The Boy Electrician

Transcriber's Note

This book was transcribed from scans of the original found at Google Books. I have rotated some images. The more complex tables are treated as images.

A BOY’S WIRELESS OUTFIT MADE UP OF THE APPARATUS DESCRIBED IN CHAPTER XIV. THE JUNIOR DYNAMO AND A COHERER OUTFIT CAN BE SEEN ON THE LOWER PART OF THE TABLE.

The

Boy

Electrician

Practical Plans for Electrical

Apparatus for work and play, with an explanation

Of the principles of every-day electricity.

ALFRED P MORGAN

With illustrations by the author

BOSTON

LOTHROP, LEE & SHEPARD CO.

Entered at Stationers’ Hall, London

Published July, 1914

THE BOY ELECTRICIAN

NORWOOD PRESS

Berwick & Smith Co.

Norwood, Mass. U.S.A.

TO THE SELF-RELIANT

BOYS OF AMERICA,

OUR FUTURE ENGINEERS AND SCIENTISTS, THAN WHOM

NONE IN THE WHOLE WORLD ARE BETTER ABLE

TO WORK OUT AND SOLVE THE PROBLEMS

THAT EVER CONFRONT YOUNG

MANHOOD, THIS BOOK

IS CORDIALLY

DEDICATED.

THE BOY ELECTRICIAN

INTRODUCTION

Once upon a time, and this is a true tale, a boy had a whole railroad system for a toy. The train ran automatically, propelled by tiny electric motors, the signals went up and down, the station was reached, a bell rang, the train moved on again and was off on its journey around many feet of track to come back over the old route.

The boy viewed his gift with raptured eyes, and then his face changed and he cried out in the bitterness of his disappointment: "But what do I do?" The toy was so elaborate that the boy was left entirely out of the play. Of course he did not like it. His cry tells a long story.

The prime instinct of almost any boy at play is to make and to create. He will make things of such materials as he has at hand, and use the whole force of dream and fancy to create something out of nothing. The five-year-old will lay half a dozen wooden blocks together with a spool on one end and tell you it is a steam train. And it is. He has both made and created an engine, which he sees but which you don’t, for the blocks and spool are only a symbol of his creation. Give his older brother a telephone receiver, some wire and bits of brass, and he will make a wireless telegraph outfit and listen to a steamship hundreds of miles away spell out its message to the shore.

The wireless outfit is not a symbol, but something that you can both hear and see in operation even though you may not understand the whispering of the dots and dashes. And as soon as the mystery of this modern wonder more firmly grips your imagination, you perhaps may come to realize that we are living more and more in the age of electricity and mechanism. Electricity propels our trains, lights our houses and streets, makes our clothes, cures our ills, warms us, cooks for us and performs an innumerable number of other tasks at the turning of a little switch. A mere list is impossible.

Almost every boy experiments at one time or another with electricity and electrical apparatus. It is my purpose in writing this book to open this wonderland of science and present it in a manner which can be readily understood, and wherein a boy may "do something." Of course there are other books with the same purport, but they do not accomplish their end. They are not practical. I can say this because as a boy I have read and studied them and they have fallen far short of teaching me or my companions the things that we were seeking to learn. If they have failed in this respect, they have done so perhaps not through any inability of the author, but from the fact that they have not been written from the boy’s standpoint. They tell what the author thought a boy ought to know but not what he really does want to know. The apparatus described therein is for the most part imaginary. The author thought it might be possible for a boy to build motors, telegraph instruments, etc., out of old bolts and tin cans, but he never tried to do so himself.

The apparatus and experiments that I have described have been constructed and carried out by boys. Their problems and their questions have been studied and remedied. I have tried to present practical matter considered wholly from a boy’s standpoint, and to show the young experimenter just what he can do with the tools and materials in his possession or not hard to obtain.

To the boy interested in science, a wide field is open. There is no better education for any boy than to begin at the bottom of the ladder and climb the rungs of scientific knowledge, step by step. It equips him with information which may prove of inestimable worth in an opportune moment.

There is an apt illustration in the boy who watched his mother empty a jug of molasses into a bowl and replace the cork. His mother told him not to disturb the jug, as it was empty. He persisted, however, and turned the jug upside down. No more molasses came, but out crawled a fly. New developments in science will never cease. Invention will follow invention. The unexpected is often a valuable clue. The Edisons and Teslas of to-day have not discovered everything. There is a fly in the molasses, to be had by persistence. Inspiration is but a starting-point. Success means work, days, nights, weeks, and years.

There can be no boy who will follow exactly any directions given to him, or do exactly as he is told, of his own free will. He will "bolt" at the first opportunity. If forced or obliged to do as he is directed, his action will be accompanied by many a "why?" Therefore in presenting the following chapters I have not only told how to make the various motors, telegraphs, telephones, radio receivers, etc. but have also explained the principles of electricity upon which they depend for their operation, and how the same thing is accomplished in the every-day world. In giving directions or offering cautions, I have usually stated the reason for so doing, in the hope that this information may be a stimulant to the imagination of the young experimenter and a useful guide in enabling him to proceed along some of the strange roads on which he will surely go.

ALFRED P. MORGAN

UPPER MONTCLAIR, N. J.

[THE BOY ELECTRICIAN]
[The Full Project Gutenberg License]

