/ FION PICTURE HANDBOOK

' / -ID OPERATORS

DITION

H.RICHARDSON

PUB3 .

TJM' V URE WORLD

Laemmle Donation

II

MOTION PICTURE

II HANDBOOK II

II 'I

A Guide for

MANAGERS AND OPERATORS of MOTION PICTURE THEATRES

By F. H. RICHARDS'ON

THIRD EDITION

Published by THE MOVING PICTURE WORLD

Pullman Building, 17 Madison Avenue NEW YORK CITY

Copyright, 1910 by

WORLD PHOTOGRAPHIC PUBLISHING Co.

Entered at Stationers' Hall, London, England.

Copyright in the United States, 1912;

Copyright in Great Britain, 1912;

Copyright in Canada, 1912,

by

CHALMERS PUBLISHING COMPANY,

New York.

Copyright in the United States, 1916;

Copyright in Great Britain, 1916;

Copyright in Canada, 1916,

by CHALMERS PUBLISHING COMPANY,

New York. All Rights Reserved.

Index to Contents

PAGE

Aberration, Chromatic 94, 98, 124

Aberration, Spherical 94, 97, 123

A. C. Action— How to Trace It 16

A. C. and D. C, Difference Between 13

A. C and D. C., Relative Efficiency of 290, 294

A. C. or D. C, to Find Out 667

A. C Wires Must Be in Same Conduit 240

Adjusting Intermittent Sprocket 461

Adjusting the Tension Springs 463

Airdomes 669

Airdome Site, Selecting. . . . . 672

Alternating Current, Definition of 22

Alternating Current, How Generated 8

American Standard Projector, Instructions for 566

Ammeter and Voltmeter for Operating Room 235, 248

Amperage 157

Amperage, Economic Limit of 292

Ampere.

Definition of 19

Hour, Definition of 19

Term, Definition of 23

What the Term Means 26

Anchoring the Machine 236

Aperture Plate Tracks Worn 465

Aperture, Standard Size 476

Arc.

Calculating Its Candle Power 293

Comparison of Candle Power 293

Comparison of Candle Power from Mercury Arc

Rectifier and Through Rheostat. 294

Controller 303

Lamp, The 268

Position of Crater of 295

Stream 291

Voltage 31, 301, 323

Architect's Plans, Checking of 668

Asbestos Wire Lamp Leads 50, 233, 271, 313

Back Focus, Definition of 92

Back Focus, How Found 104

Back Focus, Why Important 122

Baird Projector, Instructions for 546

Batteries, Renewal of 649

790334

MOTION PICTURE HANDBOOK

PAGE

Calculations, Electrical 28

Candle Power of Arc 293

Capacity, Wire, Table of 42

Capacity, Wire, Figuring Voltage Drop 45

Carbons.

Arc Stream 291

Calculating Candle Power of Crater 293

Care of 289

Chemicalizing 288

Economizers 302

Fresh Carbons in Lamp, Effect of 301

Hard and Soft 287

Hard Spots 287

How Made 284

Inspect When Buying 287

Mushroom Cap on Lower 299

Resistance They Offer 288

Set, Best Results 301

Set for A. C 297

Setting 290

Side Lining 300

Size of 285, 287

Solid vs. Cored Lower 286

Stubs 287

Why D. C. Crater Is Larger Than A. C 290

Carpeting 647

Chair, Operator's 235, 245

Chalk Surface for Screens 189

Cheap Equipment 667

Choke Coil 344

Choke Coil, Preddy Economizer 363

Chromatic Aberration 94, 98, 124

Chromatic Aberration of Condenser Beam 124

Cleaning Carbon Clamps, Importance of 270

Cleaning Film 206

Cleaning Lenses 108

Cleaning Machine After Film Fire 208

Closets for Operator 231

Coating for Screens 183

Coefficient, Temperature 39

Coloring Incandescent Lamps 668

Commutator, Care of 372

Commutator, Definition of 21

Compensarcs, A. C 353

Compensarc, A. C, Rules for Operation 355

Condenser Holder 266

Condenser Holders, Freddy, Elbert 267

Condenser Lenses, Distance from Film 131

Condenser Lenses, Selecting 128

Conductor, Definition of 22

Conductors, To Find Area of 48

iv

FOR MANAGERS AND OPERATORS

PAGE

Conductors, Properties of 40

Conduit for Wires 212, 240

Conjugate Foci, Definition of 91

Conjugate Foci, Explanation of 95

Connections, Series and Multiple 330

Connecting to Two Sources of Supply 252

Cost of Light from A. C. Through Transformer and D. C.

