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+The Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: Electricity for Boys
+
+Author: J. S. Zerbe
+
+Release Date: September 25, 2007 [EBook #22766]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELECTRICITY FOR BOYS ***
+
+
+
+
+Produced by Joe Longo and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+
+WARNING: This book of one hundred years ago describes
+experiments which are too dangerous to attempt by either
+adults or children. It is published for historical
+interest only.
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+ELECTRICITY FOR BOYS
+
+[Illustration: Fig. 1. WORK BENCH]
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+ELECTRICITY FOR BOYS
+
+A working guide, in the successive
+steps of electricity, described in
+simple terms
+
+WITH MANY ORIGINAL ILLUSTRATIONS
+
+By J. S. ZERBE, M.E.
+
+AUTHOR OF
+CARPENTRY FOR BOYS
+PRACTICAL MECHANICS FOR BOYS
+
+[Illustration: Printer's Mark]
+
+THE NEW YORK BOOK COMPANY
+NEW YORK
+
+
+
+
+COPYRIGHT, 1914, BY
+THE NEW YORK BOOK COMPANY
+
+
+
+
+CONTENTS
+
+
+INTRODUCTORY                                                      Page 1
+
+I. ELECTRICITY CONSIDERED. BRIEF HISTORICAL
+EVENTS                                                            Page 5
+
+ The Study of Electricity. First Historical Accounts. Bottling
+ Electricity. Discovery of Galvanic Electricity. Electro-motive Force.
+ Measuring Instruments. Rapidity of Modern Progress. How to Acquire the
+ Vast Knowledge. The Means Employed.
+
+II. WHAT TOOLS AND APPARATUS ARE NEEDED                          Page 11
+
+ Preparing the Workshop. Uses of Our Workshop. What to Build. What to
+ Learn. Uses of the Electrical Devices. Tools. Magnet-winding Reel.
+
+III. MAGNETS, COILS, ARMATURES, ETC.                             Page 18
+
+ The Two Kinds of Magnets. Permanent Magnets. Electro-Magnets.
+ Magnetism. Materials for Magnets. Non-magnetic Material. Action of a
+ _Second_ Magnet. What North and South Pole Mean. Repulsion and
+ Attraction. Positives and Negatives. Magnetic Lines of Force. The
+ Earth as a Magnet. Why the Compass Points North and South. Peculiarity
+ of a Magnet. Action of the Electro-Magnet. Exterior Magnetic Influence
+ Around a Wires Carrying a Current. Parallel Wires.
+
+IV. FRICTIONAL, VOLTAIC OR GALVANIC AND ELECTRO-MAGNETIC
+ELECTRICITY                                                      Page 29
+
+ Three Electrical Sources. Frictional Electricity. Leyden Jar. Voltaic
+ or Galvanic Electricity. Voltaic Pile; How Made. Plus and Minus
+ Signs. The Common Primary Cell. Battery Resistance. Electrolyte and
+ Current. Electro-magnetic Electricity. Magnetic Radiation. Different
+ Kinds of Dynamos. Direct Current Dynamos. Simple Magnet Construction.
+ How to Wind. The Dynamo Fields. The Armature. Armature Windings.
+ Mounting the Armature. The Commutator. Commutator Brushes. Dynamo
+ Windings. The Field. Series-wound Field. Shunt-wound. Compound-wound.
+
+V. HOW TO DETECT AND MEASURE ELECTRICITY                         Page 49
+
+ Measuring Instruments. The Detector. Direction of Current. Simple
+ Current Detector. How to Place the Detector. Different Ways to Measure
+ a Current. The Sulphuric Acid Voltameter. The Copper Voltameter. The
+ Galvanoscope Electro-magnetic Method. The Calorimeter. The Light
+ Method. The Preferred Method. How to Make a Sulphuric Acid Voltameter.
+ How to Make a Copper Voltameter. Objections to the Calorimeter.
+
+VI. VOLTS, AMPERES, OHMS AND WATTS                               Page 60
+
+Understanding Terms. Intensity and Quantity. Voltage.
+Amperage Meaning of Watts and Kilowatt. A
+Standard of Measurement. The Ampere Standard. The
+Voltage Standard. The Ohm. Calculating the Voltage.
+
+VII. PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND
+LIKE APPARATUS                                                   Page 65
+
+ Simple Switches. A Two-Pole Switch. Double-Pole Switch. Sliding
+ Switch. Reversing Switch. Push Buttons. Electric Bells. How Made. How
+ Operated. Annunciators. Burglar Alarm. Wire Circuiting. Circuiting
+ System with Two Bells and Push Buttons. The Push Buttons, Annunciators
+ and Bells. Wiring Up a House.
+
+VIII. ACCUMULATORS, STORAGE OR SECONDARY BATTERIES               Page 82
+
+ Storing Up Electricity. The Accumulator. Accumulator Plates. The Grid.
+ The Negative Pole. Connecting Up the Plates. Charging the Cells. The
+ Initial Charge. The Charging Current.
+
+IX. THE TELEGRAPH                                                Page 90
+
+ Mechanism in Telegraph Circuit. The Sending Key. The Sounder.
+ Connecting Up the Key and Sounder. Two Stations in Circuit. The Double
+ Click. Illustrating the Dot and the Dash. The Morse Telegraph Code.
+ Example in Use.
+
+X. HIGH-TENSION APPARATUS, CONDENSERS, ETC.                      Page 98
+
+ Induction. Low and High Tension. Elastic Property of Electricity. The
+ Condenser. Connecting up a Condenser. The Interrupter. Uses of
+ High-tension Coils.
+
+XI. WIRELESS TELEGRAPHY                                         Page 104
+
+ Telegraphing Without Wires. Surging Character of High-tension
+ Currents. The Coherer. How Made. The Decoherer. The Sending Apparatus.
+ The Receiving Apparatus. How the Circuits are Formed.
+
+XII. THE TELEPHONE                                              Page 110
+
+ Vibrations. The Acoustic Telephone. Sound Waves. Hearing Electricity.
+ The Diaphragm in a Magnetic Field. A Simple Telephone Circuit. How to
+ Make a Telephone. Telephone Connections. Complete Installation. The
+ Microphone. Light Contact Points. How to Make a Microphone.
+ Microphone, the Father of the Transmitter. Automatic Cut-outs for
+ Telephones. Complete Circuiting with Transmitters.
+
+XIII. ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING          Page 123
+
+ Decomposing Liquids. Making Hydrogen and Oxygen. Purifying Water.
+ Rust. Oxygen as a Purifier. Composition of Water. Common Air Not a
+ Good Purifier. Pure Oxygen a Water Purifier. The Use of Hydrogen in
+ Purification. Aluminum Electrodes. Electric Hand Purifier.
+ Purification and Separation of Metals. Electroplating. Plating Iron
+ with Copper. Direction of Current.
+
+XIV. ELECTRIC HEATING. THERMO-ELECTRICITY                       Page 135
+
+ Generating Heat in a Wire. Resistance of Substances. Signs of
+ Connectors. Comparison of Metals. A Simple Electric Heater. How to
+ Arrange for Quantity of Current Used. An Electric Iron.
+ Thermo-Electricity Converting Heat Directly into Electricity Metals.
+ Electric, Positive, Negative. Thermo-electric Coupler.
+
+XV. ALTERNATING CURRENTS, CHOKING COIL, TRANSFORMER             Page 145
+
+ Direct Current. Alternating Current. The Magnetic Field. Action of a
+ Magnetized Wire. The Movement of a Current in a Charged Wire. Current
+ Reversing Itself. Self-Induction. Brushes in a Direct Current Dynamo:
+ Alternating, Positive and Negative Poles. How an Alternating Current
+ Dynamo is Made. The Windings. The Armature Wires. Choking Coils. The
+ Transformer. How the Voltage is Determined. Voltage and Amperage in
+ Transformers.
+
+XVI. ELECTRIC LIGHTING                                          Page 161
+
+ Early conditions. Fuels. Reversibility of Dynamo. Electric arc.
+ Mechanism to maintain the arc. Resistance coil. Parallel carbons for
+ making arc. Series current. Incandescent system. Multiple circuit.
+ Subdivision of electric light. The filament. The glass bulb. Metallic
+ filaments. Vapor lamps. Directions for improvements. Heat in electric
+ lighting. Curious superstitions concerning electricity. Magnetism.
+ Amber. Discovery of the properties of a magnet. Electricity in
+ mountain regions. Early beliefs as to magnetism and electricity. The
+ lightning rod. Protests against using it. Pliny's explanation of
+ electricity.
+
+XVII. POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS        Page 175
+
+ Early beliefs concerning the dynamo. Experiments with magnets.
+ Physical action of dynamo and motor. Electrical influence in windings.
+ Comparing motor and dynamo. How the current acts in a dynamo. Its
+ force in a motor. Loss in power transmission. The four ways in which
+ power is dissipated. Disadvantages of electric power. Its advantages.
+ Transmission of energy. High voltages. The transformer. Step-down
+ transformers. Electric furnaces. Welding by electricity. Merging the
+ particles of the joined ends.
+
+XVIII. X-RAY, RADIUM AND THE LIKE                               Page 184
+
+ The camera and the eye. Actinic rays. Hertzian waves. High-tension
+ apparatus. Vacuum tubes. Character of the ultra-violet rays. How
+ distinguished. The infra-red rays. Their uses. X-rays not capable of
+ reflection. Not subject to refraction. Transmission through opaque
+ substances. Reducing rates of vibration. Radium. Radio-activity.
+ Radio-active materials. Pitchblende. A new form of energy. Electrical
+ source. Healing power. Problems for scientists.
+
+
+
+
+LIST OF ILLUSTRATIONS
+
+ FIG.
+
+ 1. Work bench                                           Frontispiece
+
+                                                                 PAGE
+ 2. Top of magnet-winding reel                                     14
+ 3. Side of magnet-winding reel                                    14
+ 4. Journal block                                                  15
+ 5. Plain magnet bar                                               19
+ 6. Severed magnet                                                 20
+ 7. Reversed magnets                                               21
+ 8. Horseshoe magnet                                               22
+ 9. Earth's magnetic lines                                         23
+ 10. Two permanent magnets                                         24
+ 11. Magnets in earth's magnetic field                             24
+ 12. Armatures for magnets                                         25
+ 13. Magnetized field                                              26
+ 14. Magnetized bar                                                26
+ 15. Direction of current                                          27
+ 16. Direction of induction current                                28
+ 17. Frictional-electricity machine                                30
+ 18. Leyden jar                                                    32
+ 19. Galvanic electricity. Crown of cups                           33
+ 20. Voltaic electricity                                           34
+ 21. Primary battery                                               36
+ 22. Dynamo field and pole piece                                   39
+ 23. Base and fields assembled                                     41
+ 24. Details of the armature, core                                 42
+ 25. Details of the armature, body                                 42
+ 26. Armature Journals                                             43
+ 27. Commutator                                                    43
+ 28. End view of armature, mounted                                 44
+ 29. Top view of armature on base                                  45
+ 30. Field winding                                                 47
+ 31. Series-wound                                                  47
+ 32. Shunt-wound                                                   48
+ 33. Compound-wound                                                48
+ 34. Compass magnet, swing to the right                            50
+ 35. Magnetic compass                                              50
+ 36. Magnet, swing to the left                                     50
+ 37. Indicating direction of current                               51
+ 38. The bridge of the detector                                    52
+ 39. Details of detector                                           53
+ 40. Cross-section of detector                                     54
+ 41. Acid voltameter                                               56
+ 42. Copper voltameter                                             56
+ 43. Two-pole switch                                               66
+ 44. Double-pole switch                                            66
+ 45. Sliding switch                                                67
+ 46. Rheostat form of switch                                       68
+ 47. Reversing switch                                              69
+ 48. Push button                                                   70
+ 49. Electric bell                                                 71
+ 50. Armature of electric bell                                     72
+ 51. Vertical section of annunciator                               72
+ 52. Front view of annunciator                                     72
+ 53. Horizontal section of annunciator                             72
+ 54. Front plate of annunciator                                    72
+ 55. Alarm switch on window                                        76
+ 56. Burglar alarm on window                                       76
+ 57. Burglar alarm contact                                         77
+ 58. Neutral position of contact                                   78
+ 59. Circuiting for electric bell                                  79
+ 60. Annunciators in circuit                                       80
+ 61. Wiring system for a house                                     80
+ 62. Accumulator grids                                             83
+ 63. Assemblage of accumulator grids                               85
+ 64. Connecting up storage battery in series                       87
+ 65. Parallel series                                               88
+ 66. Charging circuit                                              88
+ 67. Telegraph sending key                                         91
+ 68. Telegraph sounder                                             92
+ 69. A telegraph circuit                                           94
+ 70. Induction coil and circuit                                    99
+ 71. Illustrating elasticity                                      100
+ 72. Condenser                                                    101
+ 73. High-tension circuit                                         102
+ 74. Current interrupter                                          103
+ 75. Wireless-telegraphy coherer                                  105
+ 76. Wireless sending-apparatus                                   107
+ 77. Wireless receiving-apparatus                                 108
+ 78. Acoustic telephone                                           111
+ 79. Illustrating vibrations                                      111
+ 80. The magnetic field                                           112
+ 81. Section of telephone receiver                                114
+ 82. The magnet and receiver head                                 115
+ 83. Simple telephone connection                                  116
+ 84. Telephone stations in circuit                                117
+ 85. Illustrating light contact points                            118
+ 86. The microphone                                               119
+ 87. The transmitter                                              119
+ 88. Complete telephone circuit                                   121
+ 89. Device for making hydrogen and oxygen                        124
+ 90. Electric-water purifier                                      127
+ 91. Portable electric purifier                                   129
+ 92. Section of positive plate                                    130
+ 93. Section of negative plate                                    130
+ 94. Positive and negative in position                            130
+ 95. Form of the insulator                                        130
+ 96. Simple electric heater                                       137
+ 97. Side view of resistance device                               139
+ 98. Top view of resistance device                                139
+ 99. Plan view of electric iron                                   140
+100. Section of electric iron                                     141
+101. Thermo-electric couple                                       143
+102. Cutting a magnetic field                                     146
+103. Alternations, first position                                 148
+104. Alternations, second position                                148
+105. Alternations, third position                                 148
+106. Alternations, fourth position                                148
+107. Increasing alternations, first view                          149
+108. Increasing alternations, second view                         149
+109. Connection of alternating dynamo armature                    150
+110. Direct current dynamo                                        151
+111. Circuit wires in direct current dynamo                       152
+112. Alternating polarity lines                                   154
+113. Alternating current dynamo                                   155
+114. Choking coil                                                 157
+115. A transformer                                                158
+116. Parallel carbons                                             164
+117. Arc-lighting circuit                                         165
+118. Interrupted conductor                                        166
+119. Incandescent circuit                                         167
+120. Magnetic action in dynamo, 1st                               177
+121. Magnetic action in dynamo, 2d                                177
+122. Magnetic action in dynamo, 3d                                178
+123. Magnetic action in dynamo, 4th                               178
+124. Magnetic action in motor, 1st                                179
+125. Magnetic action in motor, 2d                                 179
+126. Magnetic action in motor, 3d                                 180
+127. Magnetic action in motor, 4th                                180
+
+
+
+
+INTRODUCTORY
+
+
+Electricity, like every science, presents two phases to the student, one
+belonging to a theoretical knowledge, and the other which pertains to
+the practical application of that knowledge. The boy is directly
+interested in the practical use which he can make of this wonderful
+phenomenon in nature.
+
+It is, in reality, the most successful avenue by which he may obtain the
+theory, for he learns the abstract more readily from concrete examples.
+
+It is an art in which shop practice is a greater educator than can be
+possible with books. Boys are not, generally, inclined to speculate or
+theorize on phenomena apart from the work itself; but once put them into
+contact with the mechanism itself, let them become a living part of it,
+and they will commence to reason and think for themselves.
+
+It would be a dry, dull and uninteresting thing to tell a boy that
+electricity can be generated by riveting together two pieces of
+dissimilar metals, and applying heat to the juncture. But put into his
+hands the metals, and set him to perform the actual work of riveting the
+metals together, then wiring up the ends of the metals, heating them,
+and, with a galvanometer, watching for results, it will at once make him
+see something in the experiment which never occurred when the abstract
+theory was propounded.
+
+He will inquire first what metals should be used to get the best
+results, and finally, he will speculate as to the reasons for the
+phenomena. When he learns that all metals are positive-negative or
+negative-positive to each other, he has grasped a new idea in the realm
+of knowledge, which he unconsciously traces back still further, only to
+learn that he has entered a field which relates to the constitution of
+matter itself. As he follows the subject through its various channels he
+will learn that there is a common source of all things; a manifestation
+common to all matter, and that all substances in nature are linked
+together in a most wonderful way.
+
+An impulse must be given to a boy's training. The time is past for the
+rule-and-rote method. The rule can be learned better by a manual
+application than by committing a sentence to memory.
+
+In the preparation of this book, therefore, I have made practice and
+work the predominating factors. It has been my aim to suggest the best
+form in which to do the things in a practical way, and from that work,
+as the boy carries it out, to deduce certain laws and develop the
+principles which underlie them. Wherever it is deemed possible to do so,
+it is planned to have the boy make these discoveries for himself, so as
+to encourage him to become a thinker and a reasoner instead of a mere
+machine.
+
+A boy does not develop into a philosopher or a scientist through being
+told he must learn the principles of this teaching, or the fundamentals
+of that school of reasoning. He will unconsciously imbibe the spirit and
+the willingness if we but place before him the tools by which he may
+build even the simple machinery that displays the various electrical
+manifestations.
+
+
+
+
+CHAPTER I
+
+THE STUDY OF ELECTRICITY. HISTORICAL
+
+
+There is no study so profound as electricity. It is a marvel to the
+scientist as well as to the novice. It is simple in its manifestations,
+but most complex in its organization and in its ramifications. It has
+been shown that light, heat, magnetism and electricity are the same, but
+that they differ merely in their modes of motion.
+
+FIRST HISTORICAL ACCOUNT.--The first historical account of electricity
+dates back to 600 years B. C. Thales of Miletus was the first to
+describe the properties of amber, which, when rubbed, attracted and
+repelled light bodies. The ancients also described what was probably
+tourmaline, a mineral which has the same qualities. The torpedo, a fish
+which has the power of emitting electric impulses, was known in very
+early times.
+
+From that period down to about the year 1600 no accounts of any
+historical value have been given. Dr. Gilbert, of England, made a number
+of researches at that time, principally with amber and other materials,
+and Boyle, in 1650, made numerous experiments with frictional
+electricity.
+
+Sir Isaac Newton also took up the subject at about the same period. In
+1705 Hawksbee made numerous experiments; also Gray, in 1720, and a
+Welshman, Dufay, at about the same time. The Germans, from 1740 to 1780,
+made many experiments. In 1740, at Leyden, was discovered the jar which
+bears that name. Before that time, all experiments began and ended with
+frictional electricity.
+
+The first attempt to "bottle" electricity was attempted by
+Muschenbr[oe]ck, at Leyden, who conceived the idea that electricity in
+materials might be retained by surrounding them with bodies which did
+not conduct the current. He electrified some water in a jar, and
+communication having been established between the water and the prime
+conductor, his assistant, who was holding the bottle, on trying to
+disengage the communicating wire, received a sudden shock.
+
+In 1747 Sir William Watson fired gunpowder by an electric spark, and,
+later on, a party from the Royal Society, in conjunction with Watson,
+conducted a series of experiments to determine the velocity of the
+electric fluid, as it was then termed.
+
+Benjamin Franklin, in 1750, showed that lightning was electricity, and
+later on made his interesting experiments with the kite and the key.
+
+DISCOVERING GALVANIC ELECTRICITY.--The great discovery of Galvani, in
+1790, led to the recognition of a new element in electricity, called
+galvanic or voltaic (named after the experimenter, Volta), and now known
+to be identical with frictional electricity. In 1805 Poisson was the
+first to analyze electricity; and when [OE]rsted of Copenhagen, in 1820,
+discovered the magnetic action of electricity, it offered a great
+stimulus to the science, and paved the way for investigation in a new
+direction. Ampere was the first to develop the idea that a motor or a
+dynamo could be made operative by means of the electro-magnetic current;
+and Faraday, about 1830, discovered electro-magnetic rotation.
+
+ELECTRO-MAGNETIC FORCE.--From this time on the knowledge of electricity
+grew with amazing rapidity. Ohm's definition of electro-motive force,
+current strength and resistance eventuated into Ohm's law. Thomson
+greatly simplified the galvanometer, and Wheatstone invented the
+rheostat, a means of measuring resistance, about 1850. Then primary
+batteries were brought forward by Daniels, Grove, Bunsen and Thomson,
+and electrolysis by Faraday. Then came the instruments of precision--the
+electrometer, the resistance bridge, the ammeter, the voltmeter--all of
+the utmost value in the science.
+
+MEASURING INSTRUMENTS.--The perfection of measuring instruments did more
+to advance electricity than almost any other field of endeavor; so that
+after 1875 the inventors took up the subject, and by their energy
+developed and put into practical operation a most wonderful array of
+mechanism, which has become valuable in the service of man in almost
+every field of human activity.
+
+RAPIDITY OF MODERN PROGRESS.--This brief history is given merely to show
+what wonders have been accomplished in a few years. The art is really
+less than fifty years old, and yet so rapidly has it gone forward that
+it is not at all surprising to hear the remark, that the end of the
+wonders has been reached. Less than twenty-five years ago a high
+official of the United States Patent Office stated that it was probable
+the end of electrical research had been reached. The most wonderful
+developments have been made since that time; and now, as in the past,
+one discovery is but the prelude to another still more remarkable. We
+are beginning to learn that we are only on the threshold of that
+storehouse in which nature has locked her secrets, and that there is no
+limit to human ingenuity.
+
+HOW TO ACQUIRE THE VAST KNOWLEDGE.--As the boy, with his limited vision,
+surveys this vast accumulation of tools, instruments and machinery, and
+sees what has been and is now being accomplished, it is not to be
+wondered at that he should enter the field with timidity. In his mind
+the great question is, how to acquire the knowledge. There is so much to
+learn. How can it be accomplished?
+
+The answer to this is, that the student of to-day has the advantage of
+the knowledge of all who have gone before; and now the pertinent thing
+is to acquire that knowledge.
+
+THE MEANS EMPLOYED.--This brings us definitely down to an examination of
+the means that we shall employ to instil this knowledge, so that it may
+become a permanent asset to the student's store of information.
+
+The most significant thing in the history of electrical development is
+the knowledge that of all the great scientists not one of them ever
+added any knowledge to the science on purely speculative reasoning. All
+of them were experimenters. They practically applied and developed their
+theories in the laboratory or the workshop. The natural inference is,
+therefore, that the boy who starts out to acquire a knowledge of
+electricity, must not only theorize, but that he shall, primarily,
+conduct the experiments, and thereby acquire the information in a
+practical way, one example of which will make a more lasting impression
+than pages of dry text.
+
+Throughout these pages, therefore, I shall, as briefly as possible,
+point out the theories involved, as a foundation for the work, and then
+illustrate the structural types or samples; and the work is so arranged
+that what is done to-day is merely a prelude or stepping-stone to the
+next phase of the art. In reality, we shall travel, to a considerable
+extent, the course which the great investigators followed when they were
+groping for the facts and discovering the great manifestations in
+nature.
+
+
+
+
+CHAPTER II
+
+WHAT TOOLS AND APPARATUS ARE NEEDED
+
+
+PREPARING THE WORKSHOP.--Before commencing actual experiments we should
+prepare the workshop and tools. Since we are going into this work as
+pioneers, we shall have to be dependent upon our own efforts for the
+production of the electrical apparatus, so as to be able, with our
+home-made factory, to provide the power, the heat and the electricity.
+Then, finding we are successful in these enterprises, we may look
+forward for "more worlds to conquer."
+
+By this time our neighbors will become interested in and solicit work
+from us.
+
+USES OF OUR WORKSHOPS.--They may want us to test batteries, and it then
+becomes necessary to construct mechanism to detect and measure
+electricity; to install new and improved apparatus; and to put in and
+connect up electric bells in their houses, as well as burglar alarms. To
+meet the requirements, we put in a telegraph line, having learned, as
+well as we are able, how they are made and operated. But we find the
+telegraph too slow and altogether unsuited for our purposes, as well as
+for the uses of the neighborhood, so we conclude to put in a telephone
+system.
+
+WHAT TO BUILD.--It is necessary, therefore, to commence right at the
+bottom to build a telephone, a transmitter, a receiver and a
+switch-board for our system. From the telephone we soon see the
+desirability of getting into touch with the great outside world, and
+wireless telegraphy absorbs our time and energies.
+
+But as we learn more and more of the wonderful things electricity will
+do, we are brought into contact with problems which directly interest
+the home. Sanitation attracts our attention. Why cannot electricity act
+as an agent to purify our drinking water, to sterilize sewage and to
+arrest offensive odors? We must, therefore, learn something about the
+subject of electrolysis.
+
+WHAT TO LEARN.--The decomposition of water is not the only thing that we
+shall describe pertaining to this subject. We go a step further, and
+find that we can decompose metals as well as liquids, and that we can
+make a pure metal out of an impure one, as well as make the foulest
+water pure. But we shall also, in the course of our experiments, find
+that a cheap metal can be coated with a costly one by means of
+electricity--that we can electroplate by electrolysis.
+
+USES OF THE ELECTRICAL DEVICES.--While all this is progressing and our
+factory is turning out an amazing variety of useful articles, we are led
+to inquire into the uses to which we may devote our surplus electricity.
+The current may be diverted for boiling water; for welding metals; for
+heating sad-irons, as well as for other purposes which are daily
+required.
+
+TOOLS.--To do these things tools are necessary, and for the present they
+should not be expensive. A small, rigidly built bench is the first
+requirement. This may be made, as shown in Fig. 1, of three 2-inch
+planks, each 10 inches wide and 6 feet long, mounted on legs 36 inches
+in height. In the front part are three drawers for your material, or the
+small odds and ends, as well as for such little tools as you may
+accumulate. Then you will need a small vise, say, with a 2-inch jaw, and
+you will also require a hand reel for winding magnets. This will be
+fully described hereafter.
+
+You can also, probably, get a small, cheap anvil, which will be of the
+greatest service in your work. It should be mounted close up to the work
+bench. Two small hammers, one with an A-shaped peon, and the other with
+a round peon, should be selected, and also a plane and a small wood saw
+with fine teeth. A bit stock, or a ratchet drill, if you can afford it,
+with a variety of small drills; two wood chisels, say of 3/8-inch and
+3/4-inch widths; small cold chisels; hack saw, 10-inch blade; small
+iron square; pair of dividers; tin shears; wire cutters; 2 pairs of
+pliers, one flat and the other round-nosed; 2 awls, centering punch,
+wire cutters, and, finally, soldering tools.
+
+[Illustration: _Fig. 2. Top View_ MAGNET-WINDING REEL]
+
+[Illustration: _Fig. 3. Side View_ MAGNET-WINDING REEL]
+
+If a gas stove is not available, a brazing torch is an essential tool.
+Numerous small torches are being made, which are cheap and easily
+operated. A small soldering iron, with pointed end, should be provided;
+also metal shears and a small square; an awl and several sizes of
+gimlets; a screwdriver; pair of pliers and wire cutters.
+
+From the foregoing it will be seen that the cost of tools is not a very
+expensive item.
+
+This entire outfit, not including the anvil and vise, may be purchased
+new for about $20.00, so we have not been extravagant.
+
+MAGNET-WINDING REEL.--Some little preparation must be made, so we may be
+enabled to handle our work by the construction of mechanical aids.
+
+[Illustration: _Fig. 4. Journal Block._]
+
+First of these is the magnet-winding reel, a plan view of which is shown
+in Fig. 2. This, for our present work, will be made wholly of wood.
+
+Select a plank 1-1/2 inches thick and 8 inches wide, and from this cut
+off two pieces (A), each 7 inches long, and then trim off the corners
+(B, B), as shown in Fig. 4. To serve as the mandrel (C, Fig. 2), select
+a piece of broomstick 9 inches long. Bore a hole (D) in each block (A) a
+half inch below the upper margin of the block, this hole being of such
+diameter that the broomstick mandrel will fit and easily turn therein.
+
+Place a crank (E), 5 inches long, on the outer end of the mandrel, as in
+Fig. 3. Then mount one block on the end of the bench and the other block
+3 inches away. Affix them to the bench by nails or screws, preferably
+the latter.
+
+On the inner end of the mandrel put a block (F) of hard wood. This is
+done by boring a hole 1 inch deep in the center of the block, into which
+the mandrel is driven. On the outer face of the block is a square hole
+large enough to receive the head of a 3/8-inch bolt, and into the
+depression thus formed a screw (G) is driven through the block and into
+the end of the mandrel, so as to hold the block (F) and mandrel firmly
+together. When these parts are properly put together, the inner side of
+the block will rest and turn against the inner journal block (A).
+
+The tailpiece is made of a 2" × 4" scantling (H), 10 inches long, one
+end of it being nailed to a transverse block (I) 2" × 2" × 4". The inner
+face of this block has a depression in which is placed a V-shaped cup
+(J), to receive the end of the magnet core (K) or bolt, which is to be
+used for this purpose. The tailpiece (H) has a longitudinal slot (L) 5
+inches long adapted to receive a 1/2-inch bolt (M), which passes down
+through the bench, and is, therefore, adjustable, so it may be moved to
+and from the journal bearing (A), thereby providing a place for the
+bolts to be put in. These bolts are the magnet cores (K), 6 inches long,
+but they may be even longer, if you bore several holes (N) through the
+bench so you may set over the tailpiece.
+
+With a single tool made substantially like this, over a thousand of the
+finest magnets have been wound. Its value will be appreciated after you
+have had the experience of winding a few magnets.
+
+ORDER IN THE WORKSHOP.--Select a place for each tool on the rear upright
+of the bench, and make it a rule to put each tool back into its place
+after using. This, if persisted in, will soon become a habit, and will
+save you hours of time. Hunting for tools is the unprofitable part of
+any work.
+
+
+
+
+CHAPTER III
+
+MAGNETS, COILS, ARMATURES, ETC.
+
+
+THE TWO KINDS OF MAGNET.--Generally speaking, magnets are of two kinds,
+namely, permanent and electro-magnetic.
+
+PERMANENT MAGNETS.--A permanent magnet is a piece of steel in which an
+electric force is exerted at all times. An electro-magnet is a piece of
+iron which is magnetized by a winding of wire, and the magnet is
+energized only while a current of electricity is passing through the
+wire.
+
+ELECTRO-MAGNET.--The electro-magnet, therefore, is the more useful,
+because the pull of the magnet can be controlled by the current which
+actuates it.
+
+The electro-magnet is the most essential of all contrivances in the
+operation and use of electricity. It is the piece of mechanism which
+does the physical work of almost every electrical apparatus or machine.
+It is the device which has the power to convert the unseen electric
+current into motion which may be observed by the human eye. Without it
+electricity would be a useless agent to man.
+
+While the electro-magnet is, therefore, the form of device which is
+almost wholly used, it is necessary, first, to understand the principles
+of the permanent magnet.
+
+MAGNETISM.--The curious force exerted by a magnet is called magnetism,
+but its origin has never been explained. We know its manifestations
+only, and laws have been formulated to explain its various phases; how
+to make it more or less intense; how to make its pull more effective;
+the shape and form of the magnet and the material most useful in its
+construction.
+
+[Illustration: _Fig 5._ PLAIN MAGNET BAR]
+
+MATERIALS FOR MAGNETS.--Iron and steel are the best materials for
+magnets. Some metals are non-magnetic, this applying to iron if combined
+with manganese. Others, like sulphur, zinc, bismuth, antimony, gold,
+silver and copper, not only are non-magnetic, but they are actually
+repelled by magnetism. They are called the diamagnetics.
+
+NON-MAGNETIC MATERIALS.--Any non-magnetic body in the path of a magnetic
+force does not screen or diminish its action, whereas a magnetic
+substance will.
+
+In Fig. 5 we show the simplest form of magnet, merely a bar of steel (A)
+with the magnetic lines of force passing from end to end. It will be
+understood that these lines extend out on all sides, and not only along
+two sides, as shown in the drawing. The object is to explain clearly how
+the lines run.
+
+[Illustration: _Fig. 6._ SEVERED MAGNET]
+
+ACTION OF A SEVERED MAGNET.--Now, let us suppose that we sever this bar
+in the middle, as in Fig. 6, or at any other point between the ends. In
+this case each part becomes a perfect magnet, and a new north pole (N)
+and a new south pole (S) are made, so that the movement of the magnetic
+lines of force are still in the same direction in each--that is, the
+current flows from the north pole to the south pole.
+
+WHAT NORTH AND SOUTH POLES MEAN.--If these two parts are placed close
+together they will attract each other. But if, on the other hand, one of
+the pieces is reversed, as in Fig. 7, they will repel each other. From
+this comes the statement that likes repel and unlikes attract each
+other.
+
+REPULSION AND ATTRACTION.--This physical act of repulsion and attraction
+is made use of in motors, as we shall see hereinafter.
+
+It will be well to bear in mind that in treating of electricity the
+north pole is always associated with the plus sign (+) and the south
+pole with the minus sign (-). Or the N sign is positive and the S sign
+negative electricity.
+
+[Illustration: _Fig. 7._ REVERSED MAGNETS]
+
+POSITIVES AND NEGATIVES.--There is really no difference between positive
+and negative electricity, so called, but the foregoing method merely
+serves as a means of identifying or classifying the opposite ends of a
+magnet or of a wire.
+
+MAGNETIC LINES OF FORCE.--It will be noticed that the magnetic lines of
+force pass through the bar and then go from end to end through the
+atmosphere. Air is a poor conductor of electricity, so that if we can
+find a shorter way to conduct the current from the north pole to the
+south pole, the efficiency of the magnet is increased.
+
+This is accomplished by means of the well-known horseshoe magnet, where
+the two ends (N, S) are brought close together, as in Fig. 8.
+
+THE EARTH AS A MAGNET.--The earth is a huge magnet and the magnetic
+lines run from the north pole to the south pole around all sides of the
+globe.
+
+[Illustration: _Fig. 8._ HORSESHOE MAGNET]
+
+The north magnetic pole does not coincide with the true north pole or
+the pivotal point of the earth's rotation, but it is sufficiently near
+for all practical purposes. Fig. 9 shows the magnetic lines running from
+the north to the south pole.
+
+WHY THE COMPASS POINTS NORTH AND SOUTH.--Now, let us try to ascertain
+why the compass points north and south.
+
+Let us assume that we have a large magnet (A, Fig. 10), and suspend a
+small magnet (B) above it, so that it is within the magnetic field of
+the large magnet. This may be done by means of a short pin (C), which is
+located in the middle of the magnet (B), the upper end of this pin
+having thereon a loop to which a thread (D) is attached. The pin also
+carries thereon a pointer (E), which is directed toward the north pole
+of the bar (B).
+
+[Illustration: _Fig. 9._ EARTH'S MAGNETIC LINES]
+
+You will now take note of the interior magnetic lines (X), and the
+exterior magnetic lines (Z) of the large magnet (A), and compare the
+direction of their flow with the similar lines in the small magnet (B).
+
+The small magnet has both its exterior and its interior lines within the
+exterior lines (Z) of the large magnet (A), so that as the small magnet
+(B) is capable of swinging around, the N pole of the bar (B) will point
+toward the S pole of the larger bar (A). The small bar, therefore, is
+influenced by the exterior magnetic field (Z).
+
+[Illustration: _Fig. 10._ TWO PERMANENT MAGNETS]
+
+[Illustration: _Fig. 11._ MAGNETS IN THE EARTH'S MAGNETIC FIELD]
+
+Let us now take the outline represented by the earth's surface (Fig.
+11), and suspend a magnet (A) at any point, like the needle of a
+compass, and it will be seen that the needle will arrange itself north
+and south, within the magnetic field which flows from the north to the
+south pole.
+
+PECULIARITY OF A MAGNET.--One characteristic of a magnet is that, while
+apparently the magnetic field flows out at one end of the magnet, and
+moves inwardly at the other end, the power of attraction is just the
+same at both ends.
+
+In Fig. 12 are shown a bar (A) and a horseshoe magnet (B). The bar (A)
+has metal blocks (C) at each end, and each of these blocks is attracted
+to and held in contact with the ends by magnetic influence, just the
+same as the bar (D) is attracted by and held against the two ends of the
+horseshoe magnet. These blocks (C) or the bar (D) are called armatures.
+Through them is represented the visible motion produced by the magnetic
+field.
+
+[Illustration: _Fig. 12._ ARMATURES FOR MAGNETS]
+
+ACTION OF THE ELECTRO-MAGNET.--The electro-magnet exerts its force in
+the same manner as a permanent magnet, so far as attraction and
+repulsion are concerned, and it has a north and a south pole, as in the
+case with the permanent magnet. An electro-magnet is simply a bar of
+iron with a coil or coils of wire around it; when a current of
+electricity flows through the wire, the bar is magnetized. The moment
+the current is cut off, the bar is demagnetized. The question that now
+arises is, why an electric current flowing through a wire, under those
+conditions, magnetizes the bar, or _core_, as it is called.
+
+[Illustration: _Fig. 13._ MAGNETIZED FIELD]
+
+[Illustration: _Fig. 14._ MAGNETIZED BAR]
+
+In Fig. 13 is shown a piece of wire (A). Let us assume that a current of
+electricity is flowing through this wire in the direction of the darts.
+What actually takes place is that the electricity extends out beyond the
+surface of the wire in the form of the closed rings (B). If, now, this
+wire (A) is wound around an iron core (C, Fig. 14), you will observe
+that this electric field, as it is called, entirely surrounds the core,
+or rather, that the core is within the magnetic field or influence of
+the current flowing through the wire, and the core (C) thereby becomes
+magnetized, but it is magnetized only when the current passes through
+the wire coil (A).
+
+[Illustration: _Fig. 15._ DIRECTION OF CURRENT]
+
+From the foregoing, it will be understood that a wire carrying a current
+of electricity not only is affected within its body, but that it also
+has a sphere of influence exteriorly to the body of the wire, at all
+points; and advantage is taken of this phenomenon in constructing
+motors, dynamos, electrical measuring devices and almost every kind of
+electrical mechanism in existence.
+
+EXTERIOR MAGNETIC INFLUENCE AROUND A WIRE CARRYING A CURRENT.--Bear in
+mind that the wire coil (A, Fig. 14) does not come into contact with the
+core (C). It is insulated from the core, either by air or by rubber or
+other insulating substance, and a current passing from A to C under
+those conditions is a current of _induction_. On the other hand, the
+current flowing through the wire (A) from end to end is called a
+_conduction_ current. Remember these terms.
+
+In this connection there is also another thing which you will do well to
+bear in mind. In Fig. 15 you will notice a core (C) and an insulated
+wire coil (B) wound around it. The current, through the wire (B), as
+shown by the darts (D), moves in one direction, and the induced current
+in the core (C) travels in the opposite direction, as shown by the darts
+(D).
+
+[Illustration: _Fig. 16._ DIRECTION OF INDUCTION CURRENT]
+
+PARALLEL WIRES.--In like manner, if two wires (A, B, Fig. 16) are
+parallel with each other, and a current of electricity passes along the
+wire (A) in one direction, the induced current in the wire (B) will move
+in the opposite direction.
+
+These fundamental principles should be thoroughly understood and
+mastered.
+
+
+
+
+CHAPTER IV
+
+FRICTIONAL, VOLTAIC OR GALVANIC, AND ELECTRO-MAGNETIC ELECTRICITY
+
+
+THREE ELECTRICAL SOURCES.--It has been found that there are three kinds
+of electricity, or, to be more accurate, there are three ways to
+generate it. These will now be described.
+
+When man first began experimenting, he produced a current by frictional
+means, and collected the electricity in a bottle or jar. Electricity, so
+stored, could be drawn from the jar, by attaching thereto suitable
+connection. This could be effected only in one way, and that was by
+discharging the entire accumulation instantaneously. At that time they
+knew of no means whereby the current could be made to flow from the jar
+as from a battery or cell.
+
+FRICTIONAL ELECTRICITY.--With a view of explaining the principles
+involved, we show in Fig. 17 a machine for producing electricity by
+friction.
+
+
+[Illustration: _Fig. 17._ FRICTION-ELECTRICITY MACHINE]
+
+This is made up as follows: A represents the base, having thereon a flat
+member (B), on which is mounted a pair of parallel posts or standards
+(C, C), which are connected at the top by a cross piece (D). Between
+these two posts is a glass disc (E), mounted upon a shaft (F), which
+passes through the posts, this shaft having at one end a crank (G). Two
+leather collecting surfaces (H, H), which are in contact with the glass
+disc (E), are held in position by arms (I, J), the arm (I) being
+supported by the cross piece (D), and the arm (J) held by the base piece
+(B). A rod (K), U-shaped in form, passes over the structure here thus
+described, its ends being secured to the base (B). The arms (I, J) are
+both electrically connected with this rod, or conductor (K), joined to a
+main conductor (L), which has a terminating knob (M). On each side and
+close to the terminal end of each leather collector (H) is a fork-shaped
+collector (N). These two collectors are also connected electrically with
+the conductor (K). When the disc is turned electricity is generated by
+the leather flaps and accumulated by the collectors (N), after which it
+is ready to be discharged at the knob (M).
+
+In order to collect the electricity thus generated a vessel called a
+Leyden jar is used.
+
+LEYDEN JAR.--This is shown in Fig. 18. The jar (A) is of glass coated
+exteriorly at its lower end with tinfoil (B), which extends up a little
+more than halfway from the bottom. This jar has a wooden cover or top
+(C), provided centrally with a hole (D). The jar is designed to receive
+within it a tripod and standard (E) of lead. Within this lead standard
+is fitted a metal rod (F), which projects upwardly through the hole (D),
+its upper end having thereon a terminal knob (G). A sliding cork (H) on
+the rod (F) serves as a means to close the jar when not in use. When in
+use this cork is raised so the rod may not come into contact,
+electrically, with the cover (C).
+
+The jar is half filled with sulphuric acid (I), after which, in order
+to charge the jar, the knob (G) is brought into contact with the knob
+(M) of the friction generator (Fig. 17).
+
+VOLTAIC OR GALVANIC ELECTRICITY.--The second method of generating
+electricity is by chemical means, so called, because a liquid is used as
+one of the agents.
+
+[Illustration: _Fig. 18._ LEYDEN JAR]
+
+Galvani, in 1790, made the experiments which led to the generation of
+electricity by means of liquids and metals. The first battery was called
+the "crown of cups," shown in Fig. 19, and consisting of a row of glass
+cups (A), containing salt water. These cups were electrically connected
+by means of bent metal strips (B), each strip having at one end a copper
+plate (C), and at the other end a zinc plate (D). The first plate in the
+cup at one end is connected with the last plate in the cup at the other
+end by a conductor (E) to make a complete circuit.
+
+[Illustration: _Fig. 19._ GALVANIC ELECTRICITY. CROWN OF CUPS]
+
+THE CELL AND BATTERY.--From the foregoing it will be seen that within
+each cup the current flows from the zinc to the copper plates, and
+exteriorly from the copper to the zinc plates through the conductors (B
+and E).
+
+A few years afterwards Volta devised what is known as the voltaic pile
+(Fig. 20).
+
+VOLTAIC PILE--HOW MADE.--This is made of alternate discs of copper and
+zinc with a piece of cardboard of corresponding size between each zinc
+and copper plate. The cardboard discs are moistened with acidulated
+water. The bottom disc of copper has a strip which connects with a cup
+of acid, and one wire terminal (A) runs therefrom. The upper disc, which
+is of zinc, is also connected, by a strip, with a cup of acid from which
+extends the other terminal wire (B).
+
+[Illustration: _Fig. 20._ VOLTAIC ELECTRICITY]
+
+_Plus and Minus Signs._--It will be noted that the positive or copper
+disc has the plus sign (+) while the zinc disc has the minus (-) sign.
+These signs denote the positive and the negative sides of the current.
+
+The liquid in the cells, or in the moistened paper, is called the
+_electrolyte_ and the plates or discs are called _electrodes_. To define
+them more clearly, the positive plate is the _anode_, and the negative
+plate the _cathode_.
+
+The current, upon entering the zinc plate, decomposes the water in the
+electrolyte, thereby forming oxygen. The hydrogen in the water, which
+has also been formed by the decomposition, is carried to the copper
+plate, so that the plate finally is so coated with hydrogen that it is
+difficult for the current to pass through. This condition is called
+"polarization," and to prevent it has been the aim of all inventors. To
+it also we may attribute the great variety of primary batteries, each
+having some distinctive claim of merit.
+
+THE COMMON PRIMARY CELL.--The most common form of primary cell contains
+sulphuric acid, or a sulphuric acid solution, as the electrolyte, with
+zinc for the _anode_, and carbon, instead of copper, for the _cathode_.
+
+The ends of the zinc and copper plates are called _terminals_, and while
+the zinc is the anode or positive element, its _terminal_ is designated
+as the positive pole. In like manner, the carbon is the negative
+element or cathode, and its terminal is designated as negative pole.
+
+Fig. 21 will show the relative arrangement of the parts. It is customary
+to term that end or element from which the current flows as positive. A
+cell is regarded as a whole, and as the current passes out of the cell
+from the copper element, the copper terminal becomes positive.
+
+[Illustration: _Fig. 21._ PRIMARY BATTERY]
+
+BATTERY RESISTANCE, ELECTROLYTE AND CURRENT.--The following should be
+carefully memorized:
+
+A cell has reference to a single vessel. When two or more cells are
+coupled together they form a _battery_.
+
+_Resistance_ is opposition to the movement of the current. If it is
+offered by the electrolyte, it is designated "Internal Resistance." If,
+on the other hand, the opposition takes place, for instance, through the
+wire, it is then called "External Resistance."
+
+The electrolyte must be either acid, or alkaline, or saline, and the
+electrodes must be of dissimilar metals, so the electrolyte will attack
+one of them.
+
+The current is measured in amperes, and the force with which it is
+caused to flow is measured in volts. In practice the word "current" is
+used to designate ampere flow; and electromotive force, or E. M. F., is
+used instead of voltage.
+
+ELECTRO-MAGNETIC ELECTRICITY.--The third method of generating
+electricity is by electro-magnets. The value and use of induction will
+now be seen, and you will be enabled to utilize the lesson concerning
+magnetic action referred to in the previous chapter.
+
+MAGNETIC RADIATION.--You will remember that every piece of metal which
+is within the path of an electric current has a space all about its
+surface from end to end which is electrified. This electrified field
+extends out a certain distance from the metal, and is supposed to
+maintain a movement around it. If, now, another piece of metal is
+brought within range of this electric or magnetic zone and moved across
+it, so as to cut through this field, a current will be generated
+thereby, or rather added to the current already exerted, so that if we
+start with a feeble current, it can be increased by rapidly "cutting the
+lines of force," as it is called.
+
+DIFFERENT KINDS OF DYNAMO.--While there are many kinds of dynamo, they
+all, without exception, are constructed in accordance with this
+principle. There are also many varieties of current. For instance, a
+dynamo may be made to produce a high voltage and a low amperage; another
+with high amperage and low voltage; another which gives a direct current
+for lighting, heating, power, and electroplating; still another which
+generates an alternating current for high tension power, or
+transmission, arc-lighting, etc., all of which will be explained
+hereafter.
+
+In this place, however, a full description of a direct-current dynamo
+will explain the principle involved in all dynamos--that to generate a
+current of electricity makes it necessary for us to move a field of
+force, like an armature, rapidly and continuously through another field
+of force, like a magnetic field.
+
+DIRECT-CURRENT DYNAMO.--We shall now make the simplest form of dynamo,
+using for this purpose a pair of permanent magnets.
+
+[Illustration: _Fig. 22._ DYNAMO FIELD AND POLE PIECE]
+
+SIMPLE MAGNET CONSTRUCTION.--A simple way to make a pair of magnets for
+this purpose is shown in Fig. 22. A piece of round 3/4-inch steel core
+(A), 5-1/2 inches long, is threaded at both ends to receive at one end a
+nut (B), which is screwed on a sufficient distance so that the end of
+the core (A) projects a half inch beyond the nut. The other end of the
+steel core has a pole piece of iron (C) 2" × 2" × 4", with a hole
+midway between the ends, threaded entirely through, and provided along
+one side with a concave channel, within which the armature is to turn.
+Now, before the pole piece (C) is put on, we will slip on a disc (E),
+made of hard rubber, then a thin rubber tube (F), and finally a rubber
+disc (G), so as to provide a positive insulation for the wire coil which
+is wound on the bobbin thus made.
+
+HOW TO WIND.--In practice, and as you go further along in this work, you
+will learn the value, first, of winding one layer of insulated wire on
+the spool, coating it with shellac, and then putting on the next layer,
+and so on; when completely wound, the two wire terminals may be brought
+out at one end; but for our present purpose, and to render the
+explanation clearer, the wire terminals are at the opposite ends of the
+spool (H, H').
+
+THE DYNAMO FIELDS.--Two of these spools are so made and they are called
+the _fields_ of the dynamo.
+
+We will next prepare an iron bar (I), 5 inches long and 1/2 inch thick
+and 1-1/2 inches wide, then bore two holes through it so the distance
+measures 3 inches from center to center. These holes are to be threaded
+for the 3/4-inch cores (A). This bar holds together the upper ends of
+the cores, as shown in Fig. 23.
+
+[Illustration: _Fig. 23._ BASE AND FIELDS ASSEMBLED]
+
+We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches
+long and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on a
+middle line, to receive a pair of 3/4-inch cap screws (K), which pass
+upwardly through the holes in the base and screw into the pole pieces
+(C). A wooden bar (L), 1-1/2" × 1-1/2", 8 inches long, is placed under
+each pole piece, which is also provided with holes for the cap screws
+(K). The lower side of the base (J) should be countersunk, as at M, so
+the head of the nut will not project. The fields of the dynamo are now
+secured in position to the base.
+
+[Illustration: _Fig. 24._ DETAILS OF THE ARMATURE, CORE
+
+_Fig. 25._ DETAILS OF THE ARMATURE, BODY]
+
+THE ARMATURE.--A bar of iron (Fig. 24), 1" × 1" and 2-1/4 inches long,
+is next provided. Through this bar (1) are then bored two 5/16-inch
+holes 1-3/4 inches apart, and on the opposite sides of this bar are two
+half-rounded plates of iron (3) (Fig. 25).
+
+ARMATURE WINDING.--Each plate is 1/2 inch thick, 1-3/4 inches wide and 4
+inches long, each plate having holes (4) to coincide with the holes (2)
+of the bar (1), so that when the two plates are applied to opposite
+sides of the bar, and riveted together, a cylindrical member is formed,
+with two channels running longitudinally, and transversely at the ends;
+and in these channels the insulated wires are wound from end to end
+around the central block (1).
+
+MOUNTING THE ARMATURE.--It is now necessary to provide a means for
+revolving this armature. To this end a brass disc (5, Fig. 26) is made,
+2 inches in diameter, 1/8 inch thick. Centrally, at one side, is a
+projecting stem (6) of round brass, which projects out 2 inches, and the
+outer end is turned down, as at 7, to form a small bearing surface.
+
+[Illustration: _Fig. 26._ JOURNALS _Fig. 27._ COMMUTATOR,
+ARMATURE MOUNTINGS]
+
+The other end of the armature has a similar disc (8), with a central
+stem (9), 1-1/2 inches long, turned down to 1/4-inch diameter up to
+within 1/4 inch of the disc (7), so as to form a shoulder.
+
+THE COMMUTATOR.--In Fig. 27 is shown, at 10, a wooden cylinder, 1 inch
+long and 1-1/4 inches in diameter, with a hole (11) bored through
+axially, so that it will fit tightly on the stem (6) of the disc (5). On
+this wooden cylinder is driven a brass or copper tube (12), which has
+holes (13) opposite each other. Screws are used to hold the tube to the
+wooden cylinder, and after they are properly secured together, the tube
+(12) is cut by a saw, as at 14, so as to form two independent tubular
+surfaces.
+
+[Illustration: _Fig. 28._ END VIEW ARMATURE, MOUNTED]
+
+These tubular sections are called the commutator plates.
+
+[Illustration: _Fig. 29._ TOP VIEW OF ARMATURE ON BASE]
+
+In order to mount this armature, two bearings are provided, each
+comprising a bar of brass (15, Fig. 28), each 1/4 inch thick, 1/2 inch
+wide and 4-1/2 inches long. Two holes, 3 inches apart, are formed
+through this bar, to receive round-headed wood screws (16), these screws
+being 3 inches long, so they will pass through the wooden pieces (I)
+and enter the base (J). Midway between the ends, each bar (15) has an
+iron bearing block (17), 3/4" × 1/2" and 1-1/2 inches high, the 1/4-inch
+hole for the journal (7) being midway between its ends.
+
+COMMUTATOR BRUSHES.--Fig. 28 shows the base, armature and commutator
+assembled in position, and to these parts have been added the commutator
+brushes. The brush holder (18) is a horizontal bar made of hard rubber
+loosely mounted upon the journal pin (7), which is 2-1/2 inches long. At
+each end is a right-angled metal arm (19) secured to the bar (18) by
+screws (20). To these arms the brushes (21) are attached, so that their
+spring ends engage with the commutator (12). An adjusting screw (22) in
+the bearing post (17), with the head thereof bearing against the
+brush-holder (18), serves as a means for revolubly adjusting the brushes
+with relation to the commutator.
+
+DYNAMO WINDINGS.--There are several ways to wind the dynamos. These
+can be shown better by the following diagrams (Figs. 30, 31, 32, 33):
+
+THE FIELD.--If the field (A, Fig. 30) is not a permanent magnet, it must
+be excited by a cell or battery, and the wires (B, B') are connected up
+with a battery, while the wires (C, C') may be connected up to run a
+motor. This would, therefore, be what is called a "separately excited"
+dynamo. In this case the battery excites the field and the armature
+(D), cutting the lines of force at the pole pieces (E), so that the
+armature gathers the current for the wires (C, C').
+
+[Illustration: _Fig. 30._ FIELD WINDING]
+
+[Illustration: _Fig. 31._ SERIES-WOUND]
+
+SERIES-WOUND FIELD.--Fig. 31 shows a "series-wound" dynamo. The wires of
+the fields (A) are connected up in series with the brushes of the
+armature (D), and the wires (G, G') are led out and connected up with a
+lamp, motor or other mechanism. In this case, as well as in Figs. 32 and
+33, both the field and the armature are made of soft gray iron. With
+this winding and means of connecting the wires, the field is constantly
+excited by the current passing through the wires.
+
+SHUNT-WOUND FIELD.--Fig. 32 represents what is known as a "shunt-wound"
+dynamo. Here the field wires (H, H) connect with the opposite brushes
+of the armature, and the wires (I, I') are also connected with the
+brushes, these two wires being provided to perform the work required.
+This is a more useful form of winding for electroplating purposes.
+
+[Illustration: _Fig. 32._ SHUNT-WOUND _Fig. 32._ COMPOUND-WOUND]
+
+COMPOUND-WOUND FIELD.--Fig. 33 is a diagram of a "compound-wound"
+dynamo. The regular field winding (J) has its opposite ends connected
+directly with the armature brushes. There is also a winding, of a
+comparatively few turns, of a thicker wire, one terminal (K) of which is
+connected with one of the brushes and the other terminal (K') forms one
+side of the lighting circuit. A wire (L) connects with the other
+armature brush to form a complete lighting circuit.
+
+
+
+
+CHAPTER V
+
+HOW TO DETECT AND MEASURE ELECTRICITY
+
+
+MEASURING INSTRUMENTS.--The production of an electric current would not
+be of much value unless we had some way by which we might detect and
+measure it. The pound weight, the foot rule and the quart measure are
+very simple devices, but without them very little business could be
+done. There must be a standard of measurement in electricity as well as
+in dealing with iron or vegetables or fabrics.
+
+As electricity cannot be seen by the human eye, some mechanism must be
+made which will reveal its movements.
+
+THE DETECTOR.--It has been shown in the preceding chapter that a current
+of electricity passing through a wire will cause a current to pass
+through a parallel wire, if the two wires are placed close together, but
+not actually in contact with each other. An instrument which reveals
+this condition is called a _galvanometer_. It not only detects the
+presence of a current, but it shows the direction of its flow. We shall
+now see how this is done.
+
+For example, the wire (A, Fig. 35) is connected up in an electric
+circuit with a permanent magnet (B) suspended by a fine wire (C), so
+that the magnet (B) may freely revolve.
+
+[Illustration: _Fig. 34._     _Fig. 35._      _Fig. 36._
+             TO THE RIGHT,  COMPASS MAGNET,  TO THE LEFT]
+
+For convenience, the magnetic field is shown flowing in the direction of
+the darts, in which the dart (D) represents the current within the
+magnet (B) flowing toward the north pole, and the darts (E) showing the
+exterior current flowing toward the south pole. Now, if the wire (A) is
+brought up close to the magnet (B), and a current passed through A, the
+magnet (B) will be affected. Fig. 35 shows the normal condition of the
+magnetized bar (B) parallel with the wire (A) when a current is not
+passing through the latter.
+
+DIRECTION OF CURRENT.--If the current should go through the wire (A)
+from right to left, as shown in Fig. 34, the magnet (B) would swing in
+the direction taken by the hands of a clock and assume the position
+shown in Fig. 34. If, on the other hand, the current in the wire (A)
+should be reversed or flow from left to right, the magnet (B) would
+swing counter-clock-wise, and assume the position shown in Fig. 36. The
+little pointer (G) would, in either case, point in the direction of the
+flow of the current through the wire (A).
+
+[Illustration: _Fig. 37._ INDICATING DIRECTION OF CURRENT]
+
+SIMPLE CURRENT DETECTOR.--A simple current detector may be made as
+follows:
+
+Prepare a base 3' × 4' in size and 1 inch thick. At each corner of one
+end fix a binding post, as at A, A', Fig. 37. Then select 20 feet of No.
+28 cotton-insulated wire, and make a coil (B) 2 inches in diameter,
+leaving the ends free, so they may be affixed to the binding posts (A,
+A'). Now glue or nail six blocks (C) to the base, each block being 1" ×
+1" × 2", and lay the coil on these blocks. Then drive an L-shaped nail
+(D) down into each block, on the inside of the coil, as shown, so as to
+hold the latter in place.
+
+[Illustration: _Fig. 38._ THE BRIDGE]
+
+Now make a bridge (E, Fig. 38) of a strip of brass 1/2 inch wide, 1/16
+inch thick and long enough to span the coil, and bend the ends down, as
+at F, so as to form legs. A screw hole (G) is formed in each foot, so it
+may be screwed to the base.
+
+Midway between the ends this bridge has a transverse slot (H) in one
+edge, to receive therein the pivot pin of the swinging magnet. In order
+to hold the pivot pin in place, cut out an H-shaped piece of sheet brass
+(I), which, when laid on the bridge, has its ends bent around the
+latter, as shown at J, and the crossbar of the H-shaped piece then will
+prevent the pivot pin from coming out of the slot (H).
+
+[Illustration: _Fig. 39._ DETAILS OF DETECTOR]
+
+The magnet is made of a bar of steel (K, Fig. 39) 1-1/2 inches long, 3/8
+inch wide and 1/16 inch thick, a piece of a clock spring being very
+serviceable for this purpose. The pivot pin is made of an ordinary pin
+(L), and as it is difficult to solder the steel magnet (K) to the pin,
+solder only a small disc (M) to the pin (L). Then bore a hole (N)
+through the middle of the magnet (K), larger in diameter than the pin
+(L), and, after putting the pin in the hole, pour sealing wax into the
+hole, and thereby secure the two parts together. Near the upper end of
+the pin (L) solder the end of a pointer (O), this pointer being at right
+angles to the armature (K). It is better to have a metal socket for the
+lower end of the pin. When these parts are put together, as shown in
+Fig. 37, a removable glass top, or cover, should be provided.
+
+This is shown in Fig. 40, in which a square, wooden frame (P) is used,
+and a glass (Q) fitted into the frame, the glass being so arranged that
+when the cover is in position it will be in close proximity to the upper
+projecting end of the pivot pin (L), and thus prevent the magnet from
+becoming misplaced.
+
+[Illustration: _Fig. 40._ CROSS SECTION OF DETECTOR]
+
+HOW TO PLACE THE DETECTOR.--If the detector is placed north and south,
+as shown by the two markings, N and S (Fig. 37), the magnet bar will
+point north and south, being affected by the earth's magnetism; but when
+a current of electricity flows through the coil (B), the magnet will be
+deflected to the right or to the left, so that the pointer (O) will then
+show the direction in which the current is flowing through the wire (R)
+which you are testing.
+
+The next step of importance is to _measure_ the current, that is, to
+determine its strength or intensity, as well as the flow or quantity.
+
+DIFFERENT WAYS OF MEASURING A CURRENT.--There are several ways to
+measure the properties of a current, which may be defined as follows:
+
+1. THE SULPHURIC ACID VOLTAMETER.--By means of an electrolytic action,
+whereby the current decomposes an acidulated solution--that is, water
+which has in it a small amount of sulphuric acid--and then measuring the
+gas generated by the current.
+
+2. THE COPPER VOLTAMETER.--By electro-chemical means, in which the
+current passes through plates immersed in a solution of copper sulphate.
+
+3. THE GALVANOSCOPE.--By having a coil of insulated wire, with a magnet
+suspended so as to turn freely within the coil, forming what is called a
+galvanoscope.
+
+4. ELECTRO-MAGNETIC METHOD.--By using a pair of magnets and sending a
+current through the coils, and then measuring the pull on the armature.
+
+5. THE POWER OR SPEED METHOD.--By using an electric fan, and noting the
+revolutions produced by the current.
+
+6. THE CALORIMETER.--By using a coil of bare wire, immersed in paraffine
+oil, and then measuring the temperature by means of a thermometer.
+
+[Illustration: _Fig. 41._ ACID VOLTAMETER]
+
+[Illustration: _Fig. 42._ COPPER VOLTAMETER]
+
+7. THE LIGHT METHOD.--Lastly, by means of an electric light, which
+shows, by its brightness, a greater or less current.
+
+THE PREFERRED METHODS.--It has been found that the first and second
+methods are the only ones which will accurately register current
+strength, and these methods have this advantage--that the chemical
+effect produced is not dependent upon the size or shape of the apparatus
+or the plates used.
+
+HOW TO MAKE A SULPHURIC ACID VOLTAMETER.--In Fig. 41 is shown a simple
+form of sulphuric acid voltameter, to illustrate the first method. A is
+a jar, tightly closed by a cover (B). Within is a pair of platinum
+plates (C, C), each having a wire (D) through the cover. The cover has a
+vertical glass tube (E) through it, which extends down to the bottom of
+the jar, the electrolyte therein being a weak solution of sulphuric
+acid. When a current passes through the wires (D), the solution is
+partially decomposed--that is, converted into gas, which passes up into
+the vacant space (F) above the liquid, and, as it cannot escape, it
+presses the liquid downwardly, and causes the latter to flow upwardly
+into the tube (E). It is then an easy matter, after the current is on
+for a certain time, to determine its strength by the height of the
+liquid in the tube.
+
+HOW TO MAKE A COPPER VOLTAMETER.--The second, or copper voltameter, is
+shown in Fig. 42. The glass jar (A) contains a solution of copper
+sulphate, known in commerce as blue vitriol. A pair of copper plates
+(B, B') are placed in this solution, each being provided with a
+connecting wire (C). When a current passes through the wires (C), one
+copper plate (B) is eaten away and deposited on the other plate (B'). It
+is then an easy matter to take out the plates and find out how much in
+weight B' has gained, or how much B has lost.
+
+In this way, in comparing the strength of, say, two separate currents,
+one should have each current pass through the voltameter the same length
+of time as the other, so as to obtain comparative results.
+
+It is not necessary, in the first and second methods, to consider the
+shapes, the sizes of the plates or the distances between them. In the
+first method the gas produced, within a given time, will be the same,
+and in the second method the amount deposited or eaten away will be the
+same under all conditions.
+
+DISADVANTAGES OF THE GALVANOSCOPE.--With the third method (using the
+galvanoscope) it is necessary, in order to get a positively correct
+reading instrument, to follow an absolutely accurate plan in
+constructing each part, in every detail, and great care must be
+exercised, particularly in winding. It is necessary also to be very
+careful in selecting the sizes of wire used and in the number of turns
+made in the coils.
+
+This is equally true of the fourth method, using the electro-magnet,
+because the magnetic pull is dependent upon the size of wire from which
+the coils are made and the number of turns of wire.
+
+OBJECTIONS TO THE CALORIMETER.--The calorimeter, or sixth method, has
+the same objection. The galvanoscope and electro-magnet do not respond
+equally to all currents, and this is also true, even to a greater
+extent, with the calorimeter.
+
+
+
+
+CHAPTER VI
+
+VOLTS, AMPERES, OHMS AND WATTS
+
+
+UNDERSTANDING TERMS.--We must now try to ascertain the meaning of some
+of the terms so frequently used in connection with electricity. If you
+intended to sell or measure produce or goods of any kind, it would be
+essential to know how many pints or quarts are contained in a gallon, or
+in a bushel, or how many inches there are in a yard, and you also ought
+to know just what the quantity term _bushel_ or the measurement _yard_
+means.
+
+INTENSITY AND QUANTITY.--Electricity, while it has no weight, is capable
+of being measured by means of its intensity, or by its quantity. Light
+may be measured or tested by its brilliancy. If one light is of less
+intensity than another and both of them receive their impulses from the
+same source, there must be something which interferes with that light
+which shows the least brilliancy. Electricity can also be interfered
+with, and this interference is called _resistance_.
+
+VOLTAGE.--Water may be made to flow with greater or less force, or
+velocity, through a pipe, the degree of same depending upon the height
+of the water which supplies the pipe. So with electricity. It may pass
+over a wire with greater or less force under one condition than another.
+This force is called voltage. If we have a large pipe, a much greater
+quantity of water will flow through it than will pass through a small
+pipe, providing the pressure in each case is alike. This quantity in
+electricity is called _amperage_.
+
+In the case of water, a column 1" × 1", 28 inches in height, weighs 1
+pound; so that if a pipe 1 inch square draws water from the bottom it
+flows with a pressure of 1 pound. If the pipe has a measurement of 2
+square inches, double the quantity of water will flow therefrom, at the
+same pressure.
+
+AMPERAGE.--If, on the other hand, we have a pipe 1 inch square, and
+there is a depth of 56 inches of water in the reservoir, we shall get as
+much water from the reservoir as though we had a pipe of 2 square inches
+drawing water from a reservoir which is 28 inches deep.
+
+MEANING OF WATTS.--It is obvious, therefore, that if we multiply the
+height of the water in inches with the area of the pipe, we shall obtain
+a factor which will show how much water is flowing.
+
+Here are two examples:
+
+1. 28 inches = height of the water in the reservoir.
+
+2 square inches = size of the pipe.
+Multiply 28 × 2 = 56.
+
+2. 56 = height of the water in the reservoir.
+1 square inch = size of the pipe.
+Multiply 56 × 1 = 56.
+
+Thus the two problems are equal.
+
+A KILOWATT.--Now, in electricity, remembering that the height of the
+water corresponds with _voltage_ in electricity, and the size of the
+pipe with _amperage_, if we multiply volts by amperes, or amperes by
+volts, we get a result which is indicated by the term _watts_. One
+thousand of these watts make a kilowatt, and the latter is the standard
+of measurement by which a dynamo or motor is judged or rated.
+
+Thus, if we have 5 amperes and 110 volts, the result of multiplying them
+would be 550 watts, or 5 volts and 110 amperes would produce 550 watts.
+
+A STANDARD OF MEASUREMENT.--But with all this we must have some
+standard. A bushel measure is of a certain size, and a foot has a
+definite length, so in electricity there is a recognized force and
+quantity which are determined as follows:
+
+THE AMPERE STANDARD.--It is necessary, first, to determine what an
+ampere is. For this purpose a standard solution of nitrate of silver is
+used, and a current of electricity is passed through this solution. In
+doing so the current deposits silver at the rate of 0.001118 grains per
+second for each ampere.
+
+THE VOLTAGE STANDARD.--In order to determine the voltage we must know
+something of _resistance_. Different metals do not transmit a current
+with equal ease. The size of a conductor, also, is an important factor
+in the passage of a current. A large conductor will transmit a current
+much better than a small conductor. We must therefore have a standard
+for the _ohm_, which is the measure of resistance.
+
+THE OHM.--It is calculated in this way: There are several standards, but
+the one most generally employed is the _International Ohm_. To determine
+it, by this system, a column of pure mercury, 106.3 millimeters long and
+weighing 14.4521 grams, is used. This would make a square tube about 94
+inches long, and a little over 1/25 of an inch in diameter. The
+resistance to a current flow in such a column would be equal to 1 ohm.
+
+CALCULATING THE VOLTAGE.--In order to arrive at the voltage we must use
+a conductor, which, with a resistance of 1 ohm, will produce 1 ampere.
+It must be remembered that the volt is the practical unit of
+electro-motive force.
+
+While it would be difficult for the boy to conduct these experiments in
+the absence of suitable apparatus, still, it is well to understand
+thoroughly how and why these standards are made and used.
+
+
+
+
+CHAPTER VII
+
+PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND
+LIKE APPARATUS
+
+
+SIMPLE SWITCHES.--We have now gone over the simpler or elementary
+outlines of electrical phenomena, and we may commence to do some of the
+practical work in the art. We need certain apparatus to make
+connections, which will be constructed first.
+
+A TWO-POLE SWITCH.--A simple two-pole switch for a single line is made
+as follows:
+
+A base block (A, Fig. 43) 3 inches long, 2 inches wide and 3/4 inch
+thick, has on it, at one end, a binding screw (B), which holds a pair of
+fingers (C) of brass or copper, these fingers being bent upwardly and so
+arranged as to serve as fingers to hold a switch bar (D) between them.
+This bar is also of copper or brass and is pivoted to the fingers. Near
+the other end of the base is a similar binding screw (E) and fingers (F)
+to receive the blade of the switch bar. The bar has a handle (G) of
+wood. The wires are attached to the respective binding screws (B, E).
+
+DOUBLE-POLE SWITCH.--A double-pole switch or a switch for a double line
+is shown in Fig. 44. This is made similar in all respects to the one
+shown in Fig. 43, excepting that there are two switch blades (A, A)
+connected by a cross bar (B) of insulating material, and this bar
+carries the handle (C).
+
+[Illustration: _Fig. 43._ TWO-POLE SWITCH]
+
+[Illustration: _Fig. 44._ DOUBLE-POLE SWITCH]
+
+Other types of switch will be found very useful. In Fig. 45 is a simple
+sliding switch in which the base block has, at one end, a pair of copper
+plates (A, B), each held at one end to the base by a binding screw (C),
+and having a bearing or contact surface (D) at its other end. At the
+other end of the base is a copper plate (E) held by a binding screw (F),
+to the inner end of which plate is hinged a swinging switch blade (G),
+the free end of which is adapted to engage with the plates (A, B).
+
+[Illustration: _Fig. 45._ SLIDING SWITCH]
+
+SLIDING SWITCH.--This sliding switch form may have the contact plates
+(A, B and C, Fig. 46) circularly arranged and any number may be located
+on the base, so they may be engaged by a single switching lever (H). It
+is the form usually adopted for rheostats.
+
+REVERSING SWITCH.--A reversing switch is shown in Fig. 47. The base has
+two plates (A, B) at one end, to which the parallel switch bars (C, D)
+are hinged. The other end of the base has three contact plates (E, F, G)
+to engage the swinging switch bars, these latter being at such distance
+apart that they will engage with the middle and one of the outer plates.
+The inlet wires, positive and negative, are attached to the plates (A,
+B, respectively), and one of the outlet wires (H) is attached to the
+middle contact plate (F), while the other wire is connected up with both
+of the outside plates. When the switch bars (C, D) are thrown to the
+left so as to be in contact with E, F, the outside plate (E) and the
+middle plate (F) will be positive and negative, respectively; but when
+the switch is thrown to the right, as shown in the figure, plate F
+becomes positive and plate E negative, as shown.
+
+[Illustration: _Fig. 46._ RHEOSTAT FORM OF SWITCH]
+
+PUSH BUTTONS.--A push button is but a modified structure of a switch,
+and they are serviceable because they are operating, or the circuit is
+formed only while the finger is on the button.
+
+[Illustration: _Fig. 47._ REVERSING SWITCH]
+
+In its simplest form (Fig. 48) the push button has merely a circular
+base (A) of insulating material, and near one margin, on the flat side,
+is a rectangular plate (B), intended to serve as a contact plate as well
+as a means for attaching one of the wires thereto. In line with this
+plate is a spring finger (C), bent upwardly so that it is normally out
+of contact with the plate (B), its end being held by a binding screw
+(D). To effect contact, the spring end of the finger (C) is pressed
+against the bar (B), as at E. This is enclosed in a suitable casing,
+such as will readily suggest itself to the novice.
+
+ELECTRIC BELL.--One of the first things the boy wants to make, and one
+which is also an interesting piece of work, is an electric bell.
+
+To make this he will be brought, experimentally, in touch with several
+important features in electrical work. He must make a battery for the
+production of current, a pair of electro-magnets to be acted upon by the
+current, a switch to control it, and, finally, he must learn how to
+connect it up so that it may be operated not only from one, but from two
+or more push buttons.
+
+[Illustration: _Fig. 48._ PUSH BUTTON]
+
+HOW MADE.--In Fig. 49 is shown an electric bell, as usually constructed,
+so modified as to show the structure at a glance, with its connections.
+A is the base, B, B' the binding posts for the wires, C, C the
+electro-magnets, C' the bracket for holding the magnets, D the armature,
+E the thin spring which connects the armature with the post F, G the
+clapper arm, H the bell, I the adjusting screw on the post J, K the wire
+lead from the binding post B to the first magnet, L the wire which
+connects the two magnets, M the wire which runs from the second magnet
+to the post J, and N a wire leading from the armature post to the
+binding post B'.
+
+[Illustration: _Fig. 49._ ELECTRIC BELL]
+
+The principle of the electric bell is this: In looking at Fig. 49, you
+will note that the armature bar D is held against the end of the
+adjusting screw by the small spring E. When a current is turned on, it
+passes through the connections and conduits as follows: Wire K to the
+magnets, wire M to the binding post J, and set screw I, then through the
+armature to the post F, and from post F to the binding post B'.
+
+[Illustration: _Fig. 50._ ARMATURE OF ELECTRIC BELL]
+
+ELECTRIC BELL--HOW OPERATED.--The moment a current passes through the
+magnets (C, C), the core is magnetized, and the result is that the
+armature (D) is attracted to the magnets, as shown by the dotted lines
+(O), when the clapper strikes the bell. But when the armature moves over
+to the magnet, the connection is broken between the screw (I) and
+armature (D), so that the cores of the magnets are demagnetized and lose
+their pull, and the spring (E) succeeds in drawing back the armature.
+This operation of vibrating the armature is repeated with great
+rapidity, alternately breaking and re-establishing the circuit, by the
+action of the current.
+
+In making the bell, you must observe one thing, the binding posts (B,
+B') must be insulated from each other, and the post J, or the post F,
+should also be insulated from the base. For convenience we show the post
+F insulated, so as to necessitate the use of wire (N) from post (F) to
+binding post (B').
+
+The foregoing assumes that you have used a cast metal base, as most
+bells are now made; but if you use a wooden base, the binding posts (B,
+B') and the posts (F, J) are insulated from each other, and the
+construction is much simplified.
+
+It is better, in practice, to have a small spring (P, Fig. 50) between
+the armature (D) and the end of the adjusting screw (I), so as to give a
+return impetus to the clapper. The object of the adjusting screw is to
+push and hold the armature close up to the ends of the magnets, if it
+seems necessary.
+
+If two bells are placed on the base with the clapper mounted between
+them, both bells will be struck by the swinging motion of the armature.
+
+An easily removable cap or cover is usually placed over the coils and
+armature, to keep out dust.
+
+A very simple annunciator may be attached to the bell, as shown in the
+following figures:
+
+[Illustration: _Figs. 51-54._ ANNUNCIATOR]
+
+ANNUNCIATORS.--Make a box of wood, with a base (A) 4" × 5" and 1/2 inch
+thick. On this you can permanently mount the two side pieces (B) and two
+top and bottom pieces (C), respectively, so they project outwardly
+4-1/2 inches from the base. On the open front place a wood or metal
+plate (D), provided with a square opening (D), as in Fig. 54, near its
+lower end. This plate is held to the box by screws (E).
+
+Within is a magnet (F), screwed into the base (A), as shown in Fig. 51;
+and pivoted to the bottom of the box is a vertical armature (G), which
+extends upwardly and contacts with the core of the magnet. The upper end
+of the armature has a shoulder (H), which is in such position that it
+serves as a rest for a V-shaped stirrup (I), which is hinged at J to the
+base (C). This stirrup carries the number plate (K), and when it is
+raised to its highest point it is held on the shoulder (H), unless the
+electro-magnet draws the armature out of range of the stirrup. A spring
+(L) bearing against the inner side of the armature keeps its upper end
+normally away from the magnet core. When the magnet draws the armature
+inwardly, the number plate drops and exposes the numeral through the
+opening in the front of the box. In order to return the number plate to
+its original position, as shown in Fig. 51, a vertical trigger (M)
+passes up through the bottom, its upper end being within range of one of
+the limbs of the stirrup.
+
+This is easily made by the ingenious boy, and will be quite an
+acquisition to his stock of instruments. In practice, the annunciator
+may be located in any convenient place and wires run to that point.
+
+[Illustration: _Fig. 55._ ALARM SWITCH ON WINDOW]
+
+[Illustration: _Fig. 56._ BURGLAR ALARM ATTACHMENT TO WINDOW]
+
+BURGLAR ALARM.--In order to make a burglar alarm connection with a bell,
+push buttons or switches may be put in circuit to connect with the
+windows and doors, and by means of the annunciators you may locate the
+door or window which has been opened. The simplest form of switch for a
+window is shown in the following figures:
+
+The base piece (A), which may be of hard rubber or fiber, is 1/4 inch
+thick and 1" × 1-1/2" in size.
+
+[Illustration: _Fig. 57._ BURGLAR ALARM CONTACT]
+
+At one end is a brass plate (B), with a hole for a wood screw (C), this
+screw being designed to pass through the plate and also into the
+window-frame, so as to serve as a means of attaching one of the wires
+thereto. The inner end of the plate has a hole for a round-headed screw
+(C') that also goes through the base and into the window-frame. It also
+passes through the lower end of the heart-shaped metal switch-piece
+(D).
+
+The upper end of the base has a brass plate (E), also secured to the
+base and window by a screw (F) at its upper end. The heart-shaped switch
+is of such length and width at its upper end that when it is swung to
+the right with one of the lobes projecting past the edge of the
+window-frame, the other lobe will be out of contact with the plate (E).
+
+[Illustration: _Fig. 58._ NEUTRAL POSITION OF CONTACT]
+
+The window sash (G) has a removable pin (H), which, when the sash moves
+upwardly, is in the path of the lobe of the heart-shaped switch, as
+shown in Fig. 56, and in this manner the pin (H) moves the upper end of
+the switch (D) inwardly, so that the other lobe contacts with the plate
+(E), and establishes an electric circuit, as shown in Fig. 57. During
+the daytime the pin (H) may be removed, and in order to protect the
+switch the heart-shaped piece (D) is swung inwardly, as shown in Fig.
+58, so that neither of the lobes is in contact with the plate (E).
+
+WIRE CIRCUITING.--For the purpose of understanding fully the circuiting,
+diagrams will be shown of the simple electric bell with two push
+buttons; next in order, the circuiting with an annunciator and then the
+circuiting necessary for a series of windows and doors, with annunciator
+attachments.
+
+[Illustration: _Fig. 59._ CIRCUITING FOR ELECTRIC BELL]
+
+CIRCUITING SYSTEM WITH A BELL AND TWO PUSH BUTTONS.--Fig. 59 shows a
+simple circuiting system which has two push buttons, although any number
+may be used, so that the bell will ring when the circuit is closed by
+either button.
+
+THE PUSH BUTTONS AND THE ANNUNCIATOR BELLS.--Fig. 60 shows three push
+buttons and an annunciator for each button. These three circuits are
+indicated by A, B and C, so that when either button makes contact, a
+complete circuit is formed through the corresponding annunciator.
+
+[Illustration: _Fig. 60._ _Annunciators_]
+
+[Illustration: _Fig. 61._ WIRING SYSTEM FOR A HOUSE]
+
+WIRING UP A HOUSE.--The system of wiring up a house so that all doors
+and windows will be connected to form a burglar alarm outfit, is shown
+in Fig. 61. It will be understood that, in practice, the bell is mounted
+on or at the annunciator, and that, for convenience, the annunciator
+box has also a receptacle for the battery. The circuiting is shown
+diagramatically, as it is called, so as fully to explain how the lines
+are run. Two windows and a door are connected up with an annunciator
+having three drops, or numbers 1, 2, 3. The circuit runs from one pole
+of the battery to the bell and then to one post of the annunciator. From
+the other post a wire runs to one terminal of the switch at the door or
+window. The other switch terminal has a wire running to the other pole
+of the battery.
+
+A, B, C represent the circuit wires from the terminals of the window and
+door switches, to the annunciators.
+
+It is entirely immaterial which side of the battery is connected up with
+the bell.
+
+From the foregoing it will readily be understood how to connect up any
+ordinary apparatus, remembering that in all cases the magnet must be
+brought into the electric circuit.
+
+
+
+
+CHAPTER VIII
+
+ACCUMULATORS. STORAGE OR SECONDARY BATTERIES
+
+
+STORING UP ELECTRICITY.--In the foregoing chapters we have seen that,
+originally, electricity was confined in a bottle, called the Leyden jar,
+from which it was wholly discharged at a single impulse, as soon as it
+was connected up by external means. Later the primary battery and the
+dynamo were invented to generate a constant current, and after these
+came the second form of storing electricity, called the storage or
+secondary battery, and later still recognized as accumulators.
+
+THE ACCUMULATOR.--The term _accumulator_ is, strictly speaking, the more
+nearly correct, as electricity is, in reality, "_stored_" in an
+accumulator. But when an accumulator is charged by a current of
+electricity, a chemical change is gradually produced in the active
+element of which the accumulator is made. This change or decomposition
+continues so long as the charging current is on. When the accumulator is
+disconnected from the charging battery or dynamo, and its terminals are
+connected up with a lighting system, or with a motor, for instance, a
+reverse process is set up, or the particles re-form themselves into
+their original compositions, which causes a current to flow in a
+direction opposite to that of the charging current.
+
+It is immaterial to the purposes of this chapter, as to the charging
+source, whether it be by batteries or dynamos; the same principles will
+apply in either case.
+
+[Illustration: _Fig. 62._ ACCUMULATOR GRIDS]
+
+ACCUMULATOR PLATES.--The elements used for accumulator plates are red
+lead for the positive plates, and precipitated lead, or the well-known
+litharge, for the negative plates. Experience has shown that the best
+way to hold this material is by means of lead grids.
+
+Fig. 62 shows the typical form of one of these grids. It is made of
+lead, cast or molded in one piece, usually square, as at A, with a wing
+or projection (B), at one margin, extending upwardly and provided with a
+hole (C). The grid is about a quarter of an inch thick.
+
+THE GRID.--The open space, called the grid, proper, comprises cross
+bars, integral with the plate, made in a variety of shapes. Fig. 62
+shows three forms of constructing these bars or ribs, the object being
+to provide a form which will hold in the lead paste, which is pressed in
+so as to make a solid-looking plate when completed.
+
+THE POSITIVE PLATE.--The positive plate is made in the following manner:
+Make a stiff paste of red lead and sulphuric acid; using a solution,
+say, of one part of acid to two parts of water. The grid is laid on a
+flat surface and the paste forced into the perforations with a stiff
+knife or spatula. Turn over the grid so as to get the paste in evenly on
+both sides.
+
+The grid is then stood on its edge, from 18 to 20 hours, to dry, and
+afterwards immersed in a concentrated solution of chloride of lime, so
+as to convert it into lead peroxide. When the action is complete it is
+thoroughly rinsed in cold water, and is ready to use.
+
+THE NEGATIVE PLATE.--The negative plate is filled, in like manner, with
+precipitated lead. This lead is made by putting a strip of zinc into a
+standard solution of acetate of lead, and crystals will then form on the
+zinc. These will be very thin, and will adhere together, firmly, forming
+a porous mass. This, when saturated and kept under water for a short
+time, may be put into the openings of the negative plate.
+
+[Illustration: _Fig. 63._ ASSEMBLAGE OF ACCUMULATOR PLATES]
+
+CONNECTING UP THE PLATES.--The next step is to put these plates in
+position to form a battery. In Fig. 63 is shown a collection of plates
+connected together.
+
+For simplicity in illustrating, the cell is made up of glass, porcelain,
+or hard rubber, with five plates (A), A, A representing the negative and
+B, B the positive plates. A base of grooved strips (C, C) is placed in
+the batteries of the cell to receive the lower ends of the plates. The
+positive plates are held apart by means of a short section of tubing
+(D), which is clamped and held within the plates by a bolt (E), this
+bolt also being designed to hold the terminal strip (F).
+
+In like manner, the negative plates are held apart by the two tubular
+sections (G), each of which is of the same length as the section D of
+the positives. The bolt (H) holds the negatives together as well as the
+terminal (I). The terminals should be lead strips, and it would be well,
+owing to the acid fumes which are formed, to coat all brass work,
+screws, etc., with paraffine wax.
+
+The electrolyte or acid used in the cell, for working purposes, is a
+pure sulphuric acid, which should be diluted with about four times its
+weight in water. Remember, you should always add the strong acid to the
+water, and never pour the water into the acid, as the latter method
+causes a dangerous ebullition, and does not produce a good mixture.
+
+Put enough of this solution into the cell to cover the tops of the
+plates, and the cell is ready.
+
+[Illustration: _Fig. 64._ CONNECTING UP STORAGE BATTERY IN SERIES]
+
+CHARGING THE CELLS.--The charge of the current must never be less than
+2.5 volts. Each cell has an output, in voltage, of about 2 volts, hence
+if we have, say, 10 cells, we must have at least 25 volts charging
+capacity. We may arrange these in one line, or in series, as it is
+called, so far as the connections are concerned, and charge them with a
+dynamo, or other electrical source, which shows a pressure of 25 volts,
+as illustrated in Fig. 64, or, instead of this, we may put them into two
+parallel sets of 5 cells each, as shown in Fig. 65, and use 12.5 volts
+to charge with. In this case it will take double the time because we are
+charging with only one-half the voltage used in the first case.
+
+The positive pole of the dynamo should be connected with the positive
+pole of the accumulator cell, and negative with negative. When this has
+been done run up the machine until it slightly exceeds the voltage of
+the cells. Thus, if we have 50 cells in parallel, like in Fig. 64, at
+least 125 volts will be required, and the excess necessary should bring
+up the voltage in the dynamo to 135 or 140 volts.
+
+[Illustration: _Fig. 65._ PARALLEL SERIES]
+
+[Illustration: _Fig. 66._ CHARGING CIRCUIT]
+
+THE INITIAL CHARGE.--It is usual initially to charge the battery from
+periods ranging from 36 to 40 hours, and to let it stand for 12 or 15
+hours, after which to re-charge, until the positive plates have turned
+to a chocolate color, and the negative plates to a slate or gray color,
+and both plates give off large bubbles of gas.
+
+In charging, the temperature of the electrolyte should not exceed 100°
+Fahrenheit.
+
+When using the accumulators they should never be fully discharged.
+
+THE CHARGING CIRCUIT.--The diagram (Fig. 66) shows how a charging
+circuit is formed. The lamps are connected up in parallel, as
+illustrated. Each 16-candle-power 105-volt lamp will carry 1/2 ampere,
+so that, supposing we have a dynamo which gives 110 volts, and we want
+to charge a 4-volt accumulator, there will be 5-volt surplus to go to
+the accumulator. If, for instance, you want the cell to have a charge of
+2 amperes, four of these lamps should be connected up in parallel. If 3
+amperes are required, use 6 lamps, and so on.
+
+
+
+
+CHAPTER IX
+
+THE TELEGRAPH
+
+
+The telegraph is a very simple instrument. The key is nothing more or
+less than a switch which turns the current on and off alternately.
+
+The signals sent over the wires are simply the audible sounds made by
+the armature, as it moves to and from the magnets.
+
+MECHANISM IN TELEGRAPH CIRCUITS.--A telegraph circuit requires three
+pieces of mechanism at each station, namely, a key used by the sender, a
+sounder for the receiver, and a battery.
+
+THE SENDING KEY.--The base of the sending instrument is six inches long,
+four inches wide, and three-quarters of an inch thick, made of wood, or
+any suitable non-conducting material. The key (A) is a piece of brass
+three-eighths by one-half inch in thickness and six inches long. Midway
+between its ends is a cross hole, to receive the pivot pin (B), which
+also passes through a pair of metal brackets (C, D), the bracket C
+having a screw to hold one of the line wires, and the other bracket
+having a metal switch (E) hinged thereto. This switch bar, like the
+brackets, is made of brass, one-half inch wide by one-sixteenth of an
+inch thick.
+
+Below the forward end of the key (A) is a cross bar of brass (F),
+screwed to the base by a screw at one end, to receive the other line
+wire. Directly below the key (A) is a screw (G), so that the key will
+strike it when moved downwardly. The other end of the bar (F) contacts
+with the forward end of the switch bar (E) when the latter is moved
+inwardly.
+
+[Illustration: _Fig. 67._ TELEGRAPH SENDING KEY]
+
+The forward end of the key (A) has a knob (H) for the fingers, and the
+rear end has an elastic (I) attached thereto which is secured to the end
+of the base, so that, normally, the rear end is held against the base
+and away from the screw head (G). The head (J) of a screw projects from
+the base at its rear end. Key A contacts with it.
+
+When the key A contacts with the screw heads G, J, a click is produced,
+one when the key is pressed down and the other when the key is released.
+
+You will notice that the two plates C, F are connected up in circuit
+with the battery, so that, as the switch E is thrown, so as to be out of
+contact, the circuit is open, and may be closed either by the key A or
+the switch E. The use of the switch will be illustrated in connection
+with the sounder.
+
+[Illustration: _Fig. 68._ TELEGRAPH SOUNDER]
+
+When the key A is depressed, the circuit of course goes through plate C,
+key A and plate F to the station signalled.
+
+THE SOUNDER.--The sounder is the instrument which carries the
+electro-magnet.
+
+In Fig. 68 this is shown in perspective. The base is six inches long and
+four inches wide, being made, preferably, of wood. Near the forward end
+is mounted a pair of electro-magnets (A, A), with their terminal wires
+connected up with plates B, B', to which the line wires are attached.
+
+Midway between the magnets and the rear end of the base is a pair of
+upwardly projecting brackets (C). Between these are pivoted a bar (D),
+the forward end of which rests between the magnets and carries, thereon,
+a cross bar (E) which is directly above the magnets, and serves as the
+armature.
+
+The rear end of the base has a screw (F) directly beneath the bar D of
+such height that when the rear end of the bar D is in contact therewith
+the armature E will be out of contact with the magnet cores (A, A). A
+spiral spring (G) secured to the rear ends of the arm and to the base,
+respectively, serves to keep the rear end of the key normally in contact
+with the screw F.
+
+CONNECTING UP THE KEY AND SOUNDER.--Having made these two instruments,
+we must next connect them up in the circuit, or circuits, formed for
+them, as there must be a battery, a key, and a sounder at each end of
+the line.
+
+In Fig. 69 you will note two groups of those instruments. Now observe
+how the wires connect them together. There are two line wires, one (A)
+which connects up the two batteries, the wire being attached so that
+one end connects with the positive terminal of the battery, and the
+other end with the negative terminal.
+
+[Illustration: _Fig. 69._ A TELEGRAPH CIRCUIT]
+
+The other line wire (B), between the two stations, has its opposite ends
+connected with the terminals of the electro-magnet C of the sounders.
+The other terminals of each electro-magnet are connected up with one
+terminal of each key by a wire (D), and to complete the circuit at each
+station, the other terminal of the key has a wire (E) to its own
+battery.
+
+TWO STATIONS IN CIRCUIT.--The illustration shows station 2 telegraphing
+to station 1. This is indicated by the fact that the switch F' of that
+instrument is open, and the switch F of station 1 closed. When,
+therefore, the key of station 2 is depressed, a complete circuit is
+formed which transmits the current through wire E' and battery, through
+line A, then through the battery of station 1, through wire E to the
+key, and from the key, through wire D, to the sounder, and finally from
+the sounder over line wire B back to the sounder of station 2,
+completing the circuit at the key through wire D'.
+
+When the operator at station 2 closes the switch F', and the operator at
+station 1 opens the switch F, the reverse operation takes place. In both
+cases, however, the sounder is in at both ends of the line, and only the
+circuit through the key is cut out by the switch F, or F'.
+
+THE DOUBLE CLICK.--The importance of the double click of the sounder
+will be understood when it is realized that the receiving operator must
+have some means of determining if the sounder has transmitted a dot or a
+dash. Whether he depresses the key for a dot or a dash, there must be
+one click when the key is pressed down on the screw head G (Fig. 62),
+and also another click, of a different kind, when the key is raised up
+so that its rear end strikes the screw head J. This action of the key is
+instantly duplicated by the bar D (Fig. 68) of the sounder, so that the
+sounder as well as the receiver knows the time between the first and the
+second click, and by that means he learns that a dot or a dash is made.
+
+ILLUSTRATING THE DOT AND THE DASH.--To illustrate: Let us suppose, for
+convenience, that the downward movement of the lever in the key, and the
+bar in the sounder, make a sharp click, and the return of the lever and
+bar make a dull click. In this case the ear, after a little practice,
+can learn readily how to distinguish the number of downward impulses
+that have been given to the key.
+
+_The Morse Telegraph Code_
+
+A . -        N - .       & . ...
+B - ...      O ..        1 . - - .
+C .. .       P .....     2 .. - ..
+D - . .      Q .. - .    3 ... - .
+E .          R . ..      4 .... -
+F . - .      S ...       5 - - -
+G - - .      T -         6 ......
+H ....       U .. -      7 - - ..
+I ..         V ... -     8 - ....
+J - . - .    W . - -     9 - .. -
+K - . -      X . - ..    0 ---- ------
+L --         Y .. ..
+M - -        Z ... .
+
+EXAMPLE IN USE.--Let us take an example in the word "electrical."
+
+E    L    E    C    T    R    I    C    A    L
+.   --   .   .. .   -  . ..  ..  .. .  . -  --
+
+The operator first makes a dot, which means a sharp and a dull click
+close together; there is then a brief interval, then a lapse, after
+which there is a sharp click, followed, after a comparatively longer
+interval, with the dull click. Now a dash by itself may be an L, a T, or
+the figure 0, dependent upon its length. The short dash is T, and the
+longest dash the figure 0. The operator will soon learn whether it is
+either of these or the letter L, which is intermediate in length.
+
+In time the sender as well as receiver will give a uniform length to the
+dash impulse, so that it may be readily distinguished. In the same way,
+we find that R, which is indicated by a dot, is followed, after a short
+interval, by two dots. This might readily be mistaken for the single dot
+for E and the two dots for I, were it not that the time element in R is
+not as long between the first and second dots, as it ordinarily is
+between the single dot of E when followed by the two dots of I.
+
+
+
+
+CHAPTER X
+
+HIGH TENSION APPARATUS, CONDENSERS, ETC.
+
+
+INDUCTION.--One of the most remarkable things in electricity is the
+action of induction--that property of an electric current which enables
+it to pass from one conductor to another conductor through the air.
+Another singular and interesting thing is that the current so
+transmitted across spaces changes its direction of flow, and,
+furthermore, the tension of such a current may be changed by
+transmitting it from one conductor to another.
+
+LOW AND HIGH TENSION.--In order to effect this latter change--that is,
+to convert it from a low tension to a high tension--coils are used, one
+coil being wound upon the other; one of these coils is called the
+primary and the other the secondary. The primary coil receives the
+current from the battery, or source of electrical power, and the
+secondary coil receives charges, and transmits the current.
+
+For an illustration of this examine Fig. 70, in which you will note a
+coil of heavy wire (A), around which is wound a coil of fine wire (B).
+If, for instance, the primary coil has a low voltage, the secondary
+coil will have a high voltage, or tension. Advantage is taken of this
+phase to use a few cells, as a primary battery, and then, by a set of
+_Induction Coils_, as they are called, to build up a high-tension
+electro-motive force, so that the spark will jump across a gap, as shown
+at C, for the purpose of igniting the charges of gas in a gasoline
+motor; or the current may be used for medical batteries, and for other
+purposes.
+
+[Illustration: _Fig. 70._ INDUCTION COIL AND CIRCUIT]
+
+The current passes, by induction, from the primary to the secondary
+coil. It passes from a large conductor to a small conductor, the small
+conductor having a much greater resistance than the large one.
+
+ELASTIC PROPERTY OF ELECTRICITY.--While electricity has no resiliency,
+like a spring, for instance, still it acts in the manner of a cushion
+under certain conditions. It may be likened to an oscillating spring
+acted upon by a bar.
+
+Referring to Fig. 71, we will assume that the bar A in falling down upon
+the spring B compresses the latter, so that at the time of greatest
+compression the bar goes down as far as the dotted line C. It is obvious
+that the spring B will throw the bar upwardly. Now, electricity appears
+to have a kind of elasticity, which characteristic is taken advantage of
+in order to increase the efficiency of the induction in the coil.
+
+[Illustration: _Fig. 71._ ILLUSTRATING ELASTICITY]
+
+THE CONDENSER.--To make a condenser, prepare two pine boards like A,
+say, eight by ten inches and a half inch thick, and shellac thoroughly
+on all sides. Then prepare sheets of tinfoil (B), six by eight inches in
+size, and also sheets of paraffined paper (C), seven by nine inches in
+dimensions. Also cut out from the waste pieces of tinfoil strips (D),
+one inch by two inches. To build up the condenser, lay down a sheet of
+paraffined paper (C), then a sheet of tinfoil (B), and before putting
+on the next sheet of paraffined paper lay down one of the small strips
+(D) of tinfoil, as shown in the illustration, so that its end projects
+over one end of the board A; then on the second sheet of paraffine paper
+lay another sheet of tinfoil, and on this, at the opposite end, place
+one of the small strips (D), and so on, using from 50 to 100 of the
+tinfoil sheets. When the last paraffine sheet is laid on, the other
+board is placed on top, and the whole bound together, either by wrapping
+cords around the same or by clamping them together with bolts.
+
+[Illustration: _Fig. 72._ CONDENSER]
+
+You may now make a hole through the projecting ends of the strips, and
+you will have two sets of tinfoil sheets, alternately connected together
+at opposite ends of the condenser.
+
+Care should be exercised to leave the paraffine sheets perfect or
+without holes. You can make these sheets yourself by soaking them in
+melted paraffine wax.
+
+CONNECTING UP A CONDENSER.--When completed, one end of the condenser is
+connected up with one terminal of the secondary coil, and the other end
+of the condenser with the other secondary terminal.
+
+[Illustration: _Fig. 73._ HIGH-TENSION CIRCUIT]
+
+In Fig. 73 a high-tension circuit is shown. Two coils, side by side, are
+always used to show an induction coil, and a condenser is generally
+shown, as illustrated, by means of a pair of forks, one resting within
+the other.
+
+THE INTERRUPTER.--One other piece of mechanism is necessary, and that is
+an _Interrupter_, for the purpose of getting the effect of the
+pulsations given out by the secondary coil.
+
+A simple current interrupter is made as follows: Prepare a wooden base
+(A), one inch thick, six inches wide, and twelve inches long. Upon this
+mount a toothed wheel (B), six inches in diameter, of thin sheet metal,
+or a brass gear wheel will answer the purpose. The standard (C), which
+supports the wheel, may be of metal bent up to form two posts, between
+which the crankshaft (D) is journaled. The base of the posts has an
+extension plate (E), with a binding post for a wire. At the front end of
+the base is an L-shaped strip (F), with a binding post for a wire
+connection, and the upwardly projecting part of the strip contacts with
+the toothed wheel. When the wheel B is rotated the spring finger (F)
+snaps from one tooth to the next, so that, momentarily, the current is
+broken, and the frequency is dependent upon the speed imparted to the
+wheel.
+
+[Illustration: _Fig. 74._ CURRENT INTERRUPTER]
+
+USES OF HIGH-TENSION COILS.--This high-tension coil is made use of, and
+is the essential apparatus in wireless telegraphy, as we shall see in
+the chapter treating upon that subject.
+
+
+
+
+CHAPTER XI
+
+WIRELESS TELEGRAPHY
+
+
+TELEGRAPHING WITHOUT WIRES.--Wireless telegraphy is an outgrowth of the
+ordinary telegraph system. When Maxwell, and, later on, Hertz,
+discovered that electricity, magnetism, and light were transmitted
+through the ether, and that they differed only in their wave lengths,
+they laid the foundations for wireless telegraphy. Ether is a substance
+which is millions and millions of times lighter than air, and it
+pervades all space. It is so unstable that it is constantly in motion,
+and this phase led some one to suggest that if a proper electrical
+apparatus could be made, the ether would thereby be disturbed
+sufficiently so that its impulses would extend out a distance
+proportioned to the intensity of the electrical agitation thereby
+created.
+
+SURGING CHARACTER OF HIGH-TENSION CURRENTS.--When a current of
+electricity is sent through a wire, hundreds of miles in length, the
+current surges back and forth on the wire many thousands of times a
+second. Light comes to us from the sun, over 90,000,000 of miles,
+through the ether. It is as reasonable to suppose, or infer, that the
+ether can, therefore, convey an electrical impulse as readily as does a
+wire.
+
+It is on this principle that impulses are sent for thousands of miles,
+and no doubt they extend even farther, if the proper mechanism could be
+devised to detect movement of the waves so propagated.
+
+THE COHERER.--The instrument for detecting these impulses, or
+disturbances, in the ether is generally called a _coherer_, although
+detector is the term which is most satisfactory. The name coherer comes
+from the first practical instrument made for this purpose.
+
+[Illustration: _Fig. 75._ WIRELESS TELEGRAPHY COHERER]
+
+HOW MADE.--The coherer is simply a tube, say, of glass, within which is
+placed iron filings. When the oscillations surge through the secondary
+coil the pressure or potentiality of the current finally causes it to
+leap across the small space separating the filings and, as it were, it
+welds together their edges so that a current freely passes. The
+bringing together of the particles, under these conditions, is called
+cohering.
+
+Fig. 75 shows the simplest form of coherer. The posts (A) are firmly
+affixed to the base (B), each post having an adjusting screw (C) in its
+upper end, and these screw downwardly against and serve to bind a pair
+of horizontal rods (D), the inner ends of which closely approach each
+other. These may be adjusted so as to be as near together or as far
+apart as desired. E is a glass tube in which the ends of the rods (D)
+rest, and between the separated ends of the rods (D) the iron filings
+(F) are placed.
+
+THE DECOHERERS.--For the purpose of causing the metal filings to fall
+apart, or decohere, the tube is tapped lightly, and this is done by a
+little object like the clapper of an electric bell.
+
+In practice, the coils and the parts directly connected with it are put
+together on one base.
+
+THE SENDING APPARATUS.--Fig. 76 shows a section of a coil with its
+connection in the sending station. The spark gap rods (A) may be swung
+so as to bring them closer together or farther apart, but they must not
+at any time contact with each other.
+
+The induction coil has one terminal of the primary coil connected up by
+a wire (B) with one post of a telegraph key, and the other post of the
+key has a wire connection (C), with one side of a storage battery. The
+other side of the battery has a wire (D) running to the other terminal
+of the primary.
+
+[Illustration: _Fig. 76._ WIRELESS SENDING APPARATUS]
+
+The secondary coil has one of its terminals connected with a binding
+post (E). This binding post has an adjustable rod with a knob (F) on its
+end, and the other binding post (G), which is connected up with the
+other terminal of the secondary coil, carries a similar adjusting rod
+with a knob (H).
+
+From the post (E) is a wire (I), which extends upwardly, and is called
+the aerial wire, or wire for the antennæ, and this wire also connects
+with one side of the condenser by a conductor (J). The ground wire (K)
+connects with the other binding post (G), and a branch wire (L) also
+connects the ground wire (K) with one end of the condenser.
+
+[Illustration: _Fig. 77._ WIRELESS RECEIVING APPARATUS]
+
+THE RECEIVING APPARATUS.--The receiving station, on the other hand, has
+neither condenser, induction coil, nor key. When the apparatus is in
+operation, the coherer switch is closed, and the instant a current
+passes through the coherer and operates the telegraph sounder, the
+galvanometer indicates the current.
+
+Of course, when the coherer switch is closed, the battery operates the
+decoherer.
+
+HOW THE CIRCUITS ARE FORMED.--By referring again to Fig. 76, it will be
+seen that when the key is depressed, a circuit is formed from the
+battery through wire B to the primary coil, and back again to the
+battery through wire D. The secondary coil is thereby energized, and,
+when the full potential is reached, the current leaps across the gap
+formed between the two knobs (F, H), thereby setting up a disturbance in
+the ether which is transmitted through space in all directions.
+
+It is this impulse, or disturbance, which is received by the coherer at
+the receiving station, and which is indicated by the telegraph sounder.
+
+
+
+
+CHAPTER XII
+
+THE TELEPHONE
+
+
+VIBRATIONS.--Every manifestation in nature is by way of vibration. The
+beating of the heart, the action of the legs in walking, the winking of
+the eyelid; the impulses from the sun, which we call light; sound, taste
+and color appeal to our senses by vibratory means, and, as we have
+hereinbefore stated, the manifestations of electricity and magnetism are
+merely vibrations of different wave lengths.
+
+THE ACOUSTIC TELEPHONE.--That sound is merely a product of vibrations
+may be proven in many ways. One of the earliest forms of telephones was
+simply a "sound" telephone, called the _Acoustic Telephone_. The
+principle of this may be illustrated as follows:
+
+Take two cups (A, B), as in Fig. 78, punch a small hole through the
+bottom of each, and run a string or wire (C) from the hole of one cup to
+that of the other, and secure it at both ends so it may be drawn taut.
+Now, by talking into the cup (A) the bottom of it will vibrate to and
+fro, as shown by the dotted lines and thereby cause the bottom of the
+other cup (B) to vibrate in like manner, and in so vibrating it will
+receive not only the same amplitude, but also the same character of
+vibrations as the cup (A) gave forth.
+
+[Illustration: _Fig. 78._ ACOUSTIC TELEPHONE]
+
+[Illustration: _Fig. 79._ ILLUSTRATING VIBRATIONS]
+
+SOUND WAVES.--Sound waves are long and short; the long waves giving
+sounds which are low in the musical scale, and the short waves high
+musical tones. You may easily determine this by the following
+experiment:
+
+Stretch a wire, as at B (Fig. 79), fairly tight, and then vibrate it.