[A BOY’S WIRELESS OUTFIT MADE UP OF THE APPARATUS DESCRIBED IN CHAPTER XIV. THE JUNIOR DYNAMO AND A COHERER OUTFIT CAN BE SEEN ON THE LOWER PART OF THE TABLE.]
[Fig. 1.—The Card of a Mariner's Compass, Showing the "Points."]
[Fig. 2.—A Bar Magnet]
[Fig. 3.—A Horseshoe Magnet]
[Fig. 4.—A Magnetized Needle and a Bar Magnet which have been dipped in Iron Filings.]
[Fig. 5.—The Lifting Power of a Bar Magnet. It must be brought closer to the nails than the tacks because they are heavier.]
[Fig. 6.—A Simple Compass.]
[Fig. 7.—Several Different Methods of Making a Simple Compass.]
[Fig. 8.—The Attraction of an Iron Nail through Glass.]
[Fig. 9.—A Magnetic Chain.]
[Fig. 10.—An Experiment Illustrating that Like Poles Repel Each Other and Unlike Poles Attract.]
[Fig. 11.—A Magnetic Boat.]
[Fig. 12.—Repulsion between Similar Poles, Shown by Floating Needles.]
[Fig. 13.—A Magnetic "Phantom," Showing the Field of Force about a Magnet.]
[Fig. 14.—Magnetic Phantom showing the Lines of Force about a Horseshoe Magnet.]
[Fig. 15.—Lines of Force between Like and Unlike Poles.]
[Fig. 16.—A Simple Dipping Needle.]
[Fig. 17.—An Electrified Glass Rod will Attract Small Bits of Paper.]
[From the author's "Wireless Telegraphy and Telephony" by permission. A Double Lightning Discharge from a Cloud to the Earth.]
[Fig. 19.—A Piece of Dry Writing-Paper may be Electrified by Rubbing.]
[Fig. 20.—A Surprise for the Cat.]
[Fig. 21.—A Paper Electroscope.]
[Fig. 22.—A Pith-Ball Electroscope.]
[Fig. 23.—A Double Pith-Ball Electroscope.]
[Fig. 24.—A Gold-Leaf Electroscope.]
[Fig. 25.—Method of Suspending an Electrified Rod in a Wire Stirrup.]
[Fig. 26.—Similarly Electrified Bodies Repel Each Other. Dissimilarly Electrified Ones Attract Each Other.]
[Fig. 27.—The Electrophorous]
[Fig. 28.—An Electric Frog-Pond.]
[Fig. 29.—Front View of a Cylinder Electric Machine.]
[Fig. 30.—Method of Finding the Center of a Circle.]
[Fig. 31.—The "Rubber."]
[Fig. 32.—The Prime Conductor or Collector.]
[Fig. 33.—The Complete Cylinder Electric Machine.]
[Fig. 34.—Paper Pattern for laying out the Plates.]
[Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.]
[Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.]
[Fig. 37.—The Frame.]
[Fig. 38.—The Upright.]
[Fig. 39.—The Driving-Wheels and Axle.]
[Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.]
[Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.]
[Fig. 42.—A Comb or Collector.]
[Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.]
[Fig. 44.—The Complete Wimshurst Electric Machine. B B B B, Brushes. C C, Combs. D B, Discharge Ball. I I, Glass Rods. H, Handle. Q Q, Quadrant Rods. S S S S S, Sectors. S G, Spark-Gap. P P, Driving-Wheels. For the sake of clearness, several of the sectors are not shown.]
[Fig. 45.—The Leyden Jar.]
[Fig. 46.—A Wooden Mortar for Igniting Gunpowder.]
[Fig. 47.—An Electric Umbrella.]
[Fig. 48.—A Lightning Board.]
[Fig. 49.—An Electric Dance.]
[Fig. 50.—An Electric Whirl.]
[Fig. 51.—Lichtenberg's Figures.]
[Fig. 52.—The Voltaic Cell.]
[Fig. 53.—The Elements of Simple Voltaic Cell.]
[Fig. 54.—A Home-Made Voltaic Cell.]
[Fig. 55.—Carbon-Cylinder Cell, and Cylinder.]
[Fig. 56.—A Leclanche Cell, showing the Porous Cup.]
[Fig. 57.—A Dry Cell.]
[Fig. 58.—The Different Operations involved in Making a Dry Cell.]
[Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.]
[Fig. 60.—A Method of making a Cell Element from Carbon Rods.]
[Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.]
[Fig. 62. A Method of Mounting four Carbon Plates.]
[Fig. 63.—A Battery Element arranged for three Cells.]
[Fig. 64.—A Plunge Battery, with Windlass.]
[Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63. They may be lifted out and placed on the "Arms" to drain.]
[Fig. 66.—An Edison-Lalande Cell.]
[Fig. 67.—A Tomato-Can Cell; Sectional View.]
[Fig. 68.—The Tomato-Can Cell Complete.]
[Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.]
[Fig. 70.—Small Storage Cells.]
[Fig. 71.—How to make the Plates for a Storage Cell.]
[Fig. 72.—The Wood Separator.]
[Fig. 73.—The Complete Element for a Storage Cell.]
[Fig. 74.—A Battery of Home-Made Storage Cells.]
[Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.]
[Fig. 76.—A Current of Electricity flowing through a Wire will deflect a Compass Needle.]
[Fig. 77.—If a Loop of Wire is formed about a Compass Needle, the Deflection will be greater.]
[Fig. 78.—Iron Filings clustered on a Wire carrying a Current of Electricity.]
[Fig. 79.—Magnetic Phantom formed about a Wire carrying a Current of Electricity.]
[Fig. 80.—Magnetic Phantom formed about several Turns of wire.]
[Fig. 81.—Paper Tube wrapped with Wire for Experimental Purposes.]
[Fig. 82.—Showing how the Lines of Force "Leak" at the sides of the coil, from a Coil of Wire, and how they are concentrated by an Iron Core.]
[Fig. 83.—The Principle of an Electro-Magnet.]
[Fig. 84.—if you wrap some insulated Wire around an Ordinary Nail and connect it to a Battery, it will become an Electro-Magnet.]
[Fig. 85.—If you wind the Wire around a small Paper Tube into which a Nail will slide easily, the Coil will draw the Nail in when the Current is turned on.]
[By permission, from "Solenoids" by C. R. Underhill. Lifting-Magnets of the type known as Plate, Billet, and Ingot Magnets.]
[Fig. 86.—Showing how a Current of Electricity may be induced by a Bar Magnet and a Coil.]
[Fig. 87.—A Horseshoe Magnet and a Coil arranged to produce Electric Currents by Induction.]
[Fig. 88.—Graphic Representation of a Direct and an Alternating Current.]
[Fig. 89.—Staples and Wooden Cleat used for running Low Voltage Wires.]
[Fig. 90.—Porcelain Insulators to support Electric Light Wires.]
[Fig. 91.—Glass Insulator Binding-Posts and Pin used to support Telegraph and Telephone wires.]
[Fig. 92.—Types of Binding-Posts.]
[Fig. 93.—Home-made Binding-Posts.]
[Fig. 94.—Binding-Post removed from the Carbon of a Dry Cell.]
[Fig. 95.—Simple Switches. A, Single-Point Switch. B, Two-Point Switch. C, Three-Point Switch. D, Five-Point Switch. E, Lever with End Rolled up to form Handle. F, Lever with Handle made from part of a Spool.]
[Fig. 96.—Knife Switches.]
[Fig. 97.—Metal Parts for the Knife Switches.]
[Fig. 98.—Simple Fuses. A, Fuse-Block with plain Wire Fuse. D, Fuse-Block with Mica Fuse in position.]
[Fig. 99.—Lightning-Arrester and Ground-Wire Switch.]
[Fig. 100.—Home-made Lightning-Arrester.]
[Fig. 101.—Lightning-Arrester for Telephone Wires.]
[Fig. 102.—A, Base, showing Slot. B and C, Sides and Top of the Bobbin. D, Base and Bobbin in Position.]
[Fig. 103.—Arrangement of the Needle and Pointer.]
[Fig. 104.—A, Bearings. B, How the Needle is mounted.]
[Fig. 105.—The Completed Meter.]
[Fig. 106.—Details of the Bobbin.]
