Electricity for Boys
by J. S. Zerbe
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A working guide, in the successive steps of electricity, described in simple terms


By J. S. ZERBE, M.E.







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.


Preparing the Workshop. Uses of Our Workshop. What to Build. What to Learn. Uses of the Electrical Devices. Tools. Magnet-winding Reel.


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.


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.


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.


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.


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.


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.


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.


Induction. Low and High Tension. Elastic Property of Electricity. The Condenser. Connecting up a Condenser. The Interrupter. Uses of High-tension Coils.


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.


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.


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.


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.


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.


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.


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.


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.



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


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.



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.



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.

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.

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.



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.

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.

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.

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.

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).

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).

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.

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.

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).

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).

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.



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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

These tubular sections are called the commutator plates.

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').

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.

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.



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.

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).

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.

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).

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.

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.

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.



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.



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).

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).

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.

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.

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.

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'.

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'.

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:

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.

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.

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).

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.

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.

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.



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.

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.

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.

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.

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.



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.

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.

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.

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.

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