FIGURE 211.
Strips.—Strips are used for the illumination of special parts of the scenery. They usually contain from one to twelve lights. A strip is subject to rough usage and should be strongly made. Cuts of several kinds of strips are given in Figure 212. The chief trouble with strips is found to be in the working loose of screws which hold the sockets in place, and the connection at the point at which the cable leaves the strip.
Must be constructed of steel of a thickness not less than No. 20 U. S. sheet metal gauge, treated to prevent oxidation, and suitably stayed and supported and so designed that flanges will protect the lamps.
FIGURE 212.
Cables must be bushed in a suitable manner where passing through the metal, and must be properly secured to prevent serious mechanical strain on the connections.
Must be wired in approved conduit or armored cable, each lamp receptacle being enclosed within an approved outlet box, or the lamp receptacles may be mounted in an iron or steel box, metal to be of a thickness not less than No. 20 U. S. sheet metal gauge, treated to prevent oxidation, so constructed as to enclose all wires. Wires to be soldered to lugs of receptacles.
FIG. 213.
Sunrise.—Sunrise effects may be produced by means of the Sciopticon, but a cheaper method is often resorted to. This is illustrated in Figure 213 and consists of a roll of suitably colored silk which may be unrolled in front of an arc lamp. To produce sunrise it is unrolled in one direction, the darkest colors coming first and gradually giving way to lighter. For sunset it is worked the other way. 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 raised, thus producing the same effect with more impressiveness, but with a much greater quantity of light.
Switches.—Knife switches on the stage are generally required to be enclosed. It is not sufficient to provide a box with a cover that can be closed, but the switch should be in a box which need not be opened to operate the switch. See Figure 214. Often it is necessary to install switches in a length of stage cable so that the switch may be portable. Such switches should be installed as shown in Figure 215, in which a flush switch is shown in a regular metal enclosure.
FIGURE 216.
Table Lamps.—The table lamp is a small device, but it causes a great deal of annoyance and trouble. The bottom of the lamp should be enclosed with metal, especially if there are any splices. The stem where the wire enters should be well reamed out (see the arrow in Figure 216) and there should be a strong well-fastened bushing where the wire leaves the lamp. The hard-rubber bushings which come with the common table lamps do not remain in place very long and are frequently broken or lost. Stage cable is generally required upon the stage, but it is customary, in connection with these lamps, to allow a good grade of reinforced cord or even fine silk-covered cord, provided it is not long enough to trail on the floor where it might be stepped upon. The glass shades which are often called for in connection with the lamps also cause much trouble; and to avoid this trouble, colored gelatine has been used, backed up with fine wire screen to keep it in place. This of course cannot always be done because many lamps are not suited to it.
Time Beaters.—This is a small keyboard located at the orchestra leader’s stand; it controls the light which may be back of the stage and indicates the time to the chorus behind scenes.
Water Falls.—The devices shown in Figure 204 for use as moonlight on the water can also be used to produce the effect of a waterfall or of water rippling downstream.
One turn of the crank runs off 1 foot of film.
One foot of film contains 16 pictures.
The audience sees about 960 different pictures in every minute that a film is being run.
The relative number of revolutions made by two pulleys connected together by belting or friction is in proportion to their diameters.
The relative number of revolutions made by two gears connected together is in proportion to their number of teeth.
A theater seat occupies from 4 to 5 square feet.
One 25-watt tungsten lamp or its equivalent provided for every 20 seats will give fairly good illumination in a small theater.
3 to 5 watts per cubic foot will be required to heat small spaces by electricity.
Direct current equals e.m.f. divided by resistance.
Alternating current equals e.m.f. divided by impedance.
Electromotive force, d.c., equals current time resistance.
Electromotive force, a.c., equals current time impedance.
Resistance equals e.m.f. divided by current.
Impedance equals e.m.f. divided by current.