[Fig. 107.—The Bobbin partly cut away so as to show the Bearing. Details of the Armature and Shaft.]
[Fig. 108.—Completed Voltmeter.]
[Fig. 109.—Circuits for Calibrating the Ammeter and Voltmeter.]
[Fig. 110.—Simple Compass Galvanoscope.]
[Fig. 111.—Galvanoscope.]
[Fig. 112.—Astatic Galvanoscope.]
[Fig. 113.—Astatic Needles.]
[Fig. 114.—Bobbin for Astatic Galvanometer.]
[Fig. 115.—Completed Astatic Galvanometer.]
[Fig. 116.—Wheatstone Bridge.]
[Fig. 117.—Knife-Contact.]
[Fig. 118.—Resistance-Coil. A shows how the Wire is doubled and wound on the Spool. B is the completed Coil.]
[Fig. 119.—Details of the Magnet Spools, and Yoke for an Electric Bell.]
[Fig. 120.—Details of the Armature, and Contact Screw.]
[Fig. 121.—The Completed Bell.]
[Fig. 122.—Diagram showing how to connect a Bell, Battery, and Push-Button.]
[Fig. 123.—Two Simple Push-Buttons.]
[Fig. 124.—Diagram showing how to arrange a Bell System of Return Signals.]
[Fig. 125.—Burglar-Alarm Trap.]
[Fig. 126.—An Early-Riser’s Electric Alarm Attachment for a Clock.]
[Fig. 127.—Details of the Chain Electrodes, etc.]
[Fig. 128.—An Annunciator Drop.]
[Fig 129.—Details of the Drop-Frame and Armature.]
[Fig. 130.—A Typical Telegraph Key, showing the Various Parts.]
[Fig. 131.—A Typical Telegraph Sounder, showing the Various Parts.]
[Fig. 132.—A Simple Home-made Telegraph Key.]
[Fig. 133.—A Simple Home-made Telegraph Sounder.]
[Fig. 134.—A Diagram showing how to connect two Simple Telegraph Stations.]
[Fig. 135.—A Complete Telegraph Set, consisting of a Keyboard and a Sounder.]
[Fig. 136.—Details of the Telegraph Set shown in Figure 135.]
[Fig. 137.—A Diagram showing how to connect two Complete Telegraph Sets, using one Line Wire and a Ground. The Two-Point Switches throw the Batteries out of Circuit when the Line is not in use.]
[Fig. 138.—Details of the Relay Parts.]
[Fig. 139.—The Completed Relay.]
[Fig. 140.—A Diagram showing how to connect a Relay, Sounder, and Key. Closing the Key will operate the Relay. The Relay will then operate the Sounder in turn.]
[Fig. 141.—How to hold a Telegraph Key.]
[Fig. 142.—The Morse Telegraphic Code.]
[Fig. 143.—A Microphone connected to a Telephone Receiver, and a Battery.]
[Fig. 144.—A Very Sensitive Form of Microphone, with which the Footsteps of a Fly can be heard.]
[Fig. 145.—A Telephone System, consisting of a Receiver, Transmitter, and a Battery connected in Series. Words spoken into the Transmitter are reproduced by the Receiver.]
[Fig. 146.—A Watch-Case Telephone Receiver.]
[Fig. 147.—A Simple Form of Telephone Receiver.]
[Fig. 148.—A Home-made Telephone Transmitter.]
[Fig. 149.—A Complete Telephone Instrument. Two Instruments such as this are necessary to form a simple Telephone System.]
[Fig. 150.—Diagram of Connection for the Telephone Instrument shown in Fig. 149.]
[Fig. 151.—A Desk-Stand Type of Telephone.]
[Fig. 152.—A Telephone Induction Coil.]
[Fig. 153.—Diagram of Connection for a Telephone System employing an Induction Coil at each Station.]
[Fig. 154.—Details of Various Parts of a Medical Coil.]
[Fig. 155.—Details of Interrupter for Medical Coil.]
[Fig. 156.—Completed Medical Coil.]
[Fig. 157.—Diagram showing Essential Parts of Induction Coil.]
[Fig. 158.—Empty Paper Tube, and Tube filled with Core Wire preparatory to winding on the Primary.]
[Fig. 159.—Illustrating the Various Steps in winding on the Primary and fastening the Ends of the Wire.]
[Fig. 160.—Complete Primary Winding and Core.]
[Fig. 161.—The Primary covered with Insulating Layer of Paper ready for the Secondary.]
[Fig. 162.—Simple Winding Device for winding the Secondary.]
[Fig. 163.—Completed Secondary Winding.]
[Fig. 164.—Interrupter Parts.]
[Fig. 165.—Condenser.]
[Fig. 166.—Completed Coil.]
[Fig. 167.—Diagram showing how to connect the Apparatus for the "Electric Hands" Experiment.]
[Fig. 168.—Geissler Tubes.]
[Fig. 169.—The Bulb will emit a Peculiar Greenish Light.]
[Fig. 170.—An Electrified Garbage-can.]
[Fig. 171.—Jacob's Ladder.]
[Fig. 172.—An X-Ray Tube.]
[Fig. 173.—Fluoroscope.]
[Fig. 174.—How to connect an X-Ray Tube to a Spark-Coil.]
[An X-Ray Photograph of the hand taken with the Outfit shown in Figure 174. The arrows point to injuries to the bone of the third finger near the middle Joint Resulting in a Stiff Joint.]
[Fig. 175.—Comparison between Electric Current and Flow of Water.]
[Fig. 176.—Alternating Current System for Light and Power.]
[Fig. 177.—Motor Generator Set for changing Alternating Current to Direct Current.]
[Fig. 178.—Step-Up Transformer.]
[Fig. 179.—Step-Down Transformer.]
[Fig. 180.—Core Dimensions.]
[Fig. 181.—The Core, Assembled and Taped.]
[Fig. 182.—Transformer Leg.]
[Fig. 183.—Fiber Head.]
[Fig. 184.—Leg with Heads in Position for Winding.]
[Fig. 185.—How to make a Tap in the Primary by soldering a Copper Strip to the Wire.]
[Fig. 186.—The Transformer completely Wound and ready for Assembling.]
[Fig. 187.—Wooden Strips for mounting the Transformer on the Base.]
[Fig. 188.—Details of the Switch Parts.]
[Fig. 189.—The Complete Switch.]
[Fig. 190.—Diagram of Connections.]
[Fig. 191.—Top View of the Transformer.]
[Fig. 192.—Side View of the Transformer.]
[Fig. 193.—Little Waves spread out from the Spot.]
[Fig. 194.—A Simple Transmitter.]
[Fig. 195.—A Simple Receptor.]
[Fig. 196.—Molded Aerial Insulator]
[Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.]
[Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.]
[Fig. 199.—Various Types of Aerials.]
[Fig. 200.—A Ground Clamp for Pipes.]
[Fig. 201.—Details of the Tuning Coil.]
[Fig. 202.—Side and End Views of the Tuning Coil.]
[Fig. 203.—Complete Double-Slider Tuning Coil.]
[Fig. 204.—A Simple Loose Coupler.]
[Fig. 205.—Details of the Wooden Parts.]
[Fig. 206.—Side View of the Loose Coupler.]
[Fig. 207.—Top View of the Loose Coupler.]
[Fig. 208.—End Views of the Loose Coupler.]
[Fig. 209.—Complete Loose Coupler.]
[Fig. 210.—A Crystal Detector.]
[Fig. 211.—Details of the Crystal Detector.]
[A Double Slider Tuning Coil.]
[A Junior Loose Coupler.]
[Crystal Detectors.]
[Fig. 212 Details of the "Cat Whisker" Detector.]
[Fig. 213.—Another Form of the "Cat-Whisker" Detector.]
[Fig. 214.—"Cat-Whisker" Detector.]
[Fig. 215.—Building up a Fixed Condenser.]
[Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.]
[Fig. 217.—A Telephone Head Set.]
[Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.]
[Fig. 219.—Circuit showing how to connect a Loose Coupler.]
[Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.]
[Fig. 221.—A Wireless Spark Coil.]
[Fig. 222.—Small Spark Gaps.]
[Fig. 223.—Diagram showing how to connect a Simple Transmitter.]
[Fig. 224.—A Test-Tube Leyden Jar.]
[Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.]
[Fig. 226.—A Helix and Clip.]
[Fig. 227.—An Oscillation Transformer.]
[AN OSCILLATION HELIX.]