Through Rheostat 294

Coulomb, Definition of 19

Crater, Position of 295

Cycle, Definition of 22

Diameter of Objective Lens •„ 110

Difference Between A. C. and D. C 13

Dimmer, Definition of 22

Direct Current, Definition of 22

Direct Current, How Generated 11

Dissolving Moving Picture 606

Dissolving Shutter 605

Dissolving Stereopticon 603

Distance Condenser to Film 131

Door of Operating Room 213

Double Sets of Fuses 86, 252

Double Spot, One Reason for 297

Double Throw Connection for Projector 250

Dynamo, Principle of Operation 11

Edison, Model D, Instructions for 579

Economizer, Hallberg A. C 360

Edison Economy Transformer 356

Edison Super-Kinetoscope 477

Efficiency, How Calculated 23

Efficiency of A. C. and D. C 290, 294

Electric Conductors, Properties of 40

Electric Meters 655

Electrical Terms 18

Electrical Terms, Explanation of 24

Electricity, How Generated 5

Electro Magnetic Field, Definition of 22

Electro Motive Force, Definition of 22

Emergency Announcement Slides 239

Emergency Light Circuit, Fusing 86

Employes 661

Emulsion Deposit on Tension Springs 464

End Play in Intermittent Sprocket 462

Equipment Operating Room 231

Equivalent Focus, Definition of 93

Equivalent Focus, How Measured 104, 108

Exit Lights: 640

Eye Strain 153, 175, 472

I7easter Non-Rewind Machine 318

Figuring Seating Capacity 643

v

MOTION PICTURE HANDBOOK

Film. PAGE

Cement Formulas 197

Cleaner, Mortimer 206

Cleaner, Ideal 207

Cleaning 206

Containers 596

Description of 192

Inspection of 201

Leader and Tailpiece 199

Life of 208

Measuring 210

Mending 195

Moistening When Dry 204

Notching Pliers 203

Perforations 194

Stretched 204

Thickness of 194

Where to Keep 203

Fire-proofing Solution 189

Fire Shutters for Ports 222

Floor of Operating Room 214

Floor, Slope of Auditorium 640

Focus, In and Out, Cause of 466

Foot-pounds, Definition of 19

Formostat, The 365

Fort Wayne A. C. to D. C. and D. C. to D. C. Compensarcs. 382

Fuses 76

Cartridge 79

Copper 83

Emergency System 86

In Case of Trouble 84

Link 80

Plug 80

Projection Circuit 81

Table of Sizes 82

Where Installed 85

Fusing for Motor Generator 82

Graphite.

