/ 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 I 7 easter 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 speed of the armature. Of course, there are other details of construction, such as the kind of iron in the magnets, size of magnets, kind of arma- ture core, etc., which are of great importance, but these items only have to do with the efficiency of the machine, not its operating principle. The magnet of this type of machine is what is termed a "permanent magnet." That is to say, the iron of its magnets remains magnetized after the armature has come to rest. The slight magnetism retained by the iron after the armature has stopped is termed "residual magnetism," and it is this residual magnetism which enables the machine to start up without having its magnets excited from an outside source. The residual magnetism is, however, very weak, and, in practice, running at normal speed, the average dynamo would generate five or at the most ten volts when operating merely on the residual magnetism of its field magnet, which would be totally inadequate for commercial purposes. Now the voltage generated by the armature will depend upon the number of lines of magnetic force which the con- ductors upon that armature cut per second. The number of lines of force cut per second, and in consequence the voltage could, of course, be increased by increasing the number of coils on the armature, but in practice this would require an armature of huge proportions. The same effect could be had by increasing the speed of the armature, but there, too, is a 12 MOTION PICTURE HANDBOOK limit, and high speeds are objectionable. It therefore follows that the really practical method of increasing the number of lines of force cut per second is to establish the speed of the armature and the number of coils thereon, and then increase the density of the magnetic field until the desired result is at- tained, and this is the method which is adopted. It is done as follows: Examining Fig. 3 you will observe there is a wire coil around the top part of the poles of the field magnet. This wire connects with one brush, passes thence to one end of coils of resistance wire, known as the "field rheostat," and from the other end of these coils to and several times around one of the poles of the field magnet, across the air gap to and several times around the other pole of the field magnet, and thence to the opposite brush. This circuit is known as the "field circuit" or "shunt field circuit." Now, it is a well known fact if a wire be wound around the poles of a magnet and an electric current be passed through the coil thus formed, the strength of the magnet will be in- creased; in other words, the magnetic field between its poles will be made more dense and powerful, or, in other words, the lines of magnetic force or the magnetic flux will be made greater; and this will continue as the current is increased until the point of saturation (iron is said to be "saturated" with magnetism when it will receive no more) is reached. As applied to the dynamo, the operation of the field circuit is as follows: In starting up, the armature is revolved and brought up to speed by an engine or some other source of power. The armature coils cutting through the weak field created by the residual magnetism generate a slight voltage, and, the resistance of the field rheostat (See Fig. 3) having first been eliminated by means provided, a current is set up in the field coils, which, in compliance with the facts before set forth, instantly increases the strength of the magnetic field, and thus the armature coils are made to cut a greater number of lines of magnetic force per second and the voltage is increased, and so on until the voltage at which the machine is intended to operate has been reached, whereupon the handle of the field rheostat is moved, and resistance is cut into the field circuit in such amount as will just regulate the flow of current in the field circuit to the value which will hold the strength of the magnet field at a point which will cause the armature to cut just enough lines of force per second to maintain the desired voltage. It will, of course, be readily seen that as the load on the generator changes an alteration of the strength of the magnetic FOR MANAGERS AND OPERATORS 13 field will be necessary, or, in other words, variations in load of the generator will require the altering of the amount of resistance in its field circuit, which in some dynamos is ac- complished automatically, while in others it must be done by hand. All the foregoing applies in practice to the shunt-wound dynamo, and also very largely to the compound wound dyna- mo, but, no matter what the type of generator may be, the principle set forth holds good. The current for the field circuit is taken direct from the armature of the generator, but this comprises a very small fraction of the total output of the machine considerably less than 10 per cent. It is not designed to do more than give a comprehensive understanding of the method by which electricity is generated. There are many excellent works on dynamo action and con- struction, which may be consulted at the public library of your city and the student can go as far as he likes in such matters. In this work I can only find space for such practical things with relation to dynamos as may be expected to be of direct assistance to operators who are obliged to manage and care for generators or a motor generator set. THE DIFFERENCE BETWEEN ALTERNATING AND DIRECT CURRENT Direct current, commonly called "D. C.," acts continuously in one direction, presumably from positive to negative. The electrical impulse or, putting it another way, the flow of cur- rent is, theoretically, outward from the positive brush of the generator to the positive wire of the circuit, along that wire to and through the various lamps, motors, etc., to the negative, and back on the negative wire of the circuit to the negative brush of the generator. Direct current is very seldom of higher voltage than 500, since above that pressure it becomes exceedingly difficult to effectively insulate the commutator bars of the generator from each other. Another reason why we do not find D. C. at high voltage lies in the fact that after leaving the generator its pressure cannot be raised without the use of machines having moving parts, which is impractical by reason of the expense of installation and operation, as well as the necessary loss inherent in such a device. Alternating current is commonly known by the abbrevia- tion "A. C." As has already been set forth, the current in the armature of all generators is alternating; that is to say, the 14 MOTION PICTURE HANDBOOK current in the armature coils constantly reverses its direction, and "alternating current" (A. C.) is nothing more or less than the unrectified current which is sent out on the circuit just as it is generated in the armature coils of the dynamo, so that the current in the whole circuit reverses its direction as often as the current is reversed in the armature coils of the dynamo. There are several reasons why A. C. is very largely used, the main one being the fact that it may be generated at rela- tively high pressure; also the pressure (voltage) may be readily increased or reduced after the current has left the dynamo and this may be accomplished by means of a very simple device known as a "transformer," which has no mov- ing parts, requires practically no care or attention, lasts in- definitely if not overloaded, and accomplishes its work of in- creasing or decreasing the voltage with comparatively little loss of energy. The advantage of high voltage lies in the fact that while a wire of given size is rated at a certain, definite number of amperes and no more (See Table 1, Page 42), it will carry those amperes at any voltage. Electric energy, by which is meant the ability of the current to perform work, is measured in "watts." One watt is equal to 1/746 of a horse power. It therefore follows that 746 watts is equal to 1 horse power. Watts are found by multiplying volts by amperes, thus: 5 amperes at 110 volts equals (5 X HO) watts. Horse power equals volts multiplied by amperes divided by 746. Referring to Table 1, Page 42, we find that a No. 6 rubber covered wire must not be allowed to carry more than 50 am- peres of current. Now suppose .we have a No. 6 wire carry- ing 50 amperes at 110 volts: 110X50=5500 watts, which divided by 746 (watts in a horse power) gives us approx- imately iy-2. h.p. as the limit of power which can be conveyed on a No. 6 r.c. wire charged at 110 volts pressure. On the other hand, suppose we have the same No. 6 r.c. wire carry- ing 50 amperes at 2000 volts pressure. We then have 2000 X 50 = 100,000 watts, which divided by 746 equals almost 135 h.p., now being conveyed over a No. 6 r.c. wire which was loaded to capacity with 7^2 'h.p. when the pressure was 110 volts. From the foregoing it will readily be seen that there is enormous saving in copper (wire diameters) effected by using high voltage. This is a particularly important item if the power (current) is to be conveyed any considerable distance. To convey 1000 h.p. five miles by means of 110 volts pressure would entail an enormous outlay for wires of large size, since FOR MANAGERS AND OPERATORS 15 it would require nearly 7000 amperes, whereas with the current at 10,000 volts only about 75 amperes would be necessary. As has been said, A. C., unlike D. C., does not flow con- tinuously in one direction, but, quite the contrary, flows in one direction and then reverses and flows in the opposite. In other words, the current flows one way for a small fraction of a second and then reverses itself and flows in the opposite direction for an equal space of time, the period of flow in either direction varying from 1/50 to 1/266 of a second, accord- ing to the way the generator is designed. Two periods of flow that is to say, the period during which the current flows in one direction and reverses itself and flows back are called a "cycle." See definition of cycle, page 22. Alternating current dynamos may be designed to pro- duce current of any given number of cycles per second, the determining factor being the use the current is to be put to. Where light only is produced, the current frequency (number of cycles per second) may be quite high; sometimes as much as 133 cycles (266 alternations) per second; but cf late years the use of current frequency in excess of 60 has been almost entirely abandoned. Where the current generated is to be used entirely for power purposes a low frequency is much preferred, for the reason that it is more economical for driving motors. Power current runs as low as 25 cycles per second, whicL is the ideal current to apply to motors. Twenty-five cycles per second, however, is unsatisfactory for incandescent or arc lighting, since the alternations are so far apart that there is a notice- able flicker in the light. Light and power companies long ago discovered the fact that 60-cycle current produces very satis- factory results in lighting, and is at the same time fairly economical for power purposes. For this reason practically ajl generators designed to provide both light and power are what is known as 60-cycle. machines. It is essential that the operator get a clear understanding of these things, since more and more they are called upon to handle motors and generators, and moreover in some localities and under some conditions problems arise which can only be solved by one conversant with this subject. The action f alternating current is usually expressed by diagram, such as that shown in Fig. 4, and I will now try to help you to understand how to trace out the real meaning of such dia- grams. Indeed, it is very necessary that you do understand, because when one studies matters electrical, he is constantly 16 MOTION PICTURE HANDBOOK confronted with diagrams of this character, and if unable to trace out their meaning is greatly handicapped in his study. Let us consider Fig. 4. In its length the horizontal line represents time, and in its position with relation to the trian- gles above and below it represents zero voltage, or, in other words, no voltage, or, in other words, it represents the point at which the alternations of the current are completed and the voltage and amperage are both at zero. From to 1 represents the time of one alternation, which with 60-cycle current would be 1/120 of a second; the rise and fall of voltage in that alternation being represented by the Figure 4. triangular line above the horizontal line which leaves 0, mounts upward and comes back down to 1. The vertical column of figures represents voltage. Turn back to Fig. 2 and examine it and the text matter dealing therewith, so that the action of an armature coil will be fresh in your memory. Remember that when the coil in Fig. 2 is in the position shown, it is generating maximum voltage, and, conversely, when standing straight up and down it is in what we call the "neutral plane," and for an infinitesimal fraction of a second is generating nothing. Now, coming back to our diagram, Fig. 4, where the line of the triangle leaves and mounts up- ward, the coil of the armature is beginning to cut lines of force in increasing number, and the voltage is rising and con- tinues to do so until the coil is cutting the maximum lines of force, at which time the voltage has reached 110. Meanwhile time equal to half of an alternation, or, 1/120 -r- 2 = 1/240 of a second, has elapsed. Now the armature coil, begins to pass FOR MANAGERS AND OPERATORS 17 out of the magnetic field, and the voltage decreases until, fol- lowing the right-hand line of the triangle down to 1, it is at zero, and the current reverses. If we now follow the line on down on the left-hand side of the lower triangle and back up to 2, we will have traced the action of two alternations, or one cycle of current, and during that time 1/60 of a second will have elapsed. Now, in your imagination, draw a pencil point from to 1, and another pencil point round the upper triangle, and then continue the first pencil out on to 2 and run the other pencil point down around the lower triangle. If you could draw one pencil point from to 2 in 1/60 of a second, and in the same length of time trace the two triangles, one above and one below the line, to 2, with the other pencil point, you would have exactly typified the action of one cycle of alternating current, both as to time and rise and fall of vol- tage and amperage. With 25-cycle current, the action would be precisely the same, except that from to 2 would represent 1/25 of a sec- ond, instead of 1/60 of a second, and the action of the current therefore would be just that much slower. In studying the above get the fact clearly fixed in your mind that, while the action is almost inconceivably rapid, still it is a fact that with plain, single-phase alternating current, twice during each cycle, or one hundred and twenty times every second, there is absolutely no voltage, amperage, or anything else on the line. This is hard for the mind to grasp, since it is very difficult for the mind to accustom itself to such extreme rapidity of motion. The student may ask: "Well, if it is a fact that there is no voltage or amperage on the line twice during each cycle, how does it happen that the light from alternating current is con- tinuous?" In reply I would say that the light is not contin- uous, but the action is so enormously rapid that the effect of one alternation blends in the next, so that with 60-cycle current the effect is that of continuous, uninterrupted, even illumina- tion, but if the current be 25-cycle, then the action is slow enough that the eye can detect an uneveness of illumination, in the form of flicker, and that is why very low cycle alter- nating current, while ideal for power purposes, is objection- able and unsatisfactory for lighting. In handling alternating current we run into many complica- tions, one of which is the fact that we have single-phase, two-phase, and three-phase current to deal with. In Fig. 4 we have traced the action of alternating current. In Fig. 5 we see, at A, a diagrammatic representation of two-phase 18 MOTION PICTURE HANDBOOK current. Two-phase and three-phase current is produced by a peculiarity of the winding of the generator. How- ever, for the purpose of a clear understanding, we will assume that we have two generators, producing current of the same cycle, with their armatures coupled rigidly together in such manner that when the current flow of one is at zero the vol- tage of the other is at maximum. We will thus have a two- phase current delivered, and the voltage of such a circuit will never be at zero, since when the current generated by one of the machines is at zero the other is at maximum. Now, if we couple the shaft of a third dynamo to the shafts of the other Figure 5. % two, in such manner that the voltage rises and falls, as shown at B, Fig. 5, we shall have three-phase current. Two-phase current ordinarily employs four wires (two separate circuits) for its distribution. Its advantage lies in the fact that the two currents, acting like the piston of a double engine, give a steady instead of an intermittent pull on the armature of motors. Three-phase current requires three wires for its distribution. It is the ideal system for transmitting energy, through any distance, for power purposes. . It gives a prac- tically steady pull on the motor armature. Neither the two nor three phase systems has any particular advantage over single-phase 60 cycle current for lighting purposes. Electrical Terms IT is essential that the operator have a complete under- standing of certain terms used in connection with elec- trical work. It is quite difficult to impart a clear under- standing of some of the terms, but we will nevertheless do our best to make the matter at least reasonably clear. Work is the term used to describe the act of overcoming resistance through a certain distance. It is measured in foot- pounds. See foot-pounds. FpR MANAGERS AND OPERATORS 19 Foot-pounds. A foot-pound is the amount of work done or energy consumed in raising a weight of one pound one foot, or the equivalent, such as, for instance, raising one-half pound two feet, or raising two pounds one-half foot. It may also be described as overcoming a pressure of one pound through a distance of one foot. Coulomb. The coulomb is used to measure the quantity of current flowing in one second. It is the number of ^am- peres of current passing in one second. It is the product of the amperes times seconds, thus: 10 amperes flowing in 1 second multiplied by 1 second equals 10 coulombs; 10 amperes flowing for 2 seconds equals 20 coulombs. Volt-Coulomb. The volt-coulomb is the electrical unit of work. It is that amount of work performed when one ampere of current flows for a period of one second in a circuit whose resistance is one ohm, when the pressure is one volt. Ampere-Hour. One may draw a certain quantity of water, say a gallon, from a hydrant in one minute, or in ten min- utes, but, regardless of the time consumed in drawing the water, it is still one gallon, no more and no less. The same holds true in dealing with electric current. A certain given quantity may be used in one minute, or in ten minutes. The current flowing in any circuit is the relation of the quan- tity flowing to the time during which it flows, or, expressed otherwise: As has been said, coulombs equals amperes multiplied by seconds, or, 2 amperes X 10 seconds = 20 coulombs. 10 amperes X 2 seconds = 20 coulombs. 1 ampere X 20 seconds = 20 coulombs, and so on. By the foregoing you will be able to calculate that if one ampere flows for one 'hour we would have 1 ampere X 60 sec- onds = 60 coulombs, and 60 coulombs X 60 minutes = 3600 cou- lombs, so that one ampere flowing for one hour equals 3600 coulombs, and 3600 coulombs are, therefore, one ampere- hour, or a flow of 2 amperes for one-half hour would be one ampere-hour, or a flow of 4 amperes for 15 minutes would be one ampere-hour, since in either case 3600 coulombs would have been used. Ampere. Ampere is the unit rate of current flow. It repre-^ sents the quantity of current flowing through a circuit, pre- cisely the same as gallons or barrels represent the quantity or volume of water flowing through a water pipe. 20 MOTION PICTURE HANDBOOK Operators should carefully consider the distinction between the ampere and the coulomb. The term coulomb is not much used, but it is nevertheless one of much importance, since it measures the quantity of current passing in a given time. The ampere is such a rate of flow as would transmit one coulomb per second through a resistance of one ohm, under a pressure of one volt; a current of such strength as would deposit .005084 grain of copper per second. Volt The volt is the unit of electric pressure. It is the electro-motive force induced in a conductor, usually an arma- ture coil, which is cutting 100,000,000 lines of magnetic force per second. It is the term used to designate the strength of the affinity of one wire of an electric circuit to and for the other wire. It is the term used to designate and describe the intensity of electrical action. It is the term used to designate that quality or property of the electric current, or electric action, which corresponds to pressure in a steam boiler, or in a water pipe. Ohm. Ohm is the unit of resistance. It is the term used to designate and measure the opposition offered to the flow of electric current. It is the amount of resistance offered by a column of mercury 106 centimeters in length, having an area of cross section of one square millimeter, at degrees centi- grade, or 32 degrees F. This is the established international value of the ohm, designated as the "Legal Ohm." Watt. Watt is the unit of power. It is obtained by multi- plying volts by amperes: 1 volt X 1 apmere = 1 watt, hence, 10 amperes at 110 volts would be, 100 X 10= 1100 watts; 746 watts equal 1 horse power (h.p.). See kilowatt. See watt- hour. Kilowatt.