[AN OSCILLATION CONDENSER.]
[Fig 228.—Circuit showing how to connect a Helix and a Condenser.]
[Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.]
[Fig 230.—An Aerial Switch.]
[Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.]
[Fig. 232.—The Continental Alphabet.]
[Fig. 233.—A Coherer and a Decoherer.]
[Fig. 234.—Details of the Coherer.]
[Fig. 235.—The Relay.]
[Fig. 236.—The Complete Coherer Outfit.]
[Fig. 237.—A Simple Arrangement showing the Inductive Action between two Coils.]
[Fig. 238.—A Simple Wireless Telephone. Speech directed into the Transmitter can be heard in the Receiver, although there is no direct electrical connection between the two.]
[Fig. 239.—A Double-Contact Strap-Key. The Dotted Lines show how the Binding-Posts are connected.]
[Fig. 240.—The Circuit of the Wireless Telephone. When the Key is up, the Receiver is ready for Action. When the Key is pressed, the Transmitter and Battery are thrown into the Circuit.]
[Fig. 241.—A Complete Wireless Telephone and Telegraph Station for Amateurs. 1. The Telephone Coil. 2. The Telephone Transmitter. 3. Double-Contact Strap-Key. 4. The Battery. 5. Spark Coil. 6. Key. 7. Spark-Gap. 8. Aerial Switch. 9. Loose Coupler. 10. Detector, 11. Fixed Condenser. 12. Code Chart. 13. Amateur License. 14. Aerial. 15. Telephone Receivers.]
[Fig. 242.—A Simple Electric Motor which may be made in Fifteen Minutes.]
[Fig. 243.—Details of the Armature of the Simplex Motor.]
[Fig. 244.—The Armature.]
[Fig. 245.—The Field.]
[Fig. 246.—The Field and Commutator.]
[Fig. 247.—The Bearings.]
[Fig. 248.—The Complete Motor.]
[Fig. 249.—Details of the Motor.]
[Fig. 250.—Complete Motor.]
[Fig. 251—A Telephone Magneto.]
[Fig. 252.—The Principle of the Alternator and the Direct-Current Dynamo.]
[Fig. 253.—Details of the Armature, Commutator, and Brushes.]
[Fig. 254.—The Complete Generator.]
[Fig. 255.—Details of the Field Casting.]
[Fig. 256.—Details of the Armature Casting.]
[Fig. 257.—Details of the Commutator.]
[Fig. 258.—Diagram showing how to connect the Armature Winding to the Commutator.]
[Fig. 259.—Details of the Wooden Base.]
[Fig. 260.—The Pulley and Bearings.]
[Fig. 261.—The Brushes.]
[THE JUNIOR DYNAMO MOUNTED ON A LONG WOODEN BASE AND BELTED TO A GROOVED WHEEL FITTED WITH A CRANK SO THAT THE DYNAMO CAN BE RUN AT HIGH SPEED BY HAND POWER. THE ILLUSTRATION ALSO SHOWS A SMALL INCANDESCENT LAMP CONNECTED TO THE DYNAMO SO THAT WHEN THE CRANK IS TURNED THE LAMP WILL LIGHT.]
[Fig. 262.—Complete Dynamo.]
[Fig. 263.—Complete Electric Railway operated by Dry Cells. Note how the Wires from the Battery are connected to the Rails by means of the Wooden Conductors illustrated in Figure 277.]
[Fig. 264.—Details of the Floor of the Car.]
[Fig. 265.—Details of the Bearing which supports the Wheel and Axle.]
[Fig. 266.—The Wheels and Axle.]
[Fig. 267.—The Motor.]
[Fig. 268.—The Complete Truck of the Car without the Body.]
[Fig. 269.—Pattern for the Sides and Ends of the Car.]
[Fig. 270.—The Roof of the Car.]
[Fig. 271.—The Completed Car.]
[Fig. 272.–Details of a Wooden Tie.]
[Fig. 273.–Arrangement of Track.]
[Fig. 274.—Three Different Patterns for laying out the Track.]
[Fig. 275.—Details of the Base of the Cross-over.]
[Fig. 276.—The Completed Cross-over.]
[Fig. 277.—A Connector for joining the Ends of the Rails.]
[Fig. 278.—A Bumper for preventing the Car from leaving the Rails.]
[Fig. 279.—A Design for a Railway Bridge.]
[Fig. 280.—A Design for a Railway Station.]
[Fig. 281.—Miniature Carbon Battery Lamp.]
[Fig. 282.—Miniature Tungsten Battery Lamp.]
[Fig. 283.—Lamps fitted respectively with Miniature, Candelabra, and Ediswan Bases.]
[Fig. 284.—Miniature Flat-Base Porcelain Receptacle.]
[Fig. 285.—Weather-proof and Pin-Sockets.]
[Fig. 286.—Types of Battery Switches suitable for Miniature Lighting.]
[Fig. 287.—How Lamps are Connected in Multiple.]
[Fig. 288.—How Lamps are Connected in Series.]
[Fig. 289.—Three-way Wiring Diagram. The Light may be turned off or on from either Switch.]
[Fig. 290.—A Lamp Bracket for Miniature Lighting.]
[Fig. 291.—A Home-made Bracket.]
[Fig. 292.—A Hanging Lamp.]
[Fig. 293.—How the Reflector is made.]
[Fig. 294.—A Three-Cell Dry Battery for use in Hand-Lanterns, etc.]
[Fig. 295.—An Electric Hand-Lantern.]
[Fig. 296.—An Electric Ruby Lantern.]
[Fig. 297.—The Electric Ruby Lamp with Glass and Shield Removed.]
[Fig. 298.—An Electric Night-Light for telling the Time during the Night.]
[Fig. 299.—A Watch-Light.]
[Fig. 300.—A "Pea" Lamp attached to a Flexible Wire and a Plug.]
[Fig. 301.—Four Steps in Carving a Skull Scarf-Pin. 1. The Bone. 2. Hole drilled in Base. 3. Roughed out. 4. Finished.]
[Fig. 302.—The Completed Pin ready to be connected to a Battery by removing the Lamp from a Flashlight and screwing the Plug into its Place.]
[Fig. 303.—How the Copper Wires (C) and the Silver Wires (I) are twisted together in Pairs.]
[Fig. 304.—Wooden Ring.]
[Fig. 305.—Complete Thermopile. An Alcohol Lamp should be lighted and placed so that the Flame heats the Inside Ends of the Wires in the Center of the Wooden Ring.]
[Fig. 306.—A Reflectoscope.]
[Fig. 307.—How the Lens is Arranged and Mounted.]
[Fig. 308.—A View of the Reflectoscope from the Rear, showing the Door, etc.]
[Fig. 309.—A View of the Reflectoscope with the Cover removed, showing the Arrangement of the Lamps, etc.]
[Fig. 310.—A Socket for holding the Lamp.]
[Fig. 311.—The Tin Reflector.]
[Fig 312.—Top View of Lamp Bank, showing how the Circuit is arranged. A and B are the Posts to which should be connected any Device it‘s desirable to operate.]
[Fig. 313.—A Glass Jar arranged to serve as an Electro-Plating Tank.]
[Fig. 314.—A Rheostat.]
[Fig. 315.—A Pole-Changing Switch or Current Reverser. The Connecting Strip is pivoted so that the Handle will operate both the Levers, A and B.]
[COMPLETE RECEIVING SET, CONSISTING OF DOUBLE SLIDER TUNING COIL, DETECTOR AND FIXED CONDENSER.]
[COMPLETE RECEIVING SET, CONSISTING OF A LOOSE COUPLER IN PLACE OF THE TUNING COIL, DETECTOR AND FIXED CONDENSER.]
[Fig. 316. A Complete Wireless Receiving Outfit.]
[Fig. 317.—Illustrating the Principle of the Tesla Coil. A Leyden Jar discharges through the Primary Coil and a High-Frequency Spark is produced at the Secondary.]
[Fig. 318.—Details of the Wooden Rings used as the Primary Heads.]
[Fig. 319.—Details of the Cross Bars which support the Primary Winding.]
[Fig. 320.—The Secondary Head.]
[A COMPLETE COHERER OUTFIT AS DESCRIBED ON PAGE 274.]
[THE TESLA HIGH FREQUENCY COIL.]
[Fig. 321.—End View of the Complete Tesla Coil.]
[Fig. 322.—The Complete Tesla Coil.]
[Fig 323.—Showing how a Glass-Plate Condenser is built up of Alternate Sheets of Tinfoil and Glass.]
[Fig. 324.—A Diagram showing the Proper Method of Connecting a Tesla Coil.]