Cap on Lower Carbon 299

Definition of 22

For Lamp 268

Where Obtained 269

Generator, Electric 11

Glass in Ports 230

Ground, Establishing Permanent 259

Ground, Testing Rheostats for 260

Grounding Machine, Reason for 262

Grounds 255

Grounds, Definition of 22

Hallberg's D. C. to D. C. Economizer 415

Hallberg's Twentieth Century Motor Generator 419

vi

FOR MANAGERS AND OPERATORS

PAGE

Haze on Screen, Reason for 168

Heating 632

Heating and Ventilating 624

Height of Screen Above Floor 181

High-Class Projection, Importance of 151

High-Grade Lenses 110

Horse Power, Definition of 20

Inclosed Switches 64

Induction, Definition of 23

Inductor, Power's 359

Inductor, Power's, Size and Weight 360

Insulation . . 50

Definition of 23

Rubber Covered 51

Testing 52

Weather-proof 53

Intermittent Sprocket, Used Too Long. 233, 462

Keystone Effect 154

Keystone Effect, Eliminating 156, 468

Killowatt-Hour, Definition of 20

Lamp, The 268

Angle of 273

Insulation 272

Lubrication of 268

Necessary Adjustments 273

Lamps, Compared 270-1-2

Lamphouse, The 262

Arc Projector 265

Condenser Holder 266

Keeping Clean 265

Lighting Interior 302

Ventilation 262

Ventilation, Best Method 263

Ventilation, Effect of Lack of 263

Leaders for Films 199

Lens System, Matching 113

Lens Tables of Small Value 105

Lenses 91

Altering Distance Between Factors 101

Cleaning 108

Cleaning the Objective 109

Diameter of Condensing 128

Diameter of Objective 110, 122

Dirty, Loss of Light 102

Explanation of Focus 95, 101

Figuring Sizes 105

High Grade 110

How Designed 96

Improving Definition 102

Loss of Light in 159

vii

MOTION PICTURE HANDBOOK

Lenses (Continued). PAGE

Measuring 103

Measuring E. F. Accurately 108

Selecting Condenser Lenses 128

Spread of Light Ray 102

Table for Matching 141

License Law, Draft of 621

License, Operator's 617

Life of Film 208

Lighting the Auditorium 633

Limelight Projection 674

Limit of Amperage 292

Lining Cam and Sprocket Shafts 466

Lining the Optical System 112

Lining the Sprockets 460

Location of Operating Room Ports 215

Loss Through Resistance 41, 334

Lugs, Wire Terminal 87, 88

Magnetic Field, Definition of 22

Martin Rotary Converter 405

Matching Up Lens System 113

Measuring Film 210

Measuring Lenses 104

Measuring Wires 48

Mechanism, The (See "Projector") 457

Mechanism, The, General Instructions 457

Meter, Reading 657

Mill-foot Standard of Resistance 42

Minusa Screen 187

Mirror Screen 185

Mirroroid Screen 187

Mortimer Film Cleaner 206

Moistening Dry Film 204

Motiograph, Instructions for 528

Motor Drive.

Do Not Belt to Fly Wheel 277

Elbert 275

Home-made 279

Multiple Clutch 277

Preddy ' 276

Wallstad Projection Stand 280

Spring Switch 274

Motor Driven Machines 273

Motor Generator.

Ammeter and Voltmeter 372

Bearings Run Hot. . . '. 381

Care of Commutator 372

Fort Wayne 382

General Instructions 368

Hallberg's D. C to D. C. Economizer 415

Hallberg's Twentieth Century 419

viii

FOR MANAGERS AND OPERATORS

Motor Generator (Continued). PAGE

Heating 381

Locating Installation 368

Martin Rotary Converter 405

Oil 371

Sparking 374

Wagner Rotary Converter 407

Wotton Rexolux 395

Multiple Arc System 55

Musicians 663

Musicians, Light for 634

Objective Lens, Cleaning 108

Objective Lens, Description of 99

Objective Lens, Test for Distortion 100

Ohm, Definition of 20

Ohm, Explanation of 27

Oil for Projector 457

Operating Room 210

Door 213

Equipment 231

Film Storage 596

Floor 214

Model Installations : 244-6-7-8-9

Observation Port 219

Ports 215

Size of Feed Wires 239

Supplies 232, 234

Toilet Conveniences 232

Vent Flue 227

Ventilation 228

Wiring 239

Operator Remaining at Machine 235, 279

Operator's License 617

Operator's Report 623

Operator's Tool Kit 237

Optical Axis, Definition of 91

Optical System, Lining Up of 112

Outlining Screen with Black 178

Overspeeding 151

Persistence of Vision 472

Polarity 5

Changer 252

Definition of 21

Explanation of 24

Ports.

For Operating Room 215

Glass in [ 230

Observation , 7j9

Shutters for ' 222

ix

MOTION PICTURE HANDBOOK

PAGE

Power's 6B, Instructions for 491

Preddy Economizer 363

Projection 147

By Limelight 674

No Excuse for Shadows 149

Overspeeding 151

Projector, The 262

Adjusting Intermittent 461

Adjusting Sprocket Idlers 466

Adjusting Top Gate Idler 462

American Standard, Instructions for 566

Baird, Instructions 546

Edison, Model D, Instructions 579

Edison Super-Kinetoscope 477

Eliminating Keystone Effect 469

Emulsion Deposit on Tension Springs 464

End Play in Intermittent Sprocket 462

Extra Framing Carriage 462

Handling Small Screws 476

In and Out of Focus, Cause 466

Lining Magazines of 467

Lining the Sprockets 460

Lining Sprocket and Cam Shafts 466

Motiograph 528

Oil for 457

Power's 6B 491

Reels for Operating Room 467

Revolving Shutter 469

Shutter and A. C 473

Standard Aperture Size 476

Take Up 592

Take-Up Adjustment 459

Tension, Adjustment of 463

Threading the Machine 594

Upper Magazine Tension 468

Worn Aperture Plate Tracks 465

Worn Sprocket Teeth 462

Properties of Conductors 40

Properties of Resistance Metals 40

Radium Gold Fibre Screen 188

Rectifier.