- Kilowatt is merely a term of convenience, mean- ing 1000 watts. It is 1000 -f- 746 = 1.34 ihorse power. Watt-Hour. One watt-hour represents the amount of work performed by one ampere of current at one volt pressure dur- ing a period of one hour, hence, 4 amperes at 110 volts would be 440 watts, and when that amount of energy has been ex- pended for a period of one hour it would be 440 watt-hours. Horse-Power. One horse-power (h.p.) equals 33,000 foot- pounds of work per minute. It is the theoretical amount of work one strong draft horse is supposed to perform if a block and tackle be attached to a weight of 33,000 pounds and the tackle be of such proportion that the horse can, by exerting his full strength, just raise the 33,000 pounds one foot while walking outward pulling on the rope for a period of one min- ute. Under these conditions one horse-power has been ex- FOR MANAGERS AND OPERATORS 21 erted during that minute. That is the theory of the thing. One horse-power-hour is the amount of work exerted by one horse during one hour, or by 60 horses during one minute, or by 3600 horses during one second. In electrics 746 watts is supposed to represent the raising of 33,000 pounds one foot in one minute, or, in other words, one horse power. The unit was established as follows: 1 watt is equivalent to 1 joule per second (the joule is the practical C.G.S. unit of electrical energy. One joule is equal to .73734 of a foot-pound, or, .00134 h.p. -seconds; it is the quantity of electric energy necessary to raise the potential of one coulomb of electricity one volt in pressure) or 60 joules per minute, and 1 joule is equal to .73734 of a foot-pound, therefore 60 joules = 60 X .73734 = 44.24 foot-pounds. Now, since one horse-power equals 33,000 foot-pounds per minute the electrical equivalent would be 33,000^-44.24 = 746 watts. Resistance is that property of an electrical conductor by which it resists the flow of electric current. It is quite similar in its effect on electric current to the opposition water en- counters in flowing through a pipe by reason of friction with the walls of the pipe. Polarity. Polarity is the difference in condition between the positive and the negative electrodes of a battery, or of two wires attached to the positive and the negative electrodes of a battery. It is the difference in condition between the two terminals of a working dynamo, or between the wires attached thereto. It may be described as representing the ability of the two battery electrodes, dynamo terminals, or wires at- tached thereto, to perform work. Positive : from which electric impulse comes or "flows." Negative: opposite of positive. Short Circuit. The term applied to a direct, accidental cur- rent-carrying connection between two wires of opposite polarity, by means of which the current is enabled to skip a portion of its appointed path. Shunt Circuit. A subsidiary or secondary circuit on any part of a main circuit, by means of which a portion of the current leaves the main circuit and flows through the sub- sidiary or secondary circuit, as, for instance, the field magnet circuit in Fig. 3, page 10. Commutator. A device attached to the armature of a dy- namo by means of which the alternating current generated in the armature coils is changed into direct current for delivery to the outside circuit. 22 MOTION PICTURE HANDBOOK Direct Current. Current which flows continually in one direction. Alternating Current. Current which flows alternately in one direction and then in the opposite, the time of the flow in either direction varying from 1/50 of a second to 1/226 of a second, according to the construction of the generator. Conductor. A wire or metal bar used to convey electric current. Cycle. Events following each other in regular succession. One-half the number of changes in direction of alternating current per second. Two complete alternations of alternating current. Dimmer. An adjustable choke or resistance coil used for increasing or decreasing the resistance in an incandescent circuit gradually, so that the incandescent lamps attached thereto will be extinguished or lighted gradually. An adjust- able rheostat for use on incandescent light circuits. Electric Motive Force. Another name for voltage, and the one commonly employed in text books. Ground. A connection between wires of opposite polarity through the ground, having resistance low enough to allow current to pass from one wire to the other. Static Electricity. A form of electricity which is generated by friction. Main Feeder. The street circuit entering a district to which feed wires supplying the various streets are attached. Street Mains. Feed wires supplying individual house mains. Electro Magnetic Field. The field produced by an alter- nating electric current or by an electric magnet. Magnetic Field. That region of magnetic influence which surrounds the poles of a magnet or wire carrying A. C. Fuse. A short length of wire interposed in an electric cur- rent, the same being of some alloy which will melt (thus breaking the circuit and stopping the flow of current) at a temperature much less than that necessary to raise the tem- perature of a copper circuit wire to the danger point. Fuses usually melt at less than 300 degrees F. Galvanized Iron Wire. An iron wire coated with zinc, in order to resist the action of corrosion. Graphite. A condition of carbon in which it becomes an excellent lubricant, able to withstand very high temperature. FOR MANAGERS AND OPERATORS 23 In this condition it forms the "lead" of the ordinary lead pencil. Induction. The influence which a mass of iron charged with alternating current exercises upon surrounding metallic bodies, without having any actual metallic connection there- with. Insulation. The employment of any material having such high resistance that electric current is unable to pass through to the earth, or other current carrying substance, and thus reach a wire of opposite polarity. Rubber, porcelain and glass are examples of insulating materials. Magnetic Saturation. That point at which the power of a magnet cannot be further increased. Torque. That force which tends to produce a rotary move- ment around an axle, as the pulling or rotating of an electric motor's armature upon its shaft. The force applied to the rim of a dynamo pulley by a belt. Turning force. Transformer. An induction coil by means of which the vol- tage of a circuit may be changed without materially altering its wattage. A step-up transformer is one which transforms a current of given amperage and voltage to a current of less amperage and higher voltage. A step-down transformer is one which transforms a current of given amperage and vol- tage to a current of less voltage and higher amperage. Ampere Turn. A unit of magneto-motive force equal to the force resulting from the effect of one ampere passing around a single turn of a coil of wire. Voltmeter. Ah instrument by means of which the voltage or electro-motive force of a circuit is measured. Ammeter. An instrument by means of which the current flow in a circuit is measured in amperes. Wattmeter. An instrument by means of which the power being consumed in a circuit is measured in watts. Current Frequency. The number of cycles per second. Efficiency. The term used in describing the loss inherent in transformers, motors, generators, generator sets, etc. Elec- trically it is the relation of the wattage taken from the line to the wattage actually employed in the work in hand. For in- stance: If a motor takes 3000 watts from the line and only exerts a pull on the thing it is driving equal to 2000 watts, then its efficiency would be the percentage found by dividing 2000 by 3000, and 2000-^3000 = .666 or 662/3 per cent. 24 MOTION PICTURE HANDBOOK Circuit. The term commonly applied to wires of opposite polarity to which are attached other power consuming circuits or lamps, motors, etc. Synchronism. Synchronism is the term used to describe the action of A. C. alternations with relation to each other. Synchronism is sometimes referred to by electricians as "keep- ing step." It means that where two or more alternating cur- rents are coupled together, as in two or three phase current, their voltage values must rise and fall constantly with fixed relation to each other, as shown in Fig. 4, Page 16. In order to produce two or three phase current the voltage values must remain absolutely in step or synchronism with each other. When a motor is run in synchronism with a generator it means that the voltage value of the alternations in the arma- ture of the motor arc and must remain absolutely identical with the voltage value of the alternations in the armature of the generator. Once you grasp the real meaning of Fig. 5 the understanding of synchronism will be easy, therefore study Fig. 5. An Explanation of Electrical Terms, I HAVE given you the definition of certain electrical terms which the operator is likely to come into contact with in his work. In order to convey a more complete under- standing of the true meaning of certain ones of these terms, however, something more than a mere definition is necessary, therefore 1 shall elaborate by amplifying certain definitions in the form of an explanation. Polarity. Polarity and potential mean the same thing. When a wire is attached to one terminal of a working dynamo and another wire is attached to the opposite terminal of the same dynamo there is an electrical condition in these wires which enables them to perform work, or, more correctly, to cause a motor to which they are attached to perform work, or cause a lamp to which they are attached to give off light. This electrical condition is called "polarity," or "potential." It is the affinity one wire of an electric circuit has for the other wire of this circuit. It represents the inclination of the cur- rent to flow from one wire to the other wire, and this inclina- tion is so strong that in order to pass from one wire to the other the current will perform labor, and lots of it. When dealing with direct current one wire is always positive and FOR MANAGERS AND OPERATORS 25 the other is always negative; when dealing with alternating current each wire is alternately positive and negative many times each second. Voltage (E.M.F.). Electric current may be said to have both pressure and volume, and in its action in both these re- spects, as well as with regard to friction, electricity is very similar to and may be compared with water or steam. We must, however, carefully remember, when using these com- parisons, that they only hold good as applied to the laws of elec- trical action which have been determined by experiment. In other words, the similarity between electricity and water or steam exists only in their similarity of action. Water may be perceived by the senses; we can feel it and watch its action, whereas electricity is an absolutely impalpable substance, which cannot be perceived by any sense except that of touch, and even then it cannot be felt except through the "shock" occasioned by its passing over the tissues of the body. (We can see electric light, yes, but that is only the effect of the current, not the current itself.) Voltage corresponds in effect or in its action to the pressure of water in a pipe, or to the pressure of steam in a boiler. A dry battery, such as is used for electric bells, has a pressure of approximately one volt, and it imparts that pressure to wires connected to its terminals, so that if you attach two wires to such a battery they will, at any portion of their length, have a pressure of one volt. Now, if you take a second battery and connect its zinc with the carbon of the first battery by means of a short piece of wire, and then attach 'two other wires to the two remaining binding posts, you will have what is known as "series" connection, and a resultant pressure of two volts between the two wires. A third battery connected in series would raise the pressure to three volts, and so on, indefinitely. Instead of using batteries for producing light and power, which would be entirely impractical, we use a machine called a dynamo, each one of which is designed and built to produce a certain voltage, which may be anywhere from one to five hundred volts D. C, or from one to six thousand A. C. Remember that voltage corresponds to pressure, and is similar in its action to pressure in a steam boiler, but that voltage acts only between the positive and negative wires of the dynamo which generated it, and that the positive attached to one generator has no affinity or attraction to or for the negative attached to another dynamo, or for the ground, ex- cept as it offers a path to the negative of the generator to 26 MOTION PICTURE HANDBOOK which the positive is attached. Get this fact firmly fixed in your mind. Ninety-nine non-electricians out of every hundred believe current generated by a dynamo seeks to escape into the ground. This is not so, except as the ground offers a path between two wires of opposite polarity. If the positive or negative side of a dynamo generating 5000 volts be thoroughly and completely insulated (never actually the fact in practical work) you could stand on wet ground and handle the bare wire of the other side with your bare hands in perfect safety. Ampere. Ampere is the term used to denote quantity. It represents the volume of current flowing through, or along a wire, just as gallons or barrels represent the quantity of water flowing through a pipe, or cubic inches the volume of steam flowing. As a matter of fact we do not actually know that anything flows in or along the wire of an electric circuit. Eminent electricians say there is an actual flow; other equally eminent electricians say there is not, but that what we con- sider as current flow is really a "molecular bombardment." With these highly technical questions, however, we have nothing to do. For our purpose it is sufficient to say that current flows along the wire, just exactly as water flows in a pipe. The work performed is accomplished by the voltage or pressure working through the amperage or volume, and it is the pressure or voltage which is consumed never the amperes. Therefore, the higher the voltage or pressure, the greater amount of work a given volume of current can perform. For instance: If you supply a steam engine with steam at fifty pounds' pressure it will consume a certain given quantity or volume of steam to each stroke of the piston, according to the cubic capacity of the cylinder, and this quantity of steam at fifty pounds pressure will do a certain given amount of work. Now, if you raise the pressure of the steam to one hundred pounds the engine will perform twice as much work, but will not consume any greater number of cubic inches of steam. And so it is with electric current: One-half of an ampere at 50 volts will do a certain amount of work, but the same one- half ampere at 100 volts will do just twice as much. In other words, the amperage or volume of current is simply the medium through which the voltage or pressure (E.M.F.) acts, or works. In a steam engine, with the steam at given pres- sure, you can increase the power of the engine by either in- creasing the size of the engine cylinder, or by increasing the pressure of the steam. In a water motor you can increase the capacity to do work either by increasing the size of the motor or the pressure of the water. The same thing holds FOR MANAGERS AND OPERATORS 27 true with electricity. You can increase its capacity to do work either by increasing the volume of current (amperage) or by increasing the voltage. To perform a given amount of work with a low pressure (voltage) a large volume (amper- age) is necessary, but if the voltage be high the same amount of work can be performed with much less volume of current. In fact, the number of horse power of work performed by electric current is represented by the voltage times the am- peres, divided by 746. Ohm. Water in passing through a pipe encounters resist- ance, by reason of the rough sides of the pipe, as well as by reason of the internal resistance of the water itself. This resistance tends to retard the flow. Precisely the same is true with electricity. In passing through a wire electric cur- rent encounters resistance, and this resistance tends to retard the flow of current. It is measured in ohms, the definition of which is given elsewhere. The effect of resistance is to pro- duce heat. In a water pipe the resistance increases as the volume of water passing through the pipe is increased, or as the pipe is made smaller in relation to the volume of water flowing. It decreases as the pipe is made larger with refer- ence to the volume of water flowing. The same thing is true of current. Having a wire of given area, the resistance in- creases as the current flow becomes greater, and decreased as the current flow becomes less, or, having a given current flow the resistance increases as the diameter of the wire is made less or its length is increased, or decreases as the diameter of the wire is made greater or its length is decreased. Watt. Watt is the unit used to measure the amount of electrical energy expended the amount of work actually per- formed. It is found by multiplying the voltage by the am- perage, and is transformed into horse power by dividing by 746, since 746 w,atts equal one horse-power. For example: If we have 10 amperes flowing at 110 volts, the amount of energy expended would be equal to 110 X 10 = 1100 watts, which, divided by 746= 1.47 h. p. If, on the other hand, we had 110 amperes flowing at 10 volts the result would be the same. But if we had 10 amperes flowing at 10,000 volts then we would have electrical energy expended (work per- formed) as follows: 10,000X10=100,000 watts -f- 746 = 134 h. p. 28 MOTION PICTURE HANDBOOK Use of Electrical Terms in Calculation IT is quite problematical as to how much use the average operator will be able to make of electrical terms in mak- ing calculations, since, in order to find an unknown quantity he must know two other quantities. In order to cal- culate the number of amperes flowing in a circuit it is neces- sary the voltage and resistance in ohms be accurately known, and, while the operator usually knows about what the voltage is, the resistance is seldom a known quantity, or one which the operator can readily ascertain with any degree of ac- curacy. To find the number of ohms resistance, the operator must know the exact amperage and voltage, which he can, if necessary, obtain by means of a reliable voltmeter and am- meter. To find the voltage he must know the exact resistance in ohms and the exact amperage. But, notwithstanding the fact that only two of these quantities are usually known to the operator, and those two often only known approximately, the operator ought to understand how to make electrical cal- culations, particularly with relation to his projection arc cir- cuit, and I shall therefore give a somewhat extended explana- tion of the method. The operator must fix firmly in his mind the fact that where the projection lamp circuit is concerned the resistance does not lie wholly in the rheostat, or whatever takes its place. The wires, lamp arms and carbons offer small resistance, but a very considerable portion of the total is in the arc itself. The resistance of the wires, lamp arms and carbons may, for ordinary purposes, be neglected, but unless the resistance of the arc itself be taken into consideration a very serious error will result. When making electrical calculations it is customary, for the sake of brevity, to use the letters E, C and R. E stands for "electro-motive force," which is merely another name for voltage, hence E stands for voltage; C stands for current flow, meaning amperes, hence C stands for amperes; R stands for resistance in ohms, hence R stands for ohms. The operator should also remember that in a common frac- tion the horizontal line always means "divided by," thus ^ really means 1 4- 2. But I think I hear some one say you cannot divide one by two. Oh, yes, you can. It is done thusly: We put down the one, followed by a period, called a "decimal point," and then add ciphers, thus: 1.00. We now have 1.00 with a decimal point between the one and the two OOs, and 1.00 -4- 2 = .50, or, .5, which is exactly the same thing FOR MANAGERS AND OPERATORS 29 as 50/100, 5/10, or 1/2. The rule .is to count the figures or ciphers to the right of the decimal point in the number being divided, and then, beginning at the last figure of the result, count an equal number, and place the decimal to the left of the last figure counted. If there are not enough figures in the result to do this, then add ciphers to the left. E When dealing with formulas, means that the quantity C represented by E is to be divided by the quantity represented by C, E being the voltage and C amperes. If there be two or more quantities above or below the line, with no sign be- tween them, it means they are to be multiplied together, thus: E means that E (volts) is to be divided by C (amperes) C R E 15 multiplied by R (ohms), means that after 15 has been C subtracted from the quantity represented by E (volts) it is to be divided by the quantity represented by C (amperes). The student will be greatly benefited if he will practice writ- ing out formulas of this kind in letters, substituting quantities in figures and working them out. Ohms law sets forth the fact that the number of amperes flowing are equal to the voltage divided by the resistance in E ohms. We, therefore have = C, or, in other words, volts R divided by ohms equals amperes. It then follows that if E = C, C multiplied by R must equal E. It also follows that R E = R. It works out as follows: We know that the ordinary C 110-volt 16 c.p. carbon filament incandescent lamp requires approximately one-half ampere of current to bring it up to candle power. What is its resistance? Using the formula E 110 volts = R, substituting figures, we have = 220, C .5 of an ampere the