CHAPTER I MAGNETS AND MAGNETISM

Over two thousand years ago, in far-away Asia Minor, a shepherd guarding his flocks on the slope of Mount Ida suddenly found the iron-shod end of his staff adhering to a stone. Upon looking further around about him he found many other pieces of this peculiar hard black mineral, the smaller bits of which tended to cling to the nails and studs in the soles of his sandals.

This mineral, which was an ore of iron, consisting of iron and oxygen, was found in a district known as Magnesia, and in this way soon became widely known as the "Magnesstone," or magnet.

This is the story of the discovery of the magnet. It exists in legends in various forms. As more masses of this magnetic ore were discovered in various parts of the world, the stories of its attractive power became greatly exaggerated, especially during the Middle Ages. In fact, magnetic mountains which would pull the iron nails out of ships, or, later, move the compass needle far astray, did not lose their place among the terrors of the sea until nearly the eighteenth century.

For many hundreds of years the magnet-stone was of little use to mankind save as a curiosity which possessed the power of attracting small pieces of iron and steel and other magnets like itself. Then some one, no one knows who, discovered that if a magnet-stone were hung by a thread in a suitable manner it would always tend to point North and South; and so the "Magnes-stone" became also called the "lodestone," or "leading-stone."

These simple bits of lodestone suspended by a thread were the forerunners of the modern compass and were of great value to the ancient navigators, for they enabled them to steer ships in cloudy weather when the sun was obscured and on nights when the pole-star could not be seen.

The first real compasses were called gnomons, and consisted of a steel needle which had been rubbed upon a lodestone until it acquired its magnetic properties. Then it was thrust through a reed or short piece of wood which supported it on the surface of a vessel of water. If the needle was left in this receptacle, naturally it would move against the side and not point a true position. Therefore it was given a circular movement in the water, and as soon as it came to rest, the point on the horizon which the north end designated was carefully noted and the ship’s course laid accordingly.

The modern mariners’ compass is quite a different arrangement. It consists of three parts, the bowl, the card, and the needle. The bowl, which contains the card and needle, is usually a hemispherical brass receptacle, suspended in a pair of brass rings, called gimbals, in such a manner that the bowl will remain horizontal no matter how violently the ship may pitch and roll. The card, which is circular, is divided into 32 equal parts called the points of the compass. The needles, of which there are generally from two to four, are fastened to the bottom of the card.

Fig. 1.—The Card of a Mariner's Compass, Showing the "Points."

In the center of the card is a conical socket poised on an upright pin fixed in the bottom of the bowl, so that the card hanging on the pin turns freely around its center. On shipboard, the compass is so placed that a black mark, called the lubber’s line, is fixed in a position parallel to the keel. The point on the compass-card which is directly against this line indicates the direction of the ship’s head.

Experiments with Magnetism

The phenomena of magnetism and its laws form a very important branch of the study of electricity, for they play an important part in the construction of almost all electrical apparatus.

Dynamos, motors, telegraphs, telephones, wireless apparatus, voltmeters, ammeters, and so on through a practically endless list, depend upon magnetism for their operation.

Artificial Magnets are those made from steel by the application of a lodestone or some other magnetizing force.

The principal forms are the Bar and Horseshoe, so called from their shape. The process of making such a magnet is called Magnetization.

Fig. 2.—A Bar Magnet

Small horseshoe and bar magnets can be purchased at toy-stores. They can be used to perform very interesting and instructive experiments.

Fig. 3.—A Horseshoe Magnet

Stroke a large darning-needle from end to end, always in the same direction, with one end of a bar magnet. Then dip the needle in some iron filings and it will be found that the filings will cling to the needle. The needle has become a magnet.

Dip the bar magnet in some iron filings and it will be noticed that the filings cling to the magnet in irregular tufts near the ends, with few if any near the middle.

Fig. 4.—A Magnetized Needle and a Bar Magnet which have been dipped in Iron Filings.

This experiment shows that the attractive power of a magnet exists in two opposite places. These are called the poles.

There exists between magnets and bits of iron and steel a peculiar unseen force which can exert itself across space.

The power with which a magnet attracts or repels another magnet or attracts bits of iron and steel is called

Magnetic Force. The force exerted by a magnet upon a bit of iron is not the same at all distances. The force is stronger when the magnet is near the iron and weaker when it is farther away.

Fig. 5.—The Lifting Power of a Bar Magnet. It must be brought closer to the nails than the tacks because they are heavier.

Place some small carpet-tacks on a piece of paper and hold a magnet above them. Gradually lower the magnet until the tacks jump up to meet it.

Then try some nails in place of the tacks. The nails are heavier than the tacks, and it will require a greater force to lift them. The magnet will have to be brought much closer to the nails than to the tacks before they are lifted, showing that the force exerted by the magnet is strongest nearest to it.

Magnetize a needle and lay it on a piece of cork floating in a glass vessel of water. It will then be seen that the needle always comes to rest lying nearly in a north and south line, with the same end always toward the north.

Fig. 6.—A Simple Compass.

The pole of the magnet which tends to turn towards the north is called the north-seeking pole and the opposite one is called the south-seeking pole.

The name is usually abbreviated to simply the north and south poles. The north pole of a magnet is often indicated by a straight line or a letter N stamped into the metal.