+The amplitude of the vibration will be as indicated by dotted line A.
+Now, stretch it very tight, as at C, so that the amplitude of vibration
+will be as shown at E. By putting your ear close to the string you will
+find that while A has a low pitch, C is very much higher. This is the
+principle on which stringed instruments are built. You will note that
+the wave length, which represents the distance between the dotted lines
+A is much greater than E.
+
+HEARING ELECTRICITY.--In electricity, mechanism has been made to enable
+man to note the action of the current. By means of the armature,
+vibrating in front of a magnet, we can see its manifestations. It is now
+but a step to devise some means whereby we may hear it. In this, as in
+everything else electrically, the magnet comes into play.
+
+[Illustration: _Fig. 80._ THE MAGNETIC FIELD]
+
+In the chapter on magnetism, it was stated that the magnetic field
+extended out beyond the magnet, so that if we were able to see the
+magnetism, the end of a magnet would appear to us something like a
+moving field, represented by the dotted lines in Fig. 80.
+
+The magnetic field is shown in Fig. 80 at only one end, but its
+manifestations are alike at both ends. It will be seen that the magnetic
+field extends out to a considerable distance and has quite a radius of
+influence.
+
+THE DIAPHRAGM IN A MAGNETIC FIELD.--If, now, we put a diaphragm (A) in
+this magnetic field, close up to the end of the magnet, but not so close
+as to touch it, and then push it in and out, or talk into it so that the
+sound waves strike it, the movement or the vibration of the diaphragm
+(A) will disturb the magnetic field emanating from the magnet, and this
+disturbance of the magnetic field at one end of the magnet also affects
+the magnetic field at the other end in the same way, so that the
+disturbance there will be of the same amplitude. It will also display
+the same characteristics as did the magnetic field when the diaphragm
+(A) disturbed it.
+
+A SIMPLE TELEPHONE CIRCUIT.--From this simple fact grew the telephone.
+If two magnets are connected up in the same circuit, so that the
+magnetic fields of the two magnets have the same source of electric
+power, the disturbance of one diaphragm will affect the other similarly,
+just the same as the two magnetic fields of the single magnet are
+disturbed in unison.
+
+HOW TO MAKE A TELEPHONE.--For experimental and testing purposes two of
+these telephones should be made at the same time. The case or holder
+(A) may be made either of hard wood or hard rubber, so that it is of
+insulating material. The core (B) is of soft iron, 3/8 inch in diameter
+and 5 inches long, bored and threaded at one end to receive a screw (C)
+which passes through the end of the case (A).
+
+The enlarged end of the case should be, exteriorly, 2-1/4 inches in
+diameter, and the body of the case 1 inch in diameter.
+
+[Illustration: _Fig. 81._ SECTION OF TELEPHONE RECEIVER]
+
+Interiorly, the large end of the case is provided with a circular recess
+1-3/4 inches in diameter and adapted to receive therein a spool which
+is, diametrically, a little smaller than the recess. The spool fits
+fairly tight upon the end of the core, and when in position rests
+against an annular shoulder in the recess. A hollow space (F) is thus
+provided behind the spool (D), so the two wires from the magnet may
+have room where they emerge from the spool.
+
+The spool is a little shorter than the distance between the shoulder (E)
+and the end of the casing, at G, and the core projects only a short
+distance beyond the end of the spool, so that when the diaphragm (H) is
+put upon the end of the case, and held there by screws (I) it will not
+touch the end of the core. A wooden or rubber mouthpiece (J) is then
+turned up to fit over the end of the case.
+
+[Illustration: _Fig. 82._ THE MAGNET AND RECEIVER HEAD]
+
+The spool (D) is made of hard rubber, and is wound with No. 24
+silk-covered wire, the windings to be well insulated from each other.
+The two ends of the wire are brought out, and threaded through holes (K)
+drilled longitudinally through the walls of the case, and affixed to the
+end by means of screws (L), so that the two wires may be brought
+together and connected with a duplex wire (M).
+
+As the screw (C), which holds the core in place, has its head hidden
+within a recess, which can be closed up by wax, the two terminals of the
+wires are well separated so that short-circuiting cannot take place.
+
+TELEPHONE CONNECTIONS.--The simplest form of telephone connection is
+shown in Fig. 83. This has merely the two telephones (A and B), with a
+single battery (C) to supply electricity for both. One line wire (D)
+connects the two telephones directly, while the other line (E) has the
+battery in its circuit.
+
+[Illustration: _Fig. 83._ SIMPLE TELEPHONE CONNECTION]
+
+COMPLETE INSTALLATION.--To install a more complete system requires, at
+each end, a switch, a battery and an electro-magneto bell. You may use,
+for this purpose, a bell, made as shown in the chapter on bells.
+
+Fig. 84 shows such a circuit. We now dispense with one of the line
+wires, because it has been found that the ground between the two
+stations serves as a conductor, so that only one line wire (A) is
+necessary to connect directly with the telephones of the two stations.
+The telephones (B, B', respectively) have wires (C, C') running to the
+pivots of double-throw switches (D, D'), one terminal of the switches
+having wires (E, E'), which go to electric bells (F, F'), and from the
+bells are other wires (G, G'), which go to the ground. The ground wires
+also have wires (H, H'), which go to the other terminals of the switch
+(D, D'). The double-throw switch (D, D'), in the two stations, is thrown
+over so the current, if any should pass through, will go through the
+bell to the ground, through the wires (E, G or E', G').
+
+[Illustration: _Fig. 84._ TELEPHONE STATIONS IN CIRCUIT]
+
+Now, supposing the switch (D'), in station 2, should be thrown over so
+it contacts with the wire (H'). It is obvious that the current will then
+flow from the battery (I') through wires (H', C') and line (A) to
+station 1; then through wire C, switch D, wire E to the bell F, to the
+ground through wire G. From wire G the current returns through the
+ground to station 2, where it flows up wire G' to the battery, thereby
+completing the circuit.
+
+[Illustration: _Fig. 85._ ILLUSTRATING LIGHT CONTACT POINTS]
+
+The operator at station 2, having given the signal, again throws his
+switch (D') back to the position shown in Fig. 84, and the operator at
+station 1 throws on his switch (D), so as to ring the bell in station 2,
+thereby answering the signal, which means that both switches are again
+to be thrown over so they contact with the battery wires (H and H'),
+respectively. When both are thus thrown over, the bells (G, G') are cut
+out of the circuit, and the batteries are both thrown in, so that the
+telephones are now ready for talking purposes.
+
+MICROPHONE.--Originally this form of telephone system was generally
+employed, but it was found that for long distances a more sensitive
+instrument was necessary.
+
+LIGHT CONTACT POINTS.--In 1877 Professor Hughes discovered,
+accidentally, that a light contact point in an electric circuit
+augmented the sound in a telephone circuit. If, for instance, a light
+pin, or a nail (A, Fig. 85) should be used to connect the severed ends
+of a wire (B), the sounds in the telephone not only would be louder, but
+they would be more distinct, and the first instrument made practically,
+to demonstrate this, is shown in Fig. 86.
+
+[Illustration: _Fig. 86._ MICROPHONE]
+
+[Illustration: _Fig. 87._ TRANSMITTER]
+
+HOW TO MAKE A MICROPHONE.--This instrument has simply a base (A) of
+wood, and near one end is a perpendicular sounding-board (B) of wood, to
+one side of which is attached, by wax or otherwise, a pair of carbon
+blocks (C, D). The lower carbon block (C) has a cup-shaped depression in
+its upper side, and the upper block has a similar depression in its
+lower side. A carbon pencil (E) is lightly held within these cups, so
+that the lightest contact of the upper end of the pencil with the
+carbon block, makes the instrument so sensitive that a fly, walking upon
+the sounding-board, may be distinctly heard through the telephone which
+is in the circuit.
+
+MICROPHONE THE FATHER OF THE TRANSMITTER.--This instrument has been
+greatly modified, and is now used as a transmitter, the latter thereby
+taking the place of the pin (A), shown in Fig. 85.
+
+AUTOMATIC CUT-OUTS FOR TELEPHONES.--In the operation of the telephone,
+the great drawback originally was in inducing users of the lines to
+replace or adjust their instruments carefully. When switches were used,
+they would forget to throw them back, and all sorts of trouble resulted.
+
+It was found necessary to provide an automatic means for throwing in and
+cutting out an instrument, this being done by hanging the telephone on
+the hook, so that the act merely of leaving the telephone made it
+necessary, in replacing the instrument, to cut out the apparatus.
+
+Before describing the circuiting required for these improvements, we
+show, in Fig. 87, a section of a transmitter.
+
+A cup-shaped case (A) is provided, made of some insulating material,
+which has a diaphragm (B) secured at its open side. This diaphragm
+carries the carbon pencil (C) on one side and from the blocks which
+support the carbon pencil the wires run to binding posts on the case.
+Of course the carbon supporting posts must be insulated from each other,
+so the current will go through the carbon pencil (C).
+
+COMPLETE CIRCUITING WITH TRANSMITTER.--In showing the circuiting (Fig.
+88) it will not be possible to illustrate the boxes, or casings, which
+receive the various instruments. For instance, the hook which carries
+the telephone or the receiver, is hinged within the transmitter box. The
+circuiting is all that it is intended to show.
+
+[Illustration: _Fig. 88._ COMPLETE TELEPHONIC CIRCUIT]
+
+The batteries of the two stations are connected up by a wire (A), unless
+a ground circuit is used. The other side of each battery has a wire
+connection (B, B') with one terminal of the transmitter, and the other
+terminal of the transmitter has a wire (C, C') which goes to the
+receiver. From the other terminal of the receiver is a wire (D, D')
+which leads to the upper stop contact (E, E') of the telephone hook. A
+wire (F, F') from the lower stop contact (G, G') of the hook goes to one
+terminal of the bell, and from the other terminal of the bell is a wire
+(H, H') which makes connection with the line wire (A). In order to make
+a complete circuit between the two stations, a line wire (I) is run from
+the pivot of the hook in station 1 to the pivot of the hook in station
+2.
+
+In the diagram, it is assumed that the receivers are on the hooks, and
+that both hooks are, therefore, in circuit with the lower contacts (G,
+G'), so that the transmitter and receiver are both out of circuit with
+the batteries, and the bell in circuit; but the moment the receiver, for
+instance, in station 1 is taken off the hook, the latter springs up so
+that it contacts with the stop (E), thus establishing a circuit through
+the line wire (I) to the hook of station 2, and from the hook through
+line (F') to the bell. From the bell, the line (A) carries the current
+back to the battery of station (A), thence through the wire (B) to the
+transmitter wire (C) to receiver and wire (D) to the post (E), thereby
+completing the circuit.
+
+When, at station 2, the receiver is taken off the hook, and the latter
+contacts with the post (E'), the transmitter and receiver of both
+stations are in circuit with each other, but both bells are cut out.
+
+
+
+
+CHAPTER XIII
+
+ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING
+
+
+DECOMPOSING LIQUIDS.--During the earlier experiments in the field of
+electricity, after the battery or cell was discovered, it was noted that
+when a current was formed in the cell, the electrolyte was charged and
+gases evolved from it. A similar action takes place when a current of
+electricity passes through a liquid, with the result that the liquid is
+decomposed--that is, the liquid is broken up into its original
+compounds. Thus, water is composed of two parts, by bulk, of hydrogen
+and of oxygen, so that if two electrodes are placed in water, and a
+current is sent through the electrodes in either direction, all the
+water will finally disappear in the form of hydrogen and oxygen gases.
+
+MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen
+is set free at the negative pole and the oxygen at the positive pole. A
+simple apparatus, which any boy can make, to generate pure oxygen and
+pure hydrogen, is shown in Fig. 89.
+
+It is constructed of a glass or earthen jar (A), preferably square, to
+which is fitted a wooden top (B), this top being provided with a
+packing ring (C), so as to make it air-tight. Within is a vertical
+partition (D), the edges of which, below the cap, fit tightly against
+the inner walls of the jar. This partition extends down into the jar a
+sufficient distance so it will terminate below the water level. A pipe
+is fitted through the top on each side of the partition, and each pipe
+has a valve. An electrode, of any convenient metal, is secured at its
+upper end to the top of the cap, on each side of the partition. These
+electrodes extend down to the bottom of the jar, and an electric wire
+connects with each of them at the top.
+
+[Illustration: _Fig. 89._ DEVICE FOR MAKING HYDROGEN AND OXYGEN]
+
+If a current of electricity is passed through the wires and the
+electrodes, in the direction shown by the darts, hydrogen will form at
+the negative pole, and oxygen at the positive pole. These gases will
+escape upwardly, so that they will be trapped in their respective
+compartments, and may be drawn off by means of the pipes.
+
+PURIFYING WATER.--Advantage is taken of this electrolytic action, to
+purify water. Oxygen is the most wonderful chemical in nature. It is
+called the acid-maker of the universe. The name is derived from two
+words, _oxy_ and _gen_; one denoting oxydation, and the other that it
+generates. In other words, it is the _generator of oxides_. It is the
+element which, when united with any other element, produces an acid, an
+alkali or a neutral compound.
+
+RUST.--For instance, iron is largely composed of ferric acid. When
+oxygen, in a free or gaseous state, comes into contact with iron, it
+produces ferrous oxide, which is recognized as rust.
+
+OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of
+animal life, like bacteria or germs in water, succumb to free oxygen. By
+_free oxygen_ is meant oxygen in the form of gas.
+
+COMPOSITION OF WATER.--Now, water, in which harmful germs live, is
+one-third oxygen. Nevertheless, the germs thrive in water, because the
+oxygen is in a compound state, and, therefore, not an active agent. But
+if oxygen, in the form of gas, can be forced through water, it will
+attack the germs, and destroy them.
+
+COMMON AIR NOT A GOOD PURIFIER.--Water may be purified, to a certain
+extent, by forcing common air through it, and the foulest water, if run
+over rocks, will be purified, in a measure, because air is intermingled
+with it. But common air is composed of four-fifths nitrogen, and only
+one-fifth oxygen, and, as nitrogen is the staple article of food for
+bacteria, the purifying method by air is not effectual.
+
+PURE OXYGEN.--When, however, oxygen is generated from water, by means of
+electrolysis, it is pure; hence is more active and is not tainted by a
+life-giving substance for germs, such as nitrogen.
+
+The mechanism usually employed for purifying water is shown in Fig. 90.
+
+A WATER PURIFIER.--The case (A, Fig. 90) may be made of metal or of an
+insulating material. If made of metal it must be insulated within with
+slate, glass, marble or hard rubber, as shown at B. The case is provided
+with exterior flanges (C, D), with upper and lower ends, and it is
+mounted upon a base plate (E) and affixed thereto by bolts. The upper
+end has a conically-formed cap (F) bolted to the flanges (C), and this
+has an outlet to which a pipe (G) is attached. The water inlet pipe (H)
+passes through the lower end of the case (A). The electrodes (I, J) are
+secured, vertically, within the case, separated from each other
+equidistant, each alternate electrode being connected up with one wire
+(K), and the alternate electrodes with a wire (L).
+
+[Illustration: _Fig. 90._ ELECTRIC WATER PURIFIER]
+
+When the water passes upwardly, the decomposed or gaseous oxygen
+percolates through the water and thus attacks the germs and destroys
+them.
+
+THE USE OF HYDROGEN IN PURIFICATION.--On the other hand, the hydrogen
+also plays an important part in purifying the water. This depends upon
+the material of which the electrodes are made. Aluminum is by far the
+best material, as it is one of nature's most active purifiers. All clay
+contains aluminum, in what is known as the sulphate form, and water
+passing through the clay of the earth thereby becomes purified, because
+of this element.
+
+ALUMINUM ELECTRODES.--When this material is used as the electrodes in
+water, hydrate of aluminum is formed, or a compound of hydrogen and
+oxygen with aluminum. The product of decomposition is a flocculent
+matter which moves upwardly through the water, giving it a milky
+appearance. This substance is like gelatine, so that it entangles or
+enmeshes the germ life and prevents it from passing through a filter.
+
+If no filter is used, this flocculent matter, as soon as it has given
+off the gases, will settle to the bottom and carry with it all
+decomposed matter, such as germs and other organic matter attacked by
+the oxygen, which has become entangled in the aluminum hydrate.
+
+ELECTRIC HAND PURIFIER.--An interesting and serviceable little purifier
+may be made by any boy with the simplest tools, by cutting out three
+pieces of sheet aluminum. Hard rolled is best for the purpose. It is
+better to have one of the sheets (A), the middle one, thicker than the
+two outer plates (B).
+
+[Illustration: _Fig. 91._ PORTABLE ELECTRIC PURIFIER]
+
+Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half
+inch from the upper ends of the two outside plates (B, B) bore bolt
+holes (C), each of these holes being a quarter of an inch from the edge
+of the plate. The inside plate (A) has two large holes (D) corresponding
+with the small holes (C) in the outside plates. At the upper end of this
+plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a
+small hole for a bolt. Next cut out two hard-rubber blocks (F), each
+1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole
+(G) through each, corresponding with the small holes (C) in the plates
+(B). The machine is now ready to be assembled. If the inner plate is 1/8
+inch thick and the outer plates each 1/16 inch thick, use two small
+eighth-inch bolts 1-1/4 inches long, and clamp together the three
+plates with these bolts. One of the bolts may be used to attach thereto
+one of the electric wires (H), and the other wire (I) is attached by a
+bolt to the wing (E).
+
+[Illustration: _Figs. 92-95._ DETAILS OF PORTABLE PURIFIER]
+
+Such a device will answer for a 110-volt circuit, in ordinary water. Now
+fill a glass nearly full of water, and stand the purifier in the glass.
+Within a few minutes the action of electrolysis will be apparent by the
+formation of numerous bubbles on the plates, followed by the
+decomposition of the organic matter in the water. At first the
+flocculent decomposed matter will rise to the surface of the water, but
+before many minutes it will settle to the bottom of the glass and leave
+clear water above.
+
+PURIFICATION AND SEPARATION OF METALS.--This electrolytic action is
+utilized in metallurgy for the purpose of producing pure metals, but it
+is more largely used to separate copper from its base. In order to
+utilize a current for this purpose, a high ampere flow and low voltage
+are required. The sheets of copper, containing all of its impurities,
+are placed within a tank, parallel with a thin copper sheet. The impure
+sheet is connected with the positive pole of an electroplating dynamo,
+and the thin sheet of copper is connected with the negative pole. The
+electrolyte in the tank is a solution of sulphate of copper. The action
+of the current will cause the pure copper in the impure sheet to
+disintegrate and it is then carried over and deposited upon the thin
+sheet, this action continuing until the impure sheet is entirely eaten
+away. All the impurities which were in the sheet fall to the bottom of
+the tank.
+
+Other metals are treated in the same way, and this treatment has a very
+wide range of usefulness.
+
+ELECTROPLATING.--The next feature to be considered in electrolysis is a
+most interesting and useful one, because a cheap or inferior metal may
+be coated by a more expensive metal. Silver and nickel plating are
+brought about by this action of a current passing through metals, which
+are immersed in an electrolyte.
+
+PLATING IRON WITH COPPER.--We have room in this chapter for only one
+concrete example of this work, which, with suitable modifications, is an
+example of the art as practiced commercially. Iron, to a considerable
+extent, is now being coated with copper to preserve it from rust. To
+carry out this work, however, an electroplating dynamo, of large
+amperage, is required, the amperage, of course, depending upon the
+surface to be treated at one time. The pressure should not exceed 5
+volts.
+
+The iron surface to be treated should first be thoroughly cleansed, and
+then immediately put into a tank containing a cyanide of copper
+solution. Two forms of copper solution are used, namely, the cyanide,
+which is a salt solution of copper, and the sulphate, which is an acid
+solution of copper. Cyanide is first used because it does not attack the
+iron, as would be the case if the sulphate solution should first come
+into contact with the iron.
+
+A sheet of copper, termed the anode, is then placed within the tank,
+parallel with the surface to be plated, known as the cathode, and so
+mounted that it may be adjusted to or from the iron surface, or cathode.
+A direct current of electricity is then caused to flow through the
+copper plate and into the iron plate or surface, and the plating
+proceeded with until the iron surface has a thin film of copper
+deposited thereon. This is a slow process with the cyanide solution, so
+it is discontinued as soon as possible, after the iron surface has been
+completely covered with copper. This copper surface is thoroughly
+cleaned off to remove therefrom the saline or alkaline solution, and it
+is then immersed within a bath, containing a solution of sulphate of
+copper. The current is then thrown on and allowed so to remain until it
+has deposited the proper thickness of copper.
+
+DIRECTION OF CURRENT.--If a copper and an iron plate are put into a
+copper solution and connected up in circuit with each other, a primary
+battery is thereby formed, which will generate electricity. In this
+case, the iron will be positive and the copper negative, so that the
+current within such a cell would flow from the iron (in this instance,
+the anode) to the negative, or cathode.
+
+The action of electroplating reverses this process and causes the
+current to flow from the copper to the iron (in this instance, the
+cathode).
+
+
+
+
+CHAPTER XIV
+
+ELECTRIC HEATING, THERMO ELECTRICITY
+
+
+GENERATING HEAT IN A WIRE.--When a current of electricity passes through
+a conductor, like a wire, more or less heat is developed in the
+conductor. This heat may be so small that it cannot be measured, but it
+is, nevertheless, present in a greater or less degree. Conductors offer
+a resistance to the passage of a current, just the same as water finds a
+resistance in pipes through which it passes. This resistance is measured
+in ohms, as explained in a preceding chapter, and it is this resistance
+which is utilized for electric heating.
+
+RESISTANCE OF SUBSTANCES.--Silver offers less resistance to the passage
+of a current than any other metal, the next in order is copper, while
+iron is, comparatively, a poor conductor.
+
+The following is a partial list of metals, showing their relative
+conductivity:
+
+Silver              1.
+Copper              1.04 to 1.09
+Gold                1.38 to 1.41
+Aluminum            1.64
+Zinc                3.79
+Nickel              4.69
+Iron                6.56
+Tin                 8.9
+Lead               13.2
+German Silver      12.2 to 15
+
+From this table it will be seen that, for instance, iron offers six and
+a half times the resistance of silver, and that German silver has
+fifteen times the resistance of silver.
+
+This table is made up of strands of the different metals of the same
+diameters and lengths, so as to obtain their relative values.
+
+SIZES OF CONDUCTORS.--Another thing, however, must be understood. If two
+conductors of the same metal, having different diameters, receive the
+same current of electricity, the small conductor will offer a greater
+resistance than the large conductor, hence will generate more heat. This
+can be offset by increasing the diameter of the conductor. The metal
+used is, therefore, of importance, on account of the cost involved.
+
+COMPARISON OF METALS.--A conductor of aluminum, say, 10 feet long and of
+the same weight as copper, has a diameter two and a quarter times
+greater than copper; but as the resistance of aluminum is 50 per cent.
+more than that of silver, it will be seen that, weight for weight,
+copper is the cheaper, particularly as aluminum costs fully three times
+as much as copper.
+
+[Illustration: _Fig. 96._ SIMPLE ELECTRIC HEATER]
+
+The table shows that German silver has the highest resistance. Of
+course, there are other metals, like antimony, platinum and the like,
+which have still higher resistance. German silver, however, is most
+commonly used, although there are various alloys of metal made which
+have high resistance and are cheaper.
+
+The principle of all electric heaters is the same, namely, the
+resistance of a conductor to the passage of a current, and an
+illustration of a water heater will show the elementary principles in
+all of these devices.
+
+A SIMPLE ELECTRIC HEATER.--In Fig. 96 the illustration shows a cup or
+holder (A) for the wire, made of hard rubber. This may be of such
+diameter as to fit upon and form the cover for a glass (B). The rubber
+should be 1/2 inch thick. Two holes are bored through the rubber cup,
+and through them are screwed two round-headed screws (C, D), each screw
+being 1-1/2 inches long, so they will project an inch below the cap.
+Each screw should have a small hole in its lower end to receive a pin
+(E) which will prevent the resistance wire from slipping off.
+
+The resistance wire (F) is coiled for a suitable length, dependent upon
+the current used, one end being fastened by wrapping it around the screw
+(C). The other end of the wire is then brought upwardly through the
+interior of the coil and secured in like manner to the other screw (D).
+
+Caution must be used to prevent the different coils or turns from
+touching each other. When completed, the coil may be immersed in water,
+the current turned on, and left so until the water is sufficiently
+heated.
+
+[Illustration: _Figs. 97-98._ RESISTANCE DEVICE]
+
+HOW TO ARRANGE FOR QUANTITY OF CURRENT USED.--It is difficult to
+determine just the proper length the coil should be, or the sizes of the
+wire, unless you know what kind of current you have. You may, however,
+rig up your own apparatus for the purpose of making it fit your heater,
+by preparing a base of wood (A) 8 inches long, 3 inches wide and 1 inch
+thick. On this mount four electric lamp sockets (B). Then connect the
+inlet wire (C) by means of short pieces of wire (D) with all the sockets
+on one side. The outlet wire (E) should then be connected up with the
+other sides of the sockets by the short wires (F). If, now, we have one
+16-candlepower lamp in one of the sockets, there is a half ampere going
+through the wires (C, F). If there are two lamps on the board you will
+have 1 ampere, and so on. By this means you may readily determine how
+much current you are using and it will also afford you a means of
+finding out whether you have too much or too little wire in your coil to
+do the work.
+
+[Illustration: _Fig. 99._ PLAN VIEW OF ELECTRIC IRON]
+
+AN ELECTRIC IRON.--An electric iron is made in the same way. The upper
+side of a flatiron has a circular or oval depression (A) cast therein,
+and a spool of slate (B) is made so it will fit into the depression and
+the high resistance wire (C) is wound around this spool, and insulating
+material, such as asbestos, must be used to pack around it. Centrally,
+the slate spool has an upwardly projecting circular extension (D) which
+passes through the cap or cover (E) of the iron. The wires of the
+resistance coil are then brought through this circular extension and
+are connected up with the source of electrical supply. Wires are now
+sold for this purpose, which are adapted to withstand an intense heat.
+
+[Illustration: _Fig. 100._ SECTION OF ELECTRIC IRON]
+
+The foregoing example of the use of the current, through resistance
+wires, has a very wide application, and any boy, with these examples
+before him, can readily make these devices.
+
+THERMO ELECTRICITY.--It has long been the dream of scientists to convert
+heat directly into electricity. The present practice is to use a boiler
+to generate steam, an engine to provide the motion, and a dynamo to
+convert that motion into electricity. The result is that there is loss
+in the process of converting the fuel heat into steam; loss to change
+the steam into motion, and loss to make electricity out of the motion
+of the engine. By using water-power there is less actual loss; but
+water-power is not available everywhere.
+
+CONVERTING HEAT DIRECTLY INTO ELECTRICITY.--Heat may be converted
+directly into electricity without using a boiler, an engine or a dynamo,
+but it has not been successful from a commercial standpoint. It is
+interesting, however, to know and understand the subject, and for that
+reason it is explained herein.
+
+METALS; ELECTRIC POSITIVE-NEGATIVE.--To understand the principle, it may
+be stated that all metals are electrically positive-negative to each
+other. You will remember that it has hereinbefore been stated that if,
+for instance, iron and copper are put into an acid solution, a current
+will be created or generated thereby. So with zinc and copper, the usual
+primary battery elements. In all such cases an electrolyte is used.
+
+Thermo-electricity dispenses with the electrolyte, and nothing is used
+but the metallic elements and heat. The word thermo means heat. If, now,
+we can select two strips of different metals, and place them as far
+apart as possible--that is, in their positive-negative relations with
+each other, and unite the end of one with one end of other by means of a
+rivet, and then heat the riveted ends, a current will be generated in
+the strips. If, for instance, we use an iron in conjunction with a
+copper strip, the current will flow from the copper to the iron, because
+copper is positive to iron, and iron negative to copper. It is from this
+that the term positive-negative is taken.
+
+The two metals most available, which are thus farthest apart in the
+scale of positive-negative relation, are bismuth and antimony.
+
+[Illustration: _Fig. 101._ THERMO-ELECTRIC COUPLE]
+
+In Fig. 101 is shown a thermo-electric couple (A, B) riveted together,
+with thin outer ends connected by means of a wire (C) to form a circuit.
+A galvanometer (D) or other current-testing means is placed in this
+circuit. A lamp is placed below the joined ends.
+
+THERMO-ELECTRIC COUPLES.--Any number of these couples may be put
+together and joined at each end to a common wire and a fairly large flow
+of current obtained thereby.
+
+One thing must be observed: A current will be generated only so long as
+there exists a difference in temperature between the inner and the outer
+ends of the bars (A, B). This may be accomplished by water, or any other
+cooling means which may suggest itself.
+
+
+
+
+CHAPTER XV
+
+ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS AND
+RECTIFIERS
+
+
+DIRECT CURRENT.--When a current of electricity is generated by a cell,
+it is assumed to move along the wire in one direction, in a steady,
+continuous flow, and is called a _direct_ current. This direct current
+is a natural one if generated by a cell.
+
+ALTERNATING CURRENT.--On the other hand, the natural current generated
+by a dynamo is alternating in its character--that is, it is not a
+direct, steady flow in one direction, but, instead, it flows for an
+instant in one direction, then in the other direction, and so on.
+
+A direct-current dynamo such as we have shown in Chapter IV, is much
+easier to explain, hence it is illustrated to show the third method used
+in generating an electric current.
+
+It is a difficult matter to explain the principle and operation of
+alternating current machines, without becoming, in a measure, too
+technical for the purposes of this book, but it is important to know the
+fundamentals involved, so that the operation and uses of certain
+apparatus, like the choking coil, transformers, rectifiers and
+converters, may be explained.
+
+THE MAGNETIC FIELD.--It has been stated that when a wire passes through
+the magnetic field of a magnet, so as to cut the lines of force flowing
+out from the end of a magnet, the wire will receive a charge of
+electricity.
+
+[Illustration: _Fig. 102._ CUTTING A MAGNETIC FIELD]
+
+To explain this, study Fig. 102, in which is a bar magnet (A). If we
+take a metal wire (B) and bend it in the form of a loop, as shown, and
+mount the ends on journal-bearing blocks, the wire may be rotated so
+that the loop will pass through the magnetic field. When this takes
+place, the wire receives a charge of electricity, which moves, say, in
+the direction of the darts, and will make a complete circuit if the ends
+of the looped wire are joined, as shown by the conductor (D).
+
+ACTION OF THE MAGNETIZED WIRE.--You will remember, also that we have
+pointed out how, when a current passes over a wire, it has a magnetic
+field extending out around it at all points, so that while it is passing
+through the magnetic field of the magnet (A), it becomes, in a measure,
+a magnet of its own and tries to set up in business for itself as a
+generator of electricity. But when the loop leaves the magnetic field,
+the magnetic or electrical impulse in the wire also leaves it.
+
+THE MOVEMENT OF A CURRENT IN A CHARGED WIRE.--Your attention is
+directed, also, to another statement, heretofore made, namely, that when
+a current from a charged wire passes by induction to a wire across
+space, so as to charge it with an electric current, it moves along the
+charged wire in a direction opposite to that of the current in the
+charging wire.
+
+Now, the darts show the direction in which the current moves while it is
+approaching and passing through the magnetic field. But the moment the
+loop is about to pass out of the magnetic field, the current in the loop
+surges back in the opposite direction, and when the loop has made a
+revolution and is again entering the magnetic field, it must again
+change the direction of flow in the current, and thus produce
+alternations in the flow thereof.
+
+Let us illustrate this by showing the four positions of the revolving
+loop. In Fig. 103 the loop (B) is in the middle of the magnetic field,
+moving upwardly in the direction of the curved dart (A), and while in
+that position the voltage, or the electrical impulse, is the most
+intense. The current used flows in the direction of the darts (C) or to
+the left.
+
+In Fig. 104, the loop (A) has gone beyond the influence of the magnetic
+field, and now the current in the loop tries to return, or reverse
+itself, as shown by the dart (D). It is a reaction that causes the
+current to die out, so that when the loop has reached the point farthest
+from the magnet, as shown in Fig. 105, there is no current in the loop,
+or, if there is any, it moves faintly in the direction of the dart (E).
+
+[Illustration: _Figs. 103-106._ ILLUSTRATING ALTERNATIONS]
+
+CURRENT REVERSING ITSELF.--When the loop reaches its lowest point (Fig.
+106) it again comes within the magnetic field and the current commences
+to flow back to its original direction, as shown by darts (C).
+
+SELF-INDUCTION.--This tendency of a current to reverse itself, under the
+conditions cited, is called self-induction, or inductance, and it would
+be well to keep this in mind in pursuing the study of alternating
+currents.
+
+You will see from the foregoing, that the alternations, or the change of
+direction of the current, depends upon the speed of rotation of the loop
+past the end of the magnet.
+
+[Illustration: _Figs. 107-108._ FORM FOR INCREASING ALTERNATIONS]
+
+Instead, therefore, of using a single loop, we may make four loops (Fig.
+107), which at the same speed as we had in the case of the single loop,
+will give four alternations, instead of one, and still further, to
+increase the periods of alternation, we may use the four loops and two
+magnets, as in Fig. 108. By having a sufficient number of loops and of
+magnets, there may be 40, 50, 60, 80, 100 or 120 such alternating
+periods in each second. Time, therefore, is an element in the operation
+of alternating currents.
+
+Let us now illustrate the manner of connecting up and building the
+dynamo, so as to derive the current from it. In Fig. 109, the loop (A)
+shows, for convenience, a pair of bearings (B). A contact finger (C)
+rests on each, and to these the circuit wire (D) is attached. Do not
+confuse these contact fingers with the commutator brushes, shown in the
+direct-current motor, as they are there merely for the purpose of making
+contact between the revolving loop (A) and stationary wire (D).
+
+[Illustration: _Fig. 109._ CONNECTION OF ALTERNATING DYNAMO ARMATURE]
+
+BRUSHES IN A DIRECT-CURRENT DYNAMO.--The object of the brushes in the
+direct-current dynamo, in connection with a commutator, is to convert
+this _inductance_ of the wire, or this effort to reverse itself into a
+current which will go in one direction all the time, and not in both
+directions alternately.
+
+To explain this more fully attention is directed to Figs. 110 and 111.
+Let A represent the armature, with a pair of grooves (B) for the wires.
+The commutator is made of a split tube, the parts so divided being
+insulated from each other, and in Fig. 110, the upper one, we shall call
+and designate the positive (+) and the lower one the negative (-). The
+armature wire (C) has one end attached to the positive commutator
+terminal and the other end of this wire is attached to the negative
+terminal.
+
+[Illustration: _Fig. 110._ DIRECT CURRENT DYNAMO]
+
+One brush (D) contacts with the positive terminal of the commutator and
+the other brush (E) with the negative terminal. Let us assume that the
+current impulse imparted to the wire (C) is in the direction of the dart
+(F, Fig. 110). The current will then flow through the positive (+)
+terminal of the commutator to the brush (D), and from the brush (D)
+through the wire (G) to the brush (E), which contacts with the negative
+(-) terminal of the commutator. This will continue to be the case, while
+the wire (C) is passing the magnetic field, and while the brush (D) is
+in contact with the positive (+) terminal. But when the armature makes a
+half turn, or when it reaches that point where the brush (D) contacts
+with the negative (-) terminal, and the brush (E) contacts with the
+positive (+) terminal, a change in the direction of the current through
+the wire (G) takes place, unless something has happened to change it
+before it has reached the brushes (D, E).
+
+[Illustration: _Fig. 111._ CIRCUIT WIRES IN DIRECT CURRENT DYNAMO]
+
+Now, this change is just exactly what has happened in the wire (C), as
+we have explained. The current attempts to reverse itself and start out
+on business of its own, so to speak, with the result that when the
+brushes (D and E) contact with the negative and positive terminals,
+respectively, the surging current in the wire (C) is going in the
+direction of the dart (H)--that is, while, in Fig. 110, the current
+flows from the wire (C) into the positive terminal, and out of the
+negative terminal into the wire (C), the conditions are exactly reversed
+in Fig. 111. Here the current in wire C flows _into_ the negative (-)
+terminal, and _from_ the positive (+) terminal into the wire C, so that
+in either case the current will flow out of the brush D and into the
+brush E, through the external circuit (G).
+
+It will be seen, therefore, that in the direct-current motor, advantage
+is taken of the surging, or back-and-forth movement, of the current to
+pass it along in one direction, whereas in the alternating current no
+such change in direction is attempted.
+
+ALTERNATING POSITIVE AND NEGATIVE POLES.--The alternating current,
+owing to this surging movement, makes the poles alternately positive and
+negative. To express this more clearly, supposing we take a line (A,
+Fig. 112), which is called the zero line, or line of no electricity. The
+current may be represented by the zigzag line (B). The lines (B) above
+zero (A) may be designated as positive, and those below the line as
+negative. The polarity reverses at the line A, goes up to D, which is
+the maximum intensity or voltage above zero, and, when the current falls
+and crosses the line A, it goes in the opposite direction to E, which is
+its maximum voltage in the other direction. In point of time, if it
+takes one second for the current to go from C to F, on the down line,
+then it takes only a half second to go from C to G, so that the line A
+represents the time, and the line H the intensity, a complete cycle
+being formed from C, D, F, then through F, E, C, and so on.
+
+[Illustration: _Fig. 112._ ALTERNATING POLARITY LINES]
+
+HOW AN ALTERNATING DYNAMO IS MADE.--It is now necessary to apply these
+principles in the construction of an alternating-current machine. Fig.
+113 is a diagram representing the various elements, and the circuiting.
+
+[Illustration: _Fig. 113._ ALTERNATING CURRENT DYNAMO]
+
+Let A represent the ring or frame containing the inwardly projecting
+field magnet cores (B). C is the shaft on which the armature revolves,
+and this carries the wheel (D), which has as many radially disposed
+magnet cores (E) as there are of the field magnet cores (B).
+
+The shaft (C) also carries two pulleys with rings thereon. One of these
+rings (F) is for one end of the armature winding, and the other ring
+(G) for the other end of the armature wire.
+
+THE WINDINGS.--The winding is as follows: One wire, as at H, is first
+coiled around one magnet core, the turnings being to the right. The
+outlet terminal of this wire is then carried to the next magnet core and
+wound around that, in the opposite direction, and so on, so that the
+terminal of the wire is brought out, as at I, all of these wires being
+connected to binding posts (J, J'), to which, also, the working circuits
+are attached.
+
+THE ARMATURE WIRES.--The armature wires, in like manner, run from the
+ring (G) to one armature core, being wound from right to left, then to
+the next core, which is wound to the right, afterward to the next core,
+which is wound to the left, and so on, the final end of the wire being
+connected up with the other ring (F). The north (N) and the south (S)
+poles are indicated in the diagram.
+
+CHOKING COIL.--The self-induction in a current of this kind is utilized
+in transmitting electricity to great distances. Wires offer resistance,
+or they impede the flow of a current, as hereinbefore stated, so that it
+is not economical to transmit a direct current over long distances. This
+can be done more efficiently by means of the alternating current, which
+is subject to far less loss than is the case with the direct current.
+It affords a means whereby the flow of a current may be checked or
+reduced without depending upon the resistance offered by the wire over
+which it is transmitted. This is done by means of what is called a
+choking coil. It is merely a coil of wire, wound upon an iron core, and
+the current to be choked passes through the coil. To illustrate this,
+let us take an arc lamp designed to use a 50-volt current. If a current
+is supplied to it carrying 100 volts, it is obvious that there are 50
+volts more than are needed. We must take care of this excess of 50 volts
+without losing it, as would happen were we to locate a resistance of
+some kind in the circuit. This result we accomplish by the introduction
+of the choking coil, which has the effect of absorbing the excessive 50
+volts, the action being due to its quality of self-induction, referred
+to in the foregoing.
+
+[Illustration: _Fig. 114._ CHOKING COIL]
+
+In Fig. 114, A is the choking coil and B an arc lamp, connected up, in
+series, with the choking coil.
+
+THE TRANSFORMER.--It is more economical to transmit 10,000 volts a long
+distance than 1,000 volts, because the lower the pressure, or the
+voltage, the larger must be the conductor to avoid loss. It is for this
+reason that 500 volts, or more, are used on electric railways. For
+electric light purposes, where the current goes into dwellings, even
+this is too high, so a transformer is used to take a high-voltage
+current from the main line and transform it into a low voltage. This is
+done by means of two distinct coils of wire, wound upon an iron core.
+
+[Illustration: _Fig. 115._ A TRANSFORMER]
+
+In Fig. 115 the core is O-shaped, so that a primary winding (A), from
+the electrical source, can be wound upon one limb, and the secondary
+winding (B) wound around the other limb. The wires, to supply the
+lamps, run from the secondary coil. There is no electrical connection
+between the two coils, but the action from the primary to the secondary
+coil is solely by induction. When a current passes through the primary
+coil, the surging movement, heretofore explained, is transmitted to the
+iron core, and the iron core, in turn, transmits this electrical energy
+to the secondary coil.
+
+HOW THE VOLTAGE IS DETERMINED.--The voltage produced by the secondary
+coil will depend upon several things, namely, the strength of the
+magnetism transmitted to it; the rapidity, or periodicity of the
+current, and the number of turns of wire around the coil. The voltage is
+dependent upon the length of the winding. But the voltage may also be
+increased, as well as decreased. If the primary has, we will say, 100
+turns of wire, and has 200 volts, and the secondary has 50 turns of
+wire, the secondary will give forth only one-half as much as the
+primary, or 100 volts.
+
+If, on the other hand, 400 volts would be required, the secondary should
+have 200 turns in the winding.
+
+VOLTAGE AND AMPERAGE IN TRANSFORMERS.--It must not be understood that,
+by increasing the voltage in this way, we are getting that much more
+electricity. If the primary coil, with 100 turns, produces a current of
+200 volts and 50 amperes, which would be 200 × 50 = 10,000 watts, and
+the secondary coil has 50 turns, we shall have 100 volts and 100
+amperes: 100 (V.) × 100 (A.) = 10,000 watts. Or, if, on the other hand,
+our secondary winding is composed of 200 turns, we shall have 400 volts
+and 25 amperes, 400 (volts) × 25 (amperes) also gives 10,000 watts.
+
+Necessarily, there will be some loss, but the foregoing is offered as
+the theoretical basis of calculation.
+
+
+
+
+CHAPTER XVI
+
+ELECTRIC LIGHTING
+
+
+The most important step in the electric field, after the dynamo had been
+brought to a fairly workable condition, was its utilization to make
+light. It was long known prior to the discovery of practical electric
+dynamos, that the electric current would produce an intense heat.
+
+Ordinary fuels under certain favorable conditions will produce a
+temperature of 4,500 degrees of heat; but by means of the electric arc,
+as high as six, eight and ten thousand degrees are available.
+
+The fact that when a conductor, in an electric current, is severed, a
+spark will follow the drawing part of the broken ends, led many
+scientists to believe, even before the dynamo was in a practical shape,
+that electricity, sooner or later, would be employed as the great
+lighting agent.
+
+When the dynamo finally reached a stage in development where its
+operation could be depended on, and was made reversible, the first
+active steps were taken to not only produce, but to maintain an arc
+between two electrodes.
+
+It would be difficult and tedious to follow out the first experiments
+in detail, and it might, also, be useless, as information, in view of
+the present knowledge of the science. A few steps in the course of the
+development are, however, necessary to a complete understanding of the
+subject.
+
+Reference has been made in a previous chapter to what is called the
+_Electric Arc_, produced by slightly separated conductors, across which
+the electric current jumps, producing the brilliantly lighted area.
+
+This light is produced by the combustion of the carbon of which the
+electrodes are composed. Thus, the illumination is the result of
+directly burning a fuel. The current, in passing from one electrode to
+the other, through the gap, produces such an intense heat that the fuel
+through which the current passes is consumed.
+
+Carbon in a comparatively pure state is difficult to ignite, owing to
+its great resistance to heat. At about 7,000 degrees it will fuse, and
+pass into a vapor which causes the intense illumination.
+
+The earliest form of electric lighting was by means of the arc, in which
+the light is maintained so long as the electrodes were kept a certain
+distance apart.
+
+To do this requires delicate mechanism, for the reason that when contact
+is made, and the current flows through the two electrodes, which are
+connected up directly with the coils of a magnet, the cores, or
+armatures, will be magnetized. The result is that the electrode,
+connected with the armature of the magnet, is drawn away from the other
+electrode, and the arc is formed, between the separated ends.
+
+As the current also passes through a resistance coil, the moment the
+ends of the electrodes are separated too great a distance, the
+resistance prevents a flow of the normal amount of current, and the
+armature is compelled to reduce its pull. The effect is to cause the two
+electrodes to again approach each other, and in doing so the arc becomes
+brighter.
+
+It will be seen, therefore, that there is a constant fight between the
+resistance coil and the magnet, the combined action of the two being
+such, that, if properly arranged, and with powers in correct relation to
+each other, the light may be maintained without undue flickering. Such
+devices are now universally used, and they afford a steady and reliable
+means of illumination.
+
+Many improvements are made in this direction, as well as in the
+ingredients of the electrodes. A very novel device for assuring a
+perfect separation at all times between the electrodes, is by means of a
+pair of parallel carbons, held apart by a non-conductor such as clay, or
+some mixture of earth, a form of which is shown in Fig. 116.
+
+The drawing shows two electrodes, separated by a non-conducting
+material, which is of such a character that it will break down and
+crumble away, as the ends of the electrodes burn away.
+
+[Illustration: _Fig. 116. Parallel Carbons._]
+
+This device is admirable where the alternating current is used, because
+the current moves back and forth, and the two electrodes are thus burned
+away at the same rate of speed.
+
+In the direct or continuous current the movement is in one direction
+only, and as a result the positive electrode is eaten away twice as fast
+as the negative.
+
+This is the arc form of lamp universally used for lighting large spaces
+or areas, such as streets, railway stations, and the like. It is
+important also as the means for utilizing searchlight illumination, and
+frequently for locomotive headlights.
+
+Arc lights are produced by what is called the _series current_. This
+means that the lamps are all connected in a single line. This is
+illustrated by reference to Fig. 117, in which A represents the wire
+from the dynamo, and B, C the two electrodes, showing the current
+passing through from one lamp to the next.
+
+[Illustration: _Fig. 117. Arc-Lighting Circuit._]
+
+A high voltage is necessary in order to cause the current to leap across
+the gap made by the separation of the electrodes.
+
+THE INCANDESCENT SYSTEM.--This method is entirely different from the arc
+system. It has been stated that certain metals conduct electricity with
+greater facility than others, and some have higher resistance than
+others. If a certain amount of electricity is forced through some
+metals, they will become heated. This is true, also, if metals, which,
+ordinarily, will conduct a current freely, are made up into such small
+conductors that it is difficult for the current to pass.
+
+[Illustration: _Fig 118. Interrupted Conductor._]
+
+In the arc method high voltage is essential; in the incandescent plan,
+current is the important consideration. In the arc, the light is
+produced by virtue of the break in the line of the conductor; in the
+incandescent, the system is closed at all times.
+
+Supposing we have a wire A, a quarter of an inch in diameter, carrying a
+current of, say, 500 amperes, and at any point in the circuit the wire
+is made very small, as shown at B, in Fig. 118, it is obvious that the
+small wire would not be large enough to carry the current.
+
+The result would be that the small connection B would heat up, and,
+finally, be fused. While the large part of the wire would carry 500
+amperes, the small wire could not possibly carry more than, say, 10
+amperes. Now these little wires are the filaments in an electric bulb,
+and originally the attempt was made to have them so connected up that
+they could be illuminated by a single wire, as with the arc system above
+explained, one following the other as shown in Fig. 117.
+
+[Illustration: _Fig. 119. Incandescent Circuit._]
+
+It was discovered, however, that the addition of each successive lamp,
+so wired, would not give light in proportion to the addition, but at
+only about one-fourth the illumination, and such a course would,
+therefore, make electric lighting enormously expensive.
+
+This knowledge resulted in an entirely new system of wiring up the lamps
+in a circuit. This is explained in Fig. 119. In this figure A represents
+the dynamo, B, B the brushes, C, D the two line wires, E the lamps, and
+F the short-circuiting wires between the two main conductors C, D.
+
+It will be observed that the wires C, D are larger than the cross wires
+F. The object is to show that the main wires might carry a very heavy
+amperage, while the small cross wires F require only a few amperes.
+
+This is called the _multiple_ circuit, and it is obvious that the entire
+amperage produced by the dynamo will not be required to pass through
+each lamp, but, on the other hand, each lamp takes only enough necessary
+to render the filament incandescent.
+
+This invention at once solved the problem of the incandescent system and
+was called the subdivision of the electric light. By this means the cost
+was materially reduced, and the wiring up and installation of lights
+materially simplified.
+
+But the divisibility of the light did not, by any means, solve the great
+problem that has occupied the attention of electricians and
+experimenters ever since. The great question was and is to preserve the
+little filament which is heated to incandescence, and from which we get
+the light.
+
+The effort of the current to pass through the small filament meets with
+such a great resistance that the substance is heated up. If it is made
+of metal there is a point at which it will fuse, and thus the lamp is
+destroyed.
+
+It was found that carbon, properly treated, would heat to a brilliant
+white heat without fusing, or melting, so that this material was
+employed. But now followed another difficulty. As this intense heat
+consumed the particles of carbon, owing to the presence of oxygen, means
+were sought to exclude the air.
+
+This was finally accomplished by making a bulb of glass, from which the
+air was exhausted, and as such a globe had no air to support combustion,
+the filaments were finally made so that they would last a long time
+before being finally disintegrated.
+
+The quest now is, and has been, to find some material of a purely
+metallic character, which will have a very high fusing point, and which
+will, therefore, dispense with the cost of the exhausted bulb. Some
+metals, as for instance, osmium, tantalum, thorium, and others, have
+been used, and others, also, with great success, so that the march of
+improvements is now going forward with rapid strides.
+
+VAPOR LAMPS.--One of the directions in which considerable energy has
+been directed in the past, was to produce light from vapors. The Cooper
+Hewitt mercury vapor lamp is a tube filled with the vapor of mercury,
+and a current is sent through the vapor which produces a greenish
+light, and owing to that peculiar color, has not met with much success.
+
+It is merely cited to show that there are other directions than the use
+of metallic conductors and filaments which will produce light, and the
+day is no doubt close at hand when we may expect some important
+developments in the production of light by means of the Hertzian waves.
+
+DIRECTIONS FOR IMPROVEMENTS.--Electricity, however, is not a cheap
+method of illumination. The enormous heat developed is largely wasted.
+The quest of the inventor is to find a means whereby light can be
+produced without the generation of the immense heat necessary.
+
+Man has not yet found a means whereby he can make a heat without
+increasing the temperature, as nature does it in the glow worm, or in
+the firefly. A certain electric energy will produce both light and heat,
+but it is found that much more of this energy is used in the heat than
+in the light.
+
+What wonderful possibilities are in store for the inventor who can make
+a heatless light! It is a direction for the exercise of ingenuity that
+will well repay any efforts.
+
+_Curious Superstitions Concerning Electricity_
+
+Electricity, as exhibited in light, has been the great marvel of all
+times. The word electricity itself comes from the thunderbolt of the
+ancient God Zeus, which is known to be synonymous with the thunderbolt
+and the lightning.
+
+Magnetism, which we know to be only another form of electricity, was not
+regarded the same as electricity by the ancients. Iron which had the
+property to attract, was first found near the town of Magnesia, in
+Lydia, and for that reason was called magnetism.
+
+Later on, a glimmer of the truth seemed to dawn on the early scientists,
+when they saw the resemblance between the actions of the amber and the
+loadstone, as both attracted particles. And here another curious thing
+resulted. Amber will attract particles other than metals. The magnet did
+not; and from this imperfect observation and understanding, grew a
+belief that electricity, or magnetism would attract all substances, even
+human flesh, and many devices were made from magnets, and used as cures
+for the gout, and to affect the brain, or to remove pain.
+
+Even as early as 2,500 years before the birth of Christ the Chinese knew
+of the properties of the magnet, and also discovered that a bar of the
+permanent magnet would arrange itself north and south, like the
+mariners' compass. There is no evidence, however, that it was used as a
+mariner's compass until centuries afterwards.
+
+But the matter connected with light, as an electrical development, which
+interests us, is its manifestations to the ancients in the form of
+lightning. The electricity of the earth concentrates itself on the tops
+of mountains, or in sharp peaks, and accounts for the magnificent
+electrical displays always found in mountainous regions.
+
+Some years ago, a noted scientist, Dr. Siemens, while standing on the
+top of the great pyramid of Cheops, in Egypt, during a storm, noted that
+an electrical discharge flowed from his hand when extended toward the
+heavens. The current manifested itself in such a manner that the hissing
+noise was plainly perceptible.
+
+The literature of all ages and of all countries shows that this
+manifestation of electrical discharges was noted, and became the subject
+of discussions among learned men.
+
+All these displays were regarded as the bolts of an angry God, and
+historians give many accounts of instances where, in His anger, He sent
+down the lightning to destroy.
+
+Among the Romans Jupiter thus hurled forth his wrath; and among many
+ancient people, even down to the time of Charlemagne, any space struck
+by lightning was considered sacred, and made consecrated ground.
+
+From this grew the belief that it was sacrilegious to attempt to imitate
+the lightning of the sky--that Deity would visit dire punishment on any
+man who attempted to produce an electric light. Virgil relates accounts
+where certain princes attempted to imitate the lightning, and were
+struck by thunderbolts as punishments.
+
+Less than a century ago Benjamin Franklin devised the lightning rod, in
+order to prevent lightning from striking objects. The literature of that
+day abounds with instances of protests made, on the part of those who
+were as superstitions as the people in ancient times, who urged that it
+was impious to attempt to ward off Heaven's lightnings. It was argued
+that the lightning was one way in which the Creator manifested His
+displeasure, and exercised His power to strike the wicked.
+
+When such writers as Pliny will gravely set forth an explanation of the
+causes of lightning, as follows in the paragraph below, we can
+understand why it inculcated superstitious fears in the people of
+ancient times. He says:
+
+"Most men are ignorant of that secret, which, by close observation of
+the heavens, deep scholars and principal men of learning have found
+out, namely, that they are the fires of the uppermost planets, which,
+falling to the earth, are called lightning; but those especially which
+are seated in the middle, that is about Jupiter, perhaps because
+participating in the excessive cold and moisture from the upper circle
+of Saturn, and the immoderate heat of Mars, that is next beneath, by
+this means he discharges his superfluity, and therefore it is commonly
+said, 'That Jupiter shooteth and darteth lightning.' Therefore, like as
+out of a burning piece of wood a coal flieth forth with a crack, even so
+from a star is spit out, as it were, and voided forth this celestial
+fire, carrying with it presages of future things; so that the heavens
+showeth divine operations, even in these parcels and portions which are
+rejected and cast away as superfluous."
+
+
+
+
+CHAPTER XVII
+
+POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS
+
+
+It would be difficult to mention any direction in human activity where
+electricity does not serve as an agent in some form or manner. Man has
+learned that the Creator gave this great power into the hands of man to
+use, and not to curse.
+
+When the dynamo was first developed it did not appear possible that it
+could generate electricity, and then use that electricity in order to
+turn the dynamo in the opposite direction. It all seems so very natural
+to us now, that such a thing should practically follow; but man had to
+learn this.
+
+Let us try to make the statement plain by a few simple illustrations. By
+carefully going over the chapter on the making of the dynamo, it will be
+evident that the basis of the generation of the current depends on the
+changing of the direction of the flow of an electric current.
+
+Look at the simple horse-shoe magnet. If two of them are gradually moved
+toward each other, so that the north pole of one approaches the north
+pole of the other, there is a sensible attempt for them to push away
+from each other. If, however, one of them is turned, so that the north
+pole of one is opposite the south pole of the other, they will draw
+together.
+
+In this we have the foundation physical action of the dynamo and the
+motor. When power is applied to an armature, and it moves through a
+magnetic field, the action is just the same as in the case of the hand
+drawing the north and the south pole of the two approaching magnets from
+each other.
+
+The influence of the electrical disturbance produced by that act
+permeated the entire winding of the field and armature, and extended out
+on the whole line with which the dynamo was connected. In this way a
+current was established and transmitted, and with proper wires was sent
+in the form of circuits and distributed so as to do work.
+
+But an electric current, without suitable mechanism, is of no value. It
+must have mechanism to use it, as well as to make it. In the case of
+light, we have explained how the arc and the incandescent lamps utilize
+it for that purpose.
+
+But now, attempting to get something from it in the way of power, means
+another piece of mechanism. This is done by the motor, and this motor is
+simply a converter, or a device for reversing the action of the
+electricity.
+
+Attention is called to Figs. 120 and 121. Let us assume that the field
+magnets A, A are the positives, and the magnets B, B the negatives. The
+revolving armature has also four magnet coils, two of them, C, C, being
+positive, and the other two, D, D, negative, each of these magnet coils
+being so connected up that they will reverse the polarities of the
+magnets.
+
+[Illustration: _Figs. 120-121._ ACTION OF MAGNETS IN A DYNAMO]
+
+Now in the particular position of the revolving armature, in Fig. 120,
+the magnets of the armature have just passed the respective poles of the
+field magnets, and the belt E is compelled to turn the armature past the
+pole pieces by force in the direction of the arrow F. After the armature
+magnets have gone to the positions in Fig. 121, the positives A try to
+draw back the negatives D of the armature, and at the same time the
+negatives B repel the negatives D, because they are of the same
+polarities.
+
+This repulsion of the negatives A, B continues until the armature poles
+C, D have slightly passed them, when the polarities of the magnets C, D
+are changed; so that it will be seen, by reference to Fig. 122, that D
+is now retreating from B, and C is going away from A--that is, being
+forced away contrary to their natural attractive influences, and in Fig.
+123, when the complete cycle is nearly finished, the positives are again
+approaching each other and the negatives moving together.
+
+[Illustration: _Figs. 122-123._ CYCLE ACTION IN DYNAMO]
+
+In this manner, at every point, the sets of magnets are compelled to
+move against their magnetic pull. This explains the dynamo.
+
+Now take up the cycle of the motor, and note in Fig. 124 that the
+negative magnets D of the armature are closely approaching the positive
+and negative magnets, on one side; and the positive magnets C are
+nearing the positive and negatives on the other side. The positives A,
+therefore, attract the negatives D, and the negative B exert a pull on
+the positives C at the same time. The result is that the armature is
+caused to revolve, as shown by the dart G, in a direction opposite to
+the dart in Fig. 120.
+
+[Illustration: _Figs. 124-125._ ACTION OF MAGNETS IN MOTOR]
+
+When the pole pieces of the magnets C, D are about to pass magnets A, B,
+as shown in Fig. 125, it is necessary to change the polarities of the
+armature magnets C, D; so that by reference to Fig. 126, it will be seen
+that they are now indicated as C-, and D+, respectively, and have moved
+to a point midway between the poles A, B (as in Fig. 125), where the
+pull on one side, and the push on the other are again the same, and the
+last Figure 127 shows the cycle nearly completed.
+
+The shaft of the motor armature is now the element which turns the
+mechanism which is to be operated. To convert electrical impulses into
+power, as thus shown, results in great loss. The first step is to take
+the steam boiler, which is the first stage in that source which is the
+most common and universal, and by means of fuel, converting water into
+steam. The second is to use the pressure of this steam to drive an
+engine; the third is to drive the dynamo which generates the electrical
+impulse; and the fourth is the conversion from the dynamo into a motor
+shaft. Loss is met with at each step, and the great problem is to
+eliminate this waste.
+
+[Illustration: _Figs. 126-127._ POSITIONS OF MAGNETS IN MOTOR]
+
+The great advantage of electrical power is not in utilizing it for
+consumption at close ranges, but where it is desired to transmit it for
+long distances. Such illustrations may be found in electric railways,
+and where water power can be obtained as the primal source of energy,
+the cost is not excessive. It is found, however, that even with the most
+improved forms of mechanism, in electrical construction, the internal
+combustion engines are far more economical.
+
+
+_Transmission of Energy_
+
+One of the great problems has been the transmission of the current to
+great distances. By using a high voltage it may be sent hundreds of
+miles, but to use a current of that character in the cars, or shops, or
+homes, would be exceedingly dangerous.
+
+To meet this requirement transformers have been devised, which will take
+a current of very high voltage, and deliver a current of low tension,
+and capable of being used anywhere with the ordinary motors.
+
+THE TRANSFORMER.--This is an electrical device made up of a core or
+cores of thin sheet metal, around which is wound sets of insulated
+wires, one set being designed to receive the high voltage, and the other
+set to put out the low voltage, as described in a former chapter.
+
+These may be made where the original output is a very high voltage, so
+that they will be stepped down, first from one voltage to a lower, and
+then from that to the next lower stage. This is called the "Step down"
+transformer, and is now used over the entire world, where large voltages
+are generated.
+
+ELECTRIC FURNACES.--The most important development of electricity in the
+direction of heat is its use in furnaces. As before stated, an intense
+heat is capable of being generated by the electric current, so that it
+becomes the great agent to use for the treatment of refractory material.
+
+In furnaces of this kind the electric arc is the mechanical form used to
+produce the great heat, the only difference being in the size of the
+apparatus. The electric furnace is simply an immense form of arc light,
+capable of taking a high voltage, and such an arc is enclosed within a
+suitable oven of refractory material, which still further conserves the
+heat.
+
+WELDING BY ELECTRICITY.--The next step is to use the high heat thus
+capable of being produced, to fuse metals so that they may be welded
+together. It is a difficult matter to unite two large pieces of metal by
+the forging method, because the highest heat is required, owing to their
+bulk, and in addition immense hammers, weighing tons, must be employed.
+
+Electric welding offers a simple and easy method of accomplishing the
+result, and in the doing of which it avoids the oxidizing action of the
+forging heat. Instead of heating the pieces to be welded in a forge, as
+is now done, the ends to be united are simply brought into contact, and
+the current is sent through the ends until they are in a soft condition,
+after which the parts are pressed together and united by the simple
+merging of the plastic condition in which they are reduced by the high
+electric heat.
+
+This form of welding makes the most perfect joint, and requires no
+hammering, as the mass of the metal flows from one part or end to the
+other; the unity is a perfect one, and the advantage is that the metals
+can be kept in a semi-fluid state for a considerable time, thus assuring
+a perfect admixture of the two parts.
+
+With the ordinary form of welding it is necessary to drive the heated
+parts together without any delay, and at the least cooling must be
+reheated, or the joint will not be perfect.
+
+The smallest kinds of electric heating apparatus are now being made, so
+that small articles, sheet metal, small rods, and like parts can be
+united with the greatest facility.
+
+
+
+
+CHAPTER XVIII
+
+X-RAY, RADIUM, AND THE LIKE
+
+
+The camera sees things invisible to the human eye. Its most effective
+work is done with beams which are beyond human perception. The
+photographer uses the _Actinic_ rays. Ordinary light is composed of the
+seven primary colors, of which the lowest in the scale is the red, and
+the highest to violet.
+
+Those below the red are called the Infra-red, and they are the Hertzian
+waves, or those used in wireless telegraphy. Those above the violet are
+called Ultra-violet, and these are employed for X-ray work. The former
+are produced by the high tension electric apparatus, which we have
+described in the chapter relating to wireless telegraphy; and the
+latter, called also the Roentgen rays, are generated by the Crookes'
+Tube.
+
+This is a tube from which all the atmosphere has been extracted so that
+it is a practical vacuum. Within this are placed electrodes so as to
+divert the action of the electrical discharge in a particular direction,
+and this light, when discharged, is of such a peculiar character that
+its discovery made a sensation in the scientific world.
+
+The reason for this great wonder was not in the fact that it projected a
+light, but because of its character. Ordinary light, as we see it with
+the eye, is capable of being reflected, as when we look into a mirror at
+an angle. The X-ray will not reflect, but instead, pass directly through
+the glass.
+
+Then, ordinary light is capable of refraction. This is shown by a ray of
+light bending as it passes through a glass of water, which is noticed
+when the light is at an angle to the surface.
+
+The X-ray will pass through the water without being changed from a
+straight line. The foregoing being the case, it was but a simple step to
+conclude that if it were possible to find a means whereby the human eye
+could see within the ultra-violet beam, it would be possible to see
+through opaque substances.
+
+From the discovery so important and far reaching it was not long until
+it was found that if the ultra-violet rays, thus propagated, were
+transmitted through certain substances, their rates of vibration would
+be brought down to the speeds which send forth the visible rays, and now
+the eye is able to see, in a measure at least, what the actinic rays
+show.
+
+This discovery was but the forerunner of a still more important
+development, namely, the discovery of _radium_. The actual finding of
+the metal was preceded by the knowledge that certain minerals, and
+water, as well, possessed the property of radio-activity.
+
+Radio-activity is a word used to express that quality in metals or other
+material by means of which obscure rays are emitted, that have the
+capacity of discharging electrified bodies, and the power to ionize
+gases, as well as to actually affect photograph plates.
+
+Certain metals had this property to a remarkable degree, particularly
+uranium, thorium, polonium, actinium, and others, and in 1898 the
+Curies, husband and wife, French chemists, isolated an element, very
+ductile in its character, which was a white metal, and had a most
+brilliant luster.
+
+Pitchblende, the base metal from which this was extracted, was
+discovered to be highly radio-active, and on making tests of the product
+taken from it, they were surprised to find that it emitted a form of
+energy that far exceeded in calculations any computations made on the
+basis of radio-activity in the metals hitherto examined.
+
+But this was not the most remarkable part of the developments. The
+energy, whatever it was, had the power to change many other substances
+if brought into close proximity. It darkens the color of diamonds,
+quartz, mica, and glass. It changes some of the latter in color, some
+kinds being turned to brown and others into violet or purple tinges.
+
+Radium has the capacity to redden the skin, and affect the flesh of
+persons, even at some considerable distance, and it is a most powerful
+germicide, destroying bacteria, and has been found also to produce some
+remarkable cures in diseases of a cancerous nature.
+
+The remarkable similarity of the rays propagated by this substance, with
+the X-rays, lead many to believe that they are electrical in their
+character, and the whole scientific world is now striving to use this
+substance, as well as the more familiar light waves of the Roentgen
+tube, in the healing of diseases.
+
+It is not at all remarkable that this use of it should first be
+considered, as it has been the history of the electrical developments,
+from the earliest times, that each successive stage should find
+advocates who would urge its virtues to heal the sick.
+
+It was so when the dynamo was invented, when the high tension current
+was produced; and electrical therapeutics became a leading theme when
+transmission by induction became recognized as a scientific fact.
+
+It is not many years since the X-rays were discovered, and the first
+announcement was concerning its wonderful healing powers.
+
+This was particularly true in the case of radium, but for some reason,
+after the first tests, all experimenters were thwarted in their
+theories, because the science, like all others, required infinite
+patience and experience. It was discovered, in the case of the X-ray,
+that it must be used in a modified form, and accordingly, various
+modifications of the waves were introduced, called the _m_ and the _n_
+rays, as well as many others, each having some peculiar qualification.
+
+In time, no doubt, the investigators will find the right quality for
+each disease, and learn how to apply it. Thus, electricity, that most
+alluring thing which, in itself, cannot be seen, and is of such a
+character that it cannot even be defined in terms which will suit the
+exact scientific mind, is daily bringing new wonders for our
+investigation and use.
+
+It is, indeed, a study which is so broad that it has no limitations, and
+a field which never will be exhausted.
+
+THE END
+
+
+
+
+GLOSSARY OF WORDS
+USED IN TEXT OF THIS VOLUME
+
+
+Acid.             Accumulator material is sulphuric acid, diluted
+                    with water.
+
+Active            That part of the material in accumulator plates
+  Material.         which is acted upon by the electric current.
+
+Accumulator.      A cell, generally known as a storage battery, which
+                    while it initially receives a charge of electricity,
+                    is nevertheless, of such a character, owing to the
+                    active material of which it is made, that it
+                    accumulates, or, as it were, generates electricity.
+
+Aerial Wire,      The wire which, in wireless  telegraphy, is carried
+  or Conductor.     up into the air to connect the antennæ with the
+                    receiving and sending apparatus.
+
+Alarm, Burglar.   A circulating system in a building, connected up with
+                    a bell or other signaling means.
+
+Alloy.            A mixture of two or more metals; as copper and zinc
+                    to make brass; nickel and zinc to form German silver.
+
+Alternating Current. A current which goes back and forth in opposite
+                    directions, unlike a direct current which flows
+                    continuously in one direction over a wire.
+
+Alternation.      The term applied to a change in the direction of an
+                    alternating current, the frequency of the alternations
+                    ranging up to 20,000 or more vibrations per second.
+
+Amber.            A resin, yellow in color, which when rubbed with a
+                    cloth, becomes excited and gives forth negative
+                    electricity.
+
+Ammeter.          An instrument for measuring the quantity or flow of
+                    electricity.
+
+Ampere.           The unit of current; the term in which strength of
+                    the current is measured. An ampere is an
+                    electromotive force of one volt through a resistance
+                    of one ohm.
+
+Annunciator.      A device which indicates or signals a call given from
+                    some distant point.
+
+Anode.            The positive terminal in a conducting circuit, like
+                    the terminal of the carbon plate in a battery. It is
+                    a plate in an electroplating bath from which the
+                    current goes over to the cathode or negative plate or
+                    terminal.
+
+Arc.              A term employed to designate the gap, or the current
+                    which flows across between the conductors, like the
+                    space between the two carbons of an arc lamp, which
+                    gives the light.
+
+Armature.         A body of iron, or other suitable metal, which is in
+                    the magnetic field of a magnet.
+
+Armature Bar.     The piece which holds the armature. Also one of a
+                    series of bars which form the conductors in armature
+                    windings.
+
+Armature Coil.    The winding around an armature, or around the core
+                    of an armature.
+
+Armature Core.    The part in a dynamo or motor which revolves,
+                    and on which the wire coils are wound.
+
+Astatic (Galvanometer). That which has no magnetic action to direct
+                    or divert anything exterior to it.
+
+Atom.             The ultimate particle of an elementary substance.
+
+Attraction.       That property of matter which causes particles to
+                    adhere, or cohere, to each other. It is known under
+                    a variety of terms, such as gravitation, chemical
+                    affinity, electro-magnetism and dynamic attraction.
+
+Automatic Cut-out. A device which acts through the operation of the
+                    mechanism with which it is connected. It is usually
+                    applied to a device which cuts out a current when it
+                    overcharges or overloads the wire.
+
+Bath.             In electroplating, the vessel or tank which holds
+                    the electroplating solution.
+
+Battery.          A combination of two or more cells.
+
+Battery, Dry.     A primary battery in which the electrolyte is made
+                    in a solid form.
+
+Battery, Galvanic. A battery which is better known by the name of the
+                    Voltaic Pile, made up of zinc and copper plates
+                    which alternate, and with a layer of acidulated paper
+                    between each pair of plates.
+
+Battery, Storage.  A battery which accumulates
+                    electricity generated by a primary battery or a
+                    generator.
+
+Brush.            A term applied to the conducting medium that
+                    bears against the cylindrical surface of a commutator.
+
+Buzzer.           An electric call produced by a rapidly moving
+                    armature of an electro-magnet.
+
+Cable.            A number of wires or conductors assembled in one
+                    strand.
+
+Candle-power.     The amount of light given by the legal-standard
+                    candle. This standard is a sperm candle, which burns
+                    two grains a minute.
+
+Capacity.         The carrying power of a wire or circuit, without
+                    heating.  When heated there is an overload, or the
+                    _capacity_ of the wire is overtaxed.
+
+Capacity, Storage. The quantity of electricity in a secondary battery
+                    when fully charged, usually reckoned in ampere hours.
+
+Carbon.           A material, like coke, ground or crushed, and formed
+                    into sticks or plates by molding or compression. It
+                    requires a high heat to melt or burn, and is used as
+                    electrodes for arc lamps and for battery elements. It
+                    has poor conductivity, and for arc lamps is coated
+                    with copper to increase its conductivity.
+
+Cell, Electrolytic. A vessel containing an electrolyte for
+                    electroplating purposes.
+
+Charge.           The quantity of electricity on the surface of a body
+                    or conductor.
+
+Chemical Change.  When a current passes through electrodes in a
+                    solution, a change takes place which is chemical
+                    in its character. Adding sulphuric acid to water
+                    produces heat. If electrodes of opposite polarity are
+                    placed in such an acid solution, a chemical change is
+                    produced, which is transformed into electricity.
+
+Choking Coil.     An instrument in a circuit which by a form of
+                    resistance regulates the flow of the current, or
+                    returns part of it to the source of its generation.
+
+Counter-electromotive Force. Cells which are inserted in opposition to
+                    a battery to reduce high voltage.
+
+Circuit, Astatic. A circuit in an instrument so wound that the earth's
+                    magnetism will not affect it.
+
+Circuit Breaker.  Any instrument in a circuit which cuts out or
+                    interrupts the flow of a current.
+
+Circuit, External. A current flows through a wire or conductor,
+                  and also along the air outside of the conductor,
+                  the latter being the _external circuit._
+
+Circuit Indicator. An instrument, like a galvanometer, that shows
+                    the direction in which a current is flowing through
+                    a conductor.
+
+Circuit, Return.  Usually the ground return, or the negative wire from
+                    a battery.
+
+Circuit, Short.   Any connection between the mains or parallel lines
+                    of a circuit which does not go through the
+                    apparatus for which the circuit is intended.
+
+Coherer.          A tube, or other structure, containing normally
+                    high resistance particles which form a path or bridge
+                    between the opposite terminals of a circuit.
+
+Coil.             A wire, usually insulated, wound around a spool.
+
+Coil, Induction.  One of a pair of coils designed to change the
+                    voltage of a current of electricity, from a higher
+                    to a lower, or from a lower to a higher
+                    electro-motive force.
+
+Coil, Resistance. A coil so wound that it will offer a resistance
+                    to a steady current, or reduce the flow of electricity.
+
+Commutator.       A cylinder on the end of the armature of a dynamo
+                    or motor and provided with a pair of contact plates
+                    for each particular coil in the armature, in order
+                    to change the direction of the current.
+
+Compass.          An apparatus which indicates the direction or flow
+                    of the earth's magnetism.
+
+Condenser.        A device for storing up electro-static charges.
+
+Conductance.      That quality of a conductor to carry a current of
+                    electricity, dependent on its shape for the best
+                    results.
+
+Conduction.       The transmission of a current through a rod, wire
+                    or conductor.
+
+Conductivity.     That quality which has reference to the capacity
+                    to conduct a current.
+
+Conductor.        Any body, such as a bar, rod, wire, or machine,
+                    which will carry a current.
+
+Connector.        A binding post, clamp, screw, or other means to
+                    hold the end of a wire, or electric conductor.
+
+Contact.          To unite any parts in an electric circuit.
+
+Controller.       The handle of a switchboard, or other contact
+                    making and breaking means in a circuit.
+
+Converter.        An induction coil in an alternating circuit for
+                    changing potential difference, such as high
+                    alternating voltage into low direct current voltage.
+
+Convolution.      To wind like a clock spring.
+
+Core.             The inner portion of an electro-magnet. The inside
+                    part of an armature wound with wire.
+
+Core, Laminated.  When the core is built up of a number of separate
+                    pieces of the same material, but not insulated from
+                    each other.
+
+Coulomb.          The unit of electrical quantity. It is the quantity
+                    passed by a current of one ampere intensity in one
+                    second of time.
+
+Couple, Electric. Two or more electrodes in a liquid to produce an
+                    electric force.
+
+Current, Alternating. A natural current produced by the action of
+                    electro-magnets. It is a succession of short impulses
+                    in opposite directions.
+
+Current, Constant. A current which is uniformly maintained in a steady
+                    stream.
+
+Current, Induced.  A current produced by electro-dynamic induction.
+
+Current Meter.    An apparatus for indicating the strength of a current.
+                    An ammeter.
+
+Current, Oscillating. A current which periodically alternates.
+
+Current, Periodic. A periodically varying current strength.
+
+Current, Undulating. A current which has a constant direction,
+                    but has a continuously varying strength.
+
+Decomposition.    The separation of a liquid, such as an electrolyte,
+                    into its prime elements, either electrically or
+                    otherwise.
+
+Deflection.       The change of movement of a magnetic needle out of
+                    its regular direction of movement.
+
+Demagnetization.  When a current passes through a coil wound on an
+                    iron core, the core becomes magnetized. When the
+                    current ceases the core is no longer a magnet. It
+                    is then said to be _demagnetized_. It also has
+                    reference to the process for making a watch
+                    non-magnetic so that it will not be affected when
+                    in a magnetic field.
+
+Density.          The quantity of an electric charge in a
+                    conductor or substance.
+
+Depolarization.   The removal of magnetism from a permanent magnet,
+                    or a horse-shoe magnet, for instance. It is generally
+                    accomplished by applying heat.
+
+Deposition,       The act of carrying metal from one pole of a cell to
+  Electrolysis.     another pole, as in electroplating.
+
+Detector.         Mechanism for indicating the presence of a current
+                    in a circuit.
+
+Diaphragm.        A plate in a telephone, which, in the receiver, is
+                    in the magnetic field of a magnet, and in a
+                    transmitter carries the light contact points.
+
+Dielectric.       A non-conductor for an electric current, but through
+                    which electro-static induction will take place.
+                    For example: glass and rubber are dielectrics.
+
+Discharge.        The current flowing from an accumulator.
+
+Disintegration.   The breaking up of the plate or active material.
+
+Disruptive.       A static discharge passing through a dielectric.
+
+Duplex Wire.      A pair of wires usually twisted together and
+                    insulated from each other to form the conducting
+                    circuit of a system.
+
+Dynamic Electricity. The term applied to a current flowing through
+                    a wire.
+
+Dynamo.           An apparatus, consisting of core and field magnets,
+                    which, when the core is turned, will develop a
+                    current of electricity.
+
+Earth Returns.    Instead of using two wires to carry a circuit,
+                    the earth is used for what is called the _return_
+                    circuit.
+
+Efficiency.       The total electrical energy produced, in which that
+                    wasted, as well as that used, is calculated.
+
+Elasticity.       That property of any matter which, after a stress,
+                    will cause the substance to return to its original
+                    form or condition. Electricity has elasticity,
+                    which is utilized in condensers, as an instance.
+
+Electricity,      Lightning, and, in short, any current or electrical
+  Atmospheric.      impulse, like wireless telegraphic waves, is called
+                    _atmospheric_.
+
+Electricity,      Electricity with a low potentiality and large current
+   Voltaic.         density.
+
+Electrification.  The process of imparting a charge of electricity
+                    to any body.
+
+Electro-chemistry. The study of which treats of electric and chemical
+                    forces, such as electric plating, electric fusing,
+                    electrolysis, and the like.
+
+Electrode.        The terminals of a battery, or of any circuit; as,
+                    for instance, an arc light.
+
+Electrolyte.      Any material which is capable of being decomposed
+                    by an electric current.
+
+Electro-magnetism. Magnetism which is created by an electric current.
+
+Electrometer.     An instrument for measuring static electricity,
+                    differing from a galvanometer, which measures a
+                    current in a wire that acts on the magnetic needle
+                    of the galvanometer.
+
+Electro-motive    Voltage, which is the measure or unit of e. m. f.
+  Force. (E. M. F.)
+
+Electroscope.     A device for indicating not only the
+                    presence of electricity, but whether it is positive
+                    or negative.
+
+Electro-static    Surfaces separated by a dielectric for opposite
+  Accumulator.    charging of the surface.
+
+Element.          In electricity a form of matter, as, for instance,
+                    gold, or silver, that has no other matter or
+                    compound. Original elements cannot be separated,
+                    because they are not made up of two or more elements,
+                    like brass, for instance.
+
+Excessive Charge.  A storage battery charged at too high a rate.
+
+Excessive Discharge. A storage battery discharged at too high a rate.
+
+Excessive Overcharge. Charging for too long a time.
+
+Exciter.          A generator, either a dynamo or a battery, for
+                    exciting the field of a dynamo.
+
+Exhaustive Discharge. An excessive over-discharge of an accumulator.
+
+F.                The sign used to indicate the heat term Fahrenheit.
+
+Fall of Voltage.  The difference between the initial and the final
+                    voltage in a current.
+
+Field.            The space or region near a magnet or charged wire.
+                    Also the electro-magnets in a dynamo or motor.
+
+Flow.             The volume of a current going through a conductor.
+
+Force, Electro-magnetic. The pull developed by an electro-magnet.
+
+Frictional        A current produced by rubbing dissimilar
+  Electricity.      substances together.
+
+
+Full Load.        The greatest load a battery, accumulator or dynamo
+                    will sustain.
+
+Galvanic.         Pertaining to the electro-chemical relations of
+                    metals toward each other.
+
+Galvanizing.      The art of coating one metal with another, such,
+                    for instance, as immersing iron in molten zinc.
+
+Galvanometry.     An instrument having a permanently magnetized needle,
+                    which is influenced by a coil or a wire in close
+                    proximity to it.
+
+Galvanoscope.     An instrument, like a galvanometer, which determines
+                    whether or not a current is present in a tested wire.
+
+Generator.        A term used to generally indicate any device which
+                    originates a current.
+
+German Silver.    An alloy of copper, nickel and zinc.
+
+Graphite.         One form of carbon. It is made artificially by the
+                    electric current.
+
+Grid.             The metallic frame of a plate used to hold the active
+                    material of an accumulator.
+
+Gravity.          The attraction of mass for mass. Weight. The
+                    accelerating tendency of material to move toward the
+                    earth.
+
+Gutta Percha.     Caoutchouc, which has been treated with sulphur,
+                    to harden it. It is produced from the sap of
+                    tropical trees, and is a good insulator.
+
+Harmonic Receiver. A vibrating reed acted on by an electro-magnet,
+                    when tuned to its pitch.
+
+High E. M. F.     A term to indicate currents which have a high
+                    voltage, and usually low amperage.
+
+Igniter.          Mechanism composed of a battery, induction coil and
+                    a vibrator, for making a jump spark, to ignite gas,
+                    powder, etc.
+
+I. H. P.          Abbreviation, which means Indicated Horse Power.
+
+Impulse.          A sudden motion of one body acting against another.
+                    An electro-magnetic wave magnetizing soft iron,
+                    and this iron attracting another piece of iron, as an
+                    example.
+
+Incandescence,    A conductor heated up by a current so it will
+  Electric.         glow.
+
+Induced Current.  A current of electricity which sets up lines of
+                    force at right angles to the body of the wire
+                    through which the current is transmitted.
+
+Induction, Magnetic. A body within a magnetic field which is excited
+                    by the magnetism.
+
+Installation.     Everything belonging to an equipment of a building,
+                    or a circuiting system to do a certain thing.
+
+Insulation.       A material or substance which resists the passage
+                    of a current placed around a conductor.
+
+Intensity.        The strength of a magnetic field, or of a current
+                    flowing over a wire.
+
+Internal Resistance. The current strength of electricity of a wire
+                    to resist the passage.
+
+Interrupter.      A device in a wire or circuit for checking a
+                    current. It also refers to the vibrator of an
+                    induction coil.
+
+Joint.            The place where two or more conductors are united.
+
+Joint Resistance. The combined resistance offered by two or more
+                    substances or conductors.
+
+Jump Spark.       A spark, disruptive in its character, between two
+                    conducting points.
+
+Initial Charge.   The charge required to start a battery.
+
+Kathode, or Cathode. The negative plate or side of a battery. The
+                    plate on which the electro deposit is made.
+
+Key.              The arm of a telegraph sounder. A bar with a finger
+                    piece, which is hinged and so arranged that it will
+                    make and break contacts in an electric circuit.
+
+Keyboard.         A switch-board; a board on which is mounted a number
+                    of switches.
+
+Kilowatt.         A unit, representing 1,000 watts. An electric current
+                    measure, usually expressed thus: K.W.
+
+Kilowatt Hour.    The computation of work equal to the exertion of one
+                    kilowatt in one hour.
+
+Knife Switch.     A bar of a blade-like form, adapted to move down
+                    between two fingers, and thus establish metallic
+                    connections.
+
+Laminated.        Made up of thin plates of the same material, laid
+                    together, but not insulated from each other.
+
+Lamp Arc.         A voltaic arc lamp, using carbon electrodes, with
+                    mechanism for feeding the electrodes regularly.
+
+Lamp, Incandescent. A lamp with a filament heated up to a glow by the
+                    action of an electric current. The filament is within
+                    a vacuum in a glass globe.
+
+Leak.             Loss of electrical energy through a fault in wiring,
+                    or in using bare wires.
+
+Load.             The ampere current delivered by a dynamo under certain
+                    conditions.
+
+Low Frequency.    A current in which the vibrations are of
+                    few alternations per second.
+
+Magnet.           A metallic substance which has power to attract
+                    iron and steel.
+
+Magnet Bar.       A straight piece of metal.
+
+Magnet Coil.      A coil of wire, insulated, surrounding a core of
+                    iron, to receive a current of electricity.
+
+Magnet Core.      A bar of iron adapted to receive a winding of wire.
+
+
+Magnet, Field.    A magnet in a dynamo. A motor to produce electric
+                    energy.
+
+Magnet, Permanent. A short steel form, to hold magnetism for a long
+                    time.
+
+Magnetic Adherence. The adherence of particles to the
+                    poles of a magnet.
+
+Magnetic          That quality of a metal which draws metals. Also
+  Attraction and    the pulling action of unlike poles for each
+  Repulsion.        other, and pushing away of like poles when brought
+                    together.
+
+Magnetic Force.   The action exercised by a magnet of attracting
+                  or repelling.
+
+Magnetic Pole.    The earth has North and South magnetic poles.
+                    The south pole of a magnetic needle is attracted
+                    so it points to the north magnetic pole; and the north
+                    pole of the needle is attracted to point to the south
+                    magnetic pole.
+
+Magneto-generator. A permanent magnet and a revolving armature for
+                    generating a current.
+
+Maximum Voltage.  The final voltage after charging.
+
+Molecule.         Invisible particles made up of two or more atoms
+                    of different matter. An atom is a particle of one
+                    substance only.
+
+Morse Sounder.    An electric instrument designed to make a clicking
+                    sound, when the armature is drawn down by a
+                    magnet.
+
+Motor-dynamo.     A motor and a dynamo having their armatures
+                    connected together, whereby the motor is driven
+                    by the dynamo, so as to change the current into a
+                    different voltage and amperage.
+
+Motor-transformer. A motor which delivers the current like a generator.
+
+Needle.           A bar magnet horizontally poised on a vertical
+                    pivot point, like the needle of a mariner's compass.
+
+Negative          Amber, when rubbed, produces negative electricity.
+  Electricity.      A battery has positive as well as negative
+                    electricity.
+
+Negative Element. That plate in the solution of a battery
+                    cell which is not disintegrated.
+
+Normal.           The usual, or ordinary. The average. In a
+                    current the regular force required to do the work.
+
+North Pole,       The term applied to the force located near
+  Electric.        the north pole of the globe, to which a permanent
+                   magnet will point if allowed to swing freely.
+
+O.                Abbreviation for Ohm.
+
+Ohm.              The unit of resistance. Equal to the resistance of
+                    a column of mercury one square millimeter in cross
+                    section, and 106.24 centimeters in length.
+
+Ohm's Law.        It is expressed as follows:
+                  1. The current strength is equal to the electro-motive
+                       force divided by its 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.
+
+Overload.         In a motor an excess of mechanical work which causes
+                    the armature to turn too slowly and produces heat.
+
+Phase.            One complete oscillation. The special form of a
+                    wave at any instant, or at any interval of time.
+
+Plate, Condenser. In a static machine it is usually a plate of glass
+                    and revoluble.
+
+Plate, Negative.  The plate in a battery, such as carbon, copper or
+                    platinum, which is not attacked by the solution.
+
+Plating, Electro-. The method of coating one metal with another by
+                    electrolysis.
+
+Polarity.         The peculiarity, in a body, of arranging itself
+                    with reference to magnetic influence.
+
+Parallel.         When a number of cells are coupled so that their
+                    similar poles are grouped together. That is to say,
+                    as the carbon plates, for instance, are connected
+                    with one terminal, and all the zinc plates with the
+                    other terminal.
+
+Polarization.     When the cell is deprived of its electro-motive
+                    force, or any part of it, polarization is the result.
+                    It is usually caused by coating of the plates.
+
+Porosity.         Having small interstices or holes.
+
+Positive Current. One which deflects a needle to the left.
+
+Positive          Any current flowing from the active element,
+  Electricity.     such as zinc, in a battery. The negative
+                    electricity flows from the carbon to the zinc.
+
+Potential,
+  Electric.       The power which performs work in a circuit.
+
+Potential Energy. That form of force, which, when liberated, does or
+                    performs work.
+
+Power Unit.       The volt-amperes or watt.
+
+Primary.          The induction coil in induction machines, or in
+                    a transformer.
+
+Push Button.      A thumb piece which serves as a switch to
+                    close a circuit while being pressed inwardly.
+
+Quantity.         Such arrangement of electrical connections
+                    which give off the largest amount of current.
+
+Receiver.         An instrument in telephony and telegraphy which
+                    receives or takes in the sound or impulses.
+
+Relay.            The device which opens or closes a circuit so as to
+                    admit a new current which is sent to a more distant
+                    point.
+
+Repulsion,        That tendency in bodies to repel each other when
+  Electric.         similarly charged.
+
+Resilience.       The springing back to its former condition or
+                    position. Electricity has resilience.
+
+Resistance.       The quality in all conductors to oppose the passage
+                    of a current.
+
+Resistance Coil.  A coil made up of wire which prevents the passage
+                    of a current to a greater or less degree.
+
+Resistance,       The counter force in an electrolyte which seeks
+  Electrolytic.     to prevent a decomposing current to pass through it.
+
+Resistance: Internal, The opposing force to the movement of a current
+  External.         which is in the cell or generator. This is called the
+                     _internal_. That opposite action outside of the cell
+                    or generator is the _external_.
+
+Resonator,        An open-circuited conductor for electrically
+  Electric.         resounding or giving back a vibration, usually
+                   exhibited by means of a spark.
+
+Rheostat.         A device which has an adjustable resistance, so
+                    arranged that while adjusting the same the circuit
+                    will not be open.
+
+Safety Fuse.      A piece of fusible metal of such resistance that
+                    it breaks down at a certain current strength.
+
+Saturated.        When a liquid has taken up a soluble material
+                    to the fullest extent it is then completely saturated.
+
+Secondary.        One of the two coils in a transformer, or induction
+                    coil.
+
+Secondary Plates. The brown or deep red plates in a storage battery
+                    when charged.
+
+Self-excited.     Producing electricity by its own current.
+
+Series.           Arranged in regular order. From one to the other
+                    directly. If lamps, for instance, should be arranged
+                    in circuit on a single wire, they would be in series.
+
+Series, Multiple. When lamps are grouped in sets in parallel,
+                    and these sets are then connected up in series.
+
+Series Windings.  A generator or motor wound in such a manner that
+                    one of the commutator brush connections is joined
+                    to the field magnet winding, and the other end of
+                    the magnet winding joined to the outer circuit.
+
+Shunt.            Going around.
+
+Shunt Winding.    A dynamo in which the field winding is parallel with
+                    the winding of the armature.
+
+Snap Switch.      A switch so arranged that it will quickly make a
+                    break.
+
+Sounder.          The apparatus at one end of a line actuated by a key
+                    at the other end of the line.
+
+Spark Coil.       A coil, to make a spark from a low electro-motive
+                    force.
+
+Spark, Electric.  The flash caused by drawing apart the ends of a
+                    conductor.
+
+Specific Gravity. The weight or density of a body.
+
+Static Electricity. Generated by friction. Also lightning.
+                    Any current generated by a high electro-motive force.
+
+Strength of Current. The quantity of electricity in a circuit.
+
+Synchronize.      Operating together; acting in unison.
+
+Terminal.         The end of any electric circuit or of a body
+                    or machine which has a current passing through it.
+
+Thermostat, Electric. An electric thermometer. Usually made
+                    with a metal coil which expands through the action
+                    of the electricity passing through it, and, in
+                    expanding, it makes a contact and closes a circuit.
+
+Transformer.      The induction coil with a high initial E. M. F.
+                    changes into a low electro-motive force.
+
+Unit.             A standard of light, heat, electricity, or of
+                    other phenomena.
+
+Vacuum.           A space from which all matter has been exhausted.
+
+Vibrator.         Mechanism for making and breaking circuits in
+                    induction coils or other apparatus.
+
+Volt.             The unit of electro-motive force.
+
+Voltage.          Electro-motive force which is expressed in volts.
+
+Voltaic.          A term applied to electric currents and devices.
+
+Volt-meter.       An apparatus for showing the difference of
+                    potential, or E.  M. F. in the term of volts.
+
+Watt.             The unit of electrical activity. The product of
+                    amperes multiplied by volts.
+
+Watt Hour.        One watt maintained through one hour of time.
+
+Waves, Electric   Waves in the ether caused by electro-magnetic
+  Magnetic.         disturbances.
+
+X-rays.           The radiation of invisible rays of light, which
+                    penetrate or pass through opaque substances.
+
+Yoke, or Bar.     A soft iron body across the ends of a
+                    horseshoe magnet, to enable the magnet to retain its
+                    magnetism an indefinite time.
+
+Zinc Battery.     A battery which uses zinc for one of its elements.
+
+
+
+
+INDEX
+
+A
+
+Accumulated, 31.
+
+Accumulation, 29.
+
+Accumulator cell, 87.
+
+Accumulators, 82, 88, 89.
+
+Accumulators, plates, 83.
+
+Acid, 34, 37, 125.
+
+Acid maker, 125.
+
+Acid, sulphuric, 31, 84.
+
+Acidulated, 55.
+
+Acidulated water, 34.
+
+Acoustics, 110.
+
+Actinic rays, 184, 185.
+
+Actinium, 186.
+
+Active element, 82.
+
+Adjustable rod, 107.
+
+Adjusting screw, 70, 71, 72, 73, 106.
+
+Aerial wire, 108.
+
+Agents, 13, 32.
+
+Alarms, burglar, 11, 76, 80.
+
+Alkali, 125.
+
+Alkaline, 37.
+
+Alternate, 127.
+
+Alternating, 38, 149, 150, 153, 154, 155, 156.
+
+Alternating current, 145.
+
+Alternating periods, 149.
+
+Alternations, 147.
+
+Aluminum, 128, 129, 135, 137.
+
+Aluminum hydrate, 129.
+
+Amber, 5, 171.
+
+Ammeter, 7, 88.
+
+Amperage, 38, 61, 62, 132, 159, 160, 168.
+
+Ampere, 7, 37, 60, 63, 139, 140, 167.
+
+Amplitude, 111.
+
+Annunciator, 65, 74, 76, 79, 80, 81.
+
+Annunciator bells, 11.
+
+Anode, 35, 133, 134.
+
+Antennæ, 108.
+
+Antimony 137, 143.
+
+Anvil, 13, 14.
+
+Apparatus, 11, 57, 106, 139, 145.
+
+Arc, 163, 182.
+
+Arc lighting, 38, 165.
+
+Arc system, 166.
+
+Armature, 18, 25, 38, 40, 42, 43, 45, 46, 47, 48, 53, 55, 70, 72, 73,
+        74, 90, 93, 112, 151, 152, 155, 163, 176, 177, 178, 179, 180.
+
+Armature brush, 48.
+
+Armature post, 71.
+
+Armature, vertical, 75.
+
+Armature winding, 42, 43, 156.
+
+Asbestos, 140.
+
+Astatic galvanometer, 108.
+
+Atmosphere, 184.
+
+Attract, 30.
+
+Attracted, 72.
+
+Attraction, 21, 25.
+
+Attractive, 178.
+
+Automatic, 120.
+
+Auxiliary, 44.
+
+Awls, 14.
+
+
+B
+
+Bacteria, 126, 187.
+
+Bar, cross, 66.
+
+Bar, horizontal, 46.
+
+Bar, parallel switch, 67.
+
+Bar, switch, 65, 68.
+
+Base block, 66.
+
+Batteries, 11, 93, 122.
+
+Battery, 29, 30, 32, 35, 36, 46, 47, 80, 81, 82, 83, 85, 86, 88, 92, 94,
+          95, 107, 108, 116, 117, 118, 121, 134, 142.
+
+Battery charging, 82.
+
+Bearings, 45, 46.
+
+Bells, 65, 73, 76, 122.
+
+Bells, electric, 70.
+
+Bench, 13, 15, 17.
+
+Binding post, 52, 70, 71, 72, 103, 107, 108, 121.
+
+Binding screw, 65, 66.
+
+Bismuth, 18, 143.
+
+Bit, 13.
+
+Blue vitriol, 57.
+
+Brass plate, 77, 78.
+
+Brazing, 17, 65.
+
+Bridge, 52.
+
+Brush holder, 46.
+
+Brushes, 48, 150, 151, 153, 167.
+
+Burglar, 11.
+
+Burglar alarm, 76, 80.
+
+Buttons, contact, 80.
+
+Buttons, push, 65, 68, 69, 70, 76, 79.
+
+
+C
+
+Calorimeter, 56.
+
+Cancerous, 187.
+
+Candle power, 89, 139.
+
+Cap, removable, 73.
+
+Cap screws, 42.
+
+Carbon, 35, 119, 121, 162, 163, 169.
+
+Carbon block, 120.
+
+Carbon pencil, 119.
+
+Cathode, 35, 36, 133, 134.
+
+Cell, 29, 33.
+
+Cell, accumulator, 87.
+
+Cell, charging, 87.
+
+Channel, 43.
+
+Channel, concave, 40.
+
+Charged, 120.
+
+Charged battery, 82.
+
+Charging circuit, 82, 89.
+
+Charging source, 83.
+
+Charged wire, 147.
+
+Chemical, 57.
+
+Chisels, 13.
+
+Chloride of lime, 84.
+
+Choked, 157.
+
+Choking coils, 145, 146, 156, 158.
+
+Circuit, 33, 69, 73, 76, 78, 80, 81, 90, 92, 93, 109, 113, 116, 121,
+         122, 131, 134, 143, 156.
+
+Circuit, primary, 99.
+
+Circuit, secondary, 99.
+
+Circuiting, 81, 155.
+
+Circuiting system, 79.
+
+Clapper arm, 70.
+
+Closed rings, 26.
+
+Coherer, 105, 108, 109.
+
+Cohering, 106.
+
+Coils, 18, 26, 52, 55, 74, 160.
+
+Coils, choking, 145, 146, 156, 158.
+
+Coils, induction, 99, 102.
+
+Coils, primary, 109.
+
+Coils, secondary, 102, 109.
+
+Coincide, 42.
+
+Cold, 14.
+
+Collecting surfaces, 30.
+
+Collector, 31.
+
+Column, 61.
+
+Combustion, 169.
+
+Commutator, 44, 46, 151, 152.
+
+Commutator brushes, 46.
+
+Commutator plates, 45.
+
+Compass, 22, 24, 172.
+
+Composition, 83, 124.
+
+Compound wound, 47.
+
+Concave channel, 40.
+
+Condenser, 98, 100, 101, 102, 108.
+
+Conduct, 6, 108.
+
+Conduction, 135, 136, 138, 166, 170.
+
+Conduction current, 27.
+
+Conductor, 21, 31, 33, 63, 98, 116, 161, 162.
+
+Conduit, 72.
+
+Conically formed, 126.
+
+Conjunction, 143.
+
+Connecting wire, 58.
+
+Connection, 72, 76.
+
+Construction, magnet, 39.
+
+Consumption, 180.
+
+Contact, 122, 123, 152, 162.
+
+Contact finger, 150.
+
+Contact plate, 67, 68, 79.
+
+Contact screws, 93.
+
+Contact surface, 66.
+
+Continuous, 145.
+
+Converter, 176.
+
+Converting, 142, 145, 146.
+
+Copper, 18, 34, 36, 65, 66, 132, 133, 134, 135, 136, 137, 142, 143.
+
+Copper cyanide, 133.
+
+Copper plate, 33, 35, 58, 67.
+
+Copper sulphate, 57.
+
+Copper voltameter, 55, 57.
+
+Core, 27, 28, 36, 39, 40, 115.
+
+Core, magnet, 75, 93.
+
+Counter, clock-wise, 51.
+
+Coupled, 36.
+
+Crank, 30.
+
+Crookes' tube, 184.
+
+Cross bar, 52, 66.
+
+Crown of cups, 32.
+
+Crystal, 85.
+
+Current, 6, 7, 13, 18, 26, 27, 28, 35, 36, 37, 38, 47, 50, 51, 52, 55,
+  56, 57, 58, 59, 62, 63, 70, 72, 73, 90, 95, 98, 105, 108, 116, 133, 134,
+  135, 136, 138, 139, 140, 141, 142, 143, 147, 148, 149, 150, 152, 153,
+  157, 160, 161, 163, 165, 166, 170.
+
+Current, alternating, 150.
+
+Current changing, 82.
+
+Current conduction, 27.
+
+Current, continuous, 164.
+
+Current, direct, 145, 150.
+
+Current direction, 50.
+
+Current, exterior, 50, 150.
+
+Current, reversing, 148.
+
+Current strength, 7, 57.
+
+Current testing, 143.
+
+Cut-out, 120.
+
+Cutter, 14.
+
+Cutting, lines of force, 38.
+
+Cylinder, 44.
+
+Cylindrical, 43.
+
+
+D
+
+Dash, 95, 97.
+
+Decoherer, 106, 108.
+
+Decomposed, 57, 128.
+
+Decomposes, 55.
+
+Decomposing, 123.
+
+Decomposition, 12, 35, 82.
+
+Deflected, 54.
+
+Degree, 135, 162.
+
+Demagnetized, 24, 72.
+
+Deposited, 58, 133.
+
+Depression, 15, 140.
+
+Detecting current, 49.
+
+Detector, 49, 52, 54, 105.
+
+Devices, measuring, 27.
+
+Diagrams, 46, 48, 79, 89.
+
+Diagrammatically, 81.
+
+Diamagnetic, 19.
+
+Diametrically, 114.
+
+Diaphragm, 112, 113, 116, 120, 122.
+
+Diamonds, 186.
+
+Diluted, 86.
+
+Direct current, 38, 140.
+
+Direction of current, 50.
+
+Direction of flow, 98.
+
+Discharge, 172.
+
+Disintegrate, 132.
+
+Disk, 43.
+
+Dissimilar, 37.
+
+Disturbance, 176.
+
+Dividers, 14.
+
+Divisibility, 168.
+
+Dot, 96, 97.
+
+Dot and dash, 96.
+
+Double click, 95.
+
+Double line, 65.
+
+Double-pole switch, 65.
+
+Double-throw switch, 117.
+
+Drawing, 20.
+
+Drill, ratchet, 13.
+
+Drops, 81.
+
+Ductile, 186.
+
+Duplex wire, 115.
+
+Dynamo, 7, 27, 38, 42, 46, 48, 62, 82, 83, 87, 89, 132, 141, 142, 145,
+       150, 155, 161, 165, 167, 175, 176, 180, 187.
+
+Dynamo fields, 40, 41.
+
+
+E
+
+Earth, 22.
+
+Elasticity, 100, 142.
+
+Electric, 6, 31, 49, 50, 76, 78, 81, 131, 142, 158, 162, 173, 176.
+
+Electric arc, 63, 163.
+
+Electric bell, 19, 69, 70, 71, 72, 106, 117.
+
+Electric bulbs, 167.
+
+Electric circuit, 118.
+
+Electric fan, 55.
+
+Electric field, 76.
+
+Electric hand purifier, 129.
+
+Electric heating, 135, 137, 161.
+
+Electric iron, 130, 141.
+
+Electric lamp socket, 139.
+
+Electric light, 56, 66.
+
+Electric lighting, 161.
+
+Electric power, 113.
+
+Electric welding, 183.
+
+Electrical, 8, 11, 65, 96, 98, 104, 141, 159, 180, 184, 187.
+
+Electrical impulses, 105, 147, 148.
+
+Electrical manifestations, 175.
+
+Electrically, 32, 70.
+
+Electricity, 5, 6, 7, 8, 9, 12, 13, 18, 21, 26, 27, 28, 29, 38, 49, 54,
+     60, 61, 62, 82, 97, 98, 100, 104, 110, 112, 116, 123, 124, 133, 134,
+    136, 138, 145, 146, 147, 154, 156, 160, 166, 170, 171, 172, 175, 182,
+    187.
+
+Electricity measuring, 49.
+
+Electricity, thermo-, 142.
+
+Electrified, 37, 186.
+
+Electro-chemical, 55.
+
+Electrode, 35, 124, 127, 128, 161, 162, 163, 164, 165, 184.
+
+Electrolysis, 7, 123, 126, 132.
+
+Electrolyte, 33, 35, 36, 57, 86, 88, 123, 132, 142.
+
+Electrolytic, 55, 123, 125.
+
+Electro-magnet, 59, 78.
+
+Electro-magnetic, 7, 24, 25, 29, 37, 55, 92, 93, 94.
+
+Electro-magnetic force, 7.
+
+Electro-magnetic rotation, 7.
+
+Electro-magnetic switch, 116.
+
+Electro-meter, 7.
+
+Electro-motive force, 37, 63, 99.
+
+Electroplate, 12, 38, 48, 123, 132, 134.
+
+Electro-positive-negative, 142, 143.
+
+Elements, 36, 83.
+
+Engine energy, 170, 180.
+
+Equidistant, 127.
+
+Ether, 104.
+
+Example, 61.
+
+Excited, 47.
+
+Extension plate, 103.
+
+Exterior, 3.
+
+Exterior magnetic, 27.
+
+External, 37.
+
+External circuit, 153.
+
+External current, 50.
+
+External resistance, 37.
+
+
+F
+
+Factor, 61.
+
+Ferrous oxide, 125.
+
+Field, 46, 47.
+
+Field, dynamo, 40, 41.
+
+Field magnet cores, 155.
+
+Field, magnetic, 38.
+
+Field of force, 33.
+
+Field wire, 48.
+
+Filament, 168, 169, 170.
+
+Filter, 128.
+
+Flat iron, 140.
+
+Flocculent, 128.
+
+Force, 50.
+
+Formulated, 19.
+
+Friction, 32.
+
+Frictional, 6, 7, 29.
+
+Fuse, 169.
+
+
+G
+
+Galvani, 7.
+
+Galvanic, 7, 23, 30.
+
+Galvanometer, 7, 49, 108, 143.
+
+Galvanoscope, 55, 58, 59.
+
+Gaseous, 128.
+
+Gasoline, 99.
+
+Gas stove, 17.
+
+Gelatine, 128.
+
+Generate, 29, 38, 134, 136, 145.
+
+Generated, 55.
+
+Generating, 32, 134.
+
+Generation, 170.
+
+Generator, 32, 125, 147.
+
+German silver, 136, 137.
+
+Germicide, 187.
+
+Gimlets, 17.