number of ohms resistance in the filament of the lamp. 30 MOTION PICTURE HANDBOOK E 110 Again applying the formula = C, we have = .5, or ^2, as R 220 the amperage 110 volts will force through 220 ohms resistance. It seems to me all this is simple enough of understanding and application, but to make it yet more plain I will take the E formula = R, which means voltage divided by amperes equal C ohms, so that if the voltage be 50 and the amperes 10, E would mean 50, C 10, and R would be 50 -^ 10 = 5, but if the voltage' be 110 and the amperage 5, then E would mean 110, C 5 and R would be 110 -i- 5 = 22 ohms. When, however, we come to consider the projection arc circuit, a new element enters in the shape of the resistance of the arc itself, and if we propose to be absolutely accurate we must consider also the resistance of the carbon arms, wires, etc., but that degree of refinement is seldom or never neces- sary in a projection circuit calculation. In leaping the air gap between the carbon tips of the arc lamp the current encounters high resistance. In overcoming resistance voltage is consumed, as will be more thoroughly set forth and explained under "Resistance," Page 34. Tn other words, when current-flow is opposed by resistance, and that resistance is overcome, there is a consequent drop in pressure or voltage; pressure has been used, or consumed in the proc- ess. The resistance of the arc, consequently, the voltage drop in overcoming the resistance, is proportional to (a) length of arc; (b) size and characters of the carbons; (c) kind of core in the carbon; (d) number of amperes flowing. All these factors enter very decidedly into the equation, but very largely the resistance encountered is directly proportional to the length of the arc. For reasons not necessary to enter into at this time the D. C. arc, for a given amperage, is longer than the A. C. arc. It, therefore, follows that its resistance will be higher. The accepted theory is that all voltage is consumed at the arc. Whether or not this is true is a highly technical question, which it would be unprofitable to discuss in these pages. We shall accept the theory. Therefore the rheostat or whatever takes its place must cut down the voltage to just that pressure which the resistance of the arc will consume when burning normally. When an ordinary D. C. projection arc is operating at its best it consumes about 48 volts. The D. C. arc voltage varies FOR MANAGERS AND OPERATORS 31 from 45 to 55, but 48 is a fair average. In other words, the current must reach the arc at that pressure, and that pressure will be consumed in the arc. Ordinarily it is spoken of as "48 volts drop across the arc." What is the resistance of such an arc operating at 40 amperes? Knowing the voltage E (48), and amperage, we apply the formula = R, and have C 48 -T- 40 = 1 1/5 ohms arc resistance. Let us prove this out. Suppose the line voltage to be 110. The total resistance must E equal ( = R) the voltage divided by the amperes flowing; C therefore, the amperage being 40, the resistance must be 110 -r- 40, or 23/4 ohms. We have seen that the arc resistance is 1 1/5 ohms with its voltage at 48. Subtracting the arc voltage from the line voltage leaves us 62, as the drop in vol- tage there must be across the rheostat. Again applying the E formula ( = R), we have 62 -r- 40 = 1 11/20 as the ohmic re- C sistance of the rheostat. Adding this and the arc resistance together, we have a total of (1 1/5 + 1 11/20) 23/4, as the total resistance, which corresponds to the total resistance necessary to allow 40 amperes to pass through. If the amperage were 45, then the total resistance, voltage remaining the same, must be less. If the amperage were less, then the resistance would necessarily be greater. The higher the voltage the greater must be the resistance, as will E be seen by applying the formula = R, to accomplish a given C current flow. Resistance is always found by application of the formula last quoted. Arc resistance, as we have said, will vary somewhat, accord- ing to the character of carbons and cores, the amount of cur- rent flowing and the arc length, particularly the latter. How- ever, with the D. C. projection arc we are reasonably safe in taking the constant 48, for the arc drop, or arc voltage, unless the amperage is low say 30, or less, when 45 will serve better. Such a standard is necessary, even though more or less in- accurate, since the operator sel-dom has a voltmeter with which to measure the arc voltage exactly. Instead of applying 32 MOTION PICTURE HANDBOOK E the formula = R, as it stands, we first subtract the arc C voltage (using the standard 48), from E, which represents the line voltage, thus securing, at one operation, the total resist- ance other than that of the arc. The problem then reads, for E 48 any D. C. arc above 30 amperes, - '=R, but the "R" in C this case is the necessary ohmic resistance except that peculiar to the arc itself. In subtracting 48 we have accounted for the arc resistance. For an arc of 30 amperes, or less, the formula is - = R. For the ordinary A. C. projection arc, up to 60 C E 35 amperes, the formula to be used is - = R. In other C words we use 35 as the A. C. constant for arc voltage, instead of the 48 used for D. C. Suppose we wish to construct, or order a rheostat to deliver 25 amperes on 125 volts line pressure, when working in series E 45 with a D. C. projection arc. We use the formula - = R. C 125-45 Substituting figures for letters we have -- , which equals 25 the necessary ohmic resistance of the rheostat, not taking ac- count of line and carbon resistance. 125 45 = 80 and 80 -T- 25 = 3 1/5, the number of ohms resistance the rheostat must contain. If it were a 40 ampere arc we would subtract 48 instead of 45. If it were an A. C. arc we would subtract 35. Were we to connect the same rheostat between the wires of a circuit carrying the same voltage without an arc in series, or, what amounts to practically almost the same thing, freeze the carbons of the arc lamp, we would then find the 3 1/5 ohm rheostat, which delivered 25 amperes in series with E an arc, to be delivering ( = C) 110-=- 3.2 = 34.4 amperes, R almost. RULE OF THUMB There is a very simple formula, easy of application, which combines the three formulas into one. It is called the "Rule FOR MANAGERS AND OPERATORS 33 E of Thumb." It is expressed for general use as: . CR To use the formula you have but to cover the symbol or letter representing the quantity desired, and what remains will produce the answer, thus: Suppose we wish to ascertain the resistance in ohms. We cover up the "R" in the formula E and find that we have remaining, which will give R, the C desired quantity. In using this formula on projection circuits the top letter must be expressed as E minus the arc voltage, the same as in the regular formulas, thus: E-48 E 45 E 35 or for D. C. and for A. C. CR CR CR Go to your work each day as though it ^vere your first day on a new job and you had to make good. 34 MOTION PICTURE HANDBOOK Resistance ONE of the most difficult problems confronting the oper- ator and the electrician is resistance. This is a factor which is met with in almost every phase of electrical work, and, so far as light be concerned, it may be said to be the very foundation stone of the structure. How Resistance Acts. In passing through a wire, current encounters resistance, which is, in its action, very similar to that encountered by water under pressure in passing through a pipe. When water flows through a pipe it encounters resist- ance directly in proportion to the size and length of the pipe and the quantity of water flowing per minute. This resistance is to some extent the result of molecular friction within the water itself, but mostly it is caused by friction be- tween the water and the sides of the pipe. In a pipe of given diameter, resistance increases with (a) increase of the flow, or volume of water, (b) increase of the length of the pipe, and (c) with the roughness of the inside of the pipe. Con- versely it decreases with decrease of the flow, the shortening of the pipe or with increased smoothness of pipe walls. With a given flow of water, resistance increases with the length of the pipe, the decrease in its diameter or added roughness, and decreases as the pipe is made larger or shorter or smoother. Resistance consumes pressure, and pressure is consumed exactly in proportion to the amount of resistance encountered. In the second edition of my Handbook I explained this propo- sition by means of a diagram, and I do not think that particular thing can be improved upon, therefore it is herewith reproduced in somewhat different form. In the illustration we see a water main, with a pressure gauge registering 100 pounds, to which are connected three pipes A, B, and C. On A is a pressure gauge placed right up close to the main pipe and another near its outer end. We will assume the diameter of this pipe to be one-half inch. At B is a short pipe of the same diameter; at C is a pipe three inches in diameter for ten feet of its length, with a three-foot extension of half-inch pipe at its end. At the outer end of the large pipe is a pressure gauge, with another at the end FOR MANAGERS AND OPERATORS 35 of the extension. Now let us consider the action. Pipe B is short and, being open at its end, the water spurts out with great force, carrying itself almost horizontal for a consider- able distance, thus showing that the pressure at the mouth of the pipe is high. The water at the end of pipe A does not come out with such great force, and if we examine gauge No. 1 and gauge No. 2 we shall find that, whereas gauge No. 1 registers very nearly the same as the one on top of the main pipe, No. 2 will register far less. Gauges No. 1 and No. 2 are on the same pipe. What is the explanation of the differ- ence in pressure? The answer is simple. It has been used up in forcing the water at high speed against the friction of the pipe. The pipe is, under the conditions, working above its normal capac- Figure 6. ity, with the result that very high resistance is developed, and the greater the resistance the more power (pressure) is consumed in overcoming it. Examining gauge No. 3 at the end of the large section of pipe C, we find that it stands almost if not quite at equal pres- sure with the one on top of the main, although it is ten feet from the main, whereas gauge No. 4, at the end of the small three-foot section, shows considerably less. What is the rea- son for this? Again the answer is simple. The volume of water passing through the short' pipe is very great as compared with its diameter. It is rushing through at high speed, therefore the friction or resistance encountered is high, with the result that pressure is used up very rapidly in forming the water against it. On the other hand, while precisely the same 36 MOTION PICTURE HANDBOOK volume or amount of water is passing through the large sec- tion of the pipe it is moving quite slowly, hence the resistance it encounters is comparatively slight, and very little power is necessary to overcome it. The pressure at which the water might be would not affect the result, except that if it be very low not much resistance could be overcome. A pipe of given diameter will carry water up to its capacity (the capacity of a pipe may be said to have been reached zvhen its resistance to the flow of water becomes excessive, so that there is a considerable waste of power in forc- ing the water through} under any pressure sufficient 4:o move the liquid and less than that sufficient to burst the pipe. A pipe of given diameter will convey only a certain number of gallons of water per minute without excessive friction, regardless of whether the pressure be 10 or 100 pounds per square inch, but when the point is reached where resistance to flow becomes excessive, the normal capacity of the pipe is said to have been reached. True, we can still force a great deal more water through, but it will be at the expense of largely increased power consumption. It costs money to force a water pipe above its capacity, and the cost increases very rapidly in proportion to the excess of capacity; in other words, the higher the excess over capacity the greater the relative cost of overcoming the resistance. The practical method of reducing this resistance is to in- crease the diameter of the pipe until the desired flow is had with only a normal friction loss. We therefore deduce the rule that: Increasing the diameter decreases the friction, or resistance offered to a given flow, since the water is thus caused to move more slowly. But another equation enters 'here, viz., the length of the pipe. Inasmuch as friction very largely results from the rough side of a pipe, it naturally follows that the longer the pipe the more friction there will be. We have already seen that with a given flow as the diameter of the pipe is decreased (made less), the friction or resistance is increased (made greater), and conversely, as the diameter of the pipe is in- creased (made greater) the friction or resistance is decreased (made less). We may also readily see that, with a given flow: As the length of the pipe is increased the-friction (resistance} is increased, and, conversely, as the length is decreased the re- sistance is also made less. Therefore, we may increase the resistance by (a) increas- ing the flow of water; (b) decreasing the diameter of the pipe; FOR MANAGERS AND OPERATORS 37 (c) increasing the length of the pipe; (d) increasing its roughness. We may decrease the resistance by (a) decreasing the flow; (b) increasing the diameter of the pipe; (c) making the pipe shorter; (d) making the pipe smoother. All this is simple, and is or ought to.be readily understand- able. And now what has been said of the water pipe is also true with relation to current and wires. If you substitute circuits of wire for the water main and for pipes A, B, and C, with volt- meters in place of the pressure gauges, and lamps or motors instead of the open pipe-end you will get precisely the same relative result in loss of pressure (voltage) when current flow is sent through the circuits. The voltage of the current has absolutely nothing whatever to do with the necessary size of wire. You could convey current at 10,000 volts, or 50,000 volts for that matter, on a No. 40 wire, which is no larger than a very fine silk thread, but on that wire you could convey a very small quantity amper- age. Electric current in passing through wires' encounters re- sistance precisely the same as does water in passing through a pipe. A wire of given diameter will convey a certain given number of .amperes of current without excessive friction (resistance), just the same as a water pipe of given diameter will convey a certain given number of gallons of water with- out undue friction or resistance, and the point where resist- ance begins to rise above normal marks the "capacity" of the wire, just as it does the water pipe. Beyond that point the friction or resistance becomes excessive, and manifests itself in a loss of pressure or voltage. This loss in pressure has been consumed in forcing the current against resistance, pre- cisely as was the case in the water pipe. It therefore follows that loading wires beyond their normal capacity is expensive, and should be avoided for that if for no other reason, since the waste is registered on your meter and you will have to pay for it, ex- actly the same as you pay for current used in your lamps or motors. But this is not all, for if you attempt to force amperage in excess of the rated capacity, as shown by the Underwriters' table (see page 42), heat will be developed, and, if the matter be car- ried too far (which can only be done by overf using), the wires may get red, or even white hot, finally burning in two entirely and stopping all current flow and perhaps setting fire to the building in the process. 38 MOTION PICTURE HANDBOOK Exactly as was the case with the water pipe, with a given current flow the resistance of a wire is decreased as the diameter of the wire is increased, or its length made shorter, and is in- creased as the diameter of the wire is made smaller or its length decreased. Resistance increases With increased length of wire; or As diameter is decreased; or As the temperature is increased above normal; or As the composition of the wire is changed to an alloy having lower conductivity. Resistance decreases As length of wire is decreased; or As the diameter is increased. As the temperature is reduced, if it be above normal. As the composition of the wire is changed to an alloy having higher conductivity. NOTE. The difference in conductivity of different metals makes the analogy of water and current action more complete, since it corre- sponds to roughness or smoothness of walls of the water pipe. Different metals offer varying resistance to electric current as follows, taking the resistance of pure silver and pure copper as 1. Copper 1 *18% German Silver 19 Silver 1 Manganin 24 Aluminum 1.5 *30% German Silver 28 Platinum 6 *Advance Wire 28 Norway Iron 7 *Climax Wire 50 Soft Steel 8 *Nichrome 60 *Ferro Nickel 17 NOTE. The Driver-Harris Company, manufacturers of resistance wires, are authority for these figures. I know of no more reliable source for information of this kind. Star (*) indicates Driver-Harris products. In the foregoing table the figures refer to the amount of resistance each metal has, as compared to that of pure, an- nealed copper. For instance, platinum has 6 and climax wire 50 times the resistance of pure, annealed copper. I have selected for a part of this table metals and composi- tions in very general use for resistance purposes. It will, of course, be understood that the figures given in the tables are based on metals and alloys of a certain standard purity, but inasmuch as the degree of purity will, in the very nature of FOR MANAGERS AND OPERATORS 39 things, vary to some extent, the figures cannot be relied upon for absolute accuracy. It must also be understood that the resistance of nearly all metals increases with rise of temperature, whereas the resist- ance of carbon decreases as its temperature increases. The resistance of the carbon filament of the incandescent lamp of the ordinary type is about twice as much when cold as when burning at candle power. As a general proposition the re- sistance of liquids and insulating materials become less with increased temperature. TEMPERATURE COEFFICIENT HOW TO USE The resistance of a wire is not constant at all temperatures. If you increase the temperature of a metallic wire you also increase its resistance, and this increase in resistance follows a definite law, viz.: In metals increase or decrease in resistance is directly in pro- portion to increase or decrease in temperature. The factor that will enable you to calculate this increase or decrease, provided you know the difference in temperature, is called the "temperature coefficient." In all catalogs of re- sistance wire the resistance per foot of the material is given at a certain standard temperature, usually 75 degrees F, and the resistance at this standard temperature will form the basis for calculation of increased or decreased resistance by reason of temperature change. The figure given for tem- perature coefficient is the fraction of an ohm change in re- sistance for each degree F change in temperature, and this coefficient must be multiplied by the number of degrees of the temperature change from the standard 75 degrees, and the result added to or subtracted from the standard resistance, depending upon whether the material increases in resistance with heat as metal does, or decreasing with heat as some other substances, carbon, for instance, do. For example, let us assume the temperature coefficient of a given material to be .001 per degree F., and that its resistance at 75 degrees F. is 10 ohms. What will be its resistance at 175 degrees.? Subtracting 75 from 175 we find the difference in tempera- ture to be 100 degrees. If the resistance increases .001 of an ohm for each degree of increased temperature then for 100 degrees increase of temperature the increase of resistance would be .001X100 = .!. Now, multiply the resistance (10 ohms) at 75 degrees by the fractional increase, which is .1, 40 MOTION PICTURE HANDBOOK which gives us the actual total increase of 10 X .1 = 1 ohm, so that the resistance at 175 degrees F will be 10 ohms, the standard resistance, plus 1 ohm increase, or a total of 11 ohms. PROPERTIES OF CONDUCTORS Electric conductors are ordinarily selected with one of two ends in view. In one case low resistance, tensile strength, ductility, and cost are the ruling factors; in the other case comparatively high and steady resistance is the important item. In the first instance conductors for current distribution is the thing considered, and, by reason of the fact that it more nearly combines the four above-named important factors than any other metal, copper has been selected as the standard electrical conductor, an office which it shares only, to some slight extent, with aluminum, the latter being used in a few instances for high tension lines. In the second instance a material to offer resistance is the thing desired, and for a long time the metal used almost ex- clusively for this purpose was German silver. Gradually, however, German silver has been largely displaced, until it is now but little used except in alloy combinations with other metals. The materials now most generally used for resistance in motion picture projector circuits are either cast iron, made up in grid form, or some one of the nickel-steel resistance wires. Reliable data concerning the properties of cast iron is difficult, in fact practically impossible to obtain, but it may be said that it forms an excellent and cheap resistance medium where considerable variation at different temperature is not of great importance. Properties of Resistance Metals. "Normal" is 75 F. or 24 C. The resistance per mill-foot of pure