The joint resistance of two conductors connected in parallel is equal to the product of their resistances divided by their sum:
r = (r1 × r2) ÷ (r1 + r2)
The joint resistance of any number of resistances connected in parallel is the reciprocal of the sum of the reciprocals. The reciprocal of a number is 1 divided by that number:
r = 11r1 + 1r2 + 1r3 + . . . . .
The total resistance of a number of resistances in series is equal to the sum of all of them:
r = r1 + r2 + r3 + . . . . .
The heating of a rheostat is proportional to the square of the current it carries.
Drop in voltage is proportional to the product of the current and resistance for a direct-current circuit, and the product of current and impedance for an alternating-current circuit.
If a reactance is used in place of a rheostat in an alternating-current circuit, the loss of energy is greatly reduced.
If the same intensity of illumination is to be provided for pictures of different sizes, the amperage must vary about as:
(W × 1.2)2
where W is the width of picture on screen.
For a given power the current in conductors is:
| for direct current | I = WE |
| for single-phase a.c. | I = WE × p. f. |
| for two-phase a.c. | I = .5 × WE × p. f. |
| for three-phase a.c. | I = .58 × WE × p. f. |
in which I is the current in amperes, W is the watts, E is the voltage, and p. f. is the power factor.
To find the size of a picture obtainable under given conditions and lens: Multiply distance from center of lens to screen by one dimension of slide or film and divide by e.f. focal length of lens, taking all measurements in inches.
Example: Slide 23⁄4 inches. Length of throw 360 inches. e. f. 10 inches
23⁄4 × 360 ÷ 10 = 99 inches.
To find focal length needed for a given slide or film to produce a given size of picture: Multiply slide or film dimension by length of throw and divide by dimension of picture, taking all measurements in inches.
Example: Same dimensions as above:
23⁄4 × 360 ÷ 99 = 10 inches.
To find length of throw needed to obtain a certain size of picture: Multiply required picture dimension by focal length of lens and divide by slide or film dimension.
Example: Same dimensions as above:
99 × 10 ÷ 23⁄4 = 360 inches.
To find slide size necessary to produce a certain size of picture under fixed conditions: Multiply focal length of lens by size of picture and divide by length of throw.
Example: Same dimensions as above:
10 × 99 ÷ 360 = 23⁄4 inches.
To find the area of a parallelogram: Multiply the base by the altitude.
To find the area of a triangle when base and altitude are given: Multiply the base by the altitude and take half the product.
To find the area of any angular surface: Divide it into triangles and find the area of the different triangles and add them together.
To find the circumference of a circle: Multiply the diameter by π, or 3.1416.
To find the diameter of a circle when the circumference is given: Divide the circumference by π, or 3.1416.
To find the area of a circle when the radius is given: Multiply the square of the radius by 3.1416. When diameter is given: Multiply the square of the diameter by .7854.
To find the radius of a circle when the area is given: Divide the area by 3.1416 and extract the square root of the quotient.
To find the lateral area of a right prism: Multiply the perimeter of the base by the altitude.
To find the lateral area of a right cylinder: Multiply the circumference of the base by the altitude.
To find the volume of a cylinder or prism: Multiply the area of the base by the altitude.
To find the lateral area of a right pyramid: Multiply the perimeter of the base by the slant height and take half the product.
To find the lateral area of a cone: Multiply the circumference of the base by the slant height and take half the product.
To find the volume of a pyramid or cone: Multiply the area of the base by the altitude and take one-third of the product.
To find the surface of a sphere: Multiply the square of the diameter by 3.1416.
To find the volume of a sphere: Multiply the cube of the diameter by one-sixth of 3.1416 or .5236.
In a right-angled triangle, the sum of the squares of the base and the perpendicular equals the square of the hypotenuse. To find the length of the hypotenuse: Extract the square root of the sum of the squares of the base and the perpendicular.
To find the base or the perpendicular: From the square of the hypotenuse subtract the square of the other given side and extract the square root of the remainder.
