles of a battery,
-and so on to the sounder, the apparatus is ready for use. By pressing on
-the key the circuit is closed, and the magnetism of the sounder-cores
-draws the armature down with a click. On releasing the key the bar flies
-back to rest, having been pulled down by the spring, and it clicks on
-the brass tack-head. These two instruments may be placed any distance
-apart, miles if necessary, so long as sufficient current is employed to
-work the sounder. Two sets of instruments must be made if boys in
-separate houses are to have a line. Each one must have a key, sounder,
-and cell, or several cells connected in series to form a battery,
-according to the current required.
-
-In the plan of the telegraph-line connections (Fig. 7, page 196) a
-clear idea is given for the wiring; and if the line and return wires are
-to be very long, it would be best to have them of No. 14 galvanized
-telegraph-wire, copper being too expensive, although much better. These
-wires must not touch each other, and when attached to a house, barn, or
-trees, porcelain or glass insulators should be used. If nothing better
-can be had, the necks of some stout glass bottles may be held with
-wooden pins or large nails, and the wire twisted to them, as shown in
-Fig. 8. When the line is not in use the switches on both keys should be
-closed; otherwise it would be impossible for the boy having the closed
-switch to call up the boy with the open one. Take great care in wiring
-your apparatus to study the plan, for a misconnected wire will throw the
-whole system out of order.
-
-[Illustration: FIG. 7]
-
-To operate the line see that all switches are closed and that the
-connections are in good condition. When the boy in house No. 2 wants to
-call up his friend in house No. 1 he throws open the switchon key, as
-shown in the plan, and by pressing down on the finger-key his sounder
-and that in house No. 1 click simultaneously. As soon as he raises or
-releases the key the armatures rise, making the up-click. If he presses
-his key and releases it quickly the two clicks on the sounder in house
-No. 1 are close together; this makes what is called a dot. If the key is
-held down longer it makes a long time between clicks, and this is
-called a dash. The dot and dash are the two elements of the telegraphic
-code. You will understand that the boy in house No. 2 hears just what
-the one in No. 1 is hearing, since the electric current passing through
-both coils causes the magnets to act in unison. So soon as the operator
-in house No. 2 has finished he closes his switch, and the other in house
-No. 1 opens his switch on the key and begins his reply. This is the
-simple principle of the telegraph, and all the improved apparatus is
-based on it, no matter how complicated. The complete Morse alphabet is
-appended:
-
-[Illustration: =The Morse Telegraph Code=]
-
-Any persevering boy can soon learn the dot-and-dash letters of the Morse
-code, and very quickly become a fairly good operator. Telegraphic
-messages are sent and received in this way, and are read by the sound of
-the clicks. Various kinds of recording instruments are also employed, so
-that when an operator is away from his table the automatic recorder
-takes down the message on a paper tape. In the stock-ticker, employed in
-brokerage offices, the recording is done by letters and numerals, and
-the paper tape drops into a basket beside the machine, so that any one
-picking up the strip of paper can see the quotations from the opening of
-business up to the time of reading them. These quotations are sent out
-directly from the floor of the exchanges, and by the action of one man’s
-hand thousands of machines are set in operation all over the city.
-
-Perhaps the most unique and wonderful telegraphic signal-apparatus is
-that located on the floor of the New York Produce Exchange and the
-Chicago Exchange. The dials, side by side, are operated by direct wire
-from Chicago. When the New York operator flashes a quotation it appears
-simultaneously on the New York dial and simultaneously on the Chicago
-dial, and vice versa.
-
-Electrical instruments are not the only means by which the Morse
-alphabet may be transmitted, for in some instances instruments would be
-in the way, while in others the wires might be down and communication
-cut off.
-
-This is interestingly illustrated by an event in Thomas A. Edison’s
-life. When he was a boy and an apprentice telegraph operator on the
-Grand Trunk Line, an ice-jam had broken the cable between Port Huron, in
-Michigan, and Sarnia, in Canada, so that communication by electricity
-was cut off. The river at that point is a mile and a half wide, the ice
-made the passage impossible, and there was no way of repairing the
-cable. Edison impulsively jumped on a locomotive standing near the
-river-bank and seized the whistle-cord.
-
-He had an idea that blasts of the whistle might be broken into long and
-short sounds corresponding to the dots and dashes of the Morse code. In
-a moment the whistle sounded over the river: “Toot, toot, toot,
-toot,--toot, tooooot,--tooooot--tooooot--toot, toot--toot, toot.”
-“Halloo, Sarnia! Do you get me? Do you hear what I say?”
-
-No answer.
-
-“Do you hear what I say, Sarnia?”
-
-A third, fourth, and fifth time the message went across, to receive no
-response. Then suddenly the operator at Sarnia heard familiar sounds,
-and, opening the station door, he clearly caught the toot, toot of the
-far-away whistle. He found a locomotive, and, mounting to the cab,
-responded to Edison, and soon messages were tooted back and forth as
-freely as though the parted cable were again in operation.
-
-Some years ago the police of New York were mystified over a murder case.
-The man they suspected had not fled, but was still in his usual place,
-and attending to his business quite as though nothing had happened to
-connect him with the tragedy.
-
-Detectives in plain clothes had been following him and watching closely
-his every move in and out of restaurants and shops and at social
-affairs; but not the slightest proof could be secured against him.
-
-One noon-time they followed him into a café, where he had gone with a
-friend. The detectives took seats near him, but each of them sat at
-different tables in the room full of people.
-
-When in the café the suspect sat next the wall, a habit the detectives
-had noticed. Consequently, only those persons who sat at one side of him
-or directly in front could see his face. During the time they were in
-the restaurant the detectives communicated with each other by tapping on
-the table tops with a lead-pencil; and something the man said, which the
-nearest detective heard, led to the climax. One detective rose, paid his
-check, and loitered near the door; another got up a little later and
-sauntered out, but returned with a cardboard sign. Going over to the
-table where the suspected criminal and his friend sat, he deliberately
-tacked it on the wall above them, then went out again, leaving the third
-detective to watch the face of the man as he read:
-
-  $1000 REWARD
-  for information leading to the arrest of the murderer of ------------
-  on March --------, 1876
-
-The man cast a glance about the restaurant, then said to his companion:
-“Did I show any signs of agitation?” The third detective rose, stepped
-over to the man, tapped him on the shoulder, and said, “I want you.”
-There would have been a scene of violence had not the other two
-detectives closed in on the man, and within six months he paid the
-penalty of his crime.
-
-If it had not been for the dot-and-dash alphabet, tapped out with
-lead-pencils, the detectives could not have communicated; but like
-Edison, they used the means at hand to open up and carry on a silent
-conversation.
-
-
-Wireless Telegraphy
-
-Everybody nowadays understands that wireless telegraphy means the
-transmission of electrical vibrations through the ether and earth
-without the aid of wires or any visible means of conductivity. The feat
-of sending an electrical communication over thousands of miles of wire,
-or through submarine cables, is wonderful enough, for all that custom
-has made it an every-day miracle. To accomplish this same end by sending
-our messages through the apparently empty air is indeed awe-inspiring
-and almost beyond belief. And yet we know that wireless telegraphy is
-to-day a real scientific fact.
-
-At first sight it would seem that the instruments must be complicated
-and necessarily beyond the ability of the average boy to make, and far
-too expensive as well. As a matter of fact, the young electrician may
-construct his wireless apparatus at a very moderate cost, it being
-understood that the sending and receiving poles may be mounted on a
-housetop or barn.
-
-But first let us consider the theory upon which we are to work. There is
-no doubt but that electricity is the highest known form of vibration--so
-high, indeed, that as yet man has been unable to invent any instrument
-to record the number of pulsations per second. This vibration will occur
-in, and can be sent through, the ordinary form of conductor, such as
-metals, water, fluids and liquids, wet earth, air and ice. Also through
-what we call the ether.
-
-Now the ether of the atmosphere, estimated to be fifteen trillion times
-lighter than air, is the medium through which the electrical vibrations
-pass in travelling in their radial direction from a central point,
-corresponding to the ripples or wavelets formed when a pond or surface
-of still water is disturbed. Ether is so fine a substance that the
-organs of sense are not delicate enough to detect it, and it is of such
-a volatile and uneasy nature that it is continually in motion. It
-vibrates under certain conditions, and when disturbed (as by a dynamo)
-it undoubtedly forms the active principle of electricity and magnetism.
-
-James Clark Maxwell believed that magnetism, electricity, and light are
-all transmitted by vibrations in one common ether, and he finally
-demonstrated his theory by proving that pulsations of light,
-electricity, and magnetism differed only in their wave lengths. In 1887
-Professor Hertz succeeded in establishing proof positive that Maxwell’s
-theories were correct, and, after elaborate experiments, he proved that
-all these forces used ether as a common medium. Therefore, if it were
-not for the ether, wireless telegraphy, with all its wonders, would not
-be possible. We understand, then, that the waves of ether are set in
-motion from a central disturbing point, and this can be accomplished
-only by means of electrical impulse.
-
-Suppose that we strike a bell held high in the air. The sound is the
-result of the vibrations of its mass sending its pulsating energy
-through the air. The length of the sound-waves is measured in the
-direction in which the waves are travelling, and if the air is quiet and
-not disturbed by wind the sound will travel equally in all directions.
-The sound of a bell will not travel so well against a wind as it will
-with it, just as the ripples on a pond would be checked by an adverse
-set of wavelets.
-
-Now the ether can be made to vibrate in a similar manner to the air by a
-charge of electricity oscillating or surging to and fro on a wire
-several hundred thousand times in a second. These oscillations strike
-out and affect the surrounding ether, so that, according to the
-intensity of the disruptive charge at the starting-point, the ether
-waves may be made to reach near or distant points.
-
-This is, perhaps, more clearly shown by the action of a pendulum. In
-Fig. 9 the rod and ball are at rest, but if drawn to one side and
-released it swings over to the other side nearly as far away from its
-central position of rest as from the starting-point. If allowed to swing
-to and fro it will oscillate until at last it will come to rest in a
-vertical position. This same oscillation (oscillation being a form of
-vibration) takes place in the water when a stone has been flung into it,
-and in the ether when affected by the electrical discharge. In Fig. 10
-are shown the principal varieties of vibration--the oscillating,
-pulsating, and alternating.
-
-It is known that if these oscillations are damped, so that the
-over-intense agitation of the central disturbance is lessened, a new
-series of vibrations, such as the pulsating or alternating, is set up,
-and these secondary vibrations possess the power to travel around the
-world--yes, and perhaps to other worlds in the planetary cosmos.
-
-[Illustration: FIG. 9
-
-FIG. 10
-
-FIG. 11
-
-OSCILLATION AND VIBRATION]
-
-The study of ether disturbances, wave currents, oscillating currents,
-and the other phenomena dependant upon this invisible force is most
-interesting and fascinating, and were it possible to devote more space
-to this topic several chapters could be written on the scientific theory
-of wireless telegraphy.[2]
-
-  [2] For further information on this subject the student is referred to
-  such well-known books as _Signalling Across Space Without Wires_, by
-  Prof. Oliver J. Lodge, and _Wireless Telegraphy_, by C. H. Sewall.
-
-The principle difference between wire, or line, and wireless telegraphy
-is that the overhead wire, or underground or submarine cable, is
-omitted. In its stead the ether of the air is set in vibratory motion by
-properly constructed instruments, and the communication is recorded at a
-distance by instruments especially designed to receive the transmitted
-waves.
-
-It seems to be the popular impression that a wireless message sent from
-one point to another travels in a straight line, as indicated by Fig.
-11, B representing Boston, which receives the message from N. Y., or New
-York. As a matter of fact, if several sets of wireless receiving
-instruments were located on the circumference of a circle the same
-distance from New York in all directions, or even at nearer or farther
-points, they would all receive the same message. Instead of travelling
-in one direction, the ether waves are set in motion by the electrical
-disturbance, just as water is agitated by the stone thrown into it. The
-ripples, or wavelets, are started from the central point of disturbance
-and radiate out, so that instead of reaching Boston only the waves
-travel over every inch of ground, or air space, in all directions, and
-would be recorded in every town and village within the sphere of energy
-set up by the original force that put the ether waves in motion. The
-stronger this initial force the wider its field of action. This is shown
-at Fig. 12, which is an area comprising Philadelphia, Pittsburg,
-Buffalo, Washington, and other cities. Moreover, the waves of electrical
-disturbance would carry far beyond in all directions, taking in the
-cities of the north, south, and west, and at the east, going far out to
-sea, beyond Boston harbor and below Cape Hatteras, where ships carrying
-receiving instruments could pick up the messages. Like the ripples on
-the water, the radiating waves, or rings, become larger as they reach
-out farther and farther from the centre of disturbance, until at last
-they are imperceptible, and lose their shape and force.
-
-[Illustration: FIG. 12]
-
-At great distances, therefore, the ether disturbance becomes so slight
-that it is impossible to record the vibration or message sent out; and
-until some improved forms of apparatus and coherer are invented, or the
-original disturbing force is enormously increased, it will be impossible
-to send messages at longer distances than four or five thousand miles
-from a central point. Both Marconi and De Forrest assert that they are
-perfecting coherers which will make it possible to girdle the earth with
-a message, and that within the next few years an aerogram may be sent
-out from a station, and, after instantly encircling the earth and being
-recorded during its passage at all intermediate stations, it will return
-and be received at the original sending-point. This, of course, is a
-matter of future achievement; but now that messages across the Atlantic
-are a commercial fact, it seems quite possible that the greater feat of
-overriding space and reaching any point on the earth’s surface will soon
-be a reality. And now to proceed from theory to the construction of a
-practical wireless apparatus having a radial area of action over some
-ten or fifteen miles.
-
-The principal parts of a wireless apparatus include the antennas (or
-receiving and sending poles with their terminal connections), the
-induction-coil, strong primary batteries or dynamo, the coherer and
-de-coherer, the telegraph key and sounder (or a telephone receiver), and
-the necessary connection wires, binding-posts, and ground-plates.
-
-A large induction-coil with many layers of fine insulated wire will be
-necessary for the perfect operative outfit. The most practical coil for
-the amateur is a Ruhmkorff induction-coil. (See the directions and
-illustrations for constructing this coil, beginning on page 59 of
-chapter iv.)
-
-The sending apparatus is practically the same in all outfits, and
-consists of a source of electrical energy, such as a battery, or dynamo,
-the essential induction-coil and adjustable spark-gap between the brass
-balls on terminal rods, and the make-and-break switch, or telegraph-key.
-
-It is in the various forms of coherers and receiving apparatus that the
-different inventors claim superiority and originality. The systems also
-differ in their theory of harmonic tuning or vibratory sympathy. This is
-accomplished by means of coils and condensers, so that the messages sent
-out on one set of instruments will not be picked up or recorded by the
-receiving apparatus of competitors.
-
-Having made or purchased an induction-coil of proper and adequate size,
-it will now be necessary to construct the parts so that an adjustable
-spark-gap may be secured.
-
-Make a hollow wooden base for the induction-coil to rest on. It should
-be a trifle longer than the length of the coil and about seven inches
-wide. This may be made from wood half an inch thick. The base should be
-two inches high, so that it will be easy and convenient to make wire
-connections under it. Mount the induction-coil on the base and make it
-fast with screws, arranging it so that the binding-posts are on the side
-rather than at the top of the coil, as shown in Fig. 13.
-
-Cut a thin board and mount it across the top of the induction-coil on
-two short blocks, and to this attach two double-pole binding-posts (P
-P). The fine wires from the induction-coil are made fast to the foot of
-each post, and from the posts the aerial wire (A W) and ground wire (G
-W) lead out.
-
-Fasten two binding-posts at the forward corners of the base, and to them
-make connection-wires fast to the heavy or primary wires of the coil.
-Wires B and C lead out from these posts to the battery and key, and to
-complete this part of the sending, or transmitting apparatus it will be
-necessary to have two terminal rods and balls attached to the top of the
-binding-posts (P P). This part of the apparatus is generally called the
-oscillator, and the rods are balanced on the posts, so that they can be
-moved in order to increase or diminish the space (S G), or spark-gap,
-between the brass balls.
-
-When, after experiment, the proper space has been determined, the set
-screw at the top of the posts will hold the terminal rods securely in
-place.
-
-Obtain a piece of brass, copper, or German-silver rod three-sixteenths
-of an inch in diameter. Now cut two short rods, each six inches long,
-and two inches from one end flatten the rods with a hammer, as shown at
-A in Fig. 14. Flatten the rod in two places at the other end, as shown
-at B B in Fig. 14; then bore holes through the flattened parts (A), so
-that the binding-screws at the top of the posts (P P) will pass through
-them.
-
-Obtain two brass balls from one to one inch and a half in diameter. If
-they are solid or cast brass they may be attached to the ends of the
-terminal rods by threading, so that it will be easy to remove them. If
-the balls are of spun sheet-metal it will be necessary to solder them
-fast to the ends of the rods, and, when polishing the balls, the rods
-will have to be removed from the binding-posts. It is imperative that
-the balls should be kept polished and in bright condition at all times,
-to facilitate the action of the impulsive sparks.
-
-[Illustration: FIG. 13]
-
-[Illustration: FIG. 14]
-
-To counterbalance these balls there should be handles at the long ends
-of the rods. These handles may be of wood, or made of composition molded
-directly on the rods. A good composition that can be easily made and
-molded is composed of eight parts plaster of Paris and two parts of
-dextrin made into a thick paste with water. The dextrin may be purchased
-at a paint-store, and is the color of light-brown sugar. Mix the dry
-plaster and dextrin together, so that they are homogeneous; then add
-water to make the pasty mass. Use an old table-knife to apply the wet
-composition to the bars. The flattened parts will help to hold the mass
-in place until it sets. It is best to make two mixtures of the paste and
-put one on first, leaving it rough on the surface, so that the last coat
-will stick to it. When the last coat is nearly dry it may be rubbed
-smooth with the fingers and a little water, or allowed to dry hard, and
-then smoothed down with an old file and sand-paper.
-
-If solid brass balls are used for the terminals the composition handles
-may be made heavier; but in any event the proper amount of composition
-should be used, so that when the rod is balanced on a nail or piece of
-wire passed through the hole it will not tip down at one end or the
-other, but will remain in a horizontal position.
-
-The overhead part of the apparatus employed to collect the electric
-waves is called the antennæ, and in the various commercial forms of
-wireless apparatus this feature differs. The general principle, however,
-is the same, and in Figs. 15, 16, 17, and 18 some simple forms of
-construction are shown.
-
-Great care must be taken to properly insulate the rod, wire, or fingers
-of these antennæ, so that the full force of the vibration is carried
-directly down to the coherer and sounder or receiver. For this purpose,
-porcelain, glass, or gutta-percha knobs must be employed.
-
-In Fig. 15 the apparatus consists of an upright stick, a cross-stick,
-and a brace, or bracket, to hold them in proper place.
-
-Porcelain knobs are made fast to the sticks with linen string or stout
-cotton line. Then an insulated copper wire is run through the holes in
-the knobs, and from the outer knob a rod of brass, copper, or
-German-silver, or even a piece of galvanized-iron lightning-rod, is
-suspended. Care should be taken to see that the joint between rod and
-wire is soldered so as to make perfect contact. Otherwise rust or
-corrosion will cause imperfect contact of metals, and interrupted
-vibrations would be the result. The upright stick should be ten or
-fifteen feet high, and may be attached to a house-top, a chimney, or on
-the corner of a barn roof.
-
-Another form of single antenna is shown in Fig. 16. This is a rod held
-fast in a porcelain insulator with cement. The insulator, in turn, is
-slipped over the end of a staff, or pole, which is erected on a building
-top or out in the open, the same as a flag-pole. Near the foot of the
-rod, and just above the insulator, a conducting-wire is made fast and
-soldered. This is run down through porcelain insulators to the
-apparatus.
-
-If the pole is erected on a house-top it may be braced with wires, to
-stay it, but care must be taken not to have these wires come into
-contact with the rod, or conducting-wire.
-
-[Illustration: FIG. 15
-
-FIG. 16
-
-FIG. 17
-
-FIG. 18
-
-TYPES OF ANTENNÆ]
-
-Another form of antennas is shown in Fig. 17, where rods are suspended
-from a wire which, in turn, is drawn taut between two insulators. The
-insulators are held in a framework composed of two uprights and a
-cross-piece of wood.
-
-This frame may be nailed fast to a chimney and to the gable of a roof,
-as shown in the drawing; and to steady the rods, so that they will not
-swing in a high wind, the lower ends should be tied together with cotton
-string, the ends of which should be fastened to the uprights. The
-leading-in wire is made fast to the top wire, from which the rods are
-suspended, and all the exposed joints should be soldered to insure
-perfect contact and conductivity. A modified form of the Marconi antennæ
-is shown in Fig. 18. This is made of a metal hoop three of four feet in
-diameter held in shape by cross-sticks of wood, which can be lashed fast
-to the ring. Leading down from it are numerous copper wires which
-terminate in a single wire, the whole apparatus resembling a funnel. The
-upper unions where the wires join the ring need not be soldered, but at
-the bottom, where they all come together and join the leading-in wire,
-it is quite necessary that a good soldered joint be made. This funnel
-may be hung between two upright poles on a house-top, or suspended from
-the towers or chimneys.
-
-Almost any metal plate will do for the ground, or the ground-wire (G W
-in Fig. 13) may be bound to a gas or water pipe which goes down deep in
-the ground, where it is moist. Rust or white lead in the joints of
-gas-mains sometimes prevent perfect contact, but in water-pipes the
-current will flow readily through either the metal or the water. To
-insure the most perfect results, it is best to have an independent
-ground composed of metal, and connected directly with the oscillator, or
-coherer, by an insulated copper wire. A simple and easily constructed
-ground is a sheet of metal, preferably copper, brass, or zinc, to the
-upper edge of which two wires are soldered, as shown in Fig. 19. This is
-embedded in the ground three or four feet below the surface. Another
-ground-plate is a sheet of metal bent in [V] shape and then inverted.
-Two wires are soldered to the angle, and the ends brought together and
-soldered. This ground is buried three or four feet deep, and stands in a
-vertical position, as shown at Fig. 20. At Fig. 21 a flat ground is
-shown. This is a sheet of metal cut with pointed ends. The ground-wire
-is soldered to the middle of it, and it is then buried deep enough to be
-embedded in moist earth.
-
-One of the best grounds is an old broiler with a copper wire soldered to
-the ends of the handles, as shown at Fig. 22. This is buried deep in the
-ground in a vertical position, and the insulated copper wire is carried
-up to the instruments.
-
-The most important part of the wireless telegraphic apparatus is now to
-be constructed, and this requires some care and patience. The coherer is
-the delicate, sensitive part of the apparatus on which hinges success or
-failure. There are various kinds of coherers designed and used by
-different inventors, but while the materials differ and the construction
-takes various forms, the same basic principle applies to all.
-
-[Illustration: FIG. 19
-
-FIG. 20
-
-FIG. 21
-
-FIG. 22
-
-TYPES OF GROUNDS]
-
-The coherer can best be explained as a short glass tube in which iron or
-other metallic filings are enclosed. Corks are placed in both ends of
-the tube, and through these corks the ends of wire are passed, so that
-they occupy the position shown in Fig. 23, the ends being separated a
-quarter of an inch. Metal filings will not conduct an electric current
-the same as a solid rod or bar of the same metal, but resist the passage
-of current.
-
-After long periods of experimenting with various devices to detect the
-presence of feeble currents, or oscillations, in the ether, the coherer
-of metal filings was adopted. When the oscillations surge through the
-resonator, the pressure, or potential, finally breaks down the air film
-separating the little particles of metal, and then gently welds their
-sharp edges and corners together so as to form a conductor for the
-current. Before this process of cohesion takes place these fine
-particles offer a very high resistance to the electrical energy
-generated by a dry cell or battery--so much so that no current is
-permitted to pass. But once the oscillations in the ether cause them to
-cohere--presto! the resistance drops from thousands of ohms to hundreds,
-and the current from the dry cell now flows easily through the coherer
-and deflects the needle of a galvanometer. This is the common principle
-of all coherers of the granulated metal type, although there are many
-modifications of the idea.
-
-The action of the electric and oscillatory currents on particles of
-metal can best be understood by placing some fine iron filings on a
-board, as shown at Fig. 24, and then inserting the aerial and ground
-wires in the filings, but separated by an eighth or a quarter of an
-inch. A temporary connection may be made as shown in Fig. 25.
-
-[Illustration: FIG. 23]
-
-[Illustration: FIG. 26]
-
-[Illustration: FIG. 27]
-
-[Illustration: FIG. 24]
-
-[Illustration: FIG. 25]
-
-A A are aerials on both instruments; C is the open coherer, or board
-with iron filings, in which the ends of the aerial and ground wires are
-embedded; D C is a dry cell; and R is a telegraphic relay, or sounder.
-If the wire across C was not parted and covered with filings, the dry
-cell would operate R, but the high resistance of the particles of metal
-holds back the current.
-
-On the opposite side, I C is the induction-coil; K is the telegraphic
-key, or switch, which makes and breaks the current; S B is the
-storage-batteries, or source of electric energy; and S G the spark-gap
-between the brass balls on the terminal rods. By closing the circuit at
-K the current flows through the primary of the induction-coil, affects
-the secondary coil, and causes a spark to leap across the gap between
-the brass balls. This instantly sets the ether in motion from A on the
-right, and the impulse is picked up by A on the left. This oscillation
-breaks down the resistance of the filings at C, and the current from
-battery, or dry cell (D C), flows through the filings and operates the
-sounder, or relay (R). This operation takes place instantly, and the
-particles of metal are seen to cohere, or shift, so that better contact
-is established. But as soon as the spark has jumped across the gap the
-action of cohesion ceases until the key (K) is again operated to close
-the circuit and cause another spark to leap across the gap. The shifting
-of the metal particles on the board (C) is what takes place in the glass
-tube of the coherer, Fig. 23, but in this confined space the particles
-will not drop apart again as on the flat surface, but will continue to
-cohere. A de-coherer is necessary, therefore, to knock the particles
-apart, so that the next oscillatory impulse will have a strong and
-individual effect. There are several forms of de-coherers in use, but
-for the amateur telegrapher an electric-bell movement without the bell,
-or, in other words, a buzzer with a knocker on the armature, will answer
-every purpose. (See description of buzzer on page 64.) It must be
-properly mounted, so that on its back stroke, or rebound, the knocker
-will strike the glass tube and shake the particles of metal apart. For
-this purpose the vibrations of the armature should be so regulated as to
-obtain the greatest possible speed, in order that the dots and dashes
-(or short and long periods) will be accurately recorded through the
-coherer and made audible by the sounder or telephone receiver.
-
-Another form of coherer is shown in Fig. 26. This is made of a small
-piece of glass tube, two rods that will accurately fit in the tube, some
-nickel filings, two binding-posts, and a base-block three inches and a
-half long. The two binding-posts are mounted on the block, and through
-the holes in the body of the posts the rods are slipped. They pass into
-the tube, and the blunt ends press the small mass of filings together,
-as shown in the drawing. By means of the binding-posts these
-coherer-rods may be held in place and the proper pressure against the
-filings adjusted; then maintained by the set-screws. The nickel filings
-may be procured by filing the edge of a five-cent piece. Obtain a few
-filings from the edge of a dime and add them to the nickel, so that the
-mixture will be in the proportion of one part silver to nine parts
-nickel. This mixture will be found to work better than the iron filings
-alone. The aerial and ground wires are made fast to the foot-screws of
-the binding-posts, and the base on which the coherer is mounted may be
-attached to a table or ledge on which the other parts of the receiving
-and recording apparatus are also installed.
-
-Another form of coherer is shown at Fig. 27. This is constructed in a
-somewhat similar manner to the one just described. A glass tube is
-provided with two corks having holes in them to receive the
-coherer-rods. Two plugs of silver are arranged to accurately fit within
-the tube, and into these the ends of the coherer-rods are screwed or
-soldered. Between these silver plugs, or terminals, the filings of
-nickel and silver are placed, and the rods are pushed together and
-caught in the binding-posts. The aerial and ground wires are made fast
-to the foot-screws of the posts.
-
-For long-distance communication it is necessary to have a condenser
-placed in series with the sparking or sending-out apparatus. (See the
-type of condenser described and illustrated in chapter iv., page 72.)
-
-An astatic galvanometer is also a valuable part of the receiving
-apparatus, and the one described on page 111 will show clearly the
-presence of oscillatory currents by the rapid and sensitive deflections
-of the needle.
-
-For local service, where a moderately powerful battery is employed, a
-telegraph-key, such as described on page 190, will answer very well, but
-for high-tension work, where a powerful storage-battery or small dynamo
-is employed, it will be necessary to have a non-sparking key, so that
-the direct current will not form an arc between the terminals of a key.
-Most of the keys used for wireless telegraphy have high insulated
-pressure-knobs, or the make and break is done in oil, so that the spark
-or arc cannot jump or be formed between the points.
-
-The plan of a simple non-sparking dry switch is shown at Fig. 28. This
-is built up on a block three inches wide and five inches long. It
-consists of a bar (A), two spring interrupters (B and C), a spring (D),
-and the binding-posts (E E). They are arranged as shown in Fig. 28, and
-a front elevation is given in Fig. 29. The strip (B) lies flat on the
-block, and is connected with one binding-post by a wire attached under
-one screw-head and run along the under side of the base in a groove to
-the foot of the post. Strip C is of spring-brass, and is made fast to
-the base with screws. This is “dead,” as no current passes through it,
-and its only use is to interrupt. The bar (A) is arranged as explained
-for the line telegraph-key, and the remaining binding-post is connected
-to it by a wire run under the base and brought up to one of the
-angle-pieces forming the hinge. A high wood or porcelain knob is made
-fast at the forward end of the bar, so that when high-tension current is
-employed the spark will not jump from the bar to the operator’s hand.
-The complete key ready for operation is shown at Fig. 30, and to make it
-permanent it should be screwed fast to the table, or cabinet, on which
-the coil and condenser rest. The plan of a “wet” key is shown in Fig.
-31, and the complete key in Fig. 32.
-
-[Illustration: FIG. 28
-
-FIG. 29
-
-FIG. 30
-
-FIG. 31
-
-FIG. 32
-
-DRY AND WET NON-SPARKING SWITCHES]
-
-A base of wood three by five inches is made and given several coats of
-shellac. Obtain a small rubber or composition pill or salve box, and
-make it fast to the front end of the base with an oval-headed brass
-screw driven down through the centre of the box. A wire leading to one
-binding-post is arranged to come into contact with the screw, and the
-other post is connected by wire to one hinge-plate supporting the bar.
-The long machine screw, or rivet, passed down through the knob and into
-the bar, extends down below the bar for half an inch or more, so that
-when the knob is pressed down the end of the screw, or rivet, will
-strike the top of the screw at the bottom of the box without the bar
-coming in contact with the edge of the box. When in operation the
-composition box is filled with olive oil or thin machinery oil, so that
-when contact is made by pressing the knob down the circuit will be
-instantly broken, the spring at the rear end of the bar drawing it back
-to rest. The oil prevents any sparks jumping across; and also breaks an
-arc, should one form between the contact-points. With the addition of a
-good storage-battery (the strength of which must be governed by the size
-of the induction-coil and the distance the messages are sent) and a
-dry-cell or two for the receiving apparatus, the parts of the wireless
-apparatus are now ready for assembling. Full directions for making
-storage-cells is given in chapter ii., page 21, and for dry-cells in
-chapter ii., page 29. For short-distance work the plan shown in Figs. 33
-and 34 will be found a very satisfactory form of apparatus. One of each
-kind of instrument should be at every point where communication is to be
-established.
-
-In the sending apparatus (Fig. 33) S C are the storage-cells, K the key,
-and I C the induction-coil. T T are the terminals and balls, S G the
-spark-gap, and P P the posts that hold the terminal rods. A W is the
-aerial wire running up from one post, and G W the ground-wire connecting
-the other terminal post with the ground-plates.
-
-In the receiving apparatus (Fig. 34) C is the coherer, D C the
-de-coherer, T S the telegraphic sounder, or relay, and A G the astatic
-galvanometer. B is the dry-cell, or battery, and D C S the de-coherer
-switch, so that when the apparatus is not in use the dry-cell will not
-operate the buzzer or de-coherer. A W is the aerial wire and G W the
-ground-wire. Two or more storage-cells may be connected in series (that
-is, the negative of one with the positive pole of the other) until a
-sufficiently powerful source of current is secured for the transmission
-of messages.
-
-[Illustration: FIG. 33]
-
-[Illustration: FIG. 34]
-
-To operate the apparatus, the circuit is closed with K, and the current
-from S C flows around the primary coil in I C and affects the secondary
-coil, causing the spark to leap across the gap (S G). This causes a
-disturbance through the wires A W and G W, and the ether waves are set
-in oscillatory motion from the antennæ on the house-top. This affects
-the antennæ at the receiving-point, and the impression is recorded
-through the coherer (C) on the telegraphic sounder or relay (T S), which
-is operated by the current from dry-cell or battery (B), since the
-oscillations have broken the resistance of the filings in the coherer
-(C). The instant that the current passes through the coherer and
-operates T S, the astatic galvanometer indicates the presence of current
-by the deflected needle.
-
-[Illustration: FIG. 35]
-
-When the apparatus is in operation D C S is closed, so that the current
-from B operates the coherer (D C). Directly communication is broken
-off, the switch (D C S) should be opened; otherwise the buzzer would
-keep up a continuous tapping. For long-distance work a more efficient
-sending apparatus is shown in Fig. 35. This is composed of an
-induction-coil, with the terminal rods and brass balls forming the
-spark-gap, an oil key (K), and three or more large storage-cells, or a
-dynamo (if power can be had to run it). A condenser is placed in
-connection with the aerial and ground wires, so that added intensity or
-higher voltage is given the spark as it leaps across the gap. In
-operation this apparatus is similar to the one already described. Where
-contact is made with K the primary coil is charged, and by induction the
-current affects the secondary coil, the current or high voltage from
-which is stored in the condenser. When a sufficient quantity is
-accumulated the spark leaps across S G and affects wires A W and G W.
-This action is almost instantaneous, and directly the impulse sets the
-ether in motion the same impulse is recorded on the distant coherers and
-sounders.
-
-There are a great many modifications of this apparatus, but the
-principles are practically the same, and while the construction of this
-apparatus is within the ability of the average boy, many of the more
-complicated forms of coherers and other parts would be beyond his
-knowledge and skill. Marconi has realized his ambition to send messages
-across the ocean without wires, and is now doing so on a commercial
-basis, and at the rate of twenty-five words a minute. It is but the next
-step to establish communication half-way around the world, and finally
-to girdle the earth.
-
-
-Chapter X
-
-DYNAMOS AND MOTORS
-
-To adequately treat of dynamos and motors, a good-sized book rather than
-this single chapter would be necessary, and only a general survey of the
-subject is possible. Its importance is unquestionable; indeed, the whole
-science of applied electricity dates from the invention of the dynamo.
-Without mechanical production of electricity there could be no such
-thing as electric traction, heat, light, power, and electro-metallurgy,
-since the chemical generation of electricity is far too expensive for
-commercial use. Surely it is a part of ordinary education nowadays to
-have a clear and definite idea of the principles of electrical science,
-and in no department of human knowledge has there been more constant and
-rapid advance. It is only a truism to assert that the school-boy of
-to-day knows a hundredfold more about electricity and its varied
-phenomena than did the scientists and philosophers of old--Volta and
-Galvani and Benjamin Franklin. Yet it was for these forerunners to open
-and blaze the way for others to follow. A beginning must always be made,
-and the Marconis and Edisons of to-day are glad to acknowledge their
-indebtedness to the experimenters and inventors of the past. And now to
-our subject.
-
-All dynamos are constructed on practically the same principle--a field
-of force rapidly and continuously cutting another field of force, and so
-generating electric current. The common practice in all dynamos and
-motors is to have the armature fields revolve within, or cut the forces
-of the main fields of the apparatus. There are many different kinds of
-dynamos generating as many varieties of current--currents with high
-voltage and low amperage; currents with low voltage and high amperage;
-currents direct for lighting, heating, and power; currents alternating,
-for high-tension power or transmission, electro-metallurgy, and other
-uses. It is not the intention in this chapter to review all of these
-forms, nor to explain the complicated and intricate systems of winding
-fields and armatures for special purposes. Consequently, only a few of
-the simpler forms of generators and motors will be here described,
-leaving the more complex problems for the consideration of the advanced
-student. For his use a list of practical text-books is appended in a
-foot-note.[3]
-
-  [3] _First Principles of Electricity and Magnetism_, by C. H. W.
-  Biggs; _The Dynamo: How Made and Used_, by S. R. Bottone; _Dynamo
-  Electric Machinery_, by Professor S. P. Thompson; _Practical Dynamo
-  Building for Amateurs_, by Frederick Walker.
-
-
-The Uni-direction Dynamo
-
-The uni-direction current machine is about the simplest practicable
-dynamo that a boy can make. It may be operated by hand, or can be run by
-motive power. The field is a permanent magnet similar to a horseshoe
-magnet. This must be made by a blacksmith, but if a large parallel
-magnet can be purchased at a reasonable price so much the better, as
-time and trouble will be saved. This magnet should measure ten inches
-long and four inches and a half across, with a clear space seven inches
-long and one inch and three-quarters wide, inside measure. The metal
-should be half an inch thick and one inch and a quarter wide. A
-blacksmith will make and temper this magnet form; then, if there is a
-power-station near at hand where electricity is generated for traction
-or lighting purposes, one of the workmen will magnetize it for you at a
-small cost; or it can be wound with several coils of wire, one over the
-other, and a current run through it. When properly magnetized it should
-be powerful enough to raise ten pounds of iron. This may be tested by
-shutting off the current and trying its lifting power. If the magnet is
-too weak to attract the weight the current should be turned on and
-another test made a few minutes later.
-
-Before the steel is tempered there should be four holes bored in the
-magnet and countersunk, so that screws may be passed through it and into
-the wooden base below, as shown at Fig. 1. This wooden base is fourteen
-inches long, eight inches wide, and one inch in thickness. It may be
-made of pine, white-wood, birch, or any good dry wood that may be at
-hand. The blocks on which the magnet rests are an inch and a quarter
-square and seven inches long. The magnet is mounted directly in the
-middle of the base, an equal distance from both edges and ends, as shown
-in the plan drawing (Fig. 10). The blocks are attached with glue and
-brass screws driven up from the underside of the base.
-
-From a brass strip three-eighths of an inch wide and one-eighth of an
-inch thick cut a piece six inches long, and bore holes at either end
-through which long, slim, oval-headed brass screws may pass. Use brass,
-copper, or German-silver for this bar, and not iron or steel. To the
-underside, and at the middle, solder or screw fast a small block of
-brass, through which a hole is to be bored for the spindle or shaft.
-This finished bar is shown in Fig. 2. When mounted over the magnet and
-held down with brass screws driven into the wood base, its end view will
-appear as shown in Fig. 3, A being the bar, B B the screws which hold it
-down, D the base into which they are driven, and C C the blocks under
-the magnet (N S). The object of this bar is to support one end of the
-armature shaft. From brass one-eighth of an inch thick bend and form two
-angles, as shown at Fig. 4. Two holes for screws are to be drilled in
-the part that rests on the base, and one hole, for the shaft to pass
-through, is bored near the top of the upright plate. The centre of this
-last hole must be the same height from the base as is the hole in the
-bar (Fig. 2) when mounted over the magnet, as shown at Fig. 3. The
-location of these plates is shown in the plan (Fig. 10). There is one
-plate at each end of the base, as indicated at B and B B, the shaft
-passing through the hole in the brass block at the underside of the bar
-(C). These angles are the end-bearings for the armature shaft, and
-should be accurately centred so that the armature will be properly
-centred between the N and S bars of the magnet.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-FIG. 7
-
-FIG. 8
-
-FIG. 9
-
-DETAILS OF UNI-DIRECTION DYNAMO]
-
-The armature is made from soft, round iron rod one inch and a half in
-diameter and five inches long. A channel is cut all around it,
-lengthwise, five-eighths of an inch wide and half an inch deep, as shown
-in Fig. 5. This will have to be done at a machine-shop in a short
-bed-planer, since it would be a long and tedious job to cut it out with
-a hack-saw. The sharp corners should be rounded off from the central
-lug, so that they will not cut the strands of fine wire that are to be
-wound round it.
-
-Two brass disks, or washers, are to be cut, one inch and a half in
-diameter and from one-eighth to one-quarter of an inch thick, for the
-armature ends. A quarter-inch hole is to be made in the centre of each
-for the shaft to fit in, and two smaller holes must be drilled near the
-edge, and opposite each other, so that machine-screws may pass through
-them and into holes bored and threaded in the ends of the armature, as
-shown at Fig. 5. These ends will appear as shown at Fig. 6, and the
-middle hole should be threaded so as to receive the end of a shaft. When
-the shaft is screwed in tight the end that passes through the brass disk
-must be tapped with a light hammer to rivet the end, and so insure that
-the shaft will not unscrew.
-
-The shafts should be of hard brass or of steel. The one at the front
-should be one inch and a half in length, and that at the rear six inches
-long, measuring from the outer face of the brass end to the end of the
-shaft. From boxwood or maple turn a cylinder three-quarters of an inch
-in diameter and an inch long, with a quarter-inch hole through it. Over
-this slip a piece of three-quarter-inch brass or copper tubing that fits
-snugly, and at opposite sides drill holes and drive in short screws that
-will hold the tube fast to the hub. They must not be so long as to reach
-the hole through the centre. Place this hub in a vise, and with a
-hack-saw cut the tube across in two opposite places, so that you will
-have the cylinder with two half-circular shells or commutators screwed
-fast to it, as shown at Fig. 7. This hub will fit over the shaft at the
-front end of the armature, and will occupy the position shown at F in
-Fig. 10.
-
-Cut two small blocks of wood for the brushes and binding-posts, and bore
-a hole through them, so that the foot-screw of a binding-post may pass
-through the block and into the post, as shown at Fig. 8. From thin
-spring copper cut a narrow strip and bend it over the block, catching it
-at the top with a screw and lapping it under the binding-post at the
-outside.
-
-From boxwood or maple have a small wooden pulley turned, with a groove
-in it and a quarter-inch hole through the centre. This pulley should be
-half an inch wide and one inch and a half in diameter, as shown at Fig.
-9. This is to be attached at the end of the long shaft, where it will
-occupy the position shown at E in Fig. 10.
-
-All the parts are now ready for assembling except the armature, which
-must be wound. Before laying on the turns of wire the channel in the
-iron must be lined with silk, held in place with glue or shellac. A band
-of silk ribbon is given two turns about the centre of the iron, and the
-sides are so completely covered with silk that not a single strand of
-wire will come into direct contact with the iron. Great care must be
-taken, when winding on the wire, not to kink, chafe, or part the
-strands. The channel should be filled but not overcrowded, and when full
-several wraps of insulating tape should be made fast about the armature
-to hold the wire firmly in place and prevent it from working out at the
-centre when the armature is driven at high speed. The armature, when
-properly wound and wrapped, will appear as shown at A in Fig. 11, and it
-is then ready to have the ends screwed on. Several sizes of wire may be
-used to wind the armature, according to the current desired, but for
-general use it would be well to use No. 30 silk-insulated copper wire.
-
-[Illustration: FIG. 10
-
-FIG. 11
-
-PLAN OF THE UNI-DIRECTION DYNAMO]
-
-About four ounces should be enough for this armature, and the ends are
-to be passed through small holes in the brass end (B); see Fig. 11. One
-end must be soldered to one commutator, the other end to the other
-commutator. The end-piece (B) is attached to the iron armature (A) with
-machine-screws; then C is to be made fast in a similar manner.
-
-When putting the parts together, it would be well to use some shellac on
-the wooden cylinder and driving-wheel to make them hold to the shaft.
-
-By following the plan in Fig. 10, it will be an easy matter to put the
-parts together; when they are assembled the complete machine will appear
-as shown in the drawing (Fig. 12).
-
-The driving-wheel should be of wood five-eighths of an inch thick and
-six inches in diameter, and held in the frame of wood and metal brackets
-by a bolt. A short handle can be arranged with which to turn the wheel,
-and a small leather belt will transmit the power to the small wheel on
-the armature shaft. As the armature is revolved the lines of force are
-cut and the current is carried out through the wire attached to the
-binding-posts on the blocks (G G).
-
-[Illustration: FIG. 12]
-
-Considerable current may be generated if the armature is driven at
-higher speed than the hand-wheel will cause it to revolve. This can be
-accomplished by running the belt over a larger wheel, such as the
-fly-wheel of a sewing-machine, or connecting it to a large pulley on a
-water-motor. The latter may be attached to a faucet in the wash-tub if
-there is pressure enough to do the work.
-
-
-A Small Dynamo
-
-All dynamos are constructed on the same general principle as that of the
-uni-direction machine just described; but they differ in their windings,
-the quantities of metal electrified, the sizes and lengths of wire wound
-on both armature and field, and in their shape and speeds.
-
-In large dynamos it is impossible to employ steel magnets of the
-required size. In place of them soft iron cores are used and magnetized
-by external electric current; or the wiring is done in “series” or
-“shunt,” so that the fields will be self-exciting once the machine has
-been properly started.
-
-The principal difference in dynamos is, perhaps, more clearly
-illustrated by the diagrams shown in Figs. 13, 14, 15, and 16. In Fig.
-13 the arrangement of armature and field-magnet is the same as in the
-uni-direction machine, the field (F) being of magnetized steel, while
-the armature (A) is of soft iron wound with coils of fine wire, the ends
-of which are brought out at the commutators (C), through which the
-current is carried to the brushes (B and B B). If, however, the soft
-iron cores are used, a separate magnetizing electric current must be
-passed through the coils of wire wound about the field-pieces, so that
-they will become temporary magnets--the same as the cores of an electric
-bell movement, a telegraph-sounder, or the induction-coil core when a
-current is passed through the primary coil. The armature (A) is then
-driven at high speed by power, and the current is taken off for use
-through wires that lead from B and B B.
-
-In all of these figures the armatures rotate, in the space between the
-large pole-pieces of the field-magnets, in the same direction as the
-hands of a clock move. In these figure drawings the field-magnets,
-commutators, and brushes only are shown, the armature being indicated by
-the circle (A).
-
-Figure 13 represents a dynamo, the field-magnets of which are excited by
-a separate battery or generator. This is known as a “separately excited”
-machine, and is employed for various uses. The brushes (B and B B) are
-connected to the external circuit--that is, with the motor or other
-apparatus for which current is to be generated. The magnetic field in
-which the armature rotates will be constant if the exciting current is
-constant, like the magnetism in the magnet of the uni-direction current
-machine.
-
-The induced electro-motive force (which depends upon the rate at which
-the lines of force are cut) will be constant for the given speed at
-which the armature rotates. This action is the same as that described
-for the uni-direction current machine.
-
-Figure 14 is the diagram of a “series”-wound dynamo. The field and
-armature are soft gray iron, and are wound in series--that is, one end
-of the magnet-winding is made fast to the brush B, the other to the
-brush B B, and the apparatus to be operated by the current is let in
-between B B and the magnet, as shown by the indicated electric arc-light
-in the illustration. The field-magnet coils, the armature, and the
-external conductors are in series with each other, forming a simple
-circuit. When the armature is driven at high speed the field-magnets
-become self-exciting, with the result that current is generated. Its
-simple course is through B B to commutators on the hub, thence through
-one winding on the iron armature A, to B, through field F, and back to B
-B again, operating in its course any pieces of equipment designed for
-electric impulse, such as motors, or lamps, trolley-cars, trains, or
-electric machinery.
-
-[Illustration: FIG. 13]
-
-[Illustration: FIG. 14]
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-The third type, shown in Fig. 15, is known as “shunt”-winding. The
-field-magnet coils and the external resistance are in parallel, or shunt
-with each other, instead of in series. The brushes are connected with
-the external circuit, and also with the ends of the field-magnet coils.
-This is clearly shown in the drawing. The ends of the field-coils are
-connected with brushes B and B B, and the external circuit wires are
-connected also with the same brushes, and pass down to such an apparatus
-as a plating bath, in which the current runs through the electrode, the
-electrolyte, and the cathode, most of the current generated passing
-through the external circuit. The field-coils are of fine wire, and when
-the armature is rotated there will always be a current through the
-field-magnets, whether the external circuit is complete or not. If a
-break occurs in the external circuit, a more powerful current will
-consequently pass through the field-magnets.
-
-In Fig. 16 a “compound”-wound dynamo is shown. It is a combination of
-the series and the shunt machine. The field-magnet coils are composed of
-two sizes of wire. There are comparatively four turns of stout wire and
-many turns of fine wire, the ends of both being connected, as shown in
-the drawing. The stout wire leads out to lamps which are arranged in
-series, as shown at the foot of the drawing. The current developed by
-this dynamo is one of “constant potential,” and is used almost
-exclusively for incandescent lamps, the “constant” current from the
-series-wound machine being used for arc-lamps, power, and other
-commercial purposes.
-
-It will not be necessary to use the first or last systems, nor to
-experiment with the alternating current, with its phases and cycles. All
-that a boy wants is a good direct-current machine that will light lamps,
-run sewing-machines or motors, and furnish the power for long-distance
-wireless telegraphy and other apparatus requiring considerable current.
-
-To begin with, it would be better to make a small dynamo and study its
-principles as you progress; then it will be a great deal easier to
-construct a larger one. It will be necessary to have the iron parts made
-at a blacksmith-shop, since the various cutting, threading, and tapping
-operations call for the use of special iron-working tools. Soft iron
-should be used, and if a piece of cast-iron can be procured for the lugs
-or magnet ends it will give better service than wrought-iron.
-
-From three-quarter-inch round iron cut two cores, each three inches and
-a half long, and thread them at both ends, as shown at B B in Fig. 17.
-From band-iron five-eighths of an inch thick and one inch and a half
-wide cut a yoke (A), and bore the indicated holes two inches and
-three-quarters apart, centre to centre. These should be threaded so that
-the cores (B B) will screw into them. From a bar of iron cut off two
-blocks one inch and a half by one inch and a half by two inches for the
-lugs. Now, with a hack-saw and a half-round file, cut out one side of
-each lug, as shown at C. These lugs are to be bored and threaded at one
-end, so that they can be screwed on the lower ends of the cores (C C).
-
-For a larger dynamo the yoke should be made six inches long, one inch
-thick, and two inches and a half wide. The cores should be of one-inch
-iron pipe. These will be hollow, as shown at B B in Fig. 18. For the
-ends cast-iron blocks must be made or cast from a pattern two inches and
-three-quarters square and four inches high, as shown at C. The yoke (A)
-and the lugs (C) are bored and threaded to receive the one-inch pipe,
-and when set up this will constitute an iron field-magnet six inches
-wide, two inches thick, and nine inches high. This, if properly wound,
-should develop a quarter of a horse-power.
-
-[Illustration: FIG. 17]
-
-[Illustration: FIG. 18]
-
-[Illustration: FIG. 19]
-
-[Illustration: FIG. 20]
-
-[Illustration: FIG. 21]
-
-The parts shown in Fig. 17, when screwed together, will give you a
-field-magnet two by one and a half by five and three-quarter inches
-high, and will appear as shown in Fig. 19, A being the yoke at the top,
-B B the cores, C C the lugs, and D a strip of brass screwed fast across
-the back of the lugs (C C), and in which a hole is bored to act as a
-bearing for one end of the armature shaft. Between the lugs and the
-strip (D) fibre washers three-eighths of an inch in thickness are placed
-to keep the strip away from the lugs. A hole is bored directly through
-the middle of each lug, from front to rear, and it is threaded at each
-end so that a machine-screw will fit in it. The brass strip (D) is
-five-eighths of an inch wide, three-sixteenths of an inch thick, and
-four inches long. Copper or German-silver may be used in place of brass,
-but iron or steel must not be employed, since these metals are
-susceptible to magnetism. Two holes should be made in the bottom of
-each lug, and threaded, so that machine-screws may be passed through a
-wooden base and into them in order to hold the dynamo on the base.
-
-Figure 20 is an end view of the field-magnets showing the yoke at A, the
-core at B, the lug at C, and the bearing and binding-strip of yellow
-metal at D. Two blocks of hard-wood, an inch square and one inch and a
-half long, are cut and provided with holes, so that they can be fastened
-to the lugs C C with long, slim machine-screws, as shown at E E in Fig.
-21. This is a view looking down on the magnets, blocks, and straps.
-These blocks are to support the brushes and terminals, and should be
-linked across the face with a brass strap G, so that the other end of
-the armature shaft may be supported. Care must be taken, when setting
-straps D and G, to have them line. The holes, too, must be centred,
-since the armature must revolve accurately within the field-lugs (C C)
-without touching them, and there is but one-sixteenth of an inch space
-between them.
-
-From hard-wood half an inch in thickness cut a base, six by seven
-inches, and two strips an inch wide and five inches long. With glue and
-screws driven up from the underside of the strips fasten them to the
-base, as shown at Fig. 22. Then make the field-magnets fast to the base
-with long machine-screws, using washers under the heads at the underside
-of the base-board. The mounting should then appear as shown in Fig. 28.
-
-[Illustration: FIG. 28]
-
-From steel, half an inch in diameter, cut a shaft five inches long. Have
-it turned down smaller at one end for three-eighths of an inch, and at
-the other end for a distance of one inch and a half, as shown at Fig.
-23. This is for the armature, and it should fit between D and G in Fig.
-21, and should revolve easily in the holes cut to receive it in both
-straps, with not more than one-eighth of an inch play forward or
-backward. The long, projecting end should be at the rear, and should
-extend beyond strip D for three-quarters of an inch, so that the
-driving-pulley can be made fast to it.
-
-The armature is made up of segments or laminations of soft iron and
-insulated copper wire. The laminated armature works much better than
-does the solid metal ring or lug, and a pattern may be made from a piece
-of tin from which all the sections can be cut. With a compass, strike a
-two-inch circle on a clear piece of tin; then mark it off, as shown at
-Fig. 24, and cut it out with shears. The hole at the centre of the
-pattern need not be bored, but a small pinhole should be made so that a
-centre-punch can be used to indicate the middle of each plate for
-subsequent perforation. Ordinary soft band iron may be employed for this
-purpose, and the sections should not be more than one-sixteenth of an
-inch in thickness.
-
-It will take some time to cut out the required number of pieces for this
-small armature. When they are all ready they should be slipped over the
-shaft, and if they have been properly matched and cut, they should
-appear as a solid body, one inch and a half long.
-
-Arrange these laminations on the armature shaft so that when the shaft
-is in position the mass of iron will be within the lugs of the
-field-magnets. The holes through the iron plate should be so snug as to
-call for some driving to put them in place. Each disk of iron should be
-given a coat of shellac to insulate it, and between each piece there
-should be a thin cardboard or stout paper separator to keep the disks
-apart. These paper washers should be dipped in hot paraffine, or thick
-shellac may be used to obtain a good sticking effect and so solidify
-the laminations into a compact mass. When this operation is completed
-the armature core should appear as shown in Fig. 25.
-
-[Illustration: FIG. 22]
-
-[Illustration: FIG. 23]
-
-[Illustration: FIG. 24]
-
-[Illustration: FIG. 25]
-
-[Illustration: FIG. 26]
-
-[Illustration: FIG. 27]
-
-[Illustration: FIG. 29]
-
-[Illustration: FIG. 30]
-
-From maple, or other hard-wood with a close grain, make a cylinder
-three-quarters of an inch long and one inch in diameter to fit the
-shaft. Over this drive a piece of copper or brass tubing, and at four
-equal distances, near the rear or inner edge, make holes and drive
-small, round-headed screws into the wood. Then, with a hack-saw, cut the
-tube into four equal parts between the screws. This is the commutator.
-In order to hold the quarter circular plates fast to the cylinder,
-remove one screw at a time, and place thick shellac on the cylinder.
-Then press the plate firmly into place and reset the screw. Repeat this
-with the other three, and the armature will be ready for the winding.
-
-The voltage and amperage of a dynamo is reckoned by its windings, the
-size of wire, the number of turns, and the direction. This is a matter
-of figuring, and need not now concern the young electrician, since it is
-a technical and theoretical subject that may be studied later on in more
-advanced text-books.
-
-For this dynamo use No. 22 cotton-insulated copper wire for the
-armature, and No. 16 double cotton-insulated copper wire for the field.
-The armature, when properly wound and ready for assembling with the
-brushes and wiring, will appear as shown in Fig. 26.
-
-A small driving-wheel two inches in diameter and half an inch thick must
-now be turned from brass and provided with a V-shaped groove on its
-face. The hub, at one side, is fitted with a set-screw, so that it can
-be bound tightly on the shaft. This pulley is made fast to the shaft at
-the rear of the dynamo, and on the opposite end to where the commutator
-hub is attached.
-
-A diagram of the wiring is shown in Fig. 29, and in Fig. 30 the mode of
-attaching the ends of the coil wires to the commutators is indicated.
-Two complete coils of wire must be made about each channel of the
-armature, as illustrated on the drum of Fig. 30. These are separated by
-a strip of cardboard dipped in paraffine and placed at the centre of a
-channel while the winding is going on. In some armatures the coils are
-laid one over the other; but with this construction, and in the case of
-a short-circuit, a broken wire, or a burn-out, it is impossible to reach
-the under coil without removing the good one.
-
-Begin by attaching one end of the fine insulated wire to commutator No.
-1; then half fill the channel, winding the wire about the armature, as
-indicated in Fig. 30. When the required number of turns has been made,
-carry the end around the screw in commutator No. 2, baring the wire to
-insure perfect contact when caught under the screw-head. From No. 2
-carry the wire around through the channel at right angles to the first
-one, and after half filling it bring the end out to commutator No. 3.
-Carry the wire in again and fill up the other half of the first channel,
-and bring the end out to commutator No. 4. Fill up the remaining half of
-the second channel; then attach the final end to commutator No. 1, and
-the armature winding will be complete without having once broken the
-strand of wire.
-
-To keep the coils of wire in place, and to prevent them from flying out,
-under the centrifugal force of high speed, it would be well to bind the
-middle of the armature with wires or adhesive tape.
-
-After driving down the small screws over the leading-in and leading-out
-wires the armature will be ready to mount in the bearings. As the blocks
-that support the brushes and binding-posts partly close the opening to
-the cavity at the front, the armature will have to be inserted from the
-back into the strip (G) in Fig. 21. Then the back strip (D) is screwed
-in place. The armature, when properly mounted, should revolve freely and
-easily within the field-lugs without friction, and the lugs must by no
-means touch the armature. From thin spring-copper brushes may be cut and
-mounted on the block under the binding-posts, so that one will rest on
-top of the commutators while the other presses up against the underside.
-The wiring is then to be placed on the field-magnets. This is carried
-out as described for the electric magnets on pages 54-58 of chapter iv.,
-each core receiving five or seven layers, or as much as it will hold
-without overlapping the lug or yoke. The ends of the wires are connected
-as shown at Fig. 14 or Fig. 15, the ends being carried down through the
-base and up again in the right location to meet the foot of a
-binding-post. The complete dynamo will appear as shown in Fig. 28.
-
-Before the dynamo is started for the first time it would be well to run
-a strong current through the field coils. The residual magnetism
-retained by the cores and iron parts will then be ready for the next
-impulse when the dynamo is started again. Larger dynamos may be made of
-this type. With an armature, the core of which is four inches in
-diameter and six inches long, having eight instead of four channels, and
-placed within a field of proportionate size, the dynamo will develop one
-horse-power.
-
-
-A Split-ring Dynamo
-
-Another type of dynamo is shown in Fig. 31. This is composed of a
-wrought or cast iron split-ring wound for the field, an armature made
-up of laminations, and the necessary brushes, posts, commutators, and
-wire.
-
-[Illustration: FIG. 31]
-
-Have a blacksmith shape an open ring of iron, in the form of a C,
-three-eighths of an inch thick and four inches wide. The opening should
-be three inches wide, as shown in Fig. 32. This ring should measure five
-inches on its outside diameter, and the ends are to be bored and
-threaded to receive machine-screws. Two lugs are to be made from
-wrought-iron to fit on these ends. These should be four inches long, an
-inch and a half high, and three-quarters of an inch thick at top and
-bottom. They should be hollowed out at the middle, so that an armature
-two inches in diameter will have one-eighth of an inch play all around
-when arranged to revolve within them. Holes are made through the lugs to
-receive machine-screws, which are driven into the holes in the ends of
-the iron (C). Wrought-iron L pieces are made one inch and a half high
-and an inch across the bottom, and with machine-screws they are made
-fast to the backs of the lugs to act as feet on which the field-magnet
-may rest, as shown in Fig. 33. Across the back of the lugs, and set away
-from them by fibre washers, a strap of brass is made fast. This measures
-three-quarters of an inch wide and a quarter of an inch thick, and at
-the middle of it a three-eighth-inch hole is bored to receive the rear
-end of the armature shaft. This is shown in Fig. 34, which is a front
-view of the field, or C, iron, the lugs (L L) and feet (F F), the
-armature bearing (S), and the base (B), of three-quarter-inch hard-wood.
-The field-magnet is bolted to the base with lag-screws, so that it will
-be held securely in place.
-
-The laminations for the armature core are two inches in diameter, and
-are cut from soft iron one-sixteenth of an inch thick. They have eight
-channels, as shown in Fig. 35, and the tubing on the commutator hub is
-divided into four parts so that the terminals from each coil can be
-brought to a commutator, as described for Fig. 30. In the eight-channel
-armature, however, there is but one coil of wire in each channel.
-
-[Illustration: FIG. 32
-
-FIG. 33
-
-FIG. 34
-
-FIG. 35
-
-FIG. 36
-
-FIG. 37
-
-FIG. 38
-
-DETAILS OF SPLIT-RING DYNAMO]
-
-In Fig. 36 a plan of the armature is shown, S representing the shaft, B
-B the bearings, L the laminations, C the commutators and hub, P the
-driving-pulley, and N N the nuts that hold the laminations together and
-lock them to the shaft. The shaft is half an inch in diameter, the
-laminations four inches thick, and the commutator barrel one inch in
-diameter and three-quarters of an inch long. The shaft is turned down
-from the middle to where P and C are attached; then at the front end it
-is made smaller, where it passes through the front bearing.
-
-With the detailed description already given for the construction of the
-small dynamo, it should be an easy matter to carry out the work on this
-one, and a quarter horse-power generator should be the result. The
-field-magnet is wound with five or seven layers of No. 16 double
-cotton-insulated wire, and the armature with No. 22 silk or
-cotton-covered wire. The connections may be made for either the series
-or the shunt windings shown in Figs. 14 and 15. Another type of field is
-shown in Fig. 37, where two plates of iron are screwed to one core, and
-the lugs are, in turn, made fast to the inner sides of the plates within
-which the armature revolves. The “Manchester” type is shown in Fig. 38,
-where two cores, constructed by a top and bottom yoke, are excited by
-the coils, and the lugs are arranged between the cores, so that the
-armature revolves within them.
-
-
-A Small Motor
-
-The shapes, types, powers, and forms of motors are as varied and
-different as those of dynamos, each inventor designing a different type
-and claiming superiority. The one common principle, however, is the
-same--that of an armature revolving within a field, and lines of force
-cutting lines of force. A motor is the reverse of a dynamo. Instead of
-generating current to develop power or light, a current must be run
-through a motor to obtain power.
-
-Motors are divided into two classes: the D C, or direct current, and the
-A C, or alternating current. For the amateur the direct-current motor
-will meet every requirement, and since the battery, or dynamo current,
-that may be available to run a motor, is in all probability a direct
-one, it will be necessary to construct a motor that is adapted to this
-source of power and for the present avoid the complications of the
-alternating current both in generation and in use.
-
-The direct-current motor is an electrical machine driven by direct
-current, the latter being generated in any desired way. This current is
-forced through the machine by electro-motive force, or voltage; the
-higher the pressure, or voltage, the more efficient the machine. Be
-careful lest too much current (amperage) is allowed to flow, for the
-heat developed thereby will burn out the wiring.
-
-Motors are so constructed that when a current is passed through the
-field and armature coils the armature is rotated. The speed of the
-armature is regulated by the amount of amperage and voltage that passes
-through the series of magnets, and this rotating power is called the
-torque.
-
-Torque is a twisting or turning force, and when a pulley is made fast to
-the armature shaft, and belted to connect with machinery, this torque,
-or force, is employed for work.
-
-The speed of an armature when at full work is usually from twelve
-hundred to two thousand revolutions a minute. As few machines are
-designed to work at that velocity, a system of speeding down with back
-gears, or counter-shafts and pulleys, is employed. The motor itself
-cannot be slowed down without losing power. The efficiency of motors is
-due to the centrifugal motion of the mass of iron and wire in the
-armature and the momentum it develops when spurred on by the magnetism
-of the field-magnets acting upon certain electrified sections of the
-armature. The armature of a working motor is usually of such high
-resistance that the current employed to run it would heat and burn out
-the wires if the full force of the current was permitted to flow through
-it for any length of time. As the armature rotates it has counter
-electro-motive force impressed upon it. This acts like resistance, and
-reduces the current passing through. The higher the speed the less
-current it takes, so that after a motor has attained its highest, or
-normal speed, it is using less than half the current required to start
-it.
-
-Reduction of current in the armature reduces torque, so that the turning
-force of the armature is reduced as its speed of rotation increases. On
-the other hand, the momentum, or “throw,” produces power at high speed,
-together with an actual saving of current. An armature revolving at
-sixteen hundred revolutions, and giving half a horse-power on a current
-of five amperes, is more economical than one making three to five
-hundred revolutions, and giving half a horse-power on a current of
-fifteen to twenty amperes. Thus, a slowly turning armature takes more
-current and exerts higher torque than a rapidly rotating one.
-
-To protect the fine wire on the armature from burning, in high-voltage
-machines a starting-box, or rheostat, is employed. The motor begins
-working on a reduced current, and as it picks up speed more current is
-let in, and so on until the full force of the current is flowing through
-the motor. It is then turning fast enough to protect itself through the
-counter electro-motive force. This can be understood better after some
-practical experience has been had in the construction and running of
-motors. Of the various forms of motors but three will be illustrated and
-described; but the boy with ideas can readily design and construct other
-types as he comes to need them.
-
-
-The Flat-bed Motor
-
-The simplest of all motors is the flat-bed type, illustrated in Fig. 39.
-This is composed of a magnet on a shaft revolving before a fixed magnet
-attached to the upright board of the base. Where space is no object,
-this motor will develop considerable power from a number of dry-cells or
-a storage-battery. Now, in the section relating to dynamos, four
-different systems of wiring were shown. In motors of the direct-current
-type but one system will be described--that of the series-winding,
-illustrated in Fig. 40. The current, entering at A, passes to the brush
-(B), thence through the commutator (C) and the armature coils. It runs
-on through the brush (B B), the field-coils (F), and out at D. This is
-the same course the current takes in the series-wound dynamo illustrated
-in Fig. 14, page 241, and with such a dynamo current could be generated
-to run any series-wound, direct-current motor.
-
-[Illustration: FIG. 39
-
-FIG. 40
-
-FIG. 41
-
-FIG. 42
-
-FIG. 43
-
-A FLAT-BED MOTOR AND PARTS]
-
-From hard-wood half an inch thick cut a base-piece six inches and a half
-long by three inches and a half wide. Arrange this base on cross-strips
-three-quarters of an inch wide and half an inch thick, making the union
-with glue and screws driven up from the underside. To one end of this
-base attach an upright or back two inches and three-quarters high, and
-allow the lower edge to extend down to the bottom of the cross-strip, as
-shown at the left of Fig. 39. Make this fast to the end of the base and
-side of the cross-strip with glue and screws; then give the wood a coat
-of stain and shellac to properly finish it.
-
-Now have a blacksmith make two [U] pieces of soft iron for the field and
-armature cores, as shown in Fig. 41. These are of quarter-inch iron one
-inch and a half in width. They are one inch and three-quarters across
-and the same in length. One of them should have a half-inch hole bored
-in the end (at the middle), and above and below it smaller holes for
-round-headed screws to pass through. By means of these screws the [U] is
-held to the wooden back. The other [U] is to have a three-eighth-inch
-hole bored in it so that it will fit on the armature shaft. Wind the [U]
-irons with six layers of No. 20 cotton-insulated wire, having first
-covered the bare iron with several wraps of paper. Use thick shellac
-freely after each layer is on, so that the turns of wire will be well
-insulated and bound to each other. Follow the wiring diagram shown in
-Fig. 40 when winding these cores, and when the field is ready, make it
-fast to the back with three-quarter-inch round-headed brass screws.
-
-Directly in the middle of the hole through the field iron bore a
-quarter-inch hole for the armature shaft to pass through; then make an
-[L] piece, of brass, two inches high, three-quarters of an inch wide,
-and with the foot an inch long, as shown at Fig. 42. Two holes are made
-in the foot through which screws will pass into the base, and near the
-top a quarter-inch hole is to be bored, the centre of which is to line
-with that through the back, at the middle of the field core. The shaft
-is made from steel three-eighths of an inch in diameter and six inches
-and a half long. One inch from one end the shaft should be turned down
-to a quarter of an inch in diameter, and one inch and a quarter from the
-other end it must be reduced to a similar size. The short end mounts in
-the back and the long one receives the pulley, after the latter passes
-through the [L] bearing. A piece of three-eighth-inch brass tubing an
-inch long is slipped over the shaft two inches from the pulley end and
-secured with a flush set-screw. This tubing is then threaded and
-provided with two nuts, one at either end, so that when the armature [U]
-is slipped on the collar the nuts can be tightened and made to hold the
-magnet securely on the shaft. This shaft is clearly shown in the
-sectional drawings Fig. 43.
-
-At the left side the shaft (S) passes into the wood back through the
-quarter-inch hole. At the outside a brass plate with a quarter-inch hole
-is screwed fast and acts as a bearing. The shaft does not touch the
-field-magnet (F M), because the hole is large enough for the
-quarter-inch shaft to clear it. A fibre washer (F W) is placed on the
-shaft before it is slipped through the back. This prevents the shaft
-from playing too much, and deadens any sound of “jumping” while
-rotating.
-
-At the middle the shaft (S) passes through the brass collar on which the
-threads are cut. A M represents the armature magnet, and W W the washers
-and nuts employed to bind it in place. At the right, S again represents
-the shaft, B the bearing, C the commutator hub, and P the pulley, while
-R is the small block under the hub to which the brushes and
-binding-posts are attached.
-
-From the descriptions already given of dynamos, and with these figure
-drawings as a guide, it should be an easy matter to assemble this motor.
-
-The ends of the field and armature magnets should be separated an eighth
-of an inch. The hub for the commutators is three-quarters of an inch
-long and three-quarters of an inch in diameter. The commutators are made
-as described for the uni-direction current machine, care being taken to
-keep the holding screws from touching the shaft. A three-quarter-inch
-cube of wood is mounted on the base, under the commutator hub, and to
-this the brushes and binding-posts are made fast, as shown in Fig. 39.
-Unless the armature happens to be in a certain position this motor is
-not self-starting, but a twist on the pulley, as the current is turned
-on, will give it the necessary start. Its speed will then depend on the
-amount of current forced through the coils.
-
-
-Another Simple Motor
-
-Another type of motor is shown in Fig. 44, where one field-winding
-magnetizes both the core and the lugs. The frame of this motor is made
-up of two plates of soft iron a quarter of an inch thick, six inches
-long, and two inches and a half wide. Each plate is bent at one end so
-as to form a foot three-quarters of an inch long, and a half-inch hole
-is drilled one inch and a quarter up from the bottom, at the middle of
-each plate. Through this hole pass the machine-screws which hold the
-iron core in place between the side-plates. The core is made of
-three-quarter-inch round iron two inches and three-quarters long, and
-drilled and threaded at each end to receive the binding machine-screws.
-
-Two lugs are cut from iron, and hollowed at one side so that an armature
-two inches in diameter will rotate within them when made fast to the
-side-plates. The lugs are two inches and a half long, an inch wide, and
-two inches and a half high.
-
-From iron five-eighths of an inch wide and one-eighth of an inch thick
-make two side-strips with [L] ends. These are four inches long, and are
-provided with two holes so that the machine-screws which hold the lugs
-to the inside plates will also hold these strips in place, at the
-outside, as shown in Fig. 45. At the rear these strips extend half an
-inch beyond the frame. Across the back a brass strip of the same size as
-the iron strips is arranged. It is held at the ends by screws, or small
-bolts, made fast to the [L] ends of the side-strips. Directly in the
-middle of the back-strip a hole is made for the armature shaft, and
-beyond it the pulley is keyed or screwed fast to the shaft.
-
-At the front a similar strip is made and attached. This latter has a
-small hole in the middle of it to serve as a bearing for the forward end
-of the shaft. Across the top of the motor a brass strip or band is made
-fast with machine-screws; and at the angles formed by the front ends of
-the side-strips and the front cross-strips hard-wood blocks are
-attached. To these the brushes and binding-posts are made fast, so that
-one brush at the top of the left-hand block rests on the top of the
-commutator. The one at the underside of the opposite block must rest on
-the underside of the commutator.
-
-[Illustration: FIG. 44]
-
-[Illustration: FIG. 45]
-
-The armature core is made up of laminations as described for the dynamo
-armatures. In a really efficient motor the armature should have eight or
-more channels.
-
-The other parts of the motor may be assembled and wired as described on
-the preceding pages. The armature should be wound with No. 20 or 22
-insulated copper wire, and the field with No. 16 or 18. For high
-voltage, however, the armature should be wound with finer wire and a
-rheostat used to start it.
-
-
-A Third Type of Motor
-
-The third type is but a duplicate of the series-wound dynamo, the
-general plan of which is shown in Fig. 40.
-
-This motor can be made any size, but as its dimensions are increased the
-weight of the field-magnets and armature must be proportionately
-enlarged. For an efficient and powerful motor, the field should stand
-ten inches high and six inches broad. The iron cores are five inches
-long and one inch and a half in diameter. These should be made by a
-blacksmith and bolted together. The armature is three inches in diameter
-and four inches long, and should develop two-thirds of a horse-power
-when sufficient current is running through the coils to drive it at
-sixteen hundred revolutions.
-
-The wiring is carried out as shown in Fig. 40, and the armature hung and
-wound as suggested for the dynamo shown in Fig. 28, page 246.
-
-
-Chapter XI
-
-GALVANISM AND ELECTRO-PLATING
-
-
-Simple Electro-plating
-
-To the average boy experimenter, electro-plating is one of the most
-fascinating of the uses to which electricity may be put. In scientific
-language the process is known as electrolysis, and involves the
-separation of a chemical compound into its constituent parts or elements
-by the action of an electric current and the proper apparatus.
-Electrolysis cannot take place, however, unless the liquid in the tank,
-commonly called the electrolyte (no relation to electric light), is a
-conductor.
-
-Water, or water with mixtures of chemicals, such as sulphate of copper,
-sulphate of zinc, chloride of nickel, cyanide and nitrate of silver, or
-uranium and other metallic salts, are good conductors. Oil is a
-non-conductor, and a current will not pass through it, no matter what
-the pressure may be. The simplest electro-plating outfit, and the one
-that a boy should start with, is the sulphate of copper bath, such as is
-commonly employed by makers of electrotypes, and which is in extensive
-use by refiners of copper for high-grade electrical use.
-
-More than half of the total output of copper in the world is used for
-electrical work--conductors, switches, and all sorts of parts--and since
-any impurity in the copper interferes with its conducting powers, it is
-most important that it should be free from any traces of carbon or
-arsenic. The electrolytic refining of copper is now a very important
-process in connection with electric work, and about half a million tons
-of copper are treated annually to free it from all impurities. Moreover,
-the gold, silver, and other valuable metals which may be found in
-copper-ore are thus recovered.
-
-The electro-plating, electrotyping, and refining operations are one and
-the same thing; but in the first instance the object to be plated is
-left in the solution only a short time or until a blush of copper has
-been applied. In the second process the wax mold is left in long enough
-for a thin shell of copper to be deposited; and in the third, the
-kathodes are immersed until they are heavily coated with copper. To
-carry on any of these operations it will be necessary to have a small
-tank or glass jar to hold the plating-bath or electrolyte. Preferably it
-should be of a square or oblong shape. But a serviceable tank may be
-constructed from white-wood, pine, or cypress, if proper care is taken
-in making and water-proofing (Fig. 1). For experimental purposes a tank
-eighteen inches long, ten inches wide, and twelve inches deep will be
-quite large enough to use as a copper bath. For silver, nickel, or gold,
-smaller tanks should be employed, as they contain less liquid, or
-electrolyte, which in the more valuable metals is expensive.
-
-Obtain a clear plank twelve inches wide, well seasoned, and free from
-knots or sappy places. Cut two sides twenty inches long and two ends
-eight inches long. With chisel, saw, and plane shape the ends of the
-side planks as shown at Fig. 2; or if there is a mill at hand it would
-be well to have the ends cut with a buzz-saw, thus insuring that they
-will be accurate and fit snugly. Screw-holes are bored with a
-gimlet-bit, and countersunk, so that screws will pass freely through
-them and take hold in the edges of the boards. Screws and plenty of
-white-lead, or asphaltum varnish, should be used on these points to make
-them water-tight; then the lower edge of the frame is prepared for the
-bottom board. Turn the tank bottom up, and, with a fat steel-wire nail
-and a hammer, dent a groove at the middle of the edge of the planks all
-around, as shown in Fig. 3. It will not do to cut this out with a
-gouge-chisel, because it is intended that the wood should swell out
-again if necessary. The object of driving the wood down is to form a
-valley into which a line of cotton string-wicking, soaked in asphaltum
-varnish or imbedded in white-lead, may be laid. This should be done (as
-shown in Fig. 4) before the bottom is screwed on, so that afterwards (in
-the event of the joint leaking) the wood will swell and force the
-wicking out, and thus properly close the fissure.
-
-The bottom board should be provided with holes all around the edge, not
-more than two inches apart, through which screws can be driven into the
-lower edge of the tank. Treat the wood, both in and outside, to several
-successive coats of asphaltum varnish, and as a result you will have a
-tank resembling Fig. 1.
-
-Two shallow grooves are to be cut in the top of each end board of the
-tank, for the cross-bars to fit in immovably. These bars should be about
-three inches apart; and the ones holding the anodes, or flat copper
-plates, should be close to one side, leaving plenty of room for objects
-of various sizes to be properly immersed.
-
-Another manner in which the bottom of the tank can be attached is shown
-in Fig. 5, which is a view of the tank sides turned bottom up. A rabbet
-is cut from the lower edges of the sides and ends, before they are
-screwed together, and a bottom is fashioned of such shape as to
-accurately fit in the lap formed by the rabbet. This rabbet and the
-outer edge of the bottom plank should be well smeared with white-lead,
-and all put together at the same time, driving the screws into the edge
-of the bottom plank, through the lower edges of the sides and bottom,
-and also through the bottom board into the lower edges of the sides and
-ends (Fig. 6).
-
-Still another and stronger way in which to make a tank for a large bath
-is to cut the planks as shown at Fig. 7. The sides are then bolted
-together, locking the ends and bottom, so that they cannot warp or get
-away. The bolts are of three-eighth-inch round iron-rod, threaded at
-both ends and provided with nuts. Large washers are placed against the
-wood and under the nuts, so that when the nuts are screwed on tightly
-they will not tear the wood, but will bear on the washers. The points
-are all to be well smeared with white-lead or acid-proof cement (see
-Formulæ) before the parts are put together and bolted, so as to avoid
-any possibility of leakage. (Fig. 8 shows the completed tank.)
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-FIG. 7
-
-FIG. 8
-
-TANK FOR ELECTRO-PLATING]
-
-Now obtain two copper rods long enough to span the tank, with an inch or
-two projecting beyond the tank at either side. At one end of these
-attach binding-posts, to which the wires from a battery can be
-connected, leaving the opposite ends free, as shown at Fig. 9 (see page
-275). Anodes, or pure soft copper plates, are hung on the positive rod,
-while on the negative one the objects to be plated, or kathodes, are
-suspended on fine copper wires just heavy enough to properly conduct the
-current. The positive wire leads from the carbon, or copper pole, of the
-battery, while the negative one is connected with the zinc. The anodes
-are plates of soft sheet or cast copper, and should be as nearly pure as
-possible for electrolytic work; but if they are to be re-deposited, to
-free them from impurities, they may be in thin ingot form, just as the
-copper comes from the mines.
-
-The general principle of electro-refining of copper is very simple. A
-cast plate of the crude copper is hung from the positive pole in a bath
-of sulphate of copper, made by dissolving all the sulphate of copper, or
-bluestone, that the water will take up. Drop a few lumps on the bottom
-of the tank to supply any deficiency, then add an ounce of sulphuric
-acid to each gallon of liquid, to make it more active and a better
-conductor.
-
-The crude copper plate is to be the leading-in pole for the current,
-while a thin sheet of pure copper, no thicker than tissue-paper, is
-suspended from the opposite rod for the leading-out pole; or in place of
-the thin sheet, some copper wires may be suspended from the rod. The
-electrodes--that is, the copper plate and the thin sheet or wires--are
-placed close together, so that the current may pass freely and not
-cause internal resistance in the battery. The electric current, in its
-passage from the crude copper plate to the pure copper sheet or wires,
-decomposes the sulphate of copper solution and causes it to deposit its
-metallic copper on the sheet or wires; and at the same time it takes
-from the crude copper a like portion of metallic copper and converts it
-into chemical copper. The electric current really takes the copper from
-the solution and adds it to the pure copper sheet, while the remaining
-constituents of the decomposed solution help themselves to some copper
-from the crude plate. In this way the crude copper diminishes and the
-pure copper sheet increases in size, the impurities as well as the salts
-of other metals being precipitated to the bottom of the tank, or mingled
-with the solution, which must be purified or replaced from time to time
-by fresh solution. This is the process of copper-plating, and any metal
-object may be properly cleansed and coated with copper by suspending it
-in the bath and running the current through it.
-
-When the refining process is employed, any metal will answer as a
-depository for the copper, but as the intention is to produce a pure
-copper plate which can be melted and cast into ingots, it is of course
-necessary to have the original kathode of the same metal; otherwise an
-impure mixture will be the result. If, for example, a piece of cast-iron
-be used upon which to deposit the copper, then the iron will be enclosed
-in a deposit of pure copper; in other words, the result will be a
-heavily copper-plated piece of iron, and the smelting process will bring
-about a fusion of the two metals. It is not necessary to have absolutely
-pure copper for the anodes when copper-plating or electrotyping; but
-the purer the copper the less the solution is fouled, and it will not
-require replenishing so often.
-
-An object intended to receive a plating of copper need not be of metal
-at all; it may be of any material, so long as it possesses a conducting
-surface. A mold or a cast made of any plastic material, such as wax or
-cement, may have its surface made conductive by the application of
-graphite, finely pulverized carbon, or metal dusts held on by some
-medium not soluble in water. The wax molds, or impressions of type and
-cuts, are dusted with plumbago, and then suspended in the copper
-solution. A wire from the negative pole is connected so as to come in
-contact with the plumbago, and the copper deposit immediately begins to
-form on the face of the wax. When the film of copper has become heavy
-enough, the mold is drawn out of the solution, and the thin shell of
-metal removed from the wax and cut apart, so that each shell is
-separated from its neighbor and freed from marginal scraps. Flowers,
-leaves, laces, and various other objects can be given a coat of copper
-by thus preparing their surfaces, and some most beautiful effects may be
-secured by copper-coating roses; then placing them for a short time in a
-gold bath, and afterwards chemically treating the surface plating so as
-to imitate Roman, Tuscan, or ormolu gold, in bright or antique finish.
-Coins, medallions, bas-reliefs, medals, and various other things are
-reproduced by the electro-plating process, and their surfaces finished
-in gold, silver, bronze, or other effects. Years ago this was not
-possible, because the old method was to make a fac-simile cast in metal
-of the object desired, and then chase or refinish the surface. This was
-a costly and tedious task. When Brugnalelli, an Italian electrician,
-electro-gilded two silver coins in 1805, he laid the foundation for the
-modern process, but it did not come into general use until about 1839,
-when electro-plating and the electro-depositing of metals was begun on a
-practical scale. Before the invention of the dynamos for generating
-current, batteries had to be employed, and this made the process
-somewhat more expensive than the present method. Our boy amateurs,
-however, will have to be content with the battery system, since they are
-not supposed to have access to direct-current power, such as is used for
-arc or street lighting.
-
-Various forms of batteries may be used for this work, and they will be
-described in detail. For the copper-plating bath it will be necessary to
-have the anodes of soft, cast, or sheet, copper sufficiently heavy so as
-not to waste away too quickly. These should be of the proper size to fit
-within the bath, and either one large one or several small ones may be
-employed. Stout copper bands should be riveted to the top of the plates,
-by means of which they may be hung on the bar and so suspended in the
-solution (Fig. 10). The contact-points should be kept clean and bright,
-so that the current will not meet with any resistance in passing from
-the rod to the plates.
-
-In Fig. 9 a complete outfit is shown for any plating process, the
-difference being only in the solution and anodes. For silver-plating a
-silver solution and silver anodes are required, while for gold the gold
-solution and gold anodes will be necessary. In this illustration, A
-represents the tank, B the battery, C C the anodes, D D D the kathodes,
-or articles to be plated, E the positive rod, F the negative, and G, H
-the leading-in and leading-out wires.
-
-There is often a doubt in a boy’s mind as to how the battery is to be
-connected up to the bath and the articles suspended in it. But there
-will be no difficulty about it once that the principle of the process is
-thoroughly understood.
-
-[Illustration: FIG. 9.]
-
-It is well to remember that the electro-plating bath is just the reverse
-of a battery in its action. The process carried on in a battery is the
-generation of electricity by the action of the acid on the positive
-metal, accompanied by the formation of a salt on one of the elements;
-while in the plating-bath the current from an external source (the
-battery or dynamo) breaks up the salts in solution and deposits the
-metal on one of the elements (the kathode).
-
-The remaining element in the solution attacks the salts, in chemical
-lumps or granular form, and dissolves them to take the place of the
-exhausted salts; or it attacks the metal anode from which these salts
-were originally made, and eats off the portion necessary to replace the
-loss caused by the action of the current in depositing the fruits of
-this robbery in metallic form upon the article to be plated (the
-kathode). There should be no confusion in the matter of properly
-connecting the poles if one remembers that the current is flowing
-through the battery as well as through the wires and the solution in the
-tank.
-
-Get clearly in your mind that the current originates in the battery of
-zinc and carbon or zinc and copper. The zinc is electro-positive to
-carbon or copper, and at a higher electric level the current flows from
-the zinc plate inside the cell to the carbon or copper; therefore, the
-zinc is the positive pole. Now the current, having flowed through the
-battery from zinc to carbon, or the negative plate, is bound to flow out
-of the battery from the carbon through the apparatus and back again to
-the zinc in the battery. Therefore, the wire (G) attached to the carbon
-of the battery leads a positive or + current, although the carbon is
-negative; in the battery, and the wire (H) leading out is negative, or
--, although it returns the current to the positive pole of the battery.
-
-This is the simple explanation of the circulation of current; but to cut
-it down still more, always remember to attach the wire from the anode
-rod to the carbon, or copper, of the battery, and the kathode rod to the
-zinc of the battery.
-
-In copper-plating this is easy to determine without any regard to wires,
-because if the wires are misconnected there will be no deposit, and the
-kathode will turn a dark color. If everything is all right a slight
-rose-colored blush of copper will appear at once on the kathode. Too
-little current will make the process a long and tedious one, while too
-much current will deposit a brown mud on the kathode, which will have to
-be washed off or removed and the article thoroughly cleansed before a
-new action is allowed to take place.
-
-With a series of cells it is an easy matter to properly govern the
-current by cutting out some of the cells or by using resistance-coils
-(see chapter vii. on Electrical Resistance).
-
-Cells and batteries for electro-plating may be made or purchased, and
-primary batteries should be used. The use of the secondary or
-storage-battery is not necessary for plating purposes, since no great
-volume of current is needed, and it can be generated in a battery of
-cells while the work is going on.
-
-One of the best primary batteries is the Benson cell, shown in
-connection with the plating-bath, and also in Fig. 11. It consists of an
-outer glass jar (G J), which contains a cylinder of amalgamated zinc (Z
-+, or positive) covered with diluted sulphuric acid--one part acid to
-three parts water. An inner porous cup (P C) contains concentrated
-nitric acid, into which the carbon (C -, or negative) is plunged. The
-liquid in the inner cup and glass cell should be at the same level.
-
-[Illustration: FIG. 10
-
-FIG. 11
-
-FIG. 12
-
-THE BENSON CELL PRIMARY BATTERY]
-
-There is no polarizing in this cell, for the hydrogen liberated at the
-zinc plate, in passing through the nitric acid on its way to the
-carbon-pole, decomposes the nitric acid and is itself oxidized. A cell
-with a glass jar six inches in diameter and eight inches high will
-develop about two volts of electro-motive force; and as its internal
-resistance is very low it will furnish a steady current for several
-hours. Any number of these cells may be made and connected in series;
-but when not in use it would be well to remove and wash the zincs. Any
-bichromate battery will answer very well for plating, the Grenet being
-an especially good one. A well-amalgamated zinc plate forms one pole,
-and a pair of carbon plates, one on each side of the zinc and joined at
-the top, make up the other pole. When not in use the entire plunge part
-should be removed from the bichromate solution, rinsed off in water, and
-laid across the top of the jar, ready for its next employment. The zinc
-and carbons must be joined together so that they are well insulated, and
-with no chance of the zinc coming into contact with the carbons. This
-may be done with four pieces of hard-wood soaked in hot paraffine and
-then locked together with stove-bolts and nuts, as shown at Fig. 12.
-Holes must be made in the top corners of the carbons and zinc, and with
-small bolts and nuts the connecting wires can be made fast.
-
-To charge this battery, add five fluid ounces of sulphuric acid to three
-pints of cold water, pouring the acid slowly into the water and stirring
-it at the same time with a glass or carbon rod. When this becomes cold,
-after standing a few hours, add six ounces of finely pulverized
-bichromate of potash. Mix this thoroughly, and pour some of the solution
-into the glass cell until it is three-fourths full; then it will be
-ready to receive the carbons and zinc. When arranging the wood-clamps on
-the carbon and zinc plates it would be well to make two of the clamps
-longer than the others so that they will extend out far enough to rest
-on the top edge of the jar. To keep them in position at the middle of
-the jar, notches should be cut at the underside of these clamps, so that
-they will fit down over the edge of the jar. Any number of these cells
-may be connected together to obtain the desired amount of current, or
-electro-motive force.
-
-Other batteries suitable for electro-plating are the Edison primary,
-Taylor, Fuller, Daniell, gravity, Groves, and Merdingers. All of these
-may be purchased at large electrical equipment or supply houses.
-
-
-The Cleansing Process
-
-One of the most important operations of the plating process is to
-properly cleanse the articles to be plated before they are placed in the
-bath. When once cleaned the surfaces of these objects must not be
-touched with the fingers, or any dusty or greasy object; otherwise the
-electro-deposited metal will not hold on the surface, but will peel off,
-in time, or blister. A very small trace of foreign matter is sufficient
-to prevent the deposit from adhering to the surface to be plated;
-therefore, great care must be taken to eliminate all trace of anything
-that would interfere with the perfect transmission of metallic molecules
-to the prepared surfaces. Acids are chiefly employed to remove foreign
-matter from new metallic surfaces; and for copper, brass, iron, zinc,
-gold, and silver a table is given on page 281 which will show the right
-proportion of acids to water in order to cleanse the various metals. In
-the following scale the numerals stand for parts. For example: the
-first one means 100 parts water, 50 parts nitric acid, 100 parts
-sulphuric acid, and 2 parts hydrochloric acid--making in all 252 parts.
-These can be measured in a glass graduate.
-
-  ----------------+-----+------+---------+------------
-                  |     |Nitric|Sulphuric|Hydrochloric
-                  |Water| Acid |  Acid   |   Acid
-  ----------------+-----+------+---------+------------
-  Copper and brass| 100 |  50  |   100   |      2
-  Gold            | 100 | ...  |   ...   |     15
-  Silver          | 100 |  10  |   ...   |    ...
-  Wrought-iron    | 100 |   2  |     8   |      2
-  Cast-iron       | 100 |   3  |    12   |      3
-  Zinc            | 100 | ...  |    10   |    ...
-  ----------------+-----+------+---------+------------
-
-Twist a piece of fine copper wire about part of the object to be cleaned
-and plated; then dip it in the acid and rinse off in clean warm or hot
-water, and rub the surface briskly with a brush dipped in the liquid.
-Dip it again several times, and rinse in the same manner; then, when it
-is bright and clean, place it in the bath, twist the loose end of the
-wire around the negative rod, and start the current flowing, taking care
-that the object is thoroughly immersed.
-
-Tarnished gold or silver articles may be cleaned by immersing them in a
-hot solution of cyanide of potassium; or a strong warm solution of
-carbonate of ammonia will loosen the tarnish on silver, so that it can
-be brushed off. Corroded brass, copper, German-silver, and bronze should
-be cleansed in a solution composed of sulphuric acid, three ounces;
-nitric acid, one and three-quarters ounces; and water, four ounces. This
-soon loosens and dissolves the corrosion; then the article should be
-brushed off, dipped in hot water, and rinsed. Then replace it in the
-solution for a minute or two and rinse again, when it will be ready for
-the plating-bath.
-
-Corroded zinc should be immersed in a solution of sulphuric acid, one
-ounce; hydrochloric acid, two ounces; and distilled or rain water, one
-gallon. It should be well brushed after the acid has bitten off the
-corrosion.
-
-Rusty iron or steel should be pickled in a solution of sulphuric acid,
-six ounces, hydrochloric acid, one ounce, and water, one gallon. When
-the rust has been removed, immerse the object in a solution composed of
-sulphuric acid, one pint, and distilled water, one gallon. Before the
-acid is added to the water dissolve one-quarter-pound of sulphate of
-zinc in the water; then add the acid, pouring it slowly and stirring the
-water.
-
-Lead, tin, pewter, and their compounds may be cleansed by immersing them
-in a hot solution of caustic soda or potash, then rinsing in hot water.
-Take great care if caustic is used, as it will burn the skin and tissues
-of the body. Do not let the fingers come into contact with any cleansed
-article, because the oily secretions of the body will stick to the metal
-and cause the coat of deposited metal to strip off or present a spotted
-appearance.
-
-
-The Plating-bath
-
-The object to be plated should not touch the bottom or sides of the
-plating-vat, and it should be far enough away from the anodes to avoid
-any possibility of coming into contact with them. It will not do to
-place the anode and kathode too close together, as the plate will be
-deposited unevenly; the thicker coating will appear on the parts
-closest to the anode. Neither should they be separated too far, as the
-resistance of the cell is thereby increased, and of course this means a
-waste of energy. The knowledge of how to arrange the anode and kathode
-is a matter to be learned by experience, but by carefully watching the
-deposit it will not be a difficult matter to determine the proper
-positions.
-
-For many reasons the glass tank is preferable for amateur
-electro-plating work, since the objects may be watched without
-disturbing their electric connections and without removing them from the
-liquid. A very good plan for the copper bath, when spherical,
-cylindrical, or hollow objects are to be plated, is to line the inside
-of the tank with strips or a sheet of copper, hung on hooks that will
-catch on the sides; then connect the positive wire directly to these
-strips. With this arrangement but one rod, the negative, is in use, and
-the objects to be plated are suspended from it. It follows that the
-objects will take up the copper deposit from all sides, and a more
-evenly distributed coating will be the result.
-
-It is better to start up the current gradually, rather than to put on at
-the beginning a large amount of electro-motive force. By watching the
-character of the deposit you can soon tell if you have the proper
-strength of current. If everything is working properly the copper
-deposit will have a beautiful flesh tint; but if the current is too
-strong it takes on a dark-red tone and resembles the surface of a brick.
-This is not right, and the object must be removed and washed off, the
-current reduced, and the object replaced in the bath.
-
-When a sufficiently heavy coating of the copper has been applied, remove
-the object and wash thoroughly in running or warm water to free it from
-any remaining copper fluid. If this is not done the surface, in drying,
-will turn a dull brown, and will have to be bitten off with the acid
-solution for cleansing copper.
-
-The finer the copper deposit the better and smoother it will be; the
-grain will be smaller, and it will not present a rough surface, which is
-always difficult to plate over with silver or gold, unless a frosted
-effect is desired. Non-conducting objects are usually plated with copper
-first, and then replated with the metal desired for the final finish.
-
-To make the surface conductive, finely powdered black-lead, or plumbago
-of the best kind, or finely pulverized gas-carbon is brushed over the
-surface. This must be thoroughly done; and if the deposit is slow about
-appearing at any spot it may be hastened by touching it with the end of
-an insulated wire attached to the main conductor. This, of course, will
-only answer for objects strong enough to stand the brushing treatment;
-it will not do for flowers, insects, and other delicate things, that are
-to be silver or gold plated. These should be given a film of silver by
-soaking in a solution of alcohol and nitrate of silver, made by shaking
-two parts of the chemical into one hundred parts of grain-alcohol, with
-the aid of heat and in a well-corked bottle. When dry, the object should
-be subjected to a bath of sulphuretted hydrogen gas under a hood. The
-sulphuretted hydrogen is made by bringing a bar of wrought-iron to a
-white-heat in the kitchen range or furnace fire, and touching it with a
-stick of sulphur. The iron will melt and drop like wax. These drops
-should be collected in a bottle. Now pour over them diluted sulphuric
-acid, one part acid to three parts water, and the gas will at once rise.
-It will be quickly recognized by its odor, which is similar to that of
-over-ripe eggs. It can be led off through a tube to the place where you
-wish to use it, and when through, the operation of gas-generation may be
-stopped by pouring off the liquid.
-
-All objects prepared in this way should be given a preliminary coating
-of thin copper before they are plated with any other metal.
-
-
-Silver-plating
-
-Plating in silver is done in practically the same way as described for
-the coppering process. Thin strips or sheets of pure silver are used for
-the anodes, and the electrolyte is composed of nitrate of silver,
-cyanide of potassium, and water.
-
-Dissolve three and one-half ounces of nitrate of silver in one gallon of
-water; or if more water is needed to fill the tank, add it in the
-proportion of three and one-half ounces of the nitrate to each gallon of
-water. Dissolve two ounces of cyanide of potassium in a quart of water,
-and slowly add this to the nitrate solution. A precipitate of cyanide of
-silver will be formed. Keep adding and stirring until no more
-precipitate is formed, but be careful not to get an excess of the
-cyanide in the solution.
-
-Gather this precipitate, and wash it on filtering-paper by pouring water
-over it. The filter-paper should be rolled in a funnel shape thus
-permitting the water to run away and leaving the precipitate in the
-paper. This precipitate is to be dissolved in more cyanide solution, and
-added to the quantity in the tank. There should be about two ounces of
-the potassium cyanide per gallon over and above what was originally put
-in.
-
-The silver anodes show the condition of the fluid. If the solution is in
-good order they will have a clear, creamy appearance, but will tarnish
-or turn pink if there is not sufficient free cyanide in the solution.
-
-The proper strength of current is indicated by the appearance of the
-plated objects. A clear white surface shows that everything is all
-right, the solution in proper working order, and the proper current to
-do the work. Too much current will make the color of the kathodes yellow
-or gray, while too little current will act slowly and require a long
-time to deposit the silver.
-
-The adhesion of silver-plate is rendered more perfect by amalgamating
-the objects in a solution of nitrate of mercury, one ounce to one gallon
-of water. After the objects have been properly cleansed they are
-immersed in this solution for a minute, then placed in the silver-bath
-and connected with the negative-rod, so that the electro-depositing
-action begins at once.
-
-
-Gold-plating
-
-The gold-bath is made in the same manner as the silver one just
-described, with the exception that chloride of gold is used in place of
-the nitrate of silver in the first solution. This solution must be
-heated to 150° Fahrenheit when the process is going on; or a cold bath
-may be made of water, 5000 parts; potassium cyanide, one hundred parts;
-and pure gold, fifty parts. The gold must be dissolved in hydrochloric
-acid, and added to the water and potassium.
-
-Very pretty effects may be obtained in gold-plating by changing the
-tones from yellow to a greenish hue by the addition of a little cyanide
-of silver to the solution, or by the use of a silver anode. A reddish
-tinge may be had by adding a small portion of sulphate of copper to the
-solution, or hanging a small copper anode beside the gold one. In the
-hot gold-bath the articles should be kept in motion, or the solution
-stirred about them with a glass rod.
-
-When the solution is perfectly balanced and working right the anodes
-should be a clear dead yellow, and the articles in process of plating
-should be of the same hue.
-
-A gold-plating outfit is shown in Fig. 13, and consists of the tank and
-bath, a cell, and a resistance-coil (R), through which the strength of
-the current is regulated.
-
-The current, passing out of the cell from the carbon (C), is regulated
-through the resistance-coils (R) by the switch (S). From thence it
-passes to the rod from which the anode (A) is suspended, across the
-electrolyte (E) to the kathode (K), on which the metal is deposited, and
-then returns through the negative wire to the zinc (Z) in the cell. If
-the hot bath is used the gold solution may be contained in a glazed
-earthen jar or a porcelain-lined metal jar or kettle. But if the latter
-is used care must be taken to see that none of the enamel is chipped, or
-a short-circuit will be established between the rods. This jar or kettle
-may then be placed on a gas-stove, and a thermometer should be
-suspended so that the mercury bulb is half an inch below the surface of
-the liquid, as shown at T in Fig. 13. As the liquid simmers or
-evaporates away a little water should be added from time to time to keep
-the bulk of the liquid up to its normal or original quantity.
-
-[Illustration: FIG. 13]
-
-
-Nickel-plating
-
-The nickel-plating process is similar, in a general way, to the others;
-it is carried on in a cold bath--that is, at the normal temperature,
-without being heated or chilled artificially.
-
-There are a great many formulæ for the nickel as well as for the other
-baths, but the generally accepted one is composed of double nickel
-ammonium-sulphate, three parts; ammonium carbonate, three parts; and
-water, one hundred parts. Another good one is composed of nickel
-sulphate, nitrate, or chloride, one part; sodium bisulphate, one part;
-and water, twenty parts.
-
-Nickel anodes are used in bath to maintain the strength, and great care
-must be taken to have the bath perfectly balanced--that is, not too acid
-nor too alkaline.
-
-To test this, have some blue-and-red litmus paper. If the blue paper is
-dipped in an acid solution, it will turn red; and back to blue again if
-placed in an alkaline solution. If the nickel solution is too strong
-with alkali, a trifle more of the nickel salts must be added, so that
-both the red-and-blue litmus paper, when dipped in the liquid, will not
-change color. If the bath is too alkaline, it will give a disagreeable
-yellowish color to the deposit of metal on the kathode; and if too acid,
-the metal will not adhere properly to the kathode, and will strip, peel,
-or blister off.
-
-
-Finishing
-
-When the articles have been plated they will have a somewhat different
-appearance to what may have been expected. For instance, copper-plated
-articles will have a bright fleshy-pink hue; silver, an opaque
-creamy-white; gold, a dead lemon-yellow color, and nickel much the
-appearance of the silver, but slightly bluer in its tone. Articles
-removed from the bath should be shaken over the bath so as to remove
-the solution; then they should be immediately plunged into hot water,
-rinsed thoroughly, and allowed to dry slowly.
-
-When a silvered or gilded object is perfectly dry it should be rubbed
-rapidly with a brush and some fine silver-polishing powder until the
-opaque white or yellow gives place to a silver or gold lustre. It will
-then be ready for burnishing with a steel burnisher, or the article may
-be left with a frosted silver or gold surface. Steel burnishers can be
-had at any tool-supply house, and when used they should be frequently
-dipped in castile soapy water to lubricate them. They will then glide
-smoothly over the surface of the deposited metal, driving the grain down
-and making it bright at the same time. If the soapy water were not used
-the action of the hard burnisher over the plate would have a tendency to
-tear away the film of deposited metal. The burnisher must always be
-clean and bright, otherwise it would scratch the plated articles; and,
-when not in use, keep the bright polishing surfaces wrapped in a piece
-of oiled flannel.
-
-Small articles, such as sleeve-buttons, rings, studs, and other things
-not larger than a twenty-five-cent piece, may be polished by being
-tumbled in a sawdust bag. A cotton bag is made, three feet long and six
-inches in diameter, closed at one end and half-filled with fine sawdust.
-The articles are then put in the bag and the end closed. Grasp the ends
-of the bag with both hands, as if to jump rope with it; then swing it to
-and fro, until the articles have had a good tumbling. Look at them to
-see if they are bright enough; if not, keep up the tumbling.
-
-When old work is to be re-plated, or gone over, it will be necessary to
-remove all of the old plate before a really good job can be done. In
-some cases it may be removed with a scratch-brush or pumice-stone; but,
-as a rule, it can be removed much quicker and more satisfactorily with
-acids.
-
-Silver may be removed from copper, brass, or German-silver with a
-solution of sulphuric acid, with one ounce of nitrate of potash to each
-two quarts of acid. Stir the potash into the acid, then immerse the
-article. If the action becomes weak before the silver is all off, then
-heat the solution and add more of the potash (saltpetre). Gold may be
-removed from silver by heating the article to a cherry-red, and dropping
-it into diluted sulphuric acid--one part acid to two parts water. This
-will cause the gold to peel and fall off easily.
-
-
-Electrotyping
-
-The term electrotyping is interpreted in several ways, but, in general,
-it means the process of electro-plating an article, or mold, with a
-metal coating, generally copper, of sufficient thickness, so that when
-it is removed, or separated from its original, it forms an independent
-object which, to all appearances, will be a fac-simile of the original.
-
-To obtain a positive copy a cast has to be taken from a negative or
-reverse. This negative is called the mold or matrix, and can be of
-plaster, glue, wax, or other compositions. There are a number of
-processes in use, but the Adams process (no relation to the author) will
-give a boy a clear idea of this electro-chemical and mechanical art.
-This process was patented in 1870, and is said to give a perfect
-conduction to wax and other molds, with greater certainty and rapidity
-than any other, and will accomplish in a few minutes that which plumbago
-(black-lead) alone would require from two to four hours to effect.
-
-As applied to the electrotyping of type, and cuts for illustration, the
-warm wax impression is taken by pressing the chase or form of type into
-a bed of wax by power or hydraulic pressure. Then remove it, and while
-the wax is still warm, powdered tin, bronze, or white bronze powder is
-freely dusted all over it with a soft hair-brush, until the surface
-presents a bright, metallic appearance. The superfluous powder is then
-dusted off, and the mold is immersed in alcohol, and afterwards washed
-in water to remove the air from the surface. It is then placed in the
-copper bath and the connection made from the negative pole to the face
-of the mold, so that the current will flow over its entire surface. A
-deposit of copper will quickly appear, and become heavier as the mold is
-left in longer.
-
-When a mold has received the required deposit it should be taken from
-the bath and the copper film removed from it. This is done by placing
-the mold in an inclined position and passing a stream of hot water over
-the back of the copper film. This softens the wax and enables one to
-strip the film off, taking care at the same time not to crack or bend
-the thin copper positive.
-
-The thin coating of wax, which adheres to the face of the copper, can be
-removed by placing it, face up, on a wire rack and pouring a solution of
-caustic potash over it, which, in draining through, will fall into a
-vessel or tank beneath the rack.
-
-The potash dissolves the wax in a short time, and the electro-deposited
-shell may then be rinsed in several changes of cold water, or held under
-the faucet until thoroughly freed from the caustic.
-
-As many, if not all, of the chemicals used in the various plating
-processes, and also the cleaning fluids, are highly poisonous, great
-care should be taken when handling them. Do not let the fingers or hands
-come in contact with caustic solutions or cyanide baths.
-
-Never use any of these solutions if you have recently cut your fingers
-or hands, and do not allow the cyanides or caustics to get under the
-finger-nails. Never add any acid to liquids containing cyanide or
-ferro-cyanide while in a closed room. This should always be done in the
-open air, where the fumes can pass away, for the gases which rise from
-these admixtures are poisonous when inhaled.
-
-
-Chapter XII
-
-MISCELLANEOUS APPARATUS
-
-The field of applied electricity is such a wide one as to preclude any
-exhaustive handling of the subject in a book of this size. The aim has
-been to acquaint the young student with the basic principles of the
-science, and it is his part to develop these principles along the lines
-indicated in the preceding pages. But there are some practical
-applications that may be properly grouped under the heading of this
-chapter. They may serve as a stimulus to the inventive faculties of the
-youthful experimenter, and since the pieces of apparatus now to be
-described are useful in themselves, the time spent in their construction
-will not be wasted.
-
-
-A Rotary Glass-cutter
-
-When making a circle of glass it is generally best to let a glazier cut
-the disk, otherwise many panes are likely to get broken before the young
-workman succeeds in getting out a perfect one. But with a rotary
-glass-cutter the task is a comparatively simple one, and the tool is
-really an indispensable piece of apparatus in every electrician’s kit.
-(See Figs. 1 and 2.)
-
-The wooden form is turned from pine or white-wood, and is three inches
-in diameter at the large end, or bottom, one inch in diameter at the
-top, and two inches high. It is covered with felt held on with glue.
-Directly in the middle of the top a small hole is bored one-eighth of an
-inch in diameter, and in this aperture an awl or marker is placed,
-handle up, as shown in Fig. 2. Notice that the awl is not made fast to
-the form, but is removable at pleasure. A hard brass strip twelve inches
-long, five-eighths of an inch wide, and one-eighth of an inch thick is
-cut at the end to receive a steel-wheel glass-cutter, as shown at the
-foot of Fig. 1.
-
-A number of one-eighth-inch holes are bored along the strip, and half an
-inch apart, measuring from centre to centre. To cut a disk of glass the
-form is placed at the centre of the pane, the latter being imposed on a
-smooth table-top over a piece of cloth. The strip, or arm, is laid on
-the form, and over a small washer, so that one of the holes lines with
-that in the form. The awl is passed down through the strip and into the
-block, and the cutter is arranged in the slot at the end of the arm.
-Press down lightly on the handle of the awl, to keep the form from
-slipping; then the cutter is drawn around the glass, describing the
-circle, and cutting the surface of the glass, as shown by the solid line
-in Fig. 4. The disk must not be removed from the pane until the margin
-is broken away. With a straight-edge and a cutter score the glass across
-the corners, as indicated by the dotted lines in Fig. 4; then tap the
-glass at the underside along the line and break off the corners. After
-the corners have been removed tap the glass again, following the line of
-the circle; then break away the remaining fragments and smooth the
-edge.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-GLASS-CUTTING APPLIANCES]
-
-
-To Smooth Glass Edges
-
-To smooth the rough edge of glass there are several methods. The
-simplest way is to hold the disk or straight-edge against a fine
-grindstone and use plenty of water. The glass must be held edgewise, as
-shown in Fig. 5, and _not_ flatwise, as shown in Fig. 6. To properly
-grind a disk two workmen are necessary, one to turn the stone, and the
-other to hold the disk by spreading the hands and grasping it at the
-middle on both sides (see Fig. 5). In this manner the glass may be held
-securely, and slowly turned, so that an even surface will be ground.
-When the flat edge is smoothed, tilt the glass first to one side and
-then the other, and grind off the sharp edges.
-
-Another method is to lay the glass on a table, upon a piece of felt or
-cloth, and allow the edge to project over the table for two or three
-inches. Hold the glass down with one hand to prevent its slipping; then,
-with a piece of corundum, or a rough whetstone and glycerine, work down
-the edge until it is smooth, turning the glass continually so that the
-edge you are working on hangs over the table. This process of grinding
-is somewhat tedious, but perseverance and patience will win out.
-
-
-To Cut Holes in Glass
-
-Holes may be cut in glass in several ways by an expert, but the boy who
-is a novice in this line should stick to slow and sure methods and take
-no chances. Fortunately, glass is little used in voltaic electricity,
-but it is indispensable in the construction of the frictional machines,
-Leyden-jars, and condensers, where glass is used as the dielectric, also
-for the covering-plates to instruments.
-
-The simplest method is that of rotating a copper tube forward and
-backward over the glass, using fine emery dust for the cutting medium
-and oil of turpentine as a lubricant. The copper tube must be held in a
-rack, so that its location will not shift during the rotating or cutting
-motion. The rack in which the tube is held may be of any size, but to
-take a disk or square of glass, twenty inches across, the frame should
-be twenty-two inches long, ten inches wide, and twelve inches high, as
-shown in Fig. 3.
-
-The side-plates are eleven inches high and ten inches wide, the top is
-twenty-two inches long and ten inches wide, while the under ledge is
-twenty and a quarter inches long by ten inches wide. This frame is put
-together with glue and screws. Across the back, from the corners down to
-the middle of the under ledge, battens or braces are made fast to
-prevent the frame from racking. A hole is made through the middle of the
-top and under ledge for the copper tube to pass through. If
-different-sized tubes are to be used, blocks to fit the top and under
-board are to be cut and bored, so that they may be held in place with
-screws when in use. To cut a hole in glass, place the disk or pane on a
-felt or cloth-covered table, and over it arrange the frame, so that the
-tube will rest on the spot to be drilled. Drop the copper tube down
-through the hole, having first spread the bottom of the tube slightly,
-so that it will not split the glass. Now put some emery inside the tube
-so that it will fall on the glass; then place a wooden plug in the top
-of the tube and arrange an awl, or hand-plate, so that the tube may be
-pressed down. Take one turn about the tube with a linen line, or
-gut-thong, and make the ends fast to a bow, so that it will draw the
-string taut but not too tight. Lubricate the foot of the tube with oil
-of turpentine, and draw the bow back and forth. At first the motion will
-cause the copper to scratch the glass, and then cut it, until finally a
-perfectly drilled hole is formed. During the operation both glass and
-frame must be held securely, and the bow drawn evenly and without any
-jerking motion. Holes of different sizes may be cut with tubes of
-various diameters. Small holes may be cut with a highly tempered
-steel-drill and glycerine, the drill being held in a hand-drilling tool
-or in a brace.
-
-
-Anti-hum Device for Metallic Lines
-
-In overhead wires, where galvanized or hard copper wire is used, the hum
-due to the tension of the wires, and the wind blowing through them,
-causes a musical vibration which becomes most annoying at times. This
-can be overcome by a simple device known as an “anti-hum.” It consists
-of a knob made of wood or rubber, through which a hole is bored, and
-around which a groove is cut. One end of the wire is passed through the
-hole and a loop formed, the loose end being wrapped about the incoming
-wire. The other end of the line is passed around the knob in the groove,
-and the end twisted about the line-wire. The knob is then an insulator
-and a sound-deadener at the same time. To complete the metallic circuit
-a loop of wire is passed under the knob, the ends of which are made fast
-to the line-wires, as shown at Fig. 7.
-
-[Illustration: FIG. 7]
-
-[Illustration: FIG. 8]
-
-
-A Reel-car for Wire
-
-It is not always convenient nor possible to carry about a heavy roll of
-wire when hanging a line, especially if it is No. 12 galvanized wire, of
-which there are from fifty to a hundred pounds in one roll. Wire should
-be unwound as it is paid out, and not slipped off from the coil, since
-it is liable to kink; therefore, some portable means of transporting it
-should be provided. Line-wires over long distances are paid out from a
-reel-truck drawn by horses. For the use of the amateur electrician the
-reel-car shown in Fig. 8 should meet all requirements.
-
-The reel is made from two six-inch boards, a barrel-head or a round
-platform of boards, four trunk-rollers, and a bolt. From a six-inch
-board cut two pieces five feet long. Eighteen inches from either end cut
-one edge away so as to form handles, as shown at C C C C in Fig. 8,
-rounding the upper and under edges to take off the sharp corners. Cut
-four cross-pieces sixteen inches long; and from two-by-four-inch spruce
-joist cut four legs twelve inches long, and plane the four sides.
-
-Nail two of the cross-pieces to the legs; then nail on the side-boards
-and so form the frame of the reel. Bore a half-inch hole through a piece
-of joist; then nail it between the remaining two cross-boards, taking
-care to get it in the centre, as shown at A. Arrange these pieces at the
-middle of the frame, making them fast with nails driven through the
-side-boards and into the ends of these cross-pieces. Drive some pieces
-of matched boards together, and with a string, a nail, and a pencil
-describe a circle twenty inches in diameter. With a compass-saw cut the
-boards on the line, and join them with four battens made fast at the
-underside with nails. Do not make the battens so that they will extend
-out to the edge of the circle, but keep them in an inch or two, so that
-the under edge of the turn-table will rest on four trunk-rollers screwed
-fast to the top edges of the side-boards and end cross-pieces, as shown
-at B. A half-inch bolt is passed down through a hole made at the middle
-of the table, and through the block. Between the block and the underside
-of the table several large iron washers should be placed on the bolt,
-so that they will keep the table slightly above the rollers, the main
-weight of the table and its load of wire being held by the middle
-cross-brace. The object of the trunk-rollers is to relieve the side
-strain on the bolt, and also to prevent friction between the edge of the
-table and the frame, in case the tension on the wire pulls it to one
-side. Bore six holes in the table, on a circle of twelve inches, and
-drive hard-wood pegs in them, as shown in Fig. 8. When a roll of wire is
-lying on the table two boys can easily lift and carry the car, and as
-they do so the wire will pay out. Give all the wood-work a coat of
-dark-green paint, and oil the trunk-rollers and the wood where the bolt
-passes through. A pair of nuts should be placed on the lower end of the
-bolt and a washer under its head. These lock-nuts must be screwed on
-with two monkey-wrenches, forced in opposite directions, so that one nut
-will be driven tightly against the other. This is to prevent the turning
-of the table from unscrewing the nuts.
-
-
-Insulators
-
-For telegraph and telephone lines, where pole, tree, or building
-attachments are necessary, insulators must be used to carry the wires
-without loss of current. The regular glass, porcelain, or hard rubber
-insulators, made for pole and bracket use, are of course the best. They
-can be purchased at any supply-house for a few cents each, but there are
-other devices which will answer equally well and which will cost little
-or nothing.
-
-Obtain some bottles of stout glass, the green or dark glass being the
-toughest; then carefully break the bottle part away. In doing this hold
-the bottle by the neck, with a piece of old cloth wrapped about it, to
-prevent the glass chips from flying. Save all of the neck and part of
-the shoulder, as shown in Fig. 9, so that the wire and its anchoring
-loop will not slip off and fall down on the peg or cross-tree.
-
-Hard-wood pegs cut from sticks one inch and a half square should be
-whittled down so that they will fit in the neck and come up to the top.
-The pegs should be long enough at the bottom to permit of their being
-fastened to the supporting poles, trees, or building. In Fig. 10 three
-ways of attaching insulators are shown. At A the peg is nailed to the
-top of a pole, or a hole is bored in the pole and the peg driven down in
-it. At B two sticks with peg ends are nailed to a pole in the form of a
-[V], and across the sticks a cross-brace is made fast to prevent the
-sticks from spreading or dropping down. This cross-brace is made fast to
-both the sticks and the pole so as to form a rigid triangle. At C the
-usual form of cross-tree, or [T] brace, is shown. The pegs may be nailed
-to the face of the cross-plate, or holes may be bored in the top and the
-pegs driven down into them. If the cross-piece is more than two feet
-long, bracket-iron should be screwed fast to the pole and brace at both
-sides, as shown at C. Where a cross-plate is made fast to a pole, a lap
-should be cut out so that the plate can lie against a flat surface
-rather than on a round one (see D in Fig. 10).
-
-The shoulder of the bottle-necks must not rest on a cross-piece, or
-touch anything that would lead to the ground or to other wires. The
-shoulder acts as a collar, and so sheds water that in wet weather the
-current cannot be grounded through the rain. The underside of the collar
-should always be dry, and also that part of the peg protected by the
-collar, thereby insuring against the loss of current. The relative
-position of insulator and peg is shown at Fig. 9, and if the pegs are
-cut carefully the bottle-necks should fit them accurately.
-
-
-Joints and Splices
-
-It is essential in electrical work to have joints, splices, unions, and
-contacts made perfectly tight, so that the current will flow through
-them uninterruptedly. A poor contact or weak joint may throw a whole
-system out of order. For this reason all joints should be soldered
-wherever practicable. In line work, however, this is impossible, except
-where trolley-wires are joined, and these are brazed in the open air by
-an apparatus especially designed for the purpose. In telegraph and
-telephone lines perfect contact is absolutely necessary, and where
-attachments are made to insulators the main-line should never be turned
-around the insulator. The wire is brought up against the insulator, and
-with a [U] wire the main-line is tightly bound to it, as shown at Fig.
-11. If it is necessary to bind the main-line more securely to the
-insulator, one or two turns may be taken around the insulator with the
-[U] or anchoring wire; then with a pair of plyers a tight wrap is made.
-
-When joining two ends of wire together, never make loops as shown in
-Fig. 12 A. This construction gives poor contact, for the wire loops
-will wear and finally break apart. Moreover, the rust that forms between
-the loops will often cause an open circuit and one difficult to locate.
-Care must be taken to make all splices secure and with perfect contact
-of wires, and the only manner in which this can be done is to pass the
-ends of wires together for three or four inches, as shown in Fig. 12 B.
-
-[Illustration: FIG. 9]
-
-[Illustration: FIG. 10]
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 12]
-
-[Illustration: FIG. 13]
-
-Grasp one wire with a pair of plyers, and with the fingers start the
-coil or twist, then with another pair of plyers finish the wrapping
-evenly and snugly. Treat the other end in a similar manner, and as a
-result you will have the splice pictured in Fig. 12 B, the many wraps
-insuring perfect contact. This same method is to be employed for inside
-wires, and after the wrap is made heat the joint and touch it with
-soldering solution. The solder will run in between the coils and
-permanently unite the joint. The bare wires should then be covered with
-adhesive tape.
-
-Avoid sharp turns and angles in lines, and where it is not possible to
-arrange them otherwise it would be well to put in a curved loop, as
-shown at Fig. 13. A represents a pole, B B the line, and C the
-quarter-circular loop let in to avoid the sharp turn about the
-insulator. The current will pass around the angle as well as through the
-loop, but a galvanometer test would show that the greater current passed
-through the loop and avoided the sharp turn.