nickel is 64.3 ohms at normal. Climax resistance wire, made by the Driver- Harris Company, Harrison, N. J., has a resistance per mill- foot of 525 ohms at normal; its temperature coefficient is .0004 per degree F. It is a nickel steel alloy with a resistance fifty times that of copper. This metal is excellent for rheostat coils. German silver is a composition containing 18 per cent, of nickel. It is known as "18 per cent. German silver." Its re- sistance varies somewhat with different lots. Its mill-foot resistance is 218 ohms at normal; its temperature coefficient .00017 per degree F. FOR MANAGERS AND OPERATORS 41 Ferro nickel has a mill-foot resistance of 170 ohms at normal; temperature coefficient is .00115 per degree F. Yankee silver is a new alloy, put out by the Driver-Harris firm, which is claimed to be an improvement on the 18 per cent. German silver in that it withstands rapid heating and cooling well, and gives good service where German silver fails. Its resistance is 200 ohms per mill-foot; its tempera- ture coefficient is very low, being .000086 per degree F. Nichrome, also a Driver-Harris product, is a practically non-corrosive alloy with high melting point about 2600 de- grees F. It is designed for use where high temperatures are the rule, such as heating coils, etc. Its mill-foot resistance is 600 ohms; its temperature coefficient .00024 per degree F. Advance wire, a Driver-Harris product, is a copper-nickel alloy containing no zinc. It is claimed to be constant in its resistance under all conditions of service; therefore it has no temperature coefficient. Resistance per mill-foot is 294 ohms. It is particularly recommended for electrical instruments where the resistance is subjected to repeated heating and cooling. LOSS THROUGH RESISTANCE It is highly desirable and under certain conditions very necessary that the operator be able to figure the resistance of the various circuits in the theatre or of the feed-wires lead- ing thereto. As has already been pointed out, the overcoming of resistance consumes voltage. All wires offer resistance to current, and voltage will be consumed in (a) proportion to the size of the wire; (b) the length of the wire; (c) the amount of current flowing; (d) composition of the wire. Up to a certain point the resistance of the wire remains without change; that is to say, the resistance offered to one ampere or ten amperes will be identical, but when the load becomes such that the temperature of the wire begins to rise, then the resistance also begins to rise, and the effect is, as has already, been explained, a loss in voltage, with the result that the lamps will not burn to candle power and the meter is registering wattage which is being wasted in overcoming the excessive resistance of the wires. Copper wire used for electric current can carry a certain number of amperes without causing any appreciable rise in temperature, and the National Board of Fire Underwriters, which is the controlling factor, has adopted the amperage rating recommended by the American Institute of Electrical Engineers. This determines the number of amperes which 42 MOTION PICTURE HANDBOOK any wire may be allowed to carry, which are set forth in Table No. 1, in which "B. & S." means "Brown & Sharpe Wire Gauge." For reasons why more current is allowed on weather-proof than on rubber-covered see "Insulation," page 50. TABLE NO. 1. WIRE CAPACITIES. Rubber Other Insulation Insulations Circular B. & S. Amperes Amperes Mills 18 3 5 1,624 16 6 10 2,583 14 15 20 4,107 12 20 25 6,530 10 25 30 10,380 8 35 50 16,510 6 50 70 26,250 5 55 80 33,088 4 70 90 41,740 3 80 100 52,630 2 90 125 66,370 1 100 150 83,690 125 200 105,500 00 IsO 225 133,100 000 175 275 167,800 0000 225 325 211,600 For insulated aluminum allow 84 per cent, of above table ratings. The Board of Fire Underwriters does not recognize anything of less size than No. 18 wire, and nothing less than No. 14 can be used for interior circuit wires. The figuring of the resistance of a wire of any size or length is a simple matter, provided the standard of resistance for that particular material be known. MILL-FOOT STANDARD OF RESISTANCE The accepted standard of resistance is the resistance of a wire one circular mill in cross-section (one one-thousandth of an inch in diameter) and one foot in length, made of the same material as the wire it is proposed to measure. This is what is known as the "Mill-foot standard of resistance." The resistance of such a wire, when made of ordinary commercial copper, is given by standard text books as 10.5 ohms. That is to say, a wire one foot in length and one one-thousandth of an inch in diameter (one mill cross-section), made of ordinary commercial copper, at normal temperature (75 F. or 24 C), will have a resistance of 10.5 ohms. FOR MANAGERS AND OPERATORS 43 TABLE NO. 2 RESISTANCE OF COPPER WIRE So Resistance at 75 F., International Units Sri R. Ohms Feet 6 . Ohms per per Ohms per Lb. per Mile Ohm 1000 Feet 000000 0.03122 0.1649 32036. 0.00003070 00000 0.03937 0.2079 25398. 0.00004881 0000 0.04964 0.2621 20147. 0.00007758 000 0.06261 0.3306 15972. 0.0001234 00 0.07894 0.4168 12668. 0.0001962 6 0.09945 0.5251 10055. 0.0003114 1 0.1255 0.6627 7968. 0.0004960 2 0.1583 0.8360 6316. 0.0007894 3 0.1966 1.054 5010. 0.001254 4 0.2516 1.329 3974. 0.001994 5 0.3174 1.676 3150. 0.003173 6 0.4002 2.113 2499. 0.005043 7 0.5044 2.663 1982. 0.008013 8 0.6361 3.358 1572. 0.01274 9 0.8026 4.238 1246. 0.02029 10 1.011 * 5.340 988.8 0.03220 11 1.277 6.743 783.1 0.05135 12 1.609 8.496 621.5 0.08154 13 2.026 10.70 493.6 0.1293 14 2.556 13.50 391.2 0.2058 15 3.221 17.01 310.4 0.3268 16 4.070 21.49 245.7 0.5216 17 5.118 27.02 195.4 0.8249 18 6.466 34.14 154.6 1.317 19 8.151 43.04 122.7 2.092 20 10.26 54.15 97.51 3.312 21 12.93 68.26 77.35 5.263 22 16.41 86.62 60.95 8.476 23 20.56 108.6 48.63 13.32 24 26.00 137.3 38.47 21.28 25 32.78 173.1 30.51 33.84 26 41.54 219.4 24.07 54.35 27 52.09 275.0 19.20 85.44 28 66.17 349.4 15.11 137.9 29 82.27 434.4 12.15 213.1 30 105.1 554.7 9.519 347.6 31 131.7 695.4 7.592 546.3 32 166.2 877.4 6.018 869.6 33 209.5 1106. 4.772 1383. 34 264.6 1397. 3.779 2205. 35 333.7 1762. 2.996 3507. 36 420.1 2218. 2.380 5558. 37 530.4 2801. 1.885 8860. 38 669.9 3537. 1.493 14131. 39 843.0 4451. 1.186 22378. 40 1065. 5625. 0.9387 35734. 44 MOTION PICTURE HANDBOOK FIGURING RESISTANCE OF CIRCUITS And now let us proceed to apply the foot-mill standard in measuring wires. Suppose you have a wire 400 feet in length and 1 mill-foot in cross-section (1/1000 of an inch in diameter) made of ordinary commercial copper. It is evident that if one foot of such a wire has a resistance of 10.5 ohms, 400 feet would have a resistance four hundred times as great, or 10.5X400 = 4200 ohms. The resistance of a wire of given length, however, decreases, as its diameter, area or cross-sec- tion is increased. Now if our 400-foot wire has a diameter of 250 mills it will have a cross-section equal to 250 X 250 = 62,500 C. M., and it follows that its resistance would be equal to the resistance of 400 feet of one-mill wire (4,200 ohms) divided by the C. M., cross-section of the larger wire (62,500), since it would be, in effect, equal to 62,500 wires, each one circular mill in cross-section, or one mill in diameter. From this we get the rule: To find the resistance of a copper wire, multiply its length in feet by 10.5 and divide that product by its area in circular mills. In measuring circuits, however, it is customary to take the one way length and double the mill-foot standard, thus: multiply the one way length of the circuit by 21 (10.5X2 = 21) and divide that product by the area of the wire in the circuit; expressed in circular mills. For example: What is the resistance of a two-wire oper- ating room feed circuit 300 feet in length size of the wire No. 5? Now if we were just measuring one 300-foot-long wire we would apply the above rule, using 10.5 as the standard of resistance, but as a matter of fact a circuit 300 feet long has 600 feet of wire, and, for convenience sake, we double the mill-foot standard, instead of doubling the wire length. In Table 1, page 42, we find that No. 5 wire has a cross- section of 33,088 C. M. We then .have the problem: Length of circuit X 21 300 X 21 = = 1874, or say .2 of an ohm, Area of wire 33,088 which is the resistance of the circuit. This rule is, of course, based on the proposition that the wire will not exceed 75 degrees F., or 24 degrees C. However, the rise and fall in temperature caused by ordinary climatic conditions is not sufficient to effect the result materially. In fact, resistance does not begin to rise appreciably until the temperature has increased sufficiently to be sensible to the feeling; beyond that point it increases very rapidly with the temperature. FOR MANAGERS AND OPERATORS 45 The foregoing is good for any number of amperes up to the capacity of the wire, or, in other words, until the load becomes great enough to cause a distinct rise in temperature. For instance: If you propose to carry only 5 amperes on a No. 5 wire you would have exactly the same total resistance you would have if you pulled 50. Theoretically this is not strictly true, since there is a rise in temperature with any increase in current, but it is true in prac- tice, nevertheless, by reason of -the fact that with any load less than the wire's capacity the temperature rise is too slight to have appreciable effect. When figuring copper wire resistance still another equation enters, however, and a very important one, too, viz., drop in voltage. FIGURING VOLTAGE DROP It has been laid down as a general rule that: For the transmission of any given amperage the most econom- ical condition is one where the line resistance is of such value that the value of the energy wasted in heat in overcoming the resist- ance of the line will be equal to the interest per annum on the original cost of the conductor. The question of drop in voltage in theatre circuits is usually given too little consideration. Where the length of the cir- cuit, the cross-section, or area of the wire, together with its mill-foot standard of resistance, is known, the ohmic resist- ance may be calculated according to: 21 XL Formula No. 1: R = A in which R is resistance in ohms; L the one-way length of the circuit, expressed in feet; A the cross-section, or area of the wire in circular mills, and 21 a constant equal to twice the re- sistance of the mill-foot standard for copper wire. Twenty- one and the one-way length of the circuit are used, instead of 10.5 and the total length of the two wires, merely for the sake of convenience. Formula No 2: e = IXR in which e is the voltage drop; I the current in amperes, and R the resistance of the circuit. 21 X I X L Formula No. 3: e = in volts. 46 MOTION PICTURE HANDBOOK 21 X I X L Formula No. 4: A = in circular mills. Formula No. 5: 1 = in amperes Formula No. 6: L = in feet. 21X1 When it is required to give a working formula for a given number of lamps expressed by N, each of which requires am- peres represented by I, use Formula No. 7. 21 X N X I X L Formula No. 7 : A = area in circular mills. When the drop is expressed as a percentage, the size of the wire may be determined by Formula No. 8. 2100 X I XL Formula No. 8: A = area in circular mills, E EXP being the voltage of the circuit and P the percentage drop. Where, as is often the case, the power, W, is given in watts instead of amperes, use Formula No. 9. 2100 X WXL Formula No. 9: A = area in circular mills. PXE If it is desired to find the number of lamps to which a given size of wire will supply current with a given drop use For- mula No. 10. AXe Formula No. 10: N = 21 X L X I Applying formula No. 2, let us assume a current of 100 amperes in a circuit whose resistance figures .02 of an ohm. Multiplying 100 amperes by .02 we get 2 volts as the drop in that circuit. Formulas Nos. 3, 4, 5, 6, 7, 8, 9, and 10 are ob- tained by substituting the value of R in Formula No. 2 for R in Formula No. 1. Also for convenience L (length of circuit) FOR MANAGERS AND OPERATORS 47 is made equal to 2L, so that only the distance one way need be considered. And now let us assume an example. A two-wire operating room feeder supplies 50 amperes at a distance of 200 feet from the house switchboard; the drop allowed is 5 per cent, the voltage 110. What size wire should be used? Referring to the formula, we select No. 8, and, substituting figures, the necessary size of wire is found as follows: 2100 X 50 X 200 A = 38181 circular mills. 110 X. 05 Turning to our capacity table we find that a No. 4 wire has an area of 41738 CM. and a No. 3 has 52624, so that a No. 3 would be largely in excess of the requirements and a No. 4 would be too small. If this energy were used for ten hours a day for 300 days and the cost of the energy were 8 cents per k.w. hours, the total yearly cost would be: 50 X HO X 300 X .08 == $1,320 1000 five per cent, of which is $66, which latter amount would ex- press a yearly loss due to the 5 per cent, drop when using 50 amperes at 110 volts. The cost of 400 feet of No. 4 wire would be about $21, hence the yearly loss would be more than three times the cost of the wire, and, without further calculation, it is very readily seen that No. 4 wire would not be econom- ical for this service. If, on the other hand, wires sufficiently large to only cause a four per cent, loss be used, it is no difficult matter to figure out the saving and discover the fact that it would considerably more than pay interest on the added copper cost with current at 8 cents per kilo- watt. Suppose, however, the price of electricity were 6 cents per k.w. instead of 8. The installation of such a large cable would then not be profitable, since the saving would be less, hence, less investment in copper would be necessary. This data is of much importance to both operator and man- ager, because by the use of the B. & S. wire gauge and a tape line they will be able to figure out the approximate loss in their various circuits, and in many instances it will be found that they are paying heavily for energy wasted in line resist- ance. There .are many operating room feed circuits that are giving a 5 per cent, drop, or even larger than that, and all this 48 MOTION PICTURE HANDBOOK waste energy is registered on the wattmeter. Therefore, I repeat, it is essential that the operator and manager have a good working knowledge of questions of this kind. Note: In the foregoing I neglected to include increase of cost for installing larger wires. This must be added to initial cost of wire in order to arrive at the correct result. Further data on resistance as applied to the projection lamp arc circuit will be found under the head, "Resistance Devices." Measuring Wires LECTRIC conductors of various kinds are measured as to their cross-section or area in square and circular mills, circular mills being used for round wires and square mills for square or rectangular conductors. A square measuring 1/1000 of an inch on each of its four sides is called a "square mill.'* A circle 1/1000 of an inch in diameter is called a "circular mill," commonly designated "CM." A round wire 1/1000 of an inch in diameter is said to have an area of cross-section of one circular mill. The areas of all round wires are directly proportioned to the square of their diameters, the calculation being made in mills (thousandths of an inch). "Squaring the diameter" means multiplying the diameter by itself. It therefore follows, if the areas of the circles are propor- tional to the squares of their diameters, and the area of a wire one mill in diameter is called one mill, or one "circular mill" (C.M.), then wires of other sizes have an area of cross- section, numerically equal, in circular mills, to their diameter in one one-thousandths of an inch (mills) squared, or multi- plied by itself, thus: If a wire be 10 mills in diameter, then 100 (10 X 10) is the "square" of its diameter, hence its area of cross-section in CM. Let us also consider a wire one-quarter of an inch in diam- eter. Since the wire is one-quarter inch in diameter, and one inch is equal to 1000/1000, then the diameter of the wire ex- pressed in thousandths of an inch, or mills, would be equal to 1000-^4 = 250. Such a wire would then be 250/1000 of an inch in diameter, or, expressed otherwise, 250 mills in diam- eter. And since the area of cross-section of a wire in circular mills is equal to its diameter in mills multiplied by itself (squared), it follows that the area of the wire in question would be 250 X 250 = 62,500 circular mills. FOR MANAGERS AND OPERATORS 49 The circular mill area of any round wire may be found by meas- uring its diameter in thousandths of an inch, using a micrometer caliper or wire gauge for the purpose, and multiplying the meas- urement thus obtained by itself. There are several methods of measuring wires. The ac- cepted standard for wire measurement in this country is the American Gauge, commonly known as the "Brown & Sharpe Gauge," and in practice dubbed the "B. & S." gauge, the same being illustrated in Fig. 7. In using this tool it is the slot and not the round hole that de- termines the size of the wire, and while the wire must not actually bind in the slot, it must fit snugly. The gauge, if it Figure 7. be a good one, will have the width of each slot, or, in other words, the diameter of the wire which fits the slot, stamped opposite each slot on one side of the gauge, and the number of the wire stamped opposite the slot on the other. In Fig. 7 it is the wire number side we see. The diameter in thousandths of an inch is the same thing as the diameter in mills. For instance, No. 16 wire has a diameter of fifty-one thousandths of an inch, or, in other words, 51 mills, the term thousandths of an inch and mills being interchangeable. One of the most convenient and at the same time most accurate methods of measuring wire is by means of a mi- crometer caliper. See Fig. 8. These calipers may now be had with the wire size and their equivalents in mills (thou- 50 MOTION PICTURE HANDBOOK sandths of an inch) stamped thereon. For instance, in the illustration we see "4/0," with 460.0 opposite it, which means that 0000 (called "four 0") wire is 460 mills (460 thousandths of an inch) in diameter. These tools are expensive, but, on the other hand, they are mighty good articles to own, and ought to be included, in one form or another, in every oper- ator's tool kit. Figure 8. For measuring very small wires, such as the strands of an asbestos-covered wire (usually No. 30 or 31), the slot wire gauge is not very reliable except in the hands of an expert. If you have no micrometer caliper it is better to have a machinist make the measurement for you with his. Have measurements made of three or four strands from different parts of the wire. For most purposes, however, the wire gauge, in conjunction with the wire capacity table, page 42, will answer all purposes. Insulation WHEN there is a difference in potential maintained between two wires of an electric circuit these wires have an affinity for each other and current seeks constantly to pass from one to the other. The purpose of insulation is to prevent this and to keep the wires from coming into electrical contact with any object which might furnish an electrical path to a wire of opposite polarity at- tached to the same dynamo. Such a path may be found through the ground or through any current-carrying material having electrical contact with wires of opposite polarity. In short, insulation is to protect the potential of or on a wire interference by any outside source. FOR MANAGERS AND OPERATORS 51 As we have already seen (page 38), various metals offer varying resistance to the passage of electric current. Not only is this true, but various materials other than metals offer varying resistance to the passage of electric current, and, while there is no material which is a non-conductor that is to say, through which electric current cannot be forced if the pressure (voltage) be raised sufficiently high, still there are materials which are considered! and treated as non-conductors, because no ordinary voltage will force current through them. These substances are called "insulat- ing materials," at the head of which stand, in the order named, glass, procelain, and rubber. Various natural sub- stances such as marble and slate form excellent insulating materials, and asbestos, when dry, is also a very good in- sulator. There are also various insulating compounds, the composition of which are trade secrets. In practice these compounds are used to saturate some kind of braided or other material which, after being so saturated, is used for weatherproof insulation on wires to be used out of doors, or to reinforce the rubber insulation of rubber covered wires. Procelain is, for the most part, used to line holes in brick or other walls through which it is necessary to pass wires and for knobs to carry wires which are run in open circuit through the air, or along walls. Rubber, on the other hand, is, for the most part, used for inner insulation of what is called "rubber covered" insulation of wires. Glass is used only for pole insulators on low potential, owing to its fragile nature. Rubber covered wire consists of tinned copper wire with a covering of rubber or rubber compound of homogeneous character, reinforced by an outer covering of braided cotton soaked in preservative insulating compound. Where copper wire is covered with any of the rubber compounds the tin- ning of the wire is very necessary, since the sulphur uni- versally present in rubber insulation is likely to combine with the copper and in a short time the wire would be cor- roded, and either very greatly weakened or, if a small wire, entirely destroyed. The tinning of the wire prevents thij, since tin will not combine with sulphur and the rubber in- sulation has no effect upon it. It is not, however, the purpose of this book to go into an exhaustive treatise on insulation materials, but merely to give the operator