Aberration.—The convergence to different foci, by a lens or mirror, of rays of light emanating from one and the same point or the deviation of such from a single focus.
a. c.—An abbreviation for alternating current.
Accumulator.—A term often used to designate a storage battery.
Achromatic.—Free from false coloration.
Achromatic Lens.—A lens which does not show color in the light which it projects; usually a combination of lenses of different kinds of glass.
Actinic Rays.—The rays of light that cause chemical changes.
Airdome.—A theater arranged in the open air.
Alloy.—Any compound of two or more metals.
Alternating Current.—An electric current undergoing periodical changes in direction.
Amalgam.—A compound of mercury with other metals.
Ammeter.—An instrument used for measuring the value of an electric current.
Amperage.—The number of amperes; the current strength in the circuit; not the quantity but the rate of flow.
Ampere.—The unit of current strength. It is equal to a rate of flow of electricity of one coulomb per second.
Ampere Hour.—One ampere flowing for one hour; or its equivalent.
Anamorphosis.—A grossly distorted image, such as can be obtained from a curved mirror.
Angular Velocity.—The rate at which a body revolves around a fixed axis, usually measured in radians per second. The radian is equal to 360 ÷ 2 × π degrees.
Annular Space.—The space between an inner and an outer ring or cylinder.
Annunciator.—An electric device provided with one or more magnets and indicators, which serve to indicate the points at which one or more electric contacts have been closed.
Anode.—The positive pole; a term used mostly with electrolytic devices, also with the mercury arc rectifier and the electric arc.
Aplanatic.—Free from spherical aberration.
Apparent Power.—The product of volts and amperes in an alternating-current circuit. The true power in an alternating-current circuit is always less than the apparent power if pressure and current are not in phase.
Arbor.—An axle or spindle on which a wheel turns.
Arc, Electric.—The heated portion of an electric circuit between two electrodes where the current passes from one to the other; the source of light of the electric arc lamp.
Armature.—That part of a generator, in which the electrical pressure is generated, which causes a current if the armature winding forms part of a closed circuit.
Automatic.—A term applied to machinery in which certain movements, usually made by hand, are made by the machine.
Auto-Transformer.—A transformer provided with only one winding; a part of the winding being traversed by both the primary and secondary currents.
Axis.—The straight line, real or imaginary, which passes through a body, and on which the body revolves, or may be supposed to revolve.
Axis of Lens.—The straight line passing through its center and perpendicular to its surface.
Axle.—A transverse bar connecting opposite wheels.
Babbitt Metal.—A soft white antifriction metal of varying composition; as 4 parts of copper, 8 of antimony, and 24 or 96 of tin. The larger the amount of tin, the harder the resultant alloy.
Baby Spot Lamp.—An incandescent lamp placed within a hood similar to that of a theater arc lamp; also usually provided with a lens.
Back Focus.—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 screen. See also Equivalent Focus.
Balance Wheel.—A wheel added to machinery for the purpose of preventing too sudden variations in speed; also called fly wheel.
Ball Bearing.—A journal fitted with balls upon which the shaft turns.
Balsam, Canadian.—A cement used to cement lenses, etc.
Band.—A small belt passing over two pulleys.
Battery.—A term used to describe a number of voltaic cells connected so as to act as a single cell; should never be used in reference to a single cell.
Bayonet.—A pin which plays in and out of holes made to receive it and serves to engage parts of machinery.
Bearing.—That part of a machine in contact with which a shaft moves; the journal boxes.
Bed.—The foundation or main fixed part of a machine.
Bell Crank.—A rectangular lever by which the direction of rotation is changed through an angle of ninety degrees.
Belt.—A strap or band of flexible material passing around two or more wheels and communicating motion to them.
Bevel Gear.—A gear in which the two wheels working together lie in planes that are not parallel.
Bifocal.—Having two foci.
Binocular.—Pertaining to both eyes, as binocular vision in microscope or telescope.