-
-
-“Grounds”
-
-[Illustration: FIG. 14]
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-In the chapter on wireless telegraphy several good “grounds” were
-described, any one of which would be admirably adapted to telegraph or
-telephone circuits. In Figs. 14, 15, and 16 are illustrated three other
-“grounds” that can easily be made from inexpensive material. The first
-one, Fig. 14, is an ordinary tin pan with the wire soldered to the
-middle of the bottom. The wire must be soldered to be of use, as the pan
-would soon rust around a simple hole and make the “ground” a
-high-resistance one. If the pan is buried deep enough in the earth, and
-bottom up, it will last for several years, or so long as the air does
-not get at it to induce corrosion.
-
-The star-shaped “ground” is cut from a piece of sheet zinc, copper, or
-brass, and is about twelve inches in diameter. The wire is soldered to
-the middle of it, and it is buried four feet deep, lying flat at the
-bottom of the hole.
-
-In Fig. 16 a pail or large tin can is shown with the wire passing down
-through the interior and finally reaching the bottom, where it is
-soldered fast. The can is filled with small chunks of carbon, or
-charcoal, and some holes are punched around the outer edge and bottom to
-let the water out. The can is then buried three or four feet in the
-ground. Use nothing but copper wire for “grounds,” and it should be
-heavy--nothing smaller than No. 14. The wire should be well insulated
-down to and below the surface for a foot or two, so that perfect action
-will take place and a complete “ground” secured.
-
-
-The Edison Roach-killer
-
-When Edison was a boy he invented the first electrocution apparatus on
-record. At a certain station on the Grand Trunk Railroad, where Edison
-was employed as a telegraph operator, the roaches were so thick that at
-night they would crawl up the partition between the windows and reach
-the ceiling, where they would go to sleep. During the day they were apt
-to become dizzy, lose their footing, and drop down on the heads of the
-operators. This did not suit young Edison, so he devised a scheme for
-their destruction. While watching a piece of telegraph apparatus one
-day, he saw a roach try to step from a bar charged with positive
-electricity to one through which a negative current flowed. The insect’s
-feet were moist and so made a connection between the two bars. As a
-consequence a short-circuit of high tension passed through its body and
-it dropped dead. This put an idea into Edison’s head, and the
-electrocution apparatus was soon in working order. The “killer” was the
-most simple device one could imagine, and was composed of two long,
-narrow strips of heavy tin-foil pasted side by side on a smooth board,
-with a space of one-eighth of an inch between them, as shown at Fig. 17.
-To one strip a positive wire was connected, while to the other a
-negative or ground was made fast. High-tension current, or that from an
-induction-coil, was connected with the wires, and the resulting voltage
-was strong enough to give one a severe shock if the fingers of one hand
-were placed on one plate and those of the other hand on the other plate.
-
-This device was arranged across the window-casing in the path the
-roaches were accustomed to travel on their nightly trips up the side
-wall. It was not long after dark before roach number one sauntered up
-the wall, crossed the under strip, and stepped over on the upper one.
-But he went no farther, and he, with many of his friends and relations,
-were gathered up in a dust-pan the next morning and thrown into the
-stove.
-
-[Illustration: FIG. 17]
-
-[Illustration: FIG. 18]
-
-In electricity, as in many other things, simplicity is the key-note of
-success; and from this little device to employ the alternating current
-for ridding a house of an insect nuisance sprang the grim apparatus
-known as the “death chair,” used in the execution of first-degree
-criminals in the State of New York. Many people think the mechanism for
-electrocution is a complicated one, but it is quite as simple as the
-Edison roach-killer. One pole is placed at the head of the criminal and
-the other at the feet, the latter being bound fast so that perfect
-contact can be had. Then an alternating current of fifteen hundred to
-two thousand volts is run through the body, and death is instantaneous
-and void of pain.
-
-
-An Electric Mouse-killer
-
-A modification of the simple roach-killer was recently used by the
-author in his laboratory to get rid of some troublesome mice. A piece of
-board was cut twelve inches square, the edges being bevelled so that it
-would be an easy matter for the mice to climb up on it. An inch-wide
-circle of sheet brass was prepared measuring eleven inches outside
-diameter and nine inches inside. Another circle was cut measuring eight
-inches and a half outside and six inches inside diameter. Both circles
-were attached to the board with copper tacks and polished as bright as
-possible, the finished board appearing as shown in Fig. 18.
-
-Wires were soldered to each strip, and these in turn were connected to a
-high-tension current of several thousand volts. Crumbs and small pieces
-of meat were placed on the board inside the circles, and the trap was
-set in a convenient place on the floor of the laboratory.
-
-The next morning several mice lay dead on the floor, but at some
-distance from the board, and this seemed a little mysterious. The
-following night the author worked late in the laboratory. After
-finishing what he had on hand, he turned down the lights and sat down
-and watched the trap. Presently Mr. Mouse appeared from somewhere. He
-sniffed the air, then approached closer to the board, sniffed again,
-and, evidently concluding that he was on the right trail, he climbed up
-the side of the board and stood on the outer strip. He placed one
-fore-foot on the inner strip, and, bang! up he went in the air, and
-landed on the floor a foot or more away. His jump into space was due to
-the electric action on his muscles, for the current literally tore his
-nervous system into shreds.
-
-Mr. Mouse lost a great many friends and relatives that season in the
-same manner, and the apparatus is confidently recommended as a certain
-and humane agent for the destruction of all small vermin.
-
-
-Chapter XIII
-
-FRICTIONAL ELECTRICITY
-
-Frictional electricity is high potential, current alternating, and of
-high voltage but very low amperage. Apart from certain uses in
-laboratory and medical practice, it is valueless. In its greater volume
-it is akin to the lightning-bolt and is dangerous; but in its smaller
-volume it is a comparatively harmless toy. From the glass rod, or the
-amber, rubbed on a catskin to the modern static machines is a long jump,
-and the period of exploitation covers centuries of interesting
-experiments, most of which, however, have been practically useless for
-any commercial purpose.
-
-Static or frictional electricity is generated by friction only, without
-the aid of magnets, coils of wire, or armatures rotating at high speed.
-The simple process of the glass and catskin has been variously modified,
-until at last Wimshurst invented and perfected what is known as the
-“Wimshurst Influence Machine.” It is self-charging, and does not require
-“starting.” It will work all the year round in any climate and
-temperature, and is the greatest improvement ever made in static
-electric machines.
-
-Apart from its efficiency under all conditions, it is the simplest of
-all machines to make, and can easily be constructed by a boy who is
-handy with tools, and who can obtain the glass and brass parts necessary
-in its construction. The principal parts of an influence machine are the
-glass disks, wooden bosses, driving pulleys and crank, glass standards,
-brass arms with the spark-balls at the ends, and the base with the
-uprights on which these parts are built up and held in position.
-
-
-A Wimshurst Influence Machine
-
-Obtain a stiff piece of brown paper twenty inches square, and with a
-compass describe a circle twenty inches in diameter. Inside of this
-circle make another one fourteen inches in diameter, and near the centre
-a third circle six inches in diameter. Another circle four inches in
-diameter should be drawn inside of the six-inch circle, so that when the
-bosses are made fast to the glass plates they can be properly centred.
-Also mark sixteen lines radiating from the centre, equal distances
-apart, as shown in Fig. 1.
-
-From a dealer in glass purchase two clear, white panes of glass eighteen
-inches square. Be careful not to get the green glass, as this is not
-nearly so good as the white for static machine construction. If it is
-possible to get crystal plate so much the better. The panes should be
-thin, or about one-sixteenth of an inch in thickness, and free from
-bubbles, wavy places, scratches, or other blemishes.
-
-From these panes cut two disks sixteen inches in diameter with a rotary
-cutter, as described in the chapter on Miscellaneous Apparatus, page
-294, and rub the edges with a water-stone (see chapter on Formulæ, page
-330.)
-
-From flat, thin tin-foil cut thirty-two wedge-shaped pieces four inches
-long. They should be one inch and a half wide at one end and
-three-quarters of an inch at the other, as shown at Fig. 2 A. Give each
-plate of glass two thin coats of shellac on both sides; then lay one on
-the paper pattern (Fig. 1) so that the outside edge of the glass will
-lie on the largest circle. Place a weight at the middle of the glass to
-hold it in place; then make sixteen of the tin-foil sectors fast to the
-plate, using shellac as the sticking medium. But first give one side of
-each sector a thin coat of shellac, allowing it to dry; then give it
-another coat when applying it to the glass. The sectors are to be
-symmetrically arranged on the glass, using a line of the pattern as a
-centre for each piece (as shown at A in Fig. 1), and the fourteen and
-six inch circles as the outer and inner boundaries. Each piece, as it is
-applied, should be pressed down upon the glass, so that it will stick
-smoothly, without air bubbles or creases. A very good plan is to lay a
-piece of soft blotting-paper over the sector and drive it down with a
-small squeegee-roller such as is used in photography, taking care,
-however, not to shift the sector from its proper position. When all the
-sectors are on, the plate should appear as shown in Fig. 2. After the
-shellac, which holds the sectors to the glass, is dry, run a brush full
-of shellac around the inner and outer extremities of the tin-foil strips
-for half or three-quarters of an inch in from the ends. The shellac will
-hold the sectors firmly to the glass, and will slightly insulate them as
-well, thereby preventing the escape of electricity. Apply the remaining
-sectors to the other plate of glass in a similar manner; and as a result
-two disks of glass, with the applied strips, will be ready to mount in
-the frame.
-
-[Illustration: FIG. 1
-
-FIG. 2
-
-FIG. 3
-
-FIG. 4
-
-FIG. 5
-
-FIG. 6
-
-DETAILS OF WIMSHURST INFLUENCE MACHINE]
-
-A hole three-quarters of an inch in diameter should be made in each
-glass plate, so that a three-eighths spindle may pass through them and
-into the bosses, so as to keep them in proper line. It is preferable,
-however, not to bore these holes if bosses and accurately bushed holes
-can be made in the uprights of the frame which support these disks.
-
-At a wood-working mill have two bosses made that will measure four
-inches in diameter at the large end, and one inch and a half at the
-small one. They should be of such length that when the plates and two
-bosses are arranged in line (to appear as shown in A A at Fig. 9) they
-will fill the entire space between the uprights B B. Near the small end
-a groove is turned in each boss, so that a round leather belt will fit
-in it, as shown in Fig. 3.
-
-The base is made from pine, white-wood, cypress, or any other wood that
-is soft and easily worked. It is composed of two strips twenty-four
-inches long, three inches wide, and one inch and a quarter in thickness,
-and two cross-pieces fourteen inches long, three inches wide, and one
-inch and a half thick.
-
-These are put together with glue and screws, and at both sides of the
-base notches are cut to accommodate the feet of the uprights. The
-uprights are seventeen inches high, three inches wide, and one inch and
-a half thick. The notch at the foot of each one is cut so that, when
-fitted in place, the foot of the upright will rest on a table on a line
-with the bottom of the end cross-pieces under each corner. At the foot
-of the uprights a piece of sheet rubber should be made fast, with glue
-or shellac, so that when in operation the machine will not move about or
-slide.
-
-A groove is cut at one side of each upright six inches above the bottom,
-as shown at Fig. 4 A. In this groove the driving-wheel axles fit, and
-near the top holes are made in the uprights through which the spindles
-pass, which in turn support the bosses and glass disks.
-
-At the middle of each cross-piece forming the ends of the base a
-one-inch hole, for the glass standard rods, is bored through the wood,
-as shown at Fig. 4 B B. After attaching the uprights to the base with
-glue and screws, and giving all the wood-work several successive coats
-of shellac, the frame will be ready for its mountings.
-
-The driving-wheels are of wood seven-eighths of an inch thick and seven
-inches in diameter; they should be turned on a lathe and a groove cut in
-the edge so that a round leather belt will fit in it. These wheels are
-mounted on a wooden axle that can be made from a round curtain-pole,
-with a half-inch hole bored through its entire length. The axle is as
-long as the distance between uprights B B in Fig. 9. The wheels are to
-be arranged and glued fast to the axle, so that the grooves will line
-directly under those in the bosses, as shown in Fig. 9. A half-inch axle
-is driven through the hub, and at one end it is threaded and provided
-with two washers and nuts; or a square shoulder and one washer and nut
-may be used, so that a crank and handle may be held fast. Shellac should
-be put on the shaft to make it hold fast in the hub.
-
-The complete apparatus of wheels, axle, hub, and handle is shown at Fig.
-5, and in the frame this is so hung that the iron axle rests in the
-grooves cut in the uprights. To hold this in place two metal straps, as
-shown in Fig. 6, are made and screwed fast to the wood. When finally
-adjusted the driving-wheels should rotate freely whenever the crank is
-turned. The wooden bosses, Fig. 3, are given two or three coats of
-shellac; then they are made fast to the glass disks on the same side to
-which the tin-foil sectors are attached. The disks should be placed over
-the paper plan, Fig. 1, and so adjusted that the outer line tallies with
-the large circle. Acetic glue[4] is then applied to the flat surface of
-the boss, and the latter is placed at the middle of the disk to line
-with the small circle. Place a weight on the end of the boss to hold it
-down, and leave it for ten or twelve hours or until thoroughly dry.
-
-  [4] See Formulæ, Chapter xiv., for the recipe of acetic glue.
-
-Both bosses should be set at the same time so that they may dry
-together.
-
-If the bosses are turned on a lathe a hole should be made in each one
-about half-way through from the small end. This, in turn, should be
-bushed or lined with a piece of brass tube, which should fit snugly in
-the hole. A little shellac painted on each piece of tube will make it
-stick. Pieces of steel rod that will just fit within the tubing are to
-be cut long enough to enter the full length of the hole, pass through
-the holes made in the top of the uprights, and extend half an inch
-beyond, as shown in Fig. 9. The bosses and axles will then appear as
-shown in Fig. 7.
-
-Flat places should be filed on each rod where it passes through the wood
-upright; a set-screw will then hold it fast and keep it from revolving.
-When the hole, or tubing, is oiled so that the boss and disk will
-revolve freely on the axle, the disks, bosses, and axles are ready to be
-mounted in the frame.
-
-A red fibre washer, such as is used in faucets, should be made fast to
-one glass disk at the centre, so as to separate the disks and prevent
-them from touching when they are revolving in opposite directions. These
-fibre washers can be had from a plumber or purchased at a hardware
-store. Shellac or acetic glue will hold the washers in place.
-
-[Illustration: FIG. 7]
-
-[Illustration: FIG. 8]
-
-[Illustration: FIG. 9]
-
-[Illustration: FIG. 10]
-
-Mount one disk by holding the boss with the small end opposite a hole in
-one upright, and slip an axle through from the outside of the upright.
-Hold the other disk in place, and slip the remaining axle through the
-other upright and into the boss. When both plates are in place and
-centred, turn the set-screws down on the flattened axles to hold them in
-place.
-
-To reduce the friction between the bosses and the uprights it would be
-well to place a fibre washer between them. A few drops of oil on these
-washers will lubricate them properly, and allow the machine to run
-easier. An end view of the apparatus, as so far assembled, will appear
-as shown in Fig. 9, A being the disks, bosses, and axles, B B the
-uprights supporting them, C the hub, and D D the driving-wheels. The
-handle and crank (E) extends out far enough from the side to allow a
-free swinging motion without hitting the upright or base. Having
-arranged these disks and wheels so as to revolve freely, it will now be
-necessary to construct and add the other vital parts and the connecting
-links in the chain of the complete working mechanism.
-
-From a supply-house obtain two solid glass rods an inch in diameter and
-fifteen inches long. These fit in the holes (B B) bored in the
-end-pieces of the base, Fig. 4. Procure two brass balls, two or two and
-a half inches in diameter, such as come on brass beds, and two short
-pieces of brass tubing, one inch inside diameter, that will fit over the
-ends of the rods. These tubings are to be soldered fast to the balls so
-that both tubes and balls will remain at the top of the glass rods.
-
-From brass rod three-sixteenths or a quarter of an inch in diameter make
-two forks, as shown at Fig. 8, and solder small brass balls at the ends
-of the rods. The prongs of the fork are six inches long and the shank
-four inches in length. Along the inside of the forks small holes are
-bored, and brass wires, or “points,” are soldered fast. These extend out
-for half an inch from the rods, and are known as the “comb,” or
-collectors. The forks should be so far apart that when mounted with the
-glass disks revolving between them the points will not touch or scratch
-the tin-foil sectors, and yet be as close to them as possible. A hole
-should be bored in the brass balls, and the shank of the fork passed
-through and soldered in place, as shown in Fig. 10.
-
-A three-eighth-inch hole is bored directly in the top of each brass ball
-to hold the quadrant rods, which extend over the top of the disks.
-
-In the illustration of the complete machine (Fig. 12) the arrangement of
-the glass pillars, balls, combs, and quadrant rods is shown. The rods
-are three-eighths of an inch in diameter and are loose in the holes at
-the top of the balls, so that they can be moved or shifted about,
-according as to whether it is a left or a right handed person who may be
-turning the crank.
-
-At the upper end of each rod a brass ball is soldered, one being
-three-quarters of an inch in diameter, the other two inches. The
-projecting ends of the forks should be provided with metal handles or
-brass balls, as shown in Fig. 12; these may be slipped over the end or
-soldered fast. Obtain two small brass balls with shanks, such as screw
-on iron bed-posts, and have the extending ends of the axles that support
-the bosses threaded, so that the balls will screw on them. Bore a
-quarter-inch hole through each ball, and slip a brass rod through it and
-solder it fast. Each end of these rods should be tipped with a bunch of
-tinsel or fine copper wires. These are the “neutralizers,” and the ends
-are curved so that the brushes of fine wires will just touch the disks
-when the latter are revolved, as shown in Fig. 12. The ball holding the
-rod is to be screwed fast to the axle; then the axle is pushed back into
-the boss and made fast in the head of the upright with the set-screw.
-
-[Illustration: FIG. 12]
-
-The rod-and-ball at the opposite side of the disks is arranged in a
-similar manner, but the rod points in an opposite direction to that on
-the first side. Cord or leather belts connect the driving-pulleys and
-bosses, the belt on one side running up straight over the boss and down
-again around the driving-pulley. The belt at the opposite side is
-crossed, so that the direction of the boss is reversed; and in this
-manner the disks are made to revolve in opposite directions, although
-the driving-pulleys are both going in the same direction.
-
-A portion of the sectors are omitted in the illustration (Fig. 12) so
-that a better view of the working parts may be had. When the disks are
-revolving the accumulated electricity discharges from one ball to the
-other, above the plates, in the form of bright blue sparks sufficiently
-powerful to puncture cardboard if it is held midway between the balls.
-
-
-A Large Leyden-jar
-
-When experimenting with this machine it would be well to have one or
-more Leyden-jars to accumulate static charges. A large one of
-considerable capacity is easily made from a battery jar, tin-foil, brass
-rods and chain, and some other small parts.
-
-Obtain a bluestone battery jar, and after heating it to drive all
-moisture from the surface, give it a coat of shellac inside and out.
-With tin-foil, set with shellac, cover the bottom and inside of the jar
-for two-thirds of its height from the bottom, as shown in Fig. 11. Cover
-the outside and bottom in a similar manner, and the same height from
-the bottom, and provide a cork, or wooden cap, for the top. If a large,
-flat cork cannot be had, then make a stopper by cutting two circular
-pieces of wood, each half an inch thick, the inner one to fit snugly
-within the jar, the other to lap over the edges a quarter of an inch all
-around. Fasten these pieces together with glue, as shown at Fig. 13, and
-give them several good coats of shellac. Make a small hole at the middle
-of this cap and pass a quarter-inch rod through it, leaving six inches
-above and below the cap. To the top of the rod solder a brass ball. At
-the foot a piece of brass chain is to be made fast, so that several
-links of it rest on the tin-foil at the bottom of the jar.
-
-To charge a jar from the Wimshurst machine, stand the jar on a
-glass-legged stool, and connect a copper wire between one of the
-overhead balls on the machine and the ball at the top of the rod in the
-stopper of the jar. Make another wire fast to the other ball at the top
-of the machine, and place it under the jar so that the tin-foil on the
-bottom touches it. By operating the machine the jar is charged.
-
-To discharge the jar make a [T]-yoke, as shown at Fig. 14, by nailing a
-brass rod fast to a wooden handle and soldering brass knobs, or
-hammering a lead bullet, on the ends of the rod. Hold one knob against
-the top knob of the jar and bring the other near the foil coating at the
-outside, when a spark will jump from the foil to the knob with a loud
-snap.
-
-
-A Glass-legged Stool
-
-One of the most useful accessories in playing with frictional
-electricity will be a glass-legged stool. A stool with glass feet is
-perhaps too expensive for a boy to purchase, but one may be made at
-little or no cost from a piece of stout plank, four glass telegraph
-line-insulators, and the wooden screw-pins on which they rest when
-attached to a pole.
-
-[Illustration: FIG. 11]
-
-[Illustration: FIG. 13]
-
-[Illustration: FIG. 14]
-
-[Illustration: FIG. 15]
-
-[Illustration: FIG. 16]
-
-The general plan of the stool is shown at Fig. 15, and the top measures
-twelve by fifteen by two inches. Under each corner a screw-pin is made
-fast by boring a hole in the wood and setting the pin in glue. The pins
-are cut at the top, as shown in Fig. 16, and when they are set in place
-the glass insulators may be screwed on. The wood-work should be given a
-few coats of shellac to lend it a good appearance and help to insulate
-it.
-
-There are a great many interesting experiments that may be performed
-with static or frictional electricity, and these may be looked up in the
-text-books on electricity used in school. A word of caution will not be
-misplaced. Remember that the current, in large volume, is dangerous. For
-example, a series of charged Leyden-jars may contain enough electricity
-to give a very severe shock to the nervous system of the person who
-chances to discharge it. Its medical use should be under the advice and
-supervision of a physician.
-
-
-Chapter XIV
-
-FORMULÆ
-
-In the construction of electrical apparatus there are many things, such
-as paint, cement, non-conducting compounds, and acid-proof substances,
-that are necessary in assembling the parts which make up complete
-working outfits. Accurate formulas and directions for these things will
-save the amateur trouble and expense, since they indicate the materials
-which have been put to the test of time and wear by others who have had
-abundant experience along these lines.
-
-The amateur will not need a large number of compounds, but such as are
-necessary should be of the best. Those which are described in this
-chapter can be relied upon to give working results.
-
-
-Acid-proof Cements
-
-One of the best acid-proof cements is made by adding shellac, dissolved
-in grain alcohol, to red-lead until it is at the right consistency. It
-can be used in liquid form or in a putty-like paste. The consistency is
-governed by the amount of shellac added to the red-lead. The lead should
-be pulverized and free from lumps. This cement can be mixed in a small
-tin cup or on a piece of glass, with a knife having a thin blade.
-
-It should be used as soon as it is mixed, since it “sets” as quickly as
-shellac, and then dries from the outside towards the middle. In a week
-or two it will become dry and hard like stone.
-
-Another cement, which will also dry as hard as a stone and will hold
-soapstone slabs together as if they were of one solid piece, is made of
-litharge (yellow lead) and glycerine. The glycerine is added to the
-pulverized litharge to make a paste, or it can be mixed and kneaded like
-thin putty. It should be used very soon after mixing, as it sets
-rapidly.
-
-
-Hard Cement
-
-A medium hard cement is made from plaster of Paris, six parts; silex, or
-fine sand, two parts; dextrine, two parts (by measure). Mix with water
-until soft; then work with a trowel or knife.
-
-
-Soft Cement
-
-A good soft cement is made of plaster of Paris, five parts; pulverized
-asbestos, five parts (by weight). Add water enough to make a soft paste,
-and use with a trowel or knife. This is a heat-proof compound and is
-commonly known as asbestos cement.
-
-
-Very Hard Cement
-
-One of the hardest cements that can be made is composed of hydraulic
-cement (Portland or Edison), five parts; silex, or white sand, five
-parts (by measure). Mix with water and use like plaster with a trowel or
-spatula.
-
-Care must be taken when the parts are combined to see that the cement is
-free from lumps. These must be broken before the silex, or sand, and
-water are added. Then the two parts should be mixed together at first
-and moistened afterwards. The proper way is to place some water at the
-bottom of a pan; then add the dry mixture by the handfuls, sprinkling it
-around so that the water can enter into it without forming lumps. Keep
-adding and mixing until the mass is at the right consistency to work.
-
-All these cements are acid-proof.
-
-
-Clark’s Compound
-
-For exterior insulation, where the parts are exposed to the weather, a
-superior compound is made up of mineral pitch, ten parts; silica, six
-parts; tar, one part (all parts by weight). This is called Clark’s
-compound, after the man who invented it and used it successfully.
-
-It is heated, thoroughly mixed, and used with a brush or spatula.
-
-
-Battery Fluid
-
-A depolarizing solution for use in zinc-carbon batteries like the Grenet
-is composed as follows:
-
-Dissolve one pound of bichromate potash or soda in ten pounds of water
-(by weight). When it is thoroughly dissolved add two and one-half pounds
-of sulphuric acid, slowly pouring it into the bichromate solution and
-stirring it with a glass rod. The addition of the acid will heat the
-solution. Do not use it until it has entirely cooled.
-
-
-Glass Rubbing
-
-To rub the edges of glass, such as the disks for Wimshurst machines,
-obtain a piece of hard sandstone, such as is used for sharpening knives
-or scythes. The glass is placed on a table so that the edge extends
-beyond. Oil of turpentine is rubbed or dropped on the surface of the
-stone, and the edge of the glass is moistened with a rag soaked in the
-turpentine. Hold the glass down securely with one hand, and with the
-other grasp the stone and give it a forward and backward motion,
-grinding the glass along its edge and not crosswise. With care and
-patience a rough edge can soon be brought to a smooth one, and a soft,
-rounded corner substituted for the hard, angular, cutting edge that
-makes the glass a difficult thing to handle. Use plenty of lubricant in
-the form of oil of turpentine to make the work easy.
-
-
-Acetic Glue
-
-One of the best glues for glass and wood or glass and fibre is made by
-placing some high-grade glue (either flake or granulated) in a cup or
-tin and covering it with cold water. Allow it to stand several hours
-until the glue absorbs all the water it will and becomes soft; then pour
-the water off, and add glacial acetic acid to cover the glue. The
-proportion should be eighteen parts of glue to two of acid. Heat the
-mass until it is reduced to liquid, stirring it until it is thoroughly
-mixed. When ready for use it should be poured into a bottle and well
-corked to keep the air away from it.
-
-
-Insulators
-
-Apart from glass and porcelain, insulators can be made from
-non-conducting compounds, the best of which is molded mica. Ground mica
-or mica dust is mixed with thick shellac until it is in a putty-like
-state. It may then be forced into oiled molds of any desired shape.
-Hydraulic pressure is employed for almost every form of molded mica that
-is made for commercial purposes; but as a boy cannot employ that means
-to get the best results, he must use all the pressure that his hands and
-a flat board will give.
-
-Another compound is made from pulverized asbestos and shellac, with a
-small portion of ground or pulverized mica added, in the proportion of
-asbestos, six parts; mica, four parts. Shellac is added to make a pasty
-mass, which is kneaded into a thick putty and forced into oiled molds
-until it sets. It is then removed and allowed to dry in the open air,
-and the mold used for more insulators.
-
-
-Non-conductors
-
-When working in different materials that seem adapted to electrical
-apparatus, it is necessary to know whether they can be used safely or
-not. Often a material seems to be just the thing, but if it should be a
-partial conductor, when a non-conductor is desired, it would be
-hazardous to use it. A list of non-conductors is therefore valuable to
-the amateur. Some of the principal non-conductors, among the many, are
-as follows: glass, porcelain, slate, marble, hard stone, soapstone,
-concrete (dry), hard rubber, soft rubber, composition fibre, mica,
-asbestos, pitch, tar, shellac, cotton, silk; cotton, silk and woollen
-fabrics, transite (dry), electrobestus (dry), duranoid; celluloid, dry
-wood (well seasoned), paper, pith, leather, and oil.
-
-While this account of formulæ and material might be extended, this is
-not necessary inasmuch as the formulæ and practical directions which
-have been given will answer all usual practical requirements.
-
-
-Insulating Varnish
-
-There are several good insulating varnishes that can be used in
-electrical work, the most valuable being shellac dissolved in alcohol
-and applied with a brush. To make good shellac, purchase the
-orange-colored flake shellac by the pound from a paint-store, place some
-of it in a wide-necked bottle, and cover it with alcohol; then cork the
-bottle and let it stand for a few hours. Shake the bottle occasionally
-until the shellac is thoroughly dissolved. It can be thinned by adding
-alcohol. Always keep the bottle corked, taking out only what is
-necessary from time to time.
-
-Another varnish can be made by dissolving red sealing-wax in alcohol and
-adding a small portion of shellac. This can be applied with a soft
-brush, and is a good varnish. When colors are to be applied to
-distinguish the poles, red is used for the positive current-poles and
-blue or black for the negative, if they are colored at all.
-
-A very good black varnish is made by adding lampblack to shellac;
-another consists of thick asphaltum or asphaltum varnish. This is
-waterproof, and dries hard, yet with an elastic finish.
-
-
-Battery Wax
-
-For the upper edges of glass cells, such as the Leclanché or other
-open-circuit batteries, there is nothing superior to hot paraffine
-brushed about the upper edge to prevent the sal-ammoniac or other fluids
-from creeping up over the top. The paraffine can be colored with
-red-lead, green dust, or powders of various colors if desired, but
-generally the paraffine is used without color, so that it has a
-frosted-glass appearance when it is cool and dry.
-
-A black wax for use in stopping the tops of dry cells and coating the
-tops of carbons is composed of paraffine, eight parts; pitch, one part;
-lampblack, one part. Heat the mixture and stir it until thoroughly
-mixed; then apply with a brush, or dip the parts into the warm fluid.
-
-Another good black wax is composed of tar and pitch in equal parts. They
-are made into a pasty mass with turpentine heated over a stove, but not
-over an open flame, because the ingredients are inflammable. The
-compound should be like very thick molasses, and can be worked with an
-old table-knife.
-
-
-Chapter XV
-
-ELECTRIC LIGHT, HEAT, AND POWER
-
-  For the use of the cuts in this chapter, the Publishers desire to
-  acknowledge the courtesy of the General Electric Company, the Thomson
-  Electric Welding Company, and the Cooper Hewitt Electric Company.
-
-With the discovery of the reversibility of the dynamo, the invention of
-the telephone, and the improvements in the electric light began the
-great modern development of electricity which proved that marvellous
-agent to be a master-workman.
-
-Many of the things electrical that we ordinarily think of as modern
-inventions are merely modern applications of phenomena that were
-discovered many years ago. The pioneers in the science of dynamic
-electricity performed their experiments with the electric light,
-electro-magnets, etc., by using galvanic batteries. But for practical
-purposes the consuming of zinc and chemicals in such batteries was too
-expensive a way to generate electricity, and prevented any commercial
-use of the results of their experiments until cheaper electricity could
-be had.
-
-
-The Work of the Dynamo
-
-The invention of the dynamo, with which we obtain electricity from
-mechanical power, changed all that. Instead of consuming zinc in
-primary batteries, men could obtain it by burning coal, which is much
-cheaper, under the boiler of a steam-engine used to drive the dynamo.
-Thus it is that modern electricity comes from mechanical power. It is
-really the energy of a steam-engine or a water-wheel, or some other
-“prime mover,” working through the medium of electricity, that is
-transmitted to a distance and distributed over wires. The electricity
-may then be transmuted into light, heat, or chemical energy as the case
-may be, to light our electric lamps, develop the intense heat of the
-electric furnace, and charge storage-batteries.
-
-Moreover, some time after the invention of the dynamo it was found that
-the mechanical power put into one of these machines could be transmitted
-electrically and reproduced as mechanical power. In other words, a
-dynamo could be made to revolve and give out power, as a motor, by
-supplying it with current from another dynamo. This showed the way to
-transmute electricity back again into mechanical power, to run our
-electric cars and trains, and all kinds of machinery in our factories
-and elsewhere. Nowadays the dynamo is used to generate nearly all the
-electricity that we need. Even in such comparatively old electrical
-applications as electro-plating and the telegraph and telephone, primary
-batteries are being supplanted by motor dynamos, which we shall learn
-about later.
-
-It is from the invention of the dynamo and the discovery that it was
-reversible that we date the beginning of what are known as heavy
-electrical engineering applications, including electric light, heat, and
-power. In this closing chapter it is purposed to learn a little about
-these applications, and in so doing to summarize briefly the things that
-we have already studied.
-
-
-The Electric Light
-
-In the chapter on Electrical Resistance we learned that an electric
-current always encounters a resistance in passing through a conductor,
-and that when the current is strong enough the conductor is heated up.
-The electric light is produced by the heating of a conductor of one kind
-or another to incandescence by the electrical friction of the current
-passing through it.
-
-The first electric light was made by Sir Humphry Davy over a hundred
-years ago. He discovered that when a current from a great many cells of
-battery was interrupted the spark did not simply appear for an instant
-and then go out, as it does when only a few cells are used, but remained
-playing between the terminals of the circuit. He found by experiment
-that if pieces of carbon are used as the terminals--or “electrodes,” as
-they are called--the electricity passes between them in an intensely hot
-flame, or “arc.” The latter, which is due to the electrical resistance
-of the vapor of carbon, heats up the carbon-points so that they give a
-brilliant white light.
-
-[Illustration: _=Fig. 1=_]
-
-[Illustration: _=Fig. 2=_]
-
-Before the dynamo came into use, the electric light was rarely seen,
-except as a philosophical experiment; but as soon as cheap electricity
-became available, commercial electric arc-lamps were made by many
-inventors and have been continually improved. Fig. 1 shows one form of
-modern arc-lamp, with its case removed to show the interior mechanism.
-In most arc-lamps the lamp itself consists of a pair of carbon or other
-electrodes in the form of long rods arranged vertically, with their tips
-normally in contact. When the current is turned on, the mechanism lifts
-the upper electrode away from the lower one. The interruption of the
-circuit thus caused “strikes the arc” between the tips, and the
-mechanism keeps the arc-distance unchanged as the carbons burn away.
-Some arc-lamps are made to burn on continuous-current, and others on
-alternating-current circuits. When continuous current is used, the upper
-(or positive) carbon burns away about twice as fast as the lower one,
-forming a cup, or “crater,” from which most of the light comes.
-
-
-Uses of the Arc-Light
-
-The first commercial use of the arc-light on a large scale was for
-street-lighting, to replace the old-fashioned gas-lamps. But another
-important use is in search-lights, in which the arc-lamp is fitted with
-a powerful reflector for throwing a very bright light to a distance.
-Fig. 2 is a view of a search-light arranged to go on top of a ship’s
-pilot-house. In war-time the ships carry search-lights to help them find
-the enemy’s ships and repel attack; and they are used in the army also,
-by having a portable dynamo and engine drawn by horses. The arc is also
-employed in projectors for lecture-rooms, and sometimes for the
-headlights of steam and electric locomotives and interurban electric
-cars.
-
-
-Incandescent and Other Lamps
-
-The arc-lamp came into wide use for lighting large spaces like streets,
-stores, and public halls, but was found to be too intense for lighting
-smaller places like private houses. After many experiments, Edison
-succeeded in subdividing the electric light into the small pear-shaped
-“incandescent” lamps that we now see everywhere. In this kind of
-electric lamp the light comes from a thin “filament” of carbon,
-contained in a glass globe from which all air has been removed. Since
-there is no oxygen to support combustion, the filament may be heated
-white-hot by the current without being consumed.
-
-[Illustration: _=Fig. 3=_]
-
-In certain other forms of incandescent lamps that are just coming into
-use, the filaments are made of rare metals--osmium, tantalum, etc.--that
-will stand a high temperature without melting. The Nernst lamp has a
-filament consisting of a mixture of certain materials that has to be
-heated before it will conduct electricity.
-
-Then there are the so-called “vapor” lamps, consisting of a glass tube
-full of conducting metallic vapor which gives out light when a current
-is passed through it. The best-known form is the Cooper Hewitt mercury
-vapor-lamp shown in Fig. 3, which gives a peculiar greenish light.
-
-From the point of view of efficiency, the electric light, wonderful as
-it is, leaves much to be desired. The light always comes from a hot
-resistance; and whether this resistance is a mass of conducting vapor,
-as in the arc and vapor lamps, or a solid conducting filament, as in the
-so-called “incandescent” lamps, much more heat than light is produced. A
-needed improvement, therefore, is in the direction of obtaining a
-greater percentage of light for a given amount of electrical energy.
-
-
-Electric Heat
-
-The generation of heat in electrical devices usually means wasted
-energy--sometimes a very serious waste, as we have just seen. There are
-certain kinds of electrical apparatus, however, that are designed to
-transform all of the electrical energy delivered to them into heat, for
-various industrial and household purposes.
-
-[Illustration: _=Fig. 4=_]
-
-
-Electric Furnaces
-
-By far the most important application of electric heat, as such, is in
-electric furnaces, by means of which we attain the highest temperatures
-known to man. The electric furnace consists of a chamber of “refractory”
-material, containing the substances to be acted upon by the heat, with a
-pair of big carbon electrodes thrust into the centre, as shown in Fig.
-4, which is a picture of Moissan’s electric furnace for the distillation
-of metals, and supplied with heavy continuous or alternating currents.
-The apparatus is therefore a sort of gigantic electric arc-lamp, so
-enclosed that the whole of the intense heat of the arc is confined and
-concentrated on the smelting or other work. In many places where cheap
-electric power is to be had--as in the vicinity of the great Niagara
-Falls power-plants--electric furnaces are employed in what are known as
-electrometallurgical and electrochemical manufacturing processes. By
-their aid many metals and other substances that were formerly scientific
-curiosities, or entirely unknown, are produced commercially; such as
-aluminum, certain rare metals, and calcium carbide, from which that
-wonderful illuminant, acetylene-gas, is obtained.
-
-
-Welding Metals
-
-Another useful application of electric heat is in the welding of metals.
-Instead of heating the pieces to be welded in a forge, their ends are
-simply butted together and the electricity--generally from an
-alternating-current transformer--turned on. The heat developed by the
-“contact resistance” between the pieces quickly softens the metal so
-that the pieces may be forced together, forming a perfect weld in a few
-minutes without any hammering. Fig. 5 is a view of one form of electric
-welding-machine in which this is accomplished. The electric process can
-weld certain metals that cannot be joined securely by ordinary welding
-methods, and is used in several special arts.
-
-Welding is also performed by the heat of a special electric arc-lamp,
-which a workman holds in his hand like a blow-pipe or torch. This
-process is especially useful in joining the edges of sheet-steel, in
-making tanks for electric “transformers,” etc. The workmen have to wear
-smoked glasses in order to protect their eyes from the intense glare of
-the arc.
-
-[Illustration: _=Fig. 5=_]
-
-
-Electric Car-heaters
-
-Perhaps the simplest and best-known application of electric heat is the
-electric car-heater, consisting of coils of high-resistance wire--such
-as iron or German-silver wire--mounted on an insulating, non-combustible
-frame which is placed under the seats of the car. Part of the current
-from the trolley wire or third rail passes through the resistance-coils,
-heating them up and thereby warming the air in the car.
-
-
-Household Uses
-
-Nowadays electric heat is being more and more widely utilized in what
-are known as household electric heating-appliances. One of the most
-useful of these is the electric flat-iron, shown in Fig. 6. This
-flat-iron is designed to do away with the use of a hot stove of any
-kind, and is internally heated by means of a resistance-coil of peculiar
-shape placed in the bottom of the iron close against its working face.
-The iron is connected to an electric-light socket by means of an
-attaching plug on the end of a long, flexible cord. It takes only a few
-minutes to get hot, and its use saves much time and labor.
-
-The list of special heating-appliances that are now made includes
-curling-iron heaters; heating-pads, for taking the place of hot-water
-bags in the sick-room; cigar-lighters, in which a little grid
-“resistance” is made incandescent by pressing a button; foot-warmers;
-and radiators to dry wet shoes or skirts on rainy days. For industrial
-use there are glue-pots, for bookbinders and pattern-makers; large
-flat-irons, for tailor-shops and laundries; and electric ovens, for
-drying certain parts of electrical machines and for cooking various
-kinds of “prepared foods.”
-
-Many electric cooking-utensils are made for the household, such as
-coffee-percolators, egg-boilers, ovens, disk stoves, etc. Each one is
-equipped with a resistance-coil like that in the electric flat-iron just
-described, so that it contains its own source of heat, which is under
-perfect control by means of a switch. An “electric kitchen” consists of
-a number of these utensils, wired to a convenient table or stand, as
-shown in Fig. 7.
-
-[Illustration: _=Fig. 6=_]
-
-[Illustration: _=Fig. 7=_]
-
-
-Electric Power
-
-We have seen that the modern way to generate electricity is from
-mechanical energy applied through a dynamo, and that the “electric
-power” thus generated may be transmitted over wires to a distance and
-there transformed into other forms of energy, such as light, heat, and
-chemical energy, or reproduced again as mechanical energy. The last
-mentioned of these transformations is the most important of them all,
-because it is the one that means the most for the advancement of
-civilization. Before the invention of the dynamo and the discovery that
-it was reversible, mechanical power could be employed only in the place
-where it was generated, so that its use was restricted; whereas nowadays
-the field of power is broadened and its cost reduced by electrical
-transmission and distribution.
-
-In the chapter on Dynamos and Motors we learned how to make and use
-those machines. Let us review, very briefly, just what happens in the
-double transformation--of mechanical energy into electricity and then
-back again at the end of a line of wires--that we call electric-power
-transmission. In the dynamo, the power of the water-wheel, or whatever
-other prime mover is used, is exerted in generating electricity by
-forcing the electric conductors of the machine through a magnetic field.
-The electricity is led away to a distance--a hundred miles, perhaps--by
-wires and allowed to enter another machine similar to the dynamo, but
-operating as a motor. Here the first process is reversed: the
-electricity passing through the conductors of the motor reacts upon its
-magnetic field, causing the machine to revolve and thus generating
-mechanical power again. The line-wires carry the power just as
-positively as though a long shaft ran from the prime mover to the
-receiving end of the line, and much more economically. The action that
-goes on is similar to the operation of the telephone--which is indeed a
-special case of electric-power transmission--as already explained in a
-former chapter: the sound of the voice being transformed, at the
-telephone-transmitter, into electrical energy in the form of alternating
-currents, then carried as such over the line and finally reproduced as
-sound again at the receiver.
-
-
-Power from Water-wheels
-
-“Hydro-electric” transmissions--i. e., electric transmissions of power
-from a water-wheel as prime mover--are the most important because they
-bring into use cheap water-power that formerly ran to waste. There are
-many hydro-electric transmissions in this country, Mexico, and Canada,
-some of them utilizing the power of waterfalls or rapids located in
-mountainous and inaccessible parts. The alternating current is nearly
-always used because by it men can much more easily and safely generate,
-transmit, and receive the high voltages that have to be used than by the
-continuous current. The machinery at the “main generating station”
-consists of big alternating-current dynamos, which sometimes have
-vertical shafts instead of horizontal ones, so that they may be driven
-directly by turbines. The current is generated at a moderate potential,
-which is then “stepped-up,” by “static transformers,” to the
-comparatively high-line voltage that is required in long-distance
-transmissions.
-
-[Illustration: _=Fig. 8=_]
-
-
-Transformers
-
-Fig. 8 is a view of a very large transformer of over 2500 electrical
-horse-power capacity. In the picture the containing-tank is represented
-as transparent, so as to show the transformer proper inside. The latter
-is really a special kind of induction-coil, with primary and secondary
-windings, and a core, weighing many tons, built up of thin sheets of
-steel. In this kind of transformer, the tank is filled with oil, to
-keep the transformer cool in operation, and to help insulate it against
-the high potential to which it is subjected. At the receiving end, or
-“sub-station,” the high-voltage electric power enters a set of
-“step-down” transformers, from which it is delivered again, at moderate
-potential, to the motors.
-
-Sometimes power is distributed from a single great generating station to
-several sub-stations. In the Necaxa transmission, in Mexico, over 35,000
-horse-power is taken from a waterfall in the mountains and transmitted
-at 60,000 volts potential to Mexico City, 100 miles away, and to the
-mining town of El Oro, seventy-four miles farther on.
-
-Several kinds of motors are used at the receiving end of electric-power
-transmission-lines, according to the work that they are called upon to
-do. For “stationary” work, like driving the machines in mills and
-factories, two principal kinds of alternating-current motors are
-employed--synchronous and induction motors. The former are built just
-like alternating-current dynamos, and when they are running they keep
-“in step” with the dynamo at the other end of the line; i. e., the
-motion of their field windings relatively to their armatures keeps exact
-pace with the same motion at the dynamo, just as though a long shaft ran
-from one machine to the other instead of the electric wires of the
-transmission-line. A motor of this type, at work driving an
-air-compressor, is shown in Fig. 9. The induction-motor is really a sort
-of transformer, the primary winding of which is the fixed part, or
-field, and the secondary winding the rotating armature. It does not keep
-in step with the dynamo, like the synchronous motor, but adapts its
-speed to the “load,” or amount of work that it is called upon to do,
-like a continuous-current motor.
-
-[Illustration: _=Fig. 9=_]
-
-
-Rotary Converters
-
-Sometimes alternating-current electric power is transformed at the
-sub-station into continuous-current power. This is done by a special
-kind of transformer called a “rotary converter.” The static transformers
-of which we have just been speaking are built, like ordinary
-reduction-coils, with no moving parts, and operate by taking in
-alternating currents at a given potential and giving out alternating
-currents at a different potential, higher or lower as the case may be.
-The rotary converter, however, is built something like a dynamo, with a
-stationary field and a revolving armature, and ordinarily operates by
-receiving an alternating current at a given potential and delivering a
-continuous current of the same or a different potential. This kind of
-transformation is employed wherever it is desired to obtain any large
-amount of continuous current from an alternating-current
-transmission-line; and especially to obtain “500-volt continuous
-current” for operating street and interurban electric railways, as we
-shall see under the next heading. Fig. 10 shows one form of rotary
-converter built for supplying continuous current for trolley service.
-
-[Illustration: _=Fig. 10=_]
-
-Oftentimes the sub-station of a transmission system contains both static
-transformers and rotary converters, to supply both alternating current
-and continuous current from the same high-voltage alternating-current
-line. When the continuous current has to be transformed from one voltage
-to another, a “motor dynamo” is used, consisting of an electric motor
-driving a dynamo on a common shaft.
-
-One of the most interesting features of electric-power transmission is
-the care that is taken to avoid the terrible danger from the high
-potentials, and at the same time prevent loss of power on the way. The
-electricity in the machinery and in the line-wires that extend across
-the country is veritable lightning, and has to be carefully guarded from
-doing any damage or escaping. To prevent leakage, the insulation of all
-of the station machinery and apparatus is made extra good, with “high
-dielectric strength,” so that it will not be punctured by the high
-voltage; and the line-insulators are made very large, and electrically
-and mechanically strong--quite unlike the ordinary-sized glass or
-porcelain insulators that are employed for telegraph and telephone
-lines. Each insulator before being put up is tested under a “breakdown
-voltage” much higher than it is to stand in actual service.
-
-
-Oil-switches
-
-The switching of high-voltage electric power is a knotty problem. The
-circuit cannot be interrupted by “air-break” switches, such as are used
-in ordinary electric-light stations, for any attempt to do so would
-result in a destructive arc many feet long, that could not be
-extinguished. Therefore “oil-switches” are always used to control the
-line-circuits at the main generating station and the sub-stations. In
-these oil-switches--which are designed to be operated from a distance,
-by hand-levers, or sometimes by electric motors--the circuit is made and
-broken under the surface of oil, which prevents the formation of an
-arc. Moreover, the switchboard attendant does not have to come anywhere
-near the deadly high-voltage wires, but can make the necessary
-connections at a safe distance.
-
-
-Electric Traction
-
-The use of the electric motor to propel vehicles of all kinds is called
-electric traction. It is, of course, a branch of electric power, which
-we have just been considering; and it is in many respects the most
-important branch. The wealth of a country is largely built up and
-maintained by its facilities for transportation, such as its canals,
-highways, railroads, and street and interurban car-lines.
-
-In this field electric power is playing a most important part, although
-it was not many years ago that the first experimental electric cars were
-put in to replace horses on the street-railways of our cities. The
-change was found to be so successful that the field of the trolley-car
-was widened and extended very rapidly, until now we have our great
-suburban and interurban electric railways, with cars almost or quite as
-big as those on the steam-railroads and running at even higher speeds.
-During the last few years, also, the sphere of the steam-railroad itself
-has been invaded by electricity, by the construction of powerful
-electric locomotives to draw passenger and freight trains.
-
-
-The Trolley-car
-
-Let us consider just what it is that makes a trolley-car go. Since
-electric power is only mechanical energy in another form, we know that
-the motionless copper trolley-wire, suspended over the track in our
-streets, is the means of propelling the car just as truly--though in a
-different way--as if it were a moving steel cable to which the car was
-attached. We must keep in mind the fact that the electricity is not
-itself the source of power, but only the medium of transmission. The
-engine in the power-house, by turning a dynamo there, maintains a
-constant electric pressure, or “constant potential,” as it is termed, in
-the trolley-wire. This pressure of electricity forces the power through
-the motors of the car as soon as the motorman makes the connection to
-them by turning the handle of his “controller.”
-
-[Illustration: _=Fig. 11=_]
-
-
-The Continuous-current Motor
-
-Fig. 11 is a view of one form of continuous-current motor. There is not
-much of the motor itself to be seen, because it is entirely enclosed in
-a cast-iron case. The shaft of the motor has a small “spur gear” fixed
-on one end, driving a gear-wheel which is fixed on the car axle. By this
-arrangement more than one revolution of the motor armature is required
-to make one revolution of the car-wheel, which multiplies the force
-exerted in turning the wheel.
-
-[Illustration: _=Fig. 12=_]
-
-
-The Controller
-
-Fig. 12 is a view of a type of controller that is used on the platform
-of trolley-cars. The cover is removed to show the contacts, inside, by
-which the electric power is turned on gradually by the controller
-handle. The trains of electric cars that run on the elevated structures
-and in the subways of our large cities are supplied with power from a
-“third rail” placed by the side of the track, on insulating supports,
-and the motors on all the cars are controlled from a single
-“master-controller” on the front platform of the forward car. This
-system of control, known as the “multiple-unit” system, gives electric
-trains several advantages over the old kind, drawn by steam-locomotives;
-such as they used to have on the New York elevated roads, for example.
-For one thing, the train can be started much more quickly, since all the
-motors begin to turn the car-wheels at the same instant. Then again, the
-system enables a long train of cars to be controlled as easily as a
-single car, and better “traction” between wheels and track is obtained.
-
-
-Electric Locomotives
-
-Several of the great steam-railroads are now adopting the electric
-locomotive to draw their trains. Fig. 13 is a view of one of the great
-continuous current electric locomotives that are used by the New York
-Central Railroad to handle many of its passenger-trains in and out of
-the Grand Central Station, in New York city. The motors of this
-powerful electric engine, unlike those of trolley-cars, are “gearless”;
-that is, their armatures are fixed directly on the locomotive axles so
-that they revolve at the same speed as the driving-wheels.
-
-[Illustration: _=Fig. 13=_]
-
-All of the railway motors considered thus far have been of the
-continuous-current type, although the current to operate them is often
-obtained from alternating current transmission-systems, through rotary
-converters, as described above. The alternating current is also
-beginning to be employed to drive cars and trains. One type of
-alternating current railway motor, designed for “single-phase”
-operation, is in use on several interurban systems in this country,
-running on high-voltage alternating current most of the time, but on
-continuous current when within the city limits.
-
-
-Other Forms of Electric Traction
-
-Electric traction also includes electric automobiles, supplied by
-storage-batteries; a slow-speed electric locomotive for drawing
-canal-boats, and called “the electric mule”; and an ingenious
-gasolene-electric outfit for driving cars by electric motors without any
-trolley, third rail, or storage-battery. The last-mentioned arrangement
-consists of a set of electric car-motors mounted on the trucks in the
-usual way, but supplied with current by a dynamo mounted on the car
-itself and driven by a gasolene-engine. Thus the car carries its own
-power-station about with it, and is independent of any outside source of
-electricity.
-
-       *       *       *       *       *
-
-The old alchemists sought to transmute _matter_ from one form to
-another; and especially lead and other “base metals” into gold, in order
-that they might grow rich by concentrating the precious metal in their
-own selfish hands. The modern miracle that electricity works for us, the
-transmutation of _energy_, is a higher and broader thing, because it
-multiplies and distributes the world’s good things.
-
-
-
-
-APPENDIX
-
-A DICTIONARY OF ELECTRICAL TERMS AND PHRASES
-
-
-Everybody is interested in electricity, but the ordinary reader, and
-particularly the boy who attempts to use this manual intelligently, will
-come across many technical words and terms that require explanation. It
-would be impossible to incorporate all needful definitions in the text
-proper, and the reader is therefore referred to the technical dictionary
-on the succeeding pages.
-
-Care has been taken in its compilation to make the definitions complete,
-simple, and concise. Some of the more advanced technical terms have been
-purposely omitted as not necessary in a book dealing with elementary
-principles. The student in the higher branches of the science will
-consult, of course, the more advanced text-books. But for our practical
-purposes this elementary dictionary should answer every requirement. To
-read it over is an education in itself, and the young experimenter in
-electrical science should always refer to it when he comes across a word
-or phrase that he does not fully understand.
-
-
-A
-
-=A.= An abbreviation for the word anode.
-
-=Absolute.= Complete by itself. In quantities it refers to fixed units.
-A galvanometer gives absolute readings if it is graduated to read direct
-amperes or volts. An absolute vacuum is one in which all residual gases
-are exhausted; an absolute void is the theoretical consequent. The
-absolute unit of current is measured in one, two, three, or more amperes
-or volts.
-
-=A-C.= An abbreviation expressing alternating current.
-
-=Acceleration.= The rate of change in velocity.
-
-The increase or decrease of motion when acted upon by the electric
-current.
-
-=Accumulator.= A term applied to a secondary battery, commonly called a
-storage-battery.
-
-=Accumulator, Electrostatic.= (_See_ Electrostatic Accumulator.)
-
-=Accumulator, Storage.= A storage-battery.
-
-=Acid.= A compound of hydrogen capable of uniting with a base to form
-salts.
-
-Sour, resembling vinegar.
-
-A sharp, biting fluid.
-
-=Acidometer.= A hydrometer used to determine the gravity of acids. It is
-employed chiefly in running storage-batteries to determine when the
-charge is complete.
-
-=Adapter.= A screw-coupling to engage with different size screws on
-either end, and used chiefly to connect incandescent lamps to
-gas-fixtures.
-
-=Adherence.= The attraction between surfaces of iron due to
-electro-magnetic action. The term is used in connection with electric
-brakes--electro-magnetic adherence.
-
-=Adjustment.= Any change in an apparatus rendering it more efficient and
-correct in its work.
-
-=Aerial Conductor.= A wire or electric conductor carried over housetops
-or poles, or otherwise suspended in the air, as distinguished from
-underground or submarine conductors.
-
-=Affinity.= The attraction of atoms and molecules for each other, due to
-chemical or electrical action.
-
-=Air-condenser.= A static condenser whose dielectric is air.
-
-=Air-line Wire.= In telegraphy that portion of the line-wire which is
-strung on poles and carried through the air.
-
-=Alarm, Burglar.= A system of circuits with an alarm-bell, the wires of
-which extend over a house or building, connecting the windows and doors
-with the annunciator.
-
-=Alarm, Electric.= An appliance for calling attention, generally through
-the ringing of a bell or the operating of a horn.
-
-=Alarm, Fire and Heat.= An expansion apparatus that automatically closes
-a circuit and rings a bell.
-
-=Alive, or “Live.”= A term applied to a wire or circuit that is charged
-with electricity. A “live” wire.
-
-Active circuits or wires.
-
-=Alloy.= Any mixture of two or more metals making a scientific compound.
-For example: copper and zinc to form brass; copper, tin, and zinc to
-form bronze; copper, nickel, and zinc to form German-silver.
-
-=Alternating Current.= (_See_ Current, Alternating.)
-
-=Alternating Current-power.= Electrical distribution employing the
-alternating current from dynamos or converters.
-
-=Alternation.= A change in the direction of a current; to and fro.
-Alternations may take place with a frequency ranging from 500 to 10,000
-or more vibrations per second.
-
-=Alternator.= An electric generator-dynamo supplying an alternating
-current.
-
-=Amalgam.= A combination of mercury with any other metal.
-
-=Amalgamation.= The application of mercury to a metal, the surface of
-which has been cleansed with acid. Mercury will adhere to all metals,
-except iron and steel, and particularly to zinc, which is treated with
-mercury to retard the corrosive action of acid on its surface.
-
-=Amber.= A fossil resin, valuable only in frictional electric
-experiments. Most of it is gathered on the shores of the Baltic Sea
-between Königsberg and Memel. It is also found in small quantities at
-Gay Head, Massachusetts, and in the New Jersey green sand. When rubbed
-with a cloth it becomes excited with negative electricity.
-
-=Ammeter.= The commercial name for an ampere-meter. An instrument
-designed to show, by direct reading, the number of amperes of current
-which are passing through a circuit.
-
-=Ampere.= The practical unit of electric current strength. It is the
-measure of the current produced by an electro-motive force of one volt
-through a resistance of one ohm.
-
-=Ampere-currents.= The currents theoretically assumed to be the cause of
-magnetism.
-
-=Ampere-hour.= The quantity of electricity passed by a current of one
-ampere in one hour. It is used by electric light and power companies as
-the unit of energy supplied by them, and on which they base their
-reckoning for measuring the charges for current consumed.
-
-=Ampere-ring.= A conductor forming a ring or circle. Used in electric
-balances for measuring current.
-
-=Animal Electricity.= A form of electricity of high tension generated in
-certain animal systems--the Torpedo, Gymnotus, and Célurus. The shocks
-given by these fish, and particularly the electric eel, are often very
-severe.
-
-=Annealing.= The process of softening yellow metals by heating them to a
-cherry redness, then allowing them to cool gradually in the air.
-
-Electric annealing is done by passing a current through the body to be
-annealed, and heating it to redness; then allowing it to cool gradually.
-
-=Annunciator.= An apparatus for giving a call from one place to another,
-as from a living-room to a hotel office, or for designating a window or
-door that may have been opened when protected by a burglar-alarm.
-
-=Annunciator-drop.= The little shutter which is dropped by some forms of
-annunciators, and whose fall discloses a number or letter, designating
-the location from which the call was sent.
-
-=Anode.= The positive terminal in a broken, metallic, or true conducting
-circuit.
-
-The terminal connected to the carbon-plate of a battery, or to its
-equivalent in any other form of electric generator, such as a dynamo or
-a voltaic pile.
-
-The copper, nickel, gold, or silver plates hung in an electro-plating
-bath, and from which the metal is supplied to fill the deficiency made
-by the electro-deposition of metal on the kathode or negative object in
-the bath.
-
-=Anti-hum.= A shackle inserted directly in a line-wire near a pole. It
-is provided with a washer or cushion of rubber to take up the vibrations
-of a wire. To continue the circuit a bridle, or curved piece of wire, is
-connected with the line-wires that are attached to the shackle.
-
-=Arc.= A term applied to an electric current flowing from carbon to
-carbon, or from metals separated by a short gap, as in the arc
-street-lamps.
-
-The original arc was produced by two vertical rods, through which the
-current passed up and down. When not in action the upper ends touched,
-but as the current flowed the ends were separated, so that the current,
-passing up one carbon across the gap and down the other, formed the
-segment of a circle in jumping from one tip to the other.
-
-An arc of electric flame is of brilliant and dazzling whiteness. The
-voltaic arc is the source of the most intense heat and light yet
-produced by man. The light is due principally to the incandescence of
-the ends of carbon-pencils, when a current of sufficient strength is
-passing through them and jumping over the gap. Undoubtedly the
-transferred carbon particles have much to do with its formation. The
-conductivity of the intervening air and the intense heating to which it
-is subjected, together with its coefficient of resistance, are other
-factors in the brilliant light produced.
-
-=Arc-lamp.= An electric lamp which derives its light from the voltaic
-arc, by means of carbon-pencils and a current jumping from one to the
-other.
-
-=Arc, Quiet.= An arc free from the hissing sound so common in
-arc-lights.
-
-=Arc, Simple.= A voltaic arc produced between only two electrodes.
-
-=Armature.= A body of iron or other material susceptible to
-magnetization, and which is placed on or near the poles of a magnet.
-
-That part of an electric mechanism which by magnetism is drawn to or
-repelled from a magnet.
-
-The core of a dynamo or motor which revolves within the field magnets,
-and which is the active principle in the generation of current by
-mechanical means, or in the distribution of power through electrical
-influence. Armatures are sometimes made of steel, and are permanent
-magnets. These are used in magneto-generators, telegraph instruments,
-and other apparatus.
-
-=Armature-bar.= An armature in a dynamo or motor whose winding is made
-up of conductors in the form of bars.
-
-=Armature-coil.= The insulated wire wound around the core of the
-armature of an electric current-generator or motor.
-
-=Armature-core.= The central mass of iron on which the insulated wire is
-wound; it is rotated in the field of an electric current-generator or
-motor.
-
-=Armored.= Protected by armor; as cables may be surrounded by a proper
-sheathing to guard them from injury.
-
-=Astatic.= Having no magnetic directive tendency, the latter being a
-general consequent of the earth’s magnetism.
-
-=Astatic Circuit.= (_See_ Circuit, Astatic.)
-
-=Astatic Couple.= (_See_ Couple, Astatic.)
-
-=Astatic Needle.= A combination of two magnetic needles so adjusted as
-to have as slight directive tendency as possible. The combination is
-generally made up of two needles arranged one above the other with the
-poles in opposite directions--commonly called “Nobili’s Pair.” These
-needles require but a slight electro-force to turn them one way or the
-other, and are used in astatic galvanometers.
-
-=Atmospheric Electricity.= (_See_ Electricity, Atmospheric.)
-
-=Atom.= The ultimate particle or division of an elementary substance.
-Electricity is largely responsible for the presence of atoms in the
-atmosphere.
-
-=Atomic Attraction.= The attraction of atoms for each other. Principally
-due to electric disturbance.
-
-=Attraction.= The tendency to approach and adhere or cohere which is
-shown in all forms of matter. It includes gravitation, cohesion,
-adhesion, chemical affinity, electro-magnetic and dynamic attraction.
-
-=Aurora.= A luminous electric display seen in the northern heavens. It
-is commonly thought to be the electric discharges of the earth into the
-atmosphere, due to revolution of the former and to the heat produced at
-the equator. As compared to the static machine for generating frictional
-electricity, the earth represents the revolving wheel gathering the
-current and discharging it at the poles.
-
-=Automatic Cut-out.= An electro-magnetic switch introduced into a
-circuit, so as to break the circuit of the latter should it become
-overloaded with current; it also acts in the event of a mechanical
-interruption.
-
-=Automatic Regulation.= A speed regulator worked by electricity so that
-a uniform flow of current may be secured automatically.
-
-=Ayrton’s Condenser.= This is a pile of glass plates separated by small
-pieces of glass at the four comers, so that the plates cannot touch each
-other. Tin-foil is pasted on both sides of every plate, and the two
-coatings are connected. The tin-foil on each second plate is smaller in
-area than that on the others, and the plates are connected in two sets,
-negative and positive. In this construction it will be seen that the
-glass is not the dielectric proper, but acts only as the plane to which
-the tin-foil is pasted. One set of plates are connected to a
-binding-post by strips of tin-foil, and the other set are connected to
-another binding-post in a similar manner.
-
-
-B
-
-=B.= An abbreviation for Beaumé, the inventor of the hydrometer scale.
-Thus, in speaking of the gravity of fluids, 20° B. means twenty degrees
-Beaumé.
-
-=Back Induction.= A demagnetizing force produced in a dynamo when a lead
-is given to the brushes. (_See also_ Induction, Back.)
-
-=Back Shock.= A lightning stroke received after the main discharge. It
-is caused by a charge induced in neighboring surfaces by the main
-discharge.
-
-=Bad Earth.= A poor ground connection, or one having comparatively
-strong electrical resistance.
-
-=Balance.= A proper adjustment between the apparatus and the
-electro-motive force, thus securing the best possible results.
-
-=B. & S. W-G.= Abbreviations for Brown & Sharp and wire-gauge, and
-referring to the sizes of wire and sheet-metal thicknesses that are
-considered standards in America.
-
-=Bar-armature.= An armature in which the conductors are constructed of
-bars.
-
-=Bar-magnet.= One whose core presents the appearance of a straight bar,
-or rod, without curve or bend.
-
-=Bare-carbons.= Electric light carbons whose surfaces are not
-electro-plated with copper.
-
-=Barometer.= An apparatus for measuring the pressure exerted by the
-atmosphere. It consists of a glass tube 31 inches long, closed at one
-end, filled with mercury, and then inverted, with its open end immersed
-in a cistern of mercury. The column of mercury falls to a height
-proportional to the pressure of the atmosphere. At the sea-level it
-ranges from 30 to 31 inches.
-
-=Bar-windings.= The windings of an armature constructed of copper bars.
-
-=Bath.= In electro-plating, the solution or electrolyte used for
-depositing metal on the object to be plated. It may be a solution of
-copper, silver, nickel, or other metal.
-
-In electro-therapeutics it is a bath of water with suitable electrodes
-and connections for treating patients with electricity.
-
-=Bath-stripping.= A solution used for stripping or removing the metal
-plating from an object.
-
-=Batten.= A strip of wood grooved longitudinally, in which electric
-light or power wires are set. The grooved strip is screwed to the wall,
-the wires being laid in the grooves, and then covered with a thin wooden
-strip fastened on with small nails.
-
-=Battery.= A combination of parts, or elements, for the production of
-electrical action.
-
-A number of cells connected parallel or in series for the generation of
-electricity. Under this heading there are at least one hundred different
-kinds. Nowadays the dynamo is the cheap and efficient generator of
-electricity.
-
-=Battery Cell, Elements of.= The plates of zinc and carbon, or of zinc
-and copper, in a cell are called elements. The plate unattacked by the
-solution, such as the carbon or copper, is the negative element, while
-the one attacked and corroded by the electrolyte is the positive.
-
-=Battery, Dry.= A form of open circuit cell in which the electrolyte is
-made practically solid, so that the cell may be placed in any position.
-A zinc cup is filled with the electrolyte and a carbon-rod placed in the
-middle, care being taken to avoid contact between cup and carbon at the
-bottom of the cell. The gelatinous chemical mass is then packed in
-closely about the carbon, so as to nearly fill the cup. A capping of
-asphaltum, wax, or other non-conducting and sealing material is placed
-over the electrolyte, and this hardens about the carbon and around the
-top inner edge of the zinc cup. The latter becomes the positive pole,
-the carbon the negative. Binding-posts, or connections, may be attached
-to the zinc and carbon to facilitate connections.
-
-=Battery, Galvanic.= The old name for a voltaic battery.
-
-=Battery, Gravity.= A battery in which the separation of fluids is
-obtained through their difference in specific gravity--for example, the
-bluestone cell. The sulphate of copper solution, being the more dense,
-goes to the bottom, while the zinc solution stays at the top. In its
-action the acid at the top corrodes the zinc, while at the bottom the
-solution is decomposed and deposits metallic copper on the thin copper
-plates.
-
-=Battery, Leclanché.= An open circuit battery consisting of a jar, a
-porous cup, and the carbon and zinc elements, the electrolyte of which
-is a solution of ammonium chloride (sal-ammoniac). The carbon plate is
-placed in the porous cup, and packed in with a mixture of powdered
-manganese binoxide and graphite, to serve as a depolarizer. A
-half-saturated solution of sal-ammoniac is placed in the outer jar, and
-a rod of zinc suspended in it. Another form of the battery is to omit
-the porous cup and use twice the bulk of carbon, both elements being
-suspended in the one solution of sal-ammoniac; this form of battery is
-used for open-circuit work only, such as bells, buzzers, and
-annunciators. It is not adapted for lights, power, or plating purposes.
-
-=Battery Mud.= A deposit of mud-like character which forms at the bottom
-of gravity batteries, and which consists of metallic copper precipitated
-by the zinc. It only occurs where wasteful action has taken place.
-
-=Battery of Dynamos.= A term used in speaking of a number of dynamos
-coupled to supply the same circuit. They may be coupled in series or
-parallel.
-
-=Battery, Plunge.= A battery in a cabinet or frame, so arranged that the
-active plates can be removed or raised out of the solutions. This is
-usually accomplished by having the plates attached to a movable frame
-which, by means of a ratchet-shaft and chains, can be raised or lowered.
-Its object is to prevent the corrosion of the plates when not in use.
-
-=Battery, Primary.= A voltaic cell or battery generating electric energy
-by direct consumption of material. The ordinary voltaic cell, or
-galvanic battery, is a primary battery.
-
-=Battery, Secondary.= A storage-battery, an accumulator.
-
-=Battery Solution.= The active excitant liquid, or electrolyte, placed
-within a cell to corrode the positive element. Also called
-Electropoion.
-
-=Battery, Storage.= A secondary battery; an accumulator; a battery which
-accumulates electricity generated by primary cells or a dynamo.
-
-=Battery-gauge.= A galvanometer used for testing batteries and
-connections. It is usually small in size, and may be carried in a
-pocket.
-
-=Battery-jar.= A glass, earthen, or lead vessel which contains the
-fluids and elements of each separate cell of a battery.
-
-=Baumé Hydrometer.= (_See_ Hydrometer, Baumé.)
-
-=Becquerel Ray and Radiation.= An invisible ray discovered by Becquerel,
-which is given out by some compounds and chemicals--notably uranium--and
-which has the power to penetrate many opaque bodies and objects
-impenetrable to the actinic rays of ordinary light. These rays are used
-chiefly in connection with the photographic dry-plate.
-
-=Bell, Electric.= A bell rung by electricity. The current excites an
-electro-magnet, attracting or releasing an armature which is attached to
-a vibrating or pivoted arm, on the end of which the knocker is fastened.
-
-=Bichromate of Potash.= A strong, yellowish-red chemical, used chiefly
-in battery fluids and electrolytes.
-
-=Bifilar Winding.= The method followed in winding resistance-coils. To
-prevent them from creating fields of force, the wire is doubled and the
-looped end started in the coil. Since the current passes in opposite
-senses in the two lays of the winding, no field of force is produced.
-
-=Binding.= Unattached wire wound round armature-coils to hold them in
-place.
-
-=Binding-post.= An arrangement for receiving the loose ends of wires in
-an electric circuit and securing them, by means of screws, so that
-perfect contact will be the result.
-
-=Bi-polar.= Possessing two poles.
-
-=Bi-telephone.= A pair of telephones arranged with a curved connecting
-arm or spring so that they can be simultaneously applied to both ears.
-
-=Blasting, Electric=. The ignition of a blasting charge of powder,
-dynamite, or other high explosive by an electric spark, or by the
-heating, to red or white heat, of a thin wire imbedded in the explosive.
-
-=Block System.= A system of signalling on railroads. Signal-posts are
-arranged at stated spaces, and on these signals appear automatically,
-showing the location of trains to the engineers of trains in the rear.
-
-=Bluestone.= A trade name for sulphate of copper in a crystallized
-state.
-
-=Bobbin.= A spool of wood or other non-conducting substance wound with
-insulated wire. In a tangent galvanometer the bobbin becomes a ring with
-a channel to receive the wire.
-
-=Boiling.= In secondary, or storage, batteries the escaping of hydrogen
-and oxygen gases, when the battery is fully charged, resembles water
-boiling.
-
-=Bonded Rails.= Rails used in an electric traction system, and which are
-linked or connected together to form a perfect circuit. Used principally
-in the third-rail system.
-
-=Brake, Electro-magnetic.= A brake to stop the wheels of a moving car.
-It consists of a shoe, or ring, which by magnetic force is drawn against
-a rotating wheel to stop its revolution.
-
-=Branch.= A conductor which leads off from a main line to distribute
-current locally.
-
-=Brassing.= A process of electro-depositing brass in a bath containing
-both copper and zinc. A plate of brass is used as an anode.
-
-=Brazing, Electric.= A process in which the spelter is melted by
-electric current, so that the two parts are united as one.
-
-=Break.= A point where an electric conductor is broken, as by a switch
-or a cut-out.
-
-=Bridge.= A special bar of copper connecting the dynamos with the bus
-wire in electric lighting or power stations.
-
-=Bronzing.= The deposition of bronze by electro-plating methods. The
-mixture is of copper and tin, and a cast bronze plate is used as an
-anode.
-
-=Brush.= A term applied to the pieces of copper, carbon, or other
-conducting medium in dynamos and motors, that bear against the
-cylindrical surface of the commutators to collect or feed in the
-current.
-
-=Bug.= Any fault or trouble in the connections or workings of an
-electrical apparatus. The term originated in quadruplex telegraphy, and
-probably had some connection with the Edison bug-killer that he invented
-when a boy.
-
-=Buoy, Electric.= A buoy to indicate dangerous channels in harbors and
-to mark wrecks and reefs. It is provided with an electric light at
-night, and with a gong or an electric horn by day.
-
-=Burner, Electric.= A gas-burner so arranged that the flame may be
-lighted by electricity operated by a push-button at some distance from
-the fixture, or, close at hand, by means of a chain or pull-string.
-
-=Burning.= In a dynamo, the improper contact of brushes and commutator,
-whereby a spark is produced and an arc formed which generates heat and
-causes the metal parts to burn.
-
-=Bus-rod.= A copper conductor used in power-plants to receive the
-current from the battery of dynamos. The distributing leads are
-connected to these rods.
-
-=Butt-joint.= A joint made by bringing the ends of wires together so
-that the ends butt. They are then soldered or brazed.
-
-=Button, Electric.= A form of switch that is operated by pushing a
-button mounted on a suitable base. Used principally for ringing bells,
-operating lights, etc.
-
-=Buzzer.= An electric alarm, or call, produced by the rapid vibration of
-an armature acted upon by electro-magnetism. The sound is magnified by
-enclosing the mechanism in a resonant box.
-
-An apparatus resembling an electric bell _minus_ the bell and clapper.
-The buzzer is used in places where the loud ring of a bell would be a
-nuisance.
-
-
-C
-
-=C.= An abbreviation for centigrade when speaking of thermal
-temperature. In chemistry the centigrade scale is used extensively, but
-in air temperatures the Fahrenheit scale is universally employed.
-
-=Cable, Aerial.= A cable that contains a number of wires separately
-insulated, the entire mass being protected by an external insulation. It
-is suspended in the air from pole to pole, and sometimes its weight is
-so great that a supporting wire is carried along with it (usually
-overhead), the large cable being suspended from it by cable-hangers.
-
-=Cable Box=. A box to receive cable ends and protect them; also, the box
-in which cable ends and line-wires are joined. Submarine cable boxes are
-usually near the ground, while telephone and telegraph cable boxes are
-mounted on poles, the cables running from the ground and up the poles to
-the boxes.
-
-=Cable-core.= The conductors of a cable which make up its interior
-mass. For the convenience of linemen the wires are often insulated with
-different-colored materials so that testing is not necessary when making
-connections.
-
-=Cable-hanger.= A metallic grip, usually of sheet metal, arranged to
-clasp two or more wires. It is fastened to the supporting wire by a hook
-and eye, or by small bolts with thumb-nuts.
-
-=Cable-head.= A rectangular board equipped with binding-posts and fuse
-wires so that the connections may be made between the cable ends and the
-overhead or line-wires of a system.
-
-=Cables.= An insulated electric conductor of large diameter, often
-protected by armor or metallic sheathing, and generally containing, or
-made up, of several separately insulated wires. Cables supply current to
-traction lines; power, through subterranean passages; communication, by
-submarine connection; and light, by overhead or underground conduits.
-
-=Call-bell.= A bell that is rung by pressing a button, and which is
-operated by electricity.
-
-=Calling-drop.= A drop-shutter which is worked by electricity in a
-telegraph or telephone exchange; it denotes the location from which the
-call was sent in. Small red incandescent lamps have taken the place of
-the drops in most of the large telephone exchanges, for they are
-noiseless and do not annoy the operators as the drops and buzzers did.
-
-=Candle-power.= The amount of light given by the standard candle. The
-legal English and American standard is a sperm candle burning two grains
-a minute.
-
-=Candle, Standard.= The standard of illuminating power; a flame which
-consumes two grains of sperm wax per minute, and produces a light of a
-brightness equal to one candle-power.
-
-=Caoutchouc.= India-rubber. So named because originally its chief use
-was to erase or rub off pencil marks. It is a substance existing, in a
-thick fluid state, in the sap or juices of certain tropical trees and
-vines; it possesses a very high value as an insulator for wire and
-circuits. The unworked, crude rubber is called virgin gum, but after it
-is kneaded it is called masticated or pure gum rubber.
-
-=Capacity.= A term used when speaking of the carrying power of a wire or
-circuit. The capacity of a wire, rod, bar, or other conductor is
-sufficient so long as the current does not heat it. Directly electric
-heat is generated, we speak of the conductor as being overloaded or
-having its capacity overtaxed.
-
-=Capacity of a Telegraph Conductor.= The electric capacity may be
-identical in quality with that of any other conductor. In quantity it
-varies not only in different wires, but for the same wire under
-different conditions. A wire reacting through the surrounding air, or
-other dielectric, upon the earth represents one element of a condenser,
-the earth in general representing the other. A wire placed near the
-earth has greater capacity than one strung upon high poles, although the
-wires may be of identical length and size and of the same metal. The
-effect of high capacity is to retard the transmission of current, the
-low capacity facilitates transmission.
-
-=Capacity, Storage.= In secondary batteries, the quantity of electric
-current they can supply, when fully charged, without exhaustion. This
-capacity is measured or reckoned in ampere-hours.
-
-=Carbon.= One of the elements in graphitic form used as an
-electric-current conductor. It is the only substance which conducts
-electricity, and which cannot be melted with comparative ease by
-increase of current. It exists in three modifications--charcoal,
-graphite, and the diamond. In its graphitic form it is used as an
-electro-current conductor, as in batteries and arc-light electrodes, and
-as filaments in incandescent lamps. In arc-lamp use the carbons are
-usually electro-plated on the outside with a film of copper which acts
-as a better conductor.
-
-=Carbon, Artificial.= Carbon-dust, powdered coke, or gas carbon is mixed
-with molasses, coal-tar, syrup, or some similar carbonaceous fluid, so
-that the mass is plastic. It can then be moulded or pressed into shapes,
-and heated to full redness for several hours by artificial or electric
-heat. For lamp-carbons the mixture is forced through a round die by
-heavy pressure, and is cut into suitable lengths, then fired or baked.
-
-After removing and cooling, the carbons are sometimes dipped again into
-the fluid used for cementing the original mass and re-ignited. This
-process is termed “nourishing.” All carbon is a resisting medium, but at
-high temperature the resistance is only about one-third as great; that
-is, the current will pass through a red-hot carbon three times better
-than through the cold carbon; or a current of thirty amperes will be
-conducted as easily through a hot carbon as ten amperes through a cold
-one.
-
-=Carbon-cored.= A carbon for arc-lamps, the core being of softer carbon
-than the outer surface. It is supposed to give a steadier light, and
-fixes the position of the arc.
-
-=Carbon-dioxide.= A compound gas, or carbonic-acid gas. It is a
-dielectric.
-
-=Carbon-holders.= In arc-lamps, the clamps arranged to hold the
-carbon-pencils.
-
-=Carbonization.= The ignition of an organic substance in a closed
-vessel, so as to expel all constituents from it except the carbon.
-
-A destructive distillation.
-
-=Carbon Resistance.= (_See_ Resistance, Carbon.)
-
-=Carbon Volatilization.= In arc-lamps the heat is so intense that it is
-believed a part of the carbon-pencil is volatilized, as vapor, before
-being burned or oxidized by the oxygen of the air.
-
-=Carbons, Bare=. (_See_ Bare Carbons.)
-
-=Carrying Capacity.= In a current-conductor, its carrying capacity up to
-the heating-point. It is expressed in amperes.
-
-=Cascade.= The arrangement of a series of Leyden-jars in properly
-insulated stools, or supports, for accumulating frictional electricity.
-They are arranged in a manner somewhat similar to a battery of galvanic
-cells, the inner coating of one being connected to the outer coating of
-the next, and so on through the series.
-
-=Case-hardening, Electric.= A process by which the surface of iron is
-converted into steel by applying a proper carbonaceous material to it
-while it is being heated by an electric current.
-
-=Cautery, Electric.= An electro-surgical appliance for removing diseased
-parts or arresting hemorrhages. It takes the place of the knife or other
-cutting instrument. It is a loop of platinum wire heated to whiteness by
-an electric current.
-
-=C.C.= An abbreviation commonly used for cubic-centimeter. It is usually
-written in small letters, as 50 c.c., meaning 50 cubic-centimeters.
-
-=Cell, Electrolytic.= A vessel containing the electrolyte used for
-electro-plating.
-
-=Cell, Regenerated.= A cell restored to its proper functions by a
-process of recharging.
-
-=Cell, Standard.= Meaning the same as battery. The vessel, including its
-contents, in which electricity is generated.
-
-=Cell, Storage.= Two plates of metal, or compounds of metal, whose
-chemical relations are changed by the passage of an electric current
-from one plate to the other through an electrolyte in which they are
-immersed.
-
-=Cements, Electrical.= Cements of a non-conducting nature, such as
-marine glue and sticky compounds, used in electrical work.
-
-=Centrifugal Force.= A diametric revolving force which throws a body
-away from its axis of rotation. A merry-go-round is a simple example of
-this force. The more rapidly the platform revolves the greater the
-tendency for those on it to be thrown off and out from the centre. The
-high velocity attained by the armatures in motors and dynamos would
-throw the wires out of place and cause them to rub against the surfaces
-of the field-magnets. Consequently, wire bands or binders are necessary
-to keep the coils of wire from spreading under the influence of the
-centrifugal force.
-
-=Charge.= The quantity of electricity that is present on the surface of
-a body or conductor.
-
-The component chemical parts that are employed to excite the elements of
-a cell in generating electric current.
-
-=Charge, Residual.= After a Leyden-jar, or other condenser, has been
-discharged by the ordinary methods, a second discharge (of less amount)
-can be had after a few minutes’ waiting. This is due to what is known
-as the residual charge, and is connected in some way with the molecular
-distortion of the dielectric.
-
-=Chemical Change.= When bodies unite so as to satisfy affinity, or to
-bring about the freeing of thermal or other energy, the union is usually
-accompanied by sensible heat or light. Sulphuric acid added to water
-produces heat; a match in burning produces light. Another form of
-chemical change is decomposition or separation (the reverse of
-combination), such as takes place in the voltaic-battery, the
-electro-plating bath, and other forms of electrolysis. This is not
-accompanied by heat or light, but by the evolution of electricity.
-
-=Chemical Element.= (_See_ Element, Chemical.)
-
-=Chemistry.= The science which treats of the atomic and molecular
-relations of the elements and their chemical compounds. Chemistry is
-divided into many departments, but electro-chemistry treats only of the
-science wherein electricity plays an active part, such as batteries,
-electro-plating, and electro-metallurgy.
-
-=Choking-coil.= (=See= Coil, Choking.)
-
-=Circle, Magic.= A form of electro-magnet. It is a thick circle of round
-iron used in connection with a magnetized coil to illustrate
-electro-magnetic attraction.
-
-=Circuit.= A conducting-path for electric currents. Properly speaking, a
-complete circuit has the ends joined, and includes a source of current,
-an apparatus, and other elements introduced in the path. When the
-circuit is complete it is called active. The term circuit is also
-applied to portions of a true circuit--as, an internal or external
-circuit.
-
-=Circuit, Astatic.= A circuit so wound, with reference to the direction
-of the currents passing through it, that the terrestrial or other lines
-of force have no directive effect upon it.
-
-=Circuit-breaker.= Any apparatus for opening and closing a circuit, such
-as switches, automatic cut-outs, lightning-arresters, and the like.
-
-A ratchet-wheel engaged with a spring, or wire, which rests against the
-teeth. The current passes through the wire, the wheel, and axle. The
-wheel is revolved by a crank, and as the ratchets pass the spring, or
-wire, an instantaneous make-and-break occurs. The speed of the wheel
-regulates the frequency of the interruptions.
-
-=Circuit, External.= A portion of the circuit not included within the
-generator, such as a secondary telegraph key and sounder.
-
-=Circuit, Grounded.= A circuit in which the ground is used as a
-conductor. This is common in telegraph and telephone lines, particularly
-for short distances where the conductivity of the earth does not offer
-too much resistance.
-
-=Circuit, Incandescent.= A circuit in which incandescent lamps are
-installed.
-
-=Circuit Indicator.= A pocket-compass, galvanometer, or other device for
-indicating or detecting the condition of a wire, whether it is active or
-dead, and, if active, in which direction the current is flowing. It may
-also give a general idea of its strength.
-
-=Circuit, Internal.= That portion of an electric circuit which is
-included within the generator.
-
-=Circuit Loop.= A minor circuit introduced, in series, into another
-circuit by a switch or cut-out, so that it becomes a part of the main
-circuit.
-
-=Circuit, Main.= a circuit or main line, includes the apparatus
-supplying current to it. Thus distinguished from a local circuit.
-
-=Circuit, Metallic.= A circuit in which the current outside the
-generator passes through metal parts or wire, but not through the
-ground. Electric light and power lines are always metallic circuits. An
-electro-plating apparatus may be properly termed a metallic circuit,
-although a part of the circuit is formed by the electrolyte in the bath.
-The essential meaning of the words metallic circuit is that the earth
-does not form a part of the return circuit.
-
-=Circuit, Open.= A circuit in which a switch has been opened to prevent
-the continuous flow of current, such as an electric-bell circuit, which
-normally remains open, and which is active only when the push-button is
-pressed, thereby closing the circuit and operating the bell. An
-open-circuit battery is one that remains inactive when the circuit is
-open.
-
-=Circuit, Parallel.= A term signifying a multiple circuit.
-
-=Circuit, Quadruple.= A single circuit capable of having four messages
-transmitted over it simultaneously--two in one direction, and two in the
-other.
-
-=Circuit, Return.= In telegraphy the ground is used as the return
-circuit. It is also that portion of a circuit which leads from an
-apparatus back to the terminal of a dynamo or battery, usually the
-negative wire.
-
-=Circuit, Short.= A connection between two parts of a circuit, causing
-the current to skip a great part of its appointed path. Short-circuits
-prevent the proper working of any electrical apparatus.
-
-=Circuit, Simple.= A circuit containing a single generator, the proper
-wire for carrying the current, and a switch to operate it. An
-electric-bell line, a single telegraph line, or a direct telephone line
-are all simple circuits.
-
-=Clamp.= A tool for grasping and holding the ends of wires while joining
-them.
-
-The appliance for holding the carbon-pencils in arc-lamps.
-
-=Cleats.= Blocks of wood, porcelain, or other insulating material used
-to hold wires against a wall or beam. They have one, two, and three
-notches at one side, for single, double, and three wire systems.
-
-=Clutch, Electric.= A form of magnetic brake applied to car-wheels, the
-armatures of motors, and other revolving mechanism, whereby the current,
-passing through a coil, magnetizes a mass of cast-iron, and brings it to
-bear frictionally upon the moving parts of the mechanism.
-
-=Code, Cipher.= A set of disconnected words which, in accordance with a
-prearranged key, stand for whole sentences and phrases. Commercially the
-system is used as a short-cut--ten words perhaps meaning what otherwise
-it would take forty or fifty words to express. It is used extensively in
-telegraphy, both as an abbreviated message and as a means for securing
-secrecy.
-
-=Coherer.= Conducting particles constituting a semi-conducting bridge
-between two electrodes, and serving to detect electro-magnetic waves.
-The coherer in wireless telegraphy is understood to mean that form of
-radio-receiver which, being normally at high resistance, is, under the
-influence of Hertzian-waves, changed to a low resistance, thus becoming
-relatively a conductor. Tubes of various kinds have been used for this
-purpose. Within them is a filling of carbon granules, copper filings,
-nickel and silver filings, and other substances. Marconi’s coherer
-consists of a tube one and one-half inches long and one-twelfth inch
-internal diameter. This is filled with filings--90 per cent. of nickel,
-10 per cent. of silver. A globule of mercury coats the outer surface of
-each grain with a thin film of the quicksilver. Into both ends a piece
-of pure silver wire is plugged. These latter are a quarter of an inch
-long, and fit the tube very accurately. The tube is thus sealed, and it
-is considered preferable to have a slight vacuum within it.
-
-=Coil.= A strand of wire wound in circular form about a spool, a
-soft-iron core, or in layers, as a coil of rope.
-
-An electro-magnetic generator.
-
-A helix. (_See also_ Induction, Resistance, Magnetizing.)
-
-=Coil, Choking.= A form of resistance to regulate the flow of current.
-Any coil of insulated wire wound upon a laminated or divided iron core
-forms a choking-coil. In alternating-current work special choking-coils
-are used. They have a movable iron core, and by thrusting it in or out
-the power is increased or diminished, thus raising or lowering the
-lights, the same as gas is regulated.
-
-=Coil, Faradic.= The name given to a medical induction-coil or faradic
-machine.
-
-=Coil, Induction.= A coil in which the electro-motive force of a portion
-of a circuit is, by induction, made to produce higher or lower
-electro-motive forces in an adjacent circuit, or in a circuit a part of
-which adjoins the original circuit. There are three principal parts to
-all induction-coils--the core, the primary coil, and the secondary coil.
-The core is a mass of soft iron, cast or wrought, but preferably
-divided--for example, a bundle of rods or bars. The primary coil of
-comparatively larger wire is wound about this core, each layer being
-properly insulated and varnished, or coated with melted paraffine, to
-bind the wires. The secondary coil is of fine wire, and is wound about
-the primary coil. A great many turns of the fine wire are necessary, and
-care must be taken to properly insulate each layer and shellac the
-wires. The primary must be well insulated from the secondary coil, so as
-to prevent sparking, which would destroy the insulation. A
-make-and-break is operated by the primary coil, and is constructed upon
-the general form of an electric bell or buzzer movement. Extra currents
-which interfere with the action of an induction-coil are avoided by the
-use of a condenser. (_See also_ Condenser.) The induction-coil produces
-a rapid succession of sparks which may spring across a gap of thirty or
-forty inches, according to the size of the coil. Induction-coils are
-used extensively in electric work, especially in telephone transmitters,
-wireless telegraphy, electric welding, and in the alternating-current
-system.
-
-=Coil, Magnetizing.= A coil of insulated wire so wound that a well or
-aperture will be formed. Within this well a piece of steel is placed, so
-that an electric current, passing through the wires, will magnetize the
-steel; or a steel rod may be passed in and out of the hole several times
-while a strong current is travelling through the coil, thus magnetizing
-the rod.
-
-=Coil, Resistance.= A coil so constructed that it will offer resistance
-to a steady current of too great electro-motive force for the safety of
-the apparatus. Generally the coil is made by doubling the wire without
-breaking it, then starting at the doubled end to wind it in coil or
-spring fashion. If the wire is too heavy to wind double, a single strand
-is wound on a square or triangular insulator in which notches are made.
-Then, alternately between the coils, the second strand is wound. The
-strands are joined at one end of the coil, but those at the other are
-left free for unions with other wires. (_See also_ Resistance.)
-
-=Coil, Retarding.= A choking-coil. A resistance-coil.
-
-=Coil, Ribbon.= Instead of wire, flat, thin strips of sheet-metal are
-sometimes used for resistance-coils, doubled, as explained above. The
-wraps are insulated with sheet-mica, micanite, or asbestos, to prevent
-short-circuiting.
-
-=Coil, Ruhmkorff.= A common type of induction-coil with a vibrator or
-circuit-breaker. Used with constant and direct current.
-
-A step-up transformer with a circuit-breaker attachment.
-
-=Coils, Idle.= Coils in a dynamo in which no electro-motive force is
-being generated or developed.
-
-Coils that, through broken connections or short circuits, are inactive.
-
-=Column, Electric.= An old name for the voltaic pile. The apparatus made
-up of a pile of disks of copper and zinc, separated by pieces of flannel
-wet with acidulated water.
-
-=Comb.= A bar from which a number of teeth project like the teeth of a
-comb. It is used as a collector of electricity from the plate of a
-frictional electric machine.
-
-=Commutator.= An apparatus used on motors and dynamos and
-induction-coils for changing the direction of currents. It is made in a
-variety of types, but usually in the shape of insulated bars closely
-packed about an armature shaft.
-
-=Commutator-bars.= The metallic segments of a dynamo or
-motor-commutator.
-
-=Commutators, Quiet.= Commutators that do not spark during the
-revolutions of the armature.
-
-=Compass.= An apparatus for indicating the directive force of the earth
-upon the magnetic needle. It consists of a case covered with glass, in
-which a magnetized needle, normally pointing to the north, is balanced
-on a point at the centre. Under the needle a card is arranged on which
-the degrees or points of the compass are inscribed. A valuable
-instrument in electrical work, magnetism, etc.
-
-=Compass, Liquid.= A form of marine compass. The needle is attached to a
-card or disk which floats in alcohol or other spirits, so as to check
-undue oscillation.
-
-=Compass, Mariners’.= A compass in which the needle is attached to a
-card that rotates in pointing to the north. A mark, called the “lubber’s
-mark,” is made upon the case, and this is in line with the ship’s keel,
-so that a glance at the card will indicate the direction in which the
-ship is headed.
-
-=Compass, Spirit.= A form of mariners’ compass in which the bowl, or
-case, is sealed and filled with alcohol. The compass-card works as a
-spindle, and, by a series of air compartments, floats on the alcohol.
-The friction of the pivot is thereby greatly diminished, making the
-compass a very sensitive one.
-
-=Compass, Standard.= A compass employed as a standard by which to
-compare other compasses.
-
-=Condenser.= An appliance for storing up electro-static charges; it is
-also called a static accumulator. The telegraphic condenser consists of
-a box packed full of sheets of tin-foil having a sheet of paraffined
-paper or sheet-mica between every two sheets. The alternate sheets of
-tin-foil are connected together, and each set has its binding-post.
-(_See also_ Electrostatic Accumulator.)
-
-=Condenser, Air.= (_See_ Air-condenser.)
-
-=Condenser, Ayrton’s.= (_See_ Ayrton’s Condenser.)
-
-=Condenser-plate.= (_See_ Plate, Condenser.)
-
-=Condenser, Sliding.= An apparatus in the form of a Leyden-jar whose
-coatings can be slid past each other to diminish or increase the face
-area, and also to diminish or increase the capacity of the condenser.
-
-=Conductance.= The conducting power of a mass of material, varying
-according to its shape and dimensions. The cylindrical or round
-conductor is the best type for the conveyance of electric currents.
-
-=Conduction.= The transmission of electricity through an immobile
-medium, such as a wire, or rod, or a bar.
-
-=Conductivity.= Ability to conduct electric currents. The conductivity
-of a wire is its power to conduct or transmit a current. Glass has no
-conductivity, and it is therefore a non-conductor.
-
-=Conductivity, Variable.= The change in the conducting or transmitting
-powers of metals and substances under different temperatures. Hot metal
-conducts an electric current better than cold. A hot carbon-pencil in an
-arc-light conducts the current better than when the light is first
-started, for as it warms up under the influence of the arc-flame the
-current passes more freely. Five minutes after the current is turned on
-the lamps in the circuit give a steady light, and do not sputter as when
-they first start up.
-
-=Conductor.= Anything which permits the passage of electric current. The
-term conductor is a relative one, and, excepting a vacuum, there is
-probably no substance that has not some conductive power. Metals,
-beginning with silver, are the best conductors, liquids next, glass the
-worst. The ether, or air, is a conductor of sound and electric vibratory
-disturbances, but not in the same sense as the ground. The air conducts
-frictional electricity, while the ground acts as a conductor for the
-galvanic current, or “current electricity.” By this last term is meant
-electricity which flows continually, instead of discharging all at once,
-with an accompanying spark or flash.
-
-=Conductor, Overhead.= Overhead electric lines, wires or cables, for
-conducting current. Generally poles are erected for this purpose.
-
-=Conductor, Prime.= A cylindrical or spherical body with no points or
-angles, but rounded everywhere and generally of metal. If made of other
-material, such as wood, glass, or composition, its entire surface is
-rendered conductive by being covered with sheet-metal, such as tin-foil,
-gold-leaf or tinsel, applied to it with paste, shellac, or glue. A prime
-conductor should be mounted on an insulated stand; it is employed to
-collect and retain frictional electricity generated by a static machine.
-
-=Conductor, Underground.= An insulated conductor which is placed under
-the surface of the earth, passing through conduits.
-
-=Connect.= The act of bringing two ends of wire together, either
-temporarily or permanently. Bringing one end of a conductor into contact
-with another so as to establish an electric connection.
-
-=Connector.= A sleeve, with screws or other clamping device, into which
-the ends of wires or rods may be passed and held securely. A
-binding-post and spring-jack comes under this head.
-
-=Contact.= The electrical union of two conductors, whether temporary or
-permanent. It may be established by touching the ends or terminals of a
-circuit through the agency of a push-button, a telegraph-key, an
-electric switch, etc.
-
-=Contact-breaker.= (The same as Circuit-breaker, _which see_.)
-
-=Contact, Loose.= A contact formed by two or several surfaces imposed
-one upon another and held by their weight alone.
-
-=Contact-point.= A point, or stud, often of silver or platinum, arranged
-to come into touch with a contact-spring, such as the vibrating armature
-of an electric bell.
-
-=Contact-spring.= A spring connected at one end of a lead and arranged
-to press against another spring or plate, so that a plug may be inserted
-between the contact-points.
-
-=Controller.= The lever or handle on the switch-board of a
-resistance-coil, by means of which electric current is let in or kept
-out of a circuit.
-
-=Controlling Force.= In galvanometers and similar instruments, the force
-used to bring the needle or indicator back to zero.
-
-=Converter.= An induction-coil used with the alternating current for
-changing the potential difference and inverting the available current.
-High alternating voltage may be converted into lower direct-current
-voltage, thereby increasing the amperage or current. A converter
-consists of a core of thin iron sheets, wound with a primary coil of
-fine insulated wire, with many convolutions or turns. Also, a secondary
-coil made up of coarse insulated wire with fewer convolutions. The coil
-may be jacketed with iron to increase the permanence.
-
-=Converter, Rotary.= A combined motor and dynamo whose function is to
-transform a current of high or low voltage (A-C., or D-C.) into any
-other kind of current desired.
-
-=Convolution.= The state of being convolved; a turn, wrap, fold, or
-whorl. A clock-spring is a familiar example.
-
-=Copper-bath.= A solution of sulphate of copper used in electro-plating,
-electrotyping, and copper-refining by electricity.
-
-=Cord, Flexible.= A flexible-wire conductor made up of many strands of
-fine wire and properly insulated so that it may be easily twisted, bent,
-or wrapped. Flexible wire is used as the conductors for portable
-electric lights, push-buttons, medical coils, etc.
-
-=Core.= The iron mass (generally located in the centre of a coil or
-helix) which becomes highly magnetic when a current is flowing around
-it, but which looses its magnetism immediately that the current ceases
-to flow.
-
-A conductor or the conductors of an electric cable made up of a single
-strand or many strands laid together and twisted. These may be of bare
-metal, or each one insulated from the others.
-
-=Core-disks.= Disks of thin wire, for building up armature-cores. The
-usual form of a core is round or cylindrical. A number of thin disks, or
-laminations, of iron strung upon the central shaft, and pressed firmly
-together by the end-nuts or keys. This arrangement gives a cylinder as a
-base on which to wind the insulated wire that forms a part of the
-armature.
-
-=Core-disks, Pierced.= Core-disks for an armature of a motor or dynamo,
-which have been pierced or bored out around the periphery. Tubes of
-insulating material, such as fibre, rubber, or paraffined paper, are
-inserted in the holes and through these the windings of wire are
-carried. The coils are thus imbedded in the solid mass of iron, and are
-protected from eddy currents; also they act to reduce the reluctance of
-the air-gaps. This arrangement is very good, from a mechanical point of
-view, but in practice its use is confined to small motors only, and
-dynamos generating under one hundred volts.
-
-=Core-disks, Toothed.= Core-disks of an armature or motor where notches
-are cut from the periphery. When they are locked together, to form the
-armature-core, the coils of wire lie in the grooves formed by a number
-of the disks bound together. This construction reduces the actual
-air-gaps and keeps the coils equally spaced.
-
-=Core, Laminated.= The core of an armature, an induction-coil, a
-converter, or any similar piece of apparatus, which is made up of plates
-or disks, insulated more or less perfectly from one another by means of
-mica or paraffined paper. The object of laminations is to prevent the
-formation of Foucault currents. A core built up of disks is sometimes
-called a radially laminated core.
-
-=Core, Ring.= A dynamo or motor armature-core which forms a complete
-ring.
-
-=Core, Stranded.= The core of a cable, or a conducting core made up of a
-number of separate wires or strands laid or twisted together.
-
-=Core, Tubular.= Tubes used as cores for electro-magnets, and also to
-produce small magnetizing power. Tubular cores are nearly as efficient
-as solid ones in straight magnets, because the principal reluctance is
-due to the air-path. On increasing the current, however, the tubular
-core becomes less efficient.
-
-=Coulomb.= The practical unit of electrical quantity. It is the quantity
-passed by a current of one ampere intensity in one second.
-
-=Couple.= The combination of two electrodes and a liquid, the
-electrodes being immersed in the latter, and being acted on
-differentially by the liquid. This combination constitutes a source of
-electro-motive force, and, consequently of current, and is called the
-galvanic or voltaic cell or battery.
-
-=Couple, Astatic.=. A term sometimes applied to astatic needles when
-working in pairs.
-
-=Coupling.= The union of cells or generators constituting a battery; the
-volume of current, or electro-motive force, is thereby increased.
-
-=C. P.= An abbreviation for “candle power”; also meaning “chemically
-pure,” when speaking of chemicals.
-
-=Crater.= The depression that forms in the positive carbon of a
-voltaic-arc.
-
-=Creeping.= A phenomena met with in solution batteries. The electrolyte
-creeps up the sides of the containing jar and evaporates, leaving a
-deposit of salts. Still more solution creeps up through the salts until
-it gets clear to the top and runs over. To prevent this the tops of the
-jars should be brushed with hot paraffine for a distance of two inches
-from the upper edge. The salts will not form on paraffine. Oil is
-sometimes poured on the top of the battery solution, but this affects
-the elements if it touches them, and makes their surfaces
-non-conducting.
-
-=Crucible, Electric.= A crucible for melting refractory substances, or
-for reducing ores by means of the electric arc produced within it.
-Probably the result obtained is due more to current incandescence than
-to the action of the arc.
-
-=Crystallization, Electric.= Under proper conditions many substances and
-liquids take a crystalline form. When such action is brought about by
-means of electricity the term electric crystallization may be applied
-to the phenomenon. A solution of nitrate of silver, when decomposed by a
-current, will give crystals of metallic silver. A solution of common
-salt or brine, when electrically decomposed, will produce sodium and
-chlorine. The sodium appears at the leading-out electrode and readily
-unites with carbonic-acid gas, which is injected into the apparatus. The
-result of the combination is carbonate of soda, one of the most
-important products of the alkali industry.
-
-=Current, Alternating.= A current flowing alternately in opposite
-directions. It is a succession of currents, each of short duration and
-of direction opposite to that of its predecessor. Abbreviation, A-C.
-
-=Current, Amperage.= The volume of electricity passing through any
-circuit per second, the flow being uniform.
-
-=Current, Constant.= An unvarying current. A constant-current system is
-one in which the current is uniformly maintained--for example, in
-electric light, power, and heat plants.
-
-=Current, Continuous.= A current of one direction only, or the reverse
-of an alternating current.
-
-=Current, Direct.= A current of unvarying direction, as distinguished
-from the alternating. Abbreviation, D-C.
-
-=Current Distribution, Uniform.= A steady current; a current whose
-density in a conductor is always the same at all points.
-
-=Current, Induced.= A current caused by electro-dynamic induction.
-
-=Current, Low Potential.= A current of low pressure.
-
-A term applied to low electro-motive force.
-
-=Current, Make-and-break.= A current which is continually broken or
-interrupted and started again. The term is applied only where the
-interruptions occur in rapid succession, as in the action of an
-induction-coil or pole-changer.
-
-The alternating current.
-
-=Current-meter.= An apparatus for indicating the strength of a current,
-such as an ammeter.
-
-=Current, Oscillating.= A current periodically alternating.
-
-=Current, Periodic.= A current with periodically varying strength or
-direction. A current alternating periodically.
-
-=Current, Polarizing.= A current which causes polarization.
-
-=Current-reverser.= A switch or other contrivance for reversing the
-direction of a current in a conductor.
-
-=Current, Undulating.= A current whose direction is constant but whose
-strength is continuously varying.
-
-=Currents, Eddy.= Useless currents in an armature, in the pole pieces,
-and in the magnetic cores of dynamos and motors. They are created by the
-high speed of the armature in its rotation, or by other electric
-currents induced by the armature’s motion through magnetic fields.
-
-=Currents, Faradic.= Induced currents. They take their name from Michael
-Faraday, the original investigator of the phenomena of electro-magnetic
-induction. The secondary or induced electro-magnetic currents and their
-accompanying phenomena.
-
-A series of alternating electro-static discharges from influence
-machine, such as the Holtz and Wimshurst.
-
-The simple and commonly understood Faradic currents are those produced
-in the medical battery, and used in medical therapeutics.
-
-=Currents, Foucault.= A form of currents produced in revolving
-armature-cores; sometimes called eddy currents. They are useless.
-
-=Currents, Harmonic.= Currents which alternate periodically, and vary
-harmonically. Currents which vibrate at certain pitches, as, for
-instance, the currents in wireless telegraphy. Two instruments must be
-tuned to the same pitch in order to be responsive. Thus an instrument
-sending out waves of 70,000 vibrations cannot be recorded by one tuned
-much below or above the same number.
-
-Sound waves of sympathetic or harmonic vibrations.
-
-=Currents, Positive.= (_See_ Positive Currents.)
-
-=Cut-in.= To electrically connect a piece of mechanism or a conductor
-with a circuit.
-
-=Cut-out.= The reverse of the cut-in. To remove from a circuit any
-conducting device. The cut-out may be so arranged as to leave the
-circuit complete in some other way.
-
-An appliance for removing a piece of apparatus from a circuit so that no
-more current shall pass through the former.
-
-=Cut-out, Automatic.= A safety device for automatically cutting out a
-circuit to prevent accident or the burning-out of an apparatus, due to
-an overload of current. It is worked by an electro-magnet and spring. An
-overload of current causes a magnet of high resistance to draw an
-armature towards it, and this, in turn, releases the spring of the
-cut-out device. Sometimes a strip or wire of fusible metal is employed
-which is in circuit with a switch. The excess of current fuses the
-metal, and the broken circuit releases a spring-jack, which, in turn,
-breaks the circuit.
-
-=Cut-out, Safety.= A block of non-conducting material, such as marble,
-slate, or porcelain, carrying a safety-fuse or plugs. In these is
-enclosed a piece of fusible wire, which burns out or melts and breaks
-the circuit before the apparatus is damaged.
-
-=Cut-out, Wedge.= A cut-out operated by a wedge, such as a spring-jack
-or the plugs at the end of the flexible wires on the switch-boards of
-telephone exchanges.
-
-
-D
-
-=Damper.= A frame of copper on which the wire in a galvanometer is
-sometimes coiled. It acts to check the needle oscillations.
-
-A brass or copper sheathing or tube placed between the primary and
-secondary coils of an induction-coil to cut off induction and diminish
-the current and potential of the secondary circuit. When the tube is
-drawn out gradually the induction increases. It is commonly used in
-medical coils to adjust their strength of action.
-
-=D-C.= An abbreviation for direct current.
-
-=Dead Earth.= A fault in telegraph and telephone lines which consists in
-the ground-wire being improperly grounded, or not fully connected with
-the earth.
-
-=Dead Turns.= A term applied to the ten to twenty per cent. of the
-convolutions or turns of wire on an armature which are considered to be
-dead. There are supposed to be about eighty per cent. of the turns on an
-armature that are active in magnetizing the core; the balance are
-outside the magnetic field and are termed dead, although they are
-necessary to the production of electro-motive force.
-
-=Dead Wire.= A wire in the electric circuit through which no current is
-passing.
-
-A disused or abandoned electric conductor, such as a telegraph wire, or
-a wire which may be in circuit, but through which at the time of
-speaking no electrical action is taking place.
-
-=Death, Electrical.= Death resulting from an electric current passing
-through the animal body--electrocution; accidental death by electric
-shock; premeditated death through bringing the body in direct contact
-with conductors carrying high electro-motive force. High electro-motive
-force is essential, and the alternating current is most fatal.
-
-=Decomposition, Electrolytic.= The decomposition or separation of a
-compound liquid into its constituents by electrolysis. The liquid must
-be a conductor or electrolyte, and the decomposition is carried on by
-means of electricity.
-
-The conversion of two or more chemicals into a new compound or
-substance.
-
-=Deflection.= In magnetism, the movement of the needle out of the plane.
-It is due to disturbance, or to the needle’s attraction towards a mass
-of iron or steel or another magnet.
-
-=Demagnetization.= The removal of magnetism from a paramagnetic
-substance. The process is principally in use for watches which have
-become magnetized by exposure to the magnetic field surrounding dynamos
-or motors.
-
-=Density, Electric.= The relative quantity of electricity, as a charge,
-upon a unit area of surface. It may be positive or negative.
-
-Surface density, as the charge of a Leyden-jar.
-
-=Depolarization.= A term applied to the removal of permanent magnetism,
-such as that from a horseshoe magnet, a watch, or a bar-magnet. Heat is
-the common depolarizer, but counter electro-magnetic forces are employed
-also in the various forms of apparatus known as demagnetizers.
-
-=Deposit, Electrolytic.= The metal or other substances precipitated by
-the action of a battery or other current-generator, as in the plating
-processes.
-
-=Detector.= A portable galvanometer, by means of which a current and its
-approximate strength can be detected and measured.
-
-=Diaphragm.= In telephones and microphones, a disk of iron thrown into
-motion by sound-waves or by electric impulse. It is usually a thin plate
-of japanned iron, such as is used in the ferrotype photographic process
-for making tin-types.
-
-=Dielectric.= Any substance through which electrostatic induction is
-allowed to occur, such as glass or rubber. It is a non-conductor for all
-electric currents.
-
-=Dielectric Resistance.= The resistance a body offers to perforation or
-destruction by an electric discharge.
-
-=Dimmer.= An adjustable choke or resistance coil used for regulating the
-intensity of electric incandescent lamps. It is employed extensively in
-theatres for raising or lowering the brilliancy of lights.
-
-=Dipping.= The process of cleaning articles by dipping them in acids or
-caustic soda, preparatory to electro-plating.
-
-Simple immersion, with or without current, to put a blush of metal on a
-cleaned surface.
-
-=Dipping-needle.= A magnetic needle mounted on a horizontal bearing so
-that it will dip vertically when excited by a current passing
-horizontally about it. The ordinary compass-needle is mounted on a
-point, and swings freely to the right or left only.
-
-=Direct Current.= (_See_ Current, Direct.)
-
-=Discharge.= The eruptive discharge from a Leyden-jar or accumulator of
-a volume of electricity stored within it.
-
-The abstraction of a charge from a conductor by connecting it to the
-earth or to another conductor.
-
-=Discharge, Disruptive.= The discharge of a static charge through a
-dielectric. It involves the mechanical perforation of the dielectric.
-
-=Disconnect.= To break an electric circuit or open it so as to stop the
-flow of current; to remove a part of a circuit or a piece of apparatus
-from a circuit.
-
-=Distillation, Electric.= The distilling of a liquid by the employment
-of electricity, which, by electrifying the liquid, assists the effects
-of heat. It is asserted that the process is accelerated by the
-electrification of the liquid or fluid, but it must be a conductor
-liquid or electrolyte. Oil, being a non-conductor, is not affected by
-any electric current, no matter what its specific gravity may be.
-
-=Distributing Centre.= The centre of distribution in a system having
-branch circuits, such as the electric-light or telephone outlets from a
-main station.
-
-=Door-opener, Electric.= A magnetic contrivance arranged in connection
-with a lock, by means of which the latch is released by pressing a
-distant push-button. This device is used in flats and apartment-houses
-for opening a door from any of the apartments in the house.
-
-=Double Filament Lamp.= An incandescent lamp having two filaments, one
-with a high capacity, the other with a low one. The high capacity may be
-from sixteen to fifty candle-power, the other from one to five. A turn
-of the bulb in its socket, or the pulling of a string which operates a
-switch in the socket, cuts out the current from the long filament and
-sends it through the shorter and finer one, thus giving a weaker light.
-These “hy-lo” lamps are useful as night lamps in halls, bath-rooms, or
-in sick-rooms, where a low or weak light is required all night.
-
-=Double Pole-switch=. A cut-out that is arranged to cut out the circuit
-of both the negative and positive leads at the same time.
-
-=Double-push.= A contact-push having two contacts and arranged so that
-pressure upon it opens one contact and closes the other.
-
-=Double Throw-switch.= A switch so arranged that it can be thrown into
-either one of two contacts; a throw-over switch.
-
-=Driving-pulley.= The broad-faced or channelled pulley on an armature
-shaft by means of which the power from a motor may be transmitted
-mechanically.
-
-=Dry Battery.= (_See_ Battery, Dry.)
-
-=Duct.= The space in an underground conduit for a single wire or cable.
-
-=Duplex Wire.= An insulated conductor having two distinct wires twisted
-or laid together, but properly insulated from each other.
-
-=Dynamic Electricity.= Electricity in motion or flowing, as
-distinguished from static or frictional electricity.
-
-Electricity of relatively low potential or electro-motive force in large
-quantity or amperage.
-
-=Dynamo.= An apparatus consisting of a core and field-magnets, properly
-wound with insulated wire, which, when put into operation by revolving
-the core or armature at high speed, develops electric current; a
-mechanical generator of electricity.
-
-=Dynamo, Motor.= (_See_ Motor-dynamo.)
-
-
-E
-
-=Earth.= The accidental grounding of a circuit is termed an “earth.”
-
-=Earth-plate.= A plate buried in the ground to receive the ends of
-telegraph lines and other circuits, and so give a ground connection.
-Copper plates are often used, but in houses the ground is usually formed
-by attaching a wire to the gas or water pipes.
-
-=Earth Return.= The grounding of a wire in a circuit at both ends gives
-the circuit an earth return. This method is commonly used in telegraph
-lines, both in the wire and wireless systems.
-
-=Eddy Currents.= (_See_ Currents, Eddy.)
-
-=Edison Distributing-box.= A box used in the Edison “three-wire” system,
-from which the outlets pass to local circuits.
-
-=Edison Lalande Cell.= A zinc-copper battery having a depolarizing
-coating of copper oxide on the copper element, the couple being immersed
-in an electrolyte composed of potash or caustic soda.
-
-=Ediswan.= A term applied to the incandescent lamps invented by Edison
-and Swan and used extensively in Great Britain. Also applied to other
-apparatus designed by the two inventors.
-
-=Efficiency.= The relation of work done to the electrical energy
-absorbed. The efficiency is not equal to the energy absorbed, because it
-always takes more power to generate a current than is given back in
-actual efficiency. This is due to mechanical friction and to the
-resistance of the air in a mechanism such as a dynamo when revolving at
-high speed.
-
-=Efficiency, Electrical.= In a generator it is the total electrical
-energy produced, both that wasted and that actually used in driving
-machinery or apparatus.
-
-=Efflorescence.= The dry salts on a jar or vessel containing liquid
-that collects above the water or evaporation line. This is due to
-creeping.
-
-=Elasticity.= A property in some bodies and forces through which they
-recover their former figure, shape, or dimensions when the external
-pressure or stress is removed. Water has no elasticity. Air is very
-elastic; steam has a great volume of elasticity; while electricity is
-undoubtedly the most elastic of all in its motion through air, water,
-and other conducting mediums.
-
-=Electric.= Pertaining to electricity; anything connected with the use
-of electricity. It has been a much-abused word, and its meaning has been
-garbled by the impostor, the crook, and the “business thief” in foisting
-on the public wares in which there was no electrical property whatever.
-“Electric” toothbrushes, combs, corsets, belts, and the like may contain
-a few bits of magnetized steel, but they possess no active therapeutic
-value.
-
-=Electrical Engineer.= The profession of electrical engineer calls for
-the highest knowledge of electricity, both theoretical and practical. It
-embraces the designing and installation of all kinds of electrical
-apparatus.
-
-=Electrician.= One versed in the practices and science of electricity; a
-practical lineman or wireman.
-
-=Electricity.= One of the hidden and mysterious powers of nature, which
-man has brought under control to serve his ends, and which manifests
-itself mainly through attraction and repulsion; the most powerful and
-yet the most docile force known to man, coming from nowhere and without
-form, weight, or color, invisible and inaudible; an energy which fills
-the universe and which is the active principle in heat, light,
-magnetism, chemical affinity, and mechanical motion.
-
-=Electricity, Atmospheric.= The electric currents of the atmosphere,
-variable but never absent. They include lightning, frictional
-electricity, the Aurora Borealis, the electric waves used in wireless
-telegraphy, etc. Benjamin Franklin indicated the method of drawing
-electricity from the clouds. In June, 1752, he flew a kite, and by its
-moistened cord drew an electric current from the clouds so that sparks
-were visible on a brass key at the ground end of the cord. Later, when a
-fine wire was substituted for the cord, and a kite was flown in a
-thunder-storm, the electric spark was vivid. This experiment confirmed
-his hypothesis that lightning was identical with the disruptive
-discharges of electricity.
-
-=Electricity, Latent.= The bound charge of static electricity.
-
-=Electricity, Negative.= (_See_ Negative Electricity.)
-
-=Electricity, Positive.= (_See_ Positive Electricity.)
-
-=Electricity, Voltaic.= Electricity of low potential difference and
-large current intensity.
-
-Electricity produced by a voltaic battery or dynamo as opposed to static
-electricity, which is frictional and practically uncontrollable for
-commercial purposes.
-
-=Electrification.= The process of imparting an electric charge to a
-surface. The term is applied chiefly to electro-static phenomena.
-
-=Electrization.= In electro-therapeutics, the subjection of the human
-system to electric treatment. An electric tonic imparted by
-electro-medical baths through the nervous system.
-
-=Electro-chemistry.= That branch of science which treats of the
-relations between electric and chemical forces in their different
-reactions and compounds. It deals with electro-plating, electro-fusing,
-electrolysis, etc.
-
-=Electro-culture.= The application of electricity to the cultivation of
-plants. The use of electricity has been found very beneficial in some
-forms of plant growth.
-
-=Electrocution.= Capital punishment inflicted by electric current from a
-dynamo of high electro-motive force. The current used is from 1500 to
-2000 volts, and it acts to break down the tissues of the body.
-
-=Electrode.= The terminals of an open electric circuit.
-
-The terminals between which an electric arc is formed, as in the
-arc-light.
-
-The terminals of the conductors of an electric circuit immersed in an
-electrolytic solution, such as the carbon and zinc of a battery.
-
-=Electrolier.= A fixture for supporting electric lamps, similar to a
-chandelier for gas or candles. Combination electroliers conduct both gas
-and electricity.
-
-=Electrolysis.= The separation of a chemical compound into its
-constituted parts by the action of an electric current.
-
-=Electrolyte.= A body susceptible of decomposition by the electric
-current. It must be a fluid body and a conductor capable of diffusion as
-well as composite in its make-up. An elemental body such as pure water
-cannot be an electrolyte.
-
-=Electrolytic Decomposition.= (_See_ Decomposition, Electrolytic.)
-
-=Electrolytic Deposit.= (_See_ Deposit, Electrolytic.)
-
-=Electrolytic Resistance.= (_See_ Resistance, Electrolytic.)
-
-=Electro-magnetic Induction.= (_See_ Induction, Electro-Magnetic.)
-
-=Electro-magnetism.= Magnetism created by electric current.
-
-That branch of electrical science which treats of the magnetic
-relations of a field of force produced by a current.
-
-=Electro-medical Bath.= A bath provided with connections and electrodes
-for causing a current of electricity to pass through the body of the
-patient.
-
-=Electrometer.= An instrument used for measuring static electricity.
-Electrometers are different from galvanometers, since the latter depend
-on a current flowing through wires to create an action of the magnetic
-needles.
-
-=Electro-motive Force.= Voltage. It may be compared to the pressure of
-water in hydraulic systems. The unit of electro-motive force is the
-volt.
-
-=Electro-motor.= A term sometimes applied to a current-generator, such
-as a small dynamo or voltaic battery.
-
-=Electro-plating.= (_See_ Plating, Electro.)
-
-=Electropoion Fluid.= An acid depolarizing solution for use in
-zinc-carbon couples, such as the “Grenet” and “Daniell” cells. The
-bi-chromate-of-potash and sulphuric-acid solution for battery charges is
-a good example.
-
-=Electroscope.= An apparatus for indicating the presence of an electric
-charge and whether the charge is negative or positive.
-
-=Electrostatic Accumulator.= Two conducting surfaces, separated by a
-dielectric and arranged for the opposite charging of the two surfaces. A
-faradic or static machine for accumulating frictional electricity is an
-example.
-
-=Electrostatics.= That division of electric science which treats of the
-phenomena of the electric charge, or of electricity in repose, as
-contrasted with electro-dynamics or electricity in motion.
-
-=Electrotype.= The reproduction of a form of type or engraving by the
-copper electro-plating process. The original is coated with plumbago and
-a wax impression taken of it. The face of the negative is made
-conductive with plumbago or tin dust, then suspended in a copper bath
-and connected with the current. A film of copper will be deposited on
-the face of the wax impression.
-
-=Element, Chemical.= Original forms of matter that cannot be separated
-into simple constituents by any known process. There are about seventy
-in all, but as science advances the list is constantly being revised.
-New elements are discovered and known ones are being resolved into
-simpler forms.
-
-=Elements of Battery Cell.= (_See_ Battery Cell, Elements of.)
-
-=Emergency Switch.= An auxiliary switch used as a controller on a car to
-reverse the action of the motor.
-
-=E-M-F.= An abbreviation for electro-motive force, or voltage.
-
-=Equalizer.= A term applied to a wire or bar in electro-magnetic
-mechanism for equalizing the pressure over a system.
-
-=Exciter.= A generator used for exciting the field-magnets of a dynamo.
-
-=Extension Call-bell.= A bell connected with a telephone call-bell, and
-located in another part of a building so as to give a distant summons.
