,transcriber's ,notes3 ,text printed in italics1 bold face and small capitals in the original work have been transcribed between underscores1 equal signs and ,,all ,,capitals1 respectively4 ,depending on the hard- and software used to read this text and their settings1 not all characters may display as intended4 ,more ,transcriber's ,notes may be found at the end of this text4 ,books by ,horstmann ,tousley ,motion ,picture ,operation1 ,stage ,electrics and ,illusions4 #b4jj 7,ready ,july #a1 #aiad47 ,alternating ,current ,theory1 ,practice and ,diagrams4 #b4jj ,modern ,electric ,illumination4 #b4jj ,practical ,armature and ,magnet ,winding4 #a4ej ,modern ,electrical ,construction4 #a4ej ,electrical ,wiring and ,construction ,tables4 #a4ej ,dynamo ,tending for ,engineers4 #a4ej ,modern ,wiring ,diagrams and ,descriptions4 #a4ej ,electricians' ,operating and ,testing ,manual4 #a4ej ,motion ,picture ,operation ,,stage ,,electrics ,,and ,,illusions ,a ,practical ,hand-book and ,guide for ,theater ,electricians1 ,motion ,picture ,operators and ,managers of ,theaters and ,productions ,by ,henry ,c4 ,horstmann and ,victor ,h4 ,tousley ,authors of 8,alternating ,current10 8,modern ,wiring ,diagrams10 8,modern ,electrical ,construction10 8,electrical ,wiring and ,construction ,tables10 8,practical ,armature and ,magnet ,winding10 8,electricians' ,operating and ,testing ,manual10 8,modern ,illumination40 ,,illustrated ,illustration ,chicago ,,frederick ,j4 ,,drake ,,co4 ,publishers ,copyright #aiad1 by ,,henry ,c4 ,,horstmann and ,,victor ,h4 ,,tousley ,,preface ,in this volume the authors have attempted to lay before the ,motion-,picture ,operators and ,theatrical ,employes generally1 a reference and handbook making a specialty of electrical requirements about theaters4 ,a working knowledge of electricity in general is assumed1 and therefore elementary ideas have been treated sparingly4 ,a specialty1 however1 has been made of all matters peculiar to theaters1 and it is thought that theater electricians will find in this volume everything that they need whether they be operating motion-picture machines or switchboards in first-class houses4 ,the two special chapters 8,portable ,stage ,equipment0 and 8,theater ,wiring0 have been arranged so that they are particularly valuable for reference4 ,they should be consulted before undertaking any electrical construction work1 either for the stage or for the auditorium4 ,these chapters embody all of the practical knowledge that has come to the notice of the authors in many years of actual experience with theatrical construction4 ,the aim of this volume has been to present in a simple and practical way the essential principles of ,motion-,picture ,work4 ,,the ,,authors4 ,table of ,contents ,,page ,,chapter ,i ,the ,electrical ,circuit and ,electrical ,hazards #i ,,chapter ,,ii ,the ,arc ,lamp #ai ,,chapter ,,iii ,projection #ca ,,chapter ,,iv ,motion ,pictures #ee ,,chapter ,v ,the ,motion-,picture ,machine #fb ,,chapter ,,vi ,the ,film #hi ,,chapter ,,vii ,general ,hints on ,installation1 ,operation and ,care of ,machines #if ,,chapter ,,viii ,light #aac ,,chapter ,,ix ,principles of ,vision #abb ,,chapter ,x ,reflection #abf ,,chapter ,,xi ,refraction #acg ,,chapter ,,xii ,optical ,instruments #adg ,,chapter ,,xiii ,optical ,illusions #aee ,,chapter ,,xiv ,theater ,buildings #afc ,,chapter ,,xv ,operating ,room ,equipment #agf ,,chapter ,,xvi ,current ,control for ,arc ,lamps #aij ,,chapter ,,xvii ,management of ,generators and ,motors #bac ,,chapter ,,xviii ,theater ,wiring #bah ,,chapter ,,xix ,portable ,stage ,equipment #caa ,,chapter ,,xx ,useful ,facts and ,formulas #cec ,,chapter ,,xxi ,glossary of ,electrical1 ,mechanical and ,optical ,words1 ,terms and ,phrases #ceh ,index #che ,,motion ,,picture ,,operation ,,stage ,,electrics ,,and ,,illusions ,,chapter ,i4 ,,the ,,electrical ,,circuit ,,and ,,electrical ,,hazards4 ,two and ,three-,wire ,systems4--,if the theater electrician will take the trouble to trace the circuits in the building to their supply1 he will find them entering the building either as two-wire or three-wire circuits4 ,illustration3 ,,figure #a4 ,a two-wire circuit is diagrammatically shown in ,figure #a4 ,the circuit1 coming from #a1 enters the building1 passes through the fuses #b1 and through switch #c to the lights4 ,a two-wire system will ordinarily be found operating at #aaj volts1 the current varying according to the number of lights turned on4 ,in the drawing1 for instance1 only one light is shown with the switch closed1 the other three switches being open4 ,the current in the circuit is equal to that which passes through the single lamp4 ,if another switch be closed1 another light will burn and the current will be increased1 so that the more lights be turned on1 the greater will be the current4 ,illustration3 ,,figure #b4 ,the three-wire system1 ,figure #b1 is almost universally used where the supply is from the outside and where any considerable number of lights are connected4 ,the chief advantage of the three-wire system lies in its economy of copper4 ,the middle or neutral wire ordinarily does not carry current1 but it is a necessity whenever the number of lights burning on the two sides of the system are not equal4 ,with the neutral wire omitted1 we have a straight two-wire system using double the voltage of the ordinary two-wire system and always operating two #aaj-volt lamps in series4 ,two lamps would always have to be turned on at the same time and if one of them should burn out1 the other would be extinguished also4 ,a system using double voltage requires only half the current and consequently but half the copper4 ,in order to obviate the necessity of always using two lamps together and at the same time economizing in copper1 the neutral wire is provided4 ,as long as the same number of lamps are burning on each side of the neutral wire1 the same current always passes through two lamps in series and there is no current in the neutral4 ,should1 however1 the group on one side be turned out1 the other would still continue to burn2 but the path of the current to the dynamo1 or bank of transformers1 would be through the neutral wire4 ,the system is thus seen to possess all the advantages of the ordinary two-wire system since each lamp can be operated by itself and at the low voltage1 while the actual supply voltage for the whole system is double that which is actually used at any lamp4 ,we have thus two voltages at our command2 #aaj and #bbj being the voltages in common use4 ,electrical ,hazards4--,since this work is not intended for mere beginners1 we shall not enter into elementary considerations1 but shall take up the matter of fire and life hazard1 both of which are important items to which attention cannot be too often called4 ,the electrical current may cause fire by overheating the wires4 ,this overheating may be due to the willful overloading of circuits2 and to prevent this1 no wire should ever be used to carry more current than is allowed by the table of carrying capacities given on page #bch4 ,the overheating may also be due to an unknown load which is caused by a 8ground0 or a partial short circuit4 8,ground0 is the technical term used to designate the connection of a wire to any substance over which electricity may be carried to the wire of opposite polarity4 ,a ground may be caused by a bare wire coming in contact with the iron framework of a building1 wet wood1 or moist substances of any kind4 ,one such ground on a circuit can do no harm2 but1 if one ground exists1 in the course of time another one may come on and1 when the second one appears1 if it is on the side of the circuit opposite to the first1 there will be trouble at once4 ,if the two grounds are both 8good0--that is1 if they are of low resistance--we shall have a short circuit and probably blow a fuse2 but if they are not 8good10 we may have but a small current which may continue unnoticed for months4 ,such a current may eat away the copper of the positive pole and in time cause the wire to break1 creating an electric arc and perhaps causing a fire4 ,it may also cause wet wood through which it flows to become charred and finally ignited4 ,the ground is the bane of the electrical worker4 ,if a system can be kept free of grounds1 the chances of trouble are vastly reduced4 ,the cause of most grounds is moisture4 ,nearly all substances except metals are fairly good insulators if dry2 and nearly all of them are fairly good conductors if sufficiently wet4 ,another very prolific source of fires is the electrical spark1 large and small4 ,the spark1 due to the breaking of an incandescent lamp1 often causes fires when it comes in contact with inflammable material or gases4 ,the ordinary lamp cord also causes many fires because it is easily damaged and liable to short circuits which often result in arcing4 ,short circuiting two wires or breaking a wire carrying current may easily ignite inflammable material in the vicinity4 ,the best way to reduce the fire hazard to a minimum1 is to install all electrical work carefully according to the rules laid down in the 8,national ,electrical ,code04 ,the life hazard is one which concerns the operator personally and is especially great to those traveling with shows4 ,traveling men are often obliged to get along with all sorts of make shifts1 especially in the smaller towns where one-night stands are the rule4 ,here it is often necessary to connect to trolley circuits or power lines of different voltages1 frequencies1 etc4 ,a person may suffer injury directly from a current of electricity by making himself part of the circuit4 ,if the system on which he is working is alive and grounded1 he may easily cause injury to himself by touching a live wire with his hands while standing upon anything that is grounded4 ,by so doing he completes a path for the current through his body4 ,he may also become part of a circuit by holding a wire with both hands while someone is cutting it between his two hands4 ,as long as a wire so held is intact1 no shock can be received except to ground1 but when the wire is cut or breaks1 a very high voltage may be produced for an instant which will cause a current through the body of the man holding the wire4 ,the extra high voltage is produced only if the wire is carrying current at the time it is being cut4 ,under these circumstances there will often be a strong flash1 due to the momentary increase in voltage1 produced by the breaking of the circuit1 which may be excessive1 especially if there is considerable inductance in the circuit4 ,the most frequent cause of injury is due to making contact with the two opposite polarities of a system4 ,as a rule circuits1 with which operators ordinarily have to work1 are low voltage1 i4e41 not over #bbj volts4 ,but many deaths have been caused by this voltage1 sometimes directly and at other times indirectly as1 for instance1 by causing a fall4 ,people whose hearts are in any way defective should be careful about exposing themselves to shocks even at #aaj volts4 ,it is true that many wiremen are in the habit of testing #bbj-volt circuits by allowing the current to pass through their bodies1 but it will be noticed that they are very careful not to make a good contact4 ,the current which passes through the body1 when one touches two wires of opposite polarity very lightly with the finger tips1 is but a fraction of what one would receive if he were unwittingly to grab two wires of opposite polarities with the hands1 especially if the hands were moist4 ,numerous cases are on record of persons having been killed by #aaj volts under favorable circumstances2 as1 for instance1 while in the bath receiving a shock from a so-called vibrator4 ,the body partly immersed in water and perhaps a foot resting against a water pipe forms a conductor of very low resistance1 and a comparatively strong current may pass through the body4 ,the most important precautions against injury while working on live circuits are3 7#a7 ,insulate yourself from the ground4 7#b7 ,handle only one side of a line at a time4 7#c7 ,if possible1 work with only one hand at a time in contact with the wires4 7#d7 ,use rubber gloves1 or rubber boots where necessary1 but bear in mind that they are of little value unless kept dry4 ,moisture will allow some current to pass over the surface of any substance no matter how good an insulator it may otherwise be4 7#e7 ,always place yourself so that a slight shock which might cause you to lose your balance will not give you a bad fall4 7#f7 ,remember that if once you make good contact with an alternating-current circuit1 you cannot let go4 7#g7 ,fix firmly in your mind the directions for resuscitation from electric shock1 on pages #ae-ah4 ,when energy is obtained through transformers1 there is another danger to be added to the above1 viz41 the possibility of the breaking down of the insulation between primary and secondary wires of the transformer4 ,if this happens1 we have suddenly and without warning1 instead of the #aaj or #bbj volts supposed to exist between the wires forming the circuit1 #b1jjj or #c1jjj volts4 ,such accidents are especially likely during thunder storms when lightning often breaks down transformers4 ,in order to reduce this danger to a minimum1 the secondaries of transformers are grounded4 ,it will be well for the electrician to assure himself that the secondaries of the transformers from which he is getting his supply are grounded4 ,this can be tested by an incandescent lamp4 ,connect the lamp to ground with one wire and1 with the other1 try the two sides of the circuit4 ,if the transformer secondaries are properly grounded1 the lamp will burn at full candle power from one of the wires2 this will show that the other wire is grounded4 ,a person working on such a circuit is of course more likely to receive a low voltage shock than if the secondaries were not grounded1 but he is fairly well protected against the primary voltage or lightning4 ,,resuscitation ,,from ,,electric ,,shock4 ,rules recommended by commission on resuscitation from electric shock1 representing ,the ,american ,medical ,association1 ,the ,national ,electric ,light ,association1 ,the ,american ,institute of ,electrical ,engineers3 ,dr4 ,w4 ,b4 ,cannon1 chairman2 professor of physiology1 ,harvard ,university4 ,dr4 ,yandell ,henderson1 professor of physiology1 ,yale ,university2 ,dr4 ,s4 ,j4 ,meltzer1 head of department of physiology and pharmacology1 ,rockefeller ,institute for ,medical ,research2 ,dr4 ,edw4 ,anthony ,spitzka1 director and professor of general anatomy1 ,daniel ,baugh ,institute of ,anatomy1 ,jefferson ,medical ,college2 ,dr4 ,george ,w4 ,crile1 professor of surgery1 ,western ,reserve ,university2 ,w4 ,c4 ,l4 ,eglin1 past-president ,national ,electric ,light ,association2 ,dr4 ,a4 ,e4 ,kennelly1 professor of electrical engineering1 ,harvard ,university2 ,dr4 ,elihu ,thomson1 electrician1 ,general ,electric ,company2 ,w4 ,d4 ,weaver1 secretary1 editor ,electrical ,world4 ,issued and copyrighted by ,national ,electric ,light ,association4 ,reprinted by permission4 ,follow these instructions even if victim appears dead4 ,i4 ,,immediately ,,break ,,the ,,circuit4 ,with a single quick motion1 free the victim from the current4 ,use any dry non-conductor 7clothing1 rope1 board7 to move either the victim or the wire4 ,beware of using metal or any moist material4 ,while freeing the victim from the live conductor have every effort also made to shut off the current quickly4 ,,ii4 ,,instantly ,,attend ,,to ,,the ,,victim',s ,,breathing4 #a4 ,as soon as the victim is clear of the conductor1 rapidly feel with your finger in his mouth and throat and remove any foreign body 7tobacco1 false teeth1 etc47 ,then begin artificial respiration at once4 ,do not stop to loosen the victim's clothing now2 every moment of delay is serious4 ,proceed as follows3 a4 ,lay the subject on his belly1 with arms extended as straightforward as possible and with face to one side1 so that nose and mouth are free for breathing1 see ,figure on page #ag4 ,let an assistant draw forward the subject's tongue4 ,illustration3 ,,inspiration--,,pressure ,,off4 b4 ,kneel straddling the subject's thighs and facing his head2 rest the palms of your hands on the loins 7on the muscles of the small of the back71 with fingers spread over the lowest ribs1 as in ,figure on page #ag4 c4 ,with arms held straight1 swing forward slowly so that the weight of your body is gradually1 but not violently1 brought to bear upon the subject1 see ,figure on page #ah4 ,this act should take from two to three seconds4 ,immediately swing backward so as to remove the pressure1 thus returning to the position shown in the ,figure on page #ag4 d4 ,repeat deliberately twelve to fifteen times a minute the swinging forward and back--a complete respiration in four or five seconds4 e4 ,as soon as this artificial respiration has been started1 and while it is being continued1 an assistant should loosen any tight clothing about the subject's neck1 chest or waist4 ,illustration3 ,,expiration--,,pressure ,,on4 #b4 ,continue the artificial respiration 7if necessary1 at least an hour71 without interruption1 until natural breathing is restored1 or until a physician arrives4 ,if natural breathing stops after being restored1 use artificial respiration again4 #c4 ,do not give any liquid by mouth until the subject is fully conscious4 #d4 ,give the subject fresh air1 but keep him warm4 ,,iii4 ,,send ,,for ,,nearest ,,doctor ,,as ,,soon ,,as ,,accident ,,is ,,discovered4 ,,chapter ,,ii4 ,,the ,,arc ,,lamp4 ,general ,discussion of the ,electrical ,arc4--,the name of the electrical arc lamp is derived from the arch-like appearance of the vapors which give out the light when the carbons are placed horizontally4 ,the horizontal arc was the earliest form1 hence the name which it carries to this day4 ,the arc proper is due to the vapors of volatilized carbon or other materials forming the electrodes1 which may be consumed by the passage of an electrical current from one electrode to another through the intervening medium4 ,in order that an arc may be formed1 it is necessary first to bring the electrodes together4 ,this1 if the circuit is properly arranged1 starts the current and when the circuit is partly interrupted1 as by slowly separating the points of the electrodes1 the current passes through the intervening space1 with the result that a high degree of heat 7about #c1ejj centigrade7 is produced4 ,this results in volatilizing the carbon or any other material of which one or both electrodes may consist4 ,as long as the distance between the electrode points is small1 the current will be quite strong and a hissing or frying sound will be given out4 ,in order to keep the current within bounds during the time that the electrodes are together or while they are separated only a very short distance1 some resistance1 or reactance in the case of alternating-current arcs1 is always connected in series in the circuit4 ,if this were not done1 there would be a short circuit at the time of starting or striking the arc4 ,the arc formed with very short separation of electrodes is generally spoken of as a low tension arc and requires very hard carbons and about #be volts4 ,this type of arc is very little used for illuminating purposes4 ,if the distance between the electrodes is increased gradually1 the light becomes very unsteady and flickers considerably until at a certain point it begins to improve and give the long quiet arc4 ,this condition will occur when1 with direct current1 the electrodes are about one-eighth of an inch apart4 ,it will then be found that the voltage across the arc is from #de to #ej volts1 which is the best voltage to use with open arcs4 ,if the separation be carried still further1 the arc will grow longer and become flaming until finally it breaks entirely4 ,the resistance of the arc is closely proportional to the cross section of the electrodes and increases with the distance of the arc gap4 ,it acts1 however1 very much as though there were a small counter e4 m4 f4 set up within it4 ,the color of the light given off varies with the length of the arc somewhat1 but depends mainly upon the material of which the electrodes consist4 ,in the so-called flaming arcs1 the peculiar color is obtained by certain chemicals imbedded in the material composing the electrodes4 ,whenever an arc is allowed to burn down until it reaches the electrode holders1 a greenish light is given off which is due to the volatilization of the metal--usually brass--in these holders4 ,the light of a strong arc is extremely injurious to the eyes and should only be viewed through colored glass4 ,many very painful experiences have resulted from persons gazing upon arcs of #bjj or #cjj amperes1 such as are used sometimes in cutting away metals of old buildings1 etc4 ,the most powerful arcs known at the present time are those used in some steel mills for refining steel4 ,these use upward of #aj1jjj amperes4 ,illustration3 ,,figure #c4 ,illustration3 ,,figure #d4 ,the length of the ordinary arc varies from one thirty-second of an inch to one inch4 ,the light is not of much use and is rather unsteady until the electrodes have assumed a shape somewhat similar to that shown in ,figure #c for direct current1 and ,figure #d for alternating current4 ,with direct-current arcs1 a crater is formed at the bottom of the positive electrode and1 from this crater1 about #hj per cent of the light is emitted4 ,where the light is wanted in a downward direction1 the crater is always formed at the top and for this purpose the top electrode must be made positive2 that is1 the electricity must flow from the top electrode into the lower one4 ,in some cases1 where special illumination effects are desired1 the bottom electrode is made the positive with the result that most of the light is thrown upward4 ,in such cases strong shadows are thrown against the ceiling and the lamp is said to be burning 8upside down40 ,the positive electrode can always be distinguished from the negative 7a7 by the shadows cast2 7b7 by the form of the electrodes2 and 7c7 by the fact that since it is heated to a greater degree1 it will1 when the lamp is turned off1 remain hot for some time after the negative electrode has cooled off4 ,in case the arc is drawn out very long and operated in this way for a considerable time1 the crater will almost wholly disappear and the electrodes will appear rounded off4 ,in an alternating-current circuit1 the positive and negative poles reverse generally about #abj times per second and both electrodes in the alternating-current arc are positive and negative to the same degree4 ,they are therefore very nearly alike1 except that the heat rising from the lower one increases slightly the volatilization of the upper4 ,the positive electrode in the direct-current arc is consumed approximately twice as fast as the negative electrode4 ,the consumption of the two electrodes in an alternating-current arc is about equal and a crater much smaller than the kind formed in a direct-current arc is1 therefore1 formed on each electrode1 instead of only on the positive electrode as in the case of the direct-current arc4 ,the general form of alternating-current arc carbons is given in ,figure #d4 ,the small elevations shown in the cuts are due to impurities and do not appear with first-class carbons4 ,when arc lamps are operated on alternating-current circuits1 the best voltage for the arc is about #bh2 and consequently1 for the same quantity of light1 the current must be increased so that the amperage of alternating-current lamps is always much greater than that of direct-current lamps4 ,the alternating-current arc is much noisier than the direct-current arc1 but with very high frequencies this noise ceases4 ,in general1 arc lamps do not work very well on low frequencies4 ,the time at which the current is practically zero is long enough to allow the vapor between the electrode points to cool off sufficiently to interfere with successful operation4 ,any arc light is affected by draughts of air and can even be blown out4 ,if this occurs often1 there will be rapid feeding1 a short arc1 and great waste of electrode4 ,a magnet held close to an arc can be made to blow it out or force it to one side4 ,this fact is made use of in some lightning arresters4 ,generally speaking1 arc lamps are of two kinds1 open and enclosed4 ,the enclosed arc operates at a much higher voltage and is but little used about theaters4 ,the open arc is almost universally used for stage work and this is about the only place where it is still considered useful4 ,this kind of arc lamp is1 however1 very hazardous in localities where inflammable material abounds and for this reason it is always enclosed with wire mesh when possible4 ,lens lamps can be tightly enclosed since none of the light is wanted except that which passes through the lens in front4 ,illustration3 ,,figure #e4 ,illustration3 ,,figure #f4 ,the so-called flood lamps are usually provided with wire gauze in front of the arc1 which prevents the escape of pieces of the electrodes and also prevents parts of scenery1 etc41 from coming in contact with the arc4 ,the lamp houses should be of such dimensions that1 with the highest amperage the lamp is capable of using1 the outer walls will not become excessively hot4 ,illustrations of standard lens and flood lamps1 as made by the ,chicago ,stage ,lighting ,company1 are shown in ,figures #e and #f4 ,operation of ,arc ,lamps4--,from the standpoint of operation1 arc lamps may be divided into two classes1 viz43 hand-feed and automatic-feed4 ,the hand-feed lamp is generally used in theaters and is practically the only kind admitted on the stage1 or for stage illuminating purposes4 ,only a very few houses now use arc lamps for general illumination4 ,the operation of hand-feed lamps#a is ordinarily quite simple and will be fully treated under the head of 8,projection01 so that we may now consider only the automatic lamps4 ,at the present time these are used mostly1 if at all1 for the illumination of the exterior of the theater4 #a ,full diagrams and descriptions are in another work of the authors'1 entitled 8,electricians' ,operating and ,testing ,manual10 so that no space need be given to these here1 save in a very general way4 ,the operator should first familiarize himself with the construction and principles upon which the mechanism of his lamp is based4 ,for this purpose he should remove the outer jacket1 thus exposing the working mechanism2 turn on the current2 and endeavor to learn the significance of each part4 ,it is of course necessary that the operator understand the hazards due to manipulating live wires and that he should be very careful not to make short circuits or grounds which might destroy parts of the lamp4 ,automatic-feed lamps are usually trimmed in the following manner3 ,bring the lamp within reach2 remove the globe2 take out the lower electrode2 let down the upper electrode rod and thoroughly clean it with crocus cloth4 ,this upper electrode rod is the principal thing that concerns the lamp trimmer2 it must be perfectly straight and care must be exercised not to bend it accidentally2 it must be clean so that the clutches may properly grip it2 it must not be greasy4 ,if it grows dirty or greasy1 it will soon become pitted from the current that passes from the contacts to it4 ,the next operation is to remove the upper electrode and place it in the lower electrode holder4 7,the length of electrode necessary should be known4 ,the lower one generally burns out first--it being shorter--and if the arc reaches the lower electrode holder1 will begin to consume it2 if the lower carbon is too long1 the arc is liable to reach the upper electrode holder and destroy it47 ,the upper electrode may then be placed in position and aligned with the lower4 ,to do this it is best to turn it about and try it until it aligns in all positions4 ,the two electrodes should form a straight line1 up and down1 no matter which way the upper is turned4 ,in some forms of enclosed lamps1 the clutch grips the electrode direct4 ,in such a case all of the upper electrode must be carefully examined to see that it is straight and free from burs1 and that it can pass freely into the opening at the top of the inner globe4 ,the successful operation of enclosed arcs depends upon the confinement of the gas in the inner globe4 ,this globe must1 therefore1 be kept as tight as possible without interfering with the operation of the electrodes which pass through it4 ,with enclosed arcs1 the care of the inner globe is of great importance1 because impurities are cast off which soon coat the inner globe and absorb much of the light4 ,the care of the outer globes in general is also an important matter4 ,a dirty globe looks very unsightly and absorbs much light4 ,the following points should be carefully considered in handling and trimming lamps3 7#a7 ,be sure that you understand your system and know whether it is a constant-current or a constant-potential system of distribution4 ,with constant-current systems1 the current is constant and the voltage over the arc is regulated2 while with constant-potential systems1 the voltage is constant and the current through the arc is regulated4 7#b7 ,with constant-current or series lamps1 the line must never be opened1 but must be shunted around the lamp if a lamp is to be cut out4 7#c7 ,with constant-potential lamps1 the lamp must never be shunted but the circuit must be opened4 7#d7 ,in all cases each lamp should be controlled by a double pole switch4 7#e7 ,constant-potential lamps cannot be operated without resistance in the circuit2 this resistance may be in the lamp itself or outside4 7#f7 ,never handle high tension lamps without insulating yourself from the ground2 and handle live wires only with one hand at a time4 7#g7 ,provide spark arresters for all open-arc lamps in the vicinity of inflammable material4 7#h7 ,never leave a lamp without globes where the wind can strike it4 ,it will be blown out or feed often1 thus consuming the electrodes very fast and at the same time yielding a very poor light4 ,green light emitted by the lamp will indicate that the electrode holders are burning4 ,strong shadows cast upwards indicate a lamp burning 8upside down04 ,the positive electrode retains heat longer than the negative4 ,the quality and size of electrodes has much to do with successful operation4 ,always use the kind of electrodes recommended by the maker of the lamp4 ,direct-current arc lamps do not require much in the shape of reflectors as they naturally throw most of the light downward1 when the upper electrode is positive4 ,they should as a rule be suspended high4 ,alternating-current arc lamps throw most of the light from the upper electrode slightly below the horizontal and that from the lower electrode somewhat above4 ,if the light is wanted in a downward direction1 suitable reflectors must be provided4 ,testing of ,arc ,lamps4--,the constant-potential arc lamp is usually designed for a certain current and voltage4 ,the enclosed arcs as a rule operate singly on #aaj volts1 while open arcs are run two in series on the same voltage4 ,in order to test and see that the voltage and current are right1 an ammeter and a voltmeter are needed4 ,the current and voltage can both be adjusted by altering the resistance1 which is always in series with such lamps4 ,to get the correct voltage over the arc1 be sure to connect the voltmeter to the two electrode holders so as to eliminate any other potential drops that may affect the reading4 ,testing ,carbons4--,the color of the light and the steadiness of it can of course only be determined by actual operation tests4 ,the arc obtained by using large electrodes with low current density is liable to rotate around the electrodes1 burn unsteadily1 and flicker4 ,this is due to the fact that the arc tends to establish itself at the point of least resistance4 ,in order that the arc may burn uniformly1 the current density must be great enough to force all of the electrode points into use4 ,as a rule the best electrode is the one that has the longest range from the low voltage point of hissing to the high voltage point of flaming4 ,with such an electrode the greatest range in light can be obtained without either the hissing or the flaming4 ,the same qualities that give an electrode long range1 as above1 also indicate its purity and if we make a test for range1 we shall therefore at the same time make a test for purity4 ,the test for range can be carried out by any ordinary hand-feed lamp4 ,to make it1 the electrodes are inserted and allowed to burn until their points have assumed the proper shape4 ,the arc can then be shortened until the familiar hissing sound is heard4 ,note the voltage at which this occurs1 being careful to have the voltmeter connected so as to get the voltage across the arc only4 ,now separate the electrodes slowly until they begin to flame and note this voltage4 ,ordinarily the hissing voltage will be about #db and the flaming voltage about #fb4 ,the greater the difference between the two1 the better the carbons are assumed to be4 ,in making comparative tests on electrodes in this manner1 care should be taken that all of the conditions of current and size of electrodes be the same4 ,the test for comparative life of electrodes is best made by arranging the different electrodes so that the same current will pass through each for the same length of time4 ,if this is done1 all that is necessary is to weigh the electrodes before and after burning4 ,the approximate useful life of an electrode can be easily determined by burning it for a stated length of time1 noting the length consumed and comparing it with the length available for burning4 ,,chapter ,,iii4 ,,projection4 ,setting and ,adjustment of ,carbons4--,to project a picture upon a screen properly is an art and requires close study and some knowledge of all the factors involved4 ,the most important factor is that of the light4 ,electric light is so universally used at the present time that it is hardly necessary to mention the other sources of illumination4 ,illustration3 ,,figure #g4 ,the electric current with which the operator has to deal may be either alternating or direct1 and the kind is of great importance4 ,the color of the light obtained from a direct-current arc is not only superior to that obtained from an alternating-current arc but is obtained at a much lower cost since1 as we shall presently see1 it is so much more efficient4 ,to project clear white light upon the screen is impossible1 some color will always be in it4 ,but by careful attention and by training himself to notice slight degrees of color1 the operator can learn to render a light which will be clear enough to satisfy the majority of the spectators4 ,in order to obtain this light1 the source from whence it comes should be located exactly in the optical axis of the lens system2 that is1 a straight line drawn through the center of all of the lenses should pass also directly through the center of the arc as indicated in ,figure #g4 7,for comprehensive treatise on lenses1 see ,chapter ,,xii47 ,illustration3 ,,figure #h4 ,illustration3 ,,figure #i4 ,illustration3 ,,figure #aj4 ,illustration3 ,,figure #aa4 ,illustration3 ,,figure #ab4 ,illustration3 ,,figure #ac4 ,most of the light1 we have already seen1 is emitted from the crater of an arc of which there is but one in a direct-current arc and two in an alternating current arc4 ,in order to obtain the most light with the least expenditure of current and heat in the lamp house1 the crater must be formed in such a manner as to face the center of the condensers as nearly as possible4 ,since1 however1 there are always two electrodes and the current must pass from one to the other1 the crater always tends to face the lower electrode if the upper one is positive4 ,it is1 therefore1 impossible to get the full benefit of the light for the condenser2 we must be satisfied with getting a part of it1 and to do this such settings of electrodes as are shown in ,figures #h to #ac are used4 ,about the relative merits of these various settings there is considerable dispute and the best advice that can be given to any new comer in the operating line is to make his own experiments and find out for himself4 ,the fact that a certain point is much disputed1 alone indicates that there is no exact knowledge available2 for we very seldom have any differences of opinion about the things that we can prove4 ,in the operating line very much depends upon the judgment of the operator4 ,electrode setting like that of ,figure #h may be good for an operator who is extremely careful and has a reliable machine which requires a minimum of attention4 ,but it can readily be seen that if the top electrode were fed a trifle too far forward1 the crater would form underneath and the lenses would receive but a small part of the light4 ,each of the settings given has its peculiarities and it is best for any operator who has not done so1 to try them all out and find which one best suits him and his conditions4 ,figures #h to #aj show the settings used with direct-current arcs2 while those illustrated by ,figures #aa to #ac are used with alternating-current arcs4 ,with alternating-current arcs the problem is even more difficult than with direct1 for we have here two craters to deal with2 and if we wish to use the light from both1 we shall have to be very careful about it4 ,if the electrodes are not set exactly right1 we may get a double spot and poor illumination at the center of the screen4 ,perhaps most operators will soon give up the idea of using the light of both craters and will settle down to an electrode setting something like that shown in ,a1 ,figure #g4 ,in this setting both electrodes are angled and the lower one is set a little ahead of the upper4 ,this has a tendency to draw the crater of the upper electrode forward1 thus improving the light on the condenser2 but if this be carried too far1 the lower electrode will obstruct the lower part of the lens4 ,the lower electrode must always be set so that it allows all parts of the condenser to receive direct rays of light from the crater of the upper4 ,the electrode must align perfectly in the vertical plane as shown in ,b1 ,figure #g1 or the arc will move while burning4 ,in order to enable the operator to arrange his electrodes at any angle and to bring them into the center of the optical system1 arc lamps are made up in various ways as illustrated in ,figures #ad to #ai4 ,the simpler types are used only in stage lighting lamps where the centering is not so important4 ,the more elaborate lamps are provided for motion picture arc lamps and allow of all necessary adjustments which are3 feed electrodes2 move lamps forward or back2 up or down2 sideways and angle electrodes4 ,where direct current is used1 the upper electrode must be fed approximately twice as fast as the lower2 but with alternating current1 they both feed at practically the same rate4 ,illustration3 ,,figure #ad4 ,figure #ad shows a form of ,mc,intosh stereopticon lamp4 ,illustration3 ,,figure #ae4 ,figure #ae is a ,kliegl lamp for open arc lamps4 ,illustration3 ,,figure #af4 ,figure #af is an ,edison lamp used for motion picture work4 ,illustration3 ,,figure #ag4 ,figure #ag is a ,kliegl lamp used for focusing purposes4 ,illustration3 ,,figure #ah4 ,figure #ah shows the ,powers lamp4 ,illustration3 ,,figure #ai4 ,figure #ai shows one of the ,motiograph ,company lamps4 ,optical ,system4--,in ,figure #bj we have the complete optical system of the moving picture or stereopticon outfit4 ,the crater of the arc lamp and the center of the objective lens are at the conjugate focal points 7see ,optics7 and must always be in this relation4 ,the size of the picture projected upon the screen is governed entirely by the focal length of the objective lens and the distance of the screen from this lens4 ,the shorter the focal length1 the greater will be the bulging out or rounding of the lens1 and the larger the picture projected4 ,the objective lens is always fitted with an adjusting device of some kind by which it can be moved forward or back a little to focus the picture properly4 ,illustration3 ,,figure #bj4 ,in order to project a picture properly1 it is necessary that the center of the arc or other illuminant1 the center of the condensers1 and the center of the objective1 all fall in one straight line as indicated in ,figure #bj4 ,the condensers are provided for the purpose of gathering and condensing as many of the scattering light rays of the arc lamp as possible and bringing them to bear upon the slide and the objective4 ,the light used must come either from a reasonably small source or from a larger source far enough away so that the rays can be considered as parallel4 ,the focal point for parallel rays would1 however1 differ somewhat from that of a point source and such illumination is seldom used2 in fact1 it is used only where special arrangements are made for it4 ,one of the principal points to be borne in mind in trying to project a good clear picture is to keep the arc down to as small a point as is practicable4 ,a long arc can be tolerated only when it is absolutely impossible to obtain sufficient illumination from a short arc2 as1 for instance1 in operating the ,kinemacolor machines1 in which from #hj to #ajj amperes are used with a very long arc4 ,the above expedient is imperative because the colored discs through which the light must pass absorb a great amount of it and the definition or outline of the picture is apt to be poor4 ,the position of the arc with reference to the condensers is also an important point to consider4 ,the focal length of the condensers determines the point at which the arc must be maintained4 ,the flatter the condensers are1 the farther away the arc may be1 and the less will be the heating2 but this position is accompanied with considerable loss of light4 ,for the purpose of projection we can use only the light which strikes the condensers direct from the arc4 ,rays reflected by the lamp house do not pass through the condensers in the same direction as those coming directly from the crater and will not focus with them4 ,hence1 the farther the arc is from the condensers1 the smaller will be the percentage of light used2 the shorter the focal length of the condensers1 the closer to them must the arc be maintained1 and the greater will be the percentage of light used4 ,but if the light is brought too close1 there will be undue heating of the condensers and these1 especially the one nearest the light1 will be likely to break4 ,so great is the heat produced that sometimes the two lenses are partially melted and welded together4 ,this is a frequent occurrence in cases where very heavy currents are used4 ,it must be recalled that the heat produced is proportional to the square of the current and that other things being equal1 #hj amperes would produce four times the heat of #dj amperes4 ,condenser breakage is quite an important subject and one upon which there is much argument among operators4 ,many of the theories held are1 however1 not plausible enough to merit mention4 ,the principal cause is no doubt overheating without allowing sufficient room for expansion in the setting4 ,no lens should ever be set so that it does not move freely even while it is hot4 ,even if free while cold1 the expansion1 where the heating is great1 may be sufficient to tighten it in the casing1 and this is likely to cause breakage4 ,the best methods of preventing heating are3 a large lamp house well ventilated and condensers of such focal length as to allow the arc to be maintained at some distance from them4 ,drafts of air are often given as the cause of breakage1 but the truth of this is rather problematical4 ,there is no doubt that sudden contraction1 due to rapid cooling1 would have a strong tendency to break them2 but the air in operating rooms is not often cold and is not likely to strike the lens anyway4 ,it must be noted that it is usually the inner lens1 which is ordinarily enclosed1 that breaks4 ,illustration3 ,,figure #ba4 ,in the projection of moving pictures there are two important points that must always be considered4 7#a7 the size of the spot on the gate at which the film appears1 and 7#b7 the clearness of the field or light on the screen4 ,by properly adjusting the arc1 we can make the spot any size we desire2 and the smaller we make it1 so long as it covers the whole aperture1 the brighter the light will be4 ,but if we make this spot too small1 we shall bring in the fringe of color which always appears at the outer edge4 ,color of this kind is objectionable and must be avoided as much as possible2 but it is not necessary to go to extremes4 ,a little coloring will not be noticed by the audience and will therefore not be objectionable4 ,with a given system there will thus be a certain size of spot which gives the best results obtainable4 ,considering that if the spot is increased in size1 the light becomes clearer but also less intense2 and that if the spot is decreased in size1 the light on the screen1 though more brilliant1 is liable to show coloring1 a good operator should practice distinguishing the coloring and make himself as proficient in this art as possible4 ,the customary proportions of spot and aperture are shown in ,figure #ba4 ,coloring appears1 however1 from another cause also1 viz41 improper centering or adjustment of the arc lamp with reference to the condensers4 ,if the arc is not properly adjusted1 bands of color such as are indicated in ,figure #bb may appear in any of the positions shown4 ,this is commonly spoken of as the 8ghost01 and it must be eliminated4 ,it is not possible to get rid of it entirely1 but by a little skill1 patience1 and experience1 it can be reduced to a negligible amount4 ,when the spot is right and the screen clear1 the picture may be focused by adjusting the objective lens4 ,illustration3 ,,figure #bb4 ,to focus sharply1 it is advisable to move the lens in one direction until the picture appears a trifle blurred2 then move it in the opposite direction until at this point there is also a blurred picture4 ,the exact focus will be at a point half way between the two4 ,to focus the lens in this manner is important where the slide or film has some play1 as when the aperture plate on a machine is worn and allows the film some movement4 ,current ,required4--,the measurement of the candle power of arc lamps has never been satisfactorily taken1 and the difficulties encountered in determining it for a projecting arc are especially great because only a small part of the total light can be utilized and this is constantly varying4 ,the light may1 however1 be assumed as proportional to the wattage of the arc1 hence1 we can best judge it by noting the volts and amperes4 ,where a very strong light is desirable1 the arc is usually drawn out to some length2 and as there is a rise in voltage1 with a long arc1 in such a case1 the light increases at a greater rate than the amperage4 ,in ordinary projection work1 the arc is kept quite short because of the better definition obtainable by the use of such an arc2 and we may assume that the light obtained is nearly directly proportional to the amperage4 ,this relation of light and the current input to the lamp will be practically correct1 especially if the size of the electrodes chosen is proportional to the amperage4 ,current ,required for ,projecting4--,the value of the current to be used for projection is a matter of some dispute among operators and probably much of this is caused by the absence of ammeters1 most operators merely guessing at what they are using1 or being guided by markings of rheostats or compensators4 ,in most cases something like #dj amperes seems to be the rule4 ,in order to give the reader a clear understanding of the theoretical requirements1 ,table ,i has been prepared4 ,this table is not intended to act as an accurate guide1 but merely to show the amperage theoretically required with different sized pictures1 to bring about the same illumination in each case4 ,,table ,i4 ,,current ,,required ,,for ,,different ,,size ,,pictures4 ---------------------------------------- --------- ,greatest ,amperes ,dimension ,area ----------------------- of ,picture ,illuminated4 ,direct ,alternating in feet4 ,current4 ,current4 ---------------------------------------- -------- #e #ci #h #ab #f #ef #aa #af #g #gg #ae #bb #h #ajj #bj #cj #i #abg #be #cg #aj #aeg #ca #de #aa #ahi #ch #eg #ab #bbd #de #fg #ac #bfj #eb #gh #ad #cjg #fj #ij ---------------------------------------- -------- ,two errors are very common in the computation of the light intensity for a given picture3 7#a7 the length of throw governs the amperage2 and 7#b7 the amperage depends upon the actual space to be illuminated4 ,apparently only an oblong square of exactly the proportions of the aperture in the machine is illuminated1 but in reality the light must be spread out so that its total illumination covers a circle enclosing the actual visible picture4 ,this is illustrated in ,figure #bc where the enclosed oblong square represents the space illuminated on the screen and the circle represents the area over which the light must be spread4 ,the portion shown by shading is nearly equal to the clear portion and shows that half of the light is wasted since it is blocked out by the cooling plate in the machine or the framework of the slides4 ,with increasing size of picture1 the light is1 however1 diminished in proportion to the area of the circle and not in proportion to the area of the picture4 ,if1 for instance1 the picture were to retain its width and be reduced in height by one half1 or even more1 there would still be about the same quantity of illumination required4 ,for this reason we have1 in ,table ,i1 given only the maximum dimension of the picture and have based the amperage calculation upon the area of the circle which encloses the picture4 ,illustration3 ,,figure #bc4 ,the values given are less than are generally used for small pictures and more than are generally used for large pictures4 ,as a rule much light is wasted on small pictures because the apparatus is at hand to deliver it2 with large pictures1 the illumination is often poor because transformers and rheostats are seldom fitted to deliver more than #fj amperes4 ,much light can easily be wasted if the picture is made too bright4 ,in such a case1 much of the light is reflected back to the auditorium and this in turn makes the picture appear less bright4 ,in determining the amperage necessary to show a picture properly1 the following conditions must be borne in mind1 any one of which may appreciably affect the result3 7#a7 ,nature of ,screen4--,a good screen will reflect more light than a poor one4 7#b7 ,size of ,picture4--,the larger the picture1 the more light will be required4 7#c7 ,character of ,film4--,some films are very dark and require extra illumination4 7#d7 ,house ,illumination4--,in some cities the law requires fairly bright illumination of auditoriums and this makes the picture appear less bright4 7#e7 ,atmosphere4--,where the air is full of dust1 or where smoking is allowed2 much light will be absorbed4 7#f7 ,lenses4--,some lenses are badly discolored and absorb much light4 7#g7 ,electrodes and ,electrode ,setting4--,this is a very important factor and one which a good operator will never neglect4 ,selection of ,lenses4--,upon the proper selection of lenses depends very much the quality of the picture4 ,the size of the picture1 under given circumstances1 depends entirely upon the focal length of the objective4 ,with a given distance between lens and screen there is practically but one size of picture obtainable4 ,if we wish to obtain a picture of another size by the use of the same lens1 this can be done only by sacrificing the definition and had better not be attempted4 ,very large pictures are desirable only in large halls in which portions of the audience are very far from the screen4 ,such a picture requires very much light and1 on account of its size1 shows many imperfections to those who sit in the front rows4 ,it is better to limit the size of the picture to one which can be easily illuminated1 and thus avoid such imperfections4 ,,table ,,ii4 ,,motion ,,picture ,,lenses4 ,,table ,,showing ,,size ,,of ,,screen ,,image ,,when ,,moving-,,picture ,,films ,,are ,,projected4 ,size of ,mat opening #aa-af #ae-af inch4 ---------------------------------------- ----------------- ,e4,e4 #ae #bj #be #cj #ce #dj #de #ej #fj #gj #hj #ij #ajj ,in4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ---------------------------------------- ----------------- #b-a_/h #d4h #f4d #h4j #i4faa4cab4iad4eaf4a #f4e #h4gaa4jac4bae4dag4fai4hbb4j ---------------------------------------- ----------------- #b-a_/b #e4d #f4h #h4b #i4faj4iab4cac4gaf4d #g4d #i4caa4bac4aad4iaf4hah4gbb4d ---------------------------------------- ----------------- #c #d4e #e4g #f4h #h4j #i4aaj4caa4dac4gaf4j #f4b #g4g #i4caj4iab4dad4jae4fah4gba4h ---------------------------------------- ----------------- #c-a_/b #d4i #e4h #f4h #g4h #h4h #i4haa4gac4gae4g #f4f #h4j #i4caj4fab4jac4caf4jah4gba4d ---------------------------------------- ----------------- #d #d4b #e4a #f4j #f4h #g4g #h4eaj4cab4jac4gae4d #e4h #g4j #h4a #i4caj4eaa4fad4jaf4cah4gba4j ---------------------------------------- ----------------- #d-a_/b #d4e #e4c #f4b #f4h #g4g #i4aaj4fab4bac4gae4d #f4b #g4b #h4d #i4caj4eab4dad4eaf4fah4gba4j ---------------------------------------- ----------------- #e #d4h #e4d #f4a #f4h #h4b #i4faj4iab4cac4g #f4e #g4d #h4d #i4caa4bac4jad4iaf4hah4g ---------------------------------------- ----------------- #e-a_/b #d4c #d4i #e4f #f4b #g4d #h4g #i4iaa4bab4d #e4i #f4g #g4f #h4daj4baa4iac4fae4cag4j ---------------------------------------- ----------------- #f #d4e #e4a #e4g #f4h #h4j #i4aaj4caa4d #f4b #g4j #g4g #i4caj4iab4dad4jae4f ---------------------------------------- ----------------- #f-a_/b #d4g #e4b #f4c #g4c #h4d #i4faj4f #f4d #g4a #h4faj4jaa4dac4jad4e ---------------------------------------- ----------------- #g #d4d #d4i #e4h #f4h #g4h #h4h #i4h #f4j #f4f #h4j #i4caj4fab4jac4c ---------------------------------------- ----------------- #g-a_/b #d4e #e4d #f4d #g4c #h4b #i4a #f4b #g4d #h4gaj4jaa4bab4c ---------------------------------------- ----------------- #h #e4a #f4j #f4h #g4g #h4e #g4j #h4a #i4caj4eaa4f ---------------------------------------- ----------------- ,example3 ,with a lens of #e-a_/b inch focus at a distance of #ce ft4 the screen image will be #d4ce4i2 at #dj ft41 #d4if4g2 at #de ft41 #e4fg4f2 etc4 ,note3 ,when ordering lenses1 give size of picture wanted1 and distance from machine to screen4 ,,table ,,iii4 ,,stereopticon ,,lenses4 ,,table ,,showing ,,size ,,of ,,screen ,,image ,,when ,,lantern ,,slides ,,are ,,projected4 ,size of ,mat opening #b-c_/d #c inches4 ---------------------------------------- ----------------- ,e4,f4 #ae #bj #be #cj #ce #dj #de #ej #fj #gj #hj #ij #ajj ,in4 ft4 ft4 ft4 ft ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ft4 ---------------------------------------- ----------------- #e #h4jaj4hac4eaf4cai4j #h4haa4had4hag4hbj4h ---------------------------------------- ----------------- #e-a_/bg4c #i4hab4cad4hag4cai4h #g4iaj4gac4daf4aah4hba4f ---------------------------------------- ----------------- #f #f4f #h4iaa4bac4eae4hah4abj4d #g4c #i4hab4cad4hag4cai4hbb4c ---------------------------------------- ----------------- #f-a_/bf4a #h4baj4dab4ead4faf4gah4h #f4g #i4jaa4cac4fae4iah4bbj4e ---------------------------------------- ----------------- #g #e4g #g4f #i4faa4fac4eae4eag4eai4d #f4b #h4caj4eab4fad4haf4iai4jba4b ---------------------------------------- ---------------- #g-a_/be4c #g4a #h4iaj4hab4fad4daf4cah4a #e4h #g4h #i4haa4hac4hae4hag4hai4h ---------------------------------------- ----------------- #h #f4f #h4daj4aaa4hac4eae4bag4jbj4d #g4c #i4aaa4jab4iad4haf4fah4ebb4c ---------------------------------------- ----------------- #h-a_/b #f4b #g4i #i4eaa4aab4gad4caf4jai4b #f4h #h4faj4cab4aac4iae4fag4dbj4i ---------------------------------------- ----------------- #i #e4i #g4d #h4iaj4eab4jac4eae4aah4aba4a #f4d #h4a #i4haa4dac4aad4haf4dai4hbc4a ---------------------------------------- ----------------- #i-a_/b #e4f #g4j #h4e #i4iaa4dab4had4bag4abj4j #f4a #g4f #i4baj4hab4dad4jae4eah4gba4i ---------------------------------------- ----------------- #aj #e4c #f4f #h4j #i4daj4hab4bac4eaf4cai4jba4h #e4h #g4c #h4haj4caa4hac4cad4hag4hbj4hbc4h ---------------------------------------- ----------------- #ab #e4e #f4f #g4h #h4iaj4aaa4bac4eae4hah4abj4d #f4j #g4c #h4e #i4haa4jab4cad4hag4cai4hbb4c ---------------------------------------- ----------------- #ad #e4f #f4f #g4f #h4f #i4faa4fac4eae4eag4eai4d #f4b #g4c #h4c #i4daj4eab4fad4haf4iai4jba4b ---------------------------------------- ----------------- #af #e4h #f4f #g4e #h4daj4aaa4hab4eae4bag4j #f4c #g4c #h4b #i4aaa4jab4iad4haf4fah4e ---------------------------------------- ----------------- #ah #e4a #e4i #f4f #g4d #h4iaj4eab4jac4eae4a #e4f #f4d #g4c #h4a #i4haa4dac4aad4haf4d ---------------------------------------- ----------------- #bj #e4c #f4j #f4f #h4j #i4daj4hab4bac4e #e4h #f4e #g4c #h4haj4caa4hac4cad4h ---------------------------------------- ----------------- #bb #e4d #f4j #g4c #h4e #i4haa4jab4c #e4i #f4f #g4i #i4caj4gab4jac4d ---------------------------------------- ----------------- #bd #e4e #f4f #g4h #h4iaj4aaa4b #f4j #g4c #h4e #i4haa4jab4c ---------------------------------------- ----------------- ,example3 ,with lens of #aj-;inch focus at a distance of #bj ft4 the screen image will be #e4ce4h2 at #be ft41 #f4fg4c2 at #cj ft41 #h4jh4h2 at #ej ft41 #ac4ead4h42 etc4 ,table ,,ii shows the size of picture obtainable from films1 and ,table ,,iii1 the size obtainable from lantern slides4 ,since the slide pictures must be shown upon the same screen as the film1 it can be seen from the tables that lenses of different focal length must be used for the two4 ,the aim should be to get the two pictures to match as nearly as possible1 but as they are not of the same proportions1 it is impossible to match them exactly in both directions4 ,the nearest approximation that can be brought about by standard lenses is illustrated in ,figure #bd4 ,the heavy lines show the dimension of the picture projected through the film1 and the light and dotted lines show the dimensions obtainable by the use of slides4 ,if the slide picture is matched to the height of the film1 it will be considerably narrower2 if it is matched to the sides1 it will be considerably higher4 ,it would of course be possible to trim down slides so that the dimensions of the two pictures would be exactly alike2 but as most all stereopticon slides belong to traveling actors this is not practicable4 ,illustration3 ,,figure #bd4 ,if the focal length of a lens is not known1 it can easily be measured by focusing some distant object1 an incandescent lamp for instance1 against the wall of a room or against some screen placed upon a table as shown in ,figure #be4 ,in the case of a single plano-convex lens1 the measurements must be made from both sides--first one side turned toward the light1 and then the other4 ,there will always be some difference between the two measurements and we must take the mean of the two4 ,to get the measurement accurately1 place a rule upon a table and set up some suitable object upon which the picture can be projected4 ,turn the flat side of the lens toward the screen and focus some distant object by moving the lens to a point at which the object selected will appear clearly upon the screen4 ,note the distance of the flat side of the lens from the picture4 ,now turn the lens half way around and focus again in the same manner1 noting this distance also4 ,add the two measurements and divide by two2 this will give the focal length of the lens4 ,in the case of an objective lens1 we must turn the side which bulges out most toward the screen and focus in the same manner4 ,illustration3 ,,figure #be4 ,with the objective lens we have two possible focal lengths to consider4 ,if we measure from the center of the lens to the screen1 we shall obtain what is called the equivalent focal length 7usually abbreviated ,e4,f4 or e4f474 ,if1 instead1 we take measurements from the face of the lens nearest the screen1 we shall obtain what is termed the back focus1 or b4f41 of the lens4 ,in all cases it is important1 when ordering1 to state which of the two is meant4 ,lenses may also be tested for chromatic and spherical aberration4 ,chromatic aberration is the fault of showing colors unduly4 ,it is impossible to avoid a fringe of color when using only a single lens1 but where we have a complete optical system1 consisting of two condensers and an objective1 it must be possible to adjust the combination so that practically no color is visible4 ,spherical aberration is best tested for by laying out very accurately1 as in ,figure #bf1 a set of small squares upon some material that will not be damaged by the heat of the lamp--mica for instance--and projecting this upon the screen4 ,if the lenses are all good1 the lines will all appear square2 if the lenses are poor1 the lines will appear curved a little1 or perhaps considerably4 ,illustration3 ,,figure #bf4 ,the diameter of the ordinary condenser lens is #d-a_/b inches4 ,smaller lenses than this cannot well be used because they would not cover the diagonal of lantern slides4 ,a very common focal length of condenser is #f-a_/b inches4 ,there is no very accurate relation necessary between the focal length of condenser and objective4 ,there is considerable difference of opinion on this subject and much of it is induced by the possibility of condenser breakage which is increased by using condensers of short focal length1 but in this case1 as in many others1 the operator must find out by his own experiments4 ,a very good plan--since1 on account of breakage1 extra lenses must be carried anyway--is to carry two #g-a_/b-;inch and two #f-a_/b-;inch condensers and experiment with these4 ,the two of the same diameters may be tried together and also those of different focal lengths1 using the one of shorter focal length either in front of or behind the other4 ,,hints ,,on ,,management ,,of ,,projecting ,,arcs4 ,before starting to work about the lamp1 be sure the switch is off4 ,see that the lamp house is clean and spark tight4 ,the gauze provided at the top must be kept free from dirt and carbon ash1 or the house itself may get too hot4 ,the house should be of such dimensions1 relative to the length of electrodes used1 that the latter cannot touch either at the top or bottom and thus ground the circuit on the lamp house and possibly burn a hole in it4 ,see that your lamp mechanism is well aligned so that electrodes center at all positions4 ,all of the screws and adjustments should be well lubricated frequently4 ,the heat in the lamp house soon evaporates all lubrication4 ,where lamps are used much and carry heavy currents1 the leading in wires will probably need reconnecting about once a week4 ,it is best to reconnect them some time before they burn off rather than be obliged to do this during a show4 ,see that your polarity is right4 ,with direct current1 the upper electrode will retain its heat longer than the lower if connections are made properly4 ,with alternating current the polarity is immaterial4 ,always point your electrodes1 especially the lower4 ,if the lower electrode is not pointed1 it will interfere with the light of the crater4 ,the recommendations for sizes of upper and lower electrodes vary somewhat but run mostly to #e_/h inch for upper and #a_/b inch for lower4 ,the size depends very much upon the current used4 ,if the electrodes are too large1 the arc will travel around the outside and yield a poor and uneven light4 ,always use cored carbons for alternating current4 ,the best length for electrodes is about #f inches1 if they do not strike the lamp house4 ,notch the carbon electrode a little before attempting to break it off4 ,many operators are in the habit of watching the arc1 opening the lamp-house door to look at it4 ,not only is this injurious to the eyes but it also interferes with proper judgment of the illumination of the picture4 ,a