Blinding Lights.—Lights used on the stage in certain acts to blind the audience; thus allowing persons to work behind them unseen by the audience.
Boss.—The enlarged part of a shaft on which a wheel is keyed.
Brace.—A curved tool of iron or wood adapted to turn and hold bits.
Brake.—A piece of mechanism adapted to stop or hold parts of machinery.
Brushes.—That part of a dynamo by which the current is taken to or from the commutator.
Buffer.—A cushion, with springs or other material, arranged to deaden the blow of a moving body.
Buffing Wheel.—A rapidly revolving wheel adapted to buff or polish materials.
Burner; Automatic, Electric.—An electric device, for turning on and lighting gas, which may be operated from a distance by pressing a button.
Bushing.—The lining of a hole with a ring or a perforated substance of metal or other material.
Calipers.—A compass with curved legs; used for measuring round bars or openings, the thickness of objects, and the distance between two points.
Cam.—A projecting part of a wheel or other moving piece, so shaped as to give an alternating or variable motion to another piece pressing against it.
Cam Wheel.—A wheel, or part of a wheel, of irregular outline employed to produce a variable or alternating motion in machinery.
Canadian Balsam.—A cement used to cement lenses, etc.
Candle Power.—This term, as commonly used, denotes the light-giving power of a lamp in terms of a standard candle. Its meaning is not very definite unless qualified by some of the following terms: apparent candle power; equivalent candle power; mean horizontal candle power; mean lower hemispherical candle power; mean spherical candle power; maximum candle power; mean zonular candle power. All of these terms are fully explained in “Modern Electric Illumination, Theory and Practice.”
Carbons.—The rods of artificial carbon used as electrodes in arc lamps.
Carbons, Cored.—Carbons, as above, but provided with a core of softer material.
Case Hardening.—The act or process of converting the surface of iron into steel while leaving the center soft and malleable.
Cathode.—The negative pole. A term usually used in connection with electrolytic apparatus, mercury arc rectifiers, and electric arcs.
Cell, Voltaic.—A cup or jar containing electrodes and an electrolyte either for producing an electromotive force or electrolysis. In the latter case it is called an electrolytic cell. A number of cells connected together make a battery.
Centi.—As a prefix it means the hundredth part; as centimeter.
Choke Coil.—A coil of wire wound upon an iron core in such a manner as to acquire a very high self-inductance; similar to a reactance.
Chuck.—A contrivance fixed to the mandril of a turning lathe for holding the material to be worked upon.
Clutch.—A projecting tooth, or other piece of machinery, for connecting shafts with each other or with wheels in such a manner as to be readily disengaged.
Cog Wheel.—A wheel with cogs or teeth.
Collar.—A ring-like part of a machine usually fastened to some part of it and used for keeping something in place.
Commutator.—That part of a dynamo-electric machine to which all of the armature wires are connected and in which the alternating-electromotive force, actually generated in the armature winding, is made to appear as a direct-electromotive force in the external circuit.
Compasses.—An instrument for describing circles, measuring, etc., consisting of two pointed branches fastened together at the top by a rivet or screw.
Compensarc.—A trade term used to describe a transformer or an auto-transformer; used in connection with projection-arc lamps.
Compound Winding.—A generator, 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 fields; is said to be compound wound, and the winding is referred to as a compound winding.
Concave.—Curved and hollow; the inside of a hollow sphere or cylinder.
Concentric.—Having a common center.
Condenser.—A lens or a set of lenses, used to gather the divergent rays from a source of illumination and bring them to a focus.
Conductor.—Any substance used to carry electricity. Most of the commercial conductors are of copper.
Cone.—A solid body having a plane for its base and a point for its top, the surface being formed by line segments joining every point of the outline of the base to the point top.
Conical.—Approximating a cone in shape.
Conjugate Foci.—The two points in the principal axis of a lens and at opposite sides of it; one point being the light source and the other the point at which rays of light from this source are brought to a focus.