-
-=External Circuit.= (_See_ Circuit, External.)
-
-
-F
-
-=F.= The sign commonly employed to designate Fahrenheit. Thus, 30° F.
-means 30 degrees Fahrenheit, or 30 degrees above zero.
-
-=False Magnetic Poles.= (_See_ Magnetic Poles, False.)
-
-=Faradic.= Induced current produced from induction-coils and faradic
-machines.
-
-A series of alternating electrostatic discharges, as from a Holtz
-influence machine.
-
-=Faradic Coil.= (_See_ Coil, Faradic.)
-
-=Faradic Currents.= (_See_ Currents, Faradic.)
-
-=Faradic Machine.= An apparatus designed to produce faradic current.
-
-=Feed.= To furnish an electric current, also spoken of in connection
-with the mechanism that moves the carbons in arc-lamps.
-
-=Feeders, or Feed Wires.= The conductors which convey electric currents
-at different points, as in the trolley system. The current is carried
-along in large cables strung on poles or laid underground, and at proper
-distances lines are run in to feed the trolley wire.
-
-=Field.= The space in the neighborhood of a dynamo or motor, or other
-generator of electric current, from which the apparatus takes its
-electricity, both electrostatic and magnetic.
-
-=Field-magnet.= (_See_ Magnet, Field.)
-
-=Field of Force.= The space in the neighborhood of an attracting or
-repelling mass or system. There are two kinds of fields of force--the
-electro-magnetic and the static--from which the respective pieces of
-apparatus draw their store of electricity.
-
-=Filament.= A long, thin piece of solid substance. It is generally as
-thin as a thread and flexible enough to be bent.
-
-The hairlike element in an incandescent lamp which, when heated by a
-current, glows and radiates light.
-
-=Filaments, Paper.= Filaments for incandescent lamps made of carbonized
-paper. They were the ones originally used in electric lamps, but have
-been superseded by other substances easier to handle and more durable.
-
-=Flow.= The volume of a current or stream escaping through a conductor,
-such as a wire, rod or pipe.
-
-=Fluorescence.= The property of converting ether waves of one length
-into waves of another length. The phenomenon is utilized in the
-production of Geissler tubes and X-rays.
-
-=Fluoroscope.= An apparatus for making examinations by means of the
-X-rays.
-
-=Fluoroscopic Screen.= A screen overspread with fluorescent material and
-employed for fluoroscopic examinations in connection with the X-rays.
-
-=Force.= Any change in the condition of matter with respect to motion or
-rest. Force is measured by the acceleration or change of motion that it
-can impart to a body of a unit mass in a unit of time. For instance, ten
-pounds pressure of steam will be indicated on a gauge made for measuring
-steam. That pressure of steam, with the proper volume behind it, is
-capable of instantly producing a given part of a horse-power. In the
-same way ten volts of electro-motive force is capable of pushing a
-current so as to exert a certain fraction of horse-power.
-
-=Force, Electro-magnetic.= The force of attraction or repulsion exerted
-by the electro-magnet. It is also known as electric force in the
-electro-magnetic system.
-
-=Foucault Currents.= (_See_ Currents, Foucault.)
-
-=Fractional Distillation.= The process of evaporating liquids by heat,
-the most volatile being the first treated. When that has been evaporated
-and distilled the heat is raised and the next most volatile liquid is
-evaporated, and so on until all are evaporated, leaving as a residue the
-solids that were a part of the original mass of liquid.
-
-=Friction.= The effect of rubbing, or the resistance which a moving
-body encounters when in contact with another body.
-
-=Frictional Electric Machine.= An apparatus for the development or
-generation of high-tension frictional electricity.
-
-=Frictional Electricity.= Electricity produced by the friction of
-dissimilar substances.
-
-=Full Load.= A complete load. The greatest load a machine or secondary
-battery will carry permanently. The full capacity of a motor running at
-its registered speed for its horse-power.
-
-=Furnace, Electric.= A furnace in which the heat is produced by the
-electric arc. It is the hottest furnace known to man, and temperatures
-as high as 7500° Fahrenheit have been developed in it.
-
-=Fuse, Electric.= A fuse for igniting an explosive charge by
-electricity. It is made by bringing the terminals or ends of wires close
-together, so that they will spark when a current passes through them. Or
-a thin piece of highly resistant wire may be imbedded in an explosive
-and brought to white heat by current.
-
-=Fuse-block.= An insulator having a safety-fuse made fast to it.
-
-=Fuse-box.= A box containing a safety-fuse, generally of porcelain,
-enamelled iron, or some other non-conductor.
-
-=Fuse-links.= Links composed of strips or plates of fusible metal
-serving the purpose of safety-fuses.
-
-=Fusing-current.= A current of sufficient strength to cause the blowing
-or fusing of a metal.
-
-
-G
-
-=Galvanic.= Voltaic. Relating to current electricity or the
-electro-chemical relations of metals.
-
-=Galvanic Taste.= A salty taste in the mouth resulting from the passage
-of a light current from a voltaic battery, the ends of the wires being
-held to either side of the tongue. This has been called tasting
-electricity, but it is really the decomposition of saliva on the surface
-of the tongue, due to electrolysis or the passage of a current through a
-liquid.
-
-=Galvanism.= The science of voltaic, or current, electricity.
-
-=Galvanizing.= Coating iron with a thin layer of zinc by immersing the
-object in the molten metal.
-
-=Galvano-faradic.= In medical electricity the shocking-coil. The
-application of the voltaic current, induced by a secondary current
-(induction-coil), to any part of the body.
-
-=Galvanometer.= An instrument for measuring current strength.
-
-A magnetic needle influenced by the passage of a current through a wire
-or coil located near it.
-
-=Galvanometer, Tangent.= A galvanometer provided with two magnetic
-needles differing in length, the shorter one serving to measure
-tangents, the longer being used for sine measurements of current
-strength.
-
-=Galvanoscope.= An instrument, generally of the galvanometer type, used
-to ascertain whether a current is flowing or not.
-
-=Generator.= An apparatus for maintaining an electric current, such as a
-dynamo, a faradic machine, a battery, etc.
-
-=German-silver.= An alloy of copper, nickel, and zinc. Used chiefly in
-resistance-coils, either in the form of wire or in strips of the
-sheet-metal.
-
-=Gold-bath.= A solution of gold used for depositing that metal in the
-electro-plating bath.
-
-=Graphite.= A form of carbon. It occurs in nature as a mineral, and
-also is made artificially by the agency of electric heat.
-
-=Gravity Battery.= (_See_ Battery, Gravity.)
-
-=Grounded Circuit.= (_See_ Circuit, Grounded.)
-
-=Ground-plate.= (_See_ Plate, Ground.)
-
-=Ground-wire.= The contact of a conductor, in an electric circuit, with
-the earth. It permits the escape of current if another ground-wire
-exists.
-
-=Guard Tube.= A tube inserted in a wooden or brick partition to insulate
-wires that may pass through it. These tubes are made of porcelain,
-gutta-percha, compositions of a non-conducting nature, and fibre.
-
-=Gutta-percha.= Caoutchouc treated with sulphur to harden it; sometimes
-called vulcanized rubber or vulcanite. It is a product obtained from
-tropical trees, and when properly treated it is a valuable insulator in
-electrical work, particularly in submarine cables, since it offers great
-resistance to the destructive agencies of the ocean’s depths.
-
-
-H
-
-=Hand Generator.= A magneto-generator driven by hand for the generation
-of light currents.
-
-=Harmonic Currents.= (_See_ Currents, Harmonic.)
-
-=Harmonic Receiver.= A receiver containing a vibrating reed acted on by
-an electro-magnet. Such a reed answers only to impulses tuned to its
-pitch.
-
-=Heat.= One of the force agents of nature. It is recognized in its
-effects through expansion, fusion, evaporation, and generation of
-energy.
-
-=Heat, Electric.= Caused by a resisting medium, such as carbon or
-German-silver, when too much current is forced through it. The
-principle of the car-warmers, electric iron, electric chafing-dish, etc.
-
-=Helix.= A coil of wire. Properly a coil of wire so wound as to follow
-the outlines of a screw without overlaying itself.
-
-=Horse-power, Electric.= Meaning the same as in mechanics. Referred to
-when speaking of the working capacity of a motor or the power required
-to drive a dynamo.
-
-=Horse-power Hour.= A unit or standard of electrical work theoretically
-equal to that accomplished by one horse during one hour.
-
-=Horseshoe Magnet.= (_See_ Magnet, Horseshoe.)
-
-=H-P.= Abbreviation for horse-power.
-
-=Hydrometer.= An instrument employed to determine the amount of moisture
-in the atmosphere.
-
-An instrument for determining through flotation the density or specific
-gravity of liquids and fluids. It consists of a weighted glass bulb or
-hollow metallic cylinder with a long stem on which the Baumé scale is
-marked. Dropping it into a liquid it floats in a vertical position, and
-sinks to a level consistent with the gravity of the fluid.
-
-=Hydrometer, Baumé.= An apparatus for testing the gravity of fluids. The
-zero point corresponds to the specific gravity of water for liquids
-heavier than water. A gauge, valuable in testing acids and other fluids
-used in electrical work.
-
-
-I
-
-=Igniter.= A mechanical hand apparatus, in which a battery,
-induction-coil, and vibrator are located, and whose spark, jumping
-across a gap at the end of a rod, ignites or lights a gas flame,
-blasting-powder, or dynamite.
-
-=I-H-P.= An abbreviation for indicated horse-power.
-
-=Illuminating Power.= Any source of light as compared with a standard
-light--as, for instance, the illuminating power of an electric light
-reckoned in candle-power.
-
-=Illumination.= A light given from any source and projected on a
-surface, per unit of area, directly or by reflection. It is stated in
-terms--as, for instance, the candle-power of a lamp. When speaking of an
-incandescent lamp we say it illuminates equal to four candle-power or it
-gives a light equal to sixteen candle-power.
-
-=Immersion, Simple.= Plating, without the aid of a battery, by simply
-immersing the metal in a solution of metallic salt.
-
-=Impulse.= The motion produced by the sudden or momentary action of a
-force upon a body. An electro-magnetic impulse is the action produced by
-the electro-magnetic waves in magnetizing a mass of soft iron and
-attracting to it another mass of iron or steel.
-
-An electro-motive impulse is one where the force rises so high as to
-produce an impulsive discharge such as that from a Leyden-jar.
-
-=Incandescence, Electric.= The heating of a conductor to red or white
-heat by the passage of an electric current. For example, an incandescent
-lamp.
-
-=Incandescent Circuit.= (_See_ Circuit, Incandescent.)
-
-=Incandescent Lamp-filament.= (_See_ Filament.)
-
-=India-rubber.= (_See_ Caoutchouc and Gutta-percha.)
-
-=Indicator-card.= The card used in galvanoscopes, volt and ampere
-meters, and other instruments. It is provided with a moving needle and
-is marked with a graduated scale.
-
-=Induced.= Caused by induction, and not directly.
-
-=Induced Current.= (_See_ Current, Induced.)
-
-=Inductance.= That capacity of a circuit which enables it to exercise
-induction and create lines of force.
-
-Inductance is the ratio between the total induction through a circuit to
-the current producing it.
-
-=Induction, Back.= A demagnetizing force produced in a dynamo armature
-when a lead is given to the brushes. When the brushes are so set the
-windings on the armature are virtually divided into two sets: one a
-direct magnetizing set, the other a cross-magnetizing set which exerts a
-demagnetizing action on the other set. The position of the brushes on a
-dynamo or motor is indicated by their location, and if changed back
-induction will be the result.
-
-=Induction-coil.= (_See_ Coil, Induction.)
-
-=Induction, Electro-magnetic.= When negative and positive currents are
-brought towards each other against their material repulsive tendencies
-the result is work, or energy, and the consequent energy increases the
-intensity of both currents temporarily. The variations thus temporarily
-produced in the currents are examples of electro-magnetic induction. A
-current is surrounded by lines of force. The approach of two
-circuits--one negative, the other positive--involves a change in the
-lines of force about the secondary circuit. Lines of force and current
-are so intimately connected that a change in one compels a change in the
-other. Therefore, the induced current in the secondary may be attributed
-to the change in the field of force in which it lies. The inner and
-outer coils of wire about the soft iron wire composing an
-induction-coil are the best and simplest examples of electro-magnetic
-induction.
-
-=Induction, Magnetic.= The magnetization of iron or other paramagnetic
-substances by a magnetic field. The magnetic influence of a bar excited
-under these conditions is shown by throwing iron filings upon it. They
-will adhere to both ends (that is at the negative and positive poles)
-but not at the middle.
-
-=Inductor.= A mass of iron in a current generator which is moved past a
-magnet-pole to increase the number of lines of force issuing therefrom.
-It is generally laminated, and is used in inductor dynamos and motors of
-the alternating-current type.
-
-=Influence, Electric.= Electric induction or influence which may be
-electro-static, current, or electro-magnetic.
-
-=Influence Machine.= A static electric machine worked by induction, and
-used to build up charges of opposite nature on two separate
-prime-conductors.
-
-=Installation.= The entire apparatus, building, and appurtenances of a
-technical or manufacturing plant or power-house. An electric-light
-installation would mean the machinery, street-lines, lamps, etc.
-
-=Insulating Joint.= Used for the purpose of insulating a gas-pipe from
-an electric circuit.
-
-=Insulating Varnish.= A varnish composed of insulating material, such as
-gums, shellac, or diluted rubber. Shellac dissolved in alcohol is
-perhaps the best. It is easy to make and dries quickly, making an
-insulating surface practical for almost every ordinary use.
-
-=Insulation.= The dielectric or non-conducting materials which are used
-to prevent the leakage of electricity. The covering for magnet wires,
-and overhead conduits for power lines and electric lighting.
-
-=Insulation, Oil.= Any non-combustible oil may be employed as an
-insulator to prevent electrical leakage in induction-coils,
-transformers, and the like. Its principal advantage lies in its being in
-liquid form, permitting of easy handling. Moreover, if pierced by a
-spark from a coil, it at once closes again without becoming ignited. A
-solid insulator, if pierced, is permanently injured.
-
-=Insulator.= Any insulating substance or material to prevent the escape
-of current. The knobs of porcelain or glass to which wires are made
-fast.
-
-=Insulator, Porcelain.= An insulator made of porcelain and used to
-support a wire.
-
-=Intensity.= The intensity or strength of a current is its amperage. The
-strength of a magnetic field, its power to attract or magnetize.
-
-=Internal Circuit.= (_See_ Circuit, Internal.)
-
-=Internal Resistance.= (_See_ Resistance, Internal.)
-
-=Interrupter.= A circuit-breaker. Any device which breaks or interrupts
-a circuit. It may be operated by hand or automatically.
-
-The vibrator of an induction-coil.
-
-The commutators of an armature.
-
-=Isolated Plant.= The system of supplying electric energy by independent
-generating dynamos for each house, factory, or traction line.
-
-=Isolation, Electric.= A term applied to “electric sunstroke.” Exposure
-to powerful arc-light produces effects resembling those of sunstroke.
-
-
-J
-
-=Joint.= The point where two or more electric conductors join.
-
-=Joint Resistance.= The united resistance offered by a number of
-resistances connected in parallel.
-
-=Jumper.= A short circuit-shunt employed temporarily around an
-apparatus, lamp, or motor to cut out the current.
-
-=Jump-spark.= A disruptive spark excited between two conducting surfaces
-in distinction from a spark excited by a rubbing contact.
-
-
-K
-
-=Kaolin.= A form of earth or product of decomposed feldspar composed of
-silica and alumina. It is serviceable in insulating compounds.
-
-=Kathode.= The terminal of an electric circuit whence an electrolyzing
-current passes from a solution. It is the terminal connected to the zinc
-pole of a battery or the article on which the electro-deposit is made.
-
-=Key.= The arm of a telegraphic sounder by which the circuit is made and
-broken. A pivoted lever with a finger-piece which, when depressed, makes
-contact between a point and a stationary contact on the base.
-
-=Keyboard.= A board, or table, on which keys or switches are mounted.
-
-A switchboard.
-
-=Kilowatt.= A compound unit; one thousand watts; an electric-current
-measure. Abbreviation, K-W.
-
-=Kilowatt Hour.= The result in work equal to the expenditure or exertion
-of one kilowatt in one hour.
-
-=Kinetoscope.= A photographic instrument invented by Edison for
-obtaining the effect of a panorama or moving objects by the display of
-pictures in rapid succession--in familiar parlance, “moving pictures.”
-
-=Knife Switch.= A switch with a narrow and deep, movable blade, or bar
-of copper or brass, which resembles the blade of a knife. It is forced
-between two spring-clamps attached to one terminal so as to make perfect
-contact.
-
-
-L
-
-=Laminated.= Made up of thin plates, as an armature-core.
-
-=Laminated Core.= (_See_ Core, Laminated.)
-
-=Lamp-Arc.= A lamp in which the light is produced by a voltaic arc.
-Carbon electrodes are used, and a special mechanism operates and
-regulates the space between the carbons so that a perfect arc may be
-maintained.
-
-=Lamp, Incandescent.= A lamp in which the light is produced through
-heating a filament to whiteness by the electric current. It consists of
-a glass bulb from which the air is exhausted and sealed, after the
-filament is enclosed. The ends of the filament are attached to platinum
-wires, which in turn are made fast to the contact-plates at the head of
-the lamp, so as to connect with the current.
-
-=Lamp-socket.= A receptacle for an incandescent lamp. It is generally
-made of brass and provided with a key-switch to turn the current on and
-off.
-
-=Latent Electricity.= (_See_ Electricity, Latent.)
-
-=Lead.= (Not the metal.) An insulated conductor which leads to and from
-a source of power; an insulated conductor to and from a telegraph or
-telephone instrument; a circuit, a battery, or a station. Not a part of
-the line circuit.
-
-That part of an electric light or power circuit which leads from the
-main to the lamps or motors.
-
-=Leading-in Wires.= The wires which lead into a building from an aerial
-circuit.
-
-The wires which lead in and out from a lamp, battery, or instrument.
-
-=Leak.= An escape of electrical energy through leakage. This is more
-liable to occur in bare than in insulated wires. The escape of current
-from bare trolley wires is much greater than that from the insulated
-conductors, particularly in damp or rainy weather.
-
-=Leclanché Battery.= (_See_ Battery, Leclanché.)
-
-=Leyden-jar.= A type of static condenser. Its usual form is a glass jar.
-Tin-foil is pasted about its inner and outer surfaces covering about
-half the wall. The balance of the glass is painted with shellac or
-insulating varnish. The mouth is closed with a cork stopper, and through
-its centre a brass rod is passed which, by a short chain, is connected
-with the interior coating of the jar. The top of the rod is provided
-with a brass knob or ball, and from this last the spark is drawn.
-
-=Lightning.= The electro-static discharge of clouds floating in the
-atmosphere. It is the highest form of frictional electricity,
-uncontrollable and very dangerous, since the strength of a single flash
-may run into hundreds of thousands of volts.
-
-=Lightning-arrester.= An apparatus for use with electric lines to carry
-off to earth any lightning discharges that such lines may pick up; or it
-may be a form of fuse which burns out before the current can do any harm
-to the electrical mechanism.
-
-=Line-insulator.= An insulator serving to support an aerial line.
-
-=Lineman.= A workman whose business is the practical part of electrical
-construction in lines and conducting circuits.
-
-=Link-fuse.= A plate of fusible metal in the shape of a link. It is used
-as a safety-fuse in connection with copper terminals.
-
-=Liquefaction, Electric.= The conversion of a solid into a liquid by the
-sole agency of electricity in its heat action upon the solid.
-
-=Liquid Resistance.= (_See_ Resistance, Liquid.)
-
-=Lithanode.= A block of compressed lead binoxide, with platinum
-connections, for use in a storage battery.
-
-=Litharge.= Yellow-lead. A chemical form of metallic lead.
-
-=Load.= In a dynamo, the amperes of current delivered by it under given
-conditions of speed, etc.
-
-=Local Action.= In a battery, the loss of current due to impurities in
-the zinc. The currents may circulate in exceedingly minute circles, but
-they waste zinc and chemicals and contribute nothing to the efficiency
-of the battery.
-
-In a dynamo, the loss of energy through the formation of eddy currents
-in its core or armature, in the pole pieces, or in other conducting
-bodies.
-
-=Lodestone.= The scientific name is magnetite. Some samples possess
-polarity and attract iron; these are called lodestones.
-
-=Loop.= A portion of a circuit introduced in series into another
-circuit.
-
-=Low Frequency.= A frequency (in current vibrations) of comparatively
-few alternations per second.
-
-=Low Potential Current.= (_See_ Current, Low Potential.)
-
-=Luminescence.= The power or properties some bodies have of giving out
-light when their molecular mass is excited. For example, phosphorus and
-radium.
-
-=Luminous Heat.= The radiation of heat by electric current, which at the
-same time produces light. For example, the filament in an incandescent
-lamp.
-
-=Luminous Jar.= A Leyden-jar whose coatings are of lozenge-shaped
-pieces of tin-foil between which are very short spaces. When discharged,
-sparks appear all over the surface where the small plates of metal
-nearly join.
-
-
-M
-
-=Magnet.= A substance or metal having the power to attract iron and
-steel.
-
-=Magnet-bar.= A magnet in the shape of a straight bar. (_See_
-Bar-magnet.)
-
-=Magnet-coil.= A coil of insulated wire enclosing a core of soft iron
-through which a current of electricity is passed to magnetize the iron.
-
-=Magnet-core.= An iron bar or mass of iron around which insulated wire
-is wound in order to create an electro-magnet.
-
-=Magnet, Electric.= A magnet consisting of a bar of iron, a bundle of
-iron wires, or an iron tube, around which a coil of insulated wire is
-wound. When a current is passing through the coil its influence
-magnetizes the iron core, but directly the current ceases the magnetism
-disappears.
-
-=Magnet, Field.= The electro or permanent magnet in a dynamo or motor,
-used to produce the area of electric energy.
-
-=Magnet, Horseshoe.= A magnet of U shape with the poles or ends brought
-closer together than the other parts of the limbs. A soft iron bar is
-placed across the poles when not in use, as this serves to conserve the
-magnetism.
-
-=Magnet, Permanent.= A term applied to a hard steel magnet possessing
-high retentivity, or the power to hold its magnetism indefinitely.
-
-=Magnet, Regulator.= An electro-magnet whose armature moves in such a
-manner as to automatically shift the commutator-brushes, on a motor or
-dynamo, to a position which insures the preservation of both brushes and
-commutator-bars, and also produces a constant current.
-
-=Magnet, Simple.= A magnet made of one piece of metal.
-
-=Magnet Wire.= Insulated wire used for coils. Cotton or silk covered
-wire is the most serviceable for winding magnets.
-
-=Magnetic Adherence.= The tendency of a mass of iron to adhere to the
-poles of a magnet.
-
-=Magnetic Attraction and Repulsion.= The attraction of a magnet for
-iron, steel, nickel, and cobalt; also of unlike poles of magnets for
-each other. The like poles repel.
-
-=Magnetic Circuit-breakers.= An automatic switch, or breaker, whose
-action is excited and controlled by an electro-magnet.
-
-=Magnetic Concentration of Ores.= The separation of iron and steel from
-their gangue by magnetic attraction. It is applicable only when either
-the ore or the gangue is susceptible to the magnet.
-
-=Magnetic Control.= The control of a magnetic needle, magnet, index,
-armature, or other iron indicator in a galvanometer, ammeter, or
-voltmeter by a magnetic field.
-
-=Magnetic Dip.= The inclination from the horizontal position of a
-magnetic needle that is free to move in a vertical plane.
-
-=Magnetic Field, Rotary.= A magnetic field resulting from a rotary
-current.
-
-=Magnetic Field, Shifting.= A magnetic field which rotates. Its lines of
-magnetic force vary, therefore, in position.
-
-=Magnetic Field, Uniform.= A field of uniform strength in all portions,
-such as the magnetic field of the earth.
-
-=Magnetic Force.= The power of attraction and repulsion exercised by a
-magnet; the force of attraction and repulsion which a magnet exercises,
-and which, in its ultimate essence, is unknown to science.
-
-=Magnetic Induction.= (_See_ Induction, Magnetic.)
-
-=Magnetic Needle.= A magnet having a cup or small depression at its
-centre, and poised on a sharp pin of brass, so as to be free to rotate.
-Its N pole points to the north, and its S pole to the south. A compass
-needle.
-
-=Magnetic Poles.= The terrestrial points towards which the north or
-south poles of the magnetic needle are attracted. There are two poles:
-the arctic, or negative, which attracts the positive or N pole of the
-magnetic needle; and the antarctic, or positive, which attracts the S
-pole of the needle.
-
-=Magnetic Poles, False.= It has been established that there are other
-poles on the earth that attract the magnetic needle when the latter is
-brought into their vicinity. These are called false poles, and are
-probably caused by large deposits of iron lying close to the surface of
-the earth.
-
-=Magnetic Separator.= An apparatus for separating magnetic substances
-from mixtures. It is used chiefly in separating iron ore from earth and
-rock. The mineral falls on an iron cylinder, or drum, magnetized by
-coils, and adheres there, while the earth or crushed rock drops below.
-The particles of iron are afterwards removed by a scraper. The machine
-is also used in separating iron filings and chips from brass, copper, or
-other metals, the iron adhering to the magnet, while the brass and other
-chips drop underneath.
-
-=Magnetism.= The phenomena of attraction exerted by one body for
-another. It has been commonly understood that magnetism and electricity
-are very closely related, for without electricity magnetism could not
-exist, although it has not been shown clearly that magnetism plays any
-part in the generation of electricity. Magnetism is the phenomenal force
-exerted by one body having two poles (negative and positive) for like
-bodies. The horseshoe magnet or a bar of magnetized steel are the
-simplest examples of this. If both ends of the horseshoe were positive
-they would not attract, but would repel. If both ends of a bar were
-positive they would repel; but as one is negative, or north-seeking, and
-the other positive, they exert lines of force which attract like bodies,
-such as bits of iron, nails, and needles. No energy is required to
-maintain magnetism in a tempered steel object, such as the wiring about
-a soft iron core when it has been magnetized, but electric current must
-flow about the soft iron core in order to render it a magnet. So soon as
-the current ceases to flow the magnetism ceases and the soft iron fails
-to attract.
-
-=Magnetism, Uniform.= Magnetism that is uniform throughout a mass of
-magnetic steel, or a core that is electro-magnetic.
-
-=Magnetize.= To impart magnetic property to a substance capable of
-receiving it.
-
-=Magnetizing-coil.= (_See_ Coil, Magnetizing.)
-
-=Magneto Call-bell.= A call-bell used principally in telephone systems,
-and operated by a current from a magneto-electric generator. The current
-is excited by turning the handle at the side of the telephone-box before
-removing the receiver from the hook.
-
-=Magneto-generator.= A current-generator composed of a permanent magnet
-and a revolving armature which is rotated between the poles of the
-permanent magnet.
-
-=Main Circuit.= (_See_ Circuit, Main.)
-
-=Main Feeder.= The main wire in a district to which all the feeder wires
-are attached.
-
-=Main Switch.= The switch connected to the main wire of a line, or the
-main-switch controlling a number of auxiliary switches.
-
-=Mains, Electric.= The large conductors in a system of electric light or
-power distribution.
-
-=Make and Break, Automatic.= An apparatus which enables the armature of
-a magnet to make and break its circuit automatically.
-
-=Make-and-break Current.= (_See_ Current, Make-and-break.)
-
-=Mercurial Air-pump.= An air-pump operated by mercury to obtain a high
-vacuum, and used extensively for exhausting incandescent-lamp bulbs.
-
-=Mercury Tube.= A glass tube sealed and containing mercury. It is so
-arranged as to give out fluorescent light when shaken or agitated by an
-electric current. For example, the Geissler tubes, the Cooper-Hewitt
-light, Crook’s tubes, etc.
-
-=Metallic Arc.= An arc which forms between metallic electrodes.
-
-=Metallic Circuit.= (_See_ Circuit, Metallic.)
-
-=Metallic Conductor.= A conductor composed of a metal.
-
-=Metallic Filament.= A metal wire used in an incandescent lamp--the
-filament.
-
-=Metallic Resistance.= (_See_ Resistance, Metallic.)
-
-=Metallurgy.= The art of working metals. Electro-metallurgy applies to
-the processes wherein electricity plays the most important part.
-
-=Mica.= A natural mineral of sheet form and translucent, used
-extensively as an insulator in electrical equipment and mechanism.
-
-=Mica, Moulded.= A composition composed of ground mica and shellac as a
-binder. When heated and pressed into various shapes and forms, it is a
-valuable insulator, and is employed for hooks, locks, tubes, sockets,
-and the like.
-
-=Micanite.= An insulating material made by cementing laminations of pure
-mica together and cementing them with shellac or other suitable
-non-conducting adhesives.
-
-=Molecular Adhesion.= The attraction of similar molecules for each
-other.
-
-=Molecular Attraction.= The attraction of molecules, or physical
-affinity.
-
-=Molecular Resistance.= The resistance which a mass or electrolyte
-offers when contained in an insulated vessel and a current of
-electricity is passed through it.
-
-=Molecule.= One of the invisible particles supposed to constitute matter
-of every kind; the smallest particle of matter that can exist
-independently. It is made up of atoms, but an atom cannot exist alone.
-
-=Morse Receiver.= The receiving instrument once universally used in the
-Morse system of telegraphy, but now superseded by the sounder.
-
-=Morse Recorder.= An apparatus which automatically records on a ribbon
-of paper the dots and dashes of the Morse telegraph alphabet.
-
-=Morse Sounder.= An electro-magnetic instrument designed to make a
-sharp, clicking sound when its armature lever is drawn down by the
-attraction of the magnets.
-
-=Morse System.= A telegraphic system invented by Prof. S. F. B. Morse,
-in which, by means of alternating makes and breaks of varying duration,
-the dots and dashes of the Morse alphabet are reproduced and received
-at a distance through the agency of wires and the electro-magnetic
-sounder.
-
-=Motor, Electric.= A machine or apparatus for converting electric energy
-into mechanical kinetic energy or power. The electrical energy is
-usually generated by a dynamo, and distributed on conductors to motors
-located at various points.
-
-Electric motors are of two types--the A-C., or alternating current, and
-the D-C., or direct current.
-
-=Motor-car, Electric.= A self-propelling car driven by stored
-electricity.
-
-=Motor-dynamo.= A motor driven by a dynamo whose armature is firmly
-attached or connected to that of the dynamo. It is used for modifying a
-current. If the dynamo generates an alternating current of high
-potential, the motor converts it into a direct current of lower voltage
-but increased amperage.
-
-=Motor-transformer.= A transformer which is operated by a motor.
-
-A dynamo-electric machine provided with two armature windings, one
-serving to receive current, as a motor, the other to deliver current, as
-a generator, to a secondary circuit.
-
-
-N
-
-=N.= An abbreviation for the north-seeking pole in a magnet.
-
-=Natural Magnet.= A loadstone.
-
-=Needle.= A term applied to a bar-magnet poised horizontally upon a
-vertical point.
-
-A magnetic needle, or the magnet in a mariner’s compass.
-
-=Negative.= Opposed to positive.
-
-=Negative Electricity.= The kind of electricity with which a piece of
-amber is charged by friction with flannel.
-
-In a galvanic battery or cell the surface of the zinc is charged with
-negative electricity. Negative electricity, according to the theory of
-some scientists, really means a deficiency of electricity.
-
-=Negative Electrode.= The same as Negative Element.
-
-=Negative Element.= The plate not dissolved by the solution in a voltaic
-cell; the one which is positively charged.
-
-The carbon, platinum, or copper plate or pole in a battery.
-
-=Negative Feeder.= The conductor which connects the negative mains with
-the negative poles of a generator.
-
-=Negative Plate.= (_See_ Plate, Negative.)
-
-=Negative Pole.= (_See_ Pole, Negative.)
-
-=Neutral Feeder.= The same as Neutral Wire.
-
-=Neutral Wire.= The central wire in a three-wire system.
-
-=Nickel-bath.= A bath for the electro-deposition of nickel.
-
-=Non-arcing Fuse.= A fuse-wire which is enclosed in a tube packed with
-asbestos or silk, and which does not produce an arc when it fuses or
-blows out. It is practically noiseless, save for a slight hissing sound,
-accompanied by a light puff of smoke, which escapes from a venthole in
-the side of the tube.
-
-=Non-conductor.= A material or substance offering very high resistance
-to the passage of the electric current.
-
-=Non-magnetic Steel.= Alloys of iron incapable of being magnetized. They
-are composed of iron and manganese, nickel, steel, etc.
-
-=Normal.= Regular. The average value of observed quantities. Normal
-current is a regular current without variations.
-
-The force of a current at which a system is intended to work.
-
-=Normal Voltage.= The same as Normal Current.
-
-=North Pole.= The north-seeking pole of a magnet.
-
-The pole of a magnet which tends to point to the north, and whence lines
-of force are assumed to issue on their course to the other pole of the
-magnet.
-
-
-O
-
-=O.= An abbreviation for Ohm.
-
-=Oersted’s Discovery.= Oersted discovered, in 1820, that a magnetic
-needle tended to place itself at right angles to a current of
-electricity. This fundamental principle is the basis of the
-galvanometer, the dynamo, and the motor.
-
-=Ohm.= The practical unit of resistance. A legal ohm is the resistance
-of a column of mercury one square millimetre in cross-sectional area and
-106.24 centimetres in length.
-
-=Ohm, True.= The true ohm is the resistance of a column of mercury
-106.24 centimetres long and one square millimetre in cross-sectional
-area. An ohm may be measured by a No. 30 copper wire nine feet and nine
-inches long. If larger size wire is used the piece must be
-proportionately longer, since the resistance is less.
-
-=Ohmic Resistance.= True resistance as distinguished from spurious
-resistance, or counter electro-motive force. (_See also_ Resistance,
-Ohmic.)
-
-=Ohm’s Law.= The basic law which expresses the relations between
-current, electro-motive force, and resistance in active circuits. It is
-formulated as follows:
-
-1. The current strength is equal to the electro-motive force divided by
-the resistance.
-
-2. The electro-motive force is equal to the current strength multiplied
-by the resistance.
-
-3. The resistance is equal to the electro-motive force divided by the
-current strength.
-
-=O. K.= A telegraphic signal meaning yes, or all right. It is supposed
-to be a misspelled form of all correct, “Oll Kerrekt.”
-
-=Okonite.= A form of insulation for wires and conductors; a trade name
-applied to insulations, and protected by copyright.
-
-=Open Arc.= A voltaic arc not enclosed.
-
-=Open Circuit.= (_See_ Circuit, Open.)
-
-=Oscillating Current.= (_See_ Current, Oscillating.)
-
-=Outlet.= That part of an electrolier or electric light fixture out of
-which the wires are led for attachment to incandescent light sockets.
-
-=Outside Wiring.= The wiring for an electric circuit which is located
-outside a building or other structure.
-
-=Overhead Feeders.= The same as overhead conductors.
-
-=Overhead Trolley.= The system in which the current for the propulsion
-of trolley-cars is taken from overhead feeders or wires.
-
-=Overhead Trolley-wire.= A naked, hard copper wire drawn at high
-tension, and suspended over or at the side of a car-track, and from
-which the trolley-wheel takes its current.
-
-=Overload.= In an electric motor, an excess of mechanical load prevents
-economical working, causing the armature to revolve slowly and the
-wiring to heat. In this case heating implies waste of energy.
-
-=Overload Switch.= A switch which operates automatically to open a
-circuit in line with a motor, and so save the motor from overheating or
-burning in the event of an overload.
-
-
-P
-
-=Paper Cable.= A cable insulated with waxed or paraffined paper.
-
-=Paraffine.= A residuum of petroleum oil, valuable as an insulating
-medium in electrical work.
-
-A hydro-carbon composition of the highest resistance known. It is
-extensively used in condensers and other electrical apparatus as a
-dielectric and insulator.
-
-=Parallel Distribution.= A distributing system for electricity wherein
-the receptive contrivances are adjusted between every two of a number of
-parallel conductors running to the limits of the system. When two or
-more conductors connect two mains of comparatively large size and low
-resistance, they are said to be in parallel or in multiple. This order
-is easily pictured by imagining the mains to be the sides of a ladder
-and the conductors the rungs. In the latter the lamps are placed. It
-follows that the current flows from one main to the other through the
-conductors and lamps.
-
-=Paramagnetic.= Substances which have magnetic properties, or those
-which are attracted by magnetic bodies. A paramagnetic substance has
-high multiplying power for lines of force, therefore a bar of iron which
-is a paramagnetic substance of the highest quality becomes magnetic when
-placed within a circle of electric lines of force. The first example of
-paramagnetic substance brought to the attention of man was the
-lodestone, from which the ancient mariners fashioned their crude compass
-needles.
-
-=P-C.= An abbreviation for porous cup.
-
-=Pear Push.= A push-button enclosed in a handle having the shape of a
-pear. It is generally attached to the end of a flexible wire cord.
-
-=Periodic Current.= (_See_ Current, Periodic.)
-
-=Permanency, Electric.= The power of conductors to retain their
-conductivity unaffected by the lapse of time.
-
-=Permanent Magnet.= (_See_ Magnet, Permanent.)
-
-=Phase.= One complete oscillation. The interval elapsing from the time a
-particle moves through the middle point of its course to the instant
-when the phase is to be stated.
-
-Simple harmonic motion. Oscillation.
-
-=’Phone.= An abbreviation for the word Telephone.
-
-=Phonograph.= An apparatus for reproducing sound. It is vibratory and
-not electric in its action, except that the mechanism may be driven by
-electricity. It consists of a rotating cylinder of a waxlike material
-and a glass diaphragm carrying a needle-point that lightly touches the
-surface of the waxen cylinder. If the diaphragm is agitated the needle
-vibrates, making indentations in the surface of the wax. If the needle
-is set back and the cylinder rotated so as to carry the point over the
-indentations, the sound is given back through the vibration of the
-diaphragm.
-
-=Pickle.= An acid solution used to cleanse metallic surfaces preparatory
-to electro-plating.
-
-=Pilot Wires.= Wires brought from distant parts of electric light and
-power mains, and leading to voltmeters at a central station. Through
-their agency the potential energy of every part of the system may be
-measured.
-
-=Pith-balls.= Balls made from the pith of light wood, such as elder.
-They are used in the construction of electroscopes and for other
-experiments in static electricity.
-
-=Plant.= The apparatus for generating electric current, including
-engines, boilers, dynamos, mains, and subsidiary apparatus.
-
-=Plate, Condenser.= In a static apparatus, the condenser having a flat
-piece of glass for a dielectric. It is mounted on an axle so that it may
-be revolved.
-
-=Plate, Ground.= In a lightning-arrester, the plate connected to the
-earth or ground wire.
-
-=Plate, Negative.= In a voltaic battery, the plate which is unattacked
-by the fluid. It is made of carbon, platinum, or copper.
-
-=Plate, Positive.= (_See_ Positive Plate.)
-
-=Plating-bath.= A vessel of solution for the deposition of metal by
-electrolysis. Used in electro-plating.
-
-=Plating, Electro.= The process of depositing metal on surfaces of
-metals or other substances by the aid of an electrolyte and the electric
-current.
-
-=Platinum Fuse.= A slender wire of platinum roused to incandescence by
-current, and used to explode a charge of powder or other combustible
-substance.
-
-=Plug.= A piece of metal, with a handle, used to make electric
-connections by being inserted between two slightly separated plates or
-blocks of metal.
-
-A wedge of metal, slightly tapered, and used to thrust between two
-conductors to close or complete a circuit.
-
-=Plumbago.= Soft, lustrous graphite; a native form of carbon sometimes
-chemically purified. It is used chiefly in electrotyping for dusting the
-wax moulds to make the surface an electric conductor.
-
-=Plunge-battery.= (_See_ Battery, Plunge.)
-
-=Polar.= Pertaining to one of the poles of a magnet.
-
-=Polarity.= The disposition in a body to place its axis in a particular
-direction when influenced by magnetism. For example, the attraction and
-repulsion at the opposite ends of a magnet. The N and S seeking poles of
-a compass needle is the simplest example.
-
-=Polarity, Electric.= The disposition in a paramagnetic body to be
-influenced by electric waves and lines of force. The otherwise
-non-magnetic body or mass becomes magnetic to attract or repulse when
-influenced by electricity, but ceases to retain the phenomena after the
-electric influence is removed. A piece of soft iron wire, a nail, or a
-short rod of iron will become electro-polarized when a current of
-electricity is sent through a coil of insulated wire so wound that one
-end will be N the other S. So soon as the circuit is broken the polarity
-ceases.
-
-=Polarization.= The depriving of a voltaic cell of its proper
-electro-motive force. This may be brought about through the solution
-becoming spent, or in the event of the acid being saturated with zinc,
-and so failing to act on the metallic zinc.
-
-Counter electro-motive force due to the accumulation of hydrogen on the
-negative plate.
-
-=Polarizing-current.= (_See_ Current, Polarizing.)
-
-=Polar Surface.= The surface of a magnetic substance through which the
-magnetic flux passes in or out.
-
-=Pole-changer.= An automatic, oscillating switch or contact-breaker
-which reverses the direction of the current.
-
-=Pole, Negative.= The S pole in a magnet or compass needle.
-
-=Pole, Positive.= (_See_ Positive Pole.)
-
-=Pole-switch, Single.= A switch designed to open or close one lead
-only.
-
-=Poles.= The terminals of an open electric circuit at which there
-necessarily exists a potential difference.
-
-The terminals of an open magnetic circuit, or the ends of a magnetized
-mass of iron.
-
-=Porcelain.= A fine variety of earthenware, valuable for insulators and
-insulating purposes.
-
-=Porosity.= The state or property of having small interstices or holes.
-The opposite of density.
-
-=Porous Cup or Cell.= A cup or cell made of pipe-clay or of unglazed
-earthenware through which a current of electricity can pass when wet or
-in a liquid. Porous cups are used in cells and batteries to keep two
-liquids apart, and yet permit electrolysis and electrolytic conduction.
-
-=Positive Currents.= Currents which deflect the needle to the left.
-
-=Positive Electricity.= The current that flows from the active element,
-the zinc in a battery, to the carbon. The negative electricity flows
-from the carbon to the zinc.
-
-=Positive Electrode.= The electrode which is connected with the positive
-pole of a source of electric energy.
-
-=Positive Feeders.= The lead or wire in a set of feeders which is
-connected to the positive terminal of the generator.
-
-=Positive Plate.= In a voltaic cell, the plate which is acted upon and
-corroded. The current from the positive plate is negative electricity.
-
-=Positive Pole.= The N pole in a magnet or magnetic needle. So called
-because it seeks the north or negative pole of the earth.
-
-=Positive Wire, or Conductor.= The wire, or conductor, connected with
-the positive pole of any apparatus which produces electro-motive force.
-
-=Potential, Electric.= The power to perform electric work.
-
-=Potential Energy.= Capacity for doing work. Potential energy when
-liberated becomes actual energy for the performance of work.
-
-=Power-generator.= Any source from which power is generated.
-
-=Power-house.= A station in which the plant of an electric power system
-is operated and the current distributed to local or long-distance
-points. Power-houses are either primary or secondary stations. In the
-primary station the current is generated directly by the aid of
-mechanical power, either the steam-engine or the steam-turbine. The
-secondary station, or sub-station, is located at a distance from the
-main power-house, and has no mechanical means of generating current. The
-current, usually of high alternating voltage, is supplied to the
-sub-station from the main power-house; and by means of transformers and
-converters, the high-voltage current is transformed into one of lower
-E-M-F and higher amperage, for distribution over local lines.
-
-=Power-unit.= The unit of electric power is the volt-ampere or watt.
-
-=Pressure, Electric.= Electro-motive force or voltage.
-
-=Primary.= A term used to designate the induction-coil in an
-induction-apparatus or transformer. It is an abbreviation for primary
-coil.
-
-=Primary Battery.= (_See_ Battery, Primary.)
-
-=Prime Conductor.= (_See_ Conductor, Prime.)
-
-=Push-button.= A switch for closing a circuit by means of pressure
-applied to a button. The button is provided with a spring, so that when
-pushed in and released it flies back, reopening the circuit.
-
-=Pyrogravure.= A process of engraving by the use of platinum points
-heated to redness by the electric current.
-
-
-Q
-
-=Q.= Abbreviation or symbol for electric quantity.
-
-=Quadrant.= The quarter of a circle or of its circumference.
-
-=Quadruple Circuit.= (_See_ Circuit, Quadruple.)
-
-=Quantity.= The term is applied to express arrangements of electrical
-connections for giving the largest possible amount of current.
-
-=Quantity, Electro-magnetic.= The electro-magnetic current measured by
-its intensity for a second of time.
-
-=Quick-break.= A break affected in an electric current by the employment
-of a quick-break switch.
-
-=Quickening.= The amalgamating of the surface of a metallic object
-before electro-plating it with silver. This secures better adhesion of
-the deposit, and is done by dipping the article into a solution of
-mercurial salts--one part of mercuric nitrate to one hundred parts of
-water.
-
-
-R
-
-=Radiant Energy.= Energy existing in the luminiferous ether and
-exercised in wave transmission, creating light or sound. Radium
-possesses the highest form of radiant energy.
-
-=Radiate.= To emit or send out in direct lines from a point or points,
-as radiating heat, light, or sound. The radiations are sent out in all
-directions from a central point, just as a stone thrown in a pond of
-still water will radiate waves or ripples from the central point.
-
-=Radiation.= The travelling or motion of ether waves through space.
-
-=Radiator, Electric.= A series of plates or wire-coils heated by
-current. They radiate heat and so warm the surrounding air.
-
-=Radiograph.= A photographic picture taken by the X-ray process.
-
-=Receiver.= In telephony or telegraphy, an instrument for receiving the
-message as distinguished from the instrument sending or transmitting the
-message.
-
-The telephone piece held to the ear is the receiver.
-
-=Receiving End.= The end of a line where the operative currents are
-received, as opposed to the end at which they are transmitted.
-
-=Receptacle.= A device for the installation of an attachment or
-extension plug. Used in connection with electric-lighting circuits.
-
-=Recoil Kick.= Reaction resulting from a disruptive discharge.
-
-=Recorder.= In telegraphy, the receiving apparatus for recording the
-dot-and-dash signals on a strip or tape of paper.
-
-=Reduction.= The influence exerted without apparent communication by a
-magnetic field or a charged mass upon neighboring bodies. The
-induction-coil is a simple example of this force. The current passes
-through the primary or inner coil about a core of soft iron, and in
-doing so it develops lines of force in the secondary or outer coils,
-although no current is flowing directly through them from a battery or
-dynamo.
-
-=Reduction Gear.= A gear which acts to reduce a speed below that of a
-motor in full motion without lessening its motive force.
-
-=Refract.= To break the natural course of light in an elastic medium.
-The rays of light, as they pass from a rare into a dense medium, are
-refracted.
-
-=Register, Electric.= An apparatus for registering and recording the
-movements of employés about a building. Press-buttons are arranged
-throughout the building, and when a man passes a station he presses the
-button, and the time is recorded by the apparatus.
-
-=Regulator Magnet.= (_See_ Magnet, Regulator.)
-
-=Relay.= A telegraphic or telephonic receiving instrument which opens
-and closes a local circuit through movements caused by the impulses of
-currents received. The relay battery may be very delicate so as to work
-with weak currents. The function of the relay is to open and close
-circuits for the admission of a new current to push on the sound or
-vibration to a more distant point. The main battery may be of any
-desired power.
-
-=Relay Connection.= A connection used in telegraphy, including a local
-battery, with a short circuit, normally open, but closed at will by a
-switch and sounder, or other appliance. A very weak current will work
-the apparatus.
-
-=Relay, Ordinary.= A relay that is not polarized.
-
-=Relay, Repeating.= In telegraphy, a relay for repeating the signals
-through a second line.
-
-=Reluctance.= Magnetic resistance.
-
-=Repeater.= In telegraphy, an instrument for repeating the signals
-through a second line. It is virtually a relay which is controlled by
-the sender, and which, in turn, operates the rest of the main line. It
-is usually located at about the middle of the total distance covered.
-
-=Repeating-station.= A telegraph station located on a long line, and
-occupying a position at the juncture of the sections into which the line
-is divided. The currents received through one section are repeated into
-the other sections by means of a repeater.
-
-=Repulsion, Electric.= The tendency which exists between two bodies
-charged alike to mutually repel each other.
-
-=Residual Charge.= (_See_ Charge, Residual.)
-
-=Resilience.= The power to spring back to a former position. Electricity
-is resilient, although its elasticity cannot be measured accurately.
-
-=Resin.= A solid inflammable substance or gum, and a good non-conductor
-in electrical work. It is the product obtained by distilling the sap of
-the pitch-pine. The name is also applied to the product of distilling
-the sap of other trees. Common resin, shellac, lac, Dragon’s-blood, and
-other substances of a similar nature are resins. They are all
-dielectrics, and the source of negative frictional electricity when
-rubbed with cotton, wool, flannel, silk, or fur.
-
-=Resistance.= That quality of an electric conductor in virtue of which
-it opposes the passage of an electric current, causing the disappearance
-or modification of electro-motive force, and converting electric energy
-into heat energy.
-
-=Resistance-box.= A box filled with resistance-coils connected in series
-and provided with a switch, so that any number of the coils may be cut
-out.
-
-=Resistance, Carbon.= A resistance composed of carbon as a substitute
-for a coil of wire. Carbon rods are placed close together having an air
-space between them, with alternate ends connected. Piles may be built up
-of carbon plates, whose resistance is made to vary by changing the
-pressure.
-
-=Resistance-coil.= A coil of wire metal or other substances having the
-power to resist a current of electricity.
-
-A coil of wire used to measure an unknown resistance by virtue of its
-own known resistance. (_See also_ Coil, Resistance.)
-
-=Resistance, Dielectric.= (_See_ Dielectric Resistance.)
-
-=Resistance, Electrolytic.= The resistance of an electrolyte to the
-passage of a current decomposing it. It is almost entirely due to
-electrolysis, and is intensified by counter-electro-motive force. When a
-current of a voltage so low as not to decompose an electrolyte is passed
-through the latter, the resistance appears very high and sometimes
-almost infinite. If the voltage is increased until the electrolyte is
-decomposed the resistance suddenly drops to a point lower than the true
-resistance.
-
-=Resistance, Internal.= The resistance of a battery, or generator, in an
-electric circuit as distinguished from the resistance of the rest of the
-circuit.
-
-=Resistance, Liquid.= A liquid of varying specific gravity used to
-create resistance to the passage of the electric current.
-
-Resistance effected by the use of liquid through which a current must
-pass to complete a circuit.
-
-=Resistance, Metallic.= The resistance of metals to the electric
-current.
-
-German-silver resistance as distinguished from that of water, carbon, or
-other substances.
-
-=Resistance, Ohmic.= True resistance measured in ohms as distinguished
-from counter electro-motive force. (_See also_ Ohmic Resistance.)
-
-=Resistance, Spurious.= The counter-electro-motive force. In its effect
-of opposing a current and in resisting its formation it differs from
-true resistance. True resistance diminishes current strength, absorbs
-energy, and develops heat. Spurious resistance opposes and diminishes a
-current without absorption of energy or production of heat.
-
-=Resistance, Standard.= A known resistance employed to determine unknown
-resistances by comparison.
-
-=Resistance, True.= The true resistance measured in ohms as
-distinguished from counter-electro-motive force.
-
-=Resonator, Electric.= A small, open electric circuit with ends nearly
-touching. When exposed to electric resonance, or to a sympathetic
-electric oscillating discharge, a spark passes across the gap. The spark
-is due to inductance in the resonator.
-
-=Retentiveness.= That property which enables steel to retain its
-magnetism.
-
-=Return.= A line or conductor which carries current back to its
-starting-point after it has traversed a circuit. The best definition of
-a return is a circuit on which no new apparatus is installed.
-
-=Return-circuit.= (_See_ Circuit, Return.)
-
-=Return-circuit, Railway.= A grounded circuit used in trolley systems
-for ground returns through the tracks, they being joined by links or
-flexible wires so as to form perfect conductors. It is the negative side
-of the system, the positive being in the overhead or underground
-feed-wire or rail.
-
-=Reversibility.= The principle by which any form of generator for
-producing a given form of energy may be reversed to absorb energy. The
-dynamo of the reversible type driven to generate current may be reversed
-and will develop power if a current is run through it.
-
-=Rheostat.= An adjustable resistance. An apparatus for changing the
-resistance, without opening the circuit, by throwing a switch-bar across
-contact points.
-
-=Rod Clamp.= A clamp used in the lamp rod of an arc-light to hold the
-carbon.
-
-=Röntgen Effects.= Phenomena obtained by the use of the X or Röntgen
-rays.
-
-=Röntgen-ray Screen.= A screen whose surface is covered with
-fluorescent material for the purpose of receiving and displaying the
-Röntgen image.
-
-=Röntgen Rays.= A peculiar form of light radiation discovered by
-Röntgen, and which is emitted from that portion of a high vacuum tube
-upon which the kathode rays fall.
-
-=Rotary Magnetic Field.= (_See_ Magnetic Field, Rotary.)
-
-=Ruhmkorff Coil.= (_See_ Coil, Ruhmkorff.)
-
-
-S
-
-=Safety Fuse.= A device to prevent overheating of any portion of a
-circuit by excessive current. It generally consists of a strip of
-fusible metal which, if the current attains too great strength, melts
-and opens the circuit.
-
-=Salt.= A chemical compound containing two atoms or radicals
-which saturate each other. One is electro-positive, the other
-electro-negative.
-
-Salts are decomposed by electrolysis, and in separating they combine to
-form new molecules.
-
-=Saturated.= A liquid is said to be saturated when it has dissolved all
-the salts it will take up.
-
-=Search-light.= An apparatus for producing a powerful beam of light and
-projecting it in any desired direction.
-
-=Secondary.= A term applied to the secondary coil of a transformer or
-induction-coil.
-
-=Secondary Battery.= (_See_ Battery, Secondary.)
-
-=Secondary Plates.= The plates of a secondary battery or
-storage-battery. When charged, the negative plate should be brown or
-deep reddish in color, and the positive slate-colored.
-
-=Self-excited.= Electrified by its own current.
-
-=Self-winding Clock.= A clock which automatically winds itself by
-electricity. It is operated by a small electro-magnetic motor which
-obtains its current from an outside source.
-
-=Semaphore, Electric.= An apparatus for exhibiting signals. Used in the
-railway block system.
-
-=Series.= Arranged in succession. When incandescent lamps are installed
-so that the current goes in and out of one lamp, and so on to the next
-and the succeeding ones, they are said to be arranged in series. It
-takes high E-M-F and current, or amperage, to operate such lamps.
-
-Series batteries are arranged with the zinc pole of one connected to the
-carbon pole of the next.
-
-=Series Arc Cut-out.= A device by means of which a short circuit is
-established past a defective lamp, thereby securing the undisturbed
-operation of all the other lamps in the circuit.
-
-=Series Distribution.= A distribution of electricity in which the
-receptive devices are arranged in successive order upon one conductor,
-extending the entire length of the circuit.
-
-=Series Dynamo.= A series-wound dynamo.
-
-=Series Incandescent Lamp.= An incandescent lamp adapted for service in
-a series circuit.
-
-=Series Motor.= A motor adapted for use in a series circuit; a motor
-whose field-coil winding is in series with the armature.
-
-=Series, Multiple.= An arrangement of electric apparatus in which the
-parts are grouped in sets in parallel, and these sets are connected in
-series.
-
-=Series Winding.= A method of winding a generator or motor in which one
-of the commutator brush connections is joined to the field-magnet
-winding. The other end of the magnet winding is connected with the outer
-circuit, and the second armature brush is coupled with the remaining
-terminal of the outer circuit.
-
-=Service Wires.= Wires connected to the supply circuit or main wires,
-and which run into buildings to supply current for heat, light, and
-power.
-
-=Shellac.= A resin gum, gathered from certain Asiatic trees. It is
-soluble in alcohol, and is used extensively in electric work as an
-insulator.
-
-=Shifting Magnetic Field.= (_See_ Magnetic Field, Shifting.)
-
-=Shock, Electric.= The effect upon the animal system of the discharge of
-an electric current of high potential difference. The voltage is the
-main element in a shock.
-
-=Shoe.= As applied to electric railways, the casting employed to bear on
-the third rail to take in positive current and electro-motive force.
-
-The cast-iron plate of an electric break, which, by magnetism, adheres
-to another iron surface.
-
-=Short Circuit.= (_See_ Circuit, Short.)
-
-=Shunt-box.= A resistance-box designed for use as a galvanometer shunt.
-The box contains a series of resistance-coils which can be plugged in or
-out as required.
-
-=Shunt-winding.= A dynamo or motor is shunt-wound when the field-magnet
-winding is parallel with the winding of the armature.
-
-=Silver-bath.= A solution of a salt of silver used in the
-electro-plating process.
-
-=Silver-plating.= Depositing a coating of silver on a metallic surface
-by the acid of electro-metallurgy.
-
-=Silver-stripping Bath.= An acid solution used for stripping silver
-from a metallic surface before re-plating it.
-
-=Simple Circuit.= (_See_ Circuit, Simple.)
-
-=Simple Immersion.= (_See_ Immersion, Simple.)
-
-=Simple Magnet.= (_See_ Magnet, Simple.)
-
-=Single-trolley System.= A trolley system employing only one overhead
-conducting wire, the track and ground serving as the return-circuit.
-
-=Single-wound Wire.= Wire insulated by winding or overlaying with but a
-single layer of material.
-
-=Sliding-condenser.= (_See_ Condenser, Sliding.)
-
-=Snap-switch.= A switch so contrived as to give a quick break. A spiral
-spring is fastened between the handle and arm in such a manner that when
-the handle is drawn back the spring operates and quickly draws a
-knife-bar from the keeper, breaking the contact instantly and without
-the formation of an arc.
-
-=Socket.= A receptacle for an incandescent lamp or plug.
-
-=Solenoid.= A helical coil of wire of uniform diameter or cylindrical in
-shape. It is useful in experiments with electro-magnetism.
-
-=Solution.= A fluid composed of dissolved salts; a mixture of liquids
-and fluids.
-
-=Sound Waves.= Waves produced in an elastic medium by sonorous
-vibration, as in wireless telegraphy.
-
-=Sounder.= In telegraphy, the instrument operated on by the key at the
-other end of a line. Various devices are employed to increase their
-resonance--as, for instance, hollow boxes. Sounders are generally placed
-on local circuits and are actuated by relays.
-
-=Sounder, Repeating.= A telegraphic instrument which repeats a message
-into another circuit.
-
-=S-P.= An abbreviation for single pole.
-
-=Spark-arrester.= A screen of wire-netting fitted around the carbons of
-arc-lamps to prevent the chips or hot sparks from flying.
-
-=Spark-coil.= A coil for producing a spark from a source of
-comparatively low electro-motive force. The induction-coil is an
-example.
-
-=Spark, Electric.= The phenomenon observed when a disruptive charge
-leaves an accumulator or induction-coil and passes through an air gap.
-
-=Spark-gap.= The space left between the ends of an electric resonator
-across which the spark springs.
-
-=Sparking.= The production of sparks at the commutator, between the bars
-and the brushes of dynamos and motors. They are minute voltaic arcs, and
-should not be allowed to occur, as they cut away the metal and score the
-surface of the commutator.
-
-=Spark-tube.= A tube used as a gauge to determine when the exhaustion of
-the vacuum chamber, or bulb, of an incandescent lamp is sufficiently
-high.
-
-=Specific Gravity.= The relative weight or density of a body as compared
-with a standard. Water is usually taken as a standard for solids and
-liquids, and air for gases.
-
-=Speed-counter.= An instrument which records the number of revolutions a
-shaft makes in a given time.
-
-=Spent Acid.= Acid which has become exhausted. In a battery the acid
-becomes spent from combination with zinc; it also loses its depolarizing
-power.
-
-=Spring-contact.= A spring connected to one lead of an electric circuit.
-It is arranged to press against another spring or contact, which it
-opens or closes by the introduction of a plug or wedge.
-
-=Spring-jack.= An arrangement of spring-arm conductors under which plugs
-with wires attached can be slipped to make a new connection or to cut
-out certain circuits.
-
-=Spurious Resistance.= (_See_ Resistance, Spurious.)
-
-=Standard Candle.= (_See_ Candle, Standard.)
-
-=Standard Resistance.= (_See_ Resistance, Standard.)
-
-=Starting-box.= A resistance or shunt box used for letting current pass
-gradually into motors, instead of throwing on the full current at once.
-
-=Static Electricity.= Electricity generated by friction; frictional
-electricity, such as lightning; electricity of high electro-motive force
-and practically uncontrollable for commercial purposes.
-
-=Static Shock.= A term used in electro-therapeutics for describing the
-discharge from a small condenser or Leyden-jar; also the effect produced
-by the action of the vibrator of the induction-coil.
-
-=Station, Central.= The building or place in which the electrical
-apparatus is installed for the generation of current; the headquarters
-of telephone lines.
-
-=Steady Current.= An electric current whose strength is fixed or
-invariable.
-
-=Stock-ticker.= An instrument employed to give quotations of stocks by
-telegraphic record. A paper tape runs through an electrical machine
-which prints on it the figures and letters that stand for stocks and
-their values. The whole system is operated from a station located in the
-Stock-exchange.
-
-=Storage Accumulator.= (_See_ Accumulator, Storage.)
-
-=Storage-battery.= (_See_ Battery, Storage.)
-
-=Strength of Current.= Amperage; the quantity of current in a circuit.
-
-=Stripping.= The process of removing electro-plating, or thin metal
-coatings, from an object before it is re-electro-plated.
-
-=Stripping Liquid.= The liquid in a stripping-bath used for removing
-metals from surfaces before re-plating them.
-
-=Submarine Cable.= A telegraphic cable laid at the bottom of the sea or
-any body of water.
-
-=Submarine Search-light.= An incandescent light which works under water.
-
-=Sub-station.= A generating or converting plant subsidiary to a central
-station, and placed so as to supply current in a district situated at a
-distance from the main power-house.
-
-=Subway, Electric.= An underground passageway utilized for carrying
-cables and wires.
-
-=Sweating.= A process by which the ends of cables are brought together
-and soldered.
-
-=S-W-G.= An abbreviation for standard wire gauge.
-
-=Switch.= A device for opening and closing an electric circuit. Made in
-a great variety of forms, such as push-button, telegraph-key, knife
-switch, automatic switch, lever switch, rheostat, etc.
-
-=Switch-bell.= A combined bell and switch. The bell is operated when the
-switch is opened or closed.
-
-=Switch-blade.= The blade of a switch; a conducting strip connecting two
-contact-jaws.
-
-=Switch-board.= A board or table to which wires are led and connected
-with cross-bars or other devices by which connections can be made.
-
-=Synchronize.= To agree in point of time; to effect concurrence of phase
-in two alternating-current machines, in order to combine them
-electrically.
-
-
-T
-
-=Table-push.= A push-button connected with a call-bell and fixed on a
-table for convenience in using.
-
-=Tamadine.= A form of cellulose used for making the filaments of
-incandescent lamps. The material is cut into proper shapes, carbonized,
-and flashed.
-
-=Tangent Galvanometer.= (_See_ Galvanometer, Tangent.)
-
-=Tape, Insulating.= Prepared tape used in covering the bared ends of
-wires or joints.
-
-=Tap-wires.= The conductors in trolley systems that at stated intervals,
-take the current from the mains and supply it to the bare feed-wires.
-
-=Telegraph.= A system of electric communication invented by S. F. B.
-Morse, in which the dot-and-dash characters are used. There are various
-modifications of the system--double (or duplex), multiplex, and
-quadruplex--by means of which a number of messages may be sent out over
-the same wires at one time. Communication from place to place is had
-over wires mounted on poles, or by underground or submarine cables.
-
-=Telegraphy, Wireless.= A system of telegraphy carried on without the
-aid of wires, using instead the ether waves of the atmosphere to conduct
-the vibrations overhead, and the ground, or earth, as a return. The
-present limit of its working is about four thousand miles.
-
-=Telephone.= An instrument and apparatus for the transmission of
-articulate speech by the electric current. A magnet is encased in a tube
-and is encircled at one end by a coil of fine, insulated wire. A
-diaphragm of thin iron is fixed in front of the coil and close to the
-end of the magnet. The ends of the coil-wires are connected with a
-line, at the other end of which another and similar instrument is
-installed. The voice causes the sending diaphragm to vibrate, and these
-waves are transmitted to the other instrument, where they can be heard
-through contra-vibrations of the receiving diaphragm.
-
-=Telephone, Long-distance.= A telephone of modern construction, in which
-the sound-recording mechanism is so sensitive as to make the vibrations
-of the voice audible at long distances. It will work satisfactorily at
-one thousand or even fifteen hundred miles.
-
-=Terminal.= The end of any open electric circuit, or of any electric
-apparatus, as the electrodes of a battery.
-
-=Thermostat, Electric.= An apparatus similar in some respects to a
-thermometer, and used for closing an electric circuit when the latter
-becomes heated. It is used in connection with automatic fire-alarms to
-give warning of fire. For this purpose the metal coil is arranged to
-close the contact at a temperature of 125° F. It usually consists of a
-compound strip of metal wound in the form of a spiral and fastened at
-one end. To this end one terminal of a circuit is connected. The
-expansion of the coil causes its loose end to touch a contact-point and
-close the circuit.
-
-=Third Rail.= A railway motive system which employs a third rail instead
-of an overhead trolley feed-wire. The rail is laid on or under the
-surface of the ground and properly insulated. A shoe from the car bears
-on the rail and takes up the current.
-
-=Three-wire Circuit.= A system invented by Edison for the distribution,
-from two dynamos, of current for multiple arc or constant potential
-service. One wire or lead starts from the positive pole of one dynamo,
-another from the negative pole of the other dynamo, and between the two
-dynamos the central or neutral lead is made fast.
-
-[Illustration]
-
-Now the dynamos may generate a current of 220 volts, and send it, at
-this strength, through the outer wires; but if lamps are connected
-between either of the outer and the neutral wires, the current, passing
-through the lamps, will be reduced to 110 volts.
-
-=Time-ball, Electric.= A ball which, by means of electricity, is made to
-drop from the top of a high pole, giving a visual signal for twelve
-o’clock or any other hour that may be designated.
-
-=Traction, Electric.= The propulsion of a car or conveyance by means of
-electricity.
-
-=Transformer.= In alternating-current systems, the induction-coil by
-means of which the primary current, with high initial electro-motive
-force, is changed into a secondary current with low initial
-electro-motive force.
-
-=Transmission.= The conveyance of electric energy and currents from one
-point to another by the proper means of conduction.
-
-=Transmitter.= An instrument which originates the signals which are sent
-through a line or circuit. The Morse key in telegraphy and the Blake
-transmitter in telephony are examples.
-
-=Tri-phase.= Three-phase.
-
-=Trolley.= A contact-wheel of bronze which rolls under the supply-wire
-in an overhead traction system and takes off the current necessary to
-run the car motors.
-
-=Trolley-wheel.= The same as Trolley.
-
-=Trolley-wire.= The overhead wire in a traction system which feeds the
-current through a trolley-wheel and pole to the motors of a car running
-underneath.
-
-=True Ohm.= (_See_ Ohm, True.)
-
-=True Resistance.= (_See_ Resistance, True.)
-
-=Two-wire Circuit.= The single system universally used for light and
-power transmission of current.
-
-
-U
-
-=Undulating Current.= (_See_ Current, Undulating.)
-
-=Uniform Magnetic Field.= (_See_ Magnetic Field, Uniform.)
-
-=Unipolar.= Having but one pole.
-
-=Unit.= The single standard of force, light, heat, magnetism,
-attraction, repulsion, resistance, etc.
-
-
-V
-
-=Vacuum.= A space empty or void of all matter; a space from which all
-gases have been exhausted.
-
-=Vacuum Tubes.= Tubes of glass through which electric discharges are
-passed after the gases have been partially removed; for example, the
-X-ray tube of Röntgen and the Crooke tubes.
-
-=Vibrator, Electro-magnetic.= The make-and-break mechanism used on
-induction-coils, or other similar apparatus, in which, through alternate
-attractions, an arm or spring is kept in motion.
-
-=Vitriol, Blue.= A trade name for copper sulphate. (Bluestone.)
-
-=Vitriol, Green.= A trade name for ferrous sulphate. (Copperas.)
-
-=Vitriol, White.= A trade name for zinc sulphate. (Salts of zinc.)
-
-=Volt.= The practical unit of electro-motive force; the volume and
-pressure of an electric current.
-
-=Voltage.= Electric-motive force expressed in volts--as, a voltage of
-100 volts.
-
-=Voltaic.= A term derived from the name of the Italian scientist Volta,
-and used in many ways as applied to electrical current and devices.
-Formerly the term galvanic was commonly employed.
-
-=Voltaic Electricity.= (_See_ Electricity, Voltaic.)
-
-=Voltimeter.= An instrument for measuring the voltage of a current.
-
-=Vulcanite.= Vulcanized rubber. Valuable for its insulating properties
-and inductive capability.
-
-
-W
-
-=Watt.= The practical unit of electrical activity; the rate of work or
-rate of energy. It is a unit of energy or of work represented by a
-current of one ampere urged on by one volt of electro-motive force.
-
-The volt-ampere.
-
-The standard of electrical energy corresponding to horse-power in
-mechanics.
-
-=Watt-hour.= A unit of electric energy or work; one watt exerted or
-expended through one hour.
-
-=Waves, Electro-magnetic.= Ether waves caused by electro-magnetic
-disturbances affecting the luminiferous ether.
-
-=Welding, Electric.= Welding by the use of the electric current.
-
-=Wimshurst Electric Machine.= An influence machine for producing high
-potential or static electricity. Thin disks of glass are mounted on
-insulated bearings and revolved by power. Brushes collect the
-frictional electricity, which is discharged into a Leyden-jar or
-other form of accumulator. It is of no practical use excepting in
-electro-therapeutics.
-
-=Wire, Flexible.= A cord of fine wire strands laid together and
-insulated so that it may be easily bent or wrapped.
-
-=Wiring.= Installing wires so as to form a circuit for the conveyance of
-current for light, heat, and power.
-
-
-X
-
-=X-rays.= A curious phenomenon involving the radiation of invisible rays
-of light, which have the power to travel through various opaque bodies.
-The rays are used in detecting foreign substances in the human body and
-for photographing invisible or hidden objects without disturbing their
-surroundings.
-
-=X-ray Lamp.= A high vacuum tube lamp whose interior walls are covered
-with crystals of calcium or other fluorescent substances, and which,
-when exposed to the X-rays, give out a luminous light.
-
-
-Y
-
-=Yoke.= A piece of soft iron which connects the ends of two portions of
-a core on which wire coils are wound. It is located at the ends farthest
-from the poles.
-
-The soft-iron bar placed across the ends of a horseshoe magnet to retain
-its magnetism.
-
-
-Z
-
-=Zinc-battery.= A battery which decomposes zinc in an electrolyte,
-thereby producing a current.
-
-=Zinc Currents.= Negative currents.
-
-=Zinc-plating.= The employment of zinc in electro-plating.
-
-
-THE END
-
-
-
-
-  Transcriber’s Notes
-
-
-  Inconsistent spelling, hyphenation, etc. have been retained, unless
-  mentioned under Changes Made below. Technical descriptions have been
-  kept as printed, even when they seem doubtful, wrong or dangerous.
-
-  Depending on the hard- and software and their settings used to read
-  this text, not all elements may display as intended.
-
-
-  Changes Made
-
-  Footnotes and illustrations have been moved outside text paragraphs.
-
-  Where letters (such as V or L) are used to denote a shape rather than
-  the letter, they have been transcribed as [V] or [L] for consistency
-  with other, similarly used letters such as [U].
-
-  Some minor obvious typographical errors have been corrected silently.
-
-  Page 108: "called Nobile’s pair" changed to "called Nobili’s pair".
-
-  Page 182: "shallacked" changed to "shellacked".
-
-  Page 184: "(A, B, and C) and A A, B B, and C C)" changed to "(A, B,
-  and C and A A, B B, and C C)".
-
-  Dictionary: several entries have been moved to their proper
-  alphabetical position.
-
-  Page 334: "modern applications of phenonema" changed to "applications
-  of phenomena
-
-  Page 372: "Coil, Ruhmkoff" changed to "Coil, Ruhmkorff".
-
-  Page 382: "Daniells" changed to "Daniell".
-
-  Page 396: "graphite a native; form of carbon" changed to "graphite; a
-  native form of carbon".
-
-  Page 401: "Ruhmkoff Coil. (See Coil, Ruhmkoff.)" changed to "Ruhmkorff
-  Coil. (See Coil, Ruhmkorff.)"
-
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-
-<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Harper's Electricity Book for Boys, by Joseph H. (Henry) Adams</div>
-
-<div style='display:block; margin:1em 0'>
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online
-at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you
-are not located in the United States, you will have to check the laws of the
-country where you are located before using this eBook.
-</div>
-
-<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Harper's Electricity Book for Boys</div>
-
-<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: Joseph H. (Henry) Adams</div>
-
-<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Contributor: Joseph B. Baker</div>
-
-<div style='display:block; margin:1em 0'>Release Date: February 18, 2021 [eBook #64592]</div>
-
-<div style='display:block; margin:1em 0'>Language: English</div>
-
-<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div>
-
-<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Richard Hulse, Harry Lamé and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.)</div>
-
-<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK HARPER'S ELECTRICITY BOOK FOR BOYS ***</div>
-
-<div class="tnbox">
-
-<p class="noindent">Please see the <a href="#TN">Transcriber&#8217;s Notes</a> at the end of this text.</p>
-
-<p class="noindent blankbefore75">The cover image has been created for this text and is placed in the public domain.</p>
-
-</div>
-
-<hr class="chap" />
-
-<div class="scr">
-
-<div class="container m40">
-
-<div class="figcenter nomargin">
-<img src="images/cover.jpg" alt="Cover image" />
-</div>
-
-</div><!--container-->
-
-<hr class="chap" />
-
-</div><!--scr-->
-
-<div class="catalogue">
-
-<p class="center fsize200">Harper’s Practical Books for Boys</p>
-
-<hr />
-
-<p class="center">A SERIES OF NEW HANDY-BOOKS<br />
-FOR AMERICAN BOYS</p>
-
-<p class="center highline2"><i>Each Crown 8vo, with many Illustrations.</i></p>
-
-<hr />
-
-<p class="center highline15">I</p>
-
-<p class="title">HARPER’S OUTDOOR BOOK FOR BOYS</p>
-
-<p class="descr">By Joseph H. Adams. With Additional Contributions
-by Kirk Munroe, Tappan Adney, Capt. Howard
-Patterson, L. M. Yale, and others. Cloth, $1.75.</p>
-
-<p class="center highline15">II</p>
-
-<p class="title">HARPER’S ELECTRICITY BOOK FOR BOYS</p>
-
-<p class="descr">Written and Illustrated by Joseph H. Adams. With
-a Dictionary of Electrical Terms. Cloth, $1.75.</p>
-
-<p class="center highline2"><i>IN PRESS</i></p>
-
-<p class="center highline15">III</p>
-
-<p class="title">HARPER’S HOW TO UNDERSTAND ELECTRICAL
-WORK</p>
-
-<p class="descr">A Simple Explanation of Electric Light, Heat,
-Power, and Traction in Daily Life. By Joseph
-B. Baker, Technical Editor, U. S. Geological Survey,
-formerly of the General Electric Company.</p>
-
-<p class="center highline15">IV</p>
-
-<p class="title">HARPER’S INDOOR BOOK FOR BOYS</p>
-
-<p class="descr">By Joseph H. Adams and others. Cloth, $1.75.</p>
-
-<p class="center highline15">V</p>
-
-<p class="title">HARPER’S MACHINERY BOOK FOR BOYS</p>
-
-<p class="descr">The Boy’s Own Book of Engines and Machinery.
-Cloth, $1.75.</p>
-
-<hr />
-
-<p class="center highline2 fsize90">HARPER &amp; BROTHERS, PUBLISHERS, NEW YORK</p>
-
-</div><!--catalogue-->
-
-<hr class="chap" />
-
-<div class="container m40">
-
-<div class="figcenter nomargin">
-<img src="images/illo000.jpg" alt="" />
-</div>
-
-<p class="credit right">Copyright, 1907, by Joseph H. Adams, N. Y.</p>
-
-<p class="caption edison">THOMAS A. EDISON DICTATING TO HIS GRAPHOPHONE</p>
-
-</div><!--container-->
-
-<hr class="chap" />
-
-<div class="titlepage">
-
-<h1><b><span class="fsize110 gesp2">HARPER’S</span><br />
-<span class="gesp1">ELECTRICITY BOOK<br />
-<span class="fsize90">FOR BOYS</span></span></b></h1>
-
-<p class="center highline3 blankbefore2">WRITTEN AND ILLUSTRATED BY<br />
-<span class="gesp2"><b>JOSEPH H. ADAMS</b></span></p>
-
-<p class="center fsize60 gesp2">AUTHOR OF<br />
-“HARPER’S OUTDOOR BOOK FOR BOYS”</p>
-
-<p class="center fsize90 blankbefore2"><span class="titlegesp1">WITH AN EXPLANATION OF ELECTRIC LIGHT, HEAT</span><br />
-<span class="titlegesp2 wordsp5">POWER, AND TRACTION BY JOSEPH B. BAKER</span><br />
-<span class="wordsp5">TECHNICAL EDITOR, U. S. GEOLOGICAL SURVEY</span></p>
-
-<p class="center highline2 blankbefore2 fsize90">AND<br />
-<b>A DICTIONARY OF ELECTRICAL TERMS</b></p>
-
-<div class="container m5">
-
-<div class="figcenter nomargin">
-<img src="images/illo001b.jpg" alt="Publisher's logo" />
-</div>
-
-</div><!--container-->
-
-<p class="center gesp2 blankbefore2 blankafter2">HARPER &amp; BROTHERS PUBLISHERS<br />
-NEW YORK AND LONDON<br />
-MCMVII</p>
-
-</div><!--titlepage-->
-
-<hr class="chap" />
-
-<div class="copyright">
-
-<p class="center highline2 fsize90">Copyright, 1907, by <span class="smcap">Harper &amp; Brothers</span>.<br />
-<i>All rights reserved.</i><br />
-Published November, 1907.</p>
-
-</div><!--copyright-->
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Pagevii">[vii]</span></p>
-
-<h2 class="front">CONTENTS</h2>
-
-<table class="toc" summary="ToC">
-
-<tr>
-<th>&nbsp;</th>
-<th class="right padl1">PAGE</th>
-</tr>
-
-<tr>
-<td class="chapter">INTRODUCTION</td>
-<td class="pageno"><a href="#Pagexi">xi</a></td>
-</tr>
-
-<tr>
-<td colspan="2" class="part">Part I</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER I.&mdash;SOME GENERAL EXPLANATIONS</td>
-<td class="pageno"><a href="#Page3">3</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">An Invisible World-power&mdash;Generating Electricity&mdash;What a Boy Can
-Do&mdash;Inexpensive Tools&mdash;Some Practical Advice</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER II.&mdash;CELLS AND BATTERIES</td>
-<td class="pageno"><a href="#Page12">12</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Simple and Inexpensive Cells&mdash;How to Make Cells and Batteries&mdash;A
-Plunge-battery&mdash;A Storage-battery&mdash;Dry-cells and Batteries</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER III.&mdash;PUSH-BUTTONS AND SWITCHES</td>
-<td class="pageno"><a href="#Page33">33</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">How to Make Push-buttons&mdash;Switches and Cut-outs&mdash;Table-jack
-Switches&mdash;Binding-posts and Connectors&mdash;Lightning-arresters and Fuse-blocks&mdash;Some Practical Precautions</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER IV.&mdash;MAGNETS AND INDUCTION-COILS</td>
-<td class="pageno"><a href="#Page54">54</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Simple and Horseshoe Magnets&mdash;Induction-coils&mdash;An Electric
-Buzzer&mdash;Electric Bells&mdash;A Large Induction-coil&mdash;Circuit-interrupters</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER V.&mdash;ANNUNCIATORS AND BELLS</td>
-<td class="pageno"><a href="#Page78">78</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">A Drum-sounder&mdash;A Simple Annunciator&mdash;A Double Electric Bell&mdash;An
-Electric Horn&mdash;How to Make a Burglar-alarm&mdash;Electric Call-signals&mdash;Clock-alarms&mdash;A Dining-table Call</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER VI.&mdash;CURRENT-DETECTORS AND GALVANOMETERS<span class="pagenum" id="Pageviii">[viii]</span></td>
-<td class="pageno"><a href="#Page102">102</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">How to Make Detectors&mdash;An Astatic Current-detector&mdash;An Astatic
-Galvanometer&mdash;A Tangent Galvanometer</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td colspan="2" class="part">Part II</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER VII.&mdash;ELECTRICAL RESISTANCE</td>
-<td class="pageno"><a href="#Page125">125</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Governing the Electric Current&mdash;Ohm’s Law&mdash;Resistance-coils and
-Rheostats&mdash;How to Make Simple Apparatus&mdash;Liquid Resistance&mdash;Importance of Switches&mdash;Uses of a
-House-current&mdash;Running a Sewing-machine, Fan, or Toys&mdash;An Easy Method for a Boy’s Use</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER VIII.&mdash;THE TELEPHONE</td>
-<td class="pageno"><a href="#Page156">156</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Vibratory Waves&mdash;A Bladder Telephone&mdash;A Single (Receiver) Line&mdash;Plan
-of Installation&mdash;A Double-pole Receiver&mdash;The Transmitter&mdash;Another Form of Transmitter&mdash;The Wiring
-System&mdash;A Telephone Induction-coil&mdash;An Installation Plan&mdash;A Portable Apparatus</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER IX.&mdash;LINE AND WIRELESS TELEGRAPHS</td>
-<td class="pageno"><a href="#Page190">190</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">A Ground Telegraph&mdash;How to Talk from House to House&mdash;The Morse Telegraph
-Code&mdash;A Story of Edison&mdash;How Detectives Used the Code&mdash;Wireless Telegraphy&mdash;Its True Character&mdash;How
-a Boy Can Make a Practical Apparatus&mdash;Receiving and Sending Poles&mdash;Induction-coils, Batteries, Coherers and
-De-coherers, etc.&mdash;Working Plans in Detail&mdash;Aërograms Across the Atlantic and, perhaps, Around the World</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER X.&mdash;DYNAMOS AND MOTORS</td>
-<td class="pageno"><a href="#Page229">229</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Dependence of Modern Electricity upon the Dynamo&mdash;A Field of Force Cutting
-another Field of Force&mdash;Varieties<span class="pagenum" id="Pageix">[ix]</span> of Dynamos&mdash;Simpler Forms of
-Generators and Motors&mdash;How to Make a Uni-direction Current Machine&mdash;Permanent Magnet, Armature, Shafts, Wheels,
-etc.&mdash;A Small Dynamo&mdash;Machines to Light Lamps, Run Motors, etc.&mdash;A Split-ring Dynamo&mdash;A Small
-Motor&mdash;The Flat-bed Motor&mdash;Motors of Other Types</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER XI.&mdash;GALVANISM AND ELECTRO-PLATING</td>
-<td class="pageno"><a href="#Page266">266</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">A Fascinating Use of Electricity&mdash;A Simple Electro-plating Outfit&mdash;The
-Sulphate of Copper Bath&mdash;How to Make the Tank and Other Apparatus&mdash;A Variety of Beautiful and Useful
-Results&mdash;Explanations of Various Batteries&mdash;The Cleansing Process&mdash;The
-Plating-bath&mdash;Silver-plating&mdash;Gold-plating&mdash;Nickel-plating&mdash;Finishing&mdash;Electrotyping&mdash;Practical
-Details of Interesting Work</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER XII.&mdash;MISCELLANEOUS APPARATUS</td>
-<td class="pageno"><a href="#Page294">294</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Making a Rotary Glass-cutter&mdash;To Smooth Glass Edges&mdash;Cutting Holes in
-Glass&mdash;Anti-hum Device for Metallic Lines&mdash;A Reel-car for Wire&mdash;Insulators&mdash;Joints and
-Splices&mdash;“Grounds”&mdash;The Edison Roach-killer&mdash;An Electric Mouse-killer</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER XIII.&mdash;FRICTIONAL ELECTRICITY</td>
-<td class="pageno"><a href="#Page312">312</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Its Nature&mdash;Limited Uses&mdash;Simplicity of Apparatus&mdash;A “Wimshurst
-Influence Machine”&mdash;Materials Required&mdash;Glass, Tin-foil, Spindles, Uprights, Wheels, etc.&mdash;A Large
-Leyden-jar&mdash;Apparatus for Interesting Experiments&mdash;Necessity of Caution</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER XIV.&mdash;FORMULÆ</td>
-<td class="pageno"><a href="#Page327">327</a></td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">Acid-proof Cements&mdash;Hard Cement&mdash;Soft Cement&mdash;Very Hard
-Cement&mdash;Clark’s Compound&mdash;Battery Fluid&mdash;Glass Rubbing&mdash;Acetic
-Glue&mdash;Insulators&mdash;Non-conductors&mdash;Insulating Varnish&mdash;Battery Wax</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">CHAPTER XV.&mdash;ELECTRIC LIGHT, HEAT AND POWER<span class="pagenum" id="Pagex">[x]</span></td>
-<td class="pageno"><a href="#Page334">334</a></td>
-</tr>
-
-<tr>
-<td class="center">(By Joseph B. Baker)</td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="subjects"><span class="smcap">The Work of the Dynamo&mdash;The Electric Light&mdash;Uses of the
-Arc-light&mdash;Incandescent and Other Lamps&mdash;Electric Heat&mdash;Electric Furnaces&mdash;Welding
-Metals&mdash;Electric Car-heaters&mdash;Household Uses&mdash;Electric Power&mdash;Power from
-Water-wheels&mdash;Transformers&mdash;Rotary Converters&mdash;Oil-switches&mdash;Electric Traction&mdash;The
-Trolley-car&mdash;The Continuous-current Motor&mdash;The Controller&mdash;Electric Locomotives&mdash;Other Forms of Electric
-Traction</span></td>
-<td>&nbsp;</td>
-</tr>
-
-<tr>
-<td class="chapter">A DICTIONARY OF ELECTRICAL TERMS</td>
-<td class="pageno"><a href="#Page359">359</a></td>
-</tr>
-
-</table>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Pagexi">[xi]</span></p>
-
-<h2 class="front">INTRODUCTION</h2>
-
-<p class="chapstart"><span class="largecap">I</span><span class="afterlargecap">f</span>
-a handy-book of electricity like this had fallen into
-the hands of Thomas A. Edison when he was a newsboy
-on the Grand Trunk Railway, or when he was a telegraph
-operator, he would have devoured it with the utmost eagerness.
-To be sure, at that time, in the early sixties, all that
-we knew of electricity and its applications could have been
-told in a very brief compass. It was an almost unknown
-field, and the crude form of the telegraph then in use
-represented its most important application. There were
-no electric lights; there was no telephone or phonograph;
-there were no electric motors. Telegraphing, itself, was a
-slow and difficult process. All the conditions were as far
-removed as possible from the broad field of applied electricity
-indicated in this book.</p>
-
-<p>But this does not mean that we have now accomplished
-all that there is to be done. On the contrary, the next half-century
-will be full of wonderful advances. This makes it
-more than ever essential that we should become acquainted
-with the principles and present conditions of a science which
-is being applied more and more closely to the work of every-day
-life. It is necessary to know this from the inside,
-not simply from general descriptions. Theory is all very
-well, but there is nothing like mastering principles, and
-then applying them and working out results for one’s self.<span class="pagenum" id="Pagexii">[xii]</span>
-Any active and intelligent boy with an inquiring mind
-will find a new world opened to him in the satisfaction of
-making electrical devices for himself according to the suggestions
-given in this book. This will show him the reasons
-for things in concrete form, will familiarize him with principles,
-and will develop his mechanical ingenuity. He may
-be laying the foundation for inventions of his own or for
-professional success in some of the many fields which electricity
-now offers. Work of this kind brings out what is in
-one, and there is no satisfaction greater than that of winning
-success by one’s own efforts.</p>
-
-<p>The boy who makes a push-button for his own home, or
-builds his own telephone line or wireless telegraph plant, or
-by his own ingenuity makes electricity run his mother’s
-sewing-machine and do other home work, has learned applications
-of theory which he will never forget. The new
-world which he will enter is a modern fairyland of science,
-for in the use of electricity he has added to himself the
-control of a powerful genie, a willing and most useful servant,
-who will do his errands or provide new playthings,
-who will give him manual training and a vast increase
-in general knowledge. The contents of this book, ranging
-from the preparation of simple cells to the making of
-dynamos and motors, and the delightful possibilities of
-electro-plating, shows the richness of the field which is made
-accessible by Mr. Adams’ practical explanations, his carefully
-tested working plans, and his numerous and admirable
-drawings&mdash;all of which have been made for this book.</p>
-
-<p>It is in keeping with the practical character of the <i>Electricity
-Book</i> that pains are taken throughout to show the<span class="pagenum" id="Pagexiii">[xiii]</span>
-simplest and most inexpensive way of choosing materials
-and securing results. The actual working out of these directions
-can be done at very small expense. Furthermore,
-there need be no concern whatever as to possible danger if
-the book is read with reasonable intelligence. Mr. Adams
-has taken pains to place danger-signals wherever special
-precautions are advisable, and, as a father of boys who are
-constantly working with electricity in his laboratory, he may
-be relied upon as a safe and sure counsellor and guide.</p>
-
-<p>While this book shows boys what they can do themselves,
-its scope has been enlarged by Mr. Baker’s <a href="#Page334">chapter</a> explaining
-briefly the working of electricity all about us, in light
-and heat, in the trolley-car, and other daily applications.
-In addition, Mr. Adams has prepared a Dictionary of Electrical
-Terms, and these brief definitions will be found peculiarly
-helpful in the first reading of the book. It is believed
-that there is no book in this particular field comparable to
-Harper’s <i>Electricity Book</i> in its comprehensiveness, practical
-character, and the number and usefulness of its illustrations.
-It follows the successful <i>Out-door Book for
-Boys</i> in Harper’s series of <i>Practical Books for Boys</i>, and
-it will be followed by <i>How to Understand Electrical Work</i>,
-a book, not of instructions in making electrical apparatus,
-but of explanations of the commercial uses of electricity all
-about us.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page1">[1]</span></p>
-
-<h2 class="part">Part I</h2>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page2">[2-<br />3]<a id="Page3"></a></span></p>
-
-<p class="fauxh1"><b>ELECTRICITY BOOK FOR BOYS</b></p>
-
-<hr class="sec" />
-
-<h3>Chapter I<br />
-<span class="chaptitle">SOME GENERAL EXPLANATIONS</span></h3>
-
-<p class="chapstart"><span class="largecap">W</span><span class="afterlargecap">e</span>
-are living in the age of electricity, just as our fathers
-lived in the age of steam. Electricity is the world-power,
-the most powerful and terrible of nature’s hidden
-forces. Yet, when man has learned how to harness its fiery
-energies, electricity becomes the most docile and useful
-of his servants. Unquestionably, electricity is to-day the
-most fascinating and the most profitable field for the investigator
-and the inventor. The best brains of the country
-are at work upon its problems. New discoveries are constantly
-being recorded, and no labor is thought too great if
-it but add its mite to the sum total of our knowledge. And
-yet, ridiculous as the statement may seem, we do not know
-what electricity is. We only know certain of its manifestations&mdash;what
-it can do. All we can say is that it does our
-bidding; it propels our trains, lights our houses and streets,
-warms us, cooks for us, and performs a thousand and one
-other tasks at the turn of a button or at the thrust of a
-switch. But <i>what</i> it is, we do not know. Electricity has<span class="pagenum" id="Page4">[4]</span>
-no weight, no bulk, no color. No one has seen it; it cannot
-be classified, nor analyzed, nor resolved into its ultimate
-elements by any known process of science. We must content
-ourselves with describing it as one manifestation of the
-energy which fills the universe and appears in a variety of
-forms&mdash;such as heat, light, magnetism, chemical affinity, and
-mechanical motion. In all probability it is one of those
-phenomena of nature that are destined to remain forever
-secret. Thus it stands in line with gravitation, magnetism,
-the active principle of radium, and the perpetual motion of
-the solar system.</p>
-
-<p>Electricity was known to the early Greeks; indeed, it
-derives its name from the Greek word for amber (electron).
-For many centuries amber was credited with certain special
-or magical powers. When it was rubbed with a flannel
-cloth, “the hidden spirit” came out and laid hold of small
-detached objects, such as bits of paper, thread, chips, or
-pith-balls. No one could explain this phenomenon. It
-was looked upon with superstitious awe and the amber itself
-was regarded as possessing the special attributes of divinity.
-But as time went on, it was discovered that in various other
-substances this mysterious attractive power could be excited,
-at will, through the agency of friction. Rubbing a
-piece of glass rod with silk or leather generated an “electricity”
-identical with that of the amber; or the same result
-could be obtained by exciting hard rubber with catskin.
-The conclusion followed that electricity was not a property
-of the special materials employed to generate it, but that
-it came from without, from that great reservoir of energy,
-the atmosphere. Then came Franklin with his experiment<span class="pagenum" id="Page5">[5]</span>
-of the kite, and the invention of the Leyden-jar and the
-chemical production of the electric fluid by means of
-batteries. It was shown that the properties of the new
-and strange force were the same, whether it was produced
-by the static (frictional) process or by the galvanic
-(chemical) method. Electrical science as a science, had
-begun.</p>
-
-<p>And yet, for many years, electricity was hardly more than
-a scientific toy. It was not supposed to possess any practical
-usefulness. The entertaining experiments with the
-static machine and the Leyden-jar (<a href="#Page294">chapter xiii.</a>) were confined
-to the laboratory and the lecture hall. Electricity
-was an amusing display of unknown energy, but no one ever
-dreamed that it could ever be made to serve the practical
-ends of life. It was not until about 1850 that electrical
-science became anything more than a name. The galvanic
-and voltaic batteries (<a href="#Page12">chapter ii.</a>) opened the way for “current”
-electricity, which flowed continuously, instead of
-jumping and disappearing like the spark from a Leyden-jar.
-When the continuous current became an established fact,
-the telegraph and telephone headed the line of a long series
-of developments. Finally, the generation of electricity in
-greater volume, and cheaply, made possible the application
-of its power for heating, light, traction, and the other forms
-of activity in which it now does so large a share of the
-world’s work.</p>
-
-<p>How electricity works is a question often asked, but not
-easily answered. There are certain so-called laws, but we
-shall best arrive at a conclusion by simply stating a few
-of the facts that have been established through the observation<span class="pagenum" id="Page6">[6]</span>
-and investigation of scientists and electrical engineers.<a id="FNanchor1"></a><a href="#Footnote1" class="fnanchor">[1]</a></p>
-
-<div class="footnote">
-
-<p><a id="Footnote1"></a><a href="#FNanchor1"><span class="label">[1]</span></a>
-Explanations of any technical names or phrases used in the text will
-be found in the simple <a href="#Page359">dictionary of electrical terms</a> which appears as an
-appendix.</p>
-
-</div><!--footnote-->
-
-<p>For example, electricity is always alert, ready to move,
-and continually on the lookout for a chance to obtain its
-freedom. It will never go the longest way round if there is
-a short cut; and it will heat, light, or fuse anything in its
-path that is too weak to carry or resist it. For this reason,
-it must be generated in small volume&mdash;that is, just sufficient
-to do the work required of it. If produced in larger volume,
-it must be held in check by resistance, and only so much
-allowed to escape as may be needed for the specified work.</p>
-
-<p>Again, when electricity is generated this must be done in
-one of two ways&mdash;by friction or chemically. But in both
-processes there must be air surrounding the generators, and
-the fluid must be of a nature through which oxygen and
-hydrogen can circulate freely. Water fluids are suitable for
-this purpose, but oils cannot be used, as they contain hydro-carbon
-in large quantities and are non-conductors.</p>
-
-<p>Batteries are chemical generators, dynamos are magneto-electric,
-and static machines are frictional. Now the theory
-is that electricity is drawn from the ether and, in its normal
-state, is quiet. If it be disturbed and collected by
-mechanical or chemical means, it is always on the alert to
-escape and again take its place in the atmosphere. As its
-volume is increased, so its energy to get away is multiplied,
-and this energy may be transformed, at will, into power,
-heat, or light. To express the idea in the simplest language,<span class="pagenum" id="Page7">[7]</span>
-it wants to go home, and in its effort to do so it expresses itself
-in the form of stored-up power, precisely like water behind
-a dam. It is for man’s cunning brain to devise all sorts of
-tasks that this power must perform before it can gain its
-release. It can’t go home until its work is done.</p>
-
-<p>Nearly every boy has experimented, at one time or another,
-with electricity and electrical apparatus, and whether
-it was with some of the simple frictional or galvanic toys, or
-with the more complicated induction-coils and motors, he has
-undoubtedly found it a most interesting amusement and an
-ever new and widening field for study. Then again, many
-boys would like to know something about simple electrical
-apparatus and how to make and use it. But his school-books
-relating to the general subject of electricity are
-hardly definite enough to serve as a practical manual. And
-yet there are many things in the way of electrical machinery
-and equipment that a boy can easily construct and use. In
-this book it is my purpose to show him just what can be done
-with the aid of the tools that are usually in his possession.
-While some things may have to be purchased from an electrical
-supply-house or other sources, there is still much
-material to be found about the house that may be put to
-good use by the amateur electrician.</p>
-
-<p>It is not possible or desirable to describe every variety of
-electrical equipment. We must confine ourselves to apparatus
-which can be readily understood and operated. The
-“practical” idea is the one to be borne in mind. This book
-shows a boy how to use his brains and the simple tools and
-material that may be at his command. Care and thought
-in the construction of the apparatus are the important<span class="pagenum" id="Page8">[8]</span>
-qualifications for success. The instructions are given in the
-clearest possible language; the diagrams and drawings are
-intelligible to any one who will take the trouble to study
-them. If your finished apparatus does not work properly,
-read the description again and see if you have not made some
-error. A misplaced or broken wire, a wrong connection, or
-a short circuit will mean all the difference between success
-and failure.</p>
-
-<p>Save in one short chapter, static or frictional electricity
-(see <a href="#Page359">Appendix</a>) is not considered; for outside of laboratory
-experimenting and electro-medical apparatus, frictional
-electricity is but a toy&mdash;interesting and useful when generated
-in small volume, but very dangerous and difficult of
-control when in great volume. For example, the bolt of
-lightning is but the many times multiplied spark stored in
-the Leyden-jar by the static machine. For all practical
-purposes, galvanic electricity, in its various phases of direct
-and alternating current, meets the requirements of man.
-With the improved apparatus and the rapid advancement
-along the line of invention, electricity is as easily controlled
-to-day as steam&mdash;in fact, its economical use is even more
-fully under control and its adaptability more practical.</p>
-
-<p>In the following pages there are probably illustrations
-and descriptions of many things that will seem strange to
-the boy who has not heard of them; but if a book were
-written each year on the subject of electricity, every new
-one would include principles and facts not known before.
-The field of electrical research is so broad and so many are
-working in it that new discoveries are being made continually.</p>
-
-<p><span class="pagenum" id="Page9">[9]</span></p>
-
-<p>To those familiar with the application of electricity, it is
-clearly evident that, as yet, we are only beginning to deal
-with this unknown force. For generations to come, developments
-will take place and invention follow invention until
-electricity assumes its rightful place as the motive force of
-the world. To the boy interested in this subject a wide
-field is open, and the youth of to-day, who are taking up
-this study, are destined to become the successful electrical
-engineers and inventors of the future. There is no better
-education for any boy, in the application and principles of
-electricity, than to begin at the very bottom of the ladder
-and climb up, constructing and studying as he progresses.
-When he attempts to design more technical and difficult
-apparatus the lessons learned in a practical way will be of
-inestimable value, greater by far than any theoretical principles
-deduced from books; he knows his subject from the
-ground up; he understands his machine because he has constructed
-it with his own hands.</p>
-
-<p>As I have said already, the necessary tools are few in number
-and not expensive. They may include a hammer, a
-plane, awls, pliers, wire-cutters, and tin-shears. The raw
-material is also cheap&mdash;lead, tin, wire, wood, and simple
-chemicals. The laboratory may be a corner in the attic, or
-even in a boy’s bedroom, so far as the finer work is concerned,
-while the hammering and sawing may be done in
-the cellar. The other best plan, of course, is to get the use
-of a spare room which may be fitted with shelves, drawers,
-and appliances for serious work. To enthusiastic beginners,
-as well as to those who have had some experience in electricity,
-a needed warning may be given in three words:<span class="pagenum" id="Page10">[10]</span>
-“Take no chances.” Electricity, the subtle, stealthy, and
-ever-alert force, will often deal a blow when least expected.
-For that reason, a boy should never meddle with a high-tension
-current or with the mains from dynamos. The
-current in the house, used for lighting, cooking, or heating
-purposes, is always an attractive point for the young electrician,
-but the wires should never be touched in any way.
-Too many accidents have happened, and the conductors,
-lamp-sockets, and plugs should be carefully avoided.</p>
-
-<p>The boy should keep strictly to his batteries, or small
-dynamos run by water-power from a faucet; in no case
-should the wire from power-houses be tampered with. One
-little knows what a current it may be carrying and what
-a death-dealing force it possesses. Always bear in mind
-that a naked wire falling from a trolley equipment carries
-enough force to kill anything it strikes.</p>
-
-<p>Special attention is called to the dictionary of electrical
-terms given in the <a href="#Page359">Appendix</a>. The young student should
-never pass over a word or a term that he does not thoroughly
-understand. Always look it up at once and <i>every
-time</i> it occurs, until you are sure that its meaning is fixed
-in your mind. This is an education in itself, at least so far
-as the theoretical knowledge of our subject is concerned.</p>
-
-<p>As a final word, I should like every boy interested in
-electricity to hear what Thomas A. Edison once said to me
-when I was a boy working in his laboratories. I often recall
-it when things do not go just right at first.</p>
-
-<p>I asked the great inventor one day if invention was not
-made up largely of inspiration. He looked at me quizzically
-for a moment, and then replied: “My boy, I have little use<span class="pagenum" id="Page11">[11]</span>
-for a man who works on inspiration. Invention is two parts
-inspiration and ninety-eight per cent. perspiration.”</p>
-
-<p>You will never get what you are after unless you work
-hard for it. You must stick to it until you produce results.
-If the history of the world’s most valuable inventions could
-be fully known, the fact would be clearly established that
-the vital spark of inspiration is but the starting-point.
-Then follow the days, weeks, and sometimes years of
-industrious toil, failures, and disappointments, until finally
-the desired end is attained. One must work for success;
-there is no other means of winning it.</p>
-
-<p>As the <a href="#Pagevii">table of contents</a> shows, <a href="#Page3">Part I.</a> of this book
-explains principles and the simpler forms of electrical appliances.
-From this we advance to <a href="#Page123">Part II.</a>, which deals
-with more complex forms of electrical work, most of which,
-however, are within the reach of intelligent boys who have
-followed the chapters carefully from the first. In a <a href="#Page334">final
-chapter</a> we have simple explanations of the great commercial
-uses of electricity, which we see all about us, although
-very few of us have a clear idea as to their operation.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page12">[12]</span></p>
-
-<h3>Chapter II<br />
-<span class="chaptitle">CELLS AND BATTERIES</span></h3>
-
-<h4>Simple Cells</h4>
-
-<p class="chapstart"><span class="largecap">I</span><span class="afterlargecap">n</span>
-order to generate electricity it is necessary to employ
-cells, batteries, or dynamos. Since the construction and
-operation of a dynamo is somewhat intricate, it will be better
-to start with the simpler methods of electric generation,
-and so work up to the more complicated forms. For small
-apparatus, such as electric bells and light magnets and
-motors, the zinc-carbon-sal-ammoniac cell will answer very
-well; but for larger machinery, where more current is required,
-the bluestone and the bi-chromate batteries will
-be found necessary.</p>
-
-<div class="container m40">
-<a id="FigII1"></a>
-<a id="FigII2"></a>
-<a id="FigII3"></a>
-<a id="FigII5"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo013.jpg" alt="" />
-</div>
-
-<p class="caption">SIMPLE BATTERY ELEMENTS</p>
-
-</div><!--container-->
-
-<p>A simple and inexpensive cell may be made from electric-light
-carbons, with the copper coating removed, and pencils
-of zinc, such as are used for electric-bell batteries and which
-can be purchased for five cents each. Copper wire is to be
-bound around the top of each pencil of carbon and zinc,
-and firmly fastened with the pliers, so that it will not pull
-off or become detached. It will be well to cut a groove
-with a file around the top of both the carbon and zinc, into
-which the wire will fit. The elements should then be<span class="pagenum" id="Page13">[13-<br />14]<a id="Page14"></a></span>
-clamped between two pieces of wood and held with screws,
-as shown in <a href="#FigII1">Fig. 1</a>. A more efficient carbon pole is made by
-strapping six or more short carbon pencils around one long
-one, as shown in <a href="#FigII3">Fig. 3</a>. The short pieces of electric-light
-carbons are bound to the longest carbon with heavy elastic
-bands, or cotton string dipped in paraffine or wax, to make
-the cotton impervious to water and the sal-ammoniac
-solution.</p>
-
-<p>Another arrangement of elements is shown in <a href="#FigII2">Fig. 2</a>,
-where a zinc rod is suspended between two carbons, the
-carbons being connected by a wire that must not touch the
-zinc.</p>
-
-<p>A fruit-jar, or a wide-necked pickle-bottle, may be employed
-for a cell, but before the solution is poured in, the
-upper edge of the glass should be coated with paraffine.
-This should be melted and applied with a brush, or the edge
-of the glass dipped in the paraffine.</p>
-
-<p>The solution is made by dissolving four ounces of sal-ammoniac
-in a pint of water, and the jar should be filled
-three-fourths full. In this solution the carbons and zinc
-may be suspended, as shown in the illustration (<a href="#FigII4">Fig. 4</a>) of
-the sal-ammoniac cell. The wood clamps keep the carbon
-and zinc together, and the extending ends rest on the top
-of the jar and hold the poles in suspension. Plates of zinc
-and carbon may be clamped on either side of a square stick
-and suspended in the sal-ammoniac solution, as shown in
-<a href="#FigII5">Fig. 5</a>, taking care, however, that the screws used for clamping
-do not touch each other.</p>
-
-<p>If one cell is not sufficiently powerful, several of them
-may be made and coupled up in series&mdash;that is, by carrying<span class="pagenum" id="Page15">[15]</span>
-the wire from the zinc of one to the carbon of the next cell,
-and so on to the end, taking care that the wire from the carbon
-in the first cell and that from the zinc of the last cell
-will be the ones in hand, as shown in <a href="#FigII6">Fig. 6</a>. This constitutes
-a battery. Be sure and keep the ends of the wire
-apart, to prevent galvanic action and to save the power of
-the batteries.</p>
-
-<p>This battery is an excellent one for bells and small experimental
-work, and when inactive the zincs are not eaten
-away (as they would be if suspended in a bi-chromate
-solution), for corrosion takes place only as the electricity
-is required, or when the circuit is closed. A series of batteries
-of this description will last about twelve months, if
-used for a bell, and at the end of that time will only require
-a new zinc and fresh solution.</p>
-
-<p>The cell in which the plates shown in <a href="#FigII5">Fig. 5</a> are used
-may contain a bi-chromate solution; and for experimental
-work, where electricity is required for a short time
-only, this will produce a stronger current. But remember
-that the solution eats the zinc rapidly, and the plates
-must be removed as soon as you have finished using
-them.</p>
-
-<p>The bi-chromate solution is made by slowly pouring four
-ounces of commercial sulphuric acid into a quart of cold
-water. This should be done in an earthen jar, since the
-heat generated by adding acid to water is enough to crack
-a glass bottle. Never pour the water into the acid. When
-the solution is about cold, add four ounces of bi-chromate of
-potash, and shake or mix it occasionally until dissolved;
-then place it in a bottle and label it:</p>
-
-<p><span class="pagenum" id="Page16">[16]</span></p>
-
-<p class="center highline2 blankbefore1 blankafter1"><span class="fsize80">BI-CHROMATE BATTERY FLUID</span><br />
-<span class="fsize110">POISON</span></p>
-
-<p>Before the zincs are immersed in the bi-chromate solution
-they should be well amalgamated to prevent the acid from
-eating them too rapidly.</p>
-
-<p>The amalgamating is done by immersing the zincs in a
-diluted solution of sulphuric acid for a few seconds, and
-then rubbing mercury (quicksilver) on the surfaces. The
-mercury will adhere to the chemically cleaned surfaces of
-any metal except iron and steel, and so prevent the corroding
-action of the acid. Do not get on too much mercury,
-but only enough to give the zinc a thin coat, so that it will
-present a silvery or shiny surface.</p>
-
-<p>A two-fluid cell is made with an outer glass or porcelain
-jar and an inner porous cup through which the current can
-pass when the cup is wet. <a href="#FigII7">Fig. 7</a>.</p>
-
-<div class="container m40">
-<a id="FigII4"></a>
-<a id="FigII7"></a>
-<a id="FigII8"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo017a.jpg" alt="Batteries" />
-</div>
-
-<div class="figcenter nomargin" id="FigII6">
-<img src="images/illo017b.jpg" alt="Batteries" />
-</div>
-
-</div><!--container-->
-
-<p>A porous cup is an unglazed earthen receptacle, similar
-to a flower-pot, through which moisture will pass slowly.
-The porous cup contains an amalgamated plate of zinc
-immersed in a solution of diluted sulphuric acid&mdash;one ounce
-to one pint of water. The outer cell contains a saturated
-solution of sulphate of copper in which a cylindrical piece
-of thin sheet-copper is held by a thin copper strap, bent over
-the edge of the outer cell. A few lumps or crystals of the
-copper sulphate, or bluestone, should be dropped to the
-bottom of the jar to keep the copper solution saturated at
-all times. When not in use, the zinc should be removed
-from the inner cell and washed off; and if the battery is
-not to be employed for several days, it would be well to<span class="pagenum" id="Page17">[17]</span>
-pour the solutions back into bottles and wash the several
-parts of the battery, so that it may be fresh and strong
-when next required. When in action, the solutions in both
-cups should be at the same level, and be careful never to
-allow the solutions to get mixed or the copper solution to
-touch the zinc. Coat the top of the porous cell with paraffine<span class="pagenum" id="Page18">[18]</span>
-to prevent crystallization, and also to keep it clean.
-Take great care, in handling the acid solutions, to wear old
-clothes, and do not let the liquids spatter, for they are
-strong enough to eat holes in almost anything, and even to
-char wood. The two-fluid cells are much stronger than the
-one-solution cells, and connected up in series they will develop
-considerable power.</p>
-
-<p>For telegraph-sounders, large electric bells, and as accumulators
-for charging storage-batteries, the gravity-cell
-will give the most satisfactory results. The one shown in
-<a href="#FigII8">Fig. 8</a> consists of a deep glass jar, three strips of thin copper
-riveted together, and a zinc crow-foot that is caught on the
-upper edge of the glass jar. These parts will have to be
-purchased at a supply-house, together with a pound or two
-of sulphate of copper (bluestone).</p>
-
-<p>To set up the cell, place the copper at the bottom and
-drop in enough of the crystals to generously cover the
-bottom, but do not try to imbed the metallic copper in
-the crystals; then fill the jar half full of clear water. In
-another jar dissolve two ounces of sulphate of zinc in
-enough water to complete the filling of the jar to within
-two inches of the top; then hang the zinc crow-foot on the
-edge of the jar so that it is immersed in the liquid and is
-suspended about three inches above the top of the copper
-strip. The wire that leads up from the copper should be
-insulated with a water-proof coating and well covered with
-paraffine. A number of these cells may be connected in
-series to increase the power of the current, and for a working-battery
-this will show a high efficiency. Note that at
-first the solutions will mingle. To separate them, join the<span class="pagenum" id="Page19">[19]</span>
-two wires and start the action; then, in a few hours, a dividing
-line will be seen between the white, or clear, and the
-blue solutions, and the action of the cell will be stronger.
-After long-continued use it may be necessary to draw off
-some of the clear zinc sulphate, or top solution, and replace
-it with pure water. The action of the acids reduces the
-metallic zinc to zinc sulphate and deposits metallic copper
-on the thin copper strips, and in this process an electrical
-current is generated.</p>
-
-<h4>A Plunge-battery</h4>
-
-<p>When two or more cells (in which sulphuric acid, bi-chromate
-of potash, or other strong electropoions are employed)
-are coupled in series, it would be well to arrange the
-copper and zinc, or the zinc and carbon, poles on a board,
-so that all of them may be lowered together into the solutions
-contained in the several jars. A simple arrangement
-of this kind is shown in <a href="#FigII9">Fig. 9</a>, where a rack is built for the
-jars and at the top of the end boards a projecting piece of
-wood, supported by a bracket, is made fast. A narrow piece
-of board nearly the length of the jar-rack is fitted with the
-battery-poles, as shown at <a href="#FigII9">Fig. 9</a> A. The carbon and zinc,
-or copper and zinc, poles are attached to small blocks of
-wood (as described for <a href="#FigII5">Fig. 5</a>), and this block in turn is
-fastened to the under side of the board with brass screws.
-The poles of the cells are to be connected (as explained in
-<a href="#FigII6">Fig. 6</a>), and when the battery is in use the poles are immersed
-in the solution contained in the jars. When the battery is
-at rest the narrow board should be lifted up and placed on<span class="pagenum" id="Page20">[20]</span>
-the projecting arms of the rack, so that the liquid on the
-poles may drain into the jars directly underneath. One or
-more of these battery-racks may be constructed, but they
-cannot be made to hold conveniently more than four or six
-cells each; if more cells are required, those contained in each
-rack must be coupled up in series.</p>
-
-<div class="container m40" id="FigII9">
-
-<div class="figcenter nomargin" id="FigII10">
-<img src="images/illo020.jpg" alt="Batteries" />
-</div>
-
-</div><!--container-->
-
-<p>A simpler plunge-battery is shown in <a href="#FigII10">Fig. 10</a>. A cell-rack
-is made of wood and given two or three coats of
-shellac. The narrow board (to the under side of which the
-battery-poles are attached, as explained in <a href="#FigII9">Fig. 9</a>) is hung
-on chains or flexible wires, which in turn are made fast to
-an iron shaft running the entire length of the cell-rack.
-This shaft is of half-inch round iron, and is held in place,
-at one end, by a pin and washer; while at the other the end
-is filed with a square shoulder, and a handle and crank is
-fitted to it, so that the shaft may be turned. A small hole,
-made at the side of the crank when it is hanging down, will
-receive a hard-wood peg, or a steel nail, and this will prevent
-the crank from slipping when the board holding the<span class="pagenum" id="Page21">[21]</span>
-poles is raised. If a gear-wheel and tongue can be had to fit
-on the shaft, it will then be possible to check the shaft
-securely at any part of a turn of the crank. The battery-poles
-are to be connected in series along the top of the
-portable board, as explained for <a href="#FigII6">Fig. 6</a>. When two or more
-of these plunge-batteries are used at one time, the wire from
-the carbon of one is to be connected with the zinc pole of
-the next, and so on. The wire from the zinc of the first
-battery, and the wire from the carbon of the last battery,
-will be the ones available for use.</p>
-
-<h4>A Storage-battery</h4>
-
-<p>When more current is desired than the simple batteries
-will give, a storage-battery should be employed as an accumulator.
-This result can be secured by coupling primary
-cells in series, so that they will be constantly generating
-and feeding the battery. Storage-batteries are too heavy
-to be shifted about, like single cells or small plunge-batteries;
-they should be placed in a cellar, where the charging or
-primary cells can be located close by, and, unless positively
-necessary, the battery of cells and the accumulator should
-not be moved.</p>
-
-<p>With sufficiently large insulated wires (Nos. 12, 14, or 16
-copper), the current may be carried to any part of the house
-for use in various ways&mdash;such as running a light motor or
-a fan, lighting a lamp-circuit, or fusing metals and chemicals
-for experimental purposes. While the battery to be described
-is not a light one in weight, nor as economical as the
-improved new Edison storage-battery, it is a good and<span class="pagenum" id="Page22">[22]</span>
-constant one, and, if not overcharged or abused, will last
-for several years.</p>
-
-<p>The component parts of a storage-battery are lead in
-metallic and chemical form, the electrolyte, or fluid, in
-which the plates are immersed, and the water-tight and
-chemical-proof cell or container. From a plumber, a supply-house,
-or a lead-works, obtain a quantity of three-eighth
-by one-quarter-inch strip-lead of the kind called chemical,
-or desilverized; also a larger quantity of lead-tape, one-sixty-fourth
-of an inch thick and three-eighths of an inch
-wide. This last is also known as torpedo-lead, and is kept
-by electrical supply-houses.</p>
-
-<p>If the three-eighths by quarter-inch strip-lead cannot be
-had, then purchase eight or ten pounds of heavy sheet-lead,
-and, with a tin-shears, divide it into strips three-eighths of
-an inch wide and twenty-nine inches long, taking care to
-cut it of uniform width and with true edges. From hard-wood
-three-eighths or half an inch thick, cut a block six
-by seven inches and make four countersunk holes in it, so
-that it may be screwed fast to a table or bench, as shown in
-<a href="#FigII11">Fig. 11</a> A. Around this the lead strips should be shaped
-and beaten at the corners to make the angles sharp.</p>
-
-<p>From the three-eighths by quarter-inch, or sheet-lead
-strips, make seven frames as shown in <a href="#FigII12">Fig. 12</a>. This is done
-by binding a strip of the lead around the block, as shown
-at <a href="#FigII11">Fig. 11</a> B. Where the ends come together insert a short
-piece of lead, three-eighths or half-inch, as shown at <a href="#FigII12">Fig.
-12</a> A, and solder it fast. A soldering-iron may be heated
-with a Bunsen-burner gas-flame or in a charcoal fire. However,
-if gas is available, it would be better to use the blue<span class="pagenum" id="Page23">[23]</span>
-flame from a Bunsen burner and direct the hot blast directly
-on the work with a blow-pipe, and so fuse the lead points
-together. After a little practice with the blow-pipe it will
-be used for many pieces of work in preference to the soldering-iron.
-If the sheet-lead is used for the frames in place of
-the three-eighths by quarter-inch strips, two or three strips
-will have to be taken, so as to build up the band of the frame
-to about a quarter of an inch in thickness. When soldered
-together, or fused at the edges, these built-up frames will be
-as rigid as the solid metal.</p>
-
-<div class="container m40">
-<a id="FigII11"></a>
-<a id="FigII12"></a>
-<a id="FigII13"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo023.jpg" alt="Leadwork" />
-</div>
-
-</div><!--container-->
-
-<p>Now cut a number of strips of the thin lead-tape six inches
-and a half long, and others that will necessarily be somewhat
-longer, for each frame is to be filled with straight and
-crimped pieces, as shown in <a href="#FigII13">Fig. 13</a>. If there is a fluting-iron
-in the house, the crimping may be done in the brass
-gears at one end of the machine. Or two wheels may be
-cut from hard-wood with a fret-saw, and made fast to a<span class="pagenum" id="Page24">[24]</span>
-block with screws, as shown in <a href="#FigII14">Fig. 14</a>. A handle, attached
-to one wheel, will make it possible to turn the gears; and
-they should be placed just far enough apart to allow the
-tape to pass through without tearing or squeezing. Put a
-washer between the wheel and the block to prevent friction.</p>
-
-<p>When a frame is in the position shown in <a href="#FigII13">Fig. 13</a>, and
-lying on a piece of slate or flat stone, you will first put in a
-crimped piece of tape, as shown at <a href="#FigII13">Fig. 13</a> A, and under this
-arrange a straight piece (<a href="#FigII13">Fig. 13</a> B); then, with the blow-pipe
-and flame, fuse fast to the frame and catch the flutes
-of the crimped piece to the straight one every inch or two.
-Add alternate crimped and straight strips until the frame
-is filled and presents the appearance of <a href="#FigII13">Fig. 13</a>. When the
-seven frames are ready, lay three of them aside for the
-positives and four for the negatives. Note that the positives
-are red and the negatives a dark yellow when they are
-filled with the active material.</p>
-
-<p>There are several methods of depositing the active material
-in the mesh or net-work of the plates, but some of them
-are too technical, others too complicated, and still others
-require charging machinery. The following plan will be
-the simplest and easiest for the amateur:</p>
-
-<p>At a paint-store, or from a wholesale druggist, obtain
-several pounds of oxide of lead (red-lead) and a similar
-quantity of litharge (yellow-lead). In an earthen vessel,
-or large jar, make a solution composed of water, twenty
-ounces, and commercial sulphuric acid, two ounces. This
-is the mixture commonly known as “one to ten.” Place
-some red-lead (dry) in an old saucepan or soup-plate, and
-add a little of the acid solution: then, with an old table-knife<span class="pagenum" id="Page25">[25]</span>
-or small trowel, mix the lead into a stiff paste, like
-soft putty. Do not get it too thin or it will run; nor too
-thick, as then it will not properly adhere to the lead-mesh
-of the frames. With the frame lying on its side, plaster
-in the red composition between the flutes and fill up the
-frame solid with it. Treat all three of the positive frames
-in the same manner, taking care that the exposed surfaces
-of the composition-filling is smooth and flush with the edges
-of the lead frame and mesh. Do not disturb these plates
-for a while, but let them remain in position, so as to set and
-partially dry. Add acid solution to the yellow-lead in a
-similar manner, and fill the four negative plates. When
-partially dry, the plates will be ready to combine in a pile.</p>
-
-<div class="container m40">
-<a id="FigII14"></a>
-<a id="FigII15"></a>
-<a id="FigII16"></a>
-<a id="FigII17"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo026.jpg" alt="Batteries; fluting tool" />
-</div>
-
-</div><!--container-->
-
-<p>At a supply-house obtain some sheets of cellulous fibre,
-three-sixteenths of an inch thick, or some asbestos cloth.