+
+Glass, 30, 86, 126, 186.
+
+Gold, 135.
+
+Grid, 84.
+
+Ground circuit, 121.
+
+Gunpowder, 6.
+
+
+H
+
+Hack-saw, 14.
+
+Hammer, 13.
+
+Heart-shaped switch, 77.
+
+Heater, 136.
+
+Heating, 13, 38.
+
+Hertzian rays, 170.
+
+Hertzian wave, 184.
+
+High tension, 38, 102, 184.
+
+High tension apparatus, 98.
+
+High tension coils, 103.
+
+High voltage, 158.
+
+Horizontal bar, 46.
+
+Horseshoe magnet, 22, 24, 175.
+
+Hydrate of aluminum, 129.
+
+Hydrogen, 35, 123, 125, 128.
+
+
+I
+
+Igniting, 99.
+
+Illumination, 162, 163, 165, 167, 170.
+
+Immersed, 133.
+
+Impulses, 60, 62, 96, 104, 109, 152, 179.
+
+Incandescent, 166, 168.
+
+Induced, 28.
+
+Inductance, 149, 150.
+
+Induction, 27, 37, 98, 147.
+
+Induction coils, 99, 102, 106.
+
+Influences, 178.
+
+Initial charge, 88.
+
+Insulated, 27, 28, 40, 43, 52, 55, 73, 115, 151, 180.
+
+Insulating, 66, 69, 120, 140, 164.
+
+Insulating material, 114.
+
+Insulation, 40, 116.
+
+Instruments, 49, 94, 112, 118, 120.
+
+Instruments, measuring, 8.
+
+Intensity, 55, 60, 104, 154.
+
+Interior, magnetic, 23.
+
+Internal resistance, 37.
+
+Interruption, 102, 103.
+
+Installation, 168.
+
+Ionize, 186.
+
+Iron, 19, 132, 133, 136, 142, 171.
+
+Isolated, 186.
+
+
+J
+
+Jar, 29, 31, 32.
+
+Journal, 46.
+
+Journal block, 16, 146.
+
+Jump spark, 99.
+
+
+K
+
+Key, 90, 91, 95.
+
+Key, sending, 90.
+
+Knob, 32.
+
+Knob, terminal, 31.
+
+
+L
+
+Laboratory, 9.
+
+Lead, 31, 136.
+
+Lead, precipitated, 83, 85.
+
+Lead, red, 83, 84.
+
+Lever switching, 67.
+
+Light, 104.
+
+Light method, 56.
+
+Lighting, 9, 38.
+
+Lighting circuit, 48.
+
+Lighting system, 82.
+
+Lightning, 6, 171, 172, 173.
+
+Lightning rod, 173.
+
+Lime, chloride of, 84.
+
+Line of force, 146.
+
+Line wire, 122.
+
+Line, magnetic, 22, 23.
+
+Liquid, 32.
+
+Litharge, 83.
+
+Loadstone, 17.
+
+Locomotives, 165.
+
+Low tension, 38, 98, 102, 179.
+
+
+M
+
+Magnet bar, 20.
+
+Magnet core, 16, 75, 93.
+
+Magnet, electro, 59, 78.
+
+Magnet, horseshoe, 22, 25, 175.
+
+Magnet lines, 22, 23.
+
+Magnet, permanent, 25, 38, 46, 50, 172.
+
+Magnet, reversed, 20.
+
+Magnet, steel, 53.
+
+Magnet, swinging, 53.
+
+Magnetic, 7, 19, 20, 21, 22, 25, 113, 178.
+
+Magnetic construction, 39.
+
+Magnetic exterior, 27.
+
+Magnetic field, 22, 24, 27, 38, 50, 112, 146, 148, 155.
+
+Magnetic interior, 23.
+
+Magnetic pull, 59.
+
+Magnetic radiator, 37.
+
+Magnetism, 19, 54, 104, 110, 159, 171.
+
+Magnetized, 18, 25, 27, 50.
+
+Magnetized wire, 146.
+
+Magnets, 13, 14, 18, 19, 20, 21, 22, 23, 24, 25, 39, 51, 53, 54, 70, 71,
+       73, 75, 81, 90, 93, 112, 113, 115, 147, 150, 163, 176, 177, 178.
+
+Main conductor, 31.
+
+Mandrel, 15, 16.
+
+Manganese, 19.
+
+Manifestations, 19.
+
+Mariner, 172.
+
+Material, non-conducting, 90.
+
+Maximum, 154.
+
+Measure, 55, 56, 60, 62.
+
+Measurement, 62.
+
+Measuring devices, 27.
+
+Measuring instruments, 8.
+
+Mechanism, 47, 180.
+
+Medical batteries, 99.
+
+Mercury, 63, 169.
+
+Metal base, 73.
+
+Mica, 186.
+
+Microphone, 118, 119, 120.
+
+Millimeter, 63.
+
+Minus, 34.
+
+Minus sign, 21.
+
+Morse code, 76.
+
+Motor, 7, 21, 27, 46, 47, 62, 82, 99, 150, 176, 180.
+
+Mouthpiece, 115.
+
+Mouthpiece rays, 188.
+
+Moving field, 117.
+
+Multiple, 168.
+
+Musical scale, 111.
+
+
+N
+
+Negative, 21, 35, 36, 68, 83, 86, 87, 94, 125, 151, 152, 154, 165, 177,
+    178, 179.
+
+Neutral, 125.
+
+Neutral plate, 84.
+
+Nickel, 136.
+
+Nickel plating, 132.
+
+Nitrate of silver, 62.
+
+Nitrogen, 126.
+
+Non-conducting material, 90.
+
+Non-conductor, 164.
+
+Non-magnetic, 19.
+
+North pole, 20, 21, 22, 23, 25, 50, 54, 156.
+
+Number plate, 75.
+
+N-ray, 188.
+
+
+O
+
+Ohms, 60, 63.
+
+Ohms, international, 63.
+
+Ohms law, 7.
+
+Operator, 95, 118.
+
+Oscillating, 99, 105.
+
+Osmium, 169.
+
+Oxides, 125.
+
+Oxidizing, 183.
+
+Oxygen, 35, 123, 125, 126, 128, 129, 169.
+
+
+P
+
+Packing ring, 124.
+
+Paraffine, 56, 100, 101, 102.
+
+Paraffine wax, 86.
+
+Parallel, 87, 88, 89.
+
+Parallel switch bar, 67.
+
+Parallel wires, 28, 49.
+
+Partition, 124.
+
+Peon, 13.
+
+Percolate, 128.
+
+Periodicity, 159.
+
+Periods of alternations, 149.
+
+Permanent, 18, 19, 50.
+
+Permanent magnet, 25, 38, 46, 50, 172.
+
+Phase, 19.
+
+Phenomenon, 27, 65.
+
+Photograph, 186.
+
+Physical, 21.
+
+Pile, voltaic, 33.
+
+Pipe, 61.
+
+Pitchblende, 186.
+
+Pivot pin, 53.
+
+Pivotal, 22.
+
+Plane, 13.
+
+Plate, 57, 93.
+
+Plate, contact, 67, 68, 79.
+
+Plate, copper, 33, 35, 58, 67.
+
+Plate, negative, 84.
+
+Plate, number, 75.
+
+Plate, positive, 84, 88.
+
+Plate, zinc, 33.
+
+Platinum, 13, 57, 137.
+
+Pliers, 14.
+
+Plus sign, 21, 24.
+
+Pointer, 53.
+
+Polarity, 154, 177, 178, 179.
+
+Polarization, 35.
+
+Pole, north, 20, 21, 22, 23, 25, 50, 54, 156.
+
+Pole piece, 40, 42.
+
+Pole, south, 20, 21, 22, 25, 50, 54, 156.
+
+Poles, 177, 179.
+
+Polonium, 186.
+
+Porcelain, 86.
+
+Porous, 85.
+
+Positive, 4, 21, 25, 36, 40, 68, 83, 86, 87, 94, 123, 125, 151, 152,
+   153, 155, 165.
+
+Post, binding, 52, 71.
+
+Potentiality, 105, 109.
+
+Power, 38, 186.
+
+Power, candle, 89, 139.
+
+Precipitate of lead, 83, 85.
+
+Precision, 7.
+
+Pressure, 87.
+
+Primary, 35, 62, 98, 134, 142, 159, 184.
+
+Primary battery, 7, 99.
+
+Primary circuit, 99.
+
+Primary coil, 106, 109.
+
+Prime conductor, 6.
+
+Projected, 185.
+
+Propagated, 105, 185.
+
+Properties, 55.
+
+Purification, 123, 128.
+
+Purifier, 126, 131.
+
+Push button, 65, 68, 69, 70, 76, 79.
+
+
+Q
+
+Quantity, 55, 60, 61, 138.
+
+Quartz, 186.
+
+
+R
+
+Radio-activity, 186.
+
+Radium, 184, 185, 187, 188.
+
+Ratchet drill, 13.
+
+Reaction, 148.
+
+Receiver, 12, 90, 97, 121, 122.
+
+Receiving station, 109.
+
+Rectangular, 69.
+
+Rectifiers, 146.
+
+Red lead, 83, 84.
+
+Reel, 13.
+
+Reflected, 185.
+
+Refraction, 185.
+
+Refractory, 182.
+
+Register, 57.
+
+Removable, 54.
+
+Removable cap, 73.
+
+Repel, 20.
+
+Repulsion, 21, 128.
+
+Reservoir, 61, 62.
+
+Resiliency, 99.
+
+Resistance, 7, 36, 37, 60, 63, 99, 135, 136, 137, 138, 140, 141, 156,
+   157, 163, 166, 168.
+
+Resistance bridge, 7.
+
+Resistance, external, 37.
+
+Resistance, internal, 37.
+
+Rheostat, 7.
+
+Reversed, 20, 50, 153.
+
+Reversible, 163.
+
+Reversing, 176.
+
+Reversing switch, 67.
+
+Revolubly, 46.
+
+Revolve, 179.
+
+Revolving, 177.
+
+Roentgen rays, 184.
+
+Roentgen tube, 187.
+
+Rotation, 149.
+
+Rubber, 40, 46, 77, 115, 126, 130, 138.
+
+
+S
+
+Sad-irons, 13.
+
+Saline, 133.
+
+Sanitation, 12.
+
+Saturated, 85.
+
+Screw, 15.
+
+Screw, binding, 65, 66.
+
+Screw-driver, 14.
+
+Screw, set, 72.
+
+Sealing wax, 53.
+
+Secondary, 62, 98, 105, 158, 159, 160.
+
+Secondary circuit, 99.
+
+Secondary coil, 107, 108.
+
+Self-induction, 149, 156.
+
+Sender, 90, 97.
+
+Sending apparatus, 106.
+
+Sending key, 90.
+
+Separately excited, 46.
+
+Series-wound, 47.
+
+Severed magnet, 20.
+
+Sewage, 12.
+
+Shaft, 30.
+
+Shears, 14, 17.
+
+Shellac, 40.
+
+Shunt-wound, 47.
+
+Signal, 118.
+
+Silver, 19, 63, 125.
+
+Silver nitrate, 62.
+
+Socket, 54, 139.
+
+Soldering, 14.
+
+Soldering iron, 17.
+
+Solution, 55, 57, 62, 63, 84, 86, 133, 134, 142.
+
+Sounder, 90, 92, 95, 96.
+
+Sounding board, 119.
+
+Source, charging, 83.
+
+South pole, 20, 21, 22, 25, 50, 54, 156.
+
+Spark gap, 102, 106.
+
+Spark jump, 99.
+
+Spring finger, 69.
+
+Square, 14, 17.
+
+Standard, 62, 63.
+
+Station, 94, 95, 117, 122.
+
+Steel, 18, 19.
+
+Steel magnet, 53.
+
+Sterilized, 12.
+
+Stirrup, 75.
+
+Stock bit, 13.
+
+Stock contact, 121.
+
+Storage, 82.
+
+Storage battery, 107.
+
+Storing, 82.
+
+Substances, 135.
+
+Sulphate, 55, 128, 133.
+
+Sulphur, 19.
+
+Sulphuric acid, 31, 84.
+
+Sulphuric acid voltameter, 55, 57.
+
+Superstition, 171, 173.
+
+Surging, 153, 154.
+
+Swinging magnet, 53.
+
+Swinging switch blade, 67.
+
+Switch blades, 66.
+
+Switches, 65, 66, 70, 77, 78, 90, 117.
+
+Switches, bar, 65, 68, 90, 91.
+
+Switches, bar, parallel, 67.
+
+Switches, heart-shaped, 78.
+
+Switches, piece, 77.
+
+Switches, reversing, 67.
+
+Switches, sliding, 67, 80.
+
+Switches, terminal, 8.
+
+Switches, two-pole, 65.
+
+System, circuiting, 79.
+
+
+T
+
+Tail-piece, 16.
+
+Tantalum, 169.
+
+Telegraph, 11, 90, 96.
+
+Telegraph key, 106.
+
+Telegraph sounder, 108, 109.
+
+Telegraphing, 94.
+
+Telephone, 12, 110, 113, 117, 118, 119, 120.
+
+Telephone circuit, 118.
+
+Telephone connections, 116.
+
+Telephone hook, 122.
+
+Temperature, 56, 88, 134, 161, 170.
+
+Tension, high, 38, 102, 184.
+
+Tension, low, 38, 98, 102, 179.
+
+Terminal, 31, 34, 35, 40, 48, 82, 86, 93, 95, 107, 116, 121, 122, 151,
+    152, 153, 154, 156.
+
+Terminal knob, 31.
+
+Terminal, secondary, 102.
+
+Terminal switch, 81.
+
+Theoretical, 160.
+
+Therapeutics, 187.
+
+Thermo-electric couples, 146.
+
+Thermo-electricity, 135.
+
+Thermometer, 56.
+
+Thorium, 169, 186.
+
+Thunderbolt, 171, 173.
+
+Tin, 136.
+
+Tinfoil, 31, 101.
+
+Tools, 11, 13, 17.
+
+Torch, brazing, 17.
+
+Transformer, 145, 146, 158, 159, 180, 182.
+
+Transformer, step-down, 182.
+
+Transmission, 38, 187.
+
+Transmit, 63, 95, 157.
+
+Transmitter, 12, 120, 121, 122, 123.
+
+Transverse, 16, 52.
+
+Transversely, 43.
+
+Trigger, 75.
+
+Tripod, 31.
+
+Tubular, 44, 45.
+
+Two-pole switch, 65.
+
+
+U
+
+Ultra-violet, 185.
+
+Uranium, 186.
+
+
+V
+
+Vacuum, 184.
+
+Vapor lamps, 169.
+
+Velocity, 60, 73.
+
+Vertical armature, 75.
+
+Vibration, 110, 111, 113.
+
+Vibratory, 110.
+
+Vise, 13.
+
+Voltage, 37, 38, 60, 61, 62, 63, 87, 88, 99, 147, 154, 165, 180, 182.
+
+Voltage, high, 158.
+
+Voltaic, 29, 32.
+
+Voltaic pile, 33.
+
+Voltameter, 7, 58, 88.
+
+Voltameter, sulphuric, acid, 55, 57.
+
+Volts, 60, 62, 87, 89, 132, 158, 159.
+
+
+W
+
+Water, 123, 138, 144.
+
+Water power, 142.
+
+Watts, 60, 61, 160.
+
+Wave lengths, 104, 110.
+
+Weight, 49.
+
+Welding, 13, 182.
+
+Winding, 18, 40, 47, 58, 159, 196.
+
+Winding reel, 14.
+
+Window connection, 76.
+
+Window frame, 78.
+
+Wire, 6, 18, 21, 26, 28, 156.
+
+Wire, circuiting, 79.
+
+Wire coil, 40.
+
+Wire lead, 70.
+
+Wire, parallel, 28, 49.
+
+Wireless, 12.
+
+Wireless telegraphy, 103, 104, 184.
+
+Wiring, 80.
+
+Wiring, window, 77.
+
+Workshop, 11, 17.
+
+Wound, compound, 48.
+
+Wound-series, 47.
+
+Wound-shunt, 47.
+
+
+X
+
+X-ray, 184, 185, 187, 188.
+
+
+Z
+
+Zinc, 17, 34, 35, 85, 135.
+
+Zinc plates, 33.
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+
+CARPENTRY FOR BOYS
+
+A book which treats, in a most practical and fascinating manner all
+subjects pertaining to the "King of Trades"; showing the care and use of
+tools; drawing; designing, and the laying out of work; the principles
+involved in the building of various kinds of structures, and the
+rudiments of architecture. It contains over two hundred and fifty
+illustrations made especially for this work, and includes also a
+complete glossary of the technical terms used in the art. The most
+comprehensive volume on this subject ever published for boys.
+
+
+ELECTRICITY FOR BOYS
+
+The author has adopted the unique plan of setting forth the fundamental
+principles in each phase of the science, and practically applying the
+work in the successive stages. It shows how the knowledge has been
+developed, and the reasons for the various phenomena, without using
+technical words so as to bring it within the compass of every boy. It
+has a complete glossary of terms, and is illustrated with two hundred
+original drawings.
+
+
+PRACTICAL MECHANICS FOR BOYS
+
+This book takes the beginner through a comprehensive series of practical
+shop work, in which the uses of tools, and the structure and handling of
+shop machinery are set forth; how they are utilized to perform the work,
+and the manner in which all dimensional work is carried out. Every
+subject is illustrated, and model building explained. It contains a
+glossary which comprises a new system of cross references, a feature
+that will prove a welcome departure in explaining subjects. Fully
+illustrated.
+
+
+_Price 60 cents per volume_
+
+THE NEW YORK BOOK COMPANY
+147 FOURTH AVENUE  NEW YORK
+
+
+
+
+ +-----------------------------------------------------------------+
+ | Transcriber's Note.                                             |
+ |                                                                 |
+ | Every effort has been made to replicate this text as faithfully |
+ | as possible, including obsolete and variant spellings and other |
+ | inconsistencies.                                                |
+ |                                                                 |
+ | Minor punctuation and printing errors have been corrected.      |
+ |                                                                 |
+ | The first page of the original book is an advertisement. The    |
+ | page was moved to the end of the text.                          |
+ |                                                                 |
+ | Some hyphenation inconsistencies in the text were retained:     |
+ |    16-candle-power and 16-candlepower,                          |
+ |    Electromotive and electro-motive,                            |
+ |    Electro-meter and Electrometer,                              |
+ |    Horseshoe and horse-shoe,                                    |
+ |    Switchboard and switch-board,                                |
+ |                                                                 |
+ |  Two occurrences of 'Colorimeter' for 'Calorimeter' repaired.   |
+ +-----------------------------------------------------------------+
+
+
+
+
+
+End of the Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
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+    <meta name="author" content="J. S. Zerbe, M.E." />
+    <meta name="DC.Creator" content="J. S. Zerbe, M.E." />
+    <meta name="DC.Title" content="Electricity For Boys" />
+    <meta name="DC.Date" content="2007" />
+    <meta name="DC.Language" content="en" />
+    <title>
+      The Project Gutenberg eBook of Electricity for Boys, by J. S. Zerbe, M.E.
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+
+The Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: Electricity for Boys
+
+Author: J. S. Zerbe
+
+Release Date: September 25, 2007 [EBook #22766]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELECTRICITY FOR BOYS ***
+
+
+
+
+Produced by Joe Longo and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+
+
+<h2>WARNING: This book of one hundred years ago describes<br />
+experiments which are too dangerous to attempt by either<br />
+adults or children. It is published for historical<br />
+interest only.<br /><br /><br /></h2>
+
+
+
+
+
+<h1 class="smcap">The "How-to-do-it" Books</h1>
+
+<hr class="minor" />
+
+<h1>ELECTRICITY FOR BOYS</h1>
+
+<div class="figcenter" style="width: 617px;margin-bottom:2em">
+<a id="fig1" name="fig1"></a>
+<img src="images/illus-fig1.png" width="617" height="316" alt="Fig. 1. WORK BENCH" title="Fig. 1. WORK BENCH" />
+<span class="caption"><i>Fig. 1.</i> WORK BENCH</span>
+</div>
+
+<div class="center">
+<table width="450" style="page-break-before: always;" cellpadding="2" cellspacing="0" border="1">
+  <col style="width:80%;" />
+  <tr>
+    <td align="center">
+<br /><br />
+<p class="titleblock" style="margin-top: 2px; font-weight: 600;
+ margin-bottom: .5em; font-variant: small-caps; word-spacing: 0.4em; font-size: 145%;">THE "HOW-TO-DO-IT" BOOKS</p>
+<p class="titleblock" style="font-size: 180%; margin-top: 2px; font-weight: 600; margin-bottom: 1em;">
+ELECTRICITY FOR BOYS</p>
+
+<table width="70%" cellpadding="2" cellspacing="0" border="0">
+<tr>
+<td align="left">
+<p>A working guide, in the successive
+steps of electricity, described in
+simple terms
+</p>
+<p class="titleblock"
+style="word-spacing: 0.4em; letter-spacing: 0.08em; margin-top: 1em; margin-bottom: 2em; font-size: 90%;">
+WITH MANY ORIGINAL ILLUSTRATIONS</p>
+</td>
+</tr>
+</table>
+
+<p class="titleblock" style="margin-top: 0em; font-size: 120%;">By J. S. ZERBE, M.E.</p>
+
+<p class="titleblock" style="margin-top: 2em; margin-bottom: 0em; font-size: 80%;">AUTHOR OF</p>
+<p class="titleblock" style="margin-top: .25em; margin-bottom: 3em; font-size: 80%;">
+CARPENTRY FOR BOYS<span style="margin-left:4em">PRACTICAL MECHANICS FOR BOYS</span>
+</p>
+
+
+<div class="figcenter" style="width: 119px;">
+<img src="images/nybc.png" width="119" height="116"
+alt="Printer's Mark: NYBC/Windmill" title="Printer's Mark: NYBC/Windmill" />
+</div>
+
+<p class="titleblock" style="margin-top: 3em; font-size: 90%; margin-bottom: 0em;">THE NEW YORK BOOK COMPANY</p>
+<p class="titleblock" style="font-variant: small-caps; margin-top: 0px; font-size: 90%; margin-bottom: 2em;">New York</p>
+    </td>
+  </tr>
+</table>
+</div>
+
+<p class="center" style="margin-top: 2em;" >
+<span class="smcap" style="font-size: 80%;">Copyright, 1914, by</span>
+<br /><span style="font-size: 80%;">THE NEW YORK BOOK COMPANY</span>
+</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="pi" id="pi">p. i</a></span></p>
+<h3><a name="toc" id="toc"></a>CONTENTS</h3>
+
+<table border="0" width="76%" cellpadding="1" cellspacing="0" summary="Contents">
+  <col style="width:5%;" /><col style="width:80%;" /><col style="width:15%;" />
+<tbody valign="top">
+    <tr>
+ <td align="right">&nbsp;</td>
+      <td class="chap">Introductory</td>
+      <td class="pr"><a href="#INTRODUCTORY">Page 1</a></td>
+    </tr>
+    <tr>
+      <td class="chap" colspan="2">&nbsp;</td>
+      <td class="pr">&nbsp;</td>
+    </tr>
+<tr>
+ <td align="right">I.</td>
+ <td class="chap">Electricity Considered. Brief Historical Events</td>
+ <td class="pr"><a href="#CHAPTER_I">Page 5</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>The Study of Electricity. First Historical Accounts. Bottling
+Electricity. Discovery of Galvanic Electricity. Electro-motive Force.
+Measuring Instruments. Rapidity of Modern Progress. How to Acquire the
+Vast Knowledge. The Means Employed.</p></td>
+</tr>
+<tr>
+ <td align="right">II.</td>
+ <td class="chap">What Tools and Apparatus are Needed</td>
+ <td class="pr"><a href="#CHAPTER_II">Page 11</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Preparing the Workshop. Uses of Our Workshop. What
+to Build. What to Learn. Uses of the Electrical Devices.
+Tools. Magnet-winding Reel.</p></td>
+</tr>
+<tr>
+ <td align="right">III.</td> <td class="chap">Magnets, Coils, Armatures, Etc.</td> <td class="pr"><a href="#CHAPTER_III">Page 18</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>The Two Kinds of Magnets. Permanent Magnets. Electro-Magnets.
+Magnetism. Materials for Magnets. Non-magnetic
+Material. Action of a <i>Second</i> Magnet. What
+North and South Pole Mean. Repulsion and Attraction.
+Positives and Negatives. Magnetic Lines of Force.
+The Earth as a Magnet. Why the Compass Points North
+and South. Peculiarity of a Magnet. Action of the
+Electro-Magnet. Exterior Magnetic Influence Around a
+Wires Carrying a Current. Parallel Wires.</p></td>
+</tr>
+<tr>
+ <td align="right">IV.</td> <td class="chap">Frictional, Voltaic or Galvanic and Electro-magnetic Electricity</td> <td class="pr"><a href="#CHAPTER_IV">Page 29</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Three Electrical Sources. Frictional Electricity. Leyden
+<span class='pagenum'><a name="pii" id="pii">p. ii</a></span>Jar. Voltaic or Galvanic Electricity. Voltaic Pile;
+How Made. Plus and Minus Signs. The Common
+Primary Cell. Battery Resistance. Electrolyte and
+Current. Electro-magnetic Electricity. Magnetic Radiation.
+Different Kinds of Dynamos. Direct Current
+Dynamos. Simple Magnet Construction. How to Wind.
+The Dynamo Fields. The Armature. Armature Windings.
+Mounting the Armature. The Commutator. Commutator
+Brushes. Dynamo Windings. The Field.
+Series-wound Field. Shunt-wound. Compound-wound.</p></td>
+</tr>
+<tr>
+ <td align="right">V.</td> <td class="chap">How to Detect and Measure Electricity</td> <td class="pr"><a href="#CHAPTER_V">Page 49</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Measuring Instruments. The Detector. Direction of
+Current. Simple Current Detector. How to Place the
+Detector. Different Ways to Measure a Current. The
+Sulphuric Acid Voltameter. The Copper Voltameter.
+The Galvanoscope Electro-magnetic Method. The Calorimeter.
+The Light Method. The Preferred Method.
+How to Make a Sulphuric Acid Voltameter. How to
+Make a Copper Voltameter. Objections to the Calorimeter.</p></td>
+</tr>
+<tr>
+ <td align="right">VI.</td> <td class="chap">Volts, Amperes, Ohms and Watts</td> <td class="pr"><a href="#CHAPTER_VI">Page 60</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Understanding Terms. Intensity and Quantity. Voltage.
+Amperage Meaning of Watts and Kilowatt. A
+Standard of Measurement. The Ampere Standard. The
+Voltage Standard. The Ohm. Calculating the Voltage.</p></td>
+</tr>
+<tr>
+ <td align="right">VII.</td> <td class="chap">Push Buttons, Switches, Annunciators, Bells and Like Apparatus</td> <td class="pr"><a href="#CHAPTER_VII">Page 65</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Simple Switches. A Two-Pole Switch. Double-Pole
+Switch. Sliding Switch. Reversing Switch. Push Buttons.
+<span class='pagenum'><a name="piii" id="piii">p. iii</a></span>Electric Bells. How Made. How Operated. Annunciators.
+Burglar Alarm. Wire Circuiting. Circuiting
+System with Two Bells and Push Buttons. The
+Push Buttons, Annunciators and Bells. Wiring Up a
+House.</p></td>
+</tr>
+<tr>
+ <td align="right">VIII.</td> <td class="chap">Accumulators, Storage or Secondary Batteries</td> <td class="pr"><a href="#CHAPTER_VIII">Page 82</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Storing Up Electricity. The Accumulator. Accumulator
+Plates. The Grid. The Negative Pole. Connecting Up
+the Plates. Charging the Cells. The Initial Charge.
+The Charging Current.</p></td>
+</tr>
+<tr>
+ <td align="right">IX.</td> <td class="chap">The Telegraph</td> <td class="pr"><a href="#CHAPTER_IX">Page 90</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Mechanism in Telegraph Circuit. The Sending Key. The
+Sounder. Connecting Up the Key and Sounder. Two
+Stations in Circuit. The Double Click. Illustrating
+the Dot and the Dash. The Morse Telegraph Code. Example
+in Use.</p></td>
+</tr>
+<tr>
+ <td align="right">X.</td> <td class="chap">High-tension Apparatus, Condensers, Etc.</td> <td class="pr"><a href="#CHAPTER_X">Page 98</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Induction. Low and High Tension. Elastic Property of
+Electricity. The Condenser. Connecting up a Condenser.
+The Interrupter. Uses of High-tension Coils.</p></td>
+</tr>
+<tr>
+ <td align="right">XI.</td> <td class="chap">Wireless Telegraphy</td> <td class="pr"><a href="#CHAPTER_XI">Page 104</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Telegraphing Without Wires. Surging Character of
+High-tension Currents. The Coherer. How Made. The
+Decoherer. The Sending Apparatus. The Receiving
+Apparatus. How the Circuits are Formed.</p></td>
+</tr>
+<tr>
+ <td align="right">XII.</td> <td class="chap">The Telephone</td> <td class="pr"><a href="#CHAPTER_XII">Page 110</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Vibrations. The Acoustic Telephone. Sound Waves.
+<span class='pagenum'><a name="piv" id="piv">p. iv</a></span>Hearing Electricity. The Diaphragm in a Magnetic
+Field. A Simple Telephone Circuit. How to Make a
+Telephone. Telephone Connections. Complete Installation.
+The Microphone. Light Contact Points. How to
+Make a Microphone. Microphone, the Father of the
+Transmitter. Automatic Cut-outs for Telephones. Complete
+Circuiting with Transmitters.</p></td>
+</tr>
+<tr>
+ <td align="right">XIII.</td> <td class="chap">Electrolysis, Water Purification, Electroplating</td> <td class="pr"><a href="#CHAPTER_XIII">Page 123</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Decomposing Liquids. Making Hydrogen and Oxygen.
+Purifying Water. Rust. Oxygen as a Purifier. Composition
+of Water. Common Air Not a Good Purifier.
+Pure Oxygen a Water Purifier. The Use of Hydrogen
+in Purification. Aluminum Electrodes. Electric
+Hand Purifier. Purification and Separation of Metals.
+Electroplating. Plating Iron with Copper. Direction of
+Current.</p></td>
+</tr>
+<tr>
+ <td align="right">XIV.</td> <td class="chap">Electric Heating. Thermo-Electricity</td> <td class="pr"><a href="#CHAPTER_XIV">Page 135</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Generating Heat in a Wire. Resistance of Substances.
+Signs of Connectors. Comparison of Metals. A Simple
+Electric Heater. How to Arrange for Quantity of Current
+Used. An Electric Iron. Thermo-Electricity Converting
+Heat Directly into Electricity Metals. Electric,
+Positive, Negative. Thermo-electric Coupler.</p></td>
+</tr>
+<tr>
+ <td align="right">XV.</td> <td class="chap">Alternating Currents, Choking Coil, Transformer</td> <td class="pr"><a href="#CHAPTER_XV">Page 145</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Direct Current. Alternating Current. The Magnetic
+Field. Action of a Magnetized Wire. The Movement of
+a Current in a Charged Wire. Current Reversing Itself.
+Self-Induction. Brushes in a Direct Current Dynamo:
+<span class='pagenum'><a name="pv" id="pv">p. v</a></span>Alternating, Positive and Negative Poles. How an Alternating
+Current Dynamo is Made. The Windings.
+The Armature Wires. Choking Coils. The Transformer.
+How the Voltage is Determined. Voltage and Amperage
+in Transformers.</p></td>
+</tr>
+<tr>
+ <td align="right">XVI.</td> <td class="chap">Electric Lighting</td> <td class="pr"><a href="#CHAPTER_XVI">Page 161</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Early conditions. Fuels. Reversibility of Dynamo.
+Electric arc. Mechanism to maintain the arc. Resistance
+coil. Parallel carbons for making arc. Series
+current. Incandescent system. Multiple circuit. Subdivision
+of electric light. The filament. The glass
+bulb. Metallic filaments. Vapor lamps. Directions
+for improvements. Heat in electric lighting. Curious
+superstitions concerning electricity. Magnetism. Amber.
+Discovery of the properties of a magnet. Electricity
+in mountain regions. Early beliefs as to magnetism
+and electricity. The lightning rod. Protests
+against using it. Pliny's explanation of electricity.</p></td>
+</tr>
+<tr>
+ <td align="right">XVII.</td> <td class="chap">Power, and Various Other Electrical Manifestations</td> <td class="pr"><a href="#CHAPTER_XVII">Page 175</a></td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>Early beliefs concerning the dynamo. Experiments
+with magnets. Physical action of dynamo and motor.
+Electrical influence in windings. Comparing motor
+and dynamo. How the current acts in a dynamo. Its
+force in a motor. Loss in power transmission. The
+four ways in which power is dissipated. Disadvantages
+of electric power. Its advantages. Transmission of
+energy. High voltages. The transformer. Step-down
+transformers. Electric furnaces. Welding by electricity.
+Merging the particles of the joined ends.</p></td>
+</tr>
+<tr>
+ <td align="right">XVIII.</td> <td class="chap">X-Ray, Radium and the Like</td> <td class="pr"><a href="#CHAPTER_XVIII">Page 184</a>
+<span class='pagenum'><a name="pvi" id="pvi">p. vi</a></span>
+</td>
+</tr>
+<tr>
+ <td class="abstract" colspan="3"><p>The camera and the eye. Actinic rays. Hertzian
+waves. High-tension apparatus. Vacuum tubes. Character
+of the ultra-violet rays. How distinguished.
+The infra-red rays. Their uses. X-rays not capable
+of reflection. Not subject to refraction. Transmission
+through opaque substances. Reducing rates of vibration.
+Radium. Radio-activity. Radio-active materials.
+Pitchblende. A new form of energy. Electrical source.
+Healing power. Problems for scientists.</p></td>
+</tr>
+<tr>
+ <td class="chap" colspan="2">Glossary of Words Used in the Text</td> <td class="pr"><a href="#GLOSSARY_OF_WORDS">Page 189</a>
+</td>
+</tr>
+<tr>
+ <td class="chap" colspan="2">Index</td> <td class="pr"><a href="#INDEX">Page 207</a>
+</td>
+</tr>
+  </tbody>
+</table>
+
+<p class="chapter"><span class='pagenum'><a name="pvii" id="pvii">p. vii</a></span></p>
+
+
+<hr class="chapter" />
+<h3><a name="toi" id="toi"></a>LIST OF ILLUSTRATIONS</h3>
+
+<table border="0" width="76%" cellpadding="1" cellspacing="1" summary="Illustrations">
+  <col style="width:10%;" /><col style="width:75%;" /><col style="width:15%;" />
+<tbody valign="top">
+<tr><td align="right">1.</td>
+<td align="left"> Work bench</td>
+  <td class="pr"><a href="#fig1">Frontispiece</a></td>
+</tr>
+    <tr>
+      <td align="right">&nbsp;</td>
+      <td class="imgr">&nbsp;</td>
+      <td class="pr" style="font-size: small;">PAGE</td>
+    </tr>
+<tr><td align="right">2.</td>
+<td align="left">Top of magnet-winding reel</td>
+  <td class="pr"><a href="#fig2">14</a></td>
+</tr>
+<tr><td align="right">3.</td>
+<td align="left">Side of magnet-winding reel</td>
+  <td class="pr"><a href="#fig3">14</a></td>
+</tr>
+<tr><td align="right">4.</td>
+<td align="left">Journal block</td>
+  <td class="pr"><a href="#fig4">15</a></td>
+</tr>
+<tr><td align="right">5.</td>
+<td align="left">Plain magnet bar</td>
+  <td class="pr"><a href="#fig5">19</a></td>
+</tr>
+<tr><td align="right">6.</td>
+<td align="left">Severed magnet</td>
+  <td class="pr"><a href="#fig6">20</a></td>
+</tr>
+<tr><td align="right">7.</td>
+<td align="left">Reversed magnets</td>
+  <td class="pr"><a href="#fig7">21</a></td>
+</tr>
+<tr><td align="right">8.</td>
+<td align="left">Horseshoe magnet</td>
+  <td class="pr"><a href="#fig8">22</a></td>
+</tr>
+<tr><td align="right">9.</td>
+<td align="left">Earth's magnetic lines</td>
+  <td class="pr"><a href="#fig9">23</a></td>
+</tr>
+<tr><td align="right">10.</td>
+<td align="left">Two permanent magnets</td>
+  <td class="pr"><a href="#fig10">24</a></td>
+</tr>
+<tr><td align="right">11.</td>
+<td align="left">Magnets in earth's magnetic field</td>
+  <td class="pr"><a href="#fig11">24</a></td>
+</tr>
+<tr><td align="right">12.</td>
+<td align="left">Armatures for magnets</td>
+  <td class="pr"><a href="#fig12">25</a></td>
+</tr>
+<tr><td align="right">13.</td>
+<td align="left">Magnetized field</td>
+  <td class="pr"><a href="#fig13">26</a></td>
+</tr>
+<tr><td align="right">14.</td>
+<td align="left">Magnetized bar</td>
+  <td class="pr"><a href="#fig14">26</a></td>
+</tr>
+<tr><td align="right">15.</td>
+<td align="left">Direction of current</td>
+  <td class="pr"><a href="#fig15">27</a></td>
+</tr>
+<tr><td align="right">16.</td>
+<td align="left">Direction of induction current</td>
+  <td class="pr"><a href="#fig16">28</a></td>
+</tr>
+<tr><td align="right">17.</td>
+<td align="left">Frictional-electricity machine</td>
+  <td class="pr"><a href="#fig17">30</a></td>
+</tr>
+<tr><td align="right">18.</td>
+<td align="left">Leyden jar</td>
+  <td class="pr"><a href="#fig18">32</a></td>
+</tr>
+<tr><td align="right">19.</td>
+<td align="left">Galvanic electricity. Crown of cups</td>
+  <td class="pr"><a href="#fig19">33</a></td>
+</tr>
+<tr><td align="right">20.</td>
+<td align="left">Voltaic electricity</td>
+  <td class="pr"><a href="#fig20">34</a></td>
+</tr>
+<tr><td align="right">21.</td>
+<td align="left">Primary battery</td>
+  <td class="pr"><a href="#fig21">36</a></td>
+</tr>
+<tr><td align="right">22.</td>
+<td align="left">Dynamo field and pole piece</td>
+  <td class="pr"><a href="#fig22">39</a></td>
+</tr>
+<tr><td align="right">23.</td>
+<td align="left">Base and fields assembled</td>
+  <td class="pr"><a href="#fig23">41</a></td>
+</tr>
+<tr><td align="right">24.</td>
+<td align="left">Details of the armature, core</td>
+  <td class="pr"><a href="#fig24">42</a></td>
+</tr>
+<tr><td align="right">25.</td>
+<td align="left">Details of the armature, body</td>
+  <td class="pr"><a href="#fig25">42</a></td>
+</tr>
+<tr><td align="right">26.</td>
+<td align="left">Armature Journals</td>
+  <td class="pr"><a href="#fig26">43</a>
+<span class='pagenum'><a name="pviii" id="pviii">p. viii</a></span>
+</td>
+</tr>
+<tr><td align="right">27.</td>
+<td align="left">Commutator</td>
+  <td class="pr"><a href="#fig27">43</a></td>
+</tr>
+<tr><td align="right">28.</td>
+<td align="left">End view of armature, mounted</td>
+  <td class="pr"><a href="#fig28">44</a></td>
+</tr>
+<tr><td align="right">29.</td>
+<td align="left">Top view of armature on base</td>
+  <td class="pr"><a href="#fig29">45</a></td>
+</tr>
+<tr><td align="right">30.</td>
+<td align="left">Field winding</td>
+  <td class="pr"><a href="#fig30-31">47</a></td>
+</tr>
+<tr><td align="right">31.</td>
+<td align="left">Series-wound</td>
+  <td class="pr"><a href="#fig30-31">47</a></td>
+</tr>
+<tr><td align="right">32.</td>
+<td align="left">Shunt-wound</td>
+  <td class="pr"><a href="#fig32-33">48</a></td>
+</tr>
+<tr><td align="right">33.</td>
+<td align="left">Compound-wound</td>
+  <td class="pr"><a href="#fig32-33">48</a></td>
+</tr>
+<tr><td align="right">34.</td>
+<td align="left">Compass magnet, swing to the right</td>
+  <td class="pr"><a href="#fig34-36">50</a></td>
+</tr>
+<tr><td align="right">35.</td>
+<td align="left">Magnetic compass</td>
+  <td class="pr"><a href="#fig34-36">50</a></td>
+</tr>
+<tr><td align="right">36.</td>
+<td align="left">Magnet, swing to the left</td>
+  <td class="pr"><a href="#fig34-36">50</a></td>
+</tr>
+<tr><td align="right">37.</td>
+<td align="left">Indicating direction of current</td>
+  <td class="pr"><a href="#fig37">51</a></td>
+</tr>
+<tr><td align="right">38.</td>
+<td align="left">The bridge of the detector</td>
+  <td class="pr"><a href="#fig38">52</a></td>
+</tr>
+<tr><td align="right">39.</td>
+<td align="left">Details of detector</td>
+  <td class="pr"><a href="#fig39">53</a></td>
+</tr>
+<tr><td align="right">40.</td>
+<td align="left">Cross-section of detector</td>
+  <td class="pr"><a href="#fig40">54</a></td>
+</tr>
+<tr><td align="right">41.</td>
+<td align="left">Acid voltameter</td>
+  <td class="pr"><a href="#fig41">56</a></td>
+</tr>
+<tr><td align="right">42.</td>
+<td align="left">Copper voltameter</td>
+  <td class="pr"><a href="#fig42">56</a></td>
+</tr>
+<tr><td align="right">43.</td>
+<td align="left">Two-pole switch</td>
+  <td class="pr"><a href="#fig43">66</a></td>
+</tr>
+<tr><td align="right">44.</td>
+<td align="left">Double-pole switch</td>
+  <td class="pr"><a href="#fig44">66</a></td>
+</tr>
+<tr><td align="right">45.</td>
+<td align="left">Sliding switch</td>
+  <td class="pr"><a href="#fig45">67</a></td>
+</tr>
+<tr><td align="right">46.</td>
+<td align="left">Rheostat form of switch</td>
+  <td class="pr"><a href="#fig46">68</a></td>
+</tr>
+<tr><td align="right">47.</td>
+<td align="left">Reversing switch</td>
+  <td class="pr"><a href="#fig47">69</a></td>
+</tr>
+<tr><td align="right">48.</td>
+<td align="left">Push button</td>
+  <td class="pr"><a href="#fig48">70</a></td>
+</tr>
+<tr><td align="right">49.</td>
+<td align="left">Electric bell</td>
+  <td class="pr"><a href="#fig49">71</a></td>
+</tr>
+<tr><td align="right">50.</td>
+<td align="left">Armature of electric bell</td>
+  <td class="pr"><a href="#fig50">72</a></td>
+</tr>
+<tr><td align="right">51.</td>
+<td align="left">Vertical section of annunciator</td>
+  <td class="pr"><a href="#fig51-54">72</a></td>
+</tr>
+<tr><td align="right">52.</td>
+<td align="left">Front view of annunciator</td>
+  <td class="pr"><a href="#fig51-54">72</a></td>
+</tr>
+<tr><td align="right">53.</td>
+<td align="left">Horizontal section of annunciator</td>
+  <td class="pr"><a href="#fig51-54">72</a></td>
+</tr>
+<tr><td align="right">54.</td>
+<td align="left">Front plate of annunciator</td>
+  <td class="pr"><a href="#fig51-54">72</a></td>
+</tr>
+<tr><td align="right">55.</td>
+<td align="left">Alarm switch on window</td>
+  <td class="pr"><a href="#fig55">76</a></td>
+</tr>
+<tr><td align="right">56.</td>
+<td align="left">Burglar alarm on window</td>
+  <td class="pr"><a href="#fig56">76</a></td>
+</tr>
+<tr><td align="right">57.</td>
+<td align="left">Burglar alarm contact</td>
+  <td class="pr"><a href="#fig57">77</a></td>
+</tr>
+<tr><td align="right">58.</td>
+<td align="left">Neutral position of contact</td>
+  <td class="pr"><a href="#fig58">78</a></td>
+</tr>
+<tr><td align="right">59.</td>
+<td align="left">Circuiting for electric bell</td>
+  <td class="pr"><a href="#fig59">79</a>
+<span class='pagenum'><a name="pix" id="pix">p. ix</a></span></td>
+</tr>
+<tr><td align="right">60.</td>
+<td align="left">Annunciators in circuit</td>
+  <td class="pr"><a href="#fig60">80</a></td>
+</tr>
+<tr><td align="right">61.</td>
+<td align="left">Wiring system for a house</td>
+  <td class="pr"><a href="#fig61">80</a></td>
+</tr>
+<tr><td align="right">62.</td>
+<td align="left">Accumulator grids</td>
+  <td class="pr"><a href="#fig62">83</a></td>
+</tr>
+<tr><td align="right">63.</td>
+<td align="left">Assemblage of accumulator grids</td>
+  <td class="pr"><a href="#fig63">85</a></td>
+</tr>
+<tr><td align="right">64.</td>
+<td align="left">Connecting up storage battery in series</td>
+  <td class="pr"><a href="#fig64">87</a></td>
+</tr>
+<tr><td align="right">65.</td>
+<td align="left">Parallel series</td>
+  <td class="pr"><a href="#fig65">88</a></td>
+</tr>
+<tr><td align="right">66.</td>
+<td align="left">Charging circuit</td>
+  <td class="pr"><a href="#fig66">88</a></td>
+</tr>
+<tr><td align="right">67.</td>
+<td align="left">Telegraph sending key</td>
+  <td class="pr"><a href="#fig67">91</a></td>
+</tr>
+<tr><td align="right">68.</td>
+<td align="left">Telegraph sounder</td>
+  <td class="pr"><a href="#fig68">92</a></td>
+</tr>
+<tr><td align="right">69.</td>
+<td align="left">A telegraph circuit</td>
+  <td class="pr"><a href="#fig69">94</a></td>
+</tr>
+<tr><td align="right">70.</td>
+<td align="left">Induction coil and circuit</td>
+  <td class="pr"><a href="#fig70">99</a></td>
+</tr>
+<tr><td align="right">71.</td>
+<td align="left">Illustrating elasticity</td>
+  <td class="pr"><a href="#fig71">100</a></td>
+</tr>
+<tr><td align="right">72.</td>
+<td align="left">Condenser</td>
+  <td class="pr"><a href="#fig72">101</a></td>
+</tr>
+<tr><td align="right">73.</td>
+<td align="left">High-tension circuit</td>
+  <td class="pr"><a href="#fig73">102</a></td>
+</tr>
+<tr><td align="right">74.</td>
+<td align="left">Current interrupter</td>
+  <td class="pr"><a href="#fig74">103</a></td>
+</tr>
+<tr><td align="right">75.</td>
+<td align="left">Wireless-telegraphy coherer</td>
+  <td class="pr"><a href="#fig75">105</a></td>
+</tr>
+<tr><td align="right">76.</td>
+<td align="left">Wireless sending-apparatus</td>
+  <td class="pr"><a href="#fig76">107</a></td>
+</tr>
+<tr><td align="right">77.</td>
+<td align="left">Wireless receiving-apparatus</td>
+  <td class="pr"><a href="#fig77">108</a></td>
+</tr>
+<tr><td align="right">78.</td>
+<td align="left">Acoustic telephone</td>
+  <td class="pr"><a href="#fig78">111</a></td>
+</tr>
+<tr><td align="right">79.</td>
+<td align="left">Illustrating vibrations</td>
+  <td class="pr"><a href="#fig79">111</a></td>
+</tr>
+<tr><td align="right">80.</td>
+<td align="left">The magnetic field</td>
+  <td class="pr"><a href="#fig80">112</a></td>
+</tr>
+<tr><td align="right">81.</td>
+<td align="left">Section of telephone receiver</td>
+  <td class="pr"><a href="#fig81">114</a></td>
+</tr>
+<tr><td align="right">82.</td>
+<td align="left">The magnet and receiver head</td>
+  <td class="pr"><a href="#fig82">115</a></td>
+</tr>
+<tr><td align="right">83.</td>
+<td align="left">Simple telephone connection</td>
+  <td class="pr"><a href="#fig83">116</a></td>
+</tr>
+<tr><td align="right">84.</td>
+<td align="left">Telephone stations in circuit</td>
+  <td class="pr"><a href="#fig84">117</a></td>
+</tr>
+<tr><td align="right">85.</td>
+<td align="left">Illustrating light contact points</td>
+  <td class="pr"><a href="#fig85">118</a></td>
+</tr>
+<tr><td align="right">86.</td>
+<td align="left">The microphone</td>
+  <td class="pr"><a href="#fig86">119</a></td>
+</tr>
+<tr><td align="right">87.</td>
+<td align="left">The transmitter</td>
+  <td class="pr"><a href="#fig87">119</a></td>
+</tr>
+<tr><td align="right">88.</td>
+<td align="left">Complete telephone circuit</td>
+  <td class="pr"><a href="#fig88">121</a></td>
+</tr>
+<tr><td align="right">89.</td>
+<td align="left">Device for making hydrogen and oxygen</td>
+  <td class="pr"><a href="#fig89">124</a></td>
+</tr>
+<tr><td align="right">90.</td>
+<td align="left">Electric-water purifier</td>
+  <td class="pr"><a href="#fig90">127</a></td>
+</tr>
+<tr><td align="right">91.</td>
+<td align="left">Portable electric purifier</td>
+  <td class="pr"><a href="#fig91">129</a><span class='pagenum'><a name="px" id="px">p. x</a></span>
+</td>
+</tr>
+<tr><td align="right">92.</td>
+<td align="left">Section of positive plate</td>
+  <td class="pr"><a href="#fig92-95">130</a></td>
+</tr>
+<tr><td align="right">93.</td>
+<td align="left">Section of negative plate</td>
+  <td class="pr"><a href="#fig92-95">130</a></td>
+</tr>
+<tr><td align="right">94.</td>
+<td align="left">Positive and negative in position</td>
+  <td class="pr"><a href="#fig92-95">130</a></td>
+</tr>
+<tr><td align="right">95.</td>
+<td align="left">Form of the insulator</td>
+  <td class="pr"><a href="#fig92-95">130</a></td>
+</tr>
+<tr><td align="right">96.</td>
+<td align="left">Simple electric heater</td>
+  <td class="pr"><a href="#fig96">137</a></td>
+</tr>
+<tr><td align="right">97.</td>
+<td align="left">Side view of resistance device</td>
+  <td class="pr"><a href="#fig97">139</a></td>
+</tr>
+<tr><td align="right">98.</td>
+<td align="left">Top view of resistance device</td>
+  <td class="pr"><a href="#fig98">139</a></td>
+</tr>
+<tr><td align="right">99.</td>
+<td align="left">Plan view of electric iron</td>
+  <td class="pr"><a href="#fig99">140</a></td>
+</tr>
+<tr><td align="right">100.</td>
+<td align="left">Section of electric iron</td>
+  <td class="pr"><a href="#fig100">141</a></td>
+</tr>
+<tr><td align="right">101.</td>
+<td align="left">Thermo-electric couple</td>
+  <td class="pr"><a href="#fig101">143</a></td>
+</tr>
+<tr><td align="right">102.</td>
+<td align="left">Cutting a magnetic field</td>
+  <td class="pr"><a href="#fig102">146</a></td>
+</tr>
+<tr><td align="right">103.</td>
+<td align="left">Alternations, first position</td>
+  <td class="pr"><a href="#fig103-106">148</a></td>
+</tr>
+<tr><td align="right">104.</td>
+<td align="left">Alternations, second position</td>
+  <td class="pr"><a href="#fig103-106">148</a></td>
+</tr>
+<tr><td align="right">105.</td>
+<td align="left">Alternations, third position</td>
+  <td class="pr"><a href="#fig103-106">148</a></td>
+</tr>
+<tr><td align="right">106.</td>
+<td align="left">Alternations, fourth position</td>
+  <td class="pr"><a href="#fig103-106">148</a></td>
+</tr>
+<tr><td align="right">107.</td>
+<td align="left">Increasing alternations, first view</td>
+  <td class="pr"><a href="#fig107">149</a></td>
+</tr>
+<tr><td align="right">108.</td>
+<td align="left">Increasing alternations, second view</td>
+  <td class="pr"><a href="#fig108">149</a></td>
+</tr>
+<tr><td align="right">109.</td>
+<td align="left">Connection of alternating dynamo armature</td>
+  <td class="pr"><a href="#fig109">150</a></td>
+</tr>
+<tr><td align="right">110.</td>
+<td align="left">Direct current dynamo</td>
+  <td class="pr"><a href="#fig110">151</a></td>
+</tr>
+<tr><td align="right">111.</td>
+<td align="left">Circuit wires in direct current dynamo</td>
+  <td class="pr"><a href="#fig111">152</a></td>
+</tr>
+<tr><td align="right">112.</td>
+<td align="left">Alternating polarity lines</td>
+  <td class="pr"><a href="#fig112">154</a></td>
+</tr>
+<tr><td align="right">113.</td>
+<td align="left">Alternating current dynamo</td>
+  <td class="pr"><a href="#fig113">155</a></td>
+</tr>
+<tr><td align="right">114.</td>
+<td align="left">Choking coil</td>
+  <td class="pr"><a href="#fig114">157</a></td>
+</tr>
+<tr><td align="right">115.</td>
+<td align="left">A transformer</td>
+  <td class="pr"><a href="#fig115">158</a></td>
+</tr>
+<tr><td align="right">116.</td>
+<td align="left">Parallel carbons</td>
+  <td class="pr"><a href="#fig116">164</a></td>
+</tr>
+<tr><td align="right">117.</td>
+<td align="left">Arc-lighting circuit</td>
+  <td class="pr"><a href="#fig117">165</a></td>
+</tr>
+<tr><td align="right">118.</td>
+<td align="left">Interrupted conductor</td>
+  <td class="pr"><a href="#fig118">166</a></td>
+</tr>
+<tr><td align="right">119.</td>
+<td align="left">Incandescent circuit</td>
+  <td class="pr"><a href="#fig119">167</a></td>
+</tr>
+<tr><td align="right">120.</td>
+<td align="left">Magnetic action in dynamo, 1st</td>
+  <td class="pr"><a href="#fig120">177</a></td>
+</tr>
+<tr><td align="right">121.</td>
+<td align="left">Magnetic action in dynamo, 2d</td>
+  <td class="pr"><a href="#fig121">177</a></td>
+</tr>
+<tr><td align="right">122.</td>
+<td align="left">Magnetic action in dynamo, 3d</td>
+  <td class="pr"><a href="#fig122">178</a></td>
+</tr>
+<tr><td align="right">123.</td>
+<td align="left">Magnetic action in dynamo, 4th</td>
+  <td class="pr"><a href="#fig123">178</a><span class='pagenum'><a name="pxi" id="pxi">p. xi</a></span></td>
+</tr>
+<tr><td align="right">124.</td>
+<td align="left">Magnetic action in motor, 1st</td>
+  <td class="pr"><a href="#fig124">179</a></td>
+</tr>
+<tr><td align="right">125.</td>
+<td align="left">Magnetic action in motor, 2d</td>
+  <td class="pr"><a href="#fig125">179</a></td>
+</tr>
+<tr><td align="right">126.</td>
+<td align="left">Magnetic action in motor, 3d</td>
+  <td class="pr"><a href="#fig126">180</a></td>
+</tr>
+<tr><td align="right">127.</td>
+<td align="left">Magnetic action in motor, 4th</td>
+  <td class="pr"><a href="#fig127">180</a></td>
+</tr>
+</tbody>
+</table>
+
+<p class="chapter"><span class='pagenum'><a name="p1" id="p1">p. 1</a></span></p>
+
+<hr class="chapter" />
+<h2><a name="INTRODUCTORY" id="INTRODUCTORY"></a>INTRODUCTORY</h2>
+
+
+<p>Electricity, like every science, presents two
+phases to the student, one belonging to a theoretical
+knowledge, and the other which pertains
+to the practical application of that knowledge.
+The boy is directly interested in the practical use
+which he can make of this wonderful phenomenon
+in nature.</p>
+
+<p>It is, in reality, the most successful avenue by
+which he may obtain the theory, for he learns the
+abstract more readily from concrete examples.</p>
+
+<p>It is an art in which shop practice is a greater
+educator than can be possible with books. Boys
+are not, generally, inclined to speculate or theorize
+on phenomena apart from the work itself;
+but once put them into contact with the mechanism
+itself, let them become a living part of it, and
+they will commence to reason and think for themselves.</p>
+
+<p>It would be a dry, dull and uninteresting thing
+to tell a boy that electricity can be generated by<span class='pagenum'><a name="p2" id="p2">p. 2</a></span>
+riveting together two pieces of dissimilar metals,
+and applying heat to the juncture. But put into
+his hands the metals, and set him to perform the
+actual work of riveting the metals together, then
+wiring up the ends of the metals, heating them,
+and, with a galvanometer, watching for results, it
+will at once make him see something in the experiment
+which never occurred when the abstract
+theory was propounded.</p>
+
+<p>He will inquire first what metals should be used
+to get the best results, and finally, he will speculate
+as to the reasons for the phenomena. When
+he learns that all metals are positive-negative or
+negative-positive to each other, he has grasped a
+new idea in the realm of knowledge, which he
+unconsciously traces back still further, only to
+learn that he has entered a field which relates to
+the constitution of matter itself. As he follows
+the subject through its various channels he will
+learn that there is a common source of all things;
+a manifestation common to all matter, and that all
+substances in nature are linked together in a most
+wonderful way.</p>
+
+<p>An impulse must be given to a boy's training.
+The time is past for the rule-and-rote method.
+The rule can be learned better by a manual application
+than by committing a sentence to memory.</p>
+
+<p>In the preparation of this book, therefore, I<span class='pagenum'><a name="p3" id="p3">p. 3</a></span>
+have made practice and work the predominating
+factors. It has been my aim to suggest the best
+form in which to do the things in a practical way,
+and from that work, as the boy carries it out, to
+deduce certain laws and develop the principles
+which underlie them. Wherever it is deemed
+possible to do so, it is planned to have the boy
+make these discoveries for himself, so as to encourage
+him to become a thinker and a reasoner
+instead of a mere machine.</p>
+
+<p>A boy does not develop into a philosopher or a
+scientist through being told he must learn the
+principles of this teaching, or the fundamentals
+of that school of reasoning. He will unconsciously
+imbibe the spirit and the willingness if
+we but place before him the tools by which he
+may build even the simple machinery that displays
+the various electrical manifestations.</p>
+
+<p class="pn"><span class='pagenum'><a name="p4" id="p4"></a></span></p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p5" id="p5">p. 5</a></span></p>
+
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I</h2>
+
+<h3>THE STUDY OF ELECTRICITY. HISTORICAL</h3>
+
+
+<p>There is no study so profound as electricity.
+It is a marvel to the scientist as well as to the
+novice. It is simple in its manifestations, but
+most complex in its organization and in its ramifications.
+It has been shown that light, heat, magnetism
+and electricity are the same, but that they
+differ merely in their modes of motion.</p>
+
+<p><span class="smcap">First Historical Account.</span>&mdash;The first historical
+account of electricity dates back to 600 years B. C.
+Thales of Miletus was the first to describe the
+properties of amber, which, when rubbed, attracted
+and repelled light bodies. The ancients
+also described what was probably tourmaline, a
+mineral which has the same qualities. The torpedo,
+a fish which has the power of emitting electric
+impulses, was known in very early times.</p>
+
+<p>From that period down to about the year 1600
+no accounts of any historical value have been
+given. Dr. Gilbert, of England, made a number
+of researches at that time, principally with amber
+and other materials, and Boyle, in 1650, made
+numerous experiments with frictional electricity.</p>
+
+<p>Sir Isaac Newton also took up the subject at<span class='pagenum'><a name="p6" id="p6">p. 6</a></span>
+about the same period. In 1705 Hawksbee made
+numerous experiments; also Gray, in 1720, and a
+Welshman, Dufay, at about the same time. The
+Germans, from 1740 to 1780, made many experiments.
+In 1740, at Leyden, was discovered the
+jar which bears that name. Before that time, all
+experiments began and ended with frictional electricity.</p>
+
+<p>The first attempt to "bottle" electricity was
+attempted by Muschenbr&oelig;ck, at Leyden, who conceived
+the idea that electricity in materials might
+be retained by surrounding them with bodies which
+did not conduct the current. He electrified some
+water in a jar, and communication having been
+established between the water and the prime conductor,
+his assistant, who was holding the bottle,
+on trying to disengage the communicating wire,
+received a sudden shock.</p>
+
+<p>In 1747 Sir William Watson fired gunpowder by
+an electric spark, and, later on, a party from the
+Royal Society, in conjunction with Watson, conducted
+a series of experiments to determine the
+velocity of the electric fluid, as it was then termed.</p>
+
+<p>Benjamin Franklin, in 1750, showed that lightning
+was electricity, and later on made his interesting
+experiments with the kite and the key.</p>
+
+<p><span class="smcap">Discovering Galvanic Electricity.</span>&mdash;The great
+discovery of Galvani, in 1790, led to the recognition<span class='pagenum'><a name="p7" id="p7">p. 7</a></span>
+of a new element in electricity, called galvanic
+or voltaic (named after the experimenter, Volta),
+and now known to be identical with frictional
+electricity. In 1805 Poisson was the first to
+analyze electricity; and when &OElig;rsted of Copenhagen,
+in 1820, discovered the magnetic action of
+electricity, it offered a great stimulus to the science,
+and paved the way for investigation in a
+new direction. Ampere was the first to develop
+the idea that a motor or a dynamo could be made
+operative by means of the electro-magnetic current;
+and Faraday, about 1830, discovered electro-magnetic
+rotation.</p>
+
+<p><span class="smcap">Electro-magnetic Force.</span>&mdash;From this time on
+the knowledge of electricity grew with amazing
+rapidity. Ohm's definition of electro-motive
+force, current strength and resistance eventuated
+into Ohm's law. Thomson greatly simplified the
+galvanometer, and Wheatstone invented the rheostat,
+a means of measuring resistance, about
+1850. Then primary batteries were brought forward
+by Daniels, Grove, Bunsen and Thomson,
+and electrolysis by Faraday. Then came the instruments
+of precision&mdash;the electrometer, the resistance
+bridge, the ammeter, the voltmeter&mdash;all
+of the utmost value in the science.</p>
+
+<p><span class="smcap">Measuring Instruments.</span>&mdash;The perfection of
+measuring instruments did more to advance electricity<span class='pagenum'><a name="p8" id="p8">p. 8</a></span>
+than almost any other field of endeavor;
+so that after 1875 the inventors took up the subject,
+and by their energy developed and put into
+practical operation a most wonderful array of
+mechanism, which has become valuable in the
+service of man in almost every field of human
+activity.</p>
+
+<p><span class="smcap">Rapidity of Modern Progress.</span>&mdash;This brief history
+is given merely to show what wonders have
+been accomplished in a few years. The art is
+really less than fifty years old, and yet so rapidly
+has it gone forward that it is not at all surprising
+to hear the remark, that the end of the wonders
+has been reached. Less than twenty-five
+years ago a high official of the United States
+Patent Office stated that it was probable the end
+of electrical research had been reached. The
+most wonderful developments have been made
+since that time; and now, as in the past, one discovery
+is but the prelude to another still more remarkable.
+We are beginning to learn that we
+are only on the threshold of that storehouse in
+which nature has locked her secrets, and that
+there is no limit to human ingenuity.</p>
+
+<p><span class="smcap">How to Acquire the Vast Knowledge.</span>&mdash;As the
+boy, with his limited vision, surveys this vast
+accumulation of tools, instruments and machinery,
+and sees what has been and is now being<span class='pagenum'><a name="p9" id="p9">p. 9</a></span>
+accomplished, it is not to be wondered at that
+he should enter the field with timidity. In his
+mind the great question is, how to acquire the
+knowledge. There is so much to learn. How can
+it be accomplished?</p>
+
+<p>The answer to this is, that the student of to-day
+has the advantage of the knowledge of all who
+have gone before; and now the pertinent thing is
+to acquire that knowledge.</p>
+
+<p><span class="smcap">The Means Employed.</span>&mdash;This brings us definitely
+down to an examination of the means that
+we shall employ to instil this knowledge, so that
+it may become a permanent asset to the student's
+store of information.</p>
+
+<p>The most significant thing in the history of
+electrical development is the knowledge that of
+all the great scientists not one of them ever added
+any knowledge to the science on purely speculative
+reasoning. All of them were experimenters.
+They practically applied and developed their
+theories in the laboratory or the workshop. The
+natural inference is, therefore, that the boy who
+starts out to acquire a knowledge of electricity,
+must not only theorize, but that he shall, primarily,
+conduct the experiments, and thereby acquire
+the information in a practical way, one example
+of which will make a more lasting impression than
+pages of dry text</p>
+<p class="pn"><span class='pagenum'><a name="p10" id="p10">p. 10</a></span></p>
+
+<p>Throughout these pages, therefore, I shall, as
+briefly as possible, point out the theories involved,
+as a foundation for the work, and then illustrate
+the structural types or samples; and the work is
+so arranged that what is done to-day is merely a
+prelude or stepping-stone to the next phase of the
+art. In reality, we shall travel, to a considerable
+extent, the course which the great investigators
+followed when they were groping for the facts
+and discovering the great manifestations in
+nature.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p11" id="p11">p. 11</a></span></p>
+
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>WHAT TOOLS AND APPARATUS ARE NEEDED</h3>
+
+
+<p><span class="smcap">Preparing the Workshop.</span>&mdash;Before commencing
+actual experiments we should prepare the
+workshop and tools. Since we are going into this
+work as pioneers, we shall have to be dependent
+upon our own efforts for the production of the
+electrical apparatus, so as to be able, with our
+home-made factory, to provide the power, the
+heat and the electricity. Then, finding we are
+successful in these enterprises, we may look forward
+for "more worlds to conquer."</p>
+
+<p>By this time our neighbors will become interested
+in and solicit work from us.</p>
+
+<p><span class="smcap">Uses of Our Workshops.</span>&mdash;They may want us
+to test batteries, and it then becomes necessary to
+construct mechanism to detect and measure electricity;
+to install new and improved apparatus;
+and to put in and connect up electric bells in their
+houses, as well as burglar alarms. To meet the
+requirements, we put in a telegraph line, having
+learned, as well as we are able, how they
+are made and operated. But we find the telegraph
+too slow and altogether unsuited for our
+purposes, as well as for the uses of the neighborhood,<span class='pagenum'><a name="p12" id="p12">p. 12</a></span>
+so we conclude to put in a telephone
+system.</p>
+
+<p><span class="smcap">What to Build.</span>&mdash;It is necessary, therefore, to
+commence right at the bottom to build a telephone,
+a transmitter, a receiver and a switch-board
+for our system. From the telephone we
+soon see the desirability of getting into touch
+with the great outside world, and wireless telegraphy
+absorbs our time and energies.</p>
+
+<p>But as we learn more and more of the wonderful
+things electricity will do, we are brought into
+contact with problems which directly interest the
+home. Sanitation attracts our attention. Why
+cannot electricity act as an agent to purify our
+drinking water, to sterilize sewage and to arrest
+offensive odors? We must, therefore, learn something
+about the subject of electrolysis.</p>
+
+<p><span class="smcap">What to Learn.</span>&mdash;The decomposition of water
+is not the only thing that we shall describe pertaining
+to this subject. We go a step further,
+and find that we can decompose metals as well as
+liquids, and that we can make a pure metal out
+of an impure one, as well as make the foulest
+water pure. But we shall also, in the course of
+our experiments, find that a cheap metal can be
+coated with a costly one by means of electricity&mdash;that
+we can electroplate by electrolysis.</p>
+
+<p><span class="smcap">Uses of the Electrical Devices.</span>&mdash;While all<span class='pagenum'><a name="p13" id="p13">p. 13</a></span>
+this is progressing and our factory is turning out
+an amazing variety of useful articles, we are led
+to inquire into the uses to which we may devote
+our surplus electricity. The current may be
+diverted for boiling water; for welding metals;
+for heating sad-irons, as well as for other purposes
+which are daily required.</p>
+
+<p><span class="smcap">Tools.</span>&mdash;To do these things tools are necessary,
+and for the present they should not be expensive.
+A small, rigidly built bench is the first requirement.
+This may be made, as shown in Fig. <a href="#fig1">1</a>, of
+three 2-inch planks, each 10 inches wide and 6
+feet long, mounted on legs 36 inches in height.
+In the front part are three drawers for your material,
+or the small odds and ends, as well as for such
+little tools as you may accumulate. Then you will
+need a small vise, say, with a 2-inch jaw, and
+you will also require a hand reel for winding
+magnets. This will be fully described hereafter.</p>
+
+<p>You can also, probably, get a small, cheap anvil,
+which will be of the greatest service in your work.
+It should be mounted close up to the work bench.
+Two small hammers, one with an A-shaped peon,
+and the other with a round peon, should be selected,
+and also a plane and a small wood saw with
+fine teeth. A bit stock, or a ratchet drill, if you
+can afford it, with a variety of small drills; two
+wood chisels, say of &#x215c;-inch and &frac34;-inch widths;<span class='pagenum'><a name="p14" id="p14">p. 14</a></span>
+small cold chisels; hack saw, 10-inch blade; small
+iron square; pair of dividers; tin shears; wire
+cutters; 2 pairs of pliers, one flat and the other
+round-nosed; 2 awls, centering punch, wire cutters,
+and, finally, soldering tools.</p>
+
+<div class="figcenter" style="width: 370px;">
+<a id="fig2" name="fig2"></a><a href="#p14">
+<img src="images/illus-fig2.png" width="370" height="128" alt="Fig. 2. Top View" title="Fig. 2. Top View" /></a>
+<span class="caption"><i>Fig. 2.</i></span>
+</div>
+
+<div class="figcenter" style="width: 369px;">
+<a id="fig3" name="fig3"></a><a href="#p14">
+<img src="images/illus-fig3.png" width="369" height="134" alt="Fig. 3. Side View" title="Fig. 3. Side View" /></a>
+<span class="caption"><i>Fig. 3.</i><br /><span class="smcap">Magnet-winding Reel</span></span>
+</div>
+
+<p>If a gas stove is not available, a brazing torch
+is an essential tool. Numerous small torches are
+being made, which are cheap and easily operated.
+A small soldering iron, with pointed end,
+should be provided; also metal shears and a small
+square; an awl and several sizes of gimlets; a
+screwdriver; pair of pliers and wire cutters</p>
+<p class="pn"><span class='pagenum'><a name="p15" id="p15">p. 15</a></span></p>
+
+<p>From the foregoing it will be seen that the cost
+of tools is not a very expensive item.</p>
+
+<p>This entire outfit, not including the anvil and
+vise, may be purchased new for about $20.00, so
+we have not been extravagant.</p>
+
+<p><span class="smcap">Magnet-winding Reel.</span>&mdash;Some little preparation
+must be made, so we may be enabled to handle
+our work by the construction of mechanical aids.</p>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig4" name="fig4"></a><a href="#p15">
+<img src="images/illus-fig4.png" width="353" height="100" alt="Fig. 4. Journal Block." title="Fig. 4. Journal Block." /></a>
+<span class="italcaption">Fig. 4. <span class="u">Journal</span> <span class="u">Block</span>.</span>
+</div>
+
+<p>First of these is the magnet-winding reel, a
+plan view of which is shown in Fig. <a href="#fig2">2</a>. This, for
+our present work, will be made wholly of wood.</p>
+
+<p>Select a plank 1&frac12; inches thick and 8 inches
+wide, and from this cut off two pieces (A), each
+7 inches long, and then trim off the corners (B, B),
+as shown in Fig. <a href="#fig4">4</a>. To serve as the mandrel (C,
+Fig. <a href="#fig2">2</a>), select a piece of broomstick 9 inches long.
+Bore a hole (D) in each block (A) a half inch
+below the upper margin of the block, this hole
+being of such diameter that the broomstick mandrel
+will fit and easily turn therein</p>
+<p class="pn"><span class='pagenum'><a name="p16" id="p16">p. 16</a></span></p>
+
+<p>Place a crank (E), 5 inches long, on the outer
+end of the mandrel, as in Fig. <a href="#fig3">3</a>. Then mount
+one block on the end of the bench and the other
+block 3 inches away. Affix them to the bench by
+nails or screws, preferably the latter.</p>
+
+<p>On the inner end of the mandrel put a block
+(F) of hard wood. This is done by boring a hole
+1 inch deep in the center of the block, into which
+the mandrel is driven. On the outer face of the
+block is a square hole large enough to receive the
+head of a &#x215c;-inch bolt, and into the depression thus
+formed a screw (G) is driven through the block
+and into the end of the mandrel, so as to hold the
+block (F) and mandrel firmly together. When
+these parts are properly put together, the inner
+side of the block will rest and turn against the
+inner journal block (A).</p>
+
+<p>The tailpiece is made of a 2" &times; 4" scantling
+(H), 10 inches long, one end of it being nailed
+to a transverse block (I) 2" &times; 2" &times; 4". The inner
+face of this block has a depression in which is
+placed a V-shaped cup (J), to receive the end of
+the magnet core (K) or bolt, which is to be used
+for this purpose. The tailpiece (H) has a longitudinal
+slot (L) 5 inches long adapted to receive
+a &frac12;-inch bolt (M), which passes down through
+the bench, and is, therefore, adjustable, so it may
+be moved to and from the journal bearing (A),<span class='pagenum'><a name="p17" id="p17">p. 17</a></span>
+thereby providing a place for the bolts to be put
+in. These bolts are the magnet cores (K), 6
+inches long, but they may be even longer, if you
+bore several holes (N) through the bench so you
+may set over the tailpiece.</p>
+
+<p>With a single tool made substantially like this,
+over a thousand of the finest magnets have been
+wound. Its value will be appreciated after you
+have had the experience of winding a few magnets.</p>
+
+<p><span class="smcap">Order in the Workshop.</span>&mdash;Select a place for
+each tool on the rear upright of the bench, and
+make it a rule to put each tool back into its place
+after using. This, if persisted in, will soon become
+a habit, and will save you hours of time.
+Hunting for tools is the unprofitable part of any
+work.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p18" id="p18">p. 18</a></span></p>
+
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>MAGNETS, COILS, ARMATURES, ETC.</h3>
+
+
+<p><span class="smcap">The Two Kinds of Magnet.</span>&mdash;Generally speaking,
+magnets are of two kinds, namely, permanent
+and electro-magnetic.</p>
+
+<p><span class="smcap">Permanent Magnets</span>.&mdash;A permanent magnet is
+a piece of steel in which an electric force is exerted
+at all times. An electro-magnet is a piece
+of iron which is magnetized by a winding of wire,
+and the magnet is energized only while a current
+of electricity is passing through the wire.</p>
+
+<p><span class="smcap">Electro-Magnet</span>.&mdash;The electro-magnet, therefore,
+is the more useful, because the pull of the
+magnet can be controlled by the current which
+actuates it.</p>
+
+<p>The electro-magnet is the most essential of all
+contrivances in the operation and use of electricity.
+It is the piece of mechanism which does
+the physical work of almost every electrical apparatus
+or machine. It is the device which has
+the power to convert the unseen electric current
+into motion which may be observed by the human
+eye. Without it electricity would be a useless
+agent to man.</p>
+
+<p>While the electro-magnet is, therefore, the form<span class='pagenum'><a name="p19" id="p19">p. 19</a></span>
+of device which is almost wholly used, it is necessary,
+first, to understand the principles of the
+permanent magnet.</p>
+
+<p><span class="smcap">Magnetism.</span>&mdash;The curious force exerted by a
+magnet is called magnetism, but its origin has
+never been explained. We know its manifestations
+only, and laws have been formulated to explain
+its various phases; how to make it more or
+less intense; how to make its pull more effective;
+the shape and form of the magnet and the material
+most useful in its construction.</p>
+
+<div class="figcenter" style="width: 347px;">
+<a id="fig5" name="fig5"></a><a href="#p19">
+<img src="images/illus-fig5.png" width="347" height="93" alt="Fig 5. Plain Magnet Bar" title="Fig 5. Plain Magnet Bar" /></a>
+<span class="caption"><i>Fig 5.</i> <span class="smcap">Plain Magnet Bar</span></span>
+</div>
+
+<p><span class="smcap">Materials for Magnets.</span>&mdash;Iron and steel are the
+best materials for magnets. Some metals are non-magnetic,
+this applying to iron if combined with
+manganese. Others, like sulphur, zinc, bismuth,
+antimony, gold, silver and copper, not only are
+non-magnetic, but they are actually repelled by
+magnetism. They are called the diamagnetics.</p>
+
+<p><span class="smcap">Non-magnetic Materials.</span>&mdash;Any non-magnetic
+body in the path of a magnetic force does not
+screen or diminish its action, whereas a magnetic
+substance will</p>
+<p class="pn"><span class='pagenum'><a name="p20" id="p20">p. 20</a></span></p>
+
+<p>In Fig. <a href="#fig5">5</a> we show the simplest form of magnet,
+merely a bar of steel (A) with the magnetic
+lines of force passing from end to end. It will
+be understood that these lines extend out on all
+sides, and not only along two sides, as shown in
+the drawing. The object is to explain clearly
+how the lines run.</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig6" name="fig6"></a><a href="#p20">
+<img src="images/illus-fig6.png" width="349" height="63" alt="Fig. 6. Severed Magnet" title="Fig. 6. Severed Magnet" /></a>
+<span class="caption"><i>Fig 6.</i> <span class="smcap">Severed Magnet</span></span>
+</div>
+
+<p><span class="smcap">Action of a Severed Magnet.</span>&mdash;Now, let us suppose
+that we sever this bar in the middle, as in Fig. <a href="#fig6">6</a>,
+or at any other point between the ends. In this
+case each part becomes a perfect magnet, and a
+new north pole (N) and a new south pole (S) are
+made, so that the movement of the magnetic lines
+of force are still in the same direction in each&mdash;that
+is, the current flows from the north pole to
+the south pole.</p>
+
+<p><span class="smcap">What North and South Poles Mean.</span>&mdash;If these
+two parts are placed close together they will attract
+each other. But if, on the other hand, one
+of the pieces is reversed, as in Fig. <a href="#fig7">7</a>, they will
+repel each other. From this comes the statement
+that likes repel and unlikes attract each other</p>
+<p class="pn"><span class='pagenum'><a name="p21" id="p21">p. 21</a></span></p>
+
+<p><span class="smcap">Repulsion and Attraction.</span>&mdash;This physical act
+of repulsion and attraction is made use of in
+motors, as we shall see hereinafter.</p>
+
+<p>It will be well to bear in mind that in treating
+of electricity the north pole is always associated
+with the plus sign (+) and the south pole with
+the minus sign (-). Or the N sign is positive
+and the S sign negative electricity.</p>
+
+<div class="figcenter" style="width: 337px;">
+<a id="fig7" name="fig7"></a><a href="#p21">
+<img src="images/illus-fig7.png" width="337" height="85" alt="Fig. 7. Reversed Magnets" title="Fig. 7. Reversed Magnets" /></a>
+<span class="caption"><i>Fig. 7.</i> <span class="smcap">Reversed Magnets</span></span>
+</div>
+
+<p><span class="smcap">Positives and Negatives.</span>&mdash;There is really no
+difference between positive and negative electricity,
+so called, but the foregoing method merely
+serves as a means of identifying or classifying the
+opposite ends of a magnet or of a wire.</p>
+
+<p><span class="smcap">Magnetic Lines of Force.</span>&mdash;It will be noticed
+that the magnetic lines of force pass through the
+bar and then go from end to end through the atmosphere.
+Air is a poor conductor of electricity,
+so that if we can find a shorter way to conduct
+the current from the north pole to the south pole,
+the efficiency of the magnet is increased.</p>
+
+<p>This is accomplished by means of the well-known<span class='pagenum'><a name="p22" id="p22">p. 22</a></span>
+horseshoe magnet, where the two ends
+(N, S) are brought close together, as in Fig. <a href="#fig8">8</a>.</p>
+
+<p><span class="smcap">The Earth as a Magnet.</span>&mdash;The earth is a huge
+magnet and the magnetic lines run from the north
+pole to the south pole around all sides of the globe.</p>
+
+<div class="figcenter" style="width: 340px;">
+<a id="fig8" name="fig8"></a><a href="#p22">
+<img src="images/illus-fig8.png" width="340" height="139" alt="Fig. 8. Horseshoe Magnet" title="Fig. 8. Horseshoe Magnet" /></a>
+<span class="caption"><i>Fig. 8.</i> <span class="smcap">Horseshoe Magnet</span></span>
+</div>
+
+<p>The north magnetic pole does not coincide with
+the true north pole or the pivotal point of the
+earth's rotation, but it is sufficiently near for all
+practical purposes. Fig. <a href="#fig9">9</a> shows the magnetic
+lines running from the north to the south pole.</p>
+
+<p><span class="smcap">Why the Compass Points North and South.</span>&mdash;Now,
+let us try to ascertain why the compass
+points north and south.</p>
+
+<p>Let us assume that we have a large magnet (A,
+Fig. <a href="#fig10">10</a>), and suspend a small magnet (B)
+above it, so that it is within the magnetic field of
+the large magnet. This may be done by means of
+a short pin (C), which is located in the middle<span class='pagenum'><a name="p23" id="p23">p. 23</a></span>
+of the magnet (B), the upper end of this pin
+having thereon a loop to which a thread (D) is
+attached. The pin also carries thereon a pointer
+(E), which is directed toward the north pole of
+the bar (B).</p>
+
+<div class="figcenter" style="width: 354px;">
+<a id="fig9" name="fig9"></a><a href="#p23">
+<img src="images/illus-fig9.png" width="354" height="235" alt="Fig. 9. Earth&#39;s Magnetic Lines" title="Fig. 9. Earth&#39;s Magnetic Lines" /></a>
+<span class="caption"><i>Fig. 9.</i> <span class="smcap">Earth&#39;s Magnetic Lines</span></span>
+</div>
+
+<p>You will now take note of the interior magnetic
+lines (X), and the exterior magnetic lines (Z)
+of the large magnet (A), and compare the direction
+of their flow with the similar lines in the
+small magnet (B).</p>
+
+<p>The small magnet has both its exterior and its
+interior lines within the exterior lines (Z) of the
+large magnet (A), so that as the small magnet
+(B) is capable of swinging around, the N pole of<span class='pagenum'><a name="p24" id="p24">p. 24</a></span>
+the bar (B) will point toward the S pole of the
+larger bar (A). The small bar, therefore, is influenced
+by the exterior magnetic field (Z).</p>
+
+<div class="figcenter" style="width: 363px;">
+<a id="fig10" name="fig10"></a><a href="#p24">
+<img src="images/illus-fig10.png" width="363" height="127" alt="Fig. 10. Two Permanent Magnets" title="Fig. 10. Two Permanent Magnets" /></a>
+<span class="caption"><i>Fig. 10.</i> <span class="smcap">Two Permanent Magnets</span></span>
+</div>
+
+<div class="figcenter" style="width: 363px;">
+<a id="fig11" name="fig11"></a><a href="#p24">
+<img src="images/illus-fig11.png" width="363" height="215" alt="Fig. 11. Magnets in the Earth&#39;s Magnetic Field"
+ title="Fig. 11. Magnets in the Earth&#39;s Magnetic Field" /></a>
+<span class="caption"><i>Fig. 11.</i> <span class="smcap">Magnets in the Earth&#39;s Magnetic Field</span></span>
+</div>
+
+<p>Let us now take the outline represented by the
+earth's surface (Fig. <a href="#fig11">11</a>), and suspend a magnet
+(A) at any point, like the needle of a compass,
+and it will be seen that the needle will arrange
+itself north and south, within the magnetic field
+which flows from the north to the south pole</p>
+<p class="pn"><span class='pagenum'><a name="p25" id="p25">p. 25</a></span></p>
+
+<p><span class="smcap">Peculiarity of a Magnet.</span>&mdash;One characteristic
+of a magnet is that, while apparently the magnetic
+field flows out at one end of the magnet, and
+moves inwardly at the other end, the power of
+attraction is just the same at both ends.</p>
+
+<p>In Fig. <a href="#fig12">12</a> are shown a bar (A) and a horseshoe
+magnet (B). The bar (A) has metal blocks (C)
+at each end, and each of these blocks is attracted
+to and held in contact with the ends by magnetic
+influence, just the same as the bar (D) is attracted
+by and held against the two ends of the horseshoe
+magnet. These blocks (C) or the bar (D) are
+called armatures. Through them is represented
+the visible motion produced by the magnetic field.</p>
+
+<div class="figcenter" style="width: 361px;">
+<a id="fig12" name="fig12"></a><a href="#p25">
+<img src="images/illus-fig12.png" width="361" height="111" alt="Fig. 12. Armatures for Magnets" title="Fig. 12. Armatures for Magnets" /></a>
+<span class="caption"><i>Fig. 12.</i> <span class="smcap">Armatures for Magnets</span></span>
+</div>
+
+<p><span class="smcap">Action of the Electro-Magnet.</span>&mdash;The electro-magnet
+exerts its force in the same manner
+as a permanent magnet, so far as attraction and
+repulsion are concerned, and it has a north and
+a south pole, as in the case with the permanent
+magnet. An electro-magnet is simply a bar of<span class='pagenum'><a name="p26" id="p26">p. 26</a></span>
+iron with a coil or coils of wire around it; when
+a current of electricity flows through the wire, the
+bar is magnetized. The moment the current is
+cut off, the bar is demagnetized. The question
+that now arises is, why an electric current flowing
+through a wire, under those conditions, magnetizes
+the bar, or <i>core</i>, as it is called.</p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig13" name="fig13"></a><a href="#p26">
+<img src="images/illus-fig13.png" width="350" height="80" alt="Fig. 13. Magnetized Field" title="Fig. 13. Magnetized Field" /></a>
+<span class="caption"><i>Fig. 13.</i> <span class="smcap">Magnetized Field</span></span>
+</div>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig14" name="fig14"></a><a href="#p26">
+<img src="images/illus-fig14.png" width="350" height="104" alt="Fig. 14. Magnetized Bar" title="Fig. 14. Magnetized Bar" /></a>
+<span class="caption"><i>Fig. 14.</i> <span class="smcap">Magnetized Bar</span></span>
+</div>
+
+<p>In Fig. <a href="#fig13">13</a> is shown a piece of wire (A). Let
+us assume that a current of electricity is flowing
+through this wire in the direction of the darts.
+What actually takes place is that the electricity
+extends out beyond the surface of the wire in the
+form of the closed rings (B). If, now, this wire
+(A) is wound around an iron core (C, Fig.
+<a href="#fig14">14</a>), you will observe that this electric field, as<span class='pagenum'><a name="p27" id="p27">p. 27</a></span>
+it is called, entirely surrounds the core, or rather,
+that the core is within the magnetic field or influence
+of the current flowing through the wire, and
+the core (C) thereby becomes magnetized, but
+it is magnetized only when the current passes
+through the wire coil (A).</p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig15" name="fig15"></a><a href="#p27">
+<img src="images/illus-fig15.png" width="350" height="73" alt="Fig. 15. Direction of Current" title="Fig. 15. Direction of Current" /></a>
+<span class="caption"><i>Fig. 15.</i> <span class="smcap">Direction of Current</span></span>
+</div>
+
+<p>From the foregoing, it will be understood that
+a wire carrying a current of electricity not only
+is affected within its body, but that it also has a
+sphere of influence exteriorly to the body of the
+wire, at all points; and advantage is taken of
+this phenomenon in constructing motors, dynamos,
+electrical measuring devices and almost
+every kind of electrical mechanism in existence.</p>
+
+<p><span class="smcap">Exterior Magnetic Influence Around a Wire
+Carrying a Current.</span>&mdash;Bear in mind that the wire
+coil (A, Fig. <a href="#fig14">14</a>) does not come into contact with
+the core (C). It is insulated from the core, either
+by air or by rubber or other insulating substance,
+and a current passing from A to C under those
+conditions is a current of <i>induction</i>. On the other
+hand, the current flowing through the wire (A)<span class='pagenum'><a name="p28" id="p28">p. 28</a></span>
+from end to end is called a <i>conduction</i> current.
+Remember these terms.</p>
+
+<p>In this connection there is also another thing
+which you will do well to bear in mind. In Fig.
+<a href="#fig15">15</a> you will notice a core (C) and an insulated
+wire coil (B) wound around it. The current,
+through the wire (B), as shown by the darts (D),
+moves in one direction, and the induced current in
+the core (C) travels in the opposite direction, as
+shown by the darts (D).</p>
+
+<div class="figcenter" style="width: 352px;">
+<a id="fig16" name="fig16"></a><a href="#p28">
+<img src="images/illus-fig16.png" width="352" height="124" alt="Fig. 16. Direction of Induction Current" title="Fig. 16. Direction of Induction Current" /></a>
+<span class="caption"><i>Fig. 16.</i> <span class="smcap">Direction of Induction Current</span></span>
+</div>
+
+<p><span class="smcap">Parallel Wires.</span>&mdash;In like manner, if two wires
+(A, B, Fig. <a href="#fig16">16</a>) are parallel with each other, and
+a current of electricity passes along the wire (A)
+in one direction, the induced current in the wire
+(B) will move in the opposite direction.</p>
+
+<p>These fundamental principles should be thoroughly
+understood and mastered.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p29" id="p29">p. 29</a></span></p>
+
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>FRICTIONAL, VOLTAIC OR GALVANIC, AND ELECTRO-MAGNETIC ELECTRICITY</h3>
+
+
+<p><span class="smcap">Three Electrical Sources.</span>&mdash;It has been found
+that there are three kinds of electricity, or, to be
+more accurate, there are three ways to generate it.
+These will now be described.</p>
+
+<p>When man first began experimenting, he produced
+a current by frictional means, and collected
+the electricity in a bottle or jar. Electricity, so
+stored, could be drawn from the jar, by attaching
+thereto suitable connection. This could be effected
+only in one way, and that was by discharging
+the entire accumulation instantaneously. At that
+time they knew of no means whereby the current
+could be made to flow from the jar as from a battery
+or cell.</p>
+
+<p><span class="smcap">Frictional Electricity.</span>&mdash;With a view of explaining
+the principles involved, we show in Fig.
+<a href="#fig17">17</a> a machine for producing electricity by friction.</p>
+
+
+<div class="figcenter" style="width: 355px;">
+<a id="fig17" name="fig17"></a><a href="#p29">
+<img src="images/illus-fig17.png" width="355" height="374" alt="Fig. 17. Friction-Electricity Machine" title="Fig. 17. Friction-Electricity Machine" /></a>
+<span class="caption"><i>Fig. 17.</i> <span class="smcap">Friction-Electricity Machine</span></span>
+</div>
+
+<p>This is made up as follows: A represents the
+base, having thereon a flat member (B), on which
+is mounted a pair of parallel posts or standards
+(C, C), which are connected at the top by a cross
+piece (D). Between these two posts is a glass<span class='pagenum'><a name="p30" id="p30">p. 30</a></span>
+disc (E), mounted upon a shaft (F), which passes
+through the posts, this shaft having at one end a
+crank (G). Two leather collecting surfaces (H,
+H), which are in contact with the glass disc (E),
+are held in position by arms (I, J), the arm (I)
+being supported by the cross piece (D), and the
+arm (J) held by the base piece (B). A rod (K),
+U-shaped in form, passes over the structure here
+thus described, its ends being secured to the base<span class='pagenum'><a name="p31" id="p31">p. 31</a></span>
+(B). The arms (I, J) are both electrically connected
+with this rod, or conductor (K), joined to
+a main conductor (L), which has a terminating
+knob (M). On each side and close to the terminal
+end of each leather collector (H) is a fork-shaped
+collector (N). These two collectors are also connected
+electrically with the conductor (K). When
+the disc is turned electricity is generated by the
+leather flaps and accumulated by the collectors
+(N), after which it is ready to be discharged at the
+knob (M).</p>
+
+<p>In order to collect the electricity thus generated
+a vessel called a Leyden jar is used.</p>
+
+<p><span class="smcap">Leyden Jar.</span>&mdash;This is shown in Fig. <a href="#fig18">18</a>. The jar
+(A) is of glass coated exteriorly at its lower end
+with tinfoil (B), which extends up a little more
+than halfway from the bottom. This jar has a
+wooden cover or top (C), provided centrally with
+a hole (D). The jar is designed to receive within
+it a tripod and standard (E) of lead. Within this
+lead standard is fitted a metal rod (F), which projects
+upwardly through the hole (D), its upper
+end having thereon a terminal knob (G). A sliding
+cork (H) on the rod (F) serves as a means to
+close the jar when not in use. When in use this
+cork is raised so the rod may not come into contact,
+electrically, with the cover (C).</p>
+
+<p>The jar is half filled with sulphuric acid (I),<span class='pagenum'><a name="p32" id="p32">p. 32</a></span>
+after which, in order to charge the jar, the knob
+(G) is brought into contact with the knob (M) of
+the friction generator (Fig. <a href="#fig17">17</a>).</p>
+
+<p><span class="smcap">Voltaic or Galvanic Electricity.</span>&mdash;The second
+method of generating electricity is by chemical
+means, so called, because a liquid is used as one
+of the agents.</p>
+
+<div class="figcenter" style="width: 308px;">
+<a id="fig18" name="fig18"></a><a href="#p32">
+<img src="images/illus-fig18.png" width="308" height="302" alt="Fig. 18. Leyden Jar" title="Fig. 18. Leyden Jar" /></a>
+<span class="caption"><i>Fig. 18.</i> <span class="smcap">Leyden Jar</span></span>
+</div>
+
+<p>Galvani, in 1790, made the experiments which
+led to the generation of electricity by means of
+liquids and metals. The first battery was called
+the "crown of cups," shown in Fig. <a href="#fig19">19</a>, and consisting<span class='pagenum'><a name="p33" id="p33">p. 33</a></span>
+of a row of glass cups (A), containing salt
+water. These cups were electrically connected by
+means of bent metal strips (B), each strip having
+at one end a copper plate (C), and at the other
+end a zinc plate (D). The first plate in the cup
+at one end is connected with the last plate in the
+cup at the other end by a conductor (E) to make
+a complete circuit.</p>
+
+<div class="figcenter" style="width: 361px;">
+<a id="fig19" name="fig19"></a><a href="#p33">
+<img src="images/illus-fig19.png" width="361" height="181" alt="Fig. 19. Galvanic Electricity. Crown of Cups"
+title="Fig. 19. Galvanic Electricity. Crown of Cups" /></a>
+<span class="caption"><i>Fig. 19.</i> <span class="smcap"> Galvanic Electricity. Crown of Cups</span></span>
+</div>
+
+<p><span class="smcap">The Cell and Battery.</span>&mdash;From the foregoing it
+will be seen that within each cup the current flows
+from the zinc to the copper plates, and exteriorly
+from the copper to the zinc plates through the
+conductors (B and E).</p>
+
+<p>A few years afterwards Volta devised what is
+known as the voltaic pile (Fig. <a href="#fig20">20</a>).</p>
+
+<p><span class="smcap">Voltaic Pile&mdash;How Made.</span>&mdash;This is made of alternate
+discs of copper and zinc with a piece of<span class='pagenum'><a name="p34" id="p34">p. 34</a></span>
+cardboard of corresponding size between each zinc
+and copper plate. The cardboard discs are moistened
+with acidulated water. The bottom disc of
+copper has a strip which connects with a cup of
+acid, and one wire terminal (A) runs therefrom.
+The upper disc, which is of zinc, is also connected,
+by a strip, with a cup of acid from which extends
+the other terminal wire (B).</p>
+
+<div class="figcenter" style="width: 348px;">
+<a id="fig20" name="fig20"></a><a href="#p34">
+<img src="images/illus-fig20.png" width="348" height="300" alt="Fig. 20. Voltaic Electricity" title="Fig. 20. Voltaic Electricity" /></a>
+<span class="caption"><i>Fig. 20.</i> <span class="smcap">Voltaic Electricity</span></span>
+</div>
+
+<p><i>Plus and Minus Signs.</i>&mdash;It will be noted that
+the positive or copper disc has the plus sign<span class='pagenum'><a name="p35" id="p35">p. 35</a></span>
+(+) while the zinc disc has the minus (-) sign.
+These signs denote the positive and the negative
+sides of the current.</p>
+
+<p>The liquid in the cells, or in the moistened
+paper, is called the <i>electrolyte</i> and the plates or
+discs are called <i>electrodes</i>. To define them more
+clearly, the positive plate is the <i>anode</i>, and the
+negative plate the <i>cathode</i>.</p>
+
+<p>The current, upon entering the zinc plate, decomposes
+the water in the electrolyte, thereby
+forming oxygen. The hydrogen in the water,
+which has also been formed by the decomposition,
+is carried to the copper plate, so that the plate
+finally is so coated with hydrogen that it is difficult
+for the current to pass through. This condition
+is called "polarization," and to prevent it has
+been the aim of all inventors. To it also we may
+attribute the great variety of primary batteries,
+each having some distinctive claim of merit.</p>
+
+<p><span class="smcap">The Common Primary Cell.</span>&mdash;The most common
+form of primary cell contains sulphuric acid,
+or a sulphuric acid solution, as the electrolyte,
+with zinc for the <i>anode</i>, and carbon, instead of copper,
+for the <i>cathode</i>.</p>
+
+<p>The ends of the zinc and copper plates are
+called <i>terminals</i>, and while the zinc is the anode
+or positive element, its <i>terminal</i> is designated as
+the positive pole. In like manner, the carbon is<span class='pagenum'><a name="p36" id="p36">p. 36</a></span>
+the negative element or cathode, and its terminal
+is designated as negative pole.</p>
+
+<p>Fig. 21 will show the relative arrangement of
+the parts. It is customary to term that end or element
+from which the current flows as positive.
+A cell is regarded as a whole, and as the current
+passes out of the cell from the copper element, the
+copper terminal becomes positive.</p>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig21" name="fig21"></a><a href="#p36">
+<img src="images/illus-fig21.png" width="353" height="233" alt="Fig. 21. Primary Battery" title="Fig. 21. Primary Battery" /></a>
+<span class="caption"><i>Fig. 21.</i> <span class="smcap">Primary Battery</span></span>
+</div>
+
+<p><span class="smcap">Battery Resistance, Electrolyte and Current.</span>&mdash;The
+following should be carefully memorized:</p>
+
+<p>A cell has reference to a single vessel. When
+two or more cells are coupled together they form
+a <i>battery</i></p>
+<p class="pn"><span class='pagenum'><a name="p37" id="p37">p. 37</a></span></p>
+
+<p><i>Resistance</i> is opposition to the movement of the
+current. If it is offered by the electrolyte, it is
+designated "Internal Resistance." If, on the other
+hand, the opposition takes place, for instance,
+through the wire, it is then called "External Resistance."</p>
+
+<p>The electrolyte must be either acid, or alkaline,
+or saline, and the electrodes must be of dissimilar
+metals, so the electrolyte will attack one of them.</p>
+
+<p>The current is measured in amperes, and the
+force with which it is caused to flow is measured
+in volts. In practice the word "current" is used
+to designate ampere flow; and electromotive force,
+or E. M. F., is used instead of voltage.</p>
+
+<p><span class="smcap">Electro-magnetic Electricity.</span>&mdash;The third
+method of generating electricity is by electro-magnets.
+The value and use of induction will now
+be seen, and you will be enabled to utilize the lesson
+concerning magnetic action referred to in the
+previous chapter.</p>
+
+<p><span class="smcap">Magnetic Radiation.</span>&mdash;You will remember that
+every piece of metal which is within the path of
+an electric current has a space all about its surface
+from end to end which is electrified. This
+electrified field extends out a certain distance from
+the metal, and is supposed to maintain a movement
+around it. If, now, another piece of metal is
+brought within range of this electric or magnetic<span class='pagenum'><a name="p38" id="p38">p. 38</a></span>
+zone and moved across it, so as to cut through this
+field, a current will be generated thereby, or rather
+added to the current already exerted, so that if
+we start with a feeble current, it can be increased
+by rapidly "cutting the lines of force," as it is
+called.</p>
+
+<p><span class="smcap">Different Kinds of Dynamo.</span>&mdash;While there are
+many kinds of dynamo, they all, without exception,
+are constructed in accordance with this principle.
+There are also many varieties of current.
+For instance, a dynamo may be made to produce
+a high voltage and a low amperage; another with
+high amperage and low voltage; another which
+gives a direct current for lighting, heating, power,
+and electroplating; still another which generates
+an alternating current for high tension power, or
+transmission, arc-lighting, etc., all of which will
+be explained hereafter.</p>
+
+<p>In this place, however, a full description of a direct-current
+dynamo will explain the principle involved
+in all dynamos&mdash;that to generate a current
+of electricity makes it necessary for us to move
+a field of force, like an armature, rapidly and continuously
+through another field of force, like a
+magnetic field.</p>
+
+<p><span class="smcap">Direct-Current Dynamo.</span>&mdash;We shall now make
+the simplest form of dynamo, using for this purpose
+a pair of permanent magnets</p>
+<p class="pn"><span class='pagenum'><a name="p39" id="p39">p. 39</a></span></p>
+
+<div class="figcenter" style="width: 352px;">
+<a id="fig22" name="fig22"></a><a href="#p39">
+<img src="images/illus-fig22.png" width="352" height="379" alt="Fig. 22. Dynamo Field and Pole Piece" title="Fig. 22. Dynamo Field and Pole Piece" /></a>
+<span class="caption"><i>Fig. 22.</i> <span class="smcap">Dynamo Field and Pole Piece</span></span>
+</div>
+
+<p><span class="smcap">Simple Magnet Construction.</span>&mdash;A simple way
+to make a pair of magnets for this purpose is
+shown in Fig. <a href="#fig22">22</a>. A piece of round &frac34;-inch steel
+core (A), 5&frac12; inches long, is threaded at both ends
+to receive at one end a nut (B), which is screwed
+on a sufficient distance so that the end of the core
+(A) projects a half inch beyond the nut. The
+other end of the steel core has a pole piece of<span class='pagenum'><a name="p40" id="p40">p. 40</a></span>
+iron (C) 2" &times; 2" &times; 4", with a hole midway between
+the ends, threaded entirely through, and provided
+along one side with a concave channel, within
+which the armature is to turn. Now, before the
+pole piece (C) is put on, we will slip on a disc
+(E), made of hard rubber, then a thin rubber tube
+(F), and finally a rubber disc (G), so as to provide
+a positive insulation for the wire coil which
+is wound on the bobbin thus made.</p>
+
+<p><span class="smcap">How to Wind.</span>&mdash;In practice, and as you go further
+along in this work, you will learn the value,
+first, of winding one layer of insulated wire on the
+spool, coating it with shellac, and then putting
+on the next layer, and so on; when completely
+wound, the two wire terminals may be brought
+out at one end; but for our present purpose, and
+to render the explanation clearer, the wire terminals
+are at the opposite ends of the spool (H, H').</p>
+
+<p><span class="smcap">The Dynamo Fields</span>.&mdash;Two of these spools are
+so made and they are called the <i>fields</i> of the dynamo.</p>
+
+<p>We will next prepare an iron bar (I), 5 inches
+long and &frac12; inch thick and 1&frac12; inches wide, then
+bore two holes through it so the distance measures
+3 inches from center to center. These holes are
+to be threaded for the &frac34;-inch cores (A). This
+bar holds together the upper ends of the cores,
+as shown in Fig. <a href="#fig23">23</a></p>
+<p class="pn"><span class='pagenum'><a name="p41" id="p41">p. 41</a></span></p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig23" name="fig23"></a><a href="#p41">
+<img src="images/illus-fig23.png" width="350" height="487" alt="Fig. 23. Base and Fields Assembled" title="Fig. 23. Base and Fields Assembled" /></a>
+<span class="caption"><i>Fig. 23.</i> <span class="smcap"> Base and Fields Assembled</span></span>
+</div>
+
+<p>We then prepare a base (J) of any hard wood,
+2 inches thick, 8 inches long and 8 inches wide,<span class='pagenum'><a name="p42" id="p42">p. 42</a></span>
+and bore two &frac34;-inch holes 3 inches apart on a middle
+line, to receive a pair of &frac34;-inch cap screws (K),
+which pass upwardly through the holes in the base
+and screw into the pole pieces (C). A wooden bar
+(L), 1&frac12;" &times; 1&frac12;", 8 inches long, is placed under each
+pole piece, which is also provided with holes for
+the cap screws (K). The lower side of the base
+(J) should be countersunk, as at M, so the head
+of the nut will not project. The fields of the dynamo
+are now secured in position to the base.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+   <td align="center"><a id="fig24" name="fig24"></a><a href="#p42">
+<img src="images/illus-fig24.png" width="211" height="131" alt="Fig. 24. Details of the Armature, core"
+title="Fig. 24. Details of the Armature, core" /></a></td>
+        <td align="center"><a id="fig25" name="fig25"></a><a href="#p42">
+<img src="images/illus-fig25.png" width="142" height="132" alt="Fig. 25.  Details of the Armature, body"
+title="Fig. 25.  Details of the Armature, body" /></a></td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 24-25.</i> <span class="smcap">Details of the Armature</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+
+<p><span class="smcap">The Armature.</span>&mdash;A bar of iron (Fig. <a href="#fig24">24</a>), 1" &times; 1"
+and 2&frac14; inches long, is next provided. Through this
+bar (1) are then bored two 5/16-inch holes 1&frac34;
+inches apart, and on the opposite sides of this bar
+are two half-rounded plates of iron (3) (Fig. <a href="#fig25">25</a>).</p>
+
+<p><span class="smcap">Armature Winding.</span>&mdash;Each plate is &frac12; inch thick,
+1&frac34; inches wide and 4 inches long, each plate having
+holes (4) to coincide with the holes (2) of the
+bar (1), so that when the two plates are applied to<span class='pagenum'><a name="p43" id="p43">p. 43</a></span>
+opposite sides of the bar, and riveted together,
+a cylindrical member is formed, with two channels
+running longitudinally, and transversely at the
+ends; and in these channels the insulated wires
+are wound from end to end around the central
+block (1).</p>
+
+<p><span class="smcap">Mounting the Armature.</span>&mdash;It is now necessary
+to provide a means for revolving this armature.