Comparative Results 432

General Electric 434

Installation 431

Light in Operating Room Objectionable 432

Mercury Arc 428

Trouble Chart 433

Tube, Operating Principle 429

Westinghouse 446

Reflection, Regular and Diffuse 168

Refraction, Definition of 92

x

FOR MANAGERS AND OPERATORS

PAGE

Relative Efficiency A. C. and D. C 291, 294

Report, Operator's 623

Resistance 34

As Applied to Projection Circuit 322

Circuits, of, Figuring It 44

Copper Wire, of 43

Definition of 21

Devices 337

Different Metals, of 38

How It Acts 34

Loss Through 41, 334

Materials, Properties of 40

Metals, Properties of 40

Rheostats.

A. C. and D. C 333

Adding Extra Resistance 327

Adjustable, How It Works 324

Amount of Heat Permissible 329

Coil, How to Make 327

Coils vs. Grids 329, 330

Examining Connections 328

Extremely Wasteful 333

Fan Blowing On 328

Figuring Connections 335

Fixed Resistance of Adjustable 325

Home Made of Iron Wire 329

How to Reduce Noise When Using Them on A. C. 333

Inductive Effect of A. C 333

Locate It Outside of Operating Room 328

Location of 227

Near Ceiling and Vent Flue 328

Resistance Rises with Age 336

Temporary Repair 326

Use on A. C. Bad Practice 333

Use Grid Type on A. C 333

What Happens if Spirals of Coils Touch 337

What They Do 322

Wire Coil, What They Are. 337

Why Noisy on A. C 333

Rule of Thumb 32

Screen, The 166

Areas 165

Chalk Surface 189

Character of Surface 169

Coatings 183

Distribution of Light 170

Eye Strain 175

Fire-proofing 189

Flat Surface 177

Height Above Floor 181

Illumination, D. C. and A. C 291

xi

MOTION PICTURE HANDBOOK

Screen (Continued). PAGE

Illumination Percentages 164

Interfering Light 169

Locating at Front of House 180

Metalized Surface 172

Minusa Gold Fibre 187

Mirror 173, 185

Mirroroid 186

Outlining the Picture 178

Putting on the Cloth 191

Radium Gold Fibre 188

Reason for Haze 168

Reflection of Light 168

Simpson Solar 186

Size of Picture 181

Stippled Surface 189

Stretching Its Surface 190

Table of Areas 165

Tinted Surfaces 178

Transparent 174

Where Vaudeville Is Used 181

White Wall or Sheet 171

Seating 642

Seating, Figuring Capacity 643

Seating, Loge Seats 643

Series and Multiple Connections 330

Setting the Carbons 290

Short Circuit, Definition of 21

Shunt Circuit, Definition of 21

Shutter.

Distance from Lens 474

Inside and Outside 475

Revolving, Principle of 469

Three and Two Wing and A. C 473

Side View, Effect of 154

Simplex Mechanism, Instructions for 513

Simpson Solar Screen 186

Size of Picture 181

Slide Coatings 615

Slides,

Coloring 614

Emergency 239

Handling Them 612

Making Them 612

Stereopticon 609

Slope of Auditorium Floor 640

Soldering Fluid 90

Spherical Aberration 94

Splices, Wire 89

Spotlight, The 598

FOR MANAGERS AND OPERATORS

Sprocket. PAGE

Adjusting Intermittent 461

End Play in Intermittent 462

Idlers, Adjusting 466

Teeth, Worn 462

Static Electricity, Definition of 22

Stereopticon, The 600

Coloring Slides 614

Dissolving Shutter 605

Handling the Slides 609

Making Slides 612

Slides 609

The Dissolver 603

Street Mains, Definition of 22

Supplies for Operating Room 232, 234

Switchboards 67

Switchboards, Exit and Emergency 72

Switchboards, Stage 73

Switches 63

Care of 66

Inclosed 64

Metal Cabinet for 67

Proper Location of 64

Use of Various Types 65

Synchronism, Definition of 24

Tables.