-If neither can be had, then soak some pieces of ordinary
-brown card-board in a solution of silicate of soda and let
-them dry. Lay a negative (yellow) plate on the table with
-the lug at the left (<a href="#FigII13">Fig. 13</a> C). On this place a square of
-the fibre, asbestos, or card-board; and on top of it lay a
-positive (red) plate with the lug at the right side. Continue
-in this manner until the seven plates are stacked, the four
-negative lugs being at the left and the three positives at
-the right. Tie the plates securely together with cotton
-string bound about them in both directions; then stand the
-pile up so that the lugs are at the top, as shown at <a href="#FigII15">Fig. 15</a>,
-with every alternate lug in an opposite direction. Obtain
-two lead bars three-eighths of an inch square, or cut strips
-from the sheet-lead and solder them together, turning the
-ends as shown at <a href="#FigII13">Fig. 13</a> D. Drop one of these bars into<span class="pagenum" id="Page26">[26]</span>
-the lugs of the positive plates, as shown in <a href="#FigII15">Fig. 15</a> H, and
-solder it fast at the three unions. Repeat this with the
-other bar in the lugs of the negative plates, and the pile will
-then be ready for immersion in the electrolyte. To both
-ends of each plate-bar solder binding-posts, so that the conductor-wires
-can be attached at one end and the feed-wires
-at the other. If a hard rubber or glass cell can be had for
-the battery so much the better; if not, a stout box may be<span class="pagenum" id="Page27">[27]</span>
-made from pine, white-wood, or cypress, and thoroughly
-coated with asphaltum varnish or asphaltick. At an electrical
-supply-house you can purchase some “P and B”
-compound, which is acid and water proof. This is excellent
-for the inside coating as well as for the outside of the box.</p>
-
-<p>The box should be made of wood not less than three-quarters
-of an inch thick, and the sides, ends, and bottom
-should be in one piece, free from knots, sappy places, or
-cracks. Brass screws should be used to hold the boards
-together, and before the joints are made the butt-ends of
-wood and the sides, against which they impinge, must be
-thoroughly coated with the asphaltum or compound. Put
-together the four sides first and then make the bottom fast,
-placing the screws two inches apart and countersinking the
-wood, so that the screw-heads will lie flush, as shown in <a href="#FigII16">Fig.
-16</a>. The box should be large enough to allow about one
-inch of space all around the pile, and deep enough for the
-solution to cover the plates and two inches of space above it
-to the top edge of the cell. The complete storage-battery
-will then appear as shown in <a href="#FigII17">Fig. 17</a>.</p>
-
-<p>The electrolyte is composed of sulphuric acid and water
-in the proportion of one ounce of acid to four of water,
-making a five-part solution. This should be mixed in an
-earthen or glass jar, and the acid poured slowly into the
-water, the latter being stirred while the acid is added.
-When the solution cools (for adding acid to water creates
-heat), add about two ounces of bicarbonate of soda, and
-mix the solution thoroughly.</p>
-
-<p>When the pile is in place within the box (having first
-removed the string which bound the plates together) pour<span class="pagenum" id="Page28">[28]</span>
-the electrolyte slowly into the cell, taking care that none of
-it spatters, for it will eat clothing or anything else that it
-touches. Before placing the pile, or electrolyte, in the box,
-it should be thoroughly tested for leaks by allowing water
-to stand in it for several days. Indeed, you should be very
-generous with the asphaltum, or compound, when coating
-the angles and points inside the box; for if the acid solution
-gets at the screws it will corrode them and the box will soon
-leak and fall apart. As a precaution against the acid working
-over the top of the box, the upper edge, for an inch or
-two, should be coated with paraffine over the asphaltum or
-acid-proof coating.</p>
-
-<p>A cell constructed in this way should accumulate about
-two volts and one hundred ampere-hours, and will run a
-one-sixteenth horse-power motor. The expense of making
-these plates is about twenty-five cents each, and, including
-the cell and coating materials, each storage-battery will cost
-approximately two dollars. The lasting qualities of the
-battery depend on the use or abuse it is put to; but with
-ordinary care it should last from three to five years.</p>
-
-<p>When the battery ceases to accumulate properly the pile
-should be removed, and, after washing it thoroughly, the
-bars should be cut away and new positive plates made and
-installed. The positive plates are the ones that deteriorate
-and need replacing; the negatives are almost everlasting,
-and with proper usage will live for fifteen or twenty years.</p>
-
-<p>Directly the electrolyte is in the cell, connect the poles of
-your primary cells so as to begin the accumulation of current.
-Never exhaust the charge of electricity from your
-storage-cell, and never leave it uncharged when the electrolyte<span class="pagenum" id="Page29">[29]</span>
-is in, or the plates will be ruined. A battery consisting
-of from five to twenty bluestone cells will be the best with
-which to charge this accumulator; and if more than one cell
-is desired, any number of them can be made and coupled
-up in series. Take care, when connecting the wires from
-the primary cells, to see that the positive wire is connected
-with the positive plates and the negative with the lead bar
-joining the yellow plates. If by accident you should make
-a misconnection, bubbles will rise from the electrolyte. This
-is not right, so reverse the wires and the accumulation of
-current will then take place without agitation in the cell.</p>
-
-<h4>Dry-cells and Batteries</h4>
-
-<div class="figright m20" id="FigII18">
-<img src="images/illo030.jpg" alt="Battery" />
-</div>
-
-<p>Dry-cells are extensively used nowadays, since their cleanliness,
-high efficiency, and low internal resistance make them
-preferable to the Leclanché and other open-circuit batteries
-for bells, annunciators, and other light work. In the
-dry-cell, the electrolyte, instead of being a liquid, is a gelatinous
-or semi-solid mass, which will not run nor slop over.
-When the capping of pitch or tar is in place, the cell may be
-placed in any position, with full assurance that the electrolyte
-will not become displaced nor run out. Dry-cells may
-be made of almost any size for convenience of handling, but
-those commonly used vary from one to four inches in diameter,
-and from four to fifteen inches high. For bells and
-general electric work, a cell two inches and a half in diameter
-and seven inches high will be found a convenient size to
-make and handle.</p>
-
-<p><span class="pagenum" id="Page30">[30]</span></p>
-
-<p>The component parts of a dry-cell are the cell itself (which
-is made of zinc and acts as the positive pole), the carbon, the
-electrolyte or active excitant element, and the pitch or tar
-cap to hold the electrolyte and carbon in place.</p>
-
-<p>From a tinsmith obtain some pieces of sheet zinc, and roll
-them into cylindrical form as shown in <a href="#FigII18">Fig. 18</a> A. The
-sheets should measure seven by eight inches, and when
-formed the edges are to be lapped and soldered.</p>
-
-<p>From a smaller piece of
-zinc cut round bottoms, fit
-them in the cylinders and
-solder securely in place,
-taking care to close up
-all seams or joints to prevent
-the escape of the
-electrolyte.</p>
-
-<p>From a supply-house obtain
-battery-carbons, one
-inch and a half wide by
-half or three-eighths of
-an inch thick and eight
-inches long. These should be provided with a thumb-screw
-or small bolt and nut at the top so as to make wire connections
-with the carbon. A strip of zinc should be soldered
-to the outside upper edge of the zinc cup to which wire
-attachments may be made with thumb-screws or small bolts
-and nuts. When the parts are ready to assemble, make a
-wooden mould or form a trifle larger than the carbon. This
-is intended to act as a temporary plunger, and is inserted,
-at first, in place of the carbon plate. This wooden plunger<span class="pagenum" id="Page31">[31]</span>
-should be smooth, and given a coat of shellac to prevent it
-from absorbing any moisture.</p>
-
-<p>Insert the plunger in the zinc cup and support it so that it
-will be at least half an inch above the bottom and centred
-at the middle of the cup. The electrolyte is then placed in
-the cup, and, when it has set a little, the wooden plunger
-is removed and the carbon inserted in its place.</p>
-
-<p>The electrolyte is composed as follows:</p>
-
-<table class="dontwrap fsize80" summary="Electrolyte">
-
-<tr>
-<td class="left padr3">Ammonium chloride</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Zinc chloride</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Plaster of Paris</td>
-<td class="left padl3">3 parts</td>
-</tr>
-
-<tr>
-<td class="left padr3">Flour</td>
-<td class="left padl3">¾ part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Water</td>
-<td class="left padl3">2 parts</td>
-</tr>
-
-</table>
-
-<p>Mix these together and place the compound within the zinc
-cups, so that the mass settles down and packs closely about
-the plunger. The space left unfilled about the carbon
-should be filled with a mixture composed as follows:</p>
-
-<table class="dontwrap fsize80" summary="Electrolyte">
-
-<tr>
-<td class="left padr3">Ammonium chloride</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Zinc chloride</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Manganese binoxide</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Granulated carbon</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Flour</td>
-<td class="left padl3">1 part</td>
-</tr>
-
-<tr>
-<td class="left padr3">Plaster of Paris</td>
-<td class="left padl3">3 parts</td>
-</tr>
-
-<tr>
-<td class="left padr3">Water</td>
-<td class="left padl3">2 parts</td>
-</tr>
-
-</table>
-
-<p>These proportions may be measured in a tin cup, a table-spoon,
-or any other small receptacle. Note that the measurement
-by parts is always by bulk and not by weight.</p>
-
-<p>Do not fill the zinc cup to the top, but leave an inch of
-space, so that half an inch of sealing material may be added.
-See that the inside top edge of the zinc cup is clean; then<span class="pagenum" id="Page32">[32]</span>
-melt some tar or pitch and pour it over the top of the electrolyte,
-so that it binds the zinc cup and carbon into a solid
-form. Drive an awl down through the capping material
-when it is nearly dry, and leave the holes open for the
-escapement of gases.</p>
-
-<p>Give the outer surface of the zinc cells a coat of asphaltum
-varnish, and wrap several thicknesses of heavy paper about
-them to prevent contact and short-circuiting. Protect the
-bottoms in a similar manner, and as a result you will have
-a cell that will appear as shown in <a href="#FigII18">Fig. 18</a> B. A battery
-of cells powerful enough for any light work can be made
-by connecting the cells in series, each having an electro-motive
-force of one and a half volts, with an internal resistance
-of less than one-third of an ohm.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page33">[33]</span></p>
-
-<h3>Chapter III<br />
-<span class="chaptitle">PUSH-BUTTONS AND SWITCHES</span></h3>
-
-<h4>Push-buttons</h4>
-
-<p class="chapstart"><span class="largecap">P</span><span class="afterlargecap">ush-buttons</span>
-and switches are a necessity in every
-home where electric bells, lights, or fans are used, for
-with them connections are made or broken. The telegraph-key
-and the commutators on a motor and dynamo are only
-improved forms of the push-button, and this simple little
-device is really an indispensable part of any electrical equipment.</p>
-
-<p>The simplest form of push-button is a bent piece of tin or
-thin sheet-metal screwed fast to a small block of wood, as
-shown in <a href="#FigIII1">Fig. 1</a>. Under the screw-head one end of a wire
-is caught, and the other wire end is secured by a washer and
-a screw driven into the block directly under the projecting
-end of the strip of metal. By pressing a finger on the tin
-it is brought into contact with the screw-head under it, and
-the circuit is closed; on releasing it, the tin flies up and the
-circuit is opened again.</p>
-
-<p>An enclosed push-button is shown in <a href="#FigIII2">Fig. 2</a>. It is made
-of the cover or body of a wooden box, a spool-end, and several
-other small parts. A round piece of thin wood is cut
-to fit inside the box and so form the base for the button.<span class="pagenum" id="Page34">[34]</span>
-On this the spring strip is attached with screws, and the
-wire ends are made fast, as shown in <a href="#FigIII3">Fig. 3</a>. The wires are
-carried through the bottom of the base and along grooves to
-the edge, and thence to their final destination. The end of
-a spool is cut off and glued to the top of the box, as shown
-in <a href="#FigIII2">Fig. 2</a>, and a hole is made in the box to correspond in size
-with that in the spool. Through this aperture the button
-(cut from a wooden dowel or shaped out with a knife) passes,
-so that the end projects about a quarter of an inch beyond
-the spool. To prevent the button from falling out, a small
-steel nail should be driven across the inner end, or a washer
-may be tacked to the end of the stick, as shown in <a href="#FigIII4">Fig. 4</a>.</p>
-
-<div class="container m40">
-<a id="FigIII1"></a>
-<a id="FigIII2"></a>
-<a id="FigIII3"></a>
-<a id="FigIII4"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo034.jpg" alt="Buttons" />
-</div>
-
-</div><!--container-->
-
-<p>The button is mounted by screwing the base fast to the
-door or window casing, it being understood that the wires
-have been first arranged in place. The button is then set<span class="pagenum" id="Page35">[35]</span>
-in the hole and the cap is placed over the base, covering it
-completely. By means of small screws, passed through the
-rim of the box and into the edge of the base, the cap is held
-in place. A coat of paint or varnish will finish the wood-work
-nicely, and this home-made button should then answer
-every requirement.</p>
-
-<h4 id="Ref005">Switches and Cut-outs</h4>
-
-<p>In electrical equipment and experimental work, switches
-and cut-outs will be found necessary, particularly so for
-telegraph and telephone lines. Care should be taken to
-construct them in a strong and durable fashion, for they
-will probably be subjected to considerable wear and tear.</p>
-
-<p>A simple switch (<a href="#FigIII5">Fig. 5</a>) is made from a base-block of
-wood three inches long, two wide, and half an inch in thickness,
-together with some small metal parts. It has but one
-contact-point, and that is the brass-headed tack (T in <a href="#FigIII5">Fig. 5</a>)
-driven through the binding-post, the latter being a small
-plate of brass, copper, or even tin screwed to the base-block.
-The end of a wire is caught under the screw-head before it
-is driven down. A similar binding-post is arranged at the
-lower side of the block, and the movable arm is attached to
-it with a screw. Between the arm and the post-plate there
-should be a small copper washer, to make it work more
-easily. The arm is cut from a thin piece of hard sheet brass
-or copper (tin or zinc will also answer very well), and at the
-loose end the half of a small spool is attached, with a brass
-screw and washer, to serve as a handle. The end of the
-screw that passes through a hole in the arm is riveted to the<span class="pagenum" id="Page36">[36]</span>
-under side to hold it securely in place. This arrangement
-is shown in <a href="#FigIII6">Fig. 6</a>.</p>
-
-<div class="container">
-<a id="FigIII5"></a>
-<a id="FigIII6"></a>
-<a id="FigIII7"></a>
-<a id="FigIII8"></a>
-<a id="FigIII9"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo036.jpg" alt="Switches" />
-</div>
-
-</div><!--container-->
-
-<p>The under edges of the arm may be slightly bevelled with a
-file, so that it will slip up easily on the oval head of the brass
-tack. The drawing shows an open switch; when the circuit
-is closed the arm rests on the tack-head. By means of small
-screws this switch-board may be fastened to a table or to
-any part of the wood-work in a house.</p>
-
-<p>In <a href="#FigIII7">Fig. 7</a> a complex switch is shown. This is the principle
-of the shunt-box switch, of the resistance-coil, and also of
-the commutators of a motor. A motorman’s controller on
-a trolley-car is a good example of the shunt, and, with it
-and the resistance-coils, the car can be started, stopped, or
-run at any speed, according to the current that is admitted
-to the motor.</p>
-
-<p>The complex switch is made in the same manner as described
-for the single switch, except that any number of
-binding-posts may be employed, arranged on a radial plan,
-so that the end of the arm will rest on any tack-head at will.
-Bells in various parts of the house may be rung by this<span class="pagenum" id="Page37">[37]</span>
-switch, or it may be coupled with a series of resistance-coils
-to control any amount of current.</p>
-
-<p>The simple cut-out (<a href="#FigIII8">Fig. 8</a>) is constructed in the same
-manner as the simple switch, except that there are two
-points of contact instead of one. This is the principle of
-the telephone and telegraph instrument wiring, so that a
-bell or sounder may be rung from a distance. The arm is
-then thrown over and the bell cut out, allowing the “phone”
-or key to be brought into use. In lifting the transmitter
-from the hook on a telephone, a cut-out is operated and
-the bell circuit is thrown out of action. It is in operation
-again directly the transmitter is returned to the hook.
-The switch cut-out (<a href="#FigIII9">Fig. 9</a>) is inactive when the arm is in
-the position shown in the illustration; but when it is thrown
-over (as shown by the dotted line) it connects the poles at
-opposite ends of the board. It may be thrown over in both
-directions, and is a useful switch for many purposes.</p>
-
-<p>For strong currents the lever-switch, that rests on a brass
-tack-head, will not be suitable, as the switch-bar must be
-held firmly in place to make a perfect connection. Strong
-currents throw weak switches open, causing an open or
-broken circuit.</p>
-
-<p>A single pole-switch, to carry a current up to one hundred
-and twenty-five volts and twenty-five amperes, is shown in
-<a href="#FigIII10">Fig. 10</a>. This consists of a base-block, a bar which is attached
-to the vertical ears of a binding-post, and a clutch
-that will hold the bar when it is pressed down between the
-ears.</p>
-
-<p>The base-block should be made from some non-conducting
-material, such as soapstone, marble, or slate. If a piece of<span class="pagenum" id="Page38">[38]</span>
-soapstone can be procured, that will be just the thing, since
-it is easily worked into the proper shape and size. Soapstone
-may be sawed and smoothed with a file; it is easily
-bored into with a gimlet-bit, and it is one of the best non-conducting
-substances. The base for this switch is six
-inches long, two inches wide, and as thick as the soapstone
-happens to be&mdash;say three-quarters of an inch. The top
-edge may be bevelled for the sake of appearance or left
-square.</p>
-
-<p>Two pieces of heavy sheet copper or brass are to be cut
-as shown at A in <a href="#FigIII11">Fig. 11</a>. The ears are half an inch wide,
-and the total height of the strip is two inches and a half,
-while the part with two holes in it side by side is one inch
-and a quarter long, including the half-inch width of the
-vertical strip. With round and flat-nosed pliers bend the
-long ears into shape, so as to form a keeper for the bar which
-is then to be riveted in place. Omit the holes at the ends
-of the long ears in the other plate; then bend it into shape
-to form a clutch that will hold the bar when it is pressed
-down between the ears. These binding-posts should be
-made fast to the base-block with brass machine-screws and
-nuts, which will fit in countersunk holes in the bottom of
-the soapstone. If hard-wood is used for the base, ordinary
-brass wood-screws will answer very well.</p>
-
-<p>The connection-bar is cut from metal the same thickness
-as that employed for the binding-posts and clutches; it
-should be shaped so as to appear as shown at B in <a href="#FigIII11">Fig. 11</a>.
-A handle should be driven on the slim end, and where the
-lower edge enters between the ears of the clutch, the corners
-of the bar should be rounded with a file. Countersunk<span class="pagenum" id="Page39">[39]</span>
-screw-holes are bored in the base, so that it can be made
-fast to the wood-work.</p>
-
-<div class="container m40">
-<a id="FigIII10"></a>
-<a id="FigIII11"></a>
-<a id="FigIII12"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo039.jpg" alt="Switches" />
-</div>
-
-</div><!--container-->
-
-<p>A double pole-switch is shown in <a href="#FigIII12">Fig. 12</a>, and in general
-construction it is similar to the single pole-switch described
-above. The binding posts and bars are cut and bent from
-the patterns A and B in <a href="#FigIII11">Fig. 11</a>; but in this case the long,
-slim ends of the bars are omitted. A short turn is made at
-the handle end of each bar and a hard-wood block is placed
-between the bar-ends and held in position with screws
-driven through holes made in the bars and into the ends of
-the block. A handle is made fast to the middle of the block<span class="pagenum" id="Page40">[40]</span>
-with a long and slim wood-screw; or a steel-wire nail may
-be passed through the handle and block, a burr slipped over
-the end opposite the head, and the small end riveted fast.
-When the binding-posts (to which the ends of the bars are
-attached) are screwed onto the base, be sure and see that
-the bars are parallel and the same distance apart at both
-ends. In like manner, when the cleat binding-posts are
-made fast, see that they are directly in line with the bars,
-so that the yoke will drop into the spaces between the ears
-without having to be pulled to one side or the other. This
-is a very useful switch for strong currents, and may be
-placed close to a dynamo, so that the current in both wires
-may be cut out at once.</p>
-
-<h4>Table-jack Switches</h4>
-
-<p>A table-jack switch is a most convenient piece of apparatus
-where several lines of bells, alarms, or telephone circuits
-are to be switched on and off.</p>
-
-<p>The single table-jack switch, shown in <a href="#FigIII13">Fig. 13</a>, is made of
-a hard-wood block three-quarters of an inch thick, five
-inches wide, and seven inches long. It is to be smoothed
-and varnished, or given several coats of shellac. At the
-four corners small holes are made to receive slim screws,
-and at one end of the block five short metal plates are
-screwed fast, with the heads of the screws countersunk, so
-that they will be flush with the top of the plates. These
-small plates should be half an inch wide and one inch long,
-and may be of brass, copper, or tin. But if they are of tin
-the plates are made of a longer strip tacked to the board<span class="pagenum" id="Page41">[41]</span>
-and then bent over, as shown at A in <a href="#FigIII14">Fig. 14</a>. They will
-therefore form short springs, the upper parts of which will
-rest against the long spring-arms. From spring brass or
-copper five arms are to be cut and shaped, as shown in
-<a href="#FigIII13">Fig. 13</a>. Holes are made at one end of each, and others
-again two inches from these, through which to pass screws.</p>
-
-<p>Screw-eyes are passed through copper washers and the
-end holes in the strips, and then screwed into the wood plate.
-These will act as binding-posts, while the second line of
-screws will hold the plates down to the base. The arms
-should be bent, so that when the screws are driven down the
-lower edge will press on the small plates under them.</p>
-
-<p>The outlet wires are attached to the binding-posts at the
-head of the block, and the plug (A in <a href="#FigIII13">Fig. 13</a>) is inserted
-between the arm and plate at the foot, so that contact and
-connection are made. This plug is a small plate of metal to
-which the end of a flexible wire is made fast. It should be
-of copper or brass, but for light work a strip of tin may be
-bent over with the wire caught between the plates and a
-copper tack passed through the sides and riveted, as shown
-at B in <a href="#FigIII14">Fig. 14</a>.</p>
-
-<p>A double jack-switch (<a href="#FigIII15">Fig. 15</a>) is made on the same general
-plan as the single, but it has no binding-posts. A block of
-the same size is used, and two rows of short plates are made
-fast at each end. The arms are made with two screw-holes
-near the middle, as shown in <a href="#FigIII15">Fig. 15</a>, and through these
-holes screws are driven to hold the arms down to the base.
-Several plugs are used for each end, so that the in and out
-lines can be shifted, and from one to four lines used at a
-time.</p>
-
-<p><span class="pagenum" id="Page42">[42]</span></p>
-
-<div class="container m40">
-<a id="FigIII13"></a>
-<a id="FigIII14"></a>
-<a id="FigIII16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo042a.jpg" alt="Switches" />
-</div>
-
-<div class="figcenter nomargin" id="FigIII15">
-<img src="images/illo042b.jpg" alt="Switches" />
-</div>
-
-<p class="caption">TABLE-JACK SWITCHES</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page43">[43]</span></p>
-
-<p>A convenient slip-switch for single or double line work
-is shown in <a href="#FigIII16">Fig. 16</a>. This consists of a small wooden base,
-on which a brass arm and handle are screwed fast and
-connected with a binding-post (A in <a href="#FigIII16">Fig. 16</a>). A slip-plate
-is made from a piece of sheet-brass and bent so as to form
-a pocket into which the arm will fit. This pocket piece is
-connected with the binding-post B. When the switch is
-thrown out the circuit is broken, unless a contact-point, C,
-is provided, from the under side of which a wire leads out
-to a second circuit. When the switch is in place, as shown
-in <a href="#FigIII16">Fig. 16</a>, the circuit is closed through A and B; but when
-the arm is thrown out the circuit through A and B is broken
-and that through A and C is closed.</p>
-
-<h4 id="Ref004">Binding-posts and Connectors</h4>
-
-<p>To make quick connections between wires and other
-parts of electrical apparatus, binding-posts are the most
-convenient device, since the turn of a screw binds or releases
-a wire instantly. Binding-posts may be made in many
-forms, but the simple ones that a boy will need can be made
-from screw-eyes, burrs, stove-bolts, and nuts, together with
-thin strips of metal and nails.</p>
-
-<p>Five simple posts are shown in <a href="#FigIII17">Fig. 17</a>. A is made from
-a screw and two burrs, B from a screw-eye and two burrs,
-and C from a thin plate of metal and two screws, with oval
-or round heads. This last, however is more of a connector
-than a binding-post. The ends of the wires to be connected
-should be caught under the screw-heads or between the
-burrs before the screws are driven down.</p>
-
-<p><span class="pagenum" id="Page44">[44]</span></p>
-
-<p>In D a simple arrangement of a stove-bolt and two nuts
-is shown. The under bolt is screwed down tightly against
-the wood, and under the head a wire is made fast, so that
-another wire may be caught under the upper nut. If a
-small thumb-nut can be had in place of the plain nut, it will
-be easier to bind the upper wire. In <a href="#FigIII17">Fig. 17</a> E a thin
-strip of metal may be folded over, and at the loose ends a
-hole should be punched through which a screw-eye will
-pass. The metal is held to a wood base with a screw, under
-the head of which a wire is caught. The second wire end is
-slipped between the metal plates, and a turn of the screw-eye
-will bind and hold it securely.</p>
-
-<div class="container m40">
-<a id="FigIII17"></a>
-<a id="FigIII18"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo044.jpg" alt="Connectors" />
-</div>
-
-</div><!--container-->
-
-<p>Connectors are employed to unite the ends of wires
-temporarily, and are made in many forms. A simple and
-useful one is made from a piece of spiral spring fastened to
-a block of wood by two staples, as shown at <a href="#FigIII18">Fig. 18</a> A.<span class="pagenum" id="Page45">[45]</span>
-The ends of the wires are pressed down into the coils of the
-spring and are held with sufficient security for temporary
-use. Another connector is made from a block of wood, a
-strip of thin metal, and two screw-eyes (<a href="#FigIII18">Fig. 18</a> B). The
-metal is bent around the ends of the block, and through
-holes made in the ends of the strip screw-eyes are driven into
-the block. When the ends of wires are slipped under the
-metal, a turn of the eyes will hold them fast, as shown at
-<a href="#FigIII18">Fig. 18</a> B.</p>
-
-<p>A short bolt threaded at each end and provided with four
-nuts will also act as a connector. The inner nuts are screwed
-on tightly and the outer ones are loose, so that when
-wires are placed between them they may be tightened with
-the fingers, as shown at C in <a href="#FigIII18">Fig. 18</a>. These are a few simple
-forms of connectors; the ingenious boy can devise many
-others to suit his needs and ideas.</p>
-
-<h4>Lightning-arresters and Fuse-blocks</h4>
-
-<p>All lines of exposed wire that run from out-doors into
-the house should be provided at both ends with lightning-arresters,
-particularly if they are telephone or telegraph
-lines, burglar alarms, or messenger call-boxes. In many
-instances where unprotected telephone lines have been the
-plaything of lightning, painful accidents have happened,
-and it is only the part of prudence to provide against them.
-It is better to have an arrester at both ends of a line, and
-as the cost is insignificant it is hardly worth considering as
-against its feature of safety.</p>
-
-<p>Lightning-arresters may be constructed in many ways<span class="pagenum" id="Page46">[46]</span>
-and of different materials; the ones here shown and described
-are easily made and efficient. The principle of all
-arresters is simply a fuse which burns out whenever the wire
-is carrying a greater amount of current than is required for
-the proper working of the apparatus, thereby arresting the
-current and protecting the instruments from destruction.
-Induction-coils, relays, fine windings on armatures, or a
-magnet helix are quickly destroyed if a too powerful current
-is permitted to pass through them, and it is therefore
-advisable to protect them. When a fuse burns out under a
-trolley-car, or in the shunt-box of a motor-car or engine,
-it is because a greater amount of current is trying to pass
-in than the motor will safely stand. When a fuse “blows
-out,” the apparatus or motor is put out of commission until
-the fuse is replaced, but the delicate mechanism and the fine
-wiring on the field-magnets or armatures are saved.</p>
-
-<p>The simplest form of single pole-fuse is a fine piece of
-lead wire held between two binding-posts, as shown at A in
-<a href="#FigIII19">Fig. 19</a>. The lead wire may be of any length; but for small
-instruments, where a moderate current is employed and
-where there is a possibility of lightning travelling on the
-wire, the fuse should be from two to three inches long.
-For inside work, however, where it is to be used simply as
-a safety, the wire may be shorter and finer.</p>
-
-<p>To make the lightning-arrester shown in <a href="#FigIII19">Fig. 19</a>, cut out
-a hard-wood block five inches long, an inch wide, and half
-an inch thick. Give this several coats of shellac; then place
-a piece of mica, or asbestos paper, over the top of the block,
-and make it fast with thick shellac to act as a glue. From
-small pieces of copper or brass cut two plates one-half by<span class="pagenum" id="Page47">[47]</span>
-one inch, and drill holes in them to take screws and screw-eyes.
-Place copper burrs under the screw-eyes for connectors,
-and drive two brass screws half-way down in the block
-through the holes at the inner ends of the binding-post
-plates. See that these screws fit snugly in the holes in the
-plates so that contact is perfect. If the holes are too large
-and the screws fit loosely, two copper burrs will have to be
-used and the screws driven in, so that the heads bind the
-burrs on the ends of the fuse-wire. From an electrician, or
-supply-house, purchase a few inches of fine lead fuse-wire&mdash;say
-Nos. 20, 22, or 24&mdash;and twist the ends of a length around
-the screws, as shown in the drawing. Perfect contact should
-be had between the lead wire and the screws; by way of
-precaution, a bit of solder will dispel all doubt. Just touch
-the point with a little soldering solution; then apply a
-soldering-iron having a drop or two of solder on the end.</p>
-
-<p>Perfect connection is absolutely necessary for telephone,
-telegraph, or annunciator work, and where there is a lightning-arrester
-and the line is not working well, the trouble
-may often lie in the poor contact of lead and brass or copper,
-or possibly in using wire that is too fine. Lead is a very
-poor conductor, and a fine wire would act as a check. For
-a test, first insert a piece of copper wire to see that the line
-is working properly; then use lead wire of sufficient size to
-carry the current as well as the copper did. The action of
-metals and wire, as current retarders, will be explained in
-the <a href="#Page125">chapter</a> on resistance and resistance-coils.</p>
-
-<p>For general commercial use the base-blocks of all lightning-arresters
-should be made of porcelain, slate, or some
-of the composition non-conductors, such as moulded mica,<span class="pagenum" id="Page48">[48]</span>
-silex and shellac, or fibre. As these are not always available,
-wood, with a covering of mica, will answer every purpose
-and can be readily adapted for use.</p>
-
-<p>The apparatus pictured in <a href="#FigIII19">Fig. 19</a> is known as a single-pole
-lightning-arrester, and is the simplest form of this kind
-of electrical paraphernalia. In <a href="#FigIII20">Fig. 20</a> a double-pole arrester
-is shown. This is constructed in the same manner
-as described for the single one. The block is five inches
-long, two inches wide, and half or five-eighths of an inch
-thick. A countersunk hole is made in the middle of all the
-lightning-arrester blocks through which a screw can be
-passed to hold the apparatus fast in any desired location.</p>
-
-<p>In <a href="#FigIII21">Fig. 21</a> another form of fuse is shown. It is made
-from a piece of mica three-quarters of an inch wide and four
-inches long, two pieces of thin sheet-copper, and a piece of
-lead fuse-wire. The copper is three-quarters of an inch
-wide, and one piece of it is bent in the form of a <span class="symbol">V</span>, as shown
-at A in <a href="#FigIII21">Fig. 21</a>. One end of the mica strip is dropped in the
-<span class="symbol">V</span>, and with a pair of pliers the <span class="symbol">V</span> is closed up by pinching
-it at the bottom. To further insure its staying in place, the
-top and end, or open edges, should be soldered. Punch a
-small hole through the copper ends, at the inside edge, slip
-the ends of the fuse-wire in them, and touch the union with
-a drop of solder to insure perfect contact. With shears and
-file cut a <span class="symbol">U</span> from the side of one copper band and from the
-end of the other; these will allow the copper ends to pass
-under the heads of screws, thus avoiding the necessity of
-removing the entire screw from the block in order to set the
-fuse in place.</p>
-
-<p><span class="pagenum" id="Page49">[49]</span></p>
-
-<div class="container m40">
-<a id="FigIII19"></a>
-<a id="FigIII20"></a>
-<a id="FigIII21"></a>
-<a id="FigIII22"></a>
-<a id="FigIII23"></a>
-<a id="FigIII24"></a>
-<a id="FigIII25"></a>
-<a id="FigIII26"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo049a.jpg" alt="" />
-</div>
-
-<div class="figcenter nomargin">
-<img src="images/illo049b.jpg" alt="" />
-</div>
-
-<p class="caption">LIGHTNING-ARRESTERS AND FUSE-BLOCKS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page50">[50]</span></p>
-
-<p>The block on which this fuse is held is shown in <a href="#FigIII22">Fig. 22</a>,
-and is made in a similar manner to the one shown in <a href="#FigIII19">Fig. 19</a>,
-except that the metal plates are a trifle longer and are
-bent up, as shown in the drawing. Thus the mica fuse-plate
-will be elevated above the block. If the brass or copper
-used for the binding-post plates is too thin to stand the
-pressure of the screws when the fuse ends are screwed fast,
-put a few burrs on the screws below the plates; then the
-pressure of the screws cannot bend down the extending ears
-of the plates and make an imperfect contact.</p>
-
-<p>Another form of fuse-block is shown in <a href="#FigIII23">Fig. 23</a>. The
-same sort of a fuse is employed as shown in <a href="#FigIII21">Fig. 21</a>, but
-without the <span class="symbol">U</span> cuts at the ends. The clutches are made by
-binding brass or copper plates, as shown in the drawing;
-they should then be screwed fast to a base-block five inches
-long, one inch and a half wide, and five-eighths of an inch
-thick. The opening between them should just admit the
-copper ends of the fuse, and pressure should be used to force
-the fuse in place so that the contact will be perfect.</p>
-
-<p>Still another form of fuse is shown in <a href="#FigIII24">Fig. 24</a>. This last
-may more properly be called a non-sparking fuse, for the
-lead wire is encased in a glass tube, and when it fuses no
-sparks fly and no small pieces of melted metal can get away
-from the inside of the tube. The plug is made from a piece
-of glass tube half an inch in diameter, two metal caps, and
-a short piece of lead wire. The metal caps are of thin
-sheet-copper, and are caught at the edges with solder. One
-end of the lead fuse-wire is passed through a hole in the
-end of a cap and soldered, as shown at A in <a href="#FigIII24">Fig. 24</a>. The
-wire is then passed through the tube and the cap placed
-over one end of it. This is repeated at the other end and<span class="pagenum" id="Page51">[51]</span>
-the wire soldered fast. As a result, you will have a glass
-tube with metal caps held on the ends of the tube, by means
-of the thin lead wire which runs through the middle of the
-tube. The base-block to which this fuse-plug is attached
-is of wood one inch and a half wide, five or six inches long,
-and five-eighths of an inch thick. Two metal straps are
-made and screwed fast to the block, and the circuit wires
-are attached under the copper burrs and held down by the
-screw-eyes.</p>
-
-<p>To place or replace a fuse-plug, unscrew the eyes and raise
-each strap slightly, so that the copper cap ends will pass
-under them. A turn or two of the eyes will clamp the plug
-in position and at the same time bind the circuit wires.</p>
-
-<p>A spring lightning-arrester is shown in <a href="#FigIII25">Fig. 25</a>; it is
-simply a modified form of that shown and described in <a href="#FigIII19">Fig.
-19</a>. The base-block is five by one-and-a-quarter by five-eighths
-of an inch, and is properly protected by a sheet of
-mica or asbestos. The two metal plates are cut for the
-binding-posts and screwed in place with screws, burrs, and
-screw-eyes. From spring-brass wire bend a hook and slip
-one end of it under the screw-head at the left side of the
-block. From a longer piece of wire make two or three
-turns around a piece of wood half an inch in diameter; then
-form a hook at one end and a turn at the other, so that it
-can be made fast under the screw-head of the binding-post.
-When at rest, the spring-hook should stand in an upright
-position, but when sprung and tied it occupies the position
-shown in the drawing. The spring-hook is to be bent down
-so that the two hooks are brought within an inch of each
-other. They are held in this position with a piece of lead<span class="pagenum" id="Page52">[52]</span>
-fuse-wire. This last is given a turn about the hooks and
-one or two turns about itself, close to each hook, to prevent
-the spring from tearing itself away. When the wire is fused
-by a current the spring-hook flies up and away from possible
-contact with the short hook attached to the opposite binding-post.
-This is the construction for a single-pole-spring
-lightning-arrester; a double one is made in a similar manner,
-and the parts mounted on a wider block, as shown in
-<a href="#FigIII20">Fig. 20</a>.</p>
-
-<p>For doubtful currents, where there is no means of knowing
-how strong they are, a combined fuse and single-pole
-switch is shown in <a href="#FigIII26">Fig. 26</a>. This is nothing more than a
-combination of the apparatus shown in <a href="#FigIII21">Fig. 21</a>, and the
-single-pole switch (<a href="#FigIII10">Fig. 10</a>). The base block is seven inches
-long and two inches wide. Or it may be made half an inch
-wider if it is to be bevelled at the top, as shown in the drawing.
-It should be three-quarters of an inch thick and provided
-with two countersunk holes for screws that will hold
-it in place on a ledge or against a casement. The little
-angles to hold the copper-ended mica fuse-plate are described
-for the apparatus pictured in <a href="#FigIII21">Fig. 21</a>. If it is desired
-that one of the ends should be provided with burrs and a
-screw-eye, the little plate of brass should be an inch long and
-an inch wide, with a half-inch-square piece snipped from
-one corner, as shown at A in <a href="#FigIII26">Fig. 26</a>. It is provided with
-two holes, and then bent on the dotted line, so that the part
-with the holes will lie on the block and the ear will stand in
-a vertical position. A reverse-plate made on this pattern
-will act as one side of the switch-bar clutch at the opposite
-end of the block. For the metal clutch and keeper at the<span class="pagenum" id="Page53">[53]</span>
-middle of the block the metal plate (before it is bent) will
-appear as shown at B in <a href="#FigIII26">Fig. 26</a>. The long plate with two
-holes lies on the base, while the first ear (or the one without
-the hole) forms part of the clutch for the fuse end, the ear
-with the hole acting as one side of the bar-lever strap. An
-opposite plate to this forms the other side of the clutch and
-strap, and the two plates are screwed side by side, so that
-the fuse-plate will be held securely when pushed into place.</p>
-
-<p>For the switch-bar use a piece of hard copper or brass
-four inches long, half an inch wide, and about one-eighth of
-an inch thick, or the same thickness as the copper straps at
-the ends of the mica fuse-plate. Bore a hole at one end of
-this bar, and with a copper rivet attach it between the two
-upright ears at the middle of the block. With a file cut
-away the two edges at the other end of the bar for a distance
-of an inch, so that the bar will have an end as shown at C
-in <a href="#FigIII26">Fig. 26</a>. Drive a small file-handle on this end and give
-it a coat or two of shellac; then bevel the lower edges of
-the bar with a file where it enters between the blades of the
-clutch. The circuit wires are made fast at both ends of the
-block, and the current travels through the binding-posts,
-the lead fuse-wire on the mica plate D, and the switch-bar.
-If the current is too strong, then when the switch-bar is
-pushed into the clutch the safety-fuse will burn out and
-save the apparatus; or it will arrest a flash of lightning.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page54">[54]</span></p>
-
-<h3>Chapter IV<br />
-<span class="chaptitle">MAGNETS AND INDUCTION-COILS</span></h3>
-
-<h4>Simple and Horseshoe Magnets</h4>
-
-<p class="chapstart"><span class="largecap">E</span><span class="afterlargecap">very</span>
-boy has a horseshoe magnet among his collection
-of useful odds and ends, and whether it is a large or
-small one its working principle is the same. If large enough
-it will lift a jack-knife, nails, or solid weights, such as a
-small flat-iron or an iron padlock. A horseshoe magnet is
-made of highly tempered steel and magnetized so that one
-end is a north pole and the other a south pole. In more
-scientific language these poles are known as, respectively,
-positive and negative. Once magnetized the instrument
-retains that property indefinitely, unless the power is drawn
-from it by exposure to intense heat, and even then, by successive
-heating and cooling, the magnetism may be partially
-restored.</p>
-
-<p>An electro-magnet may be made of any scrap of soft
-iron, from a piece of ordinary telegraph-wire to a gigantic
-iron shaft. When a current of electricity passes through a
-wire a magnetic “field” is produced around the wire, and
-if the latter is insulated with a covering and coiled about a
-soft iron object, such as a nail, a bolt, or a rod, that object
-becomes a magnet so long as a current of electricity is passing<span class="pagenum" id="Page55">[55]</span>
-through the coils of wire or helix. A coil of wire in the
-form of a spiral spring has a stronger field than a straight
-wire carrying the same current, for each turn or convolution
-adds its magnetic field to that of the other turns.</p>
-
-<p>A simple form of electro-magnet is made by winding
-several layers of No. 20 insulated copper wire around a
-stout nail or a carriage-bolt; by connecting the ends to a
-battery of sufficient power, some very heavy objects may
-be lifted. A single magnet, like the one shown in <a href="#FigIV1">Fig. 1</a>,
-is made with a piece of soft iron rod six inches long and
-half an inch in diameter, the ends of a large spool sawed off
-and worked on the rod, and half a pound of No. 20 insulated
-copper wire. The spool-ends are arranged as shown in
-<a href="#FigIV2">Fig. 2</a>. An end of the wire is passed through a hole in one
-flange when you begin to wind the coils, and when finished,
-the other end is passed through a hole at the outer rim of the
-same flange. This magnet may be held in the hands when
-in use; or a hand-magnet may be constructed of a longer
-piece of iron on one end of which a handle is driven and
-held in place with a nut and washer, as shown in <a href="#FigIV3">Fig. 3</a>.
-The wires from the coil pass through holes made in the
-handle and come out at the butt end, where they may be
-attached by connectors to the pole-wires of a battery. To
-protect the outer insulated coil of wire from chafing and a
-possible short-circuit, it would be well to wrap several
-thicknesses of stout paper around the coil and glue it fast;
-or a leather cover will answer as well.</p>
-
-<p><span class="pagenum" id="Page56">[56]</span></p>
-
-<div class="container m40">
-<a id="FigIV1"></a>
-<a id="FigIV2"></a>
-<a id="FigIV3"></a>
-<a id="FigIV4"></a>
-<a id="FigIV5"></a>
-<a id="FigIV6"></a>
-<a id="FigIV7"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo056.jpg" alt="" />
-</div>
-
-<p class="caption">SIMPLE AND HORSESHOE MAGNETS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page57">[57]</span></p>
-
-<p>A more powerful magnet may be made from a stout bolt,
-two nuts, and a wooden base, with about three-quarters of
-a pound of No. 18 insulated copper wire to wind about the
-body of the bolt. A block of wood an inch thick, four
-inches wide, and six inches long is provided with a hole at
-the middle for the bolt to pass through. A larger hole is
-made at the under side of the block so that a nut can be
-easily turned in it. A three-quarter-inch machine-bolt,
-with a square head, and seven inches long, is set in the
-block, head up, as shown in <a href="#FigIV4">Fig. 4</a>; and composition or thin
-wooden disks or washers are placed on the bolt to hold the
-coils of wire in place. The ends of the wire pass out through
-the bottom washer and are made fast to binding-posts on
-the block, and to these latter the battery-poles are made
-fast when the magnet is in use. Coils of wire may be wound
-on an ordinary spool, and the hole in the middle may be
-filled with lengths of soft iron wire. When a current is
-passing around the spool the wires become highly magnetic,
-but lose the magnetism directly the current ceases.</p>
-
-<p>Horseshoe electro-magnets are made by winding coils on
-the ends of <span class="symbol">U</span>-shaped pieces of soft iron, but the winding
-must be done so that the current will pass around them in
-opposite directions, otherwise you would have two negatives
-instead of a negative and positive. For a small
-horseshoe magnet a stout iron staple may be used, but for
-the larger magnets it would be best to have a blacksmith
-bend a piece of round iron in the desired shape.</p>
-
-<p>A powerful horseshoe magnet may be made from a piece
-of tire-iron bent as shown in <a href="#FigIV5">Fig. 5</a> A; when wound with
-No. 18 wire it will appear like <a href="#FigIV5">Fig. 5</a> B. A volt or two of
-current passing through the coils will render this magnet
-powerful enough to lift several pounds.</p>
-
-<p>For bells, telegraph-sounders, and other electrical equipment<span class="pagenum" id="Page58">[58]</span>
-requiring the horseshoe or double magnet, several
-kinds may be used, but the simplest is constructed from
-two carriage or machine bolts and a yoke of soft iron, as
-shown in <a href="#FigIV6">Fig. 6</a>. The yoke is five-eighths of an inch in
-width, two inches and a half long, and provided with two
-three-eighths-inch holes, one inch and a half apart from
-centre to centre. Two-inch carriage or machine bolts are
-used, and they should be three-eighths of an inch in diameter.
-The nuts are turned on the thread far enough to
-admit the yoke, and then another nut is applied to hold it
-in place and bind the three pieces into one compact mass.
-Wooden spool-ends or composition washers are placed on
-the bolts to hold the ends of the wire coils in place, and
-the winding may be done on each bolt separately and
-locked to the yoke after the winding is completed. Double
-cotton-insulated No. 20 or 22 copper wire should be used
-for the coils.</p>
-
-<p>It is a tedious and bothersome job to wind a coil by hand,
-and if possible a winder should be employed for this purpose.
-Several varieties of winders are on the market, but
-a simple one for ordinary spools may be made from a stick
-held in an upright piece of wood with staples. This idea is
-pictured in <a href="#FigIV7">Fig. 7</a>, where the round stick is shown cut with
-two grooves into which the staples fit. One end of the stick
-is made with a square shoulder, so that a handle and crank
-can be fitted to it. A few wraps of wire are taken around
-the crank to prevent it from splitting, and it is held to the
-round stick with a slim steel nail. The opposite end of the
-round stick is shaved off so that it will fit snugly in the hole
-of a spool; if it should be too small for some spools, a few<span class="pagenum" id="Page59">[59]</span>
-turns of cord around the small end will make it bind. The
-block to which the shaft and crank is attached may be held
-in a vise or screwed to the edge of a table.</p>
-
-<h4>Induction-coils</h4>
-
-<p>A simple induction or shocking coil may be made of a
-two-and-one-half by five-sixteenths-inch bolt, a thin wooden
-spool, and two sizes of insulated copper wire. An induction-coil
-is a peculiar and wonderful apparatus; it figures largely
-in electrical experimenting and is a part of every complete
-equipment.</p>
-
-<p>A piece of curtain-pole may be used for the spool. First
-bore a five-sixteenths-inch hole through the wood to receive
-the bolt; then in a lathe turn it down into a spool with less
-than one-eighth of an inch of wood about the hole and with
-flanges about one-eighth of an inch in thickness. Smooth
-the spool with sand-paper, while it is still in the lathe, and
-give it a thin coat or two of shellac.</p>
-
-<p>Slip the spool on the winder (<a href="#FigIV7">Fig. 7</a>) and wind on three
-layers of No. 24 cotton-insulated copper wire, taking care
-to wrap the coils evenly and close. Bring six inches of the
-ends out at either end of the spool through small holes
-pierced in the flanges; then wrap several thicknesses of
-brown paper around the coil. A current passing around
-this three-layer coil will magnetize the bolt. This is the
-primary coil and the one through which the battery current
-will pass.</p>
-
-<p>A secondary coil is now made over the primary one with
-eleven or thirteen layers of No. 30 insulated copper wire.<span class="pagenum" id="Page60">[60]</span>
-It will take some time to carefully put on these layers, and
-when doing so mark down each layer so as to keep an accurate
-count, for there must be the right number of layers to
-make the coil act properly. No. 30 wire is quite fine, and
-if the layers are not inclined to lie smooth, make a wrap or
-two of brown paper between each three layers. Bring six
-inches of each end of the wire out from the flanges of the
-spool, and to protect the outer coil wrap paper about the
-coils and attach it fast with thread or paraffine. Slip the
-bolt through the hole and screw the nut on the threaded
-end. Cut out a wooden block four inches long, three inches
-wide, and three-quarters of an inch thick, and with two thin
-metal straps and screws attach the coil to the middle of the
-block, as shown in <a href="#FigIV8">Fig. 8</a>. Make four binding-posts and
-screw them fast at the corners, and to A and B of <a href="#FigIV8">Fig. 8</a>
-attach the ends of the heavy wire from the primary coil,
-and to C and D of <a href="#FigIV8">Fig. 8</a> the ends of the fine wire from the
-secondary coils. The induction-coil is now ready for any
-use to which it may be put, and by mounting it on the block
-with the delicate wire ends attached to the binding-posts,
-it is in less danger of damage than if the wire ends were left
-loose for rough-and-ready connections.</p>
-
-<p>In order to get a shock from this coil it will be necessary
-to have a pair of handles and a current interrupter. The
-handles may be made from two pieces of tin rolled into the
-form of cylinders to which wires are soldered. Or, better
-yet, use pieces of thin brass tubing an inch in diameter.
-The buzzer shown in <a href="#FigIV9">Fig. 9</a> may be employed for a current
-interrupter, and a bichromate battery will furnish the current.</p>
-
-<p><span class="pagenum" id="Page61">[61]</span></p>
-
-<p>In order to make the connections, the wires from the
-handles are attached to the binding-posts C and D in <a href="#FigIV8">Fig. 8</a>&mdash;that
-is, to the wires of the secondary coil. One spool of
-the battery is connected with A of <a href="#FigIV8">Fig. 8</a> and the other
-with A of <a href="#FigIV9">Fig. 9</a>. A wire connects C of <a href="#FigIV9">Fig. 9</a> with B of <a href="#FigIV8">Fig. 8</a>,
-and the circuit is closed. The buzzer now begins to vibrate,
-and any one holding the handles will receive a shock the
-intensity of which depends on the strength of the batteries.
-A switch should be introduced somewhere in the circuit, so
-that it may be opened or closed at will; a good place for it
-is between a battery-pole and the binding-post A in <a href="#FigIV8">Fig. 8</a>.</p>
-
-<p id="Ref001">If the shock is too intense it may be weakened by drawing
-the carbon and zinc poles partly out of the bichromate
-solution; or a regulator may be made of a large glass tube
-and a glass preserving-jar filled with water. If the tube
-cannot be had, an Argand gas-burner chimney will answer
-as well.</p>
-
-<p>Solder a wire to the edge of a small tin or copper disk, as
-shown in <a href="#FigIV10">Fig. 10</a>, on which the chimney rests at the bottom
-of the jar, and another wire to a tin box-cover with some
-small holes punched in its top, this latter being suspended
-within the chimney. This second wire is passed out through
-a cork at the top of the chimney made of a disk of cardboard
-and a piece of wood. One wire is connected with A
-of <a href="#FigIV8">Fig. 8</a> and the other with a battery-pole. This apparatus
-acts the same as a resistance-coil, and by raising or lowering
-the box-cover the current is increased or diminished. The
-closer the cover comes to the disk the stronger the current,
-as there is less water for the electricity to pass through and
-therefore less resistance; while if the cover touches the disk<span class="pagenum" id="Page62">[62]</span>
-the current flows as freely as if there were no regulator and
-the wires ran directly to the cell.</p>
-
-<p>An apparatus comprising a coil, an interrupter, or armature,
-and a switch may be set on one block, and the arrangement
-of the several parts is clearly shown in the drawing of
-the complete galvano-faradic apparatus (<a href="#FigIV11">Fig. 11</a>). The block
-should be six inches long, four inches wide, and seven-eighths
-of an inch in thickness.</p>
-
-<div class="container m40">
-<a id="FigIV8"></a>
-<a id="FigIV9"></a>
-<a id="FigIV10"></a>
-<a id="FigIV11"></a>
-<a id="FigIV12"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo062.jpg" alt="Coils" />
-</div>
-
-</div><!--container-->
-
-<p>The coil is made as described for <a href="#FigIV8">Fig. 8</a>, the spool being
-three inches long and one inch and a quarter in diameter.
-A carriage-bolt three inches and a half long and five-sixteenths<span class="pagenum" id="Page63">[63]</span>
-of an inch in diameter, with a bevelled head, is made
-fast in the spool, and this coil is strapped to the block
-with two metal bands and screws. Two binding-posts (A
-and B of <a href="#FigIV11">Fig. 11</a>) are arranged at the upper corners, and to
-these the ends of the secondary coil wires are attached.
-Two more binding-posts (C and D of <a href="#FigIV11">Fig. 11</a>) are arranged
-at the lower side and provided with a switch to open and
-close the circuit. One of the primary coil wires is made
-fast to C, and the other one to a block which contains the
-set-screw that bears against the vibrating armature. Its
-arrangement and the wire connection is explained in <a href="#FigIV9">Fig.
-9</a> B.</p>
-
-<p>An armature of thin brass or tin is made and attached
-to a block (E in <a href="#FigIV11">Fig. 11</a>). At the loose end that is opposite
-the bolt-head several wraps of tin are made and soldered
-fast, or a small block of soft iron may be riveted to the
-armature. It must be of iron or tin, however, so as to be
-attracted by the electro-magnetized bolt-head. This arrangement
-may be seen in <a href="#FigIV12">Fig. 12</a>. Attach a thick piece
-of paper over the bolt-head, so that the lug at the end of the
-armature will not adhere to it through residual magnetism.</p>
-
-<p>In regular galvano-faradic machines the current regulator
-is formed of a hollow cylinder which is drawn from the core
-of the coil; but in this simple machine the water-jar regulator
-may be connected between a pole of the battery and
-the binding-posts (D or E of <a href="#FigIV11">Fig. 11</a>). The wires of the
-handles are attached to posts (A and B of <a href="#FigIV11">Fig. 11</a>), and when
-all the wires are in place and the current turned on by
-means of the switch, the vibrator begins to work and the
-shocking-current is felt through the handles. By means of<span class="pagenum" id="Page64">[64]</span>
-the regulating-screw that bears on the armature, the number
-of vibrations may be increased or diminished, but for
-faradic purposes the vibrations should be as quick as possible.
-Much amusement may be had with this apparatus,
-and a large number of people may be given a shock by getting
-them to join hands when standing or sitting in a circle.</p>
-
-<h4 id="Ref002">An Electric Buzzer</h4>
-
-<p>This piece of apparatus is, in theory, nothing more than
-the electric bell, and might properly be included in <a href="#Page78">Chapter
-V.</a>, on Annunciators and Bells. But since it is the logical
-development of principles just laid down, it has been thought
-best to give it its present position.</p>
-
-<p>The electric buzzer is constructed on the principle of the
-telegraph-sounder, but instead of making a single click or
-stroke the current is made to act on the armature and keep
-up a continuous motion so long as the electricity passes
-through the helix of the cores, the armature, and the contact-points
-of the apparatus.</p>
-
-<p>A buzzer has the same movement as an electric bell with
-the ringing apparatus removed. For offices, houses, and
-quiet calls it is often preferred to the loud ringing of a
-bell.</p>
-
-<p>The electric buzzer shown in <a href="#FigIV13">Fig. 13</a> is easy to make; it
-is operated by the aid of a cell and a push-button. Cut a
-base-block three inches and a half wide, five inches long,
-and three-quarters of an inch thick, and mount a horseshoe
-magnet made of bolts and a yoke and coils about at the
-middle of it, as shown in <a href="#FigIV9">Fig. 9</a>. The magnet is held to the<span class="pagenum" id="Page65">[65]</span>
-base by a flat wooden cleat and a screw passed down through
-a hole in the cleat and into the base, between the coils. An
-armature of soft iron, two inches long and half an inch wide,
-is riveted to a piece of spring-brass, as shown in <a href="#FigIV14">Fig. 14</a> A,
-and the end is bent so that it will fit around the corner of a
-block to which it is held fast with two screws. This armature
-is mounted so that there is a space one-sixteenth of an
-inch wide between it and the bolt-heads, as you can see
-in <a href="#FigIV9">Fig. 9</a>. The brass is bent out slightly and runs parallel
-with the armature for one inch and a quarter. Against this
-the end of the screw mounted in block B <a href="#FigIV9">Fig. 9</a> rests.</p>
-
-<div class="container m40">
-<a id="FigIV13"></a>
-<a id="FigIV14"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo065.jpg" alt="Buzzers" />
-</div>
-
-</div><!--container-->
-
-<p>The block B is a small piece of hard-wood screwed fast to
-the side of the base to hold the set-screw and also the wire
-that comes from the outside of the upper coil. A small hole
-is made in the edge of the block and the wire passed in, so
-that the end rests in the screw-hole as shown by the dotted
-line. When the screw is placed in the hole and turned, it
-comes into contact with the wire and makes a connection.
-This block and its attachment is shown in <a href="#FigIV14">Fig. 14</a> B.</p>
-
-<p>On the base, near the armature-block, a binding-post is<span class="pagenum" id="Page66">[66]</span>
-made fast, and the current, passing in through the wire A
-in <a href="#FigIV9">Fig. 9</a>, goes through the coils and around to the screw B,
-then through the armature to the block, and out through
-the wire C. In its circuit the bolts are magnetized, and they
-draw the armature, but the instant they do so the loose
-spring-brass end is pulled away from the screw-point B and
-the circuit is broken, the bolts cease to be magnetized, and
-the armature flies back under the influence of the spring-brass
-neck at D. The loose brass end, on touching the
-screw-point, conducts the current through the coils again,
-with a continual vibrating action, so long as the electric
-current is passing in at A and out at C. The greater the volume
-of current the greater the number of vibrations, and to
-properly regulate the contact the set-screw B must be adjusted
-at the right point. Paste pieces of heavy paper over
-the heads of the bolts to overcome residual magnetism.</p>
-
-<p>A single electric bell is made the same as a buzzer, but
-continuing on from the end of the armature a wire or rod is
-mounted with a ball at the end which strikes the bell as the
-current causes the armature to vibrate. The bell-block
-may be made longer, and a bell from an old clock or a bicycle
-should be mounted at the proper place on a wooden dowel
-driven into the base. A screw passes through the hole at
-the middle of the bell and into the top of the dowel. The
-ball at the end of the rod may be made of brass with a hole
-in it, and a drop of solder will hold it in place. Or it may
-be made of wire wound round the end and soldered into a
-compact mass.</p>
-
-<p><span class="pagenum" id="Page67">[67]</span></p>
-
-<h4>A Large Induction-coil</h4>
-
-<p>As has been said, the induction-coil is one of the mysterious
-phenomena of electrical science. While its practical
-value is known and recognized in all branches of voltaic
-electricity for use in transforming currents, its actual workings
-have never been clearly explained.</p>
-
-<p>The construction of a small induction-coil was explained
-in the description of a shocker or medical battery. For
-bigger equipments, wireless telegraphy and other uses, a
-large induction-coil will be necessary, and the following
-illustrations and descriptions should enable the young electrician
-to construct an apparatus that will be both simple
-and efficient in its working.</p>
-
-<p>For the tube (in which to wind the primary coils) obtain
-a piece of red fibre-tubing, one inch inside diameter and not
-more than one-eighth of an inch in thickness. The length
-should be ten inches. If fibre cannot be had use a paste-board
-tube.</p>
-
-<p>From white-wood, half an inch in thickness, saw two
-blocks four inches square and in the centre of each cut a
-hole so that the tube will pass through it and fit snugly.
-Some shellac and a few slim brass escutcheon pins will hold
-the blocks in place, as shown at <a href="#FigIV15">Fig. 15</a>. The wood blocks
-and fibre or paper tube should be treated to several successive
-coats of shellac to give them a good finish and prevent
-the absorption of moisture. Four binding-posts, with
-wood screw-ends, are to be made fast at the top edges of
-the end-blocks, as shown at <a href="#FigIV15">Fig. 15</a>. Holes bored in the
-blocks near the foot of the binding-posts will admit the<span class="pagenum" id="Page68">[68]</span>
-ends of the coil-wires so that contact can be made. The
-ends of the conductor-wires should then be placed in the
-holes in the binding-posts and held in place with the thumb-screws.</p>
-
-<div class="container m40">
-<a id="FigIV15"></a>
-<a id="FigIV16"></a>
-
-<div class="figcenter">
-<img src="images/illo068.jpg" alt="Coils" />
-</div>
-
-</div><!--container-->
-
-<p>The primary coil is made by winding four layers of No.
-20 insulated copper wire on the tube and between the end-blocks,
-as shown at <a href="#FigIV16">Fig. 16</a>. Each layer must be wound
-evenly, and the strands should lie close to each other.
-When the first layer is on give it a coat of shellac; then
-wrap a piece of thin paper about it and give that also a coat
-of shellac. When the second layer is on repeat the operation
-of shellacking and paper-coating, and continue with the
-third layer. When the fourth layer is on give the coil a
-double wrap of paper and two or three coats of shellac to
-thoroughly insulate it and keep out all moisture. The
-winding may be done by hand, but it is much easier to do it
-on a winder or reel, which can be operated to revolve the
-core, the wire unwinding from its original spool as it is
-wound on the tube.</p>
-
-<p>A convenient winder may be made on a base-board<span class="pagenum" id="Page69">[69]</span>
-which can be clamped to a table or bench. The board is
-twelve inches long, eight or ten inches wide, and seven-eighths
-of an inch thick. Two uprights, three inches wide,
-ten inches long, and three-quarters of an inch thick, are
-screwed and glued to the ends of the base-board. A notch
-is cut in the top of the end-boards, into which the spindle
-or shaft can rest; and at the top of the end-pieces two
-small plates of wood or metal are screwed down to hold
-the spindle in place when the tube and ends are being
-revolved. A small hole, bored in each upright end two
-inches above the top of the base-board, will admit a rod on
-which a spool of wire can revolve, as shown at <a href="#FigIV17">Fig. 17</a>.</p>
-
-<p>Two plugs of wood, shaped like corks, are made to fit in
-the ends of the fibre-tube. A hole is bored through each
-one so that a wire or rod spindle will pass through them
-and fit tightly. One end of the rod is bent and provided
-with a small wooden handle, by means of which the core
-may be revolved.</p>
-
-<p>This winding-rack makes it easy to handle the core-tube
-while putting on the layers of wire, and it holds the tube
-securely while the wraps of paper and shellac are applied.</p>
-
-<p>The secondary coil is laid over the primary, and should
-be of Nos. 30 to 36 insulated copper wire. The finer the
-wire the higher the resistance and the longer the spark, but
-nothing heavier than No. 30 should be used.</p>
-
-<p>Begin by making one end of the wire fast to a binding-post;
-then turn the core-tube with one hand, holding the
-wire in the other. Take care not to bind the wire nor
-stretch it, but wind it on smoothly and evenly, like the
-coils of thread on a new spool of cotton or silk. Be very<span class="pagenum" id="Page70">[70]</span>
-careful to avoid kinks, breaks, or uninsulated places in the
-wire. Should the wire become broken, give the coil a coat
-of shellac to bind the wound strands; then make a fine
-twisted point and cover it with the silk or cotton covering,
-with a coat of shellac to hold it in place, and proceed with
-the winding. Between each layer of wire place a thin sheet
-of paper and coat it with paraffine, or shellac, to make a
-perfect insulation; then proceed with the next layer.</p>
-
-<p>With a battery and small bell test the wire layers occasionally
-to see that everything is all right, and that there
-are no breaks or short circuits. This is very necessary to
-avoid making mistakes, and, considering the time and care
-spent in winding the coils, it would be a great disappointment
-if the coil were defective.</p>
-
-<div class="container m40">
-<a id="FigIV17"></a>
-<a id="FigIV18"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo070.jpg" alt="Coils" />
-</div>
-
-</div><!--container-->
-
-<p>About one pound and a half of wire should constitute
-the secondary coil, and, if possible, it is best to have it in
-one continuous strand, without splices.</p>
-
-<p>Over the last coil, after the winding is completed, several
-thicknesses of paper should be laid and well coated with<span class="pagenum" id="Page71">[71]</span>
-shellac between each wrap. This is a protector to insure
-the fine wire strands from damage. To improve the appearance
-of the coil a wrap of thin black or colored leather
-may be glued fast, with the seam or point at the under
-side.</p>
-
-<p>The ends of the wires forming the primary coil should
-be made fast to the binding-posts at one end, while those
-of the secondary coil should be attached to the posts at
-the other end.</p>
-
-<p>For the core, obtain some soft iron wire, about No. 18,
-and cut a number of lengths. Straighten these short wires
-and fill the tube with them, packing it closely, so that the
-wires will remain in place under a mutual pressure. It is
-better to make a core of a number of rods or wires rather
-than to have it of one solid piece of soft iron.</p>
-
-<p>Now, from hard-wood, cut a base three-quarters of an
-inch thick, five or six inches wide, and twelve inches long.
-Attach the coil to the base by means of screws passed up
-through the board and into the lower edges of the end-blocks.
-The wood is to be stained and given several successive
-coats of shellac.</p>
-
-<p>Now connect the wires of a battery to the binding-posts
-in contact with the primary coil, and attach two separate
-wires to the secondary coil binding-posts. Bring these ends
-near to each other, and a spark will leap across from one
-end to the other, its size or “fatness” depending on the
-strength of the battery. The completed apparatus is shown
-at <a href="#FigIV18">Fig. 18</a>.</p>
-
-<p>In producing a long spark a condenser is an important
-factor; it is used in series with an induction-coil. There<span class="pagenum" id="Page72">[72]</span>
-are several forms of condensers, but perhaps the simplest
-and most efficient is the Fizeau condenser, which is made
-up of layers of tin-foil with paraffined paper as separators.</p>
-
-<p>From a florist’s supply-house purchase one hundred and
-fifty sheets of tin-foil seven by nine inches, or sheets that
-will cut to that size without waste; also ten or twelve
-extra sheets for strips. At a paper supply-house obtain
-some clear, thin, tough paper about the thickness of good
-writing-paper. Be careful to reject any sheets that are perforated
-or have any fine holes in them. The sheets should
-be eight by ten inches, or half an inch larger all around
-than those of the tin-foil. The paper must be thoroughly
-soaked in hot paraffine to make it moisture-proof and a
-perfect non-conductor. This is done by placing about two
-hundred sheets on the bottom of a clean tin tray, or photographic
-developing-dish of porcelain. Don’t use glass or
-rubber. After placing some lumps of paraffine on the
-paper, put the tray in an oven so as to dissolve the paraffine
-and thoroughly soak the paper.</p>
-
-<p>Open the oven door and, with a pin, raise up the sheets
-one at a time, and draw them out of the liquid paraffine.
-As soon as it comes in contact with cool air the paraffine
-solidifies and the sheet of paper becomes stiffened. Select
-each sheet with care, so that those employed for the condenser
-are free from holes or imperfect places.</p>
-
-<p>From pine or white-wood, a quarter of an inch in thickness,
-cut two boards, eight by ten inches, and give them
-several good coats of shellac.</p>
-
-<p>To build up the condenser, lay one board on a table and
-on it place two sheets of paraffined paper. On this lay a<span class="pagenum" id="Page73">[73]</span>
-sheet of tin-foil, arranging it so that half an inch of paper
-will be visible around the margin. From the odd sheets
-of tin-foil cut some strips, one inch in width and three inches
-long. Place one of these strips at the left end of the first
-sheet of foil, as shown at <a href="#FigIV19">Fig. 19</a>. Over this lay a sheet of
-the paraffined paper, then another sheet of the foil. Now
-on this second sheet of foil lay the short strip to the right
-end, and so proceed until all the foil and paper is in place,
-arranging each alternate short strip at the opposite end.
-Care must be taken to observe this order if the condenser
-is to be of any use.</p>
-
-<div class="container m40">
-<a id="FigIV19"></a>
-<a id="FigIV20"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo073.jpg" alt="Condensors" />
-</div>
-
-</div><!--container-->
-
-<p>When the last piece of foil is laid on, with its short strip
-above it, add two or three thicknesses of paper, and then
-the other board. With four screw-clamps, one at each
-corner, press together the mass of foil, paper, and boards as
-closely as possible, then bind the boards about with adhesive
-tape, or stout twine, and release the clamps. Attach
-all the projecting ends of foil at one side by means of a
-binding-post, and those at the other end with another
-binding-post. The complete condenser will then appear
-as shown in <a href="#FigIV20">Fig. 20</a>.</p>
-
-<p>When in operation one wire leading from the secondary
-coil should be connected with a binding-post of the condenser,
-so that it is in series.</p>
-
-<p><span class="pagenum" id="Page74">[74]</span></p>
-
-<p>The object of the condenser is to increase the efficiency
-of induction, and it should be made in proportion to the size
-of the induction-coil with which it is to be employed.</p>
-
-<h4>Circuit-Interrupters</h4>
-
-<p>When an induction-coil is to be employed as a shocker
-(and there is no vibrating armature arranged in connection
-with the core), a circuit-interrupter must be employed to
-get the effect of the pulsations, as given out by the secondary
-coil when a current is passing through the primary.</p>
-
-<p>There are various forms of circuit-breakers that may be
-made for this purpose, but for really efficient service the type
-shown in <a href="#FigIV21">Fig. 21</a> is perhaps the best that can be devised.</p>
-
-<p>This interrupter consists of a metal cog-wheel with saw-teeth,
-a pinion or axle, and a handle. Also a base-block,
-with uprights to support it, and a piece of spring-brass wire,
-arranged so as to bear against the wheel. When the wheel
-is revolved the spring-wire will be driven out by each tooth;
-and when released it flies back to the wheel, striking the
-bevelled edge of a tooth at each trip.</p>
-
-<p>Two binding-posts, arranged on the block, will provide
-means of connecting in-and-out wires. With a coat or two
-of shellac on the wood-work and black asphaltum varnish
-on all surfaces of the metal that are not used for contact,
-this circuit-interrupter will be ready for any use in connection
-with an induction-coil.</p>
-
-<p>The base-block is of pine, white-wood, or cypress, seven-eighths
-of an inch thick, three inches wide, and five inches
-long. The uprights, which support the wheel, are half an<span class="pagenum" id="Page75">[75]</span>
-inch thick and one inch wide. The wheel is three inches in
-diameter and is made of brass one-sixteenth of an inch thick.
-The design of the wheel should be laid out with a compass
-and marked with lead-pencil or a sharp-pointed awl, which
-will leave a mark clear enough to be seen when sawing and
-filing the teeth and open places.</p>
-
-<div class="container m40">
-<a id="FigIV21"></a>
-<a id="FigIV22"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo075.jpg" alt="Interrupters" />
-</div>
-
-</div><!--container-->
-
-<p>A true plan is shown at <a href="#FigIV21">Fig. 21</a> A. Through the middle
-of the wheel a small hole is bored to receive the axle of
-brass which is to be soldered in place. When the wheel is
-set up, a metal crank and wooden handle should be soldered
-fast to one end of the axle. A piece of spring-brass wire is
-fastened to the block, with a staple, and the lower end bent
-so that the screw in one binding-post will hold it in place.
-The upper end of the wire is bent in the form of an <span class="symbol">L</span>.
-From the other binding-post, through the block and up one
-support, a wire is passed, the end of which comes into contact
-with the axle. The current, passing in through one
-binding-post, is carried through this wire to the axle, then
-to the wheel, and so on out through the spring-wire and
-remaining binding-post. When in action the circuit is<span class="pagenum" id="Page76">[76]</span>
-constantly being broken, as the spring-wire jumps from the
-end of one tooth back to the face of the next tooth. The
-pulsations are increased or diminished by the fast or slow
-speed of the wheel, as regulated by the hand motion. The
-strength of the current is regulated by the force of the
-battery and should be controlled by a water resistance, as
-described for the medical battery, or shocking-coil.</p>
-
-<p>The interrupter, shown in <a href="#FigIV22">Fig. 22</a>, is built up on a block
-six inches square and seven-eighths of an inch thick.</p>
-
-<p>A circle is cut from sheet-lead and laid on the face of the
-block, through which pins, or steel-wire nails, are driven.
-The lead circle is five inches in diameter and half an inch
-in width, making the inside diameter four inches.</p>
-
-<p>The pins or nails are driven a quarter of an inch apart,
-and should be properly and accurately separated, so that
-an even make-and-break will be the result.</p>
-
-<p>It is not necessary to bore holes in the lead, but the pins
-or nails should be driven clear through it, so that perfect
-contact can be had by the metal parts coming together.
-Otherwise the apparatus would be useless.</p>
-
-<p>Over the circle of pins a brass bridge is erected, so that
-the cross-strips will clear the heads of the pins. A hole is
-bored at the middle of the bridge so that the revolving axle
-will pass through it.</p>
-
-<p>The axle is made from a piece of stout wire, or light rod,
-and near the foot of it, and about half an inch above the
-base-board, a disk of metal is soldered fast. A piece of
-spring-brass wire is attached to this disk, so that when the
-axle is turned the end of the wire trips from pin to pin, thus
-making and breaking the circuit. The upper part of the<span class="pagenum" id="Page77">[77]</span>
-axle is bent and provided with a small wooden or porcelain
-knob.</p>
-
-<p>One wire from the secondary coil is caught under a screw
-that holds one end of the brass bridge to the base; and the
-other to a screw, which may be placed at one corner of the
-block, and from which a short wire leads to the lead ring.
-Binding-posts may be arranged to serve the same purpose,
-and, of course, they are much better than the screws, because
-they can be easily operated by the fingers and do not
-require a screw-driver every time the interrupter is placed
-in series with an induction-coil. An interrupter on this
-same order may be made from a straight strip of lead with
-the pins driven through the middle of it. One wire from
-the secondary coil is made fast to the lead plate, and the
-end of the other wire is passed along the pins, thus making
-and breaking the circuit in a primitive manner.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page78">[78]</span></p>
-
-<h3>Chapter V<br />
-<span class="chaptitle">ANNUNCIATORS AND BELLS</span></h3>
-
-<h4>A Drum Sounder</h4>
-
-<p class="chapstart"><span class="largecap">A</span> unique electric sounder that is sure to attract attention
-is in the shape of an electric-bell apparatus, with
-a drum sounder in place of a bell, or knockerless buzzer.
-<a href="#FigV1">Fig. 1</a>.</p>
-
-<p>The outfit is mounted on a block four inches and a half
-wide and seven inches long. The cores and yoke are made
-as described for the <a href="#Ref002">electric buzzer</a> (<a href="#Page54">chapter iv.</a>) and are
-wound with No. 22 cotton-insulated wire. The magnet is
-then strapped fast to the block by means of a hard-wood
-plate having a screw passed down through it; and between
-the coils and into the block an armature is made and
-mounted on a metal plate, which in turn is screwed to the
-block. Another block, with a contact-point, is arranged
-to interrupt the armature, and the series is connected as
-shown in the drawing <a href="#FigV1">Fig. 1</a>.</p>
-
-<p>The end of the wire projecting above the armature is provided
-with a hard-wood knocker which operates upon the
-head of the drum. The drum is made from a small tin can,
-having one or two small holes punched in the bottom. Over
-the top a thin membrane, such as a bladder or a piece of<span class="pagenum" id="Page79">[79]</span>
-sheep-skin or cat-skin, is drawn and lashed fast with several
-wraps of wire, having the ends twisted together securely.
-The membrane must be wet when drawn over the can end,
-and great care should be taken to get it tight and even.
-Then, when it dries, it will stretch and draw, like a drumhead,
-and hold its elastic, resonant surface so long as it does
-not become moistened or wet.</p>
-
-<p>This drum is arranged in the proper position and lashed
-fast with wires passed over the box and down through holes
-in the block; where, after several turns, the ends may be
-securely twisted together. In place of the drum a small
-wooden box may be lashed fast with its open end against
-the block, so as to form a hollow enclosure. The raps of
-the knocker against its sides will give forth a resonant
-xylophone tone.</p>
-
-<h4>An Annunciator</h4>
-
-<p>A simple annunciator may be made from a core, a helix,
-and some brass strips. A soft iron core, made of a piece of
-three-eighth-inch round iron and threaded at one end, is
-converted into a magnet by having a spool and wire coil
-arranged to enclose it. This in turn is screwed into a strip
-of brass bored and threaded to receive it. <a href="#FigV2">Fig. 2</a>.</p>
-
-<p>This brass strip is shaped as shown at <a href="#FigV3">Fig. 3</a> A, and the
-ears are bent to serve their several purposes. The lowest
-ears are turned out and the lower part of the plate is bent
-forward so as to form the hinge on which the drop-bar turns.
-The drop-bar is only a strip of metal turned up at one end,
-on which a numeral or letter can be attached; while at the
-other the metal should be bent over so as to form a core into<span class="pagenum" id="Page80">[80]</span>
-which a pin or wire may be passed and the extending ends
-bent down, after being caught through the holes in the ears.
-Above the magnet the strip is bent forward and the top or
-end ears bent up, so as to form the hinge on which the
-armature swings. Holes are made in the long ears, through
-which screws pass to hold the annunciator fast to the box
-or wood-work.</p>
-
-<p>The armature is made from a strip of brass and is shaped
-like B in <a href="#FigV3">Fig. 3</a>. The two ears at the top are bent down
-and fit within those at the top of the first strip. A screw
-or wire passed through the holes in the ears will complete
-the hinge. The strip is bent down so as to fall in front of
-the magnet, and to its inner side a button or disk of sheet-iron
-is riveted fast, so as to form an attraction-plate to be
-drawn against the magnet when the current is passing
-around it. The lower part of the armature is bent in hook
-fashion so as to hold up the drop-bar.</p>
-
-<p>A slot is cut in the drop-bar through which the hooked
-end will project. A short spring is arranged at the top of
-the annunciator so as to keep the bar and the hook in place
-when not in action. The current passing around the soft
-iron core magnetizes it and draws the iron button on the
-armature towards it. This action immediately releases the
-hook from under the edge of the metal at the forward end
-of the slot, and the bar drops, bringing the figure down and
-into plain sight. It is necessary, of course, to mount this
-annunciator so that the bar will not drop down too far.
-This may be done by having a platform or wire run
-along under a series of the drops, so that they will rest
-on it.</p>
-
-<p><span class="pagenum" id="Page81">[81]</span></p>
-
-<div class="container m40">
-<a id="FigV1"></a>
-<a id="FigV2"></a>
-<a id="FigV3"></a>
-<a id="FigV4"></a>
-<a id="FigV5"></a>
-<a id="FigV6"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo081.jpg" alt="" />
-</div>
-
-<p class="caption">ANNUNCIATORS AND BELLS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page82">[82]</span></p>
-
-<h4>A Double Electric Bell</h4>
-
-<p>For loud ringing, and to get the benefit of both the forward
-and backward stroke of the knocker, a double bell,
-similar to the one shown in <a href="#FigV4">Fig. 4</a>, may be constructed upon
-the general principle of the single-stroke buzzer already described
-(<a href="#Page54">chapter iv.</a>).</p>
-
-<p>Two soft iron cores are made, as described for the other
-bells, but instead of being yoked together with iron, so that
-the three parts will form a horseshoe magnet, the yoke is of
-brass or copper. Each core will then be an independent
-magnet.</p>
-
-<p>The spools are wound with No. 22 insulated wire and the
-ends left free, so that the coils are not connected together.
-If the drawing is examined closely you will see that the
-armature swings on a pivot at the base of the knocker-bar.
-When the bell is not in action the knocker might rest naturally
-against one bell or the other; or it might stand in the
-centre and not touch a contact-point, were it not for the
-small spring which draws it to the left. Directly the current
-is run through the coils it alternately magnetizes first
-one and then the other. This action is due to the making
-and breaking of the circuit by the spring on the armature.
-It first comes into contact with one point, and then is drawn
-away from it to come into contact with the other. <a href="#FigV4">Fig. 4</a>
-shows the knocker-bar at rest between both bells and the
-armature unattracted by either magnet. This position is
-purposely given so as to indicate the balance of the armature
-and the spaces between it and the cores and also the contact-points
-above it.</p>
-
-<p><span class="pagenum" id="Page83">[83]</span></p>
-
-<p>The small, light wire spring shown in the drawing draws
-the knocker to one side; therefore, when at rest, one circuit
-is closed. Otherwise the bell would not act when the current
-is run through the parts&mdash;in fact, the current could not
-run through at all, if one or the other contact were not made.</p>
-
-<p>The magnets are held fast to a base with a long screw and
-a small plate of wood laid across them as shown in <a href="#FigV4">Fig. 4</a>.
-The armature is a piece of soft iron one-eighth of an inch
-thick, half an inch wide, and three inches long. This has a
-spring-brass piece attached to it as shown at A A in <a href="#FigV5">Fig. 5</a>.
-Small holes are bored through the strip and the iron, and
-escutcheon pins are passed through and riveted. A small
-hole is made down through the middle of the iron plate and
-a pin is driven into it, so that a quarter of an inch projects
-at both sides.</p>
-
-<p>Another hole is made through the side of the plate for
-the knocker-bar. Then the armature is set in place so that
-there is a space of one-eighth of an inch between it and the
-magnet ends. The armature is held in place at the top by
-a bent metal strip (B B in <a href="#FigV5">Fig. 5</a>). This is screwed fast to
-the base and the bottom is countersunk into the wood.</p>
-
-<p>Two contact-points (C C in <a href="#FigV5">Fig. 5</a>) are arranged so that
-when a magnet draws the armature down it brings the
-opposite end of the armature spring into contact with a
-point.</p>
-
-<p>The wiring is at the under side of the base and is shown
-in <a href="#FigV6">Fig. 6</a>. The current enters binding-post A, and passes
-around coil and magnet No. 1 by entering at B and leaving
-at C; from thence to D, entering the armature spring at E,
-when the small spring has drawn the knocker-bar over to<span class="pagenum" id="Page84">[84]</span>
-the left. The current passes along the armature and out at
-F; then along to binding-post G, and so on around through
-battery K and push-button L, thus completing the circuit.
-Directly that this is done the magnet draws the spring end
-of the armature away from contact-point D and up against
-contact-point J, so that the circuit is broken through coil
-No. 1 and is sent through coil No. 2. This immediately
-magnetizes core No. 2 and draws the armature down to it,
-breaking its contact with J and re-establishing it with D.
-The rapid alternate making and breaking of the circuit, and
-the rapid and strong motion of the armature in its seesaw
-action, causes the knocker to rap the bells soundly each time
-it travels from right to left and back again.</p>
-
-<p>Two bells of similar size, or two drums or wooden boxes,
-may be employed for this double striker, and the more current
-that is run through the coils the more power and a corresponding
-increase of noise.</p>
-
-<h4>An Electric Horn</h4>
-
-<p>One of the most useful pieces of apparatus where a loud
-noise is required (such as in a motor-boat or an automobile)
-is the electric horn.</p>
-
-<p>It is a rearranged principle of the telephone, for instead
-of sound entering or striking against the membrane or
-tympanum to be transmitted elsewhere, the disturbance
-takes place within the horn and the sound is emitted.</p>
-
-<p>Everybody has been close to a telephone when others
-have been using it, and has heard noises, rasping sounds,
-and even the voice of the speaker at the other end of the<span class="pagenum" id="Page85">[85]</span>
-line. If a cornet were played at the other end of the line
-it could be distinctly heard through the receiver by many
-persons in the room, since its vibrations are loud enough
-to set up a forcible succession of sound-waves.</p>
-
-<p>The same principle operates in the electric horn, but
-instead of being agitated at a long distance it is done within
-the enclosure, and a very much louder vibration is consequently
-produced.</p>
-
-<p>It is quite as easy to make an electric horn as to construct
-a bell, but care must be exercised to have the parts fit
-accurately and the wiring properly done. If the drawings
-are studied and the description closely followed, there is no
-reason why a horn cannot be made that will demand any
-one’s attention from some distance away.</p>
-
-<p>The complete horn is shown in the illustration <a href="#FigV7">Fig. 7</a>,
-and as it is made of wood it is easily attached with screws
-to a boat or a motor-car.</p>
-
-<p>From white-wood, half an inch thick, cut two blocks three
-inches and a quarter square. In one of them (the rear one)
-bore a hole at the centre, of such size that a piece of three-eighth-inch
-gas-pipe can be screwed into it. In the other
-one make a hole two inches in diameter, so that the cover
-of a small tin can will fit into it. Outside this hole, and on
-one side of the block, cut the wood away and down for one-eighth
-of an inch, forming a rabbet, as shown at A in <a href="#FigV7">Fig. 7</a>.
-This will be the back of the front block.</p>
-
-<p><span class="pagenum" id="Page86">[86]</span></p>
-
-<div class="container m40">
-<a id="FigV7"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo086.jpg" alt="" />
-</div>
-
-<p class="caption">AN ELECTRIC HORN</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page87">[87]</span></p>
-
-<p>Have a gas or steam fitter cut a piece of two-inch iron
-pipe one inch and three-quarters long. This will measure
-a trifle over two inches and a quarter, outside diameter, and
-will form the cylinder or cover for the mechanism. The
-piece of pipe should fit snugly in the front board, and at
-the rear one the wood should be cut away so as to let it in
-an eighth of an inch, as shown in the sectional plan of
-<a href="#FigV7">Fig. 7</a>.</p>
-
-<p>Obtain a piece of three-eighth-inch gas-pipe, threaded at
-one end. Cut it with a hack-saw, and file the blunt end so
-that it will measure one inch and seven-eighths long, as
-shown at C in <a href="#FigV7">Fig. 7</a>. This is to be screwed into the front
-of the rear block so that it will project one inch and a half.</p>
-
-<p>Make a spool to fit the pipe, as shown at B in <a href="#FigV7">Fig. 7</a>, or
-use two wooden button-moulds attached to the pipe with
-shellac or glue. Between them wind on the coils of No. 22
-wire to form the helix.</p>
-
-<p>Cut a hole in the tin-can cover, as shown at D in <a href="#FigV7">Fig. 7</a>,
-and have a tinsmith solder a small funnel to it (for the horn,
-or bell, as it is called), cutting away the lower part of the
-funnel so that the hole in it will correspond in size with
-that in the can cover.</p>
-
-<p>This joint can be made at home by fitting the funnel in
-the hole and then turning back the edge, as shown in the
-sectional drawing at E in <a href="#FigV7">Fig. 7</a>. Then, with a spirit-lamp,
-some soldering solution, and solder, make a good joint.</p>
-
-<p>Small holes are to be made at the corners of the blocks,
-through which stove-bolts two inches and a half long will
-fit to bind the front, back, and cylinder together.</p>
-
-<p>Select a good, clean, and flat piece of tin and cut a disk
-two inches and a quarter in diameter, and through the middle
-make a small hole. Cut two pieces of iron about the
-size and thickness of a cent, and bore a small hole through
-the centre of each. Obtain a piece of stout brass wire, or<span class="pagenum" id="Page88">[88]</span>
-thin rod, and file one end of it as shown at G in <a href="#FigV7">Fig. 7</a>, so
-that the small end will fit in the holes made in the iron
-buttons. Place one button on either side of the tin disk, and
-pass the wire through; then clamp it in a vise and rivet the
-top of the rod so that you will have a disk with a button at
-each side of the centre and all attached firmly to a brass
-rod, as shown at F in <a href="#FigV7">Fig. 7</a>. The total length of this rod
-should be two inches and a half, and the lower end is to be
-threaded and provided with two small brass nuts. A piece
-of spring-brass three-eighths or half an inch wide is made
-fast to a small block at the back of the horn, as shown at H
-in <a href="#FigV7">Fig. 7</a>, and at its opposite end a contact-piece of metal,
-bent at an angle, is screwed fast. Around the back of the
-back block a wooden frame is attached to protect the rear
-mechanism of the horn.</p>
-
-<p>The parts are now ready to assemble. First see that the
-metal angle contact-point is in place with the long brass
-strip resting on it, and that this in turn is properly fastened
-to the block on the side opposite the contact-point, as shown
-at H in <a href="#FigV7">Fig. 7</a>. There should be a small hole through the
-middle of the brass strip directly in line with the middle
-of the hole in the gas-pipe. Place this back-board
-down on the table so that it will lie in a position as indicated
-in the sectional plan of <a href="#FigV7">Fig. 7</a>. The gas-pipe is then to be
-screwed onto the plate. Over this the spool with its layers
-of wire is to be slipped and made fast, and the cylinder of
-iron is then placed in position. Over this the disk F is laid,
-so that the brass rod extends down through the pipe and
-brass strip; then the nut is screwed on to hold it in place.
-Next comes the front block, with its horn or bell, and the<span class="pagenum" id="Page89">[89]</span>
-entire mass is locked together by means of the four bolts at
-the corners.</p>
-
-<p>The wiring is simple. One inlet being through block I,
-the current passes through strip J to contact-point K; then
-through the coil and out at wire L. The inlet and outlet
-wires are connected to a battery and to a push-button or
-switch, so that the horn can be operated. The proper adjustment
-of this horn depends on the nuts at the foot of the
-brass rod. They must be screwed on tight enough to draw
-the strip J so that it rests on the contact-point K.</p>
-
-<p>The current, passing in at I, through J, K, the coil, and
-out at L, magnetizes the piece of pipe and draws the iron
-buttons or disks attached to the tin disk. But so soon as
-it does so it breaks the contact between J and K, and the
-buttons fly back into place, having been drawn there by the
-rigidity of the tin disk to which they are attached. Again
-the current is closed and the magnet draws the iron buttons.
-The brass rod moves but a very slight distance up and down&mdash;enough,
-however, to make and break the contact between
-J and K. As a result of this rapid movement and the consequent
-snapping of the tin disk, a loud noise is emitted
-through the bell, which can be heard a long distance and
-closely resembles a long blast blown on a fish-horn.</p>
-
-<h4>Burglar-alarms</h4>
-
-<p>A unique burglar-alarm trap may be made from a plate
-of wood, five by six inches and half an inch thick, a movable
-lever, and a brass strip having the ends turned out.
-These are arranged as shown in <a href="#FigV8">Fig. 8</a>. The brass strip is<span class="pagenum" id="Page90">[90]</span>
-fastened to the plate with screws, and the ends extend out
-for half an inch from the board. The lever is made from a
-strip of brass, and the upper part is bent out so as to clear
-the strip and screws that are under it. A hole is made at
-the lower end of the lever, through which a brass ring and
-the end of a spring may be fastened. The opposite end of
-the spring is attached to a screw, and a wire carried from it
-to a binding-post, A. Another wire connects the back plate
-with binding-post B. A string or piece of fine picture-wire
-is made fast to the ring and carried to any part of a room.</p>
-
-<p>To set the trap, make the block fast in any convenient
-place, such as the door-casing or the surbase, and carry the
-string out from the trap and fasten the end of it. Any one
-running against it in the dark will draw the lever over to
-the right side and connect the circuit.</p>
-
-<div class="container">
-<a id="FigV8"></a>
-<a id="FigV9"></a>
-<a id="FigV10"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo090.jpg" alt="Burglar alarm" />
-</div>
-
-</div><!--container-->
-
-<p>When setting the trap, have the string adjusted so that
-the lever is in a vertical position, as shown in the drawing
-of <a href="#FigV8">Fig. 8</a>. When the string is disturbed it will pull the top<span class="pagenum" id="Page91">[91]</span>
-of the lever over to the right side; but if the string is broken
-by the person running against it, the spring attached to the
-bottom of the lever draws it over to the right side with a
-snap, and the top of the lever goes to the left side, when the
-circuit is closed and the alarm given.</p>
-
-<p>This trap is connected the same as a push-button, one
-wire leading to the bell, the other to the battery; then the
-battery and bell are connected together so that when the
-circuit is closed the bell will ring until some one throws a
-switch open to break it.</p>
-
-<p>Another form of circuit-closer is shown in the door-trap
-(<a href="#FigV9">Fig. 9</a>). This is a wooden block that rests on the floor close
-to the bottom of a door, and is held in place by means of
-four sharp-pointed nails driven down through the corners
-of the block. The points should project a quarter of an
-inch or more, according to whether the block is on a hard
-floor or on a carpet. The front edge of the block is bevelled
-so that the bottom of a door that fits closely to the
-floor will pass over it.</p>
-
-<p>The block is five by seven inches, and three-quarters of an
-inch thick. At the left side a strip of metal (A) is held close
-to the block with straps or wide staples driven over it, but
-not so close but that it can move freely back and forth. To
-the front end a round piece of wood is made fast. This is
-the bumper against which the door will strike when opened.
-At the middle of the strip a screw is riveted fast; or it may
-be a machine-screw let into a threaded hole in the metal.
-At the right side of the block another strip of metal (B) is
-attached, but this is held fast with a screw at the middle
-and a screw-eye and washer at the rear end to act as a binding-post.<span class="pagenum" id="Page92">[92]</span>
-The front end of this strip is turned up so as to
-form a stop; then a movable lever (C) mounted over both
-strips, with one end bent up, is attached to the block with a
-screw. A slot is cut at one end so that the screw in the
-movable strip (A) will move freely in it, and near the other
-end a small hole is made to receive the end of a spiral spring
-(D). To set the trap, the block is placed on the floor and
-the wires from battery and bell are made fast to the binding-posts.
-The spring D keeps the lever C away from the
-strip-end B, while at the same time it throws the strip A
-forward. When the door is opened it shoves the bumper
-and strip A back through the staples, while the screw operates
-lever C and causes its loose end to come into contact
-with the end B, thereby closing the circuit and ringing the
-bell or buzzer. When the door is closed again the spring
-draws lever C away from B, and the circuit is opened.</p>
-
-<p>The block acts as an obstruction as well as an alarm, for
-the pins will hold in the floor and the little block will stand
-its ground. A simple form of contact for doors is shown
-at <a href="#FigV10">Fig. 10</a>. This is simply two strips of spring-brass bent
-as shown, and screwed fast on either side the crack of a
-door, at the hinge side, so that when the door is opened
-one piece of metal bears on the other and the circuit is
-closed. This is to be operated in connection with a switch,
-so that the circuit may be opened in the daytime when the
-door is in use.</p>
-
-<h4>Signals and Alarms</h4>
-
-<p>There are many different kinds of electric call-signals
-used in and about the house; among these are some that a<span class="pagenum" id="Page93">[93]</span>
-boy can readily make&mdash;for example, the ordinary call-buttons
-and the signals between house and stable or other
-out-buildings.</p>
-
-<p>A portable call-bell, or alarm, is one of the most convenient
-things in any home. It may be temporarily rigged
-up from one room to another, or from one floor to the next,
-the small, flexible wire being run over the tops of door-casings,
-where it is held by slim nails or pins driven into
-the wood-work.</p>
-
-<p>The main terminal of this portable outfit consists of a
-wooden box that will hold a large dry-cell, and to the side of
-which an electric bell or buzzer may be attached. Binding-posts
-are arranged at another side, to which the ends of the
-flexible wire-cord can be made fast, and a cover fitted to the
-box to hide the battery and wiring. The complete outfit,
-except the flexible wire-cord and push-button, will appear
-as shown in <a href="#FigV11">Fig. 11</a>. No definite size can be laid down for
-the construction of this box, as dry-cells vary in size and
-shape, some being long and thin, while others are short and
-fat. By removing the cover and looking into the box, it
-will appear as shown in <a href="#FigV12">Fig. 12</a>. The carbon is connected
-with one binding-post and the zinc to one of the poles of
-the bell. The other bell-pole is connected with the remaining
-binding-post, and it requires but a switch or push-button
-to close the circuit between the two binding-posts. This is
-done by the long line of flexible wire-cord, which may be of
-the silk or cotton covered kind, having the two strands
-twisted together as is customary with flexible electric-light
-wire. A pear-shaped push-button may be connected at
-the end of the line, and this may be arranged at the head<span class="pagenum" id="Page94">[94]</span>
-of a bed or on a chair placed conveniently near an invalid’s
-couch.</p>
-
-<p>This same apparatus is a very convenient thing for a
-lecturer where a stereopticon is used. A buzzer takes the
-place of the bell, which would be too loud in a hall or
-lecture-room, and the cord, passing from the apparatus
-close to the operator, is hung over the lecturer’s stand, or
-the button held by him in the hand, to be pressed whenever
-he desires the pictures changed.</p>
-
-<div class="container m40">
-<a id="FigV11"></a>
-<a id="FigV12"></a>
-<a id="FigV13"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo094.jpg" alt="Buzzers" />
-</div>
-
-</div><!--container-->
-
-<p>This apparatus can be used also in connection with an
-alarm-clock, where the winding-key is exposed at the back,
-as it is in most of the nickel-cased clocks that are operated
-by a spring and which have to be wound each day. For this
-purpose obtain a piece of hard rubber or fibre, one-sixteenth<span class="pagenum" id="Page95">[95]</span>
-of an inch thick, an inch long, and half an inch wide. A
-piece of stout card-board or a thin piece of hard-wood soaked
-in hot paraffine will answer just as well, if the fibre or rubber
-cannot be had. Bore a small hole at the two upper corners
-and one at the middle near the lower edge. Obtain three
-garter-clips, with springs, and rivet one of them fast to the
-little plate of non-conducting material. Cut two lengths of
-old brass watch-chain, four inches long, or obtain eight
-inches of chain at a hardware-store, and divide it in
-half. Attach a garter-clip to one end of each piece, and
-make the other end fast in the holes at the corners of
-the small plate as shown in <a href="#FigV13">Fig. 13</a>. This will be the connector
-and will close the circuit when the alarm goes
-off.</p>
-
-<p>When the clock is wound and the alarm-spring is tight,
-catch one binding-post with a clip at the end of a chain
-and the other post with the remaining clip. Place the clock
-near the box and grasp the alarm-key with the clip on the
-plate. When the alarm goes off the bell on the clock will
-begin to ring, and when the key has made one revolution it
-twists the two pieces of chain together, closes the circuit,
-and the electric bell rings until some one unfastens one of
-the clips on the binding-posts and breaks the circuit. The
-great advantage in this double-alarm outfit is that it keeps
-the bell ringing until the attention of the sleeper is attracted.
-The bell on the clock will stop ringing directly the spring
-is unwound or run down; but in so doing it twists the
-chain and sets the electric mechanism in motion, to run
-until it is stopped, or until the battery polarizes or is exhausted.</p>
-
-<p><span class="pagenum" id="Page96">[96]</span></p>
-
-<h4>A Dining-table Call</h4>
-
-<p>One of the most convenient of house electric-calls is that
-between the dining-room and the butler’s pantry or the
-kitchen, its purpose being to summon the waitress without
-the necessity of ringing a bell at the table, or calling.</p>
-
-<p>There are various forms of push-buttons for this purpose&mdash;some
-embedded in the floor, others hanging from the
-centre light, and others again where the wire runs up from
-under the table, and the pear-shaped push rests on the cloth
-within easy reach. These last are good enough in their way,
-but are inconvenient, unsightly, and quite liable to get out
-of order.</p>
-
-<p>In order to use the floor-push the table must stand in
-exactly the right place; with the drop-string from a chandelier
-the cord is continually getting in the way; and as for
-the portable push that comes from under the table, one
-must be forever hunting for the button every time the table
-is set. And yet it is quite possible to avoid all these troubles
-and construct an apparatus that is always in order and
-always available, wherever the table may be placed. A
-visitor at a certain house noticed that the number of the
-family present at a meal was apt to vary largely, necessitating
-frequent lengthenings and shortenings of the table.
-And yet the waitress invariably appeared just at the right
-time, and whether one end or the other of the table was to
-be served, she was always on the spot where she was needed.
-The visitor tried to study it out, but was finally obliged to
-ask for an explanation of the mystery. The boy of the
-house smiled and intimated that he was responsible for this<span class="pagenum" id="Page97">[97]</span>
-domestic miracle; later on, when dinner was over, he
-removed the centre leaves from the table and displayed the
-simple apparatus that he had constructed and which had
-worked for several years without adjustment or repairs.</p>
-
-<p>The illustration (<a href="#FigV14">Fig. 14</a>) represents the frame of a dining-table
-with the middle cross-bar made fast to the side-rails,
-so as to support the mechanism. At both ends, and inside
-the rail, push-buttons are arranged and wires carried from
-them to binding-posts close at hand, as may be seen at the
-left side. The cross-bar at the middle of the table supports
-a large spool on which the flexible cord is wound, and kept
-taut by means of a clock-spring. This spool takes up the
-slack between the ends of the table when it is lengthened
-or shortened, while the smaller one opposite it keeps taut
-the feed-wires that come up through the floor. A short
-distance from the floor the wire is provided with a connector,
-so that when the rug is removed the feed-wires may be disconnected
-and slipped down.</p>
-
-<p>The large spool can be had at any dry-goods store where
-braids or fancy cords are kept. It should be about four
-inches long, three inches in diameter, and with sides thick
-enough to enable screws to be driven into it without fear of
-splitting the wood. An old clock-spring is attached at one
-side of the spool, while at the other two circular bands of
-brass are made fast, one within the other. An axle of stout
-wire should be driven through the spool; but if the hole is
-too large, wooden plugs may be glued in at each end so that
-a front view of the spool will appear as shown at A. The
-metal bands are cut with shears from sheet-brass, and are
-attached with fine steel nails, the heads of which are driven<span class="pagenum" id="Page98">[98-<br />99]<a id="Page99"></a></span>
-in flush with the wood. A hole is made in the side of the
-spool, close beside each band, so that the ends of wires may
-be brought through them and attached to the bands. This
-arrangement is illustrated at B, and at C the opposite end
-is shown, with its clock-spring, one end of which is made
-fast to the side of the spool and the other to the cross-rail.
-A small round piece of wood is slipped over the axle, at the
-spring side, and projects a quarter of an inch beyond the
-spring. This is to keep the spring away from the arm that
-stands out on that side to hold the spool in place.</p>
-
-<div class="container m40" id="FigV14">
-
-<div class="figcenter nomargin">
-<img src="images/illo098.jpg" alt="" />
-</div>
-
-<p class="caption">A DINING-TABLE CALL</p>
-
-</div><!--container-->
-
-<p>About half an inch of space is left between the spool and
-the arm at the opposite side, so that the spring contact-strips
-may be made fast to the arm and still have room to
-act. A view looking down on the spool and springs is
-shown at D, and E illustrates the arrangement of the circular
-strips and the spring contact-strips. If the table is to
-remain permanently in the same position, only one spool
-will be required, for the floor wires can come up and connect
-directly with the contact-strips. But if the table is to be
-moved about, a tension-spool, independent of the push-button
-wires, is necessary so that the position of the table
-may be changed without unwinding the large spool and
-dropping the cords down to the floor. The smaller spool
-is made and mounted in the same manner, and should be
-placed close to the large one. But a lighter spring will
-operate it. One end of a double wire-cord is made fast to
-binding-posts, mounted on a yoke of hard rubber or fibre,
-so that the terminals will be kept apart, as shown at F.
-The other ends are passed through the holes at one side of
-the small spool and soldered fast to the circular strips, or<span class="pagenum" id="Page100">[100]</span>
-a small screw may be passed down through the hole, binding
-the wire and touching the edge of one strip. Take care that
-it does not touch the other strip. The cord is then wound
-on the spool, and it is slipped in place so that the loose end
-of the spring is caught and held over a nail or screw-head.
-Turn the spool over several times to partially wind the
-spring; then attach the terminals to the wires that come up
-from the floor and the tension of the spring will draw the
-wires taut. The two contact-strips of brass, that rest
-against the brass circles, have insulated wires leading out
-from them in order to connect them with the corresponding
-wires leading from the strips of the larger spool.</p>
-
-<p>A simple way to mount the spools is shown at A in <a href="#FigV15">Fig.
-15</a>. A notch is cut in the face of the blocks large enough
-to admit the axle; then a face-plate is screwed over the end
-of the block to hold the axle in place. This arrangement
-makes it easy to remove the spool, in case of necessity,
-without detaching the arms from the cross-rail.</p>
-
-<div class="container m40" id="FigV15">
-
-<div class="figcenter nomargin">
-<img src="images/illo100.jpg" alt="Spools" />
-</div>
-
-</div><!--container-->
-
-<p>Two sets of wires are wound on the large spool, one leading<span class="pagenum" id="Page101">[101]</span>
-to the right-hand and the other to the left-hand push-button
-on the table-rails. The ends of the wires are arranged
-so that one leading from both directions is made
-fast to one circular strip on the spool, the other two being
-attached to the remaining band. This is more clearly
-shown at B in <a href="#FigV15">Fig. 15</a>, where the ends are visible as they
-are twisted together and pass through their respective
-holes. The spool is then turned over, and six or eight feet
-of wire wound on from each side. The spring is coiled up
-and caught on the nail or screw, and the ends of the wires
-are made fast to the binding-posts near the push-buttons.
-The wires from both push-buttons are then in connection
-with the circular bands, which in turn are connected to the
-bands on the smaller spool, and lead the current down
-through the floor wires. By pushing the button at either
-end the circuit is closed and the buzzer or bell is rung in the
-kitchen or pantry.</p>
-
-<p>Arranged in this manner, the wires are kept off the floor,
-no matter where the table is moved, and it can be drawn
-open as wide as may be found necessary to put in leaves.
-When closed again, the spring causes the large spool to revolve
-and wind up the wire.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page102">[102]</span></p>
-
-<h3>Chapter VI<br />
-<span class="chaptitle">CURRENT-DETECTORS AND GALVANOMETERS</span></h3>
-
-<p class="chapstart"><span class="largecap">A</span> current-detector is a necessary part of the
-amateur electrician’s equipment; technically, this piece
-of apparatus is called a galvanoscope.</p>
-
-<p>When a wire or a number of them are brought near a
-magnetic needle or a small compass, the needle will be
-deflected from its north and south line and will point east
-and west, or west and east, according to the direction in
-which the current is passing through the wires. All wires
-that are conducting electricity have a magnetic field, and
-when brought near the magnetized needle of a compass
-they have the power to act on it the same as another and
-stronger magnet would.</p>
-
-<p>The action of detectors depends upon two things&mdash;first,
-the magnetized needle that, when properly balanced, will
-point north and south; and, secondly, a current of electricity
-passing through a wire or wires held above the needle, or
-both above and below it. This is more clearly shown in
-<a href="#FigVI1">Fig. 1</a>, where a compass is resting on a wire connected to
-a battery. The wire also passes over the top of the compass,
-which doubles the electro-magnetic field.</p>
-
-<p>When the compass (with the needle pointing north) is<span class="pagenum" id="Page103">[103]</span>
-resting on the wire that is attached to the zinc pole of a
-battery, and when the end of the wire that passes back
-over the top of the compass is attached to the carbon pole,
-the needle will fly around and point to the east. When the
-wires are reversed, the needle will point to the west. Thus
-the combination of a battery or other source of electric
-current, a magnetic needle, and a coil of wire properly
-arranged, make an instrument that will detect electric
-currents and may be correctly called a current-detector.
-The pressure of more or less current is determined by instruments
-wound with wire of different sizes; the finer the
-wire the more sensitive the instrument, and consequently
-the more delicate. A very weak current can only be detected
-with a delicate and sensitive instrument. The
-coarser the wire and the larger the instrument, the better
-it will be for testing strong currents that would perhaps
-burn out the fine wire of the more delicate apparatus.</p>
-
-<p>This instrument, when placed between a source of electricity
-and a piece of apparatus, such as a bell, a motor, or
-lamp, does not weaken the current, for it requires no waste
-of electricity to operate the magnetic needle. Consequently,
-when a very weak current is being used for any tests, it is
-well to place a detector between the battery and the apparatus
-to show that the current is actually passing through
-the wire.</p>
-
-<p>A simple detector is made by winding fifteen or twenty
-feet of cotton-insulated copper wire No. 26 or 28 around
-the lower end of a drinking-glass. Leave six inches of each
-end loose; then after slipping the coil from the glass, tie
-the wires with thread at least four times around the circle,<span class="pagenum" id="Page104">[104]</span>
-so as to bind the wires together. Press two sides of the
-hoop together so as to flatten it; then with paraffine attach
-the coil to a square block of wood, as shown in <a href="#FigVI2">Fig. 2</a>.</p>
-
-<div class="container m40">
-<a id="FigVI1"></a>
-<a id="FigVI2"></a>
-<a id="FigVI3"></a>
-<a id="FigVI4"></a>
-<a id="FigVI5"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo104.jpg" alt="Galvanoscopes" />
-</div>
-
-</div><!--containers-->
-
-<p>From a thin clock-spring, not more than three-eighths of
-an inch wide, cut a piece two inches and a half long, and
-with a stout pair of tin-shears cut the ends so as to point
-them, as shown in <a href="#FigVI3">Fig. 3</a> A. With two pair of pliers bend a
-hump at the middle of the strip on the dotted lines shown
-in A, so that a side-view will appear like B in <a href="#FigVI3">Fig. 3</a>. Turn
-this strip over on a hard-wood block or a piece of lead, and
-with a stout steel-wire nail and a hammer dent the inverted<span class="pagenum" id="Page105">[105]</span>
-<span class="symbol">V</span> at the middle so that it will rest on the top of a needle-point
-without falling off.</p>
-
-<p>With three little pieces of wood make a bridge and attach
-it to the wooden base over the paraffine that holds the wire-coil,
-and drive a needle down in the middle of it, taking
-care that it does not go through the back and touch the
-wires underneath. On this needle hang the strip of steel
-spring, and, if it does not properly balance, trim it with the
-shears or a hard file until it is adjusted properly. Rub this
-piece of steel over the pole ends of a large horseshoe magnet,
-or place it within the helix of a large coil and turn a
-powerful current through the coil. This will magnetize the
-strip of steel, which will then become a magnetic needle and
-hold the magnetism. Attach two binding-posts to corners
-of the block, and make the loose ends of the coil-wires fast
-to them. You now have a current-detector, or galvanoscope,
-as shown in <a href="#FigVI4">Fig. 4</a>. Turn the block so that the needle
-points to north and south and parallel to the strands of wire.</p>
-
-<p>When the conductors from the poles of a battery or dynamo
-are made fast to the binding-posts, the needle will
-fly around to a position at right angles to that which it first
-occupied, as shown by the dotted line A A in <a href="#FigVI4">Fig. 4</a>. When
-the connection is broken the needle will turn around again
-and point to north and south, since the magnetic field about
-the wire ceases and disappears the instant the circuit is
-broken.</p>
-
-<p>This is one of the strange and unknown phenomena of
-electricity, for while the current exerts a force that deflects
-the needle, it does not destroy its magnetism. On the
-breaking of the contact, no matter how long it may have<span class="pagenum" id="Page106">[106]</span>
-held the needle away from its true course, it again points to
-north, and its magnetism is not affected.</p>
-
-<p>Another simple current-detector is shown in <a href="#FigVI5">Fig. 5</a>. A
-piece of broomstick is sawed in half and both pieces are
-made fast to a block which is mounted on a base of wood
-three-quarters of an inch in thickness. The vertical block
-should measure five inches long, three inches high, and five-eighths
-of an inch thick. The half-circular pieces of wood
-are mounted so that the flat surfaces are three inches apart
-and the lower edges are one inch above the base-block.
-These may be held in place with glue and screws driven
-through the back of the vertical block and into the ends
-of the projecting half-circular pieces. The base-block is
-six inches long and four inches wide, and the vertical block
-is mounted on it one inch from an edge. The pieces of
-broomstick are two inches long, and at the front ends a thin
-bar of brass or copper is screwed fast to hold them apart
-and in proper position, as shown at A in <a href="#FigVI5">Fig. 5</a>. To improve
-the appearance of this mounting, all the wood-work may be
-stained and shellacked before the metal parts are attached.</p>
-
-<p>With No. 26, 28, or 30 cotton-insulated wire make from
-fifteen to twenty wraps about the middle of the half-circular
-pieces of wood and carry the ends down through small holes
-in the base-block and thence through grooves cut at the
-under side of the block to the front corners, where they are
-to be made fast to binding-posts. A needle is to be set in
-the base-block midway between the two pieces of half-circular
-wood and through the strands of wire. Great care
-must be taken that the needle does not touch any bare
-wires, and as a precautionary measure it would be well to<span class="pagenum" id="Page107">[107]</span>
-wrap the needle with a piece of insulating-tape where it
-passes through the strands of wire. Now place on the top
-of it a magnetized piece of steel, as described for the detector
-shown in <a href="#FigVI4">Fig. 4</a>. As it may not always be convenient
-to turn the instrument so that the needle points north, a
-small bar of magnetized steel or a stout needle that has been
-magnetized with a horseshoe magnet or a helix, may be laid
-across the half-circular wood pieces, so that it is parallel with
-the top layer of wires&mdash;in fact, it should rest on top of them.</p>
-
-<p>By means of this needle, or bar, the magnetic piece of
-steel balanced on the vertical needle between the upper and
-lower strands of insulated wire may be held in one position
-no matter which way the block is turned. When the current
-passes in through one binding-post and out through
-the other (having thus travelled through the coil on the
-half-circular blocks) the needle is deflected and points out
-at the brass bar and back at the upright block.</p>
-
-<p>When making any of these pieces of apparatus, where
-delicately balanced magnetic needles are employed, all
-parts of the mounting blocks or other sections must be put
-together with glue and brass nails or screws. It will not do
-to use steel or iron nails, screw-eyes, or washers, nor pieces
-of sheet-iron, tin, or steel, for they will exert their influence
-on the vital parts of the apparatus and so destroy their usefulness.
-This is not so important when making buzzers,
-bells, motor-induction coils, or similar things, but in delicate
-instruments, where magnetic needles or electro-magnets are
-used for recording, measuring, or detecting, iron and steel
-parts should be carefully avoided, except where their use is
-expressly indicated.</p>
-
-<p><span class="pagenum" id="Page108">[108]</span></p>
-
-<h4>An Astatic Current-detector</h4>
-
-<p>Astatic current-detectors and galvanometers are those
-having two magnetic needles arranged with the poles in
-opposed directions.</p>
-
-<p>The ordinary magnetic or compass needle points to the
-North, and in order to deflect it a strong magnetic field must
-be created near it. For strong electric currents the ordinary
-single-needle current-detector meets all requirements, but
-for weak currents it will be necessary to arrange a pair of
-needles, one above the other, with their poles in opposite
-directions, and placed within or near one or two coils of
-fine wire. This apparatus will be affected by the weakest
-of currents, and will indicate their presence unerringly.</p>
-
-<p>The word “astatic” means having no magnetic directive
-tendency. If the needles of this astatic pair are separated
-and pivoted each will point to North and South, after the
-ordinary fashion. For all astatic instruments we must
-employ two magnetic needles in parallel, either side by side
-or one above another, as shown in <a href="#FigVI6">Fig. 6</a>, with the N and S
-poles arranged as indicated. This combination is usually
-called Nobili’s pair. If both needles are of equal length
-and magnetic strength, they will be astatic, for the power
-of one counterbalances that of the other. As a consequent
-neither points to North.</p>
-
-<p>A compound needle of this form requires but a very
-feeble current to turn it one way or the other, and this is
-the theory upon which all astatic instruments are constructed.</p>
-
-<p>A simple astatic current-detector may be made from a<span class="pagenum" id="Page109">[109]</span>
-single coil of fine insulated wire, a pair of magnetic needles,
-and a support from which to suspend them, together with
-a base-block.</p>
-
-<p>For the base-block obtain a piece of white-wood, pine,
-or cypress, four inches square and three-quarters of an
-inch thick. Sand-paper it smooth, and then give it two
-or three coats of shellac. From a strip of copper or brass
-(do not use tin or iron) make a bridge, in the form of an
-inverted <span class="symbol">V</span>, seven inches high, using metal one-sixteenth
-of an inch thick and half an inch wide. This bridge is to
-be screwed to the outside of the block, as shown at <a href="#FigVI7">Fig. 7</a>,
-so that it will be rigid and firm. A small hole is drilled
-through the top of the bridge to admit a screw-eye for the
-tension.</p>
-
-<p>Make a coil of No. 30 insulated wire, using ten or fifteen
-feet, and wind it about the base of a drinking-glass to
-shape it; then remove it and tie the coil, in several places,
-with cotton or silk thread, so as to hold the strands together.
-Shape it in the form of an ellipse and make it fast
-to the middle of the base-board with small brass or copper
-straps, and copper tacks or brass screws. Be very careful
-not to use iron, steel, or tin about this instrument, as the
-presence of these metals would deflect the needles and
-make them useless.</p>
-
-<p>Separate the strands at the top of the coil so that one
-of the needles may be slipped through to occupy a position
-in the middle of the coil. Ordinary large compass needles
-may be employed for this apparatus, or magnetized pieces
-of highly tempered steel piano-wire will answer just as
-well.</p>
-
-<p><span class="pagenum" id="Page110">[110]</span></p>
-
-<div class="container m40">
-<a id="FigVI6"></a>
-<a id="FigVI7"></a>
-<a id="FigVI8"></a>
-<a id="FigVI9"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo110.jpg" alt="Astatic galvanoscope" />
-</div>
-
-</div><!--container-->
-
-<p>A short piece of brass, copper, or wood will act as the
-carrier-bar for the needles. These should be pushed through
-holes made in the bar, and held in place with a drop of shellac
-or melted paraffine. A small hole is drilled at the top
-of the bar, or a small eye can be attached, through which
-to pass the end of a thread. The upper end of the thread
-is tied in a screw-eye, the screw part of which passes up
-through the hole in the bridge and into a wooden button
-or knob, which can be turned to shorten or lengthen the
-thread, and so raise or lower the needles. The lower needle<span class="pagenum" id="Page111">[111]</span>
-must be pivoted at an equal distance between the upper
-and lower parts of the coil.</p>
-
-<p>Two binding-posts are arranged at the corners of the
-base, and the ends of the coil wires are attached under the
-screw-heads. The in-and-out wires are to be made fast
-under the copper washers on the screw-eyes.</p>
-
-<p>Owing to the astatic qualities of the needles, the base-block
-does not have to be turned so that the coil may face
-North and South, as in the current-detector. When the
-slightest current of electricity passes through the coil it
-instantly affects the needles, turning them to the right or
-left according to the way in which the current is running
-through the coil.</p>
-
-<h4>An Astatic Galvanometer</h4>
-
-<p>The sensitiveness of an astatic detector may be increased
-by the added strength of the coil-field for a given current.</p>
-
-<p>There are two ways of accomplishing this result. The
-number of turns of wire may be increased in the coil, or
-two coils may be used, placed side by side. The latter
-method is the more satisfactory, since then the coil does
-not have to be opened at the top to admit the lower needle,
-the latter being dropped down between the coils. This apparatus
-is shown in the illustration of an astatic galvanometer,
-<a href="#FigVI8">Fig. 8</a>. The general arrangement of needles, bridge,
-and coils, is the same as described for the astatic current-detector.</p>
-
-<p>Each coil is made separately of ten feet of No. 30 insulated
-copper wire, wound about the base of a drinking-glass to<span class="pagenum" id="Page112">[112]</span>
-shape it; then pressed into elliptical shape, and fastened
-to a base-block with a brass or copper strip, and held down
-with small brass screws.</p>
-
-<p>The base-block should be four inches square, with the
-corners sawed off. Smooth the block with sand-paper, and
-then give it several good coats of shellac.</p>
-
-<p>The bridge is made from brass one-sixteenth of an inch
-thick and half an inch wide. The coils of wire are arranged
-about half an inch apart, and at both ends a small separator-block
-is placed between the coils, and then bound with silk
-or cotton thread. A circular indicator disk of bristol-board
-should be cut out and marked and attached to the top of
-the coils with a few drops of sealing-wax or paraffine; then
-the needles are suspended so as to hang properly, one above
-the card, the other between the coils.</p>
-
-<p>Three binding-posts are placed at one end of the block,
-and to them the end wires of the coils are led and attached.
-To the first binding-post (at the left) the strand of wire
-leading to the first coil is attached. It leads in and is coiled
-as the hands move on a clock, from left to right. The leading-out
-wire from the coil is made fast to the middle post.
-The leading-in wire to the second coil is also made fast to
-the middle post. The coil wires should have the turns in
-the same direction as the first coil; then the last wire is
-attached to the right-hand post.</p>
-
-<p>When making connections for a strong current, use an
-end and middle post. This arrangement will operate but
-one coil. For very weak currents make the leading in and
-out wires fast to the end-posts. This latter plan is more
-clearly shown in the diagram, <a href="#FigVI9">Fig. 9</a>. A and B represent<span class="pagenum" id="Page113">[113]</span>
-the coils, C, D, and E the binding-posts. The current,
-entering at C, passes through the coil A (as the hands move
-about the dial of a clock) and out at D, where connection is
-made with the wire leading in to coil B. The current passes
-through this coil in the same direction as the clock hands
-move, and out to post E. Be careful to arrange the wiring
-and connections after this exact manner, otherwise the instrument
-will not be of any use.</p>
-
-<p>The adjustment at the top of the bridge may be made
-with an inverted screw-eye and a small cork into which the
-eye can be screwed, thus raising or lowering the needles to
-the proper position. Be sure to have the needles in parallel
-when at rest.</p>
-
-<p>As the needles and coils are very sensitive it would be
-well to cover the instrument with an inverted glass jar.