+To this end a brass disc (5, Fig. <a href="#fig26">26</a>) is made, 2
+inches in diameter, &#x215b; inch thick. Centrally, at one
+side, is a projecting stem (6) of round brass,
+which projects out 2 inches, and the outer end is
+turned down, as at 7, to form a small bearing
+surface.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+   <td align="center">
+<a id="fig26" name="fig26"></a><a href="#p43">
+<img src="images/illus-fig26.png" width="230" height="148"
+alt="Fig. 26. Journals" title="Fig. 26. Journals" /></a>
+</td>
+        <td align="center">
+<a id="fig27" name="fig27"></a><a href="#p43">
+<img src="images/illus-fig27.png" width="116" height="151"
+alt="Fig. 27. Commutator" title="Fig. 27. Commutator" /></a>
+      </td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 26-27.</i> <span class="smcap">Armature Mountings</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+
+
+
+<p>The other end of the armature has a similar
+disc (8), with a central stem (9), 1&frac12; inches long,
+turned down to &frac14;-inch diameter up to within &frac14;
+inch of the disc (7), so as to form a shoulder</p>
+<p class="pn"><span class='pagenum'><a name="p44" id="p44">p. 44</a></span></p>
+
+<p><span class="smcap">The Commutator.</span>&mdash;In Fig. <a href="#fig27">27</a> is shown, at 10,
+a wooden cylinder, 1 inch long and 1&frac14; inches in
+diameter, with a hole (11) bored through axially,
+so that it will fit tightly on the stem (6) of the
+disc (5). On this wooden cylinder is driven a
+brass or copper tube (12), which has holes (13)
+opposite each other. Screws are used to hold
+the tube to the wooden cylinder, and after they are
+properly secured together, the tube (12) is cut by
+a saw, as at 14, so as to form two independent
+tubular surfaces</p>
+<p class="pn"><span class='pagenum'><a name="p45" id="p45">p. 45</a></span></p>
+
+<div class="figcenter" style="width: 355px;">
+<a id="fig28" name="fig28"></a><a href="#p45">
+<img src="images/illus-fig28.png" width="355" height="297" alt="Fig. 28. End View Armature, Mounted" title="Fig. 28. End View Armature, Mounted" /></a>
+<span class="caption"><i>Fig. 28.</i><br /> <span class="smcap">End View Armature, Mounted</span></span>
+</div>
+
+<p>These tubular sections are called the commutator
+plates.</p>
+
+<div class="figcenter" style="width: 363px;">
+<a id="fig29" name="fig29"></a><a href="#p45">
+<img src="images/illus-fig29.png" width="363" height="338" alt="Fig. 29. Top View of Armature on Base" title="Fig. 29. Top View of Armature on Base" /></a>
+<span class="caption"><i>Fig. 29.</i><br /><span class="smcap">Top View of Armature on Base</span></span>
+</div>
+
+<p>In order to mount this armature, two bearings
+are provided, each comprising a bar of brass (15,
+Fig. <a href="#fig28">28</a>), each &frac14; inch thick, &frac12; inch wide and 4&frac12;
+inches long. Two holes, 3 inches apart, are
+formed through this bar, to receive round-headed
+wood screws (16), these screws being 3 inches
+long, so they will pass through the wooden pieces<span class='pagenum'><a name="p46" id="p46">p. 46</a></span>
+(I) and enter the base (J). Midway between the
+ends, each bar (15) has an iron bearing block (17),
+&frac34;" &times; &frac12;" and 1&frac12; inches high, the &frac14;-inch hole for the
+journal (7) being midway between its ends.</p>
+
+<p><span class="smcap">Commutator Brushes.</span>&mdash;Fig. <a href="#fig28">28</a> shows the base,
+armature and commutator assembled in position,
+and to these parts have been added the commutator
+brushes. The brush holder (18) is a horizontal
+bar made of hard rubber loosely mounted
+upon the journal pin (7), which is 2&frac12; inches long.
+At each end is a right-angled metal arm (19) secured
+to the bar (18) by screws (20). To these
+arms the brushes (21) are attached, so that their
+spring ends engage with the commutator (12).
+An adjusting screw (22) in the bearing post (17),
+with the head thereof bearing against the brush-holder
+(18), serves as a means for revolubly adjusting
+the brushes with relation to the commutator.</p>
+
+<p><span class="smcap">Dynamo Windings.</span>&mdash;There are several ways to
+wind the dynamos. These can be shown better by
+the following diagrams (Figs. <a href="#fig30-31">30</a>, <a href="#fig30-31">31</a>, <a href="#fig32-33">32</a>, <a href="#fig32-33">33</a>):</p>
+
+<p><span class="smcap">The Field.</span>&mdash;If the field (A, Fig. <a href="#fig30-31">30</a>) is not a
+permanent magnet, it must be excited by a cell or
+battery, and the wires (B, B') are connected up
+with a battery, while the wires (C, C') may be connected
+up to run a motor. This would, therefore,
+be what is called a "separately excited" dynamo.<span class='pagenum'><a name="p47" id="p47">p. 47</a></span>
+In this case the battery excites the field and the
+armature (D), cutting the lines of force at the
+pole pieces (E), so that the armature gathers
+the current for the wires (C, C').</p>
+
+<div class="figcenter" style="width: 348px;">
+<a id="fig30-31" name="fig30-31"></a><a href="#p47">
+<img src="images/illus-fig30-31.png" width="348" height="169" alt="Fig. 30-31. Field Winding, Series-wound"
+title="Fig. 30-31. Field Winding, Series-wound" /></a>
+<span class="caption"><i>Figs. 30-31.</i> <span class="smcap">Field Winding, Series-wound</span></span>
+</div>
+
+
+<p><span class="smcap">Series-wound Field.</span>&mdash;Fig. <a href="#fig30-31">31</a> shows a "series-wound"
+dynamo. The wires of the fields
+(A) are connected up in series with the brushes
+of the armature (D), and the wires (G, G') are
+led out and connected up with a lamp, motor
+or other mechanism. In this case, as well as in
+Figs. <a href="#fig32-33">32</a> and <a href="#fig32-33">33</a>, both the field and the armature
+are made of soft gray iron. With this winding
+and means of connecting the wires, the field is
+constantly excited by the current passing through
+the wires.</p>
+
+<p><span class="smcap">Shunt-wound Field.</span>&mdash;Fig. <a href="#fig32-33">32</a> represents what
+is known as a "shunt-wound" dynamo. Here the<span class='pagenum'><a name="p48" id="p48">p. 48</a></span>
+field wires (H, H) connect with the opposite
+brushes of the armature, and the wires (I, I') are
+also connected with the brushes, these two wires
+being provided to perform the work required.
+This is a more useful form of winding for electroplating
+purposes.</p>
+
+<div class="figcenter" style="width: 343px;">
+<a id="fig32-33" name="fig32-33"></a><a href="#p48">
+<img src="images/illus-fig32-33.png" width="343" height="162" alt="Figs. 32-33. Shunt-wound, Compound-wound"
+title="Figs. 32-33. Shunt-wound, Compound-wound" /></a>
+<span class="caption"><i>Figs. 32-33.</i> <span class="smcap">Shunt-wound, Compound-wound</span></span>
+</div>
+
+<p><span class="smcap">Compound-wound Field.</span>&mdash;Fig. <a href="#fig32-33">33</a> is a diagram
+of a "compound-wound" dynamo. The regular
+field winding (J) has its opposite ends connected
+directly with the armature brushes. There is
+also a winding, of a comparatively few turns, of
+a thicker wire, one terminal (K) of which is connected
+with one of the brushes and the other terminal
+(K') forms one side of the lighting circuit.
+A wire (L) connects with the other armature
+brush to form a complete lighting circuit.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p49" id="p49">p. 49</a></span></p>
+
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>HOW TO DETECT AND MEASURE ELECTRICITY</h3>
+
+
+<p><span class="smcap">Measuring Instruments.</span>&mdash;The production of
+an electric current would not be of much value
+unless we had some way by which we might detect
+and measure it. The pound weight, the foot rule
+and the quart measure are very simple devices,
+but without them very little business could be
+done. There must be a standard of measurement
+in electricity as well as in dealing with iron or
+vegetables or fabrics.</p>
+
+<p>As electricity cannot be seen by the human eye,
+some mechanism must be made which will reveal
+its movements.</p>
+
+<p><span class="smcap">The Detector.</span>&mdash;It has been shown in the preceding
+chapter that a current of electricity passing
+through a wire will cause a current to pass
+through a parallel wire, if the two wires are
+placed close together, but not actually in contact
+with each other. An instrument which reveals
+this condition is called a <i>galvanometer</i>. It not
+only detects the presence of a current, but it
+shows the direction of its flow. We shall now see
+how this is done.</p>
+
+<p>For example, the wire (A, Fig. <a href="#fig34-36">35</a>) is connected<span class='pagenum'><a name="p50" id="p50">p. 50</a></span>
+up in an electric circuit with a permanent magnet
+(B) suspended by a fine wire (C), so that
+the magnet (B) may freely revolve.</p>
+
+<div class="figcenter" style="width: 354px;">
+<a id="fig34-36" name="fig34-36"></a><a href="#p50">
+<img src="images/illus-fig34-36.png" width="354" height="86" alt="Figs. 34-36.
+To the right, Compass Magnet, To the left" title="Figs. 34-36.
+To the right, Compass Magnet, To the left" /></a>
+<span class="caption"><i>Figs. 34-36.</i><br />
+To the right, <span class="smcap">Compass Magnet</span>, To the left</span>
+</div>
+
+<p>For convenience, the magnetic field is shown
+flowing in the direction of the darts, in which the
+dart (D) represents the current within the magnet
+(B) flowing toward the north pole, and the
+darts (E) showing the exterior current flowing
+toward the south pole. Now, if the wire (A) is
+brought up close to the magnet (B), and a current
+passed through A, the magnet (B) will be
+affected. Fig. <a href="#fig34-36">35</a> shows the normal condition of
+the magnetized bar (B) parallel with the wire
+(A) when a current is not passing through the
+latter.</p>
+
+<p><span class="smcap">Direction of Current.</span>&mdash;If the current should
+go through the wire (A) from right to left,
+as shown in Fig. <a href="#fig34-36">34</a>, the magnet (B) would
+swing in the direction taken by the hands
+of a clock and assume the position shown<span class='pagenum'><a name="p51" id="p51">p. 51</a></span>
+in Fig. <a href="#fig34-36">34</a>. If, on the other hand, the current
+in the wire (A) should be reversed or flow
+from left to right, the magnet (B) would swing
+counter-clock-wise, and assume the position shown
+in Fig. <a href="#fig34-36">36</a>. The little pointer (G) would, in either
+case, point in the direction of the flow of the current
+through the wire (A).</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig37" name="fig37"></a><a href="#p51">
+<img src="images/illus-fig37.png" width="351" height="364" alt="Fig. 37. Indicating Direction of Current" title="Fig. 37. Indicating Direction of Current" /></a>
+<span class="caption"><i>Fig. 37.</i> <span class="smcap">Indicating Direction of Current</span></span>
+</div>
+<p class="pn"><span class='pagenum'><a name="p52" id="p52">p. 52</a></span></p>
+
+<p><span class="smcap">Simple Current Detector.</span>&mdash;A simple current
+detector may be made as follows:</p>
+
+<p>Prepare a base 3' &times; 4' in size and 1 inch thick.
+At each corner of one end fix a binding post, as at
+A, A', Fig. <a href="#fig37">37</a>. Then select 20 feet of No. 28 cotton-insulated
+wire, and make a coil (B) 2 inches
+in diameter, leaving the ends free, so they may be
+affixed to the binding posts (A, A'). Now glue
+or nail six blocks (C) to the base, each block being
+1" &times; 1" &times; 2", and lay the coil on these blocks. Then
+drive an L-shaped nail (D) down into each block,
+on the inside of the coil, as shown, so as to hold
+the latter in place.</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig38" name="fig38"></a><a href="#p52">
+<img src="images/illus-fig38.png" width="349" height="68" alt="Fig. 38. The Bridge" title="Fig. 38. The Bridge" /></a>
+<span class="caption"><i>Fig. 38.</i> <span class="smcap">The Bridge</span></span>
+</div>
+
+<p>Now make a bridge (E, Fig. <a href="#fig38">38</a>) of a strip of
+brass &frac12; inch wide, 1/16 inch thick and long enough
+to span the coil, and bend the ends down, as at
+F, so as to form legs. A screw hole (G) is
+formed in each foot, so it may be screwed to the
+base.</p>
+
+<p>Midway between the ends this bridge has a transverse
+slot (H) in one edge, to receive therein the<span class='pagenum'><a name="p53" id="p53">p. 53</a></span>
+pivot pin of the swinging magnet. In order to
+hold the pivot pin in place, cut out an H-shaped
+piece of sheet brass (I), which, when laid on the
+bridge, has its ends bent around the latter, as
+shown at J, and the crossbar of the H-shaped
+piece then will prevent the pivot pin from coming
+out of the slot (H).</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig39" name="fig39"></a><a href="#p53">
+<img src="images/illus-fig39.png" width="351" height="97" alt="Fig. 39. Details of Detector" title="Fig. 39. Details of Detector" /></a>
+<span class="caption"><i>Fig. 39.</i> <span class="smcap">Details of Detector</span></span>
+</div>
+
+<p>The magnet is made of a bar of steel (K, Fig.
+<a href="#fig39">39</a>) 1&frac12; inches long, &#x215c; inch wide and 1/16 inch
+thick, a piece of a clock spring being very serviceable
+for this purpose. The pivot pin is made of
+an ordinary pin (L), and as it is difficult to
+solder the steel magnet (K) to the pin, solder
+only a small disc (M) to the pin (L). Then bore
+a hole (N) through the middle of the magnet (K),
+larger in diameter than the pin (L), and, after
+putting the pin in the hole, pour sealing wax into
+the hole, and thereby secure the two parts together.
+Near the upper end of the pin (L) solder
+the end of a pointer (O), this pointer being at
+right angles to the armature (K). It is better<span class='pagenum'><a name="p54" id="p54">p. 54</a></span>
+to have a metal socket for the lower end of the
+pin. When these parts are put together, as shown
+in Fig. <a href="#fig37">37</a>, a removable glass top, or cover, should
+be provided.</p>
+
+<p>This is shown in Fig. <a href="#fig40">40</a>, in which a square,
+wooden frame (P) is used, and a glass (Q) fitted
+into the frame, the glass being so arranged that
+when the cover is in position it will be in close
+proximity to the upper projecting end of the pivot
+pin (L), and thus prevent the magnet from becoming
+misplaced.</p>
+
+<div class="figcenter" style="width: 343px;">
+<a id="fig40" name="fig40"></a><a href="#p54">
+<img src="images/illus-fig40.png" width="343" height="116" alt="Fig. 40. Cross Section of Detector" title="Fig. 40. Cross Section of Detector" /></a>
+<span class="caption"><i>Fig. 40.</i> <span class="smcap">Cross Section of Detector</span></span>
+</div>
+
+<p><span class="smcap">How to Place the Detector.</span>&mdash;If the detector
+is placed north and south, as shown by the two
+markings, N and S (Fig. <a href="#fig37">37</a>), the magnet bar will
+point north and south, being affected by the earth's
+magnetism; but when a current of electricity flows
+through the coil (B), the magnet will be deflected
+to the right or to the left, so that the pointer
+(O) will then show the direction in which the<span class='pagenum'><a name="p55" id="p55">p. 55</a></span>
+current is flowing through the wire (R) which
+you are testing.</p>
+
+<p>The next step of importance is to <i>measure</i> the
+current, that is, to determine its strength or intensity,
+as well as the flow or quantity.</p>
+
+<p><span class="smcap">Different Ways of Measuring a Current.</span>&mdash;There
+are several ways to measure the properties
+of a current, which may be defined as follows:</p>
+
+<p>1. <span class="smcap">The Sulphuric Acid Voltameter.</span>&mdash;By
+means of an electrolytic action, whereby the current
+decomposes an acidulated solution&mdash;that is,
+water which has in it a small amount of sulphuric
+acid&mdash;and then measuring the gas generated by
+the current.</p>
+
+<p>2. <span class="smcap">The Copper Voltameter.</span>&mdash;By electro-chemical
+means, in which the current passes through
+plates immersed in a solution of copper sulphate.</p>
+
+<p>3. <span class="smcap">The Galvanoscope.</span>&mdash;By having a coil of insulated
+wire, with a magnet suspended so as to
+turn freely within the coil, forming what is called
+a galvanoscope.</p>
+
+<p>4. <span class="smcap">Electro-magnetic Method.</span>&mdash;By using a
+pair of magnets and sending a current through
+the coils, and then measuring the pull on the armature.</p>
+
+<p>5. <span class="smcap">The Power or Speed Method.</span>&mdash;By using an
+electric fan, and noting the revolutions produced
+by the current</p>
+<p class="pn"><span class='pagenum'><a name="p56" id="p56">p. 56</a></span></p>
+
+<p>6. <span class="smcap">The Calorimeter.</span>&mdash;By using a coil of bare
+wire, immersed in paraffine oil, and then measuring
+the temperature by means of a thermometer.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+   <td align="center">
+<a id="fig41" name="fig41"></a><a href="#p56">
+<img src="images/illus-fig41.png" width="178" height="330" alt="Fig. 41. Acid Voltameter" title="Fig. 41. Acid Voltameter" /></a>
+</td>
+        <td align="center">
+<a id="fig42" name="fig42"></a><a href="#p56">
+<img src="images/illus-fig42.png" width="175" height="326" alt="Fig. 42. Copper Voltameter" title="Fig. 42. Copper Voltameter" /></a>
+      </td>
+   </tr>
+   <tr>
+   <td class="tdnwc">
+<span class="caption"><i>Fig. 41.</i><br /><span class="smcap">Acid Voltameter</span></span>
+      </td>
+   <td class="tdnwc">
+<span class="caption"><i>Fig. 42.</i><br /><span class="smcap">Copper Voltameter</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+
+<p>7. <span class="smcap">The Light Method.</span>&mdash;Lastly, by means of
+an electric light, which shows, by its brightness, a
+greater or less current.</p>
+
+<p><span class="smcap">The Preferred Methods.</span>&mdash;It has been found
+that the first and second methods are the only<span class='pagenum'><a name="p57" id="p57">p. 57</a></span>
+ones which will accurately register current
+strength, and these methods have this advantage&mdash;that
+the chemical effect produced is not dependent
+upon the size or shape of the apparatus or
+the plates used.</p>
+
+<p><span class="smcap">How to Make a Sulphuric Acid Voltameter.</span>&mdash;In
+Fig. <a href="#fig41">41</a> is shown a simple form of sulphuric
+acid voltameter, to illustrate the first method. A
+is a jar, tightly closed by a cover (B). Within
+is a pair of platinum plates (C, C), each having
+a wire (D) through the cover. The cover has
+a vertical glass tube (E) through it, which extends
+down to the bottom of the jar, the electrolyte
+therein being a weak solution of sulphuric
+acid. When a current passes through the wires
+(D), the solution is partially decomposed&mdash;that is,
+converted into gas, which passes up into the
+vacant space (F) above the liquid, and, as
+it cannot escape, it presses the liquid downwardly,
+and causes the latter to flow upwardly
+into the tube (E). It is then an easy matter,
+after the current is on for a certain time,
+to determine its strength by the height of the
+liquid in the tube.</p>
+
+<p><span class="smcap">How to Make a Copper Voltameter.</span>&mdash;The second,
+or copper voltameter, is shown in Fig. <a href="#fig42">42</a>.
+The glass jar (A) contains a solution of copper
+sulphate, known in commerce as blue vitriol. A<span class='pagenum'><a name="p58" id="p58">p. 58</a></span>
+pair of copper plates (B, B') are placed in this
+solution, each being provided with a connecting
+wire (C). When a current passes through the
+wires (C), one copper plate (B) is eaten away
+and deposited on the other plate (B'). It is then
+an easy matter to take out the plates and find out
+how much in weight B' has gained, or how much
+B has lost.</p>
+
+<p>In this way, in comparing the strength of, say,
+two separate currents, one should have each current
+pass through the voltameter the same length
+of time as the other, so as to obtain comparative
+results.</p>
+
+<p>It is not necessary, in the first and second methods,
+to consider the shapes, the sizes of the plates
+or the distances between them. In the first
+method the gas produced, within a given time,
+will be the same, and in the second method the
+amount deposited or eaten away will be the same
+under all conditions.</p>
+
+<p><span class="smcap">Disadvantages of the Galvanoscope.</span>&mdash;With the
+third method (using the galvanoscope) it is necessary,
+in order to get a positively correct reading
+instrument, to follow an absolutely accurate plan
+in constructing each part, in every detail, and
+great care must be exercised, particularly in winding.
+It is necessary also to be very careful in<span class='pagenum'><a name="p59" id="p59">p. 59</a></span>
+selecting the sizes of wire used and in the number
+of turns made in the coils.</p>
+
+<p>This is equally true of the fourth method, using
+the electro-magnet, because the magnetic pull is
+dependent upon the size of wire from which the
+coils are made and the number of turns of wire.</p>
+
+<p><span class="smcap">Objections to the Calorimeter.</span>&mdash;The calorimeter,
+or sixth method, has the same objection.
+The galvanoscope and electro-magnet do not respond
+equally to all currents, and this is also true,
+even to a greater extent, with the calorimeter.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p60" id="p60">p. 60</a></span></p>
+
+<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>VOLTS, AMPERES, OHMS AND WATTS</h3>
+
+
+<p><span class="smcap">Understanding Terms.</span>&mdash;We must now try to
+ascertain the meaning of some of the terms
+so frequently used in connection with electricity.
+If you intended to sell or measure produce or
+goods of any kind, it would be essential to know
+how many pints or quarts are contained in a
+gallon, or in a bushel, or how many inches there
+are in a yard, and you also ought to know just
+what the quantity term <i>bushel</i> or the measurement
+<i>yard</i> means.</p>
+
+<p><span class="smcap">Intensity and Quantity.</span>&mdash;Electricity, while it
+has no weight, is capable of being measured by
+means of its intensity, or by its quantity. Light
+may be measured or tested by its brilliancy. If
+one light is of less intensity than another and both
+of them receive their impulses from the same
+source, there must be something which interferes
+with that light which shows the least brilliancy.
+Electricity can also be interfered with, and this
+interference is called <i>resistance</i>.</p>
+
+<p><span class="smcap">Voltage.</span>&mdash;Water may be made to flow with
+greater or less force, or velocity, through a pipe,
+the degree of same depending upon the height of<span class='pagenum'><a name="p61" id="p61">p. 61</a></span>
+the water which supplies the pipe. So with electricity.
+It may pass over a wire with greater or
+less force under one condition than another. This
+force is called voltage. If we have a large pipe,
+a much greater quantity of water will flow through
+it than will pass through a small pipe, providing
+the pressure in each case is alike. This quantity
+in electricity is called <i>amperage</i>.</p>
+
+<p>In the case of water, a column 1" &times; 1", 28
+inches in height, weighs 1 pound; so that if a
+pipe 1 inch square draws water from the bottom
+it flows with a pressure of 1 pound. If the pipe
+has a measurement of 2 square inches, double the
+quantity of water will flow therefrom, at the same
+pressure.</p>
+
+<p><span class="smcap">Amperage.</span>&mdash;If, on the other hand, we have a
+pipe 1 inch square, and there is a depth of 56
+inches of water in the reservoir, we shall get as
+much water from the reservoir as though we had
+a pipe of 2 square inches drawing water from a
+reservoir which is 28 inches deep.</p>
+
+<p><span class="smcap">Meaning of Watts.</span>&mdash;It is obvious, therefore,
+that if we multiply the height of the water in inches
+with the area of the pipe, we shall obtain a factor
+which will show how much water is flowing.</p>
+
+<p>Here are two examples:</p>
+
+<ol style="margin: 0 15% 0 15%">
+<li>
+<span class='pagenum'><a name="p62" id="p62">p. 62</a></span>28 inches = height of the water in the reservoir.<br />
+2 square inches = size of the pipe.<br />
+Multiply 28 &times; 2 = 56.</li>
+<li>56 = height of the water in the reservoir.<br />
+1 square inch = size of the pipe.<br />
+Multiply 56 &times; 1 = 56.</li>
+</ol>
+
+<p>Thus the two problems are equal.</p>
+
+<p><span class="smcap">A Kilowatt.</span>&mdash;Now, in electricity, remembering
+that the height of the water corresponds with <i>voltage</i>
+in electricity, and the size of the pipe with
+<i>amperage</i>, if we multiply volts by amperes, or amperes
+by volts, we get a result which is indicated
+by the term <i>watts</i>. One thousand of these watts
+make a kilowatt, and the latter is the standard
+of measurement by which a dynamo or motor is
+judged or rated.</p>
+
+<p>Thus, if we have 5 amperes and 110 volts, the
+result of multiplying them would be 550 watts,
+or 5 volts and 110 amperes would produce 550
+watts.</p>
+
+<p><span class="smcap">A Standard of Measurement.</span>&mdash;But with all
+this we must have some standard. A bushel
+measure is of a certain size, and a foot has a
+definite length, so in electricity there is a recognized
+force and quantity which are determined
+as follows:</p>
+
+<p><span class="smcap">The Ampere Standard.</span>&mdash;It is necessary, first,
+to determine what an ampere is. For this purpose
+a standard solution of nitrate of silver is<span class='pagenum'><a name="p63" id="p63">p. 63</a></span>
+used, and a current of electricity is passed through
+this solution. In doing so the current deposits
+silver at the rate of 0.001118 grains per second for
+each ampere.</p>
+
+<p><span class="smcap">The Voltage Standard.</span>&mdash;In order to determine
+the voltage we must know something of <i>resistance</i>.
+Different metals do not transmit a current with
+equal ease. The size of a conductor, also, is an
+important factor in the passage of a current. A
+large conductor will transmit a current much better
+than a small conductor. We must therefore
+have a standard for the <i>ohm</i>, which is the measure
+of resistance.</p>
+
+<p><span class="smcap">The Ohm.</span>&mdash;It is calculated in this way: There
+are several standards, but the one most generally
+employed is the <i>International Ohm</i>. To determine
+it, by this system, a column of pure mercury,
+106.3 millimeters long and weighing 14.4521
+grams, is used. This would make a square tube
+about 94 inches long, and a little over 1/25 of
+an inch in diameter. The resistance to a current
+flow in such a column would be equal to 1
+ohm.</p>
+
+<p><span class="smcap">Calculating the Voltage.</span>&mdash;In order to arrive
+at the voltage we must use a conductor, which,
+with a resistance of 1 ohm, will produce 1 ampere.
+It must be remembered that the volt is the
+practical unit of electro-motive force</p>
+<p class="pn"><span class='pagenum'><a name="p64" id="p64">p. 64</a></span></p>
+
+<p>While it would be difficult for the boy to conduct
+these experiments in the absence of suitable
+apparatus, still, it is well to understand thoroughly
+how and why these standards are made
+and used.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p65" id="p65">p. 65</a></span></p>
+
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND LIKE APPARATUS</h3>
+
+
+<p><span class="smcap">Simple Switches.</span>&mdash;We have now gone over the
+simpler or elementary outlines of electrical phenomena,
+and we may commence to do some of the
+practical work in the art. We need certain apparatus
+to make connections, which will be constructed
+first.</p>
+
+<p><span class="smcap">A Two-Pole Switch.</span>&mdash;A simple two-pole switch
+for a single line is made as follows:</p>
+
+<p>A base block (A, Fig. <a href="#fig43">43</a>) 3 inches long, 2 inches
+wide and &frac34; inch thick, has on it, at one end, a
+binding screw (B), which holds a pair of fingers
+(C) of brass or copper, these fingers being bent
+upwardly and so arranged as to serve as fingers to
+hold a switch bar (D) between them. This bar
+is also of copper or brass and is pivoted to the
+fingers. Near the other end of the base is a
+similar binding screw (E) and fingers (F) to receive
+the blade of the switch bar. The bar has a
+handle (G) of wood. The wires are attached to
+the respective binding screws (B, E).</p>
+
+<p><span class="smcap">Double-Pole Switch.</span>&mdash;A double-pole switch
+or a switch for a double line is shown in Fig. <a href="#fig44">44</a>.<span class='pagenum'><a name="p66" id="p66">p. 66</a></span>
+This is made similar in all respects to the one
+shown in Fig. <a href="#fig43">43</a>, excepting that there are two
+switch blades (A, A) connected by a cross bar
+(B) of insulating material, and this bar carries
+the handle (C).</p>
+
+<div class="figcenter" style="width: 345px;">
+<a id="fig43" name="fig43"></a><a href="#p66">
+<img src="images/illus-fig43.png" width="345" height="130" alt="Fig. 43. Two-Pole Switch" title="Fig. 43. Two-Pole Switch" /></a>
+<span class="caption"><i>Fig. 43.</i> <span class="smcap">Two-Pole Switch</span></span>
+</div>
+
+<div class="figcenter" style="width: 342px;">
+<a id="fig44" name="fig44"></a><a href="#p66">
+<img src="images/illus-fig44.png" width="342" height="151" alt="Fig. 44. Double-Pole Switch" title="Fig. 44. Double-Pole Switch" /></a>
+<span class="caption"><i>Fig. 44.</i> <span class="smcap">Double-Pole Switch</span></span>
+</div>
+
+<p>Other types of switch will be found very useful.
+In Fig. <a href="#fig45">45</a> is a simple sliding switch in which
+the base block has, at one end, a pair of copper
+plates (A, B), each held at one end to the base
+by a binding screw (C), and having a bearing or
+contact surface (D) at its other end. At the<span class='pagenum'><a name="p67" id="p67">p. 67</a></span>
+other end of the base is a copper plate (E) held
+by a binding screw (F), to the inner end of which
+plate is hinged a swinging switch blade (G), the
+free end of which is adapted to engage with the
+plates (A, B).</p>
+
+<div class="figcenter" style="width: 378px;">
+<a id="fig45" name="fig45"></a><a href="#p67">
+<img src="images/illus-fig45.png" width="378" height="188" alt="Fig. 45. Sliding Switch" title="Fig. 45. Sliding Switch" /></a>
+<span class="caption"><i>Fig. 45.</i> <span class="smcap">Sliding Switch</span></span>
+</div>
+
+<p><span class="smcap">Sliding Switch.</span>&mdash;This sliding switch form may
+have the contact plates (A, B and C, Fig. <a href="#fig46">46</a>) circularly
+arranged and any number may be located
+on the base, so they may be engaged by a single
+switching lever (H). It is the form usually
+adopted for rheostats.</p>
+
+<p><span class="smcap">Reversing Switch.</span>&mdash;A reversing switch is
+shown in Fig. <a href="#fig47">47</a>. The base has two plates (A, B)
+at one end, to which the parallel switch bars
+(C, D) are hinged. The other end of the base
+has three contact plates (E, F, G) to engage the<span class='pagenum'><a name="p68" id="p68">p. 68</a></span>
+swinging switch bars, these latter being at such
+distance apart that they will engage with the
+middle and one of the outer plates. The inlet
+wires, positive and negative, are attached to the
+plates (A, B, respectively), and one of the outlet
+wires (H) is attached to the middle contact plate
+(F), while the other wire is connected up with
+both of the outside plates. When the switch bars
+(C, D) are thrown to the left so as to be in contact
+with E, F, the outside plate (E) and the middle
+plate (F) will be positive and negative, respectively;
+but when the switch is thrown to the
+right, as shown in the figure, plate F becomes
+positive and plate E negative, as shown.</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig46" name="fig46"></a><a href="#p68">
+<img src="images/illus-fig46.png" width="349" height="184" alt="Fig. 46. Rheostat Form of Switch" title="Fig. 46. Rheostat Form of Switch" /></a>
+<span class="caption"><i>Fig. 46.</i> <span class="smcap">Rheostat Form of Switch</span></span>
+</div>
+
+<p><span class="smcap">Push Buttons.</span>&mdash;A push button is but a modified
+structure of a switch, and they are serviceable<span class='pagenum'><a name="p69" id="p69">p. 69</a></span>
+because they are operating, or the circuit is
+formed only while the finger is on the button.</p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig47" name="fig47"></a><a href="#p69">
+<img src="images/illus-fig47.png" width="350" height="186" alt="Fig. 47. Reversing Switch" title="Fig. 47. Reversing Switch" /></a>
+<span class="caption"><i>Fig. 47.</i> <span class="smcap">Reversing Switch</span></span>
+</div>
+
+<p>In its simplest form (Fig. <a href="#fig48">48</a>) the push button
+has merely a circular base (A) of insulating material,
+and near one margin, on the flat side, is a
+rectangular plate (B), intended to serve as a
+contact plate as well as a means for attaching
+one of the wires thereto. In line with this plate
+is a spring finger (C), bent upwardly so that it
+is normally out of contact with the plate (B), its
+end being held by a binding screw (D). To effect
+contact, the spring end of the finger (C) is pressed
+against the bar (B), as at E. This is enclosed
+in a suitable casing, such as will readily suggest
+itself to the novice.</p>
+
+<p><span class="smcap">Electric Bell.</span>&mdash;One of the first things the boy<span class='pagenum'><a name="p70" id="p70">p. 70</a></span>
+wants to make, and one which is also an interesting
+piece of work, is an electric bell.</p>
+
+<p>To make this he will be brought, experimentally,
+in touch with several important features in electrical
+work. He must make a battery for the
+production of current, a pair of electro-magnets
+to be acted upon by the current, a switch to control
+it, and, finally, he must learn how to connect
+it up so that it may be operated not only from
+one, but from two or more push buttons.</p>
+
+<div class="figcenter" style="width: 359px;">
+<a id="fig48" name="fig48"></a><a href="#p70">
+<img src="images/illus-fig48.png" width="359" height="127" alt="Fig. 48. Push Button" title="Fig. 48. Push Button" /></a>
+<span class="caption"><i>Fig. 48.</i> <span class="smcap">Push Button</span></span>
+</div>
+
+<p><span class="smcap">How Made.</span>&mdash;In Fig. <a href="#fig49">49</a> is shown an electric
+bell, as usually constructed, so modified as to show
+the structure at a glance, with its connections. A
+is the base, B, B' the binding posts for the wires,
+C, C the electro-magnets, C' the bracket for holding
+the magnets, D the armature, E the thin
+spring which connects the armature with the post
+F, G the clapper arm, H the bell, I the adjusting
+screw on the post J, K the wire lead from the<span class='pagenum'><a name="p71" id="p71">p. 71</a></span>
+binding post B to the first magnet, L the wire
+which connects the two magnets, M the wire which
+runs from the second magnet to the post J, and
+N a wire leading from the armature post to the
+binding post B'.</p>
+
+<div class="figcenter" style="width: 354px;">
+<a id="fig49" name="fig49"></a><a href="#p71">
+<img src="images/illus-fig49.png" width="354" height="371" alt="Fig. 49. Electric Bell" title="Fig. 49. Electric Bell" /></a>
+<span class="caption"><i>Fig. 49.</i> <span class="smcap">Electric Bell</span></span>
+</div>
+
+<p>The principle of the electric bell is this: In
+looking at Fig. <a href="#fig49">49</a>, you will note that the armature
+bar D is held against the end of the adjusting<span class='pagenum'><a name="p72" id="p72">p. 72</a></span>
+screw by the small spring E. When a current
+is turned on, it passes through the connections
+and conduits as follows: Wire K to the magnets,
+wire M to the binding post J, and set screw I,
+then through the armature to the post F, and
+from post F to the binding post B'.</p>
+
+<div class="figcenter" style="width: 364px;">
+<a id="fig50" name="fig50"></a><a href="#p72">
+<img src="images/illus-fig50.png" width="364" height="179" alt="Fig. 50. Armature of Electric Bell" title="Fig. 50. Armature of Electric Bell" /></a>
+<span class="caption"><i>Fig. 50.</i> <span class="smcap">Armature of Electric Bell</span></span>
+</div>
+
+<p><span class="smcap">Electric Bell&mdash;How Operated.</span>&mdash;The moment
+a current passes through the magnets (C, C), the
+core is magnetized, and the result is that the armature
+(D) is attracted to the magnets, as shown
+by the dotted lines (O), when the clapper strikes
+the bell. But when the armature moves over to
+the magnet, the connection is broken between the
+screw (I) and armature (D), so that the cores
+of the magnets are demagnetized and lose their
+pull, and the spring (E) succeeds in drawing<span class='pagenum'><a name="p73" id="p73">p. 73</a></span>
+back the armature. This operation of vibrating
+the armature is repeated with great rapidity,
+alternately breaking and re-establishing the circuit,
+by the action of the current.</p>
+
+<p>In making the bell, you must observe one thing,
+the binding posts (B, B') must be insulated from
+each other, and the post J, or the post F, should
+also be insulated from the base. For convenience
+we show the post F insulated, so as to necessitate
+the use of wire (N) from post (F) to binding post
+(B').</p>
+
+<p>The foregoing assumes that you have used a
+cast metal base, as most bells are now made;
+but if you use a wooden base, the binding posts
+(B, B') and the posts (F, J) are insulated from
+each other, and the construction is much simplified.</p>
+
+<p>It is better, in practice, to have a small spring
+(P, Fig. <a href="#fig50">50</a>) between the armature (D) and the
+end of the adjusting screw (I), so as to give a
+return impetus to the clapper. The object of the
+adjusting screw is to push and hold the armature
+close up to the ends of the magnets, if it seems
+necessary.</p>
+
+<p>If two bells are placed on the base with the
+clapper mounted between them, both bells will be
+struck by the swinging motion of the armature.</p>
+
+<p>An easily removable cap or cover is usually<span class='pagenum'><a name="p74" id="p74">p. 74</a></span>
+placed over the coils and armature, to keep out
+dust.</p>
+
+<p>A very simple annunciator may be attached to
+the bell, as shown in the following figures:</p>
+
+<div class="figcenter" style="width: 365px;">
+<a id="fig51-54" name="fig51-54"></a><a href="#p74">
+<img src="images/illus-fig51-54.png" width="365" height="367" alt="Figs. 51-54. Annunciator" title="Figs. 51-54. Annunciator" /></a>
+<span class="caption"><i>Figs. 51-54.</i> <span class="smcap">Annunciator</span></span>
+</div>
+
+<p><span class="smcap">Annunciators.</span>&mdash;Make a box of wood, with a
+base (A) 4" &times; 5" and &frac12; inch thick. On this you
+can permanently mount the two side pieces (B)
+and two top and bottom pieces (C), respectively,<span class='pagenum'><a name="p75" id="p75">p. 75</a></span>
+so they project outwardly 4&frac12; inches from the base.
+On the open front place a wood or metal plate
+(D), provided with a square opening (D), as in
+Fig. <a href="#fig51-54">54</a>, near its lower end. This plate is held
+to the box by screws (E).</p>
+
+<p>Within is a magnet (F), screwed into the base
+(A), as shown in Fig. <a href="#fig51-54">51</a>; and pivoted to the
+bottom of the box is a vertical armature (G),
+which extends upwardly and contacts with the
+core of the magnet. The upper end of the armature
+has a shoulder (H), which is in such position
+that it serves as a rest for a V-shaped stirrup
+(I), which is hinged at J to the base (C). This
+stirrup carries the number plate (K), and when
+it is raised to its highest point it is held on the
+shoulder (H), unless the electro-magnet draws
+the armature out of range of the stirrup. A
+spring (L) bearing against the inner side of the
+armature keeps its upper end normally away from
+the magnet core. When the magnet draws the
+armature inwardly, the number plate drops and
+exposes the numeral through the opening in the
+front of the box. In order to return the number
+plate to its original position, as shown in Fig. <a href="#fig51-54">51</a>,
+a vertical trigger (M) passes up through the bottom,
+its upper end being within range of one of
+the limbs of the stirrup.</p>
+
+<p>This is easily made by the ingenious boy, and<span class='pagenum'><a name="p76" id="p76">p. 76</a></span>
+will be quite an acquisition to his stock of instruments.
+In practice, the annunciator may be located
+in any convenient place and wires run to
+that point.</p>
+
+<div class="figcenter" style="width: 358px;">
+<a id="fig55" name="fig55"></a><a href="#p76">
+<img src="images/illus-fig55.png" width="358" height="180" alt="Fig. 55. Alarm Switch on Window" title="Fig. 55. Alarm Switch on Window" /></a>
+<span class="caption"><i>Fig. 55.</i> <span class="smcap">Alarm Switch on Window</span></span>
+</div>
+
+<div class="figcenter" style="width: 359px;">
+<a id="fig56" name="fig56"></a><a href="#p76">
+<img src="images/illus-fig56.png" width="359" height="205" alt="Fig. 56. Burglar Alarm Attachment to Window"
+title="Fig. 56. Burglar Alarm Attachment to Window" /></a>
+<span class="caption"><i>Fig. 56.</i> <span class="smcap">Burglar Alarm Attachment to Window</span></span>
+</div>
+
+<p><span class="smcap">Burglar Alarm.</span>&mdash;In order to make a burglar
+alarm connection with a bell, push buttons or
+switches may be put in circuit to connect with the<span class='pagenum'><a name="p77" id="p77">p. 77</a></span>
+windows and doors, and by means of the annunciators
+you may locate the door or window which
+has been opened. The simplest form of switch
+for a window is shown in the following figures:</p>
+
+<p>The base piece (A), which may be of hard rubber
+or fiber, is &frac14; inch thick and 1" &times; 1&frac12;" in size.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig57" name="fig57"></a><a href="#p77">
+<img src="images/illus-fig57.png" width="344" height="213" alt="Fig. 57. Burglar Alarm Contact" title="Fig. 57. Burglar Alarm Contact" /></a>
+<span class="caption"><i>Fig. 57.</i> <span class="smcap">Burglar Alarm Contact</span></span>
+</div>
+
+<p>At one end is a brass plate (B), with a hole for a
+wood screw (C), this screw being designed to pass
+through the plate and also into the window-frame,
+so as to serve as a means of attaching one of the
+wires thereto. The inner end of the plate has a
+hole for a round-headed screw (C') that also goes
+through the base and into the window-frame. It
+also passes through the lower end of the heart-shaped
+metal switch-piece (D)</p>
+<p class="pn"><span class='pagenum'><a name="p78" id="p78">p. 78</a></span></p>
+
+<p>The upper end of the base has a brass plate
+(E), also secured to the base and window by a
+screw (F) at its upper end. The heart-shaped
+switch is of such length and width at its upper
+end that when it is swung to the right with one
+of the lobes projecting past the edge of the window-frame,
+the other lobe will be out of contact
+with the plate (E).</p>
+
+<div class="figcenter" style="width: 360px;">
+<a id="fig58" name="fig58"></a><a href="#p78">
+<img src="images/illus-fig58.png" width="360" height="176" alt="Fig. 58. Neutral Position of Contact" title="Fig. 58. Neutral Position of Contact" /></a>
+<span class="caption"><i>Fig. 58.</i> <span class="smcap">Neutral Position of Contact</span></span>
+</div>
+
+<p>The window sash (G) has a removable pin (H),
+which, when the sash moves upwardly, is in the
+path of the lobe of the heart-shaped switch, as
+shown in Fig. <a href="#fig56">56</a>, and in this manner the pin (H)
+moves the upper end of the switch (D) inwardly,
+so that the other lobe contacts with the plate (E),
+and establishes an electric circuit, as shown in
+Fig. <a href="#fig57">57</a>. During the daytime the pin (H) may
+be removed, and in order to protect the switch<span class='pagenum'><a name="p79" id="p79">p. 79</a></span>
+the heart-shaped piece (D) is swung inwardly,
+as shown in Fig. <a href="#fig58">58</a>, so that neither of the lobes
+is in contact with the plate (E).</p>
+
+<p><span class="smcap">Wire Circuiting.</span>&mdash;For the purpose of understanding
+fully the circuiting, diagrams will be
+shown of the simple electric bell with two push
+buttons; next in order, the circuiting with an
+annunciator and then the circuiting necessary for
+a series of windows and doors, with annunciator
+attachments.</p>
+
+<div class="figcenter" style="width: 348px;">
+<a id="fig59" name="fig59"></a><a href="#p79">
+<img src="images/illus-fig59.png" width="348" height="172" alt="Fig. 59. Circuiting for Electric Bell" title="Fig. 59. Circuiting for Electric Bell" /></a>
+<span class="caption"><i>Fig. 59.</i> <span class="smcap">Circuiting for Electric Bell</span></span>
+</div>
+
+<p><span class="smcap">Circuiting System with a Bell and Two Push
+Buttons.</span>&mdash;Fig. <a href="#fig59">59</a> shows a simple circuiting system
+which has two push buttons, although any
+number may be used, so that the bell will ring
+when the circuit is closed by either button.</p>
+
+<p><span class="smcap">The Push Buttons and the Annunciator
+Bells.</span>&mdash;Fig. <a href="#fig60">60</a> shows three push buttons and an
+annunciator for each button. These three circuits<span class='pagenum'><a name="p80" id="p80">p. 80</a></span>
+are indicated by A, B and C, so that when
+either button makes contact, a complete circuit is
+formed through the corresponding annunciator.</p>
+
+<div class="figcenter" style="width: 401px;">
+<a id="fig60" name="fig60"></a><a href="#p80">
+<img src="images/illus-fig60.png" width="401" height="165" alt="Fig. 60. Annunciators" title="Fig. 60. Annunciators" /></a>
+<span class="caption"><i>Fig. 60.</i> <span class="smcap">Annunciators</span></span>
+</div>
+
+<div class="figcenter" style="width: 402px;">
+<a id="fig61" name="fig61"></a><a href="#p80">
+<img src="images/illus-fig61.png" width="402" height="177" alt="Fig. 61. Wiring System for a House" title="Fig. 61. Wiring System for a House" /></a>
+<span class="caption"><i>Fig. 61.</i> <span class="smcap">Wiring System for a House</span></span>
+</div>
+
+<p><span class="smcap">Wiring Up a House.</span>&mdash;The system of wiring up
+a house so that all doors and windows will be
+connected to form a burglar alarm outfit, is shown
+in Fig. <a href="#fig61">61</a>. It will be understood that, in practice,
+the bell is mounted on or at the annunciator, and<span class='pagenum'><a name="p81" id="p81">p. 81</a></span>
+that, for convenience, the annunciator box has also
+a receptacle for the battery. The circuiting is
+shown diagramatically, as it is called, so as fully
+to explain how the lines are run. Two windows
+and a door are connected up with an annunciator
+having three drops, or numbers 1, 2, 3. The circuit
+runs from one pole of the battery to the bell
+and then to one post of the annunciator. From
+the other post a wire runs to one terminal of the
+switch at the door or window. The other switch
+terminal has a wire running to the other pole of
+the battery.</p>
+
+<p>A, B, C represent the circuit wires from the terminals
+of the window and door switches, to the
+annunciators.</p>
+
+<p>It is entirely immaterial which side of the battery
+is connected up with the bell.</p>
+
+<p>From the foregoing it will readily be understood
+how to connect up any ordinary apparatus,
+remembering that in all cases the magnet must
+be brought into the electric circuit.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p82" id="p82">p. 82</a></span></p>
+
+<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>ACCUMULATORS. STORAGE OR SECONDARY BATTERIES</h3>
+
+
+<p><span class="smcap">Storing Up Electricity.</span>&mdash;In the foregoing
+chapters we have seen that, originally, electricity
+was confined in a bottle, called the Leyden jar,
+from which it was wholly discharged at a single
+impulse, as soon as it was connected up by external
+means. Later the primary battery and the
+dynamo were invented to generate a constant
+current, and after these came the second form
+of storing electricity, called the storage or secondary
+battery, and later still recognized as accumulators.</p>
+
+<p><span class="smcap">The Accumulator.</span>&mdash;The term <i>accumulator</i> is,
+strictly speaking, the more nearly correct, as electricity
+is, in reality, "<i>stored</i>" in an accumulator.
+But when an accumulator is charged by a current
+of electricity, a chemical change is gradually produced
+in the active element of which the accumulator
+is made. This change or decomposition
+continues so long as the charging current is on.
+When the accumulator is disconnected from the
+charging battery or dynamo, and its terminals
+are connected up with a lighting system, or with
+a motor, for instance, a reverse process is set<span class='pagenum'><a name="p83" id="p83">p. 83</a></span>
+up, or the particles re-form themselves into their
+original compositions, which causes a current to
+flow in a direction opposite to that of the charging
+current.</p>
+
+<p>It is immaterial to the purposes of this chapter,
+as to the charging source, whether it be by
+batteries or dynamos; the same principles will
+apply in either case.</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig62" name="fig62"></a><a href="#p83">
+<img src="images/illus-fig62.png" width="351" height="229" alt="Fig. 62. Accumulator Grids" title="Fig. 62. Accumulator Grids" /></a>
+<span class="caption"><i>Fig. 62.</i> <span class="smcap">Accumulator Grids</span></span>
+</div>
+
+<p><span class="smcap">Accumulator Plates.</span>&mdash;The elements used for
+accumulator plates are red lead for the positive
+plates, and precipitated lead, or the well-known
+litharge, for the negative plates. Experience has
+shown that the best way to hold this material is
+by means of lead grids</p>
+<p class="pn"><span class='pagenum'><a name="p84" id="p84">p. 84</a></span></p>
+
+<p>Fig. 62 shows the typical form of one of these
+grids. It is made of lead, cast or molded in one
+piece, usually square, as at A, with a wing or
+projection (B), at one margin, extending upwardly
+and provided with a hole (C). The grid is
+about a quarter of an inch thick.</p>
+
+<p><span class="smcap">The Grid.</span>&mdash;The open space, called the grid,
+proper, comprises cross bars, integral with the
+plate, made in a variety of shapes. Fig. <a href="#fig62">62</a> shows
+three forms of constructing these bars or ribs,
+the object being to provide a form which will
+hold in the lead paste, which is pressed in so
+as to make a solid-looking plate when completed.</p>
+
+<p><span class="smcap">The Positive Plate.</span>&mdash;The positive plate is made
+in the following manner: Make a stiff paste of
+red lead and sulphuric acid; using a solution, say,
+of one part of acid to two parts of water. The
+grid is laid on a flat surface and the paste forced
+into the perforations with a stiff knife or spatula.
+Turn over the grid so as to get the paste in evenly
+on both sides.</p>
+
+<p>The grid is then stood on its edge, from 18 to 20
+hours, to dry, and afterwards immersed in a concentrated
+solution of chloride of lime, so as to
+convert it into lead peroxide. When the action
+is complete it is thoroughly rinsed in cold water,
+and is ready to use.</p>
+
+<p><span class="smcap">The Negative Plate.</span>&mdash;The negative plate is<span class='pagenum'><a name="p85" id="p85">p. 85</a></span>
+filled, in like manner, with precipitated lead. This
+lead is made by putting a strip of zinc into a
+standard solution of acetate of lead, and crystals
+will then form on the zinc. These will be very
+thin, and will adhere together, firmly, forming a
+porous mass. This, when saturated and kept under
+water for a short time, may be put into the
+openings of the negative plate.</p>
+
+<div class="figcenter" style="width: 345px;">
+<a id="fig63" name="fig63"></a><a href="#p85">
+<img src="images/illus-fig63.png" width="345" height="292" alt="Fig. 63. Assemblage of Accumulator Plates"
+title="Fig. 63. Assemblage of Accumulator Plates" /></a>
+<span class="caption"><i>Fig. 63.</i> <span class="smcap">Assemblage of Accumulator Plates</span></span>
+</div>
+
+<p><span class="smcap">Connecting Up the Plates.</span>&mdash;The next step is
+to put these plates in position to form a battery.
+In Fig. <a href="#fig63">63</a> is shown a collection of plates connected
+together</p>
+<p class="pn"><span class='pagenum'><a name="p86" id="p86">p. 86</a></span></p>
+
+<p>For simplicity in illustrating, the cell is made
+up of glass, porcelain, or hard rubber, with five
+plates (A), A, A representing the negative and B,
+B the positive plates. A base of grooved strips
+(C, C) is placed in the batteries of the cell to
+receive the lower ends of the plates. The positive
+plates are held apart by means of a short
+section of tubing (D), which is clamped and held
+within the plates by a bolt (E), this bolt also
+being designed to hold the terminal strip (F).</p>
+
+<p>In like manner, the negative plates are held
+apart by the two tubular sections (G), each of
+which is of the same length as the section D of
+the positives. The bolt (H) holds the negatives
+together as well as the terminal (I). The terminals
+should be lead strips, and it would be well,
+owing to the acid fumes which are formed, to
+coat all brass work, screws, etc., with paraffine
+wax.</p>
+
+<p>The electrolyte or acid used in the cell, for
+working purposes, is a pure sulphuric acid, which
+should be diluted with about four times its weight
+in water. Remember, you should always add the
+strong acid to the water, and never pour the
+water into the acid, as the latter method causes a
+dangerous ebullition, and does not produce a good
+mixture</p>
+<p class="pn"><span class='pagenum'><a name="p87" id="p87">p. 87</a></span></p>
+
+<p>Put enough of this solution into the cell to cover
+the tops of the plates, and the cell is ready.</p>
+
+<div class="figcenter" style="width: 354px;">
+<a id="fig64" name="fig64"></a><a href="#p85">
+<img src="images/illus-fig64.png" width="354" height="118" alt="Fig. 64. Connecting Up Storage Battery in Series"
+title="Fig. 64. Connecting Up Storage Battery in Series" /></a>
+<span class="caption"><i>Fig. 64.</i> <span class="smcap">Connecting Up Storage Battery in Series</span></span>
+</div>
+
+<p><span class="smcap">Charging the Cells.</span>&mdash;The charge of the current
+must never be less than 2.5 volts. Each cell
+has an output, in voltage, of about 2 volts, hence
+if we have, say, 10 cells, we must have at least
+25 volts charging capacity. We may arrange
+these in one line, or in series, as it is called, so
+far as the connections are concerned, and charge
+them with a dynamo, or other electrical source,
+which shows a pressure of 25 volts, as illustrated
+in Fig. <a href="#fig64">64</a>, or, instead of this, we may put them
+into two parallel sets of 5 cells each, as shown in
+Fig. <a href="#fig65">65</a>, and use 12.5 volts to charge with. In
+this case it will take double the time because we
+are charging with only one-half the voltage used
+in the first case.</p>
+
+<p>The positive pole of the dynamo should be
+connected with the positive pole of the accumulator<span class='pagenum'><a name="p88" id="p88">p. 88</a></span>
+cell, and negative with negative. When
+this has been done run up the machine until it
+slightly exceeds the voltage of the cells. Thus,
+if we have 50 cells in parallel, like in Fig. <a href="#fig64">64</a>, at
+least 125 volts will be required, and the excess
+necessary should bring up the voltage in the dynamo
+to 135 or 140 volts.</p>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig65" name="fig65"></a><a href="#p88">
+<img src="images/illus-fig65.png" width="353" height="129" alt="Fig. 65. Parallel Series" title="Fig. 65. Parallel Series" /></a>
+<span class="caption"><i>Fig. 65.</i> <span class="smcap">Parallel Series</span></span>
+</div>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig66" name="fig66"></a><a href="#p88">
+<img src="images/illus-fig66.png" width="353" height="144" alt="Fig. 66. Charging Circuit" title="Fig. 66. Charging Circuit" /></a>
+<span class="caption"><i>Fig. 66.</i> <span class="smcap">Charging Circuit</span></span>
+</div>
+
+<p><span class="smcap">The Initial Charge.</span>&mdash;It is usual initially to
+charge the battery from periods ranging from 36
+to 40 hours, and to let it stand for 12 or 15 hours,
+after which to re-charge, until the positive plates
+have turned to a chocolate color, and the negative<span class='pagenum'><a name="p89" id="p89">p. 89</a></span>
+plates to a slate or gray color, and both plates
+give off large bubbles of gas.</p>
+
+<p>In charging, the temperature of the electrolyte
+should not exceed 100&deg; Fahrenheit.</p>
+
+<p>When using the accumulators they should never
+be fully discharged.</p>
+
+<p><span class="smcap">The Charging Circuit.</span>&mdash;The diagram (Fig.
+<a href="#fig66">66</a>) shows how a charging circuit is formed. The
+lamps are connected up in parallel, as illustrated.
+Each 16-candle-power 105-volt lamp will carry &frac12;
+ampere, so that, supposing we have a dynamo
+which gives 110 volts, and we want to charge a
+4-volt accumulator, there will be 5-volt surplus to
+go to the accumulator. If, for instance, you want
+the cell to have a charge of 2 amperes, four of
+these lamps should be connected up in parallel.
+If 3 amperes are required, use 6 lamps, and so on.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p90" id="p90">p. 90</a></span></p>
+
+<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>THE TELEGRAPH</h3>
+
+
+<p>The telegraph is a very simple instrument.
+The key is nothing more or less than a switch
+which turns the current on and off alternately.</p>
+
+<p>The signals sent over the wires are simply the
+audible sounds made by the armature, as it moves
+to and from the magnets.</p>
+
+<p><span class="smcap">Mechanism in Telegraph Circuits.</span>&mdash;A telegraph
+circuit requires three pieces of mechanism
+at each station, namely, a key used by the sender,
+a sounder for the receiver, and a battery.</p>
+
+<p><span class="smcap">The Sending Key.</span>&mdash;The base of the sending instrument
+is six inches long, four inches wide, and
+three-quarters of an inch thick, made of wood,
+or any suitable non-conducting material. The key
+(A) is a piece of brass three-eighths by one-half
+inch in thickness and six inches long. Midway
+between its ends is a cross hole, to receive the
+pivot pin (B), which also passes through a pair
+of metal brackets (C, D), the bracket C having
+a screw to hold one of the line wires, and the other
+bracket having a metal switch (E) hinged thereto.
+This switch bar, like the brackets, is made of<span class='pagenum'><a name="p91" id="p91">p. 91</a></span>
+brass, one-half inch wide by one-sixteenth of an
+inch thick.</p>
+
+<p>Below the forward end of the key (A) is a cross
+bar of brass (F), screwed to the base by a screw
+at one end, to receive the other line wire. Directly
+below the key (A) is a screw (G), so that the key
+will strike it when moved downwardly. The other
+end of the bar (F) contacts with the forward end
+of the switch bar (E) when the latter is moved
+inwardly.</p>
+
+<div class="figcenter" style="width: 357px;">
+<a id="fig67" name="fig67"></a><a href="#p91">
+<img src="images/illus-fig67.png" width="357" height="138" alt="Fig. 67. Telegraph Sending Key" title="Fig. 67. Telegraph Sending Key" /></a>
+<span class="caption"><i>Fig. 67.</i> <span class="smcap">Telegraph Sending Key</span></span>
+</div>
+
+<p>The forward end of the key (A) has a knob
+(H) for the fingers, and the rear end has an
+elastic (I) attached thereto which is secured to
+the end of the base, so that, normally, the rear
+end is held against the base and away from the
+screw head (G). The head (J) of a screw projects
+from the base at its rear end. Key A contacts
+with it.</p>
+
+<p>When the key A contacts with the screw heads<span class='pagenum'><a name="p92" id="p92">p. 92</a></span>
+G, J, a click is produced, one when the key is
+pressed down and the other when the key is released.</p>
+
+<p>You will notice that the two plates C, F are
+connected up in circuit with the battery, so that,
+as the switch E is thrown, so as to be out of contact,
+the circuit is open, and may be closed either
+by the key A or the switch E. The use of the
+switch will be illustrated in connection with the
+sounder.</p>
+
+<div class="figcenter" style="width: 345px;">
+<a id="fig68" name="fig68"></a><a href="#p92">
+<img src="images/illus-fig68.png" width="345" height="182" alt="Fig. 68. Telegraph Sounder" title="Fig. 68. Telegraph Sounder" /></a>
+<span class="caption"><i>Fig. 68.</i> <span class="smcap">Telegraph Sounder</span></span>
+</div>
+
+<p>When the key A is depressed, the circuit of
+course goes through plate C, key A and plate
+F to the station signalled.</p>
+
+<p><span class="smcap">The Sounder.</span>&mdash;The sounder is the instrument
+which carries the electro-magnet.</p>
+
+<p>In Fig. <a href="#fig68">68</a> this is shown in perspective. The
+base is six inches long and four inches wide, being<span class='pagenum'><a name="p93" id="p93">p. 93</a></span>
+made, preferably, of wood. Near the forward
+end is mounted a pair of electro-magnets (A, A),
+with their terminal wires connected up with plates
+B, B', to which the line wires are attached.</p>
+
+<p>Midway between the magnets and the rear end
+of the base is a pair of upwardly projecting brackets
+(C). Between these are pivoted a bar (D),
+the forward end of which rests between the magnets
+and carries, thereon, a cross bar (E) which
+is directly above the magnets, and serves as the
+armature.</p>
+
+<p>The rear end of the base has a screw (F) directly
+beneath the bar D of such height that when
+the rear end of the bar D is in contact therewith
+the armature E will be out of contact with the
+magnet cores (A, A). A spiral spring (G) secured
+to the rear ends of the arm and to the base,
+respectively, serves to keep the rear end of the
+key normally in contact with the screw F.</p>
+
+<p><span class="smcap">Connecting Up the Key and Sounder.</span>&mdash;Having
+made these two instruments, we must next
+connect them up in the circuit, or circuits, formed
+for them, as there must be a battery, a key, and
+a sounder at each end of the line.</p>
+
+<p>In Fig. <a href="#fig69">69</a> you will note two groups of those
+instruments. Now observe how the wires connect
+them together. There are two line wires, one
+(A) which connects up the two batteries, the wire<span class='pagenum'><a name="p94" id="p94">p. 94</a></span>
+being attached so that one end connects with the
+positive terminal of the battery, and the other end
+with the negative terminal.</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig69" name="fig69"></a><a href="#p94">
+<img src="images/illus-fig69.png" width="351" height="171" alt="Fig. 69. A Telegraph Circuit" title="Fig. 69. A Telegraph Circuit" /></a>
+<span class="caption"><i>Fig. 69.</i> <span class="smcap">A Telegraph Circuit</span></span>
+</div>
+
+<p>The other line wire (B), between the two stations,
+has its opposite ends connected with the
+terminals of the electro-magnet C of the sounders.
+The other terminals of each electro-magnet are
+connected up with one terminal of each key by a
+wire (D), and to complete the circuit at each
+station, the other terminal of the key has a wire
+(E) to its own battery.</p>
+
+<p><span class="smcap">Two Stations in Circuit.</span>&mdash;The illustration
+shows station 2 telegraphing to station 1. This
+is indicated by the fact that the switch F' of
+that instrument is open, and the switch F of
+station 1 closed. When, therefore, the key of
+station 2 is depressed, a complete circuit is formed<span class='pagenum'><a name="p95" id="p95">p. 95</a></span>
+which transmits the current through wire E' and
+battery, through line A, then through the battery
+of station 1, through wire E to the key, and from
+the key, through wire D, to the sounder, and
+finally from the sounder over line wire B back
+to the sounder of station 2, completing the circuit
+at the key through wire D'.</p>
+
+<p>When the operator at station 2 closes the switch
+F', and the operator at station 1 opens the switch
+F, the reverse operation takes place. In both
+cases, however, the sounder is in at both ends
+of the line, and only the circuit through the key
+is cut out by the switch F, or F'.</p>
+
+<p><span class="smcap">The Double Click.</span>&mdash;The importance of the
+double click of the sounder will be understood
+when it is realized that the receiving operator
+must have some means of determining if the
+sounder has transmitted a dot or a dash. Whether
+he depresses the key for a dot or a dash, there
+must be one click when the key is pressed down
+on the screw head G (Fig. <a href="#fig62">62</a>), and also another
+click, of a different kind, when the key is raised
+up so that its rear end strikes the screw head J.
+This action of the key is instantly duplicated by
+the bar D (Fig. <a href="#fig68">68</a>) of the sounder, so that the
+sounder as well as the receiver knows the time
+between the first and the second click, and by that
+means he learns that a dot or a dash is made</p>
+<p class="pn"><span class='pagenum'><a name="p96" id="p96">p. 96</a></span></p>
+
+<p><span class="smcap">Illustrating the Dot and the Dash.</span>&mdash;To illustrate:
+Let us suppose, for convenience, that the
+downward movement of the lever in the key, and
+the bar in the sounder, make a sharp click, and
+the return of the lever and bar make a dull click.
+In this case the ear, after a little practice, can
+learn readily how to distinguish the number of
+downward impulses that have been given to the
+key.</p>
+
+<p class="center"><i>The Morse Telegraph Code</i></p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/illus-p113-1.png" width="400" height="248" alt="Morse Code Table: A-Z, 0-9, &amp;" title="Morse Code Table: A-Z, 0-9, &amp;" />
+</div>
+
+<p><span class="smcap">Example in Use.</span>&mdash;Let us take an example in
+the word "electrical."</p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/illus-p113-2.png" width="400" height="47" alt="E L E C T R I C A L" title="E L E C T R I C A L" />
+</div>
+
+<p class="pn"><span class='pagenum'><a name="p97" id="p97">p. 97</a></span></p>
+
+<p>The operator first makes a dot, which means
+a sharp and a dull click close together; there is
+then a brief interval, then a lapse, after which
+there is a sharp click, followed, after a comparatively
+longer interval, with the dull click. Now
+a dash by itself may be an L, a T, or the figure
+0, dependent upon its length. The short dash
+is T, and the longest dash the figure 0. The operator
+will soon learn whether it is either of these
+or the letter L, which is intermediate in length.</p>
+
+<p>In time the sender as well as receiver will
+give a uniform length to the dash impulse, so
+that it may be readily distinguished. In the same
+way, we find that R, which is indicated by a dot,
+is followed, after a short interval, by two dots.
+This might readily be mistaken for the single dot
+for E and the two dots for I, were it not that
+the time element in R is not as long between the
+first and second dots, as it ordinarily is between
+the single dot of E when followed by the two
+dots of I.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p98" id="p98">p. 98</a></span></p>
+
+<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>HIGH TENSION APPARATUS, CONDENSERS, ETC.</h3>
+
+
+<p><span class="smcap">Induction.</span>&mdash;One of the most remarkable things
+in electricity is the action of induction&mdash;that property
+of an electric current which enables it to
+pass from one conductor to another conductor
+through the air. Another singular and interesting
+thing is that the current so transmitted across
+spaces changes its direction of flow, and, furthermore,
+the tension of such a current may be
+changed by transmitting it from one conductor to
+another.</p>
+
+<p><span class="smcap">Low and High Tension.</span>&mdash;In order to effect this
+latter change&mdash;that is, to convert it from a low
+tension to a high tension&mdash;coils are used, one coil
+being wound upon the other; one of these coils is
+called the primary and the other the secondary.
+The primary coil receives the current from the
+battery, or source of electrical power, and the secondary
+coil receives charges, and transmits the
+current.</p>
+
+<p>For an illustration of this examine Fig. <a href="#fig70">70</a>, in
+which you will note a coil of heavy wire (A),
+around which is wound a coil of fine wire (B).
+If, for instance, the primary coil has a low voltage,<span class='pagenum'><a name="p99" id="p99">p. 99</a></span>
+the secondary coil will have a high voltage,
+or tension. Advantage is taken of this phase to
+use a few cells, as a primary battery, and then,
+by a set of <i>Induction Coils</i>, as they are called,
+to build up a high-tension electro-motive force,
+so that the spark will jump across a gap, as shown
+at C, for the purpose of igniting the charges of
+gas in a gasoline motor; or the current may be
+used for medical batteries, and for other purposes.</p>
+
+<div class="figcenter" style="width: 347px;">
+<a id="fig70" name="fig70"></a><a href="#p99">
+<img src="images/illus-fig70.png" width="347" height="110" alt="Fig. 70. Induction Coil and Circuit" title="Fig. 70. Induction Coil and Circuit" /></a>
+<span class="caption"><i>Fig. 70.</i> <span class="smcap">Induction Coil and Circuit</span></span>
+</div>
+
+<p>The current passes, by induction, from the primary
+to the secondary coil. It passes from a
+large conductor to a small conductor, the small
+conductor having a much greater resistance than
+the large one.</p>
+
+<p><span class="smcap">Elastic Property of Electricity.</span>&mdash;While electricity
+has no resiliency, like a spring, for instance,
+still it acts in the manner of a cushion
+under certain conditions. It may be likened to an
+oscillating spring acted upon by a bar</p>
+<p class="pn"><span class='pagenum'><a name="p100" id="p100">p. 100</a></span></p>
+
+<p>Referring to Fig. <a href="#fig71">71</a>, we will assume that the
+bar A in falling down upon the spring B compresses
+the latter, so that at the time of greatest
+compression the bar goes down as far as the
+dotted line C. It is obvious that the spring B
+will throw the bar upwardly. Now, electricity
+appears to have a kind of elasticity, which characteristic
+is taken advantage of in order to increase
+the efficiency of the induction in the coil.</p>
+
+<div class="figcenter" style="width: 341px;">
+<a id="fig71" name="fig71"></a><a href="#p100">
+<img src="images/illus-fig71.png" width="341" height="126" alt="Fig. 71. Illustrating Elasticity" title="Fig. 71. Illustrating Elasticity" /></a>
+<span class="caption"><i>Fig. 71.</i> <span class="smcap">Illustrating Elasticity</span></span>
+</div>
+
+<p><span class="smcap">The Condenser.</span>&mdash;To make a condenser, prepare
+two pine boards like A, say, eight by ten
+inches and a half inch thick, and shellac thoroughly
+on all sides. Then prepare sheets of tinfoil
+(B), six by eight inches in size, and also sheets
+of paraffined paper (C), seven by nine inches in
+dimensions. Also cut out from the waste pieces
+of tinfoil strips (D), one inch by two inches.
+To build up the condenser, lay down a sheet of
+paraffined paper (C), then a sheet of tinfoil (B),<span class='pagenum'><a name="p101" id="p101">p. 101</a></span>
+and before putting on the next sheet of paraffined
+paper lay down one of the small strips (D) of
+tinfoil, as shown in the illustration, so that its
+end projects over one end of the board A; then
+on the second sheet of paraffine paper lay another
+sheet of tinfoil, and on this, at the opposite
+end, place one of the small strips (D), and so
+on, using from 50 to 100 of the tinfoil sheets.
+When the last paraffine sheet is laid on, the other
+board is placed on top, and the whole bound together,
+either by wrapping cords around the same
+or by clamping them together with bolts.</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig72" name="fig72"></a><a href="#p101">
+<img src="images/illus-fig72.png" width="349" height="172" alt="Fig. 72. Condenser" title="Fig. 72. Condenser" /></a>
+<span class="caption"><i>Fig. 72.</i> <span class="smcap">Condenser</span></span>
+</div>
+
+<p>You may now make a hole through the projecting
+ends of the strips, and you will have two
+sets of tinfoil sheets, alternately connected together
+at opposite ends of the condenser.</p>
+
+<p>Care should be exercised to leave the paraffine
+sheets perfect or without holes. You can make<span class='pagenum'><a name="p102" id="p102">p. 102</a></span>
+these sheets yourself by soaking them in melted
+paraffine wax.</p>
+
+<p><span class="smcap">Connecting Up a Condenser.</span>&mdash;When completed,
+one end of the condenser is connected
+up with one terminal of the secondary coil, and
+the other end of the condenser with the other
+secondary terminal.</p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig73" name="fig73"></a><a href="#p102">
+<img src="images/illus-fig73.png" width="350" height="121" alt="Fig. 73. High-tension Circuit" title="Fig. 73. High-tension Circuit" /></a>
+<span class="caption"><i>Fig. 73.</i> <span class="smcap">High-tension Circuit</span></span>
+</div>
+
+<p>In Fig. <a href="#fig73">73</a> a high-tension circuit is shown. Two
+coils, side by side, are always used to show an
+induction coil, and a condenser is generally shown,
+as illustrated, by means of a pair of forks, one
+resting within the other.</p>
+
+<p><span class="smcap">The Interrupter.</span>&mdash;One other piece of mechanism
+is necessary, and that is an <i>Interrupter</i>,
+for the purpose of getting the effect of the pulsations
+given out by the secondary coil.</p>
+
+<p>A simple current interrupter is made as follows:
+Prepare a wooden base (A), one inch
+thick, six inches wide, and twelve inches long.
+Upon this mount a toothed wheel (B), six inches<span class='pagenum'><a name="p103" id="p103">p. 103</a></span>
+in diameter, of thin sheet metal, or a brass gear
+wheel will answer the purpose. The standard
+(C), which supports the wheel, may be of metal
+bent up to form two posts, between which the
+crankshaft (D) is journaled. The base of the
+posts has an extension plate (E), with a binding
+post for a wire. At the front end of the base is an
+L-shaped strip (F), with a binding post for a
+wire connection, and the upwardly projecting
+part of the strip contacts with the toothed wheel.
+When the wheel B is rotated the spring finger (F)
+snaps from one tooth to the next, so that, momentarily,
+the current is broken, and the frequency
+is dependent upon the speed imparted to
+the wheel.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig74" name="fig74"></a><a href="#p103">
+<img src="images/illus-fig74.png" width="344" height="157" alt="Fig. 74. Current Interrupter" title="Fig. 74. Current Interrupter" /></a>
+<span class="caption"><i>Fig. 74.</i> <span class="smcap">Current Interrupter</span></span>
+</div>
+
+<p><span class="smcap">Uses of High-tension Coils.</span>&mdash;This high-tension
+coil is made use of, and is the essential apparatus
+in wireless telegraphy, as we shall see in
+the chapter treating upon that subject.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p104" id="p104">p. 104</a></span></p>
+
+<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>WIRELESS TELEGRAPHY</h3>
+
+
+<p><span class="smcap">Telegraphing Without Wires.</span>&mdash;Wireless telegraphy
+is an outgrowth of the ordinary telegraph
+system. When Maxwell, and, later on,
+Hertz, discovered that electricity, magnetism, and
+light were transmitted through the ether, and
+that they differed only in their wave lengths, they
+laid the foundations for wireless telegraphy.
+Ether is a substance which is millions and millions
+of times lighter than air, and it pervades
+all space. It is so unstable that it is constantly
+in motion, and this phase led some one to suggest
+that if a proper electrical apparatus could be
+made, the ether would thereby be disturbed sufficiently
+so that its impulses would extend out a
+distance proportioned to the intensity of the electrical
+agitation thereby created.</p>
+
+<p><span class="smcap">Surging Character of High-tension Currents.</span>&mdash;When
+a current of electricity is sent through
+a wire, hundreds of miles in length, the current
+surges back and forth on the wire many thousands
+of times a second. Light comes to us from
+the sun, over 90,000,000 of miles, through the
+ether. It is as reasonable to suppose, or infer,<span class='pagenum'><a name="p105" id="p105">p. 105</a></span>
+that the ether can, therefore, convey an electrical
+impulse as readily as does a wire.</p>
+
+<p>It is on this principle that impulses are sent
+for thousands of miles, and no doubt they extend
+even farther, if the proper mechanism could be
+devised to detect movement of the waves so propagated.</p>
+
+<p><span class="smcap">The Coherer.</span>&mdash;The instrument for detecting
+these impulses, or disturbances, in the ether is
+generally called a <i>coherer</i>, although detector is
+the term which is most satisfactory. The name
+coherer comes from the first practical instrument
+made for this purpose.</p>
+
+<div class="figcenter" style="width: 337px;">
+<a id="fig75" name="fig75"></a><a href="#p105">
+<img src="images/illus-fig75.png" width="337" height="125" alt="Fig. 75. Wireless Telegraphy Coherer" title="Fig. 75. Wireless Telegraphy Coherer" /></a>
+<span class="caption"><i>Fig. 75.</i> <span class="smcap">Wireless Telegraphy Coherer</span></span>
+</div>
+
+<p><span class="smcap">How Made.</span>&mdash;The coherer is simply a tube, say,
+of glass, within which is placed iron filings. When
+the oscillations surge through the secondary coil
+the pressure or potentiality of the current finally
+causes it to leap across the small space separating
+the filings and, as it were, it welds together
+their edges so that a current freely passes. The<span class='pagenum'><a name="p106" id="p106">p. 106</a></span>
+bringing together of the particles, under these
+conditions, is called cohering.</p>
+
+<p>Fig. 75 shows the simplest form of coherer. The
+posts (A) are firmly affixed to the base (B), each
+post having an adjusting screw (C) in its upper
+end, and these screw downwardly against and
+serve to bind a pair of horizontal rods (D), the
+inner ends of which closely approach each other.
+These may be adjusted so as to be as near together
+or as far apart as desired. E is a glass
+tube in which the ends of the rods (D) rest, and
+between the separated ends of the rods (D) the
+iron filings (F) are placed.</p>
+
+<p><span class="smcap">The Decoherers.</span>&mdash;For the purpose of causing
+the metal filings to fall apart, or decohere,
+the tube is tapped lightly, and this is done by a
+little object like the clapper of an electric bell.</p>
+
+<p>In practice, the coils and the parts directly connected
+with it are put together on one base.</p>
+
+<p><span class="smcap">The Sending Apparatus.</span>&mdash;Fig. <a href="#fig76">76</a> shows a section
+of a coil with its connection in the sending
+station. The spark gap rods (A) may be swung
+so as to bring them closer together or farther
+apart, but they must not at any time contact
+with each other.</p>
+
+<p>The induction coil has one terminal of the primary
+coil connected up by a wire (B) with one
+post of a telegraph key, and the other post of<span class='pagenum'><a name="p107" id="p107">p. 107</a></span>
+the key has a wire connection (C), with one side
+of a storage battery. The other side of the battery
+has a wire (D) running to the other terminal
+of the primary.</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig76" name="fig76"></a><a href="#p107">
+<img src="images/illus-fig76.png" width="349" height="332" alt="Fig. 76. Wireless Sending Apparatus" title="Fig. 76. Wireless Sending Apparatus" /></a>
+<span class="caption"><i>Fig. 76.</i> <span class="smcap">Wireless Sending Apparatus</span></span>
+</div>
+
+<p>The secondary coil has one of its terminals
+connected with a binding post (E). This binding
+post has an adjustable rod with a knob (F) on
+its end, and the other binding post (G), which
+is connected up with the other terminal of the<span class='pagenum'><a name="p108" id="p108">p. 108</a></span>
+secondary coil, carries a similar adjusting rod
+with a knob (H).</p>
+
+<p>From the post (E) is a wire (I), which extends
+upwardly, and is called the aerial wire, or wire
+for the antenn&aelig;, and this wire also connects with
+one side of the condenser by a conductor (J).
+The ground wire (K) connects with the other
+binding post (G), and a branch wire (L) also
+connects the ground wire (K) with one end of the
+condenser.</p>
+
+<div class="figcenter" style="width: 346px;">
+<a id="fig77" name="fig77"></a><a href="#p108">
+<img src="images/illus-fig77.png" width="346" height="150" alt="Fig. 77. Wireless Receiving Apparatus" title="Fig. 77. Wireless Receiving Apparatus" /></a>
+<span class="caption"><i>Fig. 77.</i> <span class="smcap">Wireless Receiving Apparatus</span></span>
+</div>
+
+<p><span class="smcap">The Receiving Apparatus.</span>&mdash;The receiving station,
+on the other hand, has neither condenser, induction
+coil, nor key. When the apparatus is in
+operation, the coherer switch is closed, and the
+instant a current passes through the coherer and
+operates the telegraph sounder, the galvanometer
+indicates the current.</p>
+
+<p>Of course, when the coherer switch is closed,
+the battery operates the decoherer</p>
+<p class="pn"><span class='pagenum'><a name="p109" id="p109">p. 109</a></span></p>
+
+<p><span class="smcap">How the Circuits are Formed.</span>&mdash;By referring
+again to Fig. <a href="#fig76">76</a>, it will be seen that when the
+key is depressed, a circuit is formed from the battery
+through wire B to the primary coil, and back
+again to the battery through wire D. The secondary
+coil is thereby energized, and, when the
+full potential is reached, the current leaps across
+the gap formed between the two knobs (F, H),
+thereby setting up a disturbance in the ether
+which is transmitted through space in all directions.</p>
+
+<p>It is this impulse, or disturbance, which is received
+by the coherer at the receiving station,
+and which is indicated by the telegraph sounder.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p110" id="p110">p. 110</a></span></p>
+
+<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>THE TELEPHONE</h3>
+
+
+<p><span class="smcap">Vibrations.</span>&mdash;Every manifestation in nature is
+by way of vibration. The beating of the heart,
+the action of the legs in walking, the winking of
+the eyelid; the impulses from the sun, which we
+call light; sound, taste and color appeal to our
+senses by vibratory means, and, as we have hereinbefore
+stated, the manifestations of electricity
+and magnetism are merely vibrations of different
+wave lengths.</p>
+
+<p><span class="smcap">The Acoustic Telephone.</span>&mdash;That sound is
+merely a product of vibrations may be proven in
+many ways. One of the earliest forms of telephones
+was simply a "sound" telephone, called
+the <i>Acoustic Telephone</i>. The principle of this
+may be illustrated as follows:</p>
+
+<p>Take two cups (A, B), as in Fig. <a href="#fig78">78</a>, punch a
+small hole through the bottom of each, and run a
+string or wire (C) from the hole of one cup to
+that of the other, and secure it at both ends so
+it may be drawn taut. Now, by talking into the
+cup (A) the bottom of it will vibrate to and
+fro, as shown by the dotted lines and thereby
+cause the bottom of the other cup (B) to vibrate<span class='pagenum'><a name="p111" id="p111">p. 111</a></span>
+in like manner, and in so vibrating it will receive
+not only the same amplitude, but also the same
+character of vibrations as the cup (A) gave forth.</p>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig78" name="fig78"></a><a href="#p111">
+<img src="images/illus-fig78.png" width="353" height="137" alt="Fig. 78. Acoustic Telephone" title="Fig. 78. Acoustic Telephone" /></a>
+<span class="caption"><i>Fig. 78.</i> <span class="smcap">Acoustic Telephone</span></span>
+</div>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig79" name="fig79"></a><a href="#p111">
+<img src="images/illus-fig79.png" width="353" height="100" alt="Fig. 79. Illustrating Vibrations" title="Fig. 79. Illustrating Vibrations" /></a>
+<span class="caption"><i>Fig. 79.</i> <span class="smcap">Illustrating Vibrations</span></span>
+</div>
+
+<p><span class="smcap">Sound Waves.</span>&mdash;Sound waves are long and
+short; the long waves giving sounds which are
+low in the musical scale, and the short waves high
+musical tones. You may easily determine this by
+the following experiment:</p>
+
+<p>Stretch a wire, as at B (Fig. <a href="#fig79">79</a>), fairly tight,
+and then vibrate it. The amplitude of the vibration
+will be as indicated by dotted line A. Now,
+stretch it very tight, as at C, so that the amplitude
+of vibration will be as shown at E. By putting
+your ear close to the string you will find that while
+A has a low pitch, C is very much higher. This<span class='pagenum'><a name="p112" id="p112">p. 112</a></span>
+is the principle on which stringed instruments are
+built. You will note that the wave length, which
+represents the distance between the dotted lines
+A is much greater than E.</p>
+
+<p><span class="smcap">Hearing Electricity.</span>&mdash;In electricity, mechanism
+has been made to enable man to note the action
+of the current. By means of the armature,
+vibrating in front of a magnet, we can see its
+manifestations. It is now but a step to devise
+some means whereby we may hear it. In this,
+as in everything else electrically, the magnet
+comes into play.</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig80" name="fig80"></a><a href="#p112">
+<img src="images/illus-fig80.png" width="351" height="149" alt="Fig. 80 .The Magnetic Field" title="Fig. 80. The Magnetic Field" /></a>
+<span class="caption"><i>Fig. 80.</i> <span class="smcap">The Magnetic Field</span></span>
+</div>
+
+<p>In the chapter on magnetism, it was stated that
+the magnetic field extended out beyond the magnet,
+so that if we were able to see the magnetism,
+the end of a magnet would appear to us something
+like a moving field, represented by the dotted lines
+in Fig. <a href="#fig80">80</a>.</p>
+
+<p>The magnetic field is shown in Fig. <a href="#fig80">80</a> at only<span class='pagenum'><a name="p113" id="p113">p. 113</a></span>
+one end, but its manifestations are alike at both
+ends. It will be seen that the magnetic field extends
+out to a considerable distance and has quite
+a radius of influence.</p>
+
+<p><span class="smcap">The Diaphragm in a Magnetic Field.</span>&mdash;If, now,
+we put a diaphragm (A) in this magnetic field,
+close up to the end of the magnet, but not so
+close as to touch it, and then push it in and out,
+or talk into it so that the sound waves strike it,
+the movement or the vibration of the diaphragm
+(A) will disturb the magnetic field emanating
+from the magnet, and this disturbance of the magnetic
+field at one end of the magnet also affects
+the magnetic field at the other end in the same
+way, so that the disturbance there will be of the
+same amplitude. It will also display the same
+characteristics as did the magnetic field when the
+diaphragm (A) disturbed it.</p>
+
+<p><span class="smcap">A Simple Telephone Circuit.</span>&mdash;From this simple
+fact grew the telephone. If two magnets are
+connected up in the same circuit, so that the magnetic
+fields of the two magnets have the same
+source of electric power, the disturbance of one
+diaphragm will affect the other similarly, just the
+same as the two magnetic fields of the single
+magnet are disturbed in unison.</p>
+
+<p><span class="smcap">How to Make a Telephone.</span>&mdash;For experimental
+and testing purposes two of these telephones<span class='pagenum'><a name="p114" id="p114">p. 114</a></span>
+should be made at the same time. The case or
+holder (A) may be made either of hard wood or
+hard rubber, so that it is of insulating material.
+The core (B) is of soft iron, &#x215c; inch in diameter
+and 5 inches long, bored and threaded at one end
+to receive a screw (C) which passes through the
+end of the case (A).</p>
+
+<p>The enlarged end of the case should be, exteriorly,
+2&frac14; inches in diameter, and the body of the
+case 1 inch in diameter.</p>
+
+<div class="figcenter" style="width: 369px;">
+<a id="fig81" name="fig81"></a><a href="#p114">
+<img src="images/illus-fig81.png" width="369" height="172" alt="Fig. 81. Section of Telephone Receiver" title="Fig. 81. Section of Telephone Receiver" /></a>
+<span class="caption"><i>Fig. 81.</i> <span class="smcap">Section of Telephone Receiver</span></span>
+</div>
+
+<p>Interiorly, the large end of the case is provided
+with a circular recess 1&frac34; inches in diameter and
+adapted to receive therein a spool which is,
+diametrically, a little smaller than the recess. The
+spool fits fairly tight upon the end of the core,
+and when in position rests against an annular
+shoulder in the recess. A hollow space (F) is thus
+provided behind the spool (D), so the two wires<span class='pagenum'><a name="p115" id="p115">p. 115</a></span>
+from the magnet may have room where they
+emerge from the spool.</p>
+
+<p>The spool is a little shorter than the distance
+between the shoulder (E) and the end of the casing,
+at G, and the core projects only a short distance
+beyond the end of the spool, so that when
+the diaphragm (H) is put upon the end of the
+case, and held there by screws (I) it will not
+touch the end of the core. A wooden or rubber
+mouthpiece (J) is then turned up to fit over the
+end of the case.</p>
+
+<div class="figcenter" style="width: 352px;">
+<a id="fig82" name="fig82"></a><a href="#p115">
+<img src="images/illus-fig82.png" width="352" height="142" alt="Fig. 82. The Magnet and Receiver Head" title="Fig. 82. The Magnet and Receiver Head" /></a>
+<span class="caption"><i>Fig. 82.</i> <span class="smcap">The Magnet and Receiver Head</span></span>
+</div>
+
+<p>The spool (D) is made of hard rubber, and is
+wound with No. 24 silk-covered wire, the windings
+to be well insulated from each other. The
+two ends of the wire are brought out, and threaded
+through holes (K) drilled longitudinally through
+the walls of the case, and affixed to the end by
+means of screws (L), so that the two wires may be
+brought together and connected with a duplex
+wire (M)</p>
+<p class="pn"><span class='pagenum'><a name="p116" id="p116">p. 116</a></span></p>
+
+<p>As the screw (C), which holds the core in place,
+has its head hidden within a recess, which can be
+closed up by wax, the two terminals of the wires
+are well separated so that short-circuiting cannot
+take place.</p>
+
+<p><span class="smcap">Telephone Connections.</span>&mdash;The simplest form
+of telephone connection is shown in Fig. <a href="#fig83">83</a>. This
+has merely the two telephones (A and B), with a
+single battery (C) to supply electricity for both.
+One line wire (D) connects the two telephones
+directly, while the other line (E) has the battery
+in its circuit.</p>
+
+<div class="figcenter" style="width: 350px;">
+<a id="fig83" name="fig83"></a><a href="#p116">
+<img src="images/illus-fig83.png" width="350" height="85" alt="Fig. 83. Simple Telephone Connection" title="Fig. 83. Simple Telephone Connection" /></a>
+<span class="caption"><i>Fig. 83.</i> <span class="smcap">Simple Telephone Connection</span></span>
+</div>
+
+<p><span class="smcap">Complete Installation.</span>&mdash;To install a more
+complete system requires, at each end, a switch,
+a battery and an electro-magneto bell. You may
+use, for this purpose, a bell, made as shown in
+the chapter on bells.</p>
+
+<p>Fig. 84 shows such a circuit. We now dispense
+with one of the line wires, because it has been
+found that the ground between the two stations
+serves as a conductor, so that only one line wire
+(A) is necessary to connect directly with the telephones<span class='pagenum'><a name="p117" id="p117">p. 117</a></span>
+of the two stations. The telephones
+(B, B', respectively) have wires (C, C') running
+to the pivots of double-throw switches (D, D'),
+one terminal of the switches having wires (E, E'),
+which go to electric bells (F, F'), and from the
+bells are other wires (G, G'), which go to the
+ground. The ground wires also have wires (H,
+H'), which go to the other terminals of the switch
+(D, D'). The double-throw switch (D, D'), in the
+two stations, is thrown over so the current, if
+any should pass through, will go through the bell
+to the ground, through the wires (E, G or E', G').</p>
+
+<div class="figcenter" style="width: 349px;">
+<a id="fig84" name="fig84"></a><a href="#p117">
+<img src="images/illus-fig84.png" width="349" height="132" alt="Fig. 84. Telephone Stations in Circuit" title="Fig. 84. Telephone Stations in Circuit" /></a>
+<span class="caption"><i>Fig. 84.</i> <span class="smcap">Telephone Stations in Circuit</span></span>
+</div>
+
+<p>Now, supposing the switch (D'), in station 2,
+should be thrown over so it contacts with the wire
+(H'). It is obvious that the current will then
+flow from the battery (I') through wires (H', C')
+and line (A) to station 1; then through wire
+C, switch D, wire E to the bell F, to the
+ground through wire G. From wire G the current
+returns through the ground to station 2,<span class='pagenum'><a name="p118" id="p118">p. 118</a></span>
+where it flows up wire G' to the battery, thereby
+completing the circuit.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig85" name="fig85"></a><a href="#p118">
+<img src="images/illus-fig85.png" width="344" height="87" alt="Fig. 85. Illustrating Light Contact Points" title="Fig. 85. Illustrating Light Contact Points" /></a>
+<span class="caption"><i>Fig. 85.</i> <span class="smcap">Illustrating Light Contact Points</span></span>
+</div>
+
+<p>The operator at station 2, having given the
+signal, again throws his switch (D') back to the
+position shown in Fig. <a href="#fig84">84</a>, and the operator at
+station 1 throws on his switch (D), so as to ring
+the bell in station 2, thereby answering the signal,
+which means that both switches are again to be
+thrown over so they contact with the battery wires
+(H and H'), respectively. When both are thus
+thrown over, the bells (G, G') are cut out of the
+circuit, and the batteries are both thrown in, so
+that the telephones are now ready for talking purposes.</p>
+
+<p><span class="smcap">Microphone.</span>&mdash;Originally this form of telephone
+system was generally employed, but it was found
+that for long distances a more sensitive instrument
+was necessary.</p>
+
+<p><span class="smcap">Light Contact Points.</span>&mdash;In 1877 Professor
+Hughes discovered, accidentally, that a light contact
+point in an electric circuit augmented the
+sound in a telephone circuit. If, for instance, a<span class='pagenum'><a name="p119" id="p119">p. 119</a></span>
+light pin, or a nail (A, Fig. <a href="#fig85">85</a>) should be used
+to connect the severed ends of a wire (B), the
+sounds in the telephone not only would be louder,
+but they would be more distinct, and the first instrument
+made practically, to demonstrate this, is
+shown in Fig. <a href="#fig86">86</a>.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+   <td align="center">
+<a id="fig86" name="fig86"></a><a href="#p119">
+<img src="images/illus-fig86.png" width="210" height="197" alt="Fig. 86. Microphone" title="Fig. 86. Microphone" /></a></td>
+        <td align="center">
+<a id="fig87" name="fig87"></a><a href="#p119">
+<img src="images/illus-fig87.png" width="134" height="196" alt="Fig. 87. Transmitter" title="Fig. 87. Transmitter" /></a>
+      </td>
+   </tr>
+   <tr>
+   <td class="tdnwc">
+<span class="caption"><i>Fig. 86.</i> <span class="smcap">Microphone</span></span>
+      </td>
+   <td class="tdnwc">
+<span class="caption"><i>Fig. 87.</i> <span class="smcap">Transmitter</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+
+<p><span class="smcap">How to Make a Microphone.</span>&mdash;This instrument
+has simply a base (A) of wood, and near one end
+is a perpendicular sounding-board (B) of wood,
+to one side of which is attached, by wax or otherwise,
+a pair of carbon blocks (C, D). The lower
+carbon block (C) has a cup-shaped depression in
+its upper side, and the upper block has a similar
+depression in its lower side. A carbon pencil
+(E) is lightly held within these cups, so that the
+lightest contact of the upper end of the pencil<span class='pagenum'><a name="p120" id="p120">p. 120</a></span>
+with the carbon block, makes the instrument so
+sensitive that a fly, walking upon the sounding-board,
+may be distinctly heard through the telephone
+which is in the circuit.</p>
+
+<p><span class="smcap">Microphone the Father of the Transmitter.</span>&mdash;This
+instrument has been greatly modified, and
+is now used as a transmitter, the latter thereby
+taking the place of the pin (A), shown in Fig. <a href="#fig85">85</a>.</p>
+
+<p><span class="smcap">Automatic Cut-outs for Telephones.</span>&mdash;In the
+operation of the telephone, the great drawback
+originally was in inducing users of the lines to
+replace or adjust their instruments carefully.
+When switches were used, they would forget to
+throw them back, and all sorts of trouble resulted.</p>
+
+<p>It was found necessary to provide an automatic
+means for throwing in and cutting out an instrument,
+this being done by hanging the telephone
+on the hook, so that the act merely of leaving the
+telephone made it necessary, in replacing the instrument,
+to cut out the apparatus.</p>
+
+<p>Before describing the circuiting required for
+these improvements, we show, in Fig. <a href="#fig87">87</a>, a section
+of a transmitter.</p>
+
+<p>A cup-shaped case (A) is provided, made of
+some insulating material, which has a diaphragm
+(B) secured at its open side. This diaphragm
+carries the carbon pencil (C) on one side and
+from the blocks which support the carbon pencil<span class='pagenum'><a name="p121" id="p121">p. 121</a></span>
+the wires run to binding posts on the case. Of
+course the carbon supporting posts must be insulated
+from each other, so the current will go
+through the carbon pencil (C).</p>
+
+<p><span class="smcap">Complete Circuiting with Transmitter.</span>&mdash;In
+showing the circuiting (Fig. <a href="#fig88">88</a>) it will not be possible
+to illustrate the boxes, or casings, which receive
+the various instruments. For instance, the
+hook which carries the telephone or the receiver,
+is hinged within the transmitter box. The circuiting
+is all that it is intended to show.</p>
+
+<div class="figcenter" style="width: 347px;">
+<a id="fig88" name="fig88"></a><a href="#p121">
+<img src="images/illus-fig88.png" width="347" height="140" alt="Fig. 88. Complete Telephonic Circuit" title="Fig. 88. Complete Telephonic Circuit" /></a>
+<span class="caption"><i>Fig. 88.</i> <span class="smcap">Complete Telephonic Circuit</span></span>
+</div>
+
+<p>The batteries of the two stations are connected
+up by a wire (A), unless a ground circuit is used.
+The other side of each battery has a wire connection
+(B, B') with one terminal of the transmitter,
+and the other terminal of the transmitter has a
+wire (C, C') which goes to the receiver. From
+the other terminal of the receiver is a wire (D, D')
+which leads to the upper stop contact (E, E') of<span class='pagenum'><a name="p122" id="p122">p. 122</a></span>
+the telephone hook. A wire (F, F') from the
+lower stop contact (G, G') of the hook goes to one
+terminal of the bell, and from the other terminal
+of the bell is a wire (H, H') which makes connection
+with the line wire (A). In order to make a
+complete circuit between the two stations, a line
+wire (I) is run from the pivot of the hook in station
+1 to the pivot of the hook in station 2.</p>
+
+<p>In the diagram, it is assumed that the receivers
+are on the hooks, and that both hooks are, therefore,
+in circuit with the lower contacts (G, G'), so
+that the transmitter and receiver are both out of
+circuit with the batteries, and the bell in circuit;
+but the moment the receiver, for instance, in station
+1 is taken off the hook, the latter springs up
+so that it contacts with the stop (E), thus establishing
+a circuit through the line wire (I) to the
+hook of station 2, and from the hook through line
+(F') to the bell. From the bell, the line (A) carries
+the current back to the battery of station (A),
+thence through the wire (B) to the transmitter
+wire (C) to receiver and wire (D) to the post (E),
+thereby completing the circuit.</p>
+
+<p>When, at station 2, the receiver is taken off the
+hook, and the latter contacts with the post (E'),
+the transmitter and receiver of both stations are
+in circuit with each other, but both bells are cut
+out.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p123" id="p123">p. 123</a></span></p>
+
+<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING</h3>
+
+
+<p><span class="smcap">Decomposing Liquids.</span>&mdash;During the earlier experiments
+in the field of electricity, after the battery
+or cell was discovered, it was noted that
+when a current was formed in the cell, the electrolyte
+was charged and gases evolved from it. A
+similar action takes place when a current of electricity
+passes through a liquid, with the result
+that the liquid is decomposed&mdash;that is, the liquid
+is broken up into its original compounds. Thus,
+water is composed of two parts, by bulk, of hydrogen
+and of oxygen, so that if two electrodes are
+placed in water, and a current is sent through the
+electrodes in either direction, all the water will
+finally disappear in the form of hydrogen and oxygen
+gases.</p>
+
+<p><span class="smcap">Making Hydrogen and Oxygen.</span>&mdash;During this
+electrical action, the hydrogen is set free at the
+negative pole and the oxygen at the positive pole.
+A simple apparatus, which any boy can make, to
+generate pure oxygen and pure hydrogen, is
+shown in Fig. <a href="#fig89">89</a>.</p>
+
+<p>It is constructed of a glass or earthen jar (A),
+preferably square, to which is fitted a wooden top<span class='pagenum'><a name="p124" id="p124">p. 124</a></span>
+(B), this top being provided with a packing ring
+(C), so as to make it air-tight. Within is a vertical
+partition (D), the edges of which, below the
+cap, fit tightly against the inner walls of the jar.
+This partition extends down into the jar a sufficient
+distance so it will terminate below the water
+level. A pipe is fitted through the top on each
+side of the partition, and each pipe has a valve.
+An electrode, of any convenient metal, is secured
+at its upper end to the top of the cap, on each side
+of the partition. These electrodes extend down
+to the bottom of the jar, and an electric wire connects
+with each of them at the top.</p>
+
+<div class="figcenter" style="width: 343px;">
+<a id="fig89" name="fig89"></a><a href="#p124">
+<img src="images/illus-fig89.png" width="343" height="216" alt="Fig. 89. Device for Making Hydrogen and Oxygen"
+title="Fig. 89. Device for Making Hydrogen and Oxygen" /></a>
+<span class="caption"><i>Fig. 89.</i> <span class="smcap">Device for Making Hydrogen and Oxygen</span></span>
+</div>
+
+<p>If a current of electricity is passed through the
+wires and the electrodes, in the direction shown<span class='pagenum'><a name="p125" id="p125">p. 125</a></span>
+by the darts, hydrogen will form at the negative
+pole, and oxygen at the positive pole. These
+gases will escape upwardly, so that they will be
+trapped in their respective compartments, and
+may be drawn off by means of the pipes.</p>
+
+<p><span class="smcap">Purifying Water.</span>&mdash;Advantage is taken of this
+electrolytic action, to purify water. Oxygen is
+the most wonderful chemical in nature. It is
+called the acid-maker of the universe. The name
+is derived from two words, <i>oxy</i> and <i>gen</i>; one denoting
+oxydation, and the other that it generates.
+In other words, it is the <i>generator of oxides</i>. It
+is the element which, when united with any other
+element, produces an acid, an alkali or a neutral
+compound.</p>
+
+<p><span class="smcap">Rust.</span>&mdash;For instance, iron is largely composed
+of ferric acid. When oxygen, in a free or gaseous
+state, comes into contact with iron, it produces
+ferrous oxide, which is recognized as rust.</p>
+
+<p><span class="smcap">Oxygen as a Purifier</span>.&mdash;But oxygen is also a
+purifier. All low forms of animal life, like bacteria
+or germs in water, succumb to free oxygen.
+By <i>free oxygen</i> is meant oxygen in the form of
+gas.</p>
+
+<p><span class="smcap">Composition of Water.</span>&mdash;Now, water, in which
+harmful germs live, is one-third oxygen. Nevertheless,
+the germs thrive in water, because the
+oxygen is in a compound state, and, therefore, not<span class='pagenum'><a name="p126" id="p126">p. 126</a></span>
+an active agent. But if oxygen, in the form of
+gas, can be forced through water, it will attack the
+germs, and destroy them.</p>
+
+<p><span class="smcap">Common Air Not a Good Purifier.</span>&mdash;Water may
+be purified, to a certain extent, by forcing common
+air through it, and the foulest water, if run
+over rocks, will be purified, in a measure, because
+air is intermingled with it. But common air is
+composed of four-fifths nitrogen, and only one-fifth
+oxygen, and, as nitrogen is the staple article
+of food for bacteria, the purifying method by air
+is not effectual.</p>
+
+<p><span class="smcap">Pure Oxygen.</span>&mdash;When, however, oxygen is generated
+from water, by means of electrolysis, it is
+pure; hence is more active and is not tainted by a
+life-giving substance for germs, such as nitrogen.</p>
+
+<p>The mechanism usually employed for purifying
+water is shown in Fig. <a href="#fig90">90</a>.</p>
+
+<p><span class="smcap">A Water Purifier.</span>&mdash;The case (A, Fig. <a href="#fig90">90</a>) may
+be made of metal or of an insulating material.
+If made of metal it must be insulated within with
+slate, glass, marble or hard rubber, as shown at
+B. The case is provided with exterior flanges
+(C, D), with upper and lower ends, and it is
+mounted upon a base plate (E) and affixed thereto
+by bolts. The upper end has a conically-formed
+cap (F) bolted to the flanges (C), and this has
+an outlet to which a pipe (G) is attached. The<span class='pagenum'><a name="p127" id="p127">p. 127</a></span>
+water inlet pipe (H) passes through the lower
+end of the case (A). The electrodes (I, J) are
+secured, vertically, within the case, separated
+from each other equidistant, each alternate electrode
+being connected up with one wire (K), and
+the alternate electrodes with a wire (L).</p>
+
+<div class="figcenter" style="width: 351px;">
+<a id="fig90" name="fig90"></a><a href="#p127">
+<img src="images/illus-fig90.png" width="351" height="389" alt="Fig. 90. Electric Water Purifier" title="Fig. 90. Electric Water Purifier" /></a>
+<span class="caption"><i>Fig. 90.</i> <span class="smcap">Electric Water Purifier</span></span>
+</div>
+<p class="pn"><span class='pagenum'><a name="p128" id="p128">p. 128</a></span></p>
+
+<p>When the water passes upwardly, the decomposed
+or gaseous oxygen percolates through the
+water and thus attacks the germs and destroys
+them.</p>
+
+<p><span class="smcap">The Use of Hydrogen in Purification.</span>&mdash;On
+the other hand, the hydrogen also plays an important
+part in purifying the water. This depends
+upon the material of which the electrodes are
+made. Aluminum is by far the best material, as
+it is one of nature's most active purifiers. All
+clay contains aluminum, in what is known as the
+sulphate form, and water passing through the
+clay of the earth thereby becomes purified, because
+of this element.</p>
+
+<p><span class="smcap">Aluminum Electrodes.</span>&mdash;When this material is
+used as the electrodes in water, hydrate of aluminum
+is formed, or a compound of hydrogen and
+oxygen with aluminum. The product of decomposition
+is a flocculent matter which moves upwardly
+through the water, giving it a milky appearance.
+This substance is like gelatine, so that
+it entangles or enmeshes the germ life and prevents
+it from passing through a filter.</p>
+
+<p>If no filter is used, this flocculent matter, as
+soon as it has given off the gases, will settle to
+the bottom and carry with it all decomposed matter,
+such as germs and other organic matter attacked<span class='pagenum'><a name="p129" id="p129">p. 129</a></span>
+by the oxygen, which has become entangled
+in the aluminum hydrate.</p>
+
+<p><span class="smcap">Electric Hand Purifier.</span>&mdash;An interesting and
+serviceable little purifier may be made by any
+boy with the simplest tools, by cutting out three
+pieces of sheet aluminum. Hard rolled is best
+for the purpose. It is better to have one of the
+sheets (A), the middle one, thicker than the two
+outer plates (B).</p>
+
+<div class="figcenter" style="width: 346px;">
+<a id="fig91" name="fig91"></a><a href="#p129">
+<img src="images/illus-fig91.png" width="346" height="294" alt="Fig. 91. Portable Electric Purifier" title="Fig. 91. Portable Electric Purifier" /></a>
+<span class="caption"><i>Fig. 91.</i> <span class="smcap">Portable Electric Purifier</span></span>
+</div>
+
+<p>Let each sheet be 1&frac12; inches wide and 5&frac12; inches
+thick. One-half inch from the upper ends of the<span class='pagenum'><a name="p130" id="p130">p. 130</a></span>
+two outside plates (B, B) bore bolt holes (C), each
+of these holes being a quarter of an inch from
+the edge of the plate. The inside plate (A) has
+two large holes (D) corresponding with the small
+holes (C) in the outside plates. At the upper
+end of this plate form a wing (E), &frac12; inch wide
+and &frac12; inch long, provided with a small hole for a
+bolt. Next cut out two hard-rubber blocks (F),
+each 1&frac12; inches long, 1 inch wide and &#x215c; inch thick,
+and then bore a hole (G) through each, corresponding
+with the small holes (C) in the plates
+(B). The machine is now ready to be assembled.
+If the inner plate is &#x215b; inch thick and the outer
+plates each 1/16 inch thick, use two small eighth-inch<span class='pagenum'><a name="p131" id="p131">p. 131</a></span>
+bolts 1&frac14; inches long, and clamp together the
+three plates with these bolts. One of the bolts may
+be used to attach thereto one of the electric wires
+(H), and the other wire (I) is attached by a bolt
+to the wing (E).</p>
+
+<div class="figcenter" style="width: 388px;">
+<a id="fig92-95" name="fig92-95"></a><a href="#p130">
+<img src="images/illus-fig92-95.png" width="388" height="226" alt="Figs. 92-95. Details of Portable Purifier"
+title="Figs. 92-95. Details of Portable Purifier" /></a>
+<span class="caption"><i>Figs. 92-95.</i> <span class="smcap">Details of Portable Purifier</span></span>
+</div>
+
+<p>Such a device will answer for a 110-volt circuit,
+in ordinary water. Now fill a glass nearly full
+of water, and stand the purifier in the glass.