Carbon Sizes 287

Experiments with Arc 301

Millimeter Equivalents 289

Screen Areas 165

Screen Illumination Percentages 164

Small Wire Diameters 314

Stereo Lenses 107

To Match Lenses 141

Wire Capacities 42

Take-Up Adjustment 459

Take-Up, Faults of Old Style 592

Temperature Coefficient 39

Temporary Show, Connecting Up for 664

Tension Spring, Adjusting 463

Terminals, Wire .....87, 88

Terms, Electrical, Definitions 18

Terms, Electrical, Explanation of 24

Test Lamp for Grounds 257

Testing Insulation 52

Testing Objective Lens for Distortion 100

Testing Rheostat for Ground 260

Testing Voltage 666

Threading the Machine 594

Three-Phase Current 17

xiii

MOTION PICTURE HANDBOOK

PAGE

Three-Wire System 56

Three- Wire System, Connecting Arcs 242

Toilet Conveniences for Operating Room 232

Toledo Non-Rewind 315

Tools in Order 238

Tool Kit for Operator 237

Torque, Definition of 23

Transformer, The , . 343

Action of 345

Auto 346

Compensarcs 353

Construction of 343

Definition of 23

Edison Economy 356

Fusing 351

Hallberg A. C. Economizer 360

How Amperage Is Changed 349

Power's Inductor 359

Primary vs. Secondary Terms 344, 349

The Formostat 365

Theory It Utilizes 345

Wiring of Compensarc 354

Two-Phase Current 18

Two-Wire System

Use of Electrical Terms in Calculations 28

Vent Flue for Operating Room 227

Ventilation and Heating 624

Ventilation for Operating Room 228

Ventilation, Winter 633

Volt-Coulomb, Definition of 19

Volt, Definition of 20

Voltage Drop, Figuring It 45

Voltage, Explanation of 25

Warning, A 668

Watt, Definition of 20

Watt, Explanation of Term 27

Watt-Hour, Definition of 20

Watt Meter, Definition of 23

Weather-proof Insulation 53

Wire.

Capacity, Figuring Voltage Drop 45

Capacity, Table of 42

Gauges 49

Measuring 48

Splices 89

Systems 54

Terminals '. 87, 88

Wiring the Operating Room 239

Worn Machine Parts, Do not Use Them 233

Worn Sprocket Teeth 233, 462

Wotton Vertical Rexolux. 395

xir

Acknowledgement Is Hereby Made

to Mr. B. M. SPENCER,

Attleboro, Mass.,

For the Drawings for a Large

Number of the Cuts in

This Handbook.

xv

Author's Note

TO FIRST EDITION

THIS book is dedicated to the motion picture operator as a token of appreciation of the important part he plays in the presentation of the photoplay. That it may be helpful in hastening the day of perfect motion picture pro- jection is the desire of the writer, and he trusts that a careful perusal of its pages may stir the ambition and increase the ability of every reader.

October, 1910.

Publishers Note

TO FIRST EDITION

THE remarkable vogue of the motion picture and the rapid strides it has made in public favor as an enter- tainment and educational factor have had their draw- backs. Chief among these has been the impossibility of securing a sufficient number of men with the necessary knowledge and experience to fill important positions.

THE MOVING PICTURE WORLD has, in no small measure, con- tributed to the success of the picture, and the articles in this book were written to give helpful information in regard to the many problems that may arise in connection with the duties of the manager and operator. With a few exceptions, the articles have already appeared in THE MOVING PICTURE WORLD, but they have been revised and amplified and are herewith presented in compact form to comply with popular request.

Mr. Richardson has avoided technical terms, and his plain language and matter-of-fact style bespeak for this book the same degree of popularity which attaches to the Operators' Column which he still conducts in the pages of

THE MOVING PICTURE WORLD. October, 1910.

