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diff --git a/old/64592-0.txt b/old/64592-0.txt deleted file mode 100644 index 34d8e24..0000000 --- a/old/64592-0.txt +++ /dev/null @@ -1,12789 +0,0 @@ -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. 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