+Within a few minutes the action of electrolysis
+will be apparent by the formation of numerous
+bubbles on the plates, followed by the decomposition
+of the organic matter in the water. At first
+the flocculent decomposed matter will rise to the
+surface of the water, but before many minutes it
+will settle to the bottom of the glass and leave
+clear water above.</p>
+
+<p><span class="smcap">Purification and Separation of Metals.</span>&mdash;This
+electrolytic action is utilized in metallurgy for the
+purpose of producing pure metals, but it is more
+largely used to separate copper from its base.
+In order to utilize a current for this purpose, a
+high ampere flow and low voltage are required.
+The sheets of copper, containing all of its impurities,
+are placed within a tank, parallel with a thin
+copper sheet. The impure sheet is connected with
+the positive pole of an electroplating dynamo, and
+the thin sheet of copper is connected with the
+negative pole. The electrolyte in the tank is a<span class='pagenum'><a name="p132" id="p132">p. 132</a></span>
+solution of sulphate of copper. The action of
+the current will cause the pure copper in the impure
+sheet to disintegrate and it is then carried
+over and deposited upon the thin sheet, this action
+continuing until the impure sheet is entirely eaten
+away. All the impurities which were in the sheet
+fall to the bottom of the tank.</p>
+
+<p>Other metals are treated in the same way, and
+this treatment has a very wide range of usefulness.</p>
+
+<p><span class="smcap">Electroplating.</span>&mdash;The next feature to be considered
+in electrolysis is a most interesting and
+useful one, because a cheap or inferior metal may
+be coated by a more expensive metal. Silver and
+nickel plating are brought about by this action of
+a current passing through metals, which are immersed
+in an electrolyte.</p>
+
+<p><span class="smcap">Plating Iron with Copper.</span>&mdash;We have room in
+this chapter for only one concrete example of
+this work, which, with suitable modifications, is
+an example of the art as practiced commercially.
+Iron, to a considerable extent, is now being coated
+with copper to preserve it from rust. To carry
+out this work, however, an electroplating dynamo,
+of large amperage, is required, the amperage, of
+course, depending upon the surface to be treated
+at one time. The pressure should not exceed 5
+volts</p>
+<p class="pn"><span class='pagenum'><a name="p133" id="p133">p. 133</a></span></p>
+
+<p>The iron surface to be treated should first be
+thoroughly cleansed, and then immediately put
+into a tank containing a cyanide of copper solution.
+Two forms of copper solution are used, namely,
+the cyanide, which is a salt solution of copper,
+and the sulphate, which is an acid solution of
+copper. Cyanide is first used because it does not
+attack the iron, as would be the case if the sulphate
+solution should first come into contact with
+the iron.</p>
+
+<p>A sheet of copper, termed the anode, is then
+placed within the tank, parallel with the surface
+to be plated, known as the cathode, and so
+mounted that it may be adjusted to or from the
+iron surface, or cathode. A direct current of
+electricity is then caused to flow through the copper
+plate and into the iron plate or surface, and
+the plating proceeded with until the iron surface
+has a thin film of copper deposited thereon. This
+is a slow process with the cyanide solution, so
+it is discontinued as soon as possible, after the
+iron surface has been completely covered with
+copper. This copper surface is thoroughly
+cleaned off to remove therefrom the saline or alkaline
+solution, and it is then immersed within a
+bath, containing a solution of sulphate of copper.
+The current is then thrown on and allowed so<span class='pagenum'><a name="p134" id="p134">p. 134</a></span>
+to remain until it has deposited the proper thickness
+of copper.</p>
+
+<p><span class="smcap">Direction of Current.</span>&mdash;If a copper and an
+iron plate are put into a copper solution and connected
+up in circuit with each other, a primary
+battery is thereby formed, which will generate
+electricity. In this case, the iron will be positive
+and the copper negative, so that the current
+within such a cell would flow from the iron (in
+this instance, the anode) to the negative, or
+cathode.</p>
+
+<p>The action of electroplating reverses this process
+and causes the current to flow from the copper
+to the iron (in this instance, the cathode).</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p135" id="p135">p. 135</a></span></p>
+
+<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>ELECTRIC HEATING, THERMO ELECTRICITY</h3>
+
+
+<p><span class="smcap">Generating Heat in a Wire.</span>&mdash;When a current
+of electricity passes through a conductor, like a
+wire, more or less heat is developed in the conductor.
+This heat may be so small that it cannot
+be measured, but it is, nevertheless, present
+in a greater or less degree. Conductors offer a
+resistance to the passage of a current, just the
+same as water finds a resistance in pipes through
+which it passes. This resistance is measured in
+ohms, as explained in a preceding chapter, and
+it is this resistance which is utilized for electric
+heating.</p>
+
+<p><span class="smcap">Resistance of Substances.</span>&mdash;Silver offers less
+resistance to the passage of a current than any
+other metal, the next in order is copper, while
+iron is, comparatively, a poor conductor.</p>
+
+<p>The following is a partial list of metals, showing
+their relative conductivity:</p>
+
+<div class="center" style="font-size:90%">
+<table border="0" width="50%" cellpadding="1" cellspacing="0">
+  <col style="width:50%;" /><col style="width:50%;" />
+<tbody valign="top">
+    <tr> <td align="left">Silver</td> <td align="left">&nbsp; &nbsp;1.</td></tr>
+    <tr> <td align="left">Copper</td> <td align="left">&nbsp; &nbsp;1.04 to 1.09</td></tr>
+    <tr> <td align="left">Gold</td> <td align="left">&nbsp; &nbsp;1.38 to 1.41</td></tr>
+    <tr> <td align="left">Aluminum</td> <td align="left">&nbsp; &nbsp;1.64<span class='pagenum'><a name="p136" id="p136">p. 136</a></span></td></tr>
+    <tr> <td align="left">Zinc</td> <td align="left">&nbsp; &nbsp;3.79</td></tr>
+    <tr> <td align="left">Nickel</td> <td align="left">&nbsp; &nbsp;4.69</td></tr>
+    <tr> <td align="left">Iron</td> <td align="left">&nbsp; &nbsp;6.56</td></tr>
+    <tr> <td align="left">Tin</td> <td align="left">&nbsp; &nbsp;8.9</td></tr>
+    <tr> <td align="left">Lead</td> <td align="left">13.2</td></tr>
+    <tr> <td align="left">German Silver</td> <td align="left">12.2 to 15</td></tr>
+</tbody>
+</table>
+</div>
+
+<p>From this table it will be seen that, for instance,
+iron offers six and a half times the resistance of
+silver, and that German silver has fifteen times
+the resistance of silver.</p>
+
+<p>This table is made up of strands of the different
+metals of the same diameters and lengths, so as
+to obtain their relative values.</p>
+
+<p><span class="smcap">Sizes of Conductors.</span>&mdash;Another thing, however,
+must be understood. If two conductors of the
+same metal, having different diameters, receive
+the same current of electricity, the small conductor
+will offer a greater resistance than the large
+conductor, hence will generate more heat. This
+can be offset by increasing the diameter of the
+conductor. The metal used is, therefore, of importance,
+on account of the cost involved.</p>
+
+<p><span class="smcap">Comparison of Metals.</span>&mdash;A conductor of aluminum,
+say, 10 feet long and of the same weight
+as copper, has a diameter two and a quarter times
+greater than copper; but as the resistance of
+aluminum is 50 per cent. more than that of silver,
+it will be seen that, weight for weight, copper is<span class='pagenum'><a name="p137" id="p137">p. 137</a></span>
+the cheaper, particularly as aluminum costs fully
+three times as much as copper.</p>
+
+<div class="figcenter" style="width: 338px;">
+<a id="fig96" name="fig96"></a><a href="#p137">
+<img src="images/illus-fig96.png" width="338" height="310" alt="Fig. 96. Simple Electric Heater" title="Fig. 96. Simple Electric Heater" /></a>
+<span class="caption"><i>Fig. 96.</i> <span class="smcap">Simple Electric Heater</span></span>
+</div>
+
+<p>The table shows that German silver has the
+highest resistance. Of course, there are other
+metals, like antimony, platinum and the like, which
+have still higher resistance. German silver,
+however, is most commonly used, although there
+are various alloys of metal made which have
+high resistance and are cheaper.</p>
+
+<p>The principle of all electric heaters is the same,<span class='pagenum'><a name="p138" id="p138">p. 138</a></span>
+namely, the resistance of a conductor to the passage
+of a current, and an illustration of a water
+heater will show the elementary principles in all
+of these devices.</p>
+
+<p><span class="smcap">A Simple Electric Heater</span>.&mdash;In Fig. <a href="#fig96">96</a> the
+illustration shows a cup or holder (A) for the
+wire, made of hard rubber. This may be of such
+diameter as to fit upon and form the cover for a
+glass (B). The rubber should be &frac12; inch thick.
+Two holes are bored through the rubber cup, and
+through them are screwed two round-headed
+screws (C, D), each screw being 1&frac12; inches long,
+so they will project an inch below the cap. Each
+screw should have a small hole in its lower end to
+receive a pin (E) which will prevent the resistance
+wire from slipping off.</p>
+
+<p>The resistance wire (F) is coiled for a suitable
+length, dependent upon the current used, one end
+being fastened by wrapping it around the screw
+(C). The other end of the wire is then brought
+upwardly through the interior of the coil and
+secured in like manner to the other screw (D).</p>
+
+<p>Caution must be used to prevent the different
+coils or turns from touching each other. When
+completed, the coil may be immersed in water, the
+current turned on, and left so until the water is
+sufficiently heated.</p>
+
+
+<div class="figcenter" style="width: 331px;">
+<a id="fig97" name="fig97"></a><a href="#p138">
+<img src="images/illus-fig97.png" width="331" height="113" alt="Fig. 97. Side view of resistance device" title="Fig. 97. Side view of resistance device" /></a>
+<span class="caption"><i>Fig. 97.</i> <span class="smcap">Resistance Device</span></span>
+</div>
+
+<div class="figcenter" style="width: 328px;">
+<a id="fig98" name="fig98"></a><a href="#p138">
+<img src="images/illus-fig98.png" width="328" height="107" alt="Fig. 98. Top view of resistance device" title="Fig. 98. Top view of resistance device" /></a>
+<span class="caption"><i>Fig. 98.</i> <span class="smcap">Resistance Device</span></span>
+</div>
+
+<p><span class="smcap">How to Arrange for Quantity of Current<span class='pagenum'><a name="p139" id="p139">p. 139</a></span></span>
+<span class="smcap">Used.</span>&mdash;It is difficult to determine just the proper
+length the coil should be, or the sizes of the wire,
+unless you know what kind of current you have.
+You may, however, rig up your own apparatus
+for the purpose of making it fit your heater, by
+preparing a base of wood (A) 8 inches long, 3
+inches wide and 1 inch thick. On this mount
+four electric lamp sockets (B). Then connect
+the inlet wire (C) by means of short pieces of wire
+(D) with all the sockets on one side. The outlet
+wire (E) should then be connected up with the
+other sides of the sockets by the short wires (F).
+If, now, we have one 16-candlepower lamp in one
+of the sockets, there is a half ampere going
+through the wires (C, F). If there are two lamps<span class='pagenum'><a name="p140" id="p140">p. 140</a></span>
+on the board you will have 1 ampere, and so on.
+By this means you may readily determine how
+much current you are using and it will also afford
+you a means of finding out whether you have too
+much or too little wire in your coil to do the
+work.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig99" name="fig99"></a><a href="#p140">
+<img src="images/illus-fig99.png" width="344" height="183" alt="Fig. 99. Plan View of Electric Iron" title="Fig. 99. Plan View of Electric Iron" /></a>
+<span class="caption"><i>Fig. 99.</i> <span class="smcap">Plan View of Electric Iron</span></span>
+</div>
+
+
+<p><span class="smcap">An Electric Iron.</span>&mdash;An electric iron is made in
+the same way. The upper side of a flatiron has
+a circular or oval depression (A) cast therein,
+and a spool of slate (B) is made so it will fit into
+the depression and the high resistance wire (C)
+is wound around this spool, and insulating material,
+such as asbestos, must be used to pack
+around it. Centrally, the slate spool has an upwardly
+projecting circular extension (D) which
+passes through the cap or cover (E) of the iron.
+The wires of the resistance coil are then brought<span class='pagenum'><a name="p141" id="p141">p. 141</a></span>
+through this circular extension and are connected
+up with the source of electrical supply. Wires
+are now sold for this purpose, which are adapted
+to withstand an intense heat.</p>
+
+<div class="figcenter" style="width: 347px;">
+<a id="fig100" name="fig100"></a><a href="#p141">
+<img src="images/illus-fig100.png" width="347" height="188" alt="Fig. 100. Section of Electric Iron" title="Fig. 100. Section of Electric Iron" /></a>
+<span class="caption"><i>Fig. 100.</i> <span class="smcap">Section of Electric Iron</span></span>
+</div>
+
+<p>The foregoing example of the use of the current,
+through resistance wires, has a very wide
+application, and any boy, with these examples
+before him, can readily make these devices.</p>
+
+<p><span class="smcap">Thermo Electricity.</span>&mdash;It has long been the
+dream of scientists to convert heat directly into
+electricity. The present practice is to use a boiler
+to generate steam, an engine to provide the motion,
+and a dynamo to convert that motion into
+electricity. The result is that there is loss in
+the process of converting the fuel heat into steam;
+loss to change the steam into motion, and loss to<span class='pagenum'><a name="p142" id="p142">p. 142</a></span>
+make electricity out of the motion of the engine.
+By using water-power there is less actual loss;
+but water-power is not available everywhere.</p>
+
+<p><span class="smcap">Converting Heat Directly Into Electricity.</span>&mdash;Heat
+may be converted directly into electricity
+without using a boiler, an engine or a dynamo,
+but it has not been successful from a commercial
+standpoint. It is interesting, however, to know
+and understand the subject, and for that reason
+it is explained herein.</p>
+
+<p><span class="smcap">Metals; Electric Positive-Negative.</span>&mdash;To understand
+the principle, it may be stated that all
+metals are electrically positive-negative to each
+other. You will remember that it has hereinbefore
+been stated that if, for instance, iron and
+copper are put into an acid solution, a current will
+be created or generated thereby. So with zinc
+and copper, the usual primary battery elements.
+In all such cases an electrolyte is used.</p>
+
+<p>Thermo-electricity dispenses with the electrolyte,
+and nothing is used but the metallic elements
+and heat. The word thermo means heat. If,
+now, we can select two strips of different
+metals, and place them as far apart as possible&mdash;that
+is, in their positive-negative relations with
+each other, and unite the end of one with one
+end of other by means of a rivet, and then heat
+the riveted ends, a current will be generated in<span class='pagenum'><a name="p143" id="p143">p. 143</a></span>
+the strips. If, for instance, we use an iron in
+conjunction with a copper strip, the current will
+flow from the copper to the iron, because copper
+is positive to iron, and iron negative to copper.
+It is from this that the term positive-negative is
+taken.</p>
+
+<p>The two metals most available, which are thus
+farthest apart in the scale of positive-negative
+relation, are bismuth and antimony.</p>
+
+<div class="figcenter" style="width: 345px;">
+<a id="fig101" name="fig101"></a><a href="#p143">
+<img src="images/illus-fig101.png" width="345" height="112" alt="Fig. 101. Thermo-Electric Couple" title="Fig. 101. Thermo-Electric Couple" /></a>
+<span class="caption"><i>Fig. 101.</i> <span class="smcap">Thermo-Electric Couple</span></span>
+</div>
+
+<p>In Fig. <a href="#fig101">101</a> is shown a thermo-electric couple
+(A, B) riveted together, with thin outer ends
+connected by means of a wire (C) to form a
+circuit. A galvanometer (D) or other current-testing
+means is placed in this circuit. A lamp
+is placed below the joined ends.</p>
+
+<p><span class="smcap">Thermo-Electric Couples.</span>&mdash;Any number of
+these couples may be put together and joined at
+each end to a common wire and a fairly large flow
+of current obtained thereby.</p>
+
+<p>One thing must be observed: A current will<span class='pagenum'><a name="p144" id="p144">p. 144</a></span>
+be generated only so long as there exists a difference
+in temperature between the inner and the
+outer ends of the bars (A, B). This may be accomplished
+by water, or any other cooling means
+which may suggest itself.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p145" id="p145">p. 145</a></span></p>
+
+<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS AND RECTIFIERS</h3>
+
+
+<p><span class="smcap">Direct Current.</span>&mdash;When a current of electricity
+is generated by a cell, it is assumed to move along
+the wire in one direction, in a steady, continuous
+flow, and is called a <i>direct</i> current. This direct
+current is a natural one if generated by a
+cell.</p>
+
+<p><span class="smcap">Alternating Current.</span>&mdash;On the other hand, the
+natural current generated by a dynamo is alternating
+in its character&mdash;that is, it is not a direct,
+steady flow in one direction, but, instead, it flows
+for an instant in one direction, then in the other
+direction, and so on.</p>
+
+<p>A direct-current dynamo such as we have shown
+in Chapter IV, is much easier to explain, hence it
+is illustrated to show the third method used in
+generating an electric current.</p>
+
+<p>It is a difficult matter to explain the principle
+and operation of alternating current machines,
+without becoming, in a measure, too technical for
+the purposes of this book, but it is important to
+know the fundamentals involved, so that the operation
+and uses of certain apparatus, like the choking<span class='pagenum'><a name="p146" id="p146">p. 146</a></span>
+coil, transformers, rectifiers and converters,
+may be explained.</p>
+
+<p><span class="smcap">The Magnetic Field.</span>&mdash;It has been stated that
+when a wire passes through the magnetic field of a
+magnet, so as to cut the lines of force flowing out
+from the end of a magnet, the wire will receive
+a charge of electricity.</p>
+
+<div class="figcenter" style="width: 341px;">
+<a id="fig102" name="fig102"></a><a href="#p146">
+<img src="images/illus-fig102.png" width="341" height="89" alt="Fig. 102. Cutting a Magnetic Field" title="Fig. 102. Cutting a Magnetic Field" /></a>
+<span class="caption"><i>Fig. 102.</i> <span class="smcap">Cutting a Magnetic Field</span></span>
+</div>
+
+<p>To explain this, study Fig. <a href="#fig102">102</a>, in which is a
+bar magnet (A). If we take a metal wire (B)
+and bend it in the form of a loop, as shown, and
+mount the ends on journal-bearing blocks, the wire
+may be rotated so that the loop will pass through
+the magnetic field. When this takes place, the
+wire receives a charge of electricity, which moves,
+say, in the direction of the darts, and will make a
+complete circuit if the ends of the looped wire
+are joined, as shown by the conductor (D).</p>
+
+<p><span class="smcap">Action of the Magnetized Wire.</span>&mdash;You will remember,
+also that we have pointed out how, when
+a current passes over a wire, it has a magnetic
+field extending out around it at all points, so that
+while it is passing through the magnetic field of<span class='pagenum'><a name="p147" id="p147">p. 147</a></span>
+the magnet (A), it becomes, in a measure, a magnet
+of its own and tries to set up in business for
+itself as a generator of electricity. But when the
+loop leaves the magnetic field, the magnetic or
+electrical impulse in the wire also leaves it.</p>
+
+<p><span class="smcap">The Movement of a Current in a Charged Wire.</span>&mdash;Your
+attention is directed, also, to another
+statement, heretofore made, namely, that
+when a current from a charged wire passes by
+induction to a wire across space, so as to charge
+it with an electric current, it moves along the
+charged wire in a direction opposite to that of
+the current in the charging wire.</p>
+
+<p>Now, the darts show the direction in which the
+current moves while it is approaching and passing
+through the magnetic field. But the moment
+the loop is about to pass out of the magnetic field,
+the current in the loop surges back in the opposite
+direction, and when the loop has made a revolution
+and is again entering the magnetic field, it
+must again change the direction of flow in the
+current, and thus produce alternations in the flow
+thereof.</p>
+
+<p>Let us illustrate this by showing the four positions
+of the revolving loop. In Fig. <a href="#fig103-106">103</a> the loop
+(B) is in the middle of the magnetic field, moving
+upwardly in the direction of the curved dart
+(A), and while in that position the voltage, or the<span class='pagenum'><a name="p148" id="p148">p. 148</a></span>
+electrical impulse, is the most intense. The current
+used flows in the direction of the darts (C)
+or to the left.</p>
+
+<p>In Fig. <a href="#fig103-106">104</a>, the loop (A) has gone beyond the
+influence of the magnetic field, and now the current
+in the loop tries to return, or reverse itself,
+as shown by the dart (D). It is a reaction that
+causes the current to die out, so that when the
+loop has reached the point farthest from the magnet,
+as shown in Fig. <a href="#fig103-106">105</a>, there is no current in
+the loop, or, if there is any, it moves faintly in the
+direction of the dart (E).</p>
+
+<div class="figcenter" style="width: 360px;">
+<a id="fig103-106" name="fig103-106"></a><a href="#p148">
+<img src="images/illus-fig103-106.png" width="360" height="174" alt="Fig. 13-106. Illustrating Alternations" title="Fig. 103-106. Illustrating Alternations" /></a>
+<span class="caption"><i>Fig. 103-106.</i> <span class="smcap">Illustrating Alternations</span></span>
+</div>
+
+<p><span class="smcap">Current Reversing Itself.</span>&mdash;When the loop
+reaches its lowest point (Fig. <a href="#fig103-106">106</a>) it again comes
+within the magnetic field and the current commences
+to flow back to its original direction, as
+shown by darts (C)</p>
+<p class="pn"><span class='pagenum'><a name="p149" id="p149">p. 149</a></span></p>
+
+<p><span class="smcap">Self-Induction.</span>&mdash;This tendency of a current
+to reverse itself, under the conditions cited, is
+called self-induction, or inductance, and it would
+be well to keep this in mind in pursuing the
+study of alternating currents.</p>
+
+<p>You will see from the foregoing, that the alternations,
+or the change of direction of the current,
+depends upon the speed of rotation of the loop
+past the end of the magnet.</p>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig107" name="fig107"></a><a href="#p149">
+<img src="images/illus-fig107.png" width="353" height="94" alt="Fig. 107. Form for Increasing Alternations" title="Fig. 107. Form for Increasing Alternations" /></a>
+<span class="caption"><i>Fig. 107.</i> <span class="smcap">Form for Increasing Alternations</span></span>
+</div>
+
+<div class="figcenter" style="width: 353px;">
+<a id="fig108" name="fig108"></a><a href="#p149">
+<img src="images/illus-fig108.png" width="353" height="107" alt="Fig. 108. Form for Increasing Alternations" title="Fig. 108. Form for Increasing Alternations" /></a>
+<span class="caption"><i>Fig. 108.</i> <span class="smcap">Form for Increasing Alternations</span></span>
+</div>
+
+<p>Instead, therefore, of using a single loop, we
+may make four loops (Fig. <a href="#fig107">107</a>), which at the
+same speed as we had in the case of the single
+loop, will give four alternations, instead of one,
+and still further, to increase the periods of alternation,
+we may use the four loops and two magnets,<span class='pagenum'><a name="p150" id="p150">p. 150</a></span>
+as in Fig. <a href="#fig108">108</a>. By having a sufficient number
+of loops and of magnets, there may be 40,
+50, 60, 80, 100 or 120 such alternating periods in
+each second. Time, therefore, is an element in
+the operation of alternating currents.</p>
+
+<p>Let us now illustrate the manner of connecting
+up and building the dynamo, so as to derive the
+current from it. In Fig. <a href="#fig109">109</a>, the loop (A) shows,
+for convenience, a pair of bearings (B). A contact
+finger (C) rests on each, and to these the
+circuit wire (D) is attached. Do not confuse
+these contact fingers with the commutator brushes,
+shown in the direct-current motor, as they are
+there merely for the purpose of making contact
+between the revolving loop (A) and stationary
+wire (D).</p>
+
+<div class="figcenter" style="width: 346px;">
+<a id="fig109" name="fig109"></a><a href="#p150">
+<img src="images/illus-fig109.png" width="346" height="93" alt="Fig. 109. Connection of Alternating Dynamo Armature" title="Fig. 109. Connection of Alternating Dynamo Armature" /></a>
+<span class="caption"><i>Fig. 109.</i> <span class="smcap">Connection of Alternating Dynamo Armature</span></span>
+</div>
+
+<p><span class="smcap">Brushes in a Direct-Current Dynamo.</span>&mdash;The
+object of the brushes in the direct-current dynamo,
+in connection with a commutator, is to convert
+this <i>inductance</i> of the wire, or this effort to reverse
+itself into a current which will go in one<span class='pagenum'><a name="p151" id="p151">p. 151</a></span>
+direction all the time, and not in both directions
+alternately.</p>
+
+<p>To explain this more fully attention is directed
+to Figs. <a href="#fig110">110</a> and <a href="#fig111">111</a>. Let A represent the armature,
+with a pair of grooves (B) for the wires.
+The commutator is made of a split tube, the parts
+so divided being insulated from each other, and
+in Fig. <a href="#fig110">110</a>, the upper one, we shall call and designate
+the positive (+) and the lower one the negative
+(-). The armature wire (C) has one end
+attached to the positive commutator terminal and
+the other end of this wire is attached to the negative
+terminal.</p>
+
+<div class="figcenter" style="width: 346px;">
+<a id="fig110" name="fig110"></a><a href="#p151">
+<img src="images/illus-fig110.png" width="346" height="214" alt="Fig. 110. Direct Current Dynamo" title="Fig. 110. Direct Current Dynamo" /></a>
+<span class="caption"><i>Fig. 110.</i> <span class="smcap">Direct Current Dynamo</span></span>
+</div>
+
+<p>One brush (D) contacts with the positive terminal
+of the commutator and the other brush<span class='pagenum'><a name="p152" id="p152">p. 152</a></span>
+(E) with the negative terminal. Let us assume
+that the current impulse imparted to the wire
+(C) is in the direction of the dart (F, Fig. <a href="#fig110">110</a>).
+The current will then flow through the positive
+(+) terminal of the commutator to the brush (D),
+and from the brush (D) through the wire (G) to
+the brush (E), which contacts with the negative
+(-) terminal of the commutator. This will continue
+to be the case, while the wire (C) is passing
+the magnetic field, and while the brush (D) is
+in contact with the positive (+) terminal. But
+when the armature makes a half turn, or when it
+reaches that point where the brush (D) contacts
+with the negative (-) terminal, and the brush
+(E) contacts with the positive (+) terminal, a<span class='pagenum'><a name="p153" id="p153">p. 153</a></span>
+change in the direction of the current through the
+wire (G) takes place, unless something has happened
+to change it before it has reached the
+brushes (D, E).</p>
+
+<div class="figcenter" style="width: 348px;">
+<a id="fig111" name="fig111"></a><a href="#p153">
+<img src="images/illus-fig111.png" width="348" height="210" alt="Fig. 111. Circuit Wires in Direct Current Dynamo" title="Fig. 111. Circuit Wires in Direct Current Dynamo" /></a>
+<span class="caption"><i>Fig. 111.</i> <span class="smcap">Circuit Wires in Direct Current Dynamo</span></span>
+</div>
+
+<p>Now, this change is just exactly what has happened
+in the wire (C), as we have explained.
+The current attempts to reverse itself and start
+out on business of its own, so to speak, with the
+result that when the brushes (D and E) contact
+with the negative and positive terminals, respectively,
+the surging current in the wire (C) is
+going in the direction of the dart (H)&mdash;that is,
+while, in Fig. <a href="#fig110">110</a>, the current flows from the wire
+(C) into the positive terminal, and out of the negative
+terminal into the wire (C), the conditions
+are exactly reversed in Fig. <a href="#fig111">111</a>. Here the current
+in wire C flows <i>into</i> the negative (-) terminal,
+and <i>from</i> the positive (+) terminal into
+the wire C, so that in either case the current will
+flow out of the brush D and into the brush E,
+through the external circuit (G).</p>
+
+<p>It will be seen, therefore, that in the direct-current
+motor, advantage is taken of the surging,
+or back-and-forth movement, of the current to
+pass it along in one direction, whereas in the
+alternating current no such change in direction
+is attempted.</p>
+
+<p><span class="smcap">Alternating Positive and Negative Poles.<span class='pagenum'><a name="p154" id="p154">p. 154</a></span></span>&mdash;The
+alternating current, owing to this surging
+movement, makes the poles alternately positive
+and negative. To express this more clearly, supposing
+we take a line (A, Fig. <a href="#fig112">112</a>), which is
+called the zero line, or line of no electricity. The
+current may be represented by the zigzag line
+(B). The lines (B) above zero (A) may be designated
+as positive, and those below the line as
+negative. The polarity reverses at the line A,
+goes up to D, which is the maximum intensity or
+voltage above zero, and, when the current falls
+and crosses the line A, it goes in the opposite
+direction to E, which is its maximum voltage in
+the other direction. In point of time, if it takes
+one second for the current to go from C to F,
+on the down line, then it takes only a half second
+to go from C to G, so that the line A represents
+the time, and the line H the intensity, a complete
+cycle being formed from C, D, F, then through
+F, E, C, and so on.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig112" name="fig112"></a><a href="#p154">
+<img src="images/illus-fig112.png" width="344" height="105" alt="Fig. 112. Alternating Polarity Lines" title="Fig. 112. Alternating Polarity Lines" /></a>
+<span class="caption"><i>Fig. 112.</i> <span class="smcap">Alternating Polarity Lines</span></span>
+</div>
+
+<p class="pn"><span class='pagenum'><a name="p155" id="p155">p. 155</a></span></p>
+
+<p><span class="smcap">How an Alternating Dynamo Is Made.</span>&mdash;It is
+now necessary to apply these principles in the construction
+of an alternating-current machine. Fig.
+<a href="#fig113">113</a> is a diagram representing the various elements,
+and the circuiting.</p>
+
+<div class="figcenter" style="width: 341px;">
+<a id="fig113" name="fig113"></a><a href="#p155">
+<img src="images/illus-fig113.png" width="341" height="268" alt="Fig. 113. Alternating Current Dynamo" title="Fig. 113. Alternating Current Dynamo" /></a>
+<span class="caption"><i>Fig. 113.</i> <span class="smcap">Alternating Current Dynamo</span></span>
+</div>
+
+<p>Let A represent the ring or frame containing
+the inwardly projecting field magnet cores (B). C
+is the shaft on which the armature revolves, and
+this carries the wheel (D), which has as many
+radially disposed magnet cores (E) as there are
+of the field magnet cores (B).</p>
+
+<p>The shaft (C) also carries two pulleys with
+rings thereon. One of these rings (F) is for one<span class='pagenum'><a name="p156" id="p156">p. 156</a></span>
+end of the armature winding, and the other ring
+(G) for the other end of the armature wire.</p>
+
+<p><span class="smcap">The Windings.</span>&mdash;The winding is as follows:
+One wire, as at H, is first coiled around one magnet
+core, the turnings being to the right. The
+outlet terminal of this wire is then carried to the
+next magnet core and wound around that, in the
+opposite direction, and so on, so that the terminal
+of the wire is brought out, as at I, all of these
+wires being connected to binding posts (J, J'),
+to which, also, the working circuits are attached.</p>
+
+<p><span class="smcap">The Armature Wires.</span>&mdash;The armature wires, in
+like manner, run from the ring (G) to one armature
+core, being wound from right to left, then
+to the next core, which is wound to the right, afterward
+to the next core, which is wound to the left,
+and so on, the final end of the wire being connected
+up with the other ring (F). The north
+(N) and the south (S) poles are indicated in the
+diagram.</p>
+
+<p><span class="smcap">Choking Coil.</span>&mdash;The self-induction in a current
+of this kind is utilized in transmitting electricity
+to great distances. Wires offer resistance, or
+they impede the flow of a current, as hereinbefore
+stated, so that it is not economical to transmit a
+direct current over long distances. This can be
+done more efficiently by means of the alternating
+current, which is subject to far less loss than is<span class='pagenum'><a name="p157" id="p157">p. 157</a></span>
+the case with the direct current. It affords a
+means whereby the flow of a current may be
+checked or reduced without depending upon the
+resistance offered by the wire over which it is
+transmitted. This is done by means of what is
+called a choking coil. It is merely a coil of wire,
+wound upon an iron core, and the current to be
+choked passes through the coil. To illustrate this,
+let us take an arc lamp designed to use a 50-volt
+current. If a current is supplied to it carrying
+100 volts, it is obvious that there are 50 volts more
+than are needed. We must take care of this excess
+of 50 volts without losing it, as would happen
+were we to locate a resistance of some kind in the
+circuit. This result we accomplish by the introduction
+of the choking coil, which has the effect
+of absorbing the excessive 50 volts, the action being
+due to its quality of self-induction, referred to
+in the foregoing.</p>
+
+<div class="figcenter" style="width: 342px;">
+<a id="fig114" name="fig114"></a><a href="#p157">
+<img src="images/illus-fig114.png" width="342" height="116" alt="Fig. 114. Choking Coil" title="Fig. 114. Choking Coil" /></a>
+<span class="caption"><i>Fig. 114.</i> <span class="smcap">Choking Coil</span></span>
+</div>
+
+<p>In Fig. <a href="#fig114">114</a>, A is the choking coil and B an arc<span class='pagenum'><a name="p158" id="p158">p. 158</a></span>
+lamp, connected up, in series, with the choking
+coil.</p>
+
+<p><span class="smcap">The Transformer.</span>&mdash;It is more economical to
+transmit 10,000 volts a long distance than 1,000
+volts, because the lower the pressure, or the
+voltage, the larger must be the conductor to avoid
+loss. It is for this reason that 500 volts, or more,
+are used on electric railways. For electric light
+purposes, where the current goes into dwellings,
+even this is too high, so a transformer is used
+to take a high-voltage current from the main line
+and transform it into a low voltage. This is done
+by means of two distinct coils of wire, wound
+upon an iron core.</p>
+
+<div class="figcenter" style="width: 337px;">
+<a id="fig115" name="fig115"></a><a href="#p158">
+<img src="images/illus-fig115.png" width="337" height="165" alt="Fig. 115. A Transformer" title="Fig. 115. A Transformer" /></a>
+<span class="caption"><i>Fig. 115.</i> <span class="smcap">A Transformer</span></span>
+</div>
+
+<p>In Fig. <a href="#fig115">115</a> the core is O-shaped, so that a primary
+winding (A), from the electrical source, can
+be wound upon one limb, and the secondary winding<span class='pagenum'><a name="p159" id="p159">p. 159</a></span>
+(B) wound around the other limb. The wires,
+to supply the lamps, run from the secondary coil.
+There is no electrical connection between the two
+coils, but the action from the primary to the secondary
+coil is solely by induction. When a current
+passes through the primary coil, the surging
+movement, heretofore explained, is transmitted
+to the iron core, and the iron core, in
+turn, transmits this electrical energy to the secondary
+coil.</p>
+
+<p><span class="smcap">How the Voltage Is Determined.</span>&mdash;The voltage
+produced by the secondary coil will depend
+upon several things, namely, the strength of the
+magnetism transmitted to it; the rapidity, or periodicity
+of the current, and the number of turns of
+wire around the coil. The voltage is dependent
+upon the length of the winding. But the voltage
+may also be increased, as well as decreased. If
+the primary has, we will say, 100 turns of wire,
+and has 200 volts, and the secondary has 50 turns
+of wire, the secondary will give forth only one-half
+as much as the primary, or 100 volts.</p>
+
+<p>If, on the other hand, 400 volts would be required,
+the secondary should have 200 turns in
+the winding.</p>
+
+<p><span class="smcap">Voltage and Amperage in Transformers.</span>&mdash;It
+must not be understood that, by increasing the
+voltage in this way, we are getting that much<span class='pagenum'><a name="p160" id="p160">p. 160</a></span>
+more electricity. If the primary coil, with 100
+turns, produces a current of 200 volts and 50 amperes,
+which would be 200 &times; 50 = 10,000 watts,
+and the secondary coil has 50 turns, we shall have
+100 volts and 100 amperes: 100 (V.) &times; 100 (A.)
+= 10,000 watts. Or, if, on the other hand, our
+secondary winding is composed of 200 turns, we
+shall have 400 volts and 25 amperes, 400 (volts)
+&times; 25 (amperes) also gives 10,000 watts.</p>
+
+<p>Necessarily, there will be some loss, but the
+foregoing is offered as the theoretical basis of
+calculation.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p161" id="p161">p. 161</a></span></p>
+
+
+
+
+<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>ELECTRIC LIGHTING</h3>
+
+
+<p>The most important step in the electric field,
+after the dynamo had been brought to a fairly
+workable condition, was its utilization to make
+light. It was long known prior to the discovery
+of practical electric dynamos, that the electric
+current would produce an intense heat.</p>
+
+<p>Ordinary fuels under certain favorable conditions
+will produce a temperature of 4,500 degrees
+of heat; but by means of the electric arc, as high
+as six, eight and ten thousand degrees are available.</p>
+
+<p>The fact that when a conductor, in an electric
+current, is severed, a spark will follow the drawing
+part of the broken ends, led many scientists to
+believe, even before the dynamo was in a practical
+shape, that electricity, sooner or later, would
+be employed as the great lighting agent.</p>
+
+<p>When the dynamo finally reached a stage in development
+where its operation could be depended
+on, and was made reversible, the first active steps
+were taken to not only produce, but to maintain
+an arc between two electrodes.</p>
+
+<p>It would be difficult and tedious to follow out the<span class='pagenum'><a name="p162" id="p162">p. 162</a></span>
+first experiments in detail, and it might, also, be
+useless, as information, in view of the present
+knowledge of the science. A few steps in the
+course of the development are, however, necessary
+to a complete understanding of the subject.</p>
+
+<p>Reference has been made in a previous chapter
+to what is called the <i>Electric Arc</i>, produced by
+slightly separated conductors, across which the
+electric current jumps, producing the brilliantly
+lighted area.</p>
+
+<p>This light is produced by the combustion of the
+carbon of which the electrodes are composed.
+Thus, the illumination is the result of directly
+burning a fuel. The current, in passing from one
+electrode to the other, through the gap, produces
+such an intense heat that the fuel through which
+the current passes is consumed.</p>
+
+<p>Carbon in a comparatively pure state is difficult
+to ignite, owing to its great resistance to heat.
+At about 7,000 degrees it will fuse, and pass into
+a vapor which causes the intense illumination.</p>
+
+<p>The earliest form of electric lighting was by
+means of the arc, in which the light is maintained
+so long as the electrodes were kept a certain distance
+apart.</p>
+
+<p>To do this requires delicate mechanism, for the
+reason that when contact is made, and the current
+flows through the two electrodes, which are connected<span class='pagenum'><a name="p163" id="p163">p. 163</a></span>
+up directly with the coils of a magnet, the
+cores, or armatures, will be magnetized. The result
+is that the electrode, connected with the
+armature of the magnet, is drawn away from the
+other electrode, and the arc is formed, between
+the separated ends.</p>
+
+<p>As the current also passes through a resistance
+coil, the moment the ends of the electrodes are
+separated too great a distance, the resistance prevents
+a flow of the normal amount of current,
+and the armature is compelled to reduce its pull.
+The effect is to cause the two electrodes to again
+approach each other, and in doing so the arc becomes
+brighter.</p>
+
+<p>It will be seen, therefore, that there is a constant
+fight between the resistance coil and the
+magnet, the combined action of the two being such,
+that, if properly arranged, and with powers in
+correct relation to each other, the light may be
+maintained without undue flickering. Such devices
+are now universally used, and they afford
+a steady and reliable means of illumination.</p>
+
+<p>Many improvements are made in this direction,
+as well as in the ingredients of the electrodes. A
+very novel device for assuring a perfect separation
+at all times between the electrodes, is by
+means of a pair of parallel carbons, held apart by
+a non-conductor such as clay, or some mixture of<span class='pagenum'><a name="p164" id="p164">p. 164</a></span>
+earth, a form of which is shown in Fig. <a href="#fig116">116</a>.</p>
+
+<p>The drawing shows two electrodes, separated
+by a non-conducting material, which is of such
+a character that it will break down and
+crumble away, as the ends of the electrodes burn
+away.</p>
+
+<div class="figcenter" style="width: 344px;">
+<a id="fig116" name="fig116"></a><a href="#p164">
+<img src="images/illus-fig116.png" width="344" height="287" alt="Fig. 116. Parallel Carbons." title="Fig. 116. Parallel Carbons." /></a>
+<span class="italcaption">Fig. 116. Parallel Carbons.</span>
+</div>
+
+<p>This device is admirable where the alternating
+current is used, because the current moves back
+and forth, and the two electrodes are thus burned
+away at the same rate of speed.</p>
+
+<p>In the direct or continuous current the movement<span class='pagenum'><a name="p165" id="p165">p. 165</a></span>
+is in one direction only, and as a result the
+positive electrode is eaten away twice as fast as
+the negative.</p>
+
+<p>This is the arc form of lamp universally used
+for lighting large spaces or areas, such as streets,
+railway stations, and the like. It is important also
+as the means for utilizing searchlight illumination,
+and frequently for locomotive headlights.</p>
+
+<p>Arc lights are produced by what is called the
+<i>series current</i>. This means that the lamps are all
+connected in a single line. This is illustrated by
+reference to Fig. <a href="#fig117">117</a>, in which A represents the
+wire from the dynamo, and B, C the two electrodes,
+showing the current passing through from
+one lamp to the next.</p>
+
+<div class="figcenter" style="width: 356px;">
+<a id="fig117" name="fig117"></a><a href="#p165">
+<img src="images/illus-fig117.png" width="356" height="154" alt="Fig. 117. Arc-Lighting Circuit." title="Fig. 117. Arc-Lighting Circuit." /></a>
+<span class="italcaption">Fig. 117. Arc-Lighting Circuit.</span>
+</div>
+
+<p>A high voltage is necessary in order to cause the
+current to leap across the gap made by the separation
+of the electrodes</p>
+<p class="pn"><span class='pagenum'><a name="p166" id="p166">p. 166</a></span></p>
+
+<p><span class="smcap">The Incandescent System.</span>&mdash;This method is entirely
+different from the arc system. It has been
+stated that certain metals conduct electricity
+with greater facility than others, and some have
+higher resistance than others. If a certain amount
+of electricity is forced through some metals, they
+will become heated. This is true, also, if metals,
+which, ordinarily, will conduct a current freely, are
+made up into such small conductors that it is
+difficult for the current to pass.</p>
+
+<div class="figcenter" style="width: 352px;">
+<a id="fig118" name="fig118"></a><a href="#p166">
+<img src="images/illus-fig118.png" width="352" height="81" alt="Fig 118. Interrupted Conductor." title="Fig 118. Interrupted Conductor." /></a>
+<span class="italcaption">Fig. 118. Interrupted Conductor.</span>
+</div>
+
+<p>In the arc method high voltage is essential; in
+the incandescent plan, current is the important
+consideration. In the arc, the light is produced
+by virtue of the break in the line of the conductor;
+in the incandescent, the system is closed at all
+times.</p>
+
+<p>Supposing we have a wire A, a quarter of an
+inch in diameter, carrying a current of, say, 500
+amperes, and at any point in the circuit the wire
+is made very small, as shown at B, in Fig. <a href="#fig118">118</a>, it
+is obvious that the small wire would not be large
+enough to carry the current.</p>
+
+<p>The result would be that the small connection<span class='pagenum'><a name="p167" id="p167">p. 167</a></span>
+B would heat up, and, finally, be fused. While the
+large part of the wire would carry 500 amperes,
+the small wire could not possibly carry more than,
+say, 10 amperes. Now these little wires are the
+filaments in an electric bulb, and originally the attempt
+was made to have them so connected up
+that they could be illuminated by a single wire,
+as with the arc system above explained, one following
+the other as shown in Fig. <a href="#fig117">117</a>.</p>
+
+<div class="figcenter" style="width: 348px;">
+<a id="fig119" name="fig119"></a><a href="#p167">
+<img src="images/illus-fig119.png" width="348" height="177" alt="Fig. 119. Incandescent Circuit." title="Fig. 119. Incandescent Circuit." /></a>
+<span class="italcaption">Fig. 119. Incandescent Circuit.</span>
+</div>
+
+<p>It was discovered, however, that the addition of
+each successive lamp, so wired, would not give
+light in proportion to the addition, but at only
+about one-fourth the illumination, and such a
+course would, therefore, make electric lighting
+enormously expensive.</p>
+
+<p>This knowledge resulted in an entirely new system
+of wiring up the lamps in a circuit. This is
+explained in Fig. <a href="#fig119">119</a>. In this figure A represents
+the dynamo, B, B the brushes, C, D the two line<span class='pagenum'><a name="p168" id="p168">p. 168</a></span>
+wires, E the lamps, and F the short-circuiting
+wires between the two main conductors
+C, D.</p>
+
+<p>It will be observed that the wires C, D are
+larger than the cross wires F. The object is to
+show that the main wires might carry a very heavy
+amperage, while the small cross wires F require
+only a few amperes.</p>
+
+<p>This is called the <i>multiple</i> circuit, and it is obvious
+that the entire amperage produced by the
+dynamo will not be required to pass through each
+lamp, but, on the other hand, each lamp takes only
+enough necessary to render the filament incandescent.</p>
+
+<p>This invention at once solved the problem of the
+incandescent system and was called the subdivision
+of the electric light. By this means the cost
+was materially reduced, and the wiring up and
+installation of lights materially simplified.</p>
+
+<p>But the divisibility of the light did not, by any
+means, solve the great problem that has occupied
+the attention of electricians and experimenters
+ever since. The great question was and is to preserve
+the little filament which is heated to incandescence,
+and from which we get the light.</p>
+
+<p>The effort of the current to pass through the
+small filament meets with such a great resistance
+that the substance is heated up. If it is made of<span class='pagenum'><a name="p169" id="p169">p. 169</a></span>
+metal there is a point at which it will fuse, and
+thus the lamp is destroyed.</p>
+
+<p>It was found that carbon, properly treated,
+would heat to a brilliant white heat without fusing,
+or melting, so that this material was employed.
+But now followed another difficulty. As this intense
+heat consumed the particles of carbon, owing
+to the presence of oxygen, means were sought to
+exclude the air.</p>
+
+<p>This was finally accomplished by making a bulb
+of glass, from which the air was exhausted, and as
+such a globe had no air to support combustion,
+the filaments were finally made so that they would
+last a long time before being finally disintegrated.</p>
+
+<p>The quest now is, and has been, to find some material
+of a purely metallic character, which will
+have a very high fusing point, and which will,
+therefore, dispense with the cost of the exhausted
+bulb. Some metals, as for instance, osmium, tantalum,
+thorium, and others, have been used, and
+others, also, with great success, so that the march
+of improvements is now going forward with rapid
+strides.</p>
+
+<p><span class="smcap">Vapor Lamps</span>.&mdash;One of the directions in which
+considerable energy has been directed in the past,
+was to produce light from vapors. The Cooper
+Hewitt mercury vapor lamp is a tube filled with
+the vapor of mercury, and a current is sent through<span class='pagenum'><a name="p170" id="p170">p. 170</a></span>
+the vapor which produces a greenish light, and
+owing to that peculiar color, has not met with much
+success.</p>
+
+<p>It is merely cited to show that there are other directions
+than the use of metallic conductors and
+filaments which will produce light, and the day
+is no doubt close at hand when we may expect
+some important developments in the production
+of light by means of the Hertzian waves.</p>
+
+<p><span class="smcap">Directions for Improvements</span>.&mdash;Electricity,
+however, is not a cheap method of illumination.
+The enormous heat developed is largely wasted.
+The quest of the inventor is to find a means whereby
+light can be produced without the generation
+of the immense heat necessary.</p>
+
+<p>Man has not yet found a means whereby he can
+make a heat without increasing the temperature,
+as nature does it in the glow worm, or in the firefly.
+A certain electric energy will produce both
+light and heat, but it is found that much more of
+this energy is used in the heat than in the
+light.</p>
+
+<p>What wonderful possibilities are in store for the
+inventor who can make a heatless light! It is a
+direction for the exercise of ingenuity that will
+well repay any efforts</p>
+<p class="pn"><span class='pagenum'><a name="p171" id="p171">p. 171</a></span></p>
+
+<p class="center"><i>Curious Superstitions Concerning Electricity</i></p>
+
+<p>Electricity, as exhibited in light, has been the
+great marvel of all times. The word electricity
+itself comes from the thunderbolt of the ancient
+God Zeus, which is known to be synonymous with
+the thunderbolt and the lightning.</p>
+
+<p>Magnetism, which we know to be only another
+form of electricity, was not regarded the same as
+electricity by the ancients. Iron which had the
+property to attract, was first found near the town
+of Magnesia, in Lydia, and for that reason was
+called magnetism.</p>
+
+<p>Later on, a glimmer of the truth seemed to dawn
+on the early scientists, when they saw the resemblance
+between the actions of the amber and the
+loadstone, as both attracted particles. And here
+another curious thing resulted. Amber will attract
+particles other than metals. The magnet
+did not; and from this imperfect observation and
+understanding, grew a belief that electricity, or
+magnetism would attract all substances, even human
+flesh, and many devices were made from magnets,
+and used as cures for the gout, and to affect
+the brain, or to remove pain.</p>
+
+<p>Even as early as 2,500 years before the birth
+of Christ the Chinese knew of the properties of
+the magnet, and also discovered that a bar of the<span class='pagenum'><a name="p172" id="p172">p. 172</a></span>
+permanent magnet would arrange itself north and
+south, like the mariners' compass. There is no
+evidence, however, that it was used as a mariner's
+compass until centuries afterwards.</p>
+
+<p>But the matter connected with light, as an electrical
+development, which interests us, is its manifestations
+to the ancients in the form of lightning.
+The electricity of the earth concentrates itself on
+the tops of mountains, or in sharp peaks, and accounts
+for the magnificent electrical displays
+always found in mountainous regions.</p>
+
+<p>Some years ago, a noted scientist, Dr. Siemens,
+while standing on the top of the great pyramid of
+Cheops, in Egypt, during a storm, noted that an
+electrical discharge flowed from his hand when extended
+toward the heavens. The current manifested
+itself in such a manner that the hissing
+noise was plainly perceptible.</p>
+
+<p>The literature of all ages and of all countries
+shows that this manifestation of electrical discharges
+was noted, and became the subject of discussions
+among learned men.</p>
+
+<p>All these displays were regarded as the bolts
+of an angry God, and historians give many accounts
+of instances where, in His anger, He sent
+down the lightning to destroy.</p>
+
+<p>Among the Romans Jupiter thus hurled forth
+his wrath; and among many ancient people, even<span class='pagenum'><a name="p173" id="p173">p. 173</a></span>
+down to the time of Charlemagne, any space
+struck by lightning was considered sacred, and
+made consecrated ground.</p>
+
+<p>From this grew the belief that it was sacrilegious
+to attempt to imitate the lightning of the sky&mdash;that
+Deity would visit dire punishment on any
+man who attempted to produce an electric light.
+Virgil relates accounts where certain princes attempted
+to imitate the lightning, and were struck
+by thunderbolts as punishments.</p>
+
+<p>Less than a century ago Benjamin Franklin devised
+the lightning rod, in order to prevent lightning
+from striking objects. The literature of that
+day abounds with instances of protests made, on
+the part of those who were as superstitions as the
+people in ancient times, who urged that it was
+impious to attempt to ward off Heaven's lightnings.
+It was argued that the lightning was one
+way in which the Creator manifested His displeasure,
+and exercised His power to strike the wicked.</p>
+
+<p>When such writers as Pliny will gravely set
+forth an explanation of the causes of lightning, as
+follows in the paragraph below, we can understand
+why it inculcated superstitious fears in the people
+of ancient times. He says:</p>
+
+<p>"Most men are ignorant of that secret, which,
+by close observation of the heavens, deep scholars
+and principal men of learning have found out,<span class='pagenum'><a name="p174" id="p174">p. 174</a></span>
+namely, that they are the fires of the uppermost
+planets, which, falling to the earth, are called lightning;
+but those especially which are seated in the
+middle, that is about Jupiter, perhaps because participating
+in the excessive cold and moisture from
+the upper circle of Saturn, and the immoderate
+heat of Mars, that is next beneath, by this means
+he discharges his superfluity, and therefore it is
+commonly said, 'That Jupiter shooteth and darteth
+lightning.' Therefore, like as out of a burning
+piece of wood a coal flieth forth with a crack, even
+so from a star is spit out, as it were, and voided
+forth this celestial fire, carrying with it presages
+of future things; so that the heavens showeth divine
+operations, even in these parcels and portions
+which are rejected and cast away as superfluous."</p>
+
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p175" id="p175">p. 175</a></span></p>
+
+<h2><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS</h3>
+
+
+<p>It would be difficult to mention any direction in
+human activity where electricity does not serve as
+an agent in some form or manner. Man has
+learned that the Creator gave this great power
+into the hands of man to use, and not to curse.</p>
+
+<p>When the dynamo was first developed it did not
+appear possible that it could generate electricity,
+and then use that electricity in order to turn the
+dynamo in the opposite direction. It all seems so
+very natural to us now, that such a thing should
+practically follow; but man had to learn this.</p>
+
+<p>Let us try to make the statement plain by a few
+simple illustrations. By carefully going over the
+chapter on the making of the dynamo, it will be
+evident that the basis of the generation of the current
+depends on the changing of the direction of
+the flow of an electric current.</p>
+
+<p>Look at the simple horse-shoe magnet. If two
+of them are gradually moved toward each other,
+so that the north pole of one approaches the north
+pole of the other, there is a sensible attempt for
+them to push away from each other. If, however,<span class='pagenum'><a name="p176" id="p176">p. 176</a></span>
+one of them is turned, so that the north pole of
+one is opposite the south pole of the other, they
+will draw together.</p>
+
+<p>In this we have the foundation physical action
+of the dynamo and the motor. When power is applied
+to an armature, and it moves through a magnetic
+field, the action is just the same as in the case
+of the hand drawing the north and the south pole
+of the two approaching magnets from each other.</p>
+
+<p>The influence of the electrical disturbance produced
+by that act permeated the entire winding of
+the field and armature, and extended out on the
+whole line with which the dynamo was connected.
+In this way a current was established and transmitted,
+and with proper wires was sent in the form
+of circuits and distributed so as to do work.</p>
+
+<p>But an electric current, without suitable mechanism,
+is of no value. It must have mechanism to
+use it, as well as to make it. In the case of
+light, we have explained how the arc and the incandescent
+lamps utilize it for that purpose.</p>
+
+<p>But now, attempting to get something from it
+in the way of power, means another piece of mechanism.
+This is done by the motor, and this motor
+is simply a converter, or a device for reversing
+the action of the electricity.</p>
+
+<p>Attention is called to Figs. <a href="#fig120">120</a> and <a href="#fig121">121</a>. Let us
+assume that the field magnets A, A are the positives,<span class='pagenum'><a name="p177" id="p177">p. 177</a></span>
+and the magnets B, B the negatives. The revolving
+armature has also four magnet coils, two
+of them, C, C, being positive, and the other two,
+D, D, negative, each of these magnet coils being so
+connected up that they will reverse the polarities
+of the magnets.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+<td align="center">
+<a id="fig120" name="fig120"></a><a href="#p177">
+<img src="images/illus-fig120.png" width="179" height="182" alt="Fig. 120. Action of Magnets in a Dynamo" title="Fig. 120. Action of Magnets in a Dynamo" /></a>
+</td>
+<td align="center">
+<a id="fig121" name="fig121"></a><a href="#p177">
+<img src="images/illus-fig121.png" width="176" height="182" alt="Fig. 121. Action of Magnets in a Dynamo" title="Fig. 121. Action of Magnets in a Dynamo" /></a>
+</td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 120-121.</i> <span class="smcap">Action of Magnets in a Dynamo</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+
+<p>Now in the particular position of the revolving
+armature, in Fig. <a href="#fig120">120</a>, the magnets of the armature
+have just passed the respective poles of the field
+magnets, and the belt E is compelled to turn the
+armature past the pole pieces by force in the direction
+of the arrow F. After the armature magnets
+have gone to the positions in Fig. <a href="#fig121">121</a>, the positives
+A try to draw back the negatives D of the
+armature, and at the same time the negatives B
+repel the negatives D, because they are of the same
+polarities</p>
+<p class="pn"><span class='pagenum'><a name="p178" id="p178">p. 178</a></span></p>
+
+<p>This repulsion of the negatives A, B continues
+until the armature poles C, D have slightly passed
+them, when the polarities of the magnets C, D are
+changed; so that it will be seen, by reference to
+Fig. <a href="#fig122">122</a>, that D is now retreating from B, and C
+is going away from A&mdash;that is, being forced away
+contrary to their natural attractive influences, and
+in Fig. <a href="#fig123">123</a>, when the complete cycle is nearly finished,
+the positives are again approaching each
+other and the negatives moving together.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+<td align="center">
+<a id="fig122" name="fig122"></a><a href="#p178">
+<img src="images/illus-fig122.png" width="179" height="183" alt="Fig. 122.  Cycle Action in Dynamo" title="Fig. 122.  Cycle Action in Dynamo" /></a>
+</td>
+<td align="center">
+<a id="fig123" name="fig123"></a><a href="#p178">
+<img src="images/illus-fig123.png" width="173" height="181" alt="Fig. 123. Cycle Action in Dynamo" title="Fig. 123. Cycle Action in Dynamo" /></a>
+</td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 122-123.</i> <span class="smcap">Cycle Action in Dynamo</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+
+</div>
+<p>In this manner, at every point, the sets of magnets
+are compelled to move against their magnetic
+pull. This explains the dynamo.</p>
+
+<p>Now take up the cycle of the motor, and note in
+Fig. <a href="#fig124">124</a> that the negative magnets D of the armature
+are closely approaching the positive and negative<span class='pagenum'><a name="p179" id="p179">p. 179</a></span>
+magnets, on one side; and the positive magnets
+C are nearing the positive and negatives on
+the other side. The positives A, therefore, attract
+the negatives D, and the negative B exert a pull
+on the positives C at the same time. The result is
+that the armature is caused to revolve, as shown
+by the dart G, in a direction opposite to the dart in
+Fig. <a href="#fig120">120</a>.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+<td align="center">
+<a id="fig124" name="fig124"></a><a href="#p179">
+<img src="images/illus-fig124.png" width="178" height="192" alt="Fig. 124. Action of Magnets in Motor" title="Fig. 124. Action of Magnets in Motor" /></a>
+</td>
+<td align="center">
+<a id="fig125" name="fig125"></a><a href="#p179">
+<img src="images/illus-fig125.png" width="175" height="192" alt="Fig. 125. Action of Magnets in Motor" title="Fig. 125. Action of Magnets in Motor" /></a>
+</td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 124-125.</i> <span class="smcap">Action of Magnets in Motor</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+</div>
+<p>When the pole pieces of the magnets C, D are
+about to pass magnets A, B, as shown in Fig. <a href="#fig125">125</a>,
+it is necessary to change the polarities of the armature
+magnets C, D; so that by reference to Fig.
+<a href="#fig126">126</a>, it will be seen that they are now indicated as
+C-, and D+, respectively, and have moved to a
+point midway between the poles A, B (as in Fig.
+<a href="#fig125">125</a>), where the pull on one side, and the push on<span class='pagenum'><a name="p180" id="p180">p. 180</a></span>
+the other are again the same, and the last Figure
+127 shows the cycle nearly completed.</p>
+
+<p>The shaft of the motor armature is now the element
+which turns the mechanism which is to be operated.
+To convert electrical impulses into power,
+as thus shown, results in great loss. The first step
+is to take the steam boiler, which is the first stage
+in that source which is the most common and universal,
+and by means of fuel, converting water into
+steam. The second is to use the pressure of this
+steam to drive an engine; the third is to drive the
+dynamo which generates the electrical impulse;
+and the fourth is the conversion from the dynamo
+into a motor shaft. Loss is met with at each step,
+and the great problem is to eliminate this waste.</p>
+
+<div class="center">
+<table border="0" width="390" cellpadding="0" cellspacing="0">
+<tbody valign="top">
+   <tr>
+<td align="center">
+<a id="fig126" name="fig126"></a><a href="#p180">
+<img src="images/illus-fig126.png" width="179" height="181" alt="Fig. 126. Positions of Magnets in Motor" title="Fig. 126. Positions of Magnets in Motor" /></a>
+</td>
+<td align="center">
+<a id="fig127" name="fig127"></a><a href="#p180">
+<img src="images/illus-fig127.png" width="168" height="181" alt="Fig. 127. Positions of Magnets in Motor" title="Fig. 127. Positions of Magnets in Motor" /></a>
+</td>
+   </tr>
+   <tr>
+   <td class="tdnwc" colspan="2">
+<span class="caption"><i>Figs. 126-127.</i> <span class="smcap"> Positions of Magnets in Motor</span></span>
+      </td>
+   </tr>
+</tbody>
+</table>
+</div>
+<p>The great advantage of electrical power is not in<span class='pagenum'><a name="p181" id="p181">p. 181</a></span>
+utilizing it for consumption at close ranges, but
+where it is desired to transmit it for long distances.
+Such illustrations may be found in electric
+railways, and where water power can be obtained
+as the primal source of energy, the cost is not excessive.
+It is found, however, that even with the
+most improved forms of mechanism, in electrical
+construction, the internal combustion engines are
+far more economical.</p>
+
+
+<p class="center"><i>Transmission of Energy</i></p>
+
+<p>One of the great problems has been the transmission
+of the current to great distances. By using a
+high voltage it may be sent hundreds of miles, but
+to use a current of that character in the cars, or
+shops, or homes, would be exceedingly dangerous.</p>
+
+<p>To meet this requirement transformers have
+been devised, which will take a current of very
+high voltage, and deliver a current of low tension,
+and capable of being used anywhere with the ordinary
+motors.</p>
+
+<p><span class="smcap">The Transformer.</span>&mdash;This is an electrical device
+made up of a core or cores of thin sheet metal,
+around which is wound sets of insulated wires, one
+set being designed to receive the high voltage, and
+the other set to put out the low voltage, as described
+in a former chapter</p>
+<p class="pn"><span class='pagenum'><a name="p182" id="p182">p. 182</a></span></p>
+
+<p>These may be made where the original output is
+a very high voltage, so that they will be stepped
+down, first from one voltage to a lower, and then
+from that to the next lower stage. This is called
+the "Step down" transformer, and is now used
+over the entire world, where large voltages are
+generated.</p>
+
+<p><span class="smcap">Electric Furnaces.</span>&mdash;The most important development
+of electricity in the direction of heat is
+its use in furnaces. As before stated, an intense
+heat is capable of being generated by the electric
+current, so that it becomes the great agent to use
+for the treatment of refractory material.</p>
+
+<p>In furnaces of this kind the electric arc is the
+mechanical form used to produce the great heat,
+the only difference being in the size of the apparatus.
+The electric furnace is simply an immense
+form of arc light, capable of taking a high
+voltage, and such an arc is enclosed within a suitable
+oven of refractory material, which still further
+conserves the heat.</p>
+
+<p><span class="smcap">Welding By Electricity.</span>&mdash;The next step is to
+use the high heat thus capable of being produced,
+to fuse metals so that they may be welded together.
+It is a difficult matter to unite two large pieces of
+metal by the forging method, because the highest
+heat is required, owing to their bulk, and in addition<span class='pagenum'><a name="p183" id="p183">p. 183</a></span>
+immense hammers, weighing tons, must be
+employed.</p>
+
+<p>Electric welding offers a simple and easy
+method of accomplishing the result, and in the
+doing of which it avoids the oxidizing action of
+the forging heat. Instead of heating the pieces to
+be welded in a forge, as is now done, the ends to
+be united are simply brought into contact, and the
+current is sent through the ends until they are in
+a soft condition, after which the parts are pressed
+together and united by the simple merging of the
+plastic condition in which they are reduced by the
+high electric heat.</p>
+
+<p>This form of welding makes the most perfect
+joint, and requires no hammering, as the mass of
+the metal flows from one part or end to the other;
+the unity is a perfect one, and the advantage is
+that the metals can be kept in a semi-fluid state for
+a considerable time, thus assuring a perfect admixture
+of the two parts.</p>
+
+<p>With the ordinary form of welding it is necessary
+to drive the heated parts together without
+any delay, and at the least cooling must be reheated,
+or the joint will not be perfect.</p>
+
+<p>The smallest kinds of electric heating apparatus
+are now being made, so that small articles, sheet
+metal, small rods, and like parts can be united
+with the greatest facility.</p>
+
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p184" id="p184">p. 184</a></span></p>
+
+<h2><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII<span class="totoc"><a href="#toc">ToC</a></span></h2>
+<h3>X-RAY, RADIUM, AND THE LIKE</h3>
+
+
+<p>The camera sees things invisible to the human
+eye. Its most effective work is done with beams
+which are beyond human perception. The photographer
+uses the <i>Actinic</i> rays. Ordinary light is
+composed of the seven primary colors, of which
+the lowest in the scale is the red, and the highest
+to violet.</p>
+
+<p>Those below the red are called the Infra-red,
+and they are the Hertzian waves, or those used in
+wireless telegraphy. Those above the violet are
+called Ultra-violet, and these are employed for
+X-ray work. The former are produced by the high
+tension electric apparatus, which we have described
+in the chapter relating to wireless telegraphy;
+and the latter, called also the Roentgen
+rays, are generated by the Crookes' Tube.</p>
+
+<p>This is a tube from which all the atmosphere has
+been extracted so that it is a practical vacuum.
+Within this are placed electrodes so as to divert
+the action of the electrical discharge in a particular
+direction, and this light, when discharged, is
+of such a peculiar character that its discovery
+made a sensation in the scientific world</p>
+<p class="pn"><span class='pagenum'><a name="p185" id="p185">p. 185</a></span></p>
+
+<p>The reason for this great wonder was not in the
+fact that it projected a light, but because of its
+character. Ordinary light, as we see it with the
+eye, is capable of being reflected, as when we look
+into a mirror at an angle. The X-ray will not reflect,
+but instead, pass directly through the glass.</p>
+
+<p>Then, ordinary light is capable of refraction.
+This is shown by a ray of light bending as it passes
+through a glass of water, which is noticed when
+the light is at an angle to the surface.</p>
+
+<p>The X-ray will pass through the water without
+being changed from a straight line. The foregoing
+being the case, it was but a simple step to conclude
+that if it were possible to find a means whereby
+the human eye could see within the ultra-violet
+beam, it would be possible to see through opaque
+substances.</p>
+
+<p>From the discovery so important and far reaching
+it was not long until it was found that if the
+ultra-violet rays, thus propagated, were transmitted
+through certain substances, their rates of vibration
+would be brought down to the speeds which
+send forth the visible rays, and now the eye is
+able to see, in a measure at least, what the actinic
+rays show.</p>
+
+<p>This discovery was but the forerunner of a still
+more important development, namely, the discovery
+of <i>radium</i>. The actual finding of the metal<span class='pagenum'><a name="p186" id="p186">p. 186</a></span>
+was preceded by the knowledge that certain minerals,
+and water, as well, possessed the property
+of radio-activity.</p>
+
+<p>Radio-activity is a word used to express that
+quality in metals or other material by means of
+which obscure rays are emitted, that have the capacity
+of discharging electrified bodies, and the
+power to ionize gases, as well as to actually affect
+photograph plates.</p>
+
+<p>Certain metals had this property to a remarkable
+degree, particularly uranium, thorium, polonium,
+actinium, and others, and in 1898 the Curies,
+husband and wife, French chemists, isolated an
+element, very ductile in its character, which was a
+white metal, and had a most brilliant luster.</p>
+
+<p>Pitchblende, the base metal from which this
+was extracted, was discovered to be highly radio-active,
+and on making tests of the product taken
+from it, they were surprised to find that it emitted
+a form of energy that far exceeded in calculations
+any computations made on the basis of radio-activity
+in the metals hitherto examined.</p>
+
+<p>But this was not the most remarkable part of
+the developments. The energy, whatever it was,
+had the power to change many other substances if
+brought into close proximity. It darkens the color
+of diamonds, quartz, mica, and glass. It changes
+some of the latter in color, some kinds being<span class='pagenum'><a name="p187" id="p187">p. 187</a></span>
+turned to brown and others into violet or purple
+tinges.</p>
+
+<p>Radium has the capacity to redden the skin, and
+affect the flesh of persons, even at some considerable
+distance, and it is a most powerful germicide,
+destroying bacteria, and has been found also to
+produce some remarkable cures in diseases of a
+cancerous nature.</p>
+
+<p>The remarkable similarity of the rays propagated
+by this substance, with the X-rays, lead
+many to believe that they are electrical in their
+character, and the whole scientific world is now
+striving to use this substance, as well as the more
+familiar light waves of the Roentgen tube, in the
+healing of diseases.</p>
+
+<p>It is not at all remarkable that this use of it
+should first be considered, as it has been the history
+of the electrical developments, from the
+earliest times, that each successive stage should
+find advocates who would urge its virtues to heal
+the sick.</p>
+
+<p>It was so when the dynamo was invented, when
+the high tension current was produced; and electrical
+therapeutics became a leading theme when
+transmission by induction became recognized as
+a scientific fact.</p>
+
+<p>It is not many years since the X-rays were discovered,<span class='pagenum'><a name="p188" id="p188">p. 188</a></span>
+and the first announcement was concerning
+its wonderful healing powers.</p>
+
+<p>This was particularly true in the case of radium,
+but for some reason, after the first tests, all experimenters
+were thwarted in their theories, because
+the science, like all others, required infinite
+patience and experience. It was discovered, in the
+case of the X-ray, that it must be used in a modified
+form, and accordingly, various modifications
+of the waves were introduced, called the <i>m</i> and the
+<i>n</i> rays, as well as many others, each having some
+peculiar qualification.</p>
+
+<p>In time, no doubt, the investigators will find the
+right quality for each disease, and learn how to
+apply it. Thus, electricity, that most alluring
+thing which, in itself, cannot be seen, and is of
+such a character that it cannot even be defined in
+terms which will suit the exact scientific mind, is
+daily bringing new wonders for our investigation
+and use.</p>
+
+<p>It is, indeed, a study which is so broad that it
+has no limitations, and a field which never will be
+exhausted.</p>
+
+<p class="center">THE END</p>
+<hr class="chapter" />
+<p class="chapter"><span class='pagenum'><a name="p189" id="p189">p. 189</a></span></p>
+
+<h3><a name="GLOSSARY_OF_WORDS" id="GLOSSARY_OF_WORDS"></a>GLOSSARY OF WORDS
+USED IN TEXT OF THIS VOLUME<span class="totoc"><a href="#toc">ToC</a></span></h3>
+
+<div class="index">
+<table border="0" cellpadding="2" width="76%" cellspacing="0" summary="Glossary">
+<col style="width:15%;" />
+<col style="width:85%;" />
+<tbody valign="top">
+
+<tr><td align='left'>Acid.</td><td align='left'>Accumulator material is sulphuric acid, diluted with
+water.</td></tr>
+<tr><td align='left'>Active Material.</td><td align='left'>That part of the material in accumulator plates
+which is acted upon by the electric current.</td></tr>
+<tr><td align='left'>Accumulator.</td><td align='left'>A cell, generally known as a storage battery, which
+while it initially receives a charge of electricity, is
+nevertheless, of such a character, owing to the
+active material of which it is made, that it accumulates,
+or, as it were, generates electricity.</td></tr>
+<tr><td align='left'>Aerial Wire, or Conductor.</td><td align='left'>The wire which, in wireless telegraphy, is carried up
+into the air to connect the antenn&aelig; with the receiving and sending apparatus.</td></tr>
+<tr><td align='left'>Alarm, Burglar.</td><td align='left'>A circulating system in a building, connected up
+with a bell or other signaling means.</td></tr>
+<tr><td align='left'>Alloy.</td><td align='left'>A mixture of two or more metals; as copper and
+zinc to make brass; nickel and zinc to form German silver.</td></tr>
+<tr><td align='left'>Alternating Current.</td><td align='left'>A current which goes back and forth in opposite directions,
+unlike a direct current which flows continuously
+in one direction over a wire.</td></tr>
+<tr><td align='left'>Alternation.</td><td align='left'>The term applied to a change in the direction of an
+alternating current, the frequency of the alternations
+ranging up to 20,000 or more vibrations
+per second.</td></tr>
+<tr><td align='left'>Amber.</td><td align='left'>A resin, yellow in color, which when rubbed with a
+cloth, becomes excited and gives forth negative
+<span class='pagenum'><a name="p190" id="p190">p. 190</a></span>electricity.</td></tr>
+<tr><td align='left'>Ammeter.</td><td align='left'>An instrument for measuring the quantity or flow of
+electricity.</td></tr>
+<tr><td align='left'>Ampere.</td><td align='left'>The unit of current; the term in which strength of
+the current is measured. An ampere is an electromotive
+force of one volt through a resistance of one ohm.</td></tr>
+<tr><td align='left'>Annunciator.</td><td align='left'>A device which indicates or signals a call given
+from some distant point.</td></tr>
+<tr><td align='left'>Anode.</td><td align='left'>The positive terminal in a conducting circuit, like
+the terminal of the carbon plate in a battery. It
+is a plate in an electroplating bath from which
+the current goes over to the cathode or negative
+plate or terminal.</td></tr>
+<tr><td align='left'>Arc.</td><td align='left'>A term employed to designate the gap, or the current
+which flows across between the conductors,
+like the space between the two carbons of an arc
+lamp, which gives the light.</td></tr>
+<tr><td align='left'>Armature.</td><td align='left'>A body of iron, or other suitable metal, which is in
+the magnetic field of a magnet.</td></tr>
+<tr><td align='left'>Armature Bar.</td><td align='left'>The piece which holds the armature. Also one of a
+series of bars which form the conductors in armature
+windings.</td></tr>
+<tr><td align='left'>Armature Coil.</td><td align='left'>The winding around an armature, or around the core
+of an armature.</td></tr>
+<tr><td align='left'>Armature Core.</td><td align='left'>The part in a dynamo or motor which revolves, and
+on which the wire coils are wound.</td></tr>
+<tr><td align='left'>Astatic (Galvanometer).</td><td align='left'>That which has no magnetic action to direct or divert
+anything exterior to it.</td></tr>
+<tr><td align='left'>Atom.</td><td align='left'>The ultimate particle of an elementary substance.</td></tr>
+<tr><td align='left'>Attraction.</td><td align='left'>That property of matter which causes particles to
+adhere, or cohere, to each other. It is known
+<span class='pagenum'><a name="p191" id="p191">p. 191</a></span>under a variety of terms, such as gravitation, chemical
+affinity, electro-magnetism and dynamic attraction.</td></tr>
+<tr><td align='left'>Automatic Cut-out.</td><td align='left'>A device which acts through the operation of the
+mechanism with which it is connected. It is usually
+applied to a device which cuts out a current
+when it overcharges or overloads the wire.</td></tr>
+<tr><td align='left'>Bath.</td><td align='left'>In electroplating, the vessel or tank which holds the
+electroplating solution.</td></tr>
+<tr><td align='left'>Battery.</td><td align='left'>A combination of two or more cells.</td></tr>
+<tr><td align='left'>Battery, Dry.</td><td align='left'>A primary battery in which the electrolyte is made
+in a solid form.</td></tr>
+<tr><td align='left'>Battery, Galvanic.</td><td align='left'>A battery which is better known by the name of the
+Voltaic Pile, made up of zinc and copper plates
+which alternate, and with a layer of acidulated paper
+between each pair of plates.</td></tr>
+<tr><td align='left'>Battery, Storage.</td><td align='left'>A battery which accumulates electricity generated by
+a primary battery or a generator.</td></tr>
+<tr><td align='left'>Brush.</td><td align='left'>A term applied to the conducting medium that bears
+against the cylindrical surface of a commutator.</td></tr>
+<tr><td align='left'>Buzzer.</td><td align='left'>An electric call produced by a rapidly moving armature
+of an electro-magnet.</td></tr>
+<tr><td align='left'>Cable.</td><td align='left'>A number of wires or conductors assembled in one
+strand.</td></tr>
+<tr><td align='left'>Candle-power.</td><td align='left'>The amount of light given by the legal-standard candle.
+This standard is a sperm candle, which burns
+two grains a minute.</td></tr>
+<tr><td align='left'>Capacity.</td><td align='left'>The carrying power of a wire or circuit, without
+heating. When heated there is an overload, or the
+<i>capacity</i> of the wire is overtaxed.</td></tr>
+<tr><td align='left'>Capacity, Storage.</td><td align='left'>The quantity of electricity in a secondary battery
+when fully charged, usually reckoned in ampere
+<span class='pagenum'><a name="p192" id="p192">p. 192</a></span>hours.</td></tr>
+<tr><td align='left'>Carbon.</td><td align='left'>A material, like coke, ground or crushed, and formed
+into sticks or plates by molding or compression.
+It requires a high heat to melt or burn, and is used
+as electrodes for arc lamps and for battery elements.
+It has poor conductivity, and for arc lamps
+is coated with copper to increase its conductivity.</td></tr>
+<tr><td align='left'>Cell, Electrolytic.</td><td align='left'>A vessel containing an electrolyte for electroplating
+purposes.</td></tr>
+<tr><td align='left'>Charge.</td><td align='left'>The quantity of electricity on the surface of a body
+or conductor.</td></tr>
+<tr><td align='left'>Chemical Change.</td><td align='left'>When a current passes through electrodes in a solution,
+a change takes place which is chemical in
+its character. Adding sulphuric acid to water produces
+heat. If electrodes of opposite polarity are
+placed in such an acid solution, a chemical change
+is produced, which is transformed into electricity.</td></tr>
+<tr><td align='left'>Choking Coil.</td><td align='left'>An instrument in a circuit which by a form of resistance
+regulates the flow of the current, or returns
+part of it to the source of its generation.</td></tr>
+<tr><td align='left'>Counter-electromotive Force.</td><td align='left'>Cells which are inserted in opposition to a battery
+to reduce high voltage.</td></tr>
+<tr><td align='left'>Circuit, Astatic.</td><td align='left'>A circuit in an instrument so wound that the earth's
+magnetism will not affect it.</td></tr>
+<tr><td align='left'>Circuit Breaker.</td><td align='left'>Any instrument in a circuit which cuts out or interrupts
+the flow of a current.</td></tr>
+<tr><td align='left'>Circuit, External.</td><td align='left'>A current flows through a wire or conductor, and
+also along the air outside of the conductor, the
+latter being the <i>external circuit.</i></td></tr>
+<tr><td align='left'>Circuit Indicator.</td><td align='left'>An instrument, like a galvanometer, that shows the
+direction in which a current is flowing through a
+<span class='pagenum'><a name="p193" id="p193">p. 193</a></span>conductor.</td></tr>
+<tr><td align='left'>Circuit, Return.</td><td align='left'>Usually the ground return, or the negative wire from
+a battery.</td></tr>
+<tr><td align='left'>Circuit, Short.</td><td align='left'>Any connection between the mains or parallel lines
+of a circuit which does not go through the apparatus
+for which the circuit is intended.</td></tr>
+<tr><td align='left'>Coherer.</td><td align='left'>A tube, or other structure, containing normally high
+resistance particles which form a path or bridge
+between the opposite terminals of a circuit.</td></tr>
+<tr><td align='left'>Coil.</td><td align='left'>A wire, usually insulated, wound around a spool.</td></tr>
+<tr><td align='left'>Coil, Induction.</td><td align='left'>One of a pair of coils designed to change the voltage
+of a current of electricity, from a higher to a
+lower, or from a lower to a higher electro-motive
+force.</td></tr>
+<tr><td align='left'>Coil, Resistance.</td><td align='left'>A coil so wound that it will offer a resistance to a
+steady current, or reduce the flow of electricity.</td></tr>
+<tr><td align='left'>Commutator.</td><td align='left'>A cylinder on the end of the armature of a dynamo
+or motor and provided with a pair of contact
+plates for each particular coil in the armature, in
+order to change the direction of the current.</td></tr>
+<tr><td align='left'>Compass.</td><td align='left'>An apparatus which indicates the direction or flow
+of the earth's magnetism.</td></tr>
+<tr><td align='left'>Condenser.</td><td align='left'>A device for storing up electro-static charges.</td></tr>
+<tr><td align='left'>Conductance.</td><td align='left'>That quality of a conductor to carry a current of
+electricity, dependent on its shape for the best
+results.</td></tr>
+<tr><td align='left'>Conduction.</td><td align='left'>The transmission of a current through a rod, wire or
+conductor.</td></tr>
+<tr><td align='left'>Conductivity.</td><td align='left'>That quality which has reference to the capacity to
+conduct a current.</td></tr>
+<tr><td align='left'>Conductor.</td><td align='left'>Any body, such as a bar, rod, wire, or machine,
+which will carry a current.</td></tr>
+<tr><td align='left'>Connector.</td><td align='left'>A binding post, clamp, screw, or other means to hold
+<span class='pagenum'><a name="p194" id="p194">p. 194</a></span>the end of a wire, or electric conductor.</td></tr>
+<tr><td align='left'>Contact.</td><td align='left'>To unite any parts in an electric circuit.</td></tr>
+<tr><td align='left'>Controller.</td><td align='left'>The handle of a switchboard, or other contact making
+and breaking means in a circuit.</td></tr>
+<tr><td align='left'>Converter.</td><td align='left'>An induction coil in an alternating circuit for changing
+potential difference, such as high alternating
+voltage into low direct current voltage.</td></tr>
+<tr><td align='left'>Convolution.</td><td align='left'>To wind like a clock spring.</td></tr>
+<tr><td align='left'>Core.</td><td align='left'>The inner portion of an electro-magnet. The inside
+part of an armature wound with wire.</td></tr>
+<tr><td align='left'>Core, Laminated.</td><td align='left'>When the core is built up of a number of separate
+pieces of the same material, but not insulated from
+each other.</td></tr>
+<tr><td align='left'>Coulomb.</td><td align='left'>The unit of electrical quantity. It is the quantity
+passed by a current of one ampere intensity in
+one second of time.</td></tr>
+<tr><td align='left'>Couple, Electric.</td><td align='left'>Two or more electrodes in a liquid to produce an
+electric force.</td></tr>
+<tr><td align='left'>Current, Alternating.</td><td align='left'>A natural current produced by the action of electro-magnets.
+It is a succession of short impulses in
+opposite directions.</td></tr>
+<tr><td align='left'>Current, Constant.</td><td align='left'>A current which is uniformly maintained in a steady
+stream.</td></tr>
+<tr><td align='left'>Current, Induced.</td><td align='left'>A current produced by electro-dynamic induction.</td></tr>
+<tr><td align='left'>Current Meter.</td><td align='left'>An apparatus for indicating the strength of a current.
+An ammeter.</td></tr>
+<tr><td align='left'>Current, Oscillating.</td><td align='left'>A current which periodically alternates.</td></tr>
+
+<tr><td align='left'>Current, Periodic.</td><td align='left'>A periodically varying current strength.</td></tr>
+
+<tr><td align='left'>Current, Undulating.</td><td align='left'>A current which has a constant direction, but has a
+<span class='pagenum'><a name="p195" id="p195">p. 195</a></span>continuously varying strength.</td></tr>
+<tr><td align='left'>Decomposition.</td><td align='left'>The separation of a liquid, such as an electrolyte,
+into its prime elements, either electrically or otherwise.</td></tr>
+<tr><td align='left'>Deflection.</td><td align='left'>The change of movement of a magnetic needle out of
+its regular direction of movement.</td></tr>
+<tr><td align='left'>Demagnetization.</td><td align='left'>When a current passes through a coil wound on an
+iron core, the core becomes magnetized. When the
+current ceases the core is no longer a magnet. It
+is then said to be <i>demagnetized</i>. It also has reference
+to the process for making a watch non-magnetic
+so that it will not be affected when in
+a magnetic field.</td></tr>
+<tr><td align='left'>Density.</td><td align='left'>The quantity of an electric charge in a conductor
+or substance.</td></tr>
+<tr><td align='left'>Depolarization.</td><td align='left'>The removal of magnetism from a permanent magnet,
+or a horse-shoe magnet, for instance. It is
+generally accomplished by applying heat.</td></tr>
+<tr><td align='left'>Deposition, Electrolysis.</td><td align='left'>The act of carrying metal from one pole of a cell
+to another pole, as in electroplating.</td></tr>
+<tr><td align='left'>Detector.</td><td align='left'>Mechanism for indicating the presence of a current
+in a circuit.</td></tr>
+<tr><td align='left'>Diaphragm.</td><td align='left'>A plate in a telephone, which, in the receiver, is
+in the magnetic field of a magnet, and in a transmitter
+carries the light contact points.</td></tr>
+<tr><td align='left'>Dielectric.</td><td align='left'>A non-conductor for an electric current, but through
+which electro-static induction will take place. For
+example: glass and rubber are dielectrics.</td></tr>
+<tr><td align='left'>Discharge.</td><td align='left'>The current flowing from an accumulator.</td></tr>
+<tr><td align='left'>Disintegration.</td><td align='left'>The breaking up of the plate or active material.</td></tr>
+<tr><td align='left'>Disruptive.</td><td align='left'>A static discharge passing through a dielectric.</td></tr>
+<tr><td align='left'>Duplex Wire.</td><td align='left'>A pair of wires usually twisted together and insulated
+from each other to form the conducting
+<span class='pagenum'><a name="p196" id="p196">p. 196</a></span>circuit of a system.</td></tr>
+<tr><td align='left'>Dynamic Electricity.</td><td align='left'>The term applied to a current flowing through a
+wire.</td></tr>
+<tr><td align='left'>Dynamo.</td><td align='left'>An apparatus, consisting of core and field magnets,
+which, when the core is turned, will develop a
+current of electricity.</td></tr>
+<tr><td align='left'>Earth Returns.</td><td align='left'>Instead of using two wires to carry a circuit, the
+earth is used for what is called the <i>return</i> circuit.</td></tr>
+<tr><td align='left'>Efficiency.</td><td align='left'>The total electrical energy produced, in which that
+wasted, as well as that used, is calculated.</td></tr>
+<tr><td align='left'>Elasticity.</td><td align='left'>That property of any matter which, after a stress,
+will cause the substance to return to its original
+form or condition. Electricity has elasticity, which
+is utilized in condensers, as an instance.</td></tr>
+<tr><td align='left'>Electricity, Atmospheric.</td><td align='left'>Lightning, and, in short, any current or electrical
+impulse, like wireless telegraphic waves, is called
+<i>atmospheric</i>.</td></tr>
+<tr><td align='left'>Electricity, Voltaic.</td><td align='left'>Electricity with a low potentiality and large current
+density.</td></tr>
+<tr><td align='left'>Electrification.</td><td align='left'>The process of imparting a charge of electricity to
+any body.</td></tr>
+<tr><td align='left'>Electro-chemistry.</td><td align='left'>The study of which treats of electric and chemical
+forces, such as electric plating, electric fusing,
+electrolysis, and the like.</td></tr>
+<tr><td align='left'>Electrode.</td><td align='left'>The terminals of a battery, or of any circuit; as, for
+instance, an arc light.</td></tr>
+<tr><td align='left'>Electrolyte.</td><td align='left'>Any material which is capable of being decomposed by
+an electric current.</td></tr>
+<tr><td align='left'>Electro-magnetism.</td><td align='left'>Magnetism which is created by an electric current.</td></tr>
+<tr><td align='left'>Electrometer.</td><td align='left'>An instrument for measuring static electricity, differing
+from a galvanometer, which measures a current
+in a wire that acts on the magnetic needle
+<span class='pagenum'><a name="p197" id="p197">p. 197</a></span>of the galvanometer.</td></tr>
+<tr><td align='left'>Electro-motive Force.</td><td align='left'>(E. M. F.) Voltage, which is the measure or unit
+of e. m. f.</td></tr>
+<tr><td align='left'>Electroscope.</td><td align='left'>A device for indicating not only the presence of
+electricity, but whether it is positive or negative.</td></tr>
+<tr><td align='left'>Electro-static Accumulator.</td><td align='left'>Surfaces separated by a dielectric for opposite charging
+of the surface.</td></tr>
+<tr><td align='left'>Element.</td><td align='left'>In electricity a form of matter, as, for instance, gold,
+or silver, that has no other matter or compound.
+Original elements cannot be separated, because
+they are not made up of two or more elements,
+like brass, for instance.</td></tr>
+<tr><td align='left'>Excessive Charge.</td><td align='left'>A storage battery charged at too high a rate.</td></tr>
+<tr><td align='left'>Excessive Discharge.</td><td align='left'>A storage battery discharged at too high a rate.</td></tr>
+<tr><td align='left'>Excessive Overcharge.</td><td align='left'>Charging for too long a time.</td></tr>
+<tr><td align='left'>Exciter.</td><td align='left'>A generator, either a dynamo or a battery, for exciting
+the field of a dynamo.</td></tr>
+<tr><td align='left'>Exhaustive Discharge.</td><td align='left'>An excessive over-discharge of an accumulator.</td></tr>
+<tr><td align='left'>F.</td><td align='left'>The sign used to indicate the heat term Fahrenheit.</td></tr>
+<tr><td align='left'>Fall of Voltage.</td><td align='left'>The difference between the initial and the final voltage
+in a current.</td></tr>
+<tr><td align='left'>Field.</td><td align='left'>The space or region near a magnet or charged wire.
+Also the electro-magnets in a dynamo or motor.</td></tr>
+<tr><td align='left'>Flow.</td><td align='left'>The volume of a current going through a conductor.</td></tr>
+<tr><td align='left'>Force, Electro-magnetic.</td><td align='left'>The pull developed by an electro-magnet.</td></tr>
+<tr><td align='left'>Frictional Electricity.</td><td align='left'>A current produced by rubbing dissimilar substances
+together.</td></tr>
+<tr><td align='left'>Full Load.</td><td align='left'>The greatest load a battery, accumulator or dynamo
+<span class='pagenum'><a name="p198" id="p198">p. 198</a></span>will sustain.</td></tr>
+<tr><td align='left'>Galvanic.</td><td align='left'>Pertaining to the electro-chemical relations of metals
+toward each other.</td></tr>
+<tr><td align='left'>Galvanizing.</td><td align='left'>The art of coating one metal with another, such, for
+instance, as immersing iron in molten zinc.</td></tr>
+<tr><td align='left'>Galvanometry.</td><td align='left'>An instrument having a permanently magnetized
+needle, which is influenced by a coil or a wire in
+close proximity to it.</td></tr>
+<tr><td align='left'>Galvanoscope.</td><td align='left'>An instrument, like a galvanometer, which determines
+whether or not a current is present in a
+tested wire.</td></tr>
+<tr><td align='left'>Generator.</td><td align='left'>A term used to generally indicate any device which
+originates a current.</td></tr>
+<tr><td align='left'>German Silver.</td><td align='left'>An alloy of copper, nickel and zinc.</td></tr>
+<tr><td align='left'>Graphite.</td><td align='left'>One form of carbon. It is made artificially by the
+electric current.</td></tr>
+<tr><td align='left'>Grid.</td><td align='left'>The metallic frame of a plate used to hold the active
+material of an accumulator.</td></tr>
+<tr><td align='left'>Gravity.</td><td align='left'>The attraction of mass for mass. Weight. The accelerating
+tendency of material to move toward
+the earth.</td></tr>
+<tr><td align='left'>Gutta Percha.</td><td align='left'>Caoutchouc, which has been treated with sulphur, to
+harden it. It is produced from the sap of tropical
+trees, and is a good insulator.</td></tr>
+<tr><td align='left'>Harmonic Receiver.</td><td align='left'>A vibrating reed acted on by an electro-magnet, when
+tuned to its pitch.</td></tr>
+<tr><td align='left'>High E. M. F.</td><td align='left'>A term to indicate currents which have a high voltage,
+and usually low amperage.</td></tr>
+<tr><td align='left'>Igniter.</td><td align='left'>Mechanism composed of a battery, induction coil and
+a vibrator, for making a jump spark, to ignite
+gas, powder, etc.</td></tr>
+<tr><td align='left'>I. H. P.</td><td align='left'>Abbreviation, which means Indicated Horse Power.</td></tr>
+<tr><td align='left'>Impulse.</td><td align='left'>A sudden motion of one body acting against another.
+<span class='pagenum'><a name="p199" id="p199">p. 199</a></span>An electro-magnetic wave magnetizing soft iron,
+and this iron attracting another piece of iron, as an example.</td></tr>
+<tr><td align='left'>Incandescence, Electric.</td><td align='left'>A conductor heated up by a current so it will glow.</td></tr>
+<tr><td align='left'>Induced Current.</td><td align='left'>A current of electricity which sets up lines of force
+at right angles to the body of the wire through
+which the current is transmitted.</td></tr>
+<tr><td align='left'>Induction, Magnetic.</td><td align='left'>A body within a magnetic field which is excited by
+the magnetism.</td></tr>
+<tr><td align='left'>Installation.</td><td align='left'>Everything belonging to an equipment of a building,
+or a circuiting system to do a certain thing.</td></tr>
+<tr><td align='left'>Insulation.</td><td align='left'>A material or substance which resists the passage of
+a current placed around a conductor.</td></tr>
+<tr><td align='left'>Intensity.</td><td align='left'>The strength of a magnetic field, or of a current flowing
+over a wire.</td></tr>
+<tr><td align='left'>Internal Resistance.</td><td align='left'>The current strength of electricity of a wire to resist
+the passage.</td></tr>
+<tr><td align='left'>Interrupter.</td><td align='left'>A device in a wire or circuit for checking a current.
+It also refers to the vibrator of an induction coil.</td></tr>
+<tr><td align='left'>Joint.</td><td align='left'>The place where two or more conductors are united.</td></tr>
+<tr><td align='left'>Joint Resistance.</td><td align='left'>The combined resistance offered by two or more substances
+or conductors.</td></tr>
+<tr><td align='left'>Jump Spark.</td><td align='left'>A spark, disruptive in its character, between two
+conducting points.</td></tr>
+<tr><td align='left'>Initial Charge.</td><td align='left'>The charge required to start a battery.</td></tr>
+<tr><td align='left'>Kathode, or Cathode.</td><td align='left'>The negative plate or side of a battery. The plate
+on which the electro deposit is made.</td></tr>
+<tr><td align='left'>Key.</td><td align='left'>The arm of a telegraph sounder. A bar with a finger
+piece, which is hinged and so arranged that it will
+make and break contacts in an electric circuit.</td></tr>
+<tr><td align='left'>Keyboard.</td><td align='left'>A switch-board; a board on which is mounted a number
+<span class='pagenum'><a name="p200" id="p200">p. 200</a></span>of switches.</td></tr>
+<tr><td align='left'>Kilowatt.</td><td align='left'>A unit, representing 1,000 watts. An electric current
+measure, usually expressed thus: K.W.</td></tr>
+<tr><td align='left'>Kilowatt Hour.</td><td align='left'>The computation of work equal to the exertion of
+one kilowatt in one hour.</td></tr>
+<tr><td align='left'>Knife Switch.</td><td align='left'>A bar of a blade-like form, adapted to move down
+between two fingers, and thus establish metallic
+connections.</td></tr>
+<tr><td align='left'>Laminated.</td><td align='left'>Made up of thin plates of the same material, laid
+together, but not insulated from each other.</td></tr>
+<tr><td align='left'>Lamp Arc.</td><td align='left'>A voltaic arc lamp, using carbon electrodes, with
+mechanism for feeding the electrodes regularly.</td></tr>
+<tr><td align='left'>Lamp, Incandescent.</td><td align='left'>A lamp with a filament heated up to a glow by the
+action of an electric current. The filament is within
+a vacuum in a glass globe.</td></tr>
+<tr><td align='left'>Leak.</td><td align='left'>Loss of electrical energy through a fault in wiring,
+or in using bare wires.</td></tr>
+<tr><td align='left'>Load.</td><td align='left'>The ampere current delivered by a dynamo under certain
+conditions.</td></tr>
+<tr><td align='left'>Low Frequency.</td><td align='left'>A current in which the vibrations are of few alternations
+per second.</td></tr>
+<tr><td align='left'>Magnet.</td><td align='left'>A metallic substance which has power to attract iron
+and steel.</td></tr>
+<tr><td align='left'>Magnet Bar.</td><td align='left'>A straight piece of metal.</td></tr>
+<tr><td align='left'>Magnet Coil.</td><td align='left'>A coil of wire, insulated, surrounding a core of iron,
+to receive a current of electricity.</td></tr>
+<tr><td align='left'>Magnet Core.</td><td align='left'>A bar of iron adapted to receive a winding of wire.</td></tr>
+<tr><td align='left'>Magnet, Field.</td><td align='left'>A magnet in a dynamo. A motor to produce electric
+energy.</td></tr>
+<tr><td align='left'>Magnet, Permanent.</td><td align='left'>A short steel form, to hold magnetism for a long
+time.</td></tr>
+<tr><td align='left'>Magnetic Adherence.</td><td align='left'>The adherence of particles to the poles of a magnet.
+<span class='pagenum'><a name="p201" id="p201">p. 201</a></span></td></tr>
+<tr><td align='left'>Magnetic Attraction and Repulsion.</td><td align='left'>That quality of a metal which draws metals. Also
+the pulling action of unlike poles for each other,
+and pushing away of like poles when brought together.</td></tr>
+<tr><td align='left'>Magnetic Force.</td><td align='left'>The action exercised by a magnet of attracting or
+repelling.</td></tr>
+<tr><td align='left'>Magnetic Pole.</td><td align='left'>The earth has North and South magnetic poles. The
+south pole of a magnetic needle is attracted so it
+points to the north magnetic pole; and the north
+pole of the needle is attracted to point to the
+south magnetic pole.</td></tr>
+<tr><td align='left'>Magneto-generator.</td><td align='left'>A permanent magnet and a revolving armature for
+generating a current.</td></tr>
+<tr><td align='left'>Maximum Voltage.</td><td align='left'>The final voltage after charging.</td></tr>
+<tr><td align='left'>Molecule.</td><td align='left'>Invisible particles made up of two or more atoms of
+different matter. An atom is a particle of one substance only.</td></tr>
+<tr><td align='left'>Morse Sounder.</td><td align='left'>An electric instrument designed to make a clicking
+sound, when the armature is drawn down by a
+magnet.</td></tr>
+<tr><td align='left'>Motor-dynamo.</td><td align='left'>A motor and a dynamo having their armatures connected
+together, whereby the motor is driven by
+the dynamo, so as to change the current into a
+different voltage and amperage.</td></tr>
+<tr><td align='left'>Motor-transformer.</td><td align='left'>A motor which delivers the current like a generator.</td></tr>
+<tr><td align='left'>Needle.</td><td align='left'>A bar magnet horizontally poised on a vertical pivot
+point, like the needle of a mariner's compass.</td></tr>
+<tr><td align='left'>Negative Electricity.</td><td align='left'>Amber, when rubbed, produces negative electricity.
+<span class='pagenum'><a name="p202" id="p202">p. 202</a></span>A battery has positive as well as negative electricity.</td></tr>
+<tr><td align='left'>Negative Element.</td><td align='left'>That plate in the solution of a battery cell which is
+not disintegrated.</td></tr>
+<tr><td align='left'>Normal.</td><td align='left'>The usual, or ordinary. The average. In a current
+the regular force required to do the work.</td></tr>
+<tr><td align='left'>North Pole, Electric.</td><td align='left'>The term applied to the force located near the north
+pole of the globe, to which a permanent magnet
+will point if allowed to swing freely.</td></tr>
+<tr><td align='left'>O.</td><td align='left'>Abbreviation for Ohm.</td></tr>
+<tr><td align='left'>Ohm.</td><td align='left'>The unit of resistance. Equal to the resistance of a
+column of mercury one square millimeter in cross
+section, and 106.24 centimeters in length.</td></tr>
+<tr><td align='left'>Ohm's Law.</td><td align='left'>It is expressed as follows:
+<ol><li>The current strength is equal to the electro-motive
+force divided by its resistance.</li>
+<li>The electro-motive force is equal to the current
+strength multiplied by the resistance.</li>
+<li>The resistance is equal to the electro-motive
+force divided by the current strength.</li>
+</ol>
+</td></tr>
+<tr><td align='left'>Overload.</td><td align='left'>In a motor an excess of mechanical work which
+causes the armature to turn too slowly and produces
+heat.</td></tr>
+<tr><td align='left'>Phase.</td><td align='left'>One complete oscillation. The special form of a wave
+at any instant, or at any interval of time.</td></tr>
+<tr><td align='left'>Plate, Condenser.</td><td align='left'>In a static machine it is usually a plate of glass and
+revoluble.</td></tr>
+<tr><td align='left'>Plate, Negative.</td><td align='left'>The plate in a battery, such as carbon, copper or
+platinum, which is not attacked by the solution.</td></tr>
+<tr><td align='left'>Plating, Electro-.</td><td align='left'>The method of coating one metal with another by
+electrolysis.</td></tr>
+<tr><td align='left'>Polarity.</td><td align='left'>The peculiarity, in a body, of arranging itself with
+reference to magnetic influence.</td></tr>
+<tr><td align='left'>Parallel.</td><td align='left'>When a number of cells are coupled so that their
+<span class='pagenum'><a name="p203" id="p203">p. 203</a></span>similar poles are grouped together. That is to
+say, as the carbon plates, for instance, are connected
+with one terminal, and all the zinc plates
+with the other terminal.</td></tr>
+<tr><td align='left'>Polarization.</td><td align='left'>When the cell is deprived of its electro-motive force,
+or any part of it, polarization is the result. It is
+usually caused by coating of the plates.</td></tr>
+<tr><td align='left'>Porosity.</td><td align='left'>Having small interstices or holes.</td></tr>
+<tr><td align='left'>Positive Current.</td><td align='left'>One which deflects a needle to the left.</td></tr>
+<tr><td align='left'>Positive Electricity.</td><td align='left'>Any current flowing from the active element, such as
+zinc, in a battery. The negative electricity flows
+from the carbon to the zinc.</td></tr>
+<tr><td align='left'>Potential, Electric.</td><td align='left'>The power which performs work in a circuit.</td></tr>
+<tr><td align='left'>Potential Energy.</td><td align='left'>That form of force, which, when liberated, does or
+performs work.</td></tr>
+<tr><td align='left'>Power Unit.</td><td align='left'>The volt-amperes or watt.</td></tr>
+<tr><td align='left'>Primary.</td><td align='left'>The induction coil in induction machines, or in a
+transformer.</td></tr>
+<tr><td align='left'>Push Button.</td><td align='left'>A thumb piece which serves as a switch to close a
+circuit while being pressed inwardly.</td></tr>
+<tr><td align='left'>Quantity.</td><td align='left'>Such arrangement of electrical connections which
+give off the largest amount of current.</td></tr>
+<tr><td align='left'>Receiver.</td><td align='left'>An instrument in telephony and telegraphy which
+receives or takes in the sound or impulses.</td></tr>
+<tr><td align='left'>Relay.</td><td align='left'>The device which opens or closes a circuit so as to
+admit a new current which is sent to a more distant
+point.</td></tr>
+<tr><td align='left'>Repulsion, Electric.</td><td align='left'>That tendency in bodies to repel each other when
+similarly charged.</td></tr>
+<tr><td align='left'>Resilience.</td><td align='left'>The springing back to its former condition or position.