A magnetized needle floating on a cork in a basin of water is a simple form of

Fig. 7.—Several Different Methods of Making a Simple Compass.

Compass. Figure 7 shows several other different ways of making compasses. The first method is to suspend a magnetized needle from a fine silk fiber or thread.

The second method illustrates a very sensitive compass made from paper. Two magnetized needles are stuck through the sides with their north poles both at the same end. The paper support is mounted upon a third needle stuck through a cork.

A compass which more nearly approaches the familiar type known as a pocket compass may be made from a small piece of watch-spring or clock-spring.

The center of the needle is annealed or softened by holding it in the flame of an alcohol lamp and then allowing it to cool.

Lay the needle on a piece of soft metal such as copper or brass, and dent it in the center with a punch.

Balance the needle on the end of a pin stuck through the bottom of a pill-box.

Magnetic Substances are those which are attracted by a magnet. Experiment with a number of different materials, such as paper, wood, brass, iron, copper, zinc, rubber, steel, chalk, etc. It will be found that only iron and steel are capable of being attracted by your magnet. Ordinary magnets attract but very few substances. Iron, steel, cobalt, and nickel are about the only ones worthy of mention.

Attraction through Bodies. A magnet will attract a nail or a tack through a piece of paper, just as if nothing intervened.

Fig. 8.—The Attraction of an Iron Nail through Glass.

It will also attract through glass, wood, brass, and all other substances. Through an iron plate, however, the attraction is reduced or entirely checked because the iron takes up the magnetic effect itself and prevents the force from passing through and reaching the nail.

A number of carpet-tacks may be supported from a magnet in the form of a chain. Each individual tack in the series becomes a temporary magnet by induction.

If the tack in contact with the magnet be taken in the hand and the magnet suddenly withdrawn, the tacks will at once lose their magnetism and fall apart.

Fig. 9.—A Magnetic Chain.

It will furthermore be found that a certain magnet will support a certain number of tacks in the form of a chain, but that if a second magnet is placed beneath the chain, so that its south pole is under the north pole of the original magnet, the chain may be lengthened by the addition of several other tacks.

The reason for this is that the magnetism in the tacks is increased by induction.

Magnets will Attract or Repel each other, depending upon which poles are nearest.

Magnetize a sewing-needle and hang it from a thread. Bring the north pole of a bar magnet near the lower end of the needle. If the lower end of the needle happens to be a south pole it will be attracted by the north pole of the bar magnet. If, on the other hand, it is a north pole, it will be repelled and you cannot touch it with the north pole of the bar magnet unless you catch it and hold it.

This fact gives rise to the general law of magnetism: Like poles repel each other and unlike poles attract each other.

Fig. 10.—An Experiment Illustrating that Like Poles Repel Each Other and Unlike Poles Attract.

Another interesting way of illustrating this same law is by making a small boat from cigar-box wood and laying a bar magnet on it. Place the north pole of the bar magnet in the bow of the boat.

Float the boat in a basin of water. Bring the south pole of a second magnet near the stern of the boat and it will sail away to the opposite side of the basin. Present the north pole of the magnet and it will sail back again.

Fig. 11.—A Magnetic Boat.

If the south pole of the magnet is presented to the bow of the boat the little ship will follow the magnet all around the basin.

The repulsion of similar poles may be also illustrated by a number of magnetized sewing-needles fixed in small corks so that they will float in a basin of water with their points down.

Fig. 12.—Repulsion between Similar Poles, Shown by Floating Needles.

The needles will then arrange themselves in different symmetrical groups, according to their number.

A bar magnet thrust among them will attract or repel them depending upon its polarity.

The upper ends of the needles should all have the same polarity, that is, all be either north or south poles.

Magnetism flows along certain lines called

Lines of Magnetic Force. These lines always form closed paths or circuits. The region in the neighborhood of a magnet through which these lines are passing is called the field of force, and the path through which they flow is called the

Magnetic Circuit. The paths of the lines of force can be easily demonstrated by placing a piece of paper over a bar magnet and then sprinkling iron filings over the paper, which should be jarred slightly in order that the filings may be drawn into the magnetic paths.

Fig. 13.—A Magnetic "Phantom," Showing the Field of Force about a Magnet.

The filings will arrange themselves in curved lines, diverging from one pole of the magnet and meeting again at the opposite pole. The lines of force are considered as extending outward from the north pole of the magnet, curving around through the air to the south pole and completing the circuit back through the magnet.

Fig. 14.—Magnetic Phantom showing the Lines of Force about a Horseshoe Magnet.

Figure 14 shows the lines of force about a horseshoe magnet. It will be noticed that the lines cross directly between the north and south poles.

The difference between the magnetic fields produced by like and unlike poles is shown in Figure 15.

Fig. 15.—Lines of Force between Like and Unlike Poles.

A study of this illustration will greatly assist the mind in conceiving how attraction and repulsion of magnetic poles take place.

It will be noticed the lines of force between two north poles resist each other and meet abruptly at the center. The lines between a north and a south pole pass in regular curves.

The Earth is a Great Magnet. The direction assumed by a compass needle is called the magnetic meridian.

The action of the earth on a compass needle is exactly the same as that of a permanent magnet. The fact that a magnetized needle places itself in the magnetic meridian is because the earth is a great magnet with lines of force passing in a north and south direction.

The compass needle does not generally point exactly toward the true North. This is because the magnetic pole of the earth toward which the needle points is not situated at the same place as the geographical pole.

Magnetic Dip. If a sewing-needle is balanced so as to be perfectly horizontal when suspended from a silk thread and is then magnetized, it will be found that it has lost its balance and that the north end points slightly downward.

Fig. 16.—A Simple Dipping Needle.

This is due to the fact that the earth is round and that the magnetic pole which is situated in the far North is therefore not on a horizontal line with the compass, but below such a line.

A magnetic needle mounted so as to move freely in a vertical plane, and provided with a scale for measuring the inclination, is called a

Dipping Needle. A dipping needle may be easily made by thrusting a knitting-needle through a cork before it has been magnetized.

A second needle is thrust through at right angles to the first and the arrangement carefully balanced, so that it will remain horizontal when resting on the edge of two glasses.

Then magnetize the first needle by stroking it with a bar magnet. When it is again rested on the glasses it will be found that the needle no longer balances, but dips downward.

Permanent Magnets have a number of useful applications in the construction of scientific instruments, voltmeters, ammeters, telephone receivers, magnetos and a number of other devices.

In order to secure a very powerful magnet for some purposes a number of steel bars are magnetized separately, and then riveted together. A magnet made in this way is called a compound magnet, and may have either a bar or a horse-shoe shape.

Magnets are usually provided with a soft piece of iron called an armature or "keeper." The "keeper" is laid across the poles of the magnet when the latter is not in use and preserves its magnetism.

A blow or a fall will disturb the magnetic arrangement of the molecules of a magnet and greatly weaken it. The most powerful magnet becomes absolutely demagnetized at a red heat, and remains so after cooling.

Therefore if you wish to preserve the strength of a magnetic appliance or the efficiency of any electrical instrument provided with a magnet, do not allow it to receive rough usage.