Author's Note

TO SECOND EDITION

LIKE the former edition, this book is dedicated to the moving picture operator, upon whose skill in the pro- jection of the magnificent work of our modern pro- ducers so very much depends. Since the inception of the Projection Department of THE MOVING PICTURE WORLD and the publication of the first book rapid strides have been made in the perfection of projection. The author hopes and believes that this work will serve to even further advance and perfect projection to the end that the photoplay may become still more firmly fixed in the affections of the amusement- loving public.

October 30, 1912.

Publisher's Note

TO SECOND EDITION

THE enormous increase in popularity of the motion picture during the 'past few years in all countries is one of the marvels of the day. The moving picture is now far in advance of all other forms of public entertain- ment among all classes and draws a daily patronage that is beyond belief.

In no other country, however, do the pictures have quite as good a hold on the public favor as in the United States. This is in great measure due to the enterprise and higher ideals of the film manufacturers in this country. It is also due in great measure to the care and attention given to programs, theater management and especially the projection of the pictures by the exhibitors throughout the United States and Canada.

The first edition of this work was published over two years since and has been of immense value and help to operators throughout the country. This edition has been greatly en- larged and will be found much more complete in every way. It will undoubtedly remain the standard work in its field for many years and is a worthy monument to its author's ability and painstaking effort.

CHALMERS PUBLISHING COMPANY.

November, 1912.

Author's Note

TO THIRD EDITION

AS in the case of the first and second editions, I believe it is but right and proper that this, my latest effort, should be dedicated to the moving picture operator, upon whose shoulders rest, in large degree, the welfare of the entire moving picture industry. The author has faith to believe that this book will be favorably received by the fraternity and trusts it will accomplish a large amount of good for all students of projection.

In order to do justice to the magnificent productions of today it is necessary that the moving picture operator have a wide range of knowledge and that he be capable of apply- ing that knowledge in the best possible way. The day of guesswork in projection is past. The author feels that while this book will be of great aid to the moving picture operator, it will also indirectly be of equally great help to the pro- ducers and all others connected with the industry by reason of the fact that it is the finished product which is placed in the hands of the moving picture operator, who may either reproduce it on the screen as a magnificent spectacle or a shadowy, jumping travesty on the original.

November, 1915.

Publisher's Note

TO THIRD EDITION

THERE is little to add by the Publishers in introducing this new edition. The first and second editions of this work were most complete and instructive at the time of their publication. Each edition was an improve- ment over the previous one, and this book much more than either of its predecessors not only reflects the wonderful progress and improvement in moving picture projection but points the way to still greater advancement.

The author has spent all of his time for many years in the study of projection, and we confidently believe this com- prehensive work will meet with the unqualified approval of every reader. CHALMERS PUBLISHING COMPANY.

December, 1915.

Go to your work each day as though it were your first day on a new job and you had to make good.

Polarity

IN order to have a comprehensive understanding of elec- trical action it is essential that the operator have a very clear and thorough understanding as to precisely what polarity means, and how it acts, because the whole super- structure of electrical action rests thereon.

The electric circuit with which the operator comes into con- tact consists of two wires no more and no less. There may appear to be more, as, for instance, in a three-wire system, but, as a matter of fact, so far as electrical action be con- cerned, every electric circuit is composed of two wires, viz.: the positive and the negative, and it is the affinity these two wires (which represent the poles of the dynamo) have for each other which constitutes "polarity." There always has been and still is controversy between eminent theoretical electricians as to the exact nature of the action which takes place as between the positive and the negative wire. To avoid all confusion, however, we will lay aside technical questions and accept the common statement that current seeks always to flow from the positive to the negative. Having accepted this as the fact it may be further said that the inclination of the current to escape from the positive to the negative is similar to the efforts of steam to escape from the boiler into the open air. When steam escapes from the boiler to the open air it loses its pressure in the process. When electrical energy escapes from the positive to the negative it does exactly the same thing, and that is why it seeks to escape; also that is why it will perform work in the process of escap- ing. The pressure in the boiler will force the steam to the open air through the cylinder of an engine, moving the piston and thus performing work in the process. The electric cur- rent will perform work in the motor or the lamp, since it can get from positive to negative by so doing and thus lose its pressure. This electrical affinity is termed "polarity," and its strength, which may be much or little, is measured in volts.