+<span class='pagenum'><a name="p204" id="p204">p. 204</a></span>Electricity has resilience.</td></tr>
+<tr><td align='left'>Resistance.</td><td align='left'>The quality in all conductors to oppose the passage
+of a current.</td></tr>
+<tr><td align='left'>Resistance Coil.</td><td align='left'>A coil made up of wire which prevents the passage
+of a current to a greater or less degree.</td></tr>
+<tr><td align='left'>Resistance, Electrolytic.</td><td align='left'>The counter force in an electrolyte which seeks to
+prevent a decomposing current to pass through it.</td></tr>
+<tr><td align='left'>Resistance: Internal, External.</td><td align='left'>The opposing force to the movement of a current
+which is in the cell or generator. This is called
+the <i>internal</i>. That opposite action outside of the
+cell or generator is the <i>external</i>.</td></tr>
+<tr><td align='left'>Resonator, Electric.</td><td align='left'>An open-circuited conductor for electrically resounding
+or giving back a vibration, usually exhibited
+by means of a spark.</td></tr>
+<tr><td align='left'>Rheostat.</td><td align='left'>A device which has an adjustable resistance, so arranged
+that while adjusting the same the circuit
+will not be open.</td></tr>
+<tr><td align='left'>Safety Fuse.</td><td align='left'>A piece of fusible metal of such resistance that it
+breaks down at a certain current strength.</td></tr>
+<tr><td align='left'>Saturated.</td><td align='left'>When a liquid has taken up a soluble material to the
+fullest extent it is then completely saturated.</td></tr>
+<tr><td align='left'>Secondary.</td><td align='left'>One of the two coils in a transformer, or induction
+coil.</td></tr>
+<tr><td align='left'>Secondary Plates.</td><td align='left'>The brown or deep red plates in a storage battery
+when charged.</td></tr>
+<tr><td align='left'>Self-excited.</td><td align='left'>Producing electricity by its own current.</td></tr>
+<tr><td align='left'>Series.</td><td align='left'>Arranged in regular order. From one to the other
+directly. If lamps, for instance, should be arranged
+in circuit on a single wire, they would be
+in series.</td></tr>
+<tr><td align='left'>Series, Multiple.</td><td align='left'>When lamps are grouped in sets in parallel, and
+<span class='pagenum'><a name="p205" id="p205">p. 205</a></span>these sets are then connected up in series.</td></tr>
+<tr><td align='left'>Series Windings.</td><td align='left'>A generator or motor wound in such a manner that
+one of the commutator brush connections is joined
+to the field magnet winding, and the other end
+of the magnet winding joined to the outer circuit.</td></tr>
+<tr><td align='left'>Shunt.</td><td align='left'>Going around.</td></tr>
+<tr><td align='left'>Shunt Winding.</td><td align='left'>A dynamo in which the field winding is parallel
+with the winding of the armature.</td></tr>
+<tr><td align='left'>Snap Switch.</td><td align='left'>A switch so arranged that it will quickly make a
+break.</td></tr>
+<tr><td align='left'>Sounder.</td><td align='left'>The apparatus at one end of a line actuated by a key
+at the other end of the line.</td></tr>
+<tr><td align='left'>Spark Coil.</td><td align='left'>A coil, to make a spark from a low electro-motive
+force.</td></tr>
+<tr><td align='left'>Spark, Electric.</td><td align='left'>The flash caused by drawing apart the ends of a conductor.</td></tr>
+<tr><td align='left'>Specific Gravity.</td><td align='left'>The weight or density of a body.</td></tr>
+<tr><td align='left'>Static Electricity.</td><td align='left'>Generated by friction. Also lightning. Any current
+generated by a high electro-motive force.</td></tr>
+<tr><td align='left'>Strength of Current.</td><td align='left'>The quantity of electricity in a circuit.</td></tr>
+<tr><td align='left'>Synchronize.</td><td align='left'>Operating together; acting in unison.</td></tr>
+<tr><td align='left'>Terminal.</td><td align='left'>The end of any electric circuit or of a body or machine
+which has a current passing through it.</td></tr>
+<tr><td align='left'>Thermostat, Electric.</td><td align='left'>An electric thermometer. Usually made with a metal
+coil which expands through the action of the electricity
+passing through it, and, in expanding, it
+makes a contact and closes a circuit.</td></tr>
+<tr><td align='left'>Transformer.</td><td align='left'>The induction coil with a high initial E. M. F. changes
+into a low electro-motive force.</td></tr>
+<tr><td align='left'>Unit.</td><td align='left'>A standard of light, heat, electricity, or of other
+<span class='pagenum'><a name="p206" id="p206">p. 206</a></span>phenomena.</td></tr>
+<tr><td align='left'>Vacuum.</td><td align='left'>A space from which all matter has been exhausted.</td></tr>
+<tr><td align='left'>Vibrator.</td><td align='left'>Mechanism for making and breaking circuits in induction
+coils or other apparatus.</td></tr>
+<tr><td align='left'>Volt.</td><td align='left'>The unit of electro-motive force.</td></tr>
+<tr><td align='left'>Voltage.</td><td align='left'>Electro-motive force which is expressed in volts.</td></tr>
+<tr><td align='left'>Voltaic.</td><td align='left'>A term applied to electric currents and devices.</td></tr>
+<tr><td align='left'>Volt-meter.</td><td align='left'>An apparatus for showing the difference of potential,
+or E. M. F. in the term of volts.</td></tr>
+<tr><td align='left'>Watt.</td><td align='left'>The unit of electrical activity. The product of amperes
+multiplied by volts.</td></tr>
+<tr><td align='left'>Watt Hour.</td><td align='left'>One watt maintained through one hour of time.</td></tr>
+<tr><td align='left'>Waves, Electric Magnetic.</td><td align='left'>Waves in the ether caused by electro-magnetic disturbances.</td></tr>
+<tr><td align='left'>X-rays.</td><td align='left'>The radiation of invisible rays of light, which penetrate
+or pass through opaque substances.</td></tr>
+<tr><td align='left'>Yoke, or Bar.</td><td align='left'>A soft iron body across the ends of a horseshoe magnet,
+to enable the magnet to retain its magnetism
+an indefinite time.</td></tr>
+<tr><td align='left'>Zinc Battery.</td><td align='left'>A battery which uses zinc for one of its elements.</td></tr>
+</tbody>
+</table>
+</div>
+
+
+<hr class="chapter" />
+<p class="chapter"><span class="pagenum"><a name="p207" id="p207">p. 207</a></span></p>
+
+<h2><a name="INDEX" id="INDEX"></a>INDEX<span class="totoc"><a href="#toc">ToC</a></span></h2>
+
+<div class="index">
+
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<h4><a id="IX_A" name="IX_A"></a>A</h4>
+<ul class="IX">
+<li>Accumulated, <a href="#p31">31</a>.</li>
+<li>Accumulation, <a href="#p29">29</a>.</li>
+<li>Accumulator cell, <a href="#p87">87</a>.</li>
+<li>Accumulators, <a href="#p82">82</a>, <a href="#p88">88</a>, <a href="#p89">89</a>.</li>
+<li>Accumulators, plates, <a href="#p83">83</a>.</li>
+<li>Acid, <a href="#p34">34</a>, <a href="#p37">37</a>, <a href="#p125">125</a>.</li>
+<li>Acid maker, <a href="#p125">125</a>.</li>
+<li>Acid, sulphuric, <a href="#p31">31</a>, <a href="#p84">84</a>.</li>
+<li>Acidulated, <a href="#p55">55</a>.</li>
+<li>Acidulated water, <a href="#p34">34</a>.</li>
+<li>Acoustics, <a href="#p110">110</a>.</li>
+<li>Actinic rays, <a href="#p184">184</a>, <a href="#p185">185</a>.</li>
+<li>Actinium, <a href="#p186">186</a>.</li>
+<li>Active element, <a href="#p82">82</a>.</li>
+<li>Adjustable rod, <a href="#p107">107</a>.</li>
+<li>Adjusting screw, <a href="#p70">70</a>, <a href="#p71">71</a>, <a href="#p72">72</a>, <a href="#p73">73</a>, <a href="#p106">106</a>.</li>
+<li>Aerial wire, <a href="#p108">108</a>.</li>
+<li>Agents, <a href="#p13">13</a>, <a href="#p32">32</a>.</li>
+<li>Alarms, burglar, <a href="#p11">11</a>, <a href="#p76">76</a>, <a href="#p80">80</a>.</li>
+
+<li>Alkali, <a href="#p125">125</a>.</li>
+
+<li>Alkaline, <a href="#p37">37</a>.</li>
+
+<li>Alternate, <a href="#p127">127</a>.</li>
+
+<li>Alternating, <a href="#p38">38</a>, <a href="#p149">149</a>, <a href="#p150">150</a>, <a href="#p153">153</a>, <a href="#p154">154</a>, <a href="#p155">155</a>, <a href="#p156">156</a>.</li>
+
+<li>Alternating current, <a href="#p145">145</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li><p></p></li>
+
+<li>Alternating periods, <a href="#p149">149</a>.</li>
+
+<li>Alternations, <a href="#p147">147</a>.</li>
+
+<li>Aluminum, <a href="#p128">128</a>, <a href="#p129">129</a>, <a href="#p135">135</a>, <a href="#p137">137</a>.</li>
+
+<li>Aluminum hydrate, <a href="#p129">129</a>.</li>
+
+<li>Amber, <a href="#p5">5</a>, <a href="#p171">171</a>.</li>
+
+<li>Ammeter, <a href="#p7">7</a>, <a href="#p88">88</a>.</li>
+
+<li>Amperage, <a href="#p38">38</a>, <a href="#p61">61</a>, <a href="#p62">62</a>, <a href="#p132">132</a>, <a href="#p159">159</a>, <a href="#p160">160</a>, <a href="#p168">168</a>.</li>
+
+<li>Ampere, <a href="#p7">7</a>, <a href="#p37">37</a>, <a href="#p60">60</a>, <a href="#p63">63</a>, <a href="#p139">139</a>, <a href="#p140">140</a>, <a href="#p167">167</a>.</li>
+
+<li>Amplitude, <a href="#p111">111</a>.</li>
+
+<li>Annunciator, <a href="#p65">65</a>, <a href="#p74">74</a>, <a href="#p76">76</a>, <a href="#p79">79</a>, <a href="#p80">80</a>, <a href="#p81">81</a>.</li>
+
+<li>Annunciator bells, <a href="#p11">11</a>.</li>
+
+<li>Anode, <a href="#p35">35</a>, <a href="#p133">133</a>, <a href="#p134">134</a>.</li>
+
+<li>Antenn&aelig;, <a href="#p108">108</a>.</li>
+
+<li>Antimony <a href="#p137">137</a>, <a href="#p143">143</a>.</li>
+
+<li>Anvil, <a href="#p13">13</a>, <a href="#p14">14</a>.</li>
+
+<li>Apparatus, <a href="#p11">11</a>, <a href="#p57">57</a>, <a href="#p106">106</a>, <a href="#p139">139</a>, <a href="#p145">145</a>.</li>
+
+<li>Arc, <a href="#p163">163</a>, <a href="#p182">182</a>.</li>
+
+<li>Arc lighting, <a href="#p38">38</a>, <a href="#p165">165</a>.</li>
+
+<li>Arc system, <a href="#p166">166</a>.</li>
+
+<li>Armature, <a href="#p18">18</a>, <a href="#p25">25</a>, <a href="#p38">38</a>, <a href="#p40">40</a>, <a href="#p42">42</a>, <a href="#p43">43</a>, <a href="#p45">45</a>, <a href="#p46">46</a>, <a href="#p47">47</a>, <a href="#p48">48</a>, <a href="#p53">53</a>, <a href="#p55">55</a>, <a href="#p70">70</a>, <a href="#p72">72</a>, <a href="#p73">73</a>, <a href="#p74">74</a>, <a href="#p90">90</a>, <a href="#p93">93</a>, <a href="#p112">112</a>, <a href="#p151">151</a>, <a href="#p152">152</a>, <a href="#p155">155</a>, <a href="#p163">163</a>, <a href="#p176">176</a>, <a href="#p177">177</a>, <a href="#p178">178</a>, <a href="#p179">179</a>, <a href="#p180">180</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+<div><span class='pagenum'><a name="p208" id="p208">p. 208</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Armature brush,  <a href="#p48">48</a>.</li>
+
+<li>Armature post, <a href="#p71">71</a>.</li>
+
+<li>Armature, vertical, <a href="#p75">75</a>.</li>
+
+<li>Armature winding, <a href="#p42">42</a>, <a href="#p43">43</a>, <a href="#p156">156</a>.</li>
+
+<li>Asbestos, <a href="#p140">140</a>.</li>
+
+<li>Astatic galvanometer, <a href="#p108">108</a>.</li>
+
+<li>Atmosphere, <a href="#p184">184</a>.</li>
+
+<li>Attract, <a href="#p30">30</a>.</li>
+
+<li>Attracted, <a href="#p72">72</a>.</li>
+
+<li>Attraction, <a href="#p21">21</a>, <a href="#p25">25</a>.</li>
+
+<li>Attractive, <a href="#p178">178</a>.</li>
+
+<li>Automatic, <a href="#p120">120</a>.</li>
+
+<li>Auxiliary, <a href="#p44">44</a>.</li>
+
+<li>Awls, <a href="#p14">14</a>.</li>
+</ul>
+
+<h4><a id="IX_B" name="IX_B"></a>B</h4>
+<ul class="IX">
+<li>Bacteria, <a href="#p126">126</a>, <a href="#p187">187</a>.</li>
+
+<li>Bar, cross, <a href="#p66">66</a>.</li>
+
+<li>Bar, horizontal, <a href="#p46">46</a>.</li>
+
+<li>Bar, parallel switch, <a href="#p67">67</a>.</li>
+
+<li>Bar, switch, <a href="#p65">65</a>, <a href="#p68">68</a>.</li>
+
+<li>Base block, <a href="#p66">66</a>.</li>
+
+<li>Batteries, <a href="#p11">11</a>, <a href="#p93">93</a>, <a href="#p122">122</a>.</li>
+
+<li>Battery, <a href="#p29">29</a>, <a href="#p30">30</a>, <a href="#p32">32</a>, <a href="#p35">35</a>, <a href="#p36">36</a>, <a href="#p46">46</a>, <a href="#p47">47</a>, <a href="#p80">80</a>, <a href="#p81">81</a>, <a href="#p82">82</a>, <a href="#p83">83</a>, <a href="#p85">85</a>, <a href="#p86">86</a>, <a href="#p88">88</a>, <a href="#p92">92</a>, <a href="#p94">94</a>, <a href="#p95">95</a>, <a href="#p107">107</a>, <a href="#p108">108</a>, <a href="#p116">116</a>, <a href="#p117">117</a>, <a href="#p118">118</a>, <a href="#p121">121</a>, <a href="#p134">134</a>, <a href="#p142">142</a>.</li>
+
+<li>Battery charging, <a href="#p82">82</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Bearings, <a href="#p45">45</a>, <a href="#p46">46</a>.</li>
+
+<li>Bells, <a href="#p65">65</a>, <a href="#p73">73</a>, <a href="#p76">76</a>, <a href="#p122">122</a>.</li>
+
+<li>Bells, electric, <a href="#p70">70</a>.</li>
+
+<li>Bench, <a href="#p13">13</a>, <a href="#p15">15</a>, <a href="#p17">17</a>.</li>
+
+<li>Binding post, <a href="#p52">52</a>, <a href="#p70">70</a>, <a href="#p71">71</a>, <a href="#p72">72</a>, <a href="#p103">103</a>, <a href="#p107">107</a>, <a href="#p108">108</a>, <a href="#p121">121</a>.</li>
+
+<li>Binding screw, <a href="#p65">65</a>, <a href="#p66">66</a>.</li>
+
+<li>Bismuth, <a href="#p18">18</a>, <a href="#p143">143</a>.</li>
+
+<li>Bit, <a href="#p13">13</a>.</li>
+
+<li>Blue vitriol, <a href="#p57">57</a>.</li>
+
+<li>Brass plate, <a href="#p77">77</a>, <a href="#p78">78</a>.</li>
+
+<li>Brazing, <a href="#p17">17</a>, <a href="#p65">65</a>.</li>
+
+<li>Bridge, <a href="#p52">52</a>.</li>
+
+<li>Brush holder, <a href="#p46">46</a>.</li>
+
+<li>Brushes, <a href="#p48">48</a>, <a href="#p150">150</a>, <a href="#p151">151</a>, <a href="#p153">153</a>, <a href="#p167">167</a>.</li>
+
+<li>Burglar, <a href="#p11">11</a>.</li>
+
+<li>Burglar alarm, <a href="#p76">76</a>, <a href="#p80">80</a>.</li>
+
+<li>Buttons, contact, <a href="#p80">80</a>.</li>
+
+<li>Buttons, push, <a href="#p65">65</a>, <a href="#p68">68</a>, <a href="#p69">69</a>, <a href="#p70">70</a>, <a href="#p76">76</a>, <a href="#p79">79</a>.</li>
+</ul>
+
+<h4><a id="IX_C" name="IX_C"></a>C</h4>
+<ul class="IX">
+<li>Calorimeter, <a href="#p56">56</a>.</li>
+
+<li>Cancerous, <a href="#p187">187</a>.</li>
+
+<li>Candle power, <a href="#p89">89</a>, <a href="#p139">139</a>.</li>
+
+<li>Cap, removable, <a href="#p73">73</a>.</li>
+
+<li>Cap screws, <a href="#p42">42</a>.</li>
+
+<li>Carbon, <a href="#p35">35</a>, <a href="#p119">119</a>, <a href="#p121">121</a>, <a href="#p162">162</a>, <a href="#p163">163</a>, <a href="#p169">169</a>.</li>
+<li>Carbon block, <a href="#p120">120</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p209" id="p209">p. 209</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Carbon pencil, <a href="#p119">119</a>.</li>
+
+<li>Cathode, <a href="#p35">35</a>, <a href="#p36">36</a>, <a href="#p133">133</a>, <a href="#p134">134</a>.</li>
+
+<li>Cell, <a href="#p29">29</a>, <a href="#p33">33</a>.</li>
+
+<li>Cell, accumulator, <a href="#p87">87</a>.</li>
+
+<li>Cell, charging, <a href="#p87">87</a>.</li>
+
+<li>Channel, <a href="#p43">43</a>.</li>
+
+<li>Channel, concave, <a href="#p40">40</a>.</li>
+
+<li>Charged, <a href="#p120">120</a>.</li>
+
+<li>Charged battery, <a href="#p82">82</a>.</li>
+
+<li>Charging circuit, <a href="#p82">82</a>, <a href="#p89">89</a>.</li>
+
+<li>Charging source, <a href="#p83">83</a>.</li>
+
+<li>Charged wire, <a href="#p147">147</a>.</li>
+
+<li>Chemical, <a href="#p57">57</a>.</li>
+
+<li>Chisels, <a href="#p13">13</a>.</li>
+
+<li>Chloride of lime, <a href="#p84">84</a>.</li>
+
+<li>Choked, <a href="#p157">157</a>.</li>
+
+<li>Choking coils, <a href="#p145">145</a>, <a href="#p146">146</a>, <a href="#p156">156</a>, <a href="#p158">158</a>.</li>
+
+<li>Circuit, <a href="#p33">33</a>, <a href="#p69">69</a>, <a href="#p73">73</a>, <a href="#p76">76</a>, <a href="#p78">78</a>, <a href="#p80">80</a>, <a href="#p81">81</a>, <a href="#p90">90</a>, <a href="#p92">92</a>, <a href="#p93">93</a>, <a href="#p109">109</a>, <a href="#p113">113</a>, <a href="#p116">116</a>, <a href="#p121">121</a>, <a href="#p122">122</a>, <a href="#p131">131</a>, <a href="#p134">134</a>, <a href="#p143">143</a>, <a href="#p156">156</a>.</li>
+
+<li>Circuit, primary, <a href="#p99">99</a>.</li>
+
+<li>Circuit, secondary, <a href="#p99">99</a>.</li>
+
+<li>Circuiting, <a href="#p81">81</a>, <a href="#p155">155</a>.</li>
+
+<li>Circuiting system, <a href="#p79">79</a>.</li>
+
+<li>Clapper arm, <a href="#p70">70</a>.</li>
+
+<li>Closed rings, <a href="#p26">26</a>.</li>
+
+<li>Coherer, <a href="#p105">105</a>, <a href="#p108">108</a>, <a href="#p109">109</a>.</li>
+
+<li>Cohering, <a href="#p106">106</a>.</li>
+
+<li>Coils, <a href="#p18">18</a>, <a href="#p26">26</a>, <a href="#p52">52</a>, <a href="#p55">55</a>, <a href="#p74">74</a>, <a href="#p160">160</a>.</li>
+
+<li>Coils, choking, <a href="#p145">145</a>, <a href="#p146">146</a>, <a href="#p156">156</a>, <a href="#p158">158</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Coils, induction, <a href="#p99">99</a>, <a href="#p102">102</a>.</li>
+
+<li>Coils, primary, <a href="#p109">109</a>.</li>
+
+<li>Coils, secondary, <a href="#p102">102</a>, <a href="#p109">109</a>.</li>
+
+<li>Coincide, <a href="#p42">42</a>.</li>
+
+<li>Cold, <a href="#p14">14</a>.</li>
+
+<li>Collecting surfaces, <a href="#p30">30</a>.</li>
+
+<li>Collector, <a href="#p31">31</a>.</li>
+
+<li>Column, <a href="#p61">61</a>.</li>
+
+<li>Combustion, <a href="#p169">169</a>.</li>
+
+<li>Commutator, <a href="#p44">44</a>, <a href="#p46">46</a>, <a href="#p151">151</a>, <a href="#p152">152</a>.</li>
+
+<li>Commutator brushes, <a href="#p46">46</a>.</li>
+
+<li>Commutator plates, <a href="#p45">45</a>.</li>
+
+<li>Compass, <a href="#p22">22</a>, <a href="#p24">24</a>, <a href="#p172">172</a>.</li>
+
+<li>Composition, <a href="#p83">83</a>, <a href="#p124">124</a>.</li>
+
+<li>Compound wound, <a href="#p47">47</a>.</li>
+
+<li>Concave channel, <a href="#p40">40</a>.</li>
+
+<li>Condenser, <a href="#p98">98</a>, <a href="#p100">100</a>, <a href="#p101">101</a>, <a href="#p102">102</a>, <a href="#p108">108</a>.</li>
+
+<li>Conduct, <a href="#p6">6</a>, <a href="#p108">108</a>.</li>
+
+<li>Conduction, <a href="#p135">135</a>, <a href="#p136">136</a>, <a href="#p138">138</a>, <a href="#p166">166</a>, <a href="#p170">170</a>.</li>
+
+<li>Conduction current, <a href="#p27">27</a>.</li>
+
+<li>Conductor, <a href="#p21">21</a>, <a href="#p31">31</a>, <a href="#p33">33</a>, <a href="#p63">63</a>, <a href="#p98">98</a>, <a href="#p116">116</a>, <a href="#p161">161</a>, <a href="#p162">162</a>.</li>
+
+<li>Conduit, <a href="#p72">72</a>.</li>
+
+<li>Conically formed, <a href="#p126">126</a>.</li>
+
+<li>Conjunction, <a href="#p143">143</a>.</li>
+
+<li>Connecting wire, <a href="#p58">58</a>.</li>
+
+<li>Connection, <a href="#p72">72</a>, <a href="#p76">76</a>.</li>
+
+<li>Construction, magnet, <a href="#p39">39</a>.</li>
+
+<li>Consumption, <a href="#p180">180</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p210" id="p210">p. 210</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Contact, <a href="#p122">122</a>, <a href="#p123">123</a>, <a href="#p152">152</a>, <a href="#p162">162</a>.</li>
+
+<li>Contact finger, <a href="#p150">150</a>.</li>
+
+<li>Contact plate, <a href="#p67">67</a>, <a href="#p68">68</a>, <a href="#p79">79</a>.</li>
+
+<li>Contact screws, <a href="#p93">93</a>.</li>
+
+<li>Contact surface, <a href="#p66">66</a>.</li>
+
+<li>Continuous, <a href="#p145">145</a>.</li>
+
+<li>Converter, <a href="#p176">176</a>.</li>
+
+<li>Converting, <a href="#p142">142</a>, <a href="#p145">145</a>, <a href="#p146">146</a>.</li>
+
+<li>Copper, <a href="#p18">18</a>, <a href="#p34">34</a>, <a href="#p36">36</a>, <a href="#p65">65</a>, <a href="#p66">66</a>, <a href="#p132">132</a>, <a href="#p133">133</a>, <a href="#p134">134</a>, <a href="#p135">135</a>, <a href="#p136">136</a>, <a href="#p137">137</a>, <a href="#p142">142</a>, <a href="#p143">143</a>.</li>
+
+<li>Copper cyanide, <a href="#p133">133</a>.</li>
+
+<li>Copper plate, <a href="#p33">33</a>, <a href="#p35">35</a>, <a href="#p58">58</a>, <a href="#p67">67</a>.</li>
+
+<li>Copper sulphate, <a href="#p57">57</a>.</li>
+
+<li>Copper voltameter, <a href="#p55">55</a>, <a href="#p57">57</a>.</li>
+
+<li>Core, <a href="#p27">27</a>, <a href="#p28">28</a>, <a href="#p36">36</a>, <a href="#p39">39</a>, <a href="#p40">40</a>, <a href="#p115">115</a>.</li>
+
+<li>Core, magnet, <a href="#p75">75</a>, <a href="#p93">93</a>.</li>
+
+<li>Counter, clock-wise, <a href="#p51">51</a>.</li>
+
+<li>Coupled, <a href="#p36">36</a>.</li>
+
+<li>Crank, <a href="#p30">30</a>.</li>
+
+<li>Crookes' tube, <a href="#p184">184</a>.</li>
+
+<li>Cross bar, <a href="#p52">52</a>, <a href="#p66">66</a>.</li>
+
+<li>Crown of cups, <a href="#p32">32</a>.</li>
+
+<li>Crystal, <a href="#p85">85</a>.</li>
+
+<li>Current, <a href="#p6">6</a>, <a href="#p7">7</a>, <a href="#p13">13</a>, <a href="#p18">18</a>, <a href="#p26">26</a>, <a href="#p27">27</a>, <a href="#p28">28</a>, <a href="#p35">35</a>, <a href="#p36">36</a>, <a href="#p37">37</a>, <a href="#p38">38</a>, <a href="#p47">47</a>, <a href="#p50">50</a>, <a href="#p51">51</a>, <a href="#p52">52</a>, <a href="#p55">55</a>, <a href="#p56">56</a>, <a href="#p57">57</a>, <a href="#p58">58</a>, <a href="#p59">59</a>, <a href="#p62">62</a>, <a href="#p63">63</a>, <a href="#p70">70</a>, <a href="#p72">72</a>, <a href="#p73">73</a>, <a href="#p90">90</a>, <a href="#p95">95</a>, <a href="#p98">98</a>, <a href="#p105">105</a>, <a href="#p108">108</a>,
+<a href="#p116">116</a>, <a href="#p133">133</a>, <a href="#p134">134</a>, <a href="#p135">135</a>, <a href="#p136">136</a>, <a href="#p138">138</a>, <a href="#p139">139</a>, <a href="#p140">140</a>, <a href="#p141">141</a>, <a href="#p142">142</a>, <a href="#p143">143</a>, <a href="#p147">147</a>, <a href="#p148">148</a>, <a href="#p149">149</a>, <a href="#p150">150</a>, <a href="#p152">152</a>, <a href="#p153">153</a>, <a href="#p157">157</a>, <a href="#p160">160</a>, <a href="#p161">161</a>, <a href="#p163">163</a>, <a href="#p165">165</a>, <a href="#p166">166</a>, <a href="#p170">170</a>.</li>
+<li>Current, alternating, <a href="#p150">150</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Current changing, <a href="#p82">82</a>.</li>
+
+<li>Current conduction, <a href="#p27">27</a>.</li>
+
+<li>Current, continuous, <a href="#p164">164</a>.</li>
+
+<li>Current, direct, <a href="#p145">145</a>, <a href="#p150">150</a>.</li>
+
+<li>Current direction, <a href="#p50">50</a>.</li>
+
+<li>Current, exterior, <a href="#p50">50</a>, <a href="#p150">150</a>.</li>
+
+<li>Current, reversing, <a href="#p148">148</a>.</li>
+
+<li>Current strength, <a href="#p7">7</a>, <a href="#p57">57</a>.</li>
+
+<li>Current testing, <a href="#p143">143</a>.</li>
+
+<li>Cut-out, <a href="#p120">120</a>.</li>
+
+<li>Cutter, <a href="#p14">14</a>.</li>
+
+<li>Cutting, lines of force, <a href="#p38">38</a>.</li>
+
+<li>Cylinder, <a href="#p44">44</a>.</li>
+
+<li>Cylindrical, <a href="#p43">43</a>.</li>
+
+
+</ul>
+<h4><a id="IX_D" name="IX_D"></a>D</h4>
+<ul class="IX">
+
+<li>Dash, <a href="#p95">95</a>, <a href="#p97">97</a>.</li>
+
+<li>Decoherer, <a href="#p106">106</a>, <a href="#p108">108</a>.</li>
+
+<li>Decomposed, <a href="#p57">57</a>, <a href="#p128">128</a>.</li>
+
+<li>Decomposes, <a href="#p55">55</a>.</li>
+
+<li>Decomposing, <a href="#p123">123</a>.</li>
+
+<li>Decomposition, <a href="#p12">12</a>, <a href="#p35">35</a>, <a href="#p82">82</a>.</li>
+
+<li>Deflected, <a href="#p54">54</a>.</li>
+
+<li>Degree, <a href="#p135">135</a>, <a href="#p162">162</a>.</li>
+
+<li>Demagnetized, <a href="#p24">24</a>, <a href="#p72">72</a>.</li>
+
+<li>Deposited, <a href="#p58">58</a>, <a href="#p133">133</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p211" id="p211">p. 211</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Depression, <a href="#p15">15</a>, <a href="#p140">140</a>.</li>
+
+<li>Detecting current, <a href="#p49">49</a>.</li>
+
+<li>Detector, <a href="#p49">49</a>, <a href="#p52">52</a>, <a href="#p54">54</a>, <a href="#p105">105</a>.</li>
+
+<li>Devices, measuring, <a href="#p27">27</a>.</li>
+
+<li>Diagrams, <a href="#p46">46</a>, <a href="#p48">48</a>, <a href="#p79">79</a>, <a href="#p89">89</a>.</li>
+
+<li>Diagrammatically, <a href="#p81">81</a>.</li>
+
+<li>Diamagnetic, <a href="#p19">19</a>.</li>
+
+<li>Diametrically, <a href="#p114">114</a>.</li>
+
+<li>Diaphragm, <a href="#p112">112</a>, <a href="#p113">113</a>, <a href="#p116">116</a>, <a href="#p120">120</a>, <a href="#p122">122</a>.</li>
+
+<li>Diamonds, <a href="#p186">186</a>.</li>
+
+<li>Diluted, <a href="#p86">86</a>.</li>
+
+<li>Direct current, <a href="#p38">38</a>, <a href="#p140">140</a>.</li>
+
+<li>Direction of current, <a href="#p50">50</a>.</li>
+
+<li>Direction of flow, <a href="#p98">98</a>.</li>
+
+<li>Discharge, <a href="#p172">172</a>.</li>
+
+<li>Disintegrate, <a href="#p132">132</a>.</li>
+
+<li>Disk, <a href="#p43">43</a>.</li>
+
+<li>Dissimilar, <a href="#p37">37</a>.</li>
+
+<li>Disturbance, <a href="#p176">176</a>.</li>
+
+<li>Dividers, <a href="#p14">14</a>.</li>
+
+<li>Divisibility, <a href="#p168">168</a>.</li>
+
+<li>Dot, <a href="#p96">96</a>, <a href="#p97">97</a>.</li>
+
+<li>Dot and dash, <a href="#p96">96</a>.</li>
+
+<li>Double click, <a href="#p95">95</a>.</li>
+
+<li>Double line, <a href="#p65">65</a>.</li>
+
+<li>Double-pole switch, <a href="#p65">65</a>.</li>
+
+<li>Double-throw switch, <a href="#p117">117</a>.</li>
+
+<li>Drawing, <a href="#p20">20</a>.</li>
+
+<li>Drill, ratchet, <a href="#p13">13</a>.</li>
+
+<li>Drops, <a href="#p81">81</a>.</li>
+
+<li>Ductile, <a href="#p186">186</a>.</li>
+
+<li>Duplex wire, <a href="#p115">115</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Dynamo, <a href="#p7">7</a>, <a href="#p27">27</a>, <a href="#p38">38</a>, <a href="#p42">42</a>, <a href="#p46">46</a>, <a href="#p48">48</a>, <a href="#p62">62</a>, <a href="#p82">82</a>, <a href="#p83">83</a>, <a href="#p87">87</a>, <a href="#p89">89</a>, <a href="#p132">132</a>, <a href="#p141">141</a>, <a href="#p142">142</a>, <a href="#p145">145</a>, <a href="#p150">150</a>, <a href="#p155">155</a>, <a href="#p161">161</a>, <a href="#p165">165</a>, <a href="#p167">167</a>, <a href="#p175">175</a>, <a href="#p176">176</a>, <a href="#p180">180</a>, <a href="#p187">187</a>.</li>
+
+<li>Dynamo fields, <a href="#p40">40</a>, <a href="#p41">41</a>.</li>
+</ul>
+<h4><a id="IX_E" name="IX_E"></a>E</h4>
+<ul class="IX">
+
+<li>Earth, <a href="#p22">22</a>.</li>
+
+<li>Elasticity, <a href="#p100">100</a>, <a href="#p142">142</a>.</li>
+
+<li>Electric, <a href="#p6">6</a>, <a href="#p31">31</a>, <a href="#p49">49</a>, <a href="#p50">50</a>, <a href="#p76">76</a>, <a href="#p78">78</a>, <a href="#p81">81</a>, <a href="#p131">131</a>, <a href="#p142">142</a>, <a href="#p158">158</a>, <a href="#p162">162</a>, <a href="#p173">173</a>, <a href="#p176">176</a>.</li>
+
+<li>Electric arc, <a href="#p63">63</a>, <a href="#p163">163</a>.</li>
+
+<li>Electric bell, <a href="#p19">19</a>, <a href="#p69">69</a>, <a href="#p70">70</a>, <a href="#p71">71</a>, <a href="#p72">72</a>, <a href="#p106">106</a>, <a href="#p117">117</a>.</li>
+
+<li>Electric bulbs, <a href="#p167">167</a>.</li>
+
+<li>Electric circuit, <a href="#p118">118</a>.</li>
+
+<li>Electric fan, <a href="#p55">55</a>.</li>
+
+<li>Electric field, <a href="#p76">76</a>.</li>
+
+<li>Electric hand purifier, <a href="#p129">129</a>.</li>
+
+<li>Electric heating, <a href="#p135">135</a>, <a href="#p137">137</a>, <a href="#p161">161</a>.</li>
+
+<li>Electric iron, <a href="#p130">130</a>, <a href="#p141">141</a>.</li>
+
+<li>Electric lamp socket, <a href="#p139">139</a>.</li>
+
+<li>Electric light, <a href="#p56">56</a>, <a href="#p66">66</a>.</li>
+
+<li>Electric lighting, <a href="#p161">161</a>.</li>
+
+<li>Electric power, <a href="#p113">113</a>.</li>
+
+<li>Electric welding, <a href="#p183">183</a>.</li>
+
+<li>Electrical, <a href="#p8">8</a>, <a href="#p11">11</a>, <a href="#p65">65</a>, <a href="#p96">96</a>, <a href="#p98">98</a>, <a href="#p104">104</a>, <a href="#p141">141</a>, <a href="#p159">159</a>, <a href="#p180">180</a>, <a href="#p184">184</a>, <a href="#p187">187</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p212" id="p212">p. 212</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Electrical impulses, <a href="#p105">105</a>, <a href="#p147">147</a>, <a href="#p148">148</a>.</li>
+
+<li>Electrical manifestations, <a href="#p175">175</a>.</li>
+
+<li>Electrically, <a href="#p32">32</a>, <a href="#p70">70</a>.</li>
+
+<li>Electricity, <a href="#p5">5</a>, <a href="#p6">6</a>, <a href="#p7">7</a>, <a href="#p8">8</a>, <a href="#p9">9</a>, <a href="#p12">12</a>, <a href="#p13">13</a>, <a href="#p18">18</a>, <a href="#p21">21</a>, <a href="#p26">26</a>, <a href="#p27">27</a>, <a href="#p28">28</a>, <a href="#p29">29</a>, <a href="#p38">38</a>, <a href="#p49">49</a>,
+ <a href="#p54">54</a>, <a href="#p60">60</a>, <a href="#p61">61</a>, <a href="#p62">62</a>, <a href="#p82">82</a>, <a href="#p97">97</a>, <a href="#p98">98</a>, <a href="#p100">100</a>, <a href="#p104">104</a>, <a href="#p110">110</a>, <a href="#p112">112</a>, <a href="#p116">116</a>, <a href="#p123">123</a>, <a href="#p124">124</a>,
+ <a href="#p133">133</a>, <a href="#p134">134</a>, <a href="#p136">136</a>, <a href="#p138">138</a>, <a href="#p145">145</a>, <a href="#p146">146</a>, <a href="#p147">147</a>, <a href="#p154">154</a>, <a href="#p156">156</a>, <a href="#p160">160</a>, <a href="#p166">166</a>, <a href="#p170">170</a>, <a href="#p171">171</a>, <a href="#p172">172</a>, <a href="#p175">175</a>, <a href="#p182">182</a>, <a href="#p187">187</a>.</li>
+<li>Electricity measuring, <a href="#p49">49</a>.</li>
+
+<li>Electricity, thermo-, <a href="#p142">142</a>.</li>
+
+<li>Electrified, <a href="#p37">37</a>, <a href="#p186">186</a>.</li>
+
+<li>Electro-chemical, <a href="#p55">55</a>.</li>
+
+<li>Electrode, <a href="#p35">35</a>, <a href="#p124">124</a>, <a href="#p127">127</a>, <a href="#p128">128</a>, <a href="#p161">161</a>, <a href="#p162">162</a>, <a href="#p163">163</a>, <a href="#p164">164</a>, <a href="#p165">165</a>, <a href="#p184">184</a>.</li>
+
+<li>Electrolysis, <a href="#p7">7</a>, <a href="#p123">123</a>, <a href="#p126">126</a>, <a href="#p132">132</a>.</li>
+
+<li>Electrolyte, <a href="#p33">33</a>, <a href="#p35">35</a>, <a href="#p36">36</a>, <a href="#p57">57</a>, <a href="#p86">86</a>, <a href="#p88">88</a>, <a href="#p123">123</a>, <a href="#p132">132</a>, <a href="#p142">142</a>.</li>
+
+<li>Electrolytic, <a href="#p55">55</a>, <a href="#p123">123</a>, <a href="#p125">125</a>.</li>
+
+<li>Electro-magnet, <a href="#p59">59</a>, <a href="#p78">78</a>.</li>
+
+<li>Electro-magnetic, <a href="#p7">7</a>, <a href="#p24">24</a>, <a href="#p25">25</a>, <a href="#p29">29</a>, <a href="#p37">37</a>, <a href="#p55">55</a>, <a href="#p92">92</a>, <a href="#p93">93</a>, <a href="#p94">94</a>.</li>
+
+<li>Electro-magnetic force, <a href="#p7">7</a>.</li>
+
+<li>Electro-magnetic rotation, <a href="#p7">7</a>.</li>
+
+<li>Electro-magnetic switch, <a href="#p116">116</a>.</li>
+
+<li>Electro-meter, <a href="#p7">7</a>.</li>
+
+<li>Electro-motive force, <a href="#p37">37</a>, <a href="#p63">63</a>, <a href="#p99">99</a>.</li>
+
+<li>Electroplate, <a href="#p12">12</a>, <a href="#p38">38</a>, <a href="#p48">48</a>, <a href="#p123">123</a>, <a href="#p132">132</a>, <a href="#p134">134</a>.</li>
+
+<li>Electro-positive-negative, <a href="#p142">142</a>, <a href="#p143">143</a>.</li>
+
+<li>Elements, <a href="#p36">36</a>, <a href="#p83">83</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Engine energy, <a href="#p170">170</a>, <a href="#p180">180</a>.</li>
+
+<li>Equidistant, <a href="#p127">127</a>.</li>
+
+<li>Ether, <a href="#p104">104</a>.</li>
+
+<li>Example, <a href="#p61">61</a>.</li>
+
+<li>Excited, <a href="#p47">47</a>.</li>
+
+<li>Extension plate, <a href="#p103">103</a>.</li>
+
+<li>Exterior, <a href="#p3">3</a>.</li>
+
+<li>Exterior magnetic, <a href="#p27">27</a>.</li>
+
+<li>External, <a href="#p37">37</a>.</li>
+
+<li>External circuit, <a href="#p153">153</a>.</li>
+
+<li>External current, <a href="#p50">50</a>.</li>
+
+<li>External resistance, <a href="#p37">37</a>.</li>
+
+
+</ul>
+<h4><a id="IX_F" name="IX_F"></a>F</h4>
+<ul class="IX">
+
+<li>Factor, <a href="#p61">61</a>.</li>
+
+<li>Ferrous oxide, <a href="#p125">125</a>.</li>
+
+<li>Field, <a href="#p46">46</a>, <a href="#p47">47</a>.</li>
+
+<li>Field, dynamo, <a href="#p40">40</a>, <a href="#p41">41</a>.</li>
+
+<li>Field magnet cores, <a href="#p155">155</a>.</li>
+
+<li>Field, magnetic, <a href="#p38">38</a>.</li>
+
+<li>Field of force, <a href="#p33">33</a>.</li>
+
+<li>Field wire, <a href="#p48">48</a>.</li>
+
+<li>Filament, <a href="#p168">168</a>, <a href="#p169">169</a>, <a href="#p170">170</a>.</li>
+
+<li>Filter, <a href="#p128">128</a>.</li>
+
+<li>Flat iron, <a href="#p140">140</a>.</li>
+
+<li>Flocculent, <a href="#p128">128</a>.</li>
+
+<li>Force, <a href="#p50">50</a>.</li>
+
+<li>Formulated, <a href="#p19">19</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p213" id="p213">p. 213</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Friction, <a href="#p32">32</a>.</li>
+
+<li>Frictional, <a href="#p6">6</a>, <a href="#p7">7</a>, <a href="#p29">29</a>.</li>
+
+<li>Fuse, <a href="#p169">169</a>.</li>
+
+
+</ul>
+<h4><a id="IX_G" name="IX_G"></a>G</h4>
+<ul class="IX">
+
+<li>Galvani, <a href="#p7">7</a>.</li>
+
+<li>Galvanic, <a href="#p7">7</a>, <a href="#p23">23</a>, <a href="#p30">30</a>.</li>
+
+<li>Galvanometer, <a href="#p7">7</a>, <a href="#p49">49</a>, <a href="#p108">108</a>, <a href="#p143">143</a>.</li>
+
+<li>Galvanoscope, <a href="#p55">55</a>, <a href="#p58">58</a>, <a href="#p59">59</a>.</li>
+
+<li>Gaseous, <a href="#p128">128</a>.</li>
+
+<li>Gasoline, <a href="#p99">99</a>.</li>
+
+<li>Gas stove, <a href="#p17">17</a>.</li>
+
+<li>Gelatine, <a href="#p128">128</a>.</li>
+
+<li>Generate, <a href="#p29">29</a>, <a href="#p38">38</a>, <a href="#p134">134</a>, <a href="#p136">136</a>, <a href="#p145">145</a>.</li>
+
+<li>Generated, <a href="#p55">55</a>.</li>
+
+<li>Generating, <a href="#p32">32</a>, <a href="#p134">134</a>.</li>
+
+<li>Generation, <a href="#p170">170</a>.</li>
+
+<li>Generator, <a href="#p32">32</a>, <a href="#p125">125</a>, <a href="#p147">147</a>.</li>
+
+<li>German silver, <a href="#p136">136</a>, <a href="#p137">137</a>.</li>
+
+<li>Germicide, <a href="#p187">187</a>.</li>
+
+<li>Gimlets, <a href="#p17">17</a>.</li>
+
+<li>Glass, <a href="#p30">30</a>, <a href="#p86">86</a>, <a href="#p126">126</a>, <a href="#p186">186</a>.</li>
+
+<li>Gold, <a href="#p135">135</a>.</li>
+
+<li>Grid, <a href="#p84">84</a>.</li>
+
+<li>Ground circuit, <a href="#p121">121</a>.</li>
+
+<li>Gunpowder, <a href="#p6">6</a>.</li>
+
+
+</ul>
+<h4><a id="IX_H" name="IX_H"></a>H</h4>
+<ul class="IX">
+
+<li>Hack-saw, <a href="#p14">14</a>.</li>
+
+<li>Hammer, <a href="#p13">13</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Heart-shaped switch, <a href="#p77">77</a>.</li>
+
+<li>Heater, <a href="#p136">136</a>.</li>
+
+<li>Heating, <a href="#p13">13</a>, <a href="#p38">38</a>.</li>
+
+<li>Hertzian rays, <a href="#p170">170</a>.</li>
+
+<li>Hertzian wave, <a href="#p184">184</a>.</li>
+
+<li>High tension, <a href="#p38">38</a>, <a href="#p102">102</a>, <a href="#p184">184</a>.</li>
+
+<li>High tension apparatus, <a href="#p98">98</a>.</li>
+
+<li>High tension coils, <a href="#p103">103</a>.</li>
+
+<li>High voltage, <a href="#p158">158</a>.</li>
+
+<li>Horizontal bar, <a href="#p46">46</a>.</li>
+
+<li>Horseshoe magnet, <a href="#p22">22</a>, <a href="#p24">24</a>, <a href="#p175">175</a>.</li>
+
+<li>Hydrate of aluminum, <a href="#p129">129</a>.</li>
+
+<li>Hydrogen, <a href="#p35">35</a>, <a href="#p123">123</a>, <a href="#p125">125</a>, <a href="#p128">128</a>.</li>
+
+
+</ul>
+<h4><a id="IX_I" name="IX_I"></a>I</h4>
+<ul class="IX">
+
+<li>Igniting, <a href="#p99">99</a>.</li>
+
+<li>Illumination, <a href="#p162">162</a>, <a href="#p163">163</a>, <a href="#p165">165</a>, <a href="#p167">167</a>, <a href="#p170">170</a>.</li>
+
+<li>Immersed, <a href="#p133">133</a>.</li>
+
+<li>Impulses, <a href="#p60">60</a>, <a href="#p62">62</a>, <a href="#p96">96</a>, <a href="#p104">104</a>, <a href="#p109">109</a>, <a href="#p152">152</a>, <a href="#p179">179</a>.</li>
+
+<li>Incandescent, <a href="#p166">166</a>, <a href="#p168">168</a>.</li>
+
+<li>Induced, <a href="#p28">28</a>.</li>
+
+<li>Inductance, <a href="#p149">149</a>, <a href="#p150">150</a>.</li>
+
+<li>Induction, <a href="#p27">27</a>, <a href="#p37">37</a>, <a href="#p98">98</a>, <a href="#p147">147</a>.</li>
+
+<li>Induction coils, <a href="#p99">99</a>, <a href="#p102">102</a>, <a href="#p106">106</a>.</li>
+
+<li>Influences, <a href="#p178">178</a>.</li>
+
+<li>Initial charge, <a href="#p88">88</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p214" id="p214">p. 214</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Insulated, 27, <a href="#p28">28</a>, <a href="#p40">40</a>, <a href="#p43">43</a>, <a href="#p52">52</a>, <a href="#p55">55</a>, <a href="#p73">73</a>, <a href="#p115">115</a>, <a href="#p151">151</a>, <a href="#p180">180</a>.</li>
+
+<li>Insulating, <a href="#p66">66</a>, <a href="#p69">69</a>, <a href="#p120">120</a>, <a href="#p140">140</a>, <a href="#p164">164</a>.</li>
+
+<li>Insulating material, <a href="#p114">114</a>.</li>
+
+<li>Insulation, <a href="#p40">40</a>, <a href="#p116">116</a>.</li>
+
+<li>Instruments, <a href="#p49">49</a>, <a href="#p94">94</a>, <a href="#p112">112</a>, <a href="#p118">118</a>, <a href="#p120">120</a>.</li>
+
+<li>Instruments, measuring, <a href="#p8">8</a>.</li>
+
+<li>Intensity, <a href="#p55">55</a>, <a href="#p60">60</a>, <a href="#p104">104</a>, <a href="#p154">154</a>.</li>
+
+<li>Interior, magnetic, <a href="#p23">23</a>.</li>
+
+<li>Internal resistance, <a href="#p37">37</a>.</li>
+
+<li>Interruption, <a href="#p102">102</a>, <a href="#p103">103</a>.</li>
+
+<li>Installation, <a href="#p168">168</a>.</li>
+
+<li>Ionize, <a href="#p186">186</a>.</li>
+
+<li>Iron, <a href="#p19">19</a>, <a href="#p132">132</a>, <a href="#p133">133</a>, <a href="#p136">136</a>, <a href="#p142">142</a>, <a href="#p171">171</a>.</li>
+
+<li>Isolated, <a href="#p186">186</a>.</li>
+
+
+</ul>
+<h4><a id="IX_J" name="IX_J"></a>J</h4>
+<ul class="IX">
+
+<li>Jar, <a href="#p29">29</a>, <a href="#p31">31</a>, <a href="#p32">32</a>.</li>
+
+<li>Journal, <a href="#p46">46</a>.</li>
+
+<li>Journal block, <a href="#p16">16</a>, <a href="#p146">146</a>.</li>
+
+<li>Jump spark, <a href="#p99">99</a>.</li>
+
+
+</ul>
+<h4><a id="IX_K" name="IX_K"></a>K</h4>
+<ul class="IX">
+
+<li>Key, <a href="#p90">90</a>, <a href="#p91">91</a>, <a href="#p95">95</a>.</li>
+
+<li>Key, sending, <a href="#p90">90</a>.</li>
+
+<li>Knob, <a href="#p32">32</a>.</li>
+
+<li>Knob, terminal, <a href="#p31">31</a>.</li>
+
+
+</ul>
+</td><td>
+
+<h4><a id="IX_L" name="IX_L"></a>L</h4>
+<ul class="IX">
+
+<li>Laboratory, <a href="#p9">9</a>.</li>
+
+<li>Lead, <a href="#p31">31</a>, <a href="#p136">136</a>.</li>
+
+<li>Lead, precipitated, <a href="#p83">83</a>, <a href="#p85">85</a>.</li>
+
+<li>Lead, red, <a href="#p83">83</a>, <a href="#p84">84</a>.</li>
+
+<li>Lever switching, <a href="#p67">67</a>.</li>
+
+<li>Light, <a href="#p104">104</a>.</li>
+
+<li>Light method, <a href="#p56">56</a>.</li>
+
+<li>Lighting, <a href="#p9">9</a>, <a href="#p38">38</a>.</li>
+
+<li>Lighting circuit, <a href="#p48">48</a>.</li>
+
+<li>Lighting system, <a href="#p82">82</a>.</li>
+
+<li>Lightning, <a href="#p6">6</a>, <a href="#p171">171</a>, <a href="#p172">172</a>, <a href="#p173">173</a>.</li>
+
+<li>Lightning rod, <a href="#p173">173</a>.</li>
+
+<li>Lime, chloride of, <a href="#p84">84</a>.</li>
+
+<li>Line of force, <a href="#p146">146</a>.</li>
+
+<li>Line wire, <a href="#p122">122</a>.</li>
+
+<li>Line, magnetic, <a href="#p22">22</a>, <a href="#p23">23</a>.</li>
+
+<li>Liquid, <a href="#p32">32</a>.</li>
+
+<li>Litharge, <a href="#p83">83</a>.</li>
+
+<li>Loadstone, <a href="#p17">17</a>.</li>
+
+<li>Locomotives, <a href="#p165">165</a>.</li>
+
+<li>Low tension, <a href="#p38">38</a>, <a href="#p98">98</a>, <a href="#p102">102</a>, <a href="#p179">179</a>.</li>
+
+
+</ul>
+<h4><a id="IX_M" name="IX_M"></a>M</h4>
+<ul class="IX">
+
+<li>Magnet bar, <a href="#p20">20</a>.</li>
+
+<li>Magnet core, <a href="#p16">16</a>, <a href="#p75">75</a>, <a href="#p93">93</a>.</li>
+
+<li>Magnet, electro, <a href="#p59">59</a>, <a href="#p78">78</a>.</li>
+
+<li>Magnet, horseshoe, <a href="#p22">22</a>, <a href="#p25">25</a>, <a href="#p175">175</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p215" id="p215">p. 215</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Magnet lines, <a href="#p22">22</a>, <a href="#p23">23</a>.</li>
+
+<li>Magnet, permanent, <a href="#p25">25</a>, <a href="#p38">38</a>, <a href="#p46">46</a>, <a href="#p50">50</a>, <a href="#p172">172</a>.</li>
+
+<li>Magnet, reversed, <a href="#p20">20</a>.</li>
+
+<li>Magnet, steel, <a href="#p53">53</a>.</li>
+
+<li>Magnet, swinging, <a href="#p53">53</a>.</li>
+
+<li>Magnetic, <a href="#p7">7</a>, <a href="#p19">19</a>, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p25">25</a>, <a href="#p113">113</a>, <a href="#p178">178</a>.</li>
+
+<li>Magnetic construction, <a href="#p39">39</a>.</li>
+
+<li>Magnetic exterior, <a href="#p27">27</a>.</li>
+
+<li>Magnetic field, <a href="#p22">22</a>, <a href="#p24">24</a>, <a href="#p27">27</a>, <a href="#p38">38</a>, <a href="#p50">50</a>, <a href="#p112">112</a>, <a href="#p146">146</a>, <a href="#p148">148</a>, <a href="#p155">155</a>.</li>
+
+<li>Magnetic interior, <a href="#p23">23</a>.</li>
+
+<li>Magnetic pull, <a href="#p59">59</a>.</li>
+
+<li>Magnetic radiator, <a href="#p37">37</a>.</li>
+
+<li>Magnetism, <a href="#p19">19</a>, <a href="#p54">54</a>, <a href="#p104">104</a>, <a href="#p110">110</a>, <a href="#p159">159</a>, <a href="#p171">171</a>.</li>
+
+<li>Magnetized, <a href="#p18">18</a>, <a href="#p25">25</a>, <a href="#p27">27</a>, <a href="#p50">50</a>.</li>
+
+<li>Magnetized wire, <a href="#p146">146</a>.</li>
+
+<li>Magnets, <a href="#p13">13</a>, <a href="#p14">14</a>, <a href="#p18">18</a>, <a href="#p19">19</a>, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p23">23</a>, <a href="#p24">24</a>, <a href="#p25">25</a>, <a href="#p39">39</a>, <a href="#p51">51</a>, <a href="#p53">53</a>, <a href="#p54">54</a>, <a href="#p70">70</a>, <a href="#p71">71</a>, <a href="#p73">73</a>, <a href="#p75">75</a>, <a href="#p81">81</a>, <a href="#p90">90</a>, <a href="#p93">93</a>, <a href="#p112">112</a>, <a href="#p113">113</a>, <a href="#p115">115</a>, <a href="#p147">147</a>, <a href="#p150">150</a>, <a href="#p163">163</a>, <a href="#p176">176</a>, <a href="#p177">177</a>, <a href="#p178">178</a>.</li>
+
+<li>Main conductor, <a href="#p31">31</a>.</li>
+
+<li>Mandrel, <a href="#p15">15</a>, <a href="#p16">16</a>.</li>
+
+<li>Manganese, <a href="#p19">19</a>.</li>
+
+<li>Manifestations, <a href="#p19">19</a>.</li>
+
+<li>Mariner, <a href="#p172">172</a>.</li>
+
+<li>Material, non-conducting, <a href="#p90">90</a>.</li>
+
+<li>Maximum, <a href="#p154">154</a>.</li>
+
+<li>Measure, <a href="#p55">55</a>, <a href="#p56">56</a>, <a href="#p60">60</a>, <a href="#p62">62</a>.</li>
+
+<li>Measurement, <a href="#p62">62</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Measuring devices, <a href="#p27">27</a>.</li>
+
+<li>Measuring instruments, <a href="#p8">8</a>.</li>
+
+<li>Mechanism, <a href="#p47">47</a>, <a href="#p180">180</a>.</li>
+
+<li>Medical batteries, <a href="#p99">99</a>.</li>
+
+<li>Mercury, <a href="#p63">63</a>, <a href="#p169">169</a>.</li>
+
+<li>Metal base, <a href="#p73">73</a>.</li>
+
+<li>Mica, <a href="#p186">186</a>.</li>
+
+<li>Microphone, <a href="#p118">118</a>, <a href="#p119">119</a>, <a href="#p120">120</a>.</li>
+
+<li>Millimeter, <a href="#p63">63</a>.</li>
+
+<li>Minus, <a href="#p34">34</a>.</li>
+
+<li>Minus sign, <a href="#p21">21</a>.</li>
+
+<li>Morse code, <a href="#p76">76</a>.</li>
+
+<li>Motor, <a href="#p7">7</a>, <a href="#p21">21</a>, <a href="#p27">27</a>, <a href="#p46">46</a>, <a href="#p47">47</a>, <a href="#p62">62</a>, <a href="#p82">82</a>, <a href="#p99">99</a>, <a href="#p150">150</a>, <a href="#p176">176</a>, <a href="#p180">180</a>.</li>
+
+<li>Mouthpiece, <a href="#p115">115</a>.</li>
+
+<li>Mouthpiece rays, <a href="#p188">188</a>.</li>
+
+<li>Moving field, <a href="#p117">117</a>.</li>
+
+<li>Multiple, <a href="#p168">168</a>.</li>
+
+<li>Musical scale, <a href="#p111">111</a>.</li>
+
+
+</ul>
+<h4><a id="IX_N" name="IX_N"></a>N</h4>
+<ul class="IX">
+
+<li>Negative, <a href="#p21">21</a>, <a href="#p35">35</a>, <a href="#p36">36</a>, <a href="#p68">68</a>, <a href="#p83">83</a>, <a href="#p86">86</a>, <a href="#p87">87</a>, <a href="#p94">94</a>, <a href="#p125">125</a>, <a href="#p151">151</a>, <a href="#p152">152</a>, <a href="#p154">154</a>, <a href="#p165">165</a>, <a href="#p177">177</a>, <a href="#p178">178</a>, <a href="#p179">179</a>.</li>
+
+<li>Neutral, <a href="#p125">125</a>.</li>
+
+<li>Neutral plate, <a href="#p84">84</a>.</li>
+
+<li>Nickel, <a href="#p136">136</a>.</li>
+
+<li>Nickel plating, <a href="#p132">132</a>.</li>
+
+<li>Nitrate of silver, <a href="#p62">62</a>.</li>
+
+<li>Nitrogen, <a href="#p126">126</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p216" id="p216">p. 216</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Non-conducting material, <a href="#p90">90</a>.</li>
+
+<li>Non-conductor, <a href="#p164">164</a>.</li>
+
+<li>Non-magnetic, <a href="#p19">19</a>.</li>
+
+<li>North pole, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p23">23</a>, <a href="#p25">25</a>, <a href="#p50">50</a>, <a href="#p54">54</a>, <a href="#p156">156</a>.</li>
+
+<li>Number plate, <a href="#p75">75</a>.</li>
+<li>N-ray, <a href="#p188">188</a>.</li>
+</ul>
+<h4><a id="IX_O" name="IX_O"></a>O</h4>
+<ul class="IX">
+
+<li>Ohms, <a href="#p60">60</a>, <a href="#p63">63</a>.</li>
+
+<li>Ohms, international, <a href="#p63">63</a>.</li>
+
+<li>Ohms law, <a href="#p7">7</a>.</li>
+
+<li>Operator, <a href="#p95">95</a>, <a href="#p118">118</a>.</li>
+
+<li>Oscillating, <a href="#p99">99</a>, <a href="#p105">105</a>.</li>
+
+<li>Osmium, <a href="#p169">169</a>.</li>
+
+<li>Oxides, <a href="#p125">125</a>.</li>
+
+<li>Oxidizing, <a href="#p183">183</a>.</li>
+
+<li>Oxygen, <a href="#p35">35</a>, <a href="#p123">123</a>, <a href="#p125">125</a>, <a href="#p126">126</a>, <a href="#p128">128</a>, <a href="#p129">129</a>, <a href="#p169">169</a>.</li>
+
+
+</ul>
+<h4><a id="IX_P" name="IX_P"></a>P</h4>
+<ul class="IX">
+
+<li>Packing ring, <a href="#p124">124</a>.</li>
+
+<li>Paraffine, <a href="#p56">56</a>, <a href="#p100">100</a>, <a href="#p101">101</a>, <a href="#p102">102</a>.</li>
+
+<li>Paraffine wax, <a href="#p86">86</a>.</li>
+
+<li>Parallel, <a href="#p87">87</a>, <a href="#p88">88</a>, <a href="#p89">89</a>.</li>
+
+<li>Parallel switch bar, <a href="#p67">67</a>.</li>
+
+<li>Parallel wires, <a href="#p28">28</a>, <a href="#p49">49</a>.</li>
+
+<li>Partition, <a href="#p124">124</a>.</li>
+
+<li>Peon, <a href="#p13">13</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Percolate, <a href="#p128">128</a>.</li>
+
+<li>Periodicity, <a href="#p159">159</a>.</li>
+
+<li>Periods of alternations, <a href="#p149">149</a>.</li>
+
+<li>Permanent, <a href="#p18">18</a>, <a href="#p19">19</a>, <a href="#p50">50</a>.</li>
+
+<li>Permanent magnet, <a href="#p25">25</a>, <a href="#p38">38</a>, <a href="#p46">46</a>, <a href="#p50">50</a>, <a href="#p172">172</a>.</li>
+
+<li>Phase, <a href="#p19">19</a>.</li>
+
+<li>Phenomenon, <a href="#p27">27</a>, <a href="#p65">65</a>.</li>
+
+<li>Photograph, <a href="#p186">186</a>.</li>
+
+<li>Physical, <a href="#p21">21</a>.</li>
+
+<li>Pile, voltaic, <a href="#p33">33</a>.</li>
+
+<li>Pipe, <a href="#p61">61</a>.</li>
+
+<li>Pitchblende, <a href="#p186">186</a>.</li>
+
+<li>Pivot pin, <a href="#p53">53</a>.</li>
+
+<li>Pivotal, <a href="#p22">22</a>.</li>
+
+<li>Plane, <a href="#p13">13</a>.</li>
+
+<li>Plate, <a href="#p57">57</a>, <a href="#p93">93</a>.</li>
+
+<li>Plate, contact, <a href="#p67">67</a>, <a href="#p68">68</a>, <a href="#p79">79</a>.</li>
+
+<li>Plate, copper, <a href="#p33">33</a>, <a href="#p35">35</a>, <a href="#p58">58</a>, <a href="#p67">67</a>.</li>
+
+<li>Plate, negative, <a href="#p84">84</a>.</li>
+
+<li>Plate, number, <a href="#p75">75</a>.</li>
+
+<li>Plate, positive, <a href="#p84">84</a>, <a href="#p88">88</a>.</li>
+
+<li>Plate, zinc, <a href="#p33">33</a>.</li>
+
+<li>Platinum, <a href="#p13">13</a>, <a href="#p57">57</a>, <a href="#p137">137</a>.</li>
+
+<li>Pliers, <a href="#p14">14</a>.</li>
+
+<li>Plus sign, <a href="#p21">21</a>, <a href="#p24">24</a>.</li>
+
+<li>Pointer, <a href="#p53">53</a>.</li>
+
+<li>Polarity, <a href="#p154">154</a>, <a href="#p177">177</a>, <a href="#p178">178</a>, <a href="#p179">179</a>.</li>
+
+<li>Polarization, <a href="#p35">35</a>.</li>
+
+<li>Pole, north, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p23">23</a>, <a href="#p25">25</a>, <a href="#p50">50</a>, <a href="#p54">54</a>, <a href="#p156">156</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p217" id="p217">p. 217</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Pole piece, <a href="#p40">40</a>, <a href="#p42">42</a>.</li>
+
+<li>Pole, south, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p25">25</a>, <a href="#p50">50</a>, <a href="#p54">54</a>, <a href="#p156">156</a>.</li>
+
+<li>Poles, <a href="#p177">177</a>, <a href="#p179">179</a>.</li>
+
+<li>Polonium, <a href="#p186">186</a>.</li>
+
+<li>Porcelain, <a href="#p86">86</a>.</li>
+
+<li>Porous, <a href="#p85">85</a>.</li>
+
+<li>Positive, <a href="#p4">4</a>, <a href="#p21">21</a>, <a href="#p25">25</a>, <a href="#p36">36</a>, <a href="#p40">40</a>, <a href="#p68">68</a>, <a href="#p83">83</a>, <a href="#p86">86</a>, <a href="#p87">87</a>, <a href="#p94">94</a>, <a href="#p123">123</a>, <a href="#p125">125</a>, <a href="#p151">151</a>, <a href="#p152">152</a>, <a href="#p153">153</a>, <a href="#p155">155</a>, <a href="#p165">165</a>.</li>
+
+<li>Post, binding, <a href="#p52">52</a>, <a href="#p71">71</a>.</li>
+
+<li>Potentiality, <a href="#p105">105</a>, <a href="#p109">109</a>.</li>
+
+<li>Power, <a href="#p38">38</a>, <a href="#p186">186</a>.</li>
+
+<li>Power, candle, <a href="#p89">89</a>, <a href="#p139">139</a>.</li>
+
+<li>Precipitate of lead, <a href="#p83">83</a>, <a href="#p85">85</a>.</li>
+
+<li>Precision, <a href="#p7">7</a>.</li>
+
+<li>Pressure, <a href="#p87">87</a>.</li>
+
+<li>Primary, <a href="#p35">35</a>, <a href="#p62">62</a>, <a href="#p98">98</a>, <a href="#p134">134</a>, <a href="#p142">142</a>, <a href="#p159">159</a>, <a href="#p184">184</a>.</li>
+
+<li>Primary battery, <a href="#p7">7</a>, <a href="#p99">99</a>.</li>
+
+<li>Primary circuit, <a href="#p99">99</a>.</li>
+
+<li>Primary coil, <a href="#p106">106</a>, <a href="#p109">109</a>.</li>
+
+<li>Prime conductor, <a href="#p6">6</a>.</li>
+
+<li>Projected, <a href="#p185">185</a>.</li>
+
+<li>Propagated, <a href="#p105">105</a>, <a href="#p185">185</a>.</li>
+
+<li>Properties, <a href="#p55">55</a>.</li>
+
+<li>Purification, <a href="#p123">123</a>, <a href="#p128">128</a>.</li>
+
+<li>Purifier, <a href="#p126">126</a>, <a href="#p131">131</a>.</li>
+
+<li>Push button, <a href="#p65">65</a>, <a href="#p68">68</a>, <a href="#p69">69</a>, <a href="#p70">70</a>, <a href="#p76">76</a>, <a href="#p79">79</a>.</li>
+
+
+</ul>
+<h4><a id="IX_Q" name="IX_Q"></a>Q</h4>
+<ul class="IX">
+
+<li>Quantity, <a href="#p55">55</a>, <a href="#p60">60</a>, <a href="#p61">61</a>, <a href="#p138">138</a>.</li>
+
+<li>Quartz, <a href="#p186">186</a>.</li>
+
+
+</ul>
+
+</td><td>
+<h4><a id="IX_R" name="IX_R"></a>R</h4>
+<ul class="IX">
+
+<li>Radio-activity, <a href="#p186">186</a>.</li>
+
+<li>Radium, <a href="#p184">184</a>, <a href="#p185">185</a>, <a href="#p187">187</a>, <a href="#p188">188</a>.</li>
+
+<li>Ratchet drill, <a href="#p13">13</a>.</li>
+
+<li>Reaction, <a href="#p148">148</a>.</li>
+
+<li>Receiver, <a href="#p12">12</a>, <a href="#p90">90</a>, <a href="#p97">97</a>, <a href="#p121">121</a>, <a href="#p122">122</a>.</li>
+
+<li>Receiving station, <a href="#p109">109</a>.</li>
+
+<li>Rectangular, <a href="#p69">69</a>.</li>
+
+<li>Rectifiers, <a href="#p146">146</a>.</li>
+
+<li>Red lead, <a href="#p83">83</a>, <a href="#p84">84</a>.</li>
+
+<li>Reel, <a href="#p13">13</a>.</li>
+
+<li>Reflected, <a href="#p185">185</a>.</li>
+
+<li>Refraction, <a href="#p185">185</a>.</li>
+
+<li>Refractory, <a href="#p182">182</a>.</li>
+
+<li>Register, <a href="#p57">57</a>.</li>
+
+<li>Removable, <a href="#p54">54</a>.</li>
+
+<li>Removable cap, <a href="#p73">73</a>.</li>
+
+<li>Repel, <a href="#p20">20</a>.</li>
+
+<li>Repulsion, <a href="#p21">21</a>, <a href="#p128">128</a>.</li>
+
+<li>Reservoir, <a href="#p61">61</a>, <a href="#p62">62</a>.</li>
+
+<li>Resiliency, <a href="#p99">99</a>.</li>
+
+<li>Resistance, <a href="#p7">7</a>, <a href="#p36">36</a>, <a href="#p37">37</a>, <a href="#p60">60</a>, <a href="#p63">63</a>, <a href="#p99">99</a>, <a href="#p135">135</a>, <a href="#p136">136</a>, <a href="#p137">137</a>, <a href="#p138">138</a>, <a href="#p140">140</a>, <a href="#p141">141</a>, <a href="#p156">156</a>, <a href="#p157">157</a>, <a href="#p163">163</a>, <a href="#p166">166</a>, <a href="#p168">168</a>.</li>
+
+<li>Resistance bridge, <a href="#p7">7</a>.</li>
+
+<li>Resistance, external, <a href="#p37">37</a>.</li>
+
+<li>Resistance, internal, <a href="#p37">37</a>.</li>
+
+<li>Rheostat, <a href="#p7">7</a>.</li>
+
+<li>Reversed, <a href="#p20">20</a>, <a href="#p50">50</a>, <a href="#p153">153</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p218" id="p218">p. 218</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Reversible, <a href="#p163">163</a>.</li>
+
+<li>Reversing, <a href="#p176">176</a>.</li>
+
+<li>Reversing switch, <a href="#p67">67</a>.</li>
+
+<li>Revolubly, <a href="#p46">46</a>.</li>
+
+<li>Revolve, <a href="#p179">179</a>.</li>
+
+<li>Revolving, <a href="#p177">177</a>.</li>
+
+<li>Roentgen rays, <a href="#p184">184</a>.</li>
+
+<li>Roentgen tube, <a href="#p187">187</a>.</li>
+
+<li>Rotation, <a href="#p149">149</a>.</li>
+
+<li>Rubber, <a href="#p40">40</a>, <a href="#p46">46</a>, <a href="#p77">77</a>, <a href="#p115">115</a>, <a href="#p126">126</a>, <a href="#p130">130</a>, <a href="#p138">138</a>.</li>
+
+
+</ul>
+<h4><a id="IX_S" name="IX_S"></a>S</h4>
+<ul class="IX">
+
+<li>Sad-irons, <a href="#p13">13</a>.</li>
+
+<li>Saline, <a href="#p133">133</a>.</li>
+
+<li>Sanitation, <a href="#p12">12</a>.</li>
+
+<li>Saturated, <a href="#p85">85</a>.</li>
+
+<li>Screw, <a href="#p15">15</a>.</li>
+
+<li>Screw, binding, <a href="#p65">65</a>, <a href="#p66">66</a>.</li>
+
+<li>Screw-driver, <a href="#p14">14</a>.</li>
+
+<li>Screw, set, <a href="#p72">72</a>.</li>
+
+<li>Sealing wax, <a href="#p53">53</a>.</li>
+
+<li>Secondary, <a href="#p62">62</a>, <a href="#p98">98</a>, <a href="#p105">105</a>, <a href="#p158">158</a>, <a href="#p159">159</a>, <a href="#p160">160</a>.</li>
+
+<li>Secondary circuit, <a href="#p99">99</a>.</li>
+
+<li>Secondary coil, <a href="#p107">107</a>, <a href="#p108">108</a>.</li>
+
+<li>Self-induction, <a href="#p149">149</a>, <a href="#p156">156</a>.</li>
+
+<li>Sender, <a href="#p90">90</a>, <a href="#p97">97</a>.</li>
+
+<li>Sending apparatus, <a href="#p106">106</a>.</li>
+
+<li>Sending key, <a href="#p90">90</a>.</li>
+
+<li>Separately excited, <a href="#p46">46</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Series-wound, <a href="#p47">47</a>.</li>
+
+<li>Severed magnet, <a href="#p20">20</a>.</li>
+
+<li>Sewage, <a href="#p12">12</a>.</li>
+
+<li>Shaft, <a href="#p30">30</a>.</li>
+
+<li>Shears, <a href="#p14">14</a>, <a href="#p17">17</a>.</li>
+
+<li>Shellac, <a href="#p40">40</a>.</li>
+
+<li>Shunt-wound, <a href="#p47">47</a>.</li>
+
+<li>Signal, <a href="#p118">118</a>.</li>
+
+<li>Silver, <a href="#p19">19</a>, <a href="#p63">63</a>, <a href="#p125">125</a>.</li>
+
+<li>Silver nitrate, <a href="#p62">62</a>.</li>
+
+<li>Socket, <a href="#p54">54</a>, <a href="#p139">139</a>.</li>
+
+<li>Soldering, <a href="#p14">14</a>.</li>
+
+<li>Soldering iron, <a href="#p17">17</a>.</li>
+
+<li>Solution, <a href="#p55">55</a>, <a href="#p57">57</a>, <a href="#p62">62</a>, <a href="#p63">63</a>, <a href="#p84">84</a>, <a href="#p86">86</a>, <a href="#p133">133</a>, <a href="#p134">134</a>, <a href="#p142">142</a>.</li>
+
+<li>Sounder, <a href="#p90">90</a>, <a href="#p92">92</a>, <a href="#p95">95</a>, <a href="#p96">96</a>.</li>
+
+<li>Sounding board, <a href="#p119">119</a>.</li>
+
+<li>Source, charging, <a href="#p83">83</a>.</li>
+
+<li>South pole, <a href="#p20">20</a>, <a href="#p21">21</a>, <a href="#p22">22</a>, <a href="#p25">25</a>, <a href="#p50">50</a>, <a href="#p54">54</a>, <a href="#p156">156</a>.</li>
+
+<li>Spark gap, <a href="#p102">102</a>, <a href="#p106">106</a>.</li>
+
+<li>Spark jump, <a href="#p99">99</a>.</li>
+
+<li>Spring finger, <a href="#p69">69</a>.</li>
+
+<li>Square, <a href="#p14">14</a>, <a href="#p17">17</a>.</li>
+
+<li>Standard, <a href="#p62">62</a>, <a href="#p63">63</a>.</li>
+
+<li>Station, <a href="#p94">94</a>, <a href="#p95">95</a>, <a href="#p117">117</a>, <a href="#p122">122</a>.</li>
+
+<li>Steel, <a href="#p18">18</a>, <a href="#p19">19</a>.</li>
+
+<li>Steel magnet, <a href="#p53">53</a>.</li>
+
+<li>Sterilized, <a href="#p12">12</a>.</li>
+
+<li>Stirrup, <a href="#p75">75</a>.</li>
+
+<li>Stock bit, <a href="#p13">13</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p219" id="p219">p. 219</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Stock contact, <a href="#p121">121</a>.</li>
+
+<li>Storage, <a href="#p82">82</a>.</li>
+
+<li>Storage battery, <a href="#p107">107</a>.</li>
+
+<li>Storing, <a href="#p82">82</a>.</li>
+
+<li>Substances, <a href="#p135">135</a>.</li>
+
+<li>Sulphate, <a href="#p55">55</a>, <a href="#p128">128</a>, <a href="#p133">133</a>.</li>
+
+<li>Sulphur, <a href="#p19">19</a>.</li>
+
+<li>Sulphuric acid, <a href="#p31">31</a>, <a href="#p84">84</a>.</li>
+
+<li>Sulphuric acid voltameter, <a href="#p55">55</a>, <a href="#p57">57</a>.</li>
+
+<li>Superstition, <a href="#p171">171</a>, <a href="#p173">173</a>.</li>
+
+<li>Surging, <a href="#p153">153</a>, <a href="#p154">154</a>.</li>
+
+<li>Swinging magnet, <a href="#p53">53</a>.</li>
+
+<li>Swinging switch blade, <a href="#p67">67</a>.</li>
+
+<li>Switch blades, <a href="#p66">66</a>.</li>
+
+<li>Switches, <a href="#p65">65</a>, <a href="#p66">66</a>, <a href="#p70">70</a>, <a href="#p77">77</a>, <a href="#p78">78</a>, <a href="#p90">90</a>, <a href="#p117">117</a>.</li>
+
+<li>Switches, bar, <a href="#p65">65</a>, <a href="#p68">68</a>, <a href="#p90">90</a>, <a href="#p91">91</a>.</li>
+
+<li>Switches, bar, parallel, <a href="#p67">67</a>.</li>
+
+<li>Switches, heart-shaped, <a href="#p78">78</a>.</li>
+
+<li>Switches, piece, <a href="#p77">77</a>.</li>
+
+<li>Switches, reversing, <a href="#p67">67</a>.</li>
+
+<li>Switches, sliding, <a href="#p67">67</a>, <a href="#p80">80</a>.</li>
+
+<li>Switches, terminal, <a href="#p8">8</a>.</li>
+
+<li>Switches, two-pole, <a href="#p65">65</a>.</li>
+
+<li>System, circuiting, <a href="#p79">79</a>.</li>
+
+
+</ul>
+<h4><a id="IX_T" name="IX_T"></a>T</h4>
+<ul class="IX">
+
+<li>Tail-piece, <a href="#p16">16</a>.</li>
+
+<li>Tantalum, <a href="#p169">169</a>.</li>
+
+<li>Telegraph, <a href="#p11">11</a>, <a href="#p90">90</a>, <a href="#p96">96</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Telegraph key, <a href="#p106">106</a>.</li>
+
+<li>Telegraph sounder, <a href="#p108">108</a>, <a href="#p109">109</a>.</li>
+
+<li>Telegraphing, <a href="#p94">94</a>.</li>
+
+<li>Telephone, <a href="#p12">12</a>, <a href="#p110">110</a>, <a href="#p113">113</a>, <a href="#p117">117</a>, <a href="#p118">118</a>, <a href="#p119">119</a>, <a href="#p120">120</a>.</li>
+
+<li>Telephone circuit, <a href="#p118">118</a>.</li>
+
+<li>Telephone connections, <a href="#p116">116</a>.</li>
+
+<li>Telephone hook, <a href="#p122">122</a>.</li>
+
+<li>Temperature, <a href="#p56">56</a>, <a href="#p88">88</a>, <a href="#p134">134</a>, <a href="#p161">161</a>, <a href="#p170">170</a>.</li>
+
+<li>Tension, high, <a href="#p38">38</a>, <a href="#p102">102</a>, <a href="#p184">184</a>.</li>
+
+<li>Tension, low, <a href="#p38">38</a>, <a href="#p98">98</a>, <a href="#p102">102</a>, <a href="#p179">179</a>.</li>
+
+<li>Terminal, <a href="#p31">31</a>, <a href="#p34">34</a>, <a href="#p35">35</a>, <a href="#p40">40</a>, <a href="#p48">48</a>, <a href="#p82">82</a>, <a href="#p86">86</a>, <a href="#p93">93</a>, <a href="#p95">95</a>, <a href="#p107">107</a>, <a href="#p116">116</a>, <a href="#p121">121</a>, <a href="#p122">122</a>, <a href="#p151">151</a>, <a href="#p152">152</a>, <a href="#p153">153</a>, <a href="#p154">154</a>, <a href="#p156">156</a>.</li>
+
+<li>Terminal knob, <a href="#p31">31</a>.</li>
+
+<li>Terminal, secondary, <a href="#p102">102</a>.</li>
+
+<li>Terminal switch, <a href="#p81">81</a>.</li>
+
+<li>Theoretical, <a href="#p160">160</a>.</li>
+
+<li>Therapeutics, <a href="#p187">187</a>.</li>
+
+<li>Thermo-electric couples, <a href="#p146">146</a>.</li>
+
+<li>Thermo-electricity, <a href="#p135">135</a>.</li>
+
+<li>Thermometer, <a href="#p56">56</a>.</li>
+
+<li>Thorium, <a href="#p169">169</a>, <a href="#p186">186</a>.</li>
+
+<li>Thunderbolt, <a href="#p171">171</a>, <a href="#p173">173</a>.</li>
+
+<li>Tin, <a href="#p136">136</a>.</li>
+
+<li>Tinfoil, <a href="#p31">31</a>, <a href="#p101">101</a>.</li>
+
+<li>Tools, <a href="#p11">11</a>, <a href="#p13">13</a>, <a href="#p17">17</a>.</li>
+
+<li>Torch, brazing, <a href="#p17">17</a>.</li>
+
+<li>Transformer, <a href="#p145">145</a>, <a href="#p146">146</a>, <a href="#p158">158</a>, <a href="#p159">159</a>, <a href="#p180">180</a>, <a href="#p182">182</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p220" id="p220">p. 220</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Transformer, step-down, <a href="#p182">182</a>.</li>
+
+<li>Transmission, <a href="#p38">38</a>, <a href="#p187">187</a>.</li>
+
+<li>Transmit, <a href="#p63">63</a>, <a href="#p95">95</a>, <a href="#p157">157</a>.</li>
+
+<li>Transmitter, <a href="#p12">12</a>, <a href="#p120">120</a>, <a href="#p121">121</a>, <a href="#p122">122</a>, <a href="#p123">123</a>.</li>
+
+<li>Transverse, <a href="#p16">16</a>, <a href="#p52">52</a>.</li>
+
+<li>Transversely, <a href="#p43">43</a>.</li>
+
+<li>Trigger, <a href="#p75">75</a>.</li>
+
+<li>Tripod, <a href="#p31">31</a>.</li>
+
+<li>Tubular, <a href="#p44">44</a>, <a href="#p45">45</a>.</li>
+
+<li>Two-pole switch, <a href="#p65">65</a>.</li>
+
+
+</ul>
+<h4><a id="IX_U" name="IX_U"></a>U</h4>
+<ul class="IX">
+
+<li>Ultra-violet, <a href="#p185">185</a>.</li>
+
+<li>Uranium, <a href="#p186">186</a>.</li>
+
+
+</ul>
+<h4><a id="IX_V" name="IX_V"></a>V</h4>
+<ul class="IX">
+
+<li>Vacuum, <a href="#p184">184</a>.</li>
+
+<li>Vapor lamps, <a href="#p169">169</a>.</li>
+
+<li>Velocity, <a href="#p60">60</a>, <a href="#p73">73</a>.</li>
+
+<li>Vertical armature, <a href="#p75">75</a>.</li>
+
+<li>Vibration, <a href="#p110">110</a>, <a href="#p111">111</a>, <a href="#p113">113</a>.</li>
+
+<li>Vibratory, <a href="#p110">110</a>.</li>
+
+<li>Vise, <a href="#p13">13</a>.</li>
+
+<li>Voltage, <a href="#p37">37</a>, <a href="#p38">38</a>, <a href="#p60">60</a>, <a href="#p61">61</a>, <a href="#p62">62</a>, <a href="#p63">63</a>, <a href="#p87">87</a>, <a href="#p88">88</a>, <a href="#p99">99</a>, <a href="#p147">147</a>, <a href="#p154">154</a>, <a href="#p165">165</a>, <a href="#p180">180</a>, <a href="#p182">182</a>.</li>
+
+<li>Voltage, high, <a href="#p158">158</a>.</li>
+
+<li>Voltaic, <a href="#p29">29</a>, <a href="#p32">32</a>.</li>
+</ul>
+</td><td>
+<ul class="IX">
+<li>Voltaic pile, <a href="#p33">33</a>.</li>
+
+<li>Voltameter, <a href="#p7">7</a>, <a href="#p58">58</a>, <a href="#p88">88</a>.</li>
+
+<li>Voltameter, sulphuric, acid, <a href="#p55">55</a>, <a href="#p57">57</a>.</li>
+
+<li>Volts, <a href="#p60">60</a>, <a href="#p62">62</a>, <a href="#p87">87</a>, <a href="#p89">89</a>, <a href="#p132">132</a>, <a href="#p158">158</a>, <a href="#p159">159</a>.</li>
+
+
+</ul>
+<h4><a id="IX_W" name="IX_W"></a>W</h4>
+<ul class="IX">
+
+<li>Water, <a href="#p123">123</a>, <a href="#p138">138</a>, <a href="#p144">144</a>.</li>
+
+<li>Water power, <a href="#p142">142</a>.</li>
+
+<li>Watts, <a href="#p60">60</a>, <a href="#p61">61</a>, <a href="#p160">160</a>.</li>
+
+<li>Wave lengths, <a href="#p104">104</a>, <a href="#p110">110</a>.</li>
+
+<li>Weight, <a href="#p49">49</a>.</li>
+
+<li>Welding, <a href="#p13">13</a>, <a href="#p182">182</a>.</li>
+
+<li>Winding, <a href="#p18">18</a>, <a href="#p40">40</a>, <a href="#p47">47</a>, <a href="#p58">58</a>, <a href="#p159">159</a>, <a href="#p196">196</a>.</li>
+
+<li>Winding reel, <a href="#p14">14</a>.</li>
+
+<li>Window connection, <a href="#p76">76</a>.</li>
+
+<li>Window frame, <a href="#p78">78</a>.</li>
+
+<li>Wire, <a href="#p6">6</a>, <a href="#p18">18</a>, <a href="#p21">21</a>, <a href="#p26">26</a>, <a href="#p28">28</a>, <a href="#p156">156</a>.</li>
+
+<li>Wire, circuiting, <a href="#p79">79</a>.</li>
+
+<li>Wire coil, <a href="#p40">40</a>.</li>
+
+<li>Wire lead, <a href="#p70">70</a>.</li>
+
+<li>Wire, parallel, <a href="#p28">28</a>, <a href="#p49">49</a>.</li>
+
+<li>Wireless, <a href="#p12">12</a>.</li>
+
+<li>Wireless telegraphy, <a href="#p103">103</a>, <a href="#p104">104</a>, <a href="#p184">184</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+<div><span class='pagenum'><a name="p221" id="p221">p. 221</a></span></div>
+<table border="0" width="76%" cellpadding="2" cellspacing="2">
+  <col style="width:50%;" /><col style="width:50%;" />
+  <tbody valign="top">
+<tr><td>
+<ul class="IX">
+<li>Wiring, <a href="#p80">80</a>.</li>
+
+<li>Wiring, window, <a href="#p77">77</a>.</li>
+
+<li>Workshop, <a href="#p11">11</a>, <a href="#p17">17</a>.</li>
+
+<li>Wound, compound, <a href="#p48">48</a>.</li>
+
+<li>Wound-series, <a href="#p47">47</a>.</li>
+
+<li>Wound-shunt, <a href="#p47">47</a>.</li>
+
+
+</ul>
+
+</td><td>
+<h4><a id="IX_X" name="IX_X"></a>X</h4>
+<ul class="IX">
+<li>X-ray, <a href="#p184">184</a>, <a href="#p185">185</a>, <a href="#p187">187</a>, <a href="#p188">188</a>.</li>
+</ul>
+<h4><a id="IX_Z" name="IX_Z"></a>Z</h4>
+<ul class="IX">
+<li>Zinc, <a href="#p17">17</a>, <a href="#p34">34</a>, <a href="#p35">35</a>, <a href="#p85">85</a>, <a href="#p135">135</a>.</li>
+<li>Zinc plates, <a href="#p33">33</a>.</li>
+</ul>
+</td></tr>
+</tbody>
+</table>
+
+
+</div>
+
+<hr class="chapter" />
+<h2>THE "HOW-TO-DO-IT" BOOKS</h2>
+<hr class="minor" />
+<h3><span class="smcap">Carpentry for Boys</span></h3>
+
+<p>A book which treats, in a most practical and fascinating manner
+all subjects pertaining to the "King of Trades"; showing the care
+and use of tools; drawing; designing, and the laying out of work;
+the principles involved in the building of various kinds of structures,
+and the rudiments of architecture. It contains over two
+hundred and fifty illustrations made especially for this work, and
+includes also a complete glossary of the technical terms used in the
+art. The most comprehensive volume on this subject ever published
+for boys.</p>
+<hr class="minor" />
+<h3><span class="smcap"><a href="#toc">Electricity for Boys</a></span></h3>
+
+<p>The author has adopted the unique plan of setting forth the fundamental
+principles in each phase of the science, and practically
+applying the work in the successive stages. It shows how the
+knowledge has been developed, and the reasons for the various
+phenomena, without using technical words so as to bring it within
+the compass of every boy. It has a complete glossary of terms, and
+is illustrated with two hundred original drawings.</p>
+<hr class="minor" />
+<h3><span class="smcap">Practical Mechanics for Boys</span></h3>
+
+<p>This book takes the beginner through a comprehensive series of
+practical shop work, in which the uses of tools, and the structure
+and handling of shop machinery are set forth; how they are utilized
+to perform the work, and the manner in which all dimensional work
+is carried out. Every subject is illustrated, and model building
+explained. It contains a glossary which comprises a new system of
+cross references, a feature that will prove a welcome departure in
+explaining subjects. Fully illustrated.</p>
+<hr class="minor" />
+
+
+<p class="center"><i>Price 60 cents per volume</i></p>
+
+<p class="titleblock">THE NEW YORK BOOK COMPANY</p>
+<p class="titleblock"><span class="smcap">147 Fourth Avenue&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;New York</span></p>
+
+<div class="tr">
+
+<p class="center" style="font-weight: bold;">Transcriber's Note:</p>
+
+<p>Every effort has been made to replicate this text as faithfully as possible, including obsolete and variant spellings and other inconsistencies.
+Obvious spelling/typographical and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external
+sources. Minor punctuation and printing errors have been amended without note.</p>
+
+<p>The first page of the original book is an advertisement. The page was moved to the end of the text.</p>
+<p>Two occurrences of 'Colorimeter' for 'Calorimeter' repaired.</p>
+<p>Some hyphenation inconsistencies in the text were retained:<br />
+&nbsp;&nbsp;&nbsp;&nbsp;16-candle-power and 16-candlepower,<br />
+&nbsp;&nbsp;&nbsp;&nbsp;Electromotive and electro-motive,<br />
+&nbsp;&nbsp;&nbsp;&nbsp;Electro-meter and Electrometer,<br />
+&nbsp;&nbsp;&nbsp;&nbsp;Horseshoe and horse-shoe,<br />
+&nbsp;&nbsp;&nbsp;&nbsp;Switchboard and switch-board.</p>
+</div>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
+
+*** END OF THIS PROJECT GUTENBERG EBOOK ELECTRICITY FOR BOYS ***
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+</body>
+</html>
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@@ -0,0 +1,6661 @@
+The Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
+
+This eBook is for the use of anyone anywhere 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
+
+
+Title: Electricity for Boys
+
+Author: J. S. Zerbe
+
+Release Date: September 25, 2007 [EBook #22766]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELECTRICITY FOR BOYS ***
+
+
+
+
+Produced by Joe Longo and the Online Distributed
+Proofreading Team at http://www.pgdp.net
+
+
+
+WARNING: This book of one hundred years ago describes
+experiments which are too dangerous to attempt by either
+adults or children. It is published for historical
+interest only.
+
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+ELECTRICITY FOR BOYS
+
+[Illustration: Fig. 1. WORK BENCH]
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+ELECTRICITY FOR BOYS
+
+A working guide, in the successive
+steps of electricity, described in
+simple terms
+
+WITH MANY ORIGINAL ILLUSTRATIONS
+
+By J. S. ZERBE, M.E.
+
+AUTHOR OF
+CARPENTRY FOR BOYS
+PRACTICAL MECHANICS FOR BOYS
+
+[Illustration: Printer's Mark]
+
+THE NEW YORK BOOK COMPANY
+NEW YORK
+
+
+
+
+COPYRIGHT, 1914, BY
+THE NEW YORK BOOK COMPANY
+
+
+
+
+CONTENTS
+
+
+INTRODUCTORY                                                      Page 1
+
+I. ELECTRICITY CONSIDERED. BRIEF HISTORICAL
+EVENTS                                                            Page 5
+
+ The Study of Electricity. First Historical Accounts. Bottling
+ Electricity. Discovery of Galvanic Electricity. Electro-motive Force.
+ Measuring Instruments. Rapidity of Modern Progress. How to Acquire the
+ Vast Knowledge. The Means Employed.
+
+II. WHAT TOOLS AND APPARATUS ARE NEEDED                          Page 11
+
+ Preparing the Workshop. Uses of Our Workshop. What to Build. What to
+ Learn. Uses of the Electrical Devices. Tools. Magnet-winding Reel.
+
+III. MAGNETS, COILS, ARMATURES, ETC.                             Page 18
+
+ The Two Kinds of Magnets. Permanent Magnets. Electro-Magnets.
+ Magnetism. Materials for Magnets. Non-magnetic Material. Action of a
+ _Second_ Magnet. What North and South Pole Mean. Repulsion and
+ Attraction. Positives and Negatives. Magnetic Lines of Force. The
+ Earth as a Magnet. Why the Compass Points North and South. Peculiarity
+ of a Magnet. Action of the Electro-Magnet. Exterior Magnetic Influence
+ Around a Wires Carrying a Current. Parallel Wires.
+
+IV. FRICTIONAL, VOLTAIC OR GALVANIC AND ELECTRO-MAGNETIC
+ELECTRICITY                                                      Page 29
+
+ Three Electrical Sources. Frictional Electricity. Leyden Jar. Voltaic
+ or Galvanic Electricity. Voltaic Pile; How Made. Plus and Minus
+ Signs. The Common Primary Cell. Battery Resistance. Electrolyte and
+ Current. Electro-magnetic Electricity. Magnetic Radiation. Different
+ Kinds of Dynamos. Direct Current Dynamos. Simple Magnet Construction.
+ How to Wind. The Dynamo Fields. The Armature. Armature Windings.
+ Mounting the Armature. The Commutator. Commutator Brushes. Dynamo
+ Windings. The Field. Series-wound Field. Shunt-wound. Compound-wound.
+
+V. HOW TO DETECT AND MEASURE ELECTRICITY                         Page 49
+
+ Measuring Instruments. The Detector. Direction of Current. Simple
+ Current Detector. How to Place the Detector. Different Ways to Measure
+ a Current. The Sulphuric Acid Voltameter. The Copper Voltameter. The
+ Galvanoscope Electro-magnetic Method. The Calorimeter. The Light
+ Method. The Preferred Method. How to Make a Sulphuric Acid Voltameter.
+ How to Make a Copper Voltameter. Objections to the Calorimeter.
+
+VI. VOLTS, AMPERES, OHMS AND WATTS                               Page 60
+
+Understanding Terms. Intensity and Quantity. Voltage.
+Amperage Meaning of Watts and Kilowatt. A
+Standard of Measurement. The Ampere Standard. The
+Voltage Standard. The Ohm. Calculating the Voltage.
+
+VII. PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND
+LIKE APPARATUS                                                   Page 65
+
+ Simple Switches. A Two-Pole Switch. Double-Pole Switch. Sliding
+ Switch. Reversing Switch. Push Buttons. Electric Bells. How Made. How
+ Operated. Annunciators. Burglar Alarm. Wire Circuiting. Circuiting
+ System with Two Bells and Push Buttons. The Push Buttons, Annunciators
+ and Bells. Wiring Up a House.
+
+VIII. ACCUMULATORS, STORAGE OR SECONDARY BATTERIES               Page 82
+
+ Storing Up Electricity. The Accumulator. Accumulator Plates. The Grid.
+ The Negative Pole. Connecting Up the Plates. Charging the Cells. The
+ Initial Charge. The Charging Current.
+
+IX. THE TELEGRAPH                                                Page 90
+
+ Mechanism in Telegraph Circuit. The Sending Key. The Sounder.
+ Connecting Up the Key and Sounder. Two Stations in Circuit. The Double
+ Click. Illustrating the Dot and the Dash. The Morse Telegraph Code.
+ Example in Use.
+
+X. HIGH-TENSION APPARATUS, CONDENSERS, ETC.                      Page 98
+
+ Induction. Low and High Tension. Elastic Property of Electricity. The
+ Condenser. Connecting up a Condenser. The Interrupter. Uses of
+ High-tension Coils.
+
+XI. WIRELESS TELEGRAPHY                                         Page 104
+
+ Telegraphing Without Wires. Surging Character of High-tension
+ Currents. The Coherer. How Made. The Decoherer. The Sending Apparatus.
+ The Receiving Apparatus. How the Circuits are Formed.
+
+XII. THE TELEPHONE                                              Page 110
+
+ Vibrations. The Acoustic Telephone. Sound Waves. Hearing Electricity.
+ The Diaphragm in a Magnetic Field. A Simple Telephone Circuit. How to
+ Make a Telephone. Telephone Connections. Complete Installation. The
+ Microphone. Light Contact Points. How to Make a Microphone.
+ Microphone, the Father of the Transmitter. Automatic Cut-outs for
+ Telephones. Complete Circuiting with Transmitters.
+
+XIII. ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING          Page 123
+
+ Decomposing Liquids. Making Hydrogen and Oxygen. Purifying Water.
+ Rust. Oxygen as a Purifier. Composition of Water. Common Air Not a
+ Good Purifier. Pure Oxygen a Water Purifier. The Use of Hydrogen in
+ Purification. Aluminum Electrodes. Electric Hand Purifier.
+ Purification and Separation of Metals. Electroplating. Plating Iron
+ with Copper. Direction of Current.
+
+XIV. ELECTRIC HEATING. THERMO-ELECTRICITY                       Page 135
+
+ Generating Heat in a Wire. Resistance of Substances. Signs of
+ Connectors. Comparison of Metals. A Simple Electric Heater. How to
+ Arrange for Quantity of Current Used. An Electric Iron.
+ Thermo-Electricity Converting Heat Directly into Electricity Metals.
+ Electric, Positive, Negative. Thermo-electric Coupler.
+
+XV. ALTERNATING CURRENTS, CHOKING COIL, TRANSFORMER             Page 145
+
+ Direct Current. Alternating Current. The Magnetic Field. Action of a
+ Magnetized Wire. The Movement of a Current in a Charged Wire. Current
+ Reversing Itself. Self-Induction. Brushes in a Direct Current Dynamo:
+ Alternating, Positive and Negative Poles. How an Alternating Current
+ Dynamo is Made. The Windings. The Armature Wires. Choking Coils. The
+ Transformer. How the Voltage is Determined. Voltage and Amperage in
+ Transformers.
+
+XVI. ELECTRIC LIGHTING                                          Page 161
+
+ Early conditions. Fuels. Reversibility of Dynamo. Electric arc.
+ Mechanism to maintain the arc. Resistance coil. Parallel carbons for
+ making arc. Series current. Incandescent system. Multiple circuit.
+ Subdivision of electric light. The filament. The glass bulb. Metallic
+ filaments. Vapor lamps. Directions for improvements. Heat in electric
+ lighting. Curious superstitions concerning electricity. Magnetism.
+ Amber. Discovery of the properties of a magnet. Electricity in
+ mountain regions. Early beliefs as to magnetism and electricity. The
+ lightning rod. Protests against using it. Pliny's explanation of
+ electricity.
+
+XVII. POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS        Page 175
+
+ Early beliefs concerning the dynamo. Experiments with magnets.
+ Physical action of dynamo and motor. Electrical influence in windings.
+ Comparing motor and dynamo. How the current acts in a dynamo. Its
+ force in a motor. Loss in power transmission. The four ways in which
+ power is dissipated. Disadvantages of electric power. Its advantages.
+ Transmission of energy. High voltages. The transformer. Step-down
+ transformers. Electric furnaces. Welding by electricity. Merging the
+ particles of the joined ends.
+
+XVIII. X-RAY, RADIUM AND THE LIKE                               Page 184
+
+ The camera and the eye. Actinic rays. Hertzian waves. High-tension
+ apparatus. Vacuum tubes. Character of the ultra-violet rays. How
+ distinguished. The infra-red rays. Their uses. X-rays not capable of
+ reflection. Not subject to refraction. Transmission through opaque
+ substances. Reducing rates of vibration. Radium. Radio-activity.
+ Radio-active materials. Pitchblende. A new form of energy. Electrical
+ source. Healing power. Problems for scientists.
+
+
+
+
+LIST OF ILLUSTRATIONS
+
+ FIG.
+
+ 1. Work bench                                           Frontispiece
+
+                                                                 PAGE
+ 2. Top of magnet-winding reel                                     14
+ 3. Side of magnet-winding reel                                    14
+ 4. Journal block                                                  15
+ 5. Plain magnet bar                                               19
+ 6. Severed magnet                                                 20
+ 7. Reversed magnets                                               21
+ 8. Horseshoe magnet                                               22
+ 9. Earth's magnetic lines                                         23
+ 10. Two permanent magnets                                         24
+ 11. Magnets in earth's magnetic field                             24
+ 12. Armatures for magnets                                         25
+ 13. Magnetized field                                              26
+ 14. Magnetized bar                                                26
+ 15. Direction of current                                          27
+ 16. Direction of induction current                                28
+ 17. Frictional-electricity machine                                30
+ 18. Leyden jar                                                    32
+ 19. Galvanic electricity. Crown of cups                           33
+ 20. Voltaic electricity                                           34
+ 21. Primary battery                                               36
+ 22. Dynamo field and pole piece                                   39
+ 23. Base and fields assembled                                     41
+ 24. Details of the armature, core                                 42
+ 25. Details of the armature, body                                 42
+ 26. Armature Journals                                             43
+ 27. Commutator                                                    43
+ 28. End view of armature, mounted                                 44
+ 29. Top view of armature on base                                  45
+ 30. Field winding                                                 47
+ 31. Series-wound                                                  47
+ 32. Shunt-wound                                                   48
+ 33. Compound-wound                                                48
+ 34. Compass magnet, swing to the right                            50
+ 35. Magnetic compass                                              50
+ 36. Magnet, swing to the left                                     50
+ 37. Indicating direction of current                               51
+ 38. The bridge of the detector                                    52
+ 39. Details of detector                                           53
+ 40. Cross-section of detector                                     54
+ 41. Acid voltameter                                               56
+ 42. Copper voltameter                                             56
+ 43. Two-pole switch                                               66
+ 44. Double-pole switch                                            66
+ 45. Sliding switch                                                67
+ 46. Rheostat form of switch                                       68
+ 47. Reversing switch                                              69
+ 48. Push button                                                   70
+ 49. Electric bell                                                 71
+ 50. Armature of electric bell                                     72
+ 51. Vertical section of annunciator                               72
+ 52. Front view of annunciator                                     72
+ 53. Horizontal section of annunciator                             72
+ 54. Front plate of annunciator                                    72
+ 55. Alarm switch on window                                        76
+ 56. Burglar alarm on window                                       76
+ 57. Burglar alarm contact                                         77
+ 58. Neutral position of contact                                   78
+ 59. Circuiting for electric bell                                  79
+ 60. Annunciators in circuit                                       80
+ 61. Wiring system for a house                                     80
+ 62. Accumulator grids                                             83
+ 63. Assemblage of accumulator grids                               85
+ 64. Connecting up storage battery in series                       87
+ 65. Parallel series                                               88
+ 66. Charging circuit                                              88
+ 67. Telegraph sending key                                         91
+ 68. Telegraph sounder                                             92
+ 69. A telegraph circuit                                           94
+ 70. Induction coil and circuit                                    99
+ 71. Illustrating elasticity                                      100
+ 72. Condenser                                                    101
+ 73. High-tension circuit                                         102
+ 74. Current interrupter                                          103
+ 75. Wireless-telegraphy coherer                                  105
+ 76. Wireless sending-apparatus                                   107
+ 77. Wireless receiving-apparatus                                 108
+ 78. Acoustic telephone                                           111
+ 79. Illustrating vibrations                                      111
+ 80. The magnetic field                                           112
+ 81. Section of telephone receiver                                114
+ 82. The magnet and receiver head                                 115
+ 83. Simple telephone connection                                  116
+ 84. Telephone stations in circuit                                117
+ 85. Illustrating light contact points                            118
+ 86. The microphone                                               119
+ 87. The transmitter                                              119
+ 88. Complete telephone circuit                                   121
+ 89. Device for making hydrogen and oxygen                        124
+ 90. Electric-water purifier                                      127
+ 91. Portable electric purifier                                   129
+ 92. Section of positive plate                                    130
+ 93. Section of negative plate                                    130
+ 94. Positive and negative in position                            130
+ 95. Form of the insulator                                        130
+ 96. Simple electric heater                                       137
+ 97. Side view of resistance device                               139
+ 98. Top view of resistance device                                139
+ 99. Plan view of electric iron                                   140
+100. Section of electric iron                                     141
+101. Thermo-electric couple                                       143
+102. Cutting a magnetic field                                     146
+103. Alternations, first position                                 148
+104. Alternations, second position                                148
+105. Alternations, third position                                 148
+106. Alternations, fourth position                                148
+107. Increasing alternations, first view                          149
+108. Increasing alternations, second view                         149
+109. Connection of alternating dynamo armature                    150
+110. Direct current dynamo                                        151
+111. Circuit wires in direct current dynamo                       152
+112. Alternating polarity lines                                   154
+113. Alternating current dynamo                                   155
+114. Choking coil                                                 157
+115. A transformer                                                158
+116. Parallel carbons                                             164
+117. Arc-lighting circuit                                         165
+118. Interrupted conductor                                        166
+119. Incandescent circuit                                         167
+120. Magnetic action in dynamo, 1st                               177
+121. Magnetic action in dynamo, 2d                                177
+122. Magnetic action in dynamo, 3d                                178
+123. Magnetic action in dynamo, 4th                               178
+124. Magnetic action in motor, 1st                                179
+125. Magnetic action in motor, 2d                                 179
+126. Magnetic action in motor, 3d                                 180
+127. Magnetic action in motor, 4th                                180
+
+
+
+
+INTRODUCTORY
+
+
+Electricity, like every science, presents two phases to the student, one
+belonging to a theoretical knowledge, and the other which pertains to
+the practical application of that knowledge. The boy is directly
+interested in the practical use which he can make of this wonderful
+phenomenon in nature.
+
+It is, in reality, the most successful avenue by which he may obtain the
+theory, for he learns the abstract more readily from concrete examples.
+
+It is an art in which shop practice is a greater educator than can be
+possible with books. Boys are not, generally, inclined to speculate or
+theorize on phenomena apart from the work itself; but once put them into
+contact with the mechanism itself, let them become a living part of it,
+and they will commence to reason and think for themselves.
+
+It would be a dry, dull and uninteresting thing to tell a boy that
+electricity can be generated by riveting together two pieces of
+dissimilar metals, and applying heat to the juncture. But put into his
+hands the metals, and set him to perform the actual work of riveting the
+metals together, then wiring up the ends of the metals, heating them,
+and, with a galvanometer, watching for results, it will at once make him
+see something in the experiment which never occurred when the abstract
+theory was propounded.
+
+He will inquire first what metals should be used to get the best
+results, and finally, he will speculate as to the reasons for the
+phenomena. When he learns that all metals are positive-negative or
+negative-positive to each other, he has grasped a new idea in the realm
+of knowledge, which he unconsciously traces back still further, only to
+learn that he has entered a field which relates to the constitution of
+matter itself. As he follows the subject through its various channels he
+will learn that there is a common source of all things; a manifestation
+common to all matter, and that all substances in nature are linked
+together in a most wonderful way.
+
+An impulse must be given to a boy's training. The time is past for the
+rule-and-rote method. The rule can be learned better by a manual
+application than by committing a sentence to memory.
+
+In the preparation of this book, therefore, I have made practice and
+work the predominating factors. It has been my aim to suggest the best
+form in which to do the things in a practical way, and from that work,
+as the boy carries it out, to deduce certain laws and develop the
+principles which underlie them. Wherever it is deemed possible to do so,
+it is planned to have the boy make these discoveries for himself, so as
+to encourage him to become a thinker and a reasoner instead of a mere
+machine.
+
+A boy does not develop into a philosopher or a scientist through being
+told he must learn the principles of this teaching, or the fundamentals
+of that school of reasoning. He will unconsciously imbibe the spirit and
+the willingness if we but place before him the tools by which he may
+build even the simple machinery that displays the various electrical
+manifestations.
+
+
+
+
+CHAPTER I
+
+THE STUDY OF ELECTRICITY. HISTORICAL
+
+
+There is no study so profound as electricity. It is a marvel to the
+scientist as well as to the novice. It is simple in its manifestations,
+but most complex in its organization and in its ramifications. It has
+been shown that light, heat, magnetism and electricity are the same, but
+that they differ merely in their modes of motion.
+
+FIRST HISTORICAL ACCOUNT.--The first historical account of electricity
+dates back to 600 years B. C. Thales of Miletus was the first to
+describe the properties of amber, which, when rubbed, attracted and
+repelled light bodies. The ancients also described what was probably
+tourmaline, a mineral which has the same qualities. The torpedo, a fish
+which has the power of emitting electric impulses, was known in very
+early times.
+
+From that period down to about the year 1600 no accounts of any
+historical value have been given. Dr. Gilbert, of England, made a number
+of researches at that time, principally with amber and other materials,
+and Boyle, in 1650, made numerous experiments with frictional
+electricity.
+
+Sir Isaac Newton also took up the subject at about the same period. In
+1705 Hawksbee made numerous experiments; also Gray, in 1720, and a
+Welshman, Dufay, at about the same time. The Germans, from 1740 to 1780,
+made many experiments. In 1740, at Leyden, was discovered the jar which
+bears that name. Before that time, all experiments began and ended with
+frictional electricity.
+
+The first attempt to "bottle" electricity was attempted by
+Muschenbr[oe]ck, at Leyden, who conceived the idea that electricity in
+materials might be retained by surrounding them with bodies which did
+not conduct the current. He electrified some water in a jar, and
+communication having been established between the water and the prime
+conductor, his assistant, who was holding the bottle, on trying to
+disengage the communicating wire, received a sudden shock.