CHAPTER II STATIC ELECTRICITY

If you take a glass rod and rub it with a piece of flannel or silk, it will be found to have acquired a property which it did not formerly possess: namely, the power of attracting to itself such light bodies as dust or bits of thread and paper.

Hold such a rod over some small bits of paper and watch them jump up to meet it, just as if the glass rod were a magnet attracting small pieces of iron instead of paper.

The agency at work to produce this mysterious power is called electricity, from the Greek word "Elektron," which means amber. Amber was the first substance found to possess this property.

Fig. 17.—An Electrified Glass Rod will Attract Small Bits of Paper.

The use of amber begins with the dawn of civilization. Amber beads have been found in the royal tombs at Mycenae and at various places throughout Sardinia, dating from at least two thousand years before our era.

Amber was used by the ancient world as a jewel and for decoration.

The ancient Syrian woman used distaffs made of amber for spinning. As the spindle whirled around it often rubbed against the spinner’s garments and thus became electrified, as amber always does when it is rubbed. Then on nearing the ground it drew to itself the dust or bits of chaff or leaves lying there, or sometimes perhaps attracted the fringe of the clothing.

The spinner easily saw this, because the bits of chaff which were thus attracted would become entangled in her thread unless she were careful. The amber spindle was, therefore, called the "harpaga" or "clutcher," for it seemed to seize such light bodies as if it had invisible talons, which not only grasped but held on.

This was probably the first intelligent observation of an electrical effect.

In the eighteenth century, when Benjamin Franklin performed his famous kite experiment, electricity was believed to be a sort of fiery atmospheric discharge which could be captured in small quantities and stored in receptacles such as Leyden jars.

Franklin was the first to prove that the lightning discharges taking place in the heavens are electrical.

The story of his experiment is very interesting.

He secured two light strips of cedar wood, placed cross-wise and covered with a silk handkerchief for a kite. To the top of the upright stick of the kite was fastened a sharp wire about a foot long. The twine was of the usual kind, but was provided with a short piece of silk ribbon and a key. The purpose of the ribbon was possible protection against the lightning running through his body, silk being a "non-conductor," as will be explained a little farther on. The key was secured to the junction of the silk ribbon and the twine, to serve as a convenient conductor from which to draw the sparks—if they came. He did not have to wait long for a thunderstorm, and as he saw it gathering he went out with his son, then a young man twenty-two years of age. The great clouds rolled up from the horizon, and the gusts of wind grew fitful and strong. The kite felt a swishing blast and began to rise steadily, swooping this way and that as the breeze caught it. The thunder muttered nearer and nearer and the rain began to patter on the grass as the kite flew higher.

The rain soon began to fall heavily, compelling Franklin and his son to take refuge under a near-by shed. The heavy kite, wet with water, was sailing sluggishly when suddenly a huge low-lying black cloud traveling overhead shot forth a forked flame and the flash of thunder shook the very earth. The kite moved upward, soaring straight into the black mass, from which the flashes began to come rapidly.

Franklin watched the silk ribbon and the key. There was not a sign. Had he failed? Suddenly the loose fibers of the twine erected themselves. The moment had come. Without a tremor he advanced his knuckle to the key. And between his knuckle and the key passed a spark! then another and another. They were the same kind of little sparks that he had made hundreds of times with a glass tube.

And then as the storm abated and the clouds swept off towards the mountains and the kite flew lazily in the blue, the face of Franklin gleamed in the glad sunshine. The great discovery was complete, his name immortal.

The cause of lightning is the accumulation of the electric charges in the clouds, the electricity residing on the surface of the particles of water in the cloud. These charges grow stronger as the particles of water join together and become larger. As the countless multitude of drops grows larger and larger the "potential" is increased, and the cloud soon becomes heavily charged.

Through the effects of a phenomenon called induction, and which we have already stumbled against in the experiment with the tacks and the magnetic chain, the force exerted by the charge grows stronger because of a charge of the opposite kind on a neighboring cloud or some object on the earth beneath. These charges continually strive to burst across the intervening air.

As soon as the charge grows strong enough a vivid flash of lightning, which may be from one to ten miles long, takes place. The heated air in the path of the lightning expands with great force; but immediately other air rushes in to fill the partial vacuum, thus producing the terrifying sounds called thunder.

In the eighteenth century, electricity was believed to be a sort of fiery atmospheric discharge, as has been said. Later it was discovered that it seemed to flow like water through certain mediums, and so was thought to be a fluid. Modern scientists believe it to be simply a vibratory motion, either between adjacent particles or in the ether surrounding those particles.

It was early discovered that electricity would travel through some mediums but not through others. These were termed respectively "conductors" and "non-conductors" or insulators. Metals such as silver, copper, gold, and other substances like charcoal, water, etc., are good conductors. Glass, silk, wool, oils, wax, etc., are non-conductors or insulators, while many other substances, like wood, marble, paper, cotton, etc., are partial conductors.

There seems to be two kinds of electricity, one called "static" and the other "current" electricity. The former is usually produced by friction while the latter is generated by batteries or dynamos.

A very simple and well-known method of generating static electricity is by shuffling or sliding the feet over the carpet. The body will then become charged, and if the knuckles are presented to some metallic object, such as a gas-jet or radiator, a stinging little spark will jump out to meet it.

From the author's "Wireless Telegraphy and Telephony" by permission. A Double Lightning Discharge from a Cloud to the Earth.

The electricity is produced by the friction of the feet sliding over the carpet and causes the body to become electrified.

Warm a piece of writing-paper, then lay it on a wooden table and rub it briskly with the hand. It soon will become stuck to the table and will not slide along as it did at first. If one corner is raised slightly it will tend to jump right back. If the paper is lifted off the table it will tend to cling to the hands and the clothing. If held near the face it will produce a tickling sensation. All these things happen because the paper is electrified. It is drawn to the other objects because they are neutral, that is, do not possess an electrical charge.

Fig. 19.—A Piece of Dry Writing-Paper may be Electrified by Rubbing.

All experiments with static electricity perform better in the winter time, when it is cool and clear, than in the summer. The reason is that the air in winter is drier than in summer. Summer air contains considerable moisture and water vapor. Water vapor is a partial conductor of electricity, and the surrounding air will therefore conduct the static electricity away from your apparatus almost as fast as it can be produced in the summer time.

Fig. 20.—A Surprise for the Cat.

Some day during the winter time, when it is cool and clear, and the cat is near a fire or a stove, stroke the cat rapidly with the hand. The fur will stand up towards the hand and a faint crackling noise will be heard. The crackling is caused by small sparks passing between the cat and the hand. If the experiment is performed in a dark room, the sparks may be plainly seen. If you present your knuckle to the cat's nose a spark will jump to your knuckle and somewhat surprise the cat.

If the day is brisk and cool, so that everything outside is frozen and dry, try combing the hair with a rubber comb. Your hair will stand up all over your head instead of lying down flat, and the faint crackling noise, showing that sparking is taking place as the comb passes through the hair, will be plainly heard. The electricity is produced by the friction between the hair and the comb.

Electricity may be produced by friction between a number of substances. A hard rubber rod, a glass rod, a rubber comb or a stick of sealing-wax may be very easily electrified by rubbing them briskly with a piece of dry, warm flannel.