better way is to punch a very small hole in the lamp house exactly opposite the arc4 ,over this opening a lens may be placed1 and a picture of the arc may be thrown against a wall or screen set up for that purpose4 ,a picture of the arc is also obtainable in another way3 ,if the lamp is once set exactly right1 a cross may be painted at the proper place on the screen which will indicate the exact point where the arc should be maintained4 ,the arc will of course appear inverted4 ,another method of keeping the arc always in view without inconvenience consists in arranging a small mirror1 at an angle to the peep glass in the door1 so that it will reflect the arc towards the operator4 ,an adjustable resistance should always be kept in reach so that the current may be varied to suit different films or stereopticon lamps4 ,keep your hands as free from carbon dust as possible4 ,this dust is responsible for much damage to films4 ,,chapter ,,iv4 ,,motion ,,pictures4 ,strictly speaking there are no pictures of motion4 ,what we see as such is simply an optical illusion4 ,this illusion is produced by presenting a series of pictures of an object in a systematic manner1 each picture showing some slight change from the preceding one4 ,if these changes be all in a certain direction and brought before our eyes in regular order1 we shall perceive the appearance of motion in that direction4 ,such pictures may be made by means of photography4 ,a very simple form of motion picture is made up in the form of a small book containing a number of leaves that may be run off under the finger of the holder4 ,if these leaves contain such a series of pictures as is mentioned above1 the holder1 on manipulating them properly1 will see motion reproduced quite naturally4 ,the manner in which the illusion of motion is produced can perhaps best be illustrated by ,figure #bg4 ,here we have an ordinary film1 or it may be any piece of white paper1 upon which are drawn a series of black dots as shown4 ,if this film--the observer being able to see only that part in the aperture ,a--be drawn downward the length of one section very quickly2 allowed to rest a moment2 then1 in the same manner1 be drawn down another section2 and this process repeated at proper speed1 until the full length of the film has passed the aperture1 we shall have received the impression that the black dot moved from the lower left-hand corner to the upper right-hand corner of the aperture4 ,in order that such an illusion might be perfect1 we should have to move the film so rapidly that the eye would not perceive the movement4 ,this is not possible except with very weak illumination and we should actually1 in the above experiment1 receive a blurred impression1 because we could not help seeing the dots while they were moving1 and our eyes would behold a mixture of stationary and moving dots4 ,in order to produce the impression of perfect motion1 it is necessary to shut off the light during the time that the film is actually in motion4 ,thus1 paradoxical as it may seem1 in order to simulate motion1 we must have the object which is to appear in motion always perfectly still before our eyes4 ,illustration3 ,,figure #bg4 ,in order that we may not notice that the film is out of sight1 it must be moved very quickly4 ,the actual time during which the picture on the average film is hidden from view1 and in which the picture is changed1 is about #a_/hjth of a second and the time during which the picture is stationary is about #d_/hjth of a second4 ,the possibility of the illusion of motion pictures depends upon a faculty of the eye known as persistence of vision4 ,the eye retains an impression for something like #a_/beth of a second4 ,when an object is in motion1 we see1 therefore1 not only one position of the object but all positions of it during the time of persistence of vision4 ,this time varies somewhat with the intensity of the light or the impression made upon the eye4 ,if it is equal to #a_/beth of a second in the case of a ball thrown at the rate of one hundred feet per second1 then we should see1 instead of one ball1 a large number of balls merging imperceptibly into one another1 or1 in other words1 a streak of balls four feet long4 ,thus1 in actual life1 we obtain from the moving ball but a blurred impression4 ,we see thus that in order to produce the impression of motion1 we must present the picture to the eye long enough to stimulate it properly2 we must very quickly remove that picture and substitute another differing to a slight extent from the former2 and we must repeat this process a number of times4 ,the ordinary moving picture film contains #af pictures per foot1 and is run off at the rate of about #fj feet per minute1 so that in one minute1 we see #ifj different pictures4 ,in order to make motion visible1 we must bring it within a certain speed limit4 ,thus1 to show the motion of a swiftly thrown ball in detail1 we must make it appear to move more slowly than it really does2 and to show the development of a growing plant1 it must appear to grow much faster than it actually does4 ,both of these requirements can easily be fulfilled by the motion picture camera and the projecting machine4 ,a man1 walking at the rate of three miles an hour1 displaces himself about three inches during the time of the exposure of one picture1 or #a_/afth of a second4 ,at this rate we obtain the impression of even and continuous motion unless he be too close to the camera4 ,in order to obtain pictures of other objects moving at faster or slower rates1 we must take them at intervals in order that the displacement between pictures will be about the same or at least not any more4 ,this means that pictures of rapidly moving objects must be taken at short intervals and those of slowly moving objects1 at long intervals4 ,a kernel of corn develops into a stalk six feet high in about ninety days4 ,if a photograph of this is taken every day during its growth and these pictures arranged in proper order1 they will be run off at normal speed in less than six seconds1 thus showing us in six seconds the growth which actually takes place in ninety days4 ,the motion picture camera enables us not only to produce the illusion of motion1 but to see in detail what actually takes place in connection with the moving object at any instant4 ,if we take pictures of a running horse1 for instance1 at short enough intervals1 we shall be able to see1 on the films1 just how he holds or places his feet or any other part of his body at any time4 ,in order to obtain a perfect picture simulating motion1 we must present the first picture long enough to stimulate the eye2 then we must shut off the light1 remove the first picture1 and substitute the second2 remove the second and substitute the third1 etc41 as long as desired4 ,during the time that the light is shut off1 the first picture must persist in our vision until the new one has appeared4 ,the two pictures thus mix until the first one has faded1 and thus we obtain the illusion of motion4 ,if the bright picture remains too long1 the pupil contracts--as explained in the chapter on ,optics--and when next the light is shut off1 the darkness is noticeable and gives rise to the disagreeable phenomenon of flicker4 ,in order to prevent this over-stimulation of the eye1 the long period of exposure is interrupted by a shutter at least once and1 in some cases1 two times2 and some machines are equipped with a three-blade shutter4 ,this three-blade shutter has a wide blade which shuts off the light while the film is in motion and two narrower blades which pass across the light during the time that the film is stationary1 to prevent the over-stimulation of the eye4 ,colored ,pictures4--,there are two general methods of producing colored motion pictures3 ,one is that of hand coloring or tinting1 and the other is what is known as the ,kinemacolor process4 ,in the latter process1 no color whatever is used on the film2 the coloring is supplied by a shutter with a green and a red blade which are alternately thrust into the light by which the picture is projected upon the screen4 ,in order that this process may be used1 the film pictures must first be taken through screens of corresponding color4 ,the film in the ,kinemacolor camera1 or projecting machine1 must run at more than double the speed of that which is used in the ordinary process2 and each alternate picture must be photographed through a red screen2 the others1 through a green screen4 ,the red screen will allow only red light to pass2 hence1 any part of an object that contains no red will not affect the photographic emulsion4 ,similarly1 the green screen will allow only green light to pass2 and such parts of the objects as contain no green will not affect the emulsion4 ,the alternate sections of film will thus be entirely different from each other4 ,in order to reproduce the original color of the object upon the screen1 it is but necessary to arrange that the pictures shall in turn be projected through the same or similar color screens4 ,in order to accomplish this1 the ,kinemacolor machine has1 in addition to the regular shutter which cuts off the light during the time the film is in motion1 an additional two-wing shutter which inserts the properly colored screens before each picture1 as it comes to a standstill in the film window4 ,thus we see in alternation1 a red picture and a green4 ,persistence of vision1 which is explained in ,chapter ,,ix1 helps us to mix the two colors and we see the object approximately in its own colors4 ,the color effect is not very good1 owing partly to the fact that only two colors are used4 ,if the three primary colors--red1 blue1 and yellow--could be used1 the effect would doubtless be better2 but the complications would be multiplied4 ,in order to get the best results with the ,kinemacolor process1 colors of a certain shade are used and the size and depth of coloring in the two shutters is variable4 ,one of the colors is adjustable and must be so arranged that when the machine is run without film1 it will throw approximately white light upon the screen4 ,the high speed with which the film must be run makes it impossible to turn the machine by hand and it is always motor-driven4 ,the colored shutters are constantly in the light and absorb a large portion of it and this must be compensated for by an extraordinary high amperage4 ,this process requires more than two times as much current as the ordinary projection of black and white pictures4 ,in order to obtain the greatest possible amount of light1 operators usually run a very long arc and this often results in imperfect definition4 ,in arranging for an exhibition1 it is important that the film and the colored screens be correctly placed with reference to each other2 to facilitate this1 an identifying mark is placed on the side of one of the colors4 ,,chapter ,v4 ,,the ,,motion-,,picture ,,machine4 ,a diagrammatic sketch of the essentials of a good motion picture machine is given in ,figure #bh4 ,this does not represent any machine in particular and no machine exactly like it will be found2 it does1 however1 show the theoretical elements necessary to the projection of motion pictures and the usual safety devices with which standard machines are provided4 ,as a variation from ,figure #bh1 the exact method of threading the film through the ,edison machine is given in ,figure #bi4 ,in ,figure #bh1 the parts are designated as follows3 ,a--feed reel or upper reel ,b--feed reel magazine or upper magazine ,c--magazine fire traps1 or film valves1 or fire valves ,d--upper steady-feed sprocket ,e--presser rollers1 or friction rollers1 or idlers ,f--upper feed loop or upper loop ,g--film-steady drum or film steadier ,h--film gate ,i--tension spring ,j--automatic fire shutter ,k--revolving shutter ,l--intermittent sprocket ,m--lower feed loop ,n--lower steady-feed sprocket ,o--take-up reel and lower magazine ,p--framing device or adjusting lever 7not shown7 ,q--film shields ,illustration3 ,,figure #bh4 ,illustration3 ,,figure #bi4 ,in addition to the above1 there are the gearing and the belting which transmit motion to the various sprockets and drums shown4 ,the whole function of the machine1 however1 is the proper moving of the film along the lines indicated in the figure1 the heavy black line representing the film4 ,the film is unwound from the upper reel by the upper steady feed sprocket ,d4 ,after forming the upper loop ,f1 it passes over ,g1 through the film gate ,h1 to the intermittent sprocket ,l4 ,this sprocket moves the film by an intermittent motion allowing the film to remain stationary in the light for about four-eightieths of a second and shifting it during about one-eightieth of a second4 ,after leaving the intermittent sprocket1 the film forms the lower loop and then passes to the lower steady feed sprocket1 which prevents the take-up from pulling the loop away from the intermittent sprocket4 ,the object of the upper and lower loops is to lighten the work of the intermittent sprocket as much as possible by making it unnecessary to move anything but the film between the two loops4 ,illustration3 ,,figure #cj4 ,all of the sprockets and the shutter ,k are connected together by a train of gears 7see ,figure #cj1 which is the gearing of the ,motiograph machine7 and when properly adjusted they all work in proper relation to each other4 ,the upper steady-feed sprocket feeds just as much film into the upper loop as the intermittent sprocket takes away2 while the lower steady-feed sprocket takes away just as much as the intermittent sprocket feeds to it4 ,the film is unwound from the upper reel and rewound upon the lower2 but before it is used again1 it must be rewound from the lower reel upon another one4 ,if it were to be exhibited from the lower reel without this rewinding1 the pictures would be exhibited backwards4 ,,discussion ,,of ,,parts4 ,a--,upper1 or ,feed ,reel4--,the feed reel is usually either #aj or #ab inches in diameter4 ,a #aj-;inch reel accommodates #a1jjj feet of film and a #ab-;inch reel1 about #b1jjj feet4 ,the reel fits loosely upon bearings in the upper magazine and the film is unwound from the reel1 which revolves1 by the upper steady-feed sprocket4 ,to prevent its unwinding more film than is wanted1 a small spring is arranged to cause a slight friction4 ,it is best to keep good reels in the operating room for use as feed reels4 ,a reel to be used for this purpose should be perfectly true and in good order2 reels sent out from the exchanges are often bent or have loose parts which cause trouble4 ,a good operator will keep a supply of good reels always on hand4 ,b--,upper ,magazine4--,the upper magazine is a steel box made up without solder and fitted with a steel door on the crank side of the machine4 ,it exists for the purpose of protecting the film against fire or injury from other causes4 ,it is important that the door be kept closed for1 without this precaution1 there is no fire protection4 ,in some cities1 it is required that the door be provided with spring hinges to keep it closed1 but it is doubtful whether this is a wise provision2 for since the door must be opened to change films and since there is nearly always great haste in making the change1 it is likely that the operator will block the door open if the spring hinges interfere with him4 ,all doors now swing to the side1 but it seems as though it would be a great improvement if the doors were arranged to drop down4 ,the door would then1 even if open1 prevent fire from below reaching the film4 ,the magazine might as well be entirely missing as to be left with the side-swinging door open4 ,many operators have the habit of opening the door to watch the progress of the reel instead of noting it on the screen1 or of preparing for a change of reel by opening the door long before necessary and starting the new run before closing the doors4 ,needless to say1 this is highly reprehensible4 ,in order to put out a fire in case it should communicate to the reel1 the magazines have been connected with water piping and a valve so arranged that the water could be turned on instantly thus filling the magazines4 ,if the door of the magazine is kept closed1 the progress of a fire will be comparatively slow4 ,c--,fire ,traps4--,the fire traps are an important adjunct4 ,their object is to prevent fire1 which often occurs at the aperture1 from reaching the film on the reel4 ,all of the various makes of fire traps have been tested and will ordinarily prevent fire from passing through them4 ,the larger the roller and the smaller the space around the film1 the better the traps seem to be4 ,the metal of the rollers has a cooling effect upon the flame and this is undoubtedly one reason why they do their work so well4 ,none of them1 however1 is absolutely sure4 ,if the opening through which the film passes is made too narrow1 the film is likely to brush one side or the other and wear grooves in it1 or cut entirely through it1 with the result that a splice may be caught in the opening and the film torn4 ,fire traps1 cut in this manner1 have been the cause of many fires4 ,this trouble is due mainly to improper alignment of the magazine with the fire traps4 ,examine them often and1 if the least wear shows1 improve the alignment4 ,it is advisable that every operator test his traps with pieces of film and assure himself that they will not1 under ordinary circumstances1 carry fire2 but he must never rely too much upon them as safeguards1 for although they will check a small blaze1 such as would result from the burning of a few inches of film1 they would probably not extinguish a fire occurring when there was much film crowded around them1 as might be the case when a take-up reel or the intermittent sprocket failed to work4 ,if the film catches fire and there is any possible chance to do so1 the operator should tear it off at the upper and lower magazines1 and thus break the communication4 ,but if there happens to be a lot of film lying loosely about1 it is advisable for the operator to get away as quick as possible4 ,d--,upper ,steady-,feed ,sprocket4--,the office of the upper steady-feed sprocket is to unwind the film from the reel and feed it toward the intermittent sprocket4 ,in order that it may do its work well and relieve the intermittent sprocket of all unnecessary strain1 there must be a loop ,f4 ,the upper steady-feed sprocket is in continual steady motion and feeds just as much film to the loop as the intermittent sprocket takes from it by periodical jerks4 ,the main trouble with all sprockets is in the wear of the teeth1 as in time they wear away near the body of the sprocket and form hooks4 ,the best sprockets have a number of teeth to engage the film4 ,in some of the older machines1 only two teeth catch the film1 in which case1 if two holes in the film are torn out1 the film may stand still4 ,e--,presser or ,friction ,rollers4--,the presser or friction rollers exist merely to hold the film in its proper place4 ,they are sometimes spoken of as friction rollers although they have nothing to do with friction4 ,f--,upper ,loop4--,the upper loop is provided for the purpose of storing slack film which the intermittent sprocket may pull away with a very rapid jerk4 ,it avoids placing unnecessary strain upon the film4 ,the upper loop often causes trouble by enlarging2 this occurs when the intermittent sprocket fails to work while the steady sprocket continues to feed4 ,the most frequent cause of this is due to faulty films4 ,in order to prevent the excess film in the upper loop from falling over in front of the light of the arc lamp 7which would quickly set it on fire71 the film shields ,q are provided4 ,in many machines they are too short or too narrow to be of much use4 ,g--,film-,steady ,drum1 or ,film ,steadier4--,the film steadier is not found in all machines4 ,if the upper portion of the machine head is properly arranged1 the film may feed directly into the gate4 ,h--,film ,gate4--,the film gate is to hold the film in position4 ,in order that the picture may be properly projected1 the film must lie perfectly flat and at a fixed distance from the lenses4 ,if this distance varies1 there will be improper focusing of the picture4 ,the film must also be held in its proper position laterally and vertically4 ,the film gate has nothing to do with the height of the film4 ,this is taken care of by the framing device4 ,the film gate wears quite rapidly and when badly worn allows the film too much play4 ,in order to avoid the wobbling of the picture1 a new gate must be provided4 ,there should be considerable metal surrounding the aperture and there should also be an air space and some little ventilation4 ,the metal surrounding the gate is subject to the heat from the arc lamp rays and1 unless properly constructed1 may overheat and damage the tension springs1 if it does not set fire to the film4 ,i--,tension ,springs4--,the tension springs are provided to hold the film flat against the film gate and also to check its motion as soon as the intermittent sprocket has stopped pulling it4 ,a certain intermittent movement is advertised to make the change from one picture to another in #a_/if of a second at normal operating speed4 ,the film moved at this rate of speed acquires considerable momentum2 and the office of the tension spring is to bring it to rest as quickly as possible4 ,if the springs are set too tight1 they will cause the machine to run hard and may also be the cause of tearing out splices4 ,they should be set just tight enough to keep the picture steady2 anything beyond this will merely cause unnecessary wear of the parts1 besides calling for unnecessary exertions on the part of the operator4 ,j--,automatic ,fire ,shutter4--,the automatic fire shutter is provided for the purpose of shutting off the light when the machine is not in motion4 ,it is required by most city ordinances4 ,the ideal fire shutter would be one so controlled by the film that it would remain up only while the film is moving at operating speed4 ,the shutters in use at the present time vary widely in details of construction4 ,some of them are raised and admit the light to the film the instant the handle is pressed sufficiently to start the machine4 ,other types are raised only after the machine has nearly attained its proper speed4 ,some operate as indicated in the figure and others operate from the side4 ,all of them are liable to become deranged at times1 and it is no unusual thing to find them tied up in some way because they failed to work properly4 ,the shutter is a great convenience when in proper order and has probably prevented many fires2 but it is good practice to consider it as entirely absent and not get into the habit of relying upon it4 ,the operator should always push his lamp to the side whenever anything is out of order4 ,this act is necessary in most houses at the end of every run of film showing stereopticon slides4 ,it would inconvenience the operator but little to do this at all times1 and then the habit would be formed and become second nature4 ,on the machines now in use1 there is no automatic shutter governed by the action of the film1 which would give protection in case the film should come to rest1 as old films often do when their sprocket holes are torn out1 or1 as often happens1 when the film splits along the row of holes4 ,in some machines the fire shutter is made up of such thin material and rests so close to the film that the light may heat it sufficiently to fire the film below it4 ,pieces of film often become detached at the aperture and remain in the light long enough to be ignited4 ,against such occurrences as these there is no protection whatever except the watchfulness of the operator4 ,if the film fits snugly into the gate and is well enclosed1 such fires do not usually spread4 ,k--,the ,revolving ,shutter4--,the revolving shutter is sometimes arranged in front of the machine and often between the film and the lenses4 ,the shutter ,k is of the 8barrel0 type and is further illustrated in ,figure #ca at the left4 ,the object of the shutter is to shut off the light during the time that the film is in motion so that the impressions made upon the eye by the succession of stationary pictures may not be blurred by the motion of the film when it is changed4 ,the ideal shutter is one that shuts the light off instantly and1 at the expiration of the necessary time1 allows it as quickly to come to view again4 ,the barrel-type shutter allows the light to pass through while it is in the position shown by solid lines1 ,figure #ca1 and has it entirely shut off when in the position indicated by broken lines4 ,when it is in motion1 the upper wing begins to shut off the light from the top and the lower from the bottom1 thus causing the total eclipse of light in one-half of the time that a single wing shutter could do it4 ,illustration3 ,,figure #ca4 ,at the right of ,figure #ca1 we have a cone shutter such as is used in the ,motiograph4 ,the stem and gearing of this shutter are set at an angle of forty-five degrees to the rays of light1 for the purpose of arranging them inside of the mechanism without taking up too much room4 ,there are two cones of the kind illustrated in ,figures #cb and #cc and they move in opposite directions1 thus shutting off the light in about the same time that a barrel shutter could be made to do it4 ,these two figures show the positions of wings just before shutting off the last vestige of light and just as they are beginning to admit it again4 ,illustration3 ,,figure #cb4 ,illustration3 ,,figure #cc4 ,the disk type of shutter is much used4 ,it may have either one1 two1 or three blades and may also be double1 i4e41 two disks revolving in opposite directions so as to shut off the light from two sides of the opening at once4 ,three types of disk shutters are shown in ,figures #cd to #cf4 ,in order to obtain a flickerless picture1 it is necessary to cut off the light not only during the time that the film is in motion1 but also during part of the time that it is standing still4 ,if the light were not interrupted during the time of exposure1 the light interval would be so long that the difference between the dark period1 when it is shut off entirely1 and the light period would be great enough to be noticed in the form of a flicker4 ,illustration3 ,,figure #cd4 ,illustration3 ,,figure #ce4 ,illustration3 ,,figure #cf4 ,if a single-blade shutter is used1 it must make two revolutions during the time that a single picture is exposed2 once to shut off the light while the film is being moved and once to interrupt the period of illumination4 ,this shutter would thus have to run twice as fast as the two- or three-blade shutter1 the three-blade shutter interrupting the light twice during the time the film is standing still4 ,the three-blade shutter has one wide blade which must be in front of the light while the film is moving and two narrower ones which interrupt the light during the time of exposure4 ,the two-blade shutter must have both blades of the same size and run one and one-half times as fast as the three-blade shutter to obtain the same effect1 i4e41 cause two interruptions of light during the time of exposure4 ,in order to shut the light off very rapidly with a blade1 which approaches the opening from one side only1 the disk shutter must be of sufficient size to produce great angular velocity4 ,it can not well be used1 therefore1 inside of the mechanism1 but is usually placed in front of the machine2 and it is much larger than the aperture which it must cover4 ,the shutters must all be set so as to shut off the light during the time that the film is in motion4 ,when the dividing line between two film pictures is in the center of the aperture1 the shutter should have it entirely covered4 ,it is possible1 however1 to arrange the shutter so that the film may move a trifle before the light is shut off and continue in motion also for a very short time after the light is again admitted4 ,this is practicable with the 8,geneva0 intermittent movement which starts and stops the film gradually4 ,a shutter should be adapted to the speed of the film movement4 ,there is no need of keeping the film covered any longer than it is in motion4 ,a quick film movement and a narrow shutter will add considerably to the light obtained from a given lamp and a given current consumption4 ,if the shutter is not properly adjusted1 there will be what is known as 8travel ghost01 8light rain01 or 8halo04 ,these are due to the improper timing of the shutter1 allowing a part of the picture to be seen while in motion4 ,the travel ghost may be seen either at the top or the bottom1 according to whether the shutter is set too fast or too slow4 ,illustration3 ,,figure #cg4 ,illustration3 ,,figure #ch4 ,l--,intermittent ,sprocket4--,the intermittent sprocket is a very important part of the machine4 ,owing to the swiftness with which it strikes the film1 the teeth on it are more subject to wear than those on the other sprockets4 ,the number of teeth that engage the film is also an important item4 ,in order to obtain the best picture with the least expenditure of light1 the film should be moved very rapidly so as to allow the greatest possible length of time for the stationary picture4 ,the film should1 furthermore1 be started slowly2 then increased in speed2 and the speed should decrease gradually until brought to rest1 and thus avoid unnecessary jerking4 ,it is also necessary to prevent all motion of the film during the time the mechanism which moves it is preparing for the next succeeding movement4 ,all of these conditions are admirably fulfilled by the 8,geneva0 movement1 ,figure #cg4 ,the pin wheel ,w is in continuous motion and the pin is so placed upon it that it enters one slot of the cross and carries it along with it1 thus causing a quarter revolution of the cross each time the pin wheel makes one revolution4 ,the cam band ,p is cut away sufficiently to allow the cross to make a quarter revolution1 but the remaining portion of it is made to fit the cross snugly1 so that when the cross is not in motion it is held rigid4 ,figure #cg shows the movement just starting and ,figure #ch shows it half completed4 ,it can be seen that the motion begins very slowly2 comes to a maximum when it is in the middle2 and ends slowly2 thus subjecting the film to the least possible strain4 ,this movement is widely used and may be arranged with one pin1 as shown1 or with two4 ,if the pin wheel is equipped with two pins1 it will move only half as fast as with one pin and thus the proportionate time that the film is in motion will be lengthened4 ,by making the pin wheel large as compared with the cross or star1 the time during which the motion takes place can be reduced as much as desired2 but the characteristic feature of starting and stopping the film gradually will be lost directly in proportion as the relative size of the pin wheel is increased4 ,illustration3 ,,figure #ci4 ,the 8,geneva0 movement requires extremely accurate construction and careful management4 ,if dusty or insufficiently lubricated1 it wears very rapidly4 ,it is often arranged so that it can be immersed in oil while running4 ,figure #ci shows a practical application of the 8,geneva0 as used in the ,motiograph4 ,the cover shown at the right entirely encloses it4 ,illustration3 ,,figure #dj4 ,illustration3 ,,figure #da4 ,illustration3 ,,figure #db4 ,illustration3 ,,figure #dc4 ,a form of intermittent movement which has lately come out and is used on the ,powers ,no4 #f ,cameragraph is shown in ,figures #dj to #db inclusive4 ,the moving element of this intermittent movement is a diamond-shaped projection on the surface of a revolving disk4 ,the driven element is a cross carrying four pins--termed a 8pin cross0--and is indicated by broken lines4 ,the raised portion ,a of the diamond strikes one of the pins of the cross and starts it in motion as indicated in ,figure #da4 ,the movement of the cross can be traced by the black dot indicating one of the pins4 ,at every revolution of the driving disk1 the cross makes one quarter of a revolution and when not in motion is held rigidly locked by the locking ring ,r1 which fits snugly between the pins4 ,this movement probably moves the film in the shortest time of any4 ,it is entirely encased1 runs in oil1 and is practically noiseless4 ,the manner in which it is installed in the machine is indicated in ,figure #dc4 ,m--,lower ,feed ,loop4--,the lower feed loop is provided to prevent the lower sprocket from pulling on the film and thus interfering with the work of the intermittent sprocket4 ,the intermittent sprocket feeds the loop1 by jerks1 three-fourths of an inch of the film at a time2 and the lower sprocket is geared to take away that much by steady motion4 ,thus1 everything working properly1 the loop remains of the same size4 ,in case the lower sprocket is not working properly1 the loop may become enlarged and the film may run onto the floor4 ,sometimes the intermittent sprocket does not work properly and the lower sprocket pulls away all of the loop4 ,n--,lower ,steady-,feed ,sprocket4--,the lower steady-feed sprocket maintains the loop and restrains the film4 ,if it were not for this sprocket1 the take-up mechanism would pull directly on the intermittent sprocket and keep the film jiggling4 ,illustration3 ,,figure #dd4 ,o--,take-up ,reel4--,the take-up reel is identical with the upper reel and1 in fact1 the two are generally used interchangeably4 ,in both cases1 only perfect reels should be used2 and reels delivered by exchanges are very often untrustworthy4 ,the principle of the take-up mechanism is shown in ,figure #dd4 ,when a run of film is started1 the diameter of the roll of film being small1 the reel must travel comparatively fast to take up the film as fast as it is unwound from the upper reel4 ,as more and more film is gathered by the lower reel1 the travel must become slower until finally1 with a twelve-inch reel1 the number of revolutions per minute are but about one-fourth as many as at the beginning4 ,in ,figure #dd1 ,a is the reel which is fastened to the spindle ,b2 ,c is a collar also fastened to the same spindle4 ,d is a loose pulley capable of revolving around the spindle without imparting motion to it and arranged so that it can be driven by a belt4 ,e is a spiral spring which is controlled by the small collar ,f1 and it presses the loose pulley against the collar ,c4 ,if the loose pulley is pressed against ,c with sufficient force1 it will cause ,c to revolve with it2 and the movement of ,c will impart motion to the reel and wind up the film which is fastened to it4 ,d must revolve fast enough so that1 even when the reel is empty1 it will take up all of the film fed to it4 ,as the film is wound up1 the size of the roll of film increases and the speed must become less2 thus ,d begins to slip a little on ,c and this slippage increases until the end of the run4 ,friction in one form or another is the only method by which take-up reels are now operated2 but in some of them this friction may be in a belt1 as well as in the two disks as shown4 ,sometimes a fiber washer is interposed between the two friction disks4 ,in the ,motiograph take-up1 ,figure #de1 the necessary friction and slip are all in the belting4 ,illustration3 ,,figure #de4 ,if the take-up is not handling the film properly1 it is due to a loose belt or to insufficient tension on the spring4 ,the take-up probably causes more trouble than any other part of the mechanism and it should be carefully watched4 ,on account of the trouble incurred from it1 there are still many operators who prefer to run films into a tank2 although the take-up saves them much time4 ,a careful operator who understands the care of machinery would have little trouble with a take-up2 while the one who has not the faculty of keeping things in order would1 perhaps1 be better off 7fire hazard neglected7 with a tank4 ,with most machines1 the take-up magazine is located where it is very difficult for the operator to watch its operation4 ,those machines in which it is located in easy sight of the operator have considerable advantage in this respect4 ,a careless operator is often compelled to open the lower magazine door and turn the reel by hand when the take-up tension is out of order4 ,remember that the take-up can cause trouble only when it is out of order and that a good operator will never allow it to get out of order and he will inspect it carefully before every show4 ,p--,framing ,device4--,the aperture in the film gate is just large enough to fit the picture on the film4 ,if the film is accurately placed1 the whole picture will show upon the screen4 ,in order to bring this about1 the machine must either be provided with a means of adjustment1 or a certain part of the film must be placed upon a certain sprocket tooth4 ,this latter method causes considerable annoyance and waste of time2 furthermore1 every splice in a film would have to be made exactly right or the whole succeeding part of the show would be 8out of frame04 ,in order to avoid these troubles1 every machine is provided with a so-called framing device4 ,somewhere about the machine1 convenient to the operator1 will be found a lever by which1 during the operation of the machine and without interruption1 the position of the film with reference to the film window and the lens may be adjusted either up or down4 ,the precise manner in which this is done varies with different machines4 ,the framing device must be capable of adjusting the film to somewhat more than the width of one picture4 ,the splice should be so made that framing becomes unnecessary and this is accomplished by cutting out full pictures so as to leave each picture with the full four holes4 ,if a picture is left1 for instance1 with only two holes1 it will appear upon the screen with the black line1 which should be hidden in the center4 ,if this happens1 by moving the framing lever either up or down1 the picture can again be centered upon the screen4 ,illustration3 ,,figure #df4 ,q--,film ,shields4--,the film shield is an important part of the machine2 although it is often very much neglected and in many machines is so small as to be practically useless4 ,it should prevent films from crowding out into the light when the loops enlarge4 ,many operators do not take kindly to machines that enclose the film too tightly2 for in case the take-up fails to work properly1 it is often a convenience to be able to handle the film4 ,this is also the case where very badly torn or old film is used4 ,many old films are so badly worn that they will not run properly on the sprockets and must be very closely watched4 ,illustration3 ,,figure #dg4 ,illustration3 ,,figure #dh4 ,it is not thought necessary or advisable to go into the details of construction of any particular machine as changes are made nearly every year so that such description would not be of great value and might1 in fact1 be misleading4 ,any person possessing a little mechanical ingenuity and taking an interest in such matters can readily learn the peculiarities of any of the machines4 ,they are1 after all1 when one has mastered the principles1 quite simple affairs4 ,all progressive manufacturers1 furthermore1 publish instruction books which are issued whenever a change is made in any machine2 and these are always obtainable4 ,illustration3 ,,figure #di4 ,in ,figure #df we have a general view of the ,edengraph machine4 ,it will be noticed that the total length of film between the two magazines is exposed to view making threading of the film very easy2 also that the revolving shutter works between the objective lens and the film gate4 ,the well-known ,edison machine is shown in ,figure #dg4 ,this is one of the best known machines2 and it is very compact and durable4 ,illustration3 ,,figure #ej4 ,the ,motiograph is shown in ,figure #dh4 ,the take-up1 shown on the lower magazine1 is different in this machine from what it is in the others4 ,this machine also has a special rewind feature4 ,by an adjustment of the operating handle1 the film1 after having been run off onto the take-up reel1 can be rewound upon the upper reel without taking it out of the magazines4 ,figure #di shows a general view of the ,powers ,no4 #f ,cameragraph mechanism4 ,the ,simplex mechanism is shown in ,figure #ej4 ,in this machine the film is entirely enclosed between the two magazines4 ,,chapter ,,vi4 ,,the ,,film4 ,film ,making and ,characteristics4--,all film is of celluloid4 ,the commercial film used for the projection of motion pictures comes in long strips1 is about one and three-eighths inches wide1 and about one two-hundredths of an inch thick4 ,upon one side of this film is a photographic emulsion of gelatine impregnated with a solution of bromide of silver4 ,this silver is sensitive to the light and has the property of turning black1 during the process of developing1 in proportion to the quantity of light that has struck the different parts of the emulsion4 ,wherever the light has been very intense or has been applied for a sufficiently long time1 the film1 after treatment with a proper developing fluid1 becomes very black2 where no light has reached it1 it remains white2 and in the intermediate portions1 the shading is in proportion to the light that has reached those parts4 ,film that has not been exposed and developed is of a creamy yellowish color and1 if immersed in a solution of hyposulphite of soda1 will turn perfectly clear and offer no obstruction to the light4 ,if1 on the other hand1 it is completely exposed and developed1 it will become solid black2 such black pieces are sometimes used as leaders and tails in connection with motion pictures4 ,the emulsion on the film melts at a temperature of about #ij degrees ,fahrenheit and will then run off the film4 ,it is also soluble in warm water4 ,the celluloid of the film is very inflammable and bursts into flame at a temperature of #bhd degrees ,fahrenheit4 ,if it is ignited while tightly wound upon a reel1 it burns somewhat slowly2 if it is ignited in a tank1 the beginning of the fire is also slow2 but as soon as the air in the tank attains the proper temperature1 the whole of the film bursts into flame at once4 ,it acts in this respect very much like gunpowder4 ,in burning1 the film gives off a dense brownish mass of poisonous smoke4 ,film will burn even when it has no access to the air and a film fire cannot be put out by smothering4 ,before sending out their films1 the manufacturers treat them with glycerine4 ,this is for the purpose of keeping them pliable as long as possible4 ,in time1 however1 a film dries out and there is then very little that can be done with it4 ,at any rate1 whatever is to be done should be done by the exchange1 as no operator has facilities for handling it4 ,some films are waterproofed and a little water will not damage them much2 but other films must be kept dry4 ,if by accident a roll of film should become wet1 it can be saved by very quickly unrolling it and spreading it out to dry4 ,if it can be spread out quickly enough1 it will not be harmed2 but if it is not spread out at once1 the emulsion will stick to the celluloid and will come off when the film is finally unwound4 ,there is also a process of fireproofing film4 ,this must not1 however1 be too thoroughly relied upon1 especially if the film is old4 ,fireproof film is a valuable aid1 but it is best to treat it exactly like other film in respect to the fire hazard4 ,on account of its inflammable character1 film should always be kept in fireproof enclosures4 ,the film contains sixteen pictures to each foot and for every picture there are four sprocket holes on each side of the film4 ,the size of the aperture plate and also the size of the actual picture on the film is #aa_/af inch high by #ae_/af inch wide4 ,if the picture on the screen is enlarged to #ah feet #i inches in width and #ac feet #i inches high1 every part of the picture on the film will appear #eg1fjj times as large on the screen as it is in the film4 ,in viewing a #ajjj-;foot film1 the audience will see #af1jjj separate pictures following each other so rapidly that the change from one to the other will be unnoticeable4 ,if a three-blade shutter is used1 the beholder will see the light shut off and turned on #dh1jjj times in the same run of film1 but will not be able to notice it if the speed with which it is done is correct4 ,new film coming directly from the exchange is likely to be too moist and cause trouble from that condition2 while old film is likely to be too dry and cause trouble by warping or bending out of shape4 ,patching ,film4--,all reels of films contain patches and but little trouble will arise from them1 provided they are properly made and reasonable care is exercised in watching them4 ,in order to obtain a satisfactory splice1 it should not be made more than #c_/af inch long2 a greater length than this will reach two sprocket teeth and this is objectionable because the splice stiffens the film and will prevent it from fitting the teeth properly4 ,the splice should be so made that it does not throw the pictures out of frame4 ,if made properly1 it will never be noticed in the running picture at all1 unless a large quantity of film is cut out4 ,if however1 the splice be made over part of a picture--as would be the case if an improper number of holes were cut out--the picture1 when projected1 would appear out of frame1 i4e41 the dividing line between two pictures would then appear on the screen and would continue to show until the framing lever had been adjusted to cover the dividing lines again4 ,care must also be taken that the film is straight after being spliced4 ,if the ends are not fitted squarely to each other1 there will be a bend in the film at the point the splice is made2 and this may cause trouble4 ,many operators have a plate of ground glass fitted into a work bench at the place where splices are to be made and a small lamp under this glass4 ,this is very convenient for1 as a rule1 the illumination in an operating room is very poor although a good light is necessary to match film properly4 ,if ground glass is used1 the rough side must be at the bottom2 otherwise it will be difficult to clean off the cement which adheres to the glass4 ,by making every splice in exactly the same order1 the operator will acquire the habit of doing it nicely and quickly4 ,most splices are made in a hurry 7before or after a show7 and in this1 as well as in all things that must be done hastily and at a moment's notice1 habit and practice are very important4 ,one does not become expert until he has practiced it often enough to be able to do it mechanically4 ,illustration3 ,,figure #ea4 ,proceed as follows and as outlined in ,figure #ea3 ,cut exactly along the dividing line of one picture and save this to become the top piece4 7,the emulsion side of the two sections of film must always be either up or down1 and for convenience it is well to form the habit of having them always one way or the other47 ,now1 with a sharp knife1 scrape the celluloid side of this piece until all of the gloss is removed for a width of a little more than #c_/af inch4 ,do not scrape any more than necessary1 but be sure that all dirt and oil are removed4 ,now take up the other part of the film and cut off the bad portion1 leaving a strip a trifle less than #c_/af inch beyond the dividing line4 ,this strip need not be scraped on the back1 but all of the emulsion must be scraped from the front side of it4 ,to scrape the front side nicely1 lay a short ruler across it to act as a guide for the knife and scrape up to this ruler4 ,scrape only to the dividing line1 but give particular attention to the sprocket holes and the edges1 for it is at the edges and sprocket holes that film first begins to work loose and where it is most difficult to secure proper adhesion4 ,both parts of the film should be so scraped that1 when finished1 each will furnish half of the dividing line4 ,now apply a liberal coating of cement to the latter section and carefully lay the first upon it1 taking great care that the sprocket holes in the two sections overlap and match perfectly4 ,it is for this matching purpose that the glass in the table 7with a small lamp underneath it7 is valuable4 ,the sprocket holes must match accurately and the films must line up straight4 ,after the upper film is placed1 it must be pressed down for a few seconds until the cement has set4 ,wipe off all superfluous cement before it has time to set4 ,be sure that there are four sprocket holes for each picture4 ,keep a knife on hand and use it for no other purpose4 ,keep also a suitable stone on which to sharpen this knife1 for1 unless the knife is very sharp1 it will do only poor work and the edge on it will not last long at any rate4 ,ordinary cement will not hold non-inflammable film1 and water-proof film must be more thoroughly scraped than ordinary film4 ,in the bench1 provide a recess into which the cement vessel may be set and where it will always remain4 ,provide also a pair of scissors for cutting the film4 ,illustration3 ,,figure #eb4 ,the ,edison film mender is shown in ,figure #eb4 ,this is made with three gates or hinges4 ,those on the right and left clamp down to hold the film1 while the narrower one in the center clamps down on the cemented edge4 ,to mend a film1 place one of the pieces to be joined in the mender4 ,place that part of the gage marked 8cut0 in position1 cutting between first and second perforations above the floor line separating the picture4 ,the remaining piece of film should be placed in the other side of the mender and cut exactly on the line4 ,set the opposite end of the gage marked 8scrape0 on the first section2 remove the emulsion2 cut to the floor line with a sharp pen knife1 moistening it so that the emulsion will come off easily4 ,after applying the cement with a brush to the scraped piece1 lay the other piece over it in the mender1 clamping it down2 and leave it for an instant to adhere4 ,,chapter ,,vii4 ,,general ,,hints ,,on ,,installation1 ,,operation1 ,,and ,,care ,,of ,,machines4 ,tools4--,first of all provide a suitable and sufficient set of tools4 ,there should be an assortment of screw drivers1 large and small1 to fit the different sizes of screws used not only with the machine but about the operating room and with other devices as well4 ,keep these screw drivers filed or ground to proper shapes4 ,a screw driver rounded off1 or too small1 or bent1 will ruin the heads of the screws4 ,there should also be a collection of pliers 7especially such as are commonly termed 8gas pliers071 files1 raps1 chisels 7for wood and metal71 punchers1 drills1 and monkey wrenches2 a hack saw1 a blow torch1 and a vise will also come in handy4 ,tools1 however1 depend upon the man who uses them4 ,there are men who would be no better off with such a collection at their disposal2 on the other hand1 a clever man would be able to make use of all these tools and show his skill thereby4 ,aligning the ,machine4--,the first thing to do in setting up a new machine1 after it has been unpacked and put together1 is to line it up properly4 ,this can be done by stretching a string from the lamp house1 through the center of the condenser opening1 film gate1 and objective lenses4 ,these must all be in such a position relative to one another that a taut string will pass through the center of each4 ,the center can be determined by measurement either with a suitable rule or a pair of calipers4 ,anchoring the ,machine4--,the next step is to anchor the machine so as to reduce vibration to a minimum4 ,vibration is often due to a flimsy floor which will not stand the strain of the unavoidable vibration and thus helps to increase it4 ,often1 however1 the vibration is due to some part of the running gear of the machine1 such as the revolving shutter1 for instance1 being out of balance4 ,if there is undue vibration1 the machinery should be looked after first1 for it is much better to prevent the vibration by removing the cause than to seek to restrain it by bolts and braces4 ,if the machine runs very badly1 it cannot be bolted down with any satisfactory results4 ,inspection4--,after the machine is lined up and running smoothly1 the next step should be to inspect every part of it thoroughly for loose screws1 pins1 gears1 or other parts4 ,it is best to do this by beginning at one end and continuing to the other so that no part may be overlooked4 ,upper ,magazine4--,see that the spring in the upper magazine1 or on the door of it1 which prevents the momentum of the upper reel from running off film after the sprocket has ceased pulling1 is in good order and the reel true4 ,a crooked reel will generally cause trouble and force the operator to keep the magazine door open so as to be able to aid the movement of the film4 ,fire ,trap4--,the fire trap must next be looked after4 ,the upper magazine1 the fire trap1 and the sprockets must all be in perfect alignment and the film must run through the trap without touching either side4 ,film wears the metal very fast and a day's run with the film brushing one side of a valve will show decided wear4 ,if it is allowed to run this way1 it will soon cut through the side of the valve1 forming an opening in which the film will run and in which it will often catch and tear splices4 ,special care must be exercised to see that the traps are kept clean and1 when not in use1 they should always be covered4 ,the film is drawn through the traps very rapidly and any kind of dirt accumulating on them is apt to scratch it4 ,after a fire1 burned film is likely to be found in the trap1 and this1 when cold1 becomes hard and is difficult to remove4 ,cleaning ,machine4--,after the machine has been used for a considerable time1 it is advisable to wash out the gears thoroughly4 ,not only the gearing1 but the bearings also1 should be reached by this process4 ,if one has plenty of gasoline and a suitable receptacle1 the quickest way is to take out the lenses and immerse the whole machine for a while in a vessel filled with gasoline4 ,it can then be taken out1 worked a little1 and immersed again2 this process being repeated until all of the old and hardened grease is worked out4 ,if facilities for immersing the machine are not at hand1 the bearings may easily be cleaned by using kerosene or gasoline to oil them and then running the machine a little2 this will work all of the old grease out of the bearings4 ,the gearing can be cleaned in the same way4 ,if gasoline is used1 it will quickly evaporate and leave the machine in good order4 ,oiling ,machine4--,after the machine is thoroughly cleaned1 it may be oiled again4 ,the best lubricants to be used range all the way from sewing-machine oil to beeswax4 ,beeswax is used only for the gearing and only where that is somewhat worn4 ,it is solid enough to compensate for some of the wear4 ,that part of it which works out on the sides should be wiped off at once4 ,there are many lubricants to be recommended2 in general1 however1 the particular kind to be chosen depends upon the parts to be lubricated4 ,a part moving rapidly with no great friction can be well served with a light lubricant1 but heavier parts1 or parts that fit so closely as to cause much friction are best served by some lubricant that has more body4 ,if a light oil is used1 it will of course have to be applied oftener than a heavy oil4 ,none of the extremely light oils should be used because they run off too fast4 ,care of ,sprockets4--,having thus cleaned and oiled the machine1 the next step is to look after the sprockets4 ,in an old machine it is likely that the sprocket teeth will be so worn as somewhat to resemble hooks4 ,a little wear of this kind will do no great harm1 but beyond a certain point of wear1 the sprocket teeth tend to carry the film farther than is necessary and in so doing tear out the holes4 ,some sprockets are made reversible and the trouble can be remedied by turning the sprocket wheel around4 ,in most cases it will1 however1 be advisable1 when the old teeth are badly worn1 to get a new set of sprockets4 ,the sprockets must also be examined for accumulation of dirt1 for in case there is much dirt on a sprocket1 it will not guide the film properly4 ,the dirt will cause it to jump1 and thus bring about an unsteady picture2 or1 if the accumulation of dirt is sufficient1 it may even cause the film to jump off the sprocket4 ,hundreds of feet of film have been ruined in this way4 ,the sprockets should be cleaned every day with a suitable brush4 ,an operator too careless to clean his machine properly1 is also as a rule too careless to watch the picture properly2 and he suddenly finds himself with a length of film ruined by sprocket teeth which have cut a row of holes through the center of it4 ,the sprocket should be made to align perfectly with the upper and lower magazines1 the fire valves1 the film gate1 and the path of the film4 ,they may be aligned with a straight edge made of a flexible piece of steel or1 if nothing else is available1 a piece of film may be placed upon the sprockets4 ,be sure to examine the film carefully before using it for this purpose2 old film is apt to be warped4 ,the film must fit perfectly in the aperture and on the different sprockets4 ,the sprockets must have little or no end play1 especially the intermittent1 or it may cause the picture to wiggle sideways4 ,the idlers1 or presser rollers1 should not fit tight enough to bind1 but must fit closely enough to hold the film securely4 ,in the adjustment of these and all other parts of a moving picture machine1 considerable practice and judgment are necessary to estimate how much freedom of movement is permissible4 ,adjusting ,intermittent ,sprocket4--,the 8,geneva0 wears rapidly when it is not well oiled or protected2 and it becomes necessary to adjust it4 ,there are other ways of doing this but generally it is done by means of an eccentric bushing which must be set to compensate for the wear4 ,in many operating rooms1 there is a wide range of temperature and1 as heat expands the metals1 they will bind unduly when they become warmed up1 if the star and cam wheel are set too close while cold4 ,in many machines the heat from the lamp warms them up irrespective of the temperature in the operating room4 ,automatic ,fire ,shutter4--,some means of adjusting and regulating the automatic fire shutter is usually provided2 this should be adjusted so that it will not rise before the machine is in motion and will fall before it has come to rest4 ,under no conditions should the stationary film be allowed in the path of the light4 ,there are fire shutters that do not depend upon the motion of the machine1 but are raised as soon as the handle is pressed to give motion to the machine4 ,this type of shutter is raised as soon as the handle is pressed and may expose the stationary film to the light4 ,such a shutter should not be tolerated at all4 ,the fire shutter should be carefully tested to see that it operates properly under all conditions4 ,if one is not acquainted with the particular type of fire shutter in use1 it is advisable for him to test it with the lamp turned on it for some time4 ,some shutters are so thin and are placed so close to the film they are supposed to protect1 that it is possible to fire the film through them4 ,the ,revolving ,shutter4--,in some machines the light is shut off before the film begins to move1 and in others a very slight movement of the film is permitted before the shutter closes out the light entirely4 ,the general object of the shutter is to shut off the light while the film is moving and to interrupt the long period of light so that it may not affect the eye too strongly and give rise to the sensation of flicker4 ,the exact manner of setting the shutter varies with different machines1 but in general the above consideration must be kept in view4 ,where a shutter has several blades1 it is always the larger one that shuts off the light while the film is moving and this is the only one to which any attention must be paid while setting4 ,the best test for the setting of the shutter is the appearance of the picture4 ,the best kind of picture with which to judge a shutter is one that has strong contrasts of light and darkness4 ,if a picture contains a very bright object1 the travel ghost will appear if there is any motion while the light is on the film4 ,if the shutter is set too late1 the travel ghost will be in the lower part of the screen2 and if too soon1 in the upper4 ,if the shutter is made too small1 the travel ghost cannot be entirely eliminated but must be divided half on the lower and half on the upper side of the picture4 ,the travel ghost and other imperfections of a picture are much more noticeable to persons close to the screen than to those far away4 ,as the operator himself is the farthest away of all spectators1 he is likely to miss many imperfections that are plainly visible to the audience4 ,for this reason many operators have opera glasses through which they view their pictures4 ,framing4--,when the machine is finally threaded1 the film should be so placed on the upper sprocket that1 with a proper loop1 the picture will be in frame when the framing lever is about in the middle position4 ,this position will allow the operator to frame either up or down without seriously affecting the loop4 ,the framing is best done by looking at the picture thrown upon the screen4 ,film ,gate4--,the film gate needs special attention when new film is being used4 ,very often new film is so damp that some of the emulsion sticks to the gate4 ,wet film running through a machine makes it work hard and is likely to cause much trouble4 ,with such film it is often necessary to stop during a run and clean off the gate and it is always necessary to do so after each run4 ,never use a sharp tool or anything that may scratch the gate or roughen the bearing surfaces where the film runs4 ,the gate must be watched closely for wear2 if worn too much1 the picture may be out of focus or jump in all directions4 ,tension ,springs4--,the tension springs will repay careful study by the operator4 ,the object of the springs is twofold3 ,first1 to hold the film flat1 and second1 to introduce sufficient friction to overcome quickly the slight momentum which the film has acquired while in motion4 ,the springs should be just tight enough to do this4 ,the pressure of the springs necessary to overcome the momentum of the film is proportional to the speed at which the film moves4 ,if the film is to be run at a high rate of speed--as is often the case when a crowd is waiting outside the doors--the tension must be increased1 unless it was originally great enough to hold the film at this rate of speed4 ,as the film varies in thickness1 the adjustment cannot be made too close2 but the springs must be made tight enough so that they will hold the film at the highest rate of speed when the thinnest part of the film is passing through4 ,if the springs are not sufficiently tight1 the picture will seem to move a trifle4 ,they must be just tight enough to prevent this at the highest rate of speed at which the machine is to operate4 ,the ,take-,up4--,the lower sprocket exists for the purpose of restraining the take-up from pulling on the intermittent sprocket4 ,there is thus actually always a strain that the one puts on the other4 ,for this reason the tension on the take-up should be no greater than necessary4 ,excessive tension will increase the wear on the machine2 may cause the tearing of many splices2 and will cause the machine to run hard1 thus imposing extra labor on the operator4 ,while the lower reel is nearly empty1 the strain is small2 but as it fills up1 the strain becomes greater4 ,the driving wheel or belt must move at a fixed rate of speed while the slip of the driven wheel becomes greater with every turn4 ,thus the energy expended in friction becomes greater as the picture progresses4 ,defective belting1 crooked reels1 or poor adjustment of tension are the most frequent cause of annoyance in the take-up and the take-up as a whole gives probably more trouble than any other part of the equipment4 ,cover4--,every machine should be covered when not in use and the cover should be dust tight4 ,getting ,ready for the ,show4--,the first thing for the operator