CHAPTER I MAGNETS AND MAGNETISM_The Boy Electrician

Produced by James Simmons.

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[Illustration: 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

_All rights reserved_

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 ...............................................

INTRODUCTION ....................................................

CHAPTER I MAGNETS AND MAGNETISM .................................

CHAPTER II STATIC ELECTRICITY ...................................

CHAPTER III STATIC ELECTRIC MACHINES ............................

CHAPTER IV CELLS AND BATTERIES ..................................

CHAPTER V ELECTRO-MAGNETISM AND MAGNETIC INDUCTION ..............

CHAPTER VI ELECTRICAL UNITS .....................................

CHAPTER VII ELECTRICAL APPURTENANCES ............................

CHAPTER VIII ELECTRICAL MEASURING INSTRUMENTS ...................

CHAPTER IX BELLS, ALARMS, AND ANNUNCIATORS ......................

CHAPTER X ELECTRIC TELEGRAPHS ...................................

CHAPTER XI MICROPHONES AND TELEPHONES ...........................

CHAPTER XII INDUCTION COILS .....................................

CHAPTER XIII TRANSFORMERS .......................................

CHAPTER VIV WIRELESS TELEGRAPHY .................................

CHAPTER XV A WIRELESS TELEPHONE .................................

CHAPTER XVI ELECTRIC MOTORS .....................................

CHAPTER XVII DYNAMOS ............................................

CHAPTER XVIII AN ELECTRIC RAILWAY ...............................

CHAPTER XIX MINIATURE LIGHTING ..................................

CHAPTER XX MISCELLANEOUS ELECTRICAL APPARATUS ...................

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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.

[Illustration: 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_.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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

[Illustration: 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.

[Illustration: 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.

[Illustration: 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._

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.

[Illustration: 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.