6 MOTION PICTURE HANDBOOK

And now let me make one point very clear. Electrical affinity or polarity only exists between the positive wire and the negative wire attached to the same dynamo or battery. There is absolutely no electrical affinity between the negative wire attached to one generator and the positive wire attached to another generator, unless the generators themselves are electrically coupled, as in the case of the three-wire system. You could set two generators running, side by side, each generating 500 volts, and touch the positive of one generator to the negative of the other machine without any effect what- ever, but the instant you touch the positive of either one to the negative of the same machine there will be fireworks.

And now let us go a little further: The general idea is that current seeks to escape from the wires into the ground. This is not true except in so far as the ground may offer a path from positive to negative. If you could have a generator and wire system working at 5000 volts, or any other voltage, thoroughly and completely insulated (a condition never found in actual practice), you could stand with your bare feet on the wet ground and handle either wire of the circuit without any danger whatever, but the instant one of the .wires develops current carrying connection with the ground and you stand on the ground and touch the other wire you get a shock, by reason of the fact that the current, leaping through your body into the earth and following the earth to the location of the ground on the opposite side, makes escape into the negative. If you happen to be holding the negative wire, that makes no difference, except that instead of escaping into your hands and passing through your body into the earth the current escapes through the ground at the positive into the earth, follows the earth to your body and up through your body to the negative.

In closing this topic let me repeat that the term polarity expresses the electrical difference between positive and negative.

How Electricity Is Generated

MORE and more it is becoming essential that the mov- ing picture operator have a comprehensive knowledge of electrical action, not only as pertains directly to the projection arc circuit, but also as relates to dynamos and motors. An ever increasing number of moving picture thea- tres are installing either motor generator sets or mercury arc rectifiers for the changing of alternating current into direct

FOR MANAGERS AND OPERATORS 7

current, or else isolated light plants consisting of a dynamo driven by a gas, gasoline, kerosene or steam engine. The operator is usually the man who is expected to take charge of and operate these isolated plants, and most certainly it is a part of his duties to handle and take care of a motor gener- ator set, or other device used for the rectifying of current. Therefore, I repeat, the up-to-date competent moving picture operator must have a very comprehensive knowledge of elec- trical action.

This, the third edition of my Handbook, is, like former editions, a work for practical men. In this book I shall, as I have in the past editions, pay a great deal more attention to practical things than to fine-spun theories and strictly tech- nical correctness.

We do not know the precise nature of the force we call electricity. We do not know what it consists of. Its com- ponent parts have never been analyzed. We only know that it is a mighty force, which apparently has neither sub- stance nor weight. It is a peculiar state, or condition, in and immediately surrounding a wire attached to a battery or generator which is not found in any wire not so attached.

We do, however, know how to handle this mysterious force, and bend it to our will. In fact, our knowledge of electrical action has become so complete that the mighty giant is as a child in our hands. We have chained it to the wheels of progress, and it has become a slave to mankind.

Electricity may be divided into three distinct classes, viz. : Static electricity, magnetism and electric current, meaning, by the latter, current which is generated by batteries or by an electric dynamo.

If you take a glass jar, of any convenient size, fill it two- thirds full of water, and then put in ordinary sal amoniac in proportion of a pound to the gallon of water, and in this solution suspend a piece of ordinary sheet copper, of con- siderable dimensions, and near to it but not touching suspend a piece of zinc, also of considerable dimensions, you will have the simplest form of what is known as an "electric battery." Now if you join the copper to the zinc by means of a piece of copper wire, current will flow between the two, or, more cor- rectly speaking, from the copper to the zinc, the copper being positive and the zinc negative. A properly proportioned bat- tery of this sort will generate about one volt pressure, and will put forth a considerable amperage while it lasts. It would be theoretically possible to construct and connect together

8

MOTION PICTURE HANDBOOK

a sufficient number of batteries of this kind to operate a pro- jection arc lamp, but, though theoretically possible, it would nevertheless be highly impractical. In practice the use of the battery is largely confined to the ringing of bells and buzzers, the operation of telegraph instruments and similar light ser- vice where but comparatively little energy is required.

Electric current used for ordinary light and power purposes is generated by what is known as a dynamo, or generator, the

two terms being inter- changeable when used in this connection. The dynamo depends for its action upon magnetism, and the fact that : When an electric conduct- or is moved in an electric field a current of electricity is generated therein which will flow in a direction at right angles to the line of motion.