to do before entering the operating room is to put away all smoking paraphernalia he may have about him4 ,no smoking tobacco or matches should ever be found inside of any operating room4 ,after taking this precaution the next thing will be to rewind and inspect the films to be used for the next performance4 ,if the reel happens to be properly wound when received1 it is not absolutely necessary to rewind it and1 in an emergency1 one may take a chance and run it through without previous inspection4 ,when possible1 however1 the operator should always inspect his film before using and also familiarize himself with its contents4 ,a film is best inspected by rewinding it slowly from one reel onto another1 gripping it with a gentle pressure1 and allowing it to run between the fingers4 ,this method will catch all splices and also all split films4 ,films are frequently split along the line of the sprocket holes4 ,the film should be run through the fingers in this manner twice3 once to catch such irregularities as make themselves manifest along the outer edge and again to catch the defects that exist only in the middle of the film4 ,every splice should be carefully inspected to note how the sprocket holes match and whether the splice will throw the picture out of frame4 ,all splices that are not properly made should be re-made as directed in ,chapter ,,vi4 ,if there is sufficient time1 it would be well to run the film through the machine in the regular way4 ,thus the operator can familiarize himself with the picture and note every place where improvements can be made by adjusting the speed1 for very often a picture may be improved by slowing down or increasing the speed in certain scenes4 ,the flicker varies with the illumination2 the brighter the light the greater will be the tendency to flicker1 if the machine is not run at proper speed4 ,the operator should know before hand just when his brightest scenes will come on so as to adjust the speed or1 in case he must run slowly1 so as to reduce the flicker by reducing the illumination4 ,running the film through will also show every place where the picture goes out of frame and all such places can be corrected4 ,all bad places should be cut out of the film1 but not more than necessary4 ,every additional section cut out of a film will increase the jerkiness of the motion4 ,a few are not noticed1 but one often sees in old reels1 scenes that are simply ridiculous because too much film has been cut out4 ,such effects are especially noticeable if a picture is run slowly4 ,the operator must always be prepared to run pictures at abnormal speeds4 ,it is bad practice to do so but often unavoidable2 for instance1 if the next number on the program is delayed1 it is desirable to extend the picture until it is ready in order that the audience may not be dissatisfied2 or if all the seats are filled and people are waiting outside1 the manager may demand extra speed so as to make room for the outsiders4 ,the operator who is wise and has had experience will provide himself with a receptacle in which he can store the pieces he cuts out of films4 ,saving such pieces and taking them to the exchange will often make an impression upon the exchange management and induce greater care in the inspection of films at the exchange4 ,such pieces will sometimes be good evidence in the hands of an operator1 too1 in case he is charged with having damaged a film4 ,while the film is being run through the machine1 it can also be measured4 ,every turn of the crank means one foot of film4 ,before the film is wound upon the reel from which it is to be exhibited1 an opaque piece of film about two feet in length should be attached to the tail end of the film4 ,this piece of film will in some cases serve a double purpose4 ,with some machines the film can be rewound from the lower magazine into the upper without taking it out of either1 if this tail piece is long enough to remain fast to the upper reel after the whole film is run off the upper reel4 ,thus the operator when through running the picture may immediately change his crank and1 without delay1 begin to rewind4 ,the main purpose of this tail piece1 however1 is to shut off the light immediately after the last section of the picture has been exhibited4 ,if the light is left on the screen while the operator slows down the machine1 it will cause a disagreeable flicker to appear before the eyes of the audience immediately after the picture is over1 and thus leave an unpleasant impression4 ,the beginning of the film should be provided with a leader from three to five feet long4 ,the purpose of this leader is to allow the operator time to frame his picture and get his lamp adjusted before the title appears1 or is finished1 so that when the picture actually begins1 everything will be running smoothly4 ,the film must be rewound upon the reel in such a manner that when threaded1 the emulsion side will face the lamp4 ,if this is not done1 the titles will read from right to left instead of from left to right as they should4 ,it will be well for the operator to form the habit of regularly testing his film by the actual projection to see that his titles are right4 ,there are often many other things to think of and cases of absent-mindedness are not uncommon4 ,if the title shows wrong1 the reel may be taken out and turned around2 this will reverse it1 but ordinarily it is best to wind it in one certain way4 ,every operator should have a full supply of good reels for use in the machine and should never let these get out of his house4 ,the reels furnished by the exchanges are often very bad and if perchance a real good one is sent out1 some wide-awake operator will surely keep it4 ,although it is best to rewind a reel as slowly as your time will permit1 it is necessary sometimes to do it very rapidly4 ,the reel from which the film is being unwound should be under a steady tension and some form of brake is often provided4 ,the practice of 8pulling down10 which is indulged in by so many operators1 is highly reprehensible4 ,it causes the emulsion side of the film to slide over the other and any dirt or dust that may be between the two is thus ground into them4 ,the scratches thus caused soon fill up with dirt and cause streaks in the picture which are commonly termed 8rain40 ,the dirt--especially the carbon dust1 which is so plentiful in an operating room and which is very sharp and cuts badly into the emulsion or the celluloid--disfigures the picture very much4 ,a good film box should be located in every operating room and it should be so conveniently located that the operator will use it in preference to anything else4 ,such a box should be provided with automatic self-closing covers and should be near the floor1 as the film is less liable to dry out there than if placed near the ceiling where the heat is greater4 ,nothing whatever should be placed upon the floor itself and it should be kept absolutely clean4 ,although it is very bad practice to run film on the floor and it should not be done1 there are occasions when it will be done and1 if the floor is clear of all obstruction1 the hazard of doing so is much reduced4 ,an operator who1 having trouble with his take-up and having run the film on the floor1 has had it entangled1 will appreciate this fact4 ,the spasmodic bursts of applause which an impatient audience is apt to offer while the show is being delayed are not especially comforting to any one in such a position4 ,under no circumstances should film ever be left exposed4 ,occasional small fires at the aperture plate are unavoidable and in such cases the operator will seek to tear off the burning film and throw it on the floor1 and it may then ignite the film lying about4 ,form the habit of keeping your film under cover2 and make up your mind that it is absolutely necessary4 ,keeping films under cover will also tend to save them from drying out and prevent accumulation of dust4 ,a slide with the words 8,just a moment please10 or some equivalent expression1 will reassure the audience2 one should always be kept in place and when any trouble causes an interruption of the show1 the lamp should be pushed over thus exhibiting this sign4 ,the habit of pushing the lamp over in case of interruption is also a very good one4 ,it is the simplest and most natural way of taking the light off the film and satisfying the audience at the same time4 ,this practice should become a habit4 ,it will be a great protection against fire in addition to the other safety devices4 ,all the work of making ready should if possible be done before a considerable part of the audience is in the house4 ,it is best to let none of them see the process of getting the show in readiness4 ,as has been stated before1 an occasional fire at the aperture is unavoidable4 ,sometimes pieces of film are torn loose1 stick where they are subject to the light1 and in time catch fire4 ,a fire thus started may easily consume all of the film between the two magazines and will progress slowly toward the lower one1 but towards the upper one very rapidly4 ,if the doors of the magazines are tightly closed and fit tight and if the fire traps are in good order1 there will be but a small chance of fire getting at the rolls of film that may be in either magazine4 ,every effort should1 however1 be made to extinguish it before it reaches the fire traps4 ,just what can be done depends upon the design of the machine4 ,in order to be prepared for such an emergency1 the operator should study his machine and decide what would be best to do4 ,in many cases the film can be torn off before the fire extends to the magazine and thus break the connection4 ,in some machines the film runs in such a narrow groove that the fire is generally extinguished there without any outside help4 ,some operators have been known to open their magazines and attempt to remove the film after a fire had started1 resulting in burning all their film4 ,it is far better to leave the film in the magazine and trust to the fire traps than to attempt to remove it4 ,no visitors should be allowed in any operating room during the time that the audience is in the house1 more especially when the time for opening the show approaches4 ,there should be nothing to distract the operator's attention from his duties4 ,the arc lamp should be started a few minutes before the show is to begin so that the electrodes may burn to their proper shape and the light be adjusted4 ,before the show begins1 the house should be made dark for a few minutes4 ,this will make the picture appear brighter4 ,in case the film tears during a run1 some operators have the habit of pinning the pieces together with the intention of making the splice after the picture is run4 ,this practice is well enough for an operator who feels sure that he will not forget about the pin1 but with one who is forgetful or absent-minded1 or who has a lot of other duties which might take his mind off the film1 it is a bad practice4 ,the film may be rewound with the pin remaining in position and cause very serious trouble4 ,it is safer to put the film on the take-up without pinning4 ,in a general way the points alluded to in the following list should be carefully looked after4 ,this is a list which is used by the ,electrical ,inspection ,bureau of the ,city of ,chicago in checking up operators and their equipment4 ,theatre address444444444444444444444444444444444 4444444444444444444444 ,perm4 ,operator's name 4444444444444444444444444444444444444444 444444444 ,temp4 ,address44444444444444444444444444444444 44 ,lic4 ,no4 4444444444444444444 ,,moving ,,picture ,,machine ,,inspection4 ,an x indicates defect2 a check1 satisfactory condition4 ---------------------------------------- --------------------------- #a ,smoking8 #be ,fan ,motor8 ---------------------------------------- --------------------------- #b ,matches8 #bf ,guards on inc4 lights8 ---------------------------------------- --------------------------- #c ,condition of ,films8 #bg ,unauthorized persons8 ---------------------------------------- --------------------------- #d ,magazine closed8 #bh ,rewind approved8 ---------------------------------------- --------------------------- #e ,film exposed8 #bi ,rewind location8 ---------------------------------------- --------------------------- #f ,arc enclosed8 #cj ,rheostat1 #e ft4 above floor8 ---------------------------------------- --------------------------- #g ,guard fastened8 #ca ,rheostat1 contacts enclosed8 ---------------------------------------- --------------------------- #h ,upper fire guard8 #cb ,rheostat1 safe location8 ---------------------------------------- --------------------------- #i ,lower fire guard8 #cc ,box for films1 approved8 ---------------------------------------- --------------------------- #aj ,upper magazine approved8 #cd ,box for films1 cover8 ---------------------------------------- --------------------------- #aa ,lower magazine approved8 #ce ,shutters1 guides8 ---------------------------------------- --------------------------- #ab ,upper magazine1 lock well8 #cf ,shutt's self-closing1 supports8 ---------------------------------------- --------------------------- #ac ,lower magazine1 lock well8 #cg ,booth lining8 ---------------------------------------- --------------------------- #ad ,light shutter8 #ch ,floor8 ---------------------------------------- --------------------------- #ae ,fuses enclosed8 #ci ,shelving8 ---------------------------------------- --------------------------- #af ,fuses1 proper size8 #dj ,general appearance8 ---------------------------------------- --------------------------- #ag ,inc4 circuit8 #da ,door1 self-closing8 ---------------------------------------- --------------------------- #ah ,arc switches1 enclosed8 #db ,box office8 ---------------------------------------- --------------------------- #ai ,arc switches1 control #dc ,unapproved display8 rheostat8 ---------------------------------------- --------------------------- #bj ,arc switches1 condition8 #dd ,main cutout cabinet8 ---------------------------------------- --------------------------- #ba ,how much open arc wire8 #de ,emergency cutout cabinet8 ---------------------------------------- --------------------------- #bb ,how much open inc4 wiring8 #df ,number emergency lights8 ---------------------------------------- --------------------------- #bc ,open contacts8 #dg ,fan motors auditorium8 ---------------------------------------- --------------------------- #bd ,flexible or ,,bx cord8 #dh ,rheostat in base4 cond48 ---------------------------------------- --------------------------- #di ,exits444448 ,gas444448 ,sperm ,oil444448 ,electric444448 ---------------------------------------- ------------------------------ 44444444444444444444444444444 ,inspector4 ,these defects must be corrected within44444444444444days4 ,the ,electrical ,inspection ,bureau must be notified as soon as repairs are made4 ,,chapter ,,viii4 ,,light4 ,light is emitted from a luminous body4 ,a luminous body is one in which all of the particles are conceived to be in violent motion1 which motion is transmitted to a supposed ether4 ,the existence of such ether cannot be demonstrated1 but it is supposed to exist because it is impossible to think of anything being transmitted except through some medium4 ,this ether is a rather imponderable substance2 it is supposed to pervade all space2 and it exists in all matter and in every vacuum4 ,it is supposed to be elastic without weight and capable of transmitting motion without loss of energy or friction4 ,it is1 however1 assumed to be modified to some extent by the matter in connection with which it exists4 ,thus the rate of transmission of light waves is different for air1 glass1 water1 and other substances through which they may pass and such bodies as are entirely opaque are supposed to suppress the ether vibrations1 resulting in light entirely4 ,light is then a mode of motion of this universal ether which pervades all space even to the farthest star4 ,the motion of this ether is conceived to be about as illustrated in ,figure #ec4 ,if we take a heavy string or a small rope and1 stretching it reasonably taut1 jerk it forward and back quickly a few times1 it will be seen to move and assume the appearance shown in the figure2 and that portion shown between the two vertical lines represents one complete wave4 ,illustration3 ,,figure #ec4 ,the assumption of this ether and the vibratory motions of it form the only explanation that is capable of accounting for all of the phenomena of light4 ,all other theories advanced have failed to stand the test2 sooner or later some phenomena have appeared which could not be explained by them4 ,light waves are known to travel through space in straight lines until they meet with some medium which is capable either of reflecting1 refracting1 or absorbing them4 ,the rectilinear propagation of light1 consisting of vibratory motion1 is one of the most difficult parts of the theory to explain4 ,it involves rather deep study and more mathematics than the scope of this work will warrant4 ,suffice it to say that the rectilinear propagation is brought about through the interference of light waves4 ,an analogy of this can be found in a stream of water4 ,it is well known that a stream of water issuing from the nozzle of a garden hose moves in a straight line until gradually forced into a spray by the resistance of the air4 ,yet the water passing through the hose is interfered with on all sides and on all sides there is a tendency to deflect it4 ,if the water were to move along slowly so that we could observe the action on one side independently of the balance of the stream1 we should see a series of waves being formed by every particle of the hose which offers resistance to the flow4 ,the waves formed in the interior of the hose on all sides are interfered with by waves from all other directions and the result is motion in a straight line4 ,in a similar way it may be conceived that the millions of light waves emitted from a luminous body interfere with each other and thus cause light rays to move in a straight line4 ,light is a form of energy and can be converted into other forms of energy4 ,it can be converted into heat1 for instance1 or can be used to produce chemical effects4 ,light differs from heat only in the rate of vibration and the length of the ether waves4 ,heat can be reflected in the same manner as light1 as the following experiment will show3 ,arrange two ordinary reflectors as shown in ,figure #ed4 ,in the focal point of one1 place a heated iron ball or something of the kind2 if this be hot enough1 it will ignite paper suspended in the focal point of the other reflector1 although a thermometer placed anywhere between the two reflectors will give only a small indication of a rise in temperature4 ,illustration3 ,,figure #ed4 ,all light rays as well as heat rays are in themselves invisible2 we can see only the object which emits or reflects them4 ,if a beam of light be allowed to enter a darkened room1 as shown in ,figure #ee1 we shall probably be able to see the whole path of the rays illuminated1 as well as the spot on the floor4 ,but this will be because of particles of dust in the air which reflect the rays to our eyes4 ,if we introduce some smoke into the room1 we shall see the light much more plainly because there are now more particles of matter to reflect it4 ,on the other hand1 if special precautions are taken to have the air absolutely clear of dust1 we shall be able to see nothing but the spot on the floor4 ,illustration3 ,,figure #ee4 ,light travels through space at the rate of about #ahf1jjj miles per second4 ,white light is a combination of light of many colors1 but the speed of transmission is the same for all colors4 ,the length of waves and the rate of vibrations1 however1 vary4 ,the red rays have the longest waves and the slowest rate of vibration2 they vibrate about three hundred ninety-five billion times per second and the wave length is about #j4jjjh millimeters4 ,the violet rays possess a wave length of about seven hundred sixty-three billion per second4 ,there are light waves which are longer than the red rays and these are known as infra red4 ,they are not visible to the eye but their existence can be proved in many ways4 ,light waves shorter than the violet are also invisible and are known as ultra violet4 ,these have much importance in photography and to this class belong the ,x ray4 ,illustration3 ,,figure #ef4 ,we have mentioned above that white light is a combination of light rays of many colors4 ,this can be proved by the following experiments3 ,if we arrange to have a beam of sunlight pass through a small hole into a darkened room1 it will pass to the wall on the opposite side in a straight line and give us white illumination upon a small spot4 ,if we now arrange a prism in the path of this ray or beam of light1 we shall find that the light no longer passes straight to the wall but that instead1 it is bent in a certain direction and furthermore shows us a brilliant array of colors4 ,this is illustrated in ,figure #ef4 ,the rays are thus shown to be separated into their constituent colors2 red is shown at the top and the following colors merge imperceptibly into one another--orange1 yellow1 green1 blue1 indigo1 and finally violet at the bottom4 ,the reason for this change is that the rays of light on entering the glass are slowed down--those of the higher rate of vibration more than the others4 ,the violet rays are thus said to be more refrangible than the red1 for instance4 ,the colors thus produced are simple colors4 ,this is proved by the fact that if the light is passed on through another prism1 it will be again reflected but will not be resolved into other colors2 although whichever color is carried to the next prism will spread out and show finer gradations in its color4 ,illustration3 ,,figure #eg4 ,the colors given above are those obtainable from the decomposition of sunlight and make up what is known as the solar spectrum4 ,if instead of sunlight some other illuminant be used1 the arrangement of colors will be different2 and it has been found possible to tell from the colors of the spectrum what substances are burning1 or heated to a luminous degree1 in the source from which the light comes4 ,this method is known as spectrum analysis4 ,there are several ways in which light1 which has thus been separated into its fundamental colors1 can be re-composed so as to give us white light again4 ,one of these methods consists in arranging an inverted prism to receive the light1 as shown in ,figure #eg4 ,the rays leave the second prism parallel and produce the effect of white light4 ,another method consists in gathering the rays from the prism by a lens1 as shown in ,figure #eh4 ,furthermore1 if we take a disc and paint the colors of the solar spectrum upon it in the proper proportions1 as indicated in ,figure #ei1 and cause this disc to be rapidly revolved1 we shall see it as almost white4 ,illustration3 ,,figure #eh4 ,illustration3 ,,figure #ei4 ,another fact which goes to prove the undulatory1 or motion1 theory of light is that two sources of light arranged to oppose each other can actually be made to produce darkness4 ,to do this1 the waves of one source of light must be made so that they exactly oppose those of the other2 thus they destroy each other and destroy what light there is in either4 ,there are other methods1 but this can be partially accomplished in the following manner3 ,two small mirrors of black glass or of metal are placed1 as shown in ,figure #fj1 very close together and so that they form an angle of nearly #ahj degrees4 ,a beam of light arranged to fall upon both of the mirrors will be reflected in such a manner that the two halves interfere with each other and cause bands of light and darkness to appear4 ,the dark lines are due to the opposition and nullification of certain of the light waves4 ,illustration3 ,,figure #fj4 ,illustration3 ,,figure #fa4 ,the intensity of light diminishes directly as the square of the distance through which it is transmitted4 ,this is illustrated in ,figure #fa4 ,the light1 starting from a point1 is limited by the size of the first square at the left2 it spreads out more and more1 and illuminates larger and larger spaces4 ,exact measurement will show that the spaces illuminated by a ray of light are always exactly proportional to the square of the distance from the point of light4 ,this law1 however1 applies strictly only if the distances considered are long compared to the source of light1 so that the light may be considered as being a mathematical point1 that is1 having no physical dimensions4 ,if the source of light1 for instance1 were of the same size as the first opening and of uniform intensity there would result the same intensity of illumination of a similar space at all distances4 ,there would1 however1 be an outer fringe of light which would be proportional to the law of inverse squares4 ,many reflectors are arranged to throw very nearly parallel rays2 and with these the intensity remains the same except for absorption1 which is ordinarily not very great4 ,we see things only through the rays of light they reflect4 ,all colored bodies have this peculiarity1 viz41 that they are capable of reflecting only such rays as make up the color the body is said to possess4 ,a red body1 for instance1 absorbs all colors except red and reflects red only4 ,a black body absorbs all rays and a perfectly dull black body is visible only by contrast2 that is1 we do not see it but we are aware that there is something invisible before our eyes4 ,when we are in a perfectly dark room1 we see nothing but we have blackness before our eyes4 ,a perfectly white body is one which reflects all of the rays of light and absorbs none4 ,when we view things through colored glasses1 we see them only in the colors which the glass will transmit4 ,if we view a red body through a green glass or under a green light1 it will appear black because it is capable of reflecting only red rays and in the green light there are no red rays2 hence there is nothing to be reflected and the red appears black4 ,,chapter ,,ix4 ,,principles ,,of ,,vision4 ,through the medium of our eyes we see objects by means of the light which is reflected from them4 ,this light enters the eye and forms an inverted image of the object upon the retina1 just as an inverted image is formed upon the ground glass of a camera4 ,this impression made upon the eye is corrected automatically1 so that1 although we see everything upside down1 we are not at all aware of so doing4 ,the proof of this peculiarity of the eye is found in cases where persons born blind have later through operations acquired sight4 ,in the eyes of slaughtered cattle also the image can be seen inverted4 ,a further proof that we are able thus to adjust ourselves is found in the experience of persons using cameras with ground glass screens4 ,the image on these screens is always inverted both horizontally and vertically4 ,the user soon learns to see his object1 although inverted1 in the natural way1 that is1 vertically1 because this is so plain that he must take it into account at every focusing4 ,he does not1 however1 accommodate himself to the reversal from right to left because this is of no consequence ordinarily and is not noticed4 ,many photographers1 who have been accustomed to the vertical inversion1 still find themselves confused when trying to locate the right and left of a view seen through the lens4 ,unless a special arrangement of lenses is provided1 all images cast upon screens through small openings appear inverted4 ,the reason for this can be seen from ,figure #fb4 ,it is obvious that no other light can reach the bottom of the screen through the pin hole ,o1 at the left of the figure1 except that coming from the flame of the candle2 also that no other light can reach the top of the screen except that reflected from the bottom of the candle at the right4 ,hence the image of the candle appears inverted4 ,illustration3 ,,figure #fb4 ,illustration3 ,,figure #fc4 ,a general understanding of the structure of the eye can be had from ,figure #fc4 ,w indicates a watery substance in the front of the eye2 ,i is the iris which has power to contract or expand and thus regulate the quantity of light admitted to the eye2 ,p is the pupil2 ,l is the lens2 and ,r is the retina which connects with the optic nerve and the brain4 ,the lens is made up of several parts having different indexes of refraction4 ,the whole resembles an ordinary convex lens but has considerable power of adjustment4 ,when looking at objects close by1 for instance1 the pupil can often be seen to bulge out which is its method of accommodating itself to objects close at hand4 ,to the iris falls the duty of regulating the quantity of light which is to reach the retina4 ,if confronted by a bright light1 it closes partially2 in a dim light1 it opens out wide4 ,when subject to a flickering light1 there is a tendency to follow the flickerings by rapid opening and closing1 which causes pain4 ,if subject to flickerings long enough1 however1 the pain becomes somewhat less1 probably because the iris has come to rest on an intermediate point4 ,an image formed upon the retina remains for some time1 the time varying with the intensity of the light4 ,very intense impressions are supposed to last about one twenty-fifth of a second2 milder ones as long as one-tenth of a second4 ,this tendency to retain images is known as the persistence of vision and can be noticed in many ways4 ,a twenty-five cycle alternating current falls to zero fifty times in one second2 and fifty times in each second there is a slight cooling off of the incandescent filament4 ,yet the variation in the intensity of the light is noticeable4 ,many of the sleight-of-hand tricks depend upon this persistence of vision and the projection of moving pictures would be impossible without it4 ,we are able to judge distance principally through the fact that we have two eyes4 ,if our eyes were immovable1 we should see two images for every object4 ,but as they are movable and as both normally point directly at the object we are looking at1 their axes form angles with each other and in this way we are enabled to judge the distance1 as well as other qualities of objects4 ,when both eyes are centered upon an object1 the impressions received by the brain from both sources are mixed1 and the picture we become conscious of is a composite of the two images in the eyes4 ,this is verified by the fact that many persons with defective vision can see much more clearly with one eye than with both4 ,they are not able to focus both eyes upon the same point and thus the perfectly clear picture which may exist in one eye is mixed with an uncertain picture in the other4 ,in youth normal eyes are able to adjust themselves to different intensities of light and different distances very rapidly4 ,this power is largely curtailed as age advances4 ,where a young person can almost instantly1 after gazing at some distant object1 turn to a newspaper and read1 the eyes of a person of advanced age generally require considerable time before they can adjust themselves in the same way4 ,quite frequently1 however1 very old people regain their powers of vision and become able to do without the glasses formerly used4 ,all of the above facts should be thoroughly understood by those having to do with illumination used by a mixed audience4 ,light that may seem perfectly satisfactory to one may be entirely unsuitable for another4 ,,chapter ,x4 ,,reflection4 ,light may be reflected from opaque or transparent bodies such as glass4 ,in the case of transparent bodies1 the reflected rays are not noticeable unless the ground behind the reflecting body is dark4 ,if there is much light behind a pane of glass1 for instance1 the pupil of the eye will be partially closed and not be able to see the faint light which is reflected4 ,as we gradually darken the space behind the glass1 the image begins to appear more and more distinct1 partly from contrast with the dark background and partly on account of the increased opening of the pupil4 ,this can be readily noticed if some evening out of a dimly-lighted room we look at some object just discernible4 ,if we then turn on the light suddenly1 the object will at once disappear but reflections will appear in the glass where there were none before4 ,the reflections from clear glass are much stronger at an angle than when the rays are thrown straight back4 ,this can be seen by placing any object directly in front of a pane of glass with a dark background4 ,if we place the eye so as to receive only those rays which are reflected directly back1 we shall obtain but a weak reflection4 ,if1 however1 we place the object a little to one side and stand close to the glass1 we shall see the object almost as plainly as in a regular mirror4 ,a ray of light is always reflected at exactly the same angle at which it strikes1 the reflecting body2 that is1 the angle of incidence is equal and opposite to the angle of reflection4 ,this can be illustrated by ,figure #fd4 ,if a mirror be attached to the pointer in the position shown at an angle of exactly ninety degrees and a beam of light be allowed to enter through the slit at the top1 it will be reflected back exactly to the spot at which it entered4 ,if we then turn the pointer slightly1 we shall notice that the reflection of the beam of light moves twice as fast as the pointer and1 when the pointer occupies the position indicated by broken lines1 the light will be reflected at right angles to the line along which it enters4 ,if the mirror is turned still more1 the same law will hold2 so that1 if the mirror were turned through an angle of nearly ninety degrees1 the reflected beam of light would in the same space of time make an angle of nearly one hundred eighty degrees4 ,illustration3 ,,figure #fd4 ,reflected light results in the formation of images in mirrors and other reflecting bodies and1 by bearing in mind the law of reflection given above1 we can readily explain how these images are formed and the manner in which they appear to us4 ,illustration3 ,,figure #fe4 ,let ,n1 ,figure #fe be an object in front of the mirror4 ,the only rays that are reflected back to the eye are those that strike the mirror at the proper angle4 ,all others are wasted with reference to the particular position of the eye4 ,if the eye and the object reflected are equally distant from the mirror1 we need but draw a line at right angles to the mirror and half way between the eye and the object and1 from these two1 draw lines to the point at which the perpendicular line strikes the mirror4 ,the two lines thus drawn will give us the path of the incident and the reflected rays4 ,the image will appear to lie in the direction from which the reflected ray comes and as far behind the mirror as the object is in front of it4 ,if the eye and the object to be reflected are not equally distant from the mirror1 it is more difficult to find the paths of the rays and it simplifies matters very much to use the following construction3 ,draw a line from the object before the mirror at right angles to the mirror and extend it behind the mirror as far as the object is in front of it4 ,from this point behind the mirror1 draw another line to the eye4 ,by drawing a third line from the object to the point in the mirror where this line1 from back of the mirror to the eye1 crosses it1 we shall obtain the paths of the rays and the position of the image in the mirror4 ,the image will exist in the mirror at the point where the reflected and incident rays meet but will have the appearance of lying some distance behind the mirror4 ,this is illustrated in ,figure #fe1 ,n being the object reflected and ,m the apparent position of the image to the eyes as located in the cut4 ,illustration3 ,,figure #ff4 ,illustration3 ,,figure #fg4 ,illustration3 ,,figure #fh4 ,in ,figures #ff and #fg the same construction is used to show the appearance of arrows as they are reflected from a mirror to the eye4 ,objects standing erect over horizontal mirrors or arranged at right angles to mirrors and looked at1 as in ,figure #fh1 always appear inverted4 ,this can be noticed in quiet ponds of clear water which give reflections of trees and other objects4 ,figure #fh shows two arrows1 one horizontal1 the other vertical2 by the construction in the figure one appears inverted1 the other not4 ,if the arrow were placed in the position indicated by broken lines1 the eye would see only the butt4 ,if the arrow were placed a little nearer the horizontal1 it would appear in its natural position2 if a little more vertical1 it would appear inverted in the mirror4 ,illustration3 ,,figure #fi4 ,all objects seen in mirrors are reversed with reference to right and left4 ,a pocket on the left side of a person facing a mirror will appear to be on the right side4 ,printed matter held before a mirror will appear just as it would if seen through the paper from the back side and will have to be read from right to left4 ,illustration3 ,,figure #gj4 ,illustration3 ,,figure #ga4 ,illustration3 ,,figure #gb4 ,if an object be placed between two parallel mirrors as ,b1 ,figure #fi1 there will be a vast number of reflections visible at the point ,d4 ,several reflections of ,b will come to the eye in the manner indicated but there will be a large number of additional reflections4 ,if the mirrors are exactly parallel and absolutely smooth1 the number of reflections would theoretically be infinite4 ,at each reflection1 however1 some light is absorbed and some diffused so that many of the reflections are not discernible4 ,two mirrors set opposite each other will also give many reflections of each other as indicated in ,figure #gj4 ,the images seen in parallel mirrors all appear arranged in straight lines on both sides1 as indicated in ,figure #fi4 ,if now one of the mirrors be inclined so as to form an angle with the other1 the long line of images will seem to become curved and finally lie in a circle4 ,if the mirrors be placed at right angles to each other1 as in ,figure #ga1 there will be three reflections of the object ,c visible and these will reach the eye by the paths shown4 ,if the mirrors be placed at an angle of sixty degrees to each other1 five images will appear as shown in ,figure #gb1 in which ,a is the object being reflected4 ,the following tabulation shows the number of images obtainable at different angles between the mirrors4 -------------------------- ,angle between ,number of mirrors images -------------------------- #ij degrees #c #gb degrees #d #fj degrees #e #de degrees #g #cj degrees #aa -------------------------- ,illustration3 ,,figure #gc4 ,instead of being plain1 mirrors may be either concave or convex4 ,a concave mirror is hollowed out in conformity with a small section of the surface of a sphere4 ,if a piece of glass be cut out of a hollow sphere1 the inner side of it will show the surface of a concave1 and the outer side1 the surface of a convex mirror4 ,a section of a concave mirror is shown in ,figure #gc4 ,c is the center of curvature and any line drawn from the surface of the mirror to this center is at right angles1 or normal1 to the curvature of the mirror4 ,a ray of light emanating from this center will be reflected straight back to it4 ,if the source of light be moved a little nearer to the mirror1 the light reflected will be spread out more and come to a focus farther back from the glass2 if it be moved farther back from the glass1 the rays will be focused nearer the mirror4 ,thus if a light be placed at ,a1 its rays will be focused at ,d and a light placed at ,d will focus at ,a4 ,this can be seen by the lines which represent the rays of light4 ,the two points at which a source of light will thus focus are known as the conjugate foci of the mirror4 ,if such a mirror receives parallel rays of light1 they will be reflected and come to a focus at a point midway between the mirror and the center of curvature4 ,this point is known as the principal focus of the mirror1 and the distance between it and the mirror is called the focal length of the mirror4 ,a source of light placed at this point will throw out parallel rays from the mirror4 ,if the light be moved closer to the mirror1 the reflected rays will spread out2 while if moved farther away1 the light will come to a focus at some distant point1 as shown above4 ,figure #gd can be used to illustrate the manner in which a concave mirror reflects the light from an object placed before it4 ,from the upper point of the large arrow1 rays of light emanate in all directions4 ,all that strike the face of the mirror are thrown to a certain point which can be found by tracing out the lines1 using the small arrows as guides4 ,at this point will appear the image of the top of the arrow4 ,it will be noted that it is inverted4 ,the rays from the lower part of the arrow are of course all reflected in the same manner4 ,illustration3 ,,figure #gd4 ,with mirrors of this kind1 the position of the object with reference to the focal length and center of curvature is of great importance4 ,if the object be placed in the position shown as the image in ,figure #gd1 the image will appear as though it were in place of the object2 it will be much enlarged and also inverted4 ,if the object is placed between the principal focus and the mirror1 it will appear to lie behind the mirror as shown in ,figure #ge4 ,in this case it will not be inverted4 ,illustration3 ,,figure #ge4 ,when concave mirrors forming large sections of spheres are used1 the rays reflected from the outer edges will not all meet exactly at the focal point4 ,there will then be a somewhat fuzzy image formed4 ,this is illustrated in ,figure #gf4 ,in order to obtain a perfectly clear and distinct image1 only the central part of concave mirrors should be used4 ,illustration3 ,,figure #gf4 ,convex mirrors are not much used4 ,sometimes glass spheres are set up to show miniature reflections of scenery2 convex mirrors are also found in the lobbies of theaters and in places of amusement to amuse the patrons with the caricatures of themselves reflected in them4 ,illustration3 ,,figure #gg4 ,all of the rays that strike a convex mirror are reflected back in such a manner that they seem to come from a common point behind the mirror4 ,this is shown in ,figure #gg4 ,the center of curvature here is behind the mirror but the paths of the various rays can be determined as before explained4 ,thus we shall find that every ray1 striking the mirror from a certain point1 is reflected back in a direction which gives it the appearance of coming from a certain point behind the mirror4 ,two such points are shown in ,figure #gg4 ,illustration3 ,,figure #gh4 ,in ,figure #gh we have drawn the arrow and the image it would produce in the mirror4 ,if the mirror forms a section of a sphere1 the object reflected will appear reduced in size in all directions4 ,if the mirror forms merely a section of a cylinder1 a person standing in front of it will appear very much shorter than natural but of full width thus presenting a ridiculous appearance4 ,convex and concave mirrors are often combined and if properly set1 a person standing in front of one may see himself either very much elongated or shortened4 ,,chapter ,,xi4 ,,refraction4 ,if a straight stick or pencil be plunged into a vessel containing water1 it will appear to be bent4 ,the reason for this appearance is given in detail in ,figure #gi4 ,the only light which can reach the eye from the lower extremity of the stick must reach it by a path similar to that of the bended ray at the left4 ,according to this1 the rays of light leaving the bottom of the stick at ,e bend at the water's edge and meet the eye as shown4 ,to the eye the rays1 by which it sees the end of the stick1 appear to come from the direction ,f2 hence the stick is seen crooked4 ,when a ray of light passes from air into a denser medium such as water or glass1 the ray appears to be bent somewhat1 as illustrated at the left of ,figure #gi4 ,this bending of the rays of light is called refraction4 ,illustration3 ,,figure #gi4 ,the fact of refraction can be further verified by placing an object ,g into an empty vessel in the position shown4 ,in this position the object is not visible to the eye4 ,by slowly filling the vessel with water1 the object will gradually appear and will seem to lie in the direction of the straight dotted line4 ,illustration3 ,,figure #hj4 ,the bending or refraction of light rays is governed by a law which holds in all cases4 ,the bending differs with different kinds of glass1 with water1 with oils1 or even with water mixed with chemicals2 but no matter how much the bending may differ with different materials1 for each material there is a fixed ratio between the angle at which the light enters and the angle at which it continues in the material4 ,this ratio is known as the index of refraction4 ,for water it is about #a4cc2 for glass about #a4e2 for the diamond about #b4e2 etc4 ,this can perhaps be most easily explained by reference to ,figure #hj4 ,here the top of the shaded space represents the surface of the glass at which the light enters4 ,the line ,e is drawn at right angles to this surface and the various lines1 meeting in the center of the circle1 represent different rays of light falling upon the glass at different angles4 ,the heavy line shows the ray of light striking the glass and passing through it4 ,similarly each line is drawn differently and the nature of the lines will act as a guide by which the angle of incidence upon the glass and the angle at which the rays continue through the glass can be traced4 ,when it is said that glass has an index of refraction of #a4e1 or #c_/b1 it means that the sine of the angle of incidence is #a4e times as great as the sine of the angle of refraction4 ,the sine of the angle of incidence is proportional to the length of a line drawn from the vertical ,e to the periphery of a circle1 outside of the glass or other substance1 to where it meets the ray2 and the sine of the angle of refraction is proportional to the length of a line drawn from the same vertical to the periphery of the same circle1 inside of the glass or other substance1 where it meets the ray4 ,in order to lay out the path of a ray through the material1 its angle of incidence being known1 we may resort to the construction shown in ,figure #hj4 ,draw the incident ray at its proper angle and the vertical line at right angles to the surface of the material4 ,from the point ,a1 where the ray enters the circle1 and at right angles to the vertical line1 draw the line #a4 ,measure the distance from ,a to the vertical line and divide it by the index of refraction2 and on a continuation of the line #a1 lay off the distance as found4 ,from the point so located1 draw a line parallel to the vertical until it intersects the circle at the bottom4 ,from the point at which the ray enters the medium1 draw another line to where the last line drawn strikes the circle4 ,this line will give the direction in which the ray is propagated in the medium4 ,for glass1 the index of refraction is taken as #c_/b2 hence the line #a must contain three parts1 while the continuation contains two of the same length4 ,upon leaving the medium1 the ray is bent back again so that it continues in a direction parallel to that at which it entered1 as shown in ,fig4 #ha2 and thus the case is reversed4 ,illustration3 ,,figure #ha4 ,illustration3 ,,figure #hb4 ,figure #hb is an illustration of how both refracted and reflected rays may be several times reflected4 ,if one will hold a match close to a mirror1 looking at it somewhat from the side1 there will be visible six or eight distinct reflections of it4 ,these will be of different intensity4 ,if a source of light has its origin in a medium denser than air1 it will be bent as shown in ,figure #hc4 ,in such a case some of the rays do not leave the medium at all but are reflected back into it1 as indicated at the right4 ,the heavy line indicates what is commonly known as the critical angle4 ,this angle varies with different substances and is the angle at which the refracted ray of light skims along the surface and does not pass out4 ,all rays emitted at a lower angle are returned back into the medium4 ,if an electric light were immersed in water1 only the rays of light at the left of the black line would be visible to an eye outside4 ,illustration3 ,,figure #hc4 ,figure #hd is an illustration of an equilateral prism4 ,here we have refraction on both surfaces and a light placed at ,a would be seen by the eye as located at ,b4 ,with prisms it is easily possible to locate a light so that it may be seen in two positions at the same time4 ,illustration3 ,,figure #hd4 ,figure #he shows a double convex lens4 ,both sides of it are segments of circles or sections of a sphere4 ,the center of curvature or the radius of one side is at ,a and that of the other at ,b4 ,each minute particle on the surface of such a part of a sphere may be looked upon as the surface of a prism1 the inclination of it being indicated by a line drawn at right angles to a line passing from the point through the center of curvature4 ,this is illustrated in the figure by the short heavy lines at right angles to the broken lines centering at ,a and ,b4 ,illustration3 ,,figure #he4 ,by using the construction explained with ,figure #hj and using for the left-hand surface the circle of broken lines and for the surface at ,e the circle of solid lines1 we find the path of the ray coming from ,c to cross the principal optical axis at ,a4 ,a similar construction for a ray at the lower side of the lens would bring it to the same point and furthermore all parallel rays would focus at this point4 ,this point is thus known as the principal focus of the lens1 and the distance between this point and the lens is called the focal length of the lens4 ,every lens has two principal foci1 one on either side and at equal distances from the lens4 ,illustration3 ,,figure #hf4 ,illustration3 ,,figure #hg4 ,if1 instead of subjecting the lens to parallel rays1 we use rays emanating from a central point on the optical axis1 they will come to a focus at some different point on the other side of the lens1 as illustrated in ,figure #hf4 ,if the light be placed at the principal focus of the lens1 the rays leaving the lens will be parallel4 ,if the light be brought nearer the lens1 the rays leaving it will spread out as shown in ,figure #hg2 they will leave the lens in a direction such as to make upon an observer from in front the impression that they are coming from the point ,c behind the lens4 ,if the light be placed beyond the principal focus of the lens1 the rays will converge to a point some distance ahead of it4 ,this distance varies with the position of the light and the two points 7light on one side and focus on the other7 are known as conjugate foci of the lens4 ,illustration3 ,,figure #hh4 ,if an object be projected through a lens as1 for instance1 the arrow at the right of ,figure #hh1 it will appear upon a screen placed on the opposite side1 but will be inverted4 ,the reason for this is that the rays of light striking the lens from the top of the arrow will be refracted as shown1 cross the focal point ,f1 and meet those which come from the same point and pass through the center of the lens in a straight line2 and thus the image of the arrow head will appear at the bottom2 in a similar manner the image of the tail of the arrow will appear at the top4 ,the flatter the lens1 the farther away will be the point at which the image is formed4 ,illustration3 ,,figure #hi4 ,if such a lens be placed over an object1 the light will come to the eye as shown in ,figure #hi4 ,the solid lines show the rays by which the eye receives the light and the broken lines show the direction from which it appears to come4 ,thus we see the object much enlarged4 ,a lens used in this manner is spoken of as a reading glass1 and the greater the curvature1 the greater its magnifying power4 ,illustration3 ,,figure #ij4 ,illustration3 ,,figure #ia4 ,in ,figure #ij is illustrated a double concave lens4 ,parallel rays entering this lens are scattered by it1 as shown4 ,therefore1 if such a lens be placed over an object1 the light from the extremity of the object will come to the eye as indicated in ,figure #ia1 but will give the appearance of coming along the lines ,h and ,i4 ,thus the object will be seen much reduced in size4 ,such lenses are sometimes used by artists to bring landscapes to a reduced size so that they may be viewed as a whole more easily4 ,illustration3 ,,figure #ib4 ,the general forms of lenses are shown in ,figure #ib1 7a7 ,is a plano-convex lens 7b7 ,is a double convex lens 7c7 ,is a convexo-concave lens1 or convex meniscus 7d7 ,is a plano-concave lens 7e7 ,is a double concave lens 7f7 ,is a concavo-convex lens1 or concave meniscus4 ,,chapter ,,xii4 ,,optical ,,instruments4 ,in most optical instruments1 lenses are used for the purpose of gathering a large number of rays of light and altering the apparent direction of the rays so that an enlarged picture may be presented to the eye4 ,in order to accomplish this1 it is necessary that the rays of light be bent or refracted4 ,this refraction1 we have already seen1 is always accompanied by a dispersion which causes the light to be dissolved into its original colors more or less4 ,this has been illustrated by means of prisms4 ,illustration3 ,,figure #ic4 ,illustration3 ,,figure #id4 ,wherever a single lens is used1 the light around the edges of the illuminated space is always more or less colored1 varying with the illuminant used4 ,such coloring is most noticeable along the edges of projected pictures but it also exists1 though to a less noticeable degree1 over the whole field1 showing least in the center4 ,the light which is thus refracted and dispersed by one prism may be gathered again by another1 as shown in ,figure #ic1 but the light rays after passing through the second prism will be exactly parallel to the ray striking the first4 ,the light coming out of the second prism will appear white but it will be impossible either to enlarge or diminish the size of a picture in this way2 hence lenses1 corrected to give white light in this manner1 would be of no use4 ,fortunately it has been found that1 with different kinds of glass1 the ratio of refraction to dispersion is different2 and by combining two pieces of glass of different nature1 it is possible to recombine the colors without causing the emergent ray to become parallel to the incident ray4 ,consider1 for instance1 ,figure #id in which we have drawn a prism made up of two different kinds of glass4 ,if the right half were of a glass having the same index of refraction as the left1 for the red rays for instance1 these would continue through both in a straight line4 ,if the dispersion were less in the right half1 i4e41 if the violet rays were refracted less--sufficiently less to cause them to approach the red--they would meet the latter at some point outside of the prism and combine into white light again1 thus eliminating the colors ordinarily visible through single glass lenses4 ,illustration3 ,,figure #ie4 ,whenever it is necessary to project especially good pictures upon a screen1 lenses corrected in some such manner as outlined above are always used and the lenses are often combined as shown in ,figure #ie4 ,in this figure1 ,r indicates the line1 through the principal axis1 at which the red rays refracted by lens #a alone would strike2 and ,v1 the line where the violet rays would be projected4 ,the addition of lens #b brings the red and violet together again at ,w4 ,a combination of two such lenses1 placed the proper distance apart and the surfaces properly proportioned1 may be made to combine any two of the colors of the spectrum4 ,hence even with these corrected lenses there is always some coloring on the screen although it is hardly noticeable4 ,illustration3 ,,figure #if4 ,illustration3 ,,figure #ig4 ,illustration3 ,,figure #ih4 ,figures #if1 #ig1 and #ih are drawings showing the manner in which objective lenses are usually made up4 ,the types at the right and left are used for camera work1 while the one shown in the center is used mostly for moving picture and stereopticon projection4 ,the end having the separate lenses is turned towards the light4 ,those shown in contact are glued together by the use of ,canadian balsam4 ,illustration3 ,,figure #ii4 ,the optical system of the ordinary telescope is shown in ,figure #ii4 ,light from the distant object ,a is gathered by the large lens ,b and an image is formed as indicated by the small arrow4 ,this image acts as the object to lens ,c and is projected to lens ,d where the rays of light are strongly refracted1 entering the eye by angles which cause an enlarged view of the object at ,e1 as indicated4 ,there must of course be some means by which the lenses may be adjusted to each other for focusing4 ,illustration3 ,,figure #ajj4 ,the arrangement of the opera glass in ,figure #ajj is quite different from the above because of the reduced size of the instrument and for the reason that an erect picture is desired1 whereas the telescope above gives an inverted one4 ,the principal difference between the two is in the eyepiece4 ,in the opera glass this is a concave lens while in the other it is a convex lens4 ,in this case it is necessary to have the eye very close to the lens to catch the rays of light4 ,the opera glass1 as well as the telescope1 must be provided with means of varying the distance between the lenses according to the distance of the object viewed1 for the purpose of focusing4 ,in some telescopes and also opera glasses1 prisms are used for the purpose of obtaining erect images4 ,figure #aja will show how the rays of light entering a prism are reflected and the image reversed thereby4 ,illustration3 ,,figure #aja4 ,figure #ajb is an explanation of the reflecting stereoscope4 ,let the black circles represent the eyes of the observer and let ,m represent two mirrors placed as shown4 ,if two pictures taken by a stereoscopic camera are placed as indicated by the arrows at the right and the left1 they will appear superimposed in the position of the arrow in the rear4 ,illustration3 ,,figure #ajb4 ,illustration3 ,,figure #ajc4 ,the refracting stereoscope is the one mostly used and the plan of it is shown in ,figure #ajc4 ,pictures for use with stereoscopes are taken by special cameras provided with two lenses placed about as far apart as the human eyes and mounted together4 ,stereoscopic effects may1 however1 be produced even without this precaution and it is possible to obtain some queer results by combining certain pictures4 ,in the so-called 8,camera ,lucida01 prisms of the type shown in ,figures #ajd and #aje are used4 ,at the left is a combination lens and reflecting prism which gives an erect image1 and ,figure #aje is a prism also designed to give erect images4 ,such instruments are used for sketching4 ,they may be made to throw an image upon a small screen where its lines may be traced out by the artist4 ,illustration3 ,,figure #ajd4 ,illustration3 ,,figure #aje4 ,the most important optical instrument with which we have to deal is the projecting arc lamp and its optical system4 ,the passage of light through this system of lenses is altogether different from that passing through a camera lens for instance4 ,in a camera lens the picture is formed upon the ground glass screen by the light reflected from the object4 ,from any single point of the object1 rays of light strike all parts of the lens1 pass through it1 and are recombined or focused at some point behind it4 ,under these conditions1 focus can be obtained only at a certain distance behind the lens1 this distance varying with the distance of the object whose light is being received by the lens4 ,illustration3 ,,figure #ajf4 ,illustration3 ,,figure #ajg4 ,illustration3 ,,figure #ajh4 ,with our projecting lens we have no reflected light leaving the object in all directions1 but instead we have rays of light having definite directions4 ,this can be seen from ,figure #ajf4 ,the light used must come from a point source1 the smaller and the more intense it is the better4 ,this light is gathered by condensers1 as shown at ,c1 which are so arranged as to focus the light in the center of the objective lens ,d4 ,in the moving-picture machine the light1 before reaching the objective lens1 is passed through the film as indicated1 the arrows representing sections of film4 ,the picture projected in this manner can be made to appear upon a screen in front of the object lenses at any distance1 but the farther away it is1 the larger it will be and the less bright the illumination of it4 ,a picture projected in this manner is always inverted1 and1 in order to have it appear right side up1 it must be placed in position upside down4 ,figures #ajg and #ajh show arrangement of lenses frequently used as condensers4 ,,chapter ,,xiii4 ,,optical ,,illusions4 ,illustration3 ,,figure #aji4 ,illustration3 ,,figure #aaj4 ,illustration3 ,,figure #aaa4 ,illustration3 ,,figure #aab4 ,the eye is easily deceived and is also very inaccurate in its judgment4 ,in ,figures #aji to #aaa1 all of the lines are of precisely the same length1 yet they appear to differ considerably4 ,the reason for this error in the estimation of objects is not known4 ,it is especially noticeable with such objects as a high hat2 almost any one will estimate the height of a silk hat as much greater than it really is4 ,in general1 white objects also appear to be much larger than black objects4 ,this can be seen by the two inscribed squares one black and the other white in ,figure #aab2 both of these are of exactly the same size4 ,probably the fact that more light reaches the eye from a light-colored object than from a dark-colored one of equal proportions causes the impression of greater size4 ,that the mind has the power of mixing contradictory or conflicting impressions made upon it is proved by many facts4 ,if a star1 ,figure #aac1 be pinned to the center of a wheel and rapidly revolved1 the center of it will appear jet black2 while the outer portions1 made up of the points and the white background1 will appear grey which will gradually fade to a lighter shade from the center black spot outward4 ,illustration3 ,,figure #aac4 ,illustration3 ,,figure #aad4 ,if a card be provided with a picture of a bird on one side and a ring on the other1 ,figure #aad1 and this be rapidly spun on one corner1 after the manner of a top1 the bird will appear to be in the center of the ring4 ,this effect is due to the persistence of vision2 an image formed upon the retina requires some time before it can be eliminated so that both images appear together4 ,this persistence of vision and the power of suggestion are made use of in a well-known act which consists of apparently throwing something1 for instance a guinea pig1 into the air and causing it to vanish4 ,to perform this trick1 the operator holds the pig in his hand and makes a few motions suggestive of tossing it into the air4 ,then1 with a final more extreme motion on the downward swing of his hand1 he drops the pig and swiftly moves his empty hand upward4 ,due to the persistence of vision1 the audience actually still sees the pig and due to the suggestion of tossing the eyes look upward1 and thus the persistence of vision and the power of suggestion create the illusion4 ,illustration3 ,,figure #aae4 ,dissolving ,views of ,living ,pictures4--,this act requires a large glass plate of good clear quality arranged upon the stage1 as shown in ,figure #aae4 ,one of the poses is arranged as at the black circle behind the glass and when illuminated is seen by the audience4 ,the other is arranged at one side4 ,the lighting of both is connected to the same dimmers in such a manner that when the light of one is increasing1 that of the other is diminishing4 ,thus the two figures are dissolved into one another4 ,the paths of the various rays of light to different parts of the auditorium are shown in the drawing and it is possible to procure perfect registry4 ,human ,figure ,floating or ,performing in ,air4--,this act is arranged by means of a large mirror