-A bluestone or gravity battery jar will answer very well,
-and after the wires are connected to the binding-posts the
-glass may be placed over the entire apparatus.</p>
-
-<h4 id="Ref003">A Tangent Galvanometer</h4>
-
-<p>For testing the various degrees of intensity of a current
-a tangent galvanometer is usually employed. In this apparatus
-the increased strength is indicated by the index-pointer
-as it plays over a scale or graduated circle.</p>
-
-<p>A simple tangent galvanometer may be made from a flat
-hoop of wood-fibre or brass, mounted on a base by means
-of two uprights, together with the necessary compass
-needle, an index-card, insulated wire, and binding-posts
-for the electrical connections. This piece of apparatus is<span class="pagenum" id="Page114">[114]</span>
-shown in <a href="#FigVI10">Fig. 10</a>. It is built on a base-block six by seven
-inches and three-quarters of an inch thick. The block
-should be of selected wood, and after it is made smooth it
-should be given several coats of shellac.</p>
-
-<p>Two upright pieces of wood, five inches long, half an inch
-thick, and one inch in width, are screwed fast to the rear
-edges of the base-block to support the hoop on which the
-insulated wire is wound. Be careful not to use any iron or
-steel in the construction of this or any other recording
-instrument, except where it is expressly stated. Screws,
-nails, staples, or any bits of anchoring wire should be of
-copper or brass. String, thread, or silk may be used, especially
-where coils of wire are to be bound or fastened to
-hoops or base-blocks. The balance of the indicating needle
-is so delicate, and the sensitiveness of the coils is so easily
-affected, that nothing about or near the instruments should
-be of iron or steel.</p>
-
-<p>The hoop may be made of very thin hickory wood,
-steamed and bent so as to form a ring six inches outside
-diameter and one inch wide. It is even possible to construct
-a satisfactory hoop from a ribbon of brown paper,
-rolled and lapped, the several thicknesses being glued as
-the turns are made.</p>
-
-<p>If a metal hoop is to be used, solder the ends of a thin,
-hard ribbon of brass, copper, or zinc. This strip should be
-provided with holes, set in pairs about four inches apart,
-all around the hoop, and where the hoop is to be attached
-to the uprights two holes should be made close to the
-margins through which brass screws may pass.</p>
-
-<p>Across the middle of the hoop a strip of wood six inches<span class="pagenum" id="Page115">[115]</span>
-long, an inch wide, and a quarter of an inch thick is made
-fast. On this the graduated card is placed, and at the
-centre the balanced magnetic needle is arranged on a pivot.</p>
-
-<p>After the cross-stick is in place, wind five turns of No. 24
-insulated copper wire about the hoop, keeping it as nearly
-in the centre as possible. One end of the wire (the beginning)
-is to be attached to the first binding-post on the front
-of the base, and the other end to the second post. The wire
-should be wound round the hoop in the same direction as
-the clock hands travel about a dial.</p>
-
-<p>Another coil, composed of ten turns of wire, is made over
-the first one, the beginning end being attached to the middle
-binding-post and the last end to the third post. This
-arrangement is shown in <a href="#FigVI11">Fig. 11</a>, D and E representing the
-coils, while A, B, and C are the binding-posts. The current
-enters at A, passes through coil D, and out at post B. The
-next passage is in at B, through E, and out at C. A current
-passing in at A will travel to B, thence through E, and out
-at C. If the leading-in wire is made fast to A, and the out
-wire to C, the current will travel through the entire coil.</p>
-
-<p>Under this plan one or both coils may be used (the short
-or long one as desired) by making connections with the first
-and second binding-posts, the second and third, or the first
-and third, as the strength of the current will warrant.</p>
-
-<p>Strong currents will deflect the needle when travelling
-through a short coil, but the weaker the current the more
-coils it will have to pass through to properly deflect the
-needle and indicating pointer.</p>
-
-<p><span class="pagenum" id="Page116">[116]</span></p>
-
-<div class="container m40">
-<a id="FigVI10"></a>
-<a id="FigVI11"></a>
-<a id="FigVI12"></a>
-<a id="FigVI13"></a>
-<a id="FigVI14"></a>
-<a id="FigVI15"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo116.jpg" alt="" />
-</div>
-
-<p class="caption">TANGENT GALVANOMETERS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page117">[117]</span></p>
-
-<p>When the coils are all on, the hoop should be attached
-to the uprights with small brass screws driven through holes
-in the hoop and into the wood. The wire is bound to the
-hoop by means of threads or silk passed through each pair
-of holes in the hoop, and then tied fast. Fine insulated
-wire may be used in place of the thread, but care should
-be taken that the insulation is in perfect shape on both
-the binding and coil wires; otherwise a short-circuit will
-quickly destroy the value of the coils.</p>
-
-<p>The hoop should not touch the base-block, but should
-clear it by a quarter or half an inch. Make the coil ends
-fast (as described for the astatic galvanometer and illustrated
-at <a href="#FigVI9">Fig. 9</a>) by means of binding-posts. The wires need
-not be carried over the top of the block, but may run through
-holes under the hoop and along grooves cut in the under side
-of the block and leading to the foot of the binding-posts.</p>
-
-<p>The graduated card should be made from a piece of stout
-bristol-board or heavy card-board having a smooth, hard
-surface. It is laid out with a pencil or pen compass, as
-shown at <a href="#FigVI12">Fig. 12</a>, and should be three inches in diameter.
-The card is placed on the wood strip or ledge, so that the
-zero marks will be at the front and rear, or at right angles
-to the hoop and coils of wire. The compass needle, when
-at rest, should lie parallel with the coils, so that the current
-will deflect the needle and send the indicator around to one
-side or the other of zero, according to the direction in which
-the current is passing through the coils.</p>
-
-<p>This is more clearly shown at <a href="#FigVI13">Fig. 13</a>. The circle represents
-the outside diameter of the card; the dark cross-piece,
-the magnetic needle; and the pointed indicator, a stiff
-paper, or very thin brass or copper strip, cut and attached
-to the needle with shellac or paraffine.</p>
-
-<p><span class="pagenum" id="Page118">[118]</span></p>
-
-<p>When at rest the magnetic needle should be parallel to
-the coils. To insure this the instrument must be moved
-so that the lines of wire forming the coil will run North and
-South. Otherwise the N-seeking end of the magnetic shaft
-will point to North, irrespective of the position occupied by
-the wire coil.</p>
-
-<p>The magnetic needle may be made as described for the
-compass (see <a href="#Page54">chapter iv.</a>, Magnets and Induction Coils).
-It should be arranged to rest on a brass pivot pressed down
-into the cross-piece of wood.</p>
-
-<p>The indicator-needle may be cut from stiff paper, thin
-sheet-fibre, or very thin cold-rolled brass or copper, the
-latter being commonly known as hard or spring-brass.
-Only one pointer is really necessary&mdash;that pointing to the
-front. But the weight of the material would have a tendency
-to upset the magnetic needle, and therefore it is better
-to carry an equally long tail or end, on the opposite side, to
-properly balance the needle.</p>
-
-<p>A very weak current, passing in through the first post
-and out at the third, will cause the indicator to be deflected
-considerably, or so that it will point from 40° to 60° on
-either side of the zero point, according to the direction in
-which the current is running through the coils.</p>
-
-<p>When not in use the magnetic needle should be removed
-from the pivot, and placed in a box or other safe place,
-where it will not become damaged.</p>
-
-<p>A differently arranged tangent galvanometer is shown at
-<a href="#FigVI14">Fig. 14</a>. As the line of binding-posts would indicate, there
-are several coils of wire about the circle or hoop.</p>
-
-<p>This galvanometer can be used for either strong or weak<span class="pagenum" id="Page119">[119]</span>
-currents, since it is wound with both coarse and fine insulated
-wire. An upright plate of wood, seven inches wide
-and eight inches high, supports the hoop and compass.
-The top corners are sawed off, and four inches above the
-bottom a straight cut is made across the plate, five inches
-wide and arched in a half-circle five inches in diameter.
-A shelf of wood a quarter of an inch thick, three inches
-wide, and five inches long is made, and attached as a ledge
-in this arched opening, so that a compass three inches in
-diameter may rest upon it.</p>
-
-<p>The shelf should be arranged so that it will hold the
-compass in the middle of the circle instead of at one side.
-The turns of wire will then be in line with the magnetic
-needle when the latter is at rest. A base-block seven inches
-long, three inches wide, and seven-eighths of an inch thick
-is cut and attached to the upright plate by driving screws
-through the bottom of the plate and into the rear edge of
-the base. The corners are to be cut from the front of the
-base, and ten small holes are to be bored half an inch out
-from the upright and about a quarter of an inch apart.
-These are for the end wires that will extend down from the
-coils, and from thence to the binding-post holes. Grooves
-may be cut in the under side of the base-block for the wires
-to rest, in, as shown at <a href="#FigVI15">Fig. 15</a>, which is a view of the inverted
-base.</p>
-
-<p>A hoop is made of brass, six inches in diameter and an
-inch wide. It is held to the upright plate with copper wire
-passed through a small hole, bored at the inner edge of the
-band, and back through two small holes bored in the plate,
-the ends being twisted together at the back of the plate.<span class="pagenum" id="Page120">[120]</span>
-A wire at the top, bottom, and both sides will be sufficient
-to hold it securely in place.</p>
-
-<p>The first coil of wire is made of No. 18 insulated, and the
-beginning end is made fast to the binding-post at the left.
-The wire is carried up through the first hole under the hoop,
-and after three turns have been made the end is carried
-down through the second hole and made fast to the foot of
-the second binding-post.</p>
-
-<p>The second coil is of No. 24 insulated copper wire. The
-beginning end is made fast to the second binding-post, carried
-up through the third hole, given five turns about the
-hoop, drawn down through the fourth hole, and attached
-to the third binding-post.</p>
-
-<p>The third coil is of the same size wire but has ten turns.
-The fourth coil has twenty turns, and the fifth, of No. 30
-insulated wire, has thirty turns, the last end being attached
-to the post at the right. In all the coils there should be a
-total of sixty-eight turns, or about one hundred and five
-feet of wire.</p>
-
-<p>For strong currents the in-and-out wires may be attached
-to posts Nos. 1 and 2 at the left, and for weaker currents to
-Nos. 2 and 3. For still weaker currents, use Nos. 3 and 4,
-and so on. To detect the very weakest currents, attach
-the in-and-out wires to the first and last post, and let the
-current travel through all the coils or the entire length of
-the wire wound about the hoop.</p>
-
-<p>The magnetic needle is made in the same manner as
-described for <a href="#FigVI10">Fig. 10</a>, and the pointer is attached in a similar
-fashion. But instead of being mounted on a pivot
-over a card, and so exposed to the open air and possible<span class="pagenum" id="Page121">[121]</span>
-draughts, the delicate mechanism is arranged within a brass
-hoop, which is made fast to the ledge. The graduated card
-is at the bottom of the hoop, or box formed by it, and to
-protect the needle and prevent it from being displaced it
-should be covered with glass. This can be done by making
-a split ring of spring-brass wire and pressing it down inside
-the hoop. Over this a round piece of glass is placed, and
-another hoop is pressed in above it to hold the glass in
-position. If the rings are carefully made and of stout wire
-they will stay in place; otherwise a drop of melted sealing-wax
-or paraffine will be necessary to keep them where they
-are wanted.</p>
-
-<p>The glass should be arranged close enough to the needle
-to prevent it from jumping or being shaken off the supporting
-pin, but not so close as to prevent its moving easily.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page122">[122-<br />123]<a id="Page123"></a></span></p>
-
-<h2 class="part">Part II</h2>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page124">[124-<br />125]<a id="Page125"></a></span></p>
-
-<h3>Chapter VII<br />
-<span class="chaptitle">ELECTRICAL RESISTANCE</span></h3>
-
-<p class="chapstart"><span class="largecap">T</span><span class="afterlargecap">he</span>
-science of controlling forces is so well understood
-and figured out that it becomes a simple mechanical
-proposition to adapt the various types of controllers to any
-form of power that may be employed. The tremendous
-force stored within the mechanism of a great transatlantic
-liner is governed by the twist of a man’s wrist. The
-locomotive that will pull a hundred cars loaded with coal,
-representing a weight of thousands of tons, is started and
-stopped by a short lever that is drawn in one direction or
-the other by a man’s hand. Great forces of all kinds are
-quite as easily controlled as the supply of gas through a
-jet&mdash;by simply turning the key that lets out so much as
-may be required, no matter what the pressure is back of
-the flow.</p>
-
-<p>This same principle applies to electricity, but the means of
-governing it is vastly different from the methods employed
-for other forces. Electricity is an unknown and unseen
-force, coming from apparently nowhere and returning to its
-undiscovered country immediately upon the completion of
-its work. The flow of steam, water, liquid air, gas, and
-compressed air through pipes is governed by a throttle or<span class="pagenum" id="Page126">[126]</span>
-cock, which allows as much or as little to pass as may be
-required; and if the joints, unions, and couplings in the pipes
-are not absolutely tight there will be a leakage. Electricity
-is controlled by resistance in its passage through solid wires,
-rods, or bars, and cannot be confined within a given space
-like water, nor held in tanks or pipes as a vapor or gas. It
-is invisible, colorless, odorless, and occupies no apparent
-space that can be measured; it is the most powerful and
-terrible and yet docile force known to man, doing his bidding
-at all times when properly governed and regulated. In
-some respects, electricity can be compared to water stored
-in a tank&mdash;for instance, if you have a tank of water containing
-fifty gallons at an elevation of twenty-five feet, and a
-pipe leading down from it, the pressure of the water at the
-outlet of the pipe will be a given number of pounds. Now
-if the tank were double the size the pressure at the outlet
-of the pipe would be proportionately greater. Now if you
-have a battery made up of a number of cells they will develop
-a given number of volts, and if the number of the cells
-be doubled the voltage will be correspondingly increased.
-Or if you have a dynamo giving a certain number of volts,
-that number may be increased by doubling the size.</p>
-
-<p>The water contained within the tank represents its pressure
-at the outlet of the pipe. The current in volts, generated
-in a battery or dynamo, represents its pressure on an
-outlet or conductor wire; and both represent the force behind
-their respective conductors. The valve, or faucet, at
-the end of the pipe plus the friction in the pipe would represent
-the resistance to the flow of water, while the resistance-coils
-or other mediums plus the size of the wire, or<span class="pagenum" id="Page127">[127]</span>
-conductor and switch, would regulate the flow of electric
-current. The flow of water in a pipe under certain pressure
-would represent its gallons per minute or hour, while with
-electricity its flow in a wire or other conductor would represent
-its amperage. It is to govern the flow of current
-that resisting mediums are employed.</p>
-
-<p>The resistance of electric current is measured in ohms, and
-it is with this phase that we are interested in this chapter.
-If there is only a small resistance put in the path of a current,
-then it requires but a small pressure or voltage to send
-it through the wires or circuit. This is easily understood
-by the boy who has experimented with small incandescent
-lamps in which short pieces of carbon-filament are contained.
-It requires the pressure of a few volts only to send
-the current through the carbon; but for the large carbon-filaments,
-measuring ten or twelve inches in length, from
-one hundred to five hundred volts may be necessary. The
-ordinary house lamps require one hundred and ten volts
-and half an ampere to give sixteen candle-power.</p>
-
-<p>It is easily understood, then, that it requires a high pressure
-or voltage to force the current through the resisting
-carbon-filament, or across the space from one carbon to the
-other in the arc-lamps used for street lighting. The shorter
-and larger the conducting wires the less the resistance, and
-consequently the lower the voltage or pressure necessary to
-force it. Contrariwise the longer and finer the conducting
-wares, the greater the resistance. As copper is the best
-commercial conductor of electric currents, it is in universal
-use, and in it the minimum of resistance is offered to the
-current. Iron wire is a poorer conductor, and is not used<span class="pagenum" id="Page128">[128]</span>
-for high voltage (such as trolleys or transmission of power),
-but is confined to telegraph and telephone lines and low-pressure
-work. German-silver wire, one of the poorest
-conductors, is not used for lines at all, but is employed
-solely as a resisting medium for controlling current.</p>
-
-<h4>Ohm’s Law</h4>
-
-<p>This is the fundamental formula expressing the relations
-between current, electro-motive force, and resistance in an
-active electric circuit. It may be expressed in several ways
-with the same result, as follows:</p>
-
-<p>1. The current strength is equal to the E. M. F. (electro-motive
-force) divided by the resistance.</p>
-
-<p>2. The E. M. F. (electro-motive force) is equal to the
-current strength multiplied by the resistance.</p>
-
-<p>3. The resistance is equal to the E. M. F. (electro-motive
-force) divided by the current strength.</p>
-
-<p>All these are different forms of the same statement; and
-when figuring electrical data, C stands for current, E for
-electro-motive force, and R for resistance.</p>
-
-<h4>Resistance-coils and Rheostats</h4>
-
-<p>The method by which electricity is controlled is resistance.
-No matter how great the voltage of a current, nor its volume
-in amperes, it can be brought down from the deadly force
-of the electric trolley-current to the mild degree needed to
-run a small fan-motor, an electric bell, or a miniature lamp.
-This is accomplished by means of resisting mediums, such<span class="pagenum" id="Page129">[129]</span>
-as fluids or wires, which hold back the current, and allow
-only the small quantity to pass that may be required to
-operate the apparatus.</p>
-
-<p>The jump from the high voltage of the trolley-current to
-the low one required for the electric bell, a lamp, or a small
-motor, is frequently made in traction-work, but in this case
-regular transformers are used. For the small apparatus,
-that may have its current supplied from a battery, or a
-small dynamo driven by a water-motor, the forms of resistance-coils
-and rheostats described on the following pages
-should meet every requirement.</p>
-
-<p>The standard unit of resistance is called an ohm, so
-named after Dr. G. S. Ohm, a German electrician, whose
-theory on the subject is accepted as the basis on which to
-calculate all electrical resistance. The legal ohm is the
-resistance of a mercury column one square millimetre in
-cross-sectional area and one hundred and six centimetres in
-length, and at a temperature of 0° Centigrade or 32° Fahrenheit,
-or the freezing-point for water. The conductivity of
-metals is dependent greatly on their temperature, a hot wire
-being a much better conductor than a cold one. Since
-counter-electro-motive force sometimes gives a spurious resistance,
-the ohmic resistance is the true standard by which
-all current is gauged.</p>
-
-<p>In technical mechanism and close readings the ohmic
-resistance counts for a great deal, but in the simple apparatus
-that a boy can make the German-silver resistance coils
-and the liquid resistance will answer every purpose.</p>
-
-<p>To give a clearer idea of the principle of the rheostats, a
-short description of the mercurial column will first be presented.<span class="pagenum" id="Page130">[130]</span>
-During the early part of the last century wires were
-not used as a resisting medium for electric currents. In their
-place, glass tubes, filled with mercury sealed at one end and
-corked at the other, were arranged in rows and supported in
-a wooden rack.</p>
-
-<div class="container m40" id="FigVII1">
-
-<div class="figcenter nomargin">
-<img src="images/illo130.jpg" alt="Rheostat" />
-</div>
-
-</div><!--container-->
-
-<p>Wires led out from the top and bottom of each tube,
-and were brought down to metal buttons arranged in a row
-along the front edge of the base-plate, as shown in the illustration
-of a mercurial rheostat (<a href="#FigVII1">Fig. 1</a>). Each tube represented
-a certain resistance&mdash;one or more ohms, as required.
-The outlet wire was attached to the button at one end of the<span class="pagenum" id="Page131">[131]</span>
-row, and the inlet could be moved along from button to
-button, until the required amount of current was obtained.</p>
-
-<p>The mercurial rheostat was an expensive, cumbersome,
-and treacherous thing to handle; it was liable to break, and
-its weight often prohibited its use in places where the more
-convenient and easily handled German-silver rheostats are
-now in universal employment. Overheating the mercury in
-the columns caused it to expand, and sometimes, before the
-switch could be thrown open, an end would be forced out
-and the mercury would climb over the edge of the glass
-columns.</p>
-
-<p>All metals have a certain amount of resistance for electric
-currents, and some have more than others. German-silver,
-for instance&mdash;a metal made of a mixture of other metals with
-about eighteen per cent. of nickel (see <a href="#Page359">Appendix</a>)&mdash;is considered
-to be the best commercial resistance medium, while
-pure copper is regarded as the best commercial conductor.
-Unalloyed copper is universally employed for electric conductors
-of high voltage; but for telegraph and telephone
-work, galvanized iron wire is still used extensively.</p>
-
-<p>The finer the wire, the higher is its resistance, and the more
-resistant the metal, the greater are the number of ohms to a
-given length. To nine feet and nine inches of No. 30 copper
-wire there is one ohm resistance, while to No. 24&mdash;which is
-six sizes coarser&mdash;there is one ohm to thirty-nine feet and
-one inch. In many cases it is necessary to use the coarser
-wire and greater length, as the current would superheat or
-burn the fine wire, while the coarser would conduct it safely.</p>
-
-<p>For very high voltage and amperage&mdash;such as used in traction
-cars, in power stations, and in manufacturing plants&mdash;castings<span class="pagenum" id="Page132">[132]</span>
-of German-silver are employed and linked in series.
-They are more easily handled than the coils of wire, and a
-greater number of them can be accommodated in a small
-space.</p>
-
-<div class="container m30" id="FigVII2">
-
-<div class="figcenter nomargin">
-<img src="images/illo132.jpg" alt="Coils" />
-</div>
-
-</div><!--container-->
-
-<p>For light currents in experimental work, where batteries
-are employed, obtain a pound or two of bare German-silver
-wire, from Nos. 24 to 30, and wind the strands on a round
-piece of stick attached to a winder (see Magnets and Induction-Coils,
-<a href="#Page54">chapter iv.</a>). Make several of these coils,
-two or three inches long, with the wire wound closely and
-evenly. When pulled apart the coils will appear as shown
-in <a href="#FigVII2">Fig. 2</a> A, and will resemble a spiral spring. This can
-be made fast over a porcelain knob and the ends caught
-down, as shown at B in <a href="#FigVII2">Fig. 2</a>, or it may be drawn over a<span class="pagenum" id="Page133">[133]</span>
-round stick, a porcelain tube, or a lug made of plaster of
-Paris and dextrine (three parts of the former to one of the
-latter), as shown at C in <a href="#FigVII2">Fig. 2</a>, and the ends securely bound
-with a strand or two of wire, twisted tight to keep the ends
-from slipping.</p>
-
-<p>The lugs may be made in a mold, using as a pattern a
-piece of broom-handle&mdash;shellacked and oiled to prevent the
-plaster from adhering to it. Obtain a small square and
-deep box, and drop some of the wet mixture down in the
-bottom; on this place the broomstick, small end down (it
-should be slightly tapered), and around it pour in the wet
-plaster mixture. While it is setting, turn the stick with the
-thumb and fingers, so as to shape the hole perfectly then
-draw it out, and a true mold will be the result. When dry
-enough, pour some shellac down into the mold and revolve
-it, so that the shellac will be evenly distributed, and
-let it harden for a day. Then saw off the end of the mold,
-so that it will be open at both ends.</p>
-
-<p>In order to make the lugs, pour in the plaster mixture,
-taking care to oil the mold before each pouring, so that
-the lug can be drawn out when the mixture has set. If it
-sticks, tap the small end gently to start it. For coils where
-there is little or no heat, ordinary pieces of broom-handle,
-or round sticks having a coat or two of shellac, will answer
-very well; but where the current heats the core, it must be
-of some material that will not char.</p>
-
-<p>Another method of making resistance-coils is to measure
-off a length of wire; then double it, and with a small staple
-attach the loop end at one end of the (wooden) core. Pay
-out the two strands of wire an equal distance apart with the<span class="pagenum" id="Page134">[134]</span>
-thumb and fingers, and with the other hand twist the core.
-At the other end of the spool catch the loose ends of the
-wire under small staples, taking great care not to let the
-staples touch or even be driven close together. This arrangement
-is shown at D in <a href="#FigVII2">Fig. 2</a>, and for a field resistance-board
-any number of these coils may be made.</p>
-
-<div class="container m30" id="FigVII3">
-
-<div class="figcenter nomargin">
-<img src="images/illo134.jpg" alt="Coils" />
-</div>
-
-</div><!--container-->
-
-<p>In <a href="#FigVII3">Fig. 3</a> the mode of connecting coils is shown. The
-dots represent contact-points to which the movable arm can
-be shifted. The wires at the bottom of coil, Nos. 1 and 2,
-are connected together, while those at the top of No. 2 and<span class="pagenum" id="Page135">[135]</span>
-3 are joined, and so on to the end. The leading-in current
-is connected at pole H and so on to J, while the leading-out
-wire is made fast to pole I. The switch-arm is moved
-on the first dot, or contact-point, and the current passes up
-wire A, down coil No. 1, up coil No. 2, down No. 3, up No.
-4, and so on to No. 6, and down wire G and out at I. Supposing
-that this offers too much resistance, the switch-arm
-is moved up one point. This cuts out coil No. 1, as the
-current passes up wire B, through coil No. 2, down No. 3,
-and so on, and out through G and pole I. Another move
-of the switch and coil No. 2 is cut out, the current passing
-up wire C, down coil No. 3, up No. 4, and so on, and out at
-I. Each move of the switch cuts out one coil, lessening the
-resistance; but when moved to the last contact-point the
-current flows without resistance&mdash;in at H, through the
-switch-arm, and out at I.</p>
-
-<p>The plan of arranging the coils suggested at <a href="#FigVII2">Fig. 2</a> B is
-shown in <a href="#FigVII4">Fig. 4</a>, where four of the coils are arranged in series
-over porcelain knobs, and the lower ends made fast to the
-base-board with small staples. Small pieces of brass are
-used for the switch contact-plates; those are provided with
-one plain and one countersunk hole for a flat and round
-headed screw.</p>
-
-<p>The screw-heads are arranged in a semicircular fashion,
-so that the switch-arm, attached at one end to the screw J,
-will touch each plate as it is moved forward or backward.</p>
-
-<p><span class="pagenum" id="Page136">[136]</span></p>
-
-<div class="container m40">
-<a id="FigVII4"></a>
-<a id="FigVII5"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo136.jpg" alt="" />
-</div>
-
-<p class="caption blankbefore75">TWO SIMPLE FORMS OF RHEOSTATS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page137">[137]</span></p>
-
-<p>The current passing in at binding-post A travels to J and
-B, the latter being the resting-plate for the switch-arm.
-A move of the arm to C sends the current up over the first
-coil and down; then over the second, third, and fourth
-coils, and out at G; through plate H (which is the rest at the
-right side), and out at I.</p>
-
-<p>A move of the switch-arm to D cuts out the first coil; a
-move to E, the first and second coils; and so on until the
-last plate is reached, when the current will pass without resistance
-in at A, through J, and out at I.</p>
-
-<p>A simple arrangement for a resistance-coil is shown in
-<a href="#FigVII5">Fig. 5</a>. This consists of a set of small metal plates in which
-two holes are made, one for a screw, the other for a screw-eye
-(see <a href="#Ref004">Binding-posts</a>, <a href="#Page33">chapter iii.</a>). Two lines of steel-wire
-nails are driven along a board, and German-silver wire
-is drawn around them in zig-zag fashion, beginning at the
-left and going towards the right side of the board. One end
-of wire is made fast under the screw-head on plate A. The
-strand is carried out around the first nail on the lower row
-and over the first one on the upper row, then down, up, down
-until six nails have been turned. The wire is then carried
-down to the screw in plate B, given two turns, and carried
-up again and over the nail on the top row, repeating the
-direction of zigzag No. 1, until six of them are made. The
-end of the wire is then made fast to plate G, and all the
-screws are driven in to hold the plates and wire securely.</p>
-
-<p>The inlet wire is attached to A, the outlet to G, and any
-degree of resistance can be had by moving the inlet wire to
-the various plates along the line, cutting out sections Nos. 1
-to 6 as desired.</p>
-
-<p>For heavier wire the arrangement as shown in <a href="#FigVII6">Fig. 6</a>
-should be satisfactory.</p>
-
-<p><span class="pagenum" id="Page138">[138]</span></p>
-
-<div class="container m40">
-<a id="FigVII6"></a>
-<a id="FigVII7"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo138.jpg" alt="Rheostat" />
-</div>
-
-</div><!--container-->
-
-<p>A frame twelve by fifteen inches is constructed of wood
-three-quarters of an inch thick and one inch and a quarter
-wide, having the ends securely fastened with glue and
-screws. Spirals are wound of German-silver wire (any size
-from No. 16 to 22), and drawn apart. The ends are caught<span class="pagenum" id="Page139">[139]</span>
-to the frame with small staples, and each alternate coil-end
-is joined, as shown in <a href="#FigVII6">Fig. 6</a>. The leading-out wires to the
-contact-points on the switch should be of insulated copper,
-and are to run down the sides of the frame, and so to the
-switch-board. To clearly illustrate, however, the plan of
-wiring, the drawing is made so as to show the leads from
-the coil-ends to the switch. Care should be taken to study
-this drawing well, so as not to make an error in connecting
-a wrong end to a contact-point, thereby causing a short
-circuit. When properly connected the current passes in at
-A and out at I; but if wires are improperly connected, the
-current will jump when the switch-arm reaches the misconnected
-contact.</p>
-
-<p>The switch is an important part of every rheostat, and
-should be carefully and accurately made. One of the
-simplest and most practical switches is constructed from a
-short, flat bar of brass or copper having a knob attached at
-one end and a hole provided at the other through which a
-screw may pass (see <a href="#Ref005">Switches</a>, <a href="#Page33">chapter iii.</a>). The contact-points
-are made from one or two copper washers, with the
-holes countersunk so that a machine screw of brass, with a
-flat head, will fit the hole snugly. The top of the head
-will then be flush with the top of the washer, as shown at
-<a href="#FigVII7">Fig. 7</a> A. The bolt is passed down through a piece of board,
-then slate or soapstone, and caught with a washer and nut,
-as shown at <a href="#FigVII7">Fig. 7</a> B. A loop of wire is passed about the
-bolt end, then another nut is screwed tightly over it to hold
-it in place, as well as to lock the first nut. The binding-posts
-that hold the inlet and outlet wires may be made of
-bolts and nuts also, as shown at <a href="#FigVII7">Fig. 7</a> B;
-but the bolt must<span class="pagenum" id="Page140">[140]</span>
-be passed through the switchboard so that the head is at
-the rear and the ends project out to receive the nuts.</p>
-
-<p>A very compact and simple rheostat and switch is shown
-in <a href="#FigVII8">Fig. 8</a>. It is composed of a base-board, eight blocks of
-hard-wood, and a top strip used as a binder to lock the upper
-ends of the blocks together. The hard-wood blocks are
-three-quarters of an inch thick, one inch and a half wide, and
-four inches long. A small hole is made near each end of
-the block and through one of them an end of the wire is
-passed. The wire is then wound round the block, taking
-care to lay it on evenly, and with about one-eighth of an
-inch of space between each strand. When the opposite
-hole is reached, pass the end of the wire through it and clip
-it. The block will then resemble <a href="#FigVII7">Fig. 7</a> C. There should
-be three or four inches of wire at each end for convenience in
-connection, and when the eight blocks are wound they are
-to be mounted on end at the rear side of a base-board measuring
-ten inches long, three inches wide at the ends, and
-nine at the middle (or across the face of the switchboard
-to the rear edge behind the blocks). Use slim steel-wire
-nails and glue to attach the blocks to the base; or slender
-screws may be employed. Across the top lay a piece of
-wood a quarter of an inch in thickness, and drive small nails
-or screws down through it and into the blocks.</p>
-
-<p><span class="pagenum" id="Page141">[141]</span></p>
-
-<div class="container m40">
-<a id="FigVII8"></a>
-<a id="FigVII9"></a>
-<a id="FigVII10"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo141.jpg" alt="" />
-</div>
-
-<p class="caption">COMPACT FORMS OF RHEOSTATS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page142">[142]</span></p>
-
-<p>Connect the ends of the coils together in series, as already
-described, and carry the wires under the base-plate in
-grooves cut with a <span class="symbol">V</span>-shaped chisel. If the sunken wires
-are bothersome, the work may be avoided by running the
-wires direct to the foot of the contact-points and elevating
-the rheostat on four small blocks that may be screwed, or
-nailed and glued, under the corners, as shown in <a href="#FigVII8">Fig. 8</a>.
-These will raise the base half an inch or more above the
-table on which the rheostat will rest so as to allow room for
-the under wires.</p>
-
-<p>A rheostat of round blocks standing on end is shown at
-<a href="#FigVII9">Fig. 9</a> A. These are pieces of curtain-pole, four inches long
-and wound with loops of No. 16 or 18 wire, as shown at
-<a href="#FigVII9">Fig. 9</a> B. The loop and loose ends are caught with staples,
-and when arranged on a base-board they are to be connected
-in series as before described. One long, slim screw
-passed up through the base-board and into the lower end
-of the block will hold each block securely in place. To
-keep it from twisting, a little glue may be placed under the
-blocks so that when the screw draws the block down to the
-base it will stay there permanently upon the hardening of
-the glue. The leading wires should be slipped under the
-washers forming the contact-points of the switch; or they
-may be carried under the board to the nuts that hold the
-lower ends of the bolts.</p>
-
-<p>Another form of rheostat (<a href="#FigVII10">Fig. 10</a> A) is made by sawing
-a one-inch curtain-pole into four-inch lengths and cross-cutting
-each piece with eight or ten notches, as shown at
-<a href="#FigVII10">Fig. 10</a> B. These pieces are screwed and glued fast along
-each side of a base-board eight inches wide and fourteen
-inches long, so that the notches face the outer edges of the
-board. The strand of wire passes round these upright blocks
-and fits into the notches so as to prevent them from falling
-down.</p>
-
-<p>The top end of wire at each pair of blocks is made fast by
-a turn or two of another piece of wire and a twist to hold it<span class="pagenum" id="Page143">[143]</span>
-securely; then the loose end is carried down through a hole
-and along under the board to the foot of a contact-point.</p>
-
-<p>Any number of these upright coils may be made, and on a
-long board the switch may be arranged at one side instead
-of at the end, as shown in <a href="#FigVII10">Fig. 10</a> A. When making ten or
-more coils it is best to use three or four sizes of wire, beginning
-with fine and ending with coarse. For instance, in a
-twelve-coil rheostat make three coils of No. 26, three of No.
-22, and three of No. 18; or if coarser wire is required use
-Nos. 20, 16, and 12.</p>
-
-<p>German-silver comes bare and insulated. It is preferable
-to have the fine wire insulated, but the heavier sizes may be
-bare, as it is cheaper; moreover, if heated too much the insulation
-will burn or char off. When cutting out the coils
-always begin at the end where the finer wire is wound;
-then as the current is admitted more freely the heavier wires
-will conduct it without becoming overheated.</p>
-
-<p>For running a sewing-machine, fan, or other small direct-current
-motor wound for low voltage, the house current (if
-electric lights are used in the house) may be brought down
-to the required voltage with German-silver rheostats similar
-to these already described. Another and very simple
-method is to arrange sixteen-candle-power lamps in series,
-as shown in <a href="#FigVII11">Fig. 11</a>. Six porcelain lamp-sockets are screwed
-fast to a wood base and the leading in and out wires
-brought to binding-posts or the contact-points of a switch.
-The leading-in wire to the series is made fast at binding-post
-A, which in turn is connected with screw B, under the head
-of which the switch-arm is held. When the switch is thrown
-over to contact-point C the current passes through lamp<span class="pagenum" id="Page144">[144]</span>
-No. 1 back to point D; through lamp No. 2 back to E; then
-through lamps Nos. 3, 4, 5, and 6, and out through point I
-to post J. A turn of the switch to D cuts out lamp No. 1, to
-E cuts out No. 2, and so on. The filaments of incandescent
-lamps in their vacuum are among the very best mediums of
-resistance, and with a short series of lamps a current of
-220 volts can quickly be cut down to a few volts for light
-experimental work or to run some small piece of apparatus.</p>
-
-<div class="container m40">
-<a id="FigVII11"></a>
-<a id="FigVII12"></a>
-<a id="FigVII14"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo144.jpg" alt="Rheostats" />
-</div>
-
-</div><!--container-->
-
-<p>Lamps in series are often used to cut down the current for
-operating electric toys and trains. The adjustment of the
-current should never be left to children, however, but should
-be attended to by some one qualified to look after the
-apparatus. Otherwise an unpleasant or even dangerous<span class="pagenum" id="Page145">[145]</span>
-shock may be received. Another simple form of resistance
-apparatus is made from the carbon pencils used for arc
-lights. Short pieces will answer very well, but if the long
-bare ones can be had they will be found preferable. Do not
-use the copper-plated ones as they would conduct the current
-too freely; they should be bare and black. Now around
-the ends of each piece take several turns of copper wire for
-the terminals and cut-out wires. Fasten those pencils down
-on a board (as shown at <a href="#FigVII12">Fig. 12</a>) by boring small holes
-through the board, passing a loop of copper wire down
-through the holes, and giving the ends a twist underneath.
-The leading wires to and from the contact-points should be
-insulated and may be above or below the board. From the
-descriptions already given, the connections of this rheostat
-can readily be understood.</p>
-
-<p>The rheostat shown in <a href="#FigVII13">Fig. 13</a> is perhaps the most complete
-and practical apparatus that a boy could make or
-would need. It is composed of a frame, six porcelain tubes,
-a switchboard, and the necessary German-silver and copper
-wire.</p>
-
-<p>From an electrical supply-house obtain six porcelain tubes
-fourteen by three-quarter inch. Porcelain tubes and rods
-warp in the firing and are seldom straight; in purchasing
-these select them as nearly perfect as possible in shape, size,
-and length.</p>
-
-<p><span class="pagenum" id="Page146">[146]</span></p>
-
-<div class="container m40" id="FigVII13">
-
-<div class="figcenter nomargin">
-<img src="images/illo146.jpg" alt="" />
-</div>
-
-<p class="caption">A PANEL RHEOSTAT</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page147">[147]</span></p>
-
-<p>Buy, also, twelve small porcelain knobs that are the right
-size to fit inside the large tubes. These should have holes
-bored through them to admit screws. Construct a frame
-of hard-wood to accommodate the tubes, as shown in the
-drawing, and leave one end loose. With slim screws make
-the porcelain knobs fast to the top and bottom strips of the
-frame, as shown in <a href="#FigVII14">Fig. 14</a>. The porcelain rods will fit over
-these and will thus be held securely in the frame, one small
-knob entering the tube at each end, as indicated by the
-dotted lines in <a href="#FigVII14">Fig. 14</a>.</p>
-
-<p>The first porcelain tube to the left is wound with No. 22
-German-silver wire, the next with No. 20, the third with
-No. 18, then Nos. 16, 14, and 12; so that in this field a broad
-range can be had for a current of 110 volts.</p>
-
-<p>The coils are connected in series, as explained for the other
-rheostats, and the leading wires brought down to the back
-of a switchboard of which <a href="#FigVII13">Fig. 13</a> A is the front and <a href="#FigVII13">Fig. 13</a>
-B the rear view. The switchboard is made of thin slate or
-soapstone; or a fibre-board may be employed. Fibre-board
-is especially made for electrical work, and can be had from
-a large supply-house in pieces of various thickness, three-eighths
-of an inch being about right for this board. Brass
-bolts and nuts and copper washers are used for the contact-poles,
-and when the ends of the leading wires are looped
-around the bolts the nuts are to be screwed down tightly so
-as to make good contacts. This rheostat may be used when
-lying on a table, or it can be hung up by means of two
-screw-eyes driven in the top of the frame, as shown in
-<a href="#FigVII13">Fig. 13</a> A.</p>
-
-<p>A convenient form of rheostat for fine wire and high
-resistance is shown in <a href="#FigVII15">Fig. 15</a>. This is on the plan of the
-well-known Wheatstone rheostat and does not require a
-switchboard nor a series of coils. Two rollers, one of wood
-the other of metal or brass-covered wood, are set in a frame,
-and by means of a handle and projecting ends with square<span class="pagenum" id="Page148">[148]</span>
-shoulders, one or the other of the rollers may be turned so
-that the wire on one winds up while on the other it unwinds.</p>
-
-<p>The wooden roller may be made from a piece of curtain-rod
-one inch in diameter, and it should have a thread cut
-on it. This will have to be done on a screw-cutting lathe,
-and any machinist will do it for a few cents. There should
-be from twelve to sixteen threads to the inch&mdash;no more&mdash;although
-there may be as few as eight. Twelve will be
-found a good number, as that does not crowd the coils and
-the risk of their touching is minimized. The ends of the
-roller should have bearings that will fit in holes made in the
-end-pieces of the frame, and at one end of each roller a
-square shoulder is to be cut, as shown at A in <a href="#FigVII16">Fig. 16</a>. A
-short handle may be made from two small pieces of wood,
-as shown at B in <a href="#FigVII16">Fig. 16</a>. It must be provided with a square
-hole so that it will fit on the roller ends. The metal roller
-may be made from a piece of light brass tubing one inch in
-diameter through which a wooden core is slipped; or it can
-be a piece of brass-covered curtain-pole with the ends shaped
-the same as the wooden one. The wood roller should have
-a collar of thin brass or copper (or other soft metal except
-lead) attached to the front end; or several turns of wire may
-be made about the roller so as to form a contact-point. A
-piece of spring brass, copper, or tin rests on this collar and
-is held fast under a binding-post, which in turn is screwed
-to the wooden frame. A similar strip of spring metal is
-held under another post on the opposite side of the frame
-and bears on the metal roller.</p>
-
-<div class="container m40">
-<a id="FigVII15"></a>
-<a id="FigVII16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo149.jpg" alt="Rheostat" />
-</div>
-
-</div><!--container-->
-
-<p>German-silver wire is wound on the wooden roller, one<span class="pagenum" id="Page149">[149]</span>
-end having been made fast to the metal collar; and when all
-the thread grooves on the wood roller are filled the opposite
-end of the wire is attached to the rear end of the metal roller.
-The current entering at binding-post No. 1 crosses on the
-strip of spring metal to the collar, travels along the coil of
-wire, and crosses to the metal roller and is conducted out
-at binding-post No. 2 (see <a href="#FigVII15">Fig. 15</a>). If the resistance is too
-great slip the handle over the end of the metal roller and
-give it several turns. The current will then pass with
-greater freedom as the wire on the wooden roller becomes
-shorter. This may be readily seen by connecting a small
-lamp in series with a battery and this rheostat. As the<span class="pagenum" id="Page150">[150]</span>
-metal cylinder is turned the current flows more freely and
-the filament becomes red, then white, and finally burns to
-its full capacity. Take care, however, not to admit too
-much current as it will burn out the lamp. Some sort of
-adjustment should be made to prevent the rollers turning
-of themselves and thus allowing the wire coils to slacken.
-This may be done by boring the two holes for the rollers to
-fit in and then, with a key-hole saw, cutting the stick as
-shown at C in <a href="#FigVII16">Fig. 16</a>, taking care not to split it at the ends.
-The result will be a long slot which, however, has nothing to
-do with the bearings. Down through the middle of the
-stick make a hole with an awl, so that the screw-eye will
-move easily in the upper half but will hold in the lower
-half. Under the head of the eye place a small copper washer;
-then with the thumb and finger drive the screw-eye down
-until the head rests on the washer.</p>
-
-<p>A slight turn of the eye when it is in the right place will
-draw the upper and lower parts of the stick together and
-bind the wood about the bearing ends of the rollers. The
-rollers should not be held too tightly as that would strain
-the wire when winding it from one to the other. It should
-be just tight enough to keep the wire taut.</p>
-
-<p>Two or more of these roller resistance-frames may be
-made and connected in series so that a close adjustment can
-be had when using battery currents for experimenting.</p>
-
-<h4>Liquid Resistance</h4>
-
-<p>Apart from metallic, mercurial, or carbon resistance a
-form of liquid apparatus is frequently used in laboratory
-and light experimental work.</p>
-
-<p><span class="pagenum" id="Page151">[151]</span></p>
-
-<div class="container m40">
-<a id="FigVII17"></a>
-<a id="FigVII19"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo151.jpg" alt="Resistances" />
-</div>
-
-</div><!--container-->
-
-<p>This style of resistance equipment is the least expensive
-to make, and will give excellent satisfaction to the boy who
-is using light currents for induction-coils, lamps, galvanometers,
-and testing in general. The simplest form of liquid
-resistance is made by using a glass bottle with the upper
-part cut away. The cutting may be done with a steel-wheel
-glass-cutter. The bottle should then be tapped on
-the cut line until the top part falls away. Go over the sharp
-edges with an old file to chafe the edge and round it; then
-solder a tin, copper, or brass disk to a piece of well-insulated
-wire and drop it down in the bottom of the receptacle, as
-shown at <a href="#FigVII17">Fig. 17</a>. Cut a smaller disk of metal, or use a
-brass button, and suspend it on a copper wire which passes
-through a small hole in a piece of wood at the top of the jar.
-Notches should be cut at the under side of this wood cross-piece<span class="pagenum" id="Page152">[152]</span>
-so that it will fit on top of the jar and stay in place.
-The jar is to be nearly filled with water, having a teaspoonful
-of sulphate of copper dissolved in it. This will turn the
-water a bluish color and make it a slightly better conductor,
-particularly when the button is lowered close to the round
-disk. If a high resistance is desired the copper may be
-omitted leaving the water in its pure state. The wires leading
-in and out of the jar should be connected between the
-apparatus and the battery so that the proper amperage can
-be had by raising or lowering the button. A series of these
-liquid resistance-jars may be made of glass tubes an inch in
-diameter and twelve inches long. One end of them may
-be stopped with a cement made of plaster of Paris six parts,
-ground silex or fine white sand two parts, and dextrine two
-parts. Mix the ingredients together when dry, taking care
-to break all small lumps in the dextrine; then add water
-until it is of a thick consistency like soft putty. Solder the
-ends of some copper wires to disks of copper or brass and set
-them on the middle of bone-buttons; these in turn are to be
-imbedded in the mixture after the wire has been passed
-through a hole in the bottom.</p>
-
-<p>Their location can be seen in the bottom of the tubes
-<a href="#FigVII18">Fig. 18</a>, and <a href="#FigVII19">Fig. 19</a> A is an enlarged figure drawing of the
-plate, button, and wire. The wires are brought out under
-the lower edge of the tubes, and enough of the composition
-is floated about the bottom and outer edge of the tube to
-form a base, as shown in the drawing. A base-board is
-made six inches wide and long enough to accommodate the
-desired number of tubes. Two pieces of wood one inch
-wide and three-quarters of an inch thick have hollow notches<span class="pagenum" id="Page153">[153]</span>
-cut from them at one side, as shown at <a href="#FigVII19">Fig. 19</a> B. In these
-notches the tubes are gripped. Screws are passed through
-one stick and into the other so as to clamp the wood and
-tubes securely together. The rear stick is supported on
-two uprights which are made fast to the rear edge of the
-base-plate with screws and glue.</p>
-
-<p>Along the front of the base-board small metal contact
-plates, or binding-posts, are arranged (see <a href="#Ref004">Binding-posts</a>,
-<a href="#Page33">chapter iii.</a>) and the wires led to them from the tubes, as
-shown in the drawing. The top or drop wires in the tubes
-are provided with metal buttons at the ends; or the end of
-the wire may be rolled up so as to form a little knob. The
-manner of connecting the wires was freely explained in the
-resistance-coil descriptions and may be studied out by
-examining the drawing closely. In this resistance-apparatus
-there are two ways of cutting out a medium&mdash;first, by lowering
-the wire in the tube so that both contact-points meet; and
-second, by cutting out the first tube altogether by connecting
-the incoming wire with the second binding-post. Then
-again the resistance may be regulated quite accurately by
-raising or lowering the wires in the liquid.</p>
-
-<p>For example, there is too much resistance if the current
-has to travel through all the tubes. If it is too strong when
-one tube is cut out, the wire in tube No. 1 is lowered so that
-the contacts are an inch apart. Then the more accurate
-adjustment is made by dropping the wire in the second tube,
-as shown in <a href="#FigVII18">Fig. 18</a>. The wires leading out at the top of the
-tubes are pinched over the edge to hold them in place. They
-should be cotton insulated and the part that is in the liquid
-should be coated with hot paraffine.</p>
-
-<p><span class="pagenum" id="Page154">[154]</span></p>
-
-<p>The water may be made a slightly better conductor if a
-small portion of sulphate of zinc, or sulphate of copper, is
-added to each tubeful.</p>
-
-<div class="container m40" id="FigVII18">
-
-<div class="figcenter nomargin">
-<img src="images/illo154.jpg" alt="Resistor" />
-</div>
-
-</div><!--container-->
-
-<p>Hittorf’s resistance-tube is one of the oldest on these lines,
-and two or more of them are coupled in series, as described<span class="pagenum" id="Page155">[155]</span>
-for this water-tube resistance; glass tubes are employed that
-have one end sealed with a permanent composition, as described
-for <a href="#FigVII18">Fig. 18</a>. A metallic cadmium electrode is placed
-at the bottom of the tube, and the tube is then filled with
-a solution of cadmium iodide one part and amylic alcohol
-nine parts, and then corked. A wire passing down through
-or at the side of the cork is attached to another small piece
-of metallic cadmium, which touches the top of or is suspended
-a short distance in the liquid.</p>
-
-<p>As the alcohol is volatile the cork cannot be left out of the
-tube, and the wire must be drawn through the cork with a
-needle so that no opening is left for evaporation. A number
-of these tubes may be made and coupled in series and the
-wires led down to the contact-points of a switch.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page156">[156]</span></p>
-
-<h3>Chapter VIII<br />
-<span class="chaptitle">THE TELEPHONE</span></h3>
-
-<p class="chapstart"><span class="largecap">F</span><span class="afterlargecap">or</span>
-direct communication over short or moderately
-long distances, nothing has been invented as yet that
-will take the place of the telephone. A few years ago, when
-this instrument was first brought out, it was the wonder of
-the times, just as wireless telegraphy is to-day. Starting
-with the simple form of the two cups with membranes across
-the ends, and a string or a wire connecting them, we have
-to-day the complex and wonderful electric telephone, giving
-perfect service up to a distance of two thousand miles.
-Some day inventors in the science of telephony will make it
-possible to communicate across or under the oceans, and
-when the boys of to-day grow to manhood they should be
-able to transact business by ’phone from San Francisco to
-the Far East, or from the cities near the Atlantic coast to
-London, Paris, or Berlin.</p>
-
-<p>It is hardly necessary to enter into the history of telephones,
-as this information may be readily found in any
-modern encyclopædia or reference work. But the boy who
-is interested in electricity wants to know how to make a
-telephone, and how to do it in the up-to-date way, with the
-wire and ground lines, switches, cut-outs, bell connections,<span class="pagenum" id="Page157">[157]</span>
-and other vital parts, properly constructed and assembled.
-In this laudable ambition we will endeavor to help him.</p>
-
-<p>The general principle of the telephone may be explained
-in the statement that it is an apparatus for the conveyance
-of the human voice, or indeed any sounds which are the
-direct result of vibration.</p>
-
-<p>Sound is due to the vibrations of matter. A piano string
-produces sound because of its vibration when struck, or
-pulled to one side and then released. This vibration sets
-the air in rapid motion, and the result is the recording of
-the sound on our ear-drums, the latter corresponding to the
-film of sheepskin or bladder drawn over the hollow cup or
-cylinder of a toy telephone. When the head of a drum is
-struck with a small stick it vibrates. In this case the
-vibrations are set in motion by the blow, while in the telephone
-a similar phenomenon is the result of vibratory waves
-falling from the voice on the thin membrane, or disk of
-metal, in the transmitter. When these vibrations reach the
-ear-drum the nervous system, corresponding to electricity
-in the mechanical telephone, carries this sound to our brains,
-where it is recorded and understood. In the telephone the
-wire, charged with electricity, carries the sound from one
-place to another, through the agencies of magnetism and
-vibration.</p>
-
-<p>Over short distances, however, magnetism and electricity
-need not be employed for the transmission of sound. A
-short-line telephone may be built on purely vibratory principles.
-Almost every boy has made a “phone” with two
-tomato-cans over which a membrane is drawn at one end
-and tied. The middle of the membrane is punctured, and<span class="pagenum" id="Page158">[158]</span>
-a button, or other small, flat object, is arranged in connection
-with the wires that lead from can to can.</p>
-
-<h4>A Bladder Telephone</h4>
-
-<p>A really practical talking apparatus of this simple nature
-may be made from two fresh beef bladders obtained from
-a slaughter-house or from the butcher. You will also need
-two boards with holes cut in them, two buttons, some tacks,
-and a length of fine, hard, brass, copper, or tinned iron wire.
-The size should be No. 22 or No. 24. The boards should
-be ten by fourteen inches and half an inch in thickness.
-Cut holes in them eight inches in diameter, having first
-struck a circle with a compass. This may be done with a
-keyhole saw and the edges sand-papered to remove rough
-places. Prepare the bladders by blowing them up and tieing
-them. Leave them inflated for a day or two until they
-have stretched, but do not let them get hard or dry.</p>
-
-<p>When the bladders are ready, cut off the necks, and also
-remove about one-third of the material, measuring from
-end to end. Soak the bladders in warm water until they
-become soft and white. Stretch them, loosely but evenly,
-over the opening in the boards, letting the inside of the
-bladder be on top, and tack them temporarily all around,
-one inch from the edge of the opening. Test for evenness
-by pushing down the bladder at the middle. If it stretches
-smoothly and without wrinkles it will do; otherwise the
-position and tacks must be changed until it sets perfectly
-smooth.</p>
-
-<p><span class="pagenum" id="Page159">[159]</span></p>
-
-<div class="container m40">
-<a id="FigVIII1"></a>
-<a id="FigVIII2"></a>
-<a id="FigVIII3"></a>
-<a id="FigVIII4"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo159.jpg" alt="Bladder telephones" />
-</div>
-
-</div><!--container-->
-
-<p>The bladder must now be permanently fastened to the
-board by means of a leather band half an inch wide and
-tacks driven closely, as shown in <a href="#FigVIII1">Fig. 1</a>. With a sharp
-knife trim away the rough edges of the bladder that extend
-beyond the circle of leather. Attach a piece of the fine wire
-to a button, as shown in <a href="#FigVIII2">Fig. 2</a>, and pass the free end
-through the centre of the bladder until the button rests on<span class="pagenum" id="Page160">[160]</span>
-its surface. Then fasten an eight-pound weight to the end
-of the wire and set in the sun for a few hours, until thoroughly
-dry, as shown at <a href="#FigVIII3">Fig. 3</a>.</p>
-
-<p>When both drums are complete, place one at each end
-of a line, and connect the short wires with the long wire,
-drawing the latter quite taut. The course of the main wire
-should be as straight as possible, and should it be too long
-it may be supported by string loops fastened to the limbs of
-trees, or suspended from the cross-piece of supports made
-in the form of a gallows-tree or letter F. To communicate
-it will be necessary to tap on the button with a lead-pencil
-or small hard-wood stick. The vibration will be heard at
-the other end of the line and will attract attention.</p>
-
-<p>By speaking close to the bladder in a clear, distinct tone,
-the sound will carry for at least a quarter of a mile, and the
-return vibrations of the voice at the other end of the line
-can be clearly recognized.</p>
-
-<h4>A Single (Receiver) Line</h4>
-
-<p>The principal parts of the modern telephone apparatus
-are the transmitter, receiver, induction-coil, signal-bell, push-button,
-batteries, and switch. The boxes, wall-plates, etc.,
-etc., are but accessories to which the active parts are attached.</p>
-
-<p>The first telephone that came into general use was the
-invention of Graham Bell, and the principle of his receiver
-has not been materially changed from that day to this, except
-that now a double-pole magnet and two fine wire coils
-are employed in place of the single magnet and one coil. A<span class="pagenum" id="Page161">[161]</span>
-practical form of single magnet receiver that any boy can
-easily construct is shown in <a href="#FigVIII4">Fig. 4</a>, and <a href="#FigVIII5">Fig. 5</a> is a sectional
-drawing of the receiver drawn as though it had been sliced
-or sawed in two, from front to rear.</p>
-
-<p>It is made from a piece of curtain-pole one inch and an
-eighth in diameter and three inches and a half long. A hole
-three-eighths of an inch in diameter is bored its entire
-length at the middle, and through this the magnet passes.
-At one end of this tube a wooden pill-box (E) is made fast
-with glue, or a wooden cup may be turned out on a lathe
-and attached to the magnet tube. If the pill-box is employed
-it should be two inches and a half in diameter, and
-at four equidistant places inside the box small lugs of wood
-are to be glued fast. Into these lugs the screws employed
-to hold the cap are driven. The walls of pill-boxes are so
-thin that without these lugs the cap could not be fastened
-over the thin disk of metal (D) unless it were tied or wired
-on, and that would not look well. If the cup is turned the
-walls should be left thick enough to pass the screws into,
-and the inside diameter should then be one inch and three-quarters.</p>
-
-<div class="container m40">
-
-<div class="figcenter nomargin" id="FigVIII5">
-<img src="images/illo162a.jpg" alt="Telephone" />
-</div>
-
-</div><!--container-->
-
-<p>The cap (B) is made from thin wood, fibre, or hard rubber.
-It is provided with a thin rim or collar to separate its inner
-side from the face of the disk (D). Four small holes are bored
-near the edge of this cap, so that the screws which hold it
-fast to the cup (E) may pass through them. The magnet (M)
-is a piece of hard steel three-eighths of an inch in diameter
-and four inches and a quarter long. This may be purchased
-at a supply-house, and if it is not hard enough a blacksmith
-can make it so by heating and plunging it in cold water<span class="pagenum" id="Page162">[162]</span>
-several times. It may be magnetized by rubbing it over
-the surface of a large horseshoe magnet, or if you live near
-a power station you can get one of the workmen to magnetize
-it for you at a trifling cost. Should you happen to possess a
-bar magnet of soft iron with a number of coils of wire, and
-also a storage-battery, the steel bar may be substituted for
-the soft iron core and the current turned on. After five<span class="pagenum" id="Page163">[163]</span>
-minutes the steel can be withdrawn. It is now a magnet,
-and will hold its magnetism indefinitely.</p>
-
-<p>Now have a thin, flat spool turned from maple or boxwood
-to fit over one end of the rod, and wind it with a number
-of layers of No. 36 copper wire insulated with silk.
-This is known in the electrical supply-houses as “phone”-receiver
-insulated wire, and will cost about fifty cents an
-ounce. One ounce will be enough for two receivers. It
-should be wound evenly and smoothly, like the strands of
-thread on a spool, and this may be done with the aid of
-the winder described on <a href="#Page58">page 58</a>.</p>
-
-<p>When the wire is in place a drop of hot paraffine will
-hold the end so that the wire will not unwind. The ends
-of this spool-winding should be made fast to heavier wires,
-which are run through small holes in the tube (A) and project
-out at the end, as shown at F F. The magnet, with its
-wire-wound spool on the end, is then pushed through the
-hole in A until the top end of the rod is slightly below the
-edges of the cup (E), so that when the metal disk (D) is laid
-over the cup (E) the space between the magnet and disk, or
-diaphragm (D), is one-sixteenth of an inch (see <a href="#FigVIII5">Fig. 5</a>). Put
-some shellac on the magnet, so that when it is in the right
-place the shellac will dry and hold it fast.</p>
-
-<p>The cap (B) holds the disk (D) in place, and protects the
-spool and its fine wire from being damaged and from collecting
-dust. After giving the exterior a coat of black paint
-and a finishing coat or two of shellac, the receiver will be
-ready for use.</p>
-
-<p>The original telephone apparatus was made up of these
-receivers only&mdash;one at each of a line in connection with<span class="pagenum" id="Page164">[164]</span>
-a battery, bell, push-button, and switch. On a window-casing,
-or the wall through which the wires passed, a lightning-arrester
-was arranged and made fast. Using receivers
-only, it was necessary to speak through the same instrument
-that one heard through, and for a few years this unhandy
-method of communication was the only one possible. Then
-the transmitter was invented.</p>
-
-<h4>Plan of Installation</h4>
-
-<p>Many of these single-receiver lines are still in use, and as
-they require but a small amount of constructive skill a
-diagram of the wiring and the plan of arrangement is shown
-in <a href="#FigVIII6">Fig. 6</a>.</p>
-
-<div class="container">
-
-<div class="figcenter nomargin" id="FigVIII6">
-<img src="images/illo162b.jpg" alt="Telephone" />
-</div>
-
-</div><!--container-->
-
-<p>At the left side, R is the receiver at one end of the line
-and R 2 that at the other, line No. 1 being a continuous
-wire between the two receivers. When the boy at R wishes
-to call his friend at R 2 he uses his push-button (P B), and
-the battery (B B) operates the electric bell (E B 2) at the
-other end. In order to have the bell connections operative,
-the switch (S 2) must be thrown over to the left when the
-line is “quiet,” while the switch (S) should be thrown to the
-right. With the switches in this position the boy at either
-end may call his friend at the opposite end.</p>
-
-<p>With the switch (S 2) thrown to the left (the position it
-should be in, except when talking over the line), the boy at
-the other end pushes his button (P B), first throwing switch
-S to the left. This makes connection for the battery (B B),
-and the circuit is closed through wires that join line No. 1
-and line No. 2 at 1 and 2. The branch lines to the bell<span class="pagenum" id="Page165">[165]</span>
-(E B 2) join the main lines at 3 and 4, through switch S 2,
-when the bar is thrown to the left. The circuit being complete,
-the batteries (B B) at one end of the line ring the bell
-(E B 2) at the other end of the line.</p>
-
-<p>In the reverse manner, when the switch (S) is thrown to
-the right, the boy at the opposite end rings the bell (E B)
-by pressing on the button (P B 2), first throwing switch S 2
-over to the right. If the boy at the left is calling up the
-boy at the right, the switch (S) should be thrown to the left,
-and he keeps ringing until the other operator throws switch
-S 2 over to the right. If now he has the receiver (R) up to
-his ear he can hear the vibration of the bell (E B 2) ringing
-through the receiver (R) at his end of the line. But when
-the boy summoned to R 2 takes up the receiver and places
-it to his ear, he throws switch S 2 over to the right side, and
-the boy at R leaves switch S over on the left side. This
-brings the lines into direct connection with the receivers in
-series. Be careful, when setting up this line, to have the
-batteries (B B) in series with B 2 B 2; otherwise there would
-be counter-action. The carbon of one cell should be connected
-with the zinc of the next cell, and so on.</p>
-
-<p>Another receiver is shown at <a href="#FigVIII7">Fig. 7</a>. The tube (A) and
-the cup are turned from one piece of wood, and the cap (B)
-from another piece. The length of the receiver is five inches,
-and the cap is two inches and a half across. The shank, or
-handle, through which the magnet is passed measures one
-inch and a quarter in diameter.</p>
-
-<p>These wood parts will have to be made by a wood-turner;
-and before the long piece is put in a lathe the hole, three-eighths
-of an inch in diameter, should be bored. It must be<span class="pagenum" id="Page166">[166]</span>
-done carefully, so that the wood shell will be of even thickness
-all around the hole. Also two small holes should be
-made the entire length of the handle, through which the
-wires leading from the coil to the binding-posts may
-pass.</p>
-
-<div class="container m40" id="FigVIII7">
-
-<div class="figcenter nomargin">
-<img src="images/illo166.jpg" alt="Telephone" />
-</div>
-
-</div><!--container-->
-
-<p>The spool for the fine insulated wire coil is turned from
-box-wood or maple, and wound as described in <a href="#Page54">chapter iv.</a>,
-on Magnets and Induction-coils. Small binding-posts (F F)
-with screw ends should be driven down into the holes at
-the end of the handle and over the bare ends of the wires
-that project out of the holes. The magnet (M) is three-eighths
-of an inch in diameter, and is provided with the
-spool and coil (C) at the large end of the receiver.</p>
-
-<p>The disk (D) is of very thin iron, and is held in place by the
-cap (B) and four small brass screws driven through the edge
-of B and into the cup end of A. A screw-eye should be
-driven into the small end of the receiver from which it may
-hang from a hook. If a double hook and bar is employed<span class="pagenum" id="Page167">[167]</span>
-the receiver will hang in the fork, being held there by the
-rim of wood turned at the small end of A.</p>
-
-<h4>A Double-pole Receiver</h4>
-
-<p>Another form of receiver is shown at <a href="#FigVIII8">Fig. 8</a>. This is a
-double-pole receiver, with the coils of fine wire arranged on
-the ends of a bent band of steel and located in the cup (A),
-so that the ends of the magnet are close to the diaphragm
-(D). <a href="#FigVIII8">Fig. 8</a> is a sectional view of an assembled receiver, but
-a good idea can be had from the drawings of the separate
-parts. The magnet (M) is of steel one-eighth of an inch thick<span class="pagenum" id="Page168">[168]</span>
-and five-eighths of an inch wide. A blacksmith will make
-this at a small cost. It should measure two and one-half
-inches wide, two and one-half inches long, the ends being
-five-eighths of an inch apart.</p>
-
-<div class="container m40" id="FigVIII8">
-
-<div class="figcenter nomargin">
-<img src="images/illo167.jpg" alt="Telephone" />
-</div>
-
-</div><!--container-->
-
-<p>Thin wooden spools are made from wood or fibre to fit
-over the steel ends, and are wound with No. 36 silk-insulated
-wire. A wooden cup, or shell (A), is turned from cherry,
-maple, or other close-grained wood, and at the back a hole
-is cut just large enough for the magnet ends to slip through
-exclusive of the coils wound on them. A plug of wood (A A)
-is driven between the ends of the magnet to hold them in
-place. Some shellac on the edges of the hole and the plug
-will harden and keep the parts in place.</p>
-
-<p>The coils (C C) are placed on the magnet ends, and the fine
-wires are made fast to the binding-posts (E E), the latter being
-screwed fast to the shell (A). The diaphragm (D) is then
-arranged in place and held with the cap (B) and the small
-screws which pass through it and into the shell (A).</p>
-
-<h4>The Transmitter</h4>
-
-<p>With any one of these receivers a more complete and
-convenient telephone can be made by the addition of a
-transmitter and an induction-coil.</p>
-
-<p>Following the invention of the receiver, several transmitters
-were designed and patented, among them being
-the Edison, Blake, Clamond, Western Union, and Hunning.
-The Edison and Hunning are the ones in general use, and
-as either of them can easily be made by a boy a simplified
-type of both is shown in <a href="#FigVIII9">Figs. 9 and 11</a>.</p>
-
-<p><span class="pagenum" id="Page169">[169]</span></p>
-
-<div class="container m40">
-<a id="FigVIII9"></a>
-<a id="FigVIII10"></a>
-<a id="FigVIII11"></a>
-<a id="FigVIII12"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo169.jpg" alt="Telephones" />
-</div>
-
-<p class="caption">SIMPLIFIED TYPE OF TRANSMITTER</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page170">[170]</span></p>
-
-<p>Some small blocks of wood, tin funnels, small screws,
-granulated or powdered carbon, some thin pieces of flat
-carbon, and a piece of very thin ferrotype plate will be the
-principal things needed in making a transmitter similar to
-the one shown in <a href="#FigVIII9">Fig. 9</a>. All that is visible from the outside
-is a plate of wood screwed to a block of wood, and a
-mouth-piece made fast to the thin board.</p>
-
-<p>In <a href="#FigVIII10">Fig. 10</a> an interior section is shown, which when once
-understood will be found extremely simple. The block (A) is
-of pine, white-wood, birch, or cherry, and is two inches and
-three-quarters square and five-eighths or three-quarters of
-an inch thick. A hole seven-eighths of an inch in diameter
-is bored in the centre of this block, half an inch deep, and
-a path is cut at the face of the block one inch and a half
-in diameter and one-eighth of an inch deep. Be careful to
-cut these holes accurately and smoothly, and if it is not
-possible to do so, it would be well to have them put in a
-lathe and turned out.</p>
-
-<p>The face-plate (B) is two inches square, with a three-quarter-inch
-hole in it, and the under-side is cut away for one-eighth
-of an inch in depth and one inch and a half in diameter.
-The object of these depressions in block A and
-face-plate B is to give space for the diaphragm (D) to
-vibrate when the voice falls on it through the mouth-piece
-(C).</p>
-
-<p>From carbon one-eighth of an inch in thickness two
-round buttons are cut measuring three-quarters of an inch
-across. A small hole is bored in the centre of each button,
-and one of them is provided with a very small brass screw
-and nut, as shown at F F. One side of the button-hole is<span class="pagenum" id="Page171">[171]</span>
-countersunk, so that the head of the screw will fit down
-into it and be flush with the face of the carbon. With a
-small three-cornered or square file cut the surface of the
-buttons with criss-cross lines, as shown at F F. When the
-buttons are mounted in the receiver these surfaces will face
-each other. Cut a small washer from felt or flannel, and
-place it in the bottom of the hole in block A. Line the side
-of the hole with a narrow strip of the same goods; then
-place the button (F F) in the hole, pass the screw through the
-hole and through the block (A), and make it fast with the
-nut, as shown at F. Place a thin, flat washer under the nut,
-and twist a fine piece of insulated copper wire between
-washer and nut for terminal connections, taking care that
-the end of the wire under the nut is bare and bright, so that
-perfect contact is assured. Since the practice of telephony
-involves such delicate and sensitive vibratory and electrical
-phenomena, it is best to solder all joints and unions wherever
-practicable, and so avoid the possibility of loose connections
-or corrosion of united wires.</p>
-
-<p>From very thin ferrotype plate cut a piece two inches
-square, and at the middle of it attach the other carbon button
-by means of a small rivet which you can make from a
-piece of copper wire. Or a very small brass machine screw
-may be passed through the button and plate; then gently
-tapped at the face of the plate to rivet it fast, as shown
-at E. Lay the block down flat and partly fill the cavity
-with carbon granules until the button is covered. Do not
-fill up to the top of the hole. Over this lay the disk (D), so
-that the carbon button at the under side of it will fit in the
-top part of the hole between the sides of felt or flannel.<span class="pagenum" id="Page172">[172]</span>
-Make the disk fast to the block (A) with small pins made by
-clipping ordinary pins in half and filing the ends.</p>
-
-<p>A slim bolt (G) is passed through the block (A), and a wire
-terminal is caught under a nut and between a washer at
-the back of the block, as described for F. The japan or
-lacquer must be scraped away from the disk (D) where the
-bolt-head touches it, so that perfect electrical contact will
-be the result.</p>
-
-<p>A small tin funnel is cut and made fast to the face-plate
-(B), or if an electrical supply-house is at hand a mouth-piece
-of hard rubber or composition may be had for a few cents.
-The block (B) is then screwed fast to A, forming the transmitter
-shown at <a href="#FigVIII9">Fig. 9</a>. When this transmitter stands in a
-vertical position the granules, or small particles of carbon,
-drop down between the buttons of carbon, packing closely
-at the bottom of the cavity. At the middle they are loosely
-placed, and at the top there are none. As the high or low
-vibrations of the voice fall on the disk (D) they act accordingly
-on the carbon granules, which in turn conduct the
-vibrations to the rear carbon button, and, by the aid of
-electricity reproduce the same sound, in high or low tone,
-through the receiver at the other end of a line.</p>
-
-<p>This improved transmitter makes it possible to talk in a
-moderate tone of voice over distances up to one thousand
-miles, while with the old form of the instrument it was
-necessary to talk very loud in order to be heard only a few
-miles away. Where a portable apparatus is desired, this
-block may be attached to a box or an upright staff.</p>
-
-<p>This transmitter will not work when on its back or so
-that the funnel is on top, because the particles of carbon<span class="pagenum" id="Page173">[173]</span>
-would settle on the rear button and not touch the front
-one. It is essential that the carbon grains should touch
-both buttons at the same time, and at the lower part of the
-cavity they should lie quite solid. It is not necessary, however,
-to pack it in, for the vibratory action of the voice, or
-other sounds, will cause the particles to adjust themselves
-and settle in a compact mass.</p>
-
-<h4>Another Form of Transmitter</h4>
-
-<p>In <a href="#FigVIII11">Fig. 11</a> another style of transmitter is shown. It is
-assembled on the front of a box. This front or cover swings
-on hinges, and can be opened so that the mechanism in the
-interior of the box may be gotten at easily.</p>
-
-<p>A sectional view of this transmitter is shown in <a href="#FigVIII12">Fig. 12</a>.
-A hole one inch and a half in diameter is cut in the cover (A).
-A round or square block (B) two inches and a quarter across
-and half an inch thick is made fast to the rear of the cover,
-and in this a hole is bored seven-eighths of an inch in diameter
-and one-quarter of an inch deep.</p>
-
-<p>The sides and bottom of this hole are lined with flannel
-or felt, and a carbon button with roughened surface, as
-shown at F F, is made fast in it by a small machine screw
-and nut (F). A diaphragm (D) is cut from thin ferrotype
-plate, and a carbon button is made fast to the middle of it
-by a small machine screw or a rivet made from soft copper
-or brass. When the block (B) has been screwed fast to A,
-place some granules of carbon in the space (H); then lay the
-diaphragm over the opening, and make it fast with small
-screws or pins driven around the edge.</p>
-
-<p><span class="pagenum" id="Page174">[174]</span></p>
-
-<p>From a small tin funnel and a tin-can cap make a mouth-piece
-(C) by cutting a hole in the cap and slipping the funnel
-through it, then cutting the end of the funnel that projects
-through the hole and bending back the ears so that they
-lap on the inner side of the cap. These small ears may be
-soldered to the cap so as to hold the mouth-piece securely in
-place. From felt or flannel cut a washer the size of the
-can top and about three-eighths of an inch in width. Lay
-this over the diaphragm; then place the mouth-piece on it
-and fasten it to the door (A) with small screws. The use of
-this washer is to prevent any false vibrations in the mouth-piece
-affecting the sensitive diaphragm. Make a small hole
-through A and B and pass a bolt (E) through this hole,
-taking care to lap a thin piece of sheet-brass on the
-diaphragm (D), bending it over so that it will lie under the
-head of the bolt (E). The diaphragm must be scraped where
-the metal touches it, so as to make perfect electrical connection
-between D and E. At the rear end of E arrange
-a washer and nut (G), so that the current passing in at G
-travels through E and D, then through the carbon buttons
-and granules, and out at F.</p>
-
-<p>From pine or white-wood one-quarter or three-eighths
-of an inch thick make a box four inches wide, six inches
-high, and two inches and a half deep. To the front of this
-attach a cover, which should measure a quarter of an inch
-larger all around than the width and height of the box.
-Use brass hinges for this work so that the cover may be
-opened. Fasten a transmitter to the front of the cover, or
-make one on the cover, as shown in <a href="#FigVIII11">Fig. 11</a>, and attach the
-box to a back-board or wall-plate five inches wide and<span class="pagenum" id="Page175">[175]</span>
-seven inches high made of pine or white-wood half an inch
-in thickness (see <a href="#FigVIII13">Fig. 13</a>).</p>
-
-<div class="container m40">
-<a id="FigVIII13"></a>
-<a id="FigVIII14"></a>
-<a id="FigVIII15"></a>
-<a id="FigVIII16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo175.jpg" alt="Telephones" />
-</div>
-
-</div><!--container-->
-
-<p>At the left side of the box cut a slot through the wood,
-so that a lever and hook may project and work up and
-down. The end of this lever is provided with a hook on
-which a receiver may be hung, as shown in <a href="#FigVIII13">Fig. 13</a>, and the<span class="pagenum" id="Page176">[176]</span>
-inside mechanism is arranged as shown at <a href="#FigVIII14">Fig. 14</a>. A is
-an angle-piece of brass or copper, which acts as a bracket
-and which is screwed fast to the inside of the box. B is the
-lever and hook, which is cut from a strip of brass. The
-attached end is made wider, and an ear (C), to which a wire
-is soldered, projects down beyond the screw.</p>
-
-<p>A view looking down on this lever and bracket is shown
-at <a href="#FigVIII15">Fig. 15</a>. A is the bracket, B the lever, and E the screw
-or bolt holding the two parts together, with a thin copper
-washer between them to prevent friction. When the lever
-and bracket are made fast to the box, a spring (D) should
-be arranged, so that when the receiver is removed from the
-hook the lever will be drawn up to the top of the slot. A
-small contact-plate (F) is made of brass, and fastened at the
-lower end of the slot. On this the lever should rest when
-the receiver is on the hook. A contact-wire is soldered to
-this plate, which in turn is screwed fast to the inside of
-the box. This mechanism is part of a make-and-break
-switch to cut out and cut in the bells or telephone, and
-will be more clearly understood by referring to the diagram
-in <a href="#FigVIII17">Fig. 17</a>. At the right side of the box a small push-button
-is made fast, and this, with two binding-posts at the top
-and four at the underside of the box, will complete the
-exterior equipment of one end of a line.</p>
-
-<p>The construction of the push-button is shown in <a href="#FigVIII16">Fig. 16</a>, A
-being the box and B the button which passes through a small
-hole made in the side of the box. C is a strip of spring-brass
-screwed fast to the box. It must be strong enough
-to press the small bone or hard rubber button towards the
-outside of the box. A wire is caught under one screw-head,<span class="pagenum" id="Page177">[177]</span>
-and another one is passed under the screw-head which holds
-the other spring (D) to the box. When the button (B) is
-pushed in, it brings spring C into contact with D, and the
-circuit is closed. Directly the finger is removed from B
-the spring (C) pushes it out and breaks the circuit. This
-button is used only in connection with the call-bells, and has
-nothing to do with the telephone. The wires leading from
-the interior of the box pass through the wall-plate and along
-in grooves to the foot of the binding-posts, which are arranged
-below the box on the back-board, as shown in <a href="#FigVIII13">Fig. 13</a>.</p>
-
-<p>A buzzer or bell is made fast to the inside of the box,
-unless it is too large to fit conveniently, in which case it
-may be attached to the wall above or below the box.</p>
-
-<h4>The Wiring System</h4>
-
-<p><a href="#FigVIII17">Fig. 17</a> shows the wiring system for this outfit, which,
-when properly set up and connected, should operate on a
-circuit or line several miles in length, provided that the
-batteries are strong enough.</p>
-
-<p>This system may be installed in the box shown in <a href="#FigVIII13">Fig. 13</a>,
-the flexible cord containing two wires being attached to the
-binding-posts at the top of the box and to the posts at the
-end of the receiver. This system differs from the one shown
-in <a href="#FigVIII6">Fig. 6</a> only in the addition of receivers T and T 2, and in
-the substitution of the automatic lever-switches (L S and
-L S 2) for the plain switches (S and S 2) in <a href="#FigVIII6">Fig. 6</a>. When the
-line is “quiet” the receiver (R) should be hanging on the
-lever-switch (L S), which rests on the contact-plate (A). At
-the opposite side of the line the receiver (R 2) hangs on the
-lever-switch (L S 2), which in turn rests on the contact-plate
-(A A). This puts the bell circuit in service.</p>
-
-<p><span class="pagenum" id="Page178">[178]</span></p>
-
-<div class="container">
-
-<div class="figcenter" id="FigVIII17">
-<img src="images/illo178.jpg" alt="" />
-</div>
-
-<p class="caption">PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTER, ELECTRIC BUZZERS OR BELLS,
-LEVER-SWITCHES, PUSH-BUTTONS AND BATTERIES FOR STATIONS NOT OVER FIVE MILES APART.</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page179">[179]</span></p>
-
-<p>If the boy at the left wishes to call up the boy at the
-right he removes the receiver (R) from the hook (L S) and
-presses on the button (P B). This closes the circuit through
-the battery (C C C), and operates the electric buzzer or bell
-(E B 2) at the other end of the system, through line No. 1
-and line No. 2. The operation may be clearly understood
-by following the lines in the drawing with a pointer. The
-boy at the left may keep on calling the boy at the right so
-long as the receiver (R 2) hangs on the lever (L S 2) and holds
-it down against the plate (A A). But directly the receiver
-(R 2) is removed, the lever (L S 2) flies up&mdash;being drawn upward
-by the spring (D) shown in <a href="#FigVIII14">Fig. 14</a>&mdash;and closes the telephone
-circuit through the spring-contact (B B), at the same
-time cutting out the bell circuit. The boy at the left having
-already removed his receiver, the telephone circuit is then
-complete through lines Nos. 1 and 2 and batteries C C C and
-C 2 C 2 C 2, the boys at both ends speaking into the transmitters
-and hearing through the receivers. The contacts
-B and B B are made from spring-brass or copper, and are
-attached inside the boxes at the back, so that when the
-levers are up contact is made, but when down the circuit
-is broken or opened. In <a href="#FigVIII18">Fig. 18</a> an interior view of a box
-is shown, the door being thrown open and the receiver left
-hanging on the hook.</p>
-
-<p><span class="pagenum" id="Page180">[180]</span></p>
-
-<div class="container m40">
-<a id="FigVIII18"></a>
-<a id="FigVIII19"></a>
-<a id="FigVIII20"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo180.jpg" alt="" />
-</div>
-
-<p class="caption">TELEPHONE INSTALLATION. INTERIOR VIEW OF BOX</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page181">[181]</span></p>
-
-<p>The arrangement of the several parts will be found convenient
-and easy of access. E B is the electric buzzer, L S
-the lever-switch, P B the push-button, T the transmitter,
-and R the receiver. Nos. 1, 2, 3, 4, 5, 6, 7, 8 are binding-posts
-or terminals, and B is the spring-contact against
-which the lever-switch (L S) strikes when drawn up by the
-spring (D).</p>
-
-<p>The wires that pass from 6 to 7 and from 4 to 8 should be
-soldered fast to one side of the hinge, and those running
-from the terminals or nuts at the back of the transmitter (T)
-to 7 and 8 should be similarly secured. Small brass hinges
-are not liable to become corroded at the joints, but to insure
-against any such possibility the ends of several fine wires
-may be soldered to each leaf of the hinge, so that when the
-door is closed the wires will be compressed between the
-hinge-plates. For long-distance communication it will be
-necessary to install an induction-coil, so that the direct current
-furnished by the batteries, in series with the transmitter,
-can by induction be transformed into alternating
-current over the lines connecting the two sets of apparatus.
-This system is somewhat more complicated and requires
-more care in making the connections, but once in operation
-it will be found far superior to either of the systems hitherto
-described.</p>
-
-<h4>A Telephone Induction-coil</h4>
-
-<p>It will be necessary to make two induction-coils, as described
-in <a href="#Page54">chapter iv.</a>, <a href="#Page62">page 62</a>, <a href="#FigVIII8">Fig. 8</a>. A telephone coil
-for moderately long-distance circuits is made on a wooden
-spool turned from a piece of wood three inches and a half
-long and one inch square, as shown at <a href="#FigVIII19">Fig. 19</a>. The core-sheath
-is turned down so that it is about one-sixteenth of
-an inch thick. This spool is given a coat or two of shellac,<span class="pagenum" id="Page182">[182]</span>
-and two holes are made at each end, as shown in the drawing.
-The first winding or primary coil is made up of two
-layers of No. 20 double-insulated copper wire, one end projecting
-from a hole at one end of the spool, the other from
-a hole at the other end. This coil is given two or three
-thin coats of shellac to bind the strands of wire and thoroughly
-insulate them, and over the layer a piece of paper
-is to be wrapped and shellacked. The secondary coil is
-made up of twelve layers of No. 34 silk-insulated copper
-wire, and between each layer a sheet of paper should be
-wound so that it will make two complete wraps. Each
-paper separator should be given a coat of shellac or hot
-paraffine; then the turns of wire should be continued just
-as thread is wound upon a spool, smoothly, closely, and
-evenly, until the last wrap is on. Three or four wraps of
-paper should be fastened on the coil to protect it, and it
-may then be screwed fast inside a box. The core-hole
-within the coil should be packed with lengths of No. 24 soft
-Swedes iron wire three inches and a half long. In <a href="#FigVIII19">Fig. 19</a>
-the wires are shown projecting from the end of a spool, and
-<a href="#FigVIII20">Fig. 20</a> depicts a completed telephone induction-coil. The
-installation of the induction-coils is shown in <a href="#FigVIII21">Fig. 21</a>.</p>
-
-<p><span class="pagenum" id="Page183">[183]</span></p>
-
-<div class="container" id="FigVIII21">
-
-<div class="figcenter nomargin">
-<img src="images/illo183.jpg" alt="" />
-</div>
-
-<p class="caption">PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTERS, ELECTRIC BUZZERS OR BELLS,
-LEVER-SWITCHES, INDUCTION-COILS, PUSH-BUTTONS, AND BATTERIES FOR STATIONS
-UP TO FIVE HUNDRED MILES APART.</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page184">[184]</span></p>
-
-<p>The wiring is comparatively simple, and may be easily
-followed if the description and plan are constantly consulted
-when setting up the line. R and R 2 are the receivers, T
-and T 2 the transmitters, C 1 and C 2 the batteries, E B and
-E B 2 the buzzers or bells, P B and P B 2 the push-buttons,
-and L S and L S 2 the lever-switches. For convenience of
-illustration the induction-coils are separated. The primary
-coil (P C) is indicated by the heavy spring line and the secondary
-coil (S C) by the fine spring line. When the line is
-“dead” both receivers are hanging from the hooks of the
-lever-switches. If the boy at the left wishes to call the boy
-at the right he lifts the receiver (R) from the hook (L S) and
-presses the button (P B). This throws the battery (C 1 C 1 C 1)
-in circuit with lines Nos. 1 and 2, and operates the buzzer
-(E B 2). When the boy at the right lifts his receiver (R 2) from
-the hook (L S 2), the bell circuit is cut out and the ’phone
-circuit is cut in. When the lever-switches are drawn up
-against the contact-springs (A, B, and C and A A, B B, and
-C C), both batteries are thrown into circuit with the transmitters
-at their respective ends through the primary coils
-(P C and P C 2). By inductance through the secondary coils
-(S C and S C 2), lines Nos. 1 and 2 are electrified, and when
-the voice strikes the disks in the transmitters the same tone
-and vibration is heard through the receivers at the other
-end of the line. While conversation is going on the batteries
-at either end are being drawn upon or depleted; but as soon
-as the receivers are hung on the hooks and the lever-switches
-are drawn away from the contact-springs, the flow of current
-is stopped. The buzzers or bells consume but a small
-amount of current when operated, and in dry cells the active
-parts recuperate quickly and depolarize. The greatest
-drain on a battery, therefore, is when the line is closed for
-conversation.</p>
-
-<h4>An Installation Plan</h4>
-
-<p>A simple manner in which to install this apparatus in
-boxes is shown in <a href="#FigVIII22">Fig. 22</a>. The box is depicted with the
-front opened and with the receiver hanging on the hook.<span class="pagenum" id="Page185">[185]</span>
-When the lever-switch (L S) is down it rests on the contact-spring
-(A), thus throwing in the bell circuit. When the boy
-at the other end of the line pushes the button on his box
-it operates the buzzer (E B). This can be understood by following
-with a pointer the wires from the buzzer to the
-outlet-posts (Nos. 1 and 3) at the bottom of the wall-plate.</p>
-
-<div class="container m40" id="FigVIII22">
-
-<div class="figcenter nomargin">
-<img src="images/illo185.jpg" alt="Telephone" />
-</div>
-
-</div><!--container-->
-
-<p>When the receiver (R) is lifted from the hook (L S), it cuts<span class="pagenum" id="Page186">[186]</span>
-out the bell circuit and cuts in the telephone circuit, through
-the spring-contacts (B and C). This circuit may easily be
-followed through the wires connecting transmitter, receiver,
-induction-coil, and batteries. The heavy lines leading out
-from the induction-coil are the primary coil wires, and the
-fine hair lines are those forming the secondary coil. The
-medium lines are those that connect the binding-posts,
-batteries, and lines.</p>
-
-<p>When the bell circuit is connected the impulse coming
-from the other end of the line enters through wire No. 10
-to post No. 3, thence to strip E and plate G, and so on to
-E B, which it operates. The current then passes from E B
-to contact A, through L S to post No. 1, and out on wire
-No. 11.</p>
-
-<p>To operate the buzzer at other end of the line the button
-(P B) is pushed in. This moves the spring (E) away from the
-plate (G), and brings it into contact with F. This connects
-the circuit through the battery wire (No. 8) to post No. 1 to
-line No. 11 without going into the box, and from wire No.
-9 to post No. 2; thence to hinge No. 7 to plate F, through
-E, down to post No. 3, and out through wire No. 10. In
-this manner the current is taken from the batteries at the
-foot of wires Nos. 8 and 9, and used to ring the buzzer at the
-other end of the line.</p>
-
-<p>When the hook (L S) is up the circuit is closed through T,
-I C, and battery. The current runs from the battery through
-wire No. 8 to post No. 1, to L S, through C and primary coil
-out to hinge No. 6, through transmitter to hinge No. 7, to
-post No. 2, and back to battery through wire No. 9.</p>
-
-<p>By inductance the sound is carried over the line, in at<span class="pagenum" id="Page187">[187]</span>
-wire No. 10, to post No. 3, through secondary coil to post
-No. 4, through receiver R to post No. 5, through B and
-L S to post No. 1, and out through wire No. 11. At the
-other end of the line it goes through the same parts
-of the apparatus.</p>
-
-<h4>A Portable Apparatus</h4>
-
-<p>For convenience it is often desirable to have a portable
-transmitter, and so avoid the inconvenience of having to
-stand while speaking. A neat portable apparatus that will
-stand on a ledge or table, and which may be moved about
-within the radius of the connecting lines, is shown in <a href="#FigVIII23">Fig. 23</a>.</p>
-
-<p>The wooden base is four inches square and the upright
-one inch and a half square. The stand is twelve inches
-high over all, and on the bottom a plate of iron or lead must
-be screwed fast to make it bottom-heavy, so that it will not
-topple over.</p>
-
-<p>The lever-switch may be arranged at the back of the
-upright and the push-button at the front near the base, as
-shown at A. The wall-box contains the buzzer and induction-coil,
-and within it the wiring is arranged from the portable
-stand to the batteries and line as shown at C. This
-illustration is too small, however, to show the complete
-wiring, and the young electrician is therefore referred to
-<a href="#FigVIII22">Fig. 22</a>. The battery (B) is composed of as many dry or
-wet cells as may be required to operate the line. These
-must be connected in series at both ends. At D a rear view
-of the upright and transmitter is shown to illustrate the
-manner in which the wiring can be done. If a hollow upright
-is made of four thin pieces of wood a much neater
-appearance may be secured by enclosing the wires.</p>
-
-<p><span class="pagenum" id="Page188">[188]</span></p>
-
-<div class="container m40" id="FigVIII23">
-
-<div class="figcenter nomargin">
-<img src="images/illo188.jpg" alt="" />
-</div>
-
-<p class="caption">A PORTABLE APPARATUS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page189">[189]</span></p>
-
-<p>In all of these telephone systems one wire must lead to
-the ground, or be connected with a water-pipe, taking care,
-however, to solder the wire to a galvanized pipe so that
-perfect contact will be the result. If the wire is carried
-directly to the ground it must be attached to a plate, which
-in turn is buried deep enough to reach moist earth, as
-described in the chapter on Line and Wireless Telegraphs,
-<a href="#Page215">page 215</a>.</p>
-
-<p>Care and accuracy will lead to success in telephony, but
-one slip or error will throw the best system out of order
-and render it useless. This, indeed, applies to all electrical
-apparatus; there can be no half-way; it will either work
-or it won’t.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page190">[190]</span></p>
-
-<h3>Chapter IX<br />
-<span class="chaptitle">LINE AND WIRELESS TELEGRAPHS</span></h3>
-
-<h4>A Ground Telegraph</h4>
-
-<p class="chapstart"><span class="largecap">N</span><span class="afterlargecap">early</span>
-every boy is interested in telegraphy, and it
-is a fascinating field for study and experimental work,
-to say nothing of the amusement to be gotten out of it.
-The instruments are not difficult to make, and two boys
-can easily have a line between their houses.</p>
-
-<p>The key is a modified form of the push-button, and is
-simply a contact maker and breaker for opening and closing
-an electrical circuit. A practical telegraph-key is
-shown in <a href="#FigIX1">Fig. 1</a>, and in <a href="#FigIX2">Fig. 2</a> is given the side elevation.</p>
-
-<p>The base-board is four inches wide, six inches long, and
-half an inch in thickness. At the front end a small metal
-connector-plate is screwed fast, and through a hole in the
-middle of it a brass-headed upholsterer’s tack is driven for
-the underside of the key to strike against. Two <span class="symbol">L</span> pieces
-of metal are bent and attached to the middle of the board
-to support the key-bar, and at the rear of the board another
-upholsterer’s tack is driven in the wood for the end
-of the bar to strike on and make a click. The bar is of
-brass or iron, measuring three-eighths by half an inch, and
-is provided with a hole bored at an equal distance from each<span class="pagenum" id="Page191">[191]</span>
-end for a small bolt to pass through, in order to pivot it
-between the <span class="symbol">L</span> plates. A hole made at the forward end
-will admit a brass screw that in turn will hold a spool-end
-to act as a finger-piece. The screw should be cut off and
-riveted at the underside. A short, strong spring is to be
-attached to the back of the base-block and to the end of
-the key-bar by means of a hook, which may be made from<span class="pagenum" id="Page192">[192]</span>
-a steel-wire nail flattened. It is bound to the top of the
-bar with wire, as shown in <a href="#FigIX2">Figs. 2</a> and <a href="#FigIX3">3</a>.</p>
-
-<div class="container m35" id="FigIX1">
-
-<div class="figcenter nomargin">
-<img src="images/illo191a.jpg" alt="Telegraph key" />
-</div>
-
-</div><!--container-->
-
-<div class="container m40" id="FigIX4">
-
-<div class="figcenter nomargin">
-<img src="images/illo191b.jpg" alt="Telegraph key" />
-</div>
-
-</div><!--container-->
-
-<p>The incoming and outgoing wires are made fast to one
-end of the connector-plate and to one of the <span class="symbol">L</span> pieces that
-support the key. When the key is at rest the circuit is
-open, but when pressed down against the brass tack it is
-closed, and whether pressed down or released it clicks at
-both movements. A simple switch may be connected with
-the <span class="symbol">L</span>-plate and the connection-post at the opposite side of
-the key-base, so that, if necessary, the circuit may be
-closed. Or an arm may be caught under the screw at the
-<span class="symbol">L</span>-plate, and brought forward so that it can be thrown in
-against a screw-head on the connector-plate, as shown in
-<a href="#FigIX3">Fig. 3</a>. The screw-head may be flattened with a file, and
-the underside of the switch bevelled at the edges, so that
-it will mount easily on the screw.</p>
-
-<p>In <a href="#FigIX4">Fig. 4</a> (page 191) a simple telegraph-sounder is shown.
-A base-board, four inches wide, six inches long, and seven-eighths
-of an inch in thickness, is made of hard-wood, and
-two holes are bored, with the centres two inches from one end,
-so that the lower nuts of the horseshoe magnet will fit in
-them, as shown in <a href="#FigIX5">Fig. 5</a>. This allows the yoke to rest flat
-on the top of the base, and with a stout screw passed down
-through a hole in the middle of the yoke and into the wood
-the magnets are held in an upright position.</p>
-
-<p>From the base-block to the top of the bolt the magnets
-are two inches and a quarter high. The bar of brass or
-iron to which the armature (A in <a href="#FigIX5">Fig. 5</a>) is attached is four
-inches and a half in length and three-eighths by half an
-inch thick. At the middle of the bar and through the<span class="pagenum" id="Page193">[193]</span>
-side a hole is bored, through which a small bolt may be
-passed to hold it between the upright blocks of wood. At
-the front end two small holes are to be bored, so that its
-armature may be riveted to it with brass escutcheon-pins
-or slim round-headed screws. The heads are at the top
-and the riveting is underneath. A small block of wood is
-cut, as shown in <a href="#FigIX6">Fig. 6</a>, against which the two upright
-pieces of wood are made fast. This block is two inches
-and a half long, one inch and a quarter high, and seven-eighths
-of an inch wide. The laps cut from each side are
-an inch wide and a quarter of an inch deep, to receive the
-uprights of the same dimensions.</p>
-
-<p>At the top of this block a brass-headed nail is driven
-for the underside of the bar to strike on. A hook and spring
-are to be attached to the rear of the sounder-bar, as described
-for the key, and at the front of the base two binding-posts
-are arranged, to which the loose ends of the coil-wires
-are attached.</p>
-
-<p>Just behind the yoke, and directly under the armature-bar,
-a long screw is driven into the base-block, as shown
-at B in <a href="#FigIX5">Fig. 5</a>. It must not touch the yoke, and the head
-should be less than one-eighth of an inch below the bar
-when at rest. On this the armature-bar strikes and clicks
-when drawn to the magnets. The armature must not
-touch the magnets; otherwise the residual magnetism
-would hold it down. The screw must be nicely adjusted,
-so that a loud, clear click will result.</p>
-
-<p><span class="pagenum" id="Page194">[194]</span></p>
-
-<div class="container m40">
-<a id="FigIX2"></a>
-<a id="FigIX3"></a>
-<a id="FigIX5"></a>
-<a id="FigIX6"></a>
-<a id="FigIX8"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo194.jpg" alt="" />
-</div>
-
-<p class="caption">TELEGRAPH KEY AND SOUNDER</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page195">[195]</span></p>
-
-<p>When the sounder is at rest the rear end lies on the brass
-tack in the block, and the armature is about a quarter of
-an inch above the top of the magnets. The armature is of
-soft iron, two inches and a half long, seven-eighths of an
-inch wide, and an eighth of an inch thick. These small
-scraps of metal may be procured at a blacksmith’s shop,
-and, for a few cents, he will bore the holes in the required
-places; or if you have a breast or hand drill the metal
-may be held in a vise and properly perforated.</p>
-
-<p>By connecting one wire from the key directly with one of
-the binding-posts of the sounder, and the other with the
-poles of a battery, and so on to the sounder, the apparatus
-is ready for use. By pressing on the key the circuit is
-closed, and the magnetism of the sounder-cores draws the
-armature down with a click. On releasing the key the bar
-flies back to rest, having been pulled down by the spring,
-and it clicks on the brass tack-head. These two instruments
-may be placed any distance apart, miles if necessary,
-so long as sufficient current is employed to work the sounder.
-Two sets of instruments must be made if boys in separate
-houses are to have a line. Each one must have a key,
-sounder, and cell, or several cells connected in series to form
-a battery, according to the current required.</p>
-
-<p>In the plan of the telegraph-line connections (<a href="#FigIX7">Fig. 7</a>, page
-196) a clear idea is given for the wiring; and if the line and
-return wires are to be very long, it would be best to have them
-of No. 14 galvanized telegraph-wire, copper being too expensive,
-although much better. These wires must not touch
-each other, and when attached to a house, barn, or trees,
-porcelain or glass insulators should be used. If nothing
-better can be had, the necks of some stout glass bottles may
-be held with wooden pins or large nails, and the wire twisted
-to them, as shown in <a href="#FigIX8">Fig. 8</a>. When the line is not in use<span class="pagenum" id="Page196">[196]</span>
-the switches on both keys should be closed; otherwise it
-would be impossible for the boy having the closed switch
-to call up the boy with the open one. Take great care in
-wiring your apparatus to study the plan, for a misconnected
-wire will throw the whole system out of order.</p>
-
-<div class="container" id="FigIX7">
-
-<div class="figcenter nomargin">
-<img src="images/illo196.jpg" alt="Telegraph line" />
-</div>
-
-</div><!--container-->
-
-<p>To operate the line see that all switches are closed and
-that the connections are in good condition. When the boy
-in house No. 2 wants to call up his friend in house No. 1
-he throws open the switchon key, as shown in the <a href="#FigIX7">plan</a>,
-and by pressing down on the finger-key his sounder and
-that in house No. 1 click simultaneously. As soon as he
-raises or releases the key the armatures rise, making the
-up-click. If he presses his key and releases it quickly the
-two clicks on the sounder in house No. 1 are close together;
-this makes what is called a dot. If the key is held down<span class="pagenum" id="Page197">[197]</span>
-longer it makes a long time between clicks, and this is called
-a dash. The dot and dash are the two elements of the
-telegraphic code. You will understand that the boy in
-house No. 2 hears just what the one in No. 1 is hearing,
-since the electric current passing through both coils causes
-the magnets to act in unison. So soon as the operator in
-house No. 2 has finished he closes his switch, and the other
-in house No. 1 opens his switch on the key and begins his
-reply. This is the simple principle of the telegraph, and
-all the improved apparatus is based on it, no matter how
-complicated. The complete Morse alphabet is appended:</p>
-
-<div class="container m30">
-
-<p class="caption morse"><b>The Morse Telegraph Code</b></p>
-
-<div class="figcenter nomargin">
-<img src="images/illo197.png" alt="" />
-</div>
-
-</div><!--container-->
-
-<p>Any persevering boy can soon learn the dot-and-dash
-letters of the Morse code, and very quickly become a fairly<span class="pagenum" id="Page198">[198]</span>
-good operator. Telegraphic messages are sent and received
-in this way, and are read by the sound of the clicks.
-Various kinds of recording instruments are also employed,
-so that when an operator is away from his table the automatic
-recorder takes down the message on a paper tape.
-In the stock-ticker, employed in brokerage offices, the
-recording is done by letters and numerals, and the paper
-tape drops into a basket beside the machine, so that any
-one picking up the strip of paper can see the quotations
-from the opening of business up to the time of reading
-them. These quotations are sent out directly from the
-floor of the exchanges, and by the action of one man’s hand
-thousands of machines are set in operation all over the city.</p>
-
-<p>Perhaps the most unique and wonderful telegraphic
-signal-apparatus is that located on the floor of the New
-York Produce Exchange and the Chicago Exchange. The
-dials, side by side, are operated by direct wire from Chicago.
-When the New York operator flashes a quotation it appears
-simultaneously on the New York dial and simultaneously
-on the Chicago dial, and vice versa.</p>
-
-<p>Electrical instruments are not the only means by which
-the Morse alphabet may be transmitted, for in some instances
-instruments would be in the way, while in others
-the wires might be down and communication cut off.</p>
-
-<p>This is interestingly illustrated by an event in Thomas
-A. Edison’s life. When he was a boy and an apprentice
-telegraph operator on the Grand Trunk Line, an ice-jam
-had broken the cable between Port Huron, in Michigan,
-and Sarnia, in Canada, so that communication by electricity
-was cut off. The river at that point is a mile and<span class="pagenum" id="Page199">[199]</span>
-a half wide, the ice made the passage impossible, and there
-was no way of repairing the cable. Edison impulsively
-jumped on a locomotive standing near the river-bank and
-seized the whistle-cord.</p>
-
-<p>He had an idea that blasts of the whistle might be broken
-into long and short sounds corresponding to the dots and
-dashes of the Morse code. In a moment the whistle sounded
-over the river: “Toot, toot, toot, toot,&mdash;toot, tooooot,&mdash;tooooot&mdash;tooooot&mdash;toot,
-toot&mdash;toot, toot.” “Halloo, Sarnia!
-Do you get me? Do you hear what I say?”</p>
-
-<p>No answer.</p>
-
-<p>“Do you hear what I say, Sarnia?”</p>
-
-<p>A third, fourth, and fifth time the message went across,
-to receive no response. Then suddenly the operator at
-Sarnia heard familiar sounds, and, opening the station door,
-he clearly caught the toot, toot of the far-away whistle.
-He found a locomotive, and, mounting to the cab, responded
-to Edison, and soon messages were tooted back and forth
-as freely as though the parted cable were again in operation.</p>
-
-<p>Some years ago the police of New York were mystified
-over a murder case. The man they suspected had not fled,
-but was still in his usual place, and attending to his business
-quite as though nothing had happened to connect him
-with the tragedy.</p>
-
-<p>Detectives in plain clothes had been following him and
-watching closely his every move in and out of restaurants
-and shops and at social affairs; but not the slightest proof
-could be secured against him.</p>
-
-<p>One noon-time they followed him into a café, where he
-had gone with a friend. The detectives took seats near<span class="pagenum" id="Page200">[200]</span>
-him, but each of them sat at different tables in the room
-full of people.</p>
-
-<p>When in the café the suspect sat next the wall, a habit
-the detectives had noticed. Consequently, only those persons
-who sat at one side of him or directly in front could
-see his face. During the time they were in the restaurant
-the detectives communicated with each other by tapping
-on the table tops with a lead-pencil; and something the
-man said, which the nearest detective heard, led to the
-climax. One detective rose, paid his check, and loitered
-near the door; another got up a little later and sauntered
-out, but returned with a cardboard sign. Going over to
-the table where the suspected criminal and his friend sat,
-he deliberately tacked it on the wall above them, then
-went out again, leaving the third detective to watch the
-face of the man as he read:</p>
-
-<p class="reward">$1000 REWARD<br />
-for information leading to the arrest of the murderer of &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
-on March &mdash;&mdash;&mdash;&mdash;, 1876</p>
-
-<p>The man cast a glance about the restaurant, then said
-to his companion: “Did I show any signs of agitation?”
-The third detective rose, stepped over to the man, tapped
-him on the shoulder, and said, “I want you.” There would
-have been a scene of violence had not the other two detectives
-closed in on the man, and within six months he
-paid the penalty of his crime.</p>
-
-<p>If it had not been for the dot-and-dash alphabet, tapped
-out with lead-pencils, the detectives could not have communicated;
-but like Edison, they used the means at hand
-to open up and carry on a silent conversation.</p>
-
-<p><span class="pagenum" id="Page201">[201]</span></p>
-
-<h4>Wireless Telegraphy</h4>
-
-<p>Everybody nowadays understands that wireless telegraphy
-means the transmission of electrical vibrations through
-the ether and earth without the aid of wires or any visible
-means of conductivity. The feat of sending an electrical
-communication over thousands of miles of wire, or through
-submarine cables, is wonderful enough, for all that custom
-has made it an every-day miracle. To accomplish this same
-end by sending our messages through the apparently empty
-air is indeed awe-inspiring and almost beyond belief. And
-yet we know that wireless telegraphy is to-day a real scientific
-fact.</p>
-
-<p>At first sight it would seem that the instruments must
-be complicated and necessarily beyond the ability of the
-average boy to make, and far too expensive as well. As a
-matter of fact, the young electrician may construct his wireless
-apparatus at a very moderate cost, it being understood
-that the sending and receiving poles may be mounted on a
-housetop or barn.</p>
-
-<p>But first let us consider the theory upon which we are
-to work. There is no doubt but that electricity is the highest
-known form of vibration&mdash;so high, indeed, that as yet
-man has been unable to invent any instrument to record
-the number of pulsations per second. This vibration will
-occur in, and can be sent through, the ordinary form of conductor,
-such as metals, water, fluids and liquids, wet earth,
-air and ice. Also through what we call the ether.</p>
-
-<p>Now the ether of the atmosphere, estimated to be fifteen
-trillion times lighter than air, is the medium through which<span class="pagenum" id="Page202">[202]</span>
-the electrical vibrations pass in travelling in their radial
-direction from a central point, corresponding to the ripples
-or wavelets formed when a pond or surface of still water
-is disturbed. Ether is so fine a substance that the organs
-of sense are not delicate enough to detect it, and
-it is of such a volatile and uneasy nature that it is
-continually in motion. It vibrates under certain conditions,
-and when disturbed (as by a dynamo) it undoubtedly
-forms the active principle of electricity and magnetism.</p>
-
-<p>James Clark Maxwell believed that magnetism, electricity,
-and light are all transmitted by vibrations in one common
-ether, and he finally demonstrated his theory by proving
-that pulsations of light, electricity, and magnetism differed
-only in their wave lengths. In 1887 Professor Hertz succeeded
-in establishing proof positive that Maxwell’s theories
-were correct, and, after elaborate experiments, he proved
-that all these forces used ether as a common medium.
-Therefore, if it were not for the ether, wireless telegraphy,
-with all its wonders, would not be possible. We understand,
-then, that the waves of ether are set in motion from a central
-disturbing point, and this can be accomplished only
-by means of electrical impulse.</p>
-
-<p>Suppose that we strike a bell held high in the air. The
-sound is the result of the vibrations of its mass sending its
-pulsating energy through the air. The length of the sound-waves
-is measured in the direction in which the waves are
-travelling, and if the air is quiet and not disturbed by
-wind the sound will travel equally in all directions. The
-sound of a bell will not travel so well against a wind as it<span class="pagenum" id="Page203">[203]</span>
-will with it, just as the ripples on a pond would be checked
-by an adverse set of wavelets.</p>
-
-<p>Now the ether can be made to vibrate in a similar manner
-to the air by a charge of electricity oscillating or surging
-to and fro on a wire several hundred thousand times in
-a second. These oscillations strike out and affect the surrounding
-ether, so that, according to the intensity of the
-disruptive charge at the starting-point, the ether waves
-may be made to reach near or distant points.</p>
-
-<p>This is, perhaps, more clearly shown by the action of a
-pendulum. In <a href="#FigIX9">Fig. 9</a> the rod and ball are at rest, but if
-drawn to one side and released it swings over to the other
-side nearly as far away from its central position of rest as
-from the starting-point. If allowed to swing to and fro it
-will oscillate until at last it will come to rest in a vertical
-position. This same oscillation (oscillation being a form of
-vibration) takes place in the water when a stone has been
-flung into it, and in the ether when affected by the electrical
-discharge. In <a href="#FigIX10">Fig. 10</a> are shown the principal varieties of
-vibration&mdash;the oscillating, pulsating, and alternating.</p>
-
-<p>It is known that if these oscillations are damped, so that
-the over-intense agitation of the central disturbance is
-lessened, a new series of vibrations, such as the pulsating or
-alternating, is set up, and these secondary vibrations possess
-the power to travel around the world&mdash;yes, and perhaps
-to other worlds in the planetary cosmos.</p>
-
-<p><span class="pagenum" id="Page204">[204]</span></p>
-
-<div class="container m30">
-<a id="FigIX9"></a>
-<a id="FigIX10"></a>
-<a id="FigIX11"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo204.png" alt="" />
-</div>
-
-<p class="caption">OSCILLATION AND VIBRATION</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page205">[205]</span></p>
-
-<p>The study of ether disturbances, wave currents, oscillating
-currents, and the other phenomena dependant upon
-this invisible force is most interesting and fascinating, and
-were it possible to devote more space to this topic several
-chapters could be written on the scientific theory of wireless
-telegraphy.<a id="FNanchor2"></a><a href="#Footnote2" class="fnanchor">[2]</a></p>
-
-<div class="footnote">
-
-<p><a id="Footnote2"></a><a href="#FNanchor2"><span class="label">[2]</span></a>
-For further information on this subject the student is referred to such
-well-known books as <i>Signalling Across Space Without Wires</i>, by Prof.
-Oliver J. Lodge, and <i>Wireless Telegraphy</i>, by C. H. Sewall.</p>
-
-</div><!--footnote-->
-
-<p>The principle difference between wire, or line, and wireless
-telegraphy is that the overhead wire, or underground or
-submarine cable, is omitted. In its stead the ether of the
-air is set in vibratory motion by properly constructed instruments,
-and the communication is recorded at a distance
-by instruments especially designed to receive the transmitted
-waves.</p>
-
-<p>It seems to be the popular impression that a wireless message
-sent from one point to another travels in a straight
-line, as indicated by <a href="#FigIX11">Fig. 11</a>, B representing Boston, which
-receives the message from N. Y., or New York. As a matter
-of fact, if several sets of wireless receiving instruments
-were located on the circumference of a circle the same distance
-from New York in all directions, or even at nearer
-or farther points, they would all receive the same message.
-Instead of travelling in one direction, the ether waves are
-set in motion by the electrical disturbance, just as water is
-agitated by the stone thrown into it. The ripples, or wavelets,
-are started from the central point of disturbance and
-radiate out, so that instead of reaching Boston only the
-waves travel over every inch of ground, or air space, in all
-directions, and would be recorded in every town and village
-within the sphere of energy set up by the original force
-that put the ether waves in motion. The stronger this
-initial force the wider its field of action. This is shown at<span class="pagenum" id="Page206">[206]</span>
-<a href="#FigIX12">Fig. 12</a>, which is an area comprising Philadelphia, Pittsburg,
-Buffalo, Washington, and other cities. Moreover, the
-waves of electrical disturbance would carry far beyond in
-all directions, taking in the cities of the north, south, and
-west, and at the east, going far out to sea, beyond Boston
-harbor and below Cape Hatteras, where ships carrying receiving
-instruments could pick up the messages. Like the<span class="pagenum" id="Page207">[207]</span>
-ripples on the water, the radiating waves, or rings, become
-larger as they reach out farther and farther from the centre
-of disturbance, until at last they are imperceptible, and
-lose their shape and force.</p>
-
-<div class="container m30" id="FigIX12">
-
-<div class="figcenter nomargin">
-<img src="images/illo206.jpg" alt="Map" />
-</div>
-
-</div><!--container-->
-
-<p>At great distances, therefore, the ether disturbance becomes
-so slight that it is impossible to record the vibration
-or message sent out; and until some improved forms of apparatus
-and coherer are invented, or the original disturbing
-force is enormously increased, it will be impossible to send
-messages at longer distances than four or five thousand
-miles from a central point. Both Marconi and De Forrest
-assert that they are perfecting coherers which will make
-it possible to girdle the earth with a message, and that
-within the next few years an aerogram may be sent out from
-a station, and, after instantly encircling the earth and being
-recorded during its passage at all intermediate stations, it
-will return and be received at the original sending-point.
-This, of course, is a matter of future achievement; but now
-that messages across the Atlantic are a commercial fact, it
-seems quite possible that the greater feat of overriding space
-and reaching any point on the earth’s surface will soon be
-a reality. And now to proceed from theory to the construction
-of a practical wireless apparatus having a radial
-area of action over some ten or fifteen miles.</p>
-
-<p>The principal parts of a wireless apparatus include the
-antennas (or receiving and sending poles with their terminal
-connections), the induction-coil, strong primary batteries
-or dynamo, the coherer and de-coherer, the telegraph
-key and sounder (or a telephone receiver), and the necessary
-connection wires, binding-posts, and ground-plates.</p>
-
-<p><span class="pagenum" id="Page208">[208]</span></p>
-
-<p>A large induction-coil with many layers of fine insulated
-wire will be necessary for the perfect operative outfit. The
-most practical coil for the amateur is a Ruhmkorff induction-coil.
-(See the directions and illustrations for constructing
-this coil, beginning on <a href="#Page59">page 59</a> of <a href="#Page54">chapter iv.</a>)</p>
-
-<p>The sending apparatus is practically the same in all outfits,
-and consists of a source of electrical energy, such as
-a battery, or dynamo, the essential induction-coil and adjustable
-spark-gap between the brass balls on terminal rods,
-and the make-and-break switch, or telegraph-key.</p>
-
-<p>It is in the various forms of coherers and receiving apparatus
-that the different inventors claim superiority and
-originality. The systems also differ in their theory of harmonic
-tuning or vibratory sympathy. This is accomplished
-by means of coils and condensers, so that the messages
-sent out on one set of instruments will not be picked up or
-recorded by the receiving apparatus of competitors.</p>
-
-<p>Having made or purchased an induction-coil of proper
-and adequate size, it will now be necessary to construct the
-parts so that an adjustable spark-gap may be secured.</p>
-
-<p>Make a hollow wooden base for the induction-coil to rest
-on. It should be a trifle longer than the length of the coil
-and about seven inches wide. This may be made from
-wood half an inch thick. The base should be two inches
-high, so that it will be easy and convenient to make wire
-connections under it. Mount the induction-coil on the
-base and make it fast with screws, arranging it so that the
-binding-posts are on the side rather than at the top of the
-coil, as shown in <a href="#FigIX13">Fig. 13</a>.</p>
-
-<p>Cut a thin board and mount it across the top of the induction-coil<span class="pagenum" id="Page209">[209]</span>
-on two short blocks, and to this attach two
-double-pole binding-posts (P P). The fine wires from the
-induction-coil are made fast to the foot of each post, and
-from the posts the aerial wire (A W) and ground wire (G W)
-lead out.</p>
-
-<p>Fasten two binding-posts at the forward corners of the
-base, and to them make connection-wires fast to the heavy
-or primary wires of the coil. Wires B and C lead out from
-these posts to the battery and key, and to complete this
-part of the sending, or transmitting apparatus it will be
-necessary to have two terminal rods and balls attached to
-the top of the binding-posts (P P). This part of the apparatus
-is generally called the oscillator, and the rods are balanced
-on the posts, so that they can be moved in order to
-increase or diminish the space (S G), or spark-gap, between
-the brass balls.</p>
-
-<p>When, after experiment, the proper space has been determined,
-the set screw at the top of the posts will hold
-the terminal rods securely in place.</p>
-
-<p>Obtain a piece of brass, copper, or German-silver rod
-three-sixteenths of an inch in diameter. Now cut two
-short rods, each six inches long, and two inches from one
-end flatten the rods with a hammer, as shown at A in <a href="#FigIX14">Fig.
-14</a>. Flatten the rod in two places at the other end, as shown
-at B B in <a href="#FigIX14">Fig. 14</a>; then bore holes through the flattened
-parts (A), so that the binding-screws at the top of the posts
-(P P) will pass through them.</p>
-
-<p>Obtain two brass balls from one to one inch and a half
-in diameter. If they are solid or cast brass they may be
-attached to the ends of the terminal rods by threading, so<span class="pagenum" id="Page210">[210]</span>
-that it will be easy to remove them. If the balls are of
-spun sheet-metal it will be necessary to solder them fast
-to the ends of the rods, and, when polishing the balls, the
-rods will have to be removed from the binding-posts. It
-is imperative that the balls should be kept polished and in
-bright condition at all times, to facilitate the action of the
-impulsive sparks.</p>
-
-<div class="container m40">
-<a id="FigIX13"></a>
-<a id="FigIX14"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo210.jpg" alt="Wireless set" />
-</div>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page211">[211]</span></p>
-
-<p>To counterbalance these balls there should be handles at
-the long ends of the rods. These handles may be of wood,
-or made of composition molded directly on the rods. A
-good composition that can be easily made and molded is
-composed of eight parts plaster of Paris and two parts of
-dextrin made into a thick paste with water. The dextrin
-may be purchased at a paint-store, and is the color of light-brown
-sugar. Mix the dry plaster and dextrin together,
-so that they are homogeneous; then add water to make
-the pasty mass. Use an old table-knife to apply the wet
-composition to the bars. The flattened parts will help
-to hold the mass in place until it sets. It is best to make
-two mixtures of the paste and put one on first, leaving it
-rough on the surface, so that the last coat will stick to it.
-When the last coat is nearly dry it may be rubbed
-smooth with the fingers and a little water, or allowed to dry
-hard, and then smoothed down with an old file and sand-paper.</p>
-
-<p>If solid brass balls are used for the terminals the composition
-handles may be made heavier; but in any event
-the proper amount of composition should be used, so that
-when the rod is balanced on a nail or piece of wire passed
-through the hole it will not tip down at one end or the
-other, but will remain in a horizontal position.</p>
-
-<p>The overhead part of the apparatus employed to collect
-the electric waves is called the antennæ, and in the various
-commercial forms of wireless apparatus this feature differs.
-The general principle, however, is the same, and in <a href="#FigIX15">Figs.
-15</a>, <a href="#FigIX16">16</a>, <a href="#FigIX17">17</a>,
-and <a href="#FigIX18">18</a> some simple forms of construction are
-shown.</p>
-
-<p><span class="pagenum" id="Page212">[212]</span></p>
-
-<p>Great care must be taken to properly insulate the rod,
-wire, or fingers of these antennæ, so that the full force of
-the vibration is carried directly down to the coherer and
-sounder or receiver. For this purpose, porcelain, glass, or
-gutta-percha knobs must be employed.</p>
-
-<p>In <a href="#FigIX15">Fig. 15</a> the apparatus consists of an upright stick, a
-cross-stick, and a brace, or bracket, to hold them in proper
-place.</p>
-
-<p>Porcelain knobs are made fast to the sticks with linen
-string or stout cotton line. Then an insulated copper wire
-is run through the holes in the knobs, and from the outer
-knob a rod of brass, copper, or German-silver, or even a
-piece of galvanized-iron lightning-rod, is suspended. Care
-should be taken to see that the joint between rod and wire
-is soldered so as to make perfect contact. Otherwise rust
-or corrosion will cause imperfect contact of metals, and interrupted
-vibrations would be the result. The upright stick
-should be ten or fifteen feet high, and may be attached to
-a house-top, a chimney, or on the corner of a barn roof.</p>
-
-<p>Another form of single antenna is shown in <a href="#FigIX16">Fig. 16</a>.
-This is a rod held fast in a porcelain insulator with cement.
-The insulator, in turn, is slipped over the end of a staff, or
-pole, which is erected on a building top or out in the open,
-the same as a flag-pole. Near the foot of the rod, and just
-above the insulator, a conducting-wire is made fast and
-soldered. This is run down through porcelain insulators
-to the apparatus.</p>
-
-<p>If the pole is erected on a house-top it may be braced with
-wires, to stay it, but care must be taken not to have these
-wires come into contact with the rod, or conducting-wire.</p>
-
-<p><span class="pagenum" id="Page213">[213]</span></p>
-
-<div class="container m40">
-<a id="FigIX15"></a>
-<a id="FigIX16"></a>
-<a id="FigIX17"></a>
-<a id="FigIX18"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo213.jpg" alt="" />
-</div>
-
-<p class="caption">TYPES OF ANTENNÆ</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page214">[214]</span></p>
-
-<p>Another form of antennas is shown in <a href="#FigIX17">Fig. 17</a>, where rods
-are suspended from a wire which, in turn, is drawn taut
-between two insulators. The insulators are held in a
-framework composed of two uprights and a cross-piece of
-wood.</p>
-
-<p>This frame may be nailed fast to a chimney and to the
-gable of a roof, as shown in the <a href="#FigIX17">drawing</a>; and to steady the
-rods, so that they will not swing in a high wind, the lower
-ends should be tied together with cotton string, the ends of
-which should be fastened to the uprights. The leading-in
-wire is made fast to the top wire, from which the rods are
-suspended, and all the exposed joints should be soldered
-to insure perfect contact and conductivity. A modified
-form of the Marconi antennæ is shown in <a href="#FigIX18">Fig. 18</a>. This is
-made of a metal hoop three of four feet in diameter held in
-shape by cross-sticks of wood, which can be lashed fast to
-the ring. Leading down from it are numerous copper wires
-which terminate in a single wire, the whole apparatus resembling
-a funnel. The upper unions where the wires join
-the ring need not be soldered, but at the bottom, where they
-all come together and join the leading-in wire, it is quite
-necessary that a good soldered joint be made. This funnel
-may be hung between two upright poles on a house-top, or
-suspended from the towers or chimneys.</p>
-
-<p>Almost any metal plate will do for the ground, or the
-ground-wire (G W in <a href="#FigIX13">Fig. 13</a>) may be bound to a gas or
-water pipe which goes down deep in the ground, where it is
-moist. Rust or white lead in the joints of gas-mains sometimes
-prevent perfect contact, but in water-pipes the current
-will flow readily through either the metal or the water.<span class="pagenum" id="Page215">[215]</span>
-To insure the most perfect results, it is best to have an independent
-ground composed of metal, and connected directly
-with the oscillator, or coherer, by an insulated copper
-wire. A simple and easily constructed ground is a sheet
-of metal, preferably copper, brass, or zinc, to the upper edge
-of which two wires are soldered, as shown in <a href="#FigIX19">Fig. 19</a>. This
-is embedded in the ground three or four feet below the surface.
-Another ground-plate is a sheet of metal bent in <span class="symbol">V</span>
-shape and then inverted. Two wires are soldered to the
-angle, and the ends brought together and soldered. This
-ground is buried three or four feet deep, and stands in a
-vertical position, as shown at <a href="#FigIX20">Fig. 20</a>. At <a href="#FigIX21">Fig. 21</a> a flat
-ground is shown. This is a sheet of metal cut with pointed
-ends. The ground-wire is soldered to the middle of it, and
-it is then buried deep enough to be embedded in moist
-earth.</p>
-
-<p>One of the best grounds is an old broiler with a copper
-wire soldered to the ends of the handles, as shown at <a href="#FigIX22">Fig.