a general understanding of the proposition. The current must be confined to the wire and made to pass from the positive to the negative through the paths provided, 52 MOTION PICTURE HANDBOOK and through them only, the said paths being motors, in- candescent globes, arc lamps, etc. The strength of insulation must increase with the potential, and its kind may vary with the service. For instance: the insulation known as "weather- proof" may be used where the wires are stretched in open air on out-door circuits. On the other hand, for interior work while this same insulation may still be used, under- neath it and next the wire there must be a coating of pure rubber or rubber compound. The insulation then becomes what is known as "rubber covered." Its disadvantage lies in the fact that rubber deteriorates rapidly under the influence of even moderate heat, and is immediately destroyed by any- thing like high temperature. The necessary strength of the insulation, either weatherproof or rubber covered, will depend upon the voltage. There are several ways of testing the insulation of wires, the test here given being that required by the National Board of Fire Underwriters for rubber covered wire. TESTING INSULATION Any one-foot sample of completed covering must show a dielectric (dielectric is defined as any substance or medium that transmits the electric force by a process different from conduction, as in the phenomena of induction; a non-con- ductor separating a body electrified by induction from the electrifying body) strength sufficient to resist, for a period of five minutes, the application of voltage proportionate to the thickness of the insulation, in accordance with the following table: TABLE NO. 3 Breakdown test on 1 foot Thickness in 64th inches Volts A. C. 1 3000 2 6000 3 9000 4 11000 5 13000 6 15000 7 16500 8 18000 10 21000 12 23500 14 26000 16 28000 FOR MANAGERS AND OPERATORS 53 In making the foregoing test the source of electro-motive force (voltage) must be a transformer of at least one kilowatt capacity. The application of the electro-motive force shall be made at 3000 volts for five minutes, and then the voltage must be increased by steps of not more than 3000 volts each, the voltage of each step being held for five minutes until the maximum for a given thickness of insulation is had, or until there is a rupture of the insulation. The test for die- lectric strength must be made on wire which has been immersed in water for seventy-two hours, one foot of the wire under test to be submerged in a conducting liquid held in a metal trough, one of the transformer terminals being connected to the copper of the wire, and the other to the metal of the trough. There are two types of weather-proof wire, viz.: weather- proof and slow-burning weather-proof. The insulation of the slow-burning weather-proof consists of two coatings, one of which is fire-proof in character, while the other is not. The fire-proof coating is on the outside and com- prises about six-tenths of the total thickness of the insula- tion. The complete covering for sizes of wire from No. 14 to No. 0000 varies from 3/64 to 5/64 of an inch. The fire- proof insulation is not as susceptible to fire as is ordinary weather-proof, nor does it as readily soften under the influ- ence of heat. It is not suitable, however, for outside work, being intended for interior work in dry, warm places such as shops and factories. There is another type of wire insulation called "slow-burning," which is still more fire-proof than is the slow-burning weather-proof. It is intended to be used in very hot places where ordinary insulation would soon per- ish. The insulation of weather-proof wire should consist of at least three layers of braid, each of which is thoroughly saturated with a dense, moisture-prool; compound, applied in such manner as to drive any atmospheric moisture out of the cotton braiding, thereby securing a covering to a great degree water-proof and of high insulating power. The outer surface of this insulation is pressed down to a hard, dense surface. This wire is for use out of doors where moisture is certain and where fire-proof qualities are not necessary. In general, weather-proof wires can be used only where the insulating supports on which the wire is mounted are de- pended on for insulation, the covering being regarded simply as a precaution against accidental contact with other wires or other objects. 54 MOTION PICTURE HANDBOOK From the foregoing it will readily be understood that the principal difference between rubber-covered and other in- sulation lies in the fact that the rubber-covered insulation may be depended upon entirely for insulating, whereas the others must depend, at least to a considerable extent, on the insulating supports for their insulation. Rubber-covered wire may be used in any place that weather-proof would be allow- able, but not in places where slow-burning insulation would be required. Double braid rubber-covered wire is the only kind that may be used in conduits, where the two wires of the circuit lie side by side. So far as the carrying capacity of copper be concerned it makes absolutely no difference what the insula- tion be composed of. The reason that rubber-covered wire is rated at lower capacity than weather-proof is by reason of the fact that rubber is easily injured by even moderate heat, hence when it is used a high margin of safety is main- tained. Under no circumstances is it permissible to use other than wire having rubber-covered insulation inside of conduits. Wire Systems IT is highly desirable that the operator have a good work- ing knowledge of the various wire systems with which he is likely to come in contact. It is not the purpose of this work to make the operator a wireman, or an electrician for that matter, but merely to give him a fairly comprehen- sive general idea of the action of electric current and the appliances, including the wire systems, with which he will have to do. On the road, particularly when playing small towns, the operator may be called upon to connect to any one of the several different wire systems, and unless posessed of knowl- edge he will be unable to proceed with any degree of certainty or confidence. There is one wire system with which it is impractical I might even say impossible to connect a projection arc, viz, the series arc system. This system is used only for street arc lighting. Instead of two wires it only has one, and each lamp carries the entire amperage of the system, or circuit. The voltage of the series arc system will depend upon the number of lamps, there being an added pressure of about 50 volts for each lamp, so that a circuit supplying ten lamps would have a pressure or voltage of 50 X 10 = 500 volts, whereas if there were eleven lamps the pressure would be SOX 11=550, FOR MANAGERS AND OPERATORS 55 and so on. Do not attempt to connect your projection lamp to the series arc system, because if you do you will fail; also you will cause serious trouble, and may succeed in getting yourself badly shocked, or possibly even killed. Fig. 9 is a diagrammatic representation of a 10 lamp series arc system. ? :

-inch lens, because it would focus parallel rays to form an image at a point 7^2 inches away; that is to say, it would do so theoretically. As a matter of fact, however, this is not precisely true, due to the fact that an uncorrected lens brings some rays to a focus nearer its surface than others. Spherical aberration in the condenser is governed by the fact that when parallel rays strike a plano-convex lens on the curved side the spherical aberration is reduced to a minimum, but if the rays be diverging, then the spherical aberration is less if they strike the piano side. This, of course, means that to secure the least spherical aberration the flat side of the rear lens must be next the arc where the rays are diverg- ing, and the convex side of the front lens must be toward the arc, since it receives approximately parallel rays from the rear lens. I mention this because some operators, though few, have a notion that they gain advantage by placing the curved side of the front lens next the machine aperture. This is an error. In fact, the actuality is the reverse, although but for the element of spherical aberration there would be little if any difference which way the lens was placed. In order to actually focus the rays of light perfectly the lens must be "corrected" by the addition of one or more lenses having negative curvature. As a matter of fact, the surface of a lens is really nothing more or less than millions of pin-points, each in effect a prism of minute dimensions. It is a well known fact that what we term "white light" is really composed of a number of colors. When white light, or what we call white light, is passed through a prism of glass, it is more or less separated into its primary 98 MOTION PICTURE HANDBOOK colors, or, in other words, the colors of which it is composed. The ordinary plano-convex is an uncorrected lens, and always carries the fault of chromatic aberration, which is the property of separating light more or less completely into its component parts or colors. This explains why you see a fringe of color at the edge of the spot on the cooling plate of the machine. Now, taking the condensing lens for example, it being an uncorrected lens, remembering that, as I have said, its surface is composed of numberless minute prisms, you will readily see that the further away from the center of the lens you go the more acute will become the angle of these prisms with relation to the light source, or the light rays emanating from the source central with the optical axis of the lens, and therefore the more nearly true prism is approached. It then follows that, since the nearer we come to the true prism the greater will be the light separating power, we shall have a greater amount of chromatic aberration at the outer edge of the lens than at its center. Near the center of the lens the prisms will be very flat. Therefore their light-separating powers will be but slight; in fact, prac- tically nothing at all. At the outer edge these powers will be considerable, and here is where one of the evil effects of spherical aberration as applied to projection makes itself apparent. As already set forth, light rays near the outer edge of a lens will focus somewhat nearer the surface of the lens than will rays from near its center. This means that the excessive chromatic aberration at the outer edge of the lens is mingled with the purer light coming through the center of the lens, and the quality of the whole is thus injured. This is one of the reasons for my belief that there is advantage in the properly matched meniscus-bi-convex condenser combination. The addition of the negative curvature in the meniscus and the extra curvature in the bi-convex makes, in effect, a three and I believe a four lens combination, which has or ought to have to a considerable extent the effect of correcting spherical aberration. I do not state this as a positive fact. It has not yet been proven to my entire satisfaction, but I nevertheless believe it to be correct. There is, however, another decided advantage in the use of the meniscus lens next the arc, viz. : with a lens of given focal length the arc will be nearer the meniscus than it would be to a piano, hence a much greater amount of light will be transmitted to the screen. It is also possible that a condensing lens with a poor, im- perfect surface would have a considerable effect in injuring the definition of the picture. This seems to be made apparent in Fig. 51, which is a photograph of the light ray from a con- FOR MANAGERS AND OPERATORS 99 denser covered with a metal plate in which about a dozen quarter-inch holes have been drilled at various points. This photograph proves conclusively that a light ray passing through any given point of the condenser is carried forward to the screen, where it occupies a corresponding and magnified area. This being true, I cannot see but that any imperfection in the condensing lens which would in the least tend to alter the direction of a ray from the path it would have taken were . the lens a perfect lens must of necessity injure the result on the screen, though Mr. Griffiths does not agree with this con- clusion. However, I do not care to go deeply into this matter at this time, not being entirely sure of my ground. The operator will have noted the fact that when the machine head is removed, and the white light projected to the screen without any objective lens, it is impossible to bring the light ray, as a whole, to a sharp point. Most operators have hereto- fore believed that the rays from the condenser were supposed to meet at a point and cross midway between the front and back factors of the objective lens. This is not true. See Page 118. The condenser does not bring the light ray as a whole to a point. It forms an image of the crater, and upon the size of the image thus formed will depend the diameter of the condenser light ray at its narrowest point. It is a mistaken idea to suppose that when we speak of a lens "focusing the rays" we mean that it brings the ray, as a whole, to a sharp point. It does not. What is really meant is illustrated in Fig. 32. All light rays emanating from any pinpoint of objective X and reaching the surface of the lens are refocused at a similar point in image Y. This image may be smaller than the original object. Study Fig. 32, and I think you will get the idea. The Objective. The objective lens of the moving picture projection machine consists of four lenses, two in the rear fac- tor and two in the front factor. The two at the front are usually cemented together with Canadian balsam, so that, at a superficial glance, they appear to be one thick lens. As a matter of fact it is one thick lens, with a thin one cemented to the front so that the surfaces of the two lenses are brought into contact. It sometimes happens that the heat will melt the balsam and cause it to run down between the lenses. When this happens it is best not to try to fix it yourself, but send the lens back to the manufacturer to be recemented. However, you can separate the lenses (though I do not advise you to try it) by proceeding as follows : Set a shallow dish, filled with water, on 100 MOTION PICTURE HANDBOOK the stove, place the lens on a large kitchen spoon or tablespoon and set the spoon in the water, so that the lens will be covered. Allow the water to come to a boil and remove the lens quickly, shoving with your thumbs on one lens and pulling with your fingers on the other. It is a pretty hot job, and you will have to use considerable force, but if you bring the water to a boil it softens the balsam and you can get the lenses apart. The balsam can then be washed off with turpentine. Distortion. Operators should carefully test their objective lenses for distortion. This may best be done by taking a per- fectly flat piece of mica, commonly known as isinglass, three or four inches long, and cutting it to the width of a film. Hav- ing done this, lay it off checkerboard fashion, as per Fig. 36, and put it in the machine, being careful to get it perfectly flat Figure 36. B over the aperture, and project its image to the screen. At A, Fig. 36, we see no distortion. At B there is what is known as barrel distortion, which amounts to a curvature of the lines. The lens which projects B is not a good lens, whereas the lens which projects A is practically perfect. The scratch marks on the mica may be made with the point of a knife blade, or any other sharp instrument. The lines on the mica must be perfectly straight, and if their image on the screen is not perfectly straight (test by streching a line) the lens is imperfect. A lens must focus all light rays passing through a pinpoint in the photograph to a corresponding though magnified point on the screen. The distance at which this focusing will be accomplished depends, within limits, upon the distance of the film from the lens the back focus at which the lens is working. FOR MANAGERS AND OPERATORS 101 This is diagrammatically illustrated in Fig. 37, in which arrow A is being projected and focused at point 1. That is to say : With the arrow at the distance from the lens, as shown, the rays will meet and cross at point 1, where they begin to diverge. If the screen be placed at point 2, arrow A remaining its original distance from the lens, instead of an image on the screen, each portion of arrow A will be represented by a blurred ring. If the distance of arrow A from lens B is altered, then the distance at which the rays meet and cross (image) will be altered, and the screen will have to be moved toward or from the lens a corresponding dis- tance. This explains Figure 37. why it is necessary to move the lens in and out in order to focus the picture on the screen. Where the back focus is short, as in a moving picture lens, a slight alteration of the distance between the lens and the film makes a decided difference in the distance at which the rays of light will focus. Doctoring Lenses. The question is often asked: "Can the E. F. of a lens be altered by shortening or lengthening the barrel, so as to alter the distance between its two factors?" Yes, but it is not advisable to try anything of that sort. The chances are that you will ruin your lens. This scheme has been known to work fairly well in some instances, but more often than not it is more or less of a complete failure. Bringing the two" combinations closer together or separating them farther apart would have the effect of altering the size of the picture on the screen at a given distance, but it is a very poor way of doing it. The author has frequently been asked whether or not the same lenses may be used to project a picture at different dis- tances. Yes. But it must be understood that if the distance be made less, then the picture will be smaller, and if the distance be made greater the picture will be larger. Also moving the screen will alter the back focus at which the lens will work. The shorter the distance between the lens and screen the farther the lens must be from the film, and vice versa. 102 MOTION PICTURE HANDBOOK Spread of Ray. It is easy to figure how much change in size of picture will be accomplished by moving the screen any given distance. Suppose you have a lens which projects a 10-foot picture at 60 feet. It is readily seen that if the width of the picture be divided by the number of feet it is projected the result will be the fraction of a foot its width increases with each foot of distance, hence in this case we have 10 -f- 60 = one- sixth of a foot, or 2 inches, which is the amount the light ray spreads for each foot of distance between the lens and screen. In proof of this, multiply 2 X 60 and we have 120 inches, or 10 feet. Now, if you move your screen back five feet farther you will have 2 X 5 = 10 inches additional width of picture, or if we brought the screen 6 feet nearer the lens, then we would have 2 X 6 = 12 inches less width of picture. Improving Definition. The work of a projection lens which does not give sharp definition may sometimes be improved by cutting a circle of stiff dark paper, just large enough to fit tightly into the front end of the lens barrel and up against the front lens. In the center of this ring cut a circular opening, the correct size of which must be determined by experiment in each individual case. Usually it is not advisable to stop down more than one-fourth the diameter of the opening. This is often of benefit in sharpening the focus where the machine sets above or to one side of the screen, because reducing the lens diameter has the effect of increasing its depth of focus. Dirty Lenses. It is of the utmost importance that the operator keep his lenses scrupulously clean. "Optical Projec- tion," by Simon Henry and Henry Phelps Gage, gives the losses by reflection from the polished surface of each surface to each lens as from 4 to 5 per cent., or a total of 8 to 10 per cent, for each lens or plate of glass, and further remarks that if the surface of the glass be not perfectly clean or perfectly polished the light loss may amount to much more say 15 per cent, at each surface. It really seems to me that this cannot be true. There being eight surfaces in an objective lens, or since two of them are in direct contact, let us say six, even taking the lowest figure, viz., 4 per cent, for each surface, we would have a total of 24 per cent, loss by reflection alone. However, without dis- cussing the probable correctness of the percentages, it is an undoubted fact that there is considerable loss through reflec- tion, and this loss will be very largely increased if the lens be dirty. Therefore, it is very much up to the operator to keep his lenses not only clean but polished as highly as possible, FOR MANAGERS AND OPERATORS I 03 Measuring Lenses is a very simple operation. In order properly to match up a projector lens system it is necessary that the operator be able to measure and determine the exact focal length of his condenser lenses, and it is often very desirable that he be able to measure the exact equivalent focus of an objective in order that he may determine what size picture it will project at a given distance. Plano-convex lenses may be measured as follows: Pin a sheet of white paper to the wall of a room, opposite a window, hold the lens up with its flat side toward the wall and, through the open window, carefully focus some building, trees, or other object located at a considerable distance outside the window, on the paper screen. It is essential to accuracy that the object being focused be a goodly distance away the farther the better because in these measurements the light rays are presumed to enter the lens in parallel lines, and unless they do enter in approximately parallel lines there will be error in the result. Be sure to get the lens in exact position where the focus of the image on the paper screen is most sharp, and then measure from the flat side of the lens to the wall, making a note of the pre- cise distance. Next turn the lens around and with the convex side toward the wall, again carefully focus the same object on the paper screen and measure from the wall to the flat side of the lens. It will be found that the two measurements will differ considerably, and their sum divided by 2 will be the focal length of the lens. For instance: Suppose one measurement to be 6 inches and the other 7 inches : 6 + 7 = 13 which divided by 2 = 6H> therefore it is a 6 l / 2 inch lens. It is not practical to measure condensing lenses with any great degree of accuracy. There is so much spherical aberra- tion in these uncorrected, comparatively cheap lenses, that the picture cannot be focused with absolute sharpness. The focal length of the lens may, however, be arrived at by the fore- going process closely enough to serve all practical purposes. The measuring of a motion picture objective or stereopticon lens is a very simple operation. The focus of a projection lens may be designated in two ways viz., back focus (common- ly expressed as b. f.) which is the measurement often used by the film exchange, and equivalent focus (commonly expressed as e. f.), which is the measurement used by the lens manufac- turer. Therefore in ordering lenses of a given focal length one should be careful to state whether the measurement given represents b. f. or e. f. The e. f. is the measurement which must be used in ordering lenses to project a picture of given distance. 