placed upon the stage as shown in ,figure #aaf4 ,in the pit out of sight of the audience is a revolving table draped in dull black and all of the pit is draped in the same manner4 ,a figure lying upon this table dressed in light clothes will appear erect in the mirror as indicated by the arrow4 ,if now the table is revolved1 the figure will be seen as turning over in the mirror4 ,the figure upon the table may perform a number of evolutions suggestive of floating1 flying1 etc4 ,the black cloth of the pit will reflect no light and only the figure will be visible4 ,if a glass plate is used instead of a mirror1 suitable scenery may be arranged back of it4 ,the figure must of course be brightly illuminated4 ,by moving the table upon which the figure rests across the pit1 the figure will appear to move along4 ,illustration3 ,,figure #aaf4 ,head ,suspended in ,air4--,this act is worked out in bright light4 ,it requires a mirror with a hole in the center of it large enough to admit the head of a person1 as shown in ,figure #aag4 ,above the mirror suitable decorations are provided which cause one looking at the mirror to imagine seeing the back wall of a room4 ,the ceiling must of course be kept out of view as much as possible4 ,a person looking on sees the head and the mirror gives him the impression of vacant space about it4 ,the head must be surrounded by a collar or drapery of some kind so that no reflection of it will be visible4 ,illustration3 ,,figure #aag4 ,illustration3 ,,figure #aah4 ,magic ,cabinet4--,in this act a person enters the cabinet1 ,figure #aah4 ,the outer doors are closed for an instant and then opened4 ,the person has disappeared6 ,the disappearance is brought about by pulling the two mirrors1 arranged inside of the cabinet1 into the position indicated by the dotted lines4 ,when the cabinet is open for inspection1 these are swung to the side and are invisible4 ,the backs are of the same design as the rest of the interior cabinet4 ,when they are pulled together and hide the person behind them1 they reflect the side walls of the cabinet and are not noticed4 ,if the cabinet is well made and the act skilfully performed1 the outer doors may even be omitted4 ,head ,resting on ,table4--,for this act a hole large enough to allow a person's head to project through is cut in the top of a table1 ,figure #aai4 ,this table has only two legs and is fitted up with mirrors1 as indicated by shading4 ,the reflection of the two legs in the mirror causes the observer to see four and imagine that the space below the table is vacant4 ,illustration3 ,,figure #aai4 ,multiplication of ,images4--,if three large mirrors be arranged in the form of an equilateral triangle1 as indicated in ,figure #abj1 a person standing in the center will see his image reflected so many times that he will receive the impression of being in the midst of a crowd4 ,he will see the reflections of reflections repeated until by absorption so much light is lost that they finally become invisible4 ,illustration3 ,,figure #abj4 ,illustration3 ,,figure #aba4 ,trick ,mirror4--,rather startling effects can be produced by a thinly coated mirror ,a1 ,figure #aba1 behind which an electric light is arranged so that it may be easily turned on4 ,the space behind the mirror being dark1 no one suspects that it is anything but a common looking glass4 ,it is1 however1 quite transparent when the light behind it is turned on4 ,the person in front viewing himself may thus suddenly be brought to see anything that is behind the mirror4 ,if another set of mirrors is arranged1 as shown by shaded lines1 the person in front of the mirror may suddenly be made to see a head floating in the air in front of him4 ,illustration3 ,,figure #abb4 ,the manner in which one can see through a brick is illustrated in ,figure #abb4 ,four mirrors reflect the light around it4 ,if the mirrors are properly arranged1 the person will imagine he is looking through the brick4 ,illustration3 ,,figure #abc4 ,the face of a person may be thrown upon a screen among clouds or other pictures in the manner shown in ,figure #abc4 ,the face occupies the space marked by a half circle and two arc lamps with condensers are trained upon it at very close range4 ,the face itself acts as a reflector projecting itself through the object lens in the center4 ,this act is very trying on the person whose face is reflected4 ,at a certain distance from a concave mirror1 an object will be seen inverted4 ,if the mirror be brought closer1 the image will gradually go out of focus and1 by bringing the mirror still closer1 it will gradually come into focus again but this time erect4 ,properly arranged such a mirror can be made to give weird effects1 for instance a skeleton1 rushing at the observer2 and the image will appear to step out of the mirror4 ,,chapter ,,xiv4 ,,theater ,,buildings4 ,general ,requirements4--,in most cities it is required that theaters be built in locations which give free space for exits on two or more sides4 ,a common requirement is that two sides adjoin public streets or alleys and one or both the other sides be provided with an open court allowing space for fire escapes and connections to street or alley4 ,the buildings are also1 as a rule1 required to be of fireproof construction and divided practically into two parts by strong fire walls2 one of these parts being the auditorium1 that portion of the building used by the public1 and the other1 the stage and its belongings4 ,the main fire hazard of course is on the stage and every possible precaution should be taken1 first to keep a fire from starting1 and second1 to keep it1 should it start1 from communicating to the auditorium4 ,in order to protect the audience in case a fire starts doing damage on the stage1 a steel and asbestos fireproof curtain is generally provided1 large enough to cover the whole proscenium opening and equipped with the necessary apparatus to lower it instantly in case of necessity4 ,in order to keep this curtain in first-class working order it is lowered at the end of every act and in the case of continuous vaudeville performances1 which are not divided into acts1 at least once or twice during each performance4 ,this curtain must be strong enough to withstand the strain of air pressure which would exist in case of a fire raging behind it4 ,this strain1 when one considers the quantity of oil-painted scenery carried by many of the large shows1 is apt to be considerable1 in case of fire4 ,in order further to protect the audience1 a large vent flue is required above the stage4 ,the purpose of this vent is to carry off the smoke and gases4 ,the ,chicago law requires the vent to be equal in area to one-twentieth of the area of the stage and to extend fifteen feet above the highest point of the roof4 ,the hazard to the audience is not so much that of the actual fire1 as of the rapid consumption of oxygen by the flames4 ,this causes strangling4 ,in the case of the ,iroquois ,theater fire the death of many was due almost entirely to this cause4 ,the flames spreading rapidly consumed all of the oxygen in the tightly closed theater2 at the same time the smoke and gases were spreading and hundreds of the audience inhaled this heated and vitiated air with almost instantly fatal results4 ,as a further precaution against fire1 it is now required in all large cities1 that all scenery be fireproofed to such an extent that it will not carry fire4 ,the usual test for this is1 to hold a match to a part of the cloth long enough to burn a hole through it4 ,the fire must go out as soon as the match is withdrawn4 ,the following are extracts from the ,chicago ordinances governing theaters of the larger class3 ,the building must be of fireproof construction4 ,it must adjoin two public highways one of which may be an alley4 ,there must be an open space on both sides of the audience room and in front4 ,all balconies1 galleries1 main floor1 and stage must connect with this open space by means of doors or fire escapes4 ,there must be an opening into this free space also from both sides of stage4 ,the floor level of the highest bank of seats on the main floor shall not be more than three feet above the sidewalk level and the lowest bank of seats not more than eight feet below this level4 ,all stairways must have a width of twenty inches for each one hundred seats in the room1 but no stairway shall be less than four feet in width4 ,an iron stairway must lead from the stage to the fly floor1 rigging loft1 and out onto the roof4 ,all openings leading from the stage to the outside must be vestibuled4 ,above the stage there must be a ventilating flue which must extend fifteen feet above the highest point of the roof and must equal in area one-twentieth of the area of the stage4 ,no seat must be less than twenty inches wide and thirty-four inches from back to back4 ,every aisle must lead directly to an exit4 ,between the stage and the auditorium there must be a wall of masonry and all openings in this wall must be equipped with self-closing doors4 ,there must be a steel curtain provided to close the main stage opening and the lowering of this curtain must be controlled at two different places4 ,the use of wood is allowed only for the stage floor and this must be at least two and three-fourths inches thick4 ,automatic sprinklers must be provided in paint room1 storeroom1 property room1 scene storage room1 carpenter shop1 and dressing rooms4 ,a special fire alarm system must be provided on the stage4 ,all scenery must be treated with a suitable fireproofing compound4 ,all parts of the building used by the audience must be equipped with two separate lighting systems1 one of which is known as the 8,emergency ,lighting0 and must be kept lighted at all times while the audience is in the building4 ,a suitable supply of axes1 pike poles1 and fire extinguishers must be kept on hand4 ,there must be regular drills of employes on the use of these appliances and in the operations of doors and vents4 ,all doors must swing to the outside4 ,illustration3 ,,figure #abd4 ,the ,stage4--,figure #abd is a floor plan of a typical stage1 showing the orchestra pit ,o1 foot lights ,f1 steel curtain ,c1 switchboard ,s1 stage pockets ,q1 proscenium side lights ,p1 and general arrangement of scenery4 ,the foot lights are not always curved but it seems advantageous to arrange them in this way4 ,the rows of seats are of necessity curved so as to face each patron squarely toward the stage4 ,if then the stage and foot lights are curved in the same way1 the actors will be able to come that much closer to the audience and can thus make themselves more easily heard4 ,the curving of the foot lights will have the further advantage of illuminating the sides of an actor more than would be the case if they were laid out in a straight line4 ,at each side of the steel curtain are the proscenium side lights4 ,in some cases these lights are arranged on the audience side of the curtain1 the object being to arrange them as far in front of the stage as possible4 ,the location of these lights is awkward and it is difficult to get light from them in a useful direction4 ,in most theaters the switchboard is located on the right-hand side of the stage1 facing the audience4 ,this is the side from which the stage manager prefers to work and the operating electrician should be close to him4 ,in most well-arranged theaters1 the switchboard is raised above the stage level so that it may not obstruct the exits of the actors4 ,where practicable1 the board should be let into the proscenium wall so as to allow the operator to stand as close to the proscenium opening as possible4 ,he should have a full view of the stage at all times1 since many of his cues are given by movements of the actors4 ,the stage pockets are laid out far enough from the center of the stage to insure their being always behind the scenery4 ,if they are brought in too close1 it is possible that1 in a panorama setting1 for instance1 they would be visible to the audience4 ,doors leading from the stage to the outside are always vestibuled in good houses4 ,the vestibule prevents the wind from blowing the drapery about unduly and also shields the actors from unpleasant drafts4 ,dressing rooms are arranged wherever the conditions of the building allow suitable space4 ,many of them are under the stage and others are arranged on one or both sides of the stage1 sometimes very high up4 ,a view of the stage looking from the rear is shown in ,figure #abe4 ,this figure shows the vent1 the method of border light suspension1 bridges for support of arc lamps or other sources of illumination1 the fly floor1 and the rigging loft1 or 8grid04 ,the rigging loft is generally constructed entirely of iron slats with open spaces between them4 ,this is necessary to insure ventilation in case of fire4 ,illustration3 ,,figure #abe4 ,in most theaters the height from stage to ceiling is about seventy feet or more4 ,the height must be great enough to allow the scenery to be hoisted out of sight above the proscenium opening4 ,there must also be sufficient space above the rigging loft to allow men to walk about straightening out ropes1 etc4 ,the total height should1 therefore1 be nearly two and one-half times that of the proscenium opening4 ,illustration3 ,,figure #abf4 ,as a rule no openings of any kind are arranged in any of the enclosing walls of the stage1 except those that are necessary as entrances4 ,in houses which are likely to originate shows1 a paint bridge is generally provided along the back wall4 ,illustration3 ,,figure #abg4 ,moving-,picture ,theater4--,figure #abf is a plan of a typical small moving-picture theater4 ,a spacious lobby is an important adjunct to any such theater and this space is often as valuable as the seating space inside4 ,it affords shelter to those who cannot be seated at the moment4 ,it is especially convenient in localities where race suicide is not yet very noticeable and where it forms a repository for many baby carriages4 ,a view showing the location of a picture-machine booth is given in ,figure #abg4 ,this is the arrangement most in use although there are localities where it is required that the operating room be at the end of the theater opposite the main entrance1 the object being to avoid the necessity of the audience passing under the fire to the outside in case a fire should occur in the operating room4 ,this plan has so many disadvantages that it is never followed except where the law requires it4 ,if a properly arranged operating room is provided1 there is no necessity whatever for it4 ,illustration3 ,,figure #abh4 ,the chief use of ,figure #abg is to illustrate the importance of adjusting the height at which the picture is thrown upon the curtain to the pitch of the floor4 ,the curved lines in the upper part of the picture indicate the floor conditions which would give each seat the same clearance over-the-one-in-front-of-it to a view at the bottom of the picture4 ,the upper line shows the bottom of the picture1 level with highest seat1 the other with the same point somewhat below it4 ,illustration3 ,,figure #abi4 ,figures #abh and #abi show the plan and the elevation of a large operating room4 ,every operating room should be of ample size to allow the operator to walk on all sides of the machine4 ,it should be strictly fireproof1 well-ventilated1 and provided with a door giving easy exit to a floor outside1 level with the floor of the room4 ,in altogether too many rooms the only means of getting in or out is by a ladder which leads directly into the room through a small trap door4 ,such an arrangement is extremely dangerous in case of fire4 ,the fumes of burning film are poisonous if inhaled and spread very fast4 ,if two men should happen to be in such a room at the time the film is ignited1 it is likely that they would wedge each other into the narrow opening and both perish4 ,the door to the operating room should open outward and be self-closing4 ,all openings in the operating room must be fitted with fireproof shutters by which they can be instantly closed in case of fire4 ,there should also be suitable ventilation to the outside to carry off all smoke from burning film4 ,the ,screen4--,the screen upon which the picture is projected should be a clear white but of a dull finish4 ,all glare should be avoided and wherever there is a polished surface1 this glare is always conspicuous4 ,there are a number of patent or special makes of screens on the market1 but it is not the purpose at this time to discuss any of them4 ,it will be sufficient to point out some of the simpler methods by which screens may be made4 ,a simple plaster wall is often used and is very serviceable1 but it must not be polished and must be coated in some way to allow of washing off occasionally4 ,perhaps1 all things considered1 a muslin screen is the best of all4 ,such a screen1 if well stretched1 gives a good flat surface entirely without glare and has the further advantage that it can easily be taken down and laundered as often as necessary4 ,it is best to provide duplicate sets so that there may be one for use while the other is in the wash4 ,the only real objection to a muslin screen is the loss of light which it entails4 ,it is not only a poor reflector of light1 but it allows much of the light to pass through it4 ,with many such screens1 the picture is as well visible behind the screen as it is in front of it4 ,this indicates a great loss of light and it is to prevent this loss of light that the other forms of screens have been devised4 ,the most noticeable of these is the mirror screen1 which is a mirror of ground glass4 ,it is very economical in light but expensive in first cost and hard to keep clean4 ,it must be washed quite frequently and careless men are apt to use too much water and get some of it on the back where it will soon begin to loosen the silver coating and ruin the mirror4 ,the screen should be surrounded so that no other light except that coming from the picture can reach the audience4 ,to this end there should be a black frame around it and this black frame must also be a dull black and without glare4 ,velvet drapery is the very best thing that can be provided and should be brought in so close from all sides that no white rim around the picture will be visible1 as such a white rim would detract greatly from the illumination of the picture4 ,the decorations around the proscenium should preferably be of a dark color and kept dull1 especially in cities where it is necessary to maintain emergency illumination4 ,if the front is light in color1 there will be considerable reflection which will detract from the picture and require a higher illumination of it4 ,wherever there is an opportunity to do so1 the screen should be set well away from the nearest row of seats4 ,this will not affect the view of those in the rear1 and it will very much improve the view of those in front4 ,it must of course be seen to that a clear view from both sides is possible4 ,,chapter ,,xv4 ,,operating ,,room ,,equipment4 ,construction and ,ventilation4--,the operating room should be built of fireproof material1 such as cement1 brick1 or tile4 ,if it is of wood1 it may be made nearly fireproof by lining the inside with heavy sheet iron4 ,it will be well if asbestos is placed between the sheet iron and the wood which it covers4 ,all woodwork1 whether window frames1 doors1 or shelving should be thus lined4 ,it may be taken as practically certain that sooner or later one or more reels of film will be burned in the room and every precaution should be taken to prevent the fire from spreading4 ,if this is done there will probably be no serious results1 for in the past there have been so many film fires which have been successfully confined to the operating room that audiences have become pretty well accustomed to them4 ,if all operating rooms are strongly built and of ample dimensions1 with all openings as small as practicable1 it will help to inspire confidence in the audience and there will be but little likelihood of a panic4 ,the chief danger is to the operator4 ,it is true that he is generally to blame1 but it is not always possible even with the utmost care to prevent a fire4 ,above all the operator should be given every possible chance to get away in case of fire4 ,an operator who feels that he can get away at the last moment is far more likely to stay and fight a fire than one who is penned up in a coop from which it is difficult to get out rapidly4 ,there are in existence1 at the present time1 operating rooms where it is necessary to crawl on hands and knees some twelve or fifteen feet to get from the machine to the exit1 and where the exit is by means of a trap door at the head of a ladder4 ,such operating rooms are an abomination and no self respecting operator would work in one of them4 ,the entrance and exit from the booth should be by means of a door at the right hand or crank side of the machine4 ,the door should be self closing and should open into a space having a floor level with the floor of the operating room4 ,the door should preferably be kept closed but if the provision illustrated in ,figure #abh is made there can be no serious objection to leaving the door open for ventilation4 ,a thin bar of iron is fastened to the door by a screw eye and is used to block the door open4 ,a person rushing out will naturally knock this away and the door will close4 ,the door could also be arranged to be held open by means of the strings1 to be described later1 which hold the shutters in place4 ,the ventilation of the operating room should be by means of a fireproof duct leading to the outer air4 ,this flue should preferably extend above the highest point of the roof and should be of good size4 ,the smoke from burning film is heavy and does not rise very fast but it is generated with extreme rapidity4 ,film burns at a temperature of #bhd degrees ,fahrenheit4 ,if it is incased in a tank and fire communicates with it1 the whole body of the film will be raised to this temperature in a very short time and will burn with the rapidity of an explosion4 ,in the magazines1 which are in general use in the newer houses1 the combustion will be slower but nevertheless will take not more than about one minute4 ,it has often been suggested that a motor be provided in the ventilating flue1 this motor to be kept running during the time the machine is in operation4 ,this would no doubt help clear away all smoke very quickly but there is no assurance that it will be running at the time when it is most needed4 ,a simple way to help out the ventilation without the expense and noise of a motor1 would be to arrange the ventilating flue directly above the arc lamps so that heat rising from these would cause a draft4 ,this can be further helped out by locating all resistances in this flue4 ,they will then be out of the way in a safe place and assist in ventilating the room4 ,the ventilating flue will need to be fitted with a damper for use in cold weather4 ,this damper should be arranged to open by gravity and be held closed by a string connected to the shutter strings so that the damper may open when the shutters close4 ,the floor of the operating room is a very important part of it4 ,it should1 above all1 be extremely rigid so that the machine may be fastened solid and thus obviate any vibration which will cause movement of the picture4 ,all floors that are constructed of wood are somewhat elastic and aid this vibration4 ,movement of the picture is especially noticeable and annoying to those compelled to sit close to it4 ,floors must furthermore be lined with fireproof material and the only material used is sheet iron which1 upon the floor1 is very noisy and can hardly be nailed sufficiently to eliminate the noise4 ,a metal floor lining has the further disadvantage of affording a good 8ground10 so that any one standing upon it and touching a live part of the lamp is liable to receive a severe electrical shock4 ,it will also soon wear through1 make pockets to catch dirt1 and allow a fire to communicate with the woodwork beneath it4 ,the best floor material is cement1 but this1 when wet1 also becomes a fairly good conductor and shocks may easily be obtained while standing upon it4 ,there is no reason1 however1 why it should ever be wet in an operating room and it is therefore advisable to use cement4 ,the floor of the operating room should be kept clear as far as possible4 ,careless operators often allow their take-up magazines to become deranged and when they fail to work1 allow the film to run on the floor4 ,a thousand feet of film scattered loosely about occupies considerable space and is very likely to become badly tangled in case there is anything on the floor for it to tangle with4 ,the writer has witnessed cases where it was necessary to take some of the film outside of the booth in order to get it straightened out4 ,any operator who has been in a similar predicament will appreciate the advantage of having every possible obstacle to a speedy re-adjustment removed4 ,above all1 resistances and other sources of heat should be kept off the floor4 ,every moving-picture machine requires at least two openings2 one through which the picture is projected1 which need not be very large2 another through which the operator must view his picture1 and this must be large enough to allow him to sit in comfort while watching the picture4 ,in some operating rooms the opening through which the picture is projected is closed by a metal funnel which covers the opening and extends back enclosing the front of the projecting lens4 ,this arrangement is very simple in the case of machines in which the revolving shutter is behind the lens4 ,with many machines1 however1 this shutter works in front of the lens and the funnel would have to be extended so as to enclose the revolving shutter4 ,there is no reason why strong clear glass could not be used in the operator's peep hole4 ,this would of course interfere slightly with the clearness of his vision for focusing1 but every operator should be provided with an opera glass for this purpose anyway1 so that this objection would be easily overcome4 ,the same considerations which apply to motion-picture machines also applies to stereopticon lamps4 ,in the more pretentious houses a spot light is generally maintained4 ,this is for the purpose of illuminating vaudeville performers4 ,the opening1 provided for this lamp1 must be large enough to allow the light to follow an actor about the stage1 and glass cannot well be used in it4 ,the best color for the operating room is green but it must be a dull dark green4 ,every vestige of light maintained in the room helps dull the vision of the operator to the light upon the screen4 ,there is1 furthermore1 much light reflected from the film where the light strikes it and it is unavoidable that the operator should be bothered by this at times4 ,all other light should be kept away from his eyes while the picture is running4 ,all of the openings in the room must be equipped with fire shutters4 ,these are generally made of heavy iron and are arranged so that1 if necessary1 they can be instantly released and made to close all the openings1 thus preventing the escape of fire and smoke into the auditorium4 ,illustration3 ,,figure #acj4 ,the best arrangement of such a shutter is illustrated in ,figure #acj at ,a4 ,the shaded portion shows the opening2 above is the iron slide1 preferably one-sixteenth inch metal held up by a string4 ,at the top is a step which will prevent the shutter from being pulled up out of the guides1 for many operators would do this if the step were not there4 ,it is best to mount the shutter on a large piece of heavy metal which can then be bolted to the wall of the room4 ,the hole in the wall can then be cut to the right proportions4 ,when the machine is in place the shutter can be placed very accurately4 ,in this way it will be possible to arrange for the smallest possible opening through which the machine can work4 ,making up the shutter1 as suggested above1 is further of great advantage in old operating rooms of flimsy wood construction4 ,if the guides in such places are fastened independently to the wall it is possible that they will not always remain in line with each other4 ,a slight giving of the flimsy wall on one side may cause them to bind the shutter and prevent its free descent4 ,if the metal on which the shutter guides are mounted is strong and heavy and the guides themselves substantially made1 there will be but little chance to get them askew4 ,in that part of the guides in which the shutter runs there must be no screws1 rivets1 or anything else that could work loose and obstruct the shutters4 ,good methods of making up the guides are shown in ,figure #acj1 at ,b and ,c4 ,they should be loose enough to work without lubrication4 ,at the bottom there should be a bumper to stop the fall at the proper place4 ,this bumper should be padded with some fireproof or slow-burning material and should be narrow4 ,if it is made wide the operator is apt to use it as a shelf for tools or other things and this would prevent it from closing properly in case of fire4 ,all of the shutters must be normally self-closing and must be held open by some arrangement which can readily be worked by the operator2 or1 in case he fails to close them1 they should be arranged so that the flames will cause them to close automatically4 ,this is often arranged for by simply attaching a light strong string to each shutter1 running it through a hook eye directly above and attaching it to a master string which is led over every place at which there is thought to be a likelihood of fire4 ,the idea is1 that the first spread of flames shall strike this string and by burning it1 release all of the shutters4 ,in order to enable the operator to drop the shutter perhaps before the flames have spread at all1 the string is carried to the door and fastened so that he1 on leaving the room1 may quickly release it4 ,it is even better to carry it still farther so that one can release it from the outside4 ,some people have recommended that these strings be soaked in oil to make them more inflammable and tarred rope has even been made mandatory for similar purposes in ordinances4 ,this might make the string more readily inflammable1 but it would at the same time make it last longer4 ,a string or rope so treated would act like a lamp wick and the better soaked or tarred it might be1 the longer would it last and thus fail to its purpose4 ,illustration3 ,,figure #aca4 ,the principle of the arrangement of strings is shown in ,figure #aca4 ,the string is fastened at the door in a manner allowing of easy and quick removal4 ,instead of the strings1 light chains may be used provided that at a sufficient number of places fusible links are inserted4 ,such links are made up of an alloy which melts at a low temperature and allows the shutters to drop just as they would in the case of a string burning in two4 ,in many cases the strings are run over grooved pulleys4 ,this is1 however1 inadvisable4 ,experience has proved that very often the string has come out of the groove and is wedged in between the shaft of the pulley and the side so that it will not allow the shutter to descend at all4 ,a substantial hook eye is much better than any pulley4 ,the strain being taken off the string when it separates1 there is no friction and it slides through the eyes very readily4 ,the door and the vent flue may all be brought under control of the same string so that all will operate together1 the vent of course opening while the others close4 ,where there is but one door there is little need of connecting it with the shutters1 since1 if it is provided with spring hinges it will naturally close after the operator has passed through it4 ,in some operating rooms1 however1 there are two doors and both are often found open4 ,in case of fire in such a booth it is extremely likely that one of the doors would be left open unless it is provided with some automatic manner of closing4 ,at ,d1 ,figure #acj is shown a shutter1 provided with strong spring hinges1 which closes over the opening from the outside4 ,such shutters should not be used where there is room for the drop shutters4 ,where it is necessary to have them1 they should always be arranged on the outside of the booth2 if on the inside there is too much chance of obstacles being in the way to prevent their closing4 ,it is very desirable that all of the shutters be closed after each show4 ,if this is done there will be strong assurance that they will be in working order in case of need and this is about the only way in which they can be kept in order4 ,the string arrangement above described is1 however1 not well suited to this purpose unless each shutter string be detachable from the main string4 ,there are also various other ways of accomplishing this which will readily suggest themselves to the operator4 ,in every operating room there should be ample provision for keeping tools but it is advisable to have all tools1 that are not kept in the lockers1 on hooks instead of shelves4 ,it is best to limit the amount of shelving to what is actually necessary4 ,shelving offers great temptation for the accumulation of rubbish4 ,there must be a shelf upon which to locate the rewinding apparatus and upon which to place the machine while looking it over or making repairs1 also a shelf to hold a small vise1 etc4 ,but this is all2 any additional shelving will be inexpedient4 ,a locker for tools can easily be arranged under the rewind shelf4 ,a good safe place is an encouragement to an operator to keep a supply of good tools and nothing is more essential to the proper management of a machine than good tools4 ,if the operating room is large enough1 it may also contain a locker for clothes but this should be fireproof4 ,preferably1 however1 the clothes locker should be outside of the room1 since a film fire gives one but little time to pick up clothes or anything else4 ,there should1 further1 be a metal pail or receptacle of some kind for hot carbons taken from the lamps from time to time4 ,a wise operator will also provide himself with a small receptacle in which he can keep the pieces of film which he finds it is necessary to cut out of films received from the exchanges4 ,the inspection of films in the exchange is often very perfunctory and many lengths are left in that should be cut out4 ,cutting them out and saving them for a time will often help an operator to win out in disputes with his film exchange4 ,there are operating rooms which have film boxes built into the wall in fireproof manner1 some of them even surrounded by water4 ,at the present time there are a number of good portable boxes on the market so that this is unnecessary4 ,wiring of ,operating ,room4--,every operating room must have at least two circuits run into it2 one for the arc lamp and another for one or more incandescent lights4 ,in the larger cities an emergency lighting system is required for all parts of the house used by the audience4 ,this system is always entirely independent of the main service and is supposed to furnish sufficient light for the audience in case the other lighting system should fail4 ,it will be well if one light connected to the emergency system is arranged in the operating room4 ,if this is done1 there must be special provisions that no cords1 fan motors1 or portables be connected to it4 ,a short circuit1 or trouble of any kind on this light might put the whole emergency system out of operation4 ,if such a light is installed1 it should be at the ceiling and protected by a strong wire guard fastened to the outlet box4 ,all wires carried into the operating room should be in conduit1 with the exception of the asbestos covered wires used with arc lamps and resistances4 ,in addition to the incandescent light above mentioned1 there should be several other lights so arranged that good light can be obtained in any part of the room4 ,the color of walls being dark there is but little reflection and a single light will only illuminate a small space4 ,one light should be arranged above the rewind reel and there is often another arranged under a piece of glass in a shelf above which films are patched4 ,only the best reinforced cord should be used and all work that is stationary should be in conduit4 ,several outlets should be arranged for portable cords so that one may have a light to bring down to the take-up reel or close to the floor if necessary4 ,every incandescent lamp in the operating room should be protected by a substantial wire guard fastened to the socket4 ,fan motors should be provided with strong brackets located near the ceiling and close to the outlet from which the motor is to be run4 ,fan motors should never be allowed upon the floor4 ,where rewinding is to be done by motor1 it will be well to arrange a separate circuit for this motor independent of all lights4 ,the commutator part of the motor should be enclosed so that there may be no possibility of a spark igniting the film4 ,illustration3 ,,figure #acb4 ,figure #acb is a sketch illustrating the arrangement of wiring by which two arc lamps may be connected to mains of sufficient carrying capacity for one only4 ,f is the fuse box in which the arc lamp fuses are enclosed and may be large enough to accommodate a set of fuses for the incandescent-lamp circuit also4 ,in many cases these are1 however1 taken from the house circuit since the meter rate for arc lamps is usually different from that for incandescent lamps4 ,s is the main arc-lamp switch by which the whole installation in the room can be cut off4 ,this is necessary especially if so-called compensarcs1 economy coils1 or transformers are used1 for these always take some current if left alive even if the arc lamp be not burning4 ,at ,c is the resistance or economy coil which serves for both lamps and at ,s is the throw-over switch4 ,this switch is provided to make it impossible to burn the two arcs at the same time as this would overload the small capacity mains4 ,the above is a cheap arrangement and is installed only where a set of mains exists which is too small to supply more than one arc at a time4 ,it is not to be advised for a new installation because it is of great advantage to be able to burn both arcs at the same time4 ,when changing rapidly from one machine to the other it is of advantage to have the second one on for a short time before the first is off1 not only to save a little time1 but also for bringing electrode points to the proper shape4 ,wherever it is possible to do so always provide mains of sufficient size to feed all of the arcs and give each lamp its own fuse1 switch1 and resistance or transformer4 ,illustration3 ,,figure #acc4 ,figure #acc shows a method by which it is possible to arrange for either one of two arcs to be run from a rectifier ,r1 indicated by the square at the left1 or transformer ,t1 at the right4 ,in case rectifiers1 heavy transformers that cannot well be raised to the ceiling1 or motor generators are to be installed1 they should be located in a separate enclosure which must be fireproof4 ,in general1 all of the wiring in the operating rooms must be installed in accordance with the rules given in the chapter on ,theater and ,stage ,wiring4 ,these are the rules of ,the ,national ,board of ,fire ,underwriters and are familiarly known as the 8,national ,electrical ,code10 or 8,n4,e4,c40 ,,chapter ,,xvi4 ,,current ,,control ,,for ,,arc ,,lamps4 ,voltages ,required4--,the commercial distribution of electrical energy is at voltages of #aaj or #bbj1 in most cases1 and occasionally runs as high as #eej4 ,the direct-current arc requires for its best operation a voltage of from #de to #ej1 while the alternating-current arc uses from #cj to #dj4 ,in order to secure satisfactory operation of arc lamps1 it becomes necessary to provide some means of reducing the voltage at the arc to the proper amount4 ,resistance ,control4--,the simplest method and the one universally applicable is that of inserting resistance in series with the arc4 ,the drop in voltage is equal to the current multiplied by the resistance2 hence1 if we wish to decrease our voltage1 say #fe volts1 as would be the case in connection with a #aaj-volt circuit and a #de-volt arc1 using #be amperes1 we should need a resistance of #b4f ohms4 ,twenty-five times #b4f equals #fe volts lost1 which leaves #de volts to operate the arc with4 ,in connection with arc lamps1 however1 it is not only necessary to lower the voltage but some provision must be made so that the current1 when the electrodes are brought together1 will not become excessive4 ,at the time the arc is struck1 i4e41 at the time the electrodes are brought in contact with each other1 the current is limited only by the extra resistance in the circuit1 for the electrodes then form a short circuit4 ,in the above case1 #aaj volts and a rheostat with #b4f ohms resistance we should obtain1 during the time the electrodes are together1 a current equal to #aaj divided by #b4f which equals about #dc amperes4 ,if it were not for this resistance the current would rise to several times this value and blow out any fuse we might provide4 ,it is not necessary that this resistance be in any particular place2 if we have a very long run of small wire from the service to the arc1 there may be sufficient resistance in this so that very little extra resistance is required4 ,somewhere1 however1 there must be some provision inserted in the circuit to prevent the current from becoming too great at the time the electrodes are brought together4 ,in passing it may be noted at this point that an arc can be started without any resistance in the circuit by bridging the space between the electrodes with a small fuse wire which will melt the instant the current is turned on and establish the arc4 ,the resistance method is very wasteful of energy1 as the following tabulation will show2 but with direct currents it is the only method available1 unless we are willing to provide a motor generator to give us the proper voltage4 ,for alternating currents1 resistances are not much used1 except with traveling shows where the portability of the control as well as its fitness for all possible conditions is an important consideration4 ,,table ,,iv4 ,,showing ,,waste ,,of ,,energy ,,with ,,use ,,of ,,resistances ,,for ,,various ,,voltages4 ---------------------------------------- -- ,volts ,current ,watts ,lost ,useful ,watts ---------------------------------------- -- #aaj #cj #aiej #acej #bbj #cj #ebej #acej #eej #cj #aeaej #acej ---------------------------------------- -- ,the tabulation in ,table ,,iv shows that the higher our voltage the greater the loss of energy caused by the use of resistances4 ,the figures apply1 as given1 only to cases where only a single arc lamp is used4 ,where several can be used in series the loss due to high voltage need not be greater than with lower voltage4 ,illustration3 ,,figure #acd4 ,in ,figure #acd we have shown diagrammatically the usual representation of a resistance4 ,the more wire there is in circuit1 the higher will be the resistance and the greater the drop caused by a given current4 ,if we lengthen the arc1 the current will be somewhat decreased and the drop in voltage over the resistance will be less1 thus allowing a rise in the voltage at the terminals of the lamp4 ,the energy lost in resistances takes the form of heat and all resistances1 used for the control of arc lamps1 give off much heat and must be located in safe places4 ,the heating also makes them objectionable in small operating rooms in summer1 but somewhat welcome in winter4 ,the heat generated in a wire is proportional to the square of the current2 hence if we double the current through a certain resistance we shall have four times the heat4 ,if several resistances are connected in series the total resistance will be equal to the sum of the individual resistances1 and the current will be correspondingly decreased4 ,if we wish to get more current than can be obtained with the use of one resistance we may connect up two or more in parallel4 ,two equal resistances connected in parallel will give approximately double the current that can be obtained through one of them4 ,illustration3 ,,figure #ace4 ,reactance ,control4--,a reactance1 shown diagrammatically in ,figure #ace1 may take the place of the resistance in alternating-current circuits and is preferable because it wastes comparatively little energy4 ,it lowers the voltage over the arc but its operation depends upon a counter e4m4f4 which opposes the impressed e4m4f4 of the circuit and must be subtracted from the latter4 ,the nature of reactances as well as of transformation1 etc41 has been fully treated in another work of the authors'1 entitled1 8,alternating ,current ,theory1 ,practice and ,diagrams0 and would carry us too far were it to be discussed in this work4 ,every reactive coil is made up of copper wire wound upon an iron core and contains both resistance and reactance4 ,so far as the resistance in it is concerned1 this causes a waste of energy1 but it is always very small4 ,there is also a waste of energy due to the hysteresis and eddy-current losses in the iron1 but this is also small4 ,the reactance is proportional to the square of the number of turns of wire1 if the iron core is fixed1 and may be controlled either by adjusting the position of an iron core in a helix1 or by adjusting the number of turns of wire around a fixed iron core4 ,the light obtainable through a reactance is not of the best quality and reactances are not much used4 ,transformation ,control4--,another method of lowering the voltage is by means of the transformer4 ,a diagram of an ordinary transformer winding is given in ,figure #acf4 ,the fine-wire winding is the primary winding or coil1 if the transformer is used to lower the voltage2 and the other is known as the secondary winding or coil4 ,the energy in both coils of the transformer1 neglecting the iron and copper losses1 is always exactly equal4 ,the ratio of voltage between the primary and secondary terminals is in direct proportion to the number of turns of wire in each4 ,if there are half as many turns in the secondary winding as in the primary1 the voltage will be just one-half1 but the current will be double4 ,the transformer is self-regulating1 within the limits of its capacity1 and whatever energy is taken from the secondary1 the primary will automatically supply4 ,illustration3 ,,figure #acf4 ,a transformer must be specially built for the voltage and frequency1 at which it is to be used2 but many of them are provided with taps1 such as shown in ,figure #acf1 by which small adjustments of voltage or current can be made4 ,a transformer must always be connected so that the switch1 when open1 will disconnect the primary wires4 ,if these remain closed there will be a small current through the primary winding which will mean a considerable waste of energy4 ,auto-transformer ,control4--,the auto-transformer is a special type of transformer used to obtain reduced voltage and increased current4 ,its principle may be gathered from ,figure #acg4 ,there is an iron core and two coils of wire as in ordinary transformers but the two coils are connected in series1 as shown in the figure4 ,it will also be noted that the arc is connected directly across one of the coils4 ,the lower portion of the winding or coil is traversed by the alternating current from the mains at all times and this current also passes through the arc lamp when the circuit through it is closed4 ,the current passing through the lower coil and the arc induces a current in the upper portion of the winding and these two currents then pass in parallel through the lamp4 ,illustration3 ,,figure #acg4 ,illustration3 ,,figure #ach4 ,when the arc circuit is open1 both coils are in series and act as choke coils so that but very little current is used4 ,the auto-transformer may be designed to reduce the voltage to any desirable amount and the current will be correspondingly increased1 neglecting all losses4 ,illustration3 ,,figure #aci4 ,if the reduced voltage were to be obtained from an ordinary transformer1 the secondary coil would be called upon to carry the full current used by the lamp1 while with this connection it carries much less4 ,if the two coils are equal1 the voltage will be reduced one-half1 the current will be doubled1 and only half of the current will pass through the secondary coil4 ,the nearer equal the primary and secondary voltages are1 the greater the saving in copper in the secondary coil4 ,if it were intended to transform from #aaj to #ajj volts1 the capacity of the secondary winding would need to be only one-eleventh of the total capacity4 ,the auto-transformer is a very useful device but on account of the fact that the high voltage exists in all of its parts1 it is not safe to use with the high commercial voltages outside4 ,illustration3 ,,figure #adj4 ,if the auto-transformer is connected as shown in ,figure #ach1 it can be used to raise the voltage2 but in this case the current will be decreased4 ,these auto-transformers1 as well as the ordinary transformer1 must always be connected to the source of energy by means of a switch so that they may be disconnected when not in use2 otherwise there will be a small current in the primary circuit all the time which will show up quite strong on the watt hour meter4 ,transformers and auto-transformers are arranged to be portable4 ,a general view is given in ,figures #aci and #adj2 the former being the ,edison and the latter the ,fort ,wayne4 ,motor-,generator ,control4--,the proper voltage for the operation of arc lamps can be obtained by the use of motor-generators4 ,a motor-generator is a generator driven by a motor1 the two armatures being placed upon one shaft or belted together4 ,the motor may be driven by a current of any voltage desired4 ,the diagram of such an outfit for direct current is shown in ,figure #ada4 ,this type of machine is used1 as a rule1 only where the supply voltage is much higher than that used at the arc4 ,resistance must be used at each arc lamp4 ,illustration3 ,,figure #ada4 ,figure #adb shows the connections of an alternating-current to a direct-current motor-generator of the ,fort ,wayne ,electric ,company4 ,the switch ,a is used to start it and is shown connected to a three-phase line4 ,aside from the field winding there are three wires leading to the generator4 ,the wire ,b carries a compound winding inside of the generator which opposes the magnetization of the shunt winding4 ,the wire ,c carries another compound winding which is arranged to strengthen the shunt field4 ,d is a box containing two resistances1 one for each arc lamp shown4 ,if only one lamp is to burn1 the switch ,e is closed and the arc started in the usual way4 ,when ready to change to the other arc lamp1 switch ,e must be opened1 the switch on the second arc lamp closed1 and the arc struck4 ,then extinguish the first arc and close the switch ,e again4 ,if both lamps are to be used continually1 switch ,e must be left open4 ,illustration3 ,,figure #adb4 ,as long as current is used through wire ,b1 there is no loss of energy in any resistance and should the current in the arc rise1 as when the electrodes are brought together1 the increased current in the series winding1 cut into this wire1 would weaken the field and thus keep the current down4 ,when current is used through the wire ,c1 the series field winding strengthens the field and builds up the voltage sufficiently so that the lamps may be operated through the resistances4 ,the field strength may be further regulated by the rheostat ,r4 ,another connection of the ,fort ,wayne motor-generator is shown in ,figure #adc4 ,in this case the lamps may be operated either from the compensarc ,c or the generator4 ,by throwing either one of the switches connected to the arc lamps up1 the corresponding arc lamp is connected to the compensarc4 ,by throwing the switch down it is fed from the generator4 ,the lamp1 by which the picture is being projected1 should be fed from the generator and when nearly ready to change1 the other may be started on the compensarc4 ,this lamp will burn with a short arc and when it is connected in parallel with the one on the generator1 it will immediately extinguish the latter4 ,no attempt must be made to burn both arcs from either the compensarc or the generator4 ,this generator is also wound to protect itself against an overload4 ,illustration3 ,,figure #adc4 ,where these connections are to be installed1 it will be best to consult the local inspection departments concerning the necessary fusing for the compensarc and the generator4 ,in some localities the possibility of throwing both arcs on either compensarc or generator1 where these have capacity for but one arc at a time1 will be considered very objectionable4 ,illustration3 ,,figure #add4 ,another combination of motor and generator sometimes used is shown in ,figure #add4 ,by tracing out the circuits it will be seen that the armatures of both are in series and that the electrodes1 when they come together1 form a shunt about ,b4 ,with the electrodes separated1 if current is turned on1 it must pass through both armatures in series4 ,thus the counter e4m4f4 of both armatures opposes that of the line and they operate at a certain speed4 ,each motor has a natural tendency to send current in opposition to that impressed upon it by the line4 ,if then the electrodes are brought together1 they at once form a short circuit around the armature of ,b4 ,the current in ,b reverses and it then begins to act as a generator and sends current through the arc lamp4 ,the current which passes through the armature of ,a also passes through the arc lamp4 ,a is then a motor and operates ,b as a generator4 ,the voltage at the arc is less than the line voltage by as much as the counter e4m4f4 of motor ,a amounts to1 neglecting the drop in voltage due to resistance4 ,no resistance is needed if the winding is properly arranged and there is not the less in heat which goes with the use of resistances4 ,this arrangement can be used with direct-current circuits only4 ,it is not suitable where the supply voltage is very much higher than the voltage used at the arc4 ,a field rheostat is provided to adjust the field strength of ,b4 ,a is equipped with the ordinary motor-starting rheostat only4 ,rotary ,converter ,control4--,this is a machine used only where the supply is alternating current4 ,the voltage delivered to the converter must be the same as that desired at the direct-current terminals4 ,this machine has an armature essentially similar to that of a direct-current dynamo4 ,alternating current is supplied to it at one set of terminals and direct current is taken from the others4 ,this armature acts as motor and generator at the same time4 ,whatever voltage regulating is necessary with this machine must be done on the alternating-current side4 ,changing the field strength does not materially affect the voltage so that no means for regulating the field strength is provided4 ,the polarity of the direct-current terminals depends upon the position the armature happens to be in when the alternating current is applied to it and is very apt to come in wrong when the machine is started4 ,it is therefore necessary to have a polarity indicating voltmeter in the circuit and to watch it when starting the machine4 ,if the polarity is wrong1 the switch must be opened and in a moment thrown in again2 and if still wrong1 this process must be repeated until the polarity comes right4 ,each arc lamp fed from a converter must be equipped with resistance4 ,illustration3 ,,figure #ade4 ,the ,martin rotary converter is especially designed for motion-picture work and may be provided with the proper connections for either single-phase1 two-phase1 or three-phase work4 ,there is a stator ring which entirely surrounds the armature4 ,this ring is made up of laminated disks with squirrel-cage bars and slots alternating4 ,the squirrel-cage bars are joined at the end to a copper bar and it is by the aid of this squirrel-cage that the motor may be started and brought into step4 ,the squirrel-cage also prevents 8hunting0 which is one of the common troubles experienced with synchronous motors or converters4 ,into the slots are wound special compensating coils to balance the armature reaction and keep the neutral point in constant position from no load to full load4 ,this prevents sparking at the brushes4 ,on the outside of this damper ring or squirrel-cage winding is the regular shunt-field winding used with direct-current motors or generators4 ,figure #ade is a diagram showing the connections of the ,martin ,rotary ,converter as installed by the ,northwestern ,electric ,company of ,chicago4 ,this switchboard is equipped to operate two moving-picture arcs1 two dissolving stereopticon lamps1 and one spot light4 ,each lamp is provided with a throw-over switch so that current may be used1 either from the alternating-current mains direct or from the direct-current side of the converter4 ,figure #adf is another panel board for moving-picture work made up by the same company4 ,in this case resistances are provided for use when the arc lamps are operated from the converter4 ,in case it is desired to run from the alternating-current mains1 transformers or compensarcs are used4 ,the emergency feature of these panel boards is highly to be recommended4 ,it must be borne in mind that one may suddenly be forced to deal with an operator who has never seen a converter and knows nothing of its operation2 and there is also always the possibility of some trouble with the machine4 ,illustration3 ,,figure #adf4 ,a ,martin rotary converter to be operated from a single-phase line is shown in ,figure #adg4 ,this machine is started through the commutator side4 ,in order to start this machine it is necessary first to close the main switch4 ,next throw the switch #b to the right and leave it there for about five seconds4 ,it may then be thrown over to the running position at the left and allowed to remain in this position4 ,if the polarity is not correct1 the switch must be opened again for an instant and closed again2 and this process must be repeated until the polarity comes in right4 ,to stop the converter1 first open the main switch and then the throw-over switch4 ,the manner in which the above machines are preferably set up is shown in ,figure #adh4 ,illustration3 ,,figure #adg4 ,illustration3 ,,figure #adh4 ,the ,mercury-,arc ,rectifier ,control4--,the mercury-arc rectifier has three essential parts3 the rectifier tube1 the main reactance1 and the panel4 ,the rectifier tube1 ,figure #adi1 is a glass vessel from which the air has been exhausted and in which there are two graphite electrodes1 ,a and ,a1 and one mercury electrode ,b4 ,from the two upper electrodes current can pass in the direction of the mercury only4 ,they are always positive and the term anode is usually applied to them4 ,b is always negative and the term cathode applies to it4 ,each anode is connected to a separate side of an alternating-current circuit and is thus subject alternately to positive or negative potential4 ,when current has once been started1 the tube is filled with ionized mercury vapor through which the electricity can flow1 from whichever of the two anodes is positive1 toward the cathode ,b4 ,under no conditions1 however1 can electricity flow from the mercury in the tube toward the anodes4 ,the action of the tube is started by tilting it sufficiently1 so that the mercury in the bottom of it connects the starting anode ,c to ,a4 ,this starts the current and when the tube is returned to its upright position1 the mercury bridge from ,c to ,a is interrupted2 but the current then continues from one or the other of the anodes4 ,should the current be interrupted1 even for an instant1 the tube would cease to work until it had been tilted again4 ,in order to provide that the current1 which is alternating and comes to zero twice in every cycle1 may never cease in the tube1 it is necessary to provide some reactance4 ,such a reactance causes the current to lag behind the e4m4f4 and in consequence lap over the time when it would otherwise fall to zero4 ,while the current from the rectifier is always in the same direction1 positive from ,b to the lamp1 it is also a pulsating current changing in value to some extent4 ,in ,figure #adi a complete diagram of the connections of the ,general ,electric ,company ,mercury ,arc ,rectifier for moving-picture arcs is given4 ,this type of rectifier is entirely automatic and is much used4 ,the front and back connections are shown in ,figure #aej4 ,the following instructions are taken from a publication of the ,general ,electric ,company3 ,the leads marked ,a ,c should be connected to the lower side of a double-pole switch located near the moving-picture machine4 ,the upper studs of the switch should be connected to the ,a ,c source of supply4 ,illustration3 ,,figure #adi4 ,the leads marked and - should be connected1 respectively1 to the positive 7upper7 and negative 7lower7 electrodes of the moving-picture lamp4 ,if the ,a ,c supply voltage is #aaj volts2 then connect the flexible lead marked ,z to stud marked #ab2 and flexible lead marked ,y to stud marked #f4 ,if the ,a ,c supply voltage is #bbj volts2 then connect lead ,z to stud #g1 and lead ,y to stud #a4 ,,note3--,do not disturb the other connections that are made on studs #a1 #f1 #g1 and #ab1 but only place leads ,y and ,z as directed4 ,illustration3 ,,figure #aej4 ,the tube holder should be reversed so that the clip and support will be turned away from the panel instead of towards the panel1 as it is when shipped4 ,remove the tube from its box1 being very careful not to handle it roughly and not to strain the seals in any way whatever4 ,care must also be taken to prevent the mercury from suddenly flowing into any of the arms2 otherwise the resultant pounding might damage them4 ,examine the tube for vacuum by noting the sound the mercury makes when allowed to roll gently about in the large chamber4 ,if it makes a clear1 metallic click1 the vacuum is good2 but1 if the sound is dull and the mercury sluggish in moving1 the vacuum is either partially or wholly destroyed4 ,if the vacuum is poor1 the life of the tube may be short or it may not start at all4 ,to insure careful handling and safe delivery1 ,mercury-,arc ,rectifier tubes are always shipped by express in the special box as they come from the factory4 ,place the tube in the holder by inserting the small part of the tube just above the anode arms in the upper clip2 then gently lower it until it rests firmly on the lower support4 ,connect the tube and beaded leads according to the above diagram4 ,adjustment of current 7number of amperes7 at the arc is obtained by connecting leads marked ,x to studs marked #aa1 #i1 #g1 #e1 #c1 or #a of the regulating reactance4 ,stud #a gives the maximum and stud #aa the minimum number of amperes4 ,in starting up the first time it is best to start with lead ,x on stud #aa and move toward the maximum position by steps until the desired current is obtained1 as indicated by the ammeter4 ,for this adjustment it is advisable to connect an ammeter in series with the arc in the moving-picture machine4 ,with the above instructions carried out1 all that is necessary to start is to close the switch in the ,a ,c line2 then bring the electrodes of the arc together4 ,the automatic shaking device should then rock the tube until the arc in the tube starts2 as soon as the arc in the tube starts separate the electrodes4 ,the best and whitest light can be obtained when a #e_/h-;inch cored-carbon electrode is used above and a #a_/b-;inch solid-carbon electrode below1 care being taken not to get solid carbons too hard4 ,the average current in the arc should not exceed #cj amperes and it will be found that excellent pictures can be obtained with #be amperes or even less and the cost of energy1 carbons1 and condensers will be less4 ,,chapter ,,xvii4 ,,management ,,of ,,generators ,,and ,,motors4 ,operation of ,generators4--,the generator should be located in a clean dry place4 ,if it is belt driven1 the belt should be run horizontal if possible and so that the slack side will be on top4 ,this increases the arc of contact with the pulleys and allows the belt to run with less tightening4 ,the frame should be provided with a slide for the purpose of adjusting and tightening4 ,the proportion between the largest and the smallest pulleys used close together should not be greater than about #f to #a4 ,to start a dynamo it is best first to disconnect it from the switchboard4 ,start it running and adjust the voltage by the field rheostat4 ,when the voltage has arisen to its proper value and everything is running smoothly1 the main switch may be closed4 ,if there is much of a load1 it will probably be found that the voltage has fallen off a little and it will be necessary to re-adjust it4 ,next1 look carefully after the brushes and set them at the points where there will be the least sparking4 ,a good modern generator should not spark at all4 ,all of the bearings must be carefully looked after and watched for heating4 ,if they are not properly oiled or in good condition1 they may heat considerably4 ,the armature should run with considerable end play as this helps to distribute the oil over the bearings and even up the wear on the commutator surface4 ,small generators sometimes lose their residual magnetism and it is then impossible to start them generating4 ,in such a case the fields may be connected to a live-lighting circuit2 or a small exciting current may be obtained from a battery4 ,one should know which is the positive pole of the field and apply the battery or line current accordingly4 ,a test for polarity may be made by placing the ends of wires of opposite polarity in a vessel with water and bringing them within an inch or so of each other4 ,under these conditions bubbles will be given off at the negative pole4 ,the polarity of the generator will vary with the polarity of the field1 the direction of rotation1 and the connection of the brushes4 ,by reversing any one of these we may reverse the polarity of the current delivered4 ,shunt dynamos cannot well be operated in parallel2 where it is desired to operate several dynamos together1 compound-wound machines are used4 ,operation of ,motors4--,the speed of a direct-current motor is always such that the counter e4m4f4 of the motor becomes nearly equal to the impressed e4m4f4 of the line4 ,in order to speed up a motor it is necessary to weaken the fields2 and conversely1 to slow it down we must strengthen the fields4 ,the above methods are necessary if the motor is to run at a nearly fixed speed with a variable load4 ,the speed can also be controlled by a variable resistance placed in the armature circuit4 ,this method1 however1 does not result in a steady speed with a variable load4 ,it has very little effect if the load is light1 and very much if it is heavy4 ,in order to start a motor it is necessary to have some resistance in the armature circuit4 ,in very small motors the armatures are usually wound with sufficient resistance so that no external resistance is required4 ,the larger motors are1 however1 equipped with starting boxes which limit the current through the armature until it has attained sufficient speed so that its counter e4m4f4 will keep the current in check4 ,these starting boxes are usually wound with fine wire and cannot stand the starting current very long4 ,the handle must be moved over steadily and slowly and not allowed to remain on an intermediate position unless it is known that the box is meant to be used as a speed controller as well as a starting box4 ,the direction of rotation of a direct-current motor can be reversed by reversing either the field or the armature current4 ,if both are reversed1 it will continue to run in the same direction4 ,alternating-,current ,motors4--,synchronous alternating-current motors are not used in theater work but the rotary converter is frequently used and may be considered as such4 ,this machine must run at a certain speed which depends upon the frequency of the current supplied and the number of poles on the machine4 ,rotary converters are of different types and may be started either from the direct-current side or from the alternating-current side4 ,some of them are provided with connections so that the alternating current may be applied on the direct-current side of the armature4 ,for starting and operating these converters1 the instruction of the maker should be consulted4 ,for motor-generators where alternating current is used1 the induction motor is generally employed4 ,it may be either single-phase1 two-phase1 or three-phase4 ,all of these are essentially constant-speed motors4 ,simple repulsion motors and single-phase induction motors that start as repulsion motors are reversed by shifting the brushes4 ,alternating-current series motors are reversed in the same manner as direct-current motors by reversing either field or armature4 ,if both are reversed1 the motor will continue to run in the same direction4 ,a three-phase induction motor will reverse its direction of rotation if any two of the line wires connected to the primary winding be reversed4 ,if all three wires are changed in order1 the direction of rotation will remain unchanged4 ,synchronous motors when started as induction motors are also governed in this way4 ,these motors of the larger size are generally started through an auto-transformer4 ,for the smaller ones1 it is customary to provide a throw-over switch1 one side only of the switch being fused4 ,the motor at starting takes very strong currents which would blow the running fuse4 ,to reverse a two-phase induction motor the two wires of one phase must be reversed4 ,,general ,,hints4 ,be sure that all belts are sufficiently tight4 ,see that all bearings are well oiled4 ,let all shafts have sufficient end play4 ,use no oil cans of iron around dynamos or motors4 ,keep files and other iron or steel away4 ,see that all connections are good and tight4 ,allow no metal dust or gritty substances to accumulate at the insulation of exposed parts4 ,see that the brushes fit properly and do not cut or scratch4 ,use no emery paper on commutators4 ,lubricate the commutators very sparingly and wipe off as much of the lubricant as you can4 ,keep everything about the machines clean and allow no oil drippings to accumulate4 ,place the starting box for a motor so you can see the motor start from the box4 ,always place a switch which will disconnect all of the wires close to the motor4 ,if possible arrange motors so they may start without load4 ,allow no motor or generator to be placed in the operating room of a moving-picture theater4 ,,chapter ,,xviii4 ,,theater ,,wiring4 ,the wireman should not fail to consult local rules or inspection departments as to whether any rules conflict with those given below4 ,he must be warned to consult local authorities or rules1 too1 because safety rules are liable to change4 ,the purpose of this chapter is to furnish a ready reference work concerning questions of electrical construction in theaters which come up daily in all progressive play houses4 ,to this end the subjects have been arranged in alphabetical order and the practical considerations1 as well as extracts from the ,national ,electrical ,code governing construction1 have been given together4 ,the aim has been to enable the workman to find all information concerning construction work grouped together1 so as to obviate the necessity of looking through various parts of the book for the information sought4 ,this order of things will probably avoid the troubles now often caused by overlooking certain points that should be considered4 ,aisle ,light4--,figure #aea is an illustration of an aisle light4 ,such lights are often placed along steps and aisles4 ,the light illuminates only the floor4 ,aisle lights should be arranged on a separate circuit and controlled by a switch at the door4 ,alternating ,current4--,all wires of any circuit or mains or sub-mains of any system must be run in the same conduit4 ,failure to do this will cause an unnecessary drop in voltage and heating of the conduit4 ,arc ,lamps4--,for treatment and construction of portable arc lamps1 see the chapter on 8,portable ,stage ,equipment04 ,permanently located arc lamps are used about theaters mostly for out-door lighting4 ,very often1 two or more lamps are arranged in front of the house4 ,such lamps are mostly of the flaming arc lamp type and are hung up high4 ,illustration3 ,,figure #aea4 ,in some of the cheaper theaters a pair of arc lamps is used on the stage1 but they do not give satisfaction4 ,the light is not even and steady enough and cannot be properly 8dimmed04 ,where arc lamps are to be arranged for stage illumination they must be suspended amid the scenery and enclosed with wire guards4 ,in some cities the use of arc lamps suspended above the stage is prohibited4 ,in the auditorium1 arc lamps are sometimes installed1 but this practice can not be recommended and1 with the present high efficiency incandescent lamps1 there is but little excuse for it4 ,the only advantage in using arc lamps lies in the first cost of wiring1 and this is more than balanced by the difficulties of trimming lamps located in such places4 ,wherever arc lamps are used it is essential that they be hung high and those that do not naturally throw the light downward must be equipped with suitable reflectors4 ,the question of drop in voltage need not be considered with arc lamps unless runs are very long4 ,national ,electrical ,code ,rules for ,arc ,lamps4 ,arc ,lamps in ,general4 ,must be provided with reliable stops to prevent carbons from falling out in case the clamps become loose4 ,all exposed parts must be carefully insulated from the circuit4 ,must1 for constant-current systems1 be provided with an approved hand switch1 and an automatic switch that will shunt the current around the carbons1 should they fail to feed properly4 ,the hand switch to be approved1 if placed anywhere except on the lamps itself1 must comply with requirements for switches on hanger-boards4 ,terminals must be designed to secure a thoroughly good and permanent contact with the supply wires1 which contact must not become loosened by motion of the lamp during trimming4 ,spark arresters must so close the upper orifice of the globe that it will be impossible for any sparks1 thrown off by the carbons1 to escape4 ,series ,arc ,lamps4 ,must be carefully isolated from inflammable material4 ,must be provided at all times with a glass globe surrounding the arc1 and securely fastened upon a closed base4 ,broken or cracked globes must not be used4 ,must be provided with a wire netting 7having a mesh not exceeding one and one-fourth inches7 around the globe and an approved spark arrester1 when readily inflammable material is in the vicinity of the lamps1 to prevent escape of sparks of carbon or melted copper4 ,outside arc lamps must be suspended at least eight feet above sidewalks4 ,inside arc lamps must be placed out of reach or suitably protected4 ,arc lamps1 when used in places where they are exposed to flyings of easily inflammable material1 must have the electrodes enclosed completely in a tight globe in such manner as to avoid the necessity for spark arresters4 8,enclosed arc0 lamps1 having tight inner globes may be used1 and the requirements of b and c above would1 of course1 not apply to them4 ,where hanger-boards are not used1 lamps must be hung from insulating supports other than their conductors4 ,lamps when arranged to be raised and lowered either for carboning or other purposes1 shall be connected up with stranded conductors from the last point of support to the lamp1 when such conductor is larger than ,no4 #ad ,b4 ,s4 gauge4 ,arc ,lamps on ,constant-,potential ,circuits4 ,must have a cut-out for each lamp or each series of lamps4 ,the branch conductors must have a carrying capacity about fifty per cent in excess of the normal current required by the lamp4 ,must only be furnished with such resistances or regulators as are enclosed in non-combustible material1 such resistances being treated as sources of heat4 ,incandescent lamps must not be used for this purpose4 ,arc ,lamps ,used as a ,part of a ,moving-,picture ,machine4 ,must be constructed1 so far as practicable1 similar to arc lamps of theaters1 and wiring to same must not be of less capacity than ,no4 #f ,b4 ,s4 gauge4 ,see 8,portable ,stage ,equipment04 ,stage and ,gallery ,pockets4 ,must be of approved type1 insulated from ground and controlled from switchboard1 each receptacle to be of not less than #ce ampere rating for arc lamps nor #ae amperes for incandescent lamps1 and each receptacle to be wired to its full capacity4 ,arc pockets to be wired with wire not smaller than ,no4 #f ,b4 ,s4 gauge and incandescent pockets with not less than ,no4 #ab ,b4 ,s4 gauge4 ,plugs for arcs and incandescent pockets must not be interchangeable4 ,armored ,cable4--,all wires in the stage part of theaters must be enclosed in conduit or armored cable4 ,armored cable is thus the only flexible conductor allowed for permanent work4 ,this cable is very convenient where wires must be 8fished01 or run around beams or other obstacles making many bends necessary4 ,it should1 however1 be used only where the rigid conduit cannot well be installed and it is advisable to use the latter1 even where the additional expense is considerable4 ,wires run in rigid conduit can be taken out and replaced by new ones at any time1 while this is not the case with armored cable4 ,should a wire incased in armored cable develop a serious fault1 the old cable would have to be abandoned and a new circuit run1 which in many cases would mean the tearing up of parts of the building4 ,illustration3 ,,figure #aeb4 ,where armored cable is to be used great care should be exercised to see that bends are not made too short1 and that each length of cable is tested for grounds1 short circuits1 and open circuits4 ,special attention must be given to the wires at the place where the armor has been cut4 ,careless workmen can do great damage at this point4 ,the manner of cutting the armor is shown in ,figure #aeb4 ,each strand of the armor is partly cut with a saw and may then be broken off1 taking care that no sharp edge is left in position to pierce the wire4 ,installation rules are given below4 ,before installing any armored cable1 be sure that it is of approved make and guaranteed to pass inspection4 ,national ,electrical ,code ,rule for ,armored ,cables4 ,must be continuous from outlet to outlet or to junction boxes or cabinets1 and the armor of the cable must properly enter and be secured to all fittings1 and the entire system must be mechanically secured in position4 ,in case of service connections and main runs1 this involves running such armored cable continuously into a main cut-out cabinet or gutter surrounding the panel board1 as the case may be4 ,must be equipped at every outlet with an approved outlet box or plate1 as required in conduit work4 ,outlet plates must not be used where it is practicable to install outlet boxes4 ,for concealed work in walls and ceilings composed of plaster on wooden joist or stud construction1 outlet boxes or plates and also cut-out cabinets must be so installed that the front edge will not be more than one-fourth inch back of the finished surface of the plaster1 and if this surface is broken or incomplete it shall be repaired so that it will not show any gaps or open spaces around the edges of the outlet box or plate or of the cut-out cabinet4 ,on wooden walls or ceilings1 outlet boxes or plates and cut-out cabinets must be so installed that the front edge will either be flush with the finished surface or project therefrom4 ,this will not apply to concealed work in walls or ceilings composed of concrete1 tile or other non-combustible material4 ,in buildings already constructed where the conditions are such that neither outlet box nor plate can be installed1 these appliances may be omitted by special permission1 provided the armored cable is firmly and rigidly secured in place4 ,must have the metal armor of cables permanently and effectually grounded to water piping1 gas piping1 or other suitable grounds1 provided that when connections are made to gas piping1 they must be on the street side of the meter4 ,if the armored cable system consists of several separate sections1 the sections must be bonded to each other1 and the system grounded1 or each section may be separately grounded1 as required above4 ,the armor of cables and gas pipes must be securely fastened in outlet boxes1 junction boxes1 and cabinets1 so as to secure good electrical connection4 ,if armor of cables and metal of couplings1 outlet boxes1 junction boxes1 cabinets1 or fittings having protective coating of non-conducting material1 such as enamel1 are used1 such coating must be thoroughly removed from threads of both couplings and the armor of cables1 and from surfaces of the boxes1 cabinets1 and fittings where the armor of cables or ground clamp is secured in order to obtain the requisite good connection4 ,grounded pipes must be cleaned of rust1 scale1 etc41 at place of attachment of ground clamp4 ,connections to grounded pipes and to armor of cables must be exposed to view or readily accessible1 and must be made by means of approved ground clamps1 to which the ground wires must be soldered4 ,ground wires must be of copper1 at least ,no4 #aj ,b4 ,s4 gauge 7where largest wire contained in cable is not greater than ,no4 #j ,b4 ,s4 gauge71 and need not be greater than ,no4 #d ,b4 ,s4 gauge 7where largest wire contained in cable is greater than ,no4 #j ,b4 ,s4 gauge74 ,they must be protected from mechanical injury4 ,the ground for the armored cable system is not to be considered as a ground for a secondary system4 ,when installed in so-called fireproof buildings in course of construction1 or afterwards if exposed to moisture1 or where it is exposed to the weather1 or in damp places1 such as breweries1 stables1 etc41 the cable must have a lead covering placed between the outer braid of the conductors and the steel armor4 ,the lead covering is not to be required when the cable is run against brick walls1 or laid in ordinary plaster walls unless same are continuously damp4 ,where entering junction boxes1 and at all other outlets1 etc41 must be provided with approved terminal fittings which will protect the insulation of the conductors from abrasion1 unless such junction or outlet boxes are specially designed and approved for use with the cable4 ,junction boxes must always be installed in such a manner as to be accessible4 ,for alternating-current systems must have the two or more conductors of the circuit enclosed in one metal armor4 ,all bends must be so made that the armor of the cable will not be injured4 ,the radius of the curve of the inner edge of any bend not to be less than #a-a_/b inches4 ,asbestos4--,as all wiring in theaters is required to be run in conduit1 and metal cabinets are compulsory in this connection1 there is but little opportunity to use asbestos4 ,wherever the use of asbestos is advisable it must conform to the general requirements as given for wooden cutout cabinets1 viz43 8for lining wooden cabinets1 one-eighth inch rigid asbestos board may be used when firmly secured in place by screws or tacks04 ,attachment ,plugs4--,attachment plugs should be used to connect all portable apparatus4 ,all plugs should be of approved type and constructed so as to pull out in case strain is put on them4 ,on the stage1 pin-plug connectors should be used in place of attachment plugs1 as none of the latter are sufficiently rugged to withstand the hard usage4 ,national ,electrical ,code ,rules for ,attachment ,plugs4 ,link fuse attachment plugs of the types now on the market are considered unsafe1 as under entirely possible conditions an arc may be produced when the fuses blow1 damaging the plug and perhaps causing fire4 ,attachment plugs are not approved for more than six hundred and sixty watts or two hundred and fifty volts4 ,auditorium4--,two separate systems of lighting are required3 ,see emergency or exit lighting4 ,metal moulding1 as well as armored cable or conduit1 is permissible in wiring the auditorium part of the theater4 ,auto-,starters4--,auto-starters perform the same service with alternating-current motors that resistances do with direct-current motors4 ,they are used with motors from two or three horse power upward1 and not generally with the smaller motors4 ,the following are extracts from the 8,national ,electrical ,code0 concerning their use3 ,in all wet1 dusty1 or linty places1 auto-starters1 unless equipped with tight casings enclosing all current-carrying parts1 must be enclosed in dust-tight fireproof cabinets4 ,where there is any liability of short circuits1 caused by accidental contacts1 across their exposed live parts a railing must be erected around them4 ,the switch on the auto-starter must provide an off position1 a running position1 and at least one starting position4 ,it must be so arranged that it will be held in off and running position1 but not in starting position or without the proper running overload-protection devices in the circuit4 ,for currents above #cj amperes1 lugs1 into which the connecting wires may be soldered1 or approved solderless connectors must be used4 ,clamps or lugs will not be required when leads are provided as a part of the device4 ,the following rules are drawn for rheostats but may also apply to auto-starters3 ,where the circuit-breaking device on the motor-starting rheostat disconnects all of the wires of the circuit1 the switch called for in this section 7to disconnect all apparatus7 may be omitted4 ,overload-release devices on motor-starting rheostats will not be considered to take the place of the cutout required to protect the motor and the rheostat4 ,balconies4--,the illumination of balconies is a difficult matter4 ,the ceilings under galleries above are always low1 and to obtain even illumination requires the use of many small candle-power lamps4 ,these should be set well back so as not to be visible too much to the audience4 ,stage-pocket capacity for one or more arc lamps should always be provided4 ,where there are galleries above1 the arc lamps used for stage illumination are generally placed there1 but it often happens that a moving-picture machine must be installed and it is very disadvantageous if this must be located in the galleries4 ,balconies require the same exit and emergency light service as is required in the auditorium4 ,batteries4--,see ,portable ,stage ,equipment4 ,bells4--,systems of call bells are generally arranged between the box office or the manager's office and the stage switch board2 also from the stage switch board to the fly floor by which signals for raising and lowering the curtain may be given2 also to the orchestra leader4 ,in some cities all of this wiring is required to be in conduit4 ,these signaling circuits should be carefully installed1 for they are as important as any part of the wiring4 ,only the very best bells and push buttons should be used1 and it is advisable to avoid the use of the ordinary annunciator wire so often seen in connection with bell work4 ,numerous diagrams and much information concerning bell wiring is given in 8,modern ,wiring ,diagrams and ,descriptions01 which should be consulted in case some complicated annunciator system is to be installed4 ,figure #aec is a diagram of a simple call-and-return-call system4 ,illustration3 ,,figure #aec4 ,illustration3 ,,figure #aed4 ,borders4--,the number of borders used in theaters varies from one to six1 the latter number being sufficient for almost any stage4 ,they are generally made of a length about equal to the proscenium opening4 ,the borders placed in the rear are of less importance than those in front and consequently are made shorter and are not provided with so many lights4 ,each border should have at least three circuits1 one for each color2 each circuit being taken through a separate dimmer so that any color may be used alone and dimmed as desired4 ,figures #aed and #aee show types of borders1 and the method of wiring is shown in ,figure #aef4 ,illustration3 ,,figure #aee4 ,illustration3 ,,figure #aef4 ,large borders are very heavy and are usually suspended by wire rope and provided with counterweights to make handling easy4 ,the wire rope should be kept well protected by oiling2 the moisture given off by fireproofed scenery is liable to rust them very fast1 and as the ropes are made up of very fine strands the rust soon cuts entirely through them4 ,the suspending ropes and also cables supplying lights must be long enough to admit of bringing the border within five or six feet of the stage floor for lamp renewals and cleaning4 ,the cleaning is very important as the dust which accumulates may absorb a large part of the light4 ,the ,national ,electrical ,code ,rules ,governing ,border and ,proscenium ,sidelight ,construction4 ,must be constructed of steel of a thickness not less than ,no4 #bj ,u4 ,s4 sheet metal gauge2 treated to prevent oxidation2 be suitably stayed and supported2 and so designed that flanges of reflectors will protect lamps4 ,must be so wired that no set of lamps requiring more than #a1cbj watts nor more than #bf receptacles shall be dependent upon one cut-out4 ,must be wired in approved conduit or armored cable1 each lamp receptacle to be enclosed within an approved outlet box1 or the lamp receptacles may be mounted in an iron or steel box1 metal to be of a thickness not less than ,no4 #bj ,u4 ,s4 sheet metal gauge treated to prevent oxidation1 so constructed as to enclose all wires4 ,wires to be soldered to lugs of receptacles4 ,must be provided with suitable guards to prevent scenery or other combustible material coming in contact with lamps4 ,cable for borders must be of approved type and suitably supported2 conduit construction must be used from switchboard to point where cables must be flexible to permit of the raising and lowering of border4 ,for the wiring of the border proper1 wire with approved slow-burning insulation must be used4 ,borders must be suitably suspended1 and if a wire rope is used same must be insulated by at least one strain insulator inserted at the border4 ,box ,office4--,the box office is often a very stuffy place in summer and very cold in winter4 ,there should be an outlet for a fan motor1 and also one for a heater4 ,very many box offices depend upon electric heating for comfort in winter4 ,plenty of light should be provided and the light should be at the ceiling1 out of the way1 and directly over the ticket window4 ,brackets4--,any brackets used in theaters should be at least seven feet above the floor4 ,brackets used for emergency or exit lights must be fitted with keyless sockets4 ,see 8,fixtures04 ,branch ,circuits4--,the term1 8branch circuit01 as here used refers to the wires leaving the last cut-outs and connecting directly to the lamps or other devices4 ,mains are often run from the switchboard to various parts of the building to feed cut-out centers1 and the branch circuits are then run from these centers4 ,this is often the cheapest method1 but it is by no means the best4 ,in a well designed theater all branch circuits lead out from the vicinity of the switchboard so that1 in case of any trouble with fuses1 they may be replaced without interfering with any part of the audience and in the shortest possible time4 ,this method of wiring involves some long runs of branch circuit wires and ,table ,v1 which shows the drop in voltage1 was prepared for the convenience of wiremen4 ,if possible the circuits should be so arranged that the lamps fed are closely together so all may receive nearly the same voltage4 ,the drop should not much exceed two per cent4 ,table showing drop in voltage due to #f amperes1 with sizes of wire and distances given3 ,,table ,v4 ,,drop ,,in ,,voltage ,,due ,,to #f ,,amperes ,,with ,,size ,,of ,,wire ,,and ,,distance ,,given4 ---------------------------------------- ------------------ ,distance #ej #ge #ajj #abe #aej #age #bjj #bbe #bej #cjj in feet ---------------------------------------- ------------------ ,size of ,wire #a4eh #b4cg #c4af #c4ie #d4gd #e4ec #f4cb #g4aa #g4ij #i4dh ,no4 #ad ---------------------------------------- ------------------ ,size of ,wire #j4ii #a4dh #a4ih #b4dg #b4ig #c4de #c4if #d4de #d4ie #e4id ,no4 #ab ---------------------------------------- ------------------ ,size of ,wire #j4fc #j4id #a4be #a4ef #a4hg #b4ai #b4ej #b4ha #c4ab #c4ge ,no4 #aj ---------------------------------------- ------------------ ,size of ,wire #j4ci #j4ei #j4gh #j4ig #a4ag #a4cf #a4ef #a4ge #a4ie #b4cd ,no4 #h ---------------------------------------- ------------------ ,national ,electrical ,code ,rules ,governing ,size of ,wire for ,branch ,circuits and ,fuses for ,same4 ,no wire smaller than ,no4 #ad ,b4 ,s4 gauge must be used4 ,each branch circuit must be protected by fuses1 which must be so placed that no set of small motors1 small heating devices1 or incandescent lamps1 whether grouped on one fixture or on several fixtures or pendants 7nor more than #af sockets or receptacles7 requiring more than #ffj watts1 will be dependent upon one cut-out4 ,by special permission1 in cases where wiring equal in size and insulation to ,no4 #ad ,b4 ,s4 gauge approved rubber-covered wire is carried direct into keyless sockets or receptacles1 and where the location of sockets and receptacles is such as to render unlikely the attachment of flexible cords thereto1 the circuits may be so arranged that not more than #a1cbj watts 7or thirty-two sockets or receptacles7 will be dependent upon the final cut-out4 ,except for signs and outline lighting1 sockets and receptacles will be considered as requiring not less than #dj watts each4 ,all branches or taps1 from any three-wire system1 which are directly connected to lamp sockets or other translating devices1 must be run as two-wire circuits if the fuses are omitted in the neutral1 or if the difference of potential between the two outside wires is over #bej volts1 and both wires of such branch or tap circuits must be protected by proper fuses4 ,the above shall also apply to motors1 except that small motors may be grouped under the protection of a single set of fuses1 provided the rated capacity of the fuses does not exceed #aj amperes4 ,when #a1cbj watts are dependent upon one fusible cut-out1 as is allowed in theater wiring1 outline lighting and large chandeliers1 the fuses may be in accordance with the following3 #abe volts or less #bj amperes #abe to #bej volts #aj amperes ,bus-,bars4--,bus-bars may be made of bare metal4 ,they must1 however1 be protected against accidental contact4 ,the metal should be ample so that it will not heat more than #ej degrees ,fahrenheit above the surrounding air4 ,it is customary to calculate the metal needed1 on the basis of #a1jjj amperes per square-inch cross section4 ,on this basis bars of the sizes given below would have the carrying capacities in amperes given in the body of the table4 ,,table ,,vi4 ,,current-,,carrying ,,capacity ,,of ,,bus-,,bars4 ---------------------------------------- ------------------ ,thickness #b_/cbc_/cbd_/cbe_/cbf_/cbg_/cbh_/cbi_/c baj_/cbab_/cbaf_/cb ---------------------------------------- ----------------- #a_/b #cj #de #fj #ge #ij #aje #abj #ace #aej #afe #ahj ---------------------------------------- ------------ #e_/h #cg #eg #ge #id #ajh #acb #aej #afh #ahh #bjf #bbe ---------------------------------------- ------------ #f_/h #de #fh #ij #aab #ace #aeh #ahj #bjb #bbe #bdh #bgj ---------------------------------------- ------------ ,width #g_/h #ec #gi #aje #acj #aeh #ahd #baj #bcf #bfc #bhi #cae ---------------------------------------- ------------ in #a4j #fj #ij #abj #aej #ahj #baj #bdj #bgj #cjj #ccj #cfj ---------------------------------------- ------------ ,in- #a-a_/d #ge #aab #aej #ahh #bbe #bfc #cjj #cch #cge #dab #dej ches ---------------------------------------- ------------ #a-a_/b #ij #ace #ahj #bbe #bgj #cae #cfj #dje #dej #die #edj ---------------------------------------- ------------ #a-c_/d #aje #aeg #baj #bfc #cae #cfg #dbj #dgc #ebe #egg #fcj ---------------------------------------- ------------ #b4jj #abj #ahj #bdj #cjj #cfj #dbj #dhj #edj #fjj #ffj #gbj ---------------------------------------- ------------ #c4jj #ahj #bgj #cfj #dej #edj #fcj #gbj #haj #ijj #iij #ajhj ---------------------------------------- ----------------- ,cabinets4--,cabinets are required to enclose all fuses4 ,it is advised that they be arranged so that it will not be necessary to open the fuse compartment to operate switches4 ,care should be exercised in locating cut-out cabinets4 ,they should be in a dry place1 easily accessible to authorized persons1 and not accessible to the general public or miscellaneous employes4 ,if too accessible they are likely to be made receptacles for all sorts of rubbish4 ,wooden or composition cabinets must not be used in theaters4 ,use only approved cabinets4 ,in some cities special rules1 governing the construction of cabinets for theaters1 exist and these should be looked up4 ,cables4--,for construction rules1 see 8,stage ,cables0 in the chapter on 8,portable ,stage ,equipment04 ,cables are required to connect border lights4 ,the cable is usually run from an outlet on the grid floor above the center of the border4 ,it must be long enough to allow the border to be lowered for the cleaning and renewal of lamps4 ,the slack cable must be taken up when the border is raised and some provision must be made to support the cable without injury to the insulation4 ,wire ropes or cables are generally used to support the borders1 but the lower end1 which is handled by the stage crew1 is of ordinary manilla rope4 ,wire cables must be insulated from the border by strain insulators4 ,canopies4--,very many theaters are provided with canopies which extend over the street4 ,sometimes these are fitted out with glass signs behind which incandescent lamps are installed4 ,often1 also1 a row of lights is arranged around the bottom of the canopy ceiling4 ,the number of lights to be used depends upon the design of the canopy1 but the effect is best if a large number of small candle-power lamps are used4 ,these lamps should be of low intrinsic brilliancy4 ,if possible1 the lamps and sockets should be arranged to be out of the weather4 ,in addition to the small outline lamps1 other lights are often placed under canopy to provide bright illumination4 ,each circuit may carry #a1cbj watts4 ,national ,electrical ,code ,rule4 ,where insulating joints are required1 fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings1 or from plaster walls or ceilings on metal lathing1 and from outlet boxes4 ,canopy insulators must be securely fastened in place1 so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated4 ,carriage ,call4--,see 8,program ,board04 ,carrying ,capacity of ,wires4--,table ,,vii is designed to help the wiremen select the proper size of wire to use in supplying a certain number of lights4 ,the first column at the left gives the ,b4 ,s4 gauge number4 ,the second column gives the number of amperes allowed on each wire according to the ,national ,electrical ,code4 ,the third column gives the distance in feet which will cause a loss of #b volts with the current given2 thus a current of #gj amperes in a ,no4 #d ,b4 ,s4 gauge wire will lose #b volts over a distance of #ef feet4 ,the proper size of wire to be used can easily be determined from the table4 ,the loss will always be in proportion to the product of distance and current4 ,the balance of the table is devoted to showing the number of watts and lamps of various sizes the wires will be allowed to supply4 ,ceiling ,fans4--,must be hung from insulated hooks1 or else there must be an insulator interposed between the motor and its support4 ,not more than #ffj watts may be on one circuit4 ,chandeliers4--,large and elaborate chandeliers are sometimes used in the center of the auditorium ceiling for purposes of illumination4 ,such chandeliers should be suspended in a manner which will admit of readily raising or lowering them for lamping up or repairs4 ,for rules governing wiring1 see 8,fixtures04 ,,table ,,vii4 ,,table ,,showing ,,carrying ,,capacity ,,of ,,wires2 ,,distance ,,to ,,which ,,full ,,load ,,may ,,be ,,carried ,,at #b ,,volts ,,drop ,,and ,,number ,,of ,,lights ,,equivalent ,,to ,,full ,,current ,,given4 ,b4 ,s4,rubber ,distance ,total ,total ,number of ,lamps of ,gage ,insu- in ,feet ,capacity in ,different ,voltages and lation ,causing ,watts ,wattages that may be supplied ,amperesa ,loss --------------------------- of #b #be-,watt #dj-,watt #fj-,watt ,volts ----------------------------------- #aaj #bbj #aaj #bbj #aaj #bbj #aaj #bbj ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ---------------------------------------- ----------------- #ad #ae #bf #afej #ccjj #ff #acb #da #hb #bg #ed #ab #bj #cj #bbjj #ddjj #hh #agf #ee #aaj #cf #gc #aj #be #ch #bgej #eejj #aaj #bbj #fh #acg #df #ia #h #ce #dc #chej #ggjj #aed #cjh #if #aib #fd #abh #f #ej #ej #eejj #aajjj #bbj #ddj #acg #bge #ia #ahc #e #ee #ef #fjej #abajj #bdb #dhd #aea #cjb #ajj #bja #d #gj #ef #ggjj #aedjj #cjh #faf #aib #che #abh #bef #c #hj #fa #hhjj #agfjj #ceb #gjd #bbj #ddj #adf #bib #b #ij #fh #iijj #aihjj #cif #gib #bdg #did #afe #ccj #a #ajj #fg #aajjj #bbjjj #ddj #hhj #bge #eej #ahc #cff #j #abe #gh #acgej #bgejj #eejaajj #cdc #fhf #bbi #deh #jj #aej #hb #afejj #ccjjj #ffjacbj #dab #hbd #bge #eej #jjj #age #hi #aibej #chejj #ggjaedj #dha #ifb #cbj #fdj #jjjj #bbe #hg #bdgej #diejj #iijaihj #fahabcf #dab #hbd #bjjjjj #bjj #ib #bbjjj #ddjjj #hhjagfj #eejaajj #cfg #gcd #cjjjjj #bge #aja #cjbej #fjejjabajbdbj #gefaeab #ejdajjh #djjjjj #cbe #aad #cegej #gaejjadcjbhfj #hicaghf #eifaaib #ejjjjj #djj #aag #ddjjj #hhjjjagfjcebjaajjbbjj #gccadee #fjjjjj #dej #abc #diejj #iijjjaihjcifjabcgbdgd #hbeafej #gjjjjj #ejj #acj #eejjjaajjjjbbjjddjjacgebgej #iafahcb #hjjjjj #eej #ace #fjejjabajjjbdbjdhdjaeabcjbdajjhbjaf #ijjjjj #fjj #aci #ffjjjacbjjjbfdjebhjafejccjjaajjbbjj #ajjjjjj #fej #adc #gaejjadcjjjbhfjegbjaghgcegdaaiabchb #aajjjjj #fij #adg #geijjaeahjjcjcffjgbahigcgidabfdbebh #abjjjjj #gcj #aea #hjcjjafjfjjcbabfdbdbjjgdjadacchbfgf #acjjjjj #ggj #aee #hdgjjafidjjcchhfggfbaagdbcdadabbhbd #adjjjjj #haj #afa #hiajjaghbjjcefdgabhbbbgddedadhebigj #aejjjjj #hej #afd #icejjahgjjjcgdjgdhjbccgdfgdaeehcaaf ---------------------------------------- ----------------- ,rubber ,distance ,total ,total ,number of ,lamps of ,insu- in ,feet ,capacity in ,different ,voltages and ,b4 ,s4lation ,causing ,watts ,wattages that may be supplied ,gage ,amperesa ,loss --------------------------- of #b #ajj-,watt#aej-,watt#bej-,watt ,volts ----------------------------------- #aaj #bbj #aaj #bbjaaj #bbjaajbbj ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ,v4 ---------------------------------------- ----------------- #ad #ae #bf #afej #ccjj #af #cc #aa #bb #f #ac #ab #bj #cj #bbjj #ddjj #bb #dd #ad #bi #h #ag #aj #be #ch #bgej #eejj #bg #ee #ah #cf #aa #bb #h #ce #dc #chej #ggjj #ch #gg #be #fa #ae #cj #f #ej #ej #eejj #aajjj #ee #aaj #cf #gc #bb #dd #e #ee #ef #fjej #abajj #fj #aba #dj #hj #bd #dh #d #gj #ef #ggjj #aedjj #gg #aed #di #ii #cj #fa #c #hj #fa #hhjj #agfjj #hh #agf #eh #aag #ce #gj #b #ij #fh #iijj #aihjj #ii #aih #ff #acb #ci #gh #a #ajj #fg #aajjj #bbjjjaaj #bbj #gc #adf #dd #hh #j #abe #gh #acgej #bgejjacg #bgd #ia #ahb #eeaaj #jj #aej #hb #afejj #ccjjjafe #ccjaaj #bbj #ffacb #jjj #age #hi #aibej #chejjaib #chdabh #bef #ggaed #jjjj #bbe #hg #bdgej #diejjbdg #djdafe #ccj #iiaih #bjjjjj #bjj #ib #bbjjj #ddjjjbbj #ddjadf #bib #hhagf #cjjjjj #bge #aja #cjbej #fjejjcjb #fjdbja #djbababdb #djjjjj #cbe #aad #cegej #gaejjceg #gadbch #dgfadcbhf #ejjjjj #djj #aag #ddjjj #hhjjjddj #hhjbic #ehfagfceb #fjjjjj #dej #abc #diejj #iijjjdie #iijccj #ffjaihcif #gjjjjj #ejj #acj #eejjjaajjjjeejaajjcff #gcbbbjddj #hjjjjj #eej #ace #fjejjabajjjfjeabajdjc #hjfbdbdhd #ijjjjj #fjj #aci #ffjjjacbjjjffjacbjddj #hhjbfdebh #ajjjjjj #fej #adc #gaejjadcjjjgaeadcjdgf #iebbhfegb #aajjjjj #fij #adg #geijjaeahjjgeiaeahejfajabcjcfjf #abjjjjj #gcj #aea #hjcjjafjfjjhjcafjfeceajgjcbafdb #acjjjjj #ggj #aee #hdgjjafidjjhdgafidefdaabhcchfgf #adjjjjj #haj #afa #hiajjaghbjjhiaaghbeidaahhcefgab #aejjjjj #hej #afd #icejjahgjjjiceahgjfbcabdfcgdgdh ---------------------------------------- ----------------- ,national ,electrical ,code ,rules for ,fusing ,chandelier ,circuits4 ,when #a1cbj watts are dependent upon one cut-out1 as is allowed in theater wiring1 outline lighting1 and large chandeliers1 the fuse may be in accordance with the following3 #abe volts or less #bj amperes #abe to #bej volts #aj amperes ,circuit ,breakers4--,circuit breakers are not used much about theaters4 ,they are used mostly in connection with motors and on switchboards of isolated plants4 ,they are more sensitive and quicker to act than fuses and1 in case of a blow-out1 can be more easily replaced4 ,where circuit breakers are used it is good practice to set them for a higher amperage than the fuses so that1 in case of a heavy short circuit1 the breaker may act while the fuse will take care of an overload which comes on more gradually4 ,national ,electrical ,code ,rides for ,circuit ,breakers4 ,with motors an automatic circuit breaker1 disconnecting all wires of the circuit1 may serve as both switch and cut-out4 ,where the circuit-breaking device on the motor-starting rheostat disconnects all wires of the circuit1 the switch may be omitted4 ,circuit breakers must not be set more than thirty per cent above the allowable carrying capacity of the wires1 unless a fusible cut-out is also installed on the circuit4 ,when installed without other automatic overload protective devices1 automatic overload circuit breakers must have the poles and trip coils so arranged as to afford complete protection against overloads and short circuits and1 if also used in place of the switch1 must be so arranged that no one pole can be opened manually without disconnecting all the wires4 ,concealed ,work4--,all concealed work must be in conduit or armored cable4 ,wherever possible1 rigid conduit should be used4 ,armored cable should be used only where the whole cable may at any time be withdrawn1 or where it is impracticable to use rigid conduit4 ,conduit ,work4--,this is now considered the standard method of construction4 ,it is1 however1 somewhat over-rated and1 especially in wet places1 has led to much disappointment4 ,it is generally recognized that wires1 placed in conduit1 will cause more trouble than those placed in any other standard manner4 ,the trouble is1 however1 confined to the interior of the conduit and1 if the conduit system be kept in good order1 and fuses at their proper limit1 there is no chance of fire from the wire confined within the conduit4 ,there are three points which1 if carefully observed1 will avoid most1 if not all1 of the conduit troubles3 ,avoid as far as possible locating conduit in wet or damp places4 ,run all conduits so that they will drain4 ,give particular attention to joints in outlet or junction boxes2 tape them heavily2 and arrange them so they are not pressed against metal more than is necessary2 use large boxes4 ,wires used in conduits must have approved rubber insulation and double braid4 ,national ,electrical ,code ,rules for ,wires and ,interior ,conduits4 ,wires for ,conduit ,work4 ,must have an approved rubber insulated covering 7,type ,letter ,r4 ,d471 and must within the conduit tubing be without splices or taps4 ,must not be drawn in until all mechanical work on the building has been1 as far as possible1 completed4 ,conductors in vertical conduit risers must be supported within the conduit system in accordance with the following3 ,no4 #ad to #j every #ajj feet ,no4 #jj to #jjjj every #hj feet ,no4 #jjjj to #cej1jjj ,c4 ,m4 every #fj feet #cej1jjj ,c4 ,m4 to #ejj1jjj ,c4 ,m4 every #ej feet #ejj1jjj ,c4 ,m4 to #gej1jjj ,c4 ,m4 every #dj feet #gej1jjj ,c4 ,m4 every #ce feet ,the following methods of supporting cables are recommended3 7#a7 ,a turn of #ij degrees in the conduit system will constitute a satisfactory support4 7#b7 ,junction boxes may be inserted in the conduit system at the required intervals1 in which insulating supports of approved type must be installed and secured in a satisfactory manner so as to withstand the weight of the conductors attached thereto1 the boxes to be provided with proper covers4 7#c7 ,cables may be supported in approved junction boxes on two or more insulating supports so placed that the conductors will be deflected at an angle of not less than #ij degrees1 and carried a distance of not less than twice the diameter of the cable from its vertical position4 ,cables so suspended may be additionally secured to these insulators by tie wires4 ,other methods may be used if specially approved4 ,must1 for alternating-current systems1 have two or more wires of a circuit drawn in the same conduit4 ,it is suggested that this be done for direct-current systems1 also1 so that they may be changed to alternating systems at any time1 induction troubles preventing such a change if the wires are in separate conduits4 ,except in the case of stage pocket and border circuits the same conduit must not contain more than four two-wire1 or three three-wire circuits of the same system1 except by special permission1 and must never contain circuits of different systems4 ,interior ,conduits4 ,no conduit smaller than one-half inch electrical-trade size shall be used4 ,must be continuous from outlet to outlet or to junction boxes or cabinets1 and the conduit must properly enter1 and be secured to all fittings and the entire system must be mechanically secured in position4 ,in case of service connections and main runs1 this involves running each conduit continuously into a main cut-out cabinet or gutter surrounding the panel board1 as the case may be4 ,departure from this rule may be authorized in case of underground services by special permission4 ,must be first installed as a complete conduit system1 without the conductors4 ,must be equipped at every outlet with an approved outlet box or plate4 ,at exposed ends of conduit 7but not at fixture outlets71 where wires pass from the conduit system without splice1 joint1 or tap1 an approved fitting1 having separately bushed holes for each conductor1 must be used4 ,departure from this rule may be authorized by special permission4 ,outlet plates must not be used where it is practicable to install outlet boxes4 ,for concealed work in walls and ceilings composed of plaster on wooden joist or stud construction1 outlet boxes or plates1 and also cut-out cabinets must be so installed that the front edge will not be more than one-fourth inch back of the finished surface of the plaster2 and if this surface is broken or incomplete it shall be repaired so that it will not show any gaps or open spaces around the edges of the outlet box or plate or of the cut-out cabinet4 ,on wooden walls or ceilings1 outlet boxes or plates and cut-out cabinets must be so installed that the front edge will either be flush with the finished surface or project therefrom4 ,this will not apply to concealed work in walls or ceilings composed of concrete1 tile or other non-combustible material4 ,in buildings already constructed where the conditions are such that neither outlet box or plate can be installed1 these appliances may be omitted1 providing the conduit ends are bushed and secured4 ,it is suggested that outlet boxes and fittings1 having conductive coatings1 be used in order to secure better electrical contact at all points through the conduit system4 ,metal conduits1 where they enter junction boxes and at all other outlets1 etc41 must be provided with approved bushings or fastening plates fitted so as to protect wire from abrasion1 except when such protection is obtained by the use of approved nipples1 properly fitted in boxes or devices4 ,must have the metal of the conduit permanently and effectually grounded to water piping1 gas piping1 or other suitable grounds1 provided that when connections are made to gas piping1 they must be on the street side of the meter4 ,if the conduit system consists of several separate sections1 the sections must be bonded to each other1 and the system grounded2 or each section may be separately grounded1 as required above4 ,where short sections of conduit 7or pipe of equivalent strength7 are used for the protection of exposed wiring on side walls1 and such conduit or pipe and wiring is installed as required by the ,code ,rules1 the conduit or pipe need not be grounded4 ,conduits and gas pipes must be securely fastened in outlet boxes1 junction boxes1 and cabinets1 so as to secure good electrical connections4 ,if conduits1 couplings1 outlet boxes1 junction boxes1 cabinets or fittings1 having protective coating of non-conducting material such as enamel1 are used1 such coating must be thoroughly removed from threads of both couplings and conduit1 and such surfaces of boxes1 cabinets1 and fittings1 where the conduit or group clamp is secured1 in order to obtain the requisite good connection4 ,grounded pipes must be cleaned of rust1 scale1 etc41 at place of attachment of ground clamp4 ,connections to grounded pipes and to conduits must be exposed to view or readily accessible1 and must be made by means of approved ground clamps to which the ground wires must be soldered4 ,ground wires must be of copper1 at least ,no4 #aj ,b4 ,s4 gauge 7where largest wire contained in conduit is not greater than ,no4 #j ,b4 ,s4 gauge71 and need not be greater than ,no4 #d ,b4 ,s4 gauge 7where largest wire contained in conduit is greater than ,no4 #j ,b4 ,s4 gauge74 ,they shall be protected from mechanical injury4 ,the ground on the conduit system is not to be considered as a ground for a secondary system4 ,junction boxes must always be installed in such a manner as to be accessible4 ,all elbows or hands must be so made that the conduit will not be injured4 ,the radius of the curve of the inner edge of any elbow must not be less than three and one-half inches1 and must have not more than the equivalent of four quarter bends from outlet to outlet1 the bends at the outlets not being counted4 ,contacts4--,must be mounted on non-combustible non-absorption insulated bases4 ,other materials than slate1 marble1 or porcelain must be submitted for special examination before being used4 ,cord4--,the use of flexible cord should be reduced to a minimum4 ,wherever drop lights are necessary they should be wired with reinforced cord or stage cable4 ,current ,taps4--,must be of approved construction and may be used if properly installed4 ,national ,electrical ,code ,rules for ,current ,taps4 ,where1 in addition to sockets or receptacles already installed1 connections are desired to lighting circuits for portable lamps1 for motors1 or other special appliances requiring only small amounts of current1 multiple-current taps may be used1 provided the entire circuit does not require more than #ffj watts1 and provided their use will not1 under any conditions1 involve a departure from the requirements of ,rule #bc-;d of the ,national ,electrical ,code4 ,current taps must not be used in key or pull sockets if the device1 controlled through such sockets1 requires more than #bej watts4 ,cut-,outs4--,all cut-outs should be on the stage switchboard4 ,this requires considerable extra wire1 but it will be profitable in the end4 ,fuses should be inspected occasionally to see that contacts are bright and screws kept tight4 ,there is everywhere a very strong tendency to over-fuse1 and the principal reason for it is the failure to keep screws tightly fastened4 ,there is no fuse better than the plug fuse but it is not permitted with voltages higher than #abe or with more than #cj amperes4 ,refillable fuses must not be used4 ,cartridge fuses1 especially1 require to be kept clean4 ,the spring contacts on these often grow weak and cause heating which helps to blow the fuse4 ,the neutral fuse in three-wire installations should be larger than the outside fuses4 ,link fuses should be avoided on account of the delay that may be caused through difficulty of installing4 ,it is advisable not to place switches in the same cabinet with fuses4 ,national ,electrical ,code ,rules for ,automatic ,cut-outs 7,fuses and ,circuit-,breakers74 ,constant-,potential ,systems4 ,must be placed on all service wires1 either overhead or underground1 in the nearest accessible place to the point where they enter the building1 inside the walls1 and arranged to cut off the entire current from the building4 ,departure from this rule may be authorized only under special permission in writing4 ,where the service switch is inside the building1 the cut-out required by this section must be placed so as to protect it4 ,for three-wire 7not three-phase7 systems the fuse in the neutral wire may be omitted1 provided the neutral wire is of equal carrying capacity to the larger of the outside wires and is grounded4 ,must be placed at every point where a change is made in the size of wire 7unless the cut-out in the larger wire will protect the smaller74 ,for three-wire direct current or single-phase systems the fuse in the neutral wire1 except that called for under ,section d1 may be omitted1 provided the neutral wire is grounded4 ,must be in plain sight1 or enclosed in an approved cabinet1 and readily accessible4 ,they must not be placed in the canopies or shells of fixtures4 ,link fuses may be used only when mounted on approved bases and must be enclosed in dust-tight1 fireproofed cabinets1 except on switchboards4 ,must be so placed that no set of small motors1 small heating devices1 or incandescent lamps1 whether grouped on one fixture or on several fixtures or pendants 7nor more than #af sockets or receptacles7 requiring more than #ffj watts1 will be dependent upon one cut-out4 ,by special permission1 in cases where wiring equal in size and insulation to ,no4 #ad ,b4 ,s4 gauge approved rubber-covered wire is carried direct into keyless sockets or receptacles1 and where the location of sockets and receptacles is such as to render unlikely the attachment of flexible cords thereto1 the circuits may be so arranged that not more than #a1cbj watts 7or thirty-two sockets or receptacles7 will be dependent upon the final cut-out4 ,except for signs and outline lighting1 sockets and receptacles will be considered as requiring not less than #dj watts each4 ,all branches or taps from any three-wire system which are directly connected to lamp sockets or other translating devices1 must be run as two-wire circuits if the fuses are omitted in the neutral or if the difference of potential between the two outside wires is over #bej volts1 and both wires of such branch or tap circuits must be protected by proper fuses4 ,the above shall also apply to motors1 except that small motors may be grouped under the protection of a single set of fuses1 provided the rated capacity of the fuses does not exceed #aj amperes4 ,when #a1cbj watts are dependent upon one fusible cut-out1 as is allowed in theater wiring1 outline lighting1 and large chandeliers1 the fuses may be in accordance with the following3 #abe volts or less #bj amperes #abe to #bej volts #aj amperes ,the rated capacity of fuses must not exceed the allowable carrying capacity of the wire4 ,circuit breakers must not be set more than #cj per cent above allowable carrying capacity of the wire1 unless a fusible cut-out is also installed on the circuit4 ,fixture wire or flexible cord of ,no4 #ah ,b4 ,s4 gauge1 will be considered as properly protected by #aj-;ampere fuses4 ,each wire of motor circuits1 except on main switchboard or when otherwise subject to competent supervision1 must be protected by an approved fuse whether automatic overload circuit breakers are installed or not4 ,single-phase motors may have one side protected by an approved automatic overload circuit breaker only if the other side is protected by an approved fuse4 ,for circuits having a maximum capacity greater than that for which enclosed fuses are approved1 circuit breakers alone will be approved4 ,the ordinary porcelain link fuse cut-out will not be approved4 ,link fuses may be used only when mounted on slate or marble bases conforming to the rules1 and must be enclosed in dust-tight1 fire-proofed cabinets1 except on switchboards located well away from combustible material1 as in the ordinary engine and dynamo room1 and where these conditions will be maintained4 ,damp ,places4--,it is best to avoid wiring in damp places if possible4 ,if wires must be run in such places1 they should be lead covered4 ,if armored cable is used1 the wires in cable must be incased in lead4 ,weatherproof sockets must be used and the use of cords should be avoided4 ,where cords must be used they should be of the brewery or packing-house type4 ,if outside of the theater1 proper open work may be used4 ,conduit work is permissible but not advisable1 except where wires are subject to mechanical injury4 ,decorative ,lighting ,systems4--,the commercial decorative lighting systems are not suitable for use inside of theaters and should be used only outside4 ,national ,electrical ,code ,rule for ,decorative ,lighting ,systems4 ,special permission may be given in writing for the temporary installation of approved systems of decorative lighting1 provided the difference of potential between the wires of any circuit shall not be over #aej volts and also provided that no group of lamps requiring more than #a1cbj watts shall be dependent on one cut-out4 ,illustration3 ,,figure #aeg4 ,dimmers4--8,dimmer0 is the name given to the resistances which are used to dim the electric lights on the stage4 ,they are usually mounted at the top or bottom of the switchboard with the operating handles in easy reach of the operator4 ,a dimmer should be provided for each color in every border light and also for the foot lights4 ,in some cases the proscenium side lights are also arranged for several colors4 ,the dimmers should be mounted so that each one is directly above the switch which controls the circuit to which it belongs4 ,they should be protected by wire guards against rubbish1 which is likely to accumulate among them if they are not enclosed4 ,good ventilation must be provided4 ,a certain dimmer can be used only while the amperage remains within the proper limitations4 ,if carbon lamps1 for instance1 are changed for tungsten1 the amperage will be much reduced and the dimmer may not work properly4 ,modern dimmers are all of the interlocking type so that the whole bank may be worked together or any one singly4 ,figure #aeg is an illustration of a small bank of dimmers4 ,door ,switches4--,door switches are used mostly in connection with dressing rooms4 ,when the light in the room is burning1 opening and closing the door will turn it out4 ,dressing ,rooms4--,many dressing rooms are wired with lights on pendant cords1 but this method is not to be recommended4 ,it is better to arrange the lights in sockets fitted into the outlet boxes4 ,it will be well if each dressing room is provided with a circuit for flatirons4 ,if this is considered too expensive1 the fuses on circuits leading into dressing rooms must be kept small enough to blow in case a flatiron is connected4 ,many actors are in the habit of carrying flatirons and will use them on incandescent-light circuits if no other circuit is provided4 ,if metal guards are fastened on securely1 much of the trouble from flatirons will be avoided1 but they must be fastened so that an ordinary screwdriver will not loosen the screws4 ,dressing room illumination1 if properly carried out1 will save the proprietor much annoyance4 ,actors have ways of obtaining the light they want by fair means or foul1 and it is much better to arrange the lighting so that it will be satisfactory to those using it1 than to have it continually tampered with4 ,a bright illumination is essential for making up and both sides of the face should be fully illuminated4 ,to accomplish this it is necessary to provide at least two lights for each mirror4 ,every lamp should be provided with a substantial guard which may be securely fastened to the outlet box4 ,this is especially necessary if small candle power lamps are furnished4 ,for1 if the light furnished is insufficient1 there will be strong efforts made to replace the small lamps by larger ones4 ,guards are also necessary as a protection against fire4 ,actors are in the habit of drying small articles of clothing on the lamps1 and fires have been known to start from this cause4 ,the guards on the lamps throw shadows on the faces of the actors1 and for this reason are not liked4 ,in order to avoid the shadows1 frosted lamps may be used1 or two lamps on each side of the mirror4 ,one lamp will then illuminate the shadows caused by the other4 ,where there are long dressing tables1 as in rooms occupied by the chorus1 mirrors may be placed between each two lamps on each side of the table and the lamps staggered vertically4 ,in this way each party will receive the benefit of at least four lamps and the shadows will be less noticeable4 ,the color value of the lamps used in dressing rooms should match that of the lamps used on the stage4 ,some stages1 for instance1 are illuminated by flaming arcs which may give an altogether different effect to a 8make up0 than the tungsten lamps1 for instance4 ,where there are a large number of sockets without lamps in them1 it is advisable to close the socket by a fuse plug from which the fuse has been removed1 or in some similar manner in order to avoid the chance of short circuits from hat pins or similar objects used in dressing rooms4 ,drop ,lights4--,drop lights should be avoided as much as possible4 ,where they must be installed reinforced cord1 armored cable1 or flexible steel armored cord should be used4 ,emergency ,lighting4--,every theater must have an emergency lighting system as outlined in the rules below4 ,the object of this is to provide a double system of illumination so as to reduce the likelihood of the theater being left in total darkness4 ,this is a frequent occurrence where the theater is supplied by an isolated plant1 and may also occur where the supply is obtained from a large outside lighting system although the latter is usually more reliable4 ,every unnecessary light that is added to an emergency system increases the likelihood of trouble4 ,a sufficient number of lights added to it to illuminate the space used by the audience in getting out is1 therefore1 necessary but more than this is a detriment rather than a help4 ,the practice of connecting all of the hall and lobby lights to the emergency system is to be condemned1 since it defeats the purpose of the rule which provides a double illumination system for every part of the theater used by the audience4 ,the two systems should be carried into the auditorium1 all stairways1 exits1 and lobby clear to the street4 ,they should1 furthermore1 be kept entirely separate1 in separate conduits and using separate meters4 ,the rule does not specify the number of exit and emergency lights required4 ,good practice requires a light for every #djj square feet or so4 ,if each of these outlets be fitted with a #ej watt lamp the illumination will interfere with many of the acts and so1 smaller lamps are generally used4 ,one emergency light for each #fj seats will fill the bill nicely4 ,illustration3 ,,figure #aeh4 ,over each exit1 an exit light must be provided1 but as these exit lights are usually incased in ruby glass such as shown in ,figure #aeh they cannot be counted as giving any illumination4 ,in many theaters gas is used for emergency and exit lighting and in many respects this seems to be a good practice4 ,in some quarters1 however1 it is believed that a fire in the scenery of a theater might create such an air pressure in the building as to overcome the low gas pressure and thus put out the gas at the very time when it is most needed4 ,the very best suggestion that can be made is that of a storage battery to supply the emergency system4 ,where alternating current is used this1 however1 introduces some complications and becomes quite expensive4 ,avoid the use of key sockets1 fan motors1 or any unnecessary device on emergency or exit light circuits4 ,national ,electrical ,code ,rules for ,services4 ,where supply may be obtained