-22</a>. This is buried deep in the ground in a vertical position,
-and the insulated copper wire is carried up to the instruments.</p>
-
-<p>The most important part of the wireless telegraphic apparatus
-is now to be constructed, and this requires some
-care and patience. The coherer is the delicate, sensitive
-part of the apparatus on which hinges success or failure.
-There are various kinds of coherers designed and used by
-different inventors, but while the materials differ and the
-construction takes various forms, the same basic principle
-applies to all.</p>
-
-<p><span class="pagenum" id="Page216">[216]</span></p>
-
-<div class="container m40">
-<a id="FigIX19"></a>
-<a id="FigIX20"></a>
-<a id="FigIX21"></a>
-<a id="FigIX22"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo216.jpg" alt="" />
-</div>
-
-<p class="caption">TYPES OF GROUNDS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page217">[217]</span></p>
-
-<p>The coherer can best be explained as a short glass tube
-in which iron or other metallic filings are enclosed. Corks
-are placed in both ends of the tube, and through these corks
-the ends of wire are passed, so that they occupy the position
-shown in <a href="#FigIX23">Fig. 23</a>, the ends being separated a quarter of an
-inch. Metal filings will not conduct an electric current
-the same as a solid rod or bar of the same metal, but resist
-the passage of current.</p>
-
-<p>After long periods of experimenting with various devices
-to detect the presence of feeble currents, or oscillations,
-in the ether, the coherer of metal filings was adopted.
-When the oscillations surge through the resonator, the
-pressure, or potential, finally breaks down the air film
-separating the little particles of metal, and then gently
-welds their sharp edges and corners together so as to form
-a conductor for the current. Before this process of cohesion
-takes place these fine particles offer a very high
-resistance to the electrical energy generated by a dry cell
-or battery&mdash;so much so that no current is permitted to
-pass. But once the oscillations in the ether cause them to
-cohere&mdash;presto! the resistance drops from thousands of
-ohms to hundreds, and the current from the dry cell now
-flows easily through the coherer and deflects the needle
-of a galvanometer. This is the common principle of all
-coherers of the granulated metal type, although there are
-many modifications of the idea.</p>
-
-<p>The action of the electric and oscillatory currents on
-particles of metal can best be understood by placing some
-fine iron filings on a board, as shown at <a href="#FigIX24">Fig. 24</a>, and
-then inserting the aerial and ground wires in the filings,
-but separated by an eighth or a quarter of an inch.<span class="pagenum" id="Page218">[218]</span>
-A temporary connection may be made as shown in
-<a href="#FigIX25">Fig. 25</a>.</p>
-
-<div class="container m40">
-<a id="FigIX23"></a>
-<a id="FigIX24"></a>
-<a id="FigIX25"></a>
-<a id="FigIX26"></a>
-<a id="FigIX27"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo218.jpg" alt="Coherers" />
-</div>
-
-</div><!--container-->
-
-<p>A A are aerials on both instruments; C is the open coherer,
-or board with iron filings, in which the ends of the
-aerial and ground wires are embedded; D C is a dry cell;
-and R is a telegraphic relay, or sounder. If the wire across
-C was not parted and covered with filings, the dry cell
-would operate R, but the high resistance of the particles
-of metal holds back the current.</p>
-
-<p>On the opposite side, I C is the induction-coil; K is the<span class="pagenum" id="Page219">[219]</span>
-telegraphic key, or switch, which makes and breaks the
-current; S B is the storage-batteries, or source of electric
-energy; and S G the spark-gap between the brass balls
-on the terminal rods. By closing the circuit at K the
-current flows through the primary of the induction-coil,
-affects the secondary coil, and causes a spark to leap across
-the gap between the brass balls. This instantly sets the
-ether in motion from A on the right, and the impulse is
-picked up by A on the left. This oscillation breaks down
-the resistance of the filings at C, and the current from battery,
-or dry cell (D C), flows through the filings and operates
-the sounder, or relay (R). This operation takes place instantly,
-and the particles of metal are seen to cohere, or
-shift, so that better contact is established. But as soon
-as the spark has jumped across the gap the action of cohesion
-ceases until the key (K) is again operated to close the
-circuit and cause another spark to leap across the gap.
-The shifting of the metal particles on the board (C) is what
-takes place in the glass tube of the coherer, <a href="#FigIX23">Fig. 23</a>, but in
-this confined space the particles will not drop apart again
-as on the flat surface, but will continue to cohere. A de-coherer
-is necessary, therefore, to knock the particles apart,
-so that the next oscillatory impulse will have a strong and
-individual effect. There are several forms of de-coherers
-in use, but for the amateur telegrapher an electric-bell
-movement without the bell, or, in other words, a buzzer
-with a knocker on the armature, will answer every purpose.
-(See description of <a href="#Ref002">buzzer</a> on <a href="#Page64">page 64</a>.) It must be properly
-mounted, so that on its back stroke, or rebound, the
-knocker will strike the glass tube and shake the particles of<span class="pagenum" id="Page220">[220]</span>
-metal apart. For this purpose the vibrations of the armature
-should be so regulated as to obtain the greatest possible
-speed, in order that the dots and dashes (or short and
-long periods) will be accurately recorded through the coherer
-and made audible by the sounder or telephone receiver.</p>
-
-<p>Another form of coherer is shown in <a href="#FigIX26">Fig. 26</a>. This is
-made of a small piece of glass tube, two rods that will accurately
-fit in the tube, some nickel filings, two binding-posts,
-and a base-block three inches and a half long. The
-two binding-posts are mounted on the block, and through
-the holes in the body of the posts the rods are slipped.
-They pass into the tube, and the blunt ends press the small
-mass of filings together, as shown in the drawing. By
-means of the binding-posts these coherer-rods may be held
-in place and the proper pressure against the filings adjusted;
-then maintained by the set-screws. The nickel
-filings may be procured by filing the edge of a five-cent
-piece. Obtain a few filings from the edge of a dime and
-add them to the nickel, so that the mixture will be in the
-proportion of one part silver to nine parts nickel. This
-mixture will be found to work better than the iron filings
-alone. The aerial and ground wires are made fast to the
-foot-screws of the binding-posts, and the base on which
-the coherer is mounted may be attached to a table or ledge
-on which the other parts of the receiving and recording
-apparatus are also installed.</p>
-
-<p>Another form of coherer is shown at <a href="#FigIX27">Fig. 27</a>. This is
-constructed in a somewhat similar manner to the one just
-described. A glass tube is provided with two corks having<span class="pagenum" id="Page221">[221]</span>
-holes in them to receive the coherer-rods. Two plugs of
-silver are arranged to accurately fit within the tube, and
-into these the ends of the coherer-rods are screwed or soldered.
-Between these silver plugs, or terminals, the filings
-of nickel and silver are placed, and the rods are pushed together
-and caught in the binding-posts. The aerial and
-ground wires are made fast to the foot-screws of the posts.</p>
-
-<p>For long-distance communication it is necessary to have
-a condenser placed in series with the sparking or sending-out
-apparatus. (See the type of condenser described and
-illustrated in <a href="#Page54">chapter iv.</a>, <a href="#Page72">page 72</a>.)</p>
-
-<p>An astatic galvanometer is also a valuable part of the
-receiving apparatus, and the one described on <a href="#Page111">page 111</a>
-will show clearly the presence of oscillatory currents by
-the rapid and sensitive deflections of the needle.</p>
-
-<p>For local service, where a moderately powerful battery is
-employed, a telegraph-key, such as described on <a href="#Page190">page 190</a>,
-will answer very well, but for high-tension work, where a
-powerful storage-battery or small dynamo is employed, it
-will be necessary to have a non-sparking key, so that the
-direct current will not form an arc between the terminals
-of a key. Most of the keys used for wireless telegraphy have
-high insulated pressure-knobs, or the make and break is
-done in oil, so that the spark or arc cannot jump or be
-formed between the points.</p>
-
-<p>The plan of a simple non-sparking dry switch is shown at
-<a href="#FigIX28">Fig. 28</a>. This is built up on a block three inches wide and
-five inches long. It consists of a bar (A), two spring interrupters
-(B and C), a spring (D), and the binding-posts (E E).
-They are arranged as shown in <a href="#FigIX28">Fig. 28</a>, and a front elevation<span class="pagenum" id="Page222">[222]</span>
-is given in <a href="#FigIX29">Fig. 29</a>. The strip (B) lies flat on the block, and
-is connected with one binding-post by a wire attached under
-one screw-head and run along the under side of the base
-in a groove to the foot of the post. Strip C is of spring-brass,
-and is made fast to the base with screws. This is “dead,” as
-no current passes through it, and its only use is to interrupt.
-The bar (A) is arranged as explained for the line telegraph-key,
-and the remaining binding-post is connected to
-it by a wire run under the base and brought up to one of
-the angle-pieces forming the hinge. A high wood or porcelain
-knob is made fast at the forward end of the bar, so
-that when high-tension current is employed the spark will
-not jump from the bar to the operator’s hand. The complete
-key ready for operation is shown at <a href="#FigIX30">Fig. 30</a>, and to
-make it permanent it should be screwed fast to the table,
-or cabinet, on which the coil and condenser rest. The plan
-of a “wet” key is shown in <a href="#FigIX31">Fig. 31</a>, and the complete key
-in <a href="#FigIX32">Fig. 32</a>.</p>
-
-<p><span class="pagenum" id="Page223">[223]</span></p>
-
-<div class="container m40">
-<a id="FigIX28"></a>
-<a id="FigIX29"></a>
-<a id="FigIX30"></a>
-<a id="FigIX31"></a>
-<a id="FigIX32"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo223.jpg" alt="" />
-</div>
-
-<p class="caption">DRY AND WET NON-SPARKING SWITCHES</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page224">[224]</span></p>
-
-<p>A base of wood three by five inches is made and given
-several coats of shellac. Obtain a small rubber or composition
-pill or salve box, and make it fast to the front end
-of the base with an oval-headed brass screw driven down
-through the centre of the box. A wire leading to one binding-post
-is arranged to come into contact with the screw,
-and the other post is connected by wire to one hinge-plate
-supporting the bar. The long machine screw, or rivet,
-passed down through the knob and into the bar, extends
-down below the bar for half an inch or more, so that when
-the knob is pressed down the end of the screw, or rivet, will
-strike the top of the screw at the bottom of the box without
-the bar coming in contact with the edge of the box.
-When in operation the composition box is filled with olive
-oil or thin machinery oil, so that when contact is made by
-pressing the knob down the circuit will be instantly broken,
-the spring at the rear end of the bar drawing it back to rest.
-The oil prevents any sparks jumping across; and also breaks
-an arc, should one form between the contact-points. With
-the addition of a good storage-battery (the strength of which
-must be governed by the size of the induction-coil and the
-distance the messages are sent) and a dry-cell or two for
-the receiving apparatus, the parts of the wireless apparatus
-are now ready for assembling. Full directions for making
-storage-cells is given in <a href="#Page12">chapter ii.</a>, <a href="#Page21">page 21</a>, and for dry-cells
-in chapter ii., <a href="#Page29">page 29</a>. For short-distance work the
-plan shown in <a href="#FigIX33">Figs. 33</a> and <a href="#FigIX34">34</a> will be found a very satisfactory
-form of apparatus. One of each kind of instrument
-should be at every point where communication is to be
-established.</p>
-
-<p>In the sending apparatus (<a href="#FigIX33">Fig. 33</a>) S C are the storage-cells,
-K the key, and I C the induction-coil. T T are the
-terminals and balls, S G the spark-gap, and P P the posts
-that hold the terminal rods. A W is the aerial wire running
-up from one post, and G W the ground-wire connecting
-the other terminal post with the ground-plates.</p>
-
-<p>In the receiving apparatus (<a href="#FigIX34">Fig. 34</a>) C is the coherer,
-D C the de-coherer, T S the telegraphic sounder, or relay,
-and A G the astatic galvanometer. B is the dry-cell, or
-battery, and D C S the de-coherer switch, so that when
-the apparatus is not in use the dry-cell will not operate the
-buzzer or de-coherer. A W is the aerial wire and G W<span class="pagenum" id="Page225">[225]</span>
-the ground-wire. Two or more storage-cells may be connected
-in series (that is, the negative of one with the positive
-pole of the other) until a sufficiently powerful source
-of current is secured for the transmission of messages.</p>
-
-<div class="container m40" id="FigIX33">
-
-<div class="figcenter nomargin">
-<img src="images/illo225.jpg" alt="Sending apparatus" />
-</div>
-
-</div><!--container-->
-
-<div class="container m40" id="FigIX34">
-
-<div class="figcenter nomargin">
-<img src="images/illo226.jpg" alt="Receiving apparatus" />
-</div>
-
-</div><!--container-->
-
-<p>To operate the apparatus, the circuit is closed with K,
-and the current from S C flows around the primary coil in<span class="pagenum" id="Page226">[226]</span>
-I C and affects the secondary coil, causing the spark to
-leap across the gap (S G). This causes a disturbance through
-the wires A W and G W, and the ether waves are set in
-oscillatory motion from the antennæ on the house-top.
-This affects the antennæ at the receiving-point, and the impression
-is recorded through the coherer (C) on the telegraphic
-sounder or relay (T S), which is operated by the
-current from dry-cell or battery (B), since the oscillations
-have broken the resistance of the filings in the coherer (C).
-The instant that the current passes through the coherer<span class="pagenum" id="Page227">[227]</span>
-and operates T S, the astatic galvanometer indicates the
-presence of current by the deflected needle.</p>
-
-<div class="container m40" id="FigIX35">
-
-<div class="figcenter nomargin">
-<img src="images/illo227.jpg" alt="Sending apparatus" />
-</div>
-
-</div><!--container-->
-
-<p>When the apparatus is in operation D C S is closed, so
-that the current from B operates the coherer (D C). Directly<span class="pagenum" id="Page228">[228]</span>
-communication is broken off, the switch (D C S) should be
-opened; otherwise the buzzer would keep up a continuous
-tapping. For long-distance work a more efficient sending
-apparatus is shown in <a href="#FigIX35">Fig. 35</a>. This is composed of an induction-coil,
-with the terminal rods and brass balls forming
-the spark-gap, an oil key (K), and three or more large
-storage-cells, or a dynamo (if power can be had to run it).
-A condenser is placed in connection with the aerial and
-ground wires, so that added intensity or higher voltage is
-given the spark as it leaps across the gap. In operation
-this apparatus is similar to the one already described.
-Where contact is made with K the primary coil is charged,
-and by induction the current affects the secondary coil, the
-current or high voltage from which is stored in the condenser.
-When a sufficient quantity is accumulated the
-spark leaps across S G and affects wires A W and G W.
-This action is almost instantaneous, and directly the impulse
-sets the ether in motion the same impulse is recorded
-on the distant coherers and sounders.</p>
-
-<p>There are a great many modifications of this apparatus,
-but the principles are practically the same, and while the construction
-of this apparatus is within the ability of the average
-boy, many of the more complicated forms of coherers
-and other parts would be beyond his knowledge and skill.
-Marconi has realized his ambition to send messages across
-the ocean without wires, and is now doing so on a commercial
-basis, and at the rate of twenty-five words a minute.
-It is but the next step to establish communication half-way
-around the world, and finally to girdle the earth.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page229">[229]</span></p>
-
-<h3>Chapter X<br />
-<span class="chaptitle">DYNAMOS AND MOTORS</span></h3>
-
-<p class="chapstart"><span class="largecap">T</span><span class="afterlargecap">o</span>
-adequately treat of dynamos and motors, a good-sized
-book rather than this single chapter would be
-necessary, and only a general survey of the subject is possible.
-Its importance is unquestionable; indeed, the whole
-science of applied electricity dates from the invention of
-the dynamo. Without mechanical production of electricity
-there could be no such thing as electric traction, heat,
-light, power, and electro-metallurgy, since the chemical
-generation of electricity is far too expensive for commercial
-use. Surely it is a part of ordinary education nowadays
-to have a clear and definite idea of the principles of
-electrical science, and in no department of human knowledge
-has there been more constant and rapid advance. It
-is only a truism to assert that the school-boy of to-day
-knows a hundredfold more about electricity and its varied
-phenomena than did the scientists and philosophers of
-old&mdash;Volta and Galvani and Benjamin Franklin. Yet it
-was for these forerunners to open and blaze the way for
-others to follow. A beginning must always be made, and
-the Marconis and Edisons of to-day are glad to acknowledge
-their indebtedness to the experimenters and inventors of
-the past. And now to our subject.</p>
-
-<p><span class="pagenum" id="Page230">[230]</span></p>
-
-<p>All dynamos are constructed on practically the same
-principle&mdash;a field of force rapidly and continuously cutting
-another field of force, and so generating electric current.
-The common practice in all dynamos and motors is to have
-the armature fields revolve within, or cut the forces of the
-main fields of the apparatus. There are many different
-kinds of dynamos generating as many varieties of current&mdash;currents
-with high voltage and low amperage; currents
-with low voltage and high amperage; currents direct for
-lighting, heating, and power; currents alternating, for high-tension
-power or transmission, electro-metallurgy, and other
-uses. It is not the intention in this chapter to review all
-of these forms, nor to explain the complicated and intricate
-systems of winding fields and armatures for special purposes.
-Consequently, only a few of the simpler forms of generators
-and motors will be here described, leaving the more complex
-problems for the consideration of the advanced student.
-For his use a list of practical text-books is appended in a
-foot-note.<a id="FNanchor3"></a><a href="#Footnote3" class="fnanchor">[3]</a></p>
-
-<div class="footnote">
-
-<p><a id="Footnote3"></a><a href="#FNanchor3"><span class="label">[3]</span></a>
-<i>First Principles of Electricity and Magnetism</i>, by C. H. W. Biggs;
-<i>The Dynamo: How Made and Used</i>, by S. R. Bottone; <i>Dynamo Electric
-Machinery</i>, by Professor S. P. Thompson; <i>Practical Dynamo Building for
-Amateurs</i>, by Frederick Walker.</p>
-
-</div><!--footnote-->
-
-<h4>The Uni-direction Dynamo</h4>
-
-<p>The uni-direction current machine is about the simplest
-practicable dynamo that a boy can make. It may be
-operated by hand, or can be run by motive power. The
-field is a permanent magnet similar to a horseshoe magnet.
-This must be made by a blacksmith, but if a large parallel<span class="pagenum" id="Page231">[231]</span>
-magnet can be purchased at a reasonable price so much the
-better, as time and trouble will be saved. This magnet
-should measure ten inches long and four inches and a half
-across, with a clear space seven inches long and one inch
-and three-quarters wide, inside measure. The metal should
-be half an inch thick and one inch and a quarter wide. A
-blacksmith will make and temper this magnet form; then,
-if there is a power-station near at hand where electricity is
-generated for traction or lighting purposes, one of the workmen
-will magnetize it for you at a small cost; or it can be
-wound with several coils of wire, one over the other, and
-a current run through it. When properly magnetized it
-should be powerful enough to raise ten pounds of iron.
-This may be tested by shutting off the current and trying
-its lifting power. If the magnet is too weak to attract the
-weight the current should be turned on and another test
-made a few minutes later.</p>
-
-<p>Before the steel is tempered there should be four holes
-bored in the magnet and countersunk, so that screws may
-be passed through it and into the wooden base below, as
-shown at <a href="#FigX1">Fig. 1</a>. This wooden base is fourteen inches long,
-eight inches wide, and one inch in thickness. It may be
-made of pine, white-wood, birch, or any good dry wood that
-may be at hand. The blocks on which the magnet rests
-are an inch and a quarter square and seven inches long.
-The magnet is mounted directly in the middle of the base,
-an equal distance from both edges and ends, as shown in the
-plan drawing (<a href="#FigX10">Fig. 10</a>). The blocks are attached with glue
-and brass screws driven up from the underside of the base.</p>
-
-<p>From a brass strip three-eighths of an inch wide and<span class="pagenum" id="Page232">[232]</span>
-one-eighth of an inch thick cut a piece six inches long,
-and bore holes at either end through which long, slim, oval-headed
-brass screws may pass. Use brass, copper, or German-silver
-for this bar, and not iron or steel. To the underside,
-and at the middle, solder or screw fast a small block of
-brass, through which a hole is to be bored for the spindle
-or shaft. This finished bar is shown in <a href="#FigX2">Fig. 2</a>. When
-mounted over the magnet and held down with brass screws
-driven into the wood base, its end view will appear as
-shown in <a href="#FigX3">Fig. 3</a>, A being the bar, B B the screws which hold
-it down, D the base into which they are driven, and C C
-the blocks under the magnet (N S). The object of this bar
-is to support one end of the armature shaft. From brass
-one-eighth of an inch thick bend and form two angles, as
-shown at <a href="#FigX4">Fig. 4</a>. Two holes for screws are to be drilled in
-the part that rests on the base, and one hole, for the shaft
-to pass through, is bored near the top of the upright plate.
-The centre of this last hole must be the same height from
-the base as is the hole in the bar (<a href="#FigX2">Fig. 2</a>) when mounted
-over the magnet, as shown at <a href="#FigX3">Fig. 3</a>. The location of these
-plates is shown in the plan (<a href="#FigX10">Fig. 10</a>). There is one plate at
-each end of the base, as indicated at B and B B, the shaft
-passing through the hole in the brass block at the underside
-of the bar (C). These angles are the end-bearings for
-the armature shaft, and should be accurately centred so
-that the armature will be properly centred between the N
-and S bars of the magnet.</p>
-
-<p><span class="pagenum" id="Page233">[233]</span></p>
-
-<div class="container m40">
-<a id="FigX1"></a>
-<a id="FigX2"></a>
-<a id="FigX3"></a>
-<a id="FigX4"></a>
-<a id="FigX5"></a>
-<a id="FigX6"></a>
-<a id="FigX7"></a>
-<a id="FigX8"></a>
-<a id="FigX9"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo233.jpg" alt="" />
-</div>
-
-<p class="caption">DETAILS OF UNI-DIRECTION DYNAMO</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page234">[234]</span></p>
-
-<p>The armature is made from soft, round iron rod one inch
-and a half in diameter and five inches long. A channel is
-cut all around it, lengthwise, five-eighths of an inch wide
-and half an inch deep, as shown in <a href="#FigX5">Fig. 5</a>. This will have
-to be done at a machine-shop in a short bed-planer, since
-it would be a long and tedious job to cut it out with a
-hack-saw. The sharp corners should be rounded off from
-the central lug, so that they will not cut the strands of fine
-wire that are to be wound round it.</p>
-
-<p>Two brass disks, or washers, are to be cut, one inch and
-a half in diameter and from one-eighth to one-quarter of
-an inch thick, for the armature ends. A quarter-inch hole
-is to be made in the centre of each for the shaft to fit in, and
-two smaller holes must be drilled near the edge, and opposite
-each other, so that machine-screws may pass through
-them and into holes bored and threaded in the ends of the
-armature, as shown at <a href="#FigX5">Fig. 5</a>. These ends will appear as
-shown at <a href="#FigX6">Fig. 6</a>, and the middle hole should be threaded so
-as to receive the end of a shaft. When the shaft is screwed
-in tight the end that passes through the brass disk must
-be tapped with a light hammer to rivet the end, and so
-insure that the shaft will not unscrew.</p>
-
-<p>The shafts should be of hard brass or of steel. The one
-at the front should be one inch and a half in length, and
-that at the rear six inches long, measuring from the outer
-face of the brass end to the end of the shaft. From boxwood
-or maple turn a cylinder three-quarters of an inch in
-diameter and an inch long, with a quarter-inch hole through
-it. Over this slip a piece of three-quarter-inch brass or
-copper tubing that fits snugly, and at opposite sides drill
-holes and drive in short screws that will hold the tube fast
-to the hub. They must not be so long as to reach the hole
-through the centre. Place this hub in a vise, and with a<span class="pagenum" id="Page235">[235]</span>
-hack-saw cut the tube across in two opposite places, so
-that you will have the cylinder with two half-circular shells
-or commutators screwed fast to it, as shown at <a href="#FigX7">Fig. 7</a>.
-This hub will fit over the shaft at the front end of the
-armature, and will occupy the position shown at F in
-<a href="#FigX10">Fig. 10</a>.</p>
-
-<p>Cut two small blocks of wood for the brushes and binding-posts,
-and bore a hole through them, so that the foot-screw
-of a binding-post may pass through the block and
-into the post, as shown at <a href="#FigX8">Fig. 8</a>. From thin spring copper
-cut a narrow strip and bend it over the block, catching it at
-the top with a screw and lapping it under the binding-post
-at the outside.</p>
-
-<p>From boxwood or maple have a small wooden pulley
-turned, with a groove in it and a quarter-inch hole through
-the centre. This pulley should be half an inch wide and
-one inch and a half in diameter, as shown at <a href="#FigX9">Fig. 9</a>. This
-is to be attached at the end of the long shaft, where it will
-occupy the position shown at E in <a href="#FigX10">Fig. 10</a>.</p>
-
-<p>All the parts are now ready for assembling except the
-armature, which must be wound. Before laying on the
-turns of wire the channel in the iron must be lined with
-silk, held in place with glue or shellac. A band of silk
-ribbon is given two turns about the centre of the iron, and
-the sides are so completely covered with silk that not a
-single strand of wire will come into direct contact with the
-iron. Great care must be taken, when winding on the
-wire, not to kink, chafe, or part the strands. The channel
-should be filled but not overcrowded, and when full several
-wraps of insulating tape should be made fast about the
-armature to hold the wire firmly in place and prevent it
-from working out at the centre when the armature is driven
-at high speed. The armature, when properly wound and
-wrapped, will appear as shown at A in <a href="#FigX11">Fig. 11</a>, and it is
-then ready to have the ends screwed on. Several sizes of
-wire may be used to wind the armature, according to the
-current desired, but for general use it would be well to use
-No. 30 silk-insulated copper wire.</p>
-
-<p><span class="pagenum" id="Page236">[236]</span></p>
-
-<div class="container m40">
-<a id="FigX10"></a>
-<a id="FigX11"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo236.jpg" alt="" />
-</div>
-
-<p class="caption">PLAN OF THE UNI-DIRECTION DYNAMO</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page237">[237]</span></p>
-
-<p>About four ounces should be enough for this armature,
-and the ends are to be passed through small holes in the
-brass end (B); see <a href="#FigX11">Fig. 11</a>. One end must be soldered to
-one commutator, the other end to the other commutator.
-The end-piece (B) is attached to the iron armature (A) with
-machine-screws; then C is to be made fast in a similar
-manner.</p>
-
-<p>When putting the parts together, it would be well to use
-some shellac on the wooden cylinder and driving-wheel to
-make them hold to the shaft.</p>
-
-<p>By following the plan in <a href="#FigX10">Fig. 10</a>, it will be an easy matter
-to put the parts together; when they are assembled the
-complete machine will appear as shown in the drawing
-(<a href="#FigX12">Fig. 12</a>).</p>
-
-<p>The driving-wheel should be of wood five-eighths of an
-inch thick and six inches in diameter, and held in the frame
-of wood and metal brackets by a bolt. A short handle can
-be arranged with which to turn the wheel, and a small
-leather belt will transmit the power to the small wheel on
-the armature shaft. As the armature is revolved the lines
-of force are cut and the current is carried out through the
-wire attached to the binding-posts on the blocks (G G).</p>
-
-<p><span class="pagenum" id="Page238">[238]</span></p>
-
-<div class="container m40" id="FigX12">
-
-<div class="figcenter nomargin">
-<img src="images/illo238.jpg" alt="Dynamo" />
-</div>
-
-</div><!--container-->
-
-<p>Considerable current may be generated if the armature
-is driven at higher speed than the hand-wheel will cause it
-to revolve. This can be accomplished by running the belt
-over a larger wheel, such as the fly-wheel of a sewing-machine,
-or connecting it to a large pulley on a water-motor.
-The latter may be attached to a faucet in the wash-tub if
-there is pressure enough to do the work.</p>
-
-<p><span class="pagenum" id="Page239">[239]</span></p>
-
-<h4>A Small Dynamo</h4>
-
-<p>All dynamos are constructed on the same general principle
-as that of the uni-direction machine just described;
-but they differ in their windings, the quantities of metal
-electrified, the sizes and lengths of wire wound on both
-armature and field, and in their shape and speeds.</p>
-
-<p>In large dynamos it is impossible to employ steel magnets
-of the required size. In place of them soft iron cores
-are used and magnetized by external electric current; or
-the wiring is done in “series” or “shunt,” so that the fields
-will be self-exciting once the machine has been properly
-started.</p>
-
-<p>The principal difference in dynamos is, perhaps, more
-clearly illustrated by the diagrams shown in <a href="#FigX13">Figs. 13</a>, <a href="#FigX14">14</a>,
-<a href="#FigX15">15</a>, and <a href="#FigX16">16</a>. In <a href="#FigX13">Fig. 13</a> the arrangement of armature and
-field-magnet is the same as in the uni-direction machine,
-the field (F) being of magnetized steel, while the armature
-(A) is of soft iron wound with coils of fine wire, the ends
-of which are brought out at the commutators (C), through
-which the current is carried to the brushes (B and B B). If,
-however, the soft iron cores are used, a separate magnetizing
-electric current must be passed through the coils of wire
-wound about the field-pieces, so that they will become temporary
-magnets&mdash;the same as the cores of an electric bell
-movement, a telegraph-sounder, or the induction-coil core
-when a current is passed through the primary coil. The
-armature (A) is then driven at high speed by power, and
-the current is taken off for use through wires that lead
-from B and B B.</p>
-
-<p><span class="pagenum" id="Page240">[240]</span></p>
-
-<p>In all of these figures the armatures rotate, in the space
-between the large pole-pieces of the field-magnets, in the
-same direction as the hands of a clock move. In these figure
-drawings the field-magnets, commutators, and brushes
-only are shown, the armature being indicated by the circle
-(A).</p>
-
-<p><a href="#FigX13">Figure 13</a> represents a dynamo, the field-magnets of
-which are excited by a separate battery or generator.
-This is known as a “separately excited” machine, and is
-employed for various uses. The brushes (B and B B) are
-connected to the external circuit&mdash;that is, with the motor
-or other apparatus for which current is to be generated.
-The magnetic field in which the armature rotates will be
-constant if the exciting current is constant, like the magnetism
-in the magnet of the uni-direction current machine.</p>
-
-<p>The induced electro-motive force (which depends upon
-the rate at which the lines of force are cut) will be constant
-for the given speed at which the armature rotates. This
-action is the same as that described for the uni-direction
-current machine.</p>
-
-<p><a href="#FigX14">Figure 14</a> is the diagram of a “series”-wound dynamo.
-The field and armature are soft gray iron, and are wound
-in series&mdash;that is, one end of the magnet-winding is made
-fast to the brush B, the other to the brush B B, and the
-apparatus to be operated by the current is let in between
-B B and the magnet, as shown by the indicated electric arc-light
-in the illustration. The field-magnet coils, the armature,
-and the external conductors are in series with each
-other, forming a simple circuit. When the armature is
-driven at high speed the field-magnets become self-exciting,<span class="pagenum" id="Page241">[241]</span>
-with the result that current is generated. Its simple course
-is through B B to commutators on the hub, thence through
-one winding on the iron armature A, to B, through field
-F, and back to B B again, operating in its course any pieces
-of equipment designed for electric impulse, such as motors,
-or lamps, trolley-cars, trains, or electric machinery.</p>
-
-<div class="container">
-<a id="FigX13"></a>
-<a id="FigX14"></a>
-<a id="FigX15"></a>
-<a id="FigX16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo241.jpg" alt="Dynamos" />
-</div>
-
-</div><!--container-->
-
-<p>The third type, shown in <a href="#FigX15">Fig. 15</a>, is known as “shunt”-winding.
-The field-magnet coils and the external resistance
-are in parallel, or shunt with each other, instead of in
-series. The brushes are connected with the external circuit,
-and also with the ends of the field-magnet coils. This
-is clearly shown in the drawing. The ends of the field-coils
-are connected with brushes B and B B, and the external
-circuit wires are connected also with the same brushes,
-and pass down to such an apparatus as a plating bath, in
-which the current runs through the electrode, the electrolyte,
-and the cathode, most of the current generated passing<span class="pagenum" id="Page242">[242]</span>
-through the external circuit. The field-coils are of fine wire,
-and when the armature is rotated there will always be a
-current through the field-magnets, whether the external
-circuit is complete or not. If a break occurs in the external
-circuit, a more powerful current will consequently pass
-through the field-magnets.</p>
-
-<p>In <a href="#FigX16">Fig. 16</a> a “compound”-wound dynamo is shown. It is
-a combination of the series and the shunt machine. The
-field-magnet coils are composed of two sizes of wire. There
-are comparatively four turns of stout wire and many turns
-of fine wire, the ends of both being connected, as shown in
-the drawing. The stout wire leads out to lamps which are
-arranged in series, as shown at the foot of the drawing.
-The current developed by this dynamo is one of “constant
-potential,” and is used almost exclusively for incandescent
-lamps, the “constant” current from the series-wound machine
-being used for arc-lamps, power, and other commercial
-purposes.</p>
-
-<p>It will not be necessary to use the first or last systems, nor
-to experiment with the alternating current, with its phases
-and cycles. All that a boy wants is a good direct-current
-machine that will light lamps, run sewing-machines or motors,
-and furnish the power for long-distance wireless telegraphy
-and other apparatus requiring considerable current.</p>
-
-<p>To begin with, it would be better to make a small dynamo
-and study its principles as you progress; then it will be a
-great deal easier to construct a larger one. It will be necessary
-to have the iron parts made at a blacksmith-shop,
-since the various cutting, threading, and tapping operations
-call for the use of special iron-working tools. Soft iron<span class="pagenum" id="Page243">[243]</span>
-should be used, and if a piece of cast-iron can be procured
-for the lugs or magnet ends it will give better service than
-wrought-iron.</p>
-
-<p>From three-quarter-inch round iron cut two cores, each
-three inches and a half long, and thread them at both ends,
-as shown at B B in <a href="#FigX17">Fig. 17</a>. From band-iron five-eighths
-of an inch thick and one inch and a half wide cut a yoke (A),
-and bore the indicated holes two inches and three-quarters
-apart, centre to centre. These should be threaded so that
-the cores (B B) will screw into them. From a bar of iron
-cut off two blocks one inch and a half by one inch and a
-half by two inches for the lugs. Now, with a hack-saw
-and a half-round file, cut out one side of each lug, as shown
-at C. These lugs are to be bored and threaded at one end,
-so that they can be screwed on the lower ends of the cores
-(C C).</p>
-
-<p>For a larger dynamo the yoke should be made six inches
-long, one inch thick, and two inches and a half wide. The
-cores should be of one-inch iron pipe. These will be hollow,
-as shown at B B in <a href="#FigX18">Fig. 18</a>. For the ends cast-iron blocks
-must be made or cast from a pattern two inches and three-quarters
-square and four inches high, as shown at C. The
-yoke (A) and the lugs (C) are bored and threaded to receive
-the one-inch pipe, and when set up this will constitute an
-iron field-magnet six inches wide, two inches thick, and
-nine inches high. This, if properly wound, should develop
-a quarter of a horse-power.</p>
-
-<p><span class="pagenum" id="Page244">[244]</span></p>
-
-<div class="container m40">
-<a id="FigX17"></a>
-<a id="FigX18"></a>
-<a id="FigX19"></a>
-<a id="FigX20"></a>
-<a id="FigX21"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo244.jpg" alt="Armatures" />
-</div>
-
-</div><!--container-->
-
-<p>The parts shown in <a href="#FigX17">Fig. 17</a>, when screwed together, will
-give you a field-magnet two by one and a half by five and
-three-quarter inches high, and will appear as shown in <a href="#FigX19">Fig.
-19</a>, A being the yoke at the top, B B the cores, C C the
-lugs, and D a strip of brass screwed fast across the back of
-the lugs (C C), and in which a hole is bored to act as a bearing
-for one end of the armature shaft. Between the lugs
-and the strip (D) fibre washers three-eighths of an inch in
-thickness are placed to keep the strip away from the lugs.
-A hole is bored directly through the middle of each lug,
-from front to rear, and it is threaded at each end so that
-a machine-screw will fit in it. The brass strip (D) is five-eighths
-of an inch wide, three-sixteenths of an inch thick,
-and four inches long. Copper or German-silver may be
-used in place of brass, but iron or steel must not be employed,
-since these metals are susceptible to magnetism.<span class="pagenum" id="Page245">[245]</span>
-Two holes should be made in the bottom of each lug, and
-threaded, so that machine-screws may be passed through a
-wooden base and into them in order to hold the dynamo on
-the base.</p>
-
-<p><a href="#FigX20">Figure 20</a> is an end view of the field-magnets showing the
-yoke at A, the core at B, the lug at C, and the bearing and
-binding-strip of yellow metal at D. Two blocks of hard-wood,
-an inch square and one inch and a half long, are cut
-and provided with holes, so that they can be fastened to the
-lugs C C with long, slim machine-screws, as shown at E E
-in <a href="#FigX21">Fig. 21</a>. This is a view looking down on the magnets,
-blocks, and straps. These blocks are to support the brushes
-and terminals, and should be linked across the face with a
-brass strap G, so that the other end of the armature shaft
-may be supported. Care must be taken, when setting straps
-D and G, to have them line. The holes, too, must be centred,
-since the armature must revolve accurately within
-the field-lugs (C C) without touching them, and there is but
-one-sixteenth of an inch space between them.</p>
-
-<p>From hard-wood half an inch in thickness cut a base,
-six by seven inches, and two strips an inch wide and five
-inches long. With glue and screws driven up from the
-underside of the strips fasten them to the base, as shown
-at <a href="#FigX22">Fig. 22</a>. Then make the field-magnets fast to the base
-with long machine-screws, using washers under the heads
-at the underside of the base-board. The mounting should
-then appear as shown in <a href="#FigX28">Fig. 28</a>.</p>
-
-<p><span class="pagenum" id="Page246">[246]</span></p>
-
-<div class="container m40" id="FigX28">
-
-<div class="figcenter nomargin">
-<img src="images/illo246.jpg" alt="" />
-</div>
-
-</div><!--container-->
-
-<p>From steel, half an inch in diameter, cut a shaft five
-inches long. Have it turned down smaller at one end for
-three-eighths of an inch, and at the other end for a distance
-of one inch and a half, as shown at <a href="#FigX23">Fig. 23</a>. This is for the
-armature, and it should fit between D and G in <a href="#FigX21">Fig. 21</a>,
-and should revolve easily in the holes cut to receive it in
-both straps, with not more than one-eighth of an inch
-play forward or backward. The long, projecting end should<span class="pagenum" id="Page247">[247]</span>
-be at the rear, and should extend beyond strip D for three-quarters
-of an inch, so that the driving-pulley can be made
-fast to it.</p>
-
-<p>The armature is made up of segments or laminations of
-soft iron and insulated copper wire. The laminated armature
-works much better than does the solid metal ring or
-lug, and a pattern may be made from a piece of tin from
-which all the sections can be cut. With a compass, strike a
-two-inch circle on a clear piece of tin; then mark it off, as
-shown at <a href="#FigX24">Fig. 24</a>, and cut it out with shears. The hole at
-the centre of the pattern need not be bored, but a small
-pinhole should be made so that a centre-punch can be used
-to indicate the middle of each plate for subsequent perforation.
-Ordinary soft band iron may be employed for
-this purpose, and the sections should not be more than one-sixteenth
-of an inch in thickness.</p>
-
-<p>It will take some time to cut out the required number of
-pieces for this small armature. When they are all ready
-they should be slipped over the shaft, and if they have been
-properly matched and cut, they should appear as a solid
-body, one inch and a half long.</p>
-
-<p>Arrange these laminations on the armature shaft so that
-when the shaft is in position the mass of iron will be within
-the lugs of the field-magnets. The holes through the iron
-plate should be so snug as to call for some driving to put
-them in place. Each disk of iron should be given a coat of
-shellac to insulate it, and between each piece there should
-be a thin cardboard or stout paper separator to keep the
-disks apart. These paper washers should be dipped in hot
-paraffine, or thick shellac may be used to obtain a good<span class="pagenum" id="Page248">[248]</span>
-sticking effect and so solidify the laminations into a compact
-mass. When this operation is completed the armature
-core should appear as shown in <a href="#FigX25">Fig. 25</a>.</p>
-
-<div class="container m40">
-<a id="FigX22"></a>
-<a id="FigX23"></a>
-<a id="FigX24"></a>
-<a id="FigX25"></a>
-<a id="FigX26"></a>
-<a id="FigX27"></a>
-<a id="FigX29"></a>
-<a id="FigX30"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo248.jpg" alt="Armature parts" />
-</div>
-
-</div><!--container-->
-
-<p>From maple, or other hard-wood with a close grain, make
-a cylinder three-quarters of an inch long and one inch in
-diameter to fit the shaft. Over this drive a piece of copper
-or brass tubing, and at four equal distances, near the rear<span class="pagenum" id="Page249">[249]</span>
-or inner edge, make holes and drive small, round-headed
-screws into the wood. Then, with a hack-saw, cut the tube
-into four equal parts between the screws. This is the
-commutator. In order to hold the quarter circular plates
-fast to the cylinder, remove one screw at a time, and place
-thick shellac on the cylinder. Then press the plate firmly
-into place and reset the screw. Repeat this with the other
-three, and the armature will be ready for the winding.</p>
-
-<p>The voltage and amperage of a dynamo is reckoned by
-its windings, the size of wire, the number of turns, and the
-direction. This is a matter of figuring, and need not now
-concern the young electrician, since it is a technical and
-theoretical subject that may be studied later on in more
-advanced text-books.</p>
-
-<p>For this dynamo use No. 22 cotton-insulated copper wire
-for the armature, and No. 16 double cotton-insulated copper
-wire for the field. The armature, when properly wound
-and ready for assembling with the brushes and wiring, will
-appear as shown in <a href="#FigX26">Fig. 26</a>.</p>
-
-<p>A small driving-wheel two inches in diameter and half
-an inch thick must now be turned from brass and provided
-with a V-shaped groove on its face. The hub, at one side,
-is fitted with a set-screw, so that it can be bound tightly on
-the shaft. This pulley is made fast to the shaft at the rear
-of the dynamo, and on the opposite end to where the commutator
-hub is attached.</p>
-
-<p>A diagram of the wiring is shown in <a href="#FigX29">Fig. 29</a>, and in <a href="#FigX30">Fig.
-30</a> the mode of attaching the ends of the coil wires to the
-commutators is indicated. Two complete coils of wire
-must be made about each channel of the armature, as illustrated<span class="pagenum" id="Page250">[250]</span>
-on the drum of <a href="#FigX30">Fig. 30</a>. These are separated by a
-strip of cardboard dipped in paraffine and placed at the
-centre of a channel while the winding is going on. In some
-armatures the coils are laid one over the other; but with
-this construction, and in the case of a short-circuit, a broken
-wire, or a burn-out, it is impossible to reach the under coil
-without removing the good one.</p>
-
-<p>Begin by attaching one end of the fine insulated wire to
-commutator No. 1; then half fill the channel, winding the
-wire about the armature, as indicated in <a href="#FigX30">Fig. 30</a>. When
-the required number of turns has been made, carry the end
-around the screw in commutator No. 2, baring the wire to
-insure perfect contact when caught under the screw-head.
-From No. 2 carry the wire around through the channel at
-right angles to the first one, and after half filling it bring
-the end out to commutator No. 3. Carry the wire in again
-and fill up the other half of the first channel, and bring the
-end out to commutator No. 4. Fill up the remaining half
-of the second channel; then attach the final end to commutator
-No. 1, and the armature winding will be complete
-without having once broken the strand of wire.</p>
-
-<p>To keep the coils of wire in place, and to prevent them
-from flying out, under the centrifugal force of high speed,
-it would be well to bind the middle of the armature with
-wires or adhesive tape.</p>
-
-<p>After driving down the small screws over the leading-in
-and leading-out wires the armature will be ready to
-mount in the bearings. As the blocks that support the
-brushes and binding-posts partly close the opening to
-the cavity at the front, the armature will have to be inserted<span class="pagenum" id="Page251">[251]</span>
-from the back into the strip (G) in <a href="#FigX21">Fig. 21</a>. Then
-the back strip (D) is screwed in place. The armature, when
-properly mounted, should revolve freely and easily within
-the field-lugs without friction, and the lugs must by no
-means touch the armature. From thin spring-copper
-brushes may be cut and mounted on the block under the
-binding-posts, so that one will rest on top of the commutators
-while the other presses up against the underside. The
-wiring is then to be placed on the field-magnets. This is
-carried out as described for the electric magnets on <a href="#Page54">pages
-54-58</a> of chapter iv., each core receiving five or seven layers,
-or as much as it will hold without overlapping the lug or
-yoke. The ends of the wires are connected as shown at
-<a href="#FigX14">Fig. 14</a> or <a href="#FigX15">Fig. 15</a>, the ends being carried down through the
-base and up again in the right location to meet the foot of
-a binding-post. The complete dynamo will appear as
-shown in <a href="#FigX28">Fig. 28</a>.</p>
-
-<p>Before the dynamo is started for the first time it would
-be well to run a strong current through the field coils.
-The residual magnetism retained by the cores and iron parts
-will then be ready for the next impulse when the dynamo
-is started again. Larger dynamos may be made of this
-type. With an armature, the core of which is four inches
-in diameter and six inches long, having eight instead of
-four channels, and placed within a field of proportionate
-size, the dynamo will develop one horse-power.</p>
-
-<h4>A Split-ring Dynamo</h4>
-
-<p>Another type of dynamo is shown in <a href="#FigX31">Fig. 31</a>. This is
-composed of a wrought or cast iron split-ring wound for the<span class="pagenum" id="Page252">[252]</span>
-field, an armature made up of laminations, and the necessary
-brushes, posts, commutators, and wire.</p>
-
-<div class="container m40" id="FigX31">
-
-<div class="figcenter nomargin">
-<img src="images/illo252.jpg" alt="Dynamo" />
-</div>
-
-</div><!--container-->
-
-<p>Have a blacksmith shape an open ring of iron, in the form
-of a C, three-eighths of an inch thick and four inches wide.
-The opening should be three inches wide, as shown in <a href="#FigX32">Fig.
-32</a>. This ring should measure five inches on its outside
-diameter, and the ends are to be bored and threaded to<span class="pagenum" id="Page253">[253]</span>
-receive machine-screws. Two lugs are to be made from
-wrought-iron to fit on these ends. These should be four
-inches long, an inch and a half high, and three-quarters of
-an inch thick at top and bottom. They should be hollowed
-out at the middle, so that an armature two inches in diameter
-will have one-eighth of an inch play all around
-when arranged to revolve within them. Holes are made
-through the lugs to receive machine-screws, which are driven
-into the holes in the ends of the iron (C). Wrought-iron L
-pieces are made one inch and a half high and an inch across
-the bottom, and with machine-screws they are made fast to
-the backs of the lugs to act as feet on which the field-magnet
-may rest, as shown in <a href="#FigX33">Fig. 33</a>. Across the back of the
-lugs, and set away from them by fibre washers, a strap of
-brass is made fast. This measures three-quarters of an
-inch wide and a quarter of an inch thick, and at the middle
-of it a three-eighth-inch hole is bored to receive the rear
-end of the armature shaft. This is shown in <a href="#FigX34">Fig. 34</a>, which
-is a front view of the field, or C, iron, the lugs (L L) and
-feet (F F), the armature bearing (S), and the base (B), of three-quarter-inch
-hard-wood. The field-magnet is bolted to the
-base with lag-screws, so that it will be held securely in place.</p>
-
-<p>The laminations for the armature core are two inches in
-diameter, and are cut from soft iron one-sixteenth of an
-inch thick. They have eight channels, as shown in <a href="#FigX35">Fig. 35</a>,
-and the tubing on the commutator hub is divided into four
-parts so that the terminals from each coil can be brought
-to a commutator, as described for <a href="#FigX30">Fig. 30</a>. In the eight-channel
-armature, however, there is but one coil of wire in
-each channel.</p>
-
-<p><span class="pagenum" id="Page254">[254]</span></p>
-
-<div class="container m40">
-<a id="FigX32"></a>
-<a id="FigX33"></a>
-<a id="FigX34"></a>
-<a id="FigX35"></a>
-<a id="FigX36"></a>
-<a id="FigX37"></a>
-<a id="FigX38"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo254.jpg" alt="" />
-</div>
-
-<p class="caption">DETAILS OF SPLIT-RING DYNAMO</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page255">[255]</span></p>
-
-<p>In <a href="#FigX36">Fig. 36</a> a plan of the armature is shown, S representing
-the shaft, B B the bearings, L the laminations, C the commutators
-and hub, P the driving-pulley, and N N the nuts
-that hold the laminations together and lock them to the
-shaft. The shaft is half an inch in diameter, the laminations
-four inches thick, and the commutator barrel one inch
-in diameter and three-quarters of an inch long. The shaft
-is turned down from the middle to where P and C are attached;
-then at the front end it is made smaller, where it
-passes through the front bearing.</p>
-
-<p>With the detailed description already given for the construction
-of the small dynamo, it should be an easy matter
-to carry out the work on this one, and a quarter horse-power
-generator should be the result. The field-magnet is wound
-with five or seven layers of No. 16 double cotton-insulated
-wire, and the armature with No. 22 silk or cotton-covered
-wire. The connections may be made for either the series
-or the shunt windings shown in <a href="#FigX14">Figs. 14 and 15</a>. Another
-type of field is shown in <a href="#FigX37">Fig. 37</a>, where two plates of iron are
-screwed to one core, and the lugs are, in turn, made fast to
-the inner sides of the plates within which the armature revolves.
-The “Manchester” type is shown in <a href="#FigX38">Fig. 38</a>, where
-two cores, constructed by a top and bottom yoke, are excited
-by the coils, and the lugs are arranged between the
-cores, so that the armature revolves within them.</p>
-
-<h4>A Small Motor</h4>
-
-<p>The shapes, types, powers, and forms of motors are as
-varied and different as those of dynamos, each inventor<span class="pagenum" id="Page256">[256]</span>
-designing a different type and claiming superiority. The
-one common principle, however, is the same&mdash;that of an
-armature revolving within a field, and lines of force cutting
-lines of force. A motor is the reverse of a dynamo. Instead
-of generating current to develop power or light, a
-current must be run through a motor to obtain power.</p>
-
-<p>Motors are divided into two classes: the D C, or direct
-current, and the A C, or alternating current. For the
-amateur the direct-current motor will meet every requirement,
-and since the battery, or dynamo current, that may
-be available to run a motor, is in all probability a direct
-one, it will be necessary to construct a motor that is adapted
-to this source of power and for the present avoid the complications
-of the alternating current both in generation and
-in use.</p>
-
-<p>The direct-current motor is an electrical machine driven
-by direct current, the latter being generated in any desired
-way. This current is forced through the machine by electro-motive
-force, or voltage; the higher the pressure, or voltage,
-the more efficient the machine. Be careful lest too much
-current (amperage) is allowed to flow, for the heat developed
-thereby will burn out the wiring.</p>
-
-<p>Motors are so constructed that when a current is passed
-through the field and armature coils the armature is rotated.
-The speed of the armature is regulated by the
-amount of amperage and voltage that passes through the
-series of magnets, and this rotating power is called the
-torque.</p>
-
-<p>Torque is a twisting or turning force, and when a pulley
-is made fast to the armature shaft, and belted to connect<span class="pagenum" id="Page257">[257]</span>
-with machinery, this torque, or force, is employed for
-work.</p>
-
-<p>The speed of an armature when at full work is usually
-from twelve hundred to two thousand revolutions a minute.
-As few machines are designed to work at that velocity, a
-system of speeding down with back gears, or counter-shafts
-and pulleys, is employed. The motor itself cannot be slowed
-down without losing power. The efficiency of motors is due
-to the centrifugal motion of the mass of iron and wire in the
-armature and the momentum it develops when spurred on
-by the magnetism of the field-magnets acting upon certain
-electrified sections of the armature. The armature of a
-working motor is usually of such high resistance that the
-current employed to run it would heat and burn out the
-wires if the full force of the current was permitted to flow
-through it for any length of time. As the armature rotates
-it has counter electro-motive force impressed upon it. This
-acts like resistance, and reduces the current passing through.
-The higher the speed the less current it takes, so that after
-a motor has attained its highest, or normal speed, it is using
-less than half the current required to start it.</p>
-
-<p>Reduction of current in the armature reduces torque, so
-that the turning force of the armature is reduced as its
-speed of rotation increases. On the other hand, the momentum,
-or “throw,” produces power at high speed, together
-with an actual saving of current. An armature revolving
-at sixteen hundred revolutions, and giving half a
-horse-power on a current of five amperes, is more economical
-than one making three to five hundred revolutions, and
-giving half a horse-power on a current of fifteen to twenty<span class="pagenum" id="Page258">[258]</span>
-amperes. Thus, a slowly turning armature takes more current
-and exerts higher torque than a rapidly rotating one.</p>
-
-<p>To protect the fine wire on the armature from burning,
-in high-voltage machines a starting-box, or rheostat, is employed.
-The motor begins working on a reduced current,
-and as it picks up speed more current is let in, and so on
-until the full force of the current is flowing through the
-motor. It is then turning fast enough to protect itself
-through the counter electro-motive force. This can be
-understood better after some practical experience has been
-had in the construction and running of motors. Of the
-various forms of motors but three will be illustrated and
-described; but the boy with ideas can readily design and
-construct other types as he comes to need them.</p>
-
-<h4>The Flat-bed Motor</h4>
-
-<p>The simplest of all motors is the flat-bed type, illustrated
-in <a href="#FigX39">Fig. 39</a>. This is composed of a magnet on a shaft revolving
-before a fixed magnet attached to the upright board
-of the base. Where space is no object, this motor will
-develop considerable power from a number of dry-cells or
-a storage-battery. Now, in the section relating to dynamos,
-four different systems of wiring were shown. In
-motors of the direct-current type but one system will be
-described&mdash;that of the series-winding, illustrated in <a href="#FigX40">Fig. 40</a>.
-The current, entering at A, passes to the brush (B), thence
-through the commutator (C) and the armature coils. It
-runs on through the brush (B B), the field-coils (F), and out
-at D. This is the same course the current takes in the
-series-wound dynamo illustrated in <a href="#FigX14">Fig. 14</a>, page 241, and
-with such a dynamo current could be generated to run any
-series-wound, direct-current motor.</p>
-
-<p><span class="pagenum" id="Page259">[259]</span></p>
-
-<div class="container m40">
-<a id="FigX39"></a>
-<a id="FigX40"></a>
-<a id="FigX41"></a>
-<a id="FigX42"></a>
-<a id="FigX43"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo259.jpg" alt="" />
-</div>
-
-<p class="caption">A FLAT-BED MOTOR AND PARTS</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page260">[260]</span></p>
-
-<p>From hard-wood half an inch thick cut a base-piece six
-inches and a half long by three inches and a half wide.
-Arrange this base on cross-strips three-quarters of an inch
-wide and half an inch thick, making the union with glue
-and screws driven up from the underside. To one end of
-this base attach an upright or back two inches and three-quarters
-high, and allow the lower edge to extend down to
-the bottom of the cross-strip, as shown at the left of <a href="#FigX39">Fig.
-39</a>. Make this fast to the end of the base and side of the
-cross-strip with glue and screws; then give the wood a
-coat of stain and shellac to properly finish it.</p>
-
-<p>Now have a blacksmith make two <span class="symbol">U</span> pieces of soft iron
-for the field and armature cores, as shown in <a href="#FigX41">Fig. 41</a>. These
-are of quarter-inch iron one inch and a half in width.
-They are one inch and three-quarters across and the same
-in length. One of them should have a half-inch hole bored
-in the end (at the middle), and above and below it smaller
-holes for round-headed screws to pass through. By means
-of these screws the <span class="symbol">U</span> is held to the wooden back. The
-other <span class="symbol">U</span> is to have a three-eighth-inch hole bored in it so
-that it will fit on the armature shaft. Wind the <span class="symbol">U</span> irons
-with six layers of No. 20 cotton-insulated wire, having first
-covered the bare iron with several wraps of paper. Use
-thick shellac freely after each layer is on, so that the turns
-of wire will be well insulated and bound to each other.
-Follow the wiring diagram shown in <a href="#FigX40">Fig. 40</a> when winding
-these cores, and when the field is ready, make it fast to<span class="pagenum" id="Page261">[261]</span>
-the back with three-quarter-inch round-headed brass
-screws.</p>
-
-<p>Directly in the middle of the hole through the field iron
-bore a quarter-inch hole for the armature shaft to pass
-through; then make an <span class="symbol">L</span> piece, of brass, two inches high,
-three-quarters of an inch wide, and with the foot an inch
-long, as shown at <a href="#FigX42">Fig. 42</a>. Two holes are made in the foot
-through which screws will pass into the base, and near the
-top a quarter-inch hole is to be bored, the centre of which
-is to line with that through the back, at the middle of the
-field core. The shaft is made from steel three-eighths of an
-inch in diameter and six inches and a half long. One inch
-from one end the shaft should be turned down to a quarter
-of an inch in diameter, and one inch and a quarter from the
-other end it must be reduced to a similar size. The short
-end mounts in the back and the long one receives the pulley,
-after the latter passes through the <span class="symbol">L</span> bearing. A piece of
-three-eighth-inch brass tubing an inch long is slipped over
-the shaft two inches from the pulley end and secured with
-a flush set-screw. This tubing is then threaded and provided
-with two nuts, one at either end, so that when the
-armature <span class="symbol">U</span> is slipped on the collar the nuts can be tightened
-and made to hold the magnet securely on the shaft. This
-shaft is clearly shown in the sectional drawings <a href="#FigX43">Fig. 43</a>.</p>
-
-<p>At the left side the shaft (S) passes into the wood back
-through the quarter-inch hole. At the outside a brass
-plate with a quarter-inch hole is screwed fast and acts as
-a bearing. The shaft does not touch the field-magnet
-(F M), because the hole is large enough for the quarter-inch
-shaft to clear it. A fibre washer (F W) is placed on the<span class="pagenum" id="Page262">[262]</span>
-shaft before it is slipped through the back. This prevents
-the shaft from playing too much, and deadens any sound of
-“jumping” while rotating.</p>
-
-<p>At the middle the shaft (S) passes through the brass collar
-on which the threads are cut. A M represents the armature
-magnet, and W W the washers and nuts employed to
-bind it in place. At the right, S again represents the shaft,
-B the bearing, C the commutator hub, and P the pulley,
-while R is the small block under the hub to which the
-brushes and binding-posts are attached.</p>
-
-<p>From the descriptions already given of dynamos, and
-with these figure drawings as a guide, it should be an easy
-matter to assemble this motor.</p>
-
-<p>The ends of the field and armature magnets should be
-separated an eighth of an inch. The hub for the commutators
-is three-quarters of an inch long and three-quarters
-of an inch in diameter. The commutators are made as described
-for the uni-direction current machine, care being
-taken to keep the holding screws from touching the shaft.
-A three-quarter-inch cube of wood is mounted on the base,
-under the commutator hub, and to this the brushes and
-binding-posts are made fast, as shown in <a href="#FigX39">Fig. 39</a>. Unless
-the armature happens to be in a certain position this motor
-is not self-starting, but a twist on the pulley, as the current
-is turned on, will give it the necessary start. Its speed will
-then depend on the amount of current forced through the
-coils.</p>
-
-<h4>Another Simple Motor</h4>
-
-<p>Another type of motor is shown in <a href="#FigX44">Fig. 44</a>, where one
-field-winding magnetizes both the core and the lugs. The<span class="pagenum" id="Page263">[263]</span>
-frame of this motor is made up of two plates of soft iron a
-quarter of an inch thick, six inches long, and two inches and
-a half wide. Each plate is bent at one end so as to form
-a foot three-quarters of an inch long, and a half-inch hole is
-drilled one inch and a quarter up from the bottom, at the
-middle of each plate. Through this hole pass the machine-screws
-which hold the iron core in place between the side-plates.
-The core is made of three-quarter-inch round iron
-two inches and three-quarters long, and drilled and threaded
-at each end to receive the binding machine-screws.</p>
-
-<p>Two lugs are cut from iron, and hollowed at one side so
-that an armature two inches in diameter will rotate within
-them when made fast to the side-plates. The lugs are two
-inches and a half long, an inch wide, and two inches and a
-half high.</p>
-
-<p>From iron five-eighths of an inch wide and one-eighth of
-an inch thick make two side-strips with <span class="symbol">L</span> ends. These are
-four inches long, and are provided with two holes so that
-the machine-screws which hold the lugs to the inside plates
-will also hold these strips in place, at the outside, as shown
-in <a href="#FigX45">Fig. 45</a>. At the rear these strips extend half an inch
-beyond the frame. Across the back a brass strip of the
-same size as the iron strips is arranged. It is held at the
-ends by screws, or small bolts, made fast to the <span class="symbol">L</span> ends of
-the side-strips. Directly in the middle of the back-strip a
-hole is made for the armature shaft, and beyond it the pulley
-is keyed or screwed fast to the shaft.</p>
-
-<p>At the front a similar strip is made and attached. This
-latter has a small hole in the middle of it to serve as a bearing
-for the forward end of the shaft. Across the top of the<span class="pagenum" id="Page264">[264]</span>
-motor a brass strip or band is made fast with machine-screws;
-and at the angles formed by the front ends of the side-strips
-and the front cross-strips hard-wood blocks are attached.
-To these the brushes and binding-posts are made fast, so
-that one brush at the top of the left-hand block rests on
-the top of the commutator. The one at the underside of
-the opposite block must rest on the underside of the commutator.</p>
-
-<div class="container m40">
-<a id="FigX44"></a>
-<a id="FigX45"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo264.jpg" alt="Motor" />
-</div>
-
-</div><!--container-->
-
-<p>The armature core is made up of laminations as described
-for the dynamo armatures. In a really efficient motor the
-armature should have eight or more channels.</p>
-
-<p>The other parts of the motor may be assembled and
-wired as described on the preceding pages. The armature
-should be wound with No. 20 or 22 insulated copper wire,<span class="pagenum" id="Page265">[265]</span>
-and the field with No. 16 or 18. For high voltage, however,
-the armature should be wound with finer wire and a rheostat
-used to start it.</p>
-
-<h4>A Third Type of Motor</h4>
-
-<p>The third type is but a duplicate of the series-wound
-dynamo, the general plan of which is shown in <a href="#FigX40">Fig. 40</a>.</p>
-
-<p>This motor can be made any size, but as its dimensions
-are increased the weight of the field-magnets and armature
-must be proportionately enlarged. For an efficient
-and powerful motor, the field should stand ten inches high
-and six inches broad. The iron cores are five inches long
-and one inch and a half in diameter. These should be made
-by a blacksmith and bolted together. The armature is three
-inches in diameter and four inches long, and should develop
-two-thirds of a horse-power when sufficient current is running
-through the coils to drive it at sixteen hundred revolutions.</p>
-
-<p>The wiring is carried out as shown in <a href="#FigX40">Fig. 40</a>, and the
-armature hung and wound as suggested for the dynamo
-shown in <a href="#FigX28">Fig. 28</a>, <a href="#Page246">page 246</a>.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page266">[266]</span></p>
-
-<h3>Chapter XI<br />
-<span class="chaptitle">GALVANISM AND ELECTRO-PLATING</span></h3>
-
-<h4>Simple Electro-plating</h4>
-
-<p class="chapstart"><span class="largecap">T</span><span class="afterlargecap">o</span>
-the average boy experimenter, electro-plating is one
-of the most fascinating of the uses to which electricity
-may be put. In scientific language the process is known as
-electrolysis, and involves the separation of a chemical compound
-into its constituent parts or elements by the action
-of an electric current and the proper apparatus. Electrolysis
-cannot take place, however, unless the liquid in
-the tank, commonly called the electrolyte (no relation to
-electric light), is a conductor.</p>
-
-<p>Water, or water with mixtures of chemicals, such as sulphate
-of copper, sulphate of zinc, chloride of nickel, cyanide
-and nitrate of silver, or uranium and other metallic salts,
-are good conductors. Oil is a non-conductor, and a current
-will not pass through it, no matter what the pressure may
-be. The simplest electro-plating outfit, and the one that
-a boy should start with, is the sulphate of copper bath,
-such as is commonly employed by makers of electrotypes,
-and which is in extensive use by refiners of copper for
-high-grade electrical use.</p>
-
-<p>More than half of the total output of copper in the world<span class="pagenum" id="Page267">[267]</span>
-is used for electrical work&mdash;conductors, switches, and all
-sorts of parts&mdash;and since any impurity in the copper interferes
-with its conducting powers, it is most important that
-it should be free from any traces of carbon or arsenic. The
-electrolytic refining of copper is now a very important
-process in connection with electric work, and about half a
-million tons of copper are treated annually to free it from
-all impurities. Moreover, the gold, silver, and other valuable
-metals which may be found in copper-ore are thus
-recovered.</p>
-
-<p>The electro-plating, electrotyping, and refining operations
-are one and the same thing; but in the first instance the
-object to be plated is left in the solution only a short time
-or until a blush of copper has been applied. In the second
-process the wax mold is left in long enough for a thin
-shell of copper to be deposited; and in the third, the
-kathodes are immersed until they are heavily coated with
-copper. To carry on any of these operations it will be
-necessary to have a small tank or glass jar to hold the
-plating-bath or electrolyte. Preferably it should be of a
-square or oblong shape. But a serviceable tank may be
-constructed from white-wood, pine, or cypress, if proper
-care is taken in making and water-proofing (<a href="#FigXI1">Fig. 1</a>). For
-experimental purposes a tank eighteen inches long, ten inches
-wide, and twelve inches deep will be quite large enough to
-use as a copper bath. For silver, nickel, or gold, smaller
-tanks should be employed, as they contain less liquid, or
-electrolyte, which in the more valuable metals is expensive.</p>
-
-<p>Obtain a clear plank twelve inches wide, well seasoned,
-and free from knots or sappy places. Cut two sides twenty<span class="pagenum" id="Page268">[268]</span>
-inches long and two ends eight inches long. With chisel,
-saw, and plane shape the ends of the side planks as shown
-at <a href="#FigXI2">Fig. 2</a>; or if there is a mill at hand it would be well to
-have the ends cut with a buzz-saw, thus insuring that they
-will be accurate and fit snugly. Screw-holes are bored
-with a gimlet-bit, and countersunk, so that screws will pass
-freely through them and take hold in the edges of the
-boards. Screws and plenty of white-lead, or asphaltum
-varnish, should be used on these points to make them
-water-tight; then the lower edge of the frame is prepared
-for the bottom board. Turn the tank bottom up, and,
-with a fat steel-wire nail and a hammer, dent a groove at
-the middle of the edge of the planks all around, as shown
-in <a href="#FigXI3">Fig. 3</a>. It will not do to cut this out with a gouge-chisel,
-because it is intended that the wood should swell
-out again if necessary. The object of driving the wood
-down is to form a valley into which a line of cotton string-wicking,
-soaked in asphaltum varnish or imbedded in
-white-lead, may be laid. This should be done (as shown
-in <a href="#FigXI4">Fig. 4</a>) before the bottom is screwed on, so that afterwards
-(in the event of the joint leaking) the wood will
-swell and force the wicking out, and thus properly close
-the fissure.</p>
-
-<p>The bottom board should be provided with holes all
-around the edge, not more than two inches apart, through
-which screws can be driven into the lower edge of the
-tank. Treat the wood, both in and outside, to several
-successive coats of asphaltum varnish, and as a result you
-will have a tank resembling <a href="#FigXI1">Fig. 1</a>.</p>
-
-<p>Two shallow grooves are to be cut in the top of each<span class="pagenum" id="Page269">[269]</span>
-end board of the tank, for the cross-bars to fit in immovably.
-These bars should be about three inches apart; and
-the ones holding the anodes, or flat copper plates, should
-be close to one side, leaving plenty of room for objects of
-various sizes to be properly immersed.</p>
-
-<p>Another manner in which the bottom of the tank can
-be attached is shown in <a href="#FigXI5">Fig. 5</a>, which is a view of the tank
-sides turned bottom up. A rabbet is cut from the lower
-edges of the sides and ends, before they are screwed together,
-and a bottom is fashioned of such shape as to
-accurately fit in the lap formed by the rabbet. This rabbet
-and the outer edge of the bottom plank should be well
-smeared with white-lead, and all put together at the same
-time, driving the screws into the edge of the bottom plank,
-through the lower edges of the sides and bottom, and also
-through the bottom board into the lower edges of the sides
-and ends (<a href="#FigXI6">Fig. 6</a>).</p>
-
-<p>Still another and stronger way in which to make a tank
-for a large bath is to cut the planks as shown at <a href="#FigXI7">Fig. 7</a>.
-The sides are then bolted together, locking the ends and
-bottom, so that they cannot warp or get away. The bolts
-are of three-eighth-inch round iron-rod, threaded at both
-ends and provided with nuts. Large washers are placed
-against the wood and under the nuts, so that when the
-nuts are screwed on tightly they will not tear the wood,
-but will bear on the washers. The points are all to be
-well smeared with white-lead or acid-proof cement (see
-Formulæ) before the parts are put together and bolted, so
-as to avoid any possibility of leakage. (<a href="#FigXI8">Fig. 8</a> shows the
-completed tank.)</p>
-
-<p><span class="pagenum" id="Page270">[270]</span></p>
-
-<div class="container m40">
-<a id="FigXI1"></a>
-<a id="FigXI2"></a>
-<a id="FigXI3"></a>
-<a id="FigXI4"></a>
-<a id="FigXI5"></a>
-<a id="FigXI6"></a>
-<a id="FigXI7"></a>
-<a id="FigXI8"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo270.jpg" alt="" />
-</div>
-
-<p class="caption">TANK FOR ELECTRO-PLATING</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page271">[271]</span></p>
-
-<p>Now obtain two copper rods long enough to span the tank,
-with an inch or two projecting beyond the tank at either
-side. At one end of these attach binding-posts, to which the
-wires from a battery can be connected, leaving the opposite
-ends free, as shown at <a href="#FigXI9">Fig. 9</a> (see <a href="#Page275">page 275</a>). Anodes, or
-pure soft copper plates, are hung on the positive rod, while
-on the negative one the objects to be plated, or kathodes,
-are suspended on fine copper wires just heavy enough to
-properly conduct the current. The positive wire leads
-from the carbon, or copper pole, of the battery, while the
-negative one is connected with the zinc. The anodes are
-plates of soft sheet or cast copper, and should be as nearly
-pure as possible for electrolytic work; but if they are to be
-re-deposited, to free them from impurities, they may be in
-thin ingot form, just as the copper comes from the mines.</p>
-
-<p>The general principle of electro-refining of copper is very
-simple. A cast plate of the crude copper is hung from the
-positive pole in a bath of sulphate of copper, made by dissolving
-all the sulphate of copper, or bluestone, that the
-water will take up. Drop a few lumps on the bottom of
-the tank to supply any deficiency, then add an ounce of
-sulphuric acid to each gallon of liquid, to make it more
-active and a better conductor.</p>
-
-<p>The crude copper plate is to be the leading-in pole for
-the current, while a thin sheet of pure copper, no thicker
-than tissue-paper, is suspended from the opposite rod for
-the leading-out pole; or in place of the thin sheet, some
-copper wires may be suspended from the rod. The electrodes&mdash;that
-is, the copper plate and the thin sheet or
-wires&mdash;are placed close together, so that the current may<span class="pagenum" id="Page272">[272]</span>
-pass freely and not cause internal resistance in the battery.
-The electric current, in its passage from the crude copper
-plate to the pure copper sheet or wires, decomposes the
-sulphate of copper solution and causes it to deposit its
-metallic copper on the sheet or wires; and at the same time
-it takes from the crude copper a like portion of metallic
-copper and converts it into chemical copper. The electric
-current really takes the copper from the solution and adds
-it to the pure copper sheet, while the remaining constituents
-of the decomposed solution help themselves to some copper
-from the crude plate. In this way the crude copper diminishes
-and the pure copper sheet increases in size, the
-impurities as well as the salts of other metals being precipitated
-to the bottom of the tank, or mingled with the
-solution, which must be purified or replaced from time to
-time by fresh solution. This is the process of copper-plating,
-and any metal object may be properly cleansed
-and coated with copper by suspending it in the bath and
-running the current through it.</p>
-
-<p>When the refining process is employed, any metal will
-answer as a depository for the copper, but as the intention
-is to produce a pure copper plate which can be melted and
-cast into ingots, it is of course necessary to have the original
-kathode of the same metal; otherwise an impure mixture
-will be the result. If, for example, a piece of cast-iron be
-used upon which to deposit the copper, then the iron will
-be enclosed in a deposit of pure copper; in other words, the
-result will be a heavily copper-plated piece of iron, and the
-smelting process will bring about a fusion of the two metals.
-It is not necessary to have absolutely pure copper for the<span class="pagenum" id="Page273">[273]</span>
-anodes when copper-plating or electrotyping; but the
-purer the copper the less the solution is fouled, and it will
-not require replenishing so often.</p>
-
-<p>An object intended to receive a plating of copper need
-not be of metal at all; it may be of any material, so long as
-it possesses a conducting surface. A mold or a cast made
-of any plastic material, such as wax or cement, may have
-its surface made conductive by the application of graphite,
-finely pulverized carbon, or metal dusts held on by some
-medium not soluble in water. The wax molds, or impressions
-of type and cuts, are dusted with plumbago, and
-then suspended in the copper solution. A wire from the
-negative pole is connected so as to come in contact with
-the plumbago, and the copper deposit immediately begins
-to form on the face of the wax. When the film of copper
-has become heavy enough, the mold is drawn out of the
-solution, and the thin shell of metal removed from the wax
-and cut apart, so that each shell is separated from its
-neighbor and freed from marginal scraps. Flowers, leaves,
-laces, and various other objects can be given a coat of
-copper by thus preparing their surfaces, and some most
-beautiful effects may be secured by copper-coating roses;
-then placing them for a short time in a gold bath, and
-afterwards chemically treating the surface plating so as
-to imitate Roman, Tuscan, or ormolu gold, in bright or
-antique finish. Coins, medallions, bas-reliefs, medals, and
-various other things are reproduced by the electro-plating
-process, and their surfaces finished in gold, silver, bronze,
-or other effects. Years ago this was not possible, because
-the old method was to make a fac-simile cast in metal of<span class="pagenum" id="Page274">[274]</span>
-the object desired, and then chase or refinish the surface.
-This was a costly and tedious task. When Brugnalelli, an
-Italian electrician, electro-gilded two silver coins in 1805,
-he laid the foundation for the modern process, but it did
-not come into general use until about 1839, when electro-plating
-and the electro-depositing of metals was begun on
-a practical scale. Before the invention of the dynamos
-for generating current, batteries had to be employed, and
-this made the process somewhat more expensive than the
-present method. Our boy amateurs, however, will have to
-be content with the battery system, since they are not supposed
-to have access to direct-current power, such as is
-used for arc or street lighting.</p>
-
-<p>Various forms of batteries may be used for this work,
-and they will be described in detail. For the copper-plating
-bath it will be necessary to have the anodes of soft,
-cast, or sheet, copper sufficiently heavy so as not to waste
-away too quickly. These should be of the proper size to
-fit within the bath, and either one large one or several
-small ones may be employed. Stout copper bands should
-be riveted to the top of the plates, by means of which they
-may be hung on the bar and so suspended in the solution
-(<a href="#FigXI10">Fig. 10</a>). The contact-points should be kept clean and
-bright, so that the current will not meet with any resistance
-in passing from the rod to the plates.</p>
-
-<p>In <a href="#FigXI9">Fig. 9</a> a complete outfit is shown for any plating process,
-the difference being only in the solution and anodes.
-For silver-plating a silver solution and silver anodes are
-required, while for gold the gold solution and gold anodes
-will be necessary. In this illustration, A represents the<span class="pagenum" id="Page275">[275]</span>
-tank, B the battery, C C the anodes, D D D the kathodes, or
-articles to be plated, E the positive rod, F the negative,
-and G, H the leading-in and leading-out wires.</p>
-
-<p>There is often a doubt in a boy’s mind as to how the
-battery is to be connected up to the bath and the articles
-suspended in it. But there will be no difficulty about it
-once that the principle of the process is thoroughly understood.</p>
-
-<div class="container m40" id="FigXI9">
-
-<div class="figcenter nomargin">
-<img src="images/illo275.jpg" alt="Electro-plating" />
-</div>
-
-</div><!--container-->
-
-<p>It is well to remember that the electro-plating bath is
-just the reverse of a battery in its action. The process
-carried on in a battery is the generation of electricity by
-the action of the acid on the positive metal, accompanied
-by the formation of a salt on one of the elements; while in
-the plating-bath the current from an external source (the
-battery or dynamo) breaks up the salts in solution and
-deposits the metal on one of the elements (the kathode).</p>
-
-<p>The remaining element in the solution attacks the salts,
-in chemical lumps or granular form, and dissolves them to
-take the place of the exhausted salts; or it attacks the<span class="pagenum" id="Page276">[276]</span>
-metal anode from which these salts were originally made,
-and eats off the portion necessary to replace the loss caused
-by the action of the current in depositing the fruits of this
-robbery in metallic form upon the article to be plated (the
-kathode). There should be no confusion in the matter of
-properly connecting the poles if one remembers that the
-current is flowing through the battery as well as through
-the wires and the solution in the tank.</p>
-
-<p>Get clearly in your mind that the current originates in
-the battery of zinc and carbon or zinc and copper. The
-zinc is electro-positive to carbon or copper, and at a higher
-electric level the current flows from the zinc plate inside
-the cell to the carbon or copper; therefore, the zinc is the
-positive pole. Now the current, having flowed through the
-battery from zinc to carbon, or the negative plate, is bound
-to flow out of the battery from the carbon through the
-apparatus and back again to the zinc in the battery. Therefore,
-the wire (G) attached to the carbon of the battery
-leads a positive or + current, although the carbon is
-negative; in the battery, and the wire (H) leading out is
-negative, or -, although it returns the current to the
-positive pole of the battery.</p>
-
-<p>This is the simple explanation of the circulation of current;
-but to cut it down still more, always remember to
-attach the wire from the anode rod to the carbon, or copper,
-of the battery, and the kathode rod to the zinc of the
-battery.</p>
-
-<p>In copper-plating this is easy to determine without any
-regard to wires, because if the wires are misconnected there
-will be no deposit, and the kathode will turn a dark color.<span class="pagenum" id="Page277">[277]</span>
-If everything is all right a slight rose-colored blush of
-copper will appear at once on the kathode. Too little
-current will make the process a long and tedious one, while
-too much current will deposit a brown mud on the kathode,
-which will have to be washed off or removed and the article
-thoroughly cleansed before a new action is allowed to take
-place.</p>
-
-<p>With a series of cells it is an easy matter to properly govern
-the current by cutting out some of the cells or by using
-resistance-coils (see <a href="#Page125">chapter vii.</a> on Electrical Resistance).</p>
-
-<p>Cells and batteries for electro-plating may be made or
-purchased, and primary batteries should be used. The use
-of the secondary or storage-battery is not necessary for
-plating purposes, since no great volume of current is needed,
-and it can be generated in a battery of cells while the work
-is going on.</p>
-
-<p>One of the best primary batteries is the Benson cell,
-shown in connection with the <a href="#FigXI9">plating-bath</a>, and also in <a href="#FigXI11">Fig.
-11</a>. It consists of an outer glass jar (G J), which contains
-a cylinder of amalgamated zinc (Z +, or positive) covered
-with diluted sulphuric acid&mdash;one part acid to three parts
-water. An inner porous cup (P C) contains concentrated
-nitric acid, into which the carbon (C -, or negative) is
-plunged. The liquid in the inner cup and glass cell should
-be at the same level.</p>
-
-<p><span class="pagenum" id="Page278">[278]</span></p>
-
-<div class="container m40">
-<a id="FigXI10"></a>
-<a id="FigXI11"></a>
-<a id="FigXI12"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo278.jpg" alt="" />
-</div>
-
-<p class="caption">THE BENSON CELL PRIMARY BATTERY</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page279">[279]</span></p>
-
-<p>There is no polarizing in this cell, for the hydrogen
-liberated at the zinc plate, in passing through the nitric
-acid on its way to the carbon-pole, decomposes the nitric
-acid and is itself oxidized. A cell with a glass jar six inches
-in diameter and eight inches high will develop about two
-volts of electro-motive force; and as its internal resistance
-is very low it will furnish a steady current for several hours.
-Any number of these cells may be made and connected in
-series; but when not in use it would be well to remove and
-wash the zincs. Any bichromate battery will answer very
-well for plating, the Grenet being an especially good one.
-A well-amalgamated zinc plate forms one pole, and a pair
-of carbon plates, one on each side of the zinc and joined at
-the top, make up the other pole. When not in use the
-entire plunge part should be removed from the bichromate
-solution, rinsed off in water, and laid across the top of the
-jar, ready for its next employment. The zinc and carbons
-must be joined together so that they are well insulated, and
-with no chance of the zinc coming into contact with the
-carbons. This may be done with four pieces of hard-wood
-soaked in hot paraffine and then locked together with
-stove-bolts and nuts, as shown at <a href="#FigXI12">Fig. 12</a>. Holes must be
-made in the top corners of the carbons and zinc, and with
-small bolts and nuts the connecting wires can be made
-fast.</p>
-
-<p>To charge this battery, add five fluid ounces of sulphuric
-acid to three pints of cold water, pouring the acid slowly
-into the water and stirring it at the same time with a glass
-or carbon rod. When this becomes cold, after standing a
-few hours, add six ounces of finely pulverized bichromate
-of potash. Mix this thoroughly, and pour some of the
-solution into the glass cell until it is three-fourths full;
-then it will be ready to receive the carbons and zinc. When
-arranging the wood-clamps on the carbon and zinc plates
-it would be well to make two of the clamps longer than the<span class="pagenum" id="Page280">[280]</span>
-others so that they will extend out far enough to rest on
-the top edge of the jar. To keep them in position at the
-middle of the jar, notches should be cut at the underside
-of these clamps, so that they will fit down over the edge of
-the jar. Any number of these cells may be connected together
-to obtain the desired amount of current, or electro-motive
-force.</p>
-
-<p>Other batteries suitable for electro-plating are the Edison
-primary, Taylor, Fuller, Daniell, gravity, Groves, and
-Merdingers. All of these may be purchased at large electrical
-equipment or supply houses.</p>
-
-<h4>The Cleansing Process</h4>
-
-<p>One of the most important operations of the plating
-process is to properly cleanse the articles to be plated
-before they are placed in the bath. When once cleaned
-the surfaces of these objects must not be touched with the
-fingers, or any dusty or greasy object; otherwise the electro-deposited
-metal will not hold on the surface, but will peel
-off, in time, or blister. A very small trace of foreign
-matter is sufficient to prevent the deposit from adhering
-to the surface to be plated; therefore, great care must be
-taken to eliminate all trace of anything that would interfere
-with the perfect transmission of metallic molecules to
-the prepared surfaces. Acids are chiefly employed to remove
-foreign matter from new metallic surfaces; and for
-copper, brass, iron, zinc, gold, and silver a table is given on
-<a href="#Page281">page 281</a> which will show the right proportion of acids to
-water in order to cleanse the various metals. In the following<span class="pagenum" id="Page281">[281]</span>
-scale the numerals stand for parts. For example: the
-first one means 100 parts water, 50 parts nitric acid, 100
-parts sulphuric acid, and 2 parts hydrochloric acid&mdash;making
-in all 252 parts. These can be measured in a glass graduate.</p>
-
-<table class="dontwrap fsize80" summary="Proportions">
-
-<tr class="bt bb">
-<th class="br">&nbsp;</th>
-<th class="w6m br">Water</th>
-<th class="w6m br">Nitric<br />Acid</th>
-<th class="w6m br">Sulphuric<br />Acid</th>
-<th class="w6m">Hydrochloric<br />Acid</th>
-</tr>
-
-<tr>
-<td class="left padr4 br">Copper and brass</td>
-<td class="center br">100</td>
-<td class="center br">&#8199;50</td>
-<td class="center br">100</td>
-<td class="center">&#8199;&#8199;2</td>
-</tr>
-
-<tr>
-<td class="left padr4 br">Gold</td>
-<td class="center br">100</td>
-<td class="center br">...</td>
-<td class="center br">...</td>
-<td class="center">&#8199;15</td>
-</tr>
-
-<tr>
-<td class="left padr4 br">Silver</td>
-<td class="center br">100</td>
-<td class="center br">&#8199;10</td>
-<td class="center br">...</td>
-<td class="center">...</td>
-</tr>
-
-<tr>
-<td class="left padr4 br">Wrought-iron</td>
-<td class="center br">100</td>
-<td class="center br">&#8199;&#8199;2</td>
-<td class="center br">&#8199;&#8199;8</td>
-<td class="center">&#8199;&#8199;2</td>
-</tr>
-
-<tr>
-<td class="left padr4 br">Cast-iron</td>
-<td class="center br">100</td>
-<td class="center br">&#8199;&#8199;3</td>
-<td class="center br">&#8199;12</td>
-<td class="center">&#8199;&#8199;3</td>
-</tr>
-
-<tr class="bb">
-<td class="left padr4 br">Zinc</td>
-<td class="center br">100</td>
-<td class="center br">...</td>
-<td class="center br">&#8199;10</td>
-<td class="center">...</td>
-</tr>
-
-</table>
-
-<p>Twist a piece of fine copper wire about part of the object
-to be cleaned and plated; then dip it in the acid and rinse
-off in clean warm or hot water, and rub the surface briskly
-with a brush dipped in the liquid. Dip it again several
-times, and rinse in the same manner; then, when it is bright
-and clean, place it in the bath, twist the loose end of the
-wire around the negative rod, and start the current flowing,
-taking care that the object is thoroughly immersed.</p>
-
-<p>Tarnished gold or silver articles may be cleaned by immersing
-them in a hot solution of cyanide of potassium;
-or a strong warm solution of carbonate of ammonia will
-loosen the tarnish on silver, so that it can be brushed off.
-Corroded brass, copper, German-silver, and bronze should
-be cleansed in a solution composed of sulphuric acid, three
-ounces; nitric acid, one and three-quarters ounces; and
-water, four ounces. This soon loosens and dissolves the
-corrosion; then the article should be brushed off, dipped in
-hot water, and rinsed. Then replace it in the solution for<span class="pagenum" id="Page282">[282]</span>
-a minute or two and rinse again, when it will be ready for
-the plating-bath.</p>
-
-<p>Corroded zinc should be immersed in a solution of sulphuric
-acid, one ounce; hydrochloric acid, two ounces; and
-distilled or rain water, one gallon. It should be well brushed
-after the acid has bitten off the corrosion.</p>
-
-<p>Rusty iron or steel should be pickled in a solution of
-sulphuric acid, six ounces, hydrochloric acid, one ounce,
-and water, one gallon. When the rust has been removed,
-immerse the object in a solution composed of sulphuric acid,
-one pint, and distilled water, one gallon. Before the acid
-is added to the water dissolve one-quarter-pound of sulphate
-of zinc in the water; then add the acid, pouring it
-slowly and stirring the water.</p>
-
-<p>Lead, tin, pewter, and their compounds may be cleansed
-by immersing them in a hot solution of caustic soda or
-potash, then rinsing in hot water. Take great care if
-caustic is used, as it will burn the skin and tissues of
-the body. Do not let the fingers come into contact with
-any cleansed article, because the oily secretions of the body
-will stick to the metal and cause the coat of deposited metal
-to strip off or present a spotted appearance.</p>
-
-<h4>The Plating-bath</h4>
-
-<p>The object to be plated should not touch the bottom or
-sides of the plating-vat, and it should be far enough away
-from the anodes to avoid any possibility of coming into
-contact with them. It will not do to place the anode and
-kathode too close together, as the plate will be deposited<span class="pagenum" id="Page283">[283]</span>
-unevenly; the thicker coating will appear on the parts
-closest to the anode. Neither should they be separated too
-far, as the resistance of the cell is thereby increased, and of
-course this means a waste of energy. The knowledge of how
-to arrange the anode and kathode is a matter to be learned
-by experience, but by carefully watching the deposit it will
-not be a difficult matter to determine the proper positions.</p>
-
-<p>For many reasons the glass tank is preferable for amateur
-electro-plating work, since the objects may be watched
-without disturbing their electric connections and without
-removing them from the liquid. A very good plan for the
-copper bath, when spherical, cylindrical, or hollow objects
-are to be plated, is to line the inside of the tank with strips
-or a sheet of copper, hung on hooks that will catch on the
-sides; then connect the positive wire directly to these strips.
-With this arrangement but one rod, the negative, is in use,
-and the objects to be plated are suspended from it. It
-follows that the objects will take up the copper deposit
-from all sides, and a more evenly distributed coating will
-be the result.</p>
-
-<p>It is better to start up the current gradually, rather than
-to put on at the beginning a large amount of electro-motive
-force. By watching the character of the deposit you can
-soon tell if you have the proper strength of current. If
-everything is working properly the copper deposit will have
-a beautiful flesh tint; but if the current is too strong it
-takes on a dark-red tone and resembles the surface of a
-brick. This is not right, and the object must be removed
-and washed off, the current reduced, and the object replaced
-in the bath.</p>
-
-<p><span class="pagenum" id="Page284">[284]</span></p>
-
-<p>When a sufficiently heavy coating of the copper has been
-applied, remove the object and wash thoroughly in running
-or warm water to free it from any remaining copper fluid.
-If this is not done the surface, in drying, will turn a dull
-brown, and will have to be bitten off with the acid solution
-for cleansing copper.</p>
-
-<p>The finer the copper deposit the better and smoother it
-will be; the grain will be smaller, and it will not present a
-rough surface, which is always difficult to plate over with
-silver or gold, unless a frosted effect is desired. Non-conducting
-objects are usually plated with copper first, and
-then replated with the metal desired for the final finish.</p>
-
-<p>To make the surface conductive, finely powdered black-lead,
-or plumbago of the best kind, or finely pulverized
-gas-carbon is brushed over the surface. This must be thoroughly
-done; and if the deposit is slow about appearing at
-any spot it may be hastened by touching it with the end of
-an insulated wire attached to the main conductor. This,
-of course, will only answer for objects strong enough to
-stand the brushing treatment; it will not do for flowers,
-insects, and other delicate things, that are to be silver or
-gold plated. These should be given a film of silver by soaking
-in a solution of alcohol and nitrate of silver, made by
-shaking two parts of the chemical into one hundred parts
-of grain-alcohol, with the aid of heat and in a well-corked
-bottle. When dry, the object should be subjected to a
-bath of sulphuretted hydrogen gas under a hood. The
-sulphuretted hydrogen is made by bringing a bar of wrought-iron
-to a white-heat in the kitchen range or furnace fire, and
-touching it with a stick of sulphur. The iron will melt and<span class="pagenum" id="Page285">[285]</span>
-drop like wax. These drops should be collected in a bottle.
-Now pour over them diluted sulphuric acid, one part acid to
-three parts water, and the gas will at once rise. It will be
-quickly recognized by its odor, which is similar to that of
-over-ripe eggs. It can be led off through a tube to the
-place where you wish to use it, and when through, the
-operation of gas-generation may be stopped by pouring off
-the liquid.</p>
-
-<p>All objects prepared in this way should be given a preliminary
-coating of thin copper before they are plated with
-any other metal.</p>
-
-<h4>Silver-plating</h4>
-
-<p>Plating in silver is done in practically the same way as
-described for the coppering process. Thin strips or sheets
-of pure silver are used for the anodes, and the electrolyte
-is composed of nitrate of silver, cyanide of potassium, and
-water.</p>
-
-<p>Dissolve three and one-half ounces of nitrate of silver in
-one gallon of water; or if more water is needed to fill the
-tank, add it in the proportion of three and one-half ounces
-of the nitrate to each gallon of water. Dissolve two ounces
-of cyanide of potassium in a quart of water, and slowly add
-this to the nitrate solution. A precipitate of cyanide of
-silver will be formed. Keep adding and stirring until no
-more precipitate is formed, but be careful not to get an
-excess of the cyanide in the solution.</p>
-
-<p>Gather this precipitate, and wash it on filtering-paper by
-pouring water over it. The filter-paper should be rolled in
-a funnel shape thus permitting the water to run away<span class="pagenum" id="Page286">[286]</span>
-and leaving the precipitate in the paper. This precipitate
-is to be dissolved in more cyanide solution, and added to
-the quantity in the tank. There should be about two
-ounces of the potassium cyanide per gallon over and above
-what was originally put in.</p>
-
-<p>The silver anodes show the condition of the fluid. If
-the solution is in good order they will have a clear, creamy
-appearance, but will tarnish or turn pink if there is not
-sufficient free cyanide in the solution.</p>
-
-<p>The proper strength of current is indicated by the appearance
-of the plated objects. A clear white surface
-shows that everything is all right, the solution in proper
-working order, and the proper current to do the work.
-Too much current will make the color of the kathodes
-yellow or gray, while too little current will act slowly and
-require a long time to deposit the silver.</p>
-
-<p>The adhesion of silver-plate is rendered more perfect by
-amalgamating the objects in a solution of nitrate of mercury,
-one ounce to one gallon of water. After the objects have
-been properly cleansed they are immersed in this solution
-for a minute, then placed in the silver-bath and connected
-with the negative-rod, so that the electro-depositing action
-begins at once.</p>
-
-<h4>Gold-plating</h4>
-
-<p>The gold-bath is made in the same manner as the silver
-one just described, with the exception that chloride of gold
-is used in place of the nitrate of silver in the first solution.
-This solution must be heated to 150° Fahrenheit when the
-process is going on; or a cold bath may be made of water,<span class="pagenum" id="Page287">[287]</span>
-5000 parts; potassium cyanide, one hundred parts; and pure
-gold, fifty parts. The gold must be dissolved in hydrochloric
-acid, and added to the water and potassium.</p>
-
-<p>Very pretty effects may be obtained in gold-plating by
-changing the tones from yellow to a greenish hue by the
-addition of a little cyanide of silver to the solution, or by
-the use of a silver anode. A reddish tinge may be had
-by adding a small portion of sulphate of copper to the
-solution, or hanging a small copper anode beside the gold
-one. In the hot gold-bath the articles should be kept in
-motion, or the solution stirred about them with a glass
-rod.</p>
-
-<p>When the solution is perfectly balanced and working
-right the anodes should be a clear dead yellow, and the
-articles in process of plating should be of the same hue.</p>
-
-<p>A gold-plating outfit is shown in <a href="#FigXI13">Fig. 13</a>, and consists of
-the tank and bath, a cell, and a resistance-coil (R), through
-which the strength of the current is regulated.</p>
-
-<p>The current, passing out of the cell from the carbon (C),
-is regulated through the resistance-coils (R) by the switch
-(S). From thence it passes to the rod from which the
-anode (A) is suspended, across the electrolyte (E) to the
-kathode (K), on which the metal is deposited, and then
-returns through the negative wire to the zinc (Z) in the
-cell. If the hot bath is used the gold solution may be contained
-in a glazed earthen jar or a porcelain-lined metal
-jar or kettle. But if the latter is used care must be taken
-to see that none of the enamel is chipped, or a short-circuit
-will be established between the rods. This jar or kettle
-may then be placed on a gas-stove, and a thermometer<span class="pagenum" id="Page288">[288]</span>
-should be suspended so that the mercury bulb is half an
-inch below the surface of the liquid, as shown at T in <a href="#FigXI13">Fig.
-13</a>. As the liquid simmers or evaporates away a little
-water should be added from time to time to keep the bulk
-of the liquid up to its normal or original quantity.</p>
-
-<div class="container m30" id="FigXI13">
-
-<div class="figcenter nomargin">
-<img src="images/illo288.jpg" alt="Gold plating" />
-</div>
-
-</div><!--container-->
-
-<h4>Nickel-plating</h4>
-
-<p>The nickel-plating process is similar, in a general way,
-to the others; it is carried on in a cold bath&mdash;that is, at the
-normal temperature, without being heated or chilled artificially.</p>
-
-<p><span class="pagenum" id="Page289">[289]</span></p>
-
-<p>There are a great many formulæ for the nickel as well
-as for the other baths, but the generally accepted one is
-composed of double nickel ammonium-sulphate, three parts;
-ammonium carbonate, three parts; and water, one hundred
-parts. Another good one is composed of nickel sulphate,
-nitrate, or chloride, one part; sodium bisulphate, one part;
-and water, twenty parts.</p>
-
-<p>Nickel anodes are used in bath to maintain the strength,
-and great care must be taken to have the bath perfectly
-balanced&mdash;that is, not too acid nor too alkaline.</p>
-
-<p>To test this, have some blue-and-red litmus paper. If
-the blue paper is dipped in an acid solution, it will turn red;
-and back to blue again if placed in an alkaline solution.
-If the nickel solution is too strong with alkali, a trifle more
-of the nickel salts must be added, so that both the red-and-blue
-litmus paper, when dipped in the liquid, will not
-change color. If the bath is too alkaline, it will give a disagreeable
-yellowish color to the deposit of metal on the
-kathode; and if too acid, the metal will not adhere properly
-to the kathode, and will strip, peel, or blister off.</p>
-
-<h4>Finishing</h4>
-
-<p>When the articles have been plated they will have a
-somewhat different appearance to what may have been
-expected. For instance, copper-plated articles will have a
-bright fleshy-pink hue; silver, an opaque creamy-white;
-gold, a dead lemon-yellow color, and nickel much the appearance
-of the silver, but slightly bluer in its tone. Articles
-removed from the bath should be shaken over the bath so<span class="pagenum" id="Page290">[290]</span>
-as to remove the solution; then they should be immediately
-plunged into hot water, rinsed thoroughly, and allowed to
-dry slowly.</p>
-
-<p>When a silvered or gilded object is perfectly dry it should
-be rubbed rapidly with a brush and some fine silver-polishing
-powder until the opaque white or yellow gives place to
-a silver or gold lustre. It will then be ready for burnishing
-with a steel burnisher, or the article may be left with a
-frosted silver or gold surface. Steel burnishers can be had
-at any tool-supply house, and when used they should be
-frequently dipped in castile soapy water to lubricate them.
-They will then glide smoothly over the surface of the deposited
-metal, driving the grain down and making it bright at the
-same time. If the soapy water were not used the action of
-the hard burnisher over the plate would have a tendency
-to tear away the film of deposited metal. The burnisher
-must always be clean and bright, otherwise it would scratch
-the plated articles; and, when not in use, keep the bright
-polishing surfaces wrapped in a piece of oiled flannel.</p>
-
-<p>Small articles, such as sleeve-buttons, rings, studs, and
-other things not larger than a twenty-five-cent piece, may
-be polished by being tumbled in a sawdust bag. A cotton
-bag is made, three feet long and six inches in diameter,
-closed at one end and half-filled with fine sawdust. The
-articles are then put in the bag and the end closed. Grasp
-the ends of the bag with both hands, as if to jump rope with
-it; then swing it to and fro, until the articles have had a
-good tumbling. Look at them to see if they are bright
-enough; if not, keep up the tumbling.</p>
-
-<p>When old work is to be re-plated, or gone over, it will be<span class="pagenum" id="Page291">[291]</span>
-necessary to remove all of the old plate before a really good
-job can be done. In some cases it may be removed with a
-scratch-brush or pumice-stone; but, as a rule, it can be
-removed much quicker and more satisfactorily with acids.</p>
-
-<p>Silver may be removed from copper, brass, or German-silver
-with a solution of sulphuric acid, with one ounce of
-nitrate of potash to each two quarts of acid. Stir the
-potash into the acid, then immerse the article. If the
-action becomes weak before the silver is all off, then heat
-the solution and add more of the potash (saltpetre). Gold
-may be removed from silver by heating the article to a
-cherry-red, and dropping it into diluted sulphuric acid&mdash;one
-part acid to two parts water. This will cause the gold
-to peel and fall off easily.</p>
-
-<h4>Electrotyping</h4>
-
-<p>The term electrotyping is interpreted in several ways,
-but, in general, it means the process of electro-plating an
-article, or mold, with a metal coating, generally copper, of
-sufficient thickness, so that when it is removed, or separated
-from its original, it forms an independent object
-which, to all appearances, will be a fac-simile of the original.</p>
-
-<p>To obtain a positive copy a cast has to be taken from a
-negative or reverse. This negative is called the mold or
-matrix, and can be of plaster, glue, wax, or other compositions.
-There are a number of processes in use, but the
-Adams process (no relation to the author) will give a boy a
-clear idea of this electro-chemical and mechanical art.
-This process was patented in 1870, and is said to give a<span class="pagenum" id="Page292">[292]</span>
-perfect conduction to wax and other molds, with greater
-certainty and rapidity than any other, and will accomplish
-in a few minutes that which plumbago (black-lead) alone
-would require from two to four hours to effect.</p>
-
-<p>As applied to the electrotyping of type, and cuts for
-illustration, the warm wax impression is taken by pressing
-the chase or form of type into a bed of wax by power or
-hydraulic pressure. Then remove it, and while the wax is
-still warm, powdered tin, bronze, or white bronze powder
-is freely dusted all over it with a soft hair-brush, until the
-surface presents a bright, metallic appearance. The superfluous
-powder is then dusted off, and the mold is immersed
-in alcohol, and afterwards washed in water to remove the
-air from the surface. It is then placed in the copper bath
-and the connection made from the negative pole to the face
-of the mold, so that the current will flow over its entire
-surface. A deposit of copper will quickly appear, and become
-heavier as the mold is left in longer.</p>
-
-<p>When a mold has received the required deposit it should
-be taken from the bath and the copper film removed from
-it. This is done by placing the mold in an inclined position
-and passing a stream of hot water over the back of the
-copper film. This softens the wax and enables one to strip
-the film off, taking care at the same time not to crack or
-bend the thin copper positive.</p>
-
-<p>The thin coating of wax, which adheres to the face of the
-copper, can be removed by placing it, face up, on a wire
-rack and pouring a solution of caustic potash over it, which,
-in draining through, will fall into a vessel or tank beneath
-the rack.</p>
-
-<p><span class="pagenum" id="Page293">[293]</span></p>
-
-<p>The potash dissolves the wax in a short time, and the
-electro-deposited shell may then be rinsed in several changes
-of cold water, or held under the faucet until thoroughly
-freed from the caustic.</p>
-
-<p>As many, if not all, of the chemicals used in the various
-plating processes, and also the cleaning fluids, are highly
-poisonous, great care should be taken when handling them.
-Do not let the fingers or hands come in contact with
-caustic solutions or cyanide baths.</p>
-
-<p>Never use any of these solutions if you have recently cut
-your fingers or hands, and do not allow the cyanides or
-caustics to get under the finger-nails. Never add any acid
-to liquids containing cyanide or ferro-cyanide while in a
-closed room. This should always be done in the open air,
-where the fumes can pass away, for the gases which rise
-from these admixtures are poisonous when inhaled.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page294">[294]</span></p>
-
-<h3>Chapter XII<br />
-<span class="chaptitle">MISCELLANEOUS APPARATUS</span></h3>
-
-<p class="chapstart"><span class="largecap">T</span><span class="afterlargecap">he</span>
-field of applied electricity is such a wide one as
-to preclude any exhaustive handling of the subject in
-a book of this size. The aim has been to acquaint the
-young student with the basic principles of the science, and
-it is his part to develop these principles along the lines indicated
-in the preceding pages. But there are some practical
-applications that may be properly grouped under the
-heading of this chapter. They may serve as a stimulus to
-the inventive faculties of the youthful experimenter, and
-since the pieces of apparatus now to be described are useful
-in themselves, the time spent in their construction will
-not be wasted.</p>
-
-<h4>A Rotary Glass-cutter</h4>
-
-<p>When making a circle of glass it is generally best to let
-a glazier cut the disk, otherwise many panes are likely to
-get broken before the young workman succeeds in getting
-out a perfect one. But with a rotary glass-cutter the task
-is a comparatively simple one, and the tool is really an
-indispensable piece of apparatus in every electrician’s kit.
-(See <a href="#FigXII1">Figs. 1</a> and <a href="#FigXII2">2</a>.)</p>
-
-<p><span class="pagenum" id="Page295">[295]</span></p>
-
-<p>The wooden form is turned from pine or white-wood, and
-is three inches in diameter at the large end, or bottom, one
-inch in diameter at the top, and two inches high. It is
-covered with felt held on with glue. Directly in the middle
-of the top a small hole is bored one-eighth of an inch
-in diameter, and in this aperture an awl or marker is placed,
-handle up, as shown in <a href="#FigXII2">Fig. 2</a>. Notice that the awl is not
-made fast to the form, but is removable at pleasure. A
-hard brass strip twelve inches long, five-eighths of an inch
-wide, and one-eighth of an inch thick is cut at the end to
-receive a steel-wheel glass-cutter, as shown at the foot of
-<a href="#FigXII1">Fig. 1</a>.</p>
-
-<p>A number of one-eighth-inch holes are bored along the
-strip, and half an inch apart, measuring from centre to
-centre. To cut a disk of glass the form is placed at the
-centre of the pane, the latter being imposed on a smooth
-table-top over a piece of cloth. The strip, or arm, is laid
-on the form, and over a small washer, so that one of the
-holes lines with that in the form. The awl is passed down
-through the strip and into the block, and the cutter is arranged
-in the slot at the end of the arm. Press down lightly
-on the handle of the awl, to keep the form from slipping;
-then the cutter is drawn around the glass, describing the
-circle, and cutting the surface of the glass, as shown by the
-solid line in <a href="#FigXII4">Fig. 4</a>. The disk must not be removed from
-the pane until the margin is broken away. With a straight-edge
-and a cutter score the glass across the corners, as indicated
-by the dotted lines in <a href="#FigXII4">Fig. 4</a>; then tap the glass at
-the underside along the line and break off the corners.
-After the corners have been removed tap the glass again,
-following the line of the circle; then break away the remaining
-fragments and smooth the edge.</p>
-
-<p><span class="pagenum" id="Page296">[296]</span></p>
-
-<div class="container m40">
-<a id="FigXII1"></a>
-<a id="FigXII2"></a>
-<a id="FigXII3"></a>
-<a id="FigXII4"></a>
-<a id="FigXII5"></a>
-<a id="FigXII6"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo296.jpg" alt="" />
-</div>
-
-<p class="caption">GLASS-CUTTING APPLIANCES</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page297">[297]</span></p>
-
-<h4>To Smooth Glass Edges</h4>
-
-<p>To smooth the rough edge of glass there are several
-methods. The simplest way is to hold the disk or straight-edge
-against a fine grindstone and use plenty of water.
-The glass must be held edgewise, as shown in <a href="#FigXII5">Fig. 5</a>, and
-<i>not</i> flatwise, as shown in <a href="#FigXII6">Fig. 6</a>. To properly grind a disk
-two workmen are necessary, one to turn the stone, and
-the other to hold the disk by spreading the hands and
-grasping it at the middle on both sides (see <a href="#FigXII5">Fig. 5</a>). In
-this manner the glass may be held securely, and slowly
-turned, so that an even surface will be ground. When the
-flat edge is smoothed, tilt the glass first to one side and
-then the other, and grind off the sharp edges.</p>
-
-<p>Another method is to lay the glass on a table, upon a
-piece of felt or cloth, and allow the edge to project over
-the table for two or three inches. Hold the glass down
-with one hand to prevent its slipping; then, with a piece
-of corundum, or a rough whetstone and glycerine, work
-down the edge until it is smooth, turning the glass continually
-so that the edge you are working on hangs over
-the table. This process of grinding is somewhat tedious,
-but perseverance and patience will win out.</p>
-
-<h4>To Cut Holes in Glass</h4>
-
-<p>Holes may be cut in glass in several ways by an expert,
-but the boy who is a novice in this line should stick to<span class="pagenum" id="Page298">[298]</span>
-slow and sure methods and take no chances. Fortunately,
-glass is little used in voltaic electricity, but it is indispensable
-in the construction of the frictional machines, Leyden-jars,
-and condensers, where glass is used as the dielectric,
-also for the covering-plates to instruments.</p>
-
-<p>The simplest method is that of rotating a copper tube
-forward and backward over the glass, using fine emery
-dust for the cutting medium and oil of turpentine as a
-lubricant. The copper tube must be held in a rack, so
-that its location will not shift during the rotating or cutting
-motion. The rack in which the tube is held may be
-of any size, but to take a disk or square of glass, twenty
-inches across, the frame should be twenty-two inches long,
-ten inches wide, and twelve inches high, as shown in <a href="#FigXII3">Fig. 3</a>.</p>
-
-<p>The side-plates are eleven inches high and ten inches
-wide, the top is twenty-two inches long and ten inches
-wide, while the under ledge is twenty and a quarter inches
-long by ten inches wide. This frame is put together with
-glue and screws. Across the back, from the corners down
-to the middle of the under ledge, battens or braces are
-made fast to prevent the frame from racking. A hole is
-made through the middle of the top and under ledge for
-the copper tube to pass through. If different-sized tubes
-are to be used, blocks to fit the top and under board are
-to be cut and bored, so that they may be held in place
-with screws when in use. To cut a hole in glass, place the
-disk or pane on a felt or cloth-covered table, and over it
-arrange the frame, so that the tube will rest on the spot to
-be drilled. Drop the copper tube down through the hole,
-having first spread the bottom of the tube slightly, so that<span class="pagenum" id="Page299">[299]</span>
-it will not split the glass. Now put some emery inside the
-tube so that it will fall on the glass; then place a wooden
-plug in the top of the tube and arrange an awl, or hand-plate,
-so that the tube may be pressed down. Take one
-turn about the tube with a linen line, or gut-thong, and
-make the ends fast to a bow, so that it will draw the string
-taut but not too tight. Lubricate the foot of the tube
-with oil of turpentine, and draw the bow back and forth.
-At first the motion will cause the copper to scratch the
-glass, and then cut it, until finally a perfectly drilled hole is
-formed. During the operation both glass and frame must
-be held securely, and the bow drawn evenly and without
-any jerking motion. Holes of different sizes may be cut
-with tubes of various diameters. Small holes may be cut
-with a highly tempered steel-drill and glycerine, the drill
-being held in a hand-drilling tool or in a brace.</p>
-
-<h4>Anti-hum Device for Metallic Lines</h4>
-
-<p>In overhead wires, where galvanized or hard copper wire
-is used, the hum due to the tension of the wires, and the
-wind blowing through them, causes a musical vibration
-which becomes most annoying at times. This can be overcome
-by a simple device known as an “anti-hum.” It consists
-of a knob made of wood or rubber, through which a
-hole is bored, and around which a groove is cut. One end
-of the wire is passed through the hole and a loop formed,
-the loose end being wrapped about the incoming wire.
-The other end of the line is passed around the knob in the
-groove, and the end twisted about the line-wire. The knob<span class="pagenum" id="Page300">[300]</span>
-is then an insulator and a sound-deadener at the same time.
-To complete the metallic circuit a loop of wire is passed
-under the knob, the ends of which are made fast to the
-line-wires, as shown at <a href="#FigXII7">Fig. 7</a>.</p>
-
-<div class="container m40">
-<a id="FigXII7"></a>
-<a id="FigXII8"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo300.jpg" alt="Anti-hum" />
-</div>
-
-</div><!--container-->
-
-<h4>A Reel-car for Wire</h4>
-
-<p>It is not always convenient nor possible to carry about
-a heavy roll of wire when hanging a line, especially if it is
-No. 12 galvanized wire, of which there are from fifty to a
-hundred pounds in one roll. Wire should be unwound as
-it is paid out, and not slipped off from the coil, since it is
-liable to kink; therefore, some portable means of transporting
-it should be provided. Line-wires over long distances
-are paid out from a reel-truck drawn by horses. For the<span class="pagenum" id="Page301">[301]</span>
-use of the amateur electrician the reel-car shown in <a href="#FigXII8">Fig. 8</a>
-should meet all requirements.</p>
-
-<p>The reel is made from two six-inch boards, a barrel-head
-or a round platform of boards, four trunk-rollers, and
-a bolt. From a six-inch board cut two pieces five feet
-long. Eighteen inches from either end cut one edge away
-so as to form handles, as shown at C C C C in <a href="#FigXII8">Fig. 8</a>, rounding
-the upper and under edges to take off the sharp corners.
-Cut four cross-pieces sixteen inches long; and from
-two-by-four-inch spruce joist cut four legs twelve inches
-long, and plane the four sides.</p>
-
-<p>Nail two of the cross-pieces to the legs; then nail on the
-side-boards and so form the frame of the reel. Bore a half-inch
-hole through a piece of joist; then nail it between the
-remaining two cross-boards, taking care to get it in the
-centre, as shown at A. Arrange these pieces at the middle
-of the frame, making them fast with nails driven through
-the side-boards and into the ends of these cross-pieces.
-Drive some pieces of matched boards together, and with
-a string, a nail, and a pencil describe a circle twenty inches
-in diameter. With a compass-saw cut the boards on the
-line, and join them with four battens made fast at the underside
-with nails. Do not make the battens so that they will
-extend out to the edge of the circle, but keep them in an
-inch or two, so that the under edge of the turn-table will
-rest on four trunk-rollers screwed fast to the top edges of
-the side-boards and end cross-pieces, as shown at B. A
-half-inch bolt is passed down through a hole made at the
-middle of the table, and through the block. Between the
-block and the underside of the table several large iron<span class="pagenum" id="Page302">[302]</span>
-washers should be placed on the bolt, so that they will keep
-the table slightly above the rollers, the main weight of the
-table and its load of wire being held by the middle cross-brace.
-The object of the trunk-rollers is to relieve the
-side strain on the bolt, and also to prevent friction between
-the edge of the table and the frame, in case the tension on
-the wire pulls it to one side. Bore six holes in the table,
-on a circle of twelve inches, and drive hard-wood pegs in
-them, as shown in <a href="#FigXII8">Fig. 8</a>. When a roll of wire is lying on
-the table two boys can easily lift and carry the car, and as
-they do so the wire will pay out. Give all the wood-work
-a coat of dark-green paint, and oil the trunk-rollers and
-the wood where the bolt passes through. A pair of nuts
-should be placed on the lower end of the bolt and a washer
-under its head. These lock-nuts must be screwed on with
-two monkey-wrenches, forced in opposite directions, so that
-one nut will be driven tightly against the other. This is to
-prevent the turning of the table from unscrewing the nuts.</p>
-
-<h4>Insulators</h4>
-
-<p>For telegraph and telephone lines, where pole, tree, or
-building attachments are necessary, insulators must be used
-to carry the wires without loss of current. The regular
-glass, porcelain, or hard rubber insulators, made for pole
-and bracket use, are of course the best. They can be purchased
-at any supply-house for a few cents each, but there
-are other devices which will answer equally well and which
-will cost little or nothing.</p>
-
-<p>Obtain some bottles of stout glass, the green or dark<span class="pagenum" id="Page303">[303]</span>
-glass being the toughest; then carefully break the bottle
-part away. In doing this hold the bottle by the neck,
-with a piece of old cloth wrapped about it, to prevent the
-glass chips from flying. Save all of the neck and part of
-the shoulder, as shown in <a href="#FigXII9">Fig. 9</a>, so that the wire and its
-anchoring loop will not slip off and fall down on the peg
-or cross-tree.</p>
-
-<p>Hard-wood pegs cut from sticks one inch and a half
-square should be whittled down so that they will fit in the
-neck and come up to the top. The pegs should be long
-enough at the bottom to permit of their being fastened to
-the supporting poles, trees, or building. In <a href="#FigXII10">Fig. 10</a> three
-ways of attaching insulators are shown. At A the peg is
-nailed to the top of a pole, or a hole is bored in the pole
-and the peg driven down in it. At B two sticks with peg
-ends are nailed to a pole in the form of a <span class="symbol">V</span>, and across
-the sticks a cross-brace is made fast to prevent the sticks
-from spreading or dropping down. This cross-brace is
-made fast to both the sticks and the pole so as to form
-a rigid triangle. At C the usual form of cross-tree, or <span class="symbol">T</span>
-brace, is shown. The pegs may be nailed to the face of the
-cross-plate, or holes may be bored in the top and the pegs
-driven down into them. If the cross-piece is more than
-two feet long, bracket-iron should be screwed fast to the
-pole and brace at both sides, as shown at C. Where a cross-plate
-is made fast to a pole, a lap should be cut out so that
-the plate can lie against a flat surface rather than on a
-round one (see D in <a href="#FigXII10">Fig. 10</a>).</p>
-
-<p>The shoulder of the bottle-necks must not rest on a cross-piece,
-or touch anything that would lead to the ground or<span class="pagenum" id="Page304">[304]</span>
-to other wires. The shoulder acts as a collar, and so sheds
-water that in wet weather the current cannot be grounded
-through the rain. The underside of the collar should always
-be dry, and also that part of the peg protected by the
-collar, thereby insuring against the loss of current. The
-relative position of insulator and peg is shown at <a href="#FigXII9">Fig. 9</a>,
-and if the pegs are cut carefully the bottle-necks should
-fit them accurately.</p>
-
-<h4>Joints and Splices</h4>
-
-<p>It is essential in electrical work to have joints, splices,
-unions, and contacts made perfectly tight, so that the current
-will flow through them uninterruptedly. A poor contact
-or weak joint may throw a whole system out of order.
-For this reason all joints should be soldered wherever practicable.
-In line work, however, this is impossible, except
-where trolley-wires are joined, and these are brazed in the
-open air by an apparatus especially designed for the purpose.
-In telegraph and telephone lines perfect contact is
-absolutely necessary, and where attachments are made to
-insulators the main-line should never be turned around
-the insulator. The wire is brought up against the insulator,
-and with a <span class="symbol">U</span> wire the main-line is tightly bound to
-it, as shown at <a href="#FigXII11">Fig. 11</a>. If it is necessary to bind the main-line
-more securely to the insulator, one or two turns may
-be taken around the insulator with the <span class="symbol">U</span> or anchoring wire;
-then with a pair of plyers a tight wrap is made.</p>
-
-<p>When joining two ends of wire together, never make
-loops as shown in <a href="#FigXII12">Fig. 12</a> A. This construction gives poor<span class="pagenum" id="Page305">[305]</span>
-contact, for the wire loops will wear and finally break
-apart. Moreover, the rust that forms between the loops
-will often cause an open circuit and one difficult to locate.
-Care must be taken to make all splices secure and with perfect
-contact of wires, and the only manner in which this can
-be done is to pass the ends of wires together for three or
-four inches, as shown in <a href="#FigXII12">Fig. 12</a> B.</p>
-
-<div class="container m40">
-<a id="FigXII9"></a>
-<a id="FigXII10"></a>
-<a id="FigXII11"></a>
-<a id="FigXII12"></a>
-<a id="FigXII13"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo305.jpg" alt="Insulators and connections" />
-</div>
-
-</div><!--container-->
-
-<p>Grasp one wire with a pair of plyers, and with the fingers
-start the coil or twist, then with another pair of plyers
-finish the wrapping evenly and snugly. Treat the other
-end in a similar manner, and as a result you will have the
-splice pictured in <a href="#FigXII12">Fig. 12</a> B, the many wraps insuring perfect
-contact. This same method is to be employed for inside
-wires, and after the wrap is made heat the joint and<span class="pagenum" id="Page306">[306]</span>
-touch it with soldering solution. The solder will run in
-between the coils and permanently unite the joint. The
-bare wires should then be covered with adhesive tape.</p>
-
-<p>Avoid sharp turns and angles in lines, and where it is not
-possible to arrange them otherwise it would be well to put
-in a curved loop, as shown at <a href="#FigXII13">Fig. 13</a>. A represents a pole,
-B B the line, and C the quarter-circular loop let in to avoid
-the sharp turn about the insulator. The current will pass
-around the angle as well as through the loop, but a galvanometer
-test would show that the greater current passed
-through the loop and avoided the sharp turn.</p>
-
-<h4>“Grounds”</h4>
-
-<div class="container m40">
-<a id="FigXII14"></a>
-<a id="FigXII15"></a>
-<a id="FigXII16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo306.jpg" alt="Grounds" />
-</div>
-
-</div><!--container-->
-
-<p>In the <a href="#Page190">chapter</a> on wireless telegraphy several good
-“grounds” were described, any one of which would be admirably
-adapted to telegraph or telephone circuits. In
-<a href="#FigXII14">Figs. 14</a>, <a href="#FigXII15">15</a>, and <a href="#FigXII16">16</a> are illustrated three other “grounds”
-that can easily be made from inexpensive material. The<span class="pagenum" id="Page307">[307]</span>
-first one, <a href="#FigXII14">Fig. 14</a>, is an ordinary tin pan with the wire
-soldered to the middle of the bottom. The wire must be
-soldered to be of use, as the pan would soon rust around a
-simple hole and make the “ground” a high-resistance one.
-If the pan is buried deep enough in the earth, and bottom
-up, it will last for several years, or so long as the air does
-not get at it to induce corrosion.</p>
-
-<p>The star-shaped “ground” is cut from a piece of sheet
-zinc, copper, or brass, and is about twelve inches in diameter.
-The wire is soldered to the middle of it, and it is
-buried four feet deep, lying flat at the bottom of the hole.</p>
-
-<p>In <a href="#FigXII16">Fig. 16</a> a pail or large tin can is shown with the wire
-passing down through the interior and finally reaching the
-bottom, where it is soldered fast. The can is filled with
-small chunks of carbon, or charcoal, and some holes are
-punched around the outer edge and bottom to let the water
-out. The can is then buried three or four feet in the
-ground. Use nothing but copper wire for “grounds,” and
-it should be heavy&mdash;nothing smaller than No. 14. The
-wire should be well insulated down to and below the surface
-for a foot or two, so that perfect action will take place
-and a complete “ground” secured.</p>
-
-<h4>The Edison Roach-killer</h4>
-
-<p>When Edison was a boy he invented the first electrocution
-apparatus on record. At a certain station on the
-Grand Trunk Railroad, where Edison was employed as a
-telegraph operator, the roaches were so thick that at night
-they would crawl up the partition between the windows<span class="pagenum" id="Page308">[308]</span>
-and reach the ceiling, where they would go to sleep. During
-the day they were apt to become dizzy, lose their footing,
-and drop down on the heads of the operators. This did not
-suit young Edison, so he devised a scheme for their destruction.