+
+In 1747 Sir William Watson fired gunpowder by an electric spark, and,
+later on, a party from the Royal Society, in conjunction with Watson,
+conducted a series of experiments to determine the velocity of the
+electric fluid, as it was then termed.
+
+Benjamin Franklin, in 1750, showed that lightning was electricity, and
+later on made his interesting experiments with the kite and the key.
+
+DISCOVERING GALVANIC ELECTRICITY.--The great discovery of Galvani, in
+1790, led to the recognition of a new element in electricity, called
+galvanic or voltaic (named after the experimenter, Volta), and now known
+to be identical with frictional electricity. In 1805 Poisson was the
+first to analyze electricity; and when [OE]rsted of Copenhagen, in 1820,
+discovered the magnetic action of electricity, it offered a great
+stimulus to the science, and paved the way for investigation in a new
+direction. Ampere was the first to develop the idea that a motor or a
+dynamo could be made operative by means of the electro-magnetic current;
+and Faraday, about 1830, discovered electro-magnetic rotation.
+
+ELECTRO-MAGNETIC FORCE.--From this time on the knowledge of electricity
+grew with amazing rapidity. Ohm's definition of electro-motive force,
+current strength and resistance eventuated into Ohm's law. Thomson
+greatly simplified the galvanometer, and Wheatstone invented the
+rheostat, a means of measuring resistance, about 1850. Then primary
+batteries were brought forward by Daniels, Grove, Bunsen and Thomson,
+and electrolysis by Faraday. Then came the instruments of precision--the
+electrometer, the resistance bridge, the ammeter, the voltmeter--all of
+the utmost value in the science.
+
+MEASURING INSTRUMENTS.--The perfection of measuring instruments did more
+to advance electricity than almost any other field of endeavor; so that
+after 1875 the inventors took up the subject, and by their energy
+developed and put into practical operation a most wonderful array of
+mechanism, which has become valuable in the service of man in almost
+every field of human activity.
+
+RAPIDITY OF MODERN PROGRESS.--This brief history is given merely to show
+what wonders have been accomplished in a few years. The art is really
+less than fifty years old, and yet so rapidly has it gone forward that
+it is not at all surprising to hear the remark, that the end of the
+wonders has been reached. Less than twenty-five years ago a high
+official of the United States Patent Office stated that it was probable
+the end of electrical research had been reached. The most wonderful
+developments have been made since that time; and now, as in the past,
+one discovery is but the prelude to another still more remarkable. We
+are beginning to learn that we are only on the threshold of that
+storehouse in which nature has locked her secrets, and that there is no
+limit to human ingenuity.
+
+HOW TO ACQUIRE THE VAST KNOWLEDGE.--As the boy, with his limited vision,
+surveys this vast accumulation of tools, instruments and machinery, and
+sees what has been and is now being accomplished, it is not to be
+wondered at that he should enter the field with timidity. In his mind
+the great question is, how to acquire the knowledge. There is so much to
+learn. How can it be accomplished?
+
+The answer to this is, that the student of to-day has the advantage of
+the knowledge of all who have gone before; and now the pertinent thing
+is to acquire that knowledge.
+
+THE MEANS EMPLOYED.--This brings us definitely down to an examination of
+the means that we shall employ to instil this knowledge, so that it may
+become a permanent asset to the student's store of information.
+
+The most significant thing in the history of electrical development is
+the knowledge that of all the great scientists not one of them ever
+added any knowledge to the science on purely speculative reasoning. All
+of them were experimenters. They practically applied and developed their
+theories in the laboratory or the workshop. The natural inference is,
+therefore, that the boy who starts out to acquire a knowledge of
+electricity, must not only theorize, but that he shall, primarily,
+conduct the experiments, and thereby acquire the information in a
+practical way, one example of which will make a more lasting impression
+than pages of dry text.
+
+Throughout these pages, therefore, I shall, as briefly as possible,
+point out the theories involved, as a foundation for the work, and then
+illustrate the structural types or samples; and the work is so arranged
+that what is done to-day is merely a prelude or stepping-stone to the
+next phase of the art. In reality, we shall travel, to a considerable
+extent, the course which the great investigators followed when they were
+groping for the facts and discovering the great manifestations in
+nature.
+
+
+
+
+CHAPTER II
+
+WHAT TOOLS AND APPARATUS ARE NEEDED
+
+
+PREPARING THE WORKSHOP.--Before commencing actual experiments we should
+prepare the workshop and tools. Since we are going into this work as
+pioneers, we shall have to be dependent upon our own efforts for the
+production of the electrical apparatus, so as to be able, with our
+home-made factory, to provide the power, the heat and the electricity.
+Then, finding we are successful in these enterprises, we may look
+forward for "more worlds to conquer."
+
+By this time our neighbors will become interested in and solicit work
+from us.
+
+USES OF OUR WORKSHOPS.--They may want us to test batteries, and it then
+becomes necessary to construct mechanism to detect and measure
+electricity; to install new and improved apparatus; and to put in and
+connect up electric bells in their houses, as well as burglar alarms. To
+meet the requirements, we put in a telegraph line, having learned, as
+well as we are able, how they are made and operated. But we find the
+telegraph too slow and altogether unsuited for our purposes, as well as
+for the uses of the neighborhood, so we conclude to put in a telephone
+system.
+
+WHAT TO BUILD.--It is necessary, therefore, to commence right at the
+bottom to build a telephone, a transmitter, a receiver and a
+switch-board for our system. From the telephone we soon see the
+desirability of getting into touch with the great outside world, and
+wireless telegraphy absorbs our time and energies.
+
+But as we learn more and more of the wonderful things electricity will
+do, we are brought into contact with problems which directly interest
+the home. Sanitation attracts our attention. Why cannot electricity act
+as an agent to purify our drinking water, to sterilize sewage and to
+arrest offensive odors? We must, therefore, learn something about the
+subject of electrolysis.
+
+WHAT TO LEARN.--The decomposition of water is not the only thing that we
+shall describe pertaining to this subject. We go a step further, and
+find that we can decompose metals as well as liquids, and that we can
+make a pure metal out of an impure one, as well as make the foulest
+water pure. But we shall also, in the course of our experiments, find
+that a cheap metal can be coated with a costly one by means of
+electricity--that we can electroplate by electrolysis.
+
+USES OF THE ELECTRICAL DEVICES.--While all this is progressing and our
+factory is turning out an amazing variety of useful articles, we are led
+to inquire into the uses to which we may devote our surplus electricity.
+The current may be diverted for boiling water; for welding metals; for
+heating sad-irons, as well as for other purposes which are daily
+required.
+
+TOOLS.--To do these things tools are necessary, and for the present they
+should not be expensive. A small, rigidly built bench is the first
+requirement. This may be made, as shown in Fig. 1, of three 2-inch
+planks, each 10 inches wide and 6 feet long, mounted on legs 36 inches
+in height. In the front part are three drawers for your material, or the
+small odds and ends, as well as for such little tools as you may
+accumulate. Then you will need a small vise, say, with a 2-inch jaw, and
+you will also require a hand reel for winding magnets. This will be
+fully described hereafter.
+
+You can also, probably, get a small, cheap anvil, which will be of the
+greatest service in your work. It should be mounted close up to the work
+bench. Two small hammers, one with an A-shaped peon, and the other with
+a round peon, should be selected, and also a plane and a small wood saw
+with fine teeth. A bit stock, or a ratchet drill, if you can afford it,
+with a variety of small drills; two wood chisels, say of 3/8-inch and
+3/4-inch widths; small cold chisels; hack saw, 10-inch blade; small
+iron square; pair of dividers; tin shears; wire cutters; 2 pairs of
+pliers, one flat and the other round-nosed; 2 awls, centering punch,
+wire cutters, and, finally, soldering tools.
+
+[Illustration: _Fig. 2. Top View_ MAGNET-WINDING REEL]
+
+[Illustration: _Fig. 3. Side View_ MAGNET-WINDING REEL]
+
+If a gas stove is not available, a brazing torch is an essential tool.
+Numerous small torches are being made, which are cheap and easily
+operated. A small soldering iron, with pointed end, should be provided;
+also metal shears and a small square; an awl and several sizes of
+gimlets; a screwdriver; pair of pliers and wire cutters.
+
+From the foregoing it will be seen that the cost of tools is not a very
+expensive item.
+
+This entire outfit, not including the anvil and vise, may be purchased
+new for about $20.00, so we have not been extravagant.
+
+MAGNET-WINDING REEL.--Some little preparation must be made, so we may be
+enabled to handle our work by the construction of mechanical aids.
+
+[Illustration: _Fig. 4. Journal Block._]
+
+First of these is the magnet-winding reel, a plan view of which is shown
+in Fig. 2. This, for our present work, will be made wholly of wood.
+
+Select a plank 1-1/2 inches thick and 8 inches wide, and from this cut
+off two pieces (A), each 7 inches long, and then trim off the corners
+(B, B), as shown in Fig. 4. To serve as the mandrel (C, Fig. 2), select
+a piece of broomstick 9 inches long. Bore a hole (D) in each block (A) a
+half inch below the upper margin of the block, this hole being of such
+diameter that the broomstick mandrel will fit and easily turn therein.
+
+Place a crank (E), 5 inches long, on the outer end of the mandrel, as in
+Fig. 3. Then mount one block on the end of the bench and the other block
+3 inches away. Affix them to the bench by nails or screws, preferably
+the latter.
+
+On the inner end of the mandrel put a block (F) of hard wood. This is
+done by boring a hole 1 inch deep in the center of the block, into which
+the mandrel is driven. On the outer face of the block is a square hole
+large enough to receive the head of a 3/8-inch bolt, and into the
+depression thus formed a screw (G) is driven through the block and into
+the end of the mandrel, so as to hold the block (F) and mandrel firmly
+together. When these parts are properly put together, the inner side of
+the block will rest and turn against the inner journal block (A).
+
+The tailpiece is made of a 2" x 4" scantling (H), 10 inches long, one
+end of it being nailed to a transverse block (I) 2" x 2" x 4". The inner
+face of this block has a depression in which is placed a V-shaped cup
+(J), to receive the end of the magnet core (K) or bolt, which is to be
+used for this purpose. The tailpiece (H) has a longitudinal slot (L) 5
+inches long adapted to receive a 1/2-inch bolt (M), which passes down
+through the bench, and is, therefore, adjustable, so it may be moved to
+and from the journal bearing (A), thereby providing a place for the
+bolts to be put in. These bolts are the magnet cores (K), 6 inches long,
+but they may be even longer, if you bore several holes (N) through the
+bench so you may set over the tailpiece.
+
+With a single tool made substantially like this, over a thousand of the
+finest magnets have been wound. Its value will be appreciated after you
+have had the experience of winding a few magnets.
+
+ORDER IN THE WORKSHOP.--Select a place for each tool on the rear upright
+of the bench, and make it a rule to put each tool back into its place
+after using. This, if persisted in, will soon become a habit, and will
+save you hours of time. Hunting for tools is the unprofitable part of
+any work.
+
+
+
+
+CHAPTER III
+
+MAGNETS, COILS, ARMATURES, ETC.
+
+
+THE TWO KINDS OF MAGNET.--Generally speaking, magnets are of two kinds,
+namely, permanent and electro-magnetic.
+
+PERMANENT MAGNETS.--A permanent magnet is a piece of steel in which an
+electric force is exerted at all times. An electro-magnet is a piece of
+iron which is magnetized by a winding of wire, and the magnet is
+energized only while a current of electricity is passing through the
+wire.
+
+ELECTRO-MAGNET.--The electro-magnet, therefore, is the more useful,
+because the pull of the magnet can be controlled by the current which
+actuates it.
+
+The electro-magnet is the most essential of all contrivances in the
+operation and use of electricity. It is the piece of mechanism which
+does the physical work of almost every electrical apparatus or machine.
+It is the device which has the power to convert the unseen electric
+current into motion which may be observed by the human eye. Without it
+electricity would be a useless agent to man.
+
+While the electro-magnet is, therefore, the form of device which is
+almost wholly used, it is necessary, first, to understand the principles
+of the permanent magnet.
+
+MAGNETISM.--The curious force exerted by a magnet is called magnetism,
+but its origin has never been explained. We know its manifestations
+only, and laws have been formulated to explain its various phases; how
+to make it more or less intense; how to make its pull more effective;
+the shape and form of the magnet and the material most useful in its
+construction.
+
+[Illustration: _Fig 5._ PLAIN MAGNET BAR]
+
+MATERIALS FOR MAGNETS.--Iron and steel are the best materials for
+magnets. Some metals are non-magnetic, this applying to iron if combined
+with manganese. Others, like sulphur, zinc, bismuth, antimony, gold,
+silver and copper, not only are non-magnetic, but they are actually
+repelled by magnetism. They are called the diamagnetics.
+
+NON-MAGNETIC MATERIALS.--Any non-magnetic body in the path of a magnetic
+force does not screen or diminish its action, whereas a magnetic
+substance will.
+
+In Fig. 5 we show the simplest form of magnet, merely a bar of steel (A)
+with the magnetic lines of force passing from end to end. It will be
+understood that these lines extend out on all sides, and not only along
+two sides, as shown in the drawing. The object is to explain clearly how
+the lines run.
+
+[Illustration: _Fig. 6._ SEVERED MAGNET]
+
+ACTION OF A SEVERED MAGNET.--Now, let us suppose that we sever this bar
+in the middle, as in Fig. 6, or at any other point between the ends. In
+this case each part becomes a perfect magnet, and a new north pole (N)
+and a new south pole (S) are made, so that the movement of the magnetic
+lines of force are still in the same direction in each--that is, the
+current flows from the north pole to the south pole.
+
+WHAT NORTH AND SOUTH POLES MEAN.--If these two parts are placed close
+together they will attract each other. But if, on the other hand, one of
+the pieces is reversed, as in Fig. 7, they will repel each other. From
+this comes the statement that likes repel and unlikes attract each
+other.
+
+REPULSION AND ATTRACTION.--This physical act of repulsion and attraction
+is made use of in motors, as we shall see hereinafter.
+
+It will be well to bear in mind that in treating of electricity the
+north pole is always associated with the plus sign (+) and the south
+pole with the minus sign (-). Or the N sign is positive and the S sign
+negative electricity.
+
+[Illustration: _Fig. 7._ REVERSED MAGNETS]
+
+POSITIVES AND NEGATIVES.--There is really no difference between positive
+and negative electricity, so called, but the foregoing method merely
+serves as a means of identifying or classifying the opposite ends of a
+magnet or of a wire.
+
+MAGNETIC LINES OF FORCE.--It will be noticed that the magnetic lines of
+force pass through the bar and then go from end to end through the
+atmosphere. Air is a poor conductor of electricity, so that if we can
+find a shorter way to conduct the current from the north pole to the
+south pole, the efficiency of the magnet is increased.
+
+This is accomplished by means of the well-known horseshoe magnet, where
+the two ends (N, S) are brought close together, as in Fig. 8.
+
+THE EARTH AS A MAGNET.--The earth is a huge magnet and the magnetic
+lines run from the north pole to the south pole around all sides of the
+globe.
+
+[Illustration: _Fig. 8._ HORSESHOE MAGNET]
+
+The north magnetic pole does not coincide with the true north pole or
+the pivotal point of the earth's rotation, but it is sufficiently near
+for all practical purposes. Fig. 9 shows the magnetic lines running from
+the north to the south pole.
+
+WHY THE COMPASS POINTS NORTH AND SOUTH.--Now, let us try to ascertain
+why the compass points north and south.
+
+Let us assume that we have a large magnet (A, Fig. 10), and suspend a
+small magnet (B) above it, so that it is within the magnetic field of
+the large magnet. This may be done by means of a short pin (C), which is
+located in the middle of the magnet (B), the upper end of this pin
+having thereon a loop to which a thread (D) is attached. The pin also
+carries thereon a pointer (E), which is directed toward the north pole
+of the bar (B).
+
+[Illustration: _Fig. 9._ EARTH'S MAGNETIC LINES]
+
+You will now take note of the interior magnetic lines (X), and the
+exterior magnetic lines (Z) of the large magnet (A), and compare the
+direction of their flow with the similar lines in the small magnet (B).
+
+The small magnet has both its exterior and its interior lines within the
+exterior lines (Z) of the large magnet (A), so that as the small magnet
+(B) is capable of swinging around, the N pole of the bar (B) will point
+toward the S pole of the larger bar (A). The small bar, therefore, is
+influenced by the exterior magnetic field (Z).
+
+[Illustration: _Fig. 10._ TWO PERMANENT MAGNETS]
+
+[Illustration: _Fig. 11._ MAGNETS IN THE EARTH'S MAGNETIC FIELD]
+
+Let us now take the outline represented by the earth's surface (Fig.
+11), and suspend a magnet (A) at any point, like the needle of a
+compass, and it will be seen that the needle will arrange itself north
+and south, within the magnetic field which flows from the north to the
+south pole.
+
+PECULIARITY OF A MAGNET.--One characteristic of a magnet is that, while
+apparently the magnetic field flows out at one end of the magnet, and
+moves inwardly at the other end, the power of attraction is just the
+same at both ends.
+
+In Fig. 12 are shown a bar (A) and a horseshoe magnet (B). The bar (A)
+has metal blocks (C) at each end, and each of these blocks is attracted
+to and held in contact with the ends by magnetic influence, just the
+same as the bar (D) is attracted by and held against the two ends of the
+horseshoe magnet. These blocks (C) or the bar (D) are called armatures.
+Through them is represented the visible motion produced by the magnetic
+field.
+
+[Illustration: _Fig. 12._ ARMATURES FOR MAGNETS]
+
+ACTION OF THE ELECTRO-MAGNET.--The electro-magnet exerts its force in
+the same manner as a permanent magnet, so far as attraction and
+repulsion are concerned, and it has a north and a south pole, as in the
+case with the permanent magnet. An electro-magnet is simply a bar of
+iron with a coil or coils of wire around it; when a current of
+electricity flows through the wire, the bar is magnetized. The moment
+the current is cut off, the bar is demagnetized. The question that now
+arises is, why an electric current flowing through a wire, under those
+conditions, magnetizes the bar, or _core_, as it is called.
+
+[Illustration: _Fig. 13._ MAGNETIZED FIELD]
+
+[Illustration: _Fig. 14._ MAGNETIZED BAR]
+
+In Fig. 13 is shown a piece of wire (A). Let us assume that a current of
+electricity is flowing through this wire in the direction of the darts.
+What actually takes place is that the electricity extends out beyond the
+surface of the wire in the form of the closed rings (B). If, now, this
+wire (A) is wound around an iron core (C, Fig. 14), you will observe
+that this electric field, as it is called, entirely surrounds the core,
+or rather, that the core is within the magnetic field or influence of
+the current flowing through the wire, and the core (C) thereby becomes
+magnetized, but it is magnetized only when the current passes through
+the wire coil (A).
+
+[Illustration: _Fig. 15._ DIRECTION OF CURRENT]
+
+From the foregoing, it will be understood that a wire carrying a current
+of electricity not only is affected within its body, but that it also
+has a sphere of influence exteriorly to the body of the wire, at all
+points; and advantage is taken of this phenomenon in constructing
+motors, dynamos, electrical measuring devices and almost every kind of
+electrical mechanism in existence.
+
+EXTERIOR MAGNETIC INFLUENCE AROUND A WIRE CARRYING A CURRENT.--Bear in
+mind that the wire coil (A, Fig. 14) does not come into contact with the
+core (C). It is insulated from the core, either by air or by rubber or
+other insulating substance, and a current passing from A to C under
+those conditions is a current of _induction_. On the other hand, the
+current flowing through the wire (A) from end to end is called a
+_conduction_ current. Remember these terms.
+
+In this connection there is also another thing which you will do well to
+bear in mind. In Fig. 15 you will notice a core (C) and an insulated
+wire coil (B) wound around it. The current, through the wire (B), as
+shown by the darts (D), moves in one direction, and the induced current
+in the core (C) travels in the opposite direction, as shown by the darts
+(D).
+
+[Illustration: _Fig. 16._ DIRECTION OF INDUCTION CURRENT]
+
+PARALLEL WIRES.--In like manner, if two wires (A, B, Fig. 16) are
+parallel with each other, and a current of electricity passes along the
+wire (A) in one direction, the induced current in the wire (B) will move
+in the opposite direction.
+
+These fundamental principles should be thoroughly understood and
+mastered.
+
+
+
+
+CHAPTER IV
+
+FRICTIONAL, VOLTAIC OR GALVANIC, AND ELECTRO-MAGNETIC ELECTRICITY
+
+
+THREE ELECTRICAL SOURCES.--It has been found that there are three kinds
+of electricity, or, to be more accurate, there are three ways to
+generate it. These will now be described.
+
+When man first began experimenting, he produced a current by frictional
+means, and collected the electricity in a bottle or jar. Electricity, so
+stored, could be drawn from the jar, by attaching thereto suitable
+connection. This could be effected only in one way, and that was by
+discharging the entire accumulation instantaneously. At that time they
+knew of no means whereby the current could be made to flow from the jar
+as from a battery or cell.
+
+FRICTIONAL ELECTRICITY.--With a view of explaining the principles
+involved, we show in Fig. 17 a machine for producing electricity by
+friction.
+
+
+[Illustration: _Fig. 17._ FRICTION-ELECTRICITY MACHINE]
+
+This is made up as follows: A represents the base, having thereon a flat
+member (B), on which is mounted a pair of parallel posts or standards
+(C, C), which are connected at the top by a cross piece (D). Between
+these two posts is a glass disc (E), mounted upon a shaft (F), which
+passes through the posts, this shaft having at one end a crank (G). Two
+leather collecting surfaces (H, H), which are in contact with the glass
+disc (E), are held in position by arms (I, J), the arm (I) being
+supported by the cross piece (D), and the arm (J) held by the base piece
+(B). A rod (K), U-shaped in form, passes over the structure here thus
+described, its ends being secured to the base (B). The arms (I, J) are
+both electrically connected with this rod, or conductor (K), joined to a
+main conductor (L), which has a terminating knob (M). On each side and
+close to the terminal end of each leather collector (H) is a fork-shaped
+collector (N). These two collectors are also connected electrically with
+the conductor (K). When the disc is turned electricity is generated by
+the leather flaps and accumulated by the collectors (N), after which it
+is ready to be discharged at the knob (M).
+
+In order to collect the electricity thus generated a vessel called a
+Leyden jar is used.
+
+LEYDEN JAR.--This is shown in Fig. 18. The jar (A) is of glass coated
+exteriorly at its lower end with tinfoil (B), which extends up a little
+more than halfway from the bottom. This jar has a wooden cover or top
+(C), provided centrally with a hole (D). The jar is designed to receive
+within it a tripod and standard (E) of lead. Within this lead standard
+is fitted a metal rod (F), which projects upwardly through the hole (D),
+its upper end having thereon a terminal knob (G). A sliding cork (H) on
+the rod (F) serves as a means to close the jar when not in use. When in
+use this cork is raised so the rod may not come into contact,
+electrically, with the cover (C).
+
+The jar is half filled with sulphuric acid (I), after which, in order
+to charge the jar, the knob (G) is brought into contact with the knob
+(M) of the friction generator (Fig. 17).
+
+VOLTAIC OR GALVANIC ELECTRICITY.--The second method of generating
+electricity is by chemical means, so called, because a liquid is used as
+one of the agents.
+
+[Illustration: _Fig. 18._ LEYDEN JAR]
+
+Galvani, in 1790, made the experiments which led to the generation of
+electricity by means of liquids and metals. The first battery was called
+the "crown of cups," shown in Fig. 19, and consisting of a row of glass
+cups (A), containing salt water. These cups were electrically connected
+by means of bent metal strips (B), each strip having at one end a copper
+plate (C), and at the other end a zinc plate (D). The first plate in the
+cup at one end is connected with the last plate in the cup at the other
+end by a conductor (E) to make a complete circuit.
+
+[Illustration: _Fig. 19._ GALVANIC ELECTRICITY. CROWN OF CUPS]
+
+THE CELL AND BATTERY.--From the foregoing it will be seen that within
+each cup the current flows from the zinc to the copper plates, and
+exteriorly from the copper to the zinc plates through the conductors (B
+and E).
+
+A few years afterwards Volta devised what is known as the voltaic pile
+(Fig. 20).
+
+VOLTAIC PILE--HOW MADE.--This is made of alternate discs of copper and
+zinc with a piece of cardboard of corresponding size between each zinc
+and copper plate. The cardboard discs are moistened with acidulated
+water. The bottom disc of copper has a strip which connects with a cup
+of acid, and one wire terminal (A) runs therefrom. The upper disc, which
+is of zinc, is also connected, by a strip, with a cup of acid from which
+extends the other terminal wire (B).
+
+[Illustration: _Fig. 20._ VOLTAIC ELECTRICITY]
+
+_Plus and Minus Signs._--It will be noted that the positive or copper
+disc has the plus sign (+) while the zinc disc has the minus (-) sign.
+These signs denote the positive and the negative sides of the current.
+
+The liquid in the cells, or in the moistened paper, is called the
+_electrolyte_ and the plates or discs are called _electrodes_. To define
+them more clearly, the positive plate is the _anode_, and the negative
+plate the _cathode_.
+
+The current, upon entering the zinc plate, decomposes the water in the
+electrolyte, thereby forming oxygen. The hydrogen in the water, which
+has also been formed by the decomposition, is carried to the copper
+plate, so that the plate finally is so coated with hydrogen that it is
+difficult for the current to pass through. This condition is called
+"polarization," and to prevent it has been the aim of all inventors. To
+it also we may attribute the great variety of primary batteries, each
+having some distinctive claim of merit.
+
+THE COMMON PRIMARY CELL.--The most common form of primary cell contains
+sulphuric acid, or a sulphuric acid solution, as the electrolyte, with
+zinc for the _anode_, and carbon, instead of copper, for the _cathode_.
+
+The ends of the zinc and copper plates are called _terminals_, and while
+the zinc is the anode or positive element, its _terminal_ is designated
+as the positive pole. In like manner, the carbon is the negative
+element or cathode, and its terminal is designated as negative pole.
+
+Fig. 21 will show the relative arrangement of the parts. It is customary
+to term that end or element from which the current flows as positive. A
+cell is regarded as a whole, and as the current passes out of the cell
+from the copper element, the copper terminal becomes positive.
+
+[Illustration: _Fig. 21._ PRIMARY BATTERY]
+
+BATTERY RESISTANCE, ELECTROLYTE AND CURRENT.--The following should be
+carefully memorized:
+
+A cell has reference to a single vessel. When two or more cells are
+coupled together they form a _battery_.
+
+_Resistance_ is opposition to the movement of the current. If it is
+offered by the electrolyte, it is designated "Internal Resistance." If,
+on the other hand, the opposition takes place, for instance, through the
+wire, it is then called "External Resistance."
+
+The electrolyte must be either acid, or alkaline, or saline, and the
+electrodes must be of dissimilar metals, so the electrolyte will attack
+one of them.
+
+The current is measured in amperes, and the force with which it is
+caused to flow is measured in volts. In practice the word "current" is
+used to designate ampere flow; and electromotive force, or E. M. F., is
+used instead of voltage.
+
+ELECTRO-MAGNETIC ELECTRICITY.--The third method of generating
+electricity is by electro-magnets. The value and use of induction will
+now be seen, and you will be enabled to utilize the lesson concerning
+magnetic action referred to in the previous chapter.
+
+MAGNETIC RADIATION.--You will remember that every piece of metal which
+is within the path of an electric current has a space all about its
+surface from end to end which is electrified. This electrified field
+extends out a certain distance from the metal, and is supposed to
+maintain a movement around it. If, now, another piece of metal is
+brought within range of this electric or magnetic zone and moved across
+it, so as to cut through this field, a current will be generated
+thereby, or rather added to the current already exerted, so that if we
+start with a feeble current, it can be increased by rapidly "cutting the
+lines of force," as it is called.
+
+DIFFERENT KINDS OF DYNAMO.--While there are many kinds of dynamo, they
+all, without exception, are constructed in accordance with this
+principle. There are also many varieties of current. For instance, a
+dynamo may be made to produce a high voltage and a low amperage; another
+with high amperage and low voltage; another which gives a direct current
+for lighting, heating, power, and electroplating; still another which
+generates an alternating current for high tension power, or
+transmission, arc-lighting, etc., all of which will be explained
+hereafter.
+
+In this place, however, a full description of a direct-current dynamo
+will explain the principle involved in all dynamos--that to generate a
+current of electricity makes it necessary for us to move a field of
+force, like an armature, rapidly and continuously through another field
+of force, like a magnetic field.
+
+DIRECT-CURRENT DYNAMO.--We shall now make the simplest form of dynamo,
+using for this purpose a pair of permanent magnets.
+
+[Illustration: _Fig. 22._ DYNAMO FIELD AND POLE PIECE]
+
+SIMPLE MAGNET CONSTRUCTION.--A simple way to make a pair of magnets for
+this purpose is shown in Fig. 22. A piece of round 3/4-inch steel core
+(A), 5-1/2 inches long, is threaded at both ends to receive at one end a
+nut (B), which is screwed on a sufficient distance so that the end of
+the core (A) projects a half inch beyond the nut. The other end of the
+steel core has a pole piece of iron (C) 2" x 2" x 4", with a hole
+midway between the ends, threaded entirely through, and provided along
+one side with a concave channel, within which the armature is to turn.
+Now, before the pole piece (C) is put on, we will slip on a disc (E),
+made of hard rubber, then a thin rubber tube (F), and finally a rubber
+disc (G), so as to provide a positive insulation for the wire coil which
+is wound on the bobbin thus made.
+
+HOW TO WIND.--In practice, and as you go further along in this work, you
+will learn the value, first, of winding one layer of insulated wire on
+the spool, coating it with shellac, and then putting on the next layer,
+and so on; when completely wound, the two wire terminals may be brought
+out at one end; but for our present purpose, and to render the
+explanation clearer, the wire terminals are at the opposite ends of the
+spool (H, H').
+
+THE DYNAMO FIELDS.--Two of these spools are so made and they are called
+the _fields_ of the dynamo.
+
+We will next prepare an iron bar (I), 5 inches long and 1/2 inch thick
+and 1-1/2 inches wide, then bore two holes through it so the distance
+measures 3 inches from center to center. These holes are to be threaded
+for the 3/4-inch cores (A). This bar holds together the upper ends of
+the cores, as shown in Fig. 23.
+
+[Illustration: _Fig. 23._ BASE AND FIELDS ASSEMBLED]
+
+We then prepare a base (J) of any hard wood, 2 inches thick, 8 inches
+long and 8 inches wide, and bore two 3/4-inch holes 3 inches apart on a
+middle line, to receive a pair of 3/4-inch cap screws (K), which pass
+upwardly through the holes in the base and screw into the pole pieces
+(C). A wooden bar (L), 1-1/2" x 1-1/2", 8 inches long, is placed under
+each pole piece, which is also provided with holes for the cap screws
+(K). The lower side of the base (J) should be countersunk, as at M, so
+the head of the nut will not project. The fields of the dynamo are now
+secured in position to the base.
+
+[Illustration: _Fig. 24._ DETAILS OF THE ARMATURE, CORE
+
+_Fig. 25._ DETAILS OF THE ARMATURE, BODY]
+
+THE ARMATURE.--A bar of iron (Fig. 24), 1" x 1" and 2-1/4 inches long,
+is next provided. Through this bar (1) are then bored two 5/16-inch
+holes 1-3/4 inches apart, and on the opposite sides of this bar are two
+half-rounded plates of iron (3) (Fig. 25).
+
+ARMATURE WINDING.--Each plate is 1/2 inch thick, 1-3/4 inches wide and 4
+inches long, each plate having holes (4) to coincide with the holes (2)
+of the bar (1), so that when the two plates are applied to opposite
+sides of the bar, and riveted together, a cylindrical member is formed,
+with two channels running longitudinally, and transversely at the ends;
+and in these channels the insulated wires are wound from end to end
+around the central block (1).
+
+MOUNTING THE ARMATURE.--It is now necessary to provide a means for
+revolving this armature. To this end a brass disc (5, Fig. 26) is made,
+2 inches in diameter, 1/8 inch thick. Centrally, at one side, is a
+projecting stem (6) of round brass, which projects out 2 inches, and the
+outer end is turned down, as at 7, to form a small bearing surface.
+
+[Illustration: _Fig. 26._ JOURNALS _Fig. 27._ COMMUTATOR,
+ARMATURE MOUNTINGS]
+
+The other end of the armature has a similar disc (8), with a central
+stem (9), 1-1/2 inches long, turned down to 1/4-inch diameter up to
+within 1/4 inch of the disc (7), so as to form a shoulder.
+
+THE COMMUTATOR.--In Fig. 27 is shown, at 10, a wooden cylinder, 1 inch
+long and 1-1/4 inches in diameter, with a hole (11) bored through
+axially, so that it will fit tightly on the stem (6) of the disc (5). On
+this wooden cylinder is driven a brass or copper tube (12), which has
+holes (13) opposite each other. Screws are used to hold the tube to the
+wooden cylinder, and after they are properly secured together, the tube
+(12) is cut by a saw, as at 14, so as to form two independent tubular
+surfaces.
+
+[Illustration: _Fig. 28._ END VIEW ARMATURE, MOUNTED]
+
+These tubular sections are called the commutator plates.
+
+[Illustration: _Fig. 29._ TOP VIEW OF ARMATURE ON BASE]
+
+In order to mount this armature, two bearings are provided, each
+comprising a bar of brass (15, Fig. 28), each 1/4 inch thick, 1/2 inch
+wide and 4-1/2 inches long. Two holes, 3 inches apart, are formed
+through this bar, to receive round-headed wood screws (16), these screws
+being 3 inches long, so they will pass through the wooden pieces (I)
+and enter the base (J). Midway between the ends, each bar (15) has an
+iron bearing block (17), 3/4" x 1/2" and 1-1/2 inches high, the 1/4-inch
+hole for the journal (7) being midway between its ends.
+
+COMMUTATOR BRUSHES.--Fig. 28 shows the base, armature and commutator
+assembled in position, and to these parts have been added the commutator
+brushes. The brush holder (18) is a horizontal bar made of hard rubber
+loosely mounted upon the journal pin (7), which is 2-1/2 inches long. At
+each end is a right-angled metal arm (19) secured to the bar (18) by
+screws (20). To these arms the brushes (21) are attached, so that their
+spring ends engage with the commutator (12). An adjusting screw (22) in
+the bearing post (17), with the head thereof bearing against the
+brush-holder (18), serves as a means for revolubly adjusting the brushes
+with relation to the commutator.
+
+DYNAMO WINDINGS.--There are several ways to wind the dynamos. These
+can be shown better by the following diagrams (Figs. 30, 31, 32, 33):
+
+THE FIELD.--If the field (A, Fig. 30) is not a permanent magnet, it must
+be excited by a cell or battery, and the wires (B, B') are connected up
+with a battery, while the wires (C, C') may be connected up to run a
+motor. This would, therefore, be what is called a "separately excited"
+dynamo. In this case the battery excites the field and the armature
+(D), cutting the lines of force at the pole pieces (E), so that the
+armature gathers the current for the wires (C, C').
+
+[Illustration: _Fig. 30._ FIELD WINDING]
+
+[Illustration: _Fig. 31._ SERIES-WOUND]
+
+SERIES-WOUND FIELD.--Fig. 31 shows a "series-wound" dynamo. The wires of
+the fields (A) are connected up in series with the brushes of the
+armature (D), and the wires (G, G') are led out and connected up with a
+lamp, motor or other mechanism. In this case, as well as in Figs. 32 and
+33, both the field and the armature are made of soft gray iron. With
+this winding and means of connecting the wires, the field is constantly
+excited by the current passing through the wires.
+
+SHUNT-WOUND FIELD.--Fig. 32 represents what is known as a "shunt-wound"
+dynamo. Here the field wires (H, H) connect with the opposite brushes
+of the armature, and the wires (I, I') are also connected with the
+brushes, these two wires being provided to perform the work required.
+This is a more useful form of winding for electroplating purposes.
+
+[Illustration: _Fig. 32._ SHUNT-WOUND _Fig. 32._ COMPOUND-WOUND]
+
+COMPOUND-WOUND FIELD.--Fig. 33 is a diagram of a "compound-wound"
+dynamo. The regular field winding (J) has its opposite ends connected
+directly with the armature brushes. There is also a winding, of a
+comparatively few turns, of a thicker wire, one terminal (K) of which is
+connected with one of the brushes and the other terminal (K') forms one
+side of the lighting circuit. A wire (L) connects with the other
+armature brush to form a complete lighting circuit.
+
+
+
+
+CHAPTER V
+
+HOW TO DETECT AND MEASURE ELECTRICITY
+
+
+MEASURING INSTRUMENTS.--The production of an electric current would not
+be of much value unless we had some way by which we might detect and
+measure it. The pound weight, the foot rule and the quart measure are
+very simple devices, but without them very little business could be
+done. There must be a standard of measurement in electricity as well as
+in dealing with iron or vegetables or fabrics.
+
+As electricity cannot be seen by the human eye, some mechanism must be
+made which will reveal its movements.
+
+THE DETECTOR.--It has been shown in the preceding chapter that a current
+of electricity passing through a wire will cause a current to pass
+through a parallel wire, if the two wires are placed close together, but
+not actually in contact with each other. An instrument which reveals
+this condition is called a _galvanometer_. It not only detects the
+presence of a current, but it shows the direction of its flow. We shall
+now see how this is done.
+
+For example, the wire (A, Fig. 35) is connected up in an electric
+circuit with a permanent magnet (B) suspended by a fine wire (C), so
+that the magnet (B) may freely revolve.
+
+[Illustration: _Fig. 34._     _Fig. 35._      _Fig. 36._
+             TO THE RIGHT,  COMPASS MAGNET,  TO THE LEFT]
+
+For convenience, the magnetic field is shown flowing in the direction of
+the darts, in which the dart (D) represents the current within the
+magnet (B) flowing toward the north pole, and the darts (E) showing the
+exterior current flowing toward the south pole. Now, if the wire (A) is
+brought up close to the magnet (B), and a current passed through A, the
+magnet (B) will be affected. Fig. 35 shows the normal condition of the
+magnetized bar (B) parallel with the wire (A) when a current is not
+passing through the latter.
+
+DIRECTION OF CURRENT.--If the current should go through the wire (A)
+from right to left, as shown in Fig. 34, the magnet (B) would swing in
+the direction taken by the hands of a clock and assume the position
+shown in Fig. 34. If, on the other hand, the current in the wire (A)
+should be reversed or flow from left to right, the magnet (B) would
+swing counter-clock-wise, and assume the position shown in Fig. 36. The
+little pointer (G) would, in either case, point in the direction of the
+flow of the current through the wire (A).
+
+[Illustration: _Fig. 37._ INDICATING DIRECTION OF CURRENT]
+
+SIMPLE CURRENT DETECTOR.--A simple current detector may be made as
+follows:
+
+Prepare a base 3' x 4' in size and 1 inch thick. At each corner of one
+end fix a binding post, as at A, A', Fig. 37. Then select 20 feet of No.
+28 cotton-insulated wire, and make a coil (B) 2 inches in diameter,
+leaving the ends free, so they may be affixed to the binding posts (A,
+A'). Now glue or nail six blocks (C) to the base, each block being 1" x
+1" x 2", and lay the coil on these blocks. Then drive an L-shaped nail
+(D) down into each block, on the inside of the coil, as shown, so as to
+hold the latter in place.
+
+[Illustration: _Fig. 38._ THE BRIDGE]
+
+Now make a bridge (E, Fig. 38) of a strip of brass 1/2 inch wide, 1/16
+inch thick and long enough to span the coil, and bend the ends down, as
+at F, so as to form legs. A screw hole (G) is formed in each foot, so it
+may be screwed to the base.
+
+Midway between the ends this bridge has a transverse slot (H) in one
+edge, to receive therein the pivot pin of the swinging magnet. In order
+to hold the pivot pin in place, cut out an H-shaped piece of sheet brass
+(I), which, when laid on the bridge, has its ends bent around the
+latter, as shown at J, and the crossbar of the H-shaped piece then will
+prevent the pivot pin from coming out of the slot (H).
+
+[Illustration: _Fig. 39._ DETAILS OF DETECTOR]
+
+The magnet is made of a bar of steel (K, Fig. 39) 1-1/2 inches long, 3/8
+inch wide and 1/16 inch thick, a piece of a clock spring being very
+serviceable for this purpose. The pivot pin is made of an ordinary pin
+(L), and as it is difficult to solder the steel magnet (K) to the pin,
+solder only a small disc (M) to the pin (L). Then bore a hole (N)
+through the middle of the magnet (K), larger in diameter than the pin
+(L), and, after putting the pin in the hole, pour sealing wax into the
+hole, and thereby secure the two parts together. Near the upper end of
+the pin (L) solder the end of a pointer (O), this pointer being at right
+angles to the armature (K). It is better to have a metal socket for the
+lower end of the pin. When these parts are put together, as shown in
+Fig. 37, a removable glass top, or cover, should be provided.
+
+This is shown in Fig. 40, in which a square, wooden frame (P) is used,
+and a glass (Q) fitted into the frame, the glass being so arranged that
+when the cover is in position it will be in close proximity to the upper
+projecting end of the pivot pin (L), and thus prevent the magnet from
+becoming misplaced.
+
+[Illustration: _Fig. 40._ CROSS SECTION OF DETECTOR]
+
+HOW TO PLACE THE DETECTOR.--If the detector is placed north and south,
+as shown by the two markings, N and S (Fig. 37), the magnet bar will
+point north and south, being affected by the earth's magnetism; but when
+a current of electricity flows through the coil (B), the magnet will be
+deflected to the right or to the left, so that the pointer (O) will then
+show the direction in which the current is flowing through the wire (R)
+which you are testing.
+
+The next step of importance is to _measure_ the current, that is, to
+determine its strength or intensity, as well as the flow or quantity.
+
+DIFFERENT WAYS OF MEASURING A CURRENT.--There are several ways to
+measure the properties of a current, which may be defined as follows:
+
+1. THE SULPHURIC ACID VOLTAMETER.--By means of an electrolytic action,
+whereby the current decomposes an acidulated solution--that is, water
+which has in it a small amount of sulphuric acid--and then measuring the
+gas generated by the current.
+
+2. THE COPPER VOLTAMETER.--By electro-chemical means, in which the
+current passes through plates immersed in a solution of copper sulphate.
+
+3. THE GALVANOSCOPE.--By having a coil of insulated wire, with a magnet
+suspended so as to turn freely within the coil, forming what is called a
+galvanoscope.
+
+4. ELECTRO-MAGNETIC METHOD.--By using a pair of magnets and sending a
+current through the coils, and then measuring the pull on the armature.
+
+5. THE POWER OR SPEED METHOD.--By using an electric fan, and noting the
+revolutions produced by the current.
+
+6. THE CALORIMETER.--By using a coil of bare wire, immersed in paraffine
+oil, and then measuring the temperature by means of a thermometer.
+
+[Illustration: _Fig. 41._ ACID VOLTAMETER]
+
+[Illustration: _Fig. 42._ COPPER VOLTAMETER]
+
+7. THE LIGHT METHOD.--Lastly, by means of an electric light, which
+shows, by its brightness, a greater or less current.
+
+THE PREFERRED METHODS.--It has been found that the first and second
+methods are the only ones which will accurately register current
+strength, and these methods have this advantage--that the chemical
+effect produced is not dependent upon the size or shape of the apparatus
+or the plates used.
+
+HOW TO MAKE A SULPHURIC ACID VOLTAMETER.--In Fig. 41 is shown a simple
+form of sulphuric acid voltameter, to illustrate the first method. A is
+a jar, tightly closed by a cover (B). Within is a pair of platinum
+plates (C, C), each having a wire (D) through the cover. The cover has a
+vertical glass tube (E) through it, which extends down to the bottom of
+the jar, the electrolyte therein being a weak solution of sulphuric
+acid. When a current passes through the wires (D), the solution is
+partially decomposed--that is, converted into gas, which passes up into
+the vacant space (F) above the liquid, and, as it cannot escape, it
+presses the liquid downwardly, and causes the latter to flow upwardly
+into the tube (E). It is then an easy matter, after the current is on
+for a certain time, to determine its strength by the height of the
+liquid in the tube.
+
+HOW TO MAKE A COPPER VOLTAMETER.--The second, or copper voltameter, is
+shown in Fig. 42. The glass jar (A) contains a solution of copper
+sulphate, known in commerce as blue vitriol. A pair of copper plates
+(B, B') are placed in this solution, each being provided with a
+connecting wire (C). When a current passes through the wires (C), one
+copper plate (B) is eaten away and deposited on the other plate (B'). It
+is then an easy matter to take out the plates and find out how much in
+weight B' has gained, or how much B has lost.
+
+In this way, in comparing the strength of, say, two separate currents,
+one should have each current pass through the voltameter the same length
+of time as the other, so as to obtain comparative results.
+
+It is not necessary, in the first and second methods, to consider the
+shapes, the sizes of the plates or the distances between them. In the
+first method the gas produced, within a given time, will be the same,
+and in the second method the amount deposited or eaten away will be the
+same under all conditions.
+
+DISADVANTAGES OF THE GALVANOSCOPE.--With the third method (using the
+galvanoscope) it is necessary, in order to get a positively correct
+reading instrument, to follow an absolutely accurate plan in
+constructing each part, in every detail, and great care must be
+exercised, particularly in winding. It is necessary also to be very
+careful in selecting the sizes of wire used and in the number of turns
+made in the coils.
+
+This is equally true of the fourth method, using the electro-magnet,
+because the magnetic pull is dependent upon the size of wire from which
+the coils are made and the number of turns of wire.
+
+OBJECTIONS TO THE CALORIMETER.--The calorimeter, or sixth method, has
+the same objection. The galvanoscope and electro-magnet do not respond
+equally to all currents, and this is also true, even to a greater
+extent, with the calorimeter.
+
+
+
+
+CHAPTER VI
+
+VOLTS, AMPERES, OHMS AND WATTS
+
+
+UNDERSTANDING TERMS.--We must now try to ascertain the meaning of some
+of the terms so frequently used in connection with electricity. If you
+intended to sell or measure produce or goods of any kind, it would be
+essential to know how many pints or quarts are contained in a gallon, or
+in a bushel, or how many inches there are in a yard, and you also ought
+to know just what the quantity term _bushel_ or the measurement _yard_
+means.
+
+INTENSITY AND QUANTITY.--Electricity, while it has no weight, is capable
+of being measured by means of its intensity, or by its quantity. Light
+may be measured or tested by its brilliancy. If one light is of less
+intensity than another and both of them receive their impulses from the
+same source, there must be something which interferes with that light
+which shows the least brilliancy. Electricity can also be interfered
+with, and this interference is called _resistance_.
+
+VOLTAGE.--Water may be made to flow with greater or less force, or
+velocity, through a pipe, the degree of same depending upon the height
+of the water which supplies the pipe. So with electricity. It may pass
+over a wire with greater or less force under one condition than another.
+This force is called voltage. If we have a large pipe, a much greater
+quantity of water will flow through it than will pass through a small
+pipe, providing the pressure in each case is alike. This quantity in
+electricity is called _amperage_.
+
+In the case of water, a column 1" x 1", 28 inches in height, weighs 1
+pound; so that if a pipe 1 inch square draws water from the bottom it
+flows with a pressure of 1 pound. If the pipe has a measurement of 2
+square inches, double the quantity of water will flow therefrom, at the
+same pressure.
+
+AMPERAGE.--If, on the other hand, we have a pipe 1 inch square, and
+there is a depth of 56 inches of water in the reservoir, we shall get as
+much water from the reservoir as though we had a pipe of 2 square inches
+drawing water from a reservoir which is 28 inches deep.
+
+MEANING OF WATTS.--It is obvious, therefore, that if we multiply the
+height of the water in inches with the area of the pipe, we shall obtain
+a factor which will show how much water is flowing.
+
+Here are two examples:
+
+1. 28 inches = height of the water in the reservoir.
+
+2 square inches = size of the pipe.
+Multiply 28 x 2 = 56.
+
+2. 56 = height of the water in the reservoir.
+1 square inch = size of the pipe.
+Multiply 56 x 1 = 56.
+
+Thus the two problems are equal.
+
+A KILOWATT.--Now, in electricity, remembering that the height of the
+water corresponds with _voltage_ in electricity, and the size of the
+pipe with _amperage_, if we multiply volts by amperes, or amperes by
+volts, we get a result which is indicated by the term _watts_. One
+thousand of these watts make a kilowatt, and the latter is the standard
+of measurement by which a dynamo or motor is judged or rated.
+
+Thus, if we have 5 amperes and 110 volts, the result of multiplying them
+would be 550 watts, or 5 volts and 110 amperes would produce 550 watts.
+
+A STANDARD OF MEASUREMENT.--But with all this we must have some
+standard. A bushel measure is of a certain size, and a foot has a
+definite length, so in electricity there is a recognized force and
+quantity which are determined as follows:
+
+THE AMPERE STANDARD.--It is necessary, first, to determine what an
+ampere is. For this purpose a standard solution of nitrate of silver is
+used, and a current of electricity is passed through this solution. In
+doing so the current deposits silver at the rate of 0.001118 grains per
+second for each ampere.
+
+THE VOLTAGE STANDARD.--In order to determine the voltage we must know
+something of _resistance_. Different metals do not transmit a current
+with equal ease. The size of a conductor, also, is an important factor
+in the passage of a current. A large conductor will transmit a current
+much better than a small conductor. We must therefore have a standard
+for the _ohm_, which is the measure of resistance.
+
+THE OHM.--It is calculated in this way: There are several standards, but
+the one most generally employed is the _International Ohm_. To determine
+it, by this system, a column of pure mercury, 106.3 millimeters long and
+weighing 14.4521 grams, is used. This would make a square tube about 94
+inches long, and a little over 1/25 of an inch in diameter. The
+resistance to a current flow in such a column would be equal to 1 ohm.
+
+CALCULATING THE VOLTAGE.--In order to arrive at the voltage we must use
+a conductor, which, with a resistance of 1 ohm, will produce 1 ampere.
+It must be remembered that the volt is the practical unit of
+electro-motive force.
+
+While it would be difficult for the boy to conduct these experiments in
+the absence of suitable apparatus, still, it is well to understand
+thoroughly how and why these standards are made and used.
+
+
+
+
+CHAPTER VII
+
+PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND
+LIKE APPARATUS
+
+
+SIMPLE SWITCHES.--We have now gone over the simpler or elementary
+outlines of electrical phenomena, and we may commence to do some of the
+practical work in the art. We need certain apparatus to make
+connections, which will be constructed first.
+
+A TWO-POLE SWITCH.--A simple two-pole switch for a single line is made
+as follows:
+
+A base block (A, Fig. 43) 3 inches long, 2 inches wide and 3/4 inch
+thick, has on it, at one end, a binding screw (B), which holds a pair of
+fingers (C) of brass or copper, these fingers being bent upwardly and so
+arranged as to serve as fingers to hold a switch bar (D) between them.
+This bar is also of copper or brass and is pivoted to the fingers. Near
+the other end of the base is a similar binding screw (E) and fingers (F)
+to receive the blade of the switch bar. The bar has a handle (G) of
+wood. The wires are attached to the respective binding screws (B, E).
+
+DOUBLE-POLE SWITCH.--A double-pole switch or a switch for a double line
+is shown in Fig. 44. This is made similar in all respects to the one
+shown in Fig. 43, excepting that there are two switch blades (A, A)
+connected by a cross bar (B) of insulating material, and this bar
+carries the handle (C).
+
+[Illustration: _Fig. 43._ TWO-POLE SWITCH]
+
+[Illustration: _Fig. 44._ DOUBLE-POLE SWITCH]
+
+Other types of switch will be found very useful. In Fig. 45 is a simple
+sliding switch in which the base block has, at one end, a pair of copper
+plates (A, B), each held at one end to the base by a binding screw (C),
+and having a bearing or contact surface (D) at its other end. At the
+other end of the base is a copper plate (E) held by a binding screw (F),
+to the inner end of which plate is hinged a swinging switch blade (G),
+the free end of which is adapted to engage with the plates (A, B).
+
+[Illustration: _Fig. 45._ SLIDING SWITCH]
+
+SLIDING SWITCH.--This sliding switch form may have the contact plates
+(A, B and C, Fig. 46) circularly arranged and any number may be located
+on the base, so they may be engaged by a single switching lever (H). It
+is the form usually adopted for rheostats.
+
+REVERSING SWITCH.--A reversing switch is shown in Fig. 47. The base has
+two plates (A, B) at one end, to which the parallel switch bars (C, D)
+are hinged. The other end of the base has three contact plates (E, F, G)
+to engage the swinging switch bars, these latter being at such distance
+apart that they will engage with the middle and one of the outer plates.
+The inlet wires, positive and negative, are attached to the plates (A,
+B, respectively), and one of the outlet wires (H) is attached to the
+middle contact plate (F), while the other wire is connected up with both
+of the outside plates. When the switch bars (C, D) are thrown to the
+left so as to be in contact with E, F, the outside plate (E) and the
+middle plate (F) will be positive and negative, respectively; but when
+the switch is thrown to the right, as shown in the figure, plate F
+becomes positive and plate E negative, as shown.
+
+[Illustration: _Fig. 46._ RHEOSTAT FORM OF SWITCH]
+
+PUSH BUTTONS.--A push button is but a modified structure of a switch,
+and they are serviceable because they are operating, or the circuit is
+formed only while the finger is on the button.
+
+[Illustration: _Fig. 47._ REVERSING SWITCH]
+
+In its simplest form (Fig. 48) the push button has merely a circular
+base (A) of insulating material, and near one margin, on the flat side,
+is a rectangular plate (B), intended to serve as a contact plate as well
+as a means for attaching one of the wires thereto. In line with this
+plate is a spring finger (C), bent upwardly so that it is normally out
+of contact with the plate (B), its end being held by a binding screw
+(D). To effect contact, the spring end of the finger (C) is pressed
+against the bar (B), as at E. This is enclosed in a suitable casing,
+such as will readily suggest itself to the novice.
+
+ELECTRIC BELL.--One of the first things the boy wants to make, and one
+which is also an interesting piece of work, is an electric bell.
+
+To make this he will be brought, experimentally, in touch with several
+important features in electrical work. He must make a battery for the
+production of current, a pair of electro-magnets to be acted upon by the
+current, a switch to control it, and, finally, he must learn how to
+connect it up so that it may be operated not only from one, but from two
+or more push buttons.
+
+[Illustration: _Fig. 48._ PUSH BUTTON]
+
+HOW MADE.--In Fig. 49 is shown an electric bell, as usually constructed,
+so modified as to show the structure at a glance, with its connections.
+A is the base, B, B' the binding posts for the wires, C, C the
+electro-magnets, C' the bracket for holding the magnets, D the armature,
+E the thin spring which connects the armature with the post F, G the
+clapper arm, H the bell, I the adjusting screw on the post J, K the wire
+lead from the binding post B to the first magnet, L the wire which
+connects the two magnets, M the wire which runs from the second magnet
+to the post J, and N a wire leading from the armature post to the
+binding post B'.
+
+[Illustration: _Fig. 49._ ELECTRIC BELL]
+
+The principle of the electric bell is this: In looking at Fig. 49, you
+will note that the armature bar D is held against the end of the
+adjusting screw by the small spring E. When a current is turned on, it
+passes through the connections and conduits as follows: Wire K to the
+magnets, wire M to the binding post J, and set screw I, then through the
+armature to the post F, and from post F to the binding post B'.
+
+[Illustration: _Fig. 50._ ARMATURE OF ELECTRIC BELL]
+
+ELECTRIC BELL--HOW OPERATED.--The moment a current passes through the
+magnets (C, C), the core is magnetized, and the result is that the
+armature (D) is attracted to the magnets, as shown by the dotted lines
+(O), when the clapper strikes the bell. But when the armature moves over
+to the magnet, the connection is broken between the screw (I) and
+armature (D), so that the cores of the magnets are demagnetized and lose
+their pull, and the spring (E) succeeds in drawing back the armature.
+This operation of vibrating the armature is repeated with great
+rapidity, alternately breaking and re-establishing the circuit, by the
+action of the current.
+
+In making the bell, you must observe one thing, the binding posts (B,
+B') must be insulated from each other, and the post J, or the post F,
+should also be insulated from the base. For convenience we show the post
+F insulated, so as to necessitate the use of wire (N) from post (F) to
+binding post (B').
+
+The foregoing assumes that you have used a cast metal base, as most
+bells are now made; but if you use a wooden base, the binding posts (B,
+B') and the posts (F, J) are insulated from each other, and the
+construction is much simplified.
+
+It is better, in practice, to have a small spring (P, Fig. 50) between
+the armature (D) and the end of the adjusting screw (I), so as to give a
+return impetus to the clapper. The object of the adjusting screw is to
+push and hold the armature close up to the ends of the magnets, if it
+seems necessary.
+
+If two bells are placed on the base with the clapper mounted between
+them, both bells will be struck by the swinging motion of the armature.
+
+An easily removable cap or cover is usually placed over the coils and
+armature, to keep out dust.
+
+A very simple annunciator may be attached to the bell, as shown in the
+following figures:
+
+[Illustration: _Figs. 51-54._ ANNUNCIATOR]
+
+ANNUNCIATORS.--Make a box of wood, with a base (A) 4" x 5" and 1/2 inch
+thick. On this you can permanently mount the two side pieces (B) and two
+top and bottom pieces (C), respectively, so they project outwardly
+4-1/2 inches from the base. On the open front place a wood or metal
+plate (D), provided with a square opening (D), as in Fig. 54, near its
+lower end. This plate is held to the box by screws (E).
+
+Within is a magnet (F), screwed into the base (A), as shown in Fig. 51;
+and pivoted to the bottom of the box is a vertical armature (G), which
+extends upwardly and contacts with the core of the magnet. The upper end
+of the armature has a shoulder (H), which is in such position that it
+serves as a rest for a V-shaped stirrup (I), which is hinged at J to the
+base (C). This stirrup carries the number plate (K), and when it is
+raised to its highest point it is held on the shoulder (H), unless the
+electro-magnet draws the armature out of range of the stirrup. A spring
+(L) bearing against the inner side of the armature keeps its upper end
+normally away from the magnet core. When the magnet draws the armature
+inwardly, the number plate drops and exposes the numeral through the
+opening in the front of the box. In order to return the number plate to
+its original position, as shown in Fig. 51, a vertical trigger (M)
+passes up through the bottom, its upper end being within range of one of
+the limbs of the stirrup.
+
+This is easily made by the ingenious boy, and will be quite an
+acquisition to his stock of instruments. In practice, the annunciator
+may be located in any convenient place and wires run to that point.
+
+[Illustration: _Fig. 55._ ALARM SWITCH ON WINDOW]
+
+[Illustration: _Fig. 56._ BURGLAR ALARM ATTACHMENT TO WINDOW]
+
+BURGLAR ALARM.--In order to make a burglar alarm connection with a bell,
+push buttons or switches may be put in circuit to connect with the
+windows and doors, and by means of the annunciators you may locate the
+door or window which has been opened. The simplest form of switch for a
+window is shown in the following figures:
+
+The base piece (A), which may be of hard rubber or fiber, is 1/4 inch
+thick and 1" x 1-1/2" in size.
+
+[Illustration: _Fig. 57._ BURGLAR ALARM CONTACT]
+
+At one end is a brass plate (B), with a hole for a wood screw (C), this
+screw being designed to pass through the plate and also into the
+window-frame, so as to serve as a means of attaching one of the wires
+thereto. The inner end of the plate has a hole for a round-headed screw
+(C') that also goes through the base and into the window-frame. It also
+passes through the lower end of the heart-shaped metal switch-piece
+(D).
+
+The upper end of the base has a brass plate (E), also secured to the
+base and window by a screw (F) at its upper end. The heart-shaped switch
+is of such length and width at its upper end that when it is swung to
+the right with one of the lobes projecting past the edge of the
+window-frame, the other lobe will be out of contact with the plate (E).
+
+[Illustration: _Fig. 58._ NEUTRAL POSITION OF CONTACT]
+
+The window sash (G) has a removable pin (H), which, when the sash moves
+upwardly, is in the path of the lobe of the heart-shaped switch, as
+shown in Fig. 56, and in this manner the pin (H) moves the upper end of
+the switch (D) inwardly, so that the other lobe contacts with the plate
+(E), and establishes an electric circuit, as shown in Fig. 57. During
+the daytime the pin (H) may be removed, and in order to protect the
+switch the heart-shaped piece (D) is swung inwardly, as shown in Fig.
+58, so that neither of the lobes is in contact with the plate (E).
+
+WIRE CIRCUITING.--For the purpose of understanding fully the circuiting,
+diagrams will be shown of the simple electric bell with two push
+buttons; next in order, the circuiting with an annunciator and then the
+circuiting necessary for a series of windows and doors, with annunciator
+attachments.
+
+[Illustration: _Fig. 59._ CIRCUITING FOR ELECTRIC BELL]
+
+CIRCUITING SYSTEM WITH A BELL AND TWO PUSH BUTTONS.--Fig. 59 shows a
+simple circuiting system which has two push buttons, although any number
+may be used, so that the bell will ring when the circuit is closed by
+either button.
+
+THE PUSH BUTTONS AND THE ANNUNCIATOR BELLS.--Fig. 60 shows three push
+buttons and an annunciator for each button. These three circuits are
+indicated by A, B and C, so that when either button makes contact, a
+complete circuit is formed through the corresponding annunciator.
+
+[Illustration: _Fig. 60._ _Annunciators_]
+
+[Illustration: _Fig. 61._ WIRING SYSTEM FOR A HOUSE]
+
+WIRING UP A HOUSE.--The system of wiring up a house so that all doors
+and windows will be connected to form a burglar alarm outfit, is shown
+in Fig. 61. It will be understood that, in practice, the bell is mounted
+on or at the annunciator, and that, for convenience, the annunciator
+box has also a receptacle for the battery. The circuiting is shown
+diagramatically, as it is called, so as fully to explain how the lines
+are run. Two windows and a door are connected up with an annunciator
+having three drops, or numbers 1, 2, 3. The circuit runs from one pole
+of the battery to the bell and then to one post of the annunciator. From
+the other post a wire runs to one terminal of the switch at the door or
+window. The other switch terminal has a wire running to the other pole
+of the battery.
+
+A, B, C represent the circuit wires from the terminals of the window and
+door switches, to the annunciators.
+
+It is entirely immaterial which side of the battery is connected up with
+the bell.
+
+From the foregoing it will readily be understood how to connect up any
+ordinary apparatus, remembering that in all cases the magnet must be
+brought into the electric circuit.
+
+
+
+
+CHAPTER VIII
+
+ACCUMULATORS. STORAGE OR SECONDARY BATTERIES
+
+
+STORING UP ELECTRICITY.--In the foregoing chapters we have seen that,
+originally, electricity was confined in a bottle, called the Leyden jar,
+from which it was wholly discharged at a single impulse, as soon as it
+was connected up by external means. Later the primary battery and the
+dynamo were invented to generate a constant current, and after these
+came the second form of storing electricity, called the storage or
+secondary battery, and later still recognized as accumulators.
+
+THE ACCUMULATOR.--The term _accumulator_ is, strictly speaking, the more
+nearly correct, as electricity is, in reality, "_stored_" in an
+accumulator. But when an accumulator is charged by a current of
+electricity, a chemical change is gradually produced in the active
+element of which the accumulator is made. This change or decomposition
+continues so long as the charging current is on. When the accumulator is
+disconnected from the charging battery or dynamo, and its terminals are
+connected up with a lighting system, or with a motor, for instance, a
+reverse process is set up, or the particles re-form themselves into
+their original compositions, which causes a current to flow in a
+direction opposite to that of the charging current.
+
+It is immaterial to the purposes of this chapter, as to the charging
+source, whether it be by batteries or dynamos; the same principles will
+apply in either case.
+
+[Illustration: _Fig. 62._ ACCUMULATOR GRIDS]
+
+ACCUMULATOR PLATES.--The elements used for accumulator plates are red
+lead for the positive plates, and precipitated lead, or the well-known
+litharge, for the negative plates. Experience has shown that the best
+way to hold this material is by means of lead grids.
+
+Fig. 62 shows the typical form of one of these grids. It is made of
+lead, cast or molded in one piece, usually square, as at A, with a wing
+or projection (B), at one margin, extending upwardly and provided with a
+hole (C). The grid is about a quarter of an inch thick.
+
+THE GRID.--The open space, called the grid, proper, comprises cross
+bars, integral with the plate, made in a variety of shapes. Fig. 62
+shows three forms of constructing these bars or ribs, the object being
+to provide a form which will hold in the lead paste, which is pressed in
+so as to make a solid-looking plate when completed.
+
+THE POSITIVE PLATE.--The positive plate is made in the following manner:
+Make a stiff paste of red lead and sulphuric acid; using a solution,
+say, of one part of acid to two parts of water. The grid is laid on a
+flat surface and the paste forced into the perforations with a stiff
+knife or spatula. Turn over the grid so as to get the paste in evenly on
+both sides.
+
+The grid is then stood on its edge, from 18 to 20 hours, to dry, and
+afterwards immersed in a concentrated solution of chloride of lime, so
+as to convert it into lead peroxide. When the action is complete it is
+thoroughly rinsed in cold water, and is ready to use.
+
+THE NEGATIVE PLATE.--The negative plate is filled, in like manner, with
+precipitated lead. This lead is made by putting a strip of zinc into a
+standard solution of acetate of lead, and crystals will then form on the
+zinc. These will be very thin, and will adhere together, firmly, forming
+a porous mass. This, when saturated and kept under water for a short
+time, may be put into the openings of the negative plate.
+
+[Illustration: _Fig. 63._ ASSEMBLAGE OF ACCUMULATOR PLATES]
+
+CONNECTING UP THE PLATES.--The next step is to put these plates in
+position to form a battery. In Fig. 63 is shown a collection of plates
+connected together.
+
+For simplicity in illustrating, the cell is made up of glass, porcelain,
+or hard rubber, with five plates (A), A, A representing the negative and
+B, B the positive plates. A base of grooved strips (C, C) is placed in
+the batteries of the cell to receive the lower ends of the plates. The
+positive plates are held apart by means of a short section of tubing
+(D), which is clamped and held within the plates by a bolt (E), this
+bolt also being designed to hold the terminal strip (F).
+
+In like manner, the negative plates are held apart by the two tubular
+sections (G), each of which is of the same length as the section D of
+the positives. The bolt (H) holds the negatives together as well as the
+terminal (I). The terminals should be lead strips, and it would be well,
+owing to the acid fumes which are formed, to coat all brass work,
+screws, etc., with paraffine wax.
+
+The electrolyte or acid used in the cell, for working purposes, is a
+pure sulphuric acid, which should be diluted with about four times its
+weight in water. Remember, you should always add the strong acid to the
+water, and never pour the water into the acid, as the latter method
+causes a dangerous ebullition, and does not produce a good mixture.
+
+Put enough of this solution into the cell to cover the tops of the
+plates, and the cell is ready.
+
+[Illustration: _Fig. 64._ CONNECTING UP STORAGE BATTERY IN SERIES]
+
+CHARGING THE CELLS.--The charge of the current must never be less than
+2.5 volts. Each cell has an output, in voltage, of about 2 volts, hence
+if we have, say, 10 cells, we must have at least 25 volts charging
+capacity. We may arrange these in one line, or in series, as it is
+called, so far as the connections are concerned, and charge them with a
+dynamo, or other electrical source, which shows a pressure of 25 volts,
+as illustrated in Fig. 64, or, instead of this, we may put them into two
+parallel sets of 5 cells each, as shown in Fig. 65, and use 12.5 volts
+to charge with. In this case it will take double the time because we are
+charging with only one-half the voltage used in the first case.
+
+The positive pole of the dynamo should be connected with the positive
+pole of the accumulator cell, and negative with negative. When this has
+been done run up the machine until it slightly exceeds the voltage of
+the cells. Thus, if we have 50 cells in parallel, like in Fig. 64, at
+least 125 volts will be required, and the excess necessary should bring
+up the voltage in the dynamo to 135 or 140 volts.
+
+[Illustration: _Fig. 65._ PARALLEL SERIES]
+
+[Illustration: _Fig. 66._ CHARGING CIRCUIT]
+
+THE INITIAL CHARGE.--It is usual initially to charge the battery from
+periods ranging from 36 to 40 hours, and to let it stand for 12 or 15
+hours, after which to re-charge, until the positive plates have turned
+to a chocolate color, and the negative plates to a slate or gray color,
+and both plates give off large bubbles of gas.
+
+In charging, the temperature of the electrolyte should not exceed 100 deg.
+Fahrenheit.
+
+When using the accumulators they should never be fully discharged.
+
+THE CHARGING CIRCUIT.--The diagram (Fig. 66) shows how a charging
+circuit is formed. The lamps are connected up in parallel, as
+illustrated. Each 16-candle-power 105-volt lamp will carry 1/2 ampere,
+so that, supposing we have a dynamo which gives 110 volts, and we want
+to charge a 4-volt accumulator, there will be 5-volt surplus to go to
+the accumulator. If, for instance, you want the cell to have a charge of
+2 amperes, four of these lamps should be connected up in parallel. If 3
+amperes are required, use 6 lamps, and so on.
+
+
+
+
+CHAPTER IX
+
+THE TELEGRAPH
+
+
+The telegraph is a very simple instrument. The key is nothing more or
+less than a switch which turns the current on and off alternately.
+
+The signals sent over the wires are simply the audible sounds made by
+the armature, as it moves to and from the magnets.
+
+MECHANISM IN TELEGRAPH CIRCUITS.--A telegraph circuit requires three
+pieces of mechanism at each station, namely, a key used by the sender, a
+sounder for the receiver, and a battery.
+
+THE SENDING KEY.--The base of the sending instrument is six inches long,
+four inches wide, and three-quarters of an inch thick, made of wood, or
+any suitable non-conducting material. The key (A) is a piece of brass
+three-eighths by one-half inch in thickness and six inches long. Midway
+between its ends is a cross hole, to receive the pivot pin (B), which
+also passes through a pair of metal brackets (C, D), the bracket C
+having a screw to hold one of the line wires, and the other bracket
+having a metal switch (E) hinged thereto. This switch bar, like the
+brackets, is made of brass, one-half inch wide by one-sixteenth of an
+inch thick.
+
+Below the forward end of the key (A) is a cross bar of brass (F),
+screwed to the base by a screw at one end, to receive the other line
+wire. Directly below the key (A) is a screw (G), so that the key will
+strike it when moved downwardly. The other end of the bar (F) contacts
+with the forward end of the switch bar (E) when the latter is moved
+inwardly.
+
+[Illustration: _Fig. 67._ TELEGRAPH SENDING KEY]
+
+The forward end of the key (A) has a knob (H) for the fingers, and the
+rear end has an elastic (I) attached thereto which is secured to the end
+of the base, so that, normally, the rear end is held against the base
+and away from the screw head (G). The head (J) of a screw projects from
+the base at its rear end. Key A contacts with it.
+
+When the key A contacts with the screw heads G, J, a click is produced,
+one when the key is pressed down and the other when the key is released.
+
+You will notice that the two plates C, F are connected up in circuit
+with the battery, so that, as the switch E is thrown, so as to be out of
+contact, the circuit is open, and may be closed either by the key A or
+the switch E. The use of the switch will be illustrated in connection
+with the sounder.
+
+[Illustration: _Fig. 68._ TELEGRAPH SOUNDER]
+
+When the key A is depressed, the circuit of course goes through plate C,
+key A and plate F to the station signalled.
+
+THE SOUNDER.--The sounder is the instrument which carries the
+electro-magnet.
+
+In Fig. 68 this is shown in perspective. The base is six inches long and
+four inches wide, being made, preferably, of wood. Near the forward end
+is mounted a pair of electro-magnets (A, A), with their terminal wires
+connected up with plates B, B', to which the line wires are attached.
+
+Midway between the magnets and the rear end of the base is a pair of
+upwardly projecting brackets (C). Between these are pivoted a bar (D),
+the forward end of which rests between the magnets and carries, thereon,
+a cross bar (E) which is directly above the magnets, and serves as the
+armature.
+
+The rear end of the base has a screw (F) directly beneath the bar D of
+such height that when the rear end of the bar D is in contact therewith
+the armature E will be out of contact with the magnet cores (A, A). A
+spiral spring (G) secured to the rear ends of the arm and to the base,
+respectively, serves to keep the rear end of the key normally in contact
+with the screw F.
+
+CONNECTING UP THE KEY AND SOUNDER.--Having made these two instruments,
+we must next connect them up in the circuit, or circuits, formed for
+them, as there must be a battery, a key, and a sounder at each end of
+the line.
+
+In Fig. 69 you will note two groups of those instruments. Now observe
+how the wires connect them together. There are two line wires, one (A)
+which connects up the two batteries, the wire being attached so that
+one end connects with the positive terminal of the battery, and the
+other end with the negative terminal.
+
+[Illustration: _Fig. 69._ A TELEGRAPH CIRCUIT]
+
+The other line wire (B), between the two stations, has its opposite ends
+connected with the terminals of the electro-magnet C of the sounders.
+The other terminals of each electro-magnet are connected up with one
+terminal of each key by a wire (D), and to complete the circuit at each
+station, the other terminal of the key has a wire (E) to its own
+battery.
+
+TWO STATIONS IN CIRCUIT.--The illustration shows station 2 telegraphing
+to station 1. This is indicated by the fact that the switch F' of that
+instrument is open, and the switch F of station 1 closed. When,
+therefore, the key of station 2 is depressed, a complete circuit is
+formed which transmits the current through wire E' and battery, through
+line A, then through the battery of station 1, through wire E to the
+key, and from the key, through wire D, to the sounder, and finally from
+the sounder over line wire B back to the sounder of station 2,
+completing the circuit at the key through wire D'.
+
+When the operator at station 2 closes the switch F', and the operator at
+station 1 opens the switch F, the reverse operation takes place. In both
+cases, however, the sounder is in at both ends of the line, and only the
+circuit through the key is cut out by the switch F, or F'.
+
+THE DOUBLE CLICK.--The importance of the double click of the sounder
+will be understood when it is realized that the receiving operator must
+have some means of determining if the sounder has transmitted a dot or a
+dash. Whether he depresses the key for a dot or a dash, there must be
+one click when the key is pressed down on the screw head G (Fig. 62),
+and also another click, of a different kind, when the key is raised up
+so that its rear end strikes the screw head J. This action of the key is
+instantly duplicated by the bar D (Fig. 68) of the sounder, so that the
+sounder as well as the receiver knows the time between the first and the
+second click, and by that means he learns that a dot or a dash is made.
+
+ILLUSTRATING THE DOT AND THE DASH.--To illustrate: Let us suppose, for
+convenience, that the downward movement of the lever in the key, and the
+bar in the sounder, make a sharp click, and the return of the lever and
+bar make a dull click. In this case the ear, after a little practice,
+can learn readily how to distinguish the number of downward impulses
+that have been given to the key.
+
+_The Morse Telegraph Code_
+
+A . -        N - .       & . ...
+B - ...      O ..        1 . - - .
+C .. .       P .....     2 .. - ..
+D - . .      Q .. - .    3 ... - .
+E .          R . ..      4 .... -
+F . - .      S ...       5 - - -
+G - - .      T -         6 ......
+H ....       U .. -      7 - - ..
+I ..         V ... -     8 - ....
+J - . - .    W . - -     9 - .. -
+K - . -      X . - ..    0 ---- ------
+L --         Y .. ..
+M - -        Z ... .
+
+EXAMPLE IN USE.--Let us take an example in the word "electrical."
+
+E    L    E    C    T    R    I    C    A    L
+.   --   .   .. .   -  . ..  ..  .. .  . -  --
+
+The operator first makes a dot, which means a sharp and a dull click
+close together; there is then a brief interval, then a lapse, after
+which there is a sharp click, followed, after a comparatively longer
+interval, with the dull click. Now a dash by itself may be an L, a T, or
+the figure 0, dependent upon its length. The short dash is T, and the
+longest dash the figure 0. The operator will soon learn whether it is
+either of these or the letter L, which is intermediate in length.
+
+In time the sender as well as receiver will give a uniform length to the
+dash impulse, so that it may be readily distinguished. In the same way,
+we find that R, which is indicated by a dot, is followed, after a short
+interval, by two dots. This might readily be mistaken for the single dot
+for E and the two dots for I, were it not that the time element in R is
+not as long between the first and second dots, as it ordinarily is
+between the single dot of E when followed by the two dots of I.
+
+
+
+
+CHAPTER X
+
+HIGH TENSION APPARATUS, CONDENSERS, ETC.
+
+
+INDUCTION.--One of the most remarkable things in electricity is the
+action of induction--that property of an electric current which enables
+it to pass from one conductor to another conductor through the air.
+Another singular and interesting thing is that the current so
+transmitted across spaces changes its direction of flow, and,
+furthermore, the tension of such a current may be changed by
+transmitting it from one conductor to another.
+
+LOW AND HIGH TENSION.--In order to effect this latter change--that is,
+to convert it from a low tension to a high tension--coils are used, one
+coil being wound upon the other; one of these coils is called the
+primary and the other the secondary. The primary coil receives the
+current from the battery, or source of electrical power, and the
+secondary coil receives charges, and transmits the current.
+
+For an illustration of this examine Fig. 70, in which you will note a
+coil of heavy wire (A), around which is wound a coil of fine wire (B).
+If, for instance, the primary coil has a low voltage, the secondary
+coil will have a high voltage, or tension. Advantage is taken of this
+phase to use a few cells, as a primary battery, and then, by a set of
+_Induction Coils_, as they are called, to build up a high-tension
+electro-motive force, so that the spark will jump across a gap, as shown
+at C, for the purpose of igniting the charges of gas in a gasoline
+motor; or the current may be used for medical batteries, and for other
+purposes.
+
+[Illustration: _Fig. 70._ INDUCTION COIL AND CIRCUIT]
+
+The current passes, by induction, from the primary to the secondary
+coil. It passes from a large conductor to a small conductor, the small
+conductor having a much greater resistance than the large one.
+
+ELASTIC PROPERTY OF ELECTRICITY.--While electricity has no resiliency,
+like a spring, for instance, still it acts in the manner of a cushion
+under certain conditions. It may be likened to an oscillating spring
+acted upon by a bar.
+
+Referring to Fig. 71, we will assume that the bar A in falling down upon
+the spring B compresses the latter, so that at the time of greatest
+compression the bar goes down as far as the dotted line C. It is obvious
+that the spring B will throw the bar upwardly. Now, electricity appears
+to have a kind of elasticity, which characteristic is taken advantage of
+in order to increase the efficiency of the induction in the coil.
+
+[Illustration: _Fig. 71._ ILLUSTRATING ELASTICITY]
+
+THE CONDENSER.--To make a condenser, prepare two pine boards like A,
+say, eight by ten inches and a half inch thick, and shellac thoroughly
+on all sides. Then prepare sheets of tinfoil (B), six by eight inches in
+size, and also sheets of paraffined paper (C), seven by nine inches in
+dimensions. Also cut out from the waste pieces of tinfoil strips (D),
+one inch by two inches. To build up the condenser, lay down a sheet of
+paraffined paper (C), then a sheet of tinfoil (B), and before putting
+on the next sheet of paraffined paper lay down one of the small strips
+(D) of tinfoil, as shown in the illustration, so that its end projects
+over one end of the board A; then on the second sheet of paraffine paper
+lay another sheet of tinfoil, and on this, at the opposite end, place
+one of the small strips (D), and so on, using from 50 to 100 of the
+tinfoil sheets. When the last paraffine sheet is laid on, the other
+board is placed on top, and the whole bound together, either by wrapping
+cords around the same or by clamping them together with bolts.
+
+[Illustration: _Fig. 72._ CONDENSER]
+
+You may now make a hole through the projecting ends of the strips, and
+you will have two sets of tinfoil sheets, alternately connected together
+at opposite ends of the condenser.
+
+Care should be exercised to leave the paraffine sheets perfect or
+without holes. You can make these sheets yourself by soaking them in
+melted paraffine wax.
+
+CONNECTING UP A CONDENSER.--When completed, one end of the condenser is
+connected up with one terminal of the secondary coil, and the other end
+of the condenser with the other secondary terminal.
+
+[Illustration: _Fig. 73._ HIGH-TENSION CIRCUIT]
+
+In Fig. 73 a high-tension circuit is shown. Two coils, side by side, are
+always used to show an induction coil, and a condenser is generally
+shown, as illustrated, by means of a pair of forks, one resting within
+the other.
+
+THE INTERRUPTER.--One other piece of mechanism is necessary, and that is
+an _Interrupter_, for the purpose of getting the effect of the
+pulsations given out by the secondary coil.
+
+A simple current interrupter is made as follows: Prepare a wooden base
+(A), one inch thick, six inches wide, and twelve inches long. Upon this
+mount a toothed wheel (B), six inches in diameter, of thin sheet metal,
+or a brass gear wheel will answer the purpose. The standard (C), which
+supports the wheel, may be of metal bent up to form two posts, between
+which the crankshaft (D) is journaled. The base of the posts has an
+extension plate (E), with a binding post for a wire. At the front end of
+the base is an L-shaped strip (F), with a binding post for a wire
+connection, and the upwardly projecting part of the strip contacts with
+the toothed wheel. When the wheel B is rotated the spring finger (F)
+snaps from one tooth to the next, so that, momentarily, the current is
+broken, and the frequency is dependent upon the speed imparted to the
+wheel.
+
+[Illustration: _Fig. 74._ CURRENT INTERRUPTER]
+
+USES OF HIGH-TENSION COILS.--This high-tension coil is made use of, and
+is the essential apparatus in wireless telegraphy, as we shall see in
+the chapter treating upon that subject.
+
+
+
+
+CHAPTER XI
+
+WIRELESS TELEGRAPHY
+
+
+TELEGRAPHING WITHOUT WIRES.--Wireless telegraphy is an outgrowth of the
+ordinary telegraph system. When Maxwell, and, later on, Hertz,
+discovered that electricity, magnetism, and light were transmitted
+through the ether, and that they differed only in their wave lengths,
+they laid the foundations for wireless telegraphy. Ether is a substance
+which is millions and millions of times lighter than air, and it
+pervades all space. It is so unstable that it is constantly in motion,
+and this phase led some one to suggest that if a proper electrical
+apparatus could be made, the ether would thereby be disturbed
+sufficiently so that its impulses would extend out a distance
+proportioned to the intensity of the electrical agitation thereby
+created.
+
+SURGING CHARACTER OF HIGH-TENSION CURRENTS.--When a current of
+electricity is sent through a wire, hundreds of miles in length, the
+current surges back and forth on the wire many thousands of times a
+second. Light comes to us from the sun, over 90,000,000 of miles,
+through the ether. It is as reasonable to suppose, or infer, that the
+ether can, therefore, convey an electrical impulse as readily as does a
+wire.
+
+It is on this principle that impulses are sent for thousands of miles,
+and no doubt they extend even farther, if the proper mechanism could be
+devised to detect movement of the waves so propagated.
+
+THE COHERER.--The instrument for detecting these impulses, or
+disturbances, in the ether is generally called a _coherer_, although
+detector is the term which is most satisfactory. The name coherer comes
+from the first practical instrument made for this purpose.
+
+[Illustration: _Fig. 75._ WIRELESS TELEGRAPHY COHERER]
+
+HOW MADE.--The coherer is simply a tube, say, of glass, within which is
+placed iron filings. When the oscillations surge through the secondary
+coil the pressure or potentiality of the current finally causes it to
+leap across the small space separating the filings and, as it were, it
+welds together their edges so that a current freely passes. The
+bringing together of the particles, under these conditions, is called
+cohering.
+
+Fig. 75 shows the simplest form of coherer. The posts (A) are firmly
+affixed to the base (B), each post having an adjusting screw (C) in its
+upper end, and these screw downwardly against and serve to bind a pair
+of horizontal rods (D), the inner ends of which closely approach each
+other. These may be adjusted so as to be as near together or as far
+apart as desired. E is a glass tube in which the ends of the rods (D)
+rest, and between the separated ends of the rods (D) the iron filings
+(F) are placed.
+
+THE DECOHERERS.--For the purpose of causing the metal filings to fall
+apart, or decohere, the tube is tapped lightly, and this is done by a
+little object like the clapper of an electric bell.
+
+In practice, the coils and the parts directly connected with it are put
+together on one base.
+
+THE SENDING APPARATUS.--Fig. 76 shows a section of a coil with its
+connection in the sending station. The spark gap rods (A) may be swung
+so as to bring them closer together or farther apart, but they must not
+at any time contact with each other.
+
+The induction coil has one terminal of the primary coil connected up by
+a wire (B) with one post of a telegraph key, and the other post of the
+key has a wire connection (C), with one side of a storage battery. The
+other side of the battery has a wire (D) running to the other terminal
+of the primary.
+
+[Illustration: _Fig. 76._ WIRELESS SENDING APPARATUS]
+
+The secondary coil has one of its terminals connected with a binding
+post (E). This binding post has an adjustable rod with a knob (F) on its
+end, and the other binding post (G), which is connected up with the
+other terminal of the secondary coil, carries a similar adjusting rod
+with a knob (H).
+
+From the post (E) is a wire (I), which extends upwardly, and is called
+the aerial wire, or wire for the antennae, and this wire also connects
+with one side of the condenser by a conductor (J). The ground wire (K)
+connects with the other binding post (G), and a branch wire (L) also
+connects the ground wire (K) with one end of the condenser.
+
+[Illustration: _Fig. 77._ WIRELESS RECEIVING APPARATUS]
+
+THE RECEIVING APPARATUS.--The receiving station, on the other hand, has
+neither condenser, induction coil, nor key. When the apparatus is in
+operation, the coherer switch is closed, and the instant a current
+passes through the coherer and operates the telegraph sounder, the
+galvanometer indicates the current.
+
+Of course, when the coherer switch is closed, the battery operates the
+decoherer.
+
+HOW THE CIRCUITS ARE FORMED.--By referring again to Fig. 76, it will be
+seen that when the key is depressed, a circuit is formed from the
+battery through wire B to the primary coil, and back again to the
+battery through wire D. The secondary coil is thereby energized, and,
+when the full potential is reached, the current leaps across the gap
+formed between the two knobs (F, H), thereby setting up a disturbance in
+the ether which is transmitted through space in all directions.
+
+It is this impulse, or disturbance, which is received by the coherer at
+the receiving station, and which is indicated by the telegraph sounder.
+
+
+
+
+CHAPTER XII
+
+THE TELEPHONE
+
+
+VIBRATIONS.--Every manifestation in nature is by way of vibration. The
+beating of the heart, the action of the legs in walking, the winking of
+the eyelid; the impulses from the sun, which we call light; sound, taste
+and color appeal to our senses by vibratory means, and, as we have
+hereinbefore stated, the manifestations of electricity and magnetism are
+merely vibrations of different wave lengths.
+
+THE ACOUSTIC TELEPHONE.--That sound is merely a product of vibrations
+may be proven in many ways. One of the earliest forms of telephones was
+simply a "sound" telephone, called the _Acoustic Telephone_. The
+principle of this may be illustrated as follows:
+
+Take two cups (A, B), as in Fig. 78, punch a small hole through the
+bottom of each, and run a string or wire (C) from the hole of one cup to
+that of the other, and secure it at both ends so it may be drawn taut.
+Now, by talking into the cup (A) the bottom of it will vibrate to and
+fro, as shown by the dotted lines and thereby cause the bottom of the
+other cup (B) to vibrate in like manner, and in so vibrating it will
+receive not only the same amplitude, but also the same character of
+vibrations as the cup (A) gave forth.
+
+[Illustration: _Fig. 78._ ACOUSTIC TELEPHONE]
+
+[Illustration: _Fig. 79._ ILLUSTRATING VIBRATIONS]
+
+SOUND WAVES.--Sound waves are long and short; the long waves giving
+sounds which are low in the musical scale, and the short waves high
+musical tones. You may easily determine this by the following
+experiment:
+
+Stretch a wire, as at B (Fig. 79), fairly tight, and then vibrate it.
+The amplitude of the vibration will be as indicated by dotted line A.
+Now, stretch it very tight, as at C, so that the amplitude of vibration
+will be as shown at E. By putting your ear close to the string you will
+find that while A has a low pitch, C is very much higher. This is the
+principle on which stringed instruments are built. You will note that
+the wave length, which represents the distance between the dotted lines
+A is much greater than E.
+
+HEARING ELECTRICITY.--In electricity, mechanism has been made to enable
+man to note the action of the current. By means of the armature,
+vibrating in front of a magnet, we can see its manifestations. It is now
+but a step to devise some means whereby we may hear it. In this, as in
+everything else electrically, the magnet comes into play.
+
+[Illustration: _Fig. 80._ THE MAGNETIC FIELD]
+
+In the chapter on magnetism, it was stated that the magnetic field
+extended out beyond the magnet, so that if we were able to see the
+magnetism, the end of a magnet would appear to us something like a
+moving field, represented by the dotted lines in Fig. 80.
+
+The magnetic field is shown in Fig. 80 at only one end, but its
+manifestations are alike at both ends. It will be seen that the magnetic
+field extends out to a considerable distance and has quite a radius of
+influence.
+
+THE DIAPHRAGM IN A MAGNETIC FIELD.--If, now, we put a diaphragm (A) in
+this magnetic field, close up to the end of the magnet, but not so close
+as to touch it, and then push it in and out, or talk into it so that the
+sound waves strike it, the movement or the vibration of the diaphragm
+(A) will disturb the magnetic field emanating from the magnet, and this
+disturbance of the magnetic field at one end of the magnet also affects
+the magnetic field at the other end in the same way, so that the
+disturbance there will be of the same amplitude. It will also display
+the same characteristics as did the magnetic field when the diaphragm
+(A) disturbed it.
+
+A SIMPLE TELEPHONE CIRCUIT.--From this simple fact grew the telephone.
+If two magnets are connected up in the same circuit, so that the
+magnetic fields of the two magnets have the same source of electric
+power, the disturbance of one diaphragm will affect the other similarly,
+just the same as the two magnetic fields of the single magnet are
+disturbed in unison.
+
+HOW TO MAKE A TELEPHONE.--For experimental and testing purposes two of
+these telephones should be made at the same time. The case or holder
+(A) may be made either of hard wood or hard rubber, so that it is of
+insulating material. The core (B) is of soft iron, 3/8 inch in diameter
+and 5 inches long, bored and threaded at one end to receive a screw (C)
+which passes through the end of the case (A).
+
+The enlarged end of the case should be, exteriorly, 2-1/4 inches in
+diameter, and the body of the case 1 inch in diameter.
+
+[Illustration: _Fig. 81._ SECTION OF TELEPHONE RECEIVER]
+
+Interiorly, the large end of the case is provided with a circular recess
+1-3/4 inches in diameter and adapted to receive therein a spool which
+is, diametrically, a little smaller than the recess. The spool fits
+fairly tight upon the end of the core, and when in position rests
+against an annular shoulder in the recess. A hollow space (F) is thus
+provided behind the spool (D), so the two wires from the magnet may
+have room where they emerge from the spool.
+
+The spool is a little shorter than the distance between the shoulder (E)
+and the end of the casing, at G, and the core projects only a short
+distance beyond the end of the spool, so that when the diaphragm (H) is
+put upon the end of the case, and held there by screws (I) it will not
+touch the end of the core. A wooden or rubber mouthpiece (J) is then
+turned up to fit over the end of the case.
+
+[Illustration: _Fig. 82._ THE MAGNET AND RECEIVER HEAD]
+
+The spool (D) is made of hard rubber, and is wound with No. 24
+silk-covered wire, the windings to be well insulated from each other.
+The two ends of the wire are brought out, and threaded through holes (K)
+drilled longitudinally through the walls of the case, and affixed to the
+end by means of screws (L), so that the two wires may be brought
+together and connected with a duplex wire (M).
+
+As the screw (C), which holds the core in place, has its head hidden
+within a recess, which can be closed up by wax, the two terminals of the
+wires are well separated so that short-circuiting cannot take place.
+
+TELEPHONE CONNECTIONS.--The simplest form of telephone connection is
+shown in Fig. 83. This has merely the two telephones (A and B), with a
+single battery (C) to supply electricity for both. One line wire (D)
+connects the two telephones directly, while the other line (E) has the
+battery in its circuit.
+
+[Illustration: _Fig. 83._ SIMPLE TELEPHONE CONNECTION]
+
+COMPLETE INSTALLATION.--To install a more complete system requires, at
+each end, a switch, a battery and an electro-magneto bell. You may use,
+for this purpose, a bell, made as shown in the chapter on bells.
+
+Fig. 84 shows such a circuit. We now dispense with one of the line
+wires, because it has been found that the ground between the two
+stations serves as a conductor, so that only one line wire (A) is
+necessary to connect directly with the telephones of the two stations.
+The telephones (B, B', respectively) have wires (C, C') running to the
+pivots of double-throw switches (D, D'), one terminal of the switches
+having wires (E, E'), which go to electric bells (F, F'), and from the
+bells are other wires (G, G'), which go to the ground. The ground wires
+also have wires (H, H'), which go to the other terminals of the switch
+(D, D'). The double-throw switch (D, D'), in the two stations, is thrown
+over so the current, if any should pass through, will go through the
+bell to the ground, through the wires (E, G or E', G').
+
+[Illustration: _Fig. 84._ TELEPHONE STATIONS IN CIRCUIT]
+
+Now, supposing the switch (D'), in station 2, should be thrown over so
+it contacts with the wire (H'). It is obvious that the current will then
+flow from the battery (I') through wires (H', C') and line (A) to
+station 1; then through wire C, switch D, wire E to the bell F, to the
+ground through wire G. From wire G the current returns through the
+ground to station 2, where it flows up wire G' to the battery, thereby
+completing the circuit.
+
+[Illustration: _Fig. 85._ ILLUSTRATING LIGHT CONTACT POINTS]
+
+The operator at station 2, having given the signal, again throws his
+switch (D') back to the position shown in Fig. 84, and the operator at
+station 1 throws on his switch (D), so as to ring the bell in station 2,
+thereby answering the signal, which means that both switches are again
+to be thrown over so they contact with the battery wires (H and H'),
+respectively. When both are thus thrown over, the bells (G, G') are cut
+out of the circuit, and the batteries are both thrown in, so that the
+telephones are now ready for talking purposes.
+
+MICROPHONE.--Originally this form of telephone system was generally
+employed, but it was found that for long distances a more sensitive
+instrument was necessary.
+
+LIGHT CONTACT POINTS.--In 1877 Professor Hughes discovered,
+accidentally, that a light contact point in an electric circuit
+augmented the sound in a telephone circuit. If, for instance, a light
+pin, or a nail (A, Fig. 85) should be used to connect the severed ends
+of a wire (B), the sounds in the telephone not only would be louder, but
+they would be more distinct, and the first instrument made practically,
+to demonstrate this, is shown in Fig. 86.
+
+[Illustration: _Fig. 86._ MICROPHONE]
+
+[Illustration: _Fig. 87._ TRANSMITTER]
+
+HOW TO MAKE A MICROPHONE.--This instrument has simply a base (A) of
+wood, and near one end is a perpendicular sounding-board (B) of wood, to
+one side of which is attached, by wax or otherwise, a pair of carbon
+blocks (C, D). The lower carbon block (C) has a cup-shaped depression in
+its upper side, and the upper block has a similar depression in its
+lower side. A carbon pencil (E) is lightly held within these cups, so
+that the lightest contact of the upper end of the pencil with the
+carbon block, makes the instrument so sensitive that a fly, walking upon
+the sounding-board, may be distinctly heard through the telephone which
+is in the circuit.
+
+MICROPHONE THE FATHER OF THE TRANSMITTER.--This instrument has been
+greatly modified, and is now used as a transmitter, the latter thereby
+taking the place of the pin (A), shown in Fig. 85.
+
+AUTOMATIC CUT-OUTS FOR TELEPHONES.--In the operation of the telephone,
+the great drawback originally was in inducing users of the lines to
+replace or adjust their instruments carefully. When switches were used,
+they would forget to throw them back, and all sorts of trouble resulted.
+
+It was found necessary to provide an automatic means for throwing in and
+cutting out an instrument, this being done by hanging the telephone on
+the hook, so that the act merely of leaving the telephone made it
+necessary, in replacing the instrument, to cut out the apparatus.
+
+Before describing the circuiting required for these improvements, we
+show, in Fig. 87, a section of a transmitter.
+
+A cup-shaped case (A) is provided, made of some insulating material,
+which has a diaphragm (B) secured at its open side. This diaphragm
+carries the carbon pencil (C) on one side and from the blocks which
+support the carbon pencil the wires run to binding posts on the case.
+Of course the carbon supporting posts must be insulated from each other,
+so the current will go through the carbon pencil (C).
+
+COMPLETE CIRCUITING WITH TRANSMITTER.--In showing the circuiting (Fig.
+88) it will not be possible to illustrate the boxes, or casings, which
+receive the various instruments. For instance, the hook which carries
+the telephone or the receiver, is hinged within the transmitter box. The
+circuiting is all that it is intended to show.
+
+[Illustration: _Fig. 88._ COMPLETE TELEPHONIC CIRCUIT]
+
+The batteries of the two stations are connected up by a wire (A), unless
+a ground circuit is used. The other side of each battery has a wire
+connection (B, B') with one terminal of the transmitter, and the other
+terminal of the transmitter has a wire (C, C') which goes to the
+receiver. From the other terminal of the receiver is a wire (D, D')
+which leads to the upper stop contact (E, E') of the telephone hook. A
+wire (F, F') from the lower stop contact (G, G') of the hook goes to one
+terminal of the bell, and from the other terminal of the bell is a wire
+(H, H') which makes connection with the line wire (A). In order to make
+a complete circuit between the two stations, a line wire (I) is run from
+the pivot of the hook in station 1 to the pivot of the hook in station
+2.
+
+In the diagram, it is assumed that the receivers are on the hooks, and
+that both hooks are, therefore, in circuit with the lower contacts (G,
+G'), so that the transmitter and receiver are both out of circuit with
+the batteries, and the bell in circuit; but the moment the receiver, for
+instance, in station 1 is taken off the hook, the latter springs up so
+that it contacts with the stop (E), thus establishing a circuit through
+the line wire (I) to the hook of station 2, and from the hook through
+line (F') to the bell. From the bell, the line (A) carries the current
+back to the battery of station (A), thence through the wire (B) to the
+transmitter wire (C) to receiver and wire (D) to the post (E), thereby
+completing the circuit.
+
+When, at station 2, the receiver is taken off the hook, and the latter
+contacts with the post (E'), the transmitter and receiver of both
+stations are in circuit with each other, but both bells are cut out.
+
+
+
+
+CHAPTER XIII
+
+ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING
+
+
+DECOMPOSING LIQUIDS.--During the earlier experiments in the field of
+electricity, after the battery or cell was discovered, it was noted that
+when a current was formed in the cell, the electrolyte was charged and
+gases evolved from it. A similar action takes place when a current of
+electricity passes through a liquid, with the result that the liquid is
+decomposed--that is, the liquid is broken up into its original
+compounds. Thus, water is composed of two parts, by bulk, of hydrogen
+and of oxygen, so that if two electrodes are placed in water, and a
+current is sent through the electrodes in either direction, all the
+water will finally disappear in the form of hydrogen and oxygen gases.
+
+MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen
+is set free at the negative pole and the oxygen at the positive pole. A
+simple apparatus, which any boy can make, to generate pure oxygen and
+pure hydrogen, is shown in Fig. 89.
+
+It is constructed of a glass or earthen jar (A), preferably square, to
+which is fitted a wooden top (B), this top being provided with a
+packing ring (C), so as to make it air-tight. Within is a vertical
+partition (D), the edges of which, below the cap, fit tightly against
+the inner walls of the jar. This partition extends down into the jar a
+sufficient distance so it will terminate below the water level. A pipe
+is fitted through the top on each side of the partition, and each pipe
+has a valve. An electrode, of any convenient metal, is secured at its
+upper end to the top of the cap, on each side of the partition. These
+electrodes extend down to the bottom of the jar, and an electric wire
+connects with each of them at the top.
+
+[Illustration: _Fig. 89._ DEVICE FOR MAKING HYDROGEN AND OXYGEN]
+
+If a current of electricity is passed through the wires and the
+electrodes, in the direction shown by the darts, hydrogen will form at
+the negative pole, and oxygen at the positive pole. These gases will
+escape upwardly, so that they will be trapped in their respective
+compartments, and may be drawn off by means of the pipes.
+
+PURIFYING WATER.--Advantage is taken of this electrolytic action, to
+purify water. Oxygen is the most wonderful chemical in nature. It is
+called the acid-maker of the universe. The name is derived from two
+words, _oxy_ and _gen_; one denoting oxydation, and the other that it
+generates. In other words, it is the _generator of oxides_. It is the
+element which, when united with any other element, produces an acid, an
+alkali or a neutral compound.
+
+RUST.--For instance, iron is largely composed of ferric acid. When
+oxygen, in a free or gaseous state, comes into contact with iron, it
+produces ferrous oxide, which is recognized as rust.
+
+OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of
+animal life, like bacteria or germs in water, succumb to free oxygen. By
+_free oxygen_ is meant oxygen in the form of gas.
+
+COMPOSITION OF WATER.--Now, water, in which harmful germs live, is
+one-third oxygen. Nevertheless, the germs thrive in water, because the
+oxygen is in a compound state, and, therefore, not an active agent. But
+if oxygen, in the form of gas, can be forced through water, it will
+attack the germs, and destroy them.
+
+COMMON AIR NOT A GOOD PURIFIER.--Water may be purified, to a certain
+extent, by forcing common air through it, and the foulest water, if run
+over rocks, will be purified, in a measure, because air is intermingled
+with it. But common air is composed of four-fifths nitrogen, and only
+one-fifth oxygen, and, as nitrogen is the staple article of food for
+bacteria, the purifying method by air is not effectual.
+
+PURE OXYGEN.--When, however, oxygen is generated from water, by means of
+electrolysis, it is pure; hence is more active and is not tainted by a
+life-giving substance for germs, such as nitrogen.
+
+The mechanism usually employed for purifying water is shown in Fig. 90.
+
+A WATER PURIFIER.--The case (A, Fig. 90) may be made of metal or of an
+insulating material. If made of metal it must be insulated within with
+slate, glass, marble or hard rubber, as shown at B. The case is provided
+with exterior flanges (C, D), with upper and lower ends, and it is
+mounted upon a base plate (E) and affixed thereto by bolts. The upper
+end has a conically-formed cap (F) bolted to the flanges (C), and this
+has an outlet to which a pipe (G) is attached. The water inlet pipe (H)
+passes through the lower end of the case (A). The electrodes (I, J) are
+secured, vertically, within the case, separated from each other
+equidistant, each alternate electrode being connected up with one wire
+(K), and the alternate electrodes with a wire (L).
+
+[Illustration: _Fig. 90._ ELECTRIC WATER PURIFIER]
+
+When the water passes upwardly, the decomposed or gaseous oxygen
+percolates through the water and thus attacks the germs and destroys
+them.
+
+THE USE OF HYDROGEN IN PURIFICATION.--On the other hand, the hydrogen
+also plays an important part in purifying the water. This depends upon
+the material of which the electrodes are made. Aluminum is by far the
+best material, as it is one of nature's most active purifiers. All clay
+contains aluminum, in what is known as the sulphate form, and water
+passing through the clay of the earth thereby becomes purified, because
+of this element.
+
+ALUMINUM ELECTRODES.--When this material is used as the electrodes in
+water, hydrate of aluminum is formed, or a compound of hydrogen and
+oxygen with aluminum. The product of decomposition is a flocculent
+matter which moves upwardly through the water, giving it a milky
+appearance. This substance is like gelatine, so that it entangles or
+enmeshes the germ life and prevents it from passing through a filter.
+
+If no filter is used, this flocculent matter, as soon as it has given
+off the gases, will settle to the bottom and carry with it all
+decomposed matter, such as germs and other organic matter attacked by
+the oxygen, which has become entangled in the aluminum hydrate.
+
+ELECTRIC HAND PURIFIER.--An interesting and serviceable little purifier
+may be made by any boy with the simplest tools, by cutting out three
+pieces of sheet aluminum. Hard rolled is best for the purpose. It is
+better to have one of the sheets (A), the middle one, thicker than the
+two outer plates (B).
+
+[Illustration: _Fig. 91._ PORTABLE ELECTRIC PURIFIER]
+
+Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half
+inch from the upper ends of the two outside plates (B, B) bore bolt
+holes (C), each of these holes being a quarter of an inch from the edge
+of the plate. The inside plate (A) has two large holes (D) corresponding
+with the small holes (C) in the outside plates. At the upper end of this
+plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a
+small hole for a bolt. Next cut out two hard-rubber blocks (F), each
+1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole
+(G) through each, corresponding with the small holes (C) in the plates
+(B). The machine is now ready to be assembled. If the inner plate is 1/8
+inch thick and the outer plates each 1/16 inch thick, use two small
+eighth-inch bolts 1-1/4 inches long, and clamp together the three
+plates with these bolts. One of the bolts may be used to attach thereto
+one of the electric wires (H), and the other wire (I) is attached by a
+bolt to the wing (E).
+
+[Illustration: _Figs. 92-95._ DETAILS OF PORTABLE PURIFIER]
+
+Such a device will answer for a 110-volt circuit, in ordinary water. Now
+fill a glass nearly full of water, and stand the purifier in the glass.
+Within a few minutes the action of electrolysis will be apparent by the
+formation of numerous bubbles on the plates, followed by the
+decomposition of the organic matter in the water. At first the
+flocculent decomposed matter will rise to the surface of the water, but
+before many minutes it will settle to the bottom of the glass and leave
+clear water above.
+
+PURIFICATION AND SEPARATION OF METALS.--This electrolytic action is
+utilized in metallurgy for the purpose of producing pure metals, but it
+is more largely used to separate copper from its base. In order to
+utilize a current for this purpose, a high ampere flow and low voltage
+are required. The sheets of copper, containing all of its impurities,
+are placed within a tank, parallel with a thin copper sheet. The impure
+sheet is connected with the positive pole of an electroplating dynamo,
+and the thin sheet of copper is connected with the negative pole. The
+electrolyte in the tank is a solution of sulphate of copper. The action
+of the current will cause the pure copper in the impure sheet to
+disintegrate and it is then carried over and deposited upon the thin
+sheet, this action continuing until the impure sheet is entirely eaten
+away. All the impurities which were in the sheet fall to the bottom of
+the tank.
+
+Other metals are treated in the same way, and this treatment has a very
+wide range of usefulness.
+
+ELECTROPLATING.--The next feature to be considered in electrolysis is a
+most interesting and useful one, because a cheap or inferior metal may
+be coated by a more expensive metal. Silver and nickel plating are
+brought about by this action of a current passing through metals, which
+are immersed in an electrolyte.