104 MOTION PICTURE HANDB6OK To measure a moving picture objective or stereopticon lens pin a sheet of white paper to a wall opposite a window. Hold the lens square with the paper screen and, through the open window, focus some building, tree, or other distant object on the paper screen; be very careful to get the image as sharp as you possibly can. Now measure from the wall to the surface of the lens nearest the screen, and that measurement will be the back focus, or b. f. of the lens. If, instead of measuring from the surface of the lens to the screen, you measure from a point half way between the front and back combinations of the lens (half way between the lenses at either end of the tube) to the paper screen, that measurement will be the equivalent focus, i I i i i r M 1 1 1 1 1 < i ' i ' i > i ' i ' i > i ' i M 1 1 Figure 38. or e. f. of the lens. In other words. the e. f. is equal to the b. f. plus half the distance between the two combinations of the lens. All this we see diagrammatically represented in Fig. 38. Again let me caution you always to focus some DISTANT object; an object which is 100 feet away will do, and even an object 25 feet away will not be close enough to affect the result very much. It is even possible to get an approximate measurement by focusing an incandescent light, provided it be at least 10 or 15 feet away, but such a measurement cannot be depended upon when accuracy is essential. Also see Page 108. The use of these measurements, as applied to the objective, becomes apparent when we learn that the size of the picture which will be projected by any lens at a given distance from the screen will be entirely dependent upon the focal length of the lens. The shorter its focal length the larger will be the FOR MANAGERS AND OPERATORS 105 picture at a given distance, and the longer its focal length the smaller will be the picture at a given distance. A lens having a 4-inch e. f. will project a much larger picture at 50 feet than will a lens having a 6-inch e. f. Nearly all machine and lens manufacturers put out tables de- signed to tell one the exact size (width) picture a lens of given focal length will project at a given distance. These tables are useful as applied to stereopticon lenses, but have slight value as applied to the moving picture objective this by reason of the fact that the size of picture is based upon a given width of aperture, which, in the case of the stereo, is supposed to be 3 inches, but which may vary widely with each set of slides (the aperture in the case of the stereopticon is the width of the standard slide mat) ; hence, by reason of the variation in the size of slide mats it is impossible to figure the size of a stereopticon picture with any degree of accuracy, and the table will therefore answer about as well as measurements. As applied to the motion picture objective, however, these tables are not at all satisfactory. As a rule operators and man- agers want their picture not approximately, but exactly a given width. Now there are at the present time two different stand- ards of motion picture machine aperture widths, viz., 15/16 and 29/32; also the aperture of the older machines of different makes, while they were presumed to be all 15/16 of an inch, really varied considerably, and a slight variation would make .considerable difference in the size of the picture on the screen, as for instance, if you used 15/16 of an inch as a basis for figuring, and the aperture really was a little more or a little less than that width, then the result would be a picture wider or narrower than your figures called for. This being the con- dition, you can readily see that tables cannot be depended upon for any very great degree of accuracy in results.. I will, how- ever, for reasons already set forth, append one of the tables for stereopticon lenses. To figure the necessary equivalent focus of a lens to project a picture of given width at a given distance proceed as follows : Have a machinist measure the aperture of your machine ac- curately with an inside caliper and a micrometer. Measure the exact distance from the lens to the screen. Multiply the dis- tance from the lens to the screen, in feet, by the width of the aperture, in fractions of an inch, and divide the result by the width of the picture you desire, in feet. The result will be the c. f. of the lens required to project a picture that width, and will be as close to it as you can get at it by figuring. For instance : Suppose you want a 15-foot picture at 60 feet, The machine 106 MOTION PICTURE HANDBOOK aperture is found to be 29/32 of an inch (the new standard) wide. First multiply the distance from the screen in feet by the width of the aperture in fractions of an inch. To multiply 60 by 29/32 we first divide by 32 and multiply the result by 29 ; 60-7-321.875; 1.875X29=54.375. Next we divide this measurement by the desired width of picture in feet: 54.375 -^ 15 = 3.625, or a 3^?-inch e. f. lens. We most likely would be un- able to get that exact focal length and would have to take, in- stead, a 524-inch e. f. lens. It must be understood, however, that the great bulk of pro- jection lenses now in use are cheap lenses, and cheap lenses, like all other cheap things, are inaccurate, therefore you can- not expect to arrive with certainty at precisely the result you desire in any other way than by actually testing the lenses. The stereopticon lens is figured exactly the same way, except that instead of measuring the aperture width, we take 3 inches as the average width of the slide mat the slide mat, in this case, being the aperture. It is also entirely practical to make other measurements of practical value as follows: Suppose you have an objective and wish to know what size picture it will project at a given dis- tance. First measure its e. f. as already directed and then: Size of Image. This can be determined by multiplying the difference between the distance from lens to screen and the focal length of the objective, by the width of the aperture and dividing the pro-rlurt by the focal length of the lens. For ex- ample: Let L be the projection distance, 40 feet (480 inches); S, the slide mat, 3 inches; F the e. f. of the lens, 12 inches; we then have the formula (in which d is the size of image) ; S (L-F) F Substituting for the letters their known values, we have: 3 (48012) =117 in., or 9^ feet, 12 as the size picture a 12-inch e. f. stereo lens will project at 40 feet, provided the slide mat be just 3 inches wide. If. how- ever, the mat be more or less than 3 inches, then the picture will be wider or less wide. Distance from Slide to Screen. With the other factors given we get this by multiplying the sum of the width of the FOR MANAGERS AND OPERATORS 107 Showing Size of Screen Image When Lantern Slides Are Projected Size of Mat Opening, 2^x3 Inches Table 7, Figure 39 Equlv. focus Inches 15 ft. 20 ft. 25 ft. 30 ft. 35 ft. 40 ft. 45 ft. bO ft. BO ft. 70 ft. 80 ft. 30 ft. 100 ft. 5 8.0 10.8 13.5 18.3 19.0 8.8 11.8 14.8 17.8 20.8 5/4 7.3 9.8 12.3 14.8 17.3 19.8 7.9 10.7 13,4 18.1 18.8 21.6 1 6.6 8.9 11.2 13.5 15.8 18.1 20.4 7.3 9.8 12.3 14.8 17.3 19.8 22.3 IK 6.1 8.2 10.4 12.5 14.6 18.7 18.8 6.7 9.0 1.1.3 13.6 15.9 18.2 20.5 1 5.7 7.6 9.6 11.6 13.5 15.5 17.5 19.4 6.2 8.3 10.5 12.6 14.8 16.9 19.0 21.2 1% 5,3 7.1 8.9 10.8 12.6 14.4 16.3 18.1 5.6 7.8 9.8 11.8 13.8 15.8 17.8 19.8 6 6.8 8.4 10.1 11.8 13.5 15.2 17.0 204 7.3 9.1 11.0 12.9 14.8 16.6 18.5 223 8% 6.2 7.9 9.5 11.1 12.7 14.3 16.0 19.2 6.8 8.8 10.3 12.1 13.9 15,6 17.4 20.9 1 5.9 7.4 8.9 10.5 12.0 13.5 15.1 18.1 21.1 6.4 8.1 9.8 11.4 13.1 14.8 16.4 19.8 23.1 BK 5.6 7.0 8.5 9.9 11.4 12.8 14.2 17.1 26.0 6.1 7.8 9.2 10.8 12.4 14.0 15.5 18.7 21.9 10 5.3 6.6 8.0 9.4 10.8 12.2 13.5 16.3 19.0 21.8 5.8 7.3 8.8 10.3 11.8 13.3 148 17.8 20.8 23.8 12 5.5 6.6 7,8 8.9 10.1 11.2 13.5 15.8 18.1 20.4 8.0 7.3 8.5 9.8 11.0 12.3 14.8 17.3 19.8 22.3 14 5.6 6.6 7.8 8.8 9.6 11.6 13.5 15.5 17.5 19.4 6.2 7.3 8.3 9.4 10.5 12.6 14.8 16.9 19.0 21.2 16 5.8 6.6 7.5 8.4 10.1 11.8 13.5 152 17.0 6.3 7.3 8.2 9.1 11.0 12.9 14.8 16.6 18.5 18 5.1 5.9 6.6 7.4 8.9 10.5 12.0 13.5 15.1 5.6 8.4 7.3 8.1 9.8 11.4 13.1 14.8 if. 4 20 5.3 6.0 8.6 8.0 9.4 10.8 12.2 13.5 5.8 8.5 7.3 8.8 10.3 11.8 13.3 14.8 22 5.4 6.0 7.3 8.5 9.8 11.0 12.3 5.9 6.6 7.9 9.3 10.7 12.0 13.4 24 5.5 6.8 7.8 8.9 10.1 11.2 6.0 7.3 8.6 9.8 11.0 12.3 EXAMPLE: With a lens of 10-inch focus at a distance of 20 ft. the screen image will be 5.3 x 5.8; at 25 ft., 6.6 x 7.3; at 30 ft., 8.0 x 8.8; at 50 ft., 13.5 x 14.8 etc. 108 MOTION PICTURE HANDBOOK image and width of the slide mat, by the focal length of the lens ; dividing this product by the width of the slide mat, thus : F(d + S) T _ ________ 12(117 + 3) Substituting values, L = 480 inches = 40 feet. 3 Measuring E. F. Accurately. Should the operator desire to measure the e. f. of his objective with absolute accuracy he may proceed as follows: Remove the mechanism and in the position the aperture of the machine occupied place a sheet of tin having an aperture about three-quarters of an inch square. Now hold the lens out at a distances about twice the length of its supposed e. f., in front of the aperture, with the light turned on, and an equal distance in front of the lens (still further out) hold a small screen, preferably dull black in color, and move the lens and the screen until the image of the aperture on the screen is exactly the same width as the actual aperture. Now measure the distance from the aperture to the screen and divide it by 4; the result will be the exact e. f. of the lens. Cleaning Lenses. It is of the utmost importance that lenses be kept scrupulously clean. Oil and fingermarks are particularly objectionable. I have been called to theaters to locate the cause of lack of sharp focus in the picture, only to find that the operator had had his objective apart to clean, and in putting it together had inadvertently lightly touched one of the interior surfaces of the lens with his finger. The mark was so slight that it could not be detected by looking through the lens, but was quite visible when the lens was taken apart and looked at from an angle. Slight as this mark was it seriously injured the definition of the picture. Oil on the surface of a lens will also operate to injure the focus of the picture. I do not think any argument is neces- sary on this particular point. It is absolutely essential to sharp definition of the picture on the screen that all lenses be kept scrupulously clean. The careful painstaking operator, whose machines run several hours each day, will clean his condensing lenses every day, par- ticularly the one next the arc. The objective lens need not be cleaned more than perhaps once a week, unless oil spatters on its rear surface, in which case it should be cleaned just as soon thereafter as possible, and if there is tendency of oil FOR MANAGERS AND OPERATORS 109 to spatter on the lens its rear end should be protected by some kind of a metal guard. I cannot tell you just now how to do this, because the method would vary with different mechanisms, but certainly the competent operator can devise ways and means to keep the oil off the rear end of his lens. In some cases a collar of tin made tight enough to clamp the rear end of the lens barrel, extending back nearly to the aperture, will answer the purpose. Unless there is oil on the lens I know of no better way of cleaning them than by breathing on the cold glass and polish- ing with a perfectly cle n chamois, or an old, clean, soft handkerchief. Always provided there be no oil present, this t will clean the surface of the lens perfectly, and will answer every purpose. If there be oil on the lens, then I recom- mend the use of a solution of one half alcohol and one half water. Wash the lens off with a cloth saturated with the solution, and polish quickly with a dry, soft, clean hand- kerchief, perferably an old one. Nothing makes a better lens cloth than an old, worn out handkerchief, after having been laundered. Some operators prefer a solution of ammonia and water or water and alcohol. The operator should, perhaps twice a year, take his ob- jective lenses apart and clean their interior surfaces, being very, very careful that in putting them back he does not touch their surface with his fingers. This latter is of the utmost importance, because the very lightest touch will leave a mark which, while invisible when looking through the lens, is likely to seriously injure its work. In replacing the ob- jective lens factors always put them together so that the heavy bulge or convex of all lenses is toward the screen. In taking out the rear combination be careful that you put them back in the same position they were in. In other words, don't get their position switched. The best way to go about this is to lay a sheet of paper on a table and write "rear lens," "inside lens," and "front lens," at different places on its surface. Now as you take the lenses out lay the rear one (next the aperture) on the space marked "rear lens," the inside one on the next space, and the front on the space marked "front lens." Then you cannot very well make any mistake. You will find a spacing ring between the two rear lenses. Be sure and get it back in its place when you put the lenses together. Fig. 40| shows the position of the lenses in an objective. The two front lenses are cemented together with Canadian balsam. (See Page 100.) 110 MOTION PICTURE HANDBOOK Selecting Condensing Lenses. See Page 127. Lens Diameter. Lens diameter is a subject of much im- portance. With a point source of light it would be quite impossible to use a very small diameter and place the arc right up close to it. Modern practice, however, is to use an amperage for the projeection of moving pictures which pro- duces a crater varying from (D. C.) one-quarter to one-half inch in diameter. This, of course, means a light source of very high temperature, and more or less naming of the car- bons, so that the light source cannot be brought very close to the lens. So far as the condenser be concerned, as a rule the diameter of the lens next the arc might be 4 inches as against a 4%-inch diameter for the rear lens without in- creasing light loss; this by reason of the fact that the condenser next the arc usually, with the arc in oper- ating position, produces a diverging ray beyond the lens, and it is only necessary that the front lens have suf- ficient diameter so that the light from it will just cover the front lens. This is not intended to mean that the author expects any change of this kind will be made. It is simply an interesting point, though in Eng- land and Germany use is made of a lens next the arc which has a smaller diameter than the front lens. Four and a half inches seems to be fairly satisfactory diameters for con- densers. Whether there would be, considering the proposi- tion as a whole, any gain in using a larger diameter con- denser I am not quite sure, but doubt it. The diameter of the objective lens is a matter of the utmost importance. See Page 121 and Fig. 49. High-Grade Lenses. The author of this work is thoroughly and completely convinced that it is a tremendous mistake to use cheap objective lenses for projecting the picture. This most emphatically is not the result of snap-shot judgment, but a conviction which has been growing for some years which was finally clinched by knowledge of the fact that the better English theaters are using lenses costing as much as 12 (approximately $60), supplemented by absolute proof that there is a very large possible gain in illumination and sharpness of focus by using a high class objective lens. Figure 40. FOR MANAGERS AND OPERATORS 111 The projection of the picture is nothing more or less than a reversal of the process of its photographing. Film manu- facturers spare no expense in procuring the best lens obtain- able for their cameras. These lenses are a magnificent ex- ample of the optician's art. They must have great "depth" and plenty of "speed." They must be corrected for about every imaginable fault, and the result is that they register on the film a wealth of detail, depth, and sharpness which are largely lost by reason of the fact that the photograph must be projected by about the cheapest lens it is possible to obtain. Authorities in England, where] they have already made considerable progress in the high-grade projection lens business, claim that in order to get a perfectly flat field it is necessary that an anastigmat lens be used. I cannot vouch for the correctness of this, but am told by lens men here in America that it is true. These same authorities who have experimented with ihigh- class objectives for the projection of pictures claim that the high-class lens will pay its additional cost within a com- paratively short time in current saving, it being the fact that these lenses give a greater illumination per ampere of cur- rent than do the ordinary objectives now being used. This I personally have seen demonstrated. Just reason with yourself for a moment. If the cheap leni is the right thing with which to project a picture, then why is it not the proper thing to take the picture with? Why take a picture with a costly, high-class lens and project it with a cheap, comparatively poor article. It doesn't sound like common sense, does it, gentlemen? I notice that no less a person than Simon Henry Gage, Cornell University, a man deeply versed in the science of optics, in his work on "Optic Projection," says there is no particular value in having a perfectly sharp picture if it is to be viewed at a considerable distance. He even says a little coarseness is an advantage. With this I cannot at all agree. I have the utmost respect for the knowledge of Professor Gage, but in this one particular thing I think he is decidedly in error, and, moreover, assuming he is right, it must be remembered that a goodly portion of the audience is seated compartively near the screen. The writer makes no claim to being an expert in lenses far from it. He does, however, claim to be the possessor of a considerable fund of common sense, and common sense tells him that the sharper the picture is the better for all 112 MOTION PICTURE HANDBOOK concerned. Moreover, flatness of field is to be highly de- sired, since curvature of field means there will be a tendency to out-of-focus effect at the edges when the center is in focus, and vice versa. This may or may not be sufficient to be noticeable, but is apt to be very much so with short focal length lenses. It is in the nature of things, and cannot be otherwise unless the lens is corrected to produce a flat field, and as I understand it that means an anastigmat lens. I would strongly advise theatre managers to purchase high- class lenses for their projectors. I would even advise them to have no hesitation in paying as much as sixty dollars for a good lens. The Kleine Optical Company, Chicago, is handling high-grade lenses. The Dallmyer lenses are handled by Burke & Jones, New York City and Chicago, and the other European manufacturers producing high-class pro- jection lenses also have their representatives in this country. Just at present it may be difficult to secure just the right kind of lens, but I have had proof of the fact that the lenses handled by Mr. Kleine, listed from thirty to sixty dollars, are a very good article, and worth every cent of their price. LINING THE OPTICAL SYSTEM In order to insure the best possible results on the screen it is essential that the light source (crater), the optical axis of both condensing lenses, and the optical axis of both com- binations of the objective be exactly in line and square with Figure 41. each other, and that a line drawn through the optical axis of the lens system shall pass precisely through the center of the aperture of the projector. FOR MANAGERS AND OPERATORS 113 In Fig. 41, A is the crater, B the lamphouse condenser opening with the condensers removed, D the aperture of the projector, E the objective lens barrel, with the lenses re- moved, and F the opening in the wall of the operating room. H is a stand of white sewing thread or a fine copper wire, G is a light metal rod placed across the opening in the opera- ting room wall, and supported by string H being drawn taut The method of procedure is as follows: First remove the condensing lenses and remove the lens factors from the objective, but leave the barrel screwed firmly in its place in the lens ring. Next attach cord or wire H to rod G, and pass the cord or wire through the lens barrel and machine