-While watching a piece of telegraph apparatus
-one day, he saw a roach try to step from a bar charged
-with positive electricity to one through which a negative
-current flowed. The insect’s feet were moist and so made
-a connection between the two bars. As a consequence a
-short-circuit of high tension passed through its body and it
-dropped dead. This put an idea into Edison’s head, and
-the electrocution apparatus was soon in working order.
-The “killer” was the most simple device one could imagine,
-and was composed of two long, narrow strips of heavy tin-foil
-pasted side by side on a smooth board, with a space of
-one-eighth of an inch between them, as shown at <a href="#FigXII17">Fig. 17</a>.
-To one strip a positive wire was connected, while to the
-other a negative or ground was made fast. High-tension
-current, or that from an induction-coil, was connected with
-the wires, and the resulting voltage was strong enough to
-give one a severe shock if the fingers of one hand were placed
-on one plate and those of the other hand on the other plate.</p>
-
-<p>This device was arranged across the window-casing in
-the path the roaches were accustomed to travel on their
-nightly trips up the side wall. It was not long after dark
-before roach number one sauntered up the wall, crossed the
-under strip, and stepped over on the upper one. But he
-went no farther, and he, with many of his friends and relations,
-were gathered up in a dust-pan the next morning and
-thrown into the stove.</p>
-
-<p><span class="pagenum" id="Page309">[309]</span></p>
-
-<div class="container m40">
-<a id="FigXII17"></a>
-<a id="FigXII18"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo309.jpg" alt="Roach killer" />
-</div>
-
-</div><!--container-->
-
-<p>In electricity, as in many other things, simplicity is the
-key-note of success; and from this little device to employ
-the alternating current for ridding a house of an insect
-nuisance sprang the grim apparatus known as the “death
-chair,” used in the execution of first-degree criminals in the
-State of New York. Many people think the mechanism for
-electrocution is a complicated one, but it is quite as simple
-as the Edison roach-killer. One pole is placed at the head
-of the criminal and the other at the feet, the latter being
-bound fast so that perfect contact can be had. Then an alternating<span class="pagenum" id="Page310">[310]</span>
-current of fifteen hundred to two thousand volts
-is run through the body, and death is instantaneous and
-void of pain.</p>
-
-<h4>An Electric Mouse-killer</h4>
-
-<p>A modification of the simple roach-killer was recently
-used by the author in his laboratory to get rid of some
-troublesome mice. A piece of board was cut twelve inches
-square, the edges being bevelled so that it would be an easy
-matter for the mice to climb up on it. An inch-wide circle
-of sheet brass was prepared measuring eleven inches
-outside diameter and nine inches inside. Another circle
-was cut measuring eight inches and a half outside and six
-inches inside diameter. Both circles were attached to the
-board with copper tacks and polished as bright as possible,
-the finished board appearing as shown in <a href="#FigXII18">Fig. 18</a>.</p>
-
-<p>Wires were soldered to each strip, and these in turn were
-connected to a high-tension current of several thousand
-volts. Crumbs and small pieces of meat were placed on the
-board inside the circles, and the trap was set in a convenient
-place on the floor of the laboratory.</p>
-
-<p>The next morning several mice lay dead on the floor, but
-at some distance from the board, and this seemed a little
-mysterious. The following night the author worked late
-in the laboratory. After finishing what he had on hand,
-he turned down the lights and sat down and watched the
-trap. Presently Mr. Mouse appeared from somewhere.
-He sniffed the air, then approached closer to the board,
-sniffed again, and, evidently concluding that he was on the<span class="pagenum" id="Page311">[311]</span>
-right trail, he climbed up the side of the board and stood
-on the outer strip. He placed one fore-foot on the inner
-strip, and, bang! up he went in the air, and landed on the
-floor a foot or more away. His jump into space was due to
-the electric action on his muscles, for the current literally
-tore his nervous system into shreds.</p>
-
-<p>Mr. Mouse lost a great many friends and relatives that
-season in the same manner, and the apparatus is confidently
-recommended as a certain and humane agent for the destruction
-of all small vermin.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page312">[312]</span></p>
-
-<h3>Chapter XIII<br />
-<span class="chaptitle">FRICTIONAL ELECTRICITY</span></h3>
-
-<p class="chapstart"><span class="largecap">F</span><span class="afterlargecap">rictional</span>
-electricity is high potential, current alternating,
-and of high voltage but very low amperage.
-Apart from certain uses in laboratory and medical practice,
-it is valueless. In its greater volume it is akin to the lightning-bolt
-and is dangerous; but in its smaller volume it is
-a comparatively harmless toy. From the glass rod, or the
-amber, rubbed on a catskin to the modern static machines
-is a long jump, and the period of exploitation covers centuries
-of interesting experiments, most of which, however,
-have been practically useless for any commercial purpose.</p>
-
-<p>Static or frictional electricity is generated by friction
-only, without the aid of magnets, coils of wire, or armatures
-rotating at high speed. The simple process of the
-glass and catskin has been variously modified, until at last
-Wimshurst invented and perfected what is known as the
-“Wimshurst Influence Machine.” It is self-charging, and
-does not require “starting.” It will work all the year
-round in any climate and temperature, and is the greatest
-improvement ever made in static electric machines.</p>
-
-<p>Apart from its efficiency under all conditions, it is the
-simplest of all machines to make, and can easily be constructed<span class="pagenum" id="Page313">[313]</span>
-by a boy who is handy with tools, and who can
-obtain the glass and brass parts necessary in its construction.
-The principal parts of an influence machine are the
-glass disks, wooden bosses, driving pulleys and crank, glass
-standards, brass arms with the spark-balls at the ends, and
-the base with the uprights on which these parts are built up
-and held in position.</p>
-
-<h4>A Wimshurst Influence Machine</h4>
-
-<p>Obtain a stiff piece of brown paper twenty inches square,
-and with a compass describe a circle twenty inches in diameter.
-Inside of this circle make another one fourteen inches
-in diameter, and near the centre a third circle six inches
-in diameter. Another circle four inches in diameter should
-be drawn inside of the six-inch circle, so that when the
-bosses are made fast to the glass plates they can be properly
-centred. Also mark sixteen lines radiating from the centre,
-equal distances apart, as shown in <a href="#FigXIII1">Fig. 1</a>.</p>
-
-<p>From a dealer in glass purchase two clear, white panes
-of glass eighteen inches square. Be careful not to get the
-green glass, as this is not nearly so good as the white for
-static machine construction. If it is possible to get crystal
-plate so much the better. The panes should be thin, or
-about one-sixteenth of an inch in thickness, and free from
-bubbles, wavy places, scratches, or other blemishes.</p>
-
-<p>From these panes cut two disks sixteen inches in diameter
-with a rotary cutter, as described in the chapter on Miscellaneous
-Apparatus, <a href="#Page294">page 294</a>, and rub the edges with a
-water-stone (see chapter on Formulæ, <a href="#Page330">page 330</a>.)</p>
-
-<p><span class="pagenum" id="Page314">[314]</span></p>
-
-<p>From flat, thin tin-foil cut thirty-two wedge-shaped
-pieces four inches long. They should be one inch and a
-half wide at one end and three-quarters of an inch at the
-other, as shown at <a href="#FigXIII2">Fig. 2</a> A. Give each plate of glass two
-thin coats of shellac on both sides; then lay one on the
-paper pattern (<a href="#FigXIII1">Fig. 1</a>) so that the outside edge of the glass
-will lie on the largest circle. Place a weight at the middle
-of the glass to hold it in place; then make sixteen of the
-tin-foil sectors fast to the plate, using shellac as the sticking
-medium. But first give one side of each sector a thin
-coat of shellac, allowing it to dry; then give it another coat
-when applying it to the glass. The sectors are to be symmetrically
-arranged on the glass, using a line of the pattern
-as a centre for each piece (as shown at A in <a href="#FigXIII1">Fig. 1</a>), and the
-fourteen and six inch circles as the outer and inner boundaries.
-Each piece, as it is applied, should be pressed down
-upon the glass, so that it will stick smoothly, without air
-bubbles or creases. A very good plan is to lay a piece of
-soft blotting-paper over the sector and drive it down with
-a small squeegee-roller such as is used in photography, taking
-care, however, not to shift the sector from its proper position.
-When all the sectors are on, the plate should appear
-as shown in <a href="#FigXIII2">Fig. 2</a>. After the shellac, which holds the
-sectors to the glass, is dry, run a brush full of shellac around
-the inner and outer extremities of the tin-foil strips for half
-or three-quarters of an inch in from the ends. The shellac
-will hold the sectors firmly to the glass, and will slightly
-insulate them as well, thereby preventing the escape of
-electricity. Apply the remaining sectors to the other plate
-of glass in a similar manner; and as a result two disks of
-glass, with the applied strips, will be ready to mount in
-the frame.</p>
-
-<p><span class="pagenum" id="Page315">[315]</span></p>
-
-<div class="container m40">
-<a id="FigXIII1"></a>
-<a id="FigXIII2"></a>
-<a id="FigXIII3"></a>
-<a id="FigXIII4"></a>
-<a id="FigXIII5"></a>
-<a id="FigXIII6"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo315.jpg" alt="" />
-</div>
-
-<p class="caption">DETAILS OF WIMSHURST INFLUENCE MACHINE</p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page316">[316]</span></p>
-
-<p>A hole three-quarters of an inch in diameter should be
-made in each glass plate, so that a three-eighths spindle may
-pass through them and into the bosses, so as to keep them
-in proper line. It is preferable, however, not to bore these
-holes if bosses and accurately bushed holes can be made
-in the uprights of the frame which support these disks.</p>
-
-<p>At a wood-working mill have two bosses made that will
-measure four inches in diameter at the large end, and one
-inch and a half at the small one. They should be of such
-length that when the plates and two bosses are arranged
-in line (to appear as shown in A A at <a href="#FigXIII9">Fig. 9</a>) they will fill
-the entire space between the uprights B B. Near the small
-end a groove is turned in each boss, so that a round leather
-belt will fit in it, as shown in <a href="#FigXIII3">Fig. 3</a>.</p>
-
-<p>The base is made from pine, white-wood, cypress, or any
-other wood that is soft and easily worked. It is composed
-of two strips twenty-four inches long, three inches wide,
-and one inch and a quarter in thickness, and two cross-pieces
-fourteen inches long, three inches wide, and one inch
-and a half thick.</p>
-
-<p>These are put together with glue and screws, and at both
-sides of the base notches are cut to accommodate the feet
-of the uprights. The uprights are seventeen inches high,
-three inches wide, and one inch and a half thick. The
-notch at the foot of each one is cut so that, when fitted in
-place, the foot of the upright will rest on a table on a line
-with the bottom of the end cross-pieces under each corner.
-At the foot of the uprights a piece of sheet rubber should be<span class="pagenum" id="Page317">[317]</span>
-made fast, with glue or shellac, so that when in operation
-the machine will not move about or slide.</p>
-
-<p>A groove is cut at one side of each upright six inches
-above the bottom, as shown at <a href="#FigXIII4">Fig. 4</a> A. In this groove
-the driving-wheel axles fit, and near the top holes are made
-in the uprights through which the spindles pass, which in
-turn support the bosses and glass disks.</p>
-
-<p>At the middle of each cross-piece forming the ends of
-the base a one-inch hole, for the glass standard rods, is
-bored through the wood, as shown at <a href="#FigXIII4">Fig. 4</a> B B. After
-attaching the uprights to the base with glue and screws,
-and giving all the wood-work several successive coats of
-shellac, the frame will be ready for its mountings.</p>
-
-<p>The driving-wheels are of wood seven-eighths of an inch
-thick and seven inches in diameter; they should be turned
-on a lathe and a groove cut in the edge so that a round
-leather belt will fit in it. These wheels are mounted on a
-wooden axle that can be made from a round curtain-pole,
-with a half-inch hole bored through its entire length. The
-axle is as long as the distance between uprights B B in
-<a href="#FigXIII9">Fig. 9</a>. The wheels are to be arranged and glued fast to
-the axle, so that the grooves will line directly under those
-in the bosses, as shown in <a href="#FigXIII9">Fig. 9</a>. A half-inch axle is
-driven through the hub, and at one end it is threaded and
-provided with two washers and nuts; or a square shoulder
-and one washer and nut may be used, so that a crank and
-handle may be held fast. Shellac should be put on the
-shaft to make it hold fast in the hub.</p>
-
-<p>The complete apparatus of wheels, axle, hub, and handle
-is shown at <a href="#FigXIII5">Fig. 5</a>, and in the frame this is so hung that the<span class="pagenum" id="Page318">[318]</span>
-iron axle rests in the grooves cut in the uprights. To hold
-this in place two metal straps, as shown in <a href="#FigXIII6">Fig. 6</a>, are made
-and screwed fast to the wood. When finally adjusted the
-driving-wheels should rotate freely whenever the crank is
-turned. The wooden bosses, <a href="#FigXIII3">Fig. 3</a>, are given two or three
-coats of shellac; then they are made fast to the glass disks
-on the same side to which the tin-foil sectors are attached.
-The disks should be placed over the paper plan, <a href="#FigXIII1">Fig. 1</a>,
-and so adjusted that the outer line tallies with the large
-circle. Acetic glue<a id="FNanchor4"></a><a href="#Footnote4" class="fnanchor">[4]</a> is then applied to the flat surface of
-the boss, and the latter is placed at the middle of the disk
-to line with the small circle. Place a weight on the end of
-the boss to hold it down, and leave it for ten or twelve
-hours or until thoroughly dry.</p>
-
-<div class="footnote">
-
-<p><a id="Footnote4"></a><a href="#FNanchor4"><span class="label">[4]</span></a>
-See <a href="#Page327">Formulæ, Chapter xiv.</a>, for the recipe of <a href="#Ref006">acetic glue</a>.</p>
-
-</div><!--footnote-->
-
-<p>Both bosses should be set at the same time so that they
-may dry together.</p>
-
-<p>If the bosses are turned on a lathe a hole should be made
-in each one about half-way through from the small end.
-This, in turn, should be bushed or lined with a piece of
-brass tube, which should fit snugly in the hole. A little
-shellac painted on each piece of tube will make it stick.
-Pieces of steel rod that will just fit within the tubing are
-to be cut long enough to enter the full length of the hole,
-pass through the holes made in the top of the uprights, and
-extend half an inch beyond, as shown in <a href="#FigXIII9">Fig. 9</a>. The bosses
-and axles will then appear as shown in <a href="#FigXIII7">Fig. 7</a>.</p>
-
-<p>Flat places should be filed on each rod where it passes
-through the wood upright; a set-screw will then hold it<span class="pagenum" id="Page319">[319]</span>
-fast and keep it from revolving. When the hole, or tubing,
-is oiled so that the boss and disk will revolve freely on the
-axle, the disks, bosses, and axles are ready to be mounted
-in the frame.</p>
-
-<p>A red fibre washer, such as is used in faucets, should be
-made fast to one glass disk at the centre, so as to separate
-the disks and prevent them from touching when they are
-revolving in opposite directions. These fibre washers can
-be had from a plumber or purchased at a hardware store.
-Shellac or acetic glue will hold the washers in place.</p>
-
-<div class="container m40">
-<a id="FigXIII7"></a>
-<a id="FigXIII8"></a>
-<a id="FigXIII9"></a>
-<a id="FigXIII10"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo319.jpg" alt="Influence machine" />
-</div>
-
-</div><!--container-->
-
-<p>Mount one disk by holding the boss with the small end
-opposite a hole in one upright, and slip an axle through
-from the outside of the upright. Hold the other disk in
-place, and slip the remaining axle through the other upright<span class="pagenum" id="Page320">[320]</span>
-and into the boss. When both plates are in place
-and centred, turn the set-screws down on the flattened axles
-to hold them in place.</p>
-
-<p>To reduce the friction between the bosses and the uprights
-it would be well to place a fibre washer between
-them. A few drops of oil on these washers will lubricate
-them properly, and allow the machine to run easier. An
-end view of the apparatus, as so far assembled, will appear
-as shown in <a href="#FigXIII9">Fig. 9</a>, A being the disks, bosses, and axles,
-B B the uprights supporting them, C the hub, and D D
-the driving-wheels. The handle and crank (E) extends out
-far enough from the side to allow a free swinging motion
-without hitting the upright or base. Having arranged these
-disks and wheels so as to revolve freely, it will now be
-necessary to construct and add the other vital parts and
-the connecting links in the chain of the complete working
-mechanism.</p>
-
-<p>From a supply-house obtain two solid glass rods an inch
-in diameter and fifteen inches long. These fit in the holes
-(B B) bored in the end-pieces of the base, <a href="#FigXIII4">Fig. 4</a>. Procure
-two brass balls, two or two and a half inches in diameter,
-such as come on brass beds, and two short pieces of brass
-tubing, one inch inside diameter, that will fit over the ends
-of the rods. These tubings are to be soldered fast to the
-balls so that both tubes and balls will remain at the top
-of the glass rods.</p>
-
-<p>From brass rod three-sixteenths or a quarter of an inch
-in diameter make two forks, as shown at <a href="#FigXIII8">Fig. 8</a>, and solder
-small brass balls at the ends of the rods. The prongs of
-the fork are six inches long and the shank four inches in<span class="pagenum" id="Page321">[321]</span>
-length. Along the inside of the forks small holes are bored,
-and brass wires, or “points,” are soldered fast. These extend
-out for half an inch from the rods, and are known as
-the “comb,” or collectors. The forks should be so far apart
-that when mounted with the glass disks revolving between
-them the points will not touch or scratch the tin-foil sectors,
-and yet be as close to them as possible. A hole should be
-bored in the brass balls, and the shank of the fork passed
-through and soldered in place, as shown in <a href="#FigXIII10">Fig. 10</a>.</p>
-
-<p>A three-eighth-inch hole is bored directly in the top of
-each brass ball to hold the quadrant rods, which extend
-over the top of the disks.</p>
-
-<p>In the illustration of the complete machine (<a href="#FigXIII12">Fig. 12</a>) the
-arrangement of the glass pillars, balls, combs, and quadrant
-rods is shown. The rods are three-eighths of an inch in
-diameter and are loose in the holes at the top of the balls,
-so that they can be moved or shifted about, according as to
-whether it is a left or a right handed person who may be
-turning the crank.</p>
-
-<p>At the upper end of each rod a brass ball is soldered, one
-being three-quarters of an inch in diameter, the other two
-inches. The projecting ends of the forks should be provided
-with metal handles or brass balls, as shown in <a href="#FigXIII12">Fig. 12</a>;
-these may be slipped over the end or soldered fast. Obtain
-two small brass balls with shanks, such as screw on iron
-bed-posts, and have the extending ends of the axles that
-support the bosses threaded, so that the balls will screw
-on them. Bore a quarter-inch hole through each ball, and
-slip a brass rod through it and solder it fast. Each end of
-these rods should be tipped with a bunch of tinsel or fine<span class="pagenum" id="Page322">[322]</span>
-copper wires. These are the “neutralizers,” and the ends
-are curved so that the brushes of fine wires will just touch
-the disks when the latter are revolved, as shown in <a href="#FigXIII12">Fig. 12</a>.
-The ball holding the rod is to be screwed fast to the axle;
-then the axle is pushed back into the boss and made fast
-in the head of the upright with the set-screw.</p>
-
-<div class="container m40" id="FigXIII12">
-
-<div class="figcenter nomargin">
-<img src="images/illo322.jpg" alt="Influence machine" />
-</div>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page323">[323]</span></p>
-
-<p>The rod-and-ball at the opposite side of the disks is
-arranged in a similar manner, but the rod points in an
-opposite direction to that on the first side. Cord or leather
-belts connect the driving-pulleys and bosses, the belt on
-one side running up straight over the boss and down again
-around the driving-pulley. The belt at the opposite side
-is crossed, so that the direction of the boss is reversed; and
-in this manner the disks are made to revolve in opposite
-directions, although the driving-pulleys are both going in
-the same direction.</p>
-
-<p>A portion of the sectors are omitted in the illustration
-(<a href="#FigXIII12">Fig. 12</a>) so that a better view of the working parts may be
-had. When the disks are revolving the accumulated electricity
-discharges from one ball to the other, above the
-plates, in the form of bright blue sparks sufficiently powerful
-to puncture cardboard if it is held midway between
-the balls.</p>
-
-<h4>A Large Leyden-jar</h4>
-
-<p>When experimenting with this machine it would be well
-to have one or more Leyden-jars to accumulate static
-charges. A large one of considerable capacity is easily
-made from a battery jar, tin-foil, brass rods and chain, and
-some other small parts.</p>
-
-<p>Obtain a bluestone battery jar, and after heating it to
-drive all moisture from the surface, give it a coat of shellac
-inside and out. With tin-foil, set with shellac, cover the
-bottom and inside of the jar for two-thirds of its height
-from the bottom, as shown in <a href="#FigXIII11">Fig. 11</a>. Cover the outside
-and bottom in a similar manner, and the same height from<span class="pagenum" id="Page324">[324]</span>
-the bottom, and provide a cork, or wooden cap, for the top.
-If a large, flat cork cannot be had, then make a stopper
-by cutting two circular pieces of wood, each half an inch
-thick, the inner one to fit snugly within the jar, the other
-to lap over the edges a quarter of an inch all around. Fasten
-these pieces together with glue, as shown at <a href="#FigXIII13">Fig. 13</a>,
-and give them several good coats of shellac. Make a small
-hole at the middle of this cap and pass a quarter-inch rod
-through it, leaving six inches above and below the cap.
-To the top of the rod solder a brass ball. At the foot a piece
-of brass chain is to be made fast, so that several links of it
-rest on the tin-foil at the bottom of the jar.</p>
-
-<p>To charge a jar from the Wimshurst machine, stand the
-jar on a glass-legged stool, and connect a copper wire between
-one of the overhead balls on the machine and the ball
-at the top of the rod in the stopper of the jar. Make another
-wire fast to the other ball at the top of the machine,
-and place it under the jar so that the tin-foil on the bottom
-touches it. By operating the machine the jar is charged.</p>
-
-<p>To discharge the jar make a <span class="symbol">T</span>-yoke, as shown at <a href="#FigXIII14">Fig. 14</a>,
-by nailing a brass rod fast to a wooden handle and soldering
-brass knobs, or hammering a lead bullet, on the ends of the
-rod. Hold one knob against the top knob of the jar and
-bring the other near the foil coating at the outside, when
-a spark will jump from the foil to the knob with a loud
-snap.</p>
-
-<h4>A Glass-legged Stool</h4>
-
-<p>One of the most useful accessories in playing with frictional
-electricity will be a glass-legged stool. A stool with<span class="pagenum" id="Page325">[325]</span>
-glass feet is perhaps too expensive for a boy to purchase,
-but one may be made at little or no cost from a piece of
-stout plank, four glass telegraph line-insulators, and the
-wooden screw-pins on which they rest when attached to a
-pole.</p>
-
-<div class="container m40">
-<a id="FigXIII11"></a>
-<a id="FigXIII13"></a>
-<a id="FigXIII14"></a>
-<a id="FigXIII15"></a>
-<a id="FigXIII16"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo325.jpg" alt="Leyden jar and glass stool" />
-</div>
-
-</div><!--container-->
-
-<p>The general plan of the stool is shown at <a href="#FigXIII15">Fig. 15</a>, and
-the top measures twelve by fifteen by two inches. Under
-each corner a screw-pin is made fast by boring a hole in<span class="pagenum" id="Page326">[326]</span>
-the wood and setting the pin in glue. The pins are cut
-at the top, as shown in <a href="#FigXIII16">Fig. 16</a>, and when they are set in
-place the glass insulators may be screwed on. The wood-work
-should be given a few coats of shellac to lend it a good
-appearance and help to insulate it.</p>
-
-<p>There are a great many interesting experiments that
-may be performed with static or frictional electricity, and
-these may be looked up in the text-books on electricity
-used in school. A word of caution will not be misplaced.
-Remember that the current, in large volume, is dangerous.
-For example, a series of charged Leyden-jars may contain
-enough electricity to give a very severe shock to the nervous
-system of the person who chances to discharge it. Its
-medical use should be under the advice and supervision of
-a physician.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page327">[327]</span></p>
-
-<h3>Chapter XIV<br />
-<span class="chaptitle">FORMULÆ</span></h3>
-
-<p class="chapstart"><span class="largecap">I</span><span class="afterlargecap">n</span>
-the construction of electrical apparatus there are
-many things, such as paint, cement, non-conducting compounds,
-and acid-proof substances, that are necessary in
-assembling the parts which make up complete working
-outfits. Accurate formulas and directions for these things
-will save the amateur trouble and expense, since they indicate
-the materials which have been put to the test of time
-and wear by others who have had abundant experience
-along these lines.</p>
-
-<p>The amateur will not need a large number of compounds,
-but such as are necessary should be of the best. Those
-which are described in this chapter can be relied upon to
-give working results.</p>
-
-<h4>Acid-proof Cements</h4>
-
-<p>One of the best acid-proof cements is made by adding
-shellac, dissolved in grain alcohol, to red-lead until it is at
-the right consistency. It can be used in liquid form or
-in a putty-like paste. The consistency is governed by the
-amount of shellac added to the red-lead. The lead should
-be pulverized and free from lumps. This cement can be<span class="pagenum" id="Page328">[328]</span>
-mixed in a small tin cup or on a piece of glass, with a knife
-having a thin blade.</p>
-
-<p>It should be used as soon as it is mixed, since it “sets”
-as quickly as shellac, and then dries from the outside towards
-the middle. In a week or two it will become dry
-and hard like stone.</p>
-
-<p>Another cement, which will also dry as hard as a stone
-and will hold soapstone slabs together as if they were of
-one solid piece, is made of litharge (yellow lead) and glycerine.
-The glycerine is added to the pulverized litharge
-to make a paste, or it can be mixed and kneaded like thin
-putty. It should be used very soon after mixing, as it sets
-rapidly.</p>
-
-<h4>Hard Cement</h4>
-
-<p>A medium hard cement is made from plaster of Paris,
-six parts; silex, or fine sand, two parts; dextrine, two parts
-(by measure). Mix with water until soft; then work with
-a trowel or knife.</p>
-
-<h4>Soft Cement</h4>
-
-<p>A good soft cement is made of plaster of Paris, five parts;
-pulverized asbestos, five parts (by weight). Add water
-enough to make a soft paste, and use with a trowel or knife.
-This is a heat-proof compound and is commonly known as
-asbestos cement.</p>
-
-<h4>Very Hard Cement</h4>
-
-<p>One of the hardest cements that can be made is composed
-of hydraulic cement (Portland or Edison), five parts;<span class="pagenum" id="Page329">[329]</span>
-silex, or white sand, five parts (by measure). Mix with
-water and use like plaster with a trowel or spatula.</p>
-
-<p>Care must be taken when the parts are combined to see
-that the cement is free from lumps. These must be broken
-before the silex, or sand, and water are added. Then the
-two parts should be mixed together at first and moistened
-afterwards. The proper way is to place some water at the
-bottom of a pan; then add the dry mixture by the handfuls,
-sprinkling it around so that the water can enter into
-it without forming lumps. Keep adding and mixing until
-the mass is at the right consistency to work.</p>
-
-<p>All these cements are acid-proof.</p>
-
-<h4>Clark’s Compound</h4>
-
-<p>For exterior insulation, where the parts are exposed to
-the weather, a superior compound is made up of mineral
-pitch, ten parts; silica, six parts; tar, one part (all parts by
-weight). This is called Clark’s compound, after the man
-who invented it and used it successfully.</p>
-
-<p>It is heated, thoroughly mixed, and used with a brush
-or spatula.</p>
-
-<h4>Battery Fluid</h4>
-
-<p>A depolarizing solution for use in zinc-carbon batteries
-like the Grenet is composed as follows:</p>
-
-<p>Dissolve one pound of bichromate potash or soda in ten
-pounds of water (by weight). When it is thoroughly dissolved
-add two and one-half pounds of sulphuric acid,
-slowly pouring it into the bichromate solution and stirring<span class="pagenum" id="Page330">[330]</span>
-it with a glass rod. The addition of the acid will heat the
-solution. Do not use it until it has entirely cooled.</p>
-
-<h4>Glass Rubbing</h4>
-
-<p>To rub the edges of glass, such as the disks for Wimshurst
-machines, obtain a piece of hard sandstone, such as is used
-for sharpening knives or scythes. The glass is placed on a
-table so that the edge extends beyond. Oil of turpentine
-is rubbed or dropped on the surface of the stone, and the
-edge of the glass is moistened with a rag soaked in the turpentine.
-Hold the glass down securely with one hand, and
-with the other grasp the stone and give it a forward and
-backward motion, grinding the glass along its edge and not
-crosswise. With care and patience a rough edge can soon
-be brought to a smooth one, and a soft, rounded corner substituted
-for the hard, angular, cutting edge that makes the
-glass a difficult thing to handle. Use plenty of lubricant in
-the form of oil of turpentine to make the work easy.</p>
-
-<h4 id="Ref006">Acetic Glue</h4>
-
-<p>One of the best glues for glass and wood or glass and
-fibre is made by placing some high-grade glue (either flake
-or granulated) in a cup or tin and covering it with cold
-water. Allow it to stand several hours until the glue absorbs
-all the water it will and becomes soft; then pour the
-water off, and add glacial acetic acid to cover the glue. The
-proportion should be eighteen parts of glue to two of acid.
-Heat the mass until it is reduced to liquid, stirring it until<span class="pagenum" id="Page331">[331]</span>
-it is thoroughly mixed. When ready for use it should be
-poured into a bottle and well corked to keep the air away
-from it.</p>
-
-<h4>Insulators</h4>
-
-<p>Apart from glass and porcelain, insulators can be made
-from non-conducting compounds, the best of which is
-molded mica. Ground mica or mica dust is mixed with
-thick shellac until it is in a putty-like state. It may then
-be forced into oiled molds of any desired shape. Hydraulic
-pressure is employed for almost every form of molded
-mica that is made for commercial purposes; but as a boy
-cannot employ that means to get the best results, he must
-use all the pressure that his hands and a flat board will
-give.</p>
-
-<p>Another compound is made from pulverized asbestos
-and shellac, with a small portion of ground or pulverized
-mica added, in the proportion of asbestos, six parts; mica,
-four parts. Shellac is added to make a pasty mass, which
-is kneaded into a thick putty and forced into oiled molds
-until it sets. It is then removed and allowed to dry in the
-open air, and the mold used for more insulators.</p>
-
-<h4>Non-conductors</h4>
-
-<p>When working in different materials that seem adapted
-to electrical apparatus, it is necessary to know whether they
-can be used safely or not. Often a material seems to be
-just the thing, but if it should be a partial conductor, when
-a non-conductor is desired, it would be hazardous to use<span class="pagenum" id="Page332">[332]</span>
-it. A list of non-conductors is therefore valuable to the
-amateur. Some of the principal non-conductors, among
-the many, are as follows: glass, porcelain, slate, marble,
-hard stone, soapstone, concrete (dry), hard rubber, soft rubber,
-composition fibre, mica, asbestos, pitch, tar, shellac,
-cotton, silk; cotton, silk and woollen fabrics, transite (dry),
-electrobestus (dry), duranoid; celluloid, dry wood (well seasoned),
-paper, pith, leather, and oil.</p>
-
-<p>While this account of formulæ and material might be extended,
-this is not necessary inasmuch as the formulæ and
-practical directions which have been given will answer all
-usual practical requirements.</p>
-
-<h4>Insulating Varnish</h4>
-
-<p>There are several good insulating varnishes that can be
-used in electrical work, the most valuable being shellac dissolved
-in alcohol and applied with a brush. To make good
-shellac, purchase the orange-colored flake shellac by the
-pound from a paint-store, place some of it in a wide-necked
-bottle, and cover it with alcohol; then cork the bottle and
-let it stand for a few hours. Shake the bottle occasionally
-until the shellac is thoroughly dissolved. It can be thinned
-by adding alcohol. Always keep the bottle corked, taking
-out only what is necessary from time to time.</p>
-
-<p>Another varnish can be made by dissolving red sealing-wax
-in alcohol and adding a small portion of shellac. This
-can be applied with a soft brush, and is a good varnish.
-When colors are to be applied to distinguish the poles, red<span class="pagenum" id="Page333">[333]</span>
-is used for the positive current-poles and blue or black for
-the negative, if they are colored at all.</p>
-
-<p>A very good black varnish is made by adding lampblack
-to shellac; another consists of thick asphaltum or asphaltum
-varnish. This is waterproof, and dries hard, yet with
-an elastic finish.</p>
-
-<h4>Battery Wax</h4>
-
-<p>For the upper edges of glass cells, such as the Leclanché
-or other open-circuit batteries, there is nothing superior to
-hot paraffine brushed about the upper edge to prevent the
-sal-ammoniac or other fluids from creeping up over the top.
-The paraffine can be colored with red-lead, green dust, or
-powders of various colors if desired, but generally the paraffine
-is used without color, so that it has a frosted-glass appearance
-when it is cool and dry.</p>
-
-<p>A black wax for use in stopping the tops of dry cells
-and coating the tops of carbons is composed of paraffine,
-eight parts; pitch, one part; lampblack, one part.
-Heat the mixture and stir it until thoroughly mixed;
-then apply with a brush, or dip the parts into the warm
-fluid.</p>
-
-<p>Another good black wax is composed of tar and pitch in
-equal parts. They are made into a pasty mass with turpentine
-heated over a stove, but not over an open flame,
-because the ingredients are inflammable. The compound
-should be like very thick molasses, and can be worked with
-an old table-knife.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page334">[334]</span></p>
-
-<h3>Chapter XV<br />
-<span class="chaptitle">ELECTRIC LIGHT, HEAT, AND POWER</span></h3>
-
-<p class="blankbefore75 blankafter1 fsize90">For the use of the cuts in this chapter, the Publishers desire to acknowledge
-the courtesy of the General Electric Company, the Thomson Electric
-Welding Company, and the Cooper Hewitt Electric Company.</p>
-
-<p class="chapstart"><span class="largecap">W</span><span class="afterlargecap">ith</span>
-the discovery of the reversibility of the dynamo,
-the invention of the telephone, and the improvements
-in the electric light began the great modern development
-of electricity which proved that marvellous agent to be a
-master-workman.</p>
-
-<p>Many of the things electrical that we ordinarily think of
-as modern inventions are merely modern applications of
-phenomena that were discovered many years ago. The
-pioneers in the science of dynamic electricity performed
-their experiments with the electric light, electro-magnets,
-etc., by using galvanic batteries. But for practical purposes
-the consuming of zinc and chemicals in such batteries
-was too expensive a way to generate electricity, and prevented
-any commercial use of the results of their experiments
-until cheaper electricity could be had.</p>
-
-<h4>The Work of the Dynamo</h4>
-
-<p>The invention of the dynamo, with which we obtain electricity
-from mechanical power, changed all that. Instead<span class="pagenum" id="Page335">[335]</span>
-of consuming zinc in primary batteries, men could obtain it
-by burning coal, which is much cheaper, under the boiler of a
-steam-engine used to drive the dynamo. Thus it is that
-modern electricity comes from mechanical power. It is
-really the energy of a steam-engine or a water-wheel, or some
-other “prime mover,” working through the medium of
-electricity, that is transmitted to a distance and distributed
-over wires. The electricity may then be transmuted into
-light, heat, or chemical energy as the case may be, to light
-our electric lamps, develop the intense heat of the electric
-furnace, and charge storage-batteries.</p>
-
-<p>Moreover, some time after the invention of the dynamo
-it was found that the mechanical power put into one of
-these machines could be transmitted electrically and reproduced
-as mechanical power. In other words, a dynamo
-could be made to revolve and give out power, as a motor,
-by supplying it with current from another dynamo. This
-showed the way to transmute electricity back again into
-mechanical power, to run our electric cars and trains, and
-all kinds of machinery in our factories and elsewhere. Nowadays
-the dynamo is used to generate nearly all the electricity
-that we need. Even in such comparatively old
-electrical applications as electro-plating and the telegraph
-and telephone, primary batteries are being supplanted
-by motor dynamos, which we shall learn about
-later.</p>
-
-<p>It is from the invention of the dynamo and the discovery
-that it was reversible that we date the beginning of what are
-known as heavy electrical engineering applications, including
-electric light, heat, and power. In this closing chapter it<span class="pagenum" id="Page336">[336]</span>
-is purposed to learn a little about these applications, and in
-so doing to summarize briefly the things that we have already
-studied.</p>
-
-<h4>The Electric Light</h4>
-
-<p>In the <a href="#Page125">chapter</a> on Electrical Resistance we learned that
-an electric current always encounters a resistance in passing
-through a conductor, and that when the current is strong
-enough the conductor is heated up. The electric light is
-produced by the heating of a conductor of one kind or another
-to incandescence by the electrical friction of the current
-passing through it.</p>
-
-<p>The first electric light was made by Sir Humphry Davy
-over a hundred years ago. He discovered that when a
-current from a great many cells of battery was interrupted
-the spark did not simply appear for an instant and
-then go out, as it does when only a few cells are used, but
-remained playing between the terminals of the circuit. He
-found by experiment that if pieces of carbon are used as
-the terminals&mdash;or “electrodes,” as they are called&mdash;the
-electricity passes between them in an intensely hot flame,
-or “arc.” The latter, which is due to the electrical resistance
-of the vapor of carbon, heats up the carbon-points
-so that they give a brilliant white light.</p>
-
-<p><span class="pagenum" id="Page337">[337]</span></p>
-
-<div class="container m40">
-<a id="FigXV1"></a>
-<a id="FigXV2"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo337.jpg" alt="Lamps" />
-</div>
-
-<div class="split3565">
-
-<div class="left3565">
-<p class="caption"><span class="sstype"><i><b>Fig. 1</b></i></span></p>
-</div>
-
-<div class="right3565">
-<p class="caption"><span class="sstype"><i><b>Fig. 2</b></i></span></p>
-</div>
-
-<p class="clearline">&nbsp;</p>
-
-</div><!--split3565-->
-
-</div><!--container-->
-
-<p>Before the dynamo came into use, the electric light was
-rarely seen, except as a philosophical experiment; but as
-soon as cheap electricity became available, commercial
-electric arc-lamps were made by many inventors and have
-been continually improved. <a href="#FigXV1">Fig. 1</a> shows one form of modern
-arc-lamp, with its case removed to show the interior
-mechanism. In most arc-lamps the lamp itself consists of
-a pair of carbon or other electrodes in the form of long rods
-arranged vertically, with their tips normally in contact.
-When the current is turned on, the mechanism lifts the upper
-electrode away from the lower one. The interruption of
-the circuit thus caused “strikes the arc” between the tips,<span class="pagenum" id="Page338">[338]</span>
-and the mechanism keeps the arc-distance unchanged as the
-carbons burn away. Some arc-lamps are made to burn on
-continuous-current, and others on alternating-current circuits.
-When continuous current is used, the upper (or
-positive) carbon burns away about twice as fast as the lower
-one, forming a cup, or “crater,” from which most of the
-light comes.</p>
-
-<h4>Uses of the Arc-Light</h4>
-
-<p>The first commercial use of the arc-light on a large scale
-was for street-lighting, to replace the old-fashioned gas-lamps.
-But another important use is in search-lights, in
-which the arc-lamp is fitted with a powerful reflector for
-throwing a very bright light to a distance. <a href="#FigXV2">Fig. 2</a> is a view
-of a search-light arranged to go on top of a ship’s pilot-house.
-In war-time the ships carry search-lights to help them find
-the enemy’s ships and repel attack; and they are used in the
-army also, by having a portable dynamo and engine drawn
-by horses. The arc is also employed in projectors for lecture-rooms,
-and sometimes for the headlights of steam and
-electric locomotives and interurban electric cars.</p>
-
-<h4>Incandescent and Other Lamps</h4>
-
-<p>The arc-lamp came into wide use for lighting large spaces
-like streets, stores, and public halls, but was found to be too
-intense for lighting smaller places like private houses. After
-many experiments, Edison succeeded in subdividing the
-electric light into the small pear-shaped “incandescent”
-lamps that we now see everywhere. In this kind of electric<span class="pagenum" id="Page339">[339]</span>
-lamp the light comes from a thin “filament” of carbon, contained
-in a glass globe from which all air has been removed.
-Since there is no oxygen to support combustion, the filament
-may be heated white-hot by the current without being
-consumed.</p>
-
-<div class="container m40" id="FigXV3">
-
-<div class="figcenter nomargin">
-<img src="images/illo339.jpg" alt="Lamp" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 3</span></i></b></p>
-
-</div><!--cotainer-->
-
-<p>In certain other forms of incandescent lamps that are
-just coming into use, the filaments are made of rare metals&mdash;osmium,
-tantalum, etc.&mdash;that will stand a high temperature<span class="pagenum" id="Page340">[340]</span>
-without melting. The Nernst lamp has a filament
-consisting of a mixture of certain materials that has to be
-heated before it will conduct electricity.</p>
-
-<p>Then there are the so-called “vapor” lamps, consisting of
-a glass tube full of conducting metallic vapor which gives
-out light when a current is passed through it. The best-known
-form is the Cooper Hewitt mercury vapor-lamp
-shown in <a href="#FigXV3">Fig. 3</a>, which gives a peculiar greenish light.</p>
-
-<p>From the point of view of efficiency, the electric light,
-wonderful as it is, leaves much to be desired. The light
-always comes from a hot resistance; and whether this resistance
-is a mass of conducting vapor, as in the arc and
-vapor lamps, or a solid conducting filament, as in the so-called
-“incandescent” lamps, much more heat than light
-is produced. A needed improvement, therefore, is in the
-direction of obtaining a greater percentage of light for a
-given amount of electrical energy.</p>
-
-<h4>Electric Heat</h4>
-
-<p>The generation of heat in electrical devices usually means
-wasted energy&mdash;sometimes a very serious waste, as we have
-just seen. There are certain kinds of electrical apparatus,
-however, that are designed to transform all of the electrical
-energy delivered to them into heat, for various industrial
-and household purposes.</p>
-
-<div class="container m40" id="FigXV4">
-
-<div class="figcenter nomargin">
-<img src="images/illo341.jpg" alt="Furnace" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 4</span></i></b></p>
-
-</div><!--container-->
-
-<h4>Electric Furnaces</h4>
-
-<p>By far the most important application of electric heat, as
-such, is in electric furnaces, by means of which we attain the<span class="pagenum" id="Page341">[341]</span>
-highest temperatures known to man. The electric furnace
-consists of a chamber of “refractory” material, containing
-the substances to be acted upon by the heat, with a pair of
-big carbon electrodes thrust into the centre, as shown in
-<a href="#FigXV4">Fig. 4</a>, which is a picture of Moissan’s electric furnace for
-the distillation of metals, and supplied with heavy continuous
-or alternating currents. The apparatus is therefore a
-sort of gigantic electric arc-lamp, so enclosed that the whole
-of the intense heat of the arc is confined and concentrated
-on the smelting or other work. In many places where cheap
-electric power is to be had&mdash;as in the vicinity of the great
-Niagara Falls power-plants&mdash;electric furnaces are employed
-in what are known as electrometallurgical and electrochemical<span class="pagenum" id="Page342">[342]</span>
-manufacturing processes. By their aid many metals and
-other substances that were formerly scientific curiosities, or
-entirely unknown, are produced commercially; such as aluminum,
-certain rare metals, and calcium carbide, from
-which that wonderful illuminant, acetylene-gas, is obtained.</p>
-
-<h4>Welding Metals</h4>
-
-<p>Another useful application of electric heat is in the welding
-of metals. Instead of heating the pieces to be welded
-in a forge, their ends are simply butted together and the
-electricity&mdash;generally from an alternating-current transformer&mdash;turned
-on. The heat developed by the “contact
-resistance” between the pieces quickly softens the metal so
-that the pieces may be forced together, forming a perfect
-weld in a few minutes without any hammering. <a href="#FigXV5">Fig. 5</a> is
-a view of one form of electric welding-machine in which this
-is accomplished. The electric process can weld certain
-metals that cannot be joined securely by ordinary welding
-methods, and is used in several special arts.</p>
-
-<p>Welding is also performed by the heat of a special electric
-arc-lamp, which a workman holds in his hand like a blow-pipe
-or torch. This process is especially useful in joining the
-edges of sheet-steel, in making tanks for electric “transformers,”
-etc. The workmen have to wear smoked glasses
-in order to protect their eyes from the intense glare of the
-arc.</p>
-
-<div class="container m40" id="FigXV5">
-
-<div class="figcenter nomargin">
-<img src="images/illo343.jpg" alt="Welder" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 5</span></i></b></p>
-
-</div><!--container-->
-
-<h4>Electric Car-heaters</h4>
-
-<p>Perhaps the simplest and best-known application of electric
-heat is the electric car-heater, consisting of coils of high-resistance<span class="pagenum" id="Page343">[343]</span>
-wire&mdash;such as iron or German-silver wire&mdash;mounted
-on an insulating, non-combustible frame which is placed
-under the seats of the car. Part of the current from the
-trolley wire or third rail passes through the resistance-coils,
-heating them up and thereby warming the air in the
-car.</p>
-
-<p><span class="pagenum" id="Page344">[344]</span></p>
-
-<h4>Household Uses</h4>
-
-<p>Nowadays electric heat is being more and more widely
-utilized in what are known as household electric heating-appliances.
-One of the most useful of these is the electric
-flat-iron, shown in <a href="#FigXV6">Fig. 6</a>. This flat-iron is designed to do
-away with the use of a hot stove of any kind, and is internally
-heated by means of a resistance-coil of peculiar shape
-placed in the bottom of the iron close against its working
-face. The iron is connected to an electric-light socket by
-means of an attaching plug on the end of a long, flexible
-cord. It takes only a few minutes to get hot, and its use
-saves much time and labor.</p>
-
-<p>The list of special heating-appliances that are now made
-includes curling-iron heaters; heating-pads, for taking the
-place of hot-water bags in the sick-room; cigar-lighters, in
-which a little grid “resistance” is made incandescent by
-pressing a button; foot-warmers; and radiators to dry wet
-shoes or skirts on rainy days. For industrial use there are
-glue-pots, for bookbinders and pattern-makers; large flat-irons,
-for tailor-shops and laundries; and electric ovens, for
-drying certain parts of electrical machines and for cooking
-various kinds of “prepared foods.”</p>
-
-<p>Many electric cooking-utensils are made for the household,
-such as coffee-percolators, egg-boilers, ovens, disk stoves, etc.
-Each one is equipped with a resistance-coil like that in the
-electric flat-iron just described, so that it contains its own
-source of heat, which is under perfect control by means of a
-switch. An “electric kitchen” consists of a number of these<span class="pagenum" id="Page345">[345]</span>
-utensils, wired to a convenient table or stand, as shown in
-<a href="#FigXV7">Fig. 7</a>.</p>
-
-<div class="container m40">
-<a id="FigXV6"></a>
-<a id="FigXV7"></a>
-
-<div class="figcenter nomargin">
-<img src="images/illo345.jpg" alt="Appliances" />
-</div>
-
-<div class="split4060">
-
-<div class="left4060">
-<p class="caption"><b><i><span class="sstype">Fig. 6</span></i></b></p>
-</div>
-
-<div class="right4060">
-<p class="caption"><b><i><span class="sstype">Fig. 7</span></i></b></p>
-</div>
-
-<p class="clearline">&nbsp;</p>
-
-</div><!--split-->
-
-</div><!--container-->
-
-<h4>Electric Power</h4>
-
-<p>We have seen that the modern way to generate electricity
-is from mechanical energy applied through a dynamo, and
-that the “electric power” thus generated may be transmitted
-over wires to a distance and there transformed into
-other forms of energy, such as light, heat, and chemical energy,
-or reproduced again as mechanical energy. The last
-mentioned of these transformations is the most important of
-them all, because it is the one that means the most for the
-advancement of civilization. Before the invention of the<span class="pagenum" id="Page346">[346]</span>
-dynamo and the discovery that it was reversible, mechanical
-power could be employed only in the place where it was
-generated, so that its use was restricted; whereas nowadays
-the field of power is broadened and its cost reduced by
-electrical transmission and distribution.</p>
-
-<p>In the <a href="#Page229">chapter</a> on Dynamos and Motors we learned how to
-make and use those machines. Let us review, very briefly,
-just what happens in the double transformation&mdash;of mechanical
-energy into electricity and then back again at the
-end of a line of wires&mdash;that we call electric-power transmission.
-In the dynamo, the power of the water-wheel, or
-whatever other prime mover is used, is exerted in generating
-electricity by forcing the electric conductors of the machine
-through a magnetic field. The electricity is led away to a
-distance&mdash;a hundred miles, perhaps&mdash;by wires and allowed
-to enter another machine similar to the dynamo, but operating
-as a motor. Here the first process is reversed: the electricity
-passing through the conductors of the motor reacts
-upon its magnetic field, causing the machine to revolve and
-thus generating mechanical power again. The line-wires
-carry the power just as positively as though a long shaft ran
-from the prime mover to the receiving end of the line, and
-much more economically. The action that goes on is
-similar to the operation of the telephone&mdash;which is indeed a
-special case of electric-power transmission&mdash;as already explained
-in a former chapter: the sound of the voice being
-transformed, at the telephone-transmitter, into electrical
-energy in the form of alternating currents, then carried
-as such over the line and finally reproduced as sound again
-at the receiver.</p>
-
-<p><span class="pagenum" id="Page347">[347]</span></p>
-
-<h4>Power from Water-wheels</h4>
-
-<p>“Hydro-electric” transmissions&mdash;i. e., electric transmissions
-of power from a water-wheel as prime mover&mdash;are the
-most important because they bring into use cheap water-power
-that formerly ran to waste. There are many hydro-electric
-transmissions in this country, Mexico, and Canada,
-some of them utilizing the power of waterfalls or rapids
-located in mountainous and inaccessible parts. The alternating
-current is nearly always used because by it men
-can much more easily and safely generate, transmit, and
-receive the high voltages that have to be used than by the
-continuous current. The machinery at the “main generating
-station” consists of big alternating-current dynamos,
-which sometimes have vertical shafts instead of horizontal
-ones, so that they may be driven directly by turbines.
-The current is generated at a moderate potential, which
-is then “stepped-up,” by “static transformers,” to the
-comparatively high-line voltage that is required in long-distance
-transmissions.</p>
-
-<div class="container m30" id="FigXV8">
-
-<div class="figcenter nomargin">
-<img src="images/illo348.jpg" alt="Transformer" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 8</span></i></b></p>
-
-</div><!--container-->
-
-<h4>Transformers</h4>
-
-<p><a href="#FigXV8">Fig. 8</a> is a view of a very large transformer of over 2500
-electrical horse-power capacity. In the picture the containing-tank
-is represented as transparent, so as to show the
-transformer proper inside. The latter is really a special kind
-of induction-coil, with primary and secondary windings, and
-a core, weighing many tons, built up of thin sheets of steel.
-In this kind of transformer, the tank is filled with oil, to<span class="pagenum" id="Page348">[348]</span>
-keep the transformer cool in operation, and to help insulate
-it against the high potential to which it is subjected. At
-the receiving end, or “sub-station,” the high-voltage electric<span class="pagenum" id="Page349">[349]</span>
-power enters a set of “step-down” transformers, from which
-it is delivered again, at moderate potential, to the motors.</p>
-
-<p>Sometimes power is distributed from a single great generating
-station to several sub-stations. In the Necaxa
-transmission, in Mexico, over 35,000 horse-power is taken
-from a waterfall in the mountains and transmitted at 60,000
-volts potential to Mexico City, 100 miles away, and
-to the mining town of El Oro, seventy-four miles farther
-on.</p>
-
-<p>Several kinds of motors are used at the receiving end of
-electric-power transmission-lines, according to the work that
-they are called upon to do. For “stationary” work, like
-driving the machines in mills and factories, two principal
-kinds of alternating-current motors are employed&mdash;synchronous
-and induction motors. The former are built just
-like alternating-current dynamos, and when they are running
-they keep “in step” with the dynamo at the other end
-of the line; i. e., the motion of their field windings relatively
-to their armatures keeps exact pace with the same motion
-at the dynamo, just as though a long shaft ran from one
-machine to the other instead of the electric wires of the transmission-line.
-A motor of this type, at work driving an air-compressor,
-is shown in <a href="#FigXV9">Fig. 9</a>. The induction-motor is
-really a sort of transformer, the primary winding of which
-is the fixed part, or field, and the secondary winding the
-rotating armature. It does not keep in step with the dynamo,
-like the synchronous motor, but adapts its speed to
-the “load,” or amount of work that it is called upon to do,
-like a continuous-current motor.</p>
-
-<div class="container m30" id="FigXV9">
-
-<div class="figcenter nomargin">
-<img src="images/illo350.jpg" alt="Compressor" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 9</span></i></b></p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page350">[350]</span></p>
-
-<h4>Rotary Converters</h4>
-
-<p>Sometimes alternating-current electric power is transformed
-at the sub-station into continuous-current power.
-This is done by a special kind of transformer called a “rotary
-converter.” The static transformers of which we have
-just been speaking are built, like ordinary reduction-coils,
-with no moving parts, and operate by taking in alternating
-currents at a given potential and giving out alternating
-currents at a different potential, higher or lower as the case
-may be. The rotary converter, however, is built something
-like a dynamo, with a stationary field and a revolving armature,
-and ordinarily operates by receiving an alternating
-current at a given potential and delivering a continuous
-current of the same or a different potential. This kind of
-transformation is employed wherever it is desired to obtain
-any large amount of continuous current from an alternating-current<span class="pagenum" id="Page351">[351]</span>
-transmission-line; and especially to obtain
-“500-volt continuous current” for operating street and interurban
-electric railways, as we shall see under the <a href="#Ref007">next
-heading</a>. <a href="#FigXV10">Fig. 10</a> shows one form of rotary converter built
-for supplying continuous current for trolley service.</p>
-
-<div class="container m40" id="FigXV10">
-
-<div class="figcenter nomargin">
-<img src="images/illo351.jpg" alt="Converter" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 10</span></i></b></p>
-
-</div><!--container-->
-
-<p>Oftentimes the sub-station of a transmission system contains
-both static transformers and rotary converters, to
-supply both alternating current and continuous current
-from the same high-voltage alternating-current line. When
-the continuous current has to be transformed from one
-voltage to another, a “motor dynamo” is used, consisting<span class="pagenum" id="Page352">[352]</span>
-of an electric motor driving a dynamo on a common
-shaft.</p>
-
-<p>One of the most interesting features of electric-power
-transmission is the care that is taken to avoid the terrible
-danger from the high potentials, and at the same time prevent
-loss of power on the way. The electricity in the machinery
-and in the line-wires that extend across the country
-is veritable lightning, and has to be carefully guarded
-from doing any damage or escaping. To prevent leakage,
-the insulation of all of the station machinery and apparatus
-is made extra good, with “high dielectric strength,” so
-that it will not be punctured by the high voltage; and the
-line-insulators are made very large, and electrically and
-mechanically strong&mdash;quite unlike the ordinary-sized glass
-or porcelain insulators that are employed for telegraph and
-telephone lines. Each insulator before being put up is
-tested under a “breakdown voltage” much higher than it is
-to stand in actual service.</p>
-
-<h4>Oil-switches</h4>
-
-<p>The switching of high-voltage electric power is a knotty
-problem. The circuit cannot be interrupted by “air-break”
-switches, such as are used in ordinary electric-light stations,
-for any attempt to do so would result in a destructive
-arc many feet long, that could not be extinguished.
-Therefore “oil-switches” are always used to control the
-line-circuits at the main generating station and the sub-stations.
-In these oil-switches&mdash;which are designed to be
-operated from a distance, by hand-levers, or sometimes
-by electric motors&mdash;the circuit is made and broken under<span class="pagenum" id="Page353">[353]</span>
-the surface of oil, which prevents the formation of an arc.
-Moreover, the switchboard attendant does not have to come
-anywhere near the deadly high-voltage wires, but can make
-the necessary connections at a safe distance.</p>
-
-<h4 id="Ref007">Electric Traction</h4>
-
-<p>The use of the electric motor to propel vehicles of all
-kinds is called electric traction. It is, of course, a branch
-of electric power, which we have just been considering; and
-it is in many respects the most important branch. The
-wealth of a country is largely built up and maintained by
-its facilities for transportation, such as its canals, highways,
-railroads, and street and interurban car-lines.</p>
-
-<p>In this field electric power is playing a most important
-part, although it was not many years ago that the first
-experimental electric cars were put in to replace horses on
-the street-railways of our cities. The change was found to
-be so successful that the field of the trolley-car was widened
-and extended very rapidly, until now we have our great
-suburban and interurban electric railways, with cars almost
-or quite as big as those on the steam-railroads and running
-at even higher speeds. During the last few years, also, the
-sphere of the steam-railroad itself has been invaded by
-electricity, by the construction of powerful electric locomotives
-to draw passenger and freight trains.</p>
-
-<h4>The Trolley-car</h4>
-
-<p>Let us consider just what it is that makes a trolley-car go.
-Since electric power is only mechanical energy in another<span class="pagenum" id="Page354">[354]</span>
-form, we know that the motionless copper trolley-wire, suspended
-over the track in our streets, is the means of propelling
-the car just as truly&mdash;though in a different way&mdash;as
-if it were a moving steel cable to which the car was
-attached. We must keep in mind the fact that the electricity
-is not itself the source of power, but only the medium
-of transmission. The engine in the power-house, by turning
-a dynamo there, maintains a constant electric pressure, or
-“constant potential,” as it is termed, in the trolley-wire.
-This pressure of electricity forces the power through the
-motors of the car as soon as the motorman makes the
-connection to them by turning the handle of his “controller.”</p>
-
-<div class="container m40" id="FigXV11">
-
-<div class="figcenter nomargin">
-<img src="images/illo354.jpg" alt="Motor" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 11</span></i></b></p>
-
-</div><!--container-->
-
-<p><span class="pagenum" id="Page355">[355]</span></p>
-
-<h4>The Continuous-current Motor</h4>
-
-<p><a href="#FigXV11">Fig. 11</a> is a view of one form of continuous-current motor.
-There is not much of the motor itself to be seen, because it
-is entirely enclosed in a cast-iron case. The shaft of the
-motor has a small “spur gear” fixed on one end, driving a
-gear-wheel which is fixed on the car axle. By this arrangement
-more than one revolution of the motor armature is<span class="pagenum" id="Page356">[356]</span>
-required to make one revolution of the car-wheel, which
-multiplies the force exerted in turning the wheel.</p>
-
-<div class="container m40" id="FigXV12">
-
-<div class="figcenter nomargin">
-<img src="images/illo355.jpg" alt="Controller" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 12</span></i></b></p>
-
-</div><!--container-->
-
-<h4>The Controller</h4>
-
-<p><a href="#FigXV12">Fig. 12</a> is a view of a type of controller that is used on the
-platform of trolley-cars. The cover is removed to show the
-contacts, inside, by which the electric power is turned on
-gradually by the controller handle. The trains of electric
-cars that run on the elevated structures and in the subways
-of our large cities are supplied with power from a “third
-rail” placed by the side of the track, on insulating supports,
-and the motors on all the cars are controlled from a single
-“master-controller” on the front platform of the forward
-car. This system of control, known as the “multiple-unit”
-system, gives electric trains several advantages over the
-old kind, drawn by steam-locomotives; such as they used
-to have on the New York elevated roads, for example. For
-one thing, the train can be started much more quickly,
-since all the motors begin to turn the car-wheels at the same
-instant. Then again, the system enables a long train of cars
-to be controlled as easily as a single car, and better “traction”
-between wheels and track is obtained.</p>
-
-<h4>Electric Locomotives</h4>
-
-<p>Several of the great steam-railroads are now adopting the
-electric locomotive to draw their trains. <a href="#FigXV13">Fig. 13</a> is a view
-of one of the great continuous current electric locomotives
-that are used by the New York Central Railroad to handle
-many of its passenger-trains in and out of the Grand Central<span class="pagenum" id="Page357">[357]</span>
-Station, in New York city. The motors of this powerful
-electric engine, unlike those of trolley-cars, are “gearless”;
-that is, their armatures are fixed directly on the locomotive
-axles so that they revolve at the same speed as the driving-wheels.</p>
-
-<div class="container m40" id="FigXV13">
-
-<div class="figcenter nomargin">
-<img src="images/illo357.jpg" alt="Locomotive" />
-</div>
-
-<p class="caption"><b><i><span class="sstype">Fig. 13</span></i></b></p>
-
-</div><!--container-->
-
-<p>All of the railway motors considered thus far have been
-of the continuous-current type, although the current to
-operate them is often obtained from alternating current
-transmission-systems, through rotary converters, as described
-above. The alternating current is also beginning to
-be employed to drive cars and trains. One type of alternating
-current railway motor, designed for “single-phase”
-operation, is in use on several interurban systems in
-this country, running on high-voltage alternating current
-most of the time, but on continuous current when within
-the city limits.</p>
-
-<p><span class="pagenum" id="Page358">[358]</span></p>
-
-<h4>Other Forms of Electric Traction</h4>
-
-<p>Electric traction also includes electric automobiles, supplied
-by storage-batteries; a slow-speed electric locomotive
-for drawing canal-boats, and called “the electric mule”;
-and an ingenious gasolene-electric outfit for driving cars by
-electric motors without any trolley, third rail, or storage-battery.
-The last-mentioned arrangement consists of a set
-of electric car-motors mounted on the trucks in the usual
-way, but supplied with current by a dynamo mounted on the
-car itself and driven by a gasolene-engine. Thus the car
-carries its own power-station about with it, and is independent
-of any outside source of electricity.</p>
-
-<p class="blankbefore75">The old alchemists sought to transmute <i>matter</i> from one
-form to another; and especially lead and other “base metals”
-into gold, in order that they might grow rich by concentrating
-the precious metal in their own selfish hands. The
-modern miracle that electricity works for us, the transmutation
-of <i>energy</i>, is a higher and broader thing, because it
-multiplies and distributes the world’s good things.</p>
-
-<hr class="chap" />
-
-<p><span class="pagenum" id="Page359">[359]</span></p>
-
-<h2 class="appendix">APPENDIX<br />
-<span class="title">A DICTIONARY OF ELECTRICAL TERMS AND PHRASES</span></h2>
-
-<p>Everybody is interested in electricity, but the ordinary reader, and
-particularly the boy who attempts to use this manual intelligently, will
-come across many technical words and terms that require explanation.
-It would be impossible to incorporate all needful definitions in the text
-proper, and the reader is therefore referred to the technical dictionary on
-the succeeding pages.</p>
-
-<p>Care has been taken in its compilation to make the definitions complete,
-simple, and concise. Some of the more advanced technical terms
-have been purposely omitted as not necessary in a book dealing with
-elementary principles. The student in the higher branches of the science
-will consult, of course, the more advanced text-books. But for our practical
-purposes this elementary dictionary should answer every requirement.
-To read it over is an education in itself, and the young experimenter
-in electrical science should always refer to it when he comes
-across a word or phrase that he does not fully understand.</p>
-
-<h3>A</h3>
-
-<p><b>A.</b> An abbreviation for the word
-anode.</p>
-
-<p><b>Absolute.</b> Complete by itself. In
-quantities it refers to fixed units. A
-galvanometer gives absolute readings
-if it is graduated to read direct amperes
-or volts. An absolute vacuum
-is one in which all residual gases are
-exhausted; an absolute void is the
-theoretical consequent. The absolute
-unit of current is measured in one,
-two, three, or more amperes or volts.</p>
-
-<p><b>A-C.</b> An abbreviation expressing
-alternating current.</p>
-
-<p><b>Acceleration.</b> The rate of change
-in velocity.</p>
-
-<p>The increase or decrease of motion
-when acted upon by the electric current.</p>
-
-<p><b>Accumulator.</b> A term applied to
-a secondary battery, commonly called
-a storage-battery.</p>
-
-<p><b>Accumulator, Electrostatic.</b> (<i>See</i>
-<a href="#Ref008">Electrostatic Accumulator</a>.)</p>
-
-<p id="Ref102"><b>Accumulator, Storage.</b> A storage-battery.</p>
-
-<p><b>Acid.</b> A compound of hydrogen
-capable of uniting with a base to
-form salts.</p>
-
-<p>Sour, resembling vinegar.</p>
-
-<p>A sharp, biting fluid.</p>
-
-<p><b>Acidometer.</b> A hydrometer used
-to determine the gravity of acids.
-It is employed chiefly in running<span class="pagenum" id="Page360">[360]</span>
-storage-batteries to determine when
-the charge is complete.</p>
-
-<p><b>Adapter.</b> A screw-coupling to
-engage with different size screws
-on either end, and used chiefly to
-connect incandescent lamps to gas-fixtures.</p>
-
-<p><b>Adherence.</b> The attraction between
-surfaces of iron due to electro-magnetic
-action. The term is used
-in connection with electric brakes&mdash;electro-magnetic
-adherence.</p>
-
-<p><b>Adjustment.</b> Any change in an
-apparatus rendering it more efficient
-and correct in its work.</p>
-
-<p><b>Aerial Conductor.</b> A wire or electric
-conductor carried over housetops
-or poles, or otherwise suspended
-in the air, as distinguished from underground
-or submarine conductors.</p>
-
-<p><b>Affinity.</b> The attraction of atoms
-and molecules for each other, due to
-chemical or electrical action.</p>
-
-<p id="Ref022"><b>Air-condenser.</b> A static condenser
-whose dielectric is air.</p>
-
-<p><b>Air-line Wire.</b> In telegraphy that
-portion of the line-wire which is
-strung on poles and carried through
-the air.</p>
-
-<p><b>Alarm, Burglar.</b> A system of circuits
-with an alarm-bell, the wires
-of which extend over a house or
-building, connecting the windows
-and doors with the annunciator.</p>
-
-<p><b>Alarm, Electric.</b> An appliance for
-calling attention, generally through
-the ringing of a bell or the operating
-of a horn.</p>
-
-<p><b>Alarm, Fire and Heat.</b> An expansion
-apparatus that automatically
-closes a circuit and rings a bell.</p>
-
-<p><b>Alive, or “Live.”</b> A term applied
-to a wire or circuit that is
-charged with electricity. A “live”
-wire.</p>
-
-<p>Active circuits or wires.</p>
-
-<p><b>Alloy.</b> Any mixture of two or
-more metals making a scientific compound.
-For example: copper and
-zinc to form brass; copper, tin, and
-zinc to form bronze; copper, nickel,
-and zinc to form German-silver.</p>
-
-<p><b>Alternating Current.</b> (<i>See</i> <a href="#Ref009">Current,
-Alternating</a>.)</p>
-
-<p><b>Alternating Current-power.</b> Electrical
-distribution employing the alternating
-current from dynamos or
-converters.</p>
-
-<p><b>Alternation.</b> A change in the
-direction of a current; to and fro.
-Alternations may take place with
-a frequency ranging from 500 to
-10,000 or more vibrations per second.</p>
-
-<p><b>Alternator.</b> An electric generator-dynamo
-supplying an alternating
-current.</p>
-
-<p><b>Amalgam.</b> A combination of mercury
-with any other metal.</p>
-
-<p><b>Amalgamation.</b> The application
-of mercury to a metal, the surface
-of which has been cleansed with acid.
-Mercury will adhere to all metals,
-except iron and steel, and particularly
-to zinc, which is treated with
-mercury to retard the corrosive
-action of acid on its surface.</p>
-
-<p><b>Amber.</b> A fossil resin, valuable
-only in frictional electric experiments.
-Most of it is gathered on
-the shores of the Baltic Sea between
-Königsberg and Memel. It is also
-found in small quantities at Gay
-Head, Massachusetts, and in the
-New Jersey green sand. When rubbed
-with a cloth it becomes excited
-with negative electricity.</p>
-
-<p><b>Ammeter.</b> The commercial name
-for an ampere-meter. An instrument
-designed to show, by direct reading,
-the number of amperes of current
-which are passing through a circuit.</p>
-
-<p><b>Ampere.</b> The practical unit of
-electric current strength. It is the
-measure of the current produced by
-an electro-motive force of one volt
-through a resistance of one ohm.</p>
-
-<p><b>Ampere-currents.</b> The currents
-theoretically assumed to be the cause
-of magnetism.</p>
-
-<p><span class="pagenum" id="Page361">[361]</span></p>
-
-<p><b>Ampere-hour.</b> The quantity of
-electricity passed by a current of one
-ampere in one hour. It is used by
-electric light and power companies
-as the unit of energy supplied by
-them, and on which they base their
-reckoning for measuring the charges
-for current consumed.</p>
-
-<p><b>Ampere-ring.</b> A conductor forming
-a ring or circle. Used in electric
-balances for measuring current.</p>
-
-<p><b>Animal Electricity.</b> A form of
-electricity of high tension generated
-in certain animal systems&mdash;the Torpedo,
-Gymnotus, and Célurus. The
-shocks given by these fish, and particularly
-the electric eel, are often
-very severe.</p>
-
-<p><b>Annealing.</b> The process of softening
-yellow metals by heating them
-to a cherry redness, then allowing
-them to cool gradually in the air.</p>
-
-<p>Electric annealing is done by passing
-a current through the body to be
-annealed, and heating it to redness;
-then allowing it to cool gradually.</p>
-
-<p><b>Annunciator.</b> An apparatus for
-giving a call from one place to another,
-as from a living-room to a
-hotel office, or for designating a
-window or door that may have been
-opened when protected by a burglar-alarm.</p>
-
-<p><b>Annunciator-drop.</b> The little
-shutter which is dropped by some
-forms of annunciators, and whose
-fall discloses a number or letter,
-designating the location from which
-the call was sent.</p>
-
-<p><b>Anode.</b> The positive terminal in
-a broken, metallic, or true conducting
-circuit.</p>
-
-<p>The terminal connected to the carbon-plate
-of a battery, or to its
-equivalent in any other form of electric
-generator, such as a dynamo or
-a voltaic pile.</p>
-
-<p>The copper, nickel, gold, or silver
-plates hung in an electro-plating
-bath, and from which the metal is
-supplied to fill the deficiency made
-by the electro-deposition of metal
-on the kathode or negative object
-in the bath.</p>
-
-<p><b>Anti-hum.</b> A shackle inserted
-directly in a line-wire near a pole.
-It is provided with a washer or
-cushion of rubber to take up the
-vibrations of a wire. To continue
-the circuit a bridle, or curved piece
-of wire, is connected with the line-wires
-that are attached to the
-shackle.</p>
-
-<p><b>Arc.</b> A term applied to an electric
-current flowing from carbon to
-carbon, or from metals separated by
-a short gap, as in the arc street-lamps.</p>
-
-<p>The original arc was produced by
-two vertical rods, through which the
-current passed up and down. When
-not in action the upper ends touched,
-but as the current flowed the ends
-were separated, so that the current,
-passing up one carbon across the
-gap and down the other, formed the
-segment of a circle in jumping from
-one tip to the other.</p>
-
-<p>An arc of electric flame is of brilliant
-and dazzling whiteness. The
-voltaic arc is the source of the most
-intense heat and light yet produced
-by man. The light is due principally
-to the incandescence of the ends
-of carbon-pencils, when a current of
-sufficient strength is passing through
-them and jumping over the gap.
-Undoubtedly the transferred carbon
-particles have much to do with its
-formation. The conductivity of the
-intervening air and the intense heating
-to which it is subjected, together
-with its coefficient of resistance, are
-other factors in the brilliant light
-produced.</p>
-
-<p><b>Arc-lamp.</b> An electric lamp
-which derives its light from the
-voltaic arc, by means of carbon-pencils
-and a current jumping from
-one to the other.</p>
-
-<p><span class="pagenum" id="Page362">[362]</span></p>
-
-<p><b>Arc, Quiet.</b> An arc free from the
-hissing sound so common in arc-lights.</p>
-
-<p><b>Arc, Simple.</b> A voltaic arc produced
-between only two electrodes.</p>
-
-<p><b>Armature.</b> A body of iron or other
-material susceptible to magnetization,
-and which is placed on or near
-the poles of a magnet.</p>
-
-<p>That part of an electric mechanism
-which by magnetism is drawn
-to or repelled from a magnet.</p>
-
-<p>The core of a dynamo or motor
-which revolves within the field
-magnets, and which is the active
-principle in the generation of current
-by mechanical means, or in
-the distribution of power through
-electrical influence. Armatures are
-sometimes made of steel, and are
-permanent magnets. These are used
-in magneto-generators, telegraph instruments,
-and other apparatus.</p>
-
-<p><b>Armature-bar.</b> An armature in a
-dynamo or motor whose winding is
-made up of conductors in the form
-of bars.</p>
-
-<p><b>Armature-coil.</b> The insulated
-wire wound around the core of the
-armature of an electric current-generator
-or motor.</p>
-
-<p><b>Armature-core.</b> The central mass
-of iron on which the insulated wire is
-wound; it is rotated in the field of an
-electric current-generator or motor.</p>
-
-<p><b>Armored.</b> Protected by armor;
-as cables may be surrounded by a
-proper sheathing to guard them from
-injury.</p>
-
-<p><b>Astatic.</b> Having no magnetic directive
-tendency, the latter being a
-general consequent of the earth’s
-magnetism.</p>
-
-<p><b>Astatic Circuit.</b> (<i>See</i> <a href="#Ref010">Circuit,
-Astatic</a>.)</p>
-
-<p><b>Astatic Couple.</b> (<i>See</i> <a href="#Ref011">Couple, Astatic</a>.)</p>
-
-<p><b>Astatic Needle.</b> A combination
-of two magnetic needles so adjusted
-as to have as slight directive tendency
-as possible. The combination is
-generally made up of two needles
-arranged one above the other with
-the poles in opposite directions&mdash;commonly
-called “Nobili’s Pair.”
-These needles require but a slight
-electro-force to turn them one way
-or the other, and are used in astatic
-galvanometers.</p>
-
-<p><b>Atmospheric Electricity.</b> (<i>See</i>
-<a href="#Ref012">Electricity, Atmospheric</a>.)</p>
-
-<p><b>Atom.</b> The ultimate particle or
-division of an elementary substance.
-Electricity is largely responsible for
-the presence of atoms in the atmosphere.</p>
-
-<p><b>Atomic Attraction.</b> The attraction
-of atoms for each other. Principally
-due to electric disturbance.</p>
-
-<p><b>Attraction.</b> The tendency to approach
-and adhere or cohere which
-is shown in all forms of matter. It
-includes gravitation, cohesion, adhesion,
-chemical affinity, electro-magnetic
-and dynamic attraction.</p>
-
-<p><b>Aurora.</b> A luminous electric display
-seen in the northern heavens.
-It is commonly thought to be the
-electric discharges of the earth into
-the atmosphere, due to revolution of
-the former and to the heat produced
-at the equator. As compared to
-the static machine for generating
-frictional electricity, the earth represents
-the revolving wheel gathering
-the current and discharging it
-at the poles.</p>
-
-<p><b>Automatic Cut-out.</b> An electro-magnetic
-switch introduced into a
-circuit, so as to break the circuit of
-the latter should it become overloaded
-with current; it also acts in
-the event of a mechanical interruption.</p>
-
-<p><b>Automatic Regulation.</b> A speed
-regulator worked by electricity so
-that a uniform flow of current may
-be secured automatically.</p>
-
-<p id="Ref023"><b>Ayrton’s Condenser.</b> This is a
-pile of glass plates separated by<span class="pagenum" id="Page363">[363]</span>
-small pieces of glass at the four
-comers, so that the plates cannot
-touch each other. Tin-foil is pasted
-on both sides of every plate, and
-the two coatings are connected.
-The tin-foil on each second plate is
-smaller in area than that on the
-others, and the plates are connected
-in two sets, negative and positive.
-In this construction it will be seen
-that the glass is not the dielectric
-proper, but acts only as the plane
-to which the tin-foil is pasted.
-One set of plates are connected to
-a binding-post by strips of tin-foil,
-and the other set are connected to
-another binding-post in a similar
-manner.</p>
-
-<h3>B</h3>
-
-<p><b>B.</b> An abbreviation for Beaumé,
-the inventor of the hydrometer scale.
-Thus, in speaking of the gravity of
-fluids, 20° B. means twenty degrees
-Beaumé.</p>
-
-<p><b>Back Induction.</b> A demagnetizing
-force produced in a dynamo
-when a lead is given to the brushes.
-(<i>See also</i> <a href="#Ref012a">Induction, Back</a>.)</p>
-
-<p><b>Back Shock.</b> A lightning stroke
-received after the main discharge.
-It is caused by a charge induced in
-neighboring surfaces by the main
-discharge.</p>
-
-<p><b>Bad Earth.</b> A poor ground connection,
-or one having comparatively
-strong electrical resistance.</p>
-
-<p><b>Balance.</b> A proper adjustment between
-the apparatus and the electro-motive
-force, thus securing the best
-possible results.</p>
-
-<p><b>B. &amp; S. W-G.</b> Abbreviations
-for Brown &amp; Sharp and wire-gauge,
-and referring to the sizes of wire
-and sheet-metal thicknesses that
-are considered standards in America.</p>
-
-<p><b>Bar-armature.</b> An armature in
-which the conductors are constructed
-of bars.</p>
-
-<p id="Ref063"><b>Bar-magnet.</b> One whose core
-presents the appearance of a straight
-bar, or rod, without curve or bend.</p>
-
-<p id="Ref015"><b>Bare-carbons.</b> Electric light carbons
-whose surfaces are not electro-plated
-with copper.</p>
-
-<p><b>Barometer.</b> An apparatus for
-measuring the pressure exerted by
-the atmosphere. It consists of a
-glass tube 31 inches long, closed at
-one end, filled with mercury, and
-then inverted, with its open end
-immersed in a cistern of mercury.
-The column of mercury falls to a
-height proportional to the pressure
-of the atmosphere. At the sea-level
-it ranges from 30 to 31 inches.</p>
-
-<p><b>Bar-windings.</b> The windings of an
-armature constructed of copper bars.</p>
-
-<p><b>Bath.</b> In electro-plating, the solution
-or electrolyte used for depositing
-metal on the object to be
-plated. It may be a solution of copper,
-silver, nickel, or other metal.</p>
-
-<p>In electro-therapeutics it is a
-bath of water with suitable electrodes
-and connections for treating
-patients with electricity.</p>
-
-<p><b>Bath-stripping.</b> A solution used
-for stripping or removing the metal
-plating from an object.</p>
-
-<p><b>Batten.</b> A strip of wood grooved
-longitudinally, in which electric
-light or power wires are set. The
-grooved strip is screwed to the wall,
-the wires being laid in the grooves,
-and then covered with a thin wooden
-strip fastened on with small nails.</p>
-
-<p><b>Battery.</b> A combination of parts,
-or elements, for the production of
-electrical action.</p>
-
-<p>A number of cells connected parallel
-or in series for the generation
-of electricity. Under this heading
-there are at least one hundred different
-kinds. Nowadays the dynamo
-is the cheap and efficient generator
-of electricity.</p>
-
-<p id="Ref038"><b>Battery Cell, Elements of.</b> The
-plates of zinc and carbon, or of zinc<span class="pagenum" id="Page364">[364]</span>
-and copper, in a cell are called elements.
-The plate unattacked by the
-solution, such as the carbon or copper,
-is the negative element, while
-the one attacked and corroded by
-the electrolyte is the positive.</p>
-
-<p id="Ref028"><b>Battery, Dry.</b> A form of open
-circuit cell in which the electrolyte
-is made practically solid, so that the
-cell may be placed in any position.
-A zinc cup is filled with the electrolyte
-and a carbon-rod placed in the
-middle, care being taken to avoid
-contact between cup and carbon at
-the bottom of the cell. The gelatinous
-chemical mass is then packed
-in closely about the carbon, so as to
-nearly fill the cup. A capping of asphaltum,
-wax, or other non-conducting
-and sealing material is placed
-over the electrolyte, and this hardens
-about the carbon and around the top
-inner edge of the zinc cup. The latter
-becomes the positive pole, the
-carbon the negative. Binding-posts,
-or connections, may be attached to
-the zinc and carbon to facilitate connections.</p>
-
-<p><b>Battery, Galvanic.</b> The old name
-for a voltaic battery.</p>
-
-<p id="Ref045"><b>Battery, Gravity.</b> A battery in
-which the separation of fluids is obtained
-through their difference in
-specific gravity&mdash;for example, the
-bluestone cell. The sulphate of copper
-solution, being the more dense,
-goes to the bottom, while the zinc
-solution stays at the top. In its action
-the acid at the top corrodes
-the zinc, while at the bottom the solution
-is decomposed and deposits
-metallic copper on the thin copper
-plates.</p>
-
-<p id="Ref060"><b>Battery, Leclanché.</b> An open circuit
-battery consisting of a jar, a
-porous cup, and the carbon and
-zinc elements, the electrolyte of
-which is a solution of ammonium
-chloride (sal-ammoniac). The carbon
-plate is placed in the porous cup,
-and packed in with a mixture of
-powdered manganese binoxide and
-graphite, to serve as a depolarizer.
-A half-saturated solution of sal-ammoniac
-is placed in the outer jar,
-and a rod of zinc suspended in it.
-Another form of the battery is to
-omit the porous cup and use twice
-the bulk of carbon, both elements
-being suspended in the one solution
-of sal-ammoniac; this form of battery
-is used for open-circuit work
-only, such as bells, buzzers, and annunciators.
-It is not adapted for
-lights, power, or plating purposes.</p>
-
-<p><b>Battery Mud.</b> A deposit of mud-like
-character which forms at the
-bottom of gravity batteries, and
-which consists of metallic copper
-precipitated by the zinc. It only
-occurs where wasteful action has
-taken place.</p>
-
-<p><b>Battery of Dynamos.</b> A term
-used in speaking of a number of
-dynamos coupled to supply the
-same circuit. They may be coupled
-in series or parallel.</p>
-
-<p id="Ref078"><b>Battery, Plunge.</b> A battery in a
-cabinet or frame, so arranged that
-the active plates can be removed
-or raised out of the solutions. This
-is usually accomplished by having
-the plates attached to a movable
-frame which, by means of a ratchet-shaft
-and chains, can be raised or
-lowered. Its object is to prevent
-the corrosion of the plates when not
-in use.</p>
-
-<p id="Ref081"><b>Battery, Primary.</b> A voltaic cell
-or battery generating electric energy
-by direct consumption of material.
-The ordinary voltaic cell, or galvanic
-battery, is a primary battery.</p>
-
-<p id="Ref092"><b>Battery, Secondary.</b> A storage-battery,
-an accumulator.</p>
-
-<p><b>Battery Solution.</b> The active excitant
-liquid, or electrolyte, placed
-within a cell to corrode the positive
-element. Also called Electropoion.</p>
-
-<p><span class="pagenum" id="Page365">[365]</span></p>
-
-<p id="Ref103"><b>Battery, Storage.</b> A secondary
-battery; an accumulator; a battery
-which accumulates electricity generated
-by primary cells or a dynamo.</p>
-
-<p><b>Battery-gauge.</b> A galvanometer
-used for testing batteries and connections.
-It is usually small in size,
-and may be carried in a pocket.</p>
-
-<p><b>Battery-jar.</b> A glass, earthen, or
-lead vessel which contains the fluids
-and elements of each separate cell
-of a battery.</p>
-
-<p><b>Baumé Hydrometer.</b> (<i>See</i> <a href="#Ref013">Hydrometer,
-Baumé</a>.)</p>
-
-<p><b>Becquerel Ray and Radiation.</b> An
-invisible ray discovered by Becquerel,
-which is given out by some
-compounds and chemicals&mdash;notably
-uranium&mdash;and which has the power
-to penetrate many opaque bodies
-and objects impenetrable to the actinic
-rays of ordinary light. These
-rays are used chiefly in connection
-with the photographic dry-plate.</p>
-
-<p><b>Bell, Electric.</b> A bell rung by
-electricity. The current excites an
-electro-magnet, attracting or releasing
-an armature which is attached
-to a vibrating or pivoted
-arm, on the end of which the knocker
-is fastened.</p>
-
-<p><b>Bichromate of Potash.</b> A strong,
-yellowish-red chemical, used chiefly
-in battery fluids and electrolytes.</p>
-
-<p><b>Bifilar Winding.</b> The method
-followed in winding resistance-coils.
-To prevent them from creating fields
-of force, the wire is doubled and the
-looped end started in the coil.
-Since the current passes in opposite
-senses in the two lays of the winding,
-no field of force is produced.</p>
-
-<p><b>Binding.</b> Unattached wire wound
-round armature-coils to hold them
-in place.</p>
-
-<p><b>Binding-post.</b> An arrangement
-for receiving the loose ends of wires
-in an electric circuit and securing
-them, by means of screws, so that
-perfect contact will be the result.</p>
-
-<p><b>Bi-polar.</b> Possessing two poles.</p>
-
-<p><b>Bi-telephone.</b> A pair of telephones
-arranged with a curved connecting
-arm or spring so that they
-can be simultaneously applied to
-both ears.</p>
-
-<p><b>Blasting, Electric</b>. The ignition
-of a blasting charge of powder,
-dynamite, or other high explosive
-by an electric spark, or by the heating,
-to red or white heat, of a thin
-wire imbedded in the explosive.</p>
-
-<p><b>Block System.</b> A system of signalling
-on railroads. Signal-posts
-are arranged at stated spaces, and
-on these signals appear automatically,
-showing the location of trains to
-the engineers of trains in the rear.</p>
-
-<p><b>Bluestone.</b> A trade name for sulphate
-of copper in a crystallized
-state.</p>
-
-<p><b>Bobbin.</b> A spool of wood or other
-non-conducting substance wound
-with insulated wire. In a tangent
-galvanometer the bobbin becomes a
-ring with a channel to receive the
-wire.</p>
-
-<p><b>Boiling.</b> In secondary, or storage,
-batteries the escaping of hydrogen
-and oxygen gases, when the battery
-is fully charged, resembles water
-boiling.</p>
-
-<p><b>Bonded Rails.</b> Rails used in an
-electric traction system, and which
-are linked or connected together to
-form a perfect circuit. Used principally
-in the third-rail system.</p>
-
-<p><b>Brake, Electro-magnetic.</b> A
-brake to stop the wheels of a moving
-car. It consists of a shoe, or
-ring, which by magnetic force is
-drawn against a rotating wheel to
-stop its revolution.</p>
-
-<p><b>Branch.</b> A conductor which leads
-off from a main line to distribute
-current locally.</p>
-
-<p><b>Brassing.</b> A process of electro-depositing
-brass in a bath containing
-both copper and zinc. A plate
-of brass is used as an anode.</p>
-
-<p><span class="pagenum" id="Page366">[366]</span></p>
-
-<p><b>Brazing, Electric.</b> A process in
-which the spelter is melted by electric
-current, so that the two parts
-are united as one.</p>
-
-<p><b>Break.</b> A point where an electric
-conductor is broken, as by a
-switch or a cut-out.</p>
-
-<p><b>Bridge.</b> A special bar of copper
-connecting the dynamos with the
-bus wire in electric lighting or power
-stations.</p>
-
-<p><b>Bronzing.</b> The deposition of
-bronze by electro-plating methods.
-The mixture is of copper and tin, and
-a cast bronze plate is used as an
-anode.</p>
-
-<p><b>Brush.</b> A term applied to the
-pieces of copper, carbon, or other
-conducting medium in dynamos and
-motors, that bear against the cylindrical
-surface of the commutators
-to collect or feed in the current.</p>
-
-<p><b>Bug.</b> Any fault or trouble in
-the connections or workings of an
-electrical apparatus. The term originated
-in quadruplex telegraphy,
-and probably had some connection
-with the Edison bug-killer that he
-invented when a boy.</p>
-
-<p><b>Buoy, Electric.</b> A buoy to indicate
-dangerous channels in harbors
-and to mark wrecks and reefs.
-It is provided with an electric light
-at night, and with a gong or an electric
-horn by day.</p>
-
-<p><b>Burner, Electric.</b> A gas-burner
-so arranged that the flame may be
-lighted by electricity operated by
-a push-button at some distance from
-the fixture, or, close at hand, by
-means of a chain or pull-string.</p>
-
-<p><b>Burning.</b> In a dynamo, the improper
-contact of brushes and commutator,
-whereby a spark is produced
-and an arc formed which
-generates heat and causes the metal
-parts to burn.</p>
-
-<p><b>Bus-rod.</b> A copper conductor
-used in power-plants to receive the
-current from the battery of dynamos.
-The distributing leads are connected
-to these rods.</p>
-
-<p><b>Butt-joint.</b> A joint made by
-bringing the ends of wires together
-so that the ends butt. They are
-then soldered or brazed.</p>
-
-<p><b>Button, Electric.</b> A form of
-switch that is operated by pushing
-a button mounted on a suitable
-base. Used principally for ringing
-bells, operating lights, etc.</p>
-
-<p><b>Buzzer.</b> An electric alarm, or
-call, produced by the rapid vibration
-of an armature acted upon by
-electro-magnetism. The sound is
-magnified by enclosing the mechanism
-in a resonant box.</p>
-
-<p>An apparatus resembling an electric
-bell <i>minus</i> the bell and clapper.
-The buzzer is used in places where
-the loud ring of a bell would be a
-nuisance.</p>
-
-<h3>C</h3>
-
-<p><b>C.</b> An abbreviation for centigrade
-when speaking of thermal
-temperature. In chemistry the
-centigrade scale is used extensively,
-but in air temperatures the Fahrenheit
-scale is universally employed.</p>
-
-<p><b>Cable, Aerial.</b> A cable that contains
-a number of wires separately
-insulated, the entire mass being protected
-by an external insulation.
-It is suspended in the air from pole
-to pole, and sometimes its weight
-is so great that a supporting wire is
-carried along with it (usually overhead),
-the large cable being suspended
-from it by cable-hangers.</p>
-
-<p><b>Cable Box</b>. A box to receive cable
-ends and protect them; also, the box
-in which cable ends and line-wires are
-joined. Submarine cable boxes are
-usually near the ground, while telephone
-and telegraph cable boxes are
-mounted on poles, the cables running
-from the ground and up the
-poles to the boxes.</p>
-
-<p><b>Cable-core.</b> The conductors of a<span class="pagenum" id="Page367">[367]</span>
-cable which make up its interior
-mass. For the convenience of linemen
-the wires are often insulated
-with different-colored materials so
-that testing is not necessary when
-making connections.</p>
-
-<p><b>Cable-hanger.</b> A metallic grip,
-usually of sheet metal, arranged to
-clasp two or more wires. It is fastened
-to the supporting wire by a
-hook and eye, or by small bolts with
-thumb-nuts.</p>
-
-<p><b>Cable-head.</b> A rectangular board
-equipped with binding-posts and
-fuse wires so that the connections
-may be made between the cable ends
-and the overhead or line-wires of a
-system.</p>
-
-<p><b>Cables.</b> An insulated electric
-conductor of large diameter, often
-protected by armor or metallic
-sheathing, and generally containing,
-or made up, of several separately
-insulated wires. Cables supply current
-to traction lines; power, through
-subterranean passages; communication,
-by submarine connection; and
-light, by overhead or underground
-conduits.</p>
-
-<p><b>Call-bell.</b> A bell that is rung by
-pressing a button, and which is
-operated by electricity.</p>
-
-<p><b>Calling-drop.</b> A drop-shutter
-which is worked by electricity in a
-telegraph or telephone exchange; it
-denotes the location from which the
-call was sent in. Small red incandescent
-lamps have taken the place
-of the drops in most of the large telephone
-exchanges, for they are noiseless
-and do not annoy the operators
-as the drops and buzzers did.</p>
-
-<p><b>Candle-power.</b> The amount of
-light given by the standard candle.
-The legal English and American
-standard is a sperm candle burning
-two grains a minute.</p>
-
-<p id="Ref100"><b>Candle, Standard.</b> The standard
-of illuminating power; a flame
-which consumes two grains of sperm
-wax per minute, and produces a light
-of a brightness equal to one candle-power.</p>
-
-<p id="Ref053"><b>Caoutchouc.</b> India-rubber. So
-named because originally its chief
-use was to erase or rub off pencil
-marks. It is a substance existing,
-in a thick fluid state, in the sap or
-juices of certain tropical trees and
-vines; it possesses a very high value
-as an insulator for wire and circuits.
-The unworked, crude rubber is called
-virgin gum, but after it is kneaded
-it is called masticated or pure gum
-rubber.</p>
-
-<p><b>Capacity.</b> A term used when
-speaking of the carrying power of a
-wire or circuit. The capacity of a
-wire, rod, bar, or other conductor
-is sufficient so long as the current
-does not heat it. Directly electric
-heat is generated, we speak of the
-conductor as being overloaded or
-having its capacity overtaxed.</p>
-
-<p><b>Capacity of a Telegraph Conductor.</b>
-The electric capacity may
-be identical in quality with that of
-any other conductor. In quantity
-it varies not only in different wires,
-but for the same wire under different
-conditions. A wire reacting through
-the surrounding air, or other dielectric,
-upon the earth represents
-one element of a condenser, the
-earth in general representing the
-other. A wire placed near the
-earth has greater capacity than one
-strung upon high poles, although
-the wires may be of identical length
-and size and of the same metal.
-The effect of high capacity is to retard
-the transmission of current,
-the low capacity facilitates transmission.</p>
-
-<p><b>Capacity, Storage.</b> In secondary
-batteries, the quantity of electric
-current they can supply, when fully
-charged, without exhaustion. This
-capacity is measured or reckoned in
-ampere-hours.</p>
-
-<p><span class="pagenum" id="Page368">[368]</span></p>
-
-<p><b>Carbon.</b> One of the elements in
-graphitic form used as an electric-current
-conductor. It is the only
-substance which conducts electricity,
-and which cannot be melted with
-comparative ease by increase of
-current. It exists in three modifications&mdash;charcoal,
-graphite, and the
-diamond. In its graphitic form it
-is used as an electro-current conductor,
-as in batteries and arc-light
-electrodes, and as filaments in incandescent
-lamps. In arc-lamp use
-the carbons are usually electro-plated
-on the outside with a film of
-copper which acts as a better conductor.</p>
-
-<p><b>Carbon, Artificial.</b> Carbon-dust,
-powdered coke, or gas carbon is
-mixed with molasses, coal-tar, syrup,
-or some similar carbonaceous fluid,
-so that the mass is plastic. It can
-then be moulded or pressed into
-shapes, and heated to full redness for
-several hours by artificial or electric
-heat. For lamp-carbons the mixture
-is forced through a round die
-by heavy pressure, and is cut into
-suitable lengths, then fired or baked.</p>
-
-<p>After removing and cooling, the
-carbons are sometimes dipped again
-into the fluid used for cementing the
-original mass and re-ignited. This
-process is termed “nourishing.” All
-carbon is a resisting medium, but at
-high temperature the resistance is
-only about one-third as great; that
-is, the current will pass through a
-red-hot carbon three times better
-than through the cold carbon; or a
-current of thirty amperes will be conducted
-as easily through a hot carbon
-as ten amperes through a cold one.</p>
-
-<p><b>Carbon-cored.</b> A carbon for arc-lamps,
-the core being of softer carbon
-than the outer surface. It is
-supposed to give a steadier light,
-and fixes the position of the arc.</p>
-
-<p><b>Carbon-dioxide.</b> A compound gas,
-or carbonic-acid gas. It is a dielectric.</p>
-
-<p><b>Carbon-holders.</b> In arc-lamps,
-the clamps arranged to hold the carbon-pencils.</p>
-
-<p><b>Carbonization.</b> The ignition of
-an organic substance in a closed vessel,
-so as to expel all constituents
-from it except the carbon.</p>
-
-<p>A destructive distillation.</p>
-
-<p><b>Carbon Resistance.</b> (<i>See</i> <a href="#Ref014">Resistance,
-Carbon</a>.)</p>
-
-<p><b>Carbon Volatilization.</b> In arc-lamps
-the heat is so intense that it
-is believed a part of the carbon-pencil
-is volatilized, as vapor, before
-being burned or oxidized by the
-oxygen of the air.</p>
-
-<p><b>Carbons, Bare</b>. (<i>See</i> <a href="#Ref015">Bare Carbons</a>.)</p>
-
-<p><b>Carrying Capacity.</b> In a current-conductor,
-its carrying capacity up
-to the heating-point. It is expressed
-in amperes.</p>
-
-<p><b>Cascade.</b> The arrangement of a
-series of Leyden-jars in properly
-insulated stools, or supports, for
-accumulating frictional electricity.
-They are arranged in a manner somewhat
-similar to a battery of galvanic
-cells, the inner coating of one being
-connected to the outer coating of
-the next, and so on through the
-series.</p>
-
-<p><b>Case-hardening, Electric.</b> A process
-by which the surface of iron is
-converted into steel by applying a
-proper carbonaceous material to it
-while it is being heated by an electric
-current.</p>
-
-<p><b>Cautery, Electric.</b> An electro-surgical
-appliance for removing diseased
-parts or arresting hemorrhages.
-It takes the place of the
-knife or other cutting instrument.
-It is a loop of platinum wire heated
-to whiteness by an electric current.</p>
-
-<p><b>C.C.</b> An abbreviation commonly
-used for cubic-centimeter. It is
-usually written in small letters, as 50
-c.c., meaning 50 cubic-centimeters.</p>
-
-<p><b>Cell, Electrolytic.</b> A vessel containing<span class="pagenum" id="Page369">[369]</span>
-the electrolyte used for electro-plating.</p>
-
-<p><b>Cell, Regenerated.</b> A cell restored
-to its proper functions by a process
-of recharging.</p>
-
-<p><b>Cell, Standard.</b> Meaning the same
-as battery. The vessel, including
-its contents, in which electricity is
-generated.</p>
-
-<p><b>Cell, Storage.</b> Two plates of
-metal, or compounds of metal, whose
-chemical relations are changed by
-the passage of an electric current
-from one plate to the other through
-an electrolyte in which they are immersed.</p>
-
-<p><b>Cements, Electrical.</b> Cements of
-a non-conducting nature, such as
-marine glue and sticky compounds,
-used in electrical work.</p>
-
-<p><b>Centrifugal Force.</b> A diametric
-revolving force which throws a
-body away from its axis of rotation.
-A merry-go-round is a simple example
-of this force. The more
-rapidly the platform revolves the
-greater the tendency for those on
-it to be thrown off and out from the
-centre. The high velocity attained
-by the armatures in motors and
-dynamos would throw the wires out
-of place and cause them to rub
-against the surfaces of the field-magnets.
-Consequently, wire bands
-or binders are necessary to keep the
-coils of wire from spreading under
-the influence of the centrifugal force.</p>
-
-<p><b>Charge.</b> The quantity of electricity
-that is present on the surface
-of a body or conductor.</p>
-
-<p>The component chemical parts
-that are employed to excite the elements
-of a cell in generating electric
-current.</p>
-
-<p id="Ref085"><b>Charge, Residual.</b> After a Leyden-jar,
-or other condenser, has been
-discharged by the ordinary methods,
-a second discharge (of less
-amount) can be had after a few
-minutes’ waiting. This is due to
-what is known as the residual
-charge, and is connected in some
-way with the molecular distortion
-of the dielectric.</p>
-
-<p><b>Chemical Change.</b> When bodies
-unite so as to satisfy affinity, or to
-bring about the freeing of thermal or
-other energy, the union is usually
-accompanied by sensible heat or
-light. Sulphuric acid added to water
-produces heat; a match in burning
-produces light. Another form
-of chemical change is decomposition
-or separation (the reverse of combination),
-such as takes place in the
-voltaic-battery, the electro-plating
-bath, and other forms of electrolysis.
-This is not accompanied by heat
-or light, but by the evolution of electricity.</p>
-
-<p><b>Chemical Element.</b> (<i>See</i> <a href="#Ref016">Element,
-Chemical</a>.)</p>
-
-<p><b>Chemistry.</b> The science which
-treats of the atomic and molecular
-relations of the elements and their
-chemical compounds. Chemistry is
-divided into many departments, but
-electro-chemistry treats only of the
-science wherein electricity plays an
-active part, such as batteries, electro-plating,
-and electro-metallurgy.</p>
-
-<p><b>Choking-coil.</b> (<b>See</b> <a href="#Ref017">Coil, Choking</a>.)</p>
-
-<p><b>Circle, Magic.</b> A form of electro-magnet.
-It is a thick circle of
-round iron used in connection with
-a magnetized coil to illustrate electro-magnetic
-attraction.</p>
-
-<p><b>Circuit.</b> A conducting-path for
-electric currents. Properly speaking,
-a complete circuit has the ends
-joined, and includes a source of current,
-an apparatus, and other elements
-introduced in the path. When
-the circuit is complete it is called
-active. The term circuit is also
-applied to portions of a true circuit&mdash;as,
-an internal or external circuit.</p>
-
-<p id="Ref010"><b>Circuit, Astatic.</b> A circuit so
-wound, with reference to the direction
-of the currents passing through<span class="pagenum" id="Page370">[370]</span>
-it, that the terrestrial or other lines
-of force have no directive effect
-upon it.</p>
-
-<p id="Ref025"><b>Circuit-breaker.</b> Any apparatus
-for opening and closing a circuit,
-such as switches, automatic cut-outs,
-lightning-arresters, and the like.</p>
-
-<p>A ratchet-wheel engaged with a
-spring, or wire, which rests against
-the teeth. The current passes
-through the wire, the wheel, and
-axle. The wheel is revolved by a
-crank, and as the ratchets pass the
-spring, or wire, an instantaneous
-make-and-break occurs. The speed
-of the wheel regulates the frequency
-of the interruptions.</p>
-
-<p id="Ref039"><b>Circuit, External.</b> A portion of
-the circuit not included within the
-generator, such as a secondary telegraph
-key and sounder.</p>
-
-<p id="Ref046"><b>Circuit, Grounded.</b> A circuit in
-which the ground is used as a conductor.
-This is common in telegraph
-and telephone lines, particularly
-for short distances where the
-conductivity of the earth does not
-offer too much resistance.</p>
-
-<p id="Ref050"><b>Circuit, Incandescent.</b> A circuit
-in which incandescent lamps are installed.</p>
-
-<p><b>Circuit Indicator.</b> A pocket-compass,
-galvanometer, or other device
-for indicating or detecting the condition
-of a wire, whether it is active
-or dead, and, if active, in which direction
-the current is flowing. It
-may also give a general idea of its
-strength.</p>
-
-<p id="Ref056"><b>Circuit, Internal.</b> That portion
-of an electric circuit which is included
-within the generator.</p>
-
-<p><b>Circuit Loop.</b> A minor circuit introduced,
-in series, into another circuit
-by a switch or cut-out, so that it
-becomes a part of the main circuit.</p>
-
-<p id="Ref066"><b>Circuit, Main.</b> a circuit or main
-line, includes the apparatus supplying
-current to it. Thus distinguished
-from a local circuit.</p>
-
-<p id="Ref068"><b>Circuit, Metallic.</b> A circuit in
-which the current outside the generator
-passes through metal parts
-or wire, but not through the ground.
-Electric light and power lines are
-always metallic circuits. An electro-plating
-apparatus may be properly
-termed a metallic circuit, although
-a part of the circuit is formed
-by the electrolyte in the bath. The
-essential meaning of the words metallic
-circuit is that the earth does not
-form a part of the return circuit.</p>
-
-<p id="Ref073"><b>Circuit, Open.</b> A circuit in which
-a switch has been opened to prevent
-the continuous flow of current,
-such as an electric-bell circuit, which
-normally remains open, and which
-is active only when the push-button
-is pressed, thereby closing the circuit
-and operating the bell. An open-circuit
-battery is one that remains
-inactive when the circuit is open.</p>
-
-<p><b>Circuit, Parallel.</b> A term signifying
-a multiple circuit.</p>
-
-<p id="Ref083"><b>Circuit, Quadruple.</b> A single circuit
-capable of having four messages
-transmitted over it simultaneously&mdash;two
-in one direction, and two in the
-other.</p>
-
-<p id="Ref089"><b>Circuit, Return.</b> In telegraphy
-the ground is used as the return circuit.
-It is also that portion of a
-circuit which leads from an apparatus
-back to the terminal of a dynamo
-or battery, usually the negative
-wire.</p>
-
-<p id="Ref094"><b>Circuit, Short.</b> A connection between
-two parts of a circuit, causing
-the current to skip a great part of
-its appointed path. Short-circuits
-prevent the proper working of any
-electrical apparatus.</p>
-
-<p id="Ref095"><b>Circuit, Simple.</b> A circuit containing
-a single generator, the proper
-wire for carrying the current, and
-a switch to operate it. An electric-bell
-line, a single telegraph line, or
-a direct telephone line are all simple
-circuits.</p>
-
-<p><span class="pagenum" id="Page371">[371]</span></p>
-
-<p><b>Clamp.</b> A tool for grasping and
-holding the ends of wires while joining
-them.</p>
-
-<p>The appliance for holding the carbon-pencils
-in arc-lamps.</p>
-
-<p><b>Cleats.</b> Blocks of wood, porcelain,
-or other insulating material
-used to hold wires against a wall or
-beam. They have one, two, and
-three notches at one side, for single,
-double, and three wire systems.</p>
-
-<p><b>Clutch, Electric.</b> A form of magnetic
-brake applied to car-wheels,
-the armatures of motors, and other
-revolving mechanism, whereby the
-current, passing through a coil,
-magnetizes a mass of cast-iron, and
-brings it to bear frictionally upon
-the moving parts of the mechanism.</p>
-
-<p><b>Code, Cipher.</b> A set of disconnected
-words which, in accordance
-with a prearranged key, stand for
-whole sentences and phrases. Commercially
-the system is used as a
-short-cut&mdash;ten words perhaps meaning
-what otherwise it would take
-forty or fifty words to express. It is
-used extensively in telegraphy, both
-as an abbreviated message and as a
-means for securing secrecy.</p>
-
-<p><b>Coherer.</b> Conducting particles
-constituting a semi-conducting
-bridge between two electrodes, and
-serving to detect electro-magnetic
-waves. The coherer in wireless
-telegraphy is understood to mean
-that form of radio-receiver which,
-being normally at high resistance, is,
-under the influence of Hertzian-waves,
-changed to a low resistance,
-thus becoming relatively a conductor.
-Tubes of various kinds
-have been used for this purpose.
-Within them is a filling of carbon
-granules, copper filings, nickel and
-silver filings, and other substances.
-Marconi’s coherer consists of a tube
-one and one-half inches long and
-one-twelfth inch internal diameter.
-This is filled with filings&mdash;90 per
-cent. of nickel, 10 per cent. of silver.
-A globule of mercury coats the outer
-surface of each grain with a thin
-film of the quicksilver. Into both
-ends a piece of pure silver wire is
-plugged. These latter are a quarter
-of an inch long, and fit the tube
-very accurately. The tube is thus
-sealed, and it is considered preferable
-to have a slight vacuum within
-it.</p>
-
-<p><b>Coil.</b> A strand of wire wound in
-circular form about a spool, a soft-iron
-core, or in layers, as a coil of
-rope.</p>
-
-<p>An electro-magnetic generator.</p>
-
-<p>A helix. (<i>See also</i> <a href="#Ref012a">Induction</a>, <a href="#Ref019">Resistance</a>,
-<a href="#Ref020">Magnetizing</a>.)</p>
-
-<p id="Ref017"><b>Coil, Choking.</b> A form of resistance
-to regulate the flow of current.
-Any coil of insulated wire wound
-upon a laminated or divided iron
-core forms a choking-coil. In alternating-current
-work special choking-coils
-are used. They have a movable
-iron core, and by thrusting it
-in or out the power is increased or
-diminished, thus raising or lowering
-the lights, the same as gas is regulated.</p>
-
-<p id="Ref041"><b>Coil, Faradic.</b> The name given
-to a medical induction-coil or faradic
-machine.</p>
-
-<p id="Ref055"><b>Coil, Induction.</b> A coil in which
-the electro-motive force of a portion
-of a circuit is, by induction, made
-to produce higher or lower electro-motive
-forces in an adjacent circuit,
-or in a circuit a part of which adjoins
-the original circuit. There
-are three principal parts to all induction-coils&mdash;the
-core, the primary
-coil, and the secondary coil.
-The core is a mass of soft iron, cast
-or wrought, but preferably divided&mdash;for
-example, a bundle of rods or
-bars. The primary coil of comparatively
-larger wire is wound
-about this core, each layer being
-properly insulated and varnished, or<span class="pagenum" id="Page372">[372]</span>
-coated with melted paraffine, to
-bind the wires. The secondary coil
-is of fine wire, and is wound about
-the primary coil. A great many
-turns of the fine wire are necessary,
-and care must be taken to properly
-insulate each layer and shellac the
-wires. The primary must be well
-insulated from the secondary coil,
-so as to prevent sparking, which
-would destroy the insulation. A
-make-and-break is operated by the
-primary coil, and is constructed
-upon the general form of an electric
-bell or buzzer movement. Extra
-currents which interfere with the
-action of an induction-coil are
-avoided by the use of a condenser.
-(<i>See also</i> <a href="#Ref021">Condenser</a>.) The induction-coil
-produces a rapid succession of
-sparks which may spring across a
-gap of thirty or forty inches, according
-to the size of the coil. Induction-coils
-are used extensively in electric
-work, especially in telephone transmitters,
-wireless telegraphy, electric
-welding, and in the alternating-current
-system.</p>
-
-<p id="Ref065"><b>Coil, Magnetizing.</b> A coil of insulated
-wire so wound that a well
-or aperture will be formed. Within
-this well a piece of steel is placed, so
-that an electric current, passing
-through the wires, will magnetize the
-steel; or a steel rod may be passed
-in and out of the hole several times
-while a strong current is travelling
-through the coil, thus magnetizing
-the rod.</p>
-
-<p id="Ref086"><b>Coil, Resistance.</b> A coil so constructed
-that it will offer resistance
-to a steady current of too great
-electro-motive force for the safety
-of the apparatus. Generally the
-coil is made by doubling the wire
-without breaking it, then starting
-at the doubled end to wind it in
-coil or spring fashion. If the wire
-is too heavy to wind double, a single
-strand is wound on a square or triangular
-insulator in which notches
-are made. Then, alternately between
-the coils, the second strand
-is wound. The strands are joined
-at one end of the coil, but those at
-the other are left free for unions with
-other wires. (<i>See also</i> <a href="#Ref019">Resistance</a>.)</p>
-
-<p><b>Coil, Retarding.</b> A choking-coil.
-A resistance-coil.</p>
-
-<p><b>Coil, Ribbon.</b> Instead of wire,
-flat, thin strips of sheet-metal are
-sometimes used for resistance-coils,
-doubled, as explained above. The
-wraps are insulated with sheet-mica,
-micanite, or asbestos, to prevent
-short-circuiting.</p>
-
-<p id="Ref091"><b>Coil, Ruhmkorff.</b> A common type
-of induction-coil with a vibrator or
-circuit-breaker. Used with constant
-and direct current.</p>
-
-<p>A step-up transformer with a circuit-breaker
-attachment.</p>
-
-<p><b>Coils, Idle.</b> Coils in a dynamo
-in which no electro-motive force is
-being generated or developed.</p>
-
-<p>Coils that, through broken connections
-or short circuits, are inactive.</p>
-
-<p><b>Column, Electric.</b> An old name
-for the voltaic pile. The apparatus
-made up of a pile of disks of copper
-and zinc, separated by pieces of flannel
-wet with acidulated water.</p>
-
-<p><b>Comb.</b> A bar from which a number
-of teeth project like the teeth
-of a comb. It is used as a collector
-of electricity from the plate of a
-frictional electric machine.</p>
-
-<p><b>Commutator.</b> An apparatus used
-on motors and dynamos and induction-coils
-for changing the direction
-of currents. It is made in
-a variety of types, but usually in
-the shape of insulated bars closely
-packed about an armature shaft.</p>
-
-<p><b>Commutator-bars.</b> The metallic
-segments of a dynamo or motor-commutator.</p>
-
-<p><b>Commutators, Quiet.</b> Commutators
-that do not spark during the
-revolutions of the armature.</p>
-
-<p><span class="pagenum" id="Page373">[373]</span></p>
-
-<p><b>Compass.</b> An apparatus for indicating
-the directive force of the
-earth upon the magnetic needle.
-It consists of a case covered with
-glass, in which a magnetized needle,
-normally pointing to the north, is
-balanced on a point at the centre.
-Under the needle a card is arranged
-on which the degrees or points of the
-compass are inscribed. A valuable
-instrument in electrical work, magnetism,
-etc.</p>
-
-<p><b>Compass, Liquid.</b> A form of
-marine compass. The needle is attached
-to a card or disk which floats
-in alcohol or other spirits, so as to
-check undue oscillation.</p>
-
-<p><b>Compass, Mariners’.</b> A compass
-in which the needle is attached to a
-card that rotates in pointing to the
-north. A mark, called the “lubber’s
-mark,” is made upon the case,
-and this is in line with the ship’s
-keel, so that a glance at the card
-will indicate the direction in which
-the ship is headed.</p>
-
-<p><b>Compass, Spirit.</b> A form of mariners’
-compass in which the bowl,
-or case, is sealed and filled with
-alcohol. The compass-card works
-as a spindle, and, by a series of
-air compartments, floats on the alcohol.
-The friction of the pivot is
-thereby greatly diminished, making
-the compass a very sensitive
-one.</p>
-
-<p><b>Compass, Standard.</b> A compass
-employed as a standard by which
-to compare other compasses.</p>
-
-<p id="Ref021"><b>Condenser.</b> An appliance for
-storing up electro-static charges; it
-is also called a static accumulator.
-The telegraphic condenser consists
-of a box packed full of sheets of tin-foil
-having a sheet of paraffined paper
-or sheet-mica between every
-two sheets. The alternate sheets of
-tin-foil are connected together, and
-each set has its binding-post. (<i>See
-also</i> <a href="#Ref008">Electrostatic Accumulator</a>.)</p>
-
-<p><b>Condenser, Air.</b> (<i>See</i> <a href="#Ref022">Air-condenser</a>.)</p>
-
-<p><b>Condenser, Ayrton’s.</b> (<i>See</i> <a href="#Ref023">Ayrton’s
-Condenser</a>.)</p>
-
-<p><b>Condenser-plate.</b> (<i>See</i> <a href="#Ref024">Plate, Condenser</a>.)</p>
-
-<p id="Ref098"><b>Condenser, Sliding.</b> An apparatus
-in the form of a Leyden-jar
-whose coatings can be slid past each
-other to diminish or increase the
-face area, and also to diminish or increase
-the capacity of the condenser.</p>
-
-<p><b>Conductance.</b> The conducting
-power of a mass of material, varying
-according to its shape and dimensions.
-The cylindrical or round
-conductor is the best type for the
-conveyance of electric currents.</p>
-
-<p><b>Conduction.</b> The transmission of
-electricity through an immobile medium,
-such as a wire, or rod, or a bar.</p>
-
-<p><b>Conductivity.</b> Ability to conduct
-electric currents. The conductivity
-of a wire is its power to conduct or
-transmit a current. Glass has no
-conductivity, and it is therefore a
-non-conductor.</p>
-
-<p><b>Conductivity, Variable.</b> The
-change in the conducting or transmitting
-powers of metals and substances
-under different temperatures.
-Hot metal conducts an electric
-current better than cold. A
-hot carbon-pencil in an arc-light
-conducts the current better than
-when the light is first started, for
-as it warms up under the influence
-of the arc-flame the current passes
-more freely. Five minutes after the
-current is turned on the lamps in the
-circuit give a steady light, and do
-not sputter as when they first start
-up.</p>
-
-<p><b>Conductor.</b> Anything which permits
-the passage of electric current.
-The term conductor is a relative one,
-and, excepting a vacuum, there is
-probably no substance that has not
-some conductive power. Metals,
-beginning with silver, are the best<span class="pagenum" id="Page374">[374]</span>
-conductors, liquids next, glass the
-worst. The ether, or air, is a conductor
-of sound and electric vibratory
-disturbances, but not in
-the same sense as the ground. The
-air conducts frictional electricity,
-while the ground acts as a conductor
-for the galvanic current, or “current
-electricity.” By this last term
-is meant electricity which flows continually,
-instead of discharging all
-at once, with an accompanying
-spark or flash.</p>
-
-<p><b>Conductor, Overhead.</b> Overhead
-electric lines, wires or cables, for
-conducting current. Generally poles
-are erected for this purpose.</p>
-
-<p id="Ref082"><b>Conductor, Prime.</b> A cylindrical
-or spherical body with no points or
-angles, but rounded everywhere
-and generally of metal. If made of
-other material, such as wood, glass,
-or composition, its entire surface is
-rendered conductive by being covered
-with sheet-metal, such as tin-foil,
-gold-leaf or tinsel, applied to it
-with paste, shellac, or glue. A
-prime conductor should be mounted
-on an insulated stand; it is employed
-to collect and retain frictional electricity
-generated by a static machine.</p>
-
-<p><b>Conductor, Underground.</b> An insulated
-conductor which is placed
-under the surface of the earth,
-passing through conduits.</p>
-
-<p><b>Connect.</b> The act of bringing two
-ends of wire together, either temporarily
-or permanently. Bringing
-one end of a conductor into contact
-with another so as to establish an
-electric connection.</p>
-
-<p><b>Connector.</b> A sleeve, with screws
-or other clamping device, into which
-the ends of wires or rods may be
-passed and held securely. A binding-post
-and spring-jack comes under
-this head.</p>
-
-<p><b>Contact.</b> The electrical union of
-two conductors, whether temporary
-or permanent. It may be established
-by touching the ends or terminals
-of a circuit through the agency of a
-push-button, a telegraph-key, an
-electric switch, etc.</p>
-
-<p><b>Contact-breaker.</b> (The same as
-<a href="#Ref025">Circuit-breaker</a>, <i>which see</i>.)</p>
-
-<p><b>Contact, Loose.</b> A contact formed
-by two or several surfaces imposed
-one upon another and held by
-their weight alone.</p>
-
-<p><b>Contact-point.</b> A point, or stud,
-often of silver or platinum, arranged
-to come into touch with a contact-spring,
-such as the vibrating armature
-of an electric bell.</p>
-
-<p><b>Contact-spring.</b> A spring connected
-at one end of a lead and arranged
-to press against another
-spring or plate, so that a plug may be
-inserted between the contact-points.</p>
-
-<p><b>Controller.</b> The lever or handle
-on the switch-board of a resistance-coil,
-by means of which electric current
-is let in or kept out of a circuit.</p>
-
-<p><b>Controlling Force.</b> In galvanometers
-and similar instruments, the
-force used to bring the needle or indicator
-back to zero.</p>
-
-<p><b>Converter.</b> An induction-coil used
-with the alternating current for
-changing the potential difference
-and inverting the available current.
-High alternating voltage may be
-converted into lower direct-current
-voltage, thereby increasing the amperage
-or current. A converter consists
-of a core of thin iron sheets,
-wound with a primary coil of fine
-insulated wire, with many convolutions
-or turns. Also, a secondary
-coil made up of coarse insulated
-wire with fewer convolutions. The
-coil may be jacketed with iron to
-increase the permanence.</p>
-
-<p><b>Converter, Rotary.</b> A combined
-motor and dynamo whose function
-is to transform a current of high or
-low voltage (A-C., or D-C.) into any
-other kind of current desired.</p>
-
-<p><span class="pagenum" id="Page375">[375]</span></p>
-
-<p><b>Convolution.</b> The state of being
-convolved; a turn, wrap, fold, or
-whorl. A clock-spring is a familiar
-example.</p>
-
-<p><b>Copper-bath.</b> A solution of sulphate
-of copper used in electro-plating,
-electrotyping, and copper-refining
-by electricity.</p>
-
-<p><b>Cord, Flexible.</b> A flexible-wire
-conductor made up of many strands
-of fine wire and properly insulated
-so that it may be easily twisted, bent,
-or wrapped. Flexible wire is used as
-the conductors for portable electric
-lights, push-buttons, medical coils,
-etc.</p>
-
-<p><b>Core.</b> The iron mass (generally
-located in the centre of a coil or
-helix) which becomes highly magnetic
-when a current is flowing
-around it, but which looses its magnetism
-immediately that the current
-ceases to flow.</p>
-
-<p>A conductor or the conductors of
-an electric cable made up of a single
-strand or many strands laid together
-and twisted. These may be
-of bare metal, or each one insulated
-from the others.</p>
-
-<p><b>Core-disks.</b> Disks of thin wire,
-for building up armature-cores.
-The usual form of a core is round or
-cylindrical. A number of thin disks,
-or laminations, of iron strung upon
-the central shaft, and pressed firmly
-together by the end-nuts or keys.
-This arrangement gives a cylinder as
-a base on which to wind the insulated
-wire that forms a part of the
-armature.</p>
-
-<p><b>Core-disks, Pierced.</b> Core-disks
-for an armature of a motor or dynamo,
-which have been pierced or
-bored out around the periphery.
-Tubes of insulating material, such
-as fibre, rubber, or paraffined paper,
-are inserted in the holes and through
-these the windings of wire are carried.
-The coils are thus imbedded
-in the solid mass of iron, and are
-protected from eddy currents; also
-they act to reduce the reluctance of
-the air-gaps. This arrangement is
-very good, from a mechanical point
-of view, but in practice its use is
-confined to small motors only, and
-dynamos generating under one hundred
-volts.</p>
-
-<p><b>Core-disks, Toothed.</b> Core-disks
-of an armature or motor where
-notches are cut from the periphery.
-When they are locked together, to
-form the armature-core, the coils of
-wire lie in the grooves formed by a
-number of the disks bound together.
-This construction reduces the actual
-air-gaps and keeps the coils
-equally spaced.</p>
-
-<p id="Ref058"><b>Core, Laminated.</b> The core of an
-armature, an induction-coil, a converter,
-or any similar piece of apparatus,
-which is made up of plates
-or disks, insulated more or less perfectly
-from one another by means of
-mica or paraffined paper. The object
-of laminations is to prevent the
-formation of Foucault currents. A
-core built up of disks is sometimes
-called a radially laminated core.</p>
-
-<p><b>Core, Ring.</b> A dynamo or motor
-armature-core which forms a complete
-ring.</p>
-
-<p><b>Core, Stranded.</b> The core of a
-cable, or a conducting core made up
-of a number of separate wires or
-strands laid or twisted together.</p>
-
-<p><b>Core, Tubular.</b> Tubes used as
-cores for electro-magnets, and also
-to produce small magnetizing power.