from two separate street mains1 two separate and distinct services must be installed1 one service to be of sufficient capacity to supply current for the entire equipment of theater1 while the other service must be at least of sufficient capacity to supply current for all emergency lights4 ,where supply cannot be obtained from two separate sources1 the feed for emergency lights must be taken from a point on the street side of main service fuses4 ,by 8emergency lights0 are meant exit lights and all lights in lobbies1 stairways1 corridors1 and other portions of theater to which the public have access1 which are normally kept lighted during the performance4 ,where the source of supply is an isolated plant within the same building1 an auxiliary service of at least sufficient capacity to supply all emergency lights must be installed from some outside source1 or a suitable storage battery within the premises may be considered the equivalent of such service4 ,illustration3 ,,figure #aei4 ,exit lights must not have more than one set of fuses between same and service fuses4 ,exit lights and all lights in halls1 corridors1 or any other part of the building used by audience1 except the general auditorium lighting1 must be fed independently of the stage lighting1 and must be controlled only from the lobby or other convenient place in front of the house4 ,all fuses must be enclosed in approved cabinets4 ,figure #aei shows a diagram of an emergency lighting system together with that of the house lighting system4 ,the main house switch is sometimes arranged with two sets of fuses1 so that it need only be thrown over when a fuse blows4 ,see ,figure #aei at the right4 ,exit ,lights4--,exit lights are usually required over all doors leading from any part of the auditorium to the lobby or outside of the theater4 ,they are usually incased in ruby glass on which the word ,,exit has been etched in large letters4 ,see also ,emergency ,lighting4 ,fan ,motors4--,in large theaters1 sometimes as many as ten or twelve fan motors are arranged along the walls of the auditorium1 to blow air toward the audience4 ,in small theaters there is a strong temptation to connect these to the emergency circuit1 but this should never be done4 ,the motors are too noisy to be allowed to run during an act and must be wired so that they can all be thrown on or off together from the stage switchboard4 ,not more than #ffj watts should be connected to any one circuit and the connection should be by means of attachment plugs and reinforced cord1 a bracket for the motor being placed as near as possible to the outlet1 so as to reduce the amount of cord required to a minimum4 ,fire ,alarm4--,in some of the cities a special signal system between stage and box office is required and it is necessary to consult authorities about this4 ,ordinarily a bell circuit1 such as shown under 8,bells10 will answer4 ,fish ,work4--,the fishing of wires incased in loom1 as is permitted in other places1 is not permissible in theaters4 ,if wires are to be 8fished0 they must be incased in metal armor4 ,fixtures4--,fixtures require careful inspection before installing4 ,it is seldom that the piping is properly reamed out as required by the rule4 ,chain fixtures especially1 must be closely watched4 ,there is little if any trouble to be expected from the wires laced among the chain links1 but there is much trouble to be looked for from the wires at the points where they leave the chain support and where they enter the socket4 ,the openings for the wires at these points are seldom large enough to admit of the proper wire being used1 and they are not well reamed either4 ,the result of these conditions is that the wire is very quickly abraded and short circuits are common4 ,fixtures may be tested for short circuit by connecting a magneto at the feed end of the wires and turning it briskly4 ,if a ring is obtained it is an indication that something in wrong4 ,the test for open circuit may be made with the same connection4 ,insert a screw driver or a plug into each socket2 if it is not possible to obtain a ring there must be an open circuit4 ,the test for 8ground0 may be made by connecting both feed wires to one pole of the magneto1 and the other pole to the metal of the fixture taking care that there is no lacquer on that part of the fixture4 ,if a ring is obtained it is an indication that some bare spot on the wire is in contact with the fixture4 ,fixtures used for emergency lighting must carry no key sockets and must not feed fan motors4 ,national ,electrical ,code ,rules for ,fixture ,wire and ,fixtures4 ,wires for ,fixture ,work4 ,must not be smaller than ,no4 #ah ,b4 ,s4 gauge1 and must have an approved rubber insulating covering4 ,in wiring certain designs of show-case fixtures1 ceiling bull-eyes1 and similar appliances in which the wiring is exposed to temperature in excess of #abj degrees ,fahrenheit 7#di degrees centigrade71 from the heat of the lamps1 approved slow-burning wire must be used4 ,all such forms of fixtures must be submitted for examination1 test and approval before being introduced for use4 ,supply conductors1 and especially the splices to fixture wires1 must be kept clear of the grounded part of gas pipes1 and1 where shells or outlet boxes are used1 they must be made sufficiently large to allow the fulfillment of this requirement4 ,must1 when fixtures are wired outside1 be so secured as not to be cut or abraded by the pressure of the fastenings or motion of the fixture4 ,wires of different systems must never be contained in or attached to the same fixture1 and under no circumstances must there be a difference of potential of more than #cjj volts between wires contained in or attached to the same fixtures4 ,on chains of similar parts where conductors are not completely enclosed in metal1 wires must be stranded and must have rubber insulation not less than one thirty-second of an inch in thickness2 or approved pendant or portable cord may be used4 ,fixtures4 ,when supported at outlets in metal conduit1 armored cable1 or metal-molding systems1 or from gas piping or any grounded metal work1 or when installed on metal walls or ceilings1 or on plaster walls or ceilings containing metal lath1 or on walls or ceilings in fireproof buildings1 fixtures must be insulated from such supports by approved insulating joints placed as close as possible to the ceilings or walls4 ,the insulating joint may be omitted in conduit1 armored cable1 or metal-molding systems with straight electric fixtures in which the insulation of conductors is the equivalent of insulation in other parts of the system1 and provided that approved sockets1 receptacles1 or wireless clusters are used of a type having porcelain or equivalent insulation between live metal parts and outer metal shells1 if any4 ,where insulating joints are required1 fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings1 or from plaster walls or ceilings on metal lathing1 and from outlet boxes4 ,canopy insulators must be securely fastened in place so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated4 ,fixtures having so-called flat canopies1 tops1 or backs1 will not be approved for installation1 except where outlet boxes are used4 ,in non-metallic fixtures wireways must be metal-lined unless approved armored conductors with suitable fittings are used4 ,flashers4--,flashers are used to economize electrical energy in sign illumination4 ,an electric sign is often just as effective if only one side or one letter is in use at a time and in such a case there is considerable saving by the use of a flasher4 ,illustration3 ,,figure #afj4 ,flashers are made up in a variety of forms1 one of them being shown in ,figure #afj4 ,the manner of wiring to the sign will be readily understood by reference to the figure4 ,the neutral wire is carried direct to the sign and fuses for that wire are often installed up in the sign1 while those for the other side of the circuits must be close to the flasher to comply with the rule which requires fuse protection where a small wire is tapped off from a larger one1 unless the fuse in the larger wire is below the carrying capacity of the smaller4 ,national ,electrical ,code ,rule for ,flashers4 ,time switches1 sign flashers1 and similar appliances must be of approved design and enclosed in approved cabinets4 ,flat ,irons4--,see ,heaters4 ,flexible ,cord4--,the ordinary flexible cord should not be used in any part of a theater4 ,it is recommended that only those cords described below be used1 each of course in its proper place4 ,approved reinforced cord for pendants4 ,approved asbestos-covered cord for portable heaters4 ,approved ,stage and ,border ,cables on ,stage4 ,see 8,stage ,cables40 ,flexible ,tubing4--,flexible tubing is not permissible in theaters4 ,floor ,pockets4--,these are always a source of trouble and their use should be avoided as much as possible4 ,if it is necessary to use any they must be of a type approved by the inspection department having jurisdiction4 ,fly ,floor4--,this is the name given to that part of the gallery above the stage upon which those employes1 whose duty it is to raise and lower curtains and scenery1 work4 ,no great illumination is required1 but the lights should be arranged so as to be convenient to the men for reading during long waits4 ,if this is not done there will always be considerable objectionable cord wiring found in this place4 ,fly-floor and rigging-loft lights should be provided with three way switches so that lights may be turned on or off either at the stage switchboard or on the fly floor4 ,footlights4--,these form the most important and effective part of the permanently located stage lights4 ,to locate them properly requires careful consideration4 ,if they are brought too high they will obstruct the view of the audience2 if located too low they will not illuminate the lower part of the stage4 ,opinion is somewhat divided as to whether they ought to be arranged in circular form or be laid out straight across the stage4 ,in large theaters there is a circular space between the front seats and the front of the stage4 ,a circular stage will utilize this space and this form of stage with footlights arranged in a similar manner will also allow the actors to approach more closely to the audience and will procure for them some illumination from the side4 ,the difficulty of making up a circular strip of footlights is somewhat greater than that of making them up in a straight line4 ,illustration3 ,,figure #afa4 ,illustration3 ,,figure #afb4 ,the footlights are generally made to extend nearly the full opening of the stage and the lights should be crowded into them as closely as possible4 ,the lighting should be divided into three groups suitable for three colors4 ,it is customary to have about half of the lights white and the remaining half divided into two equal parts for different colors4 ,a small part of the white lights should be arranged upon a separate circuit so that they may be used for rehearsals or other purposes1 when not very much light is needed4 ,no very definite recommendations concerning the type of lamp to be used can be given4 ,in some theaters the stage is very solid and tungsten lamps are used to advantage2 in others the jarring prevents their use4 ,the white lights should be arranged so that their light need not pass through the colored lamps4 ,in vaudeville houses some protection in the form of chains or guards is often provided to prevent objects from being rolled or thrown against the lights4 ,figures #afa and #afb show types of footlights and the manner of installing the sockets4 ,the ,national ,electrical ,code ,rules for ,wiring ,footlights4 ,must be wired in approved conduit or armored cable1 each lamp receptacle being enclosed within an approved outlet box1 or the lamp receptacles may be mounted in an iron or steel box1 metal to be of a thickness not less than ,no4 #bj ,u4 ,s4 sheet metal gauge treated to prevent oxidation and so constructed as to enclose all the wires4 ,wires to be soldered to lugs of receptacles4 ,must be so wired that no set of lamps requiring more than #a1cbj watts nor more than #bf receptacles shall be dependent upon one cut-out4 ,fuses4--,see 8,cut-outs40 ,gallery ,lighting4--,the proper lighting of galleries is a difficult matter where there is another gallery above4 ,in such a case the ceiling is always very low4 ,an even distribution of light requires the use of many small incandescent lamps evenly distributed4 ,this will make the wiring expensive4 ,the light should be taken pretty well from the rear so as to avoid placing lights in the range of visions of the audience4 ,emergency lights should be provided here as well as in the main auditorium4 ,gallery ,pockets4--,pockets for arc lamps are often provided1 as it often happens that a moving-picture machine must be placed in the gallery4 ,the stage pockets should be wired with number #f ,b4 ,s4 gauge wire1 this being the smallest wire allowed to feed a moving-picture arc4 ,the stage pocket should be controlled by a switch on the switchboard4 ,it often happens that the operator at the lamp has a wrong cue and his light can then be controlled by the stage manager at the stage switchboard4 ,gas ,lighting4--,electric gas lighting is very little used at the present time1 but in many theaters the emergency lighting is by gas and1 in order to save the time necessary to light these by hand before every performance1 an automatic gas lighting system has been installed in some theaters4 ,a diagram of such a system is shown in ,figure #afc4 ,a battery of considerable capacity is necessary and also a spark coil ,s4 ,at each gas jet a magnet ,m is installed which1 when energized1 is capable of turning the gas on and at the same time producing a spark4 ,this magnet is also capable of turning the gas off4 ,two buttons are provided1 one to turn the gas on and the other to turn it off4 ,illustration3 ,,figure #afc4 ,as the wiring is always used in connection with gas piping1 grounds are of frequent occurrence1 and in order to indicate a ground as soon as it comes on1 the bell and battery shown are provided4 ,if a ground causes a continuous current1 the spark coil will attract the armature1 thus causing the bell to ring continuously4 ,national ,electrical ,code ,rule for ,gas ,lighting4 ,electric gas lighting1 unless it is the frictional system1 must not be used on the same fixtures with the electric light4 ,grid ,floor4--,this is the term given to the framework which supports the pulleys over which the cables for handling curtains and scenery run4 ,it is usually made up of parallel iron slats or bars2 hence the name4 ,a fairly good illumination should be provided here and all of the lights should be arranged on three-way switches4 ,one light for every #djj square feet will be sufficient4 ,national ,electrical ,code ,rule for ,ground ,clamps4 ,connections to grounded pipes and to conduit must be exposed to view or be readily accessible1 and must be made by means of approved ground clamps to which the ground wire must be soldered4 ,national ,electrical ,code ,rule for ,grounding4 ,the metal of conduit1 armored cable1 or metal molding must be permanently and effectually grounded to water piping1 gas piping1 or other suitable grounds1 provided that1 when connections are made to gas piping1 they must be on the street side of the meter4 ,if the conduit system consists of several separate sections1 the sections must be bonded to each other1 and the system grounded2 or each section may be separately grounded1 as required above4 ,conduits and gas pipes must be securely fastened in outlet boxes1 junction boxes1 and cabinets1 so as to secure good electrical connections4 ,if conduit1 couplings1 outlet boxes1 junction boxes1 cabinets1 or fittings1 having protective coating of non-conducting material such as enamel1 are used1 such coating must be thoroughly removed from threads of both couplings and conduit and such surfaces of boxes1 cabinets and fittings where the conduit or ground clamp is secured in order to obtain the requisite good connection4 ,grounded pipes must be cleaned of rust1 scale1 etc41 at place of attachment of ground clamp4 ,connections to grounded pipes and to conduit must be exposed to view or readily accessible1 and must be made by means of approved ground clamps to which the ground wires must be soldered4 ,ground wires must be of copper1 at least ,no4 #aj ,b4 ,s4 gauge 7where largest wire contained in conduit is not greater than ,no4 #j ,b4 ,s4 gauge71 and need not be greater than ,no4 #d ,b4 ,s4 gauge 7where largest wire contained in conduit is greater than ,no4 #j ,b4 ,s4 gauge74 ,they shall be protected from mechanical injury4 ,the ground on the conduit system is not to be considered as a ground for a secondary system4 ,guards4--,a guard rail should be provided around the stage switchboard to prevent actors from coming in contact with any live part of the switchboard4 ,all incandescent lamps about the stage1 dressing rooms1 fly-floor1 grid-floor1 etc41 should be provided with guards4 ,hanger-,boards4--,hanger-boards are not compulsory but where not used1 arc lamps must be hung from insulating supports other than their conductors4 ,national ,electrical ,code ,rule for ,hanger-,boards for ,series ,arc ,lamps4 ,hanger-boards must be so constructed that all wires and current-carrying devices thereon will be exposed to view and thoroughly insulated by being mounted on a non-combustible1 non-absorptive1 insulating substance4 ,all switches attached to the same must be so constructed that they shall be automatic in their action1 cutting off both poles to the lamps1 not stopping between points when started1 and preventing an arc between points under all circumstances4 ,heaters4--,heaters are used sometimes in cold dressing rooms1 in box offices and in other small spaces where other adequate heating arrangements have not been made4 ,the fire hazard incident to the use of electric heaters is considerable and they should be carefully installed according to the rules given below4 ,from one-half to three watts per cubic foot will be required to heat a room4 ,the quantity of heat necessary to be supplied depends largely upon the ventilation4 ,it will be small in closed dressing rooms and large1 for instance1 in the box office4 ,always place a heater where the air enters a room2 never where it leaves4 ,national ,electrical ,code ,rules for ,electric ,heaters4 ,each heater of more than #f amperes or #ffj watts capacity must be protected by a cut-out1 and controlled by a switch or plug connector plainly indicating whether 8on0 or 8off0 and located within sight of the heater4 ,heaters of #f amperes or #ffj watts capacity1 or less1 may be grouped under the protection of a single set of fuses1 provided the rated capacity of the fuses does not exceed #aj amperes2 or may be connected individually to lighting circuits4 ,flexible conductors for smoothing irons and sad irons1 and for all devices requiring over #bej watts1 must have an approved insulation and covering4 ,with portable heating devices1 approved plug connectors must be used so arranged that the plug may be pulled out to open the circuit without leaving any live parts so exposed as to render likely accidental contact therewith4 ,the connector may be located at either end of the flexible conductor or inserted in the conductor itself4 ,smoothing irons1 sad irons1 and other heating devices that are intended to be applied to combustible articles1 must be provided with approved stands4 ,stationary heaters such as radiators1 ranges1 plate warmers1 etc41 must be so located as to furnish ample protection between the device and surrounding combustible material4 ,must each be provided with a name-plate1 giving the maker's name and the normal capacity in volts and amperes4 ,high ,potential4--,the ,national ,electrical ,code classifies all voltages below #eej as low4 ,nevertheless voltages above #bbj should not be considered in the auditorium1 stage1 or dressing rooms of any theater4 ,and this voltage only in connection with a three-wire system where the high voltage exists only between the outside wires1 and #aaj volts are used for lamps and other devices4 ,high potential systems should be used only on the outside4 ,illumination4--,illumination is more an art than a science and the rules that can be given have only a very general application4 ,the best practice1 where really good illumination is desired1 is to install a large number of circuits in proportion to the number of lights1 so that lamps of large candle power may be used wherever desirable4 ,the quantity of light needed in theaters varies greatly with the color of decorations and with their condition4 ,dust accumulates rapidly in theaters and may absorb half of the light4 ,if there is plenty of capacity the candle power of lamps may be changed to suit conditions and obtain any result desired4 ,the number of sockets installed in the auditorium varies widely4 ,in some of the cheaper theaters one light for each twenty seats is considered sufficient2 while in elaborately lighted houses1 there are cases where the number of sockets is equal to about half the number of seats4 ,good illumination requires that the light come from the back1 but very often the purpose is to obtain a brilliant effect by placing lights in front of the audience4 ,in such cases1 however1 the lamps are always of low candle power and should be frosted4 ,incandescent ,lamps4--,practically all incandescent lamps are now rated in watts4 ,they can be obtained in voltages ranging from #b to #bej and may be operated in series or in multiple4 ,all but the tantalum lamp operates equally well on alternating or direct current4 ,the tantalum cannot be recommended for alternating-current circuits4 ,no incandescent lamps will operate well on frequencies lower than forty cycles4 ,the natural distribution of light is mostly in the horizontal plane and for good illumination reflectors should be provided4 ,the color value is in the following order3 ,tungsten1 tantalum1 graphitized filament1 carbon filament4 ,none are equal for color-matching purposes to the intensified arc or the ,moore tube4 ,the life of all incandescent lamps varies inversely with the voltage4 ,an increase in voltage will produce an increase in the efficiency of the lamp but shorten its life4 ,the efficiency decreases with continued use1 and it is generally considered that the useful life of a lamp is over when its efficiency has fallen to #hj per cent of its original value4 ,frosting or coloring shortens the life of lamps from #cj to #ej per cent and reduces the candle power from #c to #aj per cent1 but the lamp yields a more pleasing light4 ,frosting is ordinarily used only where lamps are placed so as to come in the line of vision4 ,bowl frosting does not materially reduce the life of a lamp4 ,efficiency of ,lamps4 ,with incandescent lamps the term 8efficiency0 has a meaning quite different from that usually given1 it being the number of watts per candle power4 ,the lower the efficiency of an incandescent lamp1 the better it is and the more light it yields per watt consumed4 ,mazda ,lamp4 ,the ,mazda lamp has an efficiency of about #a4be and is the most efficient of all4 ,it may be recommended in all places where lamps may be suspended vertically2 where there is not too much jarring2 where there is ordinary care in handling2 and where the lamps are burning a large part of the time4 ,the operating expense of this lamp is low1 but the initial cost is high and the breakage is likely to be considerable4 ,if lamps are much handled and not burned much1 the cost of broken lamps may exceed the saving in energy4 ,it is best not to clean ,mazda lamps when cold4 ,shock absorbers should be used where there is much jarring4 ,the illumination should be laid out for the use of lamps not smaller than #fj watts4 ,the lamps should not be used for temporary work or for coloring4 ,arrange lamps as far as possible to be controlled by switches4 ,broken filaments can often be united again by shaking the lamps gently until the broken ends come together4 ,the current will then weld them4 ,when a bank of ,mazda lamps is turned on there is an excessive current for an instant4 ,tantalum ,lamp4 ,the efficiency of this lamp is from #a4h to #b watts per candle power4 ,this lamp is much used for street-car and similar illumination because it stands jarring very well4 ,it should not be used on alternating-current circuits4 ,the filament can often be united in the same manner as the ,mazda4 ,graphitized ,filament ,lamp4 ,this lamp has an efficiency of #b4e watts per candle power4 ,carbon ,filament ,lamp4 ,this lamp used on #aaj-volt circuits has an efficiency of from #c to #c4b watts per candle power4 ,the efficiency of the smaller sizes is from #d to #e watts per candle power4 ,the carbon filament lamp is the most expensive of all to operate1 but on account of the strength and cheapness of the lamp it can be recommended in places where the breakage is liable to be great or where the light is used for comparatively brief periods4 ,national ,electrical ,code ,rules for ,incandescent ,lamps4 ,must be provided with guards when liable to come in contact with inflammable material or subject to rough usage4 ,must be protected by vapor-proof globes where inflammable gases exist4 ,national ,electrical ,code ,rules for ,insulating ,joints4 ,when supported at outlets in metal conduit1 armored cable1 or metal molding systems1 or from gas piping or any grounded metal work2 or when installed on metal walls or ceilings1 or on plaster walls or ceilings containing metal lath1 or on walls or ceilings in fireproof buildings1 fixtures must be insulated from such supports by approved insulating joints placed as close as possible to the ceilings or walls4 ,the insulating joint may be omitted in conduit1 armored cable1 or metal molding systems with straight electric fixtures in which the insulation of conductors is the equivalent to insulation in other parts of the system1 and provided that approved sockets1 receptacles1 or wireless clusters are used of a type having porcelain or equivalent insulation between live metal parts and outer metal shells1 if any4 ,where insulating joints are required1 fixture canopies of metal must be thoroughly and permanently insulated from metal walls or ceilings1 or from plaster walls or ceilings on metal lathing1 and from outlet boxes4 ,canopy insulators must be securely fastened in place1 so as to separate the canopies thoroughly and permanently from the surfaces and outlet boxes from which they are designed to be insulated4 ,inverted ,lighting4--,in this method of lighting the light is first thrown upward against the ceiling and then reflected back4 ,this method can be used to advantage with light colored ceilings only4 ,it is especially suited for low ceilings and with high ceilings the advantage disappears4 ,the light obtained in this manner is very even and almost shadowless4 ,much light is lost through absorption but1 owing to the fact that the light is of such an even quality1 the eye readily accommodates itself to a lower quantity and the net increase in energy required to illuminate suitable spaces is not so very great4 ,those who wish to go into the subject of illumination thoroughly will find it treated fully in 8,modern ,illumination ,theory and ,practice04 ,joints4--,methods of making joints are illustrated in ,figure #afd4 ,be careful not to overheat1 especially at points where there is a strain on the wire4 ,national ,electrical ,code ,rule for ,joints4 ,wires must be so spliced or joined as to be both mechanically and electrically secure without solder4 ,the joints must then be soldered unless made with some form of approved splicing device1 and covered with an insulation equal to that on the conductors4 ,illustration3 ,,figure #afd4 ,stranded wires 7except in flexible cords7 must be soldered before being fastened under clamps or binding screws2 and1 whether stranded or solid1 when they have a conductivity greater than that of ,no4 #h ,b4 ,s4 gauge they must be soldered into lugs for all terminal connections1 except where an approved solderless terminal connector is used4 ,junction ,boxes4--,junction boxes are installed in conduit systems for the purpose of facilitating the drawing in of the wire or of branching off from a main run4 ,see 8,conduit ,work40 ,lamps4--,see 8,incandescent ,lamps40 ,lobby4--,the lobby generally requires a number of lights and the aim often is to create a lavish display4 ,very often a cut-out center is arranged at some convenient place4 ,the exit and emergency lights must be controlled from the lobby4 ,sometimes outlets are provided for electric bulletin boards or small signs4 ,lugs4--,for solderless lugs1 such as are used on rheostats or for arc lamps1 see 8,portable ,stage ,equipment40 ,national ,electrical ,code ,rule for ,lugs4 ,for fuses rated over #cj amperes lugs1 firmly screwed or bolted to the terminals and into which the conducting wires are soldered1 must be used4 ,on rheostats1 resistances1 etc41 lugs will not be required when leads are provided as a part of the device4 ,switches for current of over #cj amperes must be equipped with lugs1 firmly screwed or bolted to the switch1 and into which the conducting wires shall be soldered4 ,for the smaller sized switches simple clamps can be employed1 provided they are heavy enough to stand considerable hard usage4 ,where lugs are not provided1 a rugged double-,v groove clamp is advised4 ,a set screw gives a contact at only one point1 is more likely to become loosened1 and is almost sure to cut into the wire4 ,for the smaller sizes1 a screw and washer connection with up-turned lugs on the switch terminal gives a satisfactory contact4 ,national ,electrical ,code ,rules for ,metal ,moldings4 ,must not be used on stage side of proscenium wall4 ,must not be used for circuits carrying more than #a1cbj watts4 ,wire used must be standard rubber covered1 but may be single braid4 ,must never be concealed or run in damp places4 ,must not be used where the difference of potential exceeds #cjj volts4 ,must be continuous from outlet to outlet1 to junction boxes1 or approved fittings designed especially for use with metal moldings1 and must at all outlets be provided with approved terminal fittings which will protect the insulation of conductors from abrasion1 unless such protection is afforded by the construction of the boxes or fittings4 ,such molding where passing through a floor must be carried through an iron pipe extending from the ceiling below to a point five feet above the floor1 which will serve as an additional mechanical protection and exclude the presence of moisture often prevalent in such locations4 ,where the mechanical strength of the molding itself is adequate1 this ruling may be modified to require the protecting piping from the ceiling below to a point at least three inches above the flooring4 ,where such moldings pass through a partition the iron pipe1 required for passing through floors1 may be omitted and the molding passed directly through1 providing the partition is dry and the molding is in a continuous length with no joint or coupling within the partition4 ,backing must be secured in position by screws or bolts1 the heads of which must be flush with the metal4 ,must have the metal of molding permanently and effectually grounded to water piping1 gas piping1 or other suitable grounds1 provided that when connections are made to gas piping1 they must be on the street side of the meter4 ,if the metal molding system consists of several separate sections1 the sections must be bonded to each other and the system grounded1 or each section may be separately grounded1 as required above4 ,metal moldings and gas pipes must be securely fastened to outlet boxes1 junction boxes1 and cabinets1 so as to secure a good electrical connection4 ,molding must be so installed that adjacent lengths of molding will be mechanically and electrically secured at all points4 ,if metal molding1 couplings1 outlet boxes1 junction boxes1 cabinets1 or fittings having protective coating of non-conducting material such as enamel are used1 such coating must be thoroughly removed from threads of couplings and metal moldings1 and from the surfaces of boxes1 cabinets1 and fittings1 where the metal molding or ground clamp is secured in order to obtain the requisite good connection4 ,grounded pipes must be cleaned of rust1 scale1 etc41 at the place of attachment of the ground clamp4 ,connection to grounded pipes and to metal moldings must be exposed to view1 or readily accessible1 and must be made by means of approved ground clamps1 to which the wires must be soldered4 ,ground wires must be of copper1 at least ,no4 #aj ,b4 ,s4 gauge4 ,they shall be protected from mechanical injury4 ,illustration3 ,,figure #afe4 ,must be installed so that for alternating-current systems the two or more wires of a circuit will be in the same metal molding4 ,it is suggested that this be done for direct-current systems also so that they may be changed to the alternating-current system at any time1 induction troubles preventing such change if the wires are in separate moldings4 ,meters4--,a good job of meter setting requires that the meter fittings which are now on the market be used4 ,two separate meters will be required in each theater2 one for the general lighting and one for the emergency system4 ,meter ,reading4--,meter readings are indicated by pointers1 arranged to move over dials as shown in ,figure #afe4 ,the various pointers are connected together by gearing in such a manner1 that alternate pointers move in opposite directions1 as indicated by the figures on the dials4 ,the gearing moving the pointers in ,figure #afe is of such proportions that a total revolution of any pointer represents one-tenth of a revolution of the pointer to the left of it4 ,thus ten revolutions of one pointer causes one revolution of the one at the left4 ,illustration3 ,,figure #aff4 ,illustration3 ,,figure #afg4 ,at the top of each dial the value of the reading of that dial is shown4 ,where the figures given are followed by the letter 8s01 as in ,figures #afg and #afh1 it signifies that each division of the dial represents the amount of energy indicated by the figures at the top4 ,for instance1 in ,figure #afh each division of the dial at the right represents one-tenth of one kilowatt hour and a total revolution of the pointer ten-tenths1 or one kilowatt hour4 ,if the figures given at the top of the dial are not followed by the letter 8s01 or as shown in ,figure #aff1 each division of the dial represents one-tenth of the amount shown at the top of the dial1 the dial at the right of ,figure #aff indicating nine-tenths of ten kilowatts or nine kilowatts4 ,illustration3 ,,figure #afh4 ,the meter must always be read from right to left1 the lowest indicating dial being the one at the extreme right1 and the lower reading ones always being used to check the higher ones just at the left4 ,the following example will illustrate the manner of reading meters3 ,in ,figure #afe the right-hand pointer registers nine-tenths of #ajjj1 or #ijj watt hours2 the pointer next to it registers eight1 since it cannot be considered as fully up to any number unless the pointer at the right of it has just arrived at or passed #j4 ,by the same token the middle pointer also registers #h and as the middle pointer has not reached #j the one at the left of it must be read as one1 the last dial also indicates one and the total reading is #a1ahh1ijj4 ,on some types of meters a multiplier is used4 ,this is generally given on the meter dial and the readings given by the pointers must be multiplied by this number to obtain the correct reading of the meter4 ,motors4--,motors are used in theaters for ventilation1 for raising and lowering the steel curtain in cities where such are required1 and also in some cases for operating drop curtains1 but for this last purpose they have not found much favor4 ,in some localities motors are required to keep up a certain water pressure to be used in case of fire4 ,voltages higher than #eej are not considered in theater work4 ,national ,electrical ,code ,rules for #eej-volt ,motors and ,less4 ,motors operating at a potential of #eej volts or less must be thoroughly insulated from the ground wherever feasible4 ,wooden base frames used for this purpose1 and wooden floors1 which are depended upon for insulation where1 for any reason1 it is necessary to omit the base frames1 must be kept filled to prevent absorption of moisture1 and must be kept clean and dry4 ,where frame insulation is impracticable special permission in writing may be given for its omission1 in which case the frame must be permanently and effectively grounded4 ,the motor leads or branch circuits must be designed to carry a current at least #be per cent greater than that for which the motor is rated4 ,where the wires under this rule would be over-fused in order to provide for the starting current1 as in the case of many of the alternating-current motors1 the wires must be of such size as to be properly protected by these larger fuses4 ,each motor and resistance box must be protected by a cut-out and controlled by a switch2 said switch plainly indicating whether 8on0 or 8off04 ,small motors may be grouped under the protection of a single set of fuses1 provided the rated capacity of the fuses does not exceed #f amperes4 ,with motors of one-fourth horse power or less1 on circuits where the voltage does not exceed #cjj1 single-pole switches may be used4 ,the switch and rheostat must be located within sight of the motor1 except in cases where special permission to locate them elsewhere is given1 in writing4 ,where the circuit-breaking device on the motor-starting rheostat disconnects all wires of the circuit1 the switch called for in this section may be omitted4 ,overload-release devices on motor-starting rheostats will not be considered to take the place of the cut-out required by this section4 ,an automatic circuit-breaker disconnecting all wires of the circuit may serve as both switch and cut-out4 ,auto starters1 unless equipped with tight casings enclosing all current-carrying parts1 in all wet1 dusty1 or linty places1 must be enclosed in dust-tight1 fireproof cabinets4 ,where there is any liability of short circuits across their exposed live parts being caused by accidental contacts1 a railing must be erected around them4 ,must not be run in series-multiple or multiple-series1 except on constant-potential systems1 and then only by special permission4 ,must1 when combined with ceiling fans1 be hung from insulated hooks1 or else there must be an insulator interposed between the motor and its support4 ,must each be provided with a name-plate1 giving the maker's name1 the capacity in volts and amperes1 and the normal speed in revolutions per minute4 ,all varying 7or variable7 speed alternating-current motors except those used for railway service must be marked with the maximum current which they can safely carry for #cj minutes1 starting cold4 ,terminal blocks when used on motors must be made of approved non-combustible1 non-absorptive1 insulating material such as slate1 marble1 or porcelain4 ,adjustable-speed motors1 unless of special and appropriate design1 if controlled by means of field regulation1 must be so arranged and connected that they cannot be started under weakened field4 ,the use of soft rubber bushings to protect the lead wires coming through the frames of motors is permitted1 except when installed where oils1 grease1 oily vapors1 or other substances known to have rapid deleterious effect on rubber are present in such quantities and in such proximity to motors as may cause such bushings to be liable to rapid destruction4 ,in such cases hardwood properly filled1 or preferably porcelain or micanite bushings must be used4 ,the following table shows the sizes of wire recommended to be used with motors of the horsepower given4 ,this table is an extract from the rules of the ,department of ,gas and ,electricity of the ,city of ,chicago4 ,the column headed 8,mains0 may be used when there are a number of motors fed by a single line4 ,for all lines which supply a single motor only1 the column headed 8,branches0 must be used4 ,the difference between the two is due to the fact that it is not believed that several motors fed by a single line will all be started at the same time2 hence it is not necessary to provide the overload capacity for all of the motors as it is where but a single motor is installed4 ,,table ,,viii4 ,,size ,,of ,,wires ,,for ,,motors ,,of ,,different ,,horse ,,power4 ,,direct ,,current ---------------------------------------- -------------------------- #aaj ,volts #bbj ,volts ---------------------------------------- --------------------- ,h4 ,p4 ,full- ,size of ,size of ,full- ,size of ,size of load ,wire ,wire load ,wire ,wire ,current ,mains ,branches ,current ,mains ,branches ---------------------------------------- --------------------- #a #h #ad #ad #d #ad #ad #b #ae #ad #ab #h #ad #ad #c #bc #aj #h #ab #ad #ad #d #cj #h #f #ae #ad #ab #e #ch #f #f #ai #ab #aj #g4e #ef #e #d #bh #h #h #aj #ge #c #a #ch #f #f ---------------------------------------- --------------------- ,,single-,,phase ---------------------------------------- --------------------- #a #ab 444 #ab #f 444 #ad #b #bc 444 #h #aa 444 #ab #c #cc 444 #f #af 444 #aj #d #dd 444 #d #bb 444 #h #e #ec 444 #c #bf 444 #f ---------------------------------------- --------------------- ,,three-,,phase ---------------------------------------- --------------------- #a 444 444 444 #c #ad #ad #b 444 444 444 #e #ad #ad #c 444 444 444 #h #ad #ad #d 444 444 444 #aj #ad #ad #e 444 444 444 #ac #ad #ab #g4e 444 444 444 #ai #ab #h #aj 444 444 444 #bf #h #f ---------------------------------------- --------------------- ,music ,stands4--,music stands are used by the musicians and are generally placed between the first row of seats and the stage4 ,each musician should be provided with an individual stand1 although if necessary1 two or three can get along with one stand4 ,no first-class theater should be fitted up with less than twenty outlets for musicians' lights4 ,in the ,metropolitan ,opera ,house of ,new ,york there are one hundred4 ,houses used exclusively for vaudeville do not1 however1 need that many4 ,in houses devoted to grand opera1 often as many as one hundred or more musicians are employed at the same time4 ,to take care of such a number1 the music stands should be wired with pin-plug connectors so that connections may be made from one to the other4 ,long flexible connections are necessary for most music stands4 ,sometimes it is necessary to crowd the orchestra under the stage and at other times1 with musical comedies1 for instance1 they must be brought out where they can see the movements of the actors4 ,the more the circuits are subdivided1 and the different lights made independent of each other1 the better it will be and the less the annoyance in case a fuse blows4 ,the fuses should always be arranged at the switchboard so that it will not be necessary for the electrician to work in front of the audience in cases of trouble4 ,for this reason extra stands should also be kept on hand4 ,a main switch controlling the lights should be placed where one of the musicians can handle it4 ,in dark scenes these lights must often be turned out4 ,if these lights are left under the control of the stage electrician they will be more likely to be forgotten at the critical moment than if under the control of the men who need them4 ,an eight candle-power lamp for each stand will be sufficient and this is usually placed inside a special reflector which allows the light to fall upon the music sheet only4 ,stage cable of good quality should be used for the connections2 there is too much rough handling for reinforced cord4 ,the use of the ordinary attachment plug should be avoided2 use approved pin-plug connectors4 ,open ,work4--,open work is not allowed in theaters4 ,operating ,room4--,see special chapter on 8,operating ,room40 ,panel ,boards4--,panel boards are really small switchboards1 the switches and cut-outs being mounted usually upon slate4 ,the slate must be free of metal seams2 these1 if present1 often manifest themselves by heating4 ,panel boards1 unless located in the immediate vicinity of the main switchboard1 and where they are enclosed in a compartment1 must always be placed in standard metal cabinets4 ,national ,electrical ,code ,rules for ,panel ,boards4 ,the following specifications are intended to apply to all panel and distributing boards used for the control of light and power circuits1 but not to such switchboards in central stations1 sub-stations1 or isolated plants as directly control energy derived from generators or transforming devices4 ,design4 ,the specifications for construction of switches and cut-outs given in the following pages must be followed as far as they apply4 ,in the relative arrangement of fuses and switches1 the fuses may be placed between the bus-bars and the switches1 or between the switches and the circuits1 except in the case of service switches4 ,when the branch switches are between the fuses and the bus-bars1 the connections must be so arranged that the blades will be dead when the switches are open4 ,when there are exposed live-metal parts on the back of a board1 a space of at least one-half inch must be provided between such live metal parts and the cabinet in which the board is mounted4 ,spacings4 ,,table ,,ix4 ,,the ,,minimum ,,distance ,,that ,,must ,,be ,,maintained ,,between ,,bare ,,live ,,metal ,,parts 7,,bus-,,bars1 ,,etc47 ---------------------------------------- -------------------- ,between ,parts of ,opposite ,polarity1 ,except at ,switches and ,between ,link ,fuses ,parts of -------------------------- ,same ,polarity ,when at ,link ,mounted on ,when ,held ,fuses the ,same ,free in ,air ,surface ---------------------------------------- ,not over #abe volts #c_/d inch #a_/b inch #a_/b inch ,not over #bej volts #a-a_/d inch #c_/d inch #c_/d inch ,not over #fjj volts #b inch #a-c_/d inch ---------------------------------------- ------------------- ,at switches or enclosed fuses1 parts of the same polarity may be placed as close together as convenience in handling will allow4 ,it should be noted that the above distances are the minimum allowable1 and it is urged that greater distances be adopted wherever the conditions will permit4 ,the spacings given in the first column apply to the branch conductors where enclosed fuses are used4 ,where link fuses or knife switches are used1 the spacings must be at least as great as those given in the following section on fuse spacing4 ,the spacings given in the second column above apply to the distance between the raised main bars and between these bars and the branch bars over which they pass4 ,the spacings given in the third column are intended to prevent the melting of a link fuse by the blowing of an adjacent fuse of the same polarity4 ,panel boards of special design1 in which the insulation and separation between the bus-bars1 and between the other current-carrying parts is secured by means of barriers or insulating materials instead of by the spacings given above1 must be submitted for special examination and approved before being used4 ,fuse ,spacings4 ,spacings must be at least as great as those given in ,table ,x1 which applies only to plain1 open link fuses4 ,the spaces given are correct for fuse blocks to be used on direct-current systems1 and can therefore be safely followed in devices designed for alternating currents4 ,if the copper fuse tips overhang the edges of the fuse block terminals1 the spacings should be measured between the nearest edges of the tips4 ,a space must be maintained between fuse terminals of the same polarity of at least one-half of an inch for voltages up to #abe and of at least three-quarters of an inch for voltages from #abe to #bej4 ,this is the minimum distance allowable1 and greater separation should be provided when practicable4 ,for #bej volts1 boards1 or blocks with the ordinary front-connected terminals1 except where these have a mass of compact form equivalent to the back-connected terminals usually found in switchboard work1 a substantial barrier of insulating material1 not less than one-eighth of an inch in thickness1 must be placed in the 8break0 gap--this barrier to extend out from the base at least one-eighth of an inch farther than any bare live part of the fuse-block terminal1 including binding screws1 nuts and the like4 ,for three-wire systems cut-outs must have the break-distance required for circuits of the potential of the outside wires4 ,,table ,x4 ,,fuse ,,spacings4 ---------------------------------------- ---------------- ,minimum ,separation of ,minimum ,nearest ,metal ,parts of ,break ,opposite ,polarity ,distance ,not over #abe volts3 ----------------------------------- #aj amperes or less #c_/d inch #c_/d inch #aa-ajj amperes #a inch #c_/d inch #aja-cjj amperes #a inch #a inch #cja-a1jjj amperes #a-a_/d inches #a-a_/d inches ---------------------------------------- ---------------- ,minimum ,separation of ,minimum ,nearest ,metal ,parts of ,break ,opposite ,polarity ,distance ,not over #bej volts3 ----------------------------------- #aj amperes or less #a-a_/b inches #a-a_/d inches #aa-ajj amperes #a-c_/d inches #a-a_/d inches #aja-cjj amperes #b inches #a-a_/b inches #cja-a1jjj amperes #b-a_/b inches #b inches ---------------------------------------- ---------------- ,switch ,spacings and ,dimensions4 ,when designed with #bej-volt spacings between adjacent blades1 triple-pole switches must be marked #bej volts and may be used on #c-wire ,d4 ,c4 or single-phase systems having not more than #bej volts between adjacent wires and not more than #ejj volts between the two outside wires4 ,spacings and dimensions must be at least as great as those given below3 ,,table ,,xi ,a4 ,,switch ,,spacings ,,and ,,dimensions ,,for ,,switch-,,boards ,,and ,,panel ,,boards4 ,not ,over #abe ,volts ,d4 ,c4 and ,a4 ,c4 ---------------------------------------- -------------------- ,minimum ,separation of ,current ,width and ,thickness ,nearest ,metal ,minimum ---------------------------------- parts of ,break ,blades ,clips and ,opposite ,distance ,hinges ,polarity ---------------------------------------- ------------------- #cj amp4 #a_/b inch by #a_/b inch by #a inch #c_/d inch #fj amp4 #e_/fd inch #c_/fd inch #a-a_/d inch #a-c_/d inch ---------------------------------------- ------------------- ,,table ,,xi ,b4 ,,switch ,,spacings ,,and ,,dimensions ,,for ,,individual ,,switches4 ,not ,over #abe ,volts ,d4 ,c4 and ,a4 ,c4 ,inch ,inch ,inch ,inch #cj amperes #a_/b by #e_/fd #a_/b by #c_/fd #a-a_/d #a #fj and #ajj amperes #a-a_/b #a-a_/d #bjj amperes #b-a_/d #b #djj and #fjj amperes #b-c_/d #b-a_/b #hjj and #ajjj amperes #c #b-c_/d ,a #cjj-;ampere switch with the spacings of the #bjj-;ampere switch above may be used on switchboards4 ,,table ,,xi ,c4 ,,switch ,,spacings ,,and ,,dimensions ,,for ,,all ,,switches4 #bej ,volts ,only ,d4 ,c4 and ,a4 ,c4 ,inch ,inch ,inch ,inch #cj amperes #a_/b by #e_/fd #a_/b by #c_/fd #a-c_/d #a-a_/b ,,table ,,xi ,d4 ,,switch ,,spacings ,,and ,,dimensions ,,for ,,all ,,switches4 ,not ,over #bej ,volts ,d4 ,c4 nor ,over #ejj ,volts ,a4 ,c4 ,inch ,inch ,inch ,inch #cj amperes #e_/h by #a_/h #e_/h by #a_/af #b-a_/d #b #fj and #ajj amperes #b-a_/d #b #bjj amperes #b-a_/b #b-a_/d #djj and #fjj amperes #b-c_/d #b-a_/b #hjj and #ajjj amperes #c #b-c_/d ,a #cjj-;ampere switch with the spacings of the #bjj-;ampere switch above may be used on switchboards4 ,cut-out terminals on switches for over #bej volts must be designed and spaced for #fjj-volt fuses4 ,,table ,,xi ,e4 ,,switch ,,spacings ,,and ,,dimensions ,,for ,,all ,,switches4 ,not ,over #fjj ,volts ,d4 ,c4 and ,a4 ,c4 ,inch ,inch ,inch ,inch #cj amperes #e_/h by #a_/h #e_/h by #a_/af #d #c-a_/b #fj amperes #d #c-a_/b #ajj amperes #d-a_/b #d ,paint ,bridge4--,the paint bridge is usually a scaffold which can be raised and lowered1 and which serves the purpose of carrying scene painters at work on the curtains4 ,a long strip is the best means of illumination and it must be connected with long stage cable so as to be portable4 ,paint ,room4--,rooms in which paints are stored should not contain switches or cut-outs4 ,lamps should be incased in vapor-tight globes4 ,program ,board4--,a simple form of program board is shown in ,figure #afi4 ,except at the top and the bottom1 where three lamps are shown together in one compartment1 each lamp is incased by itself4 ,in front of the lamps is usually colored glass1 bearing numbers or letters4 ,the lamp behind any number being turned on1 that number becomes visible4 ,the top and bottom are usually labeled1 8,special01 or 8,extra04 ,illustration3 ,,figure #afi4 ,another form of program board is shown in ,figure #agj4 ,this requires much more wiring4 ,each lamp on the board is connected to a plug or switch at the operator's station4 ,whichever switch is closed on the small board at the right causes a corresponding light on the large board to appear4 ,illustration3 ,,figure #agj4 ,two program boards are usually installed1 one at each side of the stage1 facing the audience at angles1 so that one can be seen from the extreme right1 the other from the extreme left4 ,illustration3 ,,figure #aga4 ,a system that is often used for carriage call is shown in ,figure #aga4 ,the lights are arranged on circuits as indicated by numbers4 ,all lamps bearing the same number being connected to one wire leading to the controlling station4 ,thus there are eight controlling or switch wires and there is one wire common to all4 ,a special switch is provided which has a contact point for each wire4 ,paper cards1 perforated specially for the numbers they represent1 are used4 ,if a card bearing a certain number is inserted in the proper place and the switch closed1 the number printed on the card will appear on the sign4 ,if1 for instance1 the shaded circles in the card at the left of the figure allow contact to be made1 the lights indicated by black circles will light up and make the figure 8#f04 ,another form of program or call board is shown in ,figure #agb4 ,this requires more wires than the one just described1 one wire being carried to the controlling board from each lamp4 ,the connections may be made in various ways4 ,sometimes they are made with knife switches4 ,if it is desired to make the figure #a1 for instance1 only the three lights in a vertical row in the center need be lighted1 and to do this the three wires from those lamps must be connected to one switch4 ,to make the figure #b1 seven lamps would have to be lit by another switch4 ,it is capable of making any letter or number and when used as a program board only may be somewhat simplified4 ,illustration3 ,,figure #agb4 ,in connection with these signs a large number of wires may be required and attention should be given to the following rule3 ,national ,electrical ,code ,rule for ,wiring ,program and ,call ,boards4 ,except in the case of stage pockets the same conduit must never contain more than four two-wire1 or three three-wire circuits of the same system except by special permission1 and must never contain circuits of different systems4 ,proscenium ,side ,lights4--,these lights are located on each side of the stage1 as near as possible to the edge of the proscenium opening and often in front of the steel curtain4 ,they are of more use in musical productions1 where choruses spread over the whole stage1 than in dramatic productions where the interest is more in the center of the stage4 ,in some theaters the proscenium side lights extend the full height of the opening and are arranged for three colors in the same manner as footlights and borders4 ,very often1 however1 only ten or twelve lights are arranged on each side of the stage4 ,the construction rules are the same as those governing foot-lights4 ,lamps must be protected by strong wire mesh4 ,this is essential as in many cases actors are very likely to back into them while passing off the stage4 ,portable strips are sometimes used as proscenium side lights4 ,receptacles4--,see 8,stage ,pockets04 ,retiring ,rooms4--,in these places a quiet subdued illumination is usually desired4 ,there are also often quaint objects and effects to be illuminated4 ,a large number of outlets conveniently located for the use of table lamps1 fire places1 and illumination of pictures1 should be provided4 ,rheostats4 ,national ,electrical ,code ,rules for ,rheostats4 ,location4 ,must be placed on a switchboard1 or at a distance of at least one foot from combustible material1 or separated therefrom by a slab or panel of non-combustible1 non-absorptive1 insulating material such as slate1 soapstone1 or marble1 somewhat larger than the rheostat1 which must be secured in position independently of the rheostat supports4 ,bolts for supporting the rheostat shall be countersunk at least one-eighth inch below the surface at the back of the slab and the bolt heads shall be covered with insulating material4 ,for proper mechanical strength1 slab should be of a thickness consistent with the size and weight of the rheostat1 and in no case to be less than one-half inch4 ,if resistance devices are installed in rooms where dust or combustible flyings would be liable to accumulate on them1 they must be equipped with dust-proof face plates4 ,materials4 ,must be made entirely of non-combustible materials1 except such minor parts as handles1 magnet insulation1 etc4 ,all segments1 lever arms1 etc41 must be mounted on non-combustible1 non-absorptive1 insulating material4 ,connections4 ,clamps for connecting wires to the terminals must be so designed as to insure a thoroughly good connection and must be sufficiently strong and heavy to withstand hard usage4 ,for currents above #cj amperes1 lugs into which the connecting wires may be soldered1 or approved solderless connectors must be used4 ,clamps or lugs will not be required when leads are provided as a part of the device4 ,no-,voltage ,release4 ,motor-starting rheostats must be so designed that the contact arm cannot be left on intermediate segments1 and for direct-current circuits must be provided with an automatic device which will interrupt the supply circuit before the speed of the motor falls to less than one-third of its normal value4 ,in motor-starting rheostats for alternating-current circuits the automatic interrupting device may be omitted4 ,overload ,release4 ,overload-release devices which are inoperative during the process of starting a motor will not be approved1 unless other circuit-breakers or fuses are installed in connection with them4 ,signals4--,signals are necessary between the manager's office and the stage electrician's station2 for this purpose telephones are generally used4 ,in many cities a fire-alarm signal system is also required and it is specified to what part of the house it shall lead4 ,in addition to the above1 a means of signalling the fly floor and the orchestra leader must be provided4 ,buzzers are used for these signals4 ,it is best to use batteries for all these signals instead of attempting to run them from lighting circuits4 ,means of signalling the arc-lamp station in the gallery or the balcony should also be provided for use in connection with lantern slides1 etc4 ,telephone connection to this point will also be very useful in order to give instructions to the lamp operator4 ,return-call systems are advisable in all places so that the electrician can be called from any point4 ,in some cities the local laws require these wires to be in conduit so as to preclude any possibility of their communicating fire to anything4 ,at any rate the wires should be very carefully installed4 ,signs4--,in nearly all electric signs used about theaters the letters are outlined by incandescent lamps4 ,small candle-power lamps are always used4 ,they are not only economical but much more attractive because the glare from too much light is very annoying4 ,many signs are equipped with low candle-power tungsten lamps wired in series4 ,in order that the letters should show to full advantage they should be glossy white and be kept clean4 ,such letters will show as bright as the lamps4 ,it is best to wire the sign so that either side can be used independent of the other4 ,in many cases1 also1 signs are wired so that each letter is independent of the others for use with flashers4 ,attraction signs are used to advertise the attractions which appear from time to time4 ,independent portable letters are used and changed as often as the attractions change4 ,each letter must be fitted with cable and attachment plug of some kind and should have a separate circuit4 ,cut-outs are generally located on the frame and must be protected from the weather4 ,sockets4--,sockets must be of approved construction4 ,key sockets must not be used for emergency or exit lighting4 ,sockets with fiber linings must not be used unless protected by insulating joints4 ,in damp places weatherproof sockets must be used4 ,where inflammable gases exist1 lamps must be incased in vapor-proof globes4 ,porcelain sockets should not be used in theaters4 ,weatherproof sockets are generally used for portable purposes because they have no screws1 etc41 to work loose4 ,stage ,cable4--,stage cables are allowed in theaters only where flexible conductors are absolutely necessary4 ,all wiring that can possibly be installed in conduit or strip construction should be so arranged4 ,by the use of plugging boxes the quantity of stage cable necessary can be much reduced4 ,plugs for arc and incandescent lights must not be interchangeable4 ,stage ,flues4--,in most cities stage flues1 as described in the chapter on 8,theater ,buildings01 are required4 ,the requirement is also1 often1 that they be released by electrical means4 ,the rule below contemplates a circuit containing an electro-magnet and at least two switches in series4 ,the magnet must be energized to hold the ventilator closed4 ,if the current fails or a switch is opened the dampers must fly open at once4 ,where direct current is available the magnet is usually wound for #aaj volts and connected to a circuit that is always alive4 ,in case of an isolated plant which is shut down at night some arrangement for tying the dampers down should be made1 but it is not always advisable1 as once tied they are likely to remain so and sure to fail when needed4 ,magnets do not work well on alternating currents and in such cases the magnet should be wound for a small current to be obtained from a gravity battery which may be allowed to be always working4 ,locate the battery where it will not freeze4 ,national ,electrical ,code ,rules for ,control of ,stage ,flues4 ,in cases where dampers are released by an electric device1 the electric circuit operating same must be normally closed4 ,magnet operating dampers must be wound to take full voltage of circuit by which it is supplied1 using no resistance device1 and must not heat more than normal for apparatus of similar construction4 ,it must be located in loft above scenery1 and be installed in a suitable iron box with a tight1 self-closing door4 ,such dampers must be controlled by at least two standard single-pole switches mounted within approved iron boxes provided with self-closing doors without lock or latch1 and located1 one at the electrician's station and the others as designated4 ,stage and ,gallery ,pockets4--,stage pockets are usually located on each side of the stage just far enough from the center to be safely back of the scenery4 ,the more pockets there are the better it will be4 ,each pocket usually contains four circuits1 and one of these at least should be for incandescent lights4 ,it will be convenient if the stage pockets are divided into four groups1 each group under control of a separate switch and the whole again under control of a main switch4 ,this will enable the operator to throw off all of the pockets at once1 if necessary1 or to make any combination desired4 ,illustration3 ,,figure #agc4 ,sometimes lights fed through stage pockets require to be dimmed2 but it is hardly practicable to arrange dimmers for apparatus carried by traveling companies1 since a