Electricity for Boys | Page 2

Page 135
Generating Heat in a Wire. Resistance of Substances. Signs of
Connectors. Comparison of Metals. A Simple Electric Heater. How to
Arrange for Quantity of Current Used. An Electric Iron.
Thermo-Electricity Converting Heat Directly into Electricity Metals.
Electric, Positive, Negative. Thermo-electric Coupler.
XV. ALTERNATING CURRENTS, CHOKING COIL,
TRANSFORMER Page 145
Direct Current. Alternating Current. The Magnetic Field. Action of a
Magnetized Wire. The Movement of a Current in a Charged Wire.
Current Reversing Itself. Self-Induction. Brushes in a Direct Current
Dynamo: Alternating, Positive and Negative Poles. How an Alternating
Current Dynamo is Made. The Windings. The Armature Wires.
Choking Coils. The Transformer. How the Voltage is Determined.

Voltage and Amperage in Transformers.
XVI. ELECTRIC LIGHTING Page 161
Early conditions. Fuels. Reversibility of Dynamo. Electric arc.
Mechanism to maintain the arc. Resistance coil. Parallel carbons for
making arc. Series current. Incandescent system. Multiple circuit.
Subdivision of electric light. The filament. The glass bulb. Metallic
filaments. Vapor lamps. Directions for improvements. Heat in electric
lighting. Curious superstitions concerning electricity. Magnetism.
Amber. Discovery of the properties of a magnet. Electricity in
mountain regions. Early beliefs as to magnetism and electricity. The
lightning rod. Protests against using it. Pliny's explanation of
electricity.
XVII. POWER, AND VARIOUS OTHER ELECTRICAL
MANIFESTATIONS Page 175
Early beliefs concerning the dynamo. Experiments with magnets.
Physical action of dynamo and motor. Electrical influence in windings.
Comparing motor and dynamo. How the current acts in a dynamo. Its
force in a motor. Loss in power transmission. The four ways in which
power is dissipated. Disadvantages of electric power. Its advantages.
Transmission of energy. High voltages. The transformer. Step-down
transformers. Electric furnaces. Welding by electricity. Merging the
particles of the joined ends.
XVIII. X-RAY, RADIUM AND THE LIKE Page 184
The camera and the eye. Actinic rays. Hertzian waves. High-tension
apparatus. Vacuum tubes. Character of the ultra-violet rays. How
distinguished. The infra-red rays. Their uses. X-rays not capable of
reflection. Not subject to refraction. Transmission through opaque
substances. Reducing rates of vibration. Radium. Radio-activity.
Radio-active materials. Pitchblende. A new form of energy. Electrical
source. Healing power. Problems for scientists.

LIST OF ILLUSTRATIONS
FIG.
1. Work bench Frontispiece
PAGE 2. Top of magnet-winding reel 14 3. Side of magnet-winding
reel 14 4. Journal block 15 5. Plain magnet bar 19 6. Severed magnet
20 7. Reversed magnets 21 8. Horseshoe magnet 22 9. Earth's magnetic
lines 23 10. Two permanent magnets 24 11. Magnets in earth's
magnetic field 24 12. Armatures for magnets 25 13. Magnetized field
26 14. Magnetized bar 26 15. Direction of current 27 16. Direction of
induction current 28 17. Frictional-electricity machine 30 18. Leyden
jar 32 19. Galvanic electricity. Crown of cups 33 20. Voltaic electricity
34 21. Primary battery 36 22. Dynamo field and pole piece 39 23. Base
and fields assembled 41 24. Details of the armature, core 42 25. Details
of the armature, body 42 26. Armature Journals 43 27. Commutator 43
28. End view of armature, mounted 44 29. Top view of armature on
base 45 30. Field winding 47 31. Series-wound 47 32. Shunt-wound 48
33. Compound-wound 48 34. Compass magnet, swing to the right 50
35. Magnetic compass 50 36. Magnet, swing to the left 50 37.
Indicating direction of current 51 38. The bridge of the detector 52 39.
Details of detector 53 40. Cross-section of detector 54 41. Acid
voltameter 56 42. Copper voltameter 56 43. Two-pole switch 66 44.
Double-pole switch 66 45. Sliding switch 67 46. Rheostat form of
switch 68 47. Reversing switch 69 48. Push button 70 49. Electric bell
71 50. Armature of electric bell 72 51. Vertical section of annunciator
72 52. Front view of annunciator 72 53. Horizontal section of
annunciator 72 54. Front plate of annunciator 72 55. Alarm switch on
window 76 56. Burglar alarm on window 76 57. Burglar alarm contact
77 58. Neutral position of contact 78 59. Circuiting for electric bell 79
60. Annunciators in circuit 80 61. Wiring system for a house 80 62.
Accumulator grids 83 63. Assemblage of accumulator grids 85 64.
Connecting up storage battery in series 87 65. Parallel series 88 66.
Charging circuit 88 67. Telegraph sending key 91 68. Telegraph
sounder 92 69. A telegraph circuit 94 70. Induction coil and circuit 99
71. Illustrating elasticity 100 72. Condenser 101 73. High-tension

circuit 102 74. Current interrupter 103 75. Wireless-telegraphy coherer
105 76. Wireless sending-apparatus 107 77. Wireless
receiving-apparatus 108 78. Acoustic telephone 111 79. Illustrating
vibrations 111 80. The magnetic field 112 81. Section of telephone
receiver 114 82. The magnet and receiver head 115 83. Simple
telephone connection 116 84. Telephone stations in circuit 117 85.
Illustrating light contact points 118 86. The microphone 119 87. The
transmitter 119 88. Complete telephone circuit 121 89. Device for
making hydrogen and oxygen