+
+PLATING IRON WITH COPPER.--We have room in this chapter for only one
+concrete example of this work, which, with suitable modifications, is an
+example of the art as practiced commercially. Iron, to a considerable
+extent, is now being coated with copper to preserve it from rust. To
+carry out this work, however, an electroplating dynamo, of large
+amperage, is required, the amperage, of course, depending upon the
+surface to be treated at one time. The pressure should not exceed 5
+volts.
+
+The iron surface to be treated should first be thoroughly cleansed, and
+then immediately put into a tank containing a cyanide of copper
+solution. Two forms of copper solution are used, namely, the cyanide,
+which is a salt solution of copper, and the sulphate, which is an acid
+solution of copper. Cyanide is first used because it does not attack the
+iron, as would be the case if the sulphate solution should first come
+into contact with the iron.
+
+A sheet of copper, termed the anode, is then placed within the tank,
+parallel with the surface to be plated, known as the cathode, and so
+mounted that it may be adjusted to or from the iron surface, or cathode.
+A direct current of electricity is then caused to flow through the
+copper plate and into the iron plate or surface, and the plating
+proceeded with until the iron surface has a thin film of copper
+deposited thereon. This is a slow process with the cyanide solution, so
+it is discontinued as soon as possible, after the iron surface has been
+completely covered with copper. This copper surface is thoroughly
+cleaned off to remove therefrom the saline or alkaline solution, and it
+is then immersed within a bath, containing a solution of sulphate of
+copper. The current is then thrown on and allowed so to remain until it
+has deposited the proper thickness of copper.
+
+DIRECTION OF CURRENT.--If a copper and an iron plate are put into a
+copper solution and connected up in circuit with each other, a primary
+battery is thereby formed, which will generate electricity. In this
+case, the iron will be positive and the copper negative, so that the
+current within such a cell would flow from the iron (in this instance,
+the anode) to the negative, or cathode.
+
+The action of electroplating reverses this process and causes the
+current to flow from the copper to the iron (in this instance, the
+cathode).
+
+
+
+
+CHAPTER XIV
+
+ELECTRIC HEATING, THERMO ELECTRICITY
+
+
+GENERATING HEAT IN A WIRE.--When a current of electricity passes through
+a conductor, like a wire, more or less heat is developed in the
+conductor. This heat may be so small that it cannot be measured, but it
+is, nevertheless, present in a greater or less degree. Conductors offer
+a resistance to the passage of a current, just the same as water finds a
+resistance in pipes through which it passes. This resistance is measured
+in ohms, as explained in a preceding chapter, and it is this resistance
+which is utilized for electric heating.
+
+RESISTANCE OF SUBSTANCES.--Silver offers less resistance to the passage
+of a current than any other metal, the next in order is copper, while
+iron is, comparatively, a poor conductor.
+
+The following is a partial list of metals, showing their relative
+conductivity:
+
+Silver              1.
+Copper              1.04 to 1.09
+Gold                1.38 to 1.41
+Aluminum            1.64
+Zinc                3.79
+Nickel              4.69
+Iron                6.56
+Tin                 8.9
+Lead               13.2
+German Silver      12.2 to 15
+
+From this table it will be seen that, for instance, iron offers six and
+a half times the resistance of silver, and that German silver has
+fifteen times the resistance of silver.
+
+This table is made up of strands of the different metals of the same
+diameters and lengths, so as to obtain their relative values.
+
+SIZES OF CONDUCTORS.--Another thing, however, must be understood. If two
+conductors of the same metal, having different diameters, receive the
+same current of electricity, the small conductor will offer a greater
+resistance than the large conductor, hence will generate more heat. This
+can be offset by increasing the diameter of the conductor. The metal
+used is, therefore, of importance, on account of the cost involved.
+
+COMPARISON OF METALS.--A conductor of aluminum, say, 10 feet long and of
+the same weight as copper, has a diameter two and a quarter times
+greater than copper; but as the resistance of aluminum is 50 per cent.
+more than that of silver, it will be seen that, weight for weight,
+copper is the cheaper, particularly as aluminum costs fully three times
+as much as copper.
+
+[Illustration: _Fig. 96._ SIMPLE ELECTRIC HEATER]
+
+The table shows that German silver has the highest resistance. Of
+course, there are other metals, like antimony, platinum and the like,
+which have still higher resistance. German silver, however, is most
+commonly used, although there are various alloys of metal made which
+have high resistance and are cheaper.
+
+The principle of all electric heaters is the same, namely, the
+resistance of a conductor to the passage of a current, and an
+illustration of a water heater will show the elementary principles in
+all of these devices.
+
+A SIMPLE ELECTRIC HEATER.--In Fig. 96 the illustration shows a cup or
+holder (A) for the wire, made of hard rubber. This may be of such
+diameter as to fit upon and form the cover for a glass (B). The rubber
+should be 1/2 inch thick. Two holes are bored through the rubber cup,
+and through them are screwed two round-headed screws (C, D), each screw
+being 1-1/2 inches long, so they will project an inch below the cap.
+Each screw should have a small hole in its lower end to receive a pin
+(E) which will prevent the resistance wire from slipping off.
+
+The resistance wire (F) is coiled for a suitable length, dependent upon
+the current used, one end being fastened by wrapping it around the screw
+(C). The other end of the wire is then brought upwardly through the
+interior of the coil and secured in like manner to the other screw (D).
+
+Caution must be used to prevent the different coils or turns from
+touching each other. When completed, the coil may be immersed in water,
+the current turned on, and left so until the water is sufficiently
+heated.
+
+[Illustration: _Figs. 97-98._ RESISTANCE DEVICE]
+
+HOW TO ARRANGE FOR QUANTITY OF CURRENT USED.--It is difficult to
+determine just the proper length the coil should be, or the sizes of the
+wire, unless you know what kind of current you have. You may, however,
+rig up your own apparatus for the purpose of making it fit your heater,
+by preparing a base of wood (A) 8 inches long, 3 inches wide and 1 inch
+thick. On this mount four electric lamp sockets (B). Then connect the
+inlet wire (C) by means of short pieces of wire (D) with all the sockets
+on one side. The outlet wire (E) should then be connected up with the
+other sides of the sockets by the short wires (F). If, now, we have one
+16-candlepower lamp in one of the sockets, there is a half ampere going
+through the wires (C, F). If there are two lamps on the board you will
+have 1 ampere, and so on. By this means you may readily determine how
+much current you are using and it will also afford you a means of
+finding out whether you have too much or too little wire in your coil to
+do the work.
+
+[Illustration: _Fig. 99._ PLAN VIEW OF ELECTRIC IRON]
+
+AN ELECTRIC IRON.--An electric iron is made in the same way. The upper
+side of a flatiron has a circular or oval depression (A) cast therein,
+and a spool of slate (B) is made so it will fit into the depression and
+the high resistance wire (C) is wound around this spool, and insulating
+material, such as asbestos, must be used to pack around it. Centrally,
+the slate spool has an upwardly projecting circular extension (D) which
+passes through the cap or cover (E) of the iron. The wires of the
+resistance coil are then brought through this circular extension and
+are connected up with the source of electrical supply. Wires are now
+sold for this purpose, which are adapted to withstand an intense heat.
+
+[Illustration: _Fig. 100._ SECTION OF ELECTRIC IRON]
+
+The foregoing example of the use of the current, through resistance
+wires, has a very wide application, and any boy, with these examples
+before him, can readily make these devices.
+
+THERMO ELECTRICITY.--It has long been the dream of scientists to convert
+heat directly into electricity. The present practice is to use a boiler
+to generate steam, an engine to provide the motion, and a dynamo to
+convert that motion into electricity. The result is that there is loss
+in the process of converting the fuel heat into steam; loss to change
+the steam into motion, and loss to make electricity out of the motion
+of the engine. By using water-power there is less actual loss; but
+water-power is not available everywhere.
+
+CONVERTING HEAT DIRECTLY INTO ELECTRICITY.--Heat may be converted
+directly into electricity without using a boiler, an engine or a dynamo,
+but it has not been successful from a commercial standpoint. It is
+interesting, however, to know and understand the subject, and for that
+reason it is explained herein.
+
+METALS; ELECTRIC POSITIVE-NEGATIVE.--To understand the principle, it may
+be stated that all metals are electrically positive-negative to each
+other. You will remember that it has hereinbefore been stated that if,
+for instance, iron and copper are put into an acid solution, a current
+will be created or generated thereby. So with zinc and copper, the usual
+primary battery elements. In all such cases an electrolyte is used.
+
+Thermo-electricity dispenses with the electrolyte, and nothing is used
+but the metallic elements and heat. The word thermo means heat. If, now,
+we can select two strips of different metals, and place them as far
+apart as possible--that is, in their positive-negative relations with
+each other, and unite the end of one with one end of other by means of a
+rivet, and then heat the riveted ends, a current will be generated in
+the strips. If, for instance, we use an iron in conjunction with a
+copper strip, the current will flow from the copper to the iron, because
+copper is positive to iron, and iron negative to copper. It is from this
+that the term positive-negative is taken.
+
+The two metals most available, which are thus farthest apart in the
+scale of positive-negative relation, are bismuth and antimony.
+
+[Illustration: _Fig. 101._ THERMO-ELECTRIC COUPLE]
+
+In Fig. 101 is shown a thermo-electric couple (A, B) riveted together,
+with thin outer ends connected by means of a wire (C) to form a circuit.
+A galvanometer (D) or other current-testing means is placed in this
+circuit. A lamp is placed below the joined ends.
+
+THERMO-ELECTRIC COUPLES.--Any number of these couples may be put
+together and joined at each end to a common wire and a fairly large flow
+of current obtained thereby.
+
+One thing must be observed: A current will be generated only so long as
+there exists a difference in temperature between the inner and the outer
+ends of the bars (A, B). This may be accomplished by water, or any other
+cooling means which may suggest itself.
+
+
+
+
+CHAPTER XV
+
+ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS AND
+RECTIFIERS
+
+
+DIRECT CURRENT.--When a current of electricity is generated by a cell,
+it is assumed to move along the wire in one direction, in a steady,
+continuous flow, and is called a _direct_ current. This direct current
+is a natural one if generated by a cell.
+
+ALTERNATING CURRENT.--On the other hand, the natural current generated
+by a dynamo is alternating in its character--that is, it is not a
+direct, steady flow in one direction, but, instead, it flows for an
+instant in one direction, then in the other direction, and so on.
+
+A direct-current dynamo such as we have shown in Chapter IV, is much
+easier to explain, hence it is illustrated to show the third method used
+in generating an electric current.
+
+It is a difficult matter to explain the principle and operation of
+alternating current machines, without becoming, in a measure, too
+technical for the purposes of this book, but it is important to know the
+fundamentals involved, so that the operation and uses of certain
+apparatus, like the choking coil, transformers, rectifiers and
+converters, may be explained.
+
+THE MAGNETIC FIELD.--It has been stated that when a wire passes through
+the magnetic field of a magnet, so as to cut the lines of force flowing
+out from the end of a magnet, the wire will receive a charge of
+electricity.
+
+[Illustration: _Fig. 102._ CUTTING A MAGNETIC FIELD]
+
+To explain this, study Fig. 102, in which is a bar magnet (A). If we
+take a metal wire (B) and bend it in the form of a loop, as shown, and
+mount the ends on journal-bearing blocks, the wire may be rotated so
+that the loop will pass through the magnetic field. When this takes
+place, the wire receives a charge of electricity, which moves, say, in
+the direction of the darts, and will make a complete circuit if the ends
+of the looped wire are joined, as shown by the conductor (D).
+
+ACTION OF THE MAGNETIZED WIRE.--You will remember, also that we have
+pointed out how, when a current passes over a wire, it has a magnetic
+field extending out around it at all points, so that while it is passing
+through the magnetic field of the magnet (A), it becomes, in a measure,
+a magnet of its own and tries to set up in business for itself as a
+generator of electricity. But when the loop leaves the magnetic field,
+the magnetic or electrical impulse in the wire also leaves it.
+
+THE MOVEMENT OF A CURRENT IN A CHARGED WIRE.--Your attention is
+directed, also, to another statement, heretofore made, namely, that when
+a current from a charged wire passes by induction to a wire across
+space, so as to charge it with an electric current, it moves along the
+charged wire in a direction opposite to that of the current in the
+charging wire.
+
+Now, the darts show the direction in which the current moves while it is
+approaching and passing through the magnetic field. But the moment the
+loop is about to pass out of the magnetic field, the current in the loop
+surges back in the opposite direction, and when the loop has made a
+revolution and is again entering the magnetic field, it must again
+change the direction of flow in the current, and thus produce
+alternations in the flow thereof.
+
+Let us illustrate this by showing the four positions of the revolving
+loop. In Fig. 103 the loop (B) is in the middle of the magnetic field,
+moving upwardly in the direction of the curved dart (A), and while in
+that position the voltage, or the electrical impulse, is the most
+intense. The current used flows in the direction of the darts (C) or to
+the left.
+
+In Fig. 104, the loop (A) has gone beyond the influence of the magnetic
+field, and now the current in the loop tries to return, or reverse
+itself, as shown by the dart (D). It is a reaction that causes the
+current to die out, so that when the loop has reached the point farthest
+from the magnet, as shown in Fig. 105, there is no current in the loop,
+or, if there is any, it moves faintly in the direction of the dart (E).
+
+[Illustration: _Figs. 103-106._ ILLUSTRATING ALTERNATIONS]
+
+CURRENT REVERSING ITSELF.--When the loop reaches its lowest point (Fig.
+106) it again comes within the magnetic field and the current commences
+to flow back to its original direction, as shown by darts (C).
+
+SELF-INDUCTION.--This tendency of a current to reverse itself, under the
+conditions cited, is called self-induction, or inductance, and it would
+be well to keep this in mind in pursuing the study of alternating
+currents.
+
+You will see from the foregoing, that the alternations, or the change of
+direction of the current, depends upon the speed of rotation of the loop
+past the end of the magnet.
+
+[Illustration: _Figs. 107-108._ FORM FOR INCREASING ALTERNATIONS]
+
+Instead, therefore, of using a single loop, we may make four loops (Fig.
+107), which at the same speed as we had in the case of the single loop,
+will give four alternations, instead of one, and still further, to
+increase the periods of alternation, we may use the four loops and two
+magnets, as in Fig. 108. By having a sufficient number of loops and of
+magnets, there may be 40, 50, 60, 80, 100 or 120 such alternating
+periods in each second. Time, therefore, is an element in the operation
+of alternating currents.
+
+Let us now illustrate the manner of connecting up and building the
+dynamo, so as to derive the current from it. In Fig. 109, the loop (A)
+shows, for convenience, a pair of bearings (B). A contact finger (C)
+rests on each, and to these the circuit wire (D) is attached. Do not
+confuse these contact fingers with the commutator brushes, shown in the
+direct-current motor, as they are there merely for the purpose of making
+contact between the revolving loop (A) and stationary wire (D).
+
+[Illustration: _Fig. 109._ CONNECTION OF ALTERNATING DYNAMO ARMATURE]
+
+BRUSHES IN A DIRECT-CURRENT DYNAMO.--The object of the brushes in the
+direct-current dynamo, in connection with a commutator, is to convert
+this _inductance_ of the wire, or this effort to reverse itself into a
+current which will go in one direction all the time, and not in both
+directions alternately.
+
+To explain this more fully attention is directed to Figs. 110 and 111.
+Let A represent the armature, with a pair of grooves (B) for the wires.
+The commutator is made of a split tube, the parts so divided being
+insulated from each other, and in Fig. 110, the upper one, we shall call
+and designate the positive (+) and the lower one the negative (-). The
+armature wire (C) has one end attached to the positive commutator
+terminal and the other end of this wire is attached to the negative
+terminal.
+
+[Illustration: _Fig. 110._ DIRECT CURRENT DYNAMO]
+
+One brush (D) contacts with the positive terminal of the commutator and
+the other brush (E) with the negative terminal. Let us assume that the
+current impulse imparted to the wire (C) is in the direction of the dart
+(F, Fig. 110). The current will then flow through the positive (+)
+terminal of the commutator to the brush (D), and from the brush (D)
+through the wire (G) to the brush (E), which contacts with the negative
+(-) terminal of the commutator. This will continue to be the case, while
+the wire (C) is passing the magnetic field, and while the brush (D) is
+in contact with the positive (+) terminal. But when the armature makes a
+half turn, or when it reaches that point where the brush (D) contacts
+with the negative (-) terminal, and the brush (E) contacts with the
+positive (+) terminal, a change in the direction of the current through
+the wire (G) takes place, unless something has happened to change it
+before it has reached the brushes (D, E).
+
+[Illustration: _Fig. 111._ CIRCUIT WIRES IN DIRECT CURRENT DYNAMO]
+
+Now, this change is just exactly what has happened in the wire (C), as
+we have explained. The current attempts to reverse itself and start out
+on business of its own, so to speak, with the result that when the
+brushes (D and E) contact with the negative and positive terminals,
+respectively, the surging current in the wire (C) is going in the
+direction of the dart (H)--that is, while, in Fig. 110, the current
+flows from the wire (C) into the positive terminal, and out of the
+negative terminal into the wire (C), the conditions are exactly reversed
+in Fig. 111. Here the current in wire C flows _into_ the negative (-)
+terminal, and _from_ the positive (+) terminal into the wire C, so that
+in either case the current will flow out of the brush D and into the
+brush E, through the external circuit (G).
+
+It will be seen, therefore, that in the direct-current motor, advantage
+is taken of the surging, or back-and-forth movement, of the current to
+pass it along in one direction, whereas in the alternating current no
+such change in direction is attempted.
+
+ALTERNATING POSITIVE AND NEGATIVE POLES.--The alternating current,
+owing to this surging movement, makes the poles alternately positive and
+negative. To express this more clearly, supposing we take a line (A,
+Fig. 112), which is called the zero line, or line of no electricity. The
+current may be represented by the zigzag line (B). The lines (B) above
+zero (A) may be designated as positive, and those below the line as
+negative. The polarity reverses at the line A, goes up to D, which is
+the maximum intensity or voltage above zero, and, when the current falls
+and crosses the line A, it goes in the opposite direction to E, which is
+its maximum voltage in the other direction. In point of time, if it
+takes one second for the current to go from C to F, on the down line,
+then it takes only a half second to go from C to G, so that the line A
+represents the time, and the line H the intensity, a complete cycle
+being formed from C, D, F, then through F, E, C, and so on.
+
+[Illustration: _Fig. 112._ ALTERNATING POLARITY LINES]
+
+HOW AN ALTERNATING DYNAMO IS MADE.--It is now necessary to apply these
+principles in the construction of an alternating-current machine. Fig.
+113 is a diagram representing the various elements, and the circuiting.
+
+[Illustration: _Fig. 113._ ALTERNATING CURRENT DYNAMO]
+
+Let A represent the ring or frame containing the inwardly projecting
+field magnet cores (B). C is the shaft on which the armature revolves,
+and this carries the wheel (D), which has as many radially disposed
+magnet cores (E) as there are of the field magnet cores (B).
+
+The shaft (C) also carries two pulleys with rings thereon. One of these
+rings (F) is for one end of the armature winding, and the other ring
+(G) for the other end of the armature wire.
+
+THE WINDINGS.--The winding is as follows: One wire, as at H, is first
+coiled around one magnet core, the turnings being to the right. The
+outlet terminal of this wire is then carried to the next magnet core and
+wound around that, in the opposite direction, and so on, so that the
+terminal of the wire is brought out, as at I, all of these wires being
+connected to binding posts (J, J'), to which, also, the working circuits
+are attached.
+
+THE ARMATURE WIRES.--The armature wires, in like manner, run from the
+ring (G) to one armature core, being wound from right to left, then to
+the next core, which is wound to the right, afterward to the next core,
+which is wound to the left, and so on, the final end of the wire being
+connected up with the other ring (F). The north (N) and the south (S)
+poles are indicated in the diagram.
+
+CHOKING COIL.--The self-induction in a current of this kind is utilized
+in transmitting electricity to great distances. Wires offer resistance,
+or they impede the flow of a current, as hereinbefore stated, so that it
+is not economical to transmit a direct current over long distances. This
+can be done more efficiently by means of the alternating current, which
+is subject to far less loss than is the case with the direct current.
+It affords a means whereby the flow of a current may be checked or
+reduced without depending upon the resistance offered by the wire over
+which it is transmitted. This is done by means of what is called a
+choking coil. It is merely a coil of wire, wound upon an iron core, and
+the current to be choked passes through the coil. To illustrate this,
+let us take an arc lamp designed to use a 50-volt current. If a current
+is supplied to it carrying 100 volts, it is obvious that there are 50
+volts more than are needed. We must take care of this excess of 50 volts
+without losing it, as would happen were we to locate a resistance of
+some kind in the circuit. This result we accomplish by the introduction
+of the choking coil, which has the effect of absorbing the excessive 50
+volts, the action being due to its quality of self-induction, referred
+to in the foregoing.
+
+[Illustration: _Fig. 114._ CHOKING COIL]
+
+In Fig. 114, A is the choking coil and B an arc lamp, connected up, in
+series, with the choking coil.
+
+THE TRANSFORMER.--It is more economical to transmit 10,000 volts a long
+distance than 1,000 volts, because the lower the pressure, or the
+voltage, the larger must be the conductor to avoid loss. It is for this
+reason that 500 volts, or more, are used on electric railways. For
+electric light purposes, where the current goes into dwellings, even
+this is too high, so a transformer is used to take a high-voltage
+current from the main line and transform it into a low voltage. This is
+done by means of two distinct coils of wire, wound upon an iron core.
+
+[Illustration: _Fig. 115._ A TRANSFORMER]
+
+In Fig. 115 the core is O-shaped, so that a primary winding (A), from
+the electrical source, can be wound upon one limb, and the secondary
+winding (B) wound around the other limb. The wires, to supply the
+lamps, run from the secondary coil. There is no electrical connection
+between the two coils, but the action from the primary to the secondary
+coil is solely by induction. When a current passes through the primary
+coil, the surging movement, heretofore explained, is transmitted to the
+iron core, and the iron core, in turn, transmits this electrical energy
+to the secondary coil.
+
+HOW THE VOLTAGE IS DETERMINED.--The voltage produced by the secondary
+coil will depend upon several things, namely, the strength of the
+magnetism transmitted to it; the rapidity, or periodicity of the
+current, and the number of turns of wire around the coil. The voltage is
+dependent upon the length of the winding. But the voltage may also be
+increased, as well as decreased. If the primary has, we will say, 100
+turns of wire, and has 200 volts, and the secondary has 50 turns of
+wire, the secondary will give forth only one-half as much as the
+primary, or 100 volts.
+
+If, on the other hand, 400 volts would be required, the secondary should
+have 200 turns in the winding.
+
+VOLTAGE AND AMPERAGE IN TRANSFORMERS.--It must not be understood that,
+by increasing the voltage in this way, we are getting that much more
+electricity. If the primary coil, with 100 turns, produces a current of
+200 volts and 50 amperes, which would be 200 x 50 = 10,000 watts, and
+the secondary coil has 50 turns, we shall have 100 volts and 100
+amperes: 100 (V.) x 100 (A.) = 10,000 watts. Or, if, on the other hand,
+our secondary winding is composed of 200 turns, we shall have 400 volts
+and 25 amperes, 400 (volts) x 25 (amperes) also gives 10,000 watts.
+
+Necessarily, there will be some loss, but the foregoing is offered as
+the theoretical basis of calculation.
+
+
+
+
+CHAPTER XVI
+
+ELECTRIC LIGHTING
+
+
+The most important step in the electric field, after the dynamo had been
+brought to a fairly workable condition, was its utilization to make
+light. It was long known prior to the discovery of practical electric
+dynamos, that the electric current would produce an intense heat.
+
+Ordinary fuels under certain favorable conditions will produce a
+temperature of 4,500 degrees of heat; but by means of the electric arc,
+as high as six, eight and ten thousand degrees are available.
+
+The fact that when a conductor, in an electric current, is severed, a
+spark will follow the drawing part of the broken ends, led many
+scientists to believe, even before the dynamo was in a practical shape,
+that electricity, sooner or later, would be employed as the great
+lighting agent.
+
+When the dynamo finally reached a stage in development where its
+operation could be depended on, and was made reversible, the first
+active steps were taken to not only produce, but to maintain an arc
+between two electrodes.
+
+It would be difficult and tedious to follow out the first experiments
+in detail, and it might, also, be useless, as information, in view of
+the present knowledge of the science. A few steps in the course of the
+development are, however, necessary to a complete understanding of the
+subject.
+
+Reference has been made in a previous chapter to what is called the
+_Electric Arc_, produced by slightly separated conductors, across which
+the electric current jumps, producing the brilliantly lighted area.
+
+This light is produced by the combustion of the carbon of which the
+electrodes are composed. Thus, the illumination is the result of
+directly burning a fuel. The current, in passing from one electrode to
+the other, through the gap, produces such an intense heat that the fuel
+through which the current passes is consumed.
+
+Carbon in a comparatively pure state is difficult to ignite, owing to
+its great resistance to heat. At about 7,000 degrees it will fuse, and
+pass into a vapor which causes the intense illumination.
+
+The earliest form of electric lighting was by means of the arc, in which
+the light is maintained so long as the electrodes were kept a certain
+distance apart.
+
+To do this requires delicate mechanism, for the reason that when contact
+is made, and the current flows through the two electrodes, which are
+connected up directly with the coils of a magnet, the cores, or
+armatures, will be magnetized. The result is that the electrode,
+connected with the armature of the magnet, is drawn away from the other
+electrode, and the arc is formed, between the separated ends.
+
+As the current also passes through a resistance coil, the moment the
+ends of the electrodes are separated too great a distance, the
+resistance prevents a flow of the normal amount of current, and the
+armature is compelled to reduce its pull. The effect is to cause the two
+electrodes to again approach each other, and in doing so the arc becomes
+brighter.
+
+It will be seen, therefore, that there is a constant fight between the
+resistance coil and the magnet, the combined action of the two being
+such, that, if properly arranged, and with powers in correct relation to
+each other, the light may be maintained without undue flickering. Such
+devices are now universally used, and they afford a steady and reliable
+means of illumination.
+
+Many improvements are made in this direction, as well as in the
+ingredients of the electrodes. A very novel device for assuring a
+perfect separation at all times between the electrodes, is by means of a
+pair of parallel carbons, held apart by a non-conductor such as clay, or
+some mixture of earth, a form of which is shown in Fig. 116.
+
+The drawing shows two electrodes, separated by a non-conducting
+material, which is of such a character that it will break down and
+crumble away, as the ends of the electrodes burn away.
+
+[Illustration: _Fig. 116. Parallel Carbons._]
+
+This device is admirable where the alternating current is used, because
+the current moves back and forth, and the two electrodes are thus burned
+away at the same rate of speed.
+
+In the direct or continuous current the movement is in one direction
+only, and as a result the positive electrode is eaten away twice as fast
+as the negative.
+
+This is the arc form of lamp universally used for lighting large spaces
+or areas, such as streets, railway stations, and the like. It is
+important also as the means for utilizing searchlight illumination, and
+frequently for locomotive headlights.
+
+Arc lights are produced by what is called the _series current_. This
+means that the lamps are all connected in a single line. This is
+illustrated by reference to Fig. 117, in which A represents the wire
+from the dynamo, and B, C the two electrodes, showing the current
+passing through from one lamp to the next.
+
+[Illustration: _Fig. 117. Arc-Lighting Circuit._]
+
+A high voltage is necessary in order to cause the current to leap across
+the gap made by the separation of the electrodes.
+
+THE INCANDESCENT SYSTEM.--This method is entirely different from the arc
+system. It has been stated that certain metals conduct electricity with
+greater facility than others, and some have higher resistance than
+others. If a certain amount of electricity is forced through some
+metals, they will become heated. This is true, also, if metals, which,
+ordinarily, will conduct a current freely, are made up into such small
+conductors that it is difficult for the current to pass.
+
+[Illustration: _Fig 118. Interrupted Conductor._]
+
+In the arc method high voltage is essential; in the incandescent plan,
+current is the important consideration. In the arc, the light is
+produced by virtue of the break in the line of the conductor; in the
+incandescent, the system is closed at all times.
+
+Supposing we have a wire A, a quarter of an inch in diameter, carrying a
+current of, say, 500 amperes, and at any point in the circuit the wire
+is made very small, as shown at B, in Fig. 118, it is obvious that the
+small wire would not be large enough to carry the current.
+
+The result would be that the small connection B would heat up, and,
+finally, be fused. While the large part of the wire would carry 500
+amperes, the small wire could not possibly carry more than, say, 10
+amperes. Now these little wires are the filaments in an electric bulb,
+and originally the attempt was made to have them so connected up that
+they could be illuminated by a single wire, as with the arc system above
+explained, one following the other as shown in Fig. 117.
+
+[Illustration: _Fig. 119. Incandescent Circuit._]
+
+It was discovered, however, that the addition of each successive lamp,
+so wired, would not give light in proportion to the addition, but at
+only about one-fourth the illumination, and such a course would,
+therefore, make electric lighting enormously expensive.
+
+This knowledge resulted in an entirely new system of wiring up the lamps
+in a circuit. This is explained in Fig. 119. In this figure A represents
+the dynamo, B, B the brushes, C, D the two line wires, E the lamps, and
+F the short-circuiting wires between the two main conductors C, D.
+
+It will be observed that the wires C, D are larger than the cross wires
+F. The object is to show that the main wires might carry a very heavy
+amperage, while the small cross wires F require only a few amperes.
+
+This is called the _multiple_ circuit, and it is obvious that the entire
+amperage produced by the dynamo will not be required to pass through
+each lamp, but, on the other hand, each lamp takes only enough necessary
+to render the filament incandescent.
+
+This invention at once solved the problem of the incandescent system and
+was called the subdivision of the electric light. By this means the cost
+was materially reduced, and the wiring up and installation of lights
+materially simplified.
+
+But the divisibility of the light did not, by any means, solve the great
+problem that has occupied the attention of electricians and
+experimenters ever since. The great question was and is to preserve the
+little filament which is heated to incandescence, and from which we get
+the light.
+
+The effort of the current to pass through the small filament meets with
+such a great resistance that the substance is heated up. If it is made
+of metal there is a point at which it will fuse, and thus the lamp is
+destroyed.
+
+It was found that carbon, properly treated, would heat to a brilliant
+white heat without fusing, or melting, so that this material was
+employed. But now followed another difficulty. As this intense heat
+consumed the particles of carbon, owing to the presence of oxygen, means
+were sought to exclude the air.
+
+This was finally accomplished by making a bulb of glass, from which the
+air was exhausted, and as such a globe had no air to support combustion,
+the filaments were finally made so that they would last a long time
+before being finally disintegrated.
+
+The quest now is, and has been, to find some material of a purely
+metallic character, which will have a very high fusing point, and which
+will, therefore, dispense with the cost of the exhausted bulb. Some
+metals, as for instance, osmium, tantalum, thorium, and others, have
+been used, and others, also, with great success, so that the march of
+improvements is now going forward with rapid strides.
+
+VAPOR LAMPS.--One of the directions in which considerable energy has
+been directed in the past, was to produce light from vapors. The Cooper
+Hewitt mercury vapor lamp is a tube filled with the vapor of mercury,
+and a current is sent through the vapor which produces a greenish
+light, and owing to that peculiar color, has not met with much success.
+
+It is merely cited to show that there are other directions than the use
+of metallic conductors and filaments which will produce light, and the
+day is no doubt close at hand when we may expect some important
+developments in the production of light by means of the Hertzian waves.
+
+DIRECTIONS FOR IMPROVEMENTS.--Electricity, however, is not a cheap
+method of illumination. The enormous heat developed is largely wasted.
+The quest of the inventor is to find a means whereby light can be
+produced without the generation of the immense heat necessary.
+
+Man has not yet found a means whereby he can make a heat without
+increasing the temperature, as nature does it in the glow worm, or in
+the firefly. A certain electric energy will produce both light and heat,
+but it is found that much more of this energy is used in the heat than
+in the light.
+
+What wonderful possibilities are in store for the inventor who can make
+a heatless light! It is a direction for the exercise of ingenuity that
+will well repay any efforts.
+
+_Curious Superstitions Concerning Electricity_
+
+Electricity, as exhibited in light, has been the great marvel of all
+times. The word electricity itself comes from the thunderbolt of the
+ancient God Zeus, which is known to be synonymous with the thunderbolt
+and the lightning.
+
+Magnetism, which we know to be only another form of electricity, was not
+regarded the same as electricity by the ancients. Iron which had the
+property to attract, was first found near the town of Magnesia, in
+Lydia, and for that reason was called magnetism.
+
+Later on, a glimmer of the truth seemed to dawn on the early scientists,
+when they saw the resemblance between the actions of the amber and the
+loadstone, as both attracted particles. And here another curious thing
+resulted. Amber will attract particles other than metals. The magnet did
+not; and from this imperfect observation and understanding, grew a
+belief that electricity, or magnetism would attract all substances, even
+human flesh, and many devices were made from magnets, and used as cures
+for the gout, and to affect the brain, or to remove pain.
+
+Even as early as 2,500 years before the birth of Christ the Chinese knew
+of the properties of the magnet, and also discovered that a bar of the
+permanent magnet would arrange itself north and south, like the
+mariners' compass. There is no evidence, however, that it was used as a
+mariner's compass until centuries afterwards.
+
+But the matter connected with light, as an electrical development, which
+interests us, is its manifestations to the ancients in the form of
+lightning. The electricity of the earth concentrates itself on the tops
+of mountains, or in sharp peaks, and accounts for the magnificent
+electrical displays always found in mountainous regions.
+
+Some years ago, a noted scientist, Dr. Siemens, while standing on the
+top of the great pyramid of Cheops, in Egypt, during a storm, noted that
+an electrical discharge flowed from his hand when extended toward the
+heavens. The current manifested itself in such a manner that the hissing
+noise was plainly perceptible.
+
+The literature of all ages and of all countries shows that this
+manifestation of electrical discharges was noted, and became the subject
+of discussions among learned men.
+
+All these displays were regarded as the bolts of an angry God, and
+historians give many accounts of instances where, in His anger, He sent
+down the lightning to destroy.
+
+Among the Romans Jupiter thus hurled forth his wrath; and among many
+ancient people, even down to the time of Charlemagne, any space struck
+by lightning was considered sacred, and made consecrated ground.
+
+From this grew the belief that it was sacrilegious to attempt to imitate
+the lightning of the sky--that Deity would visit dire punishment on any
+man who attempted to produce an electric light. Virgil relates accounts
+where certain princes attempted to imitate the lightning, and were
+struck by thunderbolts as punishments.
+
+Less than a century ago Benjamin Franklin devised the lightning rod, in
+order to prevent lightning from striking objects. The literature of that
+day abounds with instances of protests made, on the part of those who
+were as superstitions as the people in ancient times, who urged that it
+was impious to attempt to ward off Heaven's lightnings. It was argued
+that the lightning was one way in which the Creator manifested His
+displeasure, and exercised His power to strike the wicked.
+
+When such writers as Pliny will gravely set forth an explanation of the
+causes of lightning, as follows in the paragraph below, we can
+understand why it inculcated superstitious fears in the people of
+ancient times. He says:
+
+"Most men are ignorant of that secret, which, by close observation of
+the heavens, deep scholars and principal men of learning have found
+out, namely, that they are the fires of the uppermost planets, which,
+falling to the earth, are called lightning; but those especially which
+are seated in the middle, that is about Jupiter, perhaps because
+participating in the excessive cold and moisture from the upper circle
+of Saturn, and the immoderate heat of Mars, that is next beneath, by
+this means he discharges his superfluity, and therefore it is commonly
+said, 'That Jupiter shooteth and darteth lightning.' Therefore, like as
+out of a burning piece of wood a coal flieth forth with a crack, even so
+from a star is spit out, as it were, and voided forth this celestial
+fire, carrying with it presages of future things; so that the heavens
+showeth divine operations, even in these parcels and portions which are
+rejected and cast away as superfluous."
+
+
+
+
+CHAPTER XVII
+
+POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS
+
+
+It would be difficult to mention any direction in human activity where
+electricity does not serve as an agent in some form or manner. Man has
+learned that the Creator gave this great power into the hands of man to
+use, and not to curse.
+
+When the dynamo was first developed it did not appear possible that it
+could generate electricity, and then use that electricity in order to
+turn the dynamo in the opposite direction. It all seems so very natural
+to us now, that such a thing should practically follow; but man had to
+learn this.
+
+Let us try to make the statement plain by a few simple illustrations. By
+carefully going over the chapter on the making of the dynamo, it will be
+evident that the basis of the generation of the current depends on the
+changing of the direction of the flow of an electric current.
+
+Look at the simple horse-shoe magnet. If two of them are gradually moved
+toward each other, so that the north pole of one approaches the north
+pole of the other, there is a sensible attempt for them to push away
+from each other. If, however, one of them is turned, so that the north
+pole of one is opposite the south pole of the other, they will draw
+together.
+
+In this we have the foundation physical action of the dynamo and the
+motor. When power is applied to an armature, and it moves through a
+magnetic field, the action is just the same as in the case of the hand
+drawing the north and the south pole of the two approaching magnets from
+each other.
+
+The influence of the electrical disturbance produced by that act
+permeated the entire winding of the field and armature, and extended out
+on the whole line with which the dynamo was connected. In this way a
+current was established and transmitted, and with proper wires was sent
+in the form of circuits and distributed so as to do work.
+
+But an electric current, without suitable mechanism, is of no value. It
+must have mechanism to use it, as well as to make it. In the case of
+light, we have explained how the arc and the incandescent lamps utilize
+it for that purpose.
+
+But now, attempting to get something from it in the way of power, means
+another piece of mechanism. This is done by the motor, and this motor is
+simply a converter, or a device for reversing the action of the
+electricity.
+
+Attention is called to Figs. 120 and 121. Let us assume that the field
+magnets A, A are the positives, and the magnets B, B the negatives. The
+revolving armature has also four magnet coils, two of them, C, C, being
+positive, and the other two, D, D, negative, each of these magnet coils
+being so connected up that they will reverse the polarities of the
+magnets.
+
+[Illustration: _Figs. 120-121._ ACTION OF MAGNETS IN A DYNAMO]
+
+Now in the particular position of the revolving armature, in Fig. 120,
+the magnets of the armature have just passed the respective poles of the
+field magnets, and the belt E is compelled to turn the armature past the
+pole pieces by force in the direction of the arrow F. After the armature
+magnets have gone to the positions in Fig. 121, the positives A try to
+draw back the negatives D of the armature, and at the same time the
+negatives B repel the negatives D, because they are of the same
+polarities.
+
+This repulsion of the negatives A, B continues until the armature poles
+C, D have slightly passed them, when the polarities of the magnets C, D
+are changed; so that it will be seen, by reference to Fig. 122, that D
+is now retreating from B, and C is going away from A--that is, being
+forced away contrary to their natural attractive influences, and in Fig.
+123, when the complete cycle is nearly finished, the positives are again
+approaching each other and the negatives moving together.
+
+[Illustration: _Figs. 122-123._ CYCLE ACTION IN DYNAMO]
+
+In this manner, at every point, the sets of magnets are compelled to
+move against their magnetic pull. This explains the dynamo.
+
+Now take up the cycle of the motor, and note in Fig. 124 that the
+negative magnets D of the armature are closely approaching the positive
+and negative magnets, on one side; and the positive magnets C are
+nearing the positive and negatives on the other side. The positives A,
+therefore, attract the negatives D, and the negative B exert a pull on
+the positives C at the same time. The result is that the armature is
+caused to revolve, as shown by the dart G, in a direction opposite to
+the dart in Fig. 120.
+
+[Illustration: _Figs. 124-125._ ACTION OF MAGNETS IN MOTOR]
+
+When the pole pieces of the magnets C, D are about to pass magnets A, B,
+as shown in Fig. 125, it is necessary to change the polarities of the
+armature magnets C, D; so that by reference to Fig. 126, it will be seen
+that they are now indicated as C-, and D+, respectively, and have moved
+to a point midway between the poles A, B (as in Fig. 125), where the
+pull on one side, and the push on the other are again the same, and the
+last Figure 127 shows the cycle nearly completed.
+
+The shaft of the motor armature is now the element which turns the
+mechanism which is to be operated. To convert electrical impulses into
+power, as thus shown, results in great loss. The first step is to take
+the steam boiler, which is the first stage in that source which is the
+most common and universal, and by means of fuel, converting water into
+steam. The second is to use the pressure of this steam to drive an
+engine; the third is to drive the dynamo which generates the electrical
+impulse; and the fourth is the conversion from the dynamo into a motor
+shaft. Loss is met with at each step, and the great problem is to
+eliminate this waste.
+
+[Illustration: _Figs. 126-127._ POSITIONS OF MAGNETS IN MOTOR]
+
+The great advantage of electrical power is not in utilizing it for
+consumption at close ranges, but where it is desired to transmit it for
+long distances. Such illustrations may be found in electric railways,
+and where water power can be obtained as the primal source of energy,
+the cost is not excessive. It is found, however, that even with the most
+improved forms of mechanism, in electrical construction, the internal
+combustion engines are far more economical.
+
+
+_Transmission of Energy_
+
+One of the great problems has been the transmission of the current to
+great distances. By using a high voltage it may be sent hundreds of
+miles, but to use a current of that character in the cars, or shops, or
+homes, would be exceedingly dangerous.
+
+To meet this requirement transformers have been devised, which will take
+a current of very high voltage, and deliver a current of low tension,
+and capable of being used anywhere with the ordinary motors.
+
+THE TRANSFORMER.--This is an electrical device made up of a core or
+cores of thin sheet metal, around which is wound sets of insulated
+wires, one set being designed to receive the high voltage, and the other
+set to put out the low voltage, as described in a former chapter.
+
+These may be made where the original output is a very high voltage, so
+that they will be stepped down, first from one voltage to a lower, and
+then from that to the next lower stage. This is called the "Step down"
+transformer, and is now used over the entire world, where large voltages
+are generated.
+
+ELECTRIC FURNACES.--The most important development of electricity in the
+direction of heat is its use in furnaces. As before stated, an intense
+heat is capable of being generated by the electric current, so that it
+becomes the great agent to use for the treatment of refractory material.
+
+In furnaces of this kind the electric arc is the mechanical form used to
+produce the great heat, the only difference being in the size of the
+apparatus. The electric furnace is simply an immense form of arc light,
+capable of taking a high voltage, and such an arc is enclosed within a
+suitable oven of refractory material, which still further conserves the
+heat.
+
+WELDING BY ELECTRICITY.--The next step is to use the high heat thus
+capable of being produced, to fuse metals so that they may be welded
+together. It is a difficult matter to unite two large pieces of metal by
+the forging method, because the highest heat is required, owing to their
+bulk, and in addition immense hammers, weighing tons, must be employed.
+
+Electric welding offers a simple and easy method of accomplishing the
+result, and in the doing of which it avoids the oxidizing action of the
+forging heat. Instead of heating the pieces to be welded in a forge, as
+is now done, the ends to be united are simply brought into contact, and
+the current is sent through the ends until they are in a soft condition,
+after which the parts are pressed together and united by the simple
+merging of the plastic condition in which they are reduced by the high
+electric heat.
+
+This form of welding makes the most perfect joint, and requires no
+hammering, as the mass of the metal flows from one part or end to the
+other; the unity is a perfect one, and the advantage is that the metals
+can be kept in a semi-fluid state for a considerable time, thus assuring
+a perfect admixture of the two parts.
+
+With the ordinary form of welding it is necessary to drive the heated
+parts together without any delay, and at the least cooling must be
+reheated, or the joint will not be perfect.
+
+The smallest kinds of electric heating apparatus are now being made, so
+that small articles, sheet metal, small rods, and like parts can be
+united with the greatest facility.
+
+
+
+
+CHAPTER XVIII
+
+X-RAY, RADIUM, AND THE LIKE
+
+
+The camera sees things invisible to the human eye. Its most effective
+work is done with beams which are beyond human perception. The
+photographer uses the _Actinic_ rays. Ordinary light is composed of the
+seven primary colors, of which the lowest in the scale is the red, and
+the highest to violet.
+
+Those below the red are called the Infra-red, and they are the Hertzian
+waves, or those used in wireless telegraphy. Those above the violet are
+called Ultra-violet, and these are employed for X-ray work. The former
+are produced by the high tension electric apparatus, which we have
+described in the chapter relating to wireless telegraphy; and the
+latter, called also the Roentgen rays, are generated by the Crookes'
+Tube.
+
+This is a tube from which all the atmosphere has been extracted so that
+it is a practical vacuum. Within this are placed electrodes so as to
+divert the action of the electrical discharge in a particular direction,
+and this light, when discharged, is of such a peculiar character that
+its discovery made a sensation in the scientific world.
+
+The reason for this great wonder was not in the fact that it projected a
+light, but because of its character. Ordinary light, as we see it with
+the eye, is capable of being reflected, as when we look into a mirror at
+an angle. The X-ray will not reflect, but instead, pass directly through
+the glass.
+
+Then, ordinary light is capable of refraction. This is shown by a ray of
+light bending as it passes through a glass of water, which is noticed
+when the light is at an angle to the surface.
+
+The X-ray will pass through the water without being changed from a
+straight line. The foregoing being the case, it was but a simple step to
+conclude that if it were possible to find a means whereby the human eye
+could see within the ultra-violet beam, it would be possible to see
+through opaque substances.
+
+From the discovery so important and far reaching it was not long until
+it was found that if the ultra-violet rays, thus propagated, were
+transmitted through certain substances, their rates of vibration would
+be brought down to the speeds which send forth the visible rays, and now
+the eye is able to see, in a measure at least, what the actinic rays
+show.
+
+This discovery was but the forerunner of a still more important
+development, namely, the discovery of _radium_. The actual finding of
+the metal was preceded by the knowledge that certain minerals, and
+water, as well, possessed the property of radio-activity.
+
+Radio-activity is a word used to express that quality in metals or other
+material by means of which obscure rays are emitted, that have the
+capacity of discharging electrified bodies, and the power to ionize
+gases, as well as to actually affect photograph plates.
+
+Certain metals had this property to a remarkable degree, particularly
+uranium, thorium, polonium, actinium, and others, and in 1898 the
+Curies, husband and wife, French chemists, isolated an element, very
+ductile in its character, which was a white metal, and had a most
+brilliant luster.
+
+Pitchblende, the base metal from which this was extracted, was
+discovered to be highly radio-active, and on making tests of the product
+taken from it, they were surprised to find that it emitted a form of
+energy that far exceeded in calculations any computations made on the
+basis of radio-activity in the metals hitherto examined.
+
+But this was not the most remarkable part of the developments. The
+energy, whatever it was, had the power to change many other substances
+if brought into close proximity. It darkens the color of diamonds,
+quartz, mica, and glass. It changes some of the latter in color, some
+kinds being turned to brown and others into violet or purple tinges.
+
+Radium has the capacity to redden the skin, and affect the flesh of
+persons, even at some considerable distance, and it is a most powerful
+germicide, destroying bacteria, and has been found also to produce some
+remarkable cures in diseases of a cancerous nature.
+
+The remarkable similarity of the rays propagated by this substance, with
+the X-rays, lead many to believe that they are electrical in their
+character, and the whole scientific world is now striving to use this
+substance, as well as the more familiar light waves of the Roentgen
+tube, in the healing of diseases.
+
+It is not at all remarkable that this use of it should first be
+considered, as it has been the history of the electrical developments,
+from the earliest times, that each successive stage should find
+advocates who would urge its virtues to heal the sick.
+
+It was so when the dynamo was invented, when the high tension current
+was produced; and electrical therapeutics became a leading theme when
+transmission by induction became recognized as a scientific fact.
+
+It is not many years since the X-rays were discovered, and the first
+announcement was concerning its wonderful healing powers.
+
+This was particularly true in the case of radium, but for some reason,
+after the first tests, all experimenters were thwarted in their
+theories, because the science, like all others, required infinite
+patience and experience. It was discovered, in the case of the X-ray,
+that it must be used in a modified form, and accordingly, various
+modifications of the waves were introduced, called the _m_ and the _n_
+rays, as well as many others, each having some peculiar qualification.
+
+In time, no doubt, the investigators will find the right quality for
+each disease, and learn how to apply it. Thus, electricity, that most
+alluring thing which, in itself, cannot be seen, and is of such a
+character that it cannot even be defined in terms which will suit the
+exact scientific mind, is daily bringing new wonders for our
+investigation and use.
+
+It is, indeed, a study which is so broad that it has no limitations, and
+a field which never will be exhausted.
+
+THE END
+
+
+
+
+GLOSSARY OF WORDS
+USED IN TEXT OF THIS VOLUME
+
+
+Acid.             Accumulator material is sulphuric acid, diluted
+                    with water.
+
+Active            That part of the material in accumulator plates
+  Material.         which is acted upon by the electric current.
+
+Accumulator.      A cell, generally known as a storage battery, which
+                    while it initially receives a charge of electricity,
+                    is nevertheless, of such a character, owing to the
+                    active material of which it is made, that it
+                    accumulates, or, as it were, generates electricity.
+
+Aerial Wire,      The wire which, in wireless  telegraphy, is carried
+  or Conductor.     up into the air to connect the antennae with the
+                    receiving and sending apparatus.
+
+Alarm, Burglar.   A circulating system in a building, connected up with
+                    a bell or other signaling means.
+
+Alloy.            A mixture of two or more metals; as copper and zinc
+                    to make brass; nickel and zinc to form German silver.
+
+Alternating Current. A current which goes back and forth in opposite
+                    directions, unlike a direct current which flows
+                    continuously in one direction over a wire.
+
+Alternation.      The term applied to a change in the direction of an
+                    alternating current, the frequency of the alternations
+                    ranging up to 20,000 or more vibrations per second.
+
+Amber.            A resin, yellow in color, which when rubbed with a
+                    cloth, becomes excited and gives forth negative
+                    electricity.
+
+Ammeter.          An instrument for measuring the quantity or flow of
+                    electricity.
+
+Ampere.           The unit of current; the term in which strength of
+                    the current is measured. An ampere is an
+                    electromotive force of one volt through a resistance
+                    of one ohm.
+
+Annunciator.      A device which indicates or signals a call given from
+                    some distant point.
+
+Anode.            The positive terminal in a conducting circuit, like
+                    the terminal of the carbon plate in a battery. It is
+                    a plate in an electroplating bath from which the
+                    current goes over to the cathode or negative plate or
+                    terminal.
+
+Arc.              A term employed to designate the gap, or the current
+                    which flows across between the conductors, like the
+                    space between the two carbons of an arc lamp, which
+                    gives the light.
+
+Armature.         A body of iron, or other suitable metal, which is in
+                    the magnetic field of a magnet.
+
+Armature Bar.     The piece which holds the armature. Also one of a
+                    series of bars which form the conductors in armature
+                    windings.
+
+Armature Coil.    The winding around an armature, or around the core
+                    of an armature.
+
+Armature Core.    The part in a dynamo or motor which revolves,
+                    and on which the wire coils are wound.
+
+Astatic (Galvanometer). That which has no magnetic action to direct
+                    or divert anything exterior to it.
+
+Atom.             The ultimate particle of an elementary substance.
+
+Attraction.       That property of matter which causes particles to
+                    adhere, or cohere, to each other. It is known under
+                    a variety of terms, such as gravitation, chemical
+                    affinity, electro-magnetism and dynamic attraction.
+
+Automatic Cut-out. A device which acts through the operation of the
+                    mechanism with which it is connected. It is usually
+                    applied to a device which cuts out a current when it
+                    overcharges or overloads the wire.
+
+Bath.             In electroplating, the vessel or tank which holds
+                    the electroplating solution.
+
+Battery.          A combination of two or more cells.
+
+Battery, Dry.     A primary battery in which the electrolyte is made
+                    in a solid form.
+
+Battery, Galvanic. A battery which is better known by the name of the
+                    Voltaic Pile, made up of zinc and copper plates
+                    which alternate, and with a layer of acidulated paper
+                    between each pair of plates.
+
+Battery, Storage.  A battery which accumulates
+                    electricity generated by a primary battery or a
+                    generator.
+
+Brush.            A term applied to the conducting medium that
+                    bears against the cylindrical surface of a commutator.
+
+Buzzer.           An electric call produced by a rapidly moving
+                    armature of an electro-magnet.
+
+Cable.            A number of wires or conductors assembled in one
+                    strand.
+
+Candle-power.     The amount of light given by the legal-standard
+                    candle. This standard is a sperm candle, which burns
+                    two grains a minute.
+
+Capacity.         The carrying power of a wire or circuit, without
+                    heating.  When heated there is an overload, or the
+                    _capacity_ of the wire is overtaxed.
+
+Capacity, Storage. The quantity of electricity in a secondary battery
+                    when fully charged, usually reckoned in ampere hours.
+
+Carbon.           A material, like coke, ground or crushed, and formed
+                    into sticks or plates by molding or compression. It
+                    requires a high heat to melt or burn, and is used as
+                    electrodes for arc lamps and for battery elements. It
+                    has poor conductivity, and for arc lamps is coated
+                    with copper to increase its conductivity.
+
+Cell, Electrolytic. A vessel containing an electrolyte for
+                    electroplating purposes.
+
+Charge.           The quantity of electricity on the surface of a body
+                    or conductor.
+
+Chemical Change.  When a current passes through electrodes in a
+                    solution, a change takes place which is chemical
+                    in its character. Adding sulphuric acid to water
+                    produces heat. If electrodes of opposite polarity are
+                    placed in such an acid solution, a chemical change is
+                    produced, which is transformed into electricity.
+
+Choking Coil.     An instrument in a circuit which by a form of
+                    resistance regulates the flow of the current, or
+                    returns part of it to the source of its generation.
+
+Counter-electromotive Force. Cells which are inserted in opposition to
+                    a battery to reduce high voltage.
+
+Circuit, Astatic. A circuit in an instrument so wound that the earth's
+                    magnetism will not affect it.
+
+Circuit Breaker.  Any instrument in a circuit which cuts out or
+                    interrupts the flow of a current.
+
+Circuit, External. A current flows through a wire or conductor,
+                  and also along the air outside of the conductor,
+                  the latter being the _external circuit._
+
+Circuit Indicator. An instrument, like a galvanometer, that shows
+                    the direction in which a current is flowing through
+                    a conductor.
+
+Circuit, Return.  Usually the ground return, or the negative wire from
+                    a battery.
+
+Circuit, Short.   Any connection between the mains or parallel lines
+                    of a circuit which does not go through the
+                    apparatus for which the circuit is intended.
+
+Coherer.          A tube, or other structure, containing normally
+                    high resistance particles which form a path or bridge
+                    between the opposite terminals of a circuit.
+
+Coil.             A wire, usually insulated, wound around a spool.
+
+Coil, Induction.  One of a pair of coils designed to change the
+                    voltage of a current of electricity, from a higher
+                    to a lower, or from a lower to a higher
+                    electro-motive force.
+
+Coil, Resistance. A coil so wound that it will offer a resistance
+                    to a steady current, or reduce the flow of electricity.
+
+Commutator.       A cylinder on the end of the armature of a dynamo
+                    or motor and provided with a pair of contact plates
+                    for each particular coil in the armature, in order
+                    to change the direction of the current.
+
+Compass.          An apparatus which indicates the direction or flow
+                    of the earth's magnetism.
+
+Condenser.        A device for storing up electro-static charges.
+
+Conductance.      That quality of a conductor to carry a current of
+                    electricity, dependent on its shape for the best
+                    results.
+
+Conduction.       The transmission of a current through a rod, wire
+                    or conductor.
+
+Conductivity.     That quality which has reference to the capacity
+                    to conduct a current.
+
+Conductor.        Any body, such as a bar, rod, wire, or machine,
+                    which will carry a current.
+
+Connector.        A binding post, clamp, screw, or other means to
+                    hold the end of a wire, or electric conductor.
+
+Contact.          To unite any parts in an electric circuit.
+
+Controller.       The handle of a switchboard, or other contact
+                    making and breaking means in a circuit.
+
+Converter.        An induction coil in an alternating circuit for
+                    changing potential difference, such as high
+                    alternating voltage into low direct current voltage.
+
+Convolution.      To wind like a clock spring.
+
+Core.             The inner portion of an electro-magnet. The inside
+                    part of an armature wound with wire.
+
+Core, Laminated.  When the core is built up of a number of separate
+                    pieces of the same material, but not insulated from
+                    each other.
+
+Coulomb.          The unit of electrical quantity. It is the quantity
+                    passed by a current of one ampere intensity in one
+                    second of time.
+
+Couple, Electric. Two or more electrodes in a liquid to produce an
+                    electric force.
+
+Current, Alternating. A natural current produced by the action of
+                    electro-magnets. It is a succession of short impulses
+                    in opposite directions.
+
+Current, Constant. A current which is uniformly maintained in a steady
+                    stream.
+
+Current, Induced.  A current produced by electro-dynamic induction.
+
+Current Meter.    An apparatus for indicating the strength of a current.
+                    An ammeter.
+
+Current, Oscillating. A current which periodically alternates.
+
+Current, Periodic. A periodically varying current strength.
+
+Current, Undulating. A current which has a constant direction,
+                    but has a continuously varying strength.
+
+Decomposition.    The separation of a liquid, such as an electrolyte,
+                    into its prime elements, either electrically or
+                    otherwise.
+
+Deflection.       The change of movement of a magnetic needle out of
+                    its regular direction of movement.
+
+Demagnetization.  When a current passes through a coil wound on an
+                    iron core, the core becomes magnetized. When the
+                    current ceases the core is no longer a magnet. It
+                    is then said to be _demagnetized_. It also has
+                    reference to the process for making a watch
+                    non-magnetic so that it will not be affected when
+                    in a magnetic field.
+
+Density.          The quantity of an electric charge in a
+                    conductor or substance.
+
+Depolarization.   The removal of magnetism from a permanent magnet,
+                    or a horse-shoe magnet, for instance. It is generally
+                    accomplished by applying heat.
+
+Deposition,       The act of carrying metal from one pole of a cell to
+  Electrolysis.     another pole, as in electroplating.
+
+Detector.         Mechanism for indicating the presence of a current
+                    in a circuit.
+
+Diaphragm.        A plate in a telephone, which, in the receiver, is
+                    in the magnetic field of a magnet, and in a
+                    transmitter carries the light contact points.
+
+Dielectric.       A non-conductor for an electric current, but through
+                    which electro-static induction will take place.
+                    For example: glass and rubber are dielectrics.
+
+Discharge.        The current flowing from an accumulator.
+
+Disintegration.   The breaking up of the plate or active material.
+
+Disruptive.       A static discharge passing through a dielectric.
+
+Duplex Wire.      A pair of wires usually twisted together and
+                    insulated from each other to form the conducting
+                    circuit of a system.
+
+Dynamic Electricity. The term applied to a current flowing through
+                    a wire.
+
+Dynamo.           An apparatus, consisting of core and field magnets,
+                    which, when the core is turned, will develop a
+                    current of electricity.
+
+Earth Returns.    Instead of using two wires to carry a circuit,
+                    the earth is used for what is called the _return_
+                    circuit.
+
+Efficiency.       The total electrical energy produced, in which that
+                    wasted, as well as that used, is calculated.
+
+Elasticity.       That property of any matter which, after a stress,
+                    will cause the substance to return to its original
+                    form or condition. Electricity has elasticity,
+                    which is utilized in condensers, as an instance.
+
+Electricity,      Lightning, and, in short, any current or electrical
+  Atmospheric.      impulse, like wireless telegraphic waves, is called
+                    _atmospheric_.
+
+Electricity,      Electricity with a low potentiality and large current
+   Voltaic.         density.
+
+Electrification.  The process of imparting a charge of electricity
+                    to any body.
+
+Electro-chemistry. The study of which treats of electric and chemical
+                    forces, such as electric plating, electric fusing,
+                    electrolysis, and the like.
+
+Electrode.        The terminals of a battery, or of any circuit; as,
+                    for instance, an arc light.
+
+Electrolyte.      Any material which is capable of being decomposed
+                    by an electric current.
+
+Electro-magnetism. Magnetism which is created by an electric current.
+
+Electrometer.     An instrument for measuring static electricity,
+                    differing from a galvanometer, which measures a
+                    current in a wire that acts on the magnetic needle
+                    of the galvanometer.
+
+Electro-motive    Voltage, which is the measure or unit of e. m. f.
+  Force. (E. M. F.)
+
+Electroscope.     A device for indicating not only the
+                    presence of electricity, but whether it is positive
+                    or negative.
+
+Electro-static    Surfaces separated by a dielectric for opposite
+  Accumulator.    charging of the surface.
+
+Element.          In electricity a form of matter, as, for instance,
+                    gold, or silver, that has no other matter or
+                    compound. Original elements cannot be separated,
+                    because they are not made up of two or more elements,
+                    like brass, for instance.
+
+Excessive Charge.  A storage battery charged at too high a rate.
+
+Excessive Discharge. A storage battery discharged at too high a rate.
+
+Excessive Overcharge. Charging for too long a time.
+
+Exciter.          A generator, either a dynamo or a battery, for
+                    exciting the field of a dynamo.
+
+Exhaustive Discharge. An excessive over-discharge of an accumulator.
+
+F.                The sign used to indicate the heat term Fahrenheit.
+
+Fall of Voltage.  The difference between the initial and the final
+                    voltage in a current.
+
+Field.            The space or region near a magnet or charged wire.
+                    Also the electro-magnets in a dynamo or motor.
+
+Flow.             The volume of a current going through a conductor.
+
+Force, Electro-magnetic. The pull developed by an electro-magnet.
+
+Frictional        A current produced by rubbing dissimilar
+  Electricity.      substances together.
+
+
+Full Load.        The greatest load a battery, accumulator or dynamo
+                    will sustain.
+
+Galvanic.         Pertaining to the electro-chemical relations of
+                    metals toward each other.
+
+Galvanizing.      The art of coating one metal with another, such,
+                    for instance, as immersing iron in molten zinc.
+
+Galvanometry.     An instrument having a permanently magnetized needle,
+                    which is influenced by a coil or a wire in close
+                    proximity to it.
+
+Galvanoscope.     An instrument, like a galvanometer, which determines
+                    whether or not a current is present in a tested wire.
+
+Generator.        A term used to generally indicate any device which
+                    originates a current.
+
+German Silver.    An alloy of copper, nickel and zinc.
+
+Graphite.         One form of carbon. It is made artificially by the
+                    electric current.
+
+Grid.             The metallic frame of a plate used to hold the active
+                    material of an accumulator.
+
+Gravity.          The attraction of mass for mass. Weight. The
+                    accelerating tendency of material to move toward the
+                    earth.
+
+Gutta Percha.     Caoutchouc, which has been treated with sulphur,
+                    to harden it. It is produced from the sap of
+                    tropical trees, and is a good insulator.
+
+Harmonic Receiver. A vibrating reed acted on by an electro-magnet,
+                    when tuned to its pitch.
+
+High E. M. F.     A term to indicate currents which have a high
+                    voltage, and usually low amperage.
+
+Igniter.          Mechanism composed of a battery, induction coil and
+                    a vibrator, for making a jump spark, to ignite gas,
+                    powder, etc.
+
+I. H. P.          Abbreviation, which means Indicated Horse Power.
+
+Impulse.          A sudden motion of one body acting against another.
+                    An electro-magnetic wave magnetizing soft iron,
+                    and this iron attracting another piece of iron, as an
+                    example.
+
+Incandescence,    A conductor heated up by a current so it will
+  Electric.         glow.
+
+Induced Current.  A current of electricity which sets up lines of
+                    force at right angles to the body of the wire
+                    through which the current is transmitted.
+
+Induction, Magnetic. A body within a magnetic field which is excited
+                    by the magnetism.
+
+Installation.     Everything belonging to an equipment of a building,
+                    or a circuiting system to do a certain thing.
+
+Insulation.       A material or substance which resists the passage
+                    of a current placed around a conductor.
+
+Intensity.        The strength of a magnetic field, or of a current
+                    flowing over a wire.
+
+Internal Resistance. The current strength of electricity of a wire
+                    to resist the passage.
+
+Interrupter.      A device in a wire or circuit for checking a
+                    current. It also refers to the vibrator of an
+                    induction coil.
+
+Joint.            The place where two or more conductors are united.
+
+Joint Resistance. The combined resistance offered by two or more
+                    substances or conductors.
+
+Jump Spark.       A spark, disruptive in its character, between two
+                    conducting points.
+
+Initial Charge.   The charge required to start a battery.
+
+Kathode, or Cathode. The negative plate or side of a battery. The
+                    plate on which the electro deposit is made.
+
+Key.              The arm of a telegraph sounder. A bar with a finger
+                    piece, which is hinged and so arranged that it will
+                    make and break contacts in an electric circuit.
+
+Keyboard.         A switch-board; a board on which is mounted a number
+                    of switches.
+
+Kilowatt.         A unit, representing 1,000 watts. An electric current
+                    measure, usually expressed thus: K.W.
+
+Kilowatt Hour.    The computation of work equal to the exertion of one
+                    kilowatt in one hour.
+
+Knife Switch.     A bar of a blade-like form, adapted to move down
+                    between two fingers, and thus establish metallic
+                    connections.
+
+Laminated.        Made up of thin plates of the same material, laid
+                    together, but not insulated from each other.
+
+Lamp Arc.         A voltaic arc lamp, using carbon electrodes, with
+                    mechanism for feeding the electrodes regularly.
+
+Lamp, Incandescent. A lamp with a filament heated up to a glow by the
+                    action of an electric current. The filament is within
+                    a vacuum in a glass globe.
+
+Leak.             Loss of electrical energy through a fault in wiring,
+                    or in using bare wires.
+
+Load.             The ampere current delivered by a dynamo under certain
+                    conditions.
+
+Low Frequency.    A current in which the vibrations are of
+                    few alternations per second.
+
+Magnet.           A metallic substance which has power to attract
+                    iron and steel.
+
+Magnet Bar.       A straight piece of metal.
+
+Magnet Coil.      A coil of wire, insulated, surrounding a core of
+                    iron, to receive a current of electricity.
+
+Magnet Core.      A bar of iron adapted to receive a winding of wire.
+
+
+Magnet, Field.    A magnet in a dynamo. A motor to produce electric
+                    energy.
+
+Magnet, Permanent. A short steel form, to hold magnetism for a long
+                    time.
+
+Magnetic Adherence. The adherence of particles to the
+                    poles of a magnet.
+
+Magnetic          That quality of a metal which draws metals. Also
+  Attraction and    the pulling action of unlike poles for each
+  Repulsion.        other, and pushing away of like poles when brought
+                    together.
+
+Magnetic Force.   The action exercised by a magnet of attracting
+                  or repelling.
+
+Magnetic Pole.    The earth has North and South magnetic poles.
+                    The south pole of a magnetic needle is attracted
+                    so it points to the north magnetic pole; and the north
+                    pole of the needle is attracted to point to the south
+                    magnetic pole.
+
+Magneto-generator. A permanent magnet and a revolving armature for
+                    generating a current.
+
+Maximum Voltage.  The final voltage after charging.
+
+Molecule.         Invisible particles made up of two or more atoms
+                    of different matter. An atom is a particle of one
+                    substance only.
+
+Morse Sounder.    An electric instrument designed to make a clicking
+                    sound, when the armature is drawn down by a
+                    magnet.
+
+Motor-dynamo.     A motor and a dynamo having their armatures
+                    connected together, whereby the motor is driven
+                    by the dynamo, so as to change the current into a
+                    different voltage and amperage.
+
+Motor-transformer. A motor which delivers the current like a generator.
+
+Needle.           A bar magnet horizontally poised on a vertical
+                    pivot point, like the needle of a mariner's compass.
+
+Negative          Amber, when rubbed, produces negative electricity.
+  Electricity.      A battery has positive as well as negative
+                    electricity.
+
+Negative Element. That plate in the solution of a battery
+                    cell which is not disintegrated.
+
+Normal.           The usual, or ordinary. The average. In a
+                    current the regular force required to do the work.
+
+North Pole,       The term applied to the force located near
+  Electric.        the north pole of the globe, to which a permanent
+                   magnet will point if allowed to swing freely.
+
+O.                Abbreviation for Ohm.
+
+Ohm.              The unit of resistance. Equal to the resistance of
+                    a column of mercury one square millimeter in cross
+                    section, and 106.24 centimeters in length.
+
+Ohm's Law.        It is expressed as follows:
+                  1. The current strength is equal to the electro-motive
+                       force divided by its 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.
+
+Overload.         In a motor an excess of mechanical work which causes
+                    the armature to turn too slowly and produces heat.
+
+Phase.            One complete oscillation. The special form of a
+                    wave at any instant, or at any interval of time.
+
+Plate, Condenser. In a static machine it is usually a plate of glass
+                    and revoluble.
+
+Plate, Negative.  The plate in a battery, such as carbon, copper or
+                    platinum, which is not attacked by the solution.
+
+Plating, Electro-. The method of coating one metal with another by
+                    electrolysis.
+
+Polarity.         The peculiarity, in a body, of arranging itself
+                    with reference to magnetic influence.
+
+Parallel.         When a number of cells are coupled so that their
+                    similar poles are grouped together. That is to say,
+                    as the carbon plates, for instance, are connected
+                    with one terminal, and all the zinc plates with the
+                    other terminal.
+
+Polarization.     When the cell is deprived of its electro-motive
+                    force, or any part of it, polarization is the result.
+                    It is usually caused by coating of the plates.
+
+Porosity.         Having small interstices or holes.
+
+Positive Current. One which deflects a needle to the left.
+
+Positive          Any current flowing from the active element,
+  Electricity.     such as zinc, in a battery. The negative
+                    electricity flows from the carbon to the zinc.
+
+Potential,
+  Electric.       The power which performs work in a circuit.
+
+Potential Energy. That form of force, which, when liberated, does or
+                    performs work.
+
+Power Unit.       The volt-amperes or watt.
+
+Primary.          The induction coil in induction machines, or in
+                    a transformer.
+
+Push Button.      A thumb piece which serves as a switch to
+                    close a circuit while being pressed inwardly.
+
+Quantity.         Such arrangement of electrical connections
+                    which give off the largest amount of current.
+
+Receiver.         An instrument in telephony and telegraphy which
+                    receives or takes in the sound or impulses.
+
+Relay.            The device which opens or closes a circuit so as to
+                    admit a new current which is sent to a more distant
+                    point.
+
+Repulsion,        That tendency in bodies to repel each other when
+  Electric.         similarly charged.
+
+Resilience.       The springing back to its former condition or
+                    position. Electricity has resilience.
+
+Resistance.       The quality in all conductors to oppose the passage
+                    of a current.
+
+Resistance Coil.  A coil made up of wire which prevents the passage
+                    of a current to a greater or less degree.
+
+Resistance,       The counter force in an electrolyte which seeks
+  Electrolytic.     to prevent a decomposing current to pass through it.
+
+Resistance: Internal, The opposing force to the movement of a current
+  External.         which is in the cell or generator. This is called the
+                     _internal_. That opposite action outside of the cell
+                    or generator is the _external_.
+
+Resonator,        An open-circuited conductor for electrically
+  Electric.         resounding or giving back a vibration, usually
+                   exhibited by means of a spark.
+
+Rheostat.         A device which has an adjustable resistance, so
+                    arranged that while adjusting the same the circuit
+                    will not be open.
+
+Safety Fuse.      A piece of fusible metal of such resistance that
+                    it breaks down at a certain current strength.
+
+Saturated.        When a liquid has taken up a soluble material
+                    to the fullest extent it is then completely saturated.
+
+Secondary.        One of the two coils in a transformer, or induction
+                    coil.
+
+Secondary Plates. The brown or deep red plates in a storage battery
+                    when charged.
+
+Self-excited.     Producing electricity by its own current.
+
+Series.           Arranged in regular order. From one to the other
+                    directly. If lamps, for instance, should be arranged
+                    in circuit on a single wire, they would be in series.
+
+Series, Multiple. When lamps are grouped in sets in parallel,
+                    and these sets are then connected up in series.
+
+Series Windings.  A generator or motor wound in such a manner that
+                    one of the commutator brush connections is joined
+                    to the field magnet winding, and the other end of
+                    the magnet winding joined to the outer circuit.
+
+Shunt.            Going around.
+
+Shunt Winding.    A dynamo in which the field winding is parallel with
+                    the winding of the armature.
+
+Snap Switch.      A switch so arranged that it will quickly make a
+                    break.
+
+Sounder.          The apparatus at one end of a line actuated by a key
+                    at the other end of the line.
+
+Spark Coil.       A coil, to make a spark from a low electro-motive
+                    force.
+
+Spark, Electric.  The flash caused by drawing apart the ends of a
+                    conductor.
+
+Specific Gravity. The weight or density of a body.
+
+Static Electricity. Generated by friction. Also lightning.
+                    Any current generated by a high electro-motive force.
+
+Strength of Current. The quantity of electricity in a circuit.
+
+Synchronize.      Operating together; acting in unison.
+
+Terminal.         The end of any electric circuit or of a body
+                    or machine which has a current passing through it.
+
+Thermostat, Electric. An electric thermometer. Usually made
+                    with a metal coil which expands through the action
+                    of the electricity passing through it, and, in
+                    expanding, it makes a contact and closes a circuit.
+
+Transformer.      The induction coil with a high initial E. M. F.
+                    changes into a low electro-motive force.
+
+Unit.             A standard of light, heat, electricity, or of
+                    other phenomena.
+
+Vacuum.           A space from which all matter has been exhausted.
+
+Vibrator.         Mechanism for making and breaking circuits in
+                    induction coils or other apparatus.
+
+Volt.             The unit of electro-motive force.
+
+Voltage.          Electro-motive force which is expressed in volts.
+
+Voltaic.          A term applied to electric currents and devices.
+
+Volt-meter.       An apparatus for showing the difference of
+                    potential, or E.  M. F. in the term of volts.
+
+Watt.             The unit of electrical activity. The product of
+                    amperes multiplied by volts.
+
+Watt Hour.        One watt maintained through one hour of time.
+
+Waves, Electric   Waves in the ether caused by electro-magnetic
+  Magnetic.         disturbances.
+
+X-rays.           The radiation of invisible rays of light, which
+                    penetrate or pass through opaque substances.
+
+Yoke, or Bar.     A soft iron body across the ends of a
+                    horseshoe magnet, to enable the magnet to retain its
+                    magnetism an indefinite time.
+
+Zinc Battery.     A battery which uses zinc for one of its elements.
+
+
+
+
+INDEX
+
+A
+
+Accumulated, 31.
+
+Accumulation, 29.
+
+Accumulator cell, 87.
+
+Accumulators, 82, 88, 89.
+
+Accumulators, plates, 83.
+
+Acid, 34, 37, 125.
+
+Acid maker, 125.
+
+Acid, sulphuric, 31, 84.
+
+Acidulated, 55.
+
+Acidulated water, 34.
+
+Acoustics, 110.
+
+Actinic rays, 184, 185.
+
+Actinium, 186.
+
+Active element, 82.
+
+Adjustable rod, 107.
+
+Adjusting screw, 70, 71, 72, 73, 106.
+
+Aerial wire, 108.
+
+Agents, 13, 32.
+
+Alarms, burglar, 11, 76, 80.
+
+Alkali, 125.
+
+Alkaline, 37.
+
+Alternate, 127.
+
+Alternating, 38, 149, 150, 153, 154, 155, 156.
+
+Alternating current, 145.
+
+Alternating periods, 149.
+
+Alternations, 147.
+
+Aluminum, 128, 129, 135, 137.
+
+Aluminum hydrate, 129.
+
+Amber, 5, 171.
+
+Ammeter, 7, 88.
+
+Amperage, 38, 61, 62, 132, 159, 160, 168.
+
+Ampere, 7, 37, 60, 63, 139, 140, 167.
+
+Amplitude, 111.
+
+Annunciator, 65, 74, 76, 79, 80, 81.
+
+Annunciator bells, 11.
+
+Anode, 35, 133, 134.
+
+Antennae, 108.
+
+Antimony 137, 143.
+
+Anvil, 13, 14.
+
+Apparatus, 11, 57, 106, 139, 145.
+
+Arc, 163, 182.
+
+Arc lighting, 38, 165.
+
+Arc system, 166.
+
+Armature, 18, 25, 38, 40, 42, 43, 45, 46, 47, 48, 53, 55, 70, 72, 73,
+        74, 90, 93, 112, 151, 152, 155, 163, 176, 177, 178, 179, 180.
+
+Armature brush, 48.
+
+Armature post, 71.
+
+Armature, vertical, 75.
+
+Armature winding, 42, 43, 156.
+
+Asbestos, 140.
+
+Astatic galvanometer, 108.
+
+Atmosphere, 184.
+
+Attract, 30.
+
+Attracted, 72.
+
+Attraction, 21, 25.
+
+Attractive, 178.
+
+Automatic, 120.
+
+Auxiliary, 44.
+
+Awls, 14.
+
+
+B
+
+Bacteria, 126, 187.
+
+Bar, cross, 66.
+
+Bar, horizontal, 46.
+
+Bar, parallel switch, 67.
+
+Bar, switch, 65, 68.
+
+Base block, 66.
+
+Batteries, 11, 93, 122.
+
+Battery, 29, 30, 32, 35, 36, 46, 47, 80, 81, 82, 83, 85, 86, 88, 92, 94,
+          95, 107, 108, 116, 117, 118, 121, 134, 142.
+
+Battery charging, 82.
+
+Bearings, 45, 46.
+
+Bells, 65, 73, 76, 122.
+
+Bells, electric, 70.
+
+Bench, 13, 15, 17.
+
+Binding post, 52, 70, 71, 72, 103, 107, 108, 121.
+
+Binding screw, 65, 66.
+
+Bismuth, 18, 143.
+
+Bit, 13.
+
+Blue vitriol, 57.
+
+Brass plate, 77, 78.
+
+Brazing, 17, 65.
+
+Bridge, 52.
+
+Brush holder, 46.
+
+Brushes, 48, 150, 151, 153, 167.
+
+Burglar, 11.
+
+Burglar alarm, 76, 80.
+
+Buttons, contact, 80.
+
+Buttons, push, 65, 68, 69, 70, 76, 79.
+
+
+C
+
+Calorimeter, 56.
+
+Cancerous, 187.
+
+Candle power, 89, 139.
+
+Cap, removable, 73.
+
+Cap screws, 42.
+
+Carbon, 35, 119, 121, 162, 163, 169.
+
+Carbon block, 120.
+
+Carbon pencil, 119.
+
+Cathode, 35, 36, 133, 134.
+
+Cell, 29, 33.
+
+Cell, accumulator, 87.
+
+Cell, charging, 87.
+
+Channel, 43.
+
+Channel, concave, 40.
+
+Charged, 120.
+
+Charged battery, 82.
+
+Charging circuit, 82, 89.
+
+Charging source, 83.
+
+Charged wire, 147.
+
+Chemical, 57.
+
+Chisels, 13.
+
+Chloride of lime, 84.
+
+Choked, 157.
+
+Choking coils, 145, 146, 156, 158.
+
+Circuit, 33, 69, 73, 76, 78, 80, 81, 90, 92, 93, 109, 113, 116, 121,
+         122, 131, 134, 143, 156.
+
+Circuit, primary, 99.
+
+Circuit, secondary, 99.
+
+Circuiting, 81, 155.
+
+Circuiting system, 79.
+
+Clapper arm, 70.
+
+Closed rings, 26.
+
+Coherer, 105, 108, 109.
+
+Cohering, 106.
+
+Coils, 18, 26, 52, 55, 74, 160.
+
+Coils, choking, 145, 146, 156, 158.
+
+Coils, induction, 99, 102.
+
+Coils, primary, 109.
+
+Coils, secondary, 102, 109.
+
+Coincide, 42.
+
+Cold, 14.
+
+Collecting surfaces, 30.
+
+Collector, 31.
+
+Column, 61.
+
+Combustion, 169.
+
+Commutator, 44, 46, 151, 152.
+
+Commutator brushes, 46.
+
+Commutator plates, 45.
+
+Compass, 22, 24, 172.
+
+Composition, 83, 124.
+
+Compound wound, 47.
+
+Concave channel, 40.
+
+Condenser, 98, 100, 101, 102, 108.
+
+Conduct, 6, 108.
+
+Conduction, 135, 136, 138, 166, 170.
+
+Conduction current, 27.
+
+Conductor, 21, 31, 33, 63, 98, 116, 161, 162.
+
+Conduit, 72.
+
+Conically formed, 126.
+
+Conjunction, 143.
+
+Connecting wire, 58.
+
+Connection, 72, 76.
+
+Construction, magnet, 39.
+
+Consumption, 180.
+
+Contact, 122, 123, 152, 162.
+
+Contact finger, 150.
+
+Contact plate, 67, 68, 79.
+
+Contact screws, 93.
+
+Contact surface, 66.
+
+Continuous, 145.
+
+Converter, 176.
+
+Converting, 142, 145, 146.
+
+Copper, 18, 34, 36, 65, 66, 132, 133, 134, 135, 136, 137, 142, 143.
+
+Copper cyanide, 133.
+
+Copper plate, 33, 35, 58, 67.
+
+Copper sulphate, 57.
+
+Copper voltameter, 55, 57.
+
+Core, 27, 28, 36, 39, 40, 115.
+
+Core, magnet, 75, 93.
+
+Counter, clock-wise, 51.
+
+Coupled, 36.
+
+Crank, 30.
+
+Crookes' tube, 184.
+
+Cross bar, 52, 66.
+
+Crown of cups, 32.
+
+Crystal, 85.
+
+Current, 6, 7, 13, 18, 26, 27, 28, 35, 36, 37, 38, 47, 50, 51, 52, 55,
+  56, 57, 58, 59, 62, 63, 70, 72, 73, 90, 95, 98, 105, 108, 116, 133, 134,
+  135, 136, 138, 139, 140, 141, 142, 143, 147, 148, 149, 150, 152, 153,
+  157, 160, 161, 163, 165, 166, 170.
+
+Current, alternating, 150.
+
+Current changing, 82.
+
+Current conduction, 27.
+
+Current, continuous, 164.
+
+Current, direct, 145, 150.
+
+Current direction, 50.
+
+Current, exterior, 50, 150.
+
+Current, reversing, 148.
+
+Current strength, 7, 57.
+
+Current testing, 143.
+
+Cut-out, 120.
+
+Cutter, 14.
+
+Cutting, lines of force, 38.
+
+Cylinder, 44.
+
+Cylindrical, 43.
+
+
+D
+
+Dash, 95, 97.
+
+Decoherer, 106, 108.
+
+Decomposed, 57, 128.
+
+Decomposes, 55.
+
+Decomposing, 123.
+
+Decomposition, 12, 35, 82.
+
+Deflected, 54.
+
+Degree, 135, 162.
+
+Demagnetized, 24, 72.
+
+Deposited, 58, 133.
+
+Depression, 15, 140.
+
+Detecting current, 49.
+
+Detector, 49, 52, 54, 105.
+
+Devices, measuring, 27.
+
+Diagrams, 46, 48, 79, 89.
+
+Diagrammatically, 81.
+
+Diamagnetic, 19.
+
+Diametrically, 114.
+
+Diaphragm, 112, 113, 116, 120, 122.
+
+Diamonds, 186.
+
+Diluted, 86.
+
+Direct current, 38, 140.
+
+Direction of current, 50.
+
+Direction of flow, 98.
+
+Discharge, 172.
+
+Disintegrate, 132.
+
+Disk, 43.
+
+Dissimilar, 37.
+
+Disturbance, 176.
+
+Dividers, 14.
+
+Divisibility, 168.
+
+Dot, 96, 97.
+
+Dot and dash, 96.
+
+Double click, 95.
+
+Double line, 65.
+
+Double-pole switch, 65.
+
+Double-throw switch, 117.
+
+Drawing, 20.
+
+Drill, ratchet, 13.
+
+Drops, 81.
+
+Ductile, 186.
+
+Duplex wire, 115.
+
+Dynamo, 7, 27, 38, 42, 46, 48, 62, 82, 83, 87, 89, 132, 141, 142, 145,
+       150, 155, 161, 165, 167, 175, 176, 180, 187.
+
+Dynamo fields, 40, 41.
+
+
+E
+
+Earth, 22.
+
+Elasticity, 100, 142.
+
+Electric, 6, 31, 49, 50, 76, 78, 81, 131, 142, 158, 162, 173, 176.
+
+Electric arc, 63, 163.
+
+Electric bell, 19, 69, 70, 71, 72, 106, 117.
+
+Electric bulbs, 167.
+
+Electric circuit, 118.
+
+Electric fan, 55.
+
+Electric field, 76.
+
+Electric hand purifier, 129.
+
+Electric heating, 135, 137, 161.
+
+Electric iron, 130, 141.
+
+Electric lamp socket, 139.
+
+Electric light, 56, 66.
+
+Electric lighting, 161.
+
+Electric power, 113.
+
+Electric welding, 183.
+
+Electrical, 8, 11, 65, 96, 98, 104, 141, 159, 180, 184, 187.
+
+Electrical impulses, 105, 147, 148.
+
+Electrical manifestations, 175.
+
+Electrically, 32, 70.
+
+Electricity, 5, 6, 7, 8, 9, 12, 13, 18, 21, 26, 27, 28, 29, 38, 49, 54,
+     60, 61, 62, 82, 97, 98, 100, 104, 110, 112, 116, 123, 124, 133, 134,
+    136, 138, 145, 146, 147, 154, 156, 160, 166, 170, 171, 172, 175, 182,
+    187.
+
+Electricity measuring, 49.
+
+Electricity, thermo-, 142.
+
+Electrified, 37, 186.
+
+Electro-chemical, 55.
+
+Electrode, 35, 124, 127, 128, 161, 162, 163, 164, 165, 184.
+
+Electrolysis, 7, 123, 126, 132.
+
+Electrolyte, 33, 35, 36, 57, 86, 88, 123, 132, 142.
+
+Electrolytic, 55, 123, 125.
+
+Electro-magnet, 59, 78.
+
+Electro-magnetic, 7, 24, 25, 29, 37, 55, 92, 93, 94.
+
+Electro-magnetic force, 7.
+
+Electro-magnetic rotation, 7.
+
+Electro-magnetic switch, 116.
+
+Electro-meter, 7.
+
+Electro-motive force, 37, 63, 99.
+
+Electroplate, 12, 38, 48, 123, 132, 134.
+
+Electro-positive-negative, 142, 143.
+
+Elements, 36, 83.
+
+Engine energy, 170, 180.
+
+Equidistant, 127.
+
+Ether, 104.
+
+Example, 61.
+
+Excited, 47.
+
+Extension plate, 103.
+
+Exterior, 3.
+
+Exterior magnetic, 27.
+
+External, 37.
+
+External circuit, 153.
+
+External current, 50.
+
+External resistance, 37.
+
+
+F
+
+Factor, 61.
+
+Ferrous oxide, 125.
+
+Field, 46, 47.
+
+Field, dynamo, 40, 41.
+
+Field magnet cores, 155.
+
+Field, magnetic, 38.
+
+Field of force, 33.
+
+Field wire, 48.
+
+Filament, 168, 169, 170.
+
+Filter, 128.
+
+Flat iron, 140.
+
+Flocculent, 128.
+
+Force, 50.
+
+Formulated, 19.
+
+Friction, 32.
+
+Frictional, 6, 7, 29.
+
+Fuse, 169.
+
+
+G
+
+Galvani, 7.
+
+Galvanic, 7, 23, 30.
+
+Galvanometer, 7, 49, 108, 143.
+
+Galvanoscope, 55, 58, 59.
+
+Gaseous, 128.
+
+Gasoline, 99.
+
+Gas stove, 17.
+
+Gelatine, 128.
+
+Generate, 29, 38, 134, 136, 145.
+
+Generated, 55.
+
+Generating, 32, 134.
+
+Generation, 170.
+
+Generator, 32, 125, 147.
+
+German silver, 136, 137.
+
+Germicide, 187.
+
+Gimlets, 17.
+
+Glass, 30, 86, 126, 186.
+
+Gold, 135.
+
+Grid, 84.
+
+Ground circuit, 121.
+
+Gunpowder, 6.
+
+
+H
+
+Hack-saw, 14.
+
+Hammer, 13.
+
+Heart-shaped switch, 77.
+
+Heater, 136.
+
+Heating, 13, 38.
+
+Hertzian rays, 170.
+
+Hertzian wave, 184.
+
+High tension, 38, 102, 184.
+
+High tension apparatus, 98.
+
+High tension coils, 103.
+
+High voltage, 158.
+
+Horizontal bar, 46.
+
+Horseshoe magnet, 22, 24, 175.
+
+Hydrate of aluminum, 129.
+
+Hydrogen, 35, 123, 125, 128.
+
+
+I
+
+Igniting, 99.
+
+Illumination, 162, 163, 165, 167, 170.
+
+Immersed, 133.
+
+Impulses, 60, 62, 96, 104, 109, 152, 179.
+
+Incandescent, 166, 168.
+
+Induced, 28.
+
+Inductance, 149, 150.
+
+Induction, 27, 37, 98, 147.
+
+Induction coils, 99, 102, 106.
+
+Influences, 178.
+
+Initial charge, 88.
+
+Insulated, 27, 28, 40, 43, 52, 55, 73, 115, 151, 180.
+
+Insulating, 66, 69, 120, 140, 164.
+
+Insulating material, 114.
+
+Insulation, 40, 116.
+
+Instruments, 49, 94, 112, 118, 120.
+
+Instruments, measuring, 8.
+
+Intensity, 55, 60, 104, 154.
+
+Interior, magnetic, 23.
+
+Internal resistance, 37.
+
+Interruption, 102, 103.
+
+Installation, 168.
+
+Ionize, 186.
+
+Iron, 19, 132, 133, 136, 142, 171.
+
+Isolated, 186.
+
+
+J
+
+Jar, 29, 31, 32.
+
+Journal, 46.
+
+Journal block, 16, 146.
+
+Jump spark, 99.
+
+
+K
+
+Key, 90, 91, 95.
+
+Key, sending, 90.
+
+Knob, 32.
+
+Knob, terminal, 31.
+
+
+L
+
+Laboratory, 9.
+
+Lead, 31, 136.
+
+Lead, precipitated, 83, 85.
+
+Lead, red, 83, 84.
+
+Lever switching, 67.
+
+Light, 104.
+
+Light method, 56.
+
+Lighting, 9, 38.
+
+Lighting circuit, 48.
+
+Lighting system, 82.
+
+Lightning, 6, 171, 172, 173.
+
+Lightning rod, 173.
+
+Lime, chloride of, 84.
+
+Line of force, 146.
+
+Line wire, 122.
+
+Line, magnetic, 22, 23.
+
+Liquid, 32.
+
+Litharge, 83.
+
+Loadstone, 17.
+
+Locomotives, 165.
+
+Low tension, 38, 98, 102, 179.
+
+
+M
+
+Magnet bar, 20.
+
+Magnet core, 16, 75, 93.
+
+Magnet, electro, 59, 78.
+
+Magnet, horseshoe, 22, 25, 175.
+
+Magnet lines, 22, 23.
+
+Magnet, permanent, 25, 38, 46, 50, 172.
+
+Magnet, reversed, 20.
+
+Magnet, steel, 53.
+
+Magnet, swinging, 53.
+
+Magnetic, 7, 19, 20, 21, 22, 25, 113, 178.
+
+Magnetic construction, 39.
+
+Magnetic exterior, 27.
+
+Magnetic field, 22, 24, 27, 38, 50, 112, 146, 148, 155.
+
+Magnetic interior, 23.
+
+Magnetic pull, 59.
+
+Magnetic radiator, 37.
+
+Magnetism, 19, 54, 104, 110, 159, 171.
+
+Magnetized, 18, 25, 27, 50.
+
+Magnetized wire, 146.
+
+Magnets, 13, 14, 18, 19, 20, 21, 22, 23, 24, 25, 39, 51, 53, 54, 70, 71,
+       73, 75, 81, 90, 93, 112, 113, 115, 147, 150, 163, 176, 177, 178.
+
+Main conductor, 31.
+
+Mandrel, 15, 16.
+
+Manganese, 19.
+
+Manifestations, 19.
+
+Mariner, 172.
+
+Material, non-conducting, 90.
+
+Maximum, 154.
+
+Measure, 55, 56, 60, 62.
+
+Measurement, 62.
+
+Measuring devices, 27.
+
+Measuring instruments, 8.
+
+Mechanism, 47, 180.
+
+Medical batteries, 99.
+
+Mercury, 63, 169.
+
+Metal base, 73.
+
+Mica, 186.
+
+Microphone, 118, 119, 120.
+
+Millimeter, 63.
+
+Minus, 34.
+
+Minus sign, 21.
+
+Morse code, 76.
+
+Motor, 7, 21, 27, 46, 47, 62, 82, 99, 150, 176, 180.
+
+Mouthpiece, 115.
+
+Mouthpiece rays, 188.
+
+Moving field, 117.
+
+Multiple, 168.
+
+Musical scale, 111.
+
+
+N
+
+Negative, 21, 35, 36, 68, 83, 86, 87, 94, 125, 151, 152, 154, 165, 177,
+    178, 179.
+
+Neutral, 125.
+
+Neutral plate, 84.
+
+Nickel, 136.
+
+Nickel plating, 132.
+
+Nitrate of silver, 62.
+
+Nitrogen, 126.
+
+Non-conducting material, 90.
+
+Non-conductor, 164.
+
+Non-magnetic, 19.
+
+North pole, 20, 21, 22, 23, 25, 50, 54, 156.
+
+Number plate, 75.
+
+N-ray, 188.
+
+
+O
+
+Ohms, 60, 63.
+
+Ohms, international, 63.
+
+Ohms law, 7.
+
+Operator, 95, 118.
+
+Oscillating, 99, 105.
+
+Osmium, 169.
+
+Oxides, 125.
+
+Oxidizing, 183.
+
+Oxygen, 35, 123, 125, 126, 128, 129, 169.
+
+
+P
+
+Packing ring, 124.
+
+Paraffine, 56, 100, 101, 102.
+
+Paraffine wax, 86.
+
+Parallel, 87, 88, 89.
+
+Parallel switch bar, 67.
+
+Parallel wires, 28, 49.
+
+Partition, 124.
+
+Peon, 13.
+
+Percolate, 128.
+
+Periodicity, 159.
+
+Periods of alternations, 149.
+
+Permanent, 18, 19, 50.
+
+Permanent magnet, 25, 38, 46, 50, 172.
+
+Phase, 19.
+
+Phenomenon, 27, 65.
+
+Photograph, 186.
+
+Physical, 21.
+
+Pile, voltaic, 33.
+
+Pipe, 61.
+
+Pitchblende, 186.
+
+Pivot pin, 53.
+
+Pivotal, 22.
+
+Plane, 13.
+
+Plate, 57, 93.
+
+Plate, contact, 67, 68, 79.
+
+Plate, copper, 33, 35, 58, 67.
+
+Plate, negative, 84.
+
+Plate, number, 75.
+
+Plate, positive, 84, 88.
+
+Plate, zinc, 33.
+
+Platinum, 13, 57, 137.
+
+Pliers, 14.
+
+Plus sign, 21, 24.
+
+Pointer, 53.
+
+Polarity, 154, 177, 178, 179.
+
+Polarization, 35.
+
+Pole, north, 20, 21, 22, 23, 25, 50, 54, 156.
+
+Pole piece, 40, 42.
+
+Pole, south, 20, 21, 22, 25, 50, 54, 156.
+
+Poles, 177, 179.
+
+Polonium, 186.
+
+Porcelain, 86.
+
+Porous, 85.
+
+Positive, 4, 21, 25, 36, 40, 68, 83, 86, 87, 94, 123, 125, 151, 152,
+   153, 155, 165.
+
+Post, binding, 52, 71.
+
+Potentiality, 105, 109.
+
+Power, 38, 186.
+
+Power, candle, 89, 139.
+
+Precipitate of lead, 83, 85.
+
+Precision, 7.
+
+Pressure, 87.
+
+Primary, 35, 62, 98, 134, 142, 159, 184.
+
+Primary battery, 7, 99.
+
+Primary circuit, 99.
+
+Primary coil, 106, 109.
+
+Prime conductor, 6.
+
+Projected, 185.
+
+Propagated, 105, 185.
+
+Properties, 55.
+
+Purification, 123, 128.
+
+Purifier, 126, 131.
+
+Push button, 65, 68, 69, 70, 76, 79.
+
+
+Q
+
+Quantity, 55, 60, 61, 138.
+
+Quartz, 186.
+
+
+R
+
+Radio-activity, 186.
+
+Radium, 184, 185, 187, 188.
+
+Ratchet drill, 13.
+
+Reaction, 148.
+
+Receiver, 12, 90, 97, 121, 122.
+
+Receiving station, 109.
+
+Rectangular, 69.
+
+Rectifiers, 146.
+
+Red lead, 83, 84.
+
+Reel, 13.
+
+Reflected, 185.
+
+Refraction, 185.
+
+Refractory, 182.
+
+Register, 57.
+
+Removable, 54.
+
+Removable cap, 73.
+
+Repel, 20.
+
+Repulsion, 21, 128.
+
+Reservoir, 61, 62.
+
+Resiliency, 99.
+
+Resistance, 7, 36, 37, 60, 63, 99, 135, 136, 137, 138, 140, 141, 156,
+   157, 163, 166, 168.
+
+Resistance bridge, 7.
+
+Resistance, external, 37.
+
+Resistance, internal, 37.
+
+Rheostat, 7.
+
+Reversed, 20, 50, 153.
+
+Reversible, 163.
+
+Reversing, 176.
+
+Reversing switch, 67.
+
+Revolubly, 46.
+
+Revolve, 179.
+
+Revolving, 177.
+
+Roentgen rays, 184.
+
+Roentgen tube, 187.
+
+Rotation, 149.
+
+Rubber, 40, 46, 77, 115, 126, 130, 138.
+
+
+S
+
+Sad-irons, 13.
+
+Saline, 133.
+
+Sanitation, 12.
+
+Saturated, 85.
+
+Screw, 15.
+
+Screw, binding, 65, 66.
+
+Screw-driver, 14.
+
+Screw, set, 72.
+
+Sealing wax, 53.
+
+Secondary, 62, 98, 105, 158, 159, 160.
+
+Secondary circuit, 99.
+
+Secondary coil, 107, 108.
+
+Self-induction, 149, 156.
+
+Sender, 90, 97.
+
+Sending apparatus, 106.
+
+Sending key, 90.
+
+Separately excited, 46.
+
+Series-wound, 47.
+
+Severed magnet, 20.
+
+Sewage, 12.
+
+Shaft, 30.
+
+Shears, 14, 17.
+
+Shellac, 40.
+
+Shunt-wound, 47.
+
+Signal, 118.
+
+Silver, 19, 63, 125.
+
+Silver nitrate, 62.
+
+Socket, 54, 139.
+
+Soldering, 14.
+
+Soldering iron, 17.
+
+Solution, 55, 57, 62, 63, 84, 86, 133, 134, 142.
+
+Sounder, 90, 92, 95, 96.
+
+Sounding board, 119.
+
+Source, charging, 83.
+
+South pole, 20, 21, 22, 25, 50, 54, 156.
+
+Spark gap, 102, 106.
+
+Spark jump, 99.
+
+Spring finger, 69.
+
+Square, 14, 17.
+
+Standard, 62, 63.
+
+Station, 94, 95, 117, 122.
+
+Steel, 18, 19.
+
+Steel magnet, 53.
+
+Sterilized, 12.
+
+Stirrup, 75.
+
+Stock bit, 13.
+
+Stock contact, 121.
+
+Storage, 82.
+
+Storage battery, 107.
+
+Storing, 82.
+
+Substances, 135.
+
+Sulphate, 55, 128, 133.
+
+Sulphur, 19.
+
+Sulphuric acid, 31, 84.
+
+Sulphuric acid voltameter, 55, 57.
+
+Superstition, 171, 173.
+
+Surging, 153, 154.
+
+Swinging magnet, 53.
+
+Swinging switch blade, 67.
+
+Switch blades, 66.
+
+Switches, 65, 66, 70, 77, 78, 90, 117.
+
+Switches, bar, 65, 68, 90, 91.
+
+Switches, bar, parallel, 67.
+
+Switches, heart-shaped, 78.
+
+Switches, piece, 77.
+
+Switches, reversing, 67.
+
+Switches, sliding, 67, 80.
+
+Switches, terminal, 8.
+
+Switches, two-pole, 65.
+
+System, circuiting, 79.
+
+
+T
+
+Tail-piece, 16.
+
+Tantalum, 169.
+
+Telegraph, 11, 90, 96.
+
+Telegraph key, 106.
+
+Telegraph sounder, 108, 109.
+
+Telegraphing, 94.
+
+Telephone, 12, 110, 113, 117, 118, 119, 120.
+
+Telephone circuit, 118.
+
+Telephone connections, 116.
+
+Telephone hook, 122.
+
+Temperature, 56, 88, 134, 161, 170.
+
+Tension, high, 38, 102, 184.
+
+Tension, low, 38, 98, 102, 179.
+
+Terminal, 31, 34, 35, 40, 48, 82, 86, 93, 95, 107, 116, 121, 122, 151,
+    152, 153, 154, 156.
+
+Terminal knob, 31.
+
+Terminal, secondary, 102.
+
+Terminal switch, 81.
+
+Theoretical, 160.
+
+Therapeutics, 187.
+
+Thermo-electric couples, 146.
+
+Thermo-electricity, 135.
+
+Thermometer, 56.
+
+Thorium, 169, 186.
+
+Thunderbolt, 171, 173.
+
+Tin, 136.
+
+Tinfoil, 31, 101.
+
+Tools, 11, 13, 17.
+
+Torch, brazing, 17.
+
+Transformer, 145, 146, 158, 159, 180, 182.
+
+Transformer, step-down, 182.
+
+Transmission, 38, 187.
+
+Transmit, 63, 95, 157.
+
+Transmitter, 12, 120, 121, 122, 123.
+
+Transverse, 16, 52.
+
+Transversely, 43.
+
+Trigger, 75.
+
+Tripod, 31.
+
+Tubular, 44, 45.
+
+Two-pole switch, 65.
+
+
+U
+
+Ultra-violet, 185.
+
+Uranium, 186.
+
+
+V
+
+Vacuum, 184.
+
+Vapor lamps, 169.
+
+Velocity, 60, 73.
+
+Vertical armature, 75.
+
+Vibration, 110, 111, 113.
+
+Vibratory, 110.
+
+Vise, 13.
+
+Voltage, 37, 38, 60, 61, 62, 63, 87, 88, 99, 147, 154, 165, 180, 182.
+
+Voltage, high, 158.
+
+Voltaic, 29, 32.
+
+Voltaic pile, 33.
+
+Voltameter, 7, 58, 88.
+
+Voltameter, sulphuric, acid, 55, 57.
+
+Volts, 60, 62, 87, 89, 132, 158, 159.
+
+
+W
+
+Water, 123, 138, 144.
+
+Water power, 142.
+
+Watts, 60, 61, 160.
+
+Wave lengths, 104, 110.
+
+Weight, 49.
+
+Welding, 13, 182.
+
+Winding, 18, 40, 47, 58, 159, 196.
+
+Winding reel, 14.
+
+Window connection, 76.
+
+Window frame, 78.
+
+Wire, 6, 18, 21, 26, 28, 156.
+
+Wire, circuiting, 79.
+
+Wire coil, 40.
+
+Wire lead, 70.
+
+Wire, parallel, 28, 49.
+
+Wireless, 12.
+
+Wireless telegraphy, 103, 104, 184.
+
+Wiring, 80.
+
+Wiring, window, 77.
+
+Workshop, 11, 17.
+
+Wound, compound, 48.
+
+Wound-series, 47.
+
+Wound-shunt, 47.
+
+
+X
+
+X-ray, 184, 185, 187, 188.
+
+
+Z
+
+Zinc, 17, 34, 35, 85, 135.
+
+Zinc plates, 33.
+
+
+
+
+THE "HOW-TO-DO-IT" BOOKS
+
+
+CARPENTRY FOR BOYS
+
+A book which treats, in a most practical and fascinating manner all
+subjects pertaining to the "King of Trades"; showing the care and use of
+tools; drawing; designing, and the laying out of work; the principles
+involved in the building of various kinds of structures, and the
+rudiments of architecture. It contains over two hundred and fifty
+illustrations made especially for this work, and includes also a
+complete glossary of the technical terms used in the art. The most
+comprehensive volume on this subject ever published for boys.
+
+
+ELECTRICITY FOR BOYS
+
+The author has adopted the unique plan of setting forth the fundamental
+principles in each phase of the science, and practically applying the
+work in the successive stages. It shows how the knowledge has been
+developed, and the reasons for the various phenomena, without using
+technical words so as to bring it within the compass of every boy. It
+has a complete glossary of terms, and is illustrated with two hundred
+original drawings.
+
+
+PRACTICAL MECHANICS FOR BOYS
+
+This book takes the beginner through a comprehensive series of practical
+shop work, in which the uses of tools, and the structure and handling of
+shop machinery are set forth; how they are utilized to perform the work,
+and the manner in which all dimensional work is carried out. Every
+subject is illustrated, and model building explained. It contains a
+glossary which comprises a new system of cross references, a feature
+that will prove a welcome departure in explaining subjects. Fully
+illustrated.
+
+
+_Price 60 cents per volume_
+
+THE NEW YORK BOOK COMPANY
+147 FOURTH AVENUE  NEW YORK
+
+
+
+
+ +-----------------------------------------------------------------+
+ | Transcriber's Note.                                             |
+ |                                                                 |
+ | Every effort has been made to replicate this text as faithfully |
+ | as possible, including obsolete and variant spellings and other |
+ | inconsistencies.                                                |
+ |                                                                 |
+ | Minor punctuation and printing errors have been corrected.      |
+ |                                                                 |
+ | The first page of the original book is an advertisement. The    |
+ | page was moved to the end of the text.                          |
+ |                                                                 |
+ | Some hyphenation inconsistencies in the text were retained:     |
+ |    16-candle-power and 16-candlepower,                          |
+ |    Electromotive and electro-motive,                            |
+ |    Electro-meter and Electrometer,                              |
+ |    Horseshoe and horse-shoe,                                    |
+ |    Switchboard and switch-board,                                |
+ |                                                                 |
+ |  Two occurrences of 'Colorimeter' for 'Calorimeter' repaired.   |
+ +-----------------------------------------------------------------+
+
+
+
+
+
+End of the Project Gutenberg EBook of Electricity for Boys, by J. S. Zerbe
+
+*** END OF THIS PROJECT GUTENBERG EBOOK ELECTRICITY FOR BOYS ***
+
+***** This file should be named 22766.txt or 22766.zip *****
+This and all associated files of various formats will be found in:
+        http://www.gutenberg.org/2/2/7/6/22766/
+
+Produced by Joe Longo and the Online Distributed
+Proofreading Team at http://www.pgdp.net
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