, . In Fig. 1 we see this law

illustrated, N and S being the

q north and south poles of an

f V ordinary horseshoe magnet,

the dotted lines representing magnetic "lines of force," which constantly flow between the poles of all electric mag- nets. The space occupied by these lines of force is termed a "magnetic field," and with a magnet of the type shown in Fig. 1 this field is, of course, strongest directly between the poles.

A represents an electric conductor, say an ordinary copper wire, with its ends joined by wire B, so that a continuous cir- cuit is formed. If this wire be moved upward, in the direc- tion of arrow A, an electric current will be generated therein, which will flow along the wire in the direction of arrow C, or at right angles to the line of motion. // the wires were moved downward through the magnetic field in the direction of arrow X, instead of up, the current in the wire would flow in the op- posite direction, as per dotted arrow Y, it, of course, being under- stood that the ends of the wire passing through the magnetic field must always be joined, so that a complete circuit is formed.

Figure 1.

FOR MANAGERS AND OPERATORS

No current would flow if the wire were merely a straight length, with its ends unjoined.

Now let us take a step in advance and examine Fig. 2. Re- membering that if the electrical conductor in Fig. 1 be moved upward the current will flow to the right, and if it be moved

downward it will flow to the left, transfer your gaze to Fig. 2, where you will see a loop of wire, X X, so ar- ranged that it may be rota- ted on a spindle. One end of this loop connects to ring A, and the other end to ring B, and the ends are joined by means of brushes C and D and the wire E (outside circuit) attached thereto. Now if we revolve this wire loop (armature) in the direction indicated by small crank arrow, the side next us will move upward, while the other moves downward, so that on the side of the loop next us the current will flow to the right, toward collecting ring B, whereas on the other side it will flow to

Figure 2.

NOTE.— Strictly speaking it Is vol- tage (E.M.F.) which is generated, but my purpose is served by the use of the term "current," which is less confusing to the student.

the left, away from the col- lecting ring A, but by reason of the fact that the wire is in the form of a loop the current flows clear around the coil, out through brush A, around wire E to brush B, and back into the loop again, and thus we have the electric action of a generator exemplified. This is how current is generated.

But this is not all, since at the end of one-half revolution the two sides of the coils will have changed place, and the current, still moving in the same direction with relation to the magnet, will then be flowing away from ring A, and toward ring B, which, as you will readily see, means the reversal of the current within the wire coil itself, as well as in outside circuit B, and this reversal must, perforce, occur with every half revolution of the coil, or armature. In considering this matter, bear carefully in mind the fact that, with relation to the poles of the magnet, the current will always flow in the direction indicated by the

10

MOTION PICTURE HANDBOOK

arrows; also remember that this wire coil merely represents one coil out of the many wound upon the armature of a generator, but that the electrical action in all armature coils is essentially the same as that of the one described.

I think after a careful study of the foregoing you will readily grasp the idea, and understand how current is gener- ated in an armature coil; also why the current in the armature of a dynamo constantly reverses its direction, or, in other words, is "alternating."

The current in the armature of all generators reverses its direction as above set forth, though in multipolar dynamos (generators having more than two poles) it is reversed every time the coil passes from the influence of one set of poles into the influence of another set of poles, which may occur several times to each revolution of the armature.

Figure 3.

FOR MANAGERS AND OPERATORS 11

All this is just as true of direct current generators as it is of alternating current generators, but in the case of the direct current dynamo the alternating current generated in the armature itself is rectified by what is known as the "commu- tator," so that the current on the outside circuit flows constantly in one direction, or, in other words, is direct current. As a matter of fact all electric dynamos generate alternating cur- rent in their armatures. A study of what has gone before will show that this could not possibly be otherwise.

Fig. 3 is an illustration of a simple form of dynamo, tech- nically known as a "two-pole, shunt-wound" machine. N is the north and b is the south pole of its "field magnet." The dotted lines between its pole pieces represent lines of magnetic force, and its voltage and capacity will depend upon (a) the number of lines of magnetic force passing between the two poles, or, in other words, the "strength of the magnetic field," or, in other words, the "density of the magnetic flux" per square inch of the surface of the pole pieces on the side next to the armature; (b) the number of coils of wire the armature contains, and, (c) the rotary