aperture, as shown, and bring it back and tie it around the point of the upper carbon. After all is ready pull the lamp back by its forward and backward adjustment (before beginning it should be shoved clear ahead) until string or wire H is pulled tight just tight enough so that rod G- will be held in place and the string or wire be perfectly straight. Now with caliper C carefully center cord or .wire H in con- denser opening B, machine aperture A, and both ends of objective lens barrel E, moving whatever may be necessary to accomplish the purpose. I cannot tell you what you will have to do to get the string in the center since this will vary in different cases : it will have to be left to your ingenuity. No attention should be paid to hole F in the wall as that has nothing whatever to do with the lining except to sup- port rod G which holds the string in place. The fastening of the cord to the carbon point will be facilitated by using a three cornered file and filing a small notch at N. Matching Up the Lens System THE action of light rays through a projection system has been the subject of mudh controversy, and I believe it might fairly be said that until the pro- jection Department of the Moving Picture World undertook a series of experiments and went into an exhaustive study of the matter, no very intelligent explanation of the action of light rays through the projector system had ever been promulgated that is to say, no explanation which "squared up" with what apparently actually took place. The main stumbling block in this proposition lay in the fact that the same conditions do not obtain in the projection of moving pictures that obtain in stereopticon projection; a 114 MOTION PICTURE HANDBOOK fact which opticians have failed to observe, attacking the problem of projecting moving pictures from the same stand- point as of projection lantern slides. The difference in the two problems lies in the following: In stereopticon projec- tion the object (slide) is situated right up against the con- densing lens, whereas in moving picture projection the ob- ject (film), is at, or near the crater image a foot or more away from the condenser, and at one of the conjugate foci points of the condenser system. This means that the two problems present very different angles. In order to obtain maximum illumination in stereopticon projection the crater image must 'be approximately central between the two factors of the stereopticon objective lens, whereas in moving picture projection it must be at or near the object (film). The author does not believe this matter to be, as yet, entirely solved, but he does believe that great progress Plate 1, Figure 42. has been made, and that the tables representing that progress which are hereto appended will be found to be approx- imately correct, and that they will, barring the limits imposed by present day apparatus, enable the operator to match up his projector lenses in a way to give very satisfactory results. In this connection we are especially indebted to John Griffiths, Ansonia, Conn.; W. S. James, formerly of Camden, N. J.; C. D. Armstrong, Ashland, Wis.; and L. C. LaGrow, Albany, N. Y. These men have aided very greatly in the solving of this difficult problem and Griffiths has contributed the greater portion of the theory upon which the tables are based, as well as worked out the tables themselves. FOR MANAGERS AND OPERATORS 115 The Condenser. The spacing of the two condenser lenses different distances apart has the effect of altering the equivalent focus of the combination. The further the lenses are spaced apart the longer will be the E. F. of the combination, and vice versa. It seems, however, that, in view of the fact that with the arc at ordinary operating distance from the rear condenser lens, the light ray di- verges after passing through the rear lens (see A-B, Plate 1) and that, incidently, this divergence increases with increased focal length of the rear lens, it is ad- visable that the condens- ing lenses be placed as close as possible to each other (without actual mechanical contact, which latter would tend to con- vey heat to the front P^te 2, Figure 43. lens), since the further apart the lenses are the greater must be the loss through the aforesaid divergence of the light ray. A and B, Plate 1, show a 6 l /z and a 7 l / 2 lens, with the arc the same distance from the lens, using equal amperage in both cases. Even with the lenses set so that their curved surfaces are within one-sixteenth of an inch of each other there will still be some loss, but this cannot be avoided, since if we pull the arc back far enough to bring the light rays parallel after passing through the front lens, Plate 3, Figure 44. t ^ ien we w ^ encounter still greater loss on the arc side of the lens, by reason of increased distance between the arc and the lens and the law that intensity of illumination decreases inversely with the square of the distance from the light source. 116 MOTION PICTURE HANDBOOK Plates 2 and 3 illustrate the relative loss through spacing of the lenses, Plate 2 shows the lenses set with their curved surfaces approximately one-sixteenth of an inch apart. Plate 3 shows the lenses spaced so that their curved surfaces are one-half inch apart. It will be observed that the loss of light is materially greater in Plate 3 than in Plate 2. It is also of interest to note the difference in the light beam itself. In Plate 2 the beam does not narrow down quite so much as it does in Plate 3, and the crossing point of the Diagram showing how the back focus and the size of the aperture of the objective lens determine the distance between condensers and anerture. 20 19 15 14 13 12 II 10 9 8 Distance between condensers and aperture when the buck focus of Plate 4, Figure 45. rays is much nearer to the lens, which means that the E. F. of the combination has been lengthened by spacing the lenses. However, due to reasons already set forth I believe it is better practice to work with a fixed E. F. y setting the condensing lenses so that their curved surfaces are not more than one-sixteenth of an inch to one-eighth of an inch apart, and make other conditions fit this one. Never have the lenses actually touching each other, since mechanical contact would serve to impart considerable heat to the front lens, which is decidedly undesirable. FOR MANAGERS AND OPERATORS 117 The novice would probably say that, since the light cone is shorter in Plate 3 than in Plate 2, the E. F. of the Plate 3 combination would be less. The opposite is true, however, Measurement from a point half way between the two lenses to the point where the rays begin to diverge from the main beam will show that the cone is shorter in Plate 2 than in Plate 3. It may be stated as an absolute fact that when the con- denser is made up of two factors of different focal lengths, as for instance, a 6 l / 2 and a 7 l / 2 lens, the better practice is to Showing how the objective is covered by the incident light when the directions given in the tables are followed. 1 Tmhies-back focus of objective lens. 5 6 NOTE. Line A would pass from the extreme edge of the conuenser to the extreme edge of the objective lens and just pass through the narrowest part of the machine aperture. Line B goes from the opposite extreme edge of the condenser to the opposite extreme edge of the objective. And while these two rays form an internal part of the condenser beam of light they form the extreme rays of the beam after passing the aperture. place the shorter focal length lens next the arc. This is proven by A-B, Plate 1. The only objection to so doing is that the thick lens is more apt to break than is the thinner one, but this may be very largely if not entirely overcome by the installation of a modern condenser mount, of which the Elbert or Preddy (see index) are excellent examples. In the course of the aforementioned experiment's it has been proven to the author's entire satisfaction that, provided the front lens of the condenser combination be in line with and square with the aperture and objective, the fact that the 118 MOTION PICTURE HANDBOOK rear condensing lens it not exactly square or in line with the front one does not make any serious difference, provided, of course, that the fault be not too great. I do not wish to be understood as saying that this condition ought to be allowed to obtain. The better practice is to have the entire lens system in exact line, but with present projector mounts this is ,a somewhat diffcult thing to accomplish, and failure to accomplish the lining of the two condenser factors per- fectly with each other will not be a very serious matter. Another extremely important relation between the con- densing lens and the objective is illustrated in Plate 4, in which A represents the extreme limit of light from the lower edge of the condensing lens when it is placed 16 inches from the aperture of the machine. You will observe that with the condenser at a distance from the aperture which will place the arc in focus (the point where the condenser ray begins to diverge), which is the point where the picture will receive evenly distributed illumination, the light will pass through the aperture and become a diverging beam. This is clearly shown in Plate 5, which shows the light beam as in actual projection, and is proven in Plate 6, in which the condenser is covered by a metal plate in which are two holes located diametrically opposite each other and about a half-inch from the edge of the lens. It will be seen from Plate 6 that the rays from the outer edge of the condenser lens actually do act precisely as indicated in diagram, Plate 4. In Plate 7 the same two rays are passed on through the ob- jective lens. From this the inevitable conclusion is reached that, with the crater in focus at the aperture, the closer the condenser is to the aperture the more rapid will be the divergence of the beam beyond the aperture, though the increase from this will be comparativetly slight. It will also be seen that the greater the distance from the aperture plate to the objective lens aperture the wider the light beam will be at the point it encounters the lens, See Plate 8. It therefore is an undoubted fact that the diameter of the objective lens is an exceedingly im- portant factor, particularly with long focal length lenses, and it is a factor which must be taken into very serious account in the matching up of projector lens systems. Plate 9 shows the loss of light through using a lens of too small diameter. This loss may be slight; or it may be very great. In many cases it is the latter. In this case the loss is far greater than appears, because the camera only caught the loss which fell outside the lens barrel, whereas FOR MANAGERS AND OPERATORS 119 I the actual diameter of the lens aperture is considerably less than the outside diameter of the barrel. In Plate 4, the long scale marks condenser distance, and the short scale, to the right, indicates the back focus of the objective. Any objective lens may work at any one of several 120 MOTION PICTURE HANDBOOK s I E oT D rt different distances from the film. That is something I have never been able to make fit in with any plan I could evolve for matching up a projector lens system. Like most other things, however, once you get hold of the right key FOR MANAGERS AND OPERATORS 121 it is very simple, and the key to this particular problem is "back focus." In matching up a projector lens system, first, using the well-known formula for finding the equivalent focus of the lens required to project the size picture you want at the distance your condition calls for, determine the E. F. of the lens you want, procure it, mount it in the machine, and, using any condenser, project a picture, and very carefully adjust the objective until the picture on the scree'n is in sharp focus. Having done this, stick a rule through the aperture and, with its end against the lens, measure the exact distance of the rear surface of the rear combination of the objective from the film track surface on the aperture. This measurement will be the BACK FOCUS at which your lens will work, and it is this measurement and not the equiva- lent focus, which must be used in matching up the lens system. The E. F. has absolutely no value whatever except to enable the operator to select the proper lens to project the size picture he wants at the given distance. At this point we reach an item of much importance, con- cerning w/hich positive data cannot as yet be given, viz.: The selection of an objective lens of the right diameter to fit local conditions. Excess in diameter is undesirable, in that it is likely to set up trouble in the shape of travel ghost. Insufficient diameter, on the other hand, means loss of light, and loss of light is expensive. On the whole, it is much better, I believe, to get a lens of too large than too small diameter, because it is an easy matter to stop down the large lens to just the size needed, whereas the small diameter cannot possibly be made larger. On the whole, I think the best recommendation we can make at present is that the E. F. of the required lens be found, and that a lens be ordered having a diameter equal to one-half its E. F., up to 4^ inches E. F., the diameter beyond that focal length to remain fixed at 2% inches, up to 7 inches E. F., beyond which it might possibly be increased to 2^ inches with advantage. When the lens is received, place it in the machine and focus the picture sharply on the screen, then measure the back focus, as already directed, and remove the lens. Now place a sheet of white paper inside the mechanism in the exact position occupied by the back surface of the lens, supporting it in any convenient way, without Jiaving changed the position of the lamp with relation to the condenser or of the lamp- house with relation to the aperture, strike an arc, and measure 122 MOTION PICTURE HANDBOOK the light on the paper. If the lens meas- ures 2 inches in diameter and the light measures 2 inches across, all is well. If the light measures more than 2 inches across, but only 2 inches up and down, the lens still will do fairly well, though there will be some loss. If, however, the lens measures greater than the light, stop the lens down to the diameter of the light at both ends, by means of rings of metal in which you have made a circular opening of proper size. I do not pretend to say that this advice is perfect. It is, however, the best I can offer at this time, and is, I am sure, based on the right idea. A Digression. Let me pause here, for T-; want of a more fitting place, and digress ^J for a moment to show you an interesting light ray picture. .? In Plate 10 we see a condenser with a ^ metal plate having a number of holes, each f about one-quarter inch in diameter. This o picture has no considerable value, except to allow the operator or student to trace the ^ light ray action on both sides of the ob- jective. It will be noted that the screen illumination is not complete, especially at the outer edges where there were but few holes in the metal plate. Another interest- ing point in this picture is the circle of light on the back side of the aperture plate, showing the loss of light through reflection from the polished surface of the lens. In fact, there are a number of things in this photograph that will interest the student- operator. Spherical Aberration. An examination into the effect of spherical aberration points to the fact that it operates mainly to cause impurity of the light, by reason of the fact that those rays which draw in toward the center earliest must naturally reach somewhat into the center of the spot, and coming, as they do, from the outer edge of the lens, they carry with them considerable color. FOR MANAGERS AND OPERATORS 123 This, so far as I am able to determine, is the principal practical effect of spherical aberration. It amounts to a dis- coloration of the light, and hence a diminution of its brilliancy, though it may or may not be sufficient to be perceptible to the eye in individual cases. Also spherical aberration, if excessive, will cause the spot at the aperture to consist of a series of circles of light in- stead of an evenly illuminated field, and as this plane is refocused at the screen, there will, if there is an absence of rays at the center, be a dark spot or "ghost," or if more of the rays are reaching the center of the spot than its edges, high lights will result. This is usually the result of the film cutting the beam of light too far from the actual mean focus of the crater, but there are, nevertheless, other conditions which result in high lights and shadows on the screen, and spherical aberration may result only in uneven illumination. There is practically no bad effect from spherical aberration through the stereopticon because the rays reach the slide before they are displaced, but chromatic aberration will show if the rays from the outer edges/ of the condenser pass through the slide. Chromatic Aberration of the Condenser Beam. In Plate 11, a crater is constructed by cutting an aperture in a piece of cardboard and placing a | ^CARDBOARD piece of ground glass K I/MNHOU- behind it. Back of this is placed a 100 C. P. incandescent lamp. The nLAMENT crater and screen are placed at conjugate foci of the condensers. The screen corresponds to the aperture plate of the Plate 11, Figure 52. machine. A piece of cardboard pierced with a pinhole is placed as shown in Plate 11. The results as observed upon the screen, Plate 11, are: the crater is focused in full definition on the screen, but it is colored with the shades of the spectrum in the manner shown. Now it has been demonstrated by the Kinemacolor process that all the colors of the spectrum can be reduced to ap- proximately two shades, viz: a reddish-orange and blueish- green, which for the sake of clearness we will call orange and green. In Plate 11 A are shown the same conditions described in connection with Fig. 1, except that the colors of the spectrum 124 MOTION PICTURE HANDBOOK have been reduced to the two primary shades, viz: orange and green. Notice that at the screen (or aperture) the colored rays combine and form white light. Now, if the process shown in Plate 11A be continued, and a very large number of rays be drawn, using orange and green ink, the result will appear as shown in Plate 11B, in which it is observed that the beam is inclosed by an orange envelope, Which is thickest toward the central part of the beam and comes to a point or disappears en- tirely at the aperture and the condenser. The ^ beam has a core in the center which is com- posed ofi the violet, :,.../?&xr v j, N ncys. blue, and green shades of the spectrum. The white part of the beam is caused by the mixture of the two other primary shades, but the mixture is not perfect at all positions. At the section AA, Plate 11B, the white light is most pure, but as it approaches the position of section BB, the colors at the violet end of the spec- trum commence to predominate, so that at section BB, the white zone has changed to a dirty purple. In< view of this condition it is not difficult to understand why a ghost appears in the screen when the aperture is brought back too far toward point BB. When properly located all the colors of the beam finally combine at the .aperture to form pure white light, and since it passes from .aperture to objective, all light beyond the aperture is pure white. It is also noted that the light at section AA, Plate 11B, is pure white. Plate 11A, Figure 53. Plate 11B, Figure 54. Now it must be remembered that the results shown in Plate 11B can only be approximately true, since all the colors of the spectrum, which are infinite in number, have been reduced to only two shades. Even if only seven colors had been used in the drawing, the straight lines in Plate 11B FOR MANAGERS AND OPERATORS 125 would show as curves, and more closely resemble the true shape of the actual beam. Nevertheless, when a small screen is placed at different sections of the actual beam, the results show a very close agree- ment with the theories set forth. In photographing the beam, only the white and green zones are actinic and show in the photograph, and by observing Plate 11B, it is seen that the theoretical shape of the combined white and green zones agrees very closely with the photo- graph. But even to the eye the beam has a curved shape, which is probably due to the existence of infra red at the outer edge of the orange envelope. It is finally seen, as a further point in practical application, that one of the im- portant functions of having the crater in true focus at the aperture is to purify the light and avoid color effects. The aperture may be placed a little forward of the focal plane, |^ but should never be behind it. Some of the practical effects of chro- matic aberration are seen in Plate 11C. It will be observed that whereas the holes in the metal shield covering the condenser are of equal size the lower ray is much the stronger. This is partly due to its position, but also to a very considerable extent to color in the upper ray which reduces its actinic effect on the photo- graphic plate. Another important point in connection with the condenser/is loss of light through poorly polished, unevenly finished surfaces, and through discoloration/ of the glass. Of late there have been those who have advocated the addition of yellow to the condenser lens glass, with the idea of mel- lowing light. With this I cannot agree. I think it is hardly necessary to enter into a discussion of the matter, and most emphatically advise operators to avoid the use of lenses containing discoloration of any kind. In selecting a condenser lens first examine its 126 MOTION PICTURE HANDBOOK surface, and, unless it presents a perfectly smooth, polished appearance, and evidence of having been ground to the true surface, reject the lens. In order to perform its function properly a lens must be a perfect segment of the surface of a sphere, and this perfect shape can only be