Electroscopes are devices for detecting the presence of static electricity.

Fig. 21.—A Paper Electroscope.

A very simple form of electroscope may be made in much the same manner as the paper compass described in the last chapter. It may be cut out of writing-paper and mounted on a pin stuck through a cork. If an electrified rod is held near the electroscope it may be made to whirl around in the same manner as a compass needle when a bar magnet is brought to it.

The Pith-Ball Electroscope is a very simple device, in which a ball of cork or elder pith is hung by a fine silk thread from an insulated support. A suitable electroscope may be made from a glass bottle having a piece of wire thrust into the cork to support the pith ball. When the electrified rod is presented to the pith ball, it will fly out towards the rod.

Fig. 22.—A Pith-Ball Electroscope.

If the pith ball is permitted to touch the glass rod, the latter will transfer some of its electricity and charge the ball. Almost immediately the pith ball will fly away from the glass rod, and no matter how near the rod is brought, it will refuse to be touched again.

This action is much the same as that of the magnetized needle suspended from a thread when the similar pole of the magnet is presented to it.

When the rod is first presented to the pith ball, the latter is neutral and does not possess an electrical charge. When the rod has touched the ball, however, some of the electricity from the rod passes to the ball, and after this they will repel each other.

The reason is that the rod and the ball are similarly charged and similarly charged bodies will repel each other.

Fig. 23.—A Double Pith-Ball Electroscope.

If you are a good observer you might have noticed when experimenting with an electrified rod and the small bits of paper, that some of the little papers were first attracted and flew upwards to the rod, but having once touched it, were quickly repelled.

The repulsion between two similarly electrified bodies may be shown by a double electroscope.

A double electroscope is made by hanging two pith balls on two silk threads from the same support.

Electrify a glass rod and touch it to the pith balls. They will immediately fly apart because they are electrified with the same kind of electricity.

The Gold-leaf Electroscope is one of the most sensitive means which can be employed to detect small amounts of static electricity.

Fig. 24.—A Gold-Leaf Electroscope.

It is a very simple instrument and is easily made in a short time. A couple of narrow strips of the thinnest tissue paper, or, better still, two strips of gold leaf, are hung from a support in a wide-mouthed glass bottle which serves at once to insulate and protect the strips from draughts of air.

The mouth of the jar is closed by a plug of paraffin wax, through the center of which passes a small glass tube. A stiff copper wire passes through the tube. The lower end of the wire is bent at right angles to furnish support for the strips of gold leaf. A round sheet metal disk about the size of a quarter is soldered to the upper end of the rod.

If an electrified stick of sealing-wax or a glass rod is presented to the disk of the electroscope, the strips will repel each other very strongly. If the instrument is sensitive, the strips should begin to diverge some time before the rod reaches the disk. It is possible to make an electroscope so sensitive that chips formed by sharpening a pencil will cause the strips to diverge.

There are two kinds of static electricity. Rub a glass rod with a piece of silk and then suspend it in a wire stirrup as shown in Figure 25. Excite a second rod also with a piece of silk and bring it near one end of the suspended one. The suspended rod is repelled and will swing away from the one held in the hand.

Fig. 25.—Method of Suspending an Electrified Rod in a Wire Stirrup.

Now rub a stick of sealing-wax with a piece of flannel until the sealing-wax is electrified. Then bring the stick of sealing-wax near the end of the suspended rod. The rod will be attracted to the sealing-wax.

If you experiment further you will find that two sticks of sealing-wax will repel each other.

Fig. 26.—Similarly Electrified Bodies Repel Each Other. Dissimilarly Electrified Ones Attract Each Other.

This experiment indicates that there are two kinds of electrification: one developed by rubbing glass with silk and the other developed by rubbing sealing-wax with flannel.

In the first instance, the glass rod is said to be positively electrified, and in the latter case the sealing-wax is negatively electrified.

The same law that applies to magnetism also holds true in the case of static electricity, and similarly electrified bodies will repel each other and dissimilar ones attract.

The Electrophorus is an instrument devised by Volta in 1775 for the purpose of obtaining static electricity.

Fig. 27.—The Electrophorous

It is easily constructed and will furnish a source of electricity for quite a number of interesting experiments. An electrophorus consists of two parts, a round cake of resinous material cast in a metal dish or pan, and a round metal disk which is provided with an insulating handle.

To make an electrophorus, first procure an old cake or pie tin, and fill it with bits of resin or sealing-wax. Place the pan in a warm spot upon the stove where the resin will melt, taking care not to overheat or it will spatter and possibly take fire. As the resin melts, add more until the pan is nearly full. When all is melted, remove from the fire and set it away where it may cool and harden in the pan without being disturbed.

Cut a circular disk out of sheet tin, zinc, or copper, making the diameter about two inches less than that of the pie pan. Solder a small cylinder of tin or sheet brass to the center of the disk to aid in supporting the handle. The latter is a piece of glass tubing about three-quarters of an inch in diameter and four or five inches long, placed in the center of the cylinder and secured with molten sealing-wax.

In order to use the electrophorus the resinous cake must first be beaten or briskly rubbed with a piece of warm woolen cloth or flannel. Then place the disk on the cake holding the insulating handle with the right hand. Touch the cover or the disk momentarily with the forefinger of the left hand. After the finger is removed, raise the disk from the cake by picking it up with the glass insulating handle. The disk will now be found heavily charged with positive electricity, and if the knuckles are presented to the edge, a spark will jump out to meet them.

Fig. 28.—An Electric Frog-Pond.

The cover may then be replaced, touched, and once more removed. It will yield any number of sparks, the resinous cake only needing to be recharged by rubbing once in a long while.

An Electric Frog-Pond may be experimented with by cutting out some small tissue-paper frogs. Moisten them a little and lay them on the cover of the electrophorus. Touch the electrophorus with the finger and then raise it with the insulating handle. If the "frogs" are not too wet they will jump from the cover upon the table as soon as the cover is raised.

CHAPTER III STATIC ELECTRIC MACHINES

A Cylinder Electric Machine

The electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.

An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.

The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.

Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.

Fig. 29.—Front View of a Cylinder Electric Machine.

When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.

The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.

The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.

Fig. 30.—Method of Finding the Center of a Circle.

Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the point C just touches the circumference. Draw a line from A to B where the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.

Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.

The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.

After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.

The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.

A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.

Fig. 31.—The "Rubber."

The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.

The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.

Fig. 32.—The Prime Conductor or Collector.

A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.

The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.

The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.

The leather rubber should be thinly smeared with lard and the powdered amalgam rubbed on it.

In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.

Fig. 33.—The Complete Cylinder Electric Machine.

A Wimshurst Machine

The Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.

The Glass Plates are each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.

Fig. 34.—Paper Pattern for laying out the Plates.

The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.

Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.

Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.

The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.

Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.

Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.

The Bosses will have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.

A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."

Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.

The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.

Then apply some bichromate glue to the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.

Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.

The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enough glacial acetic acid to cover the glue.

Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.

The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.

The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.

Fig. 37.—The Frame.

Notches are cut at both sides of the base to admit the feet of the uprights.

The Uprights are seventeen inches long, three inches wide, and one and one-half inches thick.

Fig. 38.—The Upright.

The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.