dimmer must be selected with respect to the amperage it is to control4 ,in addition to the rules given below1 some cities require the bottom of stage pockets to be open1 so as to avoid an accumulation of dust4 ,this is a very essential precaution1 as otherwise the pockets soon fill up or require very frequent cleaning4 ,the covers must be substantial as heavy trucks are sometimes run over them4 ,two illustrations of stage pockets are given in ,figures #agc and #agd4 ,the plugs used with these boxes are shown in ,figure #age4 ,illustration3 ,,figure #agd4 ,illustration3 ,,figure #age4 ,gallery pockets are not usually laid in the floor but along the railing4 ,the gallery pockets should be under separate control from the stage switchboard4 ,national ,electrical ,code ,rules for ,stage and ,gallery ,pockets4 ,must be of approved type1 insulated from ground and controlled from switchboard1 each receptacle to be of not less than #ce-;ampere rating for arc lamps nor #ae-;ampere for incandescent lamps1 and each receptacle to be wired to its full capacity4 ,arc pockets to be wired with wire not smaller than ,no4 #f ,b4 ,s4 gauge and incandescent pockets with not less than ,no4 #ab ,b4 ,s4 gauge4 ,plugs for arcs and incandescent pockets must not be interchangeable4 ,switches4--,all knife switches should be enclosed in cabinets unless they are located on a switchboard4 ,in exposed places1 flush switches should be used4 ,the usual height at which scattered switches are located is about four and one-half feet above floor4 ,door switches are of use principally in dressing rooms4 ,illustration3 ,,figure #agf4 ,diagrams of three-way switches are given in ,figures #agf and #agg4 ,in ,figure #agg1 the wiring by which a light can be controlled from three different points is shown4 ,the middle switch must be a pole-changing switch4 ,in this case a throw-over knife switch is wired to perform this function4 ,omitting the knife switch we have two three-way switches controlling the light4 ,when both switches 7indicated by broken lines7 connect to the same wire the light burns4 ,illustration3 ,,figure #agg4 ,in ,figure #agf1 when both switches connect to the same polarity the light is out2 when one of them is connected to the other pole the light burns4 ,under certain conditions this arrangement is more economical in wire but has the disadvantage which the other method avoids1 of bringing both poles to each switch4 ,this method cannot be used with direct-current arc lamps4 ,three-way switches are useful on stairways1 enabling one to turn on a light at the bottom of the stairway and turn it off when at the top or vice versa4 ,national ,electrical ,code ,rules for ,switches and ,connections4 ,switches4 ,must be placed on all service wires1 either overhead or underground1 in the nearest readily accessible place to the point where the wires enter the building1 and arranged to cut off the entire current4 ,departure from this rule may be authorized only under special permission in writing4 ,switches controlling emergency lighting must be located only in the lobby4 ,must when used for service switches1 indicate1 on inspection1 whether the current be 8on0 or 8off04 ,switch cabinets must be deep enough to allow the door to be closed when #cj ampere branch-circuit switches are in any position1 and when larger single-throw switches are thrown open as far as their construction and installation will permit4 ,must1 for constant-current systems1 close the main circuit and disconnect the branch wires when turned 8off02 must be so constructed that they shall be automatic in action1 not stopping between points when started1 and must prevent an arc between the points under all circumstances4 ,they must indicate whether the current be 8on0 or 8off04 ,service cut-out and switch must be arranged to cut off current from all devices including meters4 ,must always be placed in dry1 accessible places1 and be grouped as far as possible4 ,single-throw knife switches must be so placed that gravity will not tend to close them4 ,double-throw knife switches may be mounted so that the throw will be either vertical or horizontal as preferred1 but if the throw be vertical a locking device must be provided1 so constructed as to insure the blades remaining in the open position when so set4 ,when practicable switches must be so wired that blades will be 8dead0 when the switch is open4 ,when switches are used in rooms where combustible flyings would be likely to accumulate around them1 they must be enclosed in dust-tight cabinets4 ,up to #bej volts and thirty amperes1 approved indicating snap switches are suggested in preference to knife switches on lighting circuits4 ,single-pole switches must never be used as service switches nor for the control of outdoor signs or circuits located in damp places1 nor placed in the neutral wire of a three-wire system1 except in the two-wire branch or tap circuit supplying not more than #ffj watts4 ,where flush switches or receptacles are used1 whether with conduit systems or not1 they must be enclosed in an approved box constructed of iron or steel1 in addition to the porcelain enclosure of the switch or receptacle4 ,hinges of knife switches must not be used to carry current unless they are equipped with spring washers1 held by lock-nuts or pins1 or their equivalent1 so arranged that a firm and secure connection will be maintained at all positions of the switch blades4 ,spring washers must be of sufficient strength to take up any wear in the hinge and maintain a good contact at all times4 ,connections4 ,switches for currents of over thirty amperes must be equipped with lugs1 firmly screwed or bolted to the switch1 and into which the conducting wire shall be soldered4 ,for the smaller sized switches simple clamps can be employed1 provided they are heavy enough to stand considerable hard usage4 ,where lugs are not provided1 a rugged double-,v groove clamp is advised4 ,a set screw gives a contact at only one point1 is more likely to become loosened1 and is almost sure to cut into the wire4 ,for the smaller sizes1 a screw and washer connection with up-turned lugs on the switch terminal gives a satisfactory contact4 ,spacings4 ,see 8,panel ,boards04 ,switchboards4--,the stage switchboard is usually located on the right-hand side of the stage4 ,this position enables the operator to watch cues easily and handle his switches with the right hand4 ,this side is also the one from which the stage manager prefers to work4 ,it is preferable to have the board raised high enough above stage level to allow all space on the stage to be used by actors4 ,if the switchboard is located on stage level it takes up much room that is valuable and makes stage exits for actors difficult4 ,the wiring of a good switchboard should be divided into three parts1 each part independent of the others1 so that any one part can be entirely cut off without interfering with the other4 ,all of the house lights should be fed through one main switch1 and all of the stage light connected to another set of bus-bars1 but it is best not to have the stage side of the board as a whole controlled by a main switch4 ,if the stage side of the board is controlled by a single switch there exists the possibility that this switch may be used to cut off everything for a dark scene and when light is again wanted a part of the lighting of the previous setting may be left on and possibly interfere with the new scene4 ,illustration3 ,,figure #agh4 ,the stage lighting is usually divided into four groups1 viz43 three color groups and a group of stage pockets4 ,the number of white lights is usually equal to that of all of the colors4 ,figure #agh shows a well laid out switchboard4 ,all of the lights in the auditorium are controlled by switches shown in the upper right-hand corner and all of these are under the control of the main switch4 ,the house lights are usually thrown on or off as a whole and this main switch must be convenient for the operator4 ,the stage pockets are controlled by the bank of switches shown at ,e4 ,lights burning off the stage pockets generally are controlled by special operators on the stage or by actors1 and need not be so very convenient to the switchboard operator4 ,they must1 however1 be under his control when necessary2 but here also a main switch is not advisable4 ,in addition to the three groups of lights spoken of above1 there are a number of lights which should be controlled from the switchboard but must be so connected that they will be left on1 no matter what is done with either house or stage light4 ,in this group belong a few lights mounted at the top of the switchboard which enable the operator to see his switches when all else is dark4 ,these lights are generally shielded so as to throw no light in the direction of the stage opening4 ,the orchestra lights also belong in this group1 but a special switch may1 with advantage1 be arranged on this circuit to bring it under the control of one of the musicians4 ,in some dark scenes these lights are turned out for a short time1 but it is very important that they be turned on again at the proper moment1 and this is more certainly assured1 by giving the musicians control1 than by leaving it to an electrician on the stage who may be very busy with other matters at the time4 ,the lights on the fly floor and in the rigging loft1 as well as those in dressing rooms and basement1 must also be independent4 ,fan motor circuits should also be independent of the house circuit4 ,they are often needed when the house lights are thrown off4 ,with the switchboard illustrated in ,figure #agh we have shown only the switches governing the house and stage proper4 ,the switches governing the other lights are usually worked into the vacant spaces between the two groups4 ,each switch should be labeled in such a manner that a new operator can learn the board easily4 ,the most important part of the board is that part governing the stage lighting1 and this should always be placed as conveniently as possible to the operator4 ,a stage switchboard is like a house in that no one is wholly satisfied with the one he has1 but thinks he could improve it a little if he could build it over again4 ,the arrangement shown in ,figure #agh is1 however1 quite satisfactory for general purposes4 ,the white lights predominate in the ratio of two to one and are laid out in two groups ,a and ,b4 ,both groups are controlled by the switch ,c4 ,the switches ,a and ,b do not control the lights at all if the smaller throw-over switches at the right are thrown downward4 ,a diagram of these switch connections is given in ,figure #agi where the switches ,b and ,c are indicated4 ,the object of the switches ,a and ,b is to help in quickly increasing or decreasing the illumination on the stage4 ,if in the beginning of a certain scene1 for instance1 only a small quantity of light is wanted1 while a little later full illumination is desired1 the low illumination may be obtained by throwing the proper switches down2 the additional illumination which will be needed a few minutes later may be prepared for by setting the other switches needed to the upward position and at the proper moment closing switch ,b2 this will instantly produce the effect which otherwise would be possible only by operating a number of switches in succession4 ,in the same way1 by a reversal of this process1 the illumination may be reduced in any amount4 ,this feature is very valuable in many stage settings4 ,illustration3 ,,figure #agi4 ,to throw off all of the white lights the switch ,c must be opened4 ,the switches ,d and ,f are main switches controlling colored lamps4 ,all lamps of one color should be connected to one or the other of these groups unless some special color effect is desired4 ,from the three groups of switches1 circuits extend into the foot lights1 into every border1 and into the proscenium side-light strips so that the color scheme may be carried out in any of these4 ,the handles of all switches in a row should be of the same height so that the operator may more readily accustom himself to catch them quickly4 ,it is better to have switches of some excess capacity1 as the heavy metal stands the arcing much better4 ,a main switch by which the whole board may be cut off should be installed but this need not be on the front of the board4 ,,chapter ,,xix4 ,,portable ,,stage ,,equipment4 ,the general rule is that all wires in theaters must be in conduit or armored cable4 ,metal molding is not considered suitable for the stage side of the theater4 ,there are1 however1 stage requirements which make the use of some sort of flexible and portable connection necessary and for such purposes stage cables are allowed4 ,all wiring that can be permanently fastened to battens or fastened in other ways2 or that is run inside of posts or statuary1 must be in conduit or armored cable4 ,the ,national ,electrical ,code ,rules are quoted in this chapter wherever they apply and should be followed1 not only because these rules outline the best practice but because1 throughout the country1 inspections will generally be governed by these requirements4 ,even where the local rules vary somewhat from these rules1 it will be found that all apparatus constructed according to them will be favored to a considerable extent4 ,anvil ,sparks4--,these are sometimes produced by arranging the anvil as one pole of a circuit and the hammer as the other4 ,when the hammer leaves the anvil1 the spark occurs4 ,a resistance must always be inserted in the circuit if a light or power circuit is employed4 ,one of the most successful methods of producing anvil sparks is shown in ,figure #ahj4 ,when the hammer strikes the anvil the spring follows and strikes the head of the hammer2 and when it rebounds the spark occurs4 ,if it is not desired to use a power circuit the spark may be obtained from batteries by the use of a spark coil4 ,sparks in dueling scenes may be produced in much the same manner4 ,in some cities the inspection laws require all arcs or sparks1 used on the stage1 to be enclosed4 ,so far as the authors are aware no really satisfactory method of enclosing anvil sparks has ever been made up4 ,if such an enclosure is to be constructed it must be borne in mind that it must not spoil the illusion nor mar the tone in case the anvil is tuned for use in singing acts4 ,a special combination of metals is on sale at stage-supply dealers by which sparks can be produced without the use of current4 ,illustration3 ,,figure #ahj4 ,arc ,lamps4--,in ,figure #aha1 there is shown an open or flood lamp1 also known as the 8,olivet04 ,this style of lamp is used on the stage only for general illumination4 ,as the light from this lamp spreads in all directions it must be brought close to the part to be illuminated and this usually brings it close to the scenery4 ,all portable stage lamps are hand feed and require close attention on the part of operators4 ,while traveling it sometimes occurs that only high voltage such as #ejj or #fjj volts is available and in such a case a suitable number of lamps must be connected in series4 ,hand-feed arc lamps are difficult to start under such circumstances and the following method is often resorted to3 ,place the carbons of all the lamps connected in series the proper distance apart and connect a small fuse across each gap4 ,when the current is turned on it will melt the fuses and establish the arc4 ,illustration3 ,,figure #aha4 ,illustration3 ,,figure #ahb4 ,in ,figure #ahb we have an illustration of what is known as the spot or lens lamp4 ,this style of lamp is used on the stage1 on bridges1 or 8in front0 7in front being the term by which the balcony or galleries are designated in this case74 ,in the figure a 8,sciopticon0 attachment is shown which is removable4 ,even very unpretentious shows carry at least one spot lamp and the largest shows often carry #cj or #dj open and spot lamps4 ,arc lamps are often imitated by an incandescent lamp placed within a suitable globe with the hood made up in the shape of an arc lamp4 ,illustration3 ,,figure #ahc4 ,figure #ahc is a cut of a stereopticon outfit4 ,dissolving views require at least two lamps and sometimes three1 the third being for the purpose of providing a frame for the views or adding an extra effect1 such as falling snow4 ,two lamps at least are always in use at the same time and it is necessary to provide cables of sufficient carrying capacity for two or three lamps1 as the case may be4 ,the ,national ,electrical ,code ,rules for ,arc ,lamps to be ,used on the ,stage4 ,must be constructed entirely of metal except where the use of approved insulating material is necessary4 ,must be substantially constructed1 and so designed as to provide for proper ventilation1 and to prevent sparks being emitted from lamps when same are in operation2 and mica must be used for frame insulation4 ,front opening must be provided with self-closing hinged door frame1 in which wire gauze or glass must be inserted1 except in the case of lens lamps1 where the front may be stationary1 and a solid door be provided on back or side4 ,must be so constructed that neither carbons nor live parts will be brought into contact with metal of hood during operation1 and arc-lamp frames and standards must be so installed and protected as to prevent the liability of their being grounded4 ,switch on standard must be so constructed that accidental contact with any live portion of same will be impossible4 ,all stranded connections in lamp and at switch and rheostat must be provided with approved lugs4 ,rheostats must be plainly marked with their rated capacity in volts and amperes1 and1 if mounted on a standard1 must be raised to a height of at least three inches above the floor4 ,resistance must be enclosed in a substantial and properly ventilated metal case which affords a clearance of at least one inch between the case and the resistance element4 ,a competent operator must be in charge of each arc lamp1 except that one operator may have charge of two lamps1 when they are not more than ten feet apart and are so located that he can properly watch and care for both lamps4 ,each lamp should be provided with its own fuses and switch4 ,baby ,spot ,lamp4--,this is the name given to a small lens lamp in which an incandescent lamp is used instead of an arc lamp4 ,such a lamp cannot be used for projection very well but is well suited to illuminate parts of an act that do not require very bright illumination4 ,it is sometimes used to take the place of proscenium side lights4 ,in one well-known production twelve such lamps were used upon scaffolding directly above the proscenium opening4 ,the incandescent lamp is movable for the purpose of focusing2 but it not being a 8point source01 no such accurate focusing is possible as with arc lamps4 ,batteries4--,both primary and secondary1 or storage1 batteries are extensively used upon the stage4 ,small dry cells are often used to ring bells or light miniature lamps in the hair or clothes of the chorus4 ,the electromotive force of a cell is independent of the size and depends only upon the materials used2 but the current which a battery can deliver varies directly with its size4 ,if we wish to increase the voltage we must connect several cells in series1 as indicated in ,figure #ahd2 if we have sufficient voltage but lack current we must connect1 as in ,figure #ahe4 ,as a general rule1 in any circuit1 we must connect the battery so that its resistances shall most nearly equal the resistance of the device which it feeds4 ,this means that if the resistance of the device is greater than that of the battery we must connect our battery in series2 if it is less we must connect the cells in multiple1 as indicated by ,figure #ahe4 ,when connecting cells in multiple those of the same kind should always be selected4 ,any cell whose electromotive force is not fully equal to the others will absorb energy and be charged by the others4 ,the resistance of small cells is high and it is best1 where size is not objectionable1 to use large cells4 ,storage1 or secondary batteries1 have low resistance and are capable of delivering very strong currents1 even though the voltage be low4 ,the heat is proportional to the square of the current and a certain amperage1 with two volts back of it1 will produce just as much heat in given resistance as the same amperage with several hundred volts4 ,the sparking in case of a broken circuit or a fuse blowing would1 however1 be hardly noticeable with the low voltage4 ,illustration3 ,,figure #ahd4 ,illustration3 ,,figure #ahe4 ,no definite rule is given concerning the fusing of low-voltage storage batteries1 but it is good practice to insert a double-pole fuse in each branch circuit2 the fuse to be small enough to protect the smallest wire fed through it4 ,the capacity of storage batteries is usually given in 8ampere hours04 ,a #fj-;ampere-hour battery1 for instance1 can deliver three amperes for twenty hours or ten amperes for six hours4 ,with every battery there is1 however1 a certain maximum rate of discharge which should not be exceeded4 ,the battery should not be allowed to run down too low and should be kept well charged4 ,it is best to follow the instructions which the makers send out with them4 ,bells4--,electric bells are used on the stage for many purposes4 ,sometimes they are used as musical instruments1 the gongs being properly tuned2 at other times they are provided to ring in connection with certain acts2 and they are also used for the purpose of signaling4 ,when signals are to be given1 which the audience must not hear1 it is better to provide buzzers4 ,illustration3 ,,figure #ahf4 ,bells can be arranged to operate from power circuits by placing an incandescent lamp1 or some other suitable resistance1 in series with them2 but it is not advisable to do so4 ,it is not safe from a fire-hazard point of view1 and also not very practical1 since in many places alternating current only can be had and the ordinary bell does not operate well with it4 ,batteries should always be used for bells and other low-voltage devices4 ,where it is desired to operate a number of bells together1 they may be arranged in series1 as shown in ,figure #ahf1 in which the vibrator of one bell is cut out of circuit so that the vibrations of this bell are governed by those of the other4 ,sets of bells properly tuned are often scattered about and controlled from a keyboard4 ,there are usually eighteen bells in such a set4 ,blinding ,lights4--,in certain acts it is necessary for the actor to work part of the time unseen by the audience4 ,this may easily be arranged for by the use of a number of bright lights placed between him and the audience4 ,these lights1 when burning1 blind the audience so that they cannot see beyond them4 ,the lamps must be placed in reflectors which throw all light toward the audience4 ,they are arranged either upon the floor of the stage or around cabinets or other devices4 ,the blinding effect depends upon the contrast between the front and the rear of the lamps4 ,lights should be very bright but the quantity of light must not be sufficient to cause reflected light from the front to illuminate the back of the stage4 ,where emergency lights are kept burning during the performance it is quite difficult to carry out the blinding effect for any considerable length of time4 ,brackets4--,brackets are made up in any of the three ways shown in ,figure #ahg4 ,if the stem is large enough to admit the cable1 which should be used to the pin-plug connector1 no splice of any kind will be necessary4 ,if the bracket stem is too small for this1 fixture wire must be used and a connection from it to the cable must be made4 ,if this is made1 as at the extreme right1 the back of the canopy must be enclosed in substantial metal4 ,on no account should fixture wire be allowed to extend outside of the stem4 ,the bracket must have some provision by which it can be made to hold its proper position when in place4 ,sometimes hooks are provided for this purpose and at other times it is held in place by screws in the scenery1 as suggested by the back of the canopy shown at ,a4 ,national ,electrical ,code ,rule for ,lights on ,scenery4 ,where brackets are used they must be wired entirely on the inside2 fixture stem must come through to the back of the scenery and end of stem be properly bushed4 ,illustration3 ,,figure #ahg4 ,bunch ,lights4--,bunch lights are made up according to the plans shown in ,figure #ahh4 ,they are used only on the stage4 ,no very brilliant illumination can be obtained from them4 ,in one well-known production a bunch light containing one hundred #cb c4-p4 lamps was used without obtaining the result desired4 ,the light cannot be concentrated as can that from arc lamps4 ,bunch lights1 however1 have the advantage of not requiring so much attention as arc lamps and can often be used on a shallow stage where arc lamps would be out of place4 ,bunch lights are sometimes made double1 two on one stand2 two colors can thus be used at the same time and certain color changes facilitated4 ,color effects or changes in colors are brought about by inserting colored gelatine slides in front of the lights4 ,national ,electrical ,code ,rules for ,bunch ,lights4 ,must be substantially constructed of metal and must not contain any exposed wiring4 ,illustration3 ,,figure #ahh4 ,the cable1 feeding same1 must be bushed in an approved manner where passing through the metal1 and must be properly secured to prevent any mechanical strain on the connection4 ,chandeliers4--,the rule which requires all wiring about brackets to be enclosed1 naturally would apply here also4 ,in connection with chain fixtures1 which are at present very popular1 this requirement is generally overlooked if good reinforced cord is used4 ,ordinary fixture wire or flexible cord should not be used4 ,the weakest part of a chain fixture is indicated in ,figure #ahi by the arrow4 ,the opening at this place is1 as a rule1 too small and not well reamed out4 ,fixtures used on the road are constantly giving way at this point4 ,the opening should be large enough to pass reinforced cord and should be well reamed out4 ,if the opening cannot be made large enough to give the wire a little free movement1 it is advisable to wrap tape around the wire and the metal in such a way as to prevent all motion of the wire at this point4 ,the same observations also apply to the other end where the cord enters the socket4 ,illustration3 ,,figure #ahi4 ,illustration3 ,,figure #aij4 ,illustration3 ,,figure #aia4 ,another frequent source of trouble with chandeliers is found at the end of the stem where connection is made to the cable which feeds the fixture4 ,see ,figure #aij4 ,very often fixture wire is brought out here1 but this will soon break4 ,the stage cable1 or reinforced cord1 should be run down to the bottom of the fixture and connections there made to the wires leading to the various arms4 ,there are many fixture hooks made up after the manner shown in ,figure #aia which have a small opening for the wire at the point indicated by the arrow4 ,this opening is always too small and in such a case it is best to arrange a tee as shown4 ,a chandelier must always be hung in such a manner as to avoid strain coming on the electrical conductors4 ,illustration3 ,,figure #aib4 ,colors4--,where a certain color is wanted1 during the whole show1 from a certain light source1 the incandescent lamps themselves may be colored4 ,prepared colors for this purpose are on the market and it is best to use them4 ,where the colors in a scene change rapidly there must be some colored material available which can be quickly interposed between the light and the scene4 ,the manner in which this is done for bunch lights is indicated in ,figure #ahh4 ,the same method is also used in connection with open-arc lamps1 but for spot lights there is another method1 shown in ,figure #aib4 ,this is a so-called color wheel and the colors can be changed by simply revolving the wheel until the proper color is in front of the lens4 ,an automatic color wheel is on the market which allows the operator to control colors at a distance by means of an electric circuit and magnet4 ,this device cannot be used with flood lamps and has the further disadvantage of casting unavoidable shadows during the change of colors4 ,where detachable color holders are used1 it is possible to change from one color to another by almost imperceptible degrees by holding the frame in the hand and bringing it gradually from a distance to the front of the lamp4 ,in this manner the shadows cast by the frame can be avoided and the color brought very gradually into the scene4 ,illustration3 ,,figure #aic4 ,dimmer ,box4--,the dimmer box1 as the name implies is a box which contains the resistances required for dimming lights used on the stage4 ,it comes into service only with the more pretentious shows which carry foot-lights or border-lights4 ,a typical wiring diagram is shown in ,figure #aic4 ,this diagram supposes that not more than three colors are used4 ,a small candle power incandescent lamp should always be installed in the box so that the operator may see what is necessary in dark scenes4 ,this lamp should have its own fuse protection4 ,this is a point very often overlooked by operators4 ,the box is usually made of wood and lined with metal4 ,it should be deep and nearly square1 so as to occupy a minimum of space4 ,if a shallow box is used1 it will be necessary to place the switches in a separate compartment from the fuses1 so that the latter may be always enclosed1 even while the dimmers and fuses are being operated4 ,illustration3 ,,figure #aid4 ,provisions should be made for the cables to lead out through suitable bushings at the side instead of over the top of the box as is so often done4 ,in some dimmer boxes the slip connectors are fitted into the side of a box so that the male end may be inserted from outside4 ,this makes it unnecessary to bush the cables through the box4 ,electric ,sign ,imitations4--,these are used mostly in representations of city night scenes4 ,a flasher sign can be imitated by cutting small round holes in the curtain to outline the reading matter on the sign4 ,behind these holes a moon box is placed1 the lamps in it being on a flasher or controlled by 8skeedoodle0 sockets1 thus giving the effect of an electric sign on a flasher4 ,in case the effect of a steady burning sign is wanted the flasher is omitted4 ,electric signs imitating falling water have in turn been imitated according to the plan outlined in ,figure #aid4 ,on the side nearest the audience is the curtain ,a1 upon which the sign is painted and in which there are a number of holes representing the electric lamps in the original sign2 behind this curtain is a grating ,b1 also full of holes2 and behind this revolves a spiral ,c1 so arranged as to obstruct intermittently the light which is behind it4 ,the object is to imitate1 as nearly as possible1 the action of the lights in the original sign4 ,electric ,stage ,effects4--,a large number of stage effects can be produced by properly painted mica discs which are caused to move in front of the lens of a spot light arranged for the purpose4 ,a view of such a contrivance is given in ,figure #ahb and is known as the 8,sciopticon04 ,the effects are changed by clockwork which is adjustable as to speed4 ,the device is arranged to slip in front of the lenses and can be attached in a moment4 ,a list of some of the effects obtainable is given below3 ,avalanche ,climbing monkeys ,cyclone with flying objects ,falling leaves ,fireworks ,flame ,flowing water ,flying birds ,lightning ,moving clouds ,niagara ,falls ,ocean waves ,rainbow ,rain ,rising fire and smoke ,rolling lava ,sand storm ,snow storm ,swimming fish ,twinkling stars ,volcano ,water falls ,the above list is given to illustrate the possibilities of this method of producing effects4 ,they are1 however1 rather expensive and some of them require several machines to be in operation at the same time4 ,explosions4--,nearly all explosions are set off by the melting of a fuse through an electrical short circuit4 ,the explosive powder is placed above1 encloses the fuse1 and is ignited when the fuse blows4 ,illustration3 ,,figure #aie4 ,such explosions are often forbidden by inspectors but there is no danger from them if the powder1 etc41 is enclosed in a suitable wire mesh open on all sides4 ,this will not interfere with the explosion and will prevent the flame1 which lasts but an instant1 from coming in contact with scenery or people4 ,where such explosions are used they are generally the most important part of the act1 and every possible precaution must be taken to avoid the chance of failure4 ,they are1 therefore1 often arranged on two circuits with a throw-over switch so that in case one fuse fails the circuit can be immediately closed on the other4 ,see ,figure #aie4 ,it requires some time to throw-over a switch1 and in order to make doubly sure that the fuse will blow at the right time1 two fuses and two separate wires may be used and connected at the same time by a simple double-pole switch4 ,the latter arrangement has the disadvantage that one of the wires might be broken1 or the contacts bad1 without the defect ever being noticed until the other wire also fails and the explosion misses entirely4 ,it is best to use the throw-over switch and to use the wires for the first connection in alternation so that a defect may be noticed at once4 ,if the same wire were used each time the throw-over switch would be open to the same objection as the double-pole switch4 ,in selecting fuses for this work it must be borne in mind that the powder which is placed over the fuse has a certain cooling and conducting effect1 and that often1 therefore1 a fuse which would readily blow if in the open would not blow if covered with metallic powder4 ,face-,o-,graph4--,this is an arrangement of two powerful arc lamps with the necessary lenses and objective by which the face of an actor can be projected upon a screen4 ,this effect is very trying to the face and eyes of the actor4 ,the face must be brought very close to the arc lamps and must be held upside down during the performance4 ,from forty to fifty amperes are used in each arc lamp4 ,the optical principle is explained in another chapter4 ,festoons4--,festoons should be made up as shown in ,figure #aif4 ,weatherproof sockets are generally used because the common brass shell sockets have too many parts that are liable to work loose on account of the constant handling the festoons are subjected to with traveling productions4 ,the use of porcelain sockets1 however1 should be avoided2 mica sockets seem to be generally preferred4 ,the soldering also should be carefully done and only at the end1 as indicated by the arrow in the cut4 ,the branch wires are often taped to the main cable as indicated1 but often also1 circular loom is slipped over the cable in such a manner that the branch wires are supported by it4 ,short lengths of loom must be slipped on the cable before the tapes are made4 ,a really well made festoon will last a long time and give very little trouble2 while a poorly made one will cause much annoyance and much unfavorable comment from inspectors4 ,most of the festoon troubles are due to poor support of the branch wires4 ,a single festoon does not often carry more than ten or twelve lights and usually not more than six or eight4 ,illustration3 ,,figure #aif4 ,a certain style of shade is very much in vogue in connection with festoon lamps and this shade makes the use of lamp guards impossible4 ,if the shade is made of gelatine there will be but little need for the guard1 but celluloid shades should not be allowed4 ,all combustible material that is to come near the lamp or the socket should be fireproofed4 ,the ,national ,electrical ,code ,rule for ,string or ,festooned ,lights4 ,wiring of same must be of approved type2 joints to be properly made1 soldered1 and taped1 and staggered where practicable4 ,where lamps are used in lanterns or similar devices1 approved guards must be employed4 ,fire ,dance4--,this effect is generally illuminated from below the stage1 the light being thrown upward through glass4 ,special arc lamps1 equipped with powerful reflectors1 are often used and generally several of them are required to produce the proper effect4 ,if spot lamps are to be used they should not be turned upward but instead reflectors placed at an angle of forty-five degrees1 should be provided to throw the light upward4 ,see ,figure #aig4 ,if a spot lamp is turned upward1 the heat of the arc rising will be great enough to make condenser breakage a very serious problem4 ,it is also difficult to keep a horizontal arc working properly4 ,illustration3 ,,figure #aig4 ,fireflies4--,the 8fireflies0 are miniature incandescent lamps strung about among the scenery and on the clothing or in the hair of performers4 ,no attempt should be made to operate these from any other source than a low-voltage1 low-amperage battery4 ,it is best to subdivide them as much as possible to avoid short circuits4 ,a short circuit on one lamp would put out a group of one hundred as quickly as it would ten4 ,such lamps are often arranged on a keyboard by which single lamps or small groups may be lighted intermittently1 thus giving the effect of fireflies flitting about4 ,fireplaces4--,the commonest and best fireplace is made up of a few lights arranged in regular strip fashion1 the strip being placed in a practical fireplace filled with coal or large pieces of glass1 such as broken pieces of lenses4 ,for a very simple effect1 red colored globes are used4 ,the effect can be enhanced by using lamps of amber1 red1 and white and connecting each lamp to a dimmer which can be worked off the stage4 ,this is capable of producing a flaming effect4 ,a further enhancement of the effect is sometimes produced by placing colored asbestos about the lights4 ,this or other suitable material can be made to represent glowing ashes very nicely4 ,very often the illumination of the fireplace is by means of colored globes strung about among the logs4 ,for this purpose they must be equipped with strong guards and wired with stage cable4 ,actual gas flames are also often mixed in with the electric illumination4 ,in a mechanical way the effect of flame is often imitated by colored cloth so arranged that a small fan motor placed beneath it can blow it upward4 ,in a certain well-known production1 an imitation of the crater of a volcano is made by arranging a number of fan motors under a large piece of silk which rests upon a frame and revolves over the motors4 ,parts of this silk are provided with pockets and are loose so that they may be blown upward to represent flame while the major portion only undulates1 representing a sea of molten lava4 ,strips with red lights are used to intensify the effect4 ,a small motor operating a suitable ratchet has been used to imitate the sounds of wood crackling in the fire4 8,chemical smoke0 is also often used to enhance the effect4 ,this can be purchased of supply houses4 ,flat ,irons4--,see 8,heaters04 ,flowers4--,on the vaudeville stage1 electrically lighted flowers are sometimes used4 ,these are often wired by simply running fixture wire or flexible cord along a wire stem and fastening a small socket to it4 ,flowers lighted in this manner1 however1 will not be allowed in theaters where there is inspection4 ,a better method is shown in ,figure #aih4 ,armored cord is used for the stem and a miniature socket is placed at the end4 ,all splices are within the junction box which supports the stems4 ,instead of the armored cord ordinary fixture tubing may be used4 ,baskets of flowers and small bouquets are generally lighted from batteries4 ,illustration3 ,,figure #aih4 ,fountains4--,the illumination for electrically lighted fountains is sometimes obtained from incandescent lamps1 but no very showy effects can be produced with them4 ,where they are used in a manner which subjects them to moisture they must be wired in waterproof conduit and fittings and the lamps must be covered by a watertight globe4 ,for brilliant effects arc-lamp illumination is necessary and the arc must of course be below the water4 ,as arc lamps when tilted upward break condensers very rapidly1 the light is usually reflected upward by means of mirrors set as indicated in ,figure #aig4 ,fuses4--,there is no part of the electrical equipment of a traveling production so much abused as the fuse4 ,it is provided primarily for the protection of apparatus and should never be of greater capacity than is needed to carry the load put upon it4 ,there is nothing whatever gained by the use of larger fuses4 ,if the load is not in excess of six amperes1 a six ampere fuse will carry it as readily as a twenty ampere fuse4 ,if a short circuit occurs the twenty ampere fuse will blow as readily as the six ampere fuse and1 in addition1 will cause destruction of a socket or whatever may be the cause of the trouble as well as an increased fire hazard4 ,notwithstanding the above1 it is a rare exception when one finds the circuits of a traveling outfit properly fused4 ,for this there are two reasons4 ,one is that1 owing to frequent handling and moving1 fuses work loose2 and thus1 to the natural heat produced by the load1 there is added a certain amount of heat produced in the poor contacts4 ,trouble of such a nature can be lessened by the use of larger fuses1 but only to a very small extent4 ,it is far better to go over one's fuses two or three times a week and tighten the screws and contacts to avoid this trouble than to use over-large fuses4 ,another reason for the overfusing1 of plugging boxes especially1 is found in the fact that arc and incandescent plugs are interchangeable4 ,if1 therefore1 each circuit is fused at thirty amperes one need not worry about which pocket an arc lamp is connected to4 ,this practice is1 however1 very bad1 a table lamp1 for instance1 with a thirty-ampere fuse behind it would be likely to cause flash and smoke enough to alarm an audience4 ,some provisions should be made so that one can easily distinguish between arc and incandescent pockets or divisions in plugging boxes4 ,the main requisite which determines the style of fuse to be installed for stage effects is that of quick renewal in case of blow-out4 ,illustration3 ,,figure #aii4 ,gas ,globes4--,electric light is so convenient on the stage that even gas light is imitated by it4 ,in one production in which it was desirable to show the front of a theater illuminated by gas1 the gas globes were made up of cloth cut as shown in ,figure #aii4 ,behind each imitation globe a small incandescent lamp was arranged4 ,glass ,shades4--,an imitation of these for small desk or table lamps is often made by placing a strip of colored gelatine between two layers of wire mesh4 ,the wire screen keeps the gelatine straight and the whole is more serviceable than glass and less liable to break4 ,heaters4--,under this head come flatirons and water heaters4 ,flatirons are carried by many actors who cause much trouble by connecting them to lighting circuits4 ,in many places the house electrician prevents their use by fusing his lighting circuits so low that the addition of a flatiron immediately blows the fuse4 ,if used at all1 the flatirons should be of the smaller kind4 ,small heaters are also extensively used upon the stage4 ,national ,electrical ,code ,rule for ,electric ,heaters4 ,it is often desirable to connect in multiple with the heaters and between the heater and the switch controlling the same1 an incandescent lamp of low-candle power1 as this shows at a glance whether or not the switch is open1 and tends to prevent its being left closed through oversight4 ,must be protected by a cut-out and controlled by indicating switches4 ,switches must be double-pole except when the device controlled does not require more than #ffj watts of energy4 ,must never be concealed2 but must at all times be in plain sight4 ,special permission may be given in writing1 by the ,inspection ,department having jurisdiction1 for departure from this rule4 ,flexible conductors for smoothing irons and sadirons and for all devices requiring over #bej watts must have an approved insulation and covering4 ,for portable heating devices the flexible conductors must be connected to an approved plug device1 so arranged that the plug will pull out and open the circuit in case any abnormal strain is put upon the flexible conductor4 ,this device may be stationary1 or it may be placed in the cord itself4 ,the cable or cord must be attached to the heating apparatus in such a manner that it will be protected from kinking1 chafing1 or like injury at or near the point of connection4 ,smoothing irons1 sadirons1 and other heating appliances that are intended to be applied to inflammable articles1 such as clothing1 must conform to the above rules so far as they apply4 ,they must also be provided with an approved stand1 on which they should be placed when not in use4 ,stationary electric heating apparatus1 such as radiators1 ranges1 plate warmers1 etc41 must be placed in a safe location1 isolated from inflammable materials1 and be treated as sources of heat4 ,devices of this description will often require a suitable heat-resisting material placed between the device and its surroundings4 ,such protection may best be secured by installing two or more plates of tin or sheet steel with a one-inch air space between or by alternate layers of sheet steel and asbestos with a similar air space4 ,must each be provided with name-plate1 giving the maker's name and the normal capacity in volts and amperes4 ,lighthouse ,effect4--,to increase the effect of a lighthouse painted upon the scenery1 a strip of suitable length with one light at each end is provided4 ,the strip circuit contains a flasher so that both lights are turned on and off at regular intervals4 ,one lamp must be behind the head of the lighthouse1 the other where the reflection of the upper light would appear in the water4 ,lightning4--,the standard method of producing lightning effects upon the stage is by means of the device shown in ,figure #bjj4 ,a magnet and the arc-striking carbons are arranged in series and take current through a resistance4 ,normally the carbons are in contact and when the switch is closed the current passes through the magnet and carbons4 ,the current energizes the magnet and causes the upper carbon to separate from the lower1 thus striking the arc4 ,the arrangement must be such that the arc is immediately broken1 thus de-energizing the magnet2 this allows the movable carbon to close the circuit again1 thus repeating the operation4 ,this device if uninterrupted will give a rapid succession of lightning effects and it may be suspended in the wings as it is entirely automatic4 ,at the right of ,figure #bjj is shown another lightning striker which is operated by hand4 ,illustration3 ,,figure #bjj4 ,where it is not prohibited1 a very good lightning effect can be obtained by arranging a file and a piece of carbon as opposite poles of the circuit and scraping them together4 ,it is a bad practice1 however1 to strike an open arc on any stage4 ,there should always be wire mesh around it to prevent the escape of sparks4 ,automatic strikers can be purchased which will make an open arc lamp produce good lightning effects4 ,another method of producing lightning is that of flashing some of the border lights4 ,this will do in an emergency but does not compare with the other methods4 ,sometimes the effect of a bolt of lightning striking a certain place is imitated by an arc sliding swiftly down a wire4 ,in order to strike the arc at the proper moment1 the apparatus being somewhere up in the flies1 a small fuse is connected from one carbon to the other4 ,the current when turned on passes through the fuse1 melts it1 and establishes the arc4 ,the carbons are incased in a very small wire-mesh enclosure and the whole device is made to slide swiftly down a tight wire leading to the proper place4 ,the more pretentious shows often use several lightning machines to avoid the monotonous effect of all lightning strokes coming from the same direction4 ,one resistance may be made to serve for any number of lightning machines provided only one machine is used at a time4 ,illustration3 ,,figure #bja4 ,lugs4--,lugs must be provided for all leads where more than #cj amperes are used4 ,it is even more necessary to follow this rule in connection with portable theater equipment than with other wires because they are more apt to work loose4 ,for the connections to the arc lamp and rheostats it is not practicable to use soldered lugs because no solder will stand the heat4 ,two styles of lugs that may be used are shown in ,figure #bja4 ,the cuts will also explain the manner of connecting the lugs4 ,at the left1 the bare lugs are shown2 in the center the copper of the conductors is shown inserted into the lugs1 and at the right the whole conductor is shown bent back1 the metal of the lug catching over the insulation to keep it from fraying out4 ,the wires feeding arc lamps are always asbestos covered and this covering fits loosely to the wire and must be held in some such manner4 ,a stock of such lugs should always be carried1 as the leading-in wires to arc lamps1 using heavy currents1 frequently burn off4 ,illustration3 ,,figure #bjb4 ,moon ,boxes4--,these boxes are generally made up as shown at the left in ,figure #bjb4 ,the opening is from twelve to fourteen inches in diameter4 ,four lamps give very good illumination4 ,the frame must be provided with hooks so that it may be suspended at any desired part of the scenery4 ,it is always hung close behind a curtain and must be so arranged that the lamps cannot touch the curtain4 ,the wires should be entirely enclosed in metal of ,no4 #bj sheet metal gauge after the manner of strips4 ,very cheap productions often carry moon boxes made up of an incandescent lamp fastened in a tin dish1 similar to the one shown at the right in ,figure #bjb4 ,moonlight on ,water4--,this and all similar effects can be produced through the 8,sciopticon0 but this requires the use of an arc lamp and is expensive4 ,a cheap way of producing the effect is illustrated in ,figure #bjc1 which represents a metal cylinder1 perforated as shown1 inside of which there are a number of incandescent lamps colored to suit4 ,the cylinder is slowly revolved and the moving shadows and streams of light thrown upon the scene produce the effect4 ,illustration3 ,,figure #bjc4 ,illustration3 ,,figure #bjd4 ,a somewhat similar method of producing this effect1 as also that of a waterfall1 is illustrated in ,figure #bjd4 ,in this case a spiral capable of being moved by clock work is revolved about an electric lamp and gives the effect of falling water4 ,both of these devices work behind curtains4 ,musical ,acts4--,there are numerous musical acts upon the road in which the beat of the music is emphasized by lighting colored lamps in time with the tunes4 ,it is advisable to arrange all such acts to operate by batteries4 ,in many places inspectors will not allow high-voltage contacts to be used open1 and it is often difficult to enclose them in a practical manner4 ,by using dry batteries the apparatus is taken out of the jurisdiction of inspectors and all danger of fire is also eliminated4 ,musical ,bells4--,sets of musical bells properly tuned and connected to a keyboard from which they can be operated electrically are carried in stock by dealers in theatrical supplies4 ,sets are usually made up of eighteen bells and they may be played from a distance4 ,oil ,lamps4--,these have been imitated by arranging a small battery inside of the base of the lamp4 ,this battery would supply current only during the short time that the lamp was being carried about4 ,the base of the lamp is also fitted with electrical contacts which rest upon similar contacts fitted into the table1 and through which the lamp is kept burning by a storage battery while it is resting upon the table4 ,a small dry battery1 such as is placed in the base of an oil lamp1 would not keep the light burning for a long enough time4 ,pin-,plug ,connectors4--,these are provided to connect cables to effects used on the stage4 ,the essential points of a good connector are3 ,it should grip the whole cable1 thus making it unnecessary to strip the outer braid from any exposed part of the cable2 and it should offer no live screws or contacts on the outside4 ,these conditions are fulfilled by the connector shown in ,figure #bje4 ,in some of these connectors1 however1 the part that grips the cable 7indicated by the arrow7 is made of metal1 and this1 if forced down too tight1 may cut into the cable and cause a short circuit4 ,several instances of this kind have been known to occur4 ,pin-plug connectors must always be connected so that the projecting pins are dead when the plug is disconnected4 ,illustration3 ,,figure #bje4 ,illustration3 ,,figure #bjf4 ,a special warning against the use of such connectors as are illustrated at the right of ,figure #bje is necessary4 ,their cheapness brings them into use very often1 especially with acts that do not carry competent electricians4 ,the wires are always working loose2 projecting ends are bare1 and if the connector is twisted1 a short circuit results4 ,where they must be used in an emergency1 they should be heavily taped1 the tape being placed between the conductors and all around the plug1 as shown in the figure4 ,branch-off connectors such are shown in ,figure #bjf are often used to tap off lights from the main cable4 ,where plug connectors are used for arc lamps they must be made up as shown in ,figure #bjg4 ,the asbestos-covered wires necessary to be used with arc lamps cannot be used in cable but must be separately connected4 ,illustration3 ,,figure #bjg4 ,the ,national ,electrical ,code ,rules for ,pin-,plug ,connectors4 ,must be of an approved type1 so installed that the female part of the plug will be on the live end of the cable1 and must be so constructed that tension on the cable will not cause serious mechanical strain on the connections4 ,plugging ,boxes4--,plugging boxes are used to obviate the necessity of running a large number of wires over the stage to the different stage pockets4 ,they are also a necessity because many theaters are not equipped with a sufficient number of stage pockets to accommodate all of the devices large productions carry4 ,the plugging box should be fireproof2 should have self-closing doors so that there may be no liability of open fuses being left among the scenery where they are used4 ,most of the plugging boxes in use at the present time are arranged for link fuses4 ,a link fuse1 however1 requires more time to install than a cartridge fuse and the latter would therefore seem much more desirable4 ,a cut of a much-used plugging box is shown in ,figure #bjh4 ,illustration3 ,,figure #bjh4 ,the ,national ,electrical ,code ,rules for ,portable ,plugging ,boxes4 ,must be constructed so that no current-carrying part will be exposed1 and each receptacle must be protected by approved fuses mounted on slate or marble bases and enclosed in a fireproof cabinet equipped with self-closing doors4 ,each receptacle must be constructed to carry thirty amperes without undue heating1 and the bus-bars must have a carrying capacity equivalent to the current required for the total number of receptacles1 and approved lugs must be provided for the connection of the master cable4 ,rheostats4--,portable stage equipment being intended for use in all parts of the country must be adjustable to all kinds of lighting systems4 ,for this reason it is not practicable to use auto-transformers as is commonly the case where arc lamps are fed from alternating-current circuits4 ,simple rheostats or resistances are therefore always used4 ,with these it is immaterial whether the current be alternating or direct except in so far as the quantity is concerned4 ,alternating current being less efficient in the production of useful light than direct current1 the amperage must be greater and this produces a greater loss in voltage1 the loss being always proportional to the product of current times resistance4 ,the drop in voltage over a certain resistance is therefore always greater1 when an alternating-current arc is used1 than it is with direct2 but as the alternating-current arc operates at a lower voltage than the direct this is not objectionable and simple resistances give satisfactory results whether used with one kind of current or the other4 ,the traveling show must also be prepared for different voltages and a suitably arranged group of resistances is very convenient in this respect4 ,figure #bji shows a box made by the ,chicago ,stage ,lighting ,company containing a number of resistances which may be connected in various ways to obtain different results4 ,in ,figure #baj at ,a is given a diagram representing the wire in a single section4 ,one such section placed in series with an arc lamp will give a certain current4 ,if we connect two of them in parallel1 as in ,b1 we shall obtain not quite double the current1 since this arrangement does not affect the resistance of the arc which also influences the current strength4 ,if the connections are made as in ,c1 we shall have but half the current obtainable by the use of one section1 or the same current in case we are dealing with double the voltage4 ,if ,a is suitable for #aaj volts1 then ,c is suitable for #bbj volts and ,d for #eej4 ,in ,e we have the connection which would give us1 for #bbj volts1 the same current ,b would give with #aaj4 ,it can thus be seen that a group of such resistances can be made to fit an arc lamp to almost any voltage that is likely to be met with4 ,illustration3 ,,figure #bji4 ,nothing but metal and porcelain must be used in the construction of these resistances and they must be on stands which raise them well above the floor4 ,the connections to the resistances should ordinarily be made with asbestos cable4 ,it is necessary to keep close watch of the wire used to make up the resistance especially if it becomes very hot during a run4 ,a resistance in which the wire becomes red hot should not be used4 ,there are productions in which it is necessary to place the arc lamps and their rheostats directly in the way of flying paper used to make 8snow04 ,in such cases the resistances must be tightly enclosed4 ,this destroys the ventilation and they will readily become overheated4 ,for use with such productions resistances may be specially wound and arranged1 or they may be made separate from the arc and placed in a safe location4 ,illustration3 ,,figure #baj4 ,stage ,cables4--,stage cables are subject to very rough usage1 but there are some very good makes on the market1 and by purchasing the best1 one can expect long service4 ,cuts of various kinds of cable likely to be used upon the stage are given in ,figure #baa4 ,a is the ordinary stage cable2 ,b is used for heaters2 ,c is reinforced cord2 and ,d is the parallel cord4 ,the last two must not be used on the floor4 ,the size of the wire to be used depends upon the apparatus which the cable must supply and can be determined from ,table ,,vii which gives the carrying capacities4 ,only approved cables should be used4 ,illustration3 ,,figure #baa4 ,strips4--,strips are used for the illumination of special parts of the scenery4 ,they usually contain from one to twelve lights4 ,a strip is subject to rough usage and should be strongly made4 ,cuts of several kinds of strips are given in ,figure #bab4 ,the chief trouble with strips is found to be in the working loose of screws which hold the sockets in place1 and the connection at the point at which the cable leaves the strip4 ,the ,national ,electrical ,code ,rules for ,strips4 ,must be constructed of steel of a thickness not less than ,no4 #bj ,u4 ,s4 sheet metal gauge1 treated to prevent oxidation1 and suitably stayed and supported and so designed that flanges will protect the lamps4 ,illustration3 ,,figure #bab4 ,cables must be bushed in a suitable manner where passing through the metal1 and must be properly secured to prevent serious mechanical strain on the connections4 ,must be wired in approved conduit or armored cable1 each lamp receptacle being enclosed within an approved outlet box1 or the lamp receptacles may be mounted in an iron or steel box1 metal to be of a thickness not less than ,no4 #bj ,u4 ,s4 sheet metal gauge1 treated to prevent oxidation1 so constructed as to enclose all wires4 ,wires to be soldered to lugs of receptacles4 ,illustration3 ,,fig4 #bac4 ,sunrise4--,sunrise effects may be produced by means of the ,sciopticon1 but a cheaper method is often resorted to4 ,this is illustrated in ,figure #bac and consists of a roll of suitably colored silk which may be unrolled in front of an arc lamp4 ,to produce sunrise it is unrolled in one direction1 the darkest colors coming first and gradually giving way to lighter4 ,for sunset it is worked the other way4 ,in special cases a similar sheet of colored silk wide enough to cover open arcs has been stretched from the floor to the top of the scenery and several arc lamps arranged behind it in such a manner that they could be gradually raised1 thus producing the same effect with more impressiveness1 but with a much greater quantity of light4 ,illustration3 ,,figure #bad4 ,illustration3 ,,figure #bae4 ,switches4--,knife switches on the stage are generally required to be enclosed4 ,it is not sufficient to provide a box with a cover that can be closed1 but the switch should be in a box which need not be opened to operate the switch4 ,see ,figure #bad4 ,often it is necessary to install switches in a length of stage cable so that the switch may be portable4 ,such switches should be installed as shown in ,figure #bae1 in which a flush switch is shown in a regular metal enclosure4 ,illustration3 ,,figure #baf4 ,table ,lamps4--,the table lamp is a small device1 but it causes a great deal of annoyance and trouble4 ,the bottom of the lamp should be enclosed with metal1 especially if there are any splices4 ,the stem where the wire enters should be well reamed out 7see the arrow in ,figure #baf7 and there should be a strong well-fastened bushing where the wire leaves the lamp4 ,the hard-rubber bushings which come with the common table lamps do not remain in place very long and are frequently broken or lost4 ,stage cable is generally required upon the stage1 but it is customary1 in connection with these lamps1 to allow a good grade of reinforced cord or even fine silk-covered cord1 provided it is not long enough to trail on the floor where it might be stepped upon4 ,the glass shades which are often called for in connection with the lamps also cause much trouble2 and to avoid this trouble1 colored gelatine has been used1 backed up with fine wire screen to keep it in place4 ,this of course cannot always be done because many lamps are not suited to it4 ,time ,beaters4--,this is a small keyboard located at the orchestra leader's stand2 it controls the light which may be back of the stage and indicates the time to the chorus behind scenes4 ,water ,falls4--,the devices shown in ,figure #bjd for use as moonlight on the water can also be used to produce the effect of a waterfall or of water rippling downstream4 ,,chapter ,,xx4 ,,useful ,,facts ,,and ,,formulas4 ,one turn of the crank runs off #a foot of film4 ,one foot of film contains #af pictures4 ,the audience sees about #ifj different pictures in every minute that a film is being run4 ,the relative number of revolutions made by two pulleys connected together by belting or friction is in proportion to their diameters4 ,the relative number of revolutions made by two gears connected together is in proportion to their number of teeth4 ,a theater seat occupies from #d to #e square feet4 ,one #be-watt tungsten lamp or its equivalent provided for every #bj seats will give fairly good illumination in a small theater4 #c to #e watts per cubic foot will be required to heat small spaces by electricity4 ,ohm's ,law4 ,direct current equals e4m4f4 divided by resistance4 ,alternating current equals e4m4f4 divided by impedance4 ,electromotive force1 d4c41 equals current time resistance4 ,electromotive force1 a4c41 equals