obtained by grinding. k A B Plate 12, Figure 56. It cannot, by any stretch of imagination, be had by merely polishing the surface of a molded lens. Stop .and consider the matter for a moment. In order to secure even approximately perfect results in illumination at the spot it is necessary that all light rays emanating FOR MANAGERS AND OPERATORS 127 from any point on the crater and falling upon any point on the surface of the lens be so refracted that they will reach the same point in or on the spot. Now this can only be accomplished by a perfectly true lens surface, and it therefore follows that if the surface of the lens be not perfectly true, some of the rays are going to be refracted properly and some are not, and this of necessity means loss in effectiveness. With this in view I would call the attention of theatre managers to the fact that the cheap, molded condenser lenses, having an uneven, wavy surface, may be cheap in first cost, but are a mighty expensive article in the long run, because of the fact that, since it takes current to produce light, and you have to buy the current, anything which makes for ineffectiveness in illumination means a waste of current, hence you are simply saving a small sum of money in the original cost when you buy a cheap condenser lens, and are paying out money every minute you run for current to produce light which the cheap lens is wasting. Also reject any lens which does not measure exactly 4^2 inches in diameter and which has an excessively thick edge. Con- denser lenses should be exactly 4J^ inches in diameter, and should come down to an edge but little if any thicker than one-sixteenth of an inch. A thick edge means unnecessary glass; therefore unnecessary absorption of light. In Plate 12 A shows the wrong and B the right lens edge. It is im- portant that the edges of condenser lenses be of standard thickness, .and that their diameters be exactly 4H inches, because not only is excessive glass wasteful (it is impossible for manufacturing reasons to bring the edge right down to a thin edge at a 4^2 inch diameter) but with edges of varying thickness it is impossible to make the lenses fit properly in many of the machine lens holders; also any change in diameter alters the fit of the lens in the holder, and these variations will render it practically impossible for the operator to properly line up his lens system. I would sug- gest that operators pay careful attention to this matter be- cause lens manufacturers seem to think that "near or about" is good enough, both in diameters and lens edge thickness. They will only change that attitude and come down to a fixed standard when a large number -of kicks are registered by purchasers. I have pointed out the reasons why diameters and lens edge thickness should be absolutely standard. I think you will have no trouble in recognizing the fact that these reasons are sound. It is now up to you to compel lens manufacturers to produce a standard article, and I 128 MOTION PICTURE HANDBOOK suggest that you insist on an exact 4 l / 2 inch diameter and a lens edge thickness exactly one-sixteenth of an inch. It is quite true that to thus standardize lenses might add somewhat to their cost, but even so, it will be money saved in the end, no matter from what angle the proposition be viewed. In selecting your condensing lens, first examine its surface, and if it is not perfectly smooth and highly polished it is not a good lens. Next look through the lens edgewise, and if it does not show clear (has any trace of color when looked through that way) reject it. It is not a good lens. If you have any doubt whatever as to the inadvisability of using lenses containing color, either purple, greenish or yel- low, break a clear white condensing lens in half; also break a lens containing discoloration in half, put these two halves in as the front lens of your condenser combination, being certain the rear lens contains no color, and project the clear light on the screen through the stereopticon lens. I think the appearance of the screen will satisfy you thoroughly as to the advisability of rejecting any lenses containing any color what- ever. This experiment should only be tried through the stereo lens, with which the two halves can be focused at the screen. In a camera the lens receives rays directly from an object and delivers them directly to the screen (plate). In the projector there are two absolutely separate lens systems, one of which receives its rays from the other, and one of our problems is to so join these two systems that the film picture will not only receive a maximum of illumination, but also that that illumination shall be evenly distributed over the entire area of the photograph, and that the second or objective system be enabled to pick up the light rays delivered to it by the first or condenser system, with the least possible amount of loss. Now these various propositions look reasonably simple, but there are, in fact, some very intricate problems involved. With relation to the condenser system, there is one point on which we have very little accurate data, viz.: the exact diameter of the crater for a given amperage. Until this matter is accurately determined our efforts in that direction can only be approximately correct, and possibly there may always be some differences in this item since doubtless differ- ent carbons will slightly alter crater size for a given am- perage. One exceedingly important point, which must be borne care- fully in mind, is that when the source of illumination is greater FOR MANAGERS AND OPERATORS 129 than a point the light ray from the condenser can never be brought to a point, for example : Assuming the crater to be an object, and the spot on the aperture an image (which is the exact condition), if the crater be 4 inches from the apex of the curved surface of the back condenser, and the spot on the aperture 16 inches from the apex of the curved surface of the front condenser, then the diameter of the spot on the aperture will be four times the diameter of the crater, of which the spot is an image, and the spot will be the nar- rowest part of the condenser beam, since at this point the beam will begin to diverge, therefore we cannot consider the condenser beam as coming to a point further on, as it has always been supposed to do. Not only have we discovered the fact that there is a direct ratio between the diameter of the crater and the diameter of the spot on the cooling plate, but we have also found that in order to obtain the most even illumination of the entire aper- ture it is necessary that the crater be "in focus" at the aperture of the machine, or in other words, that the crater and spot be at the respective points of conjugate foci of the condenser lens. Now in order to understand this some of you must do a little studying. Take a condenser lens and hold it near the wall of a room, opposite an open window, and you will find that with the lens at a certain distance from the wall you get a fairly good image or picture of the scene out of doors on the wall. This means that the lens is at a distance from the wall equal to its focal length, or, in other words, in a posi- tion where rays emanating from a point on an object are brought to a focus in the image, not where the light beam, as a whole, is brought to a point, which it never is. Move the lens further from the wall and the ray increases in size and is quickly lost. Some may dispute this, and cite the burning glass in proof. Well, the point to which the burning glass apparently brings the rays is not a point at all, but merely an exceedingly small image of the sun. Now, taking the condenser as a whole, the crater of the carbon takes the place of the scene out of doors, and the aperture of the machine the place of the wall. Of course the image is formed much further away than was the case with the lens held near the wall, but this is by reason of the fact that the crater (object) is close to the lens, whereas the out-of-door scene was far away. If a single lens were used, instead of a double one, these distances would again be altered. 130 MOTION PICTURE HANDBOOK And now the question comes: When is the crater in focus at the aperture? This is a somewhat complicated proposition, in which we must take into consideration the known fact that spherical aberration exists in the condenser system, and the further fact that the crater does not set parallel to either the condensing lens or the film; therefore, due to the latter equation, there is bound to be precisely the same effect at the spot as there is when the machine sets at an angle to the screen. In other words, since the surface of the crater is not parallel to the lens the whole crater cannot possibly be put in sharp focus at the aperture, or anywhere else. We must therefore adopt a "mean focus point" or point of actual mean focus, since we cannot expect to get a sharp focus of the entire crater for reasons already pointed out. The point of actual focus must, due to spherical aberration, be beyond the plane where the rays from the outer edges of the spot would naturally focus, they being focused nearer the lens than the rays forming the center of the spot; therefore the plane of actual mean focus will to some extent have the appearance of back focus at the cooling plate. In fact, the focus of the crater may be assumed to occupy any position between the circle of least confusion, which may be recognized as a round spot with reasonably sharply denned edges, and a plane a few inches in front of the circle of least confusion, which latter may be recognized as a white spot surrounded by a bright blue outline. This blue spot consists of the aberrated rays on the back focus, the white spot in the center of the haze being the image of the crater. The ordinary practice of the operator is to carry a sharp, round spot at the cooling plate, rather than the actual focus of the crater, and so long as he can maintain this spot small enough, and still keep 'his arc near enough to the back con- denser to give good illumination, all is well provided he can also maintain a distance sufficiently great between the con- denser and aperture to prevent the rays in front of the aperture from diverging beyond the limits of the objective lens. See Plate 8. When the distance between the condensers and film be- comes too great to maintain a suitable size focused spot at the aperture and still keep the arc near enough to the con- denser, the only alternative is to focus the actual image of the crater, which is surrounded by a blue haze, at the aperture, and in order to do this it is necessary to utilize the whole length of the machine table, and also the shortest focal length condensers usually carried in stock, viz: two FOR MANAGERS AND OPERATORS 131 6H inch, in order that the white center be sufficiently magni- fied to fully cover the aperture. The spot produced by this arrangement will not look very picturesque on the cooling plate, but will give very superior results on the screen. If the amperage be very heavy it may be necessary to use one 6 l /2 and one 7 l /2 condenser, or if very light then one 5^ and one 6 l /2 will be best. In this we assume the limit of the machine table to be such that approximately twenty-two inches can be had between the condensers and aperture. Note. You cannot have too great a distance between the condensers and aperture, provided you keep your arc near enough to the back condenser. The tables given in this article merely provide the mini- mum, and the condensers therein named are for working w^;h the spot at the plane of least confusion only. I would suggest that any condition calling for greater focal length condensers than 6^2 and iy-2 will be better taken care of by using the spot with the blue haze and shorter condensers and the limit of dis- tance between the con- denser and film. Remember this: The spot itself is actually an image or picture of the crater. It therefore fol- lows that any attempt to use both craters with A. C. will set up diffi- culty, since it will, in the very nature of things, be extremely difficult, if not impossible, to get their images properly superimposed upon each other. Some operators have got splendid results from meniscus- bi-convex condensers, whereas others have reported no per- ceptible advantage in their use. It is all a matter of local conditions. Operators who have difficulty in getting their arc near enough to the condenser are the ones who will get best results with the meniscus-convex combination, by reason of the fact that they gain at least Y^ of an inch between the arc and the condenser, owing to the fact that the planes from which the conjugate foci are measured are changed that is to say, they are not the same with the meniscus-bi-convex as Plate 13, Figure 57. 132 MOTION PICTURE HANDBOOK they are with two plano-convex (see Plate 13). This is owing to the introduction of two more curved surfaces. The result is less enlarge- ment of the crater. On the other hand, the operator who can get near the condenser with his arc and still have a small spot will find but little benefit in the use of the meniscus-bi-convex set, pro- vided the meniscus-bi-convex and plano-convex lenses be of the same quality, except in reduction of spherical aber- ration. The theory upon which the action of light rays through the projector system, as set forth in this article, is based, is a difficult matter to ex- plain in such way that the reader or student will grasp the idea. Light action is one of the most difficult things imaginable to describe intel- ligently by reason of the fact that in drawing diagrams representing light action one is limited to the examination of the action of one, two or possibly a dozen rays out of literally millions and, as a general rule, the student has difficulty in considering the single ray or the few rays shown in the diagram as being representative of the action of countless numbers of rays which accompany it but are not shown. ' In this connection, as a di- gression, it might be interesting to know that scientists tell us that a bundle of thirty-six Plate 14, Figure 58. FOR MANAGERS AND OPERATORS 133 light rays will have approximately the same area as that of a single human hair. Beginning with a fact with which all are more or less familiar, viz.: that from each point in a light source rays radiate in all directions (in the case of a projection arc light crater it would not be literally in "all directions," but in all directions over an area covering what would be practically equal to one-half the surface of a globe) until they meet with some obstruction. After leaving the crater the first obstruction encountered is the condensing lens through which the rays must pass. This gives us countless numbers of cones of light as A-l-2, B-l-2, C-l-2, Plate 14, each cone having its apex at a point in the crater, and its base on the surface of the condensing lens. The sum of these cones represents the total light passing through the condenser. Each one of these cones is made up of diverging rays ex- clusively, up to the rear surface of the condensing lens. With; this I believe we all will agree, and thus endeth the first part. But when we come to examine into their action beyond the rear surface of the condensing lens we find that the fore- going does not fully elucidate or make clear the entire prob- lem. First: From each point on the crater we have rays enter- ing every minute pinpoint on the surface of the condenser, therefore through each point of the condenser we have pass- ing a cone of converging rays, each cone carrying a complete image of the crater, as per A-C-2, A-C-1, so that we are also entirely correct when we consider the total light passing from the crater through the condenser as consisting of countless numbers of cones of converging rays having their apex at a point on the condenser at 1-2, Plate 14. It will thus be seen that while we do not actually have two sets of rays we do have a double light action. It may very reason- ably be asked: "If the first part includes the total rays pass- ing from the crater through the condenser, and the second part merely does the same thing in a different way, why bother with the second part at! all when the action first described is more generally understood?" The reason for analyzing the action of light rays complete- ly and describing the second part is because it gives us a clearer understanding of what follows. Now having in mind one of the cones A-C-1, or A-C-2, Plate 14, it will be readily seen that rays A-l and C-l meet- ing at a point on the condenser will, even though refracted, 134 MOTION PICTURE HANDBOOK cross at the plane of the condenser. This can easily be proven by using a refractometer. It therefore follows that as the total rays entering and passing through the condenser from the crater may be considered as consisting of count- less cones having their apex at a point on the condenser, the crossing point or reversal of the image must, in the very nature of things, take place at the rear plane of the rear condenser and at no other place. Undoubtedly the rays do cross each other before reaching the condenser plane, but only when on their way to and from a point which is receiving a complete image of the crater. This action is perhaps made most clearly intelligible, and may be best adapted to use in this article by considering cone A-l-2, cone B-l-2, cone C-l-2, cone A-B-1, A-B-2 and B-C-2 (remembering that these are but representative of Plate 15, Figure 59. millions of other similar cones at other pinpoints on the crater and condenser) as being two sets of rays. Please understand that we do not mean by this that there actually are two sets of rays, but merely use that term as a con- venient medium through which to describe certain action of the light which really is the same group of rays acting in two different ways. Theory of double action may perhaps be made more un- derstandable by means of diagram, Plate 15, which is a diagrammatic representation of pinhole photography. In Plate 15, at A, we see a diagrammatic representation of pinhole photography, in which rays by the millions go in every direction from every point of arrow B-C, but only those FOR MANAGERS AND OPERATORS 135 rays striking pinhole D can pass through and form an image on the screen at E-F. That is the idea we had in mind in saying that one set of rays projected the whole crater. To get the point of view, you must consider each minute point on the back plane of the condenser as being a pinhole, and as a matter of fact it does act in exactly that way, therefore each minute pinhole point of the condenser will receive one ray from each pinpoint of the crater and will therefore project an image of the crater, as a whole, to the aperture of the machine. This same thing is shown photographically in Plate 16, in which Plate 16, Figure 60. A is the machine aperture, covered by a plate in which are two pinholes, and B the back factor of an objective, covered with a plate containing one pinhole. The action is that rays from the lower half of upper cone X pass through as ray Y, whereas from the upper half of cone X pass through as ray Y. The photo is a poor one, as it is extremely difficult to get a good picture of such weak rays. A comparison will reveal the fact that the action in A, Plate 15 and in Plate 16, is identical. The second set of rays, viz.: those emanating from a point on the crater, represented by cones A 1-2, and B 1-2, and C 1-2, Plate 14, project to the same aperture, in converging lines, rays from every infinitesimal portion of the crater, and that is the real explanation. The foregoing theory is not altogether coincided in by some, but the fact, nevertheless, remains that it is the only one by means of which we can explain one phenomenon, viz.: why the beam of light is round as it emerges from the objec- tive, and continues so for a distance varying with the focal length of the lens, and thence to the screen is rectangular. And now comes the difficult part to explain. In Plate 14 we see a diagrammatic representation of Grif- fiths' theory, as applied to the condenser system. In Plate 16 we see, in photography, precisely the same thing as applied to 136 MOTION PICTURE HANDBOOK the objective lens. Always bear in mind one fact, viz.: the optical action of the objective lens and the optical action of the condensing lens is in every respect identical. Now to follow this matter through we will consider Plate 17, which is a photographic representation of light ray action in an objective lens, in which X is a shield containing a standard machine aperture, covered by a brass plate containing two pinholes. Y is a standard projection lens, with one- half of its barrel cut away, 1 and 2 be- ing respectively the back and front factors of the lens, though 2 is hidden behind its container. This photograph is made with the aperture and the lens in actually working position, and with the light projected through the con- denser in the ordinary way, under actual operating conditions. You will observe that the light coming through the upper pinhole, Plate 17, diverges into a cone, which corresponds to cone A, 1-2, Plate 14. This cone cov- ers very nearly the full aperture of the lens. The light passing through the lower pinhole does exactly the same thing, and the two cones begin to in- termingle at L, and from there on to the lens a small central light pyramid is shown, the upper half of which is the upper edge of the lower pinhole cone, and its lower edge the lower edge of the upper pinhole cone. Be- yond the back factor of the lens, be- tween the two lens factors, you can easily trace the action. And it is made clear in this photograph that the bend which starts the final crossing or trans- position of the rays takes place at the first or back surface of the first or back combination of the objective, even as it takes place at the back surface of the rear lens, Plate 14. The action, as between the diagram, Plate FOR MANAGERS AND OPERATORS 137 i; y