-Tubular cores are nearly as efficient
-as solid ones in straight magnets,
-because the principal reluctance is
-due to the air-path. On increasing
-the current, however, the tubular
-core becomes less efficient.</p>
-
-<p><b>Coulomb.</b> The practical unit of
-electrical quantity. It is the quantity
-passed by a current of one ampere
-intensity in one second.</p>
-
-<p><b>Couple.</b> The combination of two<span class="pagenum" id="Page376">[376]</span>
-electrodes and a liquid, the electrodes
-being immersed in the latter,
-and being acted on differentially by
-the liquid. This combination constitutes
-a source of electro-motive
-force, and, consequently of current,
-and is called the galvanic or voltaic
-cell or battery.</p>
-
-<p id="Ref011"><b>Couple, Astatic.</b>. A term sometimes
-applied to astatic needles when
-working in pairs.</p>
-
-<p><b>Coupling.</b> The union of cells or
-generators constituting a battery;
-the volume of current, or electro-motive
-force, is thereby increased.</p>
-
-<p><b>C. P.</b> An abbreviation for “candle
-power”; also meaning “chemically
-pure,” when speaking of chemicals.</p>
-
-<p><b>Crater.</b> The depression that forms
-in the positive carbon of a voltaic-arc.</p>
-
-<p><b>Creeping.</b> A phenomena met with
-in solution batteries. The electrolyte
-creeps up the sides of the containing
-jar and evaporates, leaving
-a deposit of salts. Still more solution
-creeps up through the salts until
-it gets clear to the top and runs over.
-To prevent this the tops of the jars
-should be brushed with hot paraffine
-for a distance of two inches from
-the upper edge. The salts will not
-form on paraffine. Oil is sometimes
-poured on the top of the battery
-solution, but this affects the elements
-if it touches them, and makes
-their surfaces non-conducting.</p>
-
-<p><b>Crucible, Electric.</b> A crucible for
-melting refractory substances, or for
-reducing ores by means of the electric
-arc produced within it. Probably
-the result obtained is due more
-to current incandescence than to the
-action of the arc.</p>
-
-<p><b>Crystallization, Electric.</b> Under
-proper conditions many substances
-and liquids take a crystalline form.
-When such action is brought about
-by means of electricity the term
-electric crystallization may be applied
-to the phenomenon. A solution
-of nitrate of silver, when decomposed
-by a current, will give
-crystals of metallic silver. A solution
-of common salt or brine, when
-electrically decomposed, will produce
-sodium and chlorine. The
-sodium appears at the leading-out
-electrode and readily unites with
-carbonic-acid gas, which is injected
-into the apparatus. The result of
-the combination is carbonate of soda,
-one of the most important products
-of the alkali industry.</p>
-
-<p id="Ref009"><b>Current, Alternating.</b> A current
-flowing alternately in opposite directions.
-It is a succession of currents,
-each of short duration and of
-direction opposite to that of its predecessor.
-Abbreviation, A-C.</p>
-
-<p><b>Current, Amperage.</b> The volume
-of electricity passing through any
-circuit per second, the flow being
-uniform.</p>
-
-<p><b>Current, Constant.</b> An unvarying
-current. A constant-current
-system is one in which the current
-is uniformly maintained&mdash;for example,
-in electric light, power, and
-heat plants.</p>
-
-<p><b>Current, Continuous.</b> A current
-of one direction only, or the reverse
-of an alternating current.</p>
-
-<p id="Ref027"><b>Current, Direct.</b> A current of unvarying
-direction, as distinguished
-from the alternating. Abbreviation,
-D-C.</p>
-
-<p><b>Current Distribution, Uniform.</b>
-A steady current; a current whose
-density in a conductor is always the
-same at all points.</p>
-
-<p id="Ref054"><b>Current, Induced.</b> A current
-caused by electro-dynamic induction.</p>
-
-<p id="Ref062"><b>Current, Low Potential.</b> A current
-of low pressure.</p>
-
-<p>A term applied to low electro-motive
-force.</p>
-
-<p id="Ref067"><b>Current, Make-and-break.</b> A current
-which is continually broken or<span class="pagenum" id="Page377">[377]</span>
-interrupted and started again. The
-term is applied only where the interruptions
-occur in rapid succession,
-as in the action of an induction-coil
-or pole-changer.</p>
-
-<p>The alternating current.</p>
-
-<p><b>Current-meter.</b> An apparatus for
-indicating the strength of a current,
-such as an ammeter.</p>
-
-<p id="Ref074"><b>Current, Oscillating.</b> A current
-periodically alternating.</p>
-
-<p id="Ref075"><b>Current, Periodic.</b> A current with
-periodically varying strength or direction.
-A current alternating periodically.</p>
-
-<p id="Ref079"><b>Current, Polarizing.</b> A current
-which causes polarization.</p>
-
-<p><b>Current-reverser.</b> A switch or
-other contrivance for reversing the
-direction of a current in a conductor.</p>
-
-<p id="Ref107"><b>Current, Undulating.</b> A current
-whose direction is constant but
-whose strength is continuously varying.</p>
-
-<p id="Ref030"><b>Currents, Eddy.</b> Useless currents
-in an armature, in the pole pieces,
-and in the magnetic cores of dynamos
-and motors. They are created
-by the high speed of the armature
-in its rotation, or by other electric
-currents induced by the armature’s
-motion through magnetic fields.</p>
-
-<p id="Ref042"><b>Currents, Faradic.</b> Induced currents.
-They take their name from
-Michael Faraday, the original investigator
-of the phenomena of
-electro-magnetic induction. The
-secondary or induced electro-magnetic
-currents and their accompanying
-phenomena.</p>
-
-<p>A series of alternating electro-static
-discharges from influence
-machine, such as the Holtz and
-Wimshurst.</p>
-
-<p>The simple and commonly understood
-Faradic currents are those
-produced in the medical battery,
-and used in medical therapeutics.</p>
-
-<p id="Ref044"><b>Currents, Foucault.</b> A form of
-currents produced in revolving armature-cores;
-sometimes called eddy
-currents. They are useless.</p>
-
-<p id="Ref048"><b>Currents, Harmonic.</b> Currents
-which alternate periodically, and
-vary harmonically. Currents which
-vibrate at certain pitches, as, for
-instance, the currents in wireless
-telegraphy. Two instruments must
-be tuned to the same pitch in order
-to be responsive. Thus an instrument
-sending out waves of 70,000
-vibrations cannot be recorded by
-one tuned much below or above
-the same number.</p>
-
-<p>Sound waves of sympathetic or
-harmonic vibrations.</p>
-
-<p><b>Currents, Positive.</b> (<i>See</i> <a href="#Ref026">Positive
-Currents</a>.)</p>
-
-<p><b>Cut-in.</b> To electrically connect a
-piece of mechanism or a conductor
-with a circuit.</p>
-
-<p><b>Cut-out.</b> The reverse of the cut-in.
-To remove from a circuit any
-conducting device. The cut-out
-may be so arranged as to leave the
-circuit complete in some other way.</p>
-
-<p>An appliance for removing a piece
-of apparatus from a circuit so that
-no more current shall pass through
-the former.</p>
-
-<p><b>Cut-out, Automatic.</b> A safety device
-for automatically cutting out
-a circuit to prevent accident or
-the burning-out of an apparatus,
-due to an overload of current. It
-is worked by an electro-magnet and
-spring. An overload of current
-causes a magnet of high resistance
-to draw an armature towards it,
-and this, in turn, releases the spring
-of the cut-out device. Sometimes
-a strip or wire of fusible metal is
-employed which is in circuit with
-a switch. The excess of current
-fuses the metal, and the broken circuit
-releases a spring-jack, which, in
-turn, breaks the circuit.</p>
-
-<p><b>Cut-out, Safety.</b> A block of non-conducting
-material, such as marble,
-slate, or porcelain, carrying a safety-fuse<span class="pagenum" id="Page378">[378]</span>
-or plugs. In these is enclosed
-a piece of fusible wire, which burns
-out or melts and breaks the circuit
-before the apparatus is damaged.</p>
-
-<p><b>Cut-out, Wedge.</b> A cut-out operated
-by a wedge, such as a spring-jack
-or the plugs at the end of the
-flexible wires on the switch-boards
-of telephone exchanges.</p>
-
-<h3>D</h3>
-
-<p><b>Damper.</b> A frame of copper on
-which the wire in a galvanometer is
-sometimes coiled. It acts to check
-the needle oscillations.</p>
-
-<p>A brass or copper sheathing or
-tube placed between the primary
-and secondary coils of an induction-coil
-to cut off induction and diminish
-the current and potential of the
-secondary circuit. When the tube
-is drawn out gradually the induction
-increases. It is commonly
-used in medical coils to adjust their
-strength of action.</p>
-
-<p><b>D-C.</b> An abbreviation for direct
-current.</p>
-
-<p><b>Dead Earth.</b> A fault in telegraph
-and telephone lines which consists
-in the ground-wire being improperly
-grounded, or not fully connected
-with the earth.</p>
-
-<p><b>Dead Turns.</b> A term applied to
-the ten to twenty per cent. of the
-convolutions or turns of wire on
-an armature which are considered
-to be dead. There are supposed to
-be about eighty per cent. of the
-turns on an armature that are active
-in magnetizing the core; the
-balance are outside the magnetic
-field and are termed dead, although
-they are necessary to the production
-of electro-motive force.</p>
-
-<p><b>Dead Wire.</b> A wire in the electric
-circuit through which no current
-is passing.</p>
-
-<p>A disused or abandoned electric
-conductor, such as a telegraph wire,
-or a wire which may be in circuit,
-but through which at the time of
-speaking no electrical action is taking
-place.</p>
-
-<p><b>Death, Electrical.</b> Death resulting
-from an electric current passing
-through the animal body&mdash;electrocution;
-accidental death by electric
-shock; premeditated death through
-bringing the body in direct contact
-with conductors carrying high electro-motive
-force. High electro-motive
-force is essential, and the alternating
-current is most fatal.</p>
-
-<p id="Ref033"><b>Decomposition, Electrolytic.</b> The
-decomposition or separation of a
-compound liquid into its constituents
-by electrolysis. The liquid
-must be a conductor or electrolyte,
-and the decomposition is carried on
-by means of electricity.</p>
-
-<p>The conversion of two or more
-chemicals into a new compound or
-substance.</p>
-
-<p><b>Deflection.</b> In magnetism, the
-movement of the needle out of the
-plane. It is due to disturbance, or
-to the needle’s attraction towards
-a mass of iron or steel or another
-magnet.</p>
-
-<p><b>Demagnetization.</b> The removal
-of magnetism from a paramagnetic
-substance. The process is principally
-in use for watches which have become
-magnetized by exposure to the
-magnetic field surrounding dynamos
-or motors.</p>
-
-<p><b>Density, Electric.</b> The relative
-quantity of electricity, as a charge,
-upon a unit area of surface. It may
-be positive or negative.</p>
-
-<p>Surface density, as the charge of
-a Leyden-jar.</p>
-
-<p><b>Depolarization.</b> A term applied
-to the removal of permanent magnetism,
-such as that from a horseshoe
-magnet, a watch, or a bar-magnet.
-Heat is the common depolarizer,
-but counter electro-magnetic
-forces are employed also in the<span class="pagenum" id="Page379">[379]</span>
-various forms of apparatus known
-as demagnetizers.</p>
-
-<p id="Ref034"><b>Deposit, Electrolytic.</b> The metal or
-other substances precipitated by the
-action of a battery or other current-generator,
-as in the plating processes.</p>
-
-<p><b>Detector.</b> A portable galvanometer,
-by means of which a current
-and its approximate strength can
-be detected and measured.</p>
-
-<p><b>Diaphragm.</b> In telephones and
-microphones, a disk of iron thrown
-into motion by sound-waves or by
-electric impulse. It is usually a
-thin plate of japanned iron, such as
-is used in the ferrotype photographic
-process for making tin-types.</p>
-
-<p><b>Dielectric.</b> Any substance through
-which electrostatic induction is allowed
-to occur, such as glass or rubber.
-It is a non-conductor for all
-electric currents.</p>
-
-<p id="Ref087"><b>Dielectric Resistance.</b> The resistance
-a body offers to perforation or
-destruction by an electric discharge.</p>
-
-<p><b>Dimmer.</b> An adjustable choke or
-resistance coil used for regulating
-the intensity of electric incandescent
-lamps. It is employed extensively
-in theatres for raising or lowering
-the brilliancy of lights.</p>
-
-<p><b>Dipping.</b> The process of cleaning
-articles by dipping them in acids
-or caustic soda, preparatory to electro-plating.</p>
-
-<p>Simple immersion, with or without
-current, to put a blush of metal
-on a cleaned surface.</p>
-
-<p><b>Dipping-needle.</b> A magnetic needle
-mounted on a horizontal bearing
-so that it will dip vertically
-when excited by a current passing
-horizontally about it. The ordinary
-compass-needle is mounted on a
-point, and swings freely to the right
-or left only.</p>
-
-<p><b>Direct Current.</b> (<i>See</i> <a href="#Ref027">Current,
-Direct</a>.)</p>
-
-<p><b>Discharge.</b> The eruptive discharge
-from a Leyden-jar or accumulator
-of a volume of electricity stored
-within it.</p>
-
-<p>The abstraction of a charge from
-a conductor by connecting it to the
-earth or to another conductor.</p>
-
-<p><b>Discharge, Disruptive.</b> The discharge
-of a static charge through a
-dielectric. It involves the mechanical
-perforation of the dielectric.</p>
-
-<p><b>Disconnect.</b> To break an electric
-circuit or open it so as to stop the
-flow of current; to remove a part
-of a circuit or a piece of apparatus
-from a circuit.</p>
-
-<p><b>Distillation, Electric.</b> The distilling
-of a liquid by the employment
-of electricity, which, by electrifying
-the liquid, assists the effects of heat.
-It is asserted that the process is
-accelerated by the electrification of
-the liquid or fluid, but it must be a
-conductor liquid or electrolyte. Oil,
-being a non-conductor, is not affected
-by any electric current, no matter
-what its specific gravity may be.</p>
-
-<p><b>Distributing Centre.</b> The centre
-of distribution in a system having
-branch circuits, such as the electric-light
-or telephone outlets from a
-main station.</p>
-
-<p><b>Door-opener, Electric.</b> A magnetic
-contrivance arranged in connection
-with a lock, by means of
-which the latch is released by pressing
-a distant push-button. This
-device is used in flats and apartment-houses
-for opening a door
-from any of the apartments in the
-house.</p>
-
-<p><b>Double Filament Lamp.</b> An incandescent
-lamp having two filaments,
-one with a high capacity, the
-other with a low one. The high
-capacity may be from sixteen to
-fifty candle-power, the other from
-one to five. A turn of the bulb in
-its socket, or the pulling of a string
-which operates a switch in the
-socket, cuts out the current from
-the long filament and sends it<span class="pagenum" id="Page380">[380]</span>
-through the shorter and finer one,
-thus giving a weaker light. These
-“hy-lo” lamps are useful as night
-lamps in halls, bath-rooms, or in
-sick-rooms, where a low or weak light
-is required all night.</p>
-
-<p><b>Double Pole-switch</b>. A cut-out
-that is arranged to cut out the circuit
-of both the negative and positive
-leads at the same time.</p>
-
-<p><b>Double-push.</b> A contact-push
-having two contacts and arranged
-so that pressure upon it opens one
-contact and closes the other.</p>
-
-<p><b>Double Throw-switch.</b> A switch
-so arranged that it can be thrown
-into either one of two contacts; a
-throw-over switch.</p>
-
-<p><b>Driving-pulley.</b> The broad-faced
-or channelled pulley on an armature
-shaft by means of which the power
-from a motor may be transmitted
-mechanically.</p>
-
-<p><b>Dry Battery.</b> (<i>See</i> <a href="#Ref028">Battery, Dry</a>.)</p>
-
-<p><b>Duct.</b> The space in an underground
-conduit for a single wire or
-cable.</p>
-
-<p><b>Duplex Wire.</b> An insulated conductor
-having two distinct wires
-twisted or laid together, but properly
-insulated from each other.</p>
-
-<p><b>Dynamic Electricity.</b> Electricity
-in motion or flowing, as distinguished
-from static or frictional electricity.</p>
-
-<p>Electricity of relatively low potential
-or electro-motive force in
-large quantity or amperage.</p>
-
-<p><b>Dynamo.</b> An apparatus consisting
-of a core and field-magnets,
-properly wound with insulated wire,
-which, when put into operation by
-revolving the core or armature at
-high speed, develops electric current;
-a mechanical generator of electricity.</p>
-
-<p><b>Dynamo, Motor.</b> (<i>See</i> <a href="#Ref029">Motor-dynamo</a>.)</p>
-
-<h3>E</h3>
-
-<p><b>Earth.</b> The accidental grounding
-of a circuit is termed an “earth.”</p>
-
-<p><b>Earth-plate.</b> A plate buried in
-the ground to receive the ends of
-telegraph lines and other circuits,
-and so give a ground connection.
-Copper plates are often used, but
-in houses the ground is usually
-formed by attaching a wire to the
-gas or water pipes.</p>
-
-<p><b>Earth Return.</b> The grounding
-of a wire in a circuit at both ends
-gives the circuit an earth return.
-This method is commonly used in
-telegraph lines, both in the wire
-and wireless systems.</p>
-
-<p><b>Eddy Currents.</b> (<i>See</i> <a href="#Ref030">Currents,
-Eddy</a>.)</p>
-
-<p><b>Edison Distributing-box.</b> A box
-used in the Edison “three-wire”
-system, from which the outlets pass
-to local circuits.</p>
-
-<p><b>Edison Lalande Cell.</b> A zinc-copper
-battery having a depolarizing
-coating of copper oxide on the copper
-element, the couple being immersed
-in an electrolyte composed
-of potash or caustic soda.</p>
-
-<p><b>Ediswan.</b> A term applied to the
-incandescent lamps invented by Edison
-and Swan and used extensively
-in Great Britain. Also applied to
-other apparatus designed by the
-two inventors.</p>
-
-<p><b>Efficiency.</b> The relation of work
-done to the electrical energy absorbed.
-The efficiency is not equal
-to the energy absorbed, because it
-always takes more power to generate
-a current than is given back in
-actual efficiency. This is due to
-mechanical friction and to the resistance
-of the air in a mechanism
-such as a dynamo when revolving at
-high speed.</p>
-
-<p><b>Efficiency, Electrical.</b> In a generator
-it is the total electrical energy
-produced, both that wasted and
-that actually used in driving machinery
-or apparatus.</p>
-
-<p><b>Efflorescence.</b> The dry salts on
-a jar or vessel containing liquid that<span class="pagenum" id="Page381">[381]</span>
-collects above the water or evaporation
-line. This is due to creeping.</p>
-
-<p><b>Elasticity.</b> A property in some
-bodies and forces through which they
-recover their former figure, shape,
-or dimensions when the external
-pressure or stress is removed. Water
-has no elasticity. Air is very elastic;
-steam has a great volume of
-elasticity; while electricity is undoubtedly
-the most elastic of all in
-its motion through air, water, and
-other conducting mediums.</p>
-
-<p><b>Electric.</b> Pertaining to electricity;
-anything connected with the
-use of electricity. It has been a
-much-abused word, and its meaning
-has been garbled by the impostor,
-the crook, and the “business thief”
-in foisting on the public wares in
-which there was no electrical property
-whatever. “Electric” toothbrushes,
-combs, corsets, belts, and
-the like may contain a few bits of
-magnetized steel, but they possess
-no active therapeutic value.</p>
-
-<p><b>Electrical Engineer.</b> The profession
-of electrical engineer calls
-for the highest knowledge of electricity,
-both theoretical and practical.
-It embraces the designing and
-installation of all kinds of electrical
-apparatus.</p>
-
-<p><b>Electrician.</b> One versed in the
-practices and science of electricity;
-a practical lineman or wireman.</p>
-
-<p><b>Electricity.</b> One of the hidden
-and mysterious powers of nature,
-which man has brought under control
-to serve his ends, and which
-manifests itself mainly through attraction
-and repulsion; the most
-powerful and yet the most docile
-force known to man, coming from
-nowhere and without form, weight,
-or color, invisible and inaudible;
-an energy which fills the universe
-and which is the active principle
-in heat, light, magnetism, chemical
-affinity, and mechanical motion.</p>
-
-<p id="Ref012"><b>Electricity, Atmospheric.</b> The
-electric currents of the atmosphere,
-variable but never absent. They
-include lightning, frictional electricity,
-the Aurora Borealis, the electric
-waves used in wireless telegraphy,
-etc. Benjamin Franklin indicated
-the method of drawing electricity
-from the clouds. In June,
-1752, he flew a kite, and by its
-moistened cord drew an electric
-current from the clouds so that
-sparks were visible on a brass key
-at the ground end of the cord. Later,
-when a fine wire was substituted for
-the cord, and a kite was flown in a
-thunder-storm, the electric spark
-was vivid. This experiment confirmed
-his hypothesis that lightning
-was identical with the disruptive
-discharges of electricity.</p>
-
-<p id="Ref059"><b>Electricity, Latent.</b> The bound
-charge of static electricity.</p>
-
-<p><b>Electricity, Negative.</b> (<i>See</i> <a href="#Ref031">Negative
-Electricity</a>.)</p>
-
-<p><b>Electricity, Positive.</b> (<i>See</i> <a href="#Ref032">Positive
-Electricity</a>.)</p>
-
-<p id="Ref109"><b>Electricity, Voltaic.</b> Electricity
-of low potential difference and large
-current intensity.</p>
-
-<p>Electricity produced by a voltaic
-battery or dynamo as opposed to
-static electricity, which is frictional
-and practically uncontrollable for
-commercial purposes.</p>
-
-<p><b>Electrification.</b> The process of imparting
-an electric charge to a surface.
-The term is applied chiefly to
-electro-static phenomena.</p>
-
-<p><b>Electrization.</b> In electro-therapeutics,
-the subjection of the human
-system to electric treatment. An
-electric tonic imparted by electro-medical
-baths through the nervous
-system.</p>
-
-<p><b>Electro-chemistry.</b> That branch
-of science which treats of the relations
-between electric and chemical
-forces in their different reactions and
-compounds. It deals with electro-plating,<span class="pagenum" id="Page382">[382]</span>
-electro-fusing, electrolysis,
-etc.</p>
-
-<p><b>Electro-culture.</b> The application
-of electricity to the cultivation of
-plants. The use of electricity has
-been found very beneficial in some
-forms of plant growth.</p>
-
-<p><b>Electrocution.</b> Capital punishment
-inflicted by electric current
-from a dynamo of high electro-motive
-force. The current used is
-from 1500 to 2000 volts, and it
-acts to break down the tissues of
-the body.</p>
-
-<p><b>Electrode.</b> The terminals of an
-open electric circuit.</p>
-
-<p>The terminals between which an
-electric arc is formed, as in the arc-light.</p>
-
-<p>The terminals of the conductors of
-an electric circuit immersed in an
-electrolytic solution, such as the
-carbon and zinc of a battery.</p>
-
-<p><b>Electrolier.</b> A fixture for supporting
-electric lamps, similar to a
-chandelier for gas or candles. Combination
-electroliers conduct both
-gas and electricity.</p>
-
-<p><b>Electrolysis.</b> The separation of a
-chemical compound into its constituted
-parts by the action of an
-electric current.</p>
-
-<p><b>Electrolyte.</b> A body susceptible
-of decomposition by the electric current.
-It must be a fluid body and
-a conductor capable of diffusion as
-well as composite in its make-up.
-An elemental body such as pure
-water cannot be an electrolyte.</p>
-
-<p><b>Electrolytic Decomposition.</b> (<i>See</i>
-<a href="#Ref033">Decomposition, Electrolytic</a>.)</p>
-
-<p><b>Electrolytic Deposit.</b> (<i>See</i> <a href="#Ref034">Deposit,
-Electrolytic</a>.)</p>
-
-<p><b>Electrolytic Resistance.</b> (<i>See</i> <a href="#Ref035">Resistance,
-Electrolytic</a>.)</p>
-
-<p><b>Electro-magnetic Induction.</b> (<i>See</i>
-<a href="#Ref036">Induction, Electro-Magnetic</a>.)</p>
-
-<p><b>Electro-magnetism.</b> Magnetism
-created by electric current.</p>
-
-<p>That branch of electrical science
-which treats of the magnetic relations
-of a field of force produced
-by a current.</p>
-
-<p><b>Electro-medical Bath.</b> A bath
-provided with connections and electrodes
-for causing a current of electricity
-to pass through the body of
-the patient.</p>
-
-<p><b>Electrometer.</b> An instrument
-used for measuring static electricity.
-Electrometers are different from galvanometers,
-since the latter depend
-on a current flowing through wires
-to create an action of the magnetic
-needles.</p>
-
-<p><b>Electro-motive Force.</b> Voltage.
-It may be compared to the pressure
-of water in hydraulic systems. The
-unit of electro-motive force is the
-volt.</p>
-
-<p><b>Electro-motor.</b> A term sometimes
-applied to a current-generator,
-such as a small dynamo or voltaic
-battery.</p>
-
-<p><b>Electro-plating.</b> (<i>See</i> <a href="#Ref037">Plating,
-Electro</a>.)</p>
-
-<p><b>Electropoion Fluid.</b> An acid depolarizing
-solution for use in zinc-carbon
-couples, such as the “Grenet”
-and “Daniell” cells. The bi-chromate-of-potash
-and sulphuric-acid
-solution for battery charges is
-a good example.</p>
-
-<p><b>Electroscope.</b> An apparatus for
-indicating the presence of an electric
-charge and whether the charge
-is negative or positive.</p>
-
-<p id="Ref008"><b>Electrostatic Accumulator.</b> Two
-conducting surfaces, separated by
-a dielectric and arranged for the opposite
-charging of the two surfaces.
-A faradic or static machine for accumulating
-frictional electricity is
-an example.</p>
-
-<p><b>Electrostatics.</b> That division of
-electric science which treats of the
-phenomena of the electric charge, or
-of electricity in repose, as contrasted
-with electro-dynamics or electricity
-in motion.</p>
-
-<p><span class="pagenum" id="Page383">[383]</span></p>
-
-<p><b>Electrotype.</b> The reproduction
-of a form of type or engraving by
-the copper electro-plating process.
-The original is coated with plumbago
-and a wax impression taken of
-it. The face of the negative is made
-conductive with plumbago or tin
-dust, then suspended in a copper
-bath and connected with the current.
-A film of copper will be deposited
-on the face of the wax impression.</p>
-
-<p id="Ref016"><b>Element, Chemical.</b> Original
-forms of matter that cannot be
-separated into simple constituents
-by any known process. There are
-about seventy in all, but as science
-advances the list is constantly being
-revised. New elements are discovered
-and known ones are being
-resolved into simpler forms.</p>
-
-<p><b>Elements of Battery Cell.</b> (<i>See</i>
-<a href="#Ref038">Battery Cell, Elements of</a>.)</p>
-
-<p><b>Emergency Switch.</b> An auxiliary
-switch used as a controller on a car
-to reverse the action of the motor.</p>
-
-<p><b>E-M-F.</b> An abbreviation for electro-motive
-force, or voltage.</p>
-
-<p><b>Equalizer.</b> A term applied to a
-wire or bar in electro-magnetic mechanism
-for equalizing the pressure
-over a system.</p>
-
-<p><b>Exciter.</b> A generator used for exciting
-the field-magnets of a dynamo.</p>
-
-<p><b>Extension Call-bell.</b> A bell connected
-with a telephone call-bell, and
-located in another part of a building
-so as to give a distant summons.</p>
-
-<p><b>External Circuit.</b> (<i>See</i> <a href="#Ref039">Circuit,
-External</a>.)</p>
-
-<h3>F</h3>
-
-<p><b>F.</b> The sign commonly employed
-to designate Fahrenheit. Thus, 30°
-F. means 30 degrees Fahrenheit, or
-30 degrees above zero.</p>
-
-<p><b>False Magnetic Poles.</b> (<i>See</i> <a href="#Ref040">Magnetic
-Poles, False</a>.)</p>
-
-<p><b>Faradic.</b> Induced current produced
-from induction-coils and
-faradic machines.</p>
-
-<p>A series of alternating electrostatic
-discharges, as from a Holtz
-influence machine.</p>
-
-<p><b>Faradic Coil.</b> (<i>See</i> <a href="#Ref041">Coil, Faradic</a>.)</p>
-
-<p><b>Faradic Currents.</b> (<i>See</i> <a href="#Ref042">Currents,
-Faradic</a>.)</p>
-
-<p><b>Faradic Machine.</b> An apparatus
-designed to produce faradic current.</p>
-
-<p><b>Feed.</b> To furnish an electric current,
-also spoken of in connection
-with the mechanism that moves the
-carbons in arc-lamps.</p>
-
-<p><b>Feeders, or Feed Wires.</b> The conductors
-which convey electric currents
-at different points, as in the
-trolley system. The current is carried
-along in large cables strung on
-poles or laid underground, and at
-proper distances lines are run in to
-feed the trolley wire.</p>
-
-<p><b>Field.</b> The space in the neighborhood
-of a dynamo or motor, or
-other generator of electric current,
-from which the apparatus takes its
-electricity, both electrostatic and
-magnetic.</p>
-
-<p><b>Field-magnet.</b> (<i>See</i> <a href="#Ref043">Magnet,
-Field</a>.)</p>
-
-<p><b>Field of Force.</b> The space in the
-neighborhood of an attracting or
-repelling mass or system. There
-are two kinds of fields of force&mdash;the
-electro-magnetic and the static&mdash;from
-which the respective pieces of
-apparatus draw their store of electricity.</p>
-
-<p id="Ref051"><b>Filament.</b> A long, thin piece of
-solid substance. It is generally as
-thin as a thread and flexible enough
-to be bent.</p>
-
-<p>The hairlike element in an incandescent
-lamp which, when heated
-by a current, glows and radiates light.</p>
-
-<p><b>Filaments, Paper.</b> Filaments for
-incandescent lamps made of carbonized
-paper. They were the ones
-originally used in electric lamps, but
-have been superseded by other substances
-easier to handle and more
-durable.</p>
-
-<p><span class="pagenum" id="Page384">[384]</span></p>
-
-<p><b>Flow.</b> The volume of a current
-or stream escaping through a conductor,
-such as a wire, rod or pipe.</p>
-
-<p><b>Fluorescence.</b> The property of
-converting ether waves of one length
-into waves of another length. The
-phenomenon is utilized in the production
-of Geissler tubes and X-rays.</p>
-
-<p><b>Fluoroscope.</b> An apparatus for
-making examinations by means of
-the X-rays.</p>
-
-<p><b>Fluoroscopic Screen.</b> A screen
-overspread with fluorescent material
-and employed for fluoroscopic examinations
-in connection with the
-X-rays.</p>
-
-<p><b>Force.</b> Any change in the condition
-of matter with respect to
-motion or rest. Force is measured
-by the acceleration or change of
-motion that it can impart to a body
-of a unit mass in a unit of time. For
-instance, ten pounds pressure of
-steam will be indicated on a gauge
-made for measuring steam. That
-pressure of steam, with the proper
-volume behind it, is capable of instantly
-producing a given part of a
-horse-power. In the same way ten
-volts of electro-motive force is capable
-of pushing a current so as to exert
-a certain fraction of horse-power.</p>
-
-<p><b>Force, Electro-magnetic.</b> The
-force of attraction or repulsion exerted
-by the electro-magnet. It is
-also known as electric force in the
-electro-magnetic system.</p>
-
-<p><b>Foucault Currents.</b> (<i>See</i> <a href="#Ref044">Currents,
-Foucault</a>.)</p>
-
-<p><b>Fractional Distillation.</b> The process
-of evaporating liquids by heat,
-the most volatile being the first
-treated. When that has been evaporated
-and distilled the heat is raised
-and the next most volatile liquid is
-evaporated, and so on until all are
-evaporated, leaving as a residue the
-solids that were a part of the original
-mass of liquid.</p>
-
-<p><b>Friction.</b> The effect of rubbing,
-or the resistance which a moving
-body encounters when in contact
-with another body.</p>
-
-<p><b>Frictional Electric Machine.</b> An
-apparatus for the development or
-generation of high-tension frictional
-electricity.</p>
-
-<p><b>Frictional Electricity.</b> Electricity
-produced by the friction of dissimilar
-substances.</p>
-
-<p><b>Full Load.</b> A complete load.
-The greatest load a machine or
-secondary battery will carry permanently.
-The full capacity of a
-motor running at its registered
-speed for its horse-power.</p>
-
-<p><b>Furnace, Electric.</b> A furnace in
-which the heat is produced by the
-electric arc. It is the hottest furnace
-known to man, and temperatures
-as high as 7500° Fahrenheit
-have been developed in it.</p>
-
-<p><b>Fuse, Electric.</b> A fuse for igniting
-an explosive charge by electricity.
-It is made by bringing the
-terminals or ends of wires close together,
-so that they will spark
-when a current passes through them.
-Or a thin piece of highly resistant
-wire may be imbedded in an explosive
-and brought to white heat
-by current.</p>
-
-<p><b>Fuse-block.</b> An insulator having
-a safety-fuse made fast to it.</p>
-
-<p><b>Fuse-box.</b> A box containing a
-safety-fuse, generally of porcelain,
-enamelled iron, or some other non-conductor.</p>
-
-<p><b>Fuse-links.</b> Links composed of
-strips or plates of fusible metal
-serving the purpose of safety-fuses.</p>
-
-<p><b>Fusing-current.</b> A current of sufficient
-strength to cause the blowing
-or fusing of a metal.</p>
-
-<h3>G</h3>
-
-<p><b>Galvanic.</b> Voltaic. Relating to
-current electricity or the electro-chemical
-relations of metals.</p>
-
-<p><span class="pagenum" id="Page385">[385]</span></p>
-
-<p><b>Galvanic Taste.</b> A salty taste in
-the mouth resulting from the passage
-of a light current from a voltaic
-battery, the ends of the wires being
-held to either side of the tongue.
-This has been called tasting electricity,
-but it is really the decomposition
-of saliva on the surface of
-the tongue, due to electrolysis or
-the passage of a current through a
-liquid.</p>
-
-<p><b>Galvanism.</b> The science of voltaic,
-or current, electricity.</p>
-
-<p><b>Galvanizing.</b> Coating iron with
-a thin layer of zinc by immersing the
-object in the molten metal.</p>
-
-<p><b>Galvano-faradic.</b> In medical electricity
-the shocking-coil. The application
-of the voltaic current, induced
-by a secondary current (induction-coil),
-to any part of the body.</p>
-
-<p><b>Galvanometer.</b> An instrument for
-measuring current strength.</p>
-
-<p>A magnetic needle influenced by
-the passage of a current through a
-wire or coil located near it.</p>
-
-<p id="Ref104"><b>Galvanometer, Tangent.</b> A galvanometer
-provided with two magnetic
-needles differing in length, the
-shorter one serving to measure tangents,
-the longer being used for sine
-measurements of current strength.</p>
-
-<p><b>Galvanoscope.</b> An instrument,
-generally of the galvanometer type,
-used to ascertain whether a current
-is flowing or not.</p>
-
-<p><b>Generator.</b> An apparatus for maintaining
-an electric current, such as
-a dynamo, a faradic machine, a battery,
-etc.</p>
-
-<p><b>German-silver.</b> An alloy of copper,
-nickel, and zinc. Used chiefly
-in resistance-coils, either in the form
-of wire or in strips of the sheet-metal.</p>
-
-<p><b>Gold-bath.</b> A solution of gold
-used for depositing that metal in the
-electro-plating bath.</p>
-
-<p><b>Graphite.</b> A form of carbon. It
-occurs in nature as a mineral, and
-also is made artificially by the
-agency of electric heat.</p>
-
-<p><b>Gravity Battery.</b> (<i>See</i> <a href="#Ref045">Battery,
-Gravity</a>.)</p>
-
-<p><b>Grounded Circuit.</b> (<i>See</i> <a href="#Ref046">Circuit,
-Grounded</a>.)</p>
-
-<p><b>Ground-plate.</b> (<i>See</i> <a href="#Ref047">Plate,
-Ground</a>.)</p>
-
-<p><b>Ground-wire.</b> The contact of a
-conductor, in an electric circuit,
-with the earth. It permits the escape
-of current if another ground-wire
-exists.</p>
-
-<p><b>Guard Tube.</b> A tube inserted in
-a wooden or brick partition to insulate
-wires that may pass through
-it. These tubes are made of porcelain,
-gutta-percha, compositions
-of a non-conducting nature, and
-fibre.</p>
-
-<p id="Ref052"><b>Gutta-percha.</b> Caoutchouc treated
-with sulphur to harden it; sometimes
-called vulcanized rubber or
-vulcanite. It is a product obtained
-from tropical trees, and when properly
-treated it is a valuable insulator
-in electrical work, particularly in submarine
-cables, since it offers great
-resistance to the destructive agencies
-of the ocean’s depths.</p>
-
-<h3>H</h3>
-
-<p><b>Hand Generator.</b> A magneto-generator
-driven by hand for the generation
-of light currents.</p>
-
-<p><b>Harmonic Currents.</b> (<i>See</i> <a href="#Ref048">Currents,
-Harmonic</a>.)</p>
-
-<p><b>Harmonic Receiver.</b> A receiver
-containing a vibrating reed acted on
-by an electro-magnet. Such a reed
-answers only to impulses tuned to its
-pitch.</p>
-
-<p><b>Heat.</b> One of the force agents of
-nature. It is recognized in its effects
-through expansion, fusion, evaporation,
-and generation of energy.</p>
-
-<p><b>Heat, Electric.</b> Caused by a resisting
-medium, such as carbon or
-German-silver, when too much current<span class="pagenum" id="Page386">[386]</span>
-is forced through it. The principle
-of the car-warmers, electric iron,
-electric chafing-dish, etc.</p>
-
-<p><b>Helix.</b> A coil of wire. Properly
-a coil of wire so wound as to follow
-the outlines of a screw without overlaying
-itself.</p>
-
-<p><b>Horse-power, Electric.</b> Meaning
-the same as in mechanics. Referred
-to when speaking of the working
-capacity of a motor or the power
-required to drive a dynamo.</p>
-
-<p><b>Horse-power Hour.</b> A unit or
-standard of electrical work theoretically
-equal to that accomplished by
-one horse during one hour.</p>
-
-<p><b>Horseshoe Magnet.</b> (<i>See</i> <a href="#Ref049">Magnet,
-Horseshoe</a>.)</p>
-
-<p><b>H-P.</b> Abbreviation for horse-power.</p>
-
-<p><b>Hydrometer.</b> An instrument employed
-to determine the amount of
-moisture in the atmosphere.</p>
-
-<p>An instrument for determining
-through flotation the density or
-specific gravity of liquids and fluids.
-It consists of a weighted glass bulb
-or hollow metallic cylinder with a
-long stem on which the Baumé
-scale is marked. Dropping it into
-a liquid it floats in a vertical position,
-and sinks to a level consistent
-with the gravity of the fluid.</p>
-
-<p id="Ref013"><b>Hydrometer, Baumé.</b> An apparatus
-for testing the gravity of
-fluids. The zero point corresponds
-to the specific gravity of water for
-liquids heavier than water. A
-gauge, valuable in testing acids and
-other fluids used in electrical work.</p>
-
-<h3>I</h3>
-
-<p><b>Igniter.</b> A mechanical hand apparatus,
-in which a battery, induction-coil,
-and vibrator are located,
-and whose spark, jumping across a
-gap at the end of a rod, ignites or
-lights a gas flame, blasting-powder,
-or dynamite.</p>
-
-<p><b>I-H-P.</b> An abbreviation for indicated
-horse-power.</p>
-
-<p><b>Illuminating Power.</b> Any source
-of light as compared with a standard
-light&mdash;as, for instance, the illuminating
-power of an electric light
-reckoned in candle-power.</p>
-
-<p><b>Illumination.</b> A light given from
-any source and projected on a surface,
-per unit of area, directly or by
-reflection. It is stated in terms&mdash;as,
-for instance, the candle-power of
-a lamp. When speaking of an incandescent
-lamp we say it illuminates
-equal to four candle-power
-or it gives a light equal to sixteen
-candle-power.</p>
-
-<p id="Ref096"><b>Immersion, Simple.</b> Plating, without
-the aid of a battery, by simply
-immersing the metal in a solution
-of metallic salt.</p>
-
-<p><b>Impulse.</b> The motion produced
-by the sudden or momentary action
-of a force upon a body. An electro-magnetic
-impulse is the action produced
-by the electro-magnetic waves
-in magnetizing a mass of soft iron
-and attracting to it another mass
-of iron or steel.</p>
-
-<p>An electro-motive impulse is one
-where the force rises so high as to
-produce an impulsive discharge such
-as that from a Leyden-jar.</p>
-
-<p><b>Incandescence, Electric.</b> The
-heating of a conductor to red or
-white heat by the passage of an
-electric current. For example, an
-incandescent lamp.</p>
-
-<p><b>Incandescent Circuit.</b> (<i>See</i> <a href="#Ref050">Circuit,
-Incandescent</a>.)</p>
-
-<p><b>Incandescent Lamp-filament.</b>
-(<i>See</i> <a href="#Ref051">Filament</a>.)</p>
-
-<p><b>India-rubber.</b> (<i>See</i> <a href="#Ref053">Caoutchouc</a>
-and <a href="#Ref052">Gutta-percha</a>.)</p>
-
-<p><b>Indicator-card.</b> The card used
-in galvanoscopes, volt and ampere
-meters, and other instruments. It
-is provided with a moving needle
-and is marked with a graduated
-scale.</p>
-
-<p><span class="pagenum" id="Page387">[387]</span></p>
-
-<p><b>Induced.</b> Caused by induction,
-and not directly.</p>
-
-<p><b>Induced Current.</b> (<i>See</i> <a href="#Ref054">Current,
-Induced</a>.)</p>
-
-<p><b>Inductance.</b> That capacity of a
-circuit which enables it to exercise
-induction and create lines of force.</p>
-
-<p>Inductance is the ratio between
-the total induction through a circuit
-to the current producing it.</p>
-
-<p id="Ref012a"><b>Induction, Back.</b> A demagnetizing
-force produced in a dynamo
-armature when a lead is given to the
-brushes. When the brushes are so
-set the windings on the armature
-are virtually divided into two sets:
-one a direct magnetizing set, the
-other a cross-magnetizing set which
-exerts a demagnetizing action on
-the other set. The position of the
-brushes on a dynamo or motor is
-indicated by their location, and if
-changed back induction will be the
-result.</p>
-
-<p><b>Induction-coil.</b> (<i>See</i> <a href="#Ref055">Coil, Induction</a>.)</p>
-
-<p id="Ref036"><b>Induction, Electro-magnetic.</b>
-When negative and positive currents
-are brought towards each other
-against their material repulsive
-tendencies the result is work, or
-energy, and the consequent energy
-increases the intensity of both currents
-temporarily. The variations
-thus temporarily produced in the
-currents are examples of electro-magnetic
-induction. A current is
-surrounded by lines of force. The
-approach of two circuits&mdash;one negative,
-the other positive&mdash;involves a
-change in the lines of force about
-the secondary circuit. Lines of
-force and current are so intimately
-connected that a change in one
-compels a change in the other.
-Therefore, the induced current in
-the secondary may be attributed to
-the change in the field of force in
-which it lies. The inner and outer
-coils of wire about the soft iron
-wire composing an induction-coil
-are the best and simplest examples
-of electro-magnetic induction.</p>
-
-<p id="Ref064"><b>Induction, Magnetic.</b> The magnetization
-of iron or other paramagnetic
-substances by a magnetic
-field. The magnetic influence of a
-bar excited under these conditions
-is shown by throwing iron filings
-upon it. They will adhere to both
-ends (that is at the negative and
-positive poles) but not at the middle.</p>
-
-<p><b>Inductor.</b> A mass of iron in a
-current generator which is moved
-past a magnet-pole to increase the
-number of lines of force issuing therefrom.
-It is generally laminated, and
-is used in inductor dynamos and motors
-of the alternating-current type.</p>
-
-<p><b>Influence, Electric.</b> Electric induction
-or influence which may be
-electro-static, current, or electro-magnetic.</p>
-
-<p><b>Influence Machine.</b> A static electric
-machine worked by induction,
-and used to build up charges of opposite
-nature on two separate prime-conductors.</p>
-
-<p><b>Installation.</b> The entire apparatus,
-building, and appurtenances of
-a technical or manufacturing plant
-or power-house. An electric-light
-installation would mean the machinery,
-street-lines, lamps, etc.</p>
-
-<p><b>Insulating Joint.</b> Used for the
-purpose of insulating a gas-pipe
-from an electric circuit.</p>
-
-<p><b>Insulating Varnish.</b> A varnish
-composed of insulating material,
-such as gums, shellac, or diluted rubber.
-Shellac dissolved in alcohol is
-perhaps the best. It is easy to
-make and dries quickly, making an
-insulating surface practical for almost
-every ordinary use.</p>
-
-<p><b>Insulation.</b> The dielectric or non-conducting
-materials which are used
-to prevent the leakage of electricity.
-The covering for magnet wires, and<span class="pagenum" id="Page388">[388]</span>
-overhead conduits for power lines
-and electric lighting.</p>
-
-<p><b>Insulation, Oil.</b> Any non-combustible
-oil may be employed as an
-insulator to prevent electrical leakage
-in induction-coils, transformers,
-and the like. Its principal advantage
-lies in its being in liquid form,
-permitting of easy handling. Moreover,
-if pierced by a spark from a
-coil, it at once closes again without
-becoming ignited. A solid insulator,
-if pierced, is permanently injured.</p>
-
-<p><b>Insulator.</b> Any insulating substance
-or material to prevent the
-escape of current. The knobs of
-porcelain or glass to which wires
-are made fast.</p>
-
-<p><b>Insulator, Porcelain.</b> An insulator
-made of porcelain and used to
-support a wire.</p>
-
-<p><b>Intensity.</b> The intensity or
-strength of a current is its amperage.
-The strength of a magnetic
-field, its power to attract or magnetize.</p>
-
-<p><b>Internal Circuit.</b> (<i>See</i> <a href="#Ref056">Circuit,
-Internal</a>.)</p>
-
-<p><b>Internal Resistance.</b> (<i>See</i> <a href="#Ref057">Resistance,
-Internal</a>.)</p>
-
-<p><b>Interrupter.</b> A circuit-breaker.
-Any device which breaks or interrupts
-a circuit. It may be operated
-by hand or automatically.</p>
-
-<p>The vibrator of an induction-coil.</p>
-
-<p>The commutators of an armature.</p>
-
-<p><b>Isolated Plant.</b> The system of
-supplying electric energy by independent
-generating dynamos for
-each house, factory, or traction line.</p>
-
-<p><b>Isolation, Electric.</b> A term applied
-to “electric sunstroke.” Exposure
-to powerful arc-light produces
-effects resembling those of
-sunstroke.</p>
-
-<h3>J</h3>
-
-<p><b>Joint.</b> The point where two or
-more electric conductors join.</p>
-
-<p><b>Joint Resistance.</b> The united
-resistance offered by a number of
-resistances connected in parallel.</p>
-
-<p><b>Jumper.</b> A short circuit-shunt
-employed temporarily around an
-apparatus, lamp, or motor to cut
-out the current.</p>
-
-<p><b>Jump-spark.</b> A disruptive spark
-excited between two conducting surfaces
-in distinction from a spark excited
-by a rubbing contact.</p>
-
-<h3>K</h3>
-
-<p><b>Kaolin.</b> A form of earth or product
-of decomposed feldspar composed
-of silica and alumina. It is
-serviceable in insulating compounds.</p>
-
-<p><b>Kathode.</b> The terminal of an
-electric circuit whence an electrolyzing
-current passes from a solution.
-It is the terminal connected to the
-zinc pole of a battery or the article
-on which the electro-deposit is
-made.</p>
-
-<p><b>Key.</b> The arm of a telegraphic
-sounder by which the circuit is
-made and broken. A pivoted lever
-with a finger-piece which, when depressed,
-makes contact between a
-point and a stationary contact on
-the base.</p>
-
-<p><b>Keyboard.</b> A board, or table, on
-which keys or switches are mounted.</p>
-
-<p>A switchboard.</p>
-
-<p><b>Kilowatt.</b> A compound unit; one
-thousand watts; an electric-current
-measure. Abbreviation, K-W.</p>
-
-<p><b>Kilowatt Hour.</b> The result in
-work equal to the expenditure or
-exertion of one kilowatt in one hour.</p>
-
-<p><b>Kinetoscope.</b> A photographic
-instrument invented by Edison for
-obtaining the effect of a panorama
-or moving objects by the display of
-pictures in rapid succession&mdash;in familiar
-parlance, “moving pictures.”</p>
-
-<p><b>Knife Switch.</b> A switch with a
-narrow and deep, movable blade, or
-bar of copper or brass, which resembles<span class="pagenum" id="Page389">[389]</span>
-the blade of a knife. It is
-forced between two spring-clamps
-attached to one terminal so as to
-make perfect contact.</p>
-
-<h3>L</h3>
-
-<p><b>Laminated.</b> Made up of thin
-plates, as an armature-core.</p>
-
-<p><b>Laminated Core.</b> (<i>See</i> <a href="#Ref058">Core, Laminated</a>.)</p>
-
-<p><b>Lamp-Arc.</b> A lamp in which the
-light is produced by a voltaic arc.
-Carbon electrodes are used, and a
-special mechanism operates and
-regulates the space between the
-carbons so that a perfect arc may
-be maintained.</p>
-
-<p><b>Lamp, Incandescent.</b> A lamp in
-which the light is produced through
-heating a filament to whiteness by
-the electric current. It consists of
-a glass bulb from which the air is
-exhausted and sealed, after the
-filament is enclosed. The ends of
-the filament are attached to platinum
-wires, which in turn are made
-fast to the contact-plates at the
-head of the lamp, so as to connect
-with the current.</p>
-
-<p><b>Lamp-socket.</b> A receptacle for
-an incandescent lamp. It is generally
-made of brass and provided
-with a key-switch to turn the current
-on and off.</p>
-
-<p><b>Latent Electricity.</b> (<i>See</i> <a href="#Ref059">Electricity,
-Latent</a>.)</p>
-
-<p><b>Lead.</b> (Not the metal.) An insulated
-conductor which leads to
-and from a source of power; an
-insulated conductor to and from a
-telegraph or telephone instrument;
-a circuit, a battery, or a station.
-Not a part of the line circuit.</p>
-
-<p>That part of an electric light or
-power circuit which leads from the
-main to the lamps or motors.</p>
-
-<p><b>Leading-in Wires.</b> The wires
-which lead into a building from an
-aerial circuit.</p>
-
-<p>The wires which lead in and out
-from a lamp, battery, or instrument.</p>
-
-<p><b>Leak.</b> An escape of electrical energy
-through leakage. This is more
-liable to occur in bare than in insulated
-wires. The escape of current
-from bare trolley wires is much
-greater than that from the insulated
-conductors, particularly in damp or
-rainy weather.</p>
-
-<p><b>Leclanché Battery.</b> (<i>See</i> <a href="#Ref060">Battery,
-Leclanché</a>.)</p>
-
-<p><b>Leyden-jar.</b> A type of static condenser.
-Its usual form is a glass
-jar. Tin-foil is pasted about its
-inner and outer surfaces covering
-about half the wall. The balance
-of the glass is painted with shellac
-or insulating varnish. The mouth
-is closed with a cork stopper, and
-through its centre a brass rod is
-passed which, by a short chain, is
-connected with the interior coating
-of the jar. The top of the rod is provided
-with a brass knob or ball, and
-from this last the spark is drawn.</p>
-
-<p><b>Lightning.</b> The electro-static discharge
-of clouds floating in the atmosphere.
-It is the highest form
-of frictional electricity, uncontrollable
-and very dangerous, since the
-strength of a single flash may run
-into hundreds of thousands of volts.</p>
-
-<p><b>Lightning-arrester.</b> An apparatus
-for use with electric lines to carry
-off to earth any lightning discharges
-that such lines may pick up; or it
-may be a form of fuse which burns
-out before the current can do any
-harm to the electrical mechanism.</p>
-
-<p><b>Line-insulator.</b> An insulator serving
-to support an aerial line.</p>
-
-<p><b>Lineman.</b> A workman whose
-business is the practical part of electrical
-construction in lines and conducting
-circuits.</p>
-
-<p><b>Link-fuse.</b> A plate of fusible
-metal in the shape of a link. It is
-used as a safety-fuse in connection
-with copper terminals.</p>
-
-<p><span class="pagenum" id="Page390">[390]</span></p>
-
-<p><b>Liquefaction, Electric.</b> The conversion
-of a solid into a liquid by
-the sole agency of electricity in its
-heat action upon the solid.</p>
-
-<p><b>Liquid Resistance.</b> (<i>See</i> <a href="#Ref061">Resistance,
-Liquid</a>.)</p>
-
-<p><b>Lithanode.</b> A block of compressed
-lead binoxide, with platinum
-connections, for use in a storage
-battery.</p>
-
-<p><b>Litharge.</b> Yellow-lead. A chemical
-form of metallic lead.</p>
-
-<p><b>Load.</b> In a dynamo, the amperes
-of current delivered by it under
-given conditions of speed, etc.</p>
-
-<p><b>Local Action.</b> In a battery, the
-loss of current due to impurities in
-the zinc. The currents may circulate
-in exceedingly minute circles,
-but they waste zinc and chemicals
-and contribute nothing to the efficiency
-of the battery.</p>
-
-<p>In a dynamo, the loss of energy
-through the formation of eddy currents
-in its core or armature, in the
-pole pieces, or in other conducting
-bodies.</p>
-
-<p><b>Lodestone.</b> The scientific name
-is magnetite. Some samples possess
-polarity and attract iron; these are
-called lodestones.</p>
-
-<p><b>Loop.</b> A portion of a circuit introduced
-in series into another circuit.</p>
-
-<p><b>Low Frequency.</b> A frequency (in
-current vibrations) of comparatively
-few alternations per second.</p>
-
-<p><b>Low Potential Current.</b> (<i>See</i> <a href="#Ref062">Current,
-Low Potential</a>.)</p>
-
-<p><b>Luminescence.</b> The power or
-properties some bodies have of giving
-out light when their molecular
-mass is excited. For example, phosphorus
-and radium.</p>
-
-<p><b>Luminous Heat.</b> The radiation
-of heat by electric current, which at
-the same time produces light. For
-example, the filament in an incandescent
-lamp.</p>
-
-<p><b>Luminous Jar.</b> A Leyden-jar
-whose coatings are of lozenge-shaped
-pieces of tin-foil between which are
-very short spaces. When discharged,
-sparks appear all over the surface
-where the small plates of metal nearly
-join.</p>
-
-<h3>M</h3>
-
-<p><b>Magnet.</b> A substance or metal
-having the power to attract iron
-and steel.</p>
-
-<p><b>Magnet-bar.</b> A magnet in the
-shape of a straight bar. (<i>See</i> <a href="#Ref063">Bar-magnet</a>.)</p>
-
-<p><b>Magnet-coil.</b> A coil of insulated
-wire enclosing a core of soft iron
-through which a current of electricity
-is passed to magnetize the
-iron.</p>
-
-<p><b>Magnet-core.</b> An iron bar or
-mass of iron around which insulated
-wire is wound in order to create an
-electro-magnet.</p>
-
-<p><b>Magnet, Electric.</b> A magnet consisting
-of a bar of iron, a bundle of
-iron wires, or an iron tube, around
-which a coil of insulated wire is
-wound. When a current is passing
-through the coil its influence
-magnetizes the iron core, but directly
-the current ceases the magnetism
-disappears.</p>
-
-<p id="Ref043"><b>Magnet, Field.</b> The electro or
-permanent magnet in a dynamo or
-motor, used to produce the area of
-electric energy.</p>
-
-<p id="Ref049"><b>Magnet, Horseshoe.</b> A magnet
-of U shape with the poles or ends
-brought closer together than the
-other parts of the limbs. A soft
-iron bar is placed across the poles
-when not in use, as this serves to
-conserve the magnetism.</p>
-
-<p id="Ref076"><b>Magnet, Permanent.</b> A term applied
-to a hard steel magnet possessing
-high retentivity, or the power to
-hold its magnetism indefinitely.</p>
-
-<p id="Ref084"><b>Magnet, Regulator.</b> An electro-magnet
-whose armature moves in
-such a manner as to automatically<span class="pagenum" id="Page391">[391]</span>
-shift the commutator-brushes, on
-a motor or dynamo, to a position
-which insures the preservation of
-both brushes and commutator-bars,
-and also produces a constant current.</p>
-
-<p id="Ref097"><b>Magnet, Simple.</b> A magnet made
-of one piece of metal.</p>
-
-<p><b>Magnet Wire.</b> Insulated wire
-used for coils. Cotton or silk covered
-wire is the most serviceable for
-winding magnets.</p>
-
-<p><b>Magnetic Adherence.</b> The tendency
-of a mass of iron to adhere to
-the poles of a magnet.</p>
-
-<p><b>Magnetic Attraction and Repulsion.</b>
-The attraction of a magnet
-for iron, steel, nickel, and cobalt;
-also of unlike poles of magnets for
-each other. The like poles repel.</p>
-
-<p><b>Magnetic Circuit-breakers.</b> An
-automatic switch, or breaker, whose
-action is excited and controlled by
-an electro-magnet.</p>
-
-<p><b>Magnetic Concentration of Ores.</b>
-The separation of iron and steel
-from their gangue by magnetic attraction.
-It is applicable only when
-either the ore or the gangue is susceptible
-to the magnet.</p>
-
-<p><b>Magnetic Control.</b> The control of
-a magnetic needle, magnet, index,
-armature, or other iron indicator in
-a galvanometer, ammeter, or voltmeter
-by a magnetic field.</p>
-
-<p><b>Magnetic Dip.</b> The inclination
-from the horizontal position of a magnetic
-needle that is free to move in
-a vertical plane.</p>
-
-<p id="Ref090"><b>Magnetic Field, Rotary.</b> A magnetic
-field resulting from a rotary
-current.</p>
-
-<p id="Ref093"><b>Magnetic Field, Shifting.</b> A magnetic
-field which rotates. Its lines
-of magnetic force vary, therefore, in
-position.</p>
-
-<p id="Ref108"><b>Magnetic Field, Uniform.</b> A field
-of uniform strength in all portions,
-such as the magnetic field of the
-earth.</p>
-
-<p><b>Magnetic Force.</b> The power of attraction
-and repulsion exercised by
-a magnet; the force of attraction and
-repulsion which a magnet exercises,
-and which, in its ultimate essence, is
-unknown to science.</p>
-
-<p><b>Magnetic Induction.</b> (<i>See</i> <a href="#Ref064">Induction,
-Magnetic</a>.)</p>
-
-<p><b>Magnetic Needle.</b> A magnet having
-a cup or small depression at its
-centre, and poised on a sharp pin of
-brass, so as to be free to rotate. Its
-N pole points to the north, and its
-S pole to the south. A compass
-needle.</p>
-
-<p><b>Magnetic Poles.</b> The terrestrial
-points towards which the north or
-south poles of the magnetic needle
-are attracted. There are two poles:
-the arctic, or negative, which attracts
-the positive or N pole of the
-magnetic needle; and the antarctic,
-or positive, which attracts the S pole
-of the needle.</p>
-
-<p id="Ref040"><b>Magnetic Poles, False.</b> It has
-been established that there are other
-poles on the earth that attract the
-magnetic needle when the latter is
-brought into their vicinity. These
-are called false poles, and are probably
-caused by large deposits of
-iron lying close to the surface of the
-earth.</p>
-
-<p><b>Magnetic Separator.</b> An apparatus
-for separating magnetic substances
-from mixtures. It is used
-chiefly in separating iron ore from
-earth and rock. The mineral falls
-on an iron cylinder, or drum, magnetized
-by coils, and adheres there,
-while the earth or crushed rock
-drops below. The particles of iron
-are afterwards removed by a scraper.
-The machine is also used in separating
-iron filings and chips from brass,
-copper, or other metals, the iron
-adhering to the magnet, while the
-brass and other chips drop underneath.</p>
-
-<p><b>Magnetism.</b> The phenomena of attraction
-exerted by one body for
-another. It has been commonly
-understood that magnetism and
-electricity are very closely related,<span class="pagenum" id="Page392">[392]</span>
-for without electricity magnetism
-could not exist, although it has not
-been shown clearly that magnetism
-plays any part in the generation of
-electricity. Magnetism is the phenomenal
-force exerted by one body
-having two poles (negative and positive)
-for like bodies. The horseshoe
-magnet or a bar of magnetized
-steel are the simplest examples of
-this. If both ends of the horseshoe
-were positive they would not attract,
-but would repel. If both
-ends of a bar were positive they
-would repel; but as one is negative,
-or north-seeking, and the other positive,
-they exert lines of force which
-attract like bodies, such as bits of
-iron, nails, and needles. No energy
-is required to maintain magnetism
-in a tempered steel object, such as
-the wiring about a soft iron core
-when it has been magnetized, but
-electric current must flow about the
-soft iron core in order to render it
-a magnet. So soon as the current
-ceases to flow the magnetism ceases
-and the soft iron fails to attract.</p>
-
-<p><b>Magnetism, Uniform.</b> Magnetism
-that is uniform throughout a mass
-of magnetic steel, or a core that is
-electro-magnetic.</p>
-
-<p><b>Magnetize.</b> To impart magnetic
-property to a substance capable of
-receiving it.</p>
-
-<p id="Ref020"><b>Magnetizing-coil.</b> (<i>See</i> <a href="#Ref065">Coil, Magnetizing</a>.)</p>
-
-<p><b>Magneto Call-bell.</b> A call-bell
-used principally in telephone systems,
-and operated by a current
-from a magneto-electric generator.
-The current is excited by turning
-the handle at the side of the telephone-box
-before removing the receiver
-from the hook.</p>
-
-<p><b>Magneto-generator.</b> A current-generator
-composed of a permanent
-magnet and a revolving armature
-which is rotated between the poles
-of the permanent magnet.</p>
-
-<p><b>Main Circuit.</b> (<i>See</i> <a href="#Ref066">Circuit, Main</a>.)</p>
-
-<p><b>Main Feeder.</b> The main wire in
-a district to which all the feeder
-wires are attached.</p>
-
-<p><b>Main Switch.</b> The switch connected
-to the main wire of a line,
-or the main-switch controlling a
-number of auxiliary switches.</p>
-
-<p><b>Mains, Electric.</b> The large conductors
-in a system of electric light
-or power distribution.</p>
-
-<p><b>Make and Break, Automatic.</b> An
-apparatus which enables the armature
-of a magnet to make and break
-its circuit automatically.</p>
-
-<p><b>Make-and-break Current.</b> (<i>See</i>
-<a href="#Ref067">Current, Make-and-break</a>.)</p>
-
-<p><b>Mercurial Air-pump.</b> An air-pump
-operated by mercury to
-obtain a high vacuum, and used
-extensively for exhausting incandescent-lamp
-bulbs.</p>
-
-<p><b>Mercury Tube.</b> A glass tube
-sealed and containing mercury. It
-is so arranged as to give out fluorescent
-light when shaken or agitated
-by an electric current. For example,
-the Geissler tubes, the Cooper-Hewitt
-light, Crook’s tubes, etc.</p>
-
-<p><b>Metallic Arc.</b> An arc which forms
-between metallic electrodes.</p>
-
-<p><b>Metallic Circuit.</b> (<i>See</i> <a href="#Ref068">Circuit,
-Metallic</a>.)</p>
-
-<p><b>Metallic Conductor.</b> A conductor
-composed of a metal.</p>
-
-<p><b>Metallic Filament.</b> A metal wire
-used in an incandescent lamp&mdash;the
-filament.</p>
-
-<p><b>Metallic Resistance.</b> (<i>See</i> <a href="#Ref069">Resistance,
-Metallic</a>.)</p>
-
-<p><b>Metallurgy.</b> The art of working
-metals. Electro-metallurgy applies
-to the processes wherein electricity
-plays the most important part.</p>
-
-<p><b>Mica.</b> A natural mineral of sheet
-form and translucent, used extensively<span class="pagenum" id="Page393">[393]</span>
-as an insulator in electrical
-equipment and mechanism.</p>
-
-<p><b>Mica, Moulded.</b> A composition
-composed of ground mica and shellac
-as a binder. When heated and
-pressed into various shapes and
-forms, it is a valuable insulator, and
-is employed for hooks, locks, tubes,
-sockets, and the like.</p>
-
-<p><b>Micanite.</b> An insulating material
-made by cementing laminations of
-pure mica together and cementing
-them with shellac or other suitable
-non-conducting adhesives.</p>
-
-<p><b>Molecular Adhesion.</b> The attraction
-of similar molecules for each
-other.</p>
-
-<p><b>Molecular Attraction.</b> The attraction
-of molecules, or physical
-affinity.</p>
-
-<p><b>Molecular Resistance.</b> The resistance
-which a mass or electrolyte
-offers when contained in an insulated
-vessel and a current of electricity
-is passed through it.</p>
-
-<p><b>Molecule.</b> One of the invisible
-particles supposed to constitute
-matter of every kind; the smallest
-particle of matter that can exist
-independently. It is made up of
-atoms, but an atom cannot exist
-alone.</p>
-
-<p><b>Morse Receiver.</b> The receiving
-instrument once universally used in
-the Morse system of telegraphy, but
-now superseded by the sounder.</p>
-
-<p><b>Morse Recorder.</b> An apparatus
-which automatically records on a
-ribbon of paper the dots and dashes
-of the Morse telegraph alphabet.</p>
-
-<p><b>Morse Sounder.</b> An electro-magnetic
-instrument designed to make
-a sharp, clicking sound when its
-armature lever is drawn down by
-the attraction of the magnets.</p>
-
-<p><b>Morse System.</b> A telegraphic
-system invented by Prof. S. F. B.
-Morse, in which, by means of alternating
-makes and breaks of varying
-duration, the dots and dashes of the
-Morse alphabet are reproduced and
-received at a distance through the
-agency of wires and the electro-magnetic
-sounder.</p>
-
-<p><b>Motor, Electric.</b> A machine or
-apparatus for converting electric energy
-into mechanical kinetic energy
-or power. The electrical energy is
-usually generated by a dynamo, and
-distributed on conductors to motors
-located at various points.</p>
-
-<p>Electric motors are of two types&mdash;the
-A-C., or alternating current,
-and the D-C., or direct current.</p>
-
-<p><b>Motor-car, Electric.</b> A self-propelling
-car driven by stored electricity.</p>
-
-<p id="Ref029"><b>Motor-dynamo.</b> A motor driven
-by a dynamo whose armature is
-firmly attached or connected to
-that of the dynamo. It is used for
-modifying a current. If the dynamo
-generates an alternating current of
-high potential, the motor converts
-it into a direct current of lower voltage
-but increased amperage.</p>
-
-<p><b>Motor-transformer.</b> A transformer
-which is operated by a motor.</p>
-
-<p>A dynamo-electric machine provided
-with two armature windings,
-one serving to receive current, as a
-motor, the other to deliver current,
-as a generator, to a secondary circuit.</p>
-
-<h3>N</h3>
-
-<p><b>N.</b> An abbreviation for the north-seeking
-pole in a magnet.</p>
-
-<p><b>Natural Magnet.</b> A loadstone.</p>
-
-<p><b>Needle.</b> A term applied to a bar-magnet
-poised horizontally upon a
-vertical point.</p>
-
-<p>A magnetic needle, or the magnet
-in a mariner’s compass.</p>
-
-<p><b>Negative.</b> Opposed to positive.</p>
-
-<p id="Ref031"><b>Negative Electricity.</b> The kind of
-electricity with which a piece of
-amber is charged by friction with
-flannel.</p>
-
-<p>In a galvanic battery or cell the<span class="pagenum" id="Page394">[394]</span>
-surface of the zinc is charged with
-negative electricity. Negative electricity,
-according to the theory of
-some scientists, really means a deficiency
-of electricity.</p>
-
-<p><b>Negative Electrode.</b> The same as
-Negative Element.</p>
-
-<p><b>Negative Element.</b> The plate not
-dissolved by the solution in a voltaic
-cell; the one which is positively
-charged.</p>
-
-<p>The carbon, platinum, or copper
-plate or pole in a battery.</p>
-
-<p><b>Negative Feeder.</b> The conductor
-which connects the negative mains
-with the negative poles of a generator.</p>
-
-<p><b>Negative Plate.</b> (<i>See</i> <a href="#Ref070">Plate, Negative</a>.)</p>
-
-<p><b>Negative Pole.</b> (<i>See</i> <a href="#Ref071">Pole, Negative</a>.)</p>
-
-<p><b>Neutral Feeder.</b> The same as
-Neutral Wire.</p>
-
-<p><b>Neutral Wire.</b> The central wire
-in a three-wire system.</p>
-
-<p><b>Nickel-bath.</b> A bath for the
-electro-deposition of nickel.</p>
-
-<p><b>Non-arcing Fuse.</b> A fuse-wire
-which is enclosed in a tube packed
-with asbestos or silk, and which
-does not produce an arc when it
-fuses or blows out. It is practically
-noiseless, save for a slight hissing
-sound, accompanied by a light puff
-of smoke, which escapes from a venthole
-in the side of the tube.</p>
-
-<p><b>Non-conductor.</b> A material or
-substance offering very high resistance
-to the passage of the electric
-current.</p>
-
-<p><b>Non-magnetic Steel.</b> Alloys of
-iron incapable of being magnetized.
-They are composed of iron and manganese,
-nickel, steel, etc.</p>
-
-<p><b>Normal.</b> Regular. The average
-value of observed quantities. Normal
-current is a regular current without
-variations.</p>
-
-<p>The force of a current at which a
-system is intended to work.</p>
-
-<p><b>Normal Voltage.</b> The same as
-Normal Current.</p>
-
-<p><b>North Pole.</b> The north-seeking
-pole of a magnet.</p>
-
-<p>The pole of a magnet which tends
-to point to the north, and whence
-lines of force are assumed to issue
-on their course to the other pole of
-the magnet.</p>
-
-<h3>O</h3>
-
-<p><b>O.</b> An abbreviation for Ohm.</p>
-
-<p><b>Oersted’s Discovery.</b> Oersted discovered,
-in 1820, that a magnetic
-needle tended to place itself at
-right angles to a current of electricity.
-This fundamental principle
-is the basis of the galvanometer,
-the dynamo, and the motor.</p>
-
-<p><b>Ohm.</b> The practical unit of resistance.
-A legal ohm is the resistance
-of a column of mercury one
-square millimetre in cross-sectional
-area and 106.24 centimetres in
-length.</p>
-
-<p id="Ref105"><b>Ohm, True.</b> The true ohm is the
-resistance of a column of mercury
-106.24 centimetres long and one
-square millimetre in cross-sectional
-area. An ohm may be measured by
-a No. 30 copper wire nine feet and
-nine inches long. If larger size wire
-is used the piece must be proportionately
-longer, since the resistance is
-less.</p>
-
-<p id="Ref088"><b>Ohmic Resistance.</b> True resistance
-as distinguished from spurious
-resistance, or counter electro-motive
-force. (<i>See also</i> <a href="#Ref072">Resistance,
-Ohmic</a>.)</p>
-
-<p><b>Ohm’s Law.</b> The basic law which
-expresses the relations between current,
-electro-motive force, and resistance
-in active circuits. It is formulated
-as follows:</p>
-
-<p>1. The current strength is equal
-to the electro-motive force divided
-by the resistance.</p>
-
-<p>2. The electro-motive force is<span class="pagenum" id="Page395">[395]</span>
-equal to the current strength multiplied
-by the resistance.</p>
-
-<p>3. The resistance is equal to the
-electro-motive force divided by the
-current strength.</p>
-
-<p><b>O. K.</b> A telegraphic signal meaning
-yes, or all right. It is supposed
-to be a misspelled form of all correct,
-“Oll Kerrekt.”</p>
-
-<p><b>Okonite.</b> A form of insulation
-for wires and conductors; a trade
-name applied to insulations, and protected
-by copyright.</p>
-
-<p><b>Open Arc.</b> A voltaic arc not enclosed.</p>
-
-<p><b>Open Circuit.</b> (<i>See</i> <a href="#Ref073">Circuit, Open</a>.)</p>
-
-<p><b>Oscillating Current.</b> (<i>See</i> <a href="#Ref074">Current,
-Oscillating</a>.)</p>
-
-<p><b>Outlet.</b> That part of an electrolier
-or electric light fixture out
-of which the wires are led for attachment
-to incandescent light sockets.</p>
-
-<p><b>Outside Wiring.</b> The wiring for
-an electric circuit which is located
-outside a building or other structure.</p>
-
-<p><b>Overhead Feeders.</b> The same as
-overhead conductors.</p>
-
-<p><b>Overhead Trolley.</b> The system
-in which the current for the propulsion
-of trolley-cars is taken from
-overhead feeders or wires.</p>
-
-<p><b>Overhead Trolley-wire.</b> A naked,
-hard copper wire drawn at high tension,
-and suspended over or at the
-side of a car-track, and from which
-the trolley-wheel takes its current.</p>
-
-<p><b>Overload.</b> In an electric motor,
-an excess of mechanical load prevents
-economical working, causing
-the armature to revolve slowly and
-the wiring to heat. In this case
-heating implies waste of energy.</p>
-
-<p><b>Overload Switch.</b> A switch which
-operates automatically to open a
-circuit in line with a motor, and so
-save the motor from overheating or
-burning in the event of an overload.</p>
-
-<h3>P</h3>
-
-<p><b>Paper Cable.</b> A cable insulated
-with waxed or paraffined paper.</p>
-
-<p><b>Paraffine.</b> A residuum of petroleum
-oil, valuable as an insulating
-medium in electrical work.</p>
-
-<p>A hydro-carbon composition of
-the highest resistance known. It is
-extensively used in condensers and
-other electrical apparatus as a dielectric
-and insulator.</p>
-
-<p><b>Parallel Distribution.</b> A distributing
-system for electricity wherein
-the receptive contrivances are
-adjusted between every two of a
-number of parallel conductors running
-to the limits of the system.
-When two or more conductors connect
-two mains of comparatively
-large size and low resistance, they
-are said to be in parallel or in multiple.
-This order is easily pictured
-by imagining the mains to be the
-sides of a ladder and the conductors
-the rungs. In the latter the lamps
-are placed. It follows that the current
-flows from one main to the other
-through the conductors and lamps.</p>
-
-<p><b>Paramagnetic.</b> Substances which
-have magnetic properties, or those
-which are attracted by magnetic
-bodies. A paramagnetic substance
-has high multiplying power for lines
-of force, therefore a bar of iron which
-is a paramagnetic substance of the
-highest quality becomes magnetic
-when placed within a circle of electric
-lines of force. The first example
-of paramagnetic substance brought
-to the attention of man was the lodestone,
-from which the ancient mariners
-fashioned their crude compass
-needles.</p>
-
-<p><b>P-C.</b> An abbreviation for porous
-cup.</p>
-
-<p><b>Pear Push.</b> A push-button enclosed
-in a handle having the shape
-of a pear. It is generally attached
-to the end of a flexible wire cord.</p>
-
-<p><span class="pagenum" id="Page396">[396]</span></p>
-
-<p><b>Periodic Current.</b> (<i>See</i> <a href="#Ref075">Current,
-Periodic</a>.)</p>
-
-<p><b>Permanency, Electric.</b> The power
-of conductors to retain their conductivity
-unaffected by the lapse
-of time.</p>
-
-<p><b>Permanent Magnet.</b> (<i>See</i> <a href="#Ref076">Magnet,
-Permanent</a>.)</p>
-
-<p><b>Phase.</b> One complete oscillation.
-The interval elapsing from the time
-a particle moves through the middle
-point of its course to the instant
-when the phase is to be stated.</p>
-
-<p>Simple harmonic motion. Oscillation.</p>
-
-<p><b>’Phone.</b> An abbreviation for the
-word Telephone.</p>
-
-<p><b>Phonograph.</b> An apparatus for
-reproducing sound. It is vibratory
-and not electric in its action, except
-that the mechanism may be driven by
-electricity. It consists of a rotating
-cylinder of a waxlike material
-and a glass diaphragm carrying a
-needle-point that lightly touches
-the surface of the waxen cylinder.
-If the diaphragm is agitated the
-needle vibrates, making indentations
-in the surface of the wax. If
-the needle is set back and the cylinder
-rotated so as to carry the point
-over the indentations, the sound is
-given back through the vibration of
-the diaphragm.</p>
-
-<p><b>Pickle.</b> An acid solution used to
-cleanse metallic surfaces preparatory
-to electro-plating.</p>
-
-<p><b>Pilot Wires.</b> Wires brought from
-distant parts of electric light and
-power mains, and leading to voltmeters
-at a central station. Through
-their agency the potential energy of
-every part of the system may be
-measured.</p>
-
-<p><b>Pith-balls.</b> Balls made from the
-pith of light wood, such as elder.
-They are used in the construction
-of electroscopes and for other experiments
-in static electricity.</p>
-
-<p><b>Plant.</b> The apparatus for generating
-electric current, including
-engines, boilers, dynamos, mains,
-and subsidiary apparatus.</p>
-
-<p id="Ref024"><b>Plate, Condenser.</b> In a static
-apparatus, the condenser having a
-flat piece of glass for a dielectric.
-It is mounted on an axle so that it
-may be revolved.</p>
-
-<p id="Ref047"><b>Plate, Ground.</b> In a lightning-arrester,
-the plate connected to the
-earth or ground wire.</p>
-
-<p id="Ref070"><b>Plate, Negative.</b> In a voltaic
-battery, the plate which is unattacked
-by the fluid. It is made of
-carbon, platinum, or copper.</p>
-
-<p><b>Plate, Positive.</b> (<i>See</i> <a href="#Ref077">Positive
-Plate</a>.)</p>
-
-<p><b>Plating-bath.</b> A vessel of solution
-for the deposition of metal by
-electrolysis. Used in electro-plating.</p>
-
-<p id="Ref037"><b>Plating, Electro.</b> The process of
-depositing metal on surfaces of
-metals or other substances by the
-aid of an electrolyte and the electric
-current.</p>
-
-<p><b>Platinum Fuse.</b> A slender wire
-of platinum roused to incandescence
-by current, and used to explode a
-charge of powder or other combustible
-substance.</p>
-
-<p><b>Plug.</b> A piece of metal, with a
-handle, used to make electric connections
-by being inserted between
-two slightly separated plates or
-blocks of metal.</p>
-
-<p>A wedge of metal, slightly tapered,
-and used to thrust between two
-conductors to close or complete a
-circuit.</p>
-
-<p><b>Plumbago.</b> Soft, lustrous graphite;
-a native form of carbon sometimes
-chemically purified. It is used
-chiefly in electrotyping for dusting
-the wax moulds to make the surface
-an electric conductor.</p>
-
-<p><b>Plunge-battery.</b> (<i>See</i> <a href="#Ref078">Battery,
-Plunge</a>.)</p>
-
-<p><b>Polar.</b> Pertaining to one of the
-poles of a magnet.</p>
-
-<p><span class="pagenum" id="Page397">[397]</span></p>
-
-<p><b>Polarity.</b> The disposition in a
-body to place its axis in a particular
-direction when influenced by magnetism.
-For example, the attraction
-and repulsion at the opposite
-ends of a magnet. The N and S
-seeking poles of a compass needle is
-the simplest example.</p>
-
-<p><b>Polarity, Electric.</b> The disposition
-in a paramagnetic body to be
-influenced by electric waves and
-lines of force. The otherwise non-magnetic
-body or mass becomes
-magnetic to attract or repulse when
-influenced by electricity, but ceases
-to retain the phenomena after the
-electric influence is removed. A
-piece of soft iron wire, a nail, or a
-short rod of iron will become electro-polarized
-when a current of electricity
-is sent through a coil of insulated
-wire so wound that one end
-will be N the other S. So soon as
-the circuit is broken the polarity
-ceases.</p>
-
-<p><b>Polarization.</b> The depriving of a
-voltaic cell of its proper electro-motive
-force. This may be brought
-about through the solution becoming
-spent, or in the event of the acid
-being saturated with zinc, and so
-failing to act on the metallic zinc.</p>
-
-<p>Counter electro-motive force due
-to the accumulation of hydrogen on
-the negative plate.</p>
-
-<p><b>Polarizing-current.</b> (<i>See</i> <a href="#Ref079">Current,
-Polarizing</a>.)</p>
-
-<p><b>Polar Surface.</b> The surface of a
-magnetic substance through which
-the magnetic flux passes in or out.</p>
-
-<p><b>Pole-changer.</b> An automatic, oscillating
-switch or contact-breaker
-which reverses the direction of the
-current.</p>
-
-<p id="Ref071"><b>Pole, Negative.</b> The S pole in a
-magnet or compass needle.</p>
-
-<p><b>Pole, Positive.</b> (<i>See</i> <a href="#Ref080">Positive
-Pole</a>.)</p>
-
-<p><b>Pole-switch, Single.</b> A switch designed
-to open or close one lead only.</p>
-
-<p><b>Poles.</b> The terminals of an open
-electric circuit at which there necessarily
-exists a potential difference.</p>
-
-<p>The terminals of an open magnetic
-circuit, or the ends of a magnetized
-mass of iron.</p>
-
-<p><b>Porcelain.</b> A fine variety of earthenware,
-valuable for insulators and
-insulating purposes.</p>
-
-<p><b>Porosity.</b> The state or property
-of having small interstices or holes.
-The opposite of density.</p>
-
-<p><b>Porous Cup or Cell.</b> A cup or
-cell made of pipe-clay or of unglazed
-earthenware through which
-a current of electricity can pass
-when wet or in a liquid. Porous
-cups are used in cells and batteries
-to keep two liquids apart, and yet
-permit electrolysis and electrolytic
-conduction.</p>
-
-<p id="Ref026"><b>Positive Currents.</b> Currents which
-deflect the needle to the left.</p>
-
-<p id="Ref032"><b>Positive Electricity.</b> The current
-that flows from the active element,
-the zinc in a battery, to the carbon.
-The negative electricity flows from
-the carbon to the zinc.</p>
-
-<p><b>Positive Electrode.</b> The electrode
-which is connected with the positive
-pole of a source of electric energy.</p>
-
-<p><b>Positive Feeders.</b> The lead or
-wire in a set of feeders which is connected
-to the positive terminal of
-the generator.</p>
-
-<p id="Ref077"><b>Positive Plate.</b> In a voltaic cell,
-the plate which is acted upon and
-corroded. The current from the
-positive plate is negative electricity.</p>
-
-<p id="Ref080"><b>Positive Pole.</b> The N pole in a
-magnet or magnetic needle. So
-called because it seeks the north
-or negative pole of the earth.</p>
-
-<p><b>Positive Wire, or Conductor.</b> The
-wire, or conductor, connected with
-the positive pole of any apparatus
-which produces electro-motive force.</p>
-
-<p><b>Potential, Electric.</b> The power to
-perform electric work.</p>
-
-<p><b>Potential Energy.</b> Capacity for<span class="pagenum" id="Page398">[398]</span>
-doing work. Potential energy when
-liberated becomes actual energy for
-the performance of work.</p>
-
-<p><b>Power-generator.</b> Any source
-from which power is generated.</p>
-
-<p><b>Power-house.</b> A station in which
-the plant of an electric power system
-is operated and the current distributed
-to local or long-distance
-points. Power-houses are either
-primary or secondary stations. In
-the primary station the current is
-generated directly by the aid of
-mechanical power, either the steam-engine
-or the steam-turbine. The
-secondary station, or sub-station,
-is located at a distance from the
-main power-house, and has no mechanical
-means of generating current.
-The current, usually of high
-alternating voltage, is supplied to
-the sub-station from the main power-house;
-and by means of transformers
-and converters, the high-voltage
-current is transformed into one of
-lower E-M-F and higher amperage,
-for distribution over local lines.</p>
-
-<p><b>Power-unit.</b> The unit of electric
-power is the volt-ampere or watt.</p>
-
-<p><b>Pressure, Electric.</b> Electro-motive
-force or voltage.</p>
-
-<p><b>Primary.</b> A term used to designate
-the induction-coil in an induction-apparatus
-or transformer.
-It is an abbreviation for primary
-coil.</p>
-
-<p><b>Primary Battery.</b> (<i>See</i> <a href="#Ref081">Battery,
-Primary</a>.)</p>
-
-<p><b>Prime Conductor.</b> (<i>See</i> <a href="#Ref082">Conductor,
-Prime</a>.)</p>
-
-<p><b>Push-button.</b> A switch for closing
-a circuit by means of pressure
-applied to a button. The button
-is provided with a spring, so that
-when pushed in and released it flies
-back, reopening the circuit.</p>
-
-<p><b>Pyrogravure.</b> A process of engraving
-by the use of platinum points
-heated to redness by the electric
-current.</p>
-
-<h3>Q</h3>
-
-<p><b>Q.</b> Abbreviation or symbol for
-electric quantity.</p>
-
-<p><b>Quadrant.</b> The quarter of a circle
-or of its circumference.</p>
-
-<p><b>Quadruple Circuit.</b> (<i>See</i> <a href="#Ref083">Circuit,
-Quadruple</a>.)</p>
-
-<p><b>Quantity.</b> The term is applied
-to express arrangements of electrical
-connections for giving the
-largest possible amount of current.</p>
-
-<p><b>Quantity, Electro-magnetic.</b> The
-electro-magnetic current measured
-by its intensity for a second of time.</p>
-
-<p><b>Quick-break.</b> A break affected in
-an electric current by the employment
-of a quick-break switch.</p>
-
-<p><b>Quickening.</b> The amalgamating
-of the surface of a metallic object
-before electro-plating it with silver.
-This secures better adhesion of the
-deposit, and is done by dipping the
-article into a solution of mercurial
-salts&mdash;one part of mercuric nitrate
-to one hundred parts of water.</p>
-
-<h3>R</h3>
-
-<p><b>Radiant Energy.</b> Energy existing
-in the luminiferous ether and
-exercised in wave transmission, creating
-light or sound. Radium possesses
-the highest form of radiant energy.</p>
-
-<p><b>Radiate.</b> To emit or send out in
-direct lines from a point or points,
-as radiating heat, light, or sound.
-The radiations are sent out in all
-directions from a central point, just
-as a stone thrown in a pond of still
-water will radiate waves or ripples
-from the central point.</p>
-
-<p><b>Radiation.</b> The travelling or motion
-of ether waves through space.</p>
-
-<p><b>Radiator, Electric.</b> A series of
-plates or wire-coils heated by current.
-They radiate heat and so
-warm the surrounding air.</p>
-
-<p><b>Radiograph.</b> A photographic picture
-taken by the X-ray process.</p>
-
-<p><span class="pagenum" id="Page399">[399]</span></p>
-
-<p><b>Receiver.</b> In telephony or telegraphy,
-an instrument for receiving
-the message as distinguished from
-the instrument sending or transmitting
-the message.</p>
-
-<p>The telephone piece held to the
-ear is the receiver.</p>
-
-<p><b>Receiving End.</b> The end of a
-line where the operative currents
-are received, as opposed to the end
-at which they are transmitted.</p>
-
-<p><b>Receptacle.</b> A device for the installation
-of an attachment or extension
-plug. Used in connection
-with electric-lighting circuits.</p>
-
-<p><b>Recoil Kick.</b> Reaction resulting
-from a disruptive discharge.</p>
-
-<p><b>Recorder.</b> In telegraphy, the receiving
-apparatus for recording the
-dot-and-dash signals on a strip or
-tape of paper.</p>
-
-<p><b>Reduction.</b> The influence exerted
-without apparent communication
-by a magnetic field or a charged
-mass upon neighboring bodies. The
-induction-coil is a simple example of
-this force. The current passes through
-the primary or inner coil about a core
-of soft iron, and in doing so it develops
-lines of force in the secondary or outer
-coils, although no current is flowing
-directly through them from a battery
-or dynamo.</p>
-
-<p><b>Reduction Gear.</b> A gear which
-acts to reduce a speed below that of
-a motor in full motion without lessening
-its motive force.</p>
-
-<p><b>Refract.</b> To break the natural
-course of light in an elastic medium.
-The rays of light, as they pass from
-a rare into a dense medium, are refracted.</p>
-
-<p><b>Register, Electric.</b> An apparatus
-for registering and recording the
-movements of employés about a
-building. Press-buttons are arranged
-throughout the building, and
-when a man passes a station he presses
-the button, and the time is recorded
-by the apparatus.</p>
-
-<p><b>Regulator Magnet.</b> (<i>See</i> <a href="#Ref084">Magnet,
-Regulator</a>.)</p>
-
-<p><b>Relay.</b> A telegraphic or telephonic
-receiving instrument which
-opens and closes a local circuit
-through movements caused by the
-impulses of currents received. The
-relay battery may be very delicate
-so as to work with weak currents.
-The function of the relay is to open
-and close circuits for the admission
-of a new current to push on the
-sound or vibration to a more distant
-point. The main battery may
-be of any desired power.</p>
-
-<p><b>Relay Connection.</b> A connection
-used in telegraphy, including a local
-battery, with a short circuit, normally
-open, but closed at will by a
-switch and sounder, or other appliance.
-A very weak current will
-work the apparatus.</p>
-
-<p><b>Relay, Ordinary.</b> A relay that is
-not polarized.</p>
-
-<p><b>Relay, Repeating.</b> In telegraphy,
-a relay for repeating the signals
-through a second line.</p>
-
-<p><b>Reluctance.</b> Magnetic resistance.</p>
-
-<p><b>Repeater.</b> In telegraphy, an instrument
-for repeating the signals
-through a second line. It is virtually
-a relay which is controlled by the
-sender, and which, in turn, operates
-the rest of the main line. It is
-usually located at about the middle
-of the total distance covered.</p>
-
-<p><b>Repeating-station.</b> A telegraph
-station located on a long line, and
-occupying a position at the juncture
-of the sections into which the line
-is divided. The currents received
-through one section are repeated into
-the other sections by means of a
-repeater.</p>
-
-<p><b>Repulsion, Electric.</b> The tendency
-which exists between two bodies
-charged alike to mutually repel each
-other.</p>
-
-<p><b>Residual Charge.</b> (<i>See</i> <a href="#Ref085">Charge,
-Residual</a>.)</p>
-
-<p><span class="pagenum" id="Page400">[400]</span></p>
-
-<p><b>Resilience.</b> The power to spring
-back to a former position. Electricity
-is resilient, although its elasticity
-cannot be measured accurately.</p>
-
-<p><b>Resin.</b> A solid inflammable substance
-or gum, and a good non-conductor
-in electrical work. It is the
-product obtained by distilling the
-sap of the pitch-pine. The name is
-also applied to the product of distilling
-the sap of other trees. Common
-resin, shellac, lac, Dragon’s-blood,
-and other substances of a similar
-nature are resins. They are all dielectrics,
-and the source of negative
-frictional electricity when rubbed
-with cotton, wool, flannel, silk, or
-fur.</p>
-
-<p id="Ref019"><b>Resistance.</b> That quality of an
-electric conductor in virtue of which
-it opposes the passage of an electric
-current, causing the disappearance
-or modification of electro-motive
-force, and converting electric energy
-into heat energy.</p>
-
-<p><b>Resistance-box.</b> A box filled
-with resistance-coils connected in
-series and provided with a switch,
-so that any number of the coils may
-be cut out.</p>
-
-<p id="Ref014"><b>Resistance, Carbon.</b> A resistance
-composed of carbon as a substitute
-for a coil of wire. Carbon rods are
-placed close together having an air
-space between them, with alternate
-ends connected. Piles may be built
-up of carbon plates, whose resistance
-is made to vary by changing the
-pressure.</p>
-
-<p><b>Resistance-coil.</b> A coil of wire
-metal or other substances having
-the power to resist a current of
-electricity.</p>
-
-<p>A coil of wire used to measure an
-unknown resistance by virtue of its
-own known resistance. (<i>See also</i>
-<a href="#Ref086">Coil, Resistance</a>.)</p>
-
-<p><b>Resistance, Dielectric.</b> (<i>See</i> <a href="#Ref087">Dielectric
-Resistance</a>.)</p>
-
-<p id="Ref035"><b>Resistance, Electrolytic.</b> The resistance
-of an electrolyte to the passage
-of a current decomposing it. It
-is almost entirely due to electrolysis,
-and is intensified by counter-electro-motive
-force. When a current of
-a voltage so low as not to decompose
-an electrolyte is passed through
-the latter, the resistance appears
-very high and sometimes almost infinite.
-If the voltage is increased
-until the electrolyte is decomposed
-the resistance suddenly drops to a
-point lower than the true resistance.</p>
-
-<p id="Ref057"><b>Resistance, Internal.</b> The resistance
-of a battery, or generator, in
-an electric circuit as distinguished
-from the resistance of the rest of
-the circuit.</p>
-
-<p id="Ref061"><b>Resistance, Liquid.</b> A liquid of
-varying specific gravity used to
-create resistance to the passage of
-the electric current.</p>
-
-<p>Resistance effected by the use of
-liquid through which a current must
-pass to complete a circuit.</p>
-
-<p id="Ref069"><b>Resistance, Metallic.</b> The resistance
-of metals to the electric current.</p>
-
-<p>German-silver resistance as distinguished
-from that of water, carbon,
-or other substances.</p>
-
-<p id="Ref072"><b>Resistance, Ohmic.</b> True resistance
-measured in ohms as distinguished
-from counter electro-motive
-force. (<i>See also</i> <a href="#Ref088">Ohmic Resistance</a>.)</p>
-
-<p id="Ref099"><b>Resistance, Spurious.</b> The counter-electro-motive
-force. In its effect
-of opposing a current and in resisting
-its formation it differs from
-true resistance. True resistance diminishes
-current strength, absorbs
-energy, and develops heat. Spurious
-resistance opposes and diminishes a
-current without absorption of energy
-or production of heat.</p>
-
-<p id="Ref101"><b>Resistance, Standard.</b> A known
-resistance employed to determine unknown
-resistances by comparison.</p>
-
-<p id="Ref106"><b>Resistance, True.</b> The true resistance
-measured in ohms as distinguished<span class="pagenum" id="Page401">[401]</span>
-from counter-electro-motive
-force.</p>
-
-<p><b>Resonator, Electric.</b> A small,
-open electric circuit with ends nearly
-touching. When exposed to electric
-resonance, or to a sympathetic
-electric oscillating discharge, a spark
-passes across the gap. The spark
-is due to inductance in the resonator.</p>
-
-<p><b>Retentiveness.</b> That property
-which enables steel to retain its
-magnetism.</p>
-
-<p><b>Return.</b> A line or conductor
-which carries current back to its
-starting-point after it has traversed
-a circuit. The best definition of a
-return is a circuit on which no new
-apparatus is installed.</p>
-
-<p><b>Return-circuit.</b> (<i>See</i> <a href="#Ref089">Circuit, Return</a>.)</p>
-
-<p><b>Return-circuit, Railway.</b> A
-grounded circuit used in trolley
-systems for ground returns through
-the tracks, they being joined by
-links or flexible wires so as to form
-perfect conductors. It is the negative
-side of the system, the positive
-being in the overhead or underground
-feed-wire or rail.</p>
-
-<p><b>Reversibility.</b> The principle by
-which any form of generator for producing
-a given form of energy may
-be reversed to absorb energy. The
-dynamo of the reversible type driven
-to generate current may be reversed
-and will develop power if a current
-is run through it.</p>
-
-<p><b>Rheostat.</b> An adjustable resistance.
-An apparatus for changing
-the resistance, without opening the
-circuit, by throwing a switch-bar
-across contact points.</p>
-
-<p><b>Rod Clamp.</b> A clamp used in the
-lamp rod of an arc-light to hold the
-carbon.</p>
-
-<p><b>Röntgen Effects.</b> Phenomena
-obtained by the use of the X or
-Röntgen rays.</p>
-
-<p><b>Röntgen-ray Screen.</b> A screen
-whose surface is covered with fluorescent
-material for the purpose of
-receiving and displaying the Röntgen
-image.</p>
-
-<p><b>Röntgen Rays.</b> A peculiar form
-of light radiation discovered by
-Röntgen, and which is emitted
-from that portion of a high vacuum
-tube upon which the kathode rays
-fall.</p>
-
-<p><b>Rotary Magnetic Field.</b> (<i>See</i>
-<a href="#Ref090">Magnetic Field, Rotary</a>.)</p>
-
-<p><b>Ruhmkorff Coil.</b> (<i>See</i> <a href="#Ref091">Coil, Ruhmkorff</a>.)</p>
-
-<h3>S</h3>
-
-<p><b>Safety Fuse.</b> A device to prevent
-overheating of any portion of a circuit
-by excessive current. It generally
-consists of a strip of fusible
-metal which, if the current attains
-too great strength, melts and opens
-the circuit.</p>
-
-<p><b>Salt.</b> A chemical compound containing
-two atoms or radicals which
-saturate each other. One is electro-positive,
-the other electro-negative.</p>
-
-<p>Salts are decomposed by electrolysis,
-and in separating they combine
-to form new molecules.</p>
-
-<p><b>Saturated.</b> A liquid is said to be
-saturated when it has dissolved all
-the salts it will take up.</p>
-
-<p><b>Search-light.</b> An apparatus for
-producing a powerful beam of light
-and projecting it in any desired direction.</p>
-
-<p><b>Secondary.</b> A term applied to
-the secondary coil of a transformer
-or induction-coil.</p>
-
-<p><b>Secondary Battery.</b> (<i>See</i> <a href="#Ref092">Battery,
-Secondary</a>.)</p>
-
-<p><b>Secondary Plates.</b> The plates of
-a secondary battery or storage-battery.
-When charged, the negative
-plate should be brown or deep reddish
-in color, and the positive slate-colored.</p>
-
-<p><b>Self-excited.</b> Electrified by its
-own current.</p>
-
-<p><b>Self-winding Clock.</b> A clock<span class="pagenum" id="Page402">[402]</span>
-which automatically winds itself by
-electricity. It is operated by a
-small electro-magnetic motor which
-obtains its current from an outside
-source.</p>
-
-<p><b>Semaphore, Electric.</b> An apparatus
-for exhibiting signals. Used in
-the railway block system.</p>
-
-<p><b>Series.</b> Arranged in succession.
-When incandescent lamps are installed
-so that the current goes in
-and out of one lamp, and so on to
-the next and the succeeding ones,
-they are said to be arranged in
-series. It takes high E-M-F and
-current, or amperage, to operate
-such lamps.</p>
-
-<p>Series batteries are arranged with
-the zinc pole of one connected to the
-carbon pole of the next.</p>
-
-<p><b>Series Arc Cut-out.</b> A device by
-means of which a short circuit is
-established past a defective lamp,
-thereby securing the undisturbed
-operation of all the other lamps in
-the circuit.</p>
-
-<p><b>Series Distribution.</b> A distribution
-of electricity in which the receptive
-devices are arranged in successive
-order upon one conductor,
-extending the entire length of the
-circuit.</p>
-
-<p><b>Series Dynamo.</b> A series-wound
-dynamo.</p>
-
-<p><b>Series Incandescent Lamp.</b> An
-incandescent lamp adapted for service
-in a series circuit.</p>
-
-<p><b>Series Motor.</b> A motor adapted
-for use in a series circuit; a motor
-whose field-coil winding is in series
-with the armature.</p>
-
-<p><b>Series, Multiple.</b> An arrangement
-of electric apparatus in which the
-parts are grouped in sets in parallel,
-and these sets are connected in
-series.</p>
-
-<p><b>Series Winding.</b> A method of
-winding a generator or motor in
-which one of the commutator brush
-connections is joined to the field-magnet
-winding. The other end of
-the magnet winding is connected
-with the outer circuit, and the second
-armature brush is coupled with
-the remaining terminal of the outer
-circuit.</p>
-
-<p><b>Service Wires.</b> Wires connected
-to the supply circuit or main wires,
-and which run into buildings to
-supply current for heat, light, and
-power.</p>
-
-<p><b>Shellac.</b> A resin gum, gathered
-from certain Asiatic trees. It is
-soluble in alcohol, and is used extensively
-in electric work as an
-insulator.</p>
-
-<p><b>Shifting Magnetic Field.</b> (<i>See</i>
-<a href="#Ref093">Magnetic Field, Shifting</a>.)</p>
-
-<p><b>Shock, Electric.</b> The effect upon
-the animal system of the discharge
-of an electric current of high potential
-difference. The voltage is
-the main element in a shock.</p>
-
-<p><b>Shoe.</b> As applied to electric
-railways, the casting employed to
-bear on the third rail to take in
-positive current and electro-motive
-force.</p>
-
-<p>The cast-iron plate of an electric
-break, which, by magnetism, adheres
-to another iron surface.</p>
-
-<p><b>Short Circuit.</b> (<i>See</i> <a href="#Ref094">Circuit,
-Short</a>.)</p>
-
-<p><b>Shunt-box.</b> A resistance-box designed
-for use as a galvanometer
-shunt. The box contains a series of
-resistance-coils which can be plugged
-in or out as required.</p>
-
-<p><b>Shunt-winding.</b> A dynamo or
-motor is shunt-wound when the field-magnet
-winding is parallel with the
-winding of the armature.</p>
-
-<p><b>Silver-bath.</b> A solution of a salt
-of silver used in the electro-plating
-process.</p>
-
-<p><b>Silver-plating.</b> Depositing a coating
-of silver on a metallic surface by
-the acid of electro-metallurgy.</p>
-
-<p><b>Silver-stripping Bath.</b> An acid
-solution used for stripping silver<span class="pagenum" id="Page403">[403]</span>
-from a metallic surface before re-plating
-it.</p>
-
-<p><b>Simple Circuit.</b> (<i>See</i> <a href="#Ref095">Circuit,
-Simple</a>.)</p>
-
-<p><b>Simple Immersion.</b> (<i>See</i> <a href="#Ref096">Immersion,
-Simple</a>.)</p>
-
-<p><b>Simple Magnet.</b> (<i>See</i> <a href="#Ref097">Magnet,
-Simple</a>.)</p>
-
-<p><b>Single-trolley System.</b> A trolley
-system employing only one overhead
-conducting wire, the track and
-ground serving as the return-circuit.</p>
-
-<p><b>Single-wound Wire.</b> Wire insulated
-by winding or overlaying
-with but a single layer of material.</p>
-
-<p><b>Sliding-condenser.</b> (<i>See</i> <a href="#Ref098">Condenser,
-Sliding</a>.)</p>
-
-<p><b>Snap-switch.</b> A switch so contrived
-as to give a quick break. A
-spiral spring is fastened between the
-handle and arm in such a manner
-that when the handle is drawn back
-the spring operates and quickly
-draws a knife-bar from the keeper,
-breaking the contact instantly and
-without the formation of an arc.</p>
-
-<p><b>Socket.</b> A receptacle for an incandescent
-lamp or plug.</p>
-
-<p><b>Solenoid.</b> A helical coil of wire
-of uniform diameter or cylindrical
-in shape. It is useful in experiments
-with electro-magnetism.</p>
-
-<p><b>Solution.</b> A fluid composed of
-dissolved salts; a mixture of liquids
-and fluids.</p>
-
-<p><b>Sound Waves.</b> Waves produced
-in an elastic medium by sonorous
-vibration, as in wireless telegraphy.</p>
-
-<p><b>Sounder.</b> In telegraphy, the instrument
-operated on by the key at
-the other end of a line. Various devices
-are employed to increase their
-resonance&mdash;as, for instance, hollow
-boxes. Sounders are generally placed
-on local circuits and are actuated by
-relays.</p>
-
-<p><b>Sounder, Repeating.</b> A telegraphic
-instrument which repeats a message
-into another circuit.</p>
-
-<p><b>S-P.</b> An abbreviation for single
-pole.</p>
-
-<p><b>Spark-arrester.</b> A screen of wire-netting
-fitted around the carbons of
-arc-lamps to prevent the chips or
-hot sparks from flying.</p>
-
-<p><b>Spark-coil.</b> A coil for producing
-a spark from a source of comparatively
-low electro-motive force.
-The induction-coil is an example.</p>
-
-<p><b>Spark, Electric.</b> The phenomenon
-observed when a disruptive
-charge leaves an accumulator or induction-coil
-and passes through an
-air gap.</p>
-
-<p><b>Spark-gap.</b> The space left between
-the ends of an electric resonator
-across which the spark springs.</p>
-
-<p><b>Sparking.</b> The production of
-sparks at the commutator, between
-the bars and the brushes of dynamos
-and motors. They are minute voltaic
-arcs, and should not be allowed
-to occur, as they cut away the metal
-and score the surface of the commutator.</p>
-
-<p><b>Spark-tube.</b> A tube used as a
-gauge to determine when the exhaustion
-of the vacuum chamber,
-or bulb, of an incandescent lamp
-is sufficiently high.</p>
-
-<p><b>Specific Gravity.</b> The relative
-weight or density of a body as compared
-with a standard. Water is
-usually taken as a standard for
-solids and liquids, and air for gases.</p>
-
-<p><b>Speed-counter.</b> An instrument
-which records the number of revolutions
-a shaft makes in a given time.</p>
-
-<p><b>Spent Acid.</b> Acid which has become
-exhausted. In a battery the
-acid becomes spent from combination
-with zinc; it also loses its depolarizing
-power.</p>
-
-<p><b>Spring-contact.</b> A spring connected
-to one lead of an electric
-circuit. It is arranged to press
-against another spring or contact,
-which it opens or closes by the introduction
-of a plug or wedge.</p>
-
-<p><span class="pagenum" id="Page404">[404]</span></p>
-
-<p><b>Spring-jack.</b> An arrangement of
-spring-arm conductors under which
-plugs with wires attached can be
-slipped to make a new connection
-or to cut out certain circuits.</p>
-
-<p><b>Spurious Resistance.</b> (<i>See</i> <a href="#Ref099">Resistance,
-Spurious</a>.)</p>
-
-<p><b>Standard Candle.</b> (<i>See</i> <a href="#Ref100">Candle,
-Standard</a>.)</p>
-
-<p><b>Standard Resistance.</b> (<i>See</i> <a href="#Ref101">Resistance,
-Standard</a>.)</p>
-
-<p><b>Starting-box.</b> A resistance or
-shunt box used for letting current
-pass gradually into motors, instead of
-throwing on the full current at once.</p>
-
-<p><b>Static Electricity.</b> Electricity
-generated by friction; frictional electricity,
-such as lightning; electricity
-of high electro-motive force and practically
-uncontrollable for commercial
-purposes.</p>
-
-<p><b>Static Shock.</b> A term used in
-electro-therapeutics for describing
-the discharge from a small condenser
-or Leyden-jar; also the effect produced
-by the action of the vibrator
-of the induction-coil.</p>
-
-<p><b>Station, Central.</b> The building or
-place in which the electrical apparatus
-is installed for the generation
-of current; the headquarters of telephone
-lines.</p>
-
-<p><b>Steady Current.</b> An electric current
-whose strength is fixed or invariable.</p>
-
-<p><b>Stock-ticker.</b> An instrument employed
-to give quotations of stocks
-by telegraphic record. A paper tape
-runs through an electrical machine
-which prints on it the figures and
-letters that stand for stocks and
-their values. The whole system is
-operated from a station located in
-the Stock-exchange.</p>
-
-<p><b>Storage Accumulator.</b> (<i>See</i> <a href="#Ref102">Accumulator,
-Storage</a>.)</p>
-
-<p><b>Storage-battery.</b> (<i>See</i> <a href="#Ref103">Battery,
-Storage</a>.)</p>
-
-<p><b>Strength of Current.</b> Amperage;
-the quantity of current in a circuit.</p>
-
-<p><b>Stripping.</b> The process of removing
-electro-plating, or thin metal
-coatings, from an object before it is
-re-electro-plated.</p>
-
-<p><b>Stripping Liquid.</b> The liquid in
-a stripping-bath used for removing
-metals from surfaces before re-plating
-them.</p>
-
-<p><b>Submarine Cable.</b> A telegraphic
-cable laid at the bottom of the sea
-or any body of water.</p>
-
-<p><b>Submarine Search-light.</b> An incandescent
-light which works under
-water.</p>
-
-<p><b>Sub-station.</b> A generating or
-converting plant subsidiary to a
-central station, and placed so as to
-supply current in a district situated
-at a distance from the main power-house.</p>
-
-<p><b>Subway, Electric.</b> An underground
-passageway utilized for carrying
-cables and wires.</p>
-
-<p><b>Sweating.</b> A process by which
-the ends of cables are brought together
-and soldered.</p>
-
-<p><b>S-W-G.</b> An abbreviation for
-standard wire gauge.</p>
-
-<p><b>Switch.</b> A device for opening
-and closing an electric circuit.
-Made in a great variety of forms,
-such as push-button, telegraph-key,
-knife switch, automatic switch, lever
-switch, rheostat, etc.</p>
-
-<p><b>Switch-bell.</b> A combined bell
-and switch. The bell is operated
-when the switch is opened or closed.</p>
-
-<p><b>Switch-blade.</b> The blade of a
-switch; a conducting strip connecting
-two contact-jaws.</p>
-
-<p><b>Switch-board.</b> A board or table
-to which wires are led and connected
-with cross-bars or other devices
-by which connections can be
-made.</p>
-
-<p><b>Synchronize.</b> To agree in point
-of time; to effect concurrence of
-phase in two alternating-current
-machines, in order to combine them
-electrically.</p>
-
-<p><span class="pagenum" id="Page405">[405]</span></p>
-
-<h3>T</h3>
-
-<p><b>Table-push.</b> A push-button connected
-with a call-bell and fixed on
-a table for convenience in using.</p>
-
-<p><b>Tamadine.</b> A form of cellulose
-used for making the filaments of incandescent
-lamps. The material is
-cut into proper shapes, carbonized,
-and flashed.</p>
-
-<p><b>Tangent Galvanometer.</b> (<i>See</i>
-<a href="#Ref104">Galvanometer, Tangent</a>.)</p>
-
-<p><b>Tape, Insulating.</b> Prepared tape
-used in covering the bared ends of
-wires or joints.</p>
-
-<p><b>Tap-wires.</b> The conductors in
-trolley systems that at stated intervals,
-take the current from the
-mains and supply it to the bare feed-wires.</p>
-
-<p><b>Telegraph.</b> A system of electric
-communication invented by S. F.
-B. Morse, in which the dot-and-dash
-characters are used. There are
-various modifications of the system&mdash;double
-(or duplex), multiplex, and
-quadruplex&mdash;by means of which a
-number of messages may be sent
-out over the same wires at one time.
-Communication from place to place
-is had over wires mounted on poles,
-or by underground or submarine
-cables.</p>
-
-<p><b>Telegraphy, Wireless.</b> A system
-of telegraphy carried on without the
-aid of wires, using instead the ether
-waves of the atmosphere to conduct
-the vibrations overhead, and the
-ground, or earth, as a return. The
-present limit of its working is about
-four thousand miles.</p>
-
-<p><b>Telephone.</b> An instrument and
-apparatus for the transmission of
-articulate speech by the electric
-current. A magnet is encased in a
-tube and is encircled at one end by
-a coil of fine, insulated wire. A diaphragm
-of thin iron is fixed in front
-of the coil and close to the end of
-the magnet. The ends of the coil-wires
-are connected with a line, at
-the other end of which another and
-similar instrument is installed. The
-voice causes the sending diaphragm
-to vibrate, and these waves are
-transmitted to the other instrument,
-where they can be heard
-through contra-vibrations of the receiving
-diaphragm.</p>
-
-<p><b>Telephone, Long-distance.</b> A
-telephone of modern construction,
-in which the sound-recording mechanism
-is so sensitive as to make the
-vibrations of the voice audible at
-long distances. It will work satisfactorily
-at one thousand or even
-fifteen hundred miles.</p>
-
-<p><b>Terminal.</b> The end of any open
-electric circuit, or of any electric
-apparatus, as the electrodes of a
-battery.</p>
-
-<p><b>Thermostat, Electric.</b> An apparatus
-similar in some respects
-to a thermometer, and used for
-closing an electric circuit when the
-latter becomes heated. It is used
-in connection with automatic fire-alarms
-to give warning of fire. For
-this purpose the metal coil is arranged
-to close the contact at a
-temperature of 125° F. It usually
-consists of a compound strip of
-metal wound in the form of a spiral
-and fastened at one end. To this
-end one terminal of a circuit is connected.
-The expansion of the coil
-causes its loose end to touch a contact-point
-and close the circuit.</p>
-
-<p><b>Third Rail.</b> A railway motive
-system which employs a third rail
-instead of an overhead trolley feed-wire.
-The rail is laid on or under
-the surface of the ground and properly
-insulated. A shoe from the
-car bears on the rail and takes up
-the current.</p>
-
-<p><b>Three-wire Circuit.</b> A system invented
-by Edison for the distribution,
-from two dynamos, of current
-for multiple arc or constant potential<span class="pagenum" id="Page406">[406]</span>
-service. One wire or lead starts
-from the positive pole of one dynamo,
-another from the negative pole of
-the other dynamo, and between the
-two dynamos the central or neutral
-lead is made fast.</p>
-
-<div class="container m25">
-
-<div class="figcenter nomargin">
-<img src="images/illo406.png" alt="Circuit" />
-</div>
-
-</div><!--container-->
-
-<p>Now the dynamos may generate
-a current of 220 volts, and send it,
-at this strength, through the outer
-wires; but if lamps are connected
-between either of the outer and the
-neutral wires, the current, passing
-through the lamps, will be reduced
-to 110 volts.</p>
-
-<p><b>Time-ball, Electric.</b> A ball which,
-by means of electricity, is made to
-drop from the top of a high pole,
-giving a visual signal for twelve
-o’clock or any other hour that may
-be designated.</p>
-
-<p><b>Traction, Electric.</b> The propulsion
-of a car or conveyance by means
-of electricity.</p>
-
-<p><b>Transformer.</b> In alternating-current
-systems, the induction-coil by
-means of which the primary current,
-with high initial electro-motive force,
-is changed into a secondary current
-with low initial electro-motive force.</p>
-
-<p><b>Transmission.</b> The conveyance of
-electric energy and currents from
-one point to another by the proper
-means of conduction.</p>
-
-<p><b>Transmitter.</b> An instrument
-which originates the signals which
-are sent through a line or circuit.
-The Morse key in telegraphy and
-the Blake transmitter in telephony
-are examples.</p>
-
-<p><b>Tri-phase.</b> Three-phase.</p>
-
-<p><b>Trolley.</b> A contact-wheel of
-bronze which rolls under the supply-wire
-in an overhead traction
-system and takes off the current
-necessary to run the car motors.</p>
-
-<p><b>Trolley-wheel.</b> The same as Trolley.</p>
-
-<p><b>Trolley-wire.</b> The overhead
-wire in a traction system which feeds
-the current through a trolley-wheel
-and pole to the motors of a car running
-underneath.</p>
-
-<p><b>True Ohm.</b> (<i>See</i> <a href="#Ref105">Ohm, True</a>.)</p>
-
-<p><b>True Resistance.</b> (<i>See</i> <a href="#Ref106">Resistance,
-True</a>.)</p>
-
-<p><b>Two-wire Circuit.</b> The single system
-universally used for light and
-power transmission of current.</p>
-
-<h3>U</h3>
-
-<p><b>Undulating Current.</b> (<i>See</i> <a href="#Ref107">Current,
-Undulating</a>.)</p>
-
-<p><b>Uniform Magnetic Field.</b> (<i>See</i>
-<a href="#Ref108">Magnetic Field, Uniform</a>.)</p>
-
-<p><b>Unipolar.</b> Having but one pole.</p>
-
-<p><b>Unit.</b> The single standard of
-force, light, heat, magnetism, attraction,
-repulsion, resistance, etc.</p>
-
-<h3>V</h3>
-
-<p><b>Vacuum.</b> A space empty or void
-of all matter; a space from which
-all gases have been exhausted.</p>
-
-<p><b>Vacuum Tubes.</b> Tubes of glass
-through which electric discharges are
-passed after the gases have been
-partially removed; for example, the
-X-ray tube of Röntgen and the
-Crooke tubes.</p>
-
-<p><b>Vibrator, Electro-magnetic.</b> The
-make-and-break mechanism used on
-induction-coils, or other similar apparatus,
-in which, through alternate
-attractions, an arm or spring is kept
-in motion.</p>
-
-<p><b>Vitriol, Blue.</b> A trade name for
-copper sulphate. (Bluestone.)</p>
-
-<p><b>Vitriol, Green.</b> A trade name for
-ferrous sulphate. (Copperas.)</p>
-
-<p><b>Vitriol, White.</b> A trade name for
-zinc sulphate. (Salts of zinc.)</p>
-
-<p><span class="pagenum" id="Page407">[407]</span></p>
-
-<p><b>Volt.</b> The practical unit of electro-motive
-force; the volume and
-pressure of an electric current.</p>
-
-<p><b>Voltage.</b> Electric-motive force
-expressed in volts&mdash;as, a voltage of
-100 volts.</p>
-
-<p><b>Voltaic.</b> A term derived from
-the name of the Italian scientist
-Volta, and used in many ways as
-applied to electrical current and devices.
-Formerly the term galvanic
-was commonly employed.</p>
-
-<p><b>Voltaic Electricity.</b> (<i>See</i> <a href="#Ref109">Electricity,
-Voltaic</a>.)</p>
-
-<p><b>Voltimeter.</b> An instrument for
-measuring the voltage of a current.</p>
-
-<p><b>Vulcanite.</b> Vulcanized rubber.
-Valuable for its insulating properties
-and inductive capability.</p>
-
-<h3>W</h3>
-
-<p><b>Watt.</b> The practical unit of electrical
-activity; the rate of work or
-rate of energy. It is a unit of energy
-or of work represented by a
-current of one ampere urged on by
-one volt of electro-motive force.</p>
-
-<p>The volt-ampere.</p>
-
-<p>The standard of electrical energy
-corresponding to horse-power in mechanics.</p>
-
-<p><b>Watt-hour.</b> A unit of electric
-energy or work; one watt exerted
-or expended through one hour.</p>
-
-<p><b>Waves, Electro-magnetic.</b> Ether
-waves caused by electro-magnetic
-disturbances affecting the luminiferous
-ether.</p>
-
-<p><b>Welding, Electric.</b> Welding by
-the use of the electric current.</p>
-
-<p><b>Wimshurst Electric Machine.</b> An
-influence machine for producing
-high potential or static electricity.
-Thin disks of glass are mounted on
-insulated bearings and revolved by
-power. Brushes collect the frictional
-electricity, which is discharged
-into a Leyden-jar or other form of
-accumulator. It is of no practical
-use excepting in electro-therapeutics.</p>
-
-<p><b>Wire, Flexible.</b> A cord of fine
-wire strands laid together and insulated
-so that it may be easily
-bent or wrapped.</p>
-
-<p><b>Wiring.</b> Installing wires so as to
-form a circuit for the conveyance of
-current for light, heat, and power.</p>
-
-<h3>X</h3>
-
-<p><b>X-rays.</b> A curious phenomenon
-involving the radiation of invisible
-rays of light, which have the power
-to travel through various opaque
-bodies. The rays are used in detecting
-foreign substances in the
-human body and for photographing
-invisible or hidden objects without
-disturbing their surroundings.</p>
-
-<p><b>X-ray Lamp.</b> A high vacuum
-tube lamp whose interior walls are
-covered with crystals of calcium or
-other fluorescent substances, and
-which, when exposed to the X-rays,
-give out a luminous light.</p>
-
-<h3>Y</h3>
-
-<p><b>Yoke.</b> A piece of soft iron which
-connects the ends of two portions
-of a core on which wire coils are
-wound. It is located at the ends
-farthest from the poles.</p>
-
-<p>The soft-iron bar placed across
-the ends of a horseshoe magnet to
-retain its magnetism.</p>
-
-<h3>Z</h3>
-
-<p><b>Zinc-battery.</b> A battery which
-decomposes zinc in an electrolyte,
-thereby producing a current.</p>
-
-<p><b>Zinc Currents.</b> Negative currents.</p>
-
-<p><b>Zinc-plating.</b> The employment
-of zinc in electro-plating.</p>
-
-<p class="center highline5 fsize80">THE END</p>
-
-<hr class="full" />
-
-<div class="tnbot" id="TN">
-
-<h2>Transcriber&#8217;s Notes</h2>
-
-<p>Inconsistent spelling, hyphenation, etc. have been retained, unless mentioned under Changes Made below.
-Technical descriptions have been kept as printed, even when they seem
-doubtful, wrong or dangerous.</p>
-
-<p>Depending on the hard- and software and their settings used to read this text, not all elements may display
-as intended.</p>
-
-<p class="blankbefore75">Changes Made</p>
-
-<p>Footnotes and illustrations have been moved outside text paragraphs.</p>
-
-<p>Where letters (such as V or L) are used to
-denote a shape rather than the letter, they have been transcribed as <span class="symbol">V</span> or
-<span class="symbol">L</span> for consistency with other, similarly used letters such as <span class="symbol">U</span>.</p>
-
-<p>Some minor obvious typographical errors have been corrected silently.</p>
-
-<p>Page 108: "called Nobile&#8217;s pair" changed to "called Nobili&#8217;s pair".</p>
-
-<p>Page 182: "shallacked" changed to "shellacked".</p>
-
-<p>Page 184: "(A, B, and C) and A A, B B, and C C)" changed to "(A, B, and C and A A, B B, and
-C C)".</p>
-
-<p>Dictionary: several entries have been moved to their proper alphabetical position.</p>
-
-<p>Page 334: "modern applications of phenonema" changed to "applications
-of phenomena</p>
-
-<p>Page 372: "Coil, Ruhmkoff" changed to "Coil, Ruhmkorff".</p>
-
-<p>Page 382: "Daniells" changed to "Daniell".</p>
-
-<p>Page 396: "graphite a native; form of carbon" changed to "graphite; a native form of carbon".</p>
-
-<p>Page 401: "Ruhmkoff Coil. (See Coil, Ruhmkoff.)" changed to "Ruhmkorff Coil. (See Coil, Ruhmkorff.)"</p>
-
-</div><!--TN-->
-
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author	nfenwick <nfenwick@pglaf.org>	2025-01-23 09:09:40 -0800
committer	nfenwick <nfenwick@pglaf.org>	2025-01-23 09:09:40 -0800
commit	1a8142037b87be54530d6b31e18eaa312d941012 (patch)
tree	bdfcad92473ca7a9c104248bbc5507162a720bce
parent	c3f06cfa2cc619fabe563bfd7bfb8da75bd0a16b (diff)