current time impedance4 ,resistance equals e4m4f4 divided by current4 ,impedance equals e4m4f4 divided by current4 ,the joint resistance of two conductors connected in parallel is equal to the product of their resistances divided by their sum3 r 7r r7 7r r7 ,the joint resistance of any number of resistances connected in parallel is the reciprocal of the sum of the reciprocals4 ,the reciprocal of a number is #a divided by that number3 #a r -------------------------- #a #a #a ---- ---- ---- 44444 r r r ,the total resistance of a number of resistances in series is equal to the sum of all of them3 r r r r 44444 ,the heating of a rheostat is proportional to the square of the current it carries4 ,drop in voltage is proportional to the product of the current and resistance for a direct-current circuit1 and the product of current and impedance for an alternating-current circuit4 ,if a reactance is used in place of a rheostat in an alternating-current circuit1 the loss of energy is greatly reduced4 ,if the same intensity of illumination is to be provided for pictures of different sizes1 the amperage must vary about as3 7,w #a4b7 where ,w is the width of picture on screen4 ,for a given power the current in conductors is3 ,w for direct current ,i --- ,e ,w for single-phase a4c4 ,i ------------- ,e p4 f4 ,w for two-phase a4c4 ,i 4#e ------------- ,e p4 f4 ,w for three-phase a4c4 ,i 4#eh ------------- ,e p4 f4 in which ,i is the current in amperes1 ,w is the watts1 ,e is the voltage1 and p4 f4 is the power factor4 ,lens ,formulas4 ,to find the size of a picture obtainable under given conditions and lens3 ,multiply distance from center of lens to screen by one dimension of slide or film and divide by e4f4 focal length of lens1 taking all measurements in inches4 ,example3 ,slide #b-c_/d inches4 ,length of throw #cfj inches4 e4 f4 #aj inches #b-c_/d #cfj #aj #ii inches4 ,to find focal length needed for a given slide or film to produce a given size of picture3 ,multiply slide or film dimension by length of throw and divide by dimension of picture1 taking all measurements in inches4 ,example3 ,same dimensions as above3 #b-c_/d #cfj #ii #aj inches4 ,to find length of throw needed to obtain a certain size of picture3 ,multiply required picture dimension by focal length of lens and divide by slide or film dimension4 ,example3 ,same dimensions as above3 #ii #aj #b-c_/d #cfj inches4 ,to find slide size necessary to produce a certain size of picture under fixed conditions3 ,multiply focal length of lens by size of picture and divide by length of throw4 ,example3 ,same dimensions as above3 #aj #ii #cfj #b-c_/d inches4 ,measurement of ,surfaces4 ,to find the area of a parallelogram3 ,multiply the base by the altitude4 ,to find the area of a triangle when base and altitude are given3 ,multiply the base by the altitude and take half the product4 ,to find the area of any angular surface3 ,divide it into triangles and find the area of the different triangles and add them together4 ,to find the circumference of a circle3 ,multiply the diameter by 2 or #c4adaf4 ,to find the diameter of a circle when the circumference is given3 ,divide the circumference by 1 or #c4adaf4 ,to find the area of a circle when the radius is given3 ,multiply the square of the radius by #c4adaf4 ,when diameter is given3 ,multiply the square of the diameter by 4#ghed4 ,to find the radius of a circle when the area is given3 ,divide the area by #c4adaf and extract the square root of the quotient4 ,measurement of ,solids4 ,to find the lateral area of a right prism3 ,multiply the perimeter of the base by the altitude4 ,to find the lateral area of a right cylinder3 ,multiply the circumference of the base by the altitude4 ,to find the volume of a cylinder or prism3 ,multiply the area of the base by the altitude4 ,to find the lateral area of a right pyramid3 ,multiply the perimeter of the base by the slant height and take half the product4 ,to find the lateral area of a cone3 ,multiply the circumference of the base by the slant height and take half the product4 ,to find the volume of a pyramid or cone3 ,multiply the area of the base by the altitude and take one-third of the product4 ,to find the surface of a sphere3 ,multiply the square of the diameter by #c4adaf4 ,to find the volume of a sphere3 ,multiply the cube of the diameter by one-sixth of #c4adaf or 4#ebcf4 ,in a right-angled triangle1 the sum of the squares of the base and the perpendicular equals the square of the hypotenuse4 ,to find the length of the hypotenuse3 ,extract the square root of the sum of the squares of the base and the perpendicular4 ,to find the base or the perpendicular3 ,from the square of the hypotenuse subtract the square of the other given side and extract the square root of the remainder4 ,,chapter ,,xxi4 ,,glossary ,,of ,,electrical1 ,,mechanical1 ,,and ,,optical ,,words1 ,,terms1 ,,and ,,phrases4 ,aberration4--,the convergence to different foci1 by a lens or mirror1 of rays of light emanating from one and the same point or the deviation of such from a single focus4 a4 c4--,an abbreviation for alternating current4 ,accumulator4--,a term often used to designate a storage battery4 ,achromatic4--,free from false coloration4 ,achromatic ,lens4--,a lens which does not show color in the light which it projects2 usually a combination of lenses of different kinds of glass4 ,actinic ,rays4--,the rays of light that cause chemical changes4 ,airdome4--,a theater arranged in the open air4 ,alloy4--,any compound of two or more metals4 ,alternating ,current4--,an electric current undergoing periodical changes in direction4 ,amalgam4--,a compound of mercury with other metals4 ,ammeter4--,an instrument used for measuring the value of an electric current4 ,amperage4--,the number of amperes2 the current strength in the circuit2 not the quantity but the rate of flow4 ,ampere4--,the unit of current strength4 ,it is equal to a rate of flow of electricity of one coulomb per second4 ,ampere ,hour4--,one ampere flowing for one hour2 or its equivalent4 ,anamorphosis4--,a grossly distorted image1 such as can be obtained from a curved mirror4 ,angular ,velocity4--,the rate at which a body revolves around a fixed axis1 usually measured in radians per second4 ,the radian is equal to #cfj #b degrees4 ,annular ,space4--,the space between an inner and an outer ring or cylinder4 ,annunciator4--,an electric device provided with one or more magnets and indicators1 which serve to indicate the points at which one or more electric contacts have been closed4 ,anode4--,the positive pole2 a term used mostly with electrolytic devices1 also with the mercury arc rectifier and the electric arc4 ,aplanatic4--,free from spherical aberration4 ,apparent ,power4--,the product of volts and amperes in an alternating-current circuit4 ,the true power in an alternating-current circuit is always less than the apparent power if pressure and current are not in phase4 ,arbor4--,an axle or spindle on which a wheel turns4 ,arc1 ,electric4--,the heated portion of an electric circuit between two electrodes where the current passes from one to the other2 the source of light of the electric arc lamp4 ,armature4--,that part of a generator1 in which the electrical pressure is generated1 which causes a current if the armature winding forms part of a closed circuit4 ,automatic4--,a term applied to machinery in which certain movements1 usually made by hand1 are made by the machine4 ,auto-,transformer4--,a transformer provided with only one winding2 a part of the winding being traversed by both the primary and secondary currents4 ,axis4--,the straight line1 real or imaginary1 which passes through a body1 and on which the body revolves1 or may be supposed to revolve4 ,axis of ,lens4--,the straight line passing through its center and perpendicular to its surface4 ,axle4--,a transverse bar connecting opposite wheels4 ,babbitt ,metal4--,a soft white antifriction metal of varying composition2 as #d parts of copper1 #h of antimony1 and #bd or #if of tin4 ,the larger the amount of tin1 the harder the resultant alloy4 ,baby ,spot ,lamp4--,an incandescent lamp placed within a hood similar to that of a theater arc lamp2 also usually provided with a lens4 ,back ,focus4--,this term is used to designate the distance from the lens nearest the slide to the position of the slide when the picture is in focus on the screen4 ,see also ,equivalent ,focus4 ,balance ,wheel4--,a wheel added to machinery for the purpose of preventing too sudden variations in speed2 also called fly wheel4 ,ball ,bearing4--,a journal fitted with balls upon which the shaft turns4 ,balsam1 ,canadian4--,a cement used to cement lenses1 etc4 ,band4--,a small belt passing over two pulleys4 ,battery4--,a term used to describe a number of voltaic cells connected so as to act as a single cell2 should never be used in reference to a single cell4 ,bayonet4--,a pin which plays in and out of holes made to receive it and serves to engage parts of machinery4 ,bearing4--,that part of a machine in contact with which a shaft moves2 the journal boxes4 ,bed4--,the foundation or main fixed part of a machine4 ,bell ,crank4--,a rectangular lever by which the direction of rotation is changed through an angle of ninety degrees4 ,belt4--,a strap or band of flexible material passing around two or more wheels and communicating motion to them4 ,bevel ,gear4--,a gear in which the two wheels working together lie in planes that are not parallel4 ,bifocal4--,having two foci4 ,binocular4--,pertaining to both eyes1 as binocular vision in microscope or telescope4 ,blinding ,lights4--,lights used on the stage in certain acts to blind the audience2 thus allowing persons to work behind them unseen by the audience4 ,boss4--,the enlarged part of a shaft on which a wheel is keyed4 ,brace4--,a curved tool of iron or wood adapted to turn and hold bits4 ,brake4--,a piece of mechanism adapted to stop or hold parts of machinery4 ,brushes4--,that part of a dynamo by which the current is taken to or from the commutator4 ,buffer4--,a cushion1 with springs or other material1 arranged to deaden the blow of a moving body4 ,buffing ,wheel4--,a rapidly revolving wheel adapted to buff or polish materials4 ,burner2 ,automatic1 ,electric4--,an electric device1 for turning on and lighting gas1 which may be operated from a distance by pressing a button4 ,bushing4--,the lining of a hole with a ring or a perforated substance of metal or other material4 ,calipers4--,a compass with curved legs2 used for measuring round bars or openings1 the thickness of objects1 and the distance between two points4 ,cam4--,a projecting part of a wheel or other moving piece1 so shaped as to give an alternating or variable motion to another piece pressing against it4 ,cam ,wheel4--,a wheel1 or part of a wheel1 of irregular outline employed to produce a variable or alternating motion in machinery4 ,canadian ,balsam4--,a cement used to cement lenses1 etc4 ,candle ,power4--,this term1 as commonly used1 denotes the light-giving power of a lamp in terms of a standard candle4 ,its meaning is not very definite unless qualified by some of the following terms3 apparent candle power2 equivalent candle power2 mean horizontal candle power2 mean lower hemispherical candle power2 mean spherical candle power2 maximum candle power2 mean zonular candle power4 ,all of these terms are fully explained in 8,modern ,electric ,illumination1 ,theory and ,practice40 ,carbons4--,the rods of artificial carbon used as electrodes in arc lamps4 ,carbons1 ,cored4--,carbons1 as above1 but provided with a core of softer material4 ,case ,hardening4--,the act or process of converting the surface of iron into steel while leaving the center soft and malleable4 ,cathode4--,the negative pole4 ,a term usually used in connection with electrolytic apparatus1 mercury arc rectifiers1 and electric arcs4 ,cell1 ,voltaic4--,a cup or jar containing electrodes and an electrolyte either for producing an electromotive force or electrolysis4 ,in the latter case it is called an electrolytic cell4 ,a number of cells connected together make a battery4 ,centi4--,as a prefix it means the hundredth part2 as centimeter4 ,choke ,coil4--,a coil of wire wound upon an iron core in such a manner as to acquire a very high self-inductance2 similar to a reactance4 ,chuck4--,a contrivance fixed to the mandril of a turning lathe for holding the material to be worked upon4 ,clutch4--,a projecting tooth1 or other piece of machinery1 for connecting shafts with each other or with wheels in such a manner as to be readily disengaged4 ,cog ,wheel4--,a wheel with cogs or teeth4 ,collar4--,a ring-like part of a machine usually fastened to some part of it and used for keeping something in place4 ,commutator4--,that part of a dynamo-electric machine to which all of the armature wires are connected and in which the alternating-electromotive force1 actually generated in the armature winding1 is made to appear as a direct-electromotive force in the external circuit4 ,compasses4--,an instrument for describing circles1 measuring1 etc41 consisting of two pointed branches fastened together at the top by a rivet or screw4 ,compensarc4--,a trade term used to describe a transformer or an auto-transformer2 used in connection with projection-arc lamps4 ,compound ,winding4--,a generator1 in which the fields are provided with a shunt winding and in addition with a series winding which carries all of the current around the fields2 is said to be compound wound1 and the winding is referred to as a compound winding4 ,concave4--,curved and hollow2 the inside of a hollow sphere or cylinder4 ,concentric4--,having a common center4 ,condenser4--,a lens or a set of lenses1 used to gather the divergent rays from a source of illumination and bring them to a focus4 ,conductor4--,any substance used to carry electricity4 ,most of the commercial conductors are of copper4 ,cone4--,a solid body having a plane for its base and a point for its top1 the surface being formed by line segments joining every point of the outline of the base to the point top4 ,conical4--,approximating a cone in shape4 ,conjugate ,foci4--,the two points in the principal axis of a lens and at opposite sides of it2 one point being the light source and the other the point at which rays of light from this source are brought to a focus4 ,controller4--,a resistance used for controlling the speed of a motor or the field strength of a dynamo4 ,converter4--,any apparatus used for changing from one form of current to another2 generally used to indicate a synchronous or rotary converter4 ,convex4--,rising or swelling2 the outside of a sphere or cylinder4 ,convexo-,plano4--,convex on one side and plane on the other2 plano-convex is more often used4 ,cooling ,plate4--,the metal around the projection aperture of a motion-picture machine which protects the film from the rays of light4 ,cotter4--,a wedge-shaped piece of wood1 iron1 or other material used for fastening the parts of a structure2 a key4 ,cotter ,pin4--,a pin made up of doubled wire expanded at top and bottom so as to hold its place when inserted in a hole4 ,coulomb4--,the unit of quantity of electricity4 ,it is equal to the current multiplied by the time that it flows2 viz41 ampere times second4 ,countershaft4--,a secondary shaft driven from another shaft2 not the main or driving shaft4 ,countersink4--,a drill or cutting tool used to enlarge the outer edges of a hole in countersinking4 ,crown ,wheel4--,a wheel1 with cogs or teeth set at right angles to its plane4 ,cycle4--,a complete recurrence of any periodic change4 ,the two immediately succeeding half waves of an alternating current or e4m4f4 constitute a cycle4 ,damping ,coils1 ,dampers4--,coils of wire or bars of copper placed on1 or imbedded in1 the pole pieces of a dynamo-electric machine2 used mostly in connection with synchronous motors or rotary converters to prevent hunting4 ,dead ,center4--,either of the two opposite points1 in the orbit of a crank1 at which the crank and a driving rod lie in a straight line4 ,diffusing ,globes4--,globes of ground glass or other medium which causes diffusion of light4 ,used to reduce the intrinsic brilliancy of illuminants4 ,the light is emitted from a larger surface and is less trying to the eyes4 ,diffusion4--,the scattering of light by diffuse reflection1 as from an irregular surface such as ground glass4 ,diffusion ,projection4--,a method of projection sometimes resorted to when condensers are broken4 ,ground glass is used in place of the condensers4 ,direct ,current4--,a current of electricity maintained in one direction as distinguished from an alternating current which is regularly alternating in direction4 ,dog4--,a part of machinery acting as a catch or a clutch4 ,dovetail4--,to unite by a tenon1 in the form of a pigeon's tail spread out1 let into a board or timber4 ,dowel ,pin4--,a pin of wood or metal used for joining two pieces2 part of its length entering one piece1 and the rest entering a corresponding hole in the other4 ,dowser4--,a hand shutter arranged in front of the lens of an arc lamp by which the light may be shut off4 ,drift4--,a conical tool of steel for enlarging or shaping a hole in metal by being driven into or through it4 ,drill4--,a pointed instrument used for boring holes2 especially in hard substances4 ,drop in ,potential4--,a term often used to designate a loss of electrical pressure4 ,in d4c4 circuits it is equal to current times resistance4 ,in a4c4 circuits it is equal to current times impedance4 ,drum4--,a short cylinder revolving on an axis4 ,dynamo4--,a dynamo electric machine for converting electrical energy into mechanical1 or vice versa4 ,when the transformation is from electrical to mechanical energy the machine is operating as a motor2 and when the transformation is from mechanical to electrical energy the machine is operating as a generator4 e4 f4--,abbreviation for equivalent focus4 e4 m4 f4--,abbreviation for electromotive force4 ,the unit of electromotive force4 ,the unit of electromotive force is the volt4 ,eccentric4--,a wheel or disc having its axis of revolution out of its center2 used to convert circular motion into reciprocating4 ,economizer4--,a trade name applied to a transformer or auto-transformer1 used in connection with projection-arc lamps4 ,economy ,coils4--,an auto-transformer4 ,this term is used very much in connection with auto-transformers1 and also transformers used in connection with arc lamps4 ,efficiency of ,incandescent ,lamps4--,the efficiency of incandescent lamps is expressed in watts per candle power4 ,the lower the numerical expression for efficiency1 the greater is the light obtained per unit of energy4 ,electrodes4--,the terminals of an electric source2 in an arc lamp1 the two carbons4 ,electrolysis4--,chemical decomposition by an electric current4 ,the positive pole1 or anode1 is eaten away with direct current2 the effect with alternating current is very slight4 ,emergency ,lights4--,those lights arranged in theaters1 the object of which is to furnish the necessary illumination by which the audience may leave the theater in case of a failure of the regular illumination4 ,emergency and exit lights are generally grouped together but must not be confused with each other4 ,equivalent ,focus4--,the distance from the center of a set of lenses to the slide1 when the picture on the slide is in focus on the screen4 ,exit ,lights4--,the lights placed directly above exits2 usually colored red4 ,expansion ,bolt4--,a bolt adapted to be inserted into a socket which1 expanded by the insertion1 thus holds the bolt in place4 ,face ,plate4--,the disc attached to the revolving spindle of a lathe to which the work is often fastened4 ,feeders4--,the main wires extending from the supply to the distributing center4 ,field4--,a term commonly used to designate the space traversed by the lines of the force of magnetism which is supposed to exist4 ,the fields of a dynamo consist of the pole pieces around which the exciting current circulates4 ,fire ,trap4--,the arrangement of rollers and their enclosure1 usually placed on magazine or film tanks1 through which the film is led1 to prevent a flame from following the film in case of fire4 ,flange4--,a projecting edge or rim on a wheel or shaft by which it may be kept in place or fastened4 ,flasher4--,the term by which a contrivance for regularly1 and at frequent intervals1 turning lights on and off is described2 used mostly in connection with electric signs4 ,flicker4--,the unsteady illumination of a motion picture2 caused mostly by insufficient speed of film or too brilliant illumination4 ,fly ,floor4--,a floor above the stage upon which the scene shifters1 whose duty it is to raise and lower the curtains1 work4 ,footlights4--,a row of lights placed at the stage level and directly in front of the actors4 ,forging4--,a piece of metal shaped by hammering2 not a casting4 ,framing ,device4--,a device attached to every motion-picture machine by which the relative position of the film to the optical system may be adjusted to make the picture appear in its proper place on the screen4 ,frequency4--,the number of cycles per second2 also spoken of as the periodicity4 ,the most common frequencies are #be and #fj cycles per second4 ,gearing4--,the parts by which motion given to one part of a machine is transmitted to other parts4 ,in a narrower sense it refers only to cog wheels4 ,a spur gear is one in which the teeth are arranged either on the outside or inside of the rim in the direction of radii from the center of the wheel4 ,a bevel gear is one in which the shafts of the two gears are not parallel4 ,a friction gear is one in which friction takes the place of the teeth4 ,a worm gear is one in which one of the members is in the form of a screw4 ,the pitch of the screw may1 or may not1 be such as to prevent it from being turned by the other4 ,a herring-bone gear is one in which the teeth are cut across the face of the wheel at an angle4 ,the teeth may be made to converge toward the center of the face or may be cut in a line across it4 ,this gear is used where noiseless operation is required4 ,generator4--,a term frequently used to describe a dynamo-electric machine used in converting mechanical energy into electrical energy4 ,geneva4--,a form of intermittent movement first used in ,geneva1 ,switzerland2 hence the name4 ,it is the form of intermittent mechanism most used4 ,governor4--,a contrivance used in connection with machinery to regulate the speed4 ,grid1 or ,grid ,floor4--,this term refers to the topmost floor above the stage of a theater where the pulleys and the cables1 by which scenery is raised and lowered1 are placed4 ,it is usually made up of iron bars with spaces between them2 hence the name4 ,ground4---,this term is used to describe any connection of an electrical conductor to any conducting medium1 other than that to which it belongs1 which may be common to other conductors or which may convey current to the opposite pole in a manner not desired4 ,gudgeon4--,the piece of iron in the end of a wooden shaft on which it turns in a collar or on a gudgeon block4 ,heat ,shield4--,a part of a motion-picture machine which shields the film and adjacent parts from the heat of the light4 ,helix4--,see ,solenoid4 ,horsepower4--,a unit or standard by which the capability of machinery is measured4 ,power sufficient to raise one pound #cc1jjj feet in one minute is called one horsepower4 ,electrically it is equal to #gdf watts4 ,hunting4--,this term describes the regular and persistent changes in the speed of synchronous apparatus running in parallel1 which are due to fluctuations in the load on the generators or in the speed of the prime mover2 and causes cross currents4 ,in theaters they would be noticeable only in connection with rotary converters which are sometimes used to convert a4c4 into d4c4 for arc lamps4 ,idler4--,a wheel placed between two other wheels to convey motion from one to the other without changing the direction of motion4 ,impedance4--,impedance is to an alternating-current circuit what resistance is to a direct-current circuit4 ,the e4m4f4 divided by the impedance equals the current4 ,the symbol for impedance is ,z4 ,impressed e4m4f4--,the electromotive force brought to bear on any circuit to produce a current therein2 the applied e4m4f4 ,index of ,refraction4--,the index of refraction1 or the refraction index1 is the ratio the sine of the angle of incidence bears to the sine of the angle of refraction4 ,for glass the index of refraction is about #a4e4 ,indirect ,lighting4--,a system of illumination in which all of the light is first thrown to the ceiling and reflected therefrom4 ,inductance4--,that property of an electric circuit which causes a current in it to create lines of force and thus generate a counter e4m4f4 when the current changes in value4 ,induction ,motor4--,a much used alternating-current motor in which there is no electrical connection between the primary and secondary or rotor and stator windings4 ,it may be either single or polyphase4 ,intermittent ,movements4--,there are numerous types of intermittent movements but the ,geneva and the pin cross are the only ones used with the latest types of motion-picture projection machines4 ,the other movements have mostly come into use in connection with cameras4 ,the beater movement is one in which a certain length of film is pushed to one side at each movement4 ,the claw movement is one in which claws reach up and pull down a fixed amount of film at each movement4 ,other intermittent movements are known as1 the drunken screw2 ratchet2 pitman and grip4 ,they have mostly only a historical interest4 ,intrinsic ,brilliancy4--,this term refers to the candle power per unit area of a source of light4 ,a light having a large candle power in proportion to its size is said to have a high intrinsic brilliancy4 ,lamps of high intrinsic brilliancy should never be placed in the line of vision4 ,inverted ,lighting4--,synonymous with indirect lighting4 ,key4--,a wedge-shaped piece of wood or metal used1 to hold something in place2 a cotter4 ,key ,seat4--,a groove cut into a shaft to fit a similar groove in a wheel or flange1 and into which a key may be fitted4 ,key to ,curtain4--,a fictitious article1 in quest of which novices employed in theaters are often sent2 a hoax4 ,kilowatt4--#ajjj watts4 ,lagging ,current4--,a current1 the maximum value of which occurs later than that of the e4m4f4 producing it4 ,laminated4--,made up of sheets4 ,all iron parts subject to the influence of alternating fields must be laminated to reduce the losses due to ,foucault or eddy currents4 ,leading ,current4--,a current1 the maximum value of which occurs earlier than that of the e4m4f4 producing it4 ,in connection with synchronous converters the current may be made either lagging or leading by adjusting the field excitation4 ,lens4--,a piece of glass1 or other transparent substance1 ground with two opposite regular surfaces4 ,in practice the curved surfaces are generally spherical but sometimes they are made cylindrical4 ,of spherical lenses there are six varieties3 plano-concave2 double-concave2 plano-convex2 double-convex2 meniscus2 and concave-convex4 ,a double-convex lens1 with one radius six times that of the other1 is called a crossed lens4 ,a multiplying lens or glass is one consisting of a number of plane faces on one side and a convex surface on the other4 ,the plane faces are inclined to one another and each presents a different picture2 thus giving the appearance of the multiplication of images4 ,a polyzonal lens is one that is made up of a large number of pieces arranged in zones or rings4 ,this kind of lens is used only for sizes in which it is difficult to use pieces large enough to have the lens in one piece4 ,lime ,light4--,a light produced by means of a cylinder of lime which is subjected to a flame of gas or of oxygen and hydrogen4 ,lines of ,force4--,every magnetic field is supposed to be made up of imaginary lines called lines of force4 ,the number of these lines per unit area perpendicular to the field is a measure of the strength of the field4 ,lost ,motion4--,refers to the loss or irregularity of motion caused by wear of machinery or poor adjustment4 ,magic ,pane4--,this is a condenser formed of a sheet of glass1 one side of which is covered by pieces of tin foil with spaces left between4 ,the spaces between may be arranged to represent any design and on the discharge of the condenser the design is illuminated by the sparks which jump over the spaces4 ,male ,thread or ,coupling4--,in connection with piping1 hose1 etc41 a coupling arranged to enter into another1 is spoken of as 8male02 that part which is entered into is known as 8female40 ,mandrel4--,a bar of metal inserted in the work to hold it1 as in a lathe1 during the process of manufacture4 ,also the spindle which carries the center chuck of a lathe1 an arbor4 ,matched ,lenses4--,the lenses in two stereopticon lamps to be used together must be matched to give the same size of picture4 ,micrometer4--,an instrument used for measuring very small diameters or thicknesses1 the adjustments being made by a screw arranged to indicate very slight changes in the opening in which the object is inserted4 ,mil4--,the one-thousandth part of an inch4 ,the circular-mil area of a circular area1 such as the cross section of a wire1 can be found by squaring the diameter4 ,mirage4--,an optical illusion due to an unequal refraction in the lower atmosphere which causes remote objects to be seen double and suspended in the air4 ,a mirage can be arranged for by a prism or by a piece of beveled glass4 ,miter ,wheels4--,a pair of bevel wheels of equal diameter working together1 usually with their axes at right angles4 ,motion ,head4--,by this term the whole of the motion-picture machine is usually designated4 ,motor4--,see dynamo4 ,motor ,generator4--,a generator driven by a motor4 ,multiple ,series4--,a system of wiring in which several lamps are connected in series and a number of such series combinations connected in multiple4 ,neutral ,wire4--,the wire of a three-wire system which ordinarily carries no current4 ,in a three-wire system it is usually run in the center4 ,ohm4--,the ohm is the unit of electrical resistance4 ,ohmic ,drop4--,this is the loss of potential due to the resistance1 as distinguished from that due to the reactance4 ,it is always equal to the current multiplied by the resistance1 the current being measured in amperes and the resistance in ohms4 ,ohm's ,law4--,this is a statement defining the relations existing between electrical pressure1 current1 and resistance4 ,the current is equal to the electrical pressure divided by the resistance4 ,the resistance is equal to the electrical pressure divided by the current4 p4 d4--,an abbreviation for difference of potential4 ,pawl4--,a short movable piece or bar connected at one end1 by a joint1 with some part of a machine2 while the other end falls into notches or teeth on another part1 in such a manner as to permit motion in one direction only4 ,period4--,the time required for one complete cycle4 ,photometer4--,an instrument used for comparing or measuring the candle power of illuminants4 ,pinion4--,a small wheel with leaves or teeth working into the teeth of a larger wheel or rack2 especially such a wheel having its leaves formed of the substance of the arbor or spindle on which it turns2 a toothed arbor4 ,pitch4--,the distance from center to center of any two adjacent teeth of gearing measured on the pitch line4 ,the distance measured on a line parallel to the axis between two adjacent threads or convolutions of a screw4 ,pitch ,line4--,a circle concentric with the circumference of a toothed wheel and cutting its teeth at such a distance from their points as to touch the corresponding circle of the gear working with it4 ,the two circles must have a common velocity4 ,plunger4--,a part of machinery which is subject to a plunging motion4 ,polarity4--,a difference of polarity exists between any two wires1 or points in one wire1 where there is any tendency to produce a current4 ,in practice1 however1 the term is used to designate wires pertaining to the two opposite poles of a system4 ,polyphase4--,referring to more than one phase1 multiphase4 ,power4--,this term designates the rate of doing work4 ,power ,factor4--,this term expresses the ratio of the true power in an alternating-current circuit to the apparent power4 ,it is always less than #a4 ,the apparent power 7product of volts and amperes measured by independent instruments7 must be multiplied by the power factor to obtain the true power in alternating-current circuits4 ,primary ,battery4--,a battery in which the p4d4 is produced by primary action of the ingredients used1 instead of by secondary action as in secondary batteries or accumulators4 ,primary ,coil4--,that coil of a transformer1 induction motor1 or induction coil which is connected to the source of electrical energy4 ,prism4--,a transparent body usually having three rectangular faces and triangular ends4 ,it is used in experiments on optics to show refraction and may also be made to produce total reflection4 ,prismatic ,colors4--,the seven colors into which sunlight is resolved when passed through a prism4 ,an achromatic prism is one made up of two kinds of glass of different dispersive powers by which a ray of light may be refracted without showing color4 ,pulley4--,a broad-rimmed wheel used for transmitting power by means of a belt4 ,a narrow-rimmed wheel with a groove used for the same purpose is termed a sheave4 ,a cone pulley is a pulley made in the shape of a cone and used in conjunction with a similar pulley and a belt connecting them for the purpose of varying the velocity4 ,a fast pulley is one which is rigidly attached to the shaft4 ,a loose pulley is one which is used in conjunction with another pulley of the same size to carry the belt while the shaft attached to the other is still4 ,pulsating ,current4--,a current of electricity varying regularly in strength but not in direction4 ,rack and ,pinion4--,a straight bar with teeth on its edge to work with the teeth of a pinion which is to drive or follow it4 ,ratchet4--,a bar or piece of mechanism turning upon a pivot while the other end falls into the teeth of a wheel or rack allowing the latter to move in one direction only4 ,it may be used for preventing backward motion in machinery or for converting reciprocating motion into forward motion4 ,ratchet ,drill4--,a drill attached to a ratchet4 ,ratchet ,wheel4--,a wheel having teeth by which it may be moved forward as by a lever and catch1 or by a pawl arranged to engage the teeth4 ,the pawl may also be arranged to engage the teeth for the purpose of preventing backward motion4 ,reactance ,coil4--,see ,choke ,coil4 ,reactive ,drop4--,the drop in potential caused through the presence of reactance in the circuit1 as distinguished from that caused by ohmic resistance which is known as the ohmic drop4 ,rectifier4--,any apparatus used to change an alternating current to a direct current by periodically interrupting or changing the direction of the alternating current so that the derived current is always in the same direction4 ,relay4--,a device actuated by an electric current to open or close another circuit4 ,rheostat4--,an adjustable resistance4 ,rock ,shaft4--,a shaft that vibrates or oscillates instead of making complete revolutions4 ,called also rocker or rocking shaft4 ,rotary ,converter4--,a rotating machine having a field excited by a direct current and an armature winding connected to a commutator and a set of collector rings4 ,it is used to convert alternating current into direct1 or vice versa2 also called synchronous converter4 ,rotor4--,the moving part of an alternating-current generator or motor4 ,secondary ,battery4--,a storage battery2 an accumulator4 ,secondary ,coil4--,the coil of a transformer or an induction coil into which currents are induced2 the coil which is not connected to the source of energy4 ,series ,connection4--,a connection in which a number of devices are joined so that the same current passes through all of them4 ,series ,multiple4--,a system of wiring in which a number of devices are connected in multiple and several of such groups then connected in series4 ,the same current must pass through each group4 ,shaking ,coil4--,a coil used in connection with a mercury-arc rectifier for tilting or shaking the tube and starting the apparatus4 ,shunt4--,a by-pass4 ,a wire which carries part or all of the current in a circuit around some other device connected in the circuit4 ,single-,phase4--,an alternating-current system using only two wires and only one e4m4f4 ,it is sometimes termed uniphase or monophase4 ,slip of ,induction ,motor4--,the difference in the number of revolutions made by the revolving field and the rotor of the motor4 ,it is usually expressed in per cent of the synchronous speed which is that of the revolving field4 ,solenoid4--,a round coil of wire generally used to control an iron core2 an electromagnetic helix4 ,spider4--,a casting or part of a machine having projections or arms radiating from it so as somewhat to resemble a spider4 ,spindle4--,the revolving arbor of a machine tool2 an axis4 ,spiral ,gear or ,gearing4--,a gearing consisting of wheels working together with their axes at an angle to each other double that of the angle of the teeth with the axes4 ,it is sometimes used in light machinery in place of bevel gearing4 ,spiral ,wheel4--,a wheel having its teeth cut at an angle with its axis or so that they form small parts of screws or spirals4 ,spline4--,a rectangular piece fitting the key seats of a hub and shaft so that1 while the one may slide endwise on the other1 both must revolve together4 ,spur ,wheel4--,a wheel in which the teeth are perpendicular to the axis and in the direction of the radii4 ,static ,electricity4--,the name usually given to electricity generated by friction1 as from belting in machine shops1 etc4 ,stator4--,the stationary part of an alternating-current motor or generator4 ,stay ,bolt4--,a bolt connecting opposite plates to keep them from bulging4 ,stepdown ,transformer4--,a transformer used for reducing voltage4 ,stepup ,transformer4--,a transformer used for increasing voltage4 ,striking the ,arc4--,the act of bringing the carbons of an arc lamp together and immediately separating them and establishing the arc is called striking the arc4 ,stud4--,a projection of a bolt adapted to hold a lug or connection of some kind4 ,stud ,bolt4--,a bolt with threads on both ends1 to be screwed into a fixed part at one end and receive a nut upon the other4 ,sustaining ,coil4--,the name sometimes given to a reactance used in connection with a mercury-arc rectifier to cause an overlapping of the two currents from the anodes4 ,swivel or ,swivel ,joint4--,a joint1 the two pieces of which can be turned around independently of each other4 ,synchronism4--,being in time or occurring at the same time in regular order with some other event4 ,synchronous ,converter4--,see rotary converter4 ,tap ,bolt4--,a bolt with a head on one end and a thread on the other to be screwed into some part instead of passing through and being fastened with a nut4 ,three-,phase4--,refers to a system of electrical distribution making use of three separate currents4 ,these currents may be superimposed and generally only three wires are used in the transmission4 ,thumb ,screw4--,a screw arranged so that it can be set up with the fingers4 ,similar to a wing nut4 ,thumb ,spot4--,a distinguishing mark usually placed on stereopticon slides so as to mark the spot at which the thumb of the right hand should be placed when inserting the slide to insure its proper placing in the holder4 ,travel ,ghost4--,the peculiar hazy appearance often seen in a motion picture2 it is produced by the improper setting of the revolving shutter4 ,trunnion4--,projection lugs on the sides of some piece of machinery upon which it is supported and upon which it can move4 ,two-,phase4--,this term refers to an a4c4 system of electrical distribution making use of two currents of different phase4 ,it may be arranged with three or four wires4 ,unbalanced4--,this term is used in connection with three-wire and three-phase systems4 ,the three-wire system is said to be unbalanced when one of the outside wires is carrying more current than the other4 ,the three-phase system is said to be unbalanced when the load is unevenly distributed over the three-phase wires4 ,universal ,joint4--,a contrivance used for joining two shafts or parts of machinery endwise so that one may give rotary motion to the other while at an angle4 ,volt4--,the unit of electromotive force4 ,voltmeter4--,an instrument used for measuring potential difference4 ,water ,rheostat4--,a resistance in which water is used to carry the current4 ,plates of metal proportional to the current to be used are inserted in the water and by inserting them to a greater extent or moving them closer together the current can be increased4 ,watt4--,the unit of power4 ,wattless ,current4--,that part of an alternating current which is either ahead of or behind the e4 m4 f4 of the circuit4 ,watt ,meter4--,an instrument used for measuring electrical energy4 ,yoke4--,a clamp resembling an ox yoke somewhat and adapted to join two pieces of a machine4 ,,index ,,page ,aberration1 chromatic1 #ea ,aberration1 spherical1 #ea ,adjusting intermittent sprocket1 #ajj ,aisle lights1 #bah ,aligning machine1 #if ,alternating current1 #bah ,alternating current motor1 #bae ,amperage for projection1 #dc1 #dd ,amperage1 determination of1 #de1 #df ,anchoring machine1 #ig ,anvil sparks1 #caa ,arc1 color of1 #ai1 #bj1 #ca ,enclosed1 #bc ,form of carbons1 #bb ,length of1 #ba ,low tension1 #bj ,open1 #bc ,resistance of1 #bj ,upside down1 #bb ,arc lamps1 #ai1 #bah1 #cab ,automatic1 #be ,edison1 #cf ,hand feed1 #be ,kliegl1 #ce1 #cf ,mc,intosh1 #cd ,motiograph1 #cg ,operation of1 #be1 #bg ,powers1 #cg ,testing of1 #bh ,arc light1 injurious1 #ba ,armored cable1 #bbb ,asbestos1 #bbf ,attachment plugs1 #bbf ,auto-starters1 #bbg ,automatic fire shutter1 #fb1 #gj1 #ga1 #aja ,axis of lens1 #cfj ,baby spot lamp1 #caf ,balconies1 #bbh ,batteries1 #caf ,bells1 #bbh1 #cah ,blinding lights1 #cai ,borders1 #bbi ,brackets1 #bcb1 #cai ,branch circuits1 #bcb ,branch-off connectors1 #cdc ,bunch lights1 #cbj ,bus-bars1 #bcd ,cabinets1 #bce ,cables1 #bce ,call-board1 #bic ,canopies1 #bcf ,camera lucida1 #aeb ,carbons1 adjusting of1 #ca ,best to use1 #bi ,cored1 #ec ,setting of1 #ca1 #cb1 #cd ,testing of1 #bh ,care of sprockets1 #ii ,carriage call1 #bic ,carrying capacity1 #bcg ,ceiling fans1 #bcg ,chandeliers1 #bcg1 #cba1 #cbb ,chromatic aberration1 #ea ,cleaning machine1 #ih ,circuit breakers1 #bci ,colors for arc lamps1 #cbc ,colored pictures1 #ei ,comparison of stereopticon and motion picture machine pictures1 #di ,concavo-convex lens1 #adf ,concave meniscus lens1 #adf ,concealed work1 #bdj ,condensers1 #ch1 #aec ,breakage1 #dj ,diameter of1 #ea ,focal length of1 #ej ,conduit work1 #bdj ,conjugate foci of lens1 #adc ,conjugate foci of mirror1 #acc ,contacts1 #bde ,convexo-concave lens1 #adf ,convex meniscus lens1 #adf ,cord1 #bde ,corrected lenses1 #adh ,cover for machine1 #ajd ,critical angle of refraction1 #adj ,current control for arc lamps1 #aij ,auto-transformer1 #aie ,mercury-arc rectifier1 #bjg ,motor generators1 #aih ,reactances1 #aic ,resistances1 #aij ,rotary converters1 #bjb ,transformation1 #aid ,current required for projection1 #dc1 #dd ,current taps1 #bde ,cut-outs1 #bdf ,damp places1 #bdi ,decorative lighting systems1 #bdi ,dimmers1 #bej ,dimmer box1 #cbd ,door switches1 #bea ,double concave lens1 #adf ,double convex lens1 #adf ,dressing rooms1 #afh1 #bea ,drop lights1 #beb ,edengraph motion head1 #hc1 #hf ,edison motion head1 #fd1 #hd ,efficiency of incandescent lamps1 #bgj ,electric sign imitations1 #cbe ,electric stage effects1 #cbf ,emergency lighting system1 #bec ,equivalent focal length1 #ej ,exit lights1 #bef ,explosions1 #cbg ,eye1 the1 #abd ,mixing of impressions1 #abe ,regaining of vision by aged1 #abe ,face-o-graph1 #afa1 #cbh ,fan motors1 #bef ,festoons1 #cbh ,film1 #hi ,box for1 #ajh ,burning of1 #ij1 #agc1 #agg ,emulsion on1 #hi ,fire1 #aaj ,gate1 #fb1 #fi1 #gj1 #ajb ,inspection of1 #aje ,leaders and tails1 #ajf1 #ajg ,mender1 #id ,patching1 #ia1 #ic ,pictures1 per foot1 #eg ,pinning of1 #aaj ,receptacle for1 #ajf ,rewinding1 #ajh ,shields1 #fb1 #hc ,steadier drum1 #fb1 #fi ,fire alarm1 #bef ,fire dance1 #ccj ,fire hazard1 #aa ,fire flies1 #ccj ,fire places1 #cca ,fire proof film1 #ij ,fire traps1 #fb1 #fg1 #ig ,testing of1 #fh ,fish work1 #bef ,fixtures1 #beg ,flashers1 #bei ,flexible cord1 #bfa ,flexible tubing1 #bfa ,flood lamps1 #bd ,floor pockets1 #bfa ,flowers1 #ccb ,fly door1 #bfa ,focal length of concave mirror1 #acc ,focusing1 #db ,foot-lights1 #bfa1 #bfb ,formulas1 #cec ,fountains1 #ccb ,framing1 #ajb ,framing device1 #fb1 #hb ,friction rollers1 #fb1 #fi ,fuses1 #ccc ,fuse spacings1 #bhh ,gallery lighting1 #bfc ,gallery pockets1 #bfc1 #cjj ,gas globes1 #ccd ,gas lighting1 #bfd ,generators1 management of1 #bac 8,geneva0 movement1 #gf1 #gg ,getting ready for the show1 #ajd 8,ghost01 #db ,glass shades1 #ccd ,glossary of mechanical1 electrical and optical words1 terms and phrases1 #ceh ,grid floor1 #bfe ,ground1 #aa ,grounding1 #bfe ,guards1 #bff ,hanger boards1 #bff ,heat1 #aae ,heaters1 #bfg1 #cce ,high potential1 #bfh ,hints on management of projecting arcs1 #eb ,hissing voltage of arc1 #bi ,illumination1 #bfi ,illusions1 optical1 #aee ,dissolving living pictures1 #aeg ,face in clouds1 #afa ,figure floating in air1 #aeg ,head resting on table1 #afj ,head suspended in air1 #aeh ,magic cabinet1 #aei ,of motion1 #ee ,multiplication of images1 #afj ,trick mirror1 #afj ,seeing through a brick1 #afa ,image inversion1 by lens1 #add ,by pin hole1 #abc ,by prism1 #aea ,incandescent lamps1 #bfi ,index of refraction1 #ach ,inspecting films1 #aje ,inspecting machine1 #ig ,inspection memoranda1 #aab ,insulating joints1 #bgb ,interior conduit1 #bdb ,intermittent sprocket1 #fb1 #ge ,inversion of images1 #abc1 #add1 #aea ,inverted lighting1 #bgc ,iris1 the1 #abd ,joints1 #bgc ,junction boxes1 #bge ,kinemacolor process1 #ei ,lens lamp1 #bd ,lenses1 conjugate foci of1 #adc ,double concave1 #ade ,double convex1 #ada1 #adb ,focal length of1 #adb ,heating of1 #dj ,inversion of image by1 #add ,measuring focal length1 #di ,objective1 #adi ,principal focus of1 #adb ,selection of1 #df ,tables of1 #dg1 #dh ,types of1 #adf ,life hazard1 #ac ,light1 #aac ,infra red rays of1 #aag ,intensity of1 #abj ,interference of1 #abj ,law of inverse squares1 #aba ,reflection of1 #aba1 #abg ,re-composition of1 #aah1 #adh ,source best for projection1 #ci ,ultra violet rays of1 #aag ,vibratory1 theory of1 #aad ,waste of1 in projection1 #de ,wave lengths1 #aaf ,lighthouse effect1 #ccf ,lightning1 #ccf ,lobby1 #bge ,lower feed loop1 #fb1 #gi ,lower magazine1 #fb ,lower steady feed sprocket1 #fb1 #gi ,lugs1 #bge1 #cch ,magnifying glass1 #ade ,metal molding1 #bgf ,meters1 #bgh ,meter reading1 #bgi ,mirrors1 #abh ,concave1 #acb ,convex1 #acb1 #ace ,conjugate foci of1 #acc ,principal focus of1 #acc ,moon boxes1 #cci ,moonlight on water1 #cdj ,motiograph motion head1 #he ,motion pictures1 #ee ,motion picture machine1 #fb ,diagram of1 #fc ,discussion of parts of1 #ff ,gearing of1 #fe ,motors1 #bha ,operation of1 #bad ,starting boxes for1 #bae ,musical acts1 #cdj ,musical bells1 #cda ,music stands1 #bhe ,objective lenses1 #adi ,ohm's law1 #cec ,oiling machine1 #ih ,oil lamps1 imitation of1 #cda ,open work1 #bhf ,opera glass1 #aej ,operating room1 #agb ,color of1 #ahj ,construction of1 #agf ,entrance and exit1 #agg ,equipment of1 #agf ,fire shutters for1 #aha ,floor of1 #agh1 #agi ,shutter1 strings for1 #ahc ,tools for1 #ahe ,ventilation of1 #agf ,wiring for1 #ahf1 #ahi ,operation of motors1 #bad ,operation of motion picture machines1 #if ,optical illusions1 #aee ,optical instruments1 #adg ,optical system of projecting arcs1 #ch ,panel boards1 #bhf ,paint bridge1 #bia ,paint room1 #bia ,persistence of vision1 #ef1 #abd 8,pin cross0 movement1 #gg1 #gh ,pin plug connectors1 #cda ,plano-concave lens1 #adf ,plano-convex lens1 #adf ,plugging boxes1 #cdc ,portable stage equipment1 #caa ,powers motion head1 #hf ,presser rollers1 #fi ,principles of vision1 #abb ,prisms1 #aag1 #aah1 #ada1 #adg1 #aea ,program board1 #bia ,projection1 #ca ,projecting arc lamps1 #ch1 #eb ,proscenium side lights1 #afg1 #bid ,reactances1 #aic ,reading glass1 #add1 #ade ,reflection1 #abf ,inversion of image by1 #abi1 #acj ,multiplication of image by1 #acj1 #aca ,refraction1 #acg ,critical angle of1 #adj ,index of1 #ach ,paths of rays of light1 #aci ,refraction and reflection combined1 #adj ,retiring rooms1 #bie ,resistance1 #aij ,resuscitation1 #ae ,revolving shutter1 #fb1 #gb1 #aja ,setting of1 #ge ,rewinding1 #ajh ,rheostats1 #bie1 #cde ,rigging loft1 #afh ,sciopticon1 #cac ,screens1 #agc ,signals1 #big ,signs1 #big ,size of picture1 #ch ,simplex motion head1 #hg ,slides1 #aji ,sockets1 #bih ,solar spectrum1 #aah ,spectrum analysis1 #aah ,spherical aberration1 #ea ,spot on gate1 size of1 #da ,stage cable1 #bih1 #cdg ,stage flues1 #bii ,stage1 plan of1 #afg ,pockets1 #afh1 #cjj ,switchboard1 #afg1 #cje ,stereopticon lamps1 #cad ,stereoscope1 reflecting1 #aea ,refracting1 #aea ,strips1 #cdh ,sunrise1 #cej ,switch board1 #afg ,switches1 #cja1 #cej ,knife1 #cja ,spacings of1 #bhi ,three way1 #cjb ,table of amperage for projection1 #dd ,capacity of bus-bars1 #bce ,capacity of wires1 #bch ,drop due to #f amperes1 #bcc ,fuse spacings1 #bhi ,motion picture lenses1 #dg ,of multiple reflections1 #acb ,panel board spacings1 #bhg ,size of wire for motors1 #bhd ,stereopticon lenses1 #dh ,waste of energy by resistance1 #aia ,table lamps1 #cea ,take up1 #fb1 #gi1 #ajc1 #ajd ,telescope1 #aej ,tension springs1 #fb1 #gj1 #ajc ,testing arc lamps1 #bh ,carbons1 #bh1 #bi ,fire traps1 #fh ,theater buildings1 #afc ,for motion pictures1 #aga ,wiring of1 #bah ,three-wire system1 #aj ,time beaters1 #ceb ,tools for operating motion picture machine1 #if ,transformers1 #aid ,trick mirror1 #afj ,two-wire system1 #i ,upper feed reel1 #ff ,upper loop1 #fb1 #fi ,upper magazine1 #fb1 #ff1 #ig ,upper steady feed sprocket1 #fb1 #fh ,useful light of projecting arc1 #dj ,ventilating flues1 #agh ,vision1 persistence of1 #ef ,visitors1 #aaj ,water falls1 #ceb ,waterproof film1 #ij ,wire systems1 #i ,books ,that ,really ,teach you the things you want to know1 and in a simple1 practical way that you can understand ,illustration ,our illustrated catalogue1 which will be sent you free upon request1 tells all about the ,practical ,mechanical ,books for ,home ,study that we publish4 ,there are popular priced books on the operation of trains and station work1 practical mechanical drawing and machine designing1 pattern making1 electrical railroading1 power stations1 automobiles1 gas engines1 electrical wiring1 armature and magnet winding1 dynamo tending1 elementary electricity1 wireless telegraphy and telephony1 carpentry and architecture1 concrete construction1 plumbing and heating1 sign and house painting1 amusements1 etc41 etc4 ,no matter what your ambition or desire for knowledge may be1 we publish books written by authorities in their different lines that will give you just the training and information that you want and need4 ,write today for this up-to-date and complete illustrated catalogue and popular price list4 ,it is free4 ,,frederick ,j4 ,,drake ,,co4 ,,publishers ,,of ,,self-,,educational ,,books #acbe ,michigan ,avenue ,,chicago ,,frederick ,j4 ,,drake ,,co4',s ,,practical ,,mechanical ,,books ,,for ,,home ,,study ,price4 ,titles4 ,cloth4 ,lea4 ,air ,brake ,practice1 ,modern--,dukesmith4 ,illustrated #a4ej 444 ,air ,brake1 ,complete ,examinations1 ,westinghouse and ,new ,york4 444 #b4jj ,air ,brake1 ,westinghouse ,system4 #b4jj 444 ,air ,brake1 ,new ,york ,system4 #b4jj 444 ,american ,homes1 ,low ,cost--,hodgson4 ,illustrated #a4jj 444 ,architectural ,drawing1 ,self-,taught--,hodgson4 ,illustrated #b4jj 444 ,architecture1 ,easy ,steps to--,hodgson4 ,illustrated #a4ej 444 ,architecture1 ,five ,orders--,hodgson4 ,illustrated #a4jj 444 ,armature and ,magnet ,winding--,horstmann ,tousley4 444 #a4ej ,artist1 ,the ,amateur--,delamotte4 #a4jj 444 ,automobile ,hand ,book--,brookes4 ,illustrated 444 #b4jj ,automobile1 ,the ,mechanician's ,catechism--,swingle 444 #a4be ,blacksmithing1 ,modern--,holmstrom4 ,illustrated #a4jj 444 ,boat ,building1 for ,amateurs--,nelson4 ,illustrated #a4jj 444 ,bricklayers' and ,masons' ,assistant1 ,the #bjth ,century --,hodgson4 ,illustrated #a4ej 444 ,bricklaying1 ,practical1 ,self-,taught--,hodgson4 ,illustrated #a4jj 444 ,bungalows and ,low ,priced ,cottages--,hodgson #a4jj 444 ,calculation of ,horse ,power ,made ,easy--,brookes4 ,illustrated 4#ge 444 ,carpentry1 ,modern4 ,vol4 ,i--,hodgson4 ,illustrated #a4jj 444 ,carpentry1 ,modern4 ,vol4 ,,ii--,hodgson4 ,illustrated #a4jj 444 ,chemistry1 ,elementary1 ,self-,taught--,roscoe4 ,illustrated #a4jj 444 ,concretes1 ,cements1 ,plasters1 etc4--,hodgson4 ,illustrated #a4ej 444 ,correct ,measurements1 ,builders' and ,contractors' ,guide to--,hodgson4 #a4ej 444 ,catechism1 ,swingle's ,steam1 ,gas and ,electrical ,engineering 444 #a4ej ,cabinet ,maker1 ,the ,practical1 and ,furniture ,designer --,hodgson4 ,illustrated #b4jj 444 ,dynamo ,tending for ,engineers--,horstmann ,tousley4 ,illustrated #a4ej 444 ,dynamo--,electric ,machines--,swingle4 ,illustrated #a4ej 444 ,electric ,railway ,troubles and ,how ,to ,find ,them--,lowe #a4ej 444 ,electric ,power ,stations--,swingle #b4ej 444 ,electrical ,construction1 ,modern4 ,illustrated 444 #a4ej ,electrical ,dictionary4 ,handy1 ,weber4 4#be 4#ej ,electrical ,wiring and ,construction ,tables--,horstmann ,tousley4 444 #a4ej ,electricity1 ,easy ,experiments in--,dickinson4 ,illustrated #a4jj 444 ,electricity ,made ,simple--,haskins4 ,illustrated #a4jj 444 ,electric ,railroading--,aylmer-,small4 ,illustrated 444 #c4ej ,electro-,plating ,hand ,book--,weston4 ,illustrated #a4jj #a4ej ,elementary ,electricity1 ,up ,to ,date--,aylmer-,small #a4be 444 ,estimator1 ,modern1 for ,builders and ,architects--,hodgson #a4ej 444 ,examination ,questions and ,answers for ,locomotive ,firemen--,wallace4 ,illustrated 444 #a4ej ,examination ,questions and ,answers for ,marine and ,stationary ,engineers--,swingle4 ,illustrated 444 #a4ej ,elevators1 ,hydraulic and ,electric--,swingle4 ,illustrated #a4jj 444 ,electrician's ,operating and ,testing ,manual--,horstmann ,tousley4 ,illustrated 444 #a4ej ,farm ,engines and ,how to ,run ,them--,stephenson4 ,illustrated #a4jj 444 ,furniture ,making1 ,home--,raeth4 ,illustrated 4#fj 444 ,first ,steps in ,electricity1 or ,electricity for ,beginners --,harrison #a4jj 444 ,gas and ,oil ,engine ,hand ,book--,brookes4 ,illustrated #a4jj #a4ej ,hand ,book for ,engineers and ,electricians--,swingle4 ,illustrated4 ,pocket ,book ,style 444 #c4jj ,hardwood ,finishing1 ,up-to-date--,hodgson4 ,illustrated #a4jj 444 ,horse ,shoeing1 ,correct--,holmstrom4 ,illustrated #a4jj 444 ,hot ,water ,heating1 ,steam and ,gas ,fitting--,donaldson4 ,illustrated #a4ej 444 ,heating and ,lighting ,railway ,passenger ,cars--,prior #a4be 444 ,locomotive ,breakdowns1 with ,questions and ,answers-- ,wallace4 ,illustrated 444 #a4ej ,locomotive ,fireman's ,boiler ,instructor--,swingle 444 #a4ej ,locomotive ,engineering--,swingle4 ,illustrated4 ,pocket ,book ,style4 444 #c4jj ,machine ,shop ,practice--,brookes4 ,illustrated #b4jj 444 ,mechanical ,drawing and ,machine ,design--,westinghouse4 ,illustrated #b4jj 444 ,motorman1 ,how to ,become a ,successful4 ,aylmer-,small4 ,illustrated 444 #a4ej ,motorman's ,practical ,air ,brake ,instructor--,denehie4 444 #a4ej ,modern ,electric ,illumination1 ,theory and ,practice-- ,horstmann ,tousley4 ,illustrated 444 #b4jj ,millwright's ,practical ,hand ,book--,swingle4 ,illustrated #b4jj 444 ,modern ,american ,telephony ,in ,all ,its ,branches--,smith4 ,illustrated 444 #b4jj ,operation of ,trains and ,station ,work--,prior4 ,illustrated 444 #a4ej ,painting1 ,cyclopedia of--,maire4 ,illustrated #a4ej 444 ,pattern ,making and ,foundry ,practice--,hand4 ,illustrated 444 #a4ej ,picture ,making for ,pleasure and ,profit--,baldwin4 ,illustrated #a4be 444 ,plumbing1 ,practical1 ,up-to-,date--,clow4 ,illustrated #a4ej 444 ,railway ,roadbed and ,track1 ,construction and ,maintenance of--,prior4 ,illustrated 444 #b4jj ,railway ,shop ,up-to-,date--,haig4 ,illustrated #b4jj 444 ,sheet ,metal ,workers' ,instructor--,rose4 ,illustrated #b4jj 444 ,signist's ,book of ,modern ,alphabets--,delamotte #a4ej 444 ,sign ,painting1 ,the ,art of--,atkinson #c4jj 444 ,stair ,building and ,hand ,railing--,hodgson4 ,illustrated #a4jj 444 ,steam ,boilers--,swingle4 ,illustrated 444 #a4ej ,steel ,square1 ,a ,key to--,woods4 #a4ej 444 ,steel ,square1 ,vol4 ,i--,hodgson4 ,illustrated #a4jj 444 ,steel ,square1 ,vol4 ,,ii--,hodgson4 ,illustrated #a4jj 444 ,steel ,square1 ,a ,b ,c--,hodgson4 4#ej 444 ,steel ,construction1 ,practical--,hodgson4 ,illustrated 4#ej 444 ,storage ,batteries--,niblett 4#ej 444 ,sho' ,cards1 ,a ,show ,at--,atkinson and ,atkinson #c4jj 444 ,stonemasonry1 ,practical1 ,self-,taught--,hodgson4 ,illustrated #a4jj 444 ,telegraphy ,self-,taught--,edison4 ,illustrated #a4jj 444 ,telephone ,hand-,book--,baldwin4 ,illustrated #a4jj 444 ,timber ,framing1 ,light and ,heavy--,hodgson #b4jj 444 ,toolsmith and ,steel ,worker--,holford4 ,illustrated #a4ej 444 ,turbine1 ,the ,steam--,swingle4 ,illustrated #a4jj 444 ,walschaert ,valve ,gear ,breakdowns and ,how to ,adjust ,them --,swingle4 ,illustrated #a4jj 444 ,wiring ,diagrams1 ,modern--,horstmann ,tousley4 ,illustrated 444 #a4ej ,wireless ,telegraphy and ,telephony--,v4 ,h4 ,laughter #a4jj 444 ,wood ,carving1 ,practical--,hodgson4 ,illustrated #a4ej 444 ,,the ,,red ,,book ,,series ,,of ,,trade ,,school ,,manuals ,by ,f4 ,maire #af mo41 ,cloth1 ,illustrated4 ,price1 each1 #j4fj ,exterior ,painting1 ,wood1 ,iron and ,brick4 ,interior ,painting1 ,water and ,oil ,colors4 ,colors1 ,what ,they ,are and ,what to ,expect from ,them4 ,graining and ,marbling4 ,carriage ,painting4 ,the ,wood ,finisher4 ,,the ,,automobile ,,hand-,,book ,,over #bjj1jjj ,,sold ,by ,,elliott ,,brookes1 ,assisted by ,other ,well-,known ,experts ,revised and ,enlarged ,new ,edition--,the largest and most practical work published4 ,used by all up-to-date automobile schools as their every-day text-book4 over #gbj pages and over #cbi illustrations4 ,full ,leather ,limp1 ,round ,corners1 ,red ,edges4 ,price1 #b4jj4 ,illustration ,at the present time nearly all automobile troubles or breakdowns may1 in almost every case1 be traced to the lack of knowledge or carelessness of the owner or operator of the car1 rather than to the car itself4 ,the automobile hand book is a work of practical information for the use of owners1 operators and automobile mechanics1 giving full and concise information on all questions relating to the construction1 care and operation of gasoline and electric automobiles1 including road troubles1 motor troubles1 carburetor troubles1 ignition troubles1 battery troubles1 clutch troubles1 starting troubles4 ,with numerous tables1 useful rules and formul1 wiring diagrams and over #cbi illustrations4 ,special efforts have been put forth to treat the subjects of ignition1 and ignition devices1 in a manner befitting their importance4 ,a large section has been devoted to these subjects1 including batteries1 primary and secondary1 magnetos1 carburators1 spark plugs1 and in fact all devices used in connection with the production of the spark4 ,power transmission is thoroughly discussed1 and the various systems of transmitting the power from the motor to the driving axle are analyzed and compared4 ,the perusal of this work for a few minutes when troubles occur1 will often not only save time1 money1 and worry1 but give greater confidence in the car1 with regard to its going qualities on the road1 when properly and intelligently cared for4 ,a ,,word ,,to ,,the ,,wise ,the time is at hand when any person caring for and operating any kind of self-propelling vehicle in a public or private capacity1 will have to undergo a rigid examination before a state board of examiners and secure a license before they can collect their salary or get employment4 ,already ,new ,york ,state has enacted such a law and before long1 with a positive certainty every state in the ,union will pass such an ordinance for the protection of life and property4 ,remember this is a brand new book from cover to cover1 just from the press--,new ,edition--and must not be confounded with any former editions of this popular work4 ,sent prepaid to any address upon receipt of price ,,frederick ,j4 ,,drake ,,co41 ,publishers #acbe ,michigan ,avenue ,,chicago1 ,u4 ,s4 ,a4 ,,complete ,,examination ,,questions ,,and ,,answers ,,for ,,marine ,,and ,,stationary ,,engineers ,by ,calvin ,f4 ,swingle1 ,m4 ,e4 ,author of ,swingle's ,twentieth ,century ,hand ,book for ,steam ,engineers and ,electricians4 ,modern ,locomotive ,engineering ,handy ,book1 and ,steam ,boilers--,their construction1 care and management ,illustration ,this book is a compendium of useful knowledge1 and practical pointers1 for all engineers1 whether in the marine1 or stationary service4 ,for busy men and for those who are not inclined to spend any more time at study than is absolutely necessary1 the book will prove a rich mine from which they may draw nuggets of just the kind of information that they are looking for4 ,the method pursued by the author in the compilation of the work and in the arrangement of the subject matter1 is such that a man in search of any particular item of information relative to the operation of his steam or electric plant1 will experience no trouble in finding that particular item1 and he will not be under the necessity of going over a couple of hundred pages1 either1 before he finds it because the matter is systematically arranged and classified4 ,the book will be a valuable addition to any engineer's library1 not alone as a convenient reference book1 but also as a book for study4 ,it also contains a complete chapter on refrigeration for engineers4 #cfg pages fully illustrated1 durably bound in full ,persian ,morocco limp1 round corners1 red edges4 ,,price #a4ej ,sold by ,booksellers generally or sent postpaid to any address upon receipt of price by the ,publishers ,,frederick ,j4 ,,drake ,,co4 ,,chicago4 ,u4 ,s4 ,a4 ,transcriber's ,notes3 ,the structure of the printed book regarding headings1 sections and 7sub-7sub-sections was inconsistent and occasionally unclear4 ,as a consequence1 there are some sub-sub-sections that are not part of sub-sections 7for example1 sub-sub-section national code rules for grounding1 where there is no sub-section grounding71 and in-line section headers are not marked as such4 ,inconsistent spacing of abbreviations1 capitalisation1 spelling and hyphenation have been retained4 ,the alphabetic order of sections in ,chapters ,,xviii and ,,xix is not always correct1 this has not been changed4 ,on various pages there are references to other sections and rules of the ,national ,electric ,code4 ,these sections and rules are not listed as such1 and it is therefore unclear whether the section or rule referred to is given in this work4 ,page #cai3 444 which should be used to the pin-plug connector 4443 there is probably a word missing 78connect0 or similar74 ,advertisement ,automobile ,hand-,book1 444 over #gbj pages3 there is probably a word missing4 ,changes made ,illustrations have been moved out of paragraphs1 footnotes have been moved to directly below the paragraph they refer to4 ,obvious minor typographical and punctuation errors have been corrected silently4 ,other changes3 ,page #aj3 444 lights turned on 444 changed to 444 lights be turned on 444 ,page #be1 footnote3 author's changed to authors' ,page #bf3 misplaced line moved to proper place on page ,page #aic3 author's changed to authors' ,page #ee3 aperature changed to aperture 7#bx7 ,page #bji3 8,y0 changed to ,y as other reference letters ,page #bch1 last row1 column #be-,watt1 #aaj ,v43 #gdcj changed to #cgdj ,page #cgc3 misplaced line moved to proper place on page4