Controller.—A resistance used for controlling the speed of a motor or the field strength of a dynamo.
Converter.—Any apparatus used for changing from one form of current to another; generally used to indicate a synchronous or rotary converter.
Convex.—Rising or swelling; the outside of a sphere or cylinder.
Convexo-Plano.—Convex on one side and plane on the other; plano-convex is more often used.
Cooling Plate.—The metal around the projection aperture of a motion-picture machine which protects the film from the rays of light.
Cotter.—A wedge-shaped piece of wood, iron, or other material used for fastening the parts of a structure; a key.
Cotter Pin.—A pin made up of doubled wire expanded at top and bottom so as to hold its place when inserted in a hole.
Coulomb.—The unit of quantity of electricity. It is equal to the current multiplied by the time that it flows; viz., ampere times second.
Countershaft.—A secondary shaft driven from another shaft; not the main or driving shaft.
Countersink.—A drill or cutting tool used to enlarge the outer edges of a hole in countersinking.
Crown Wheel.—A wheel, with cogs or teeth set at right angles to its plane.
Cycle.—A complete recurrence of any periodic change. The two immediately succeeding half waves of an alternating current or e.m.f. constitute a cycle.
Damping Coils, Dampers.—Coils of wire or bars of copper placed on, or imbedded in, the pole pieces of a dynamo-electric machine; used mostly in connection with synchronous motors or rotary converters to prevent hunting.
Dead Center.—Either of the two opposite points, in the orbit of a crank, at which the crank and a driving rod lie in a straight line.
Diffusing Globes.—Globes of ground glass or other medium which causes diffusion of light. Used to reduce the intrinsic brilliancy of illuminants. The light is emitted from a larger surface and is less trying to the eyes.
Diffusion.—The scattering of light by diffuse reflection, as from an irregular surface such as ground glass.
Diffusion Projection.—A method of projection sometimes resorted to when condensers are broken. Ground glass is used in place of the condensers.
Direct Current.—A current of electricity maintained in one direction as distinguished from an alternating current which is regularly alternating in direction.
Dog.—A part of machinery acting as a catch or a clutch.
Dovetail.—To unite by a tenon, in the form of a pigeon’s tail spread out, let into a board or timber.
Dowel Pin.—A pin of wood or metal used for joining two pieces; part of its length entering one piece, and the rest entering a corresponding hole in the other.
Dowser.—A hand shutter arranged in front of the lens of an arc lamp by which the light may be shut off.
Drift.—A conical tool of steel for enlarging or shaping a hole in metal by being driven into or through it.
Drill.—A pointed instrument used for boring holes; especially in hard substances.
Drop in Potential.—A term often used to designate a loss of electrical pressure. In d.c. circuits it is equal to current times resistance. In a.c. circuits it is equal to current times impedance.
Drum.—A short cylinder revolving on an axis.
Dynamo.—A dynamo electric machine for converting electrical energy into mechanical, or vice versa. When the transformation is from electrical to mechanical energy the machine is operating as a motor; and when the transformation is from mechanical to electrical energy the machine is operating as a generator.
e. f.—Abbreviation for equivalent focus.
e. m. f.—Abbreviation for electromotive force. The unit of electromotive force. The unit of electromotive force is the volt.
Eccentric.—A wheel or disc having its axis of revolution out of its center; used to convert circular motion into reciprocating.
Economizer.—A trade name applied to a transformer or auto-transformer, used in connection with projection-arc lamps.
Economy Coils.—An auto-transformer. This term is used very much in connection with auto-transformers, and also transformers used in connection with arc lamps.
Efficiency of Incandescent Lamps.—The efficiency of incandescent lamps is expressed in watts per candle power. The lower the numerical expression for efficiency, the greater is the light obtained per unit of energy.
Electrodes.—The terminals of an electric source; in an arc lamp, the two carbons.
Electrolysis.—Chemical decomposition by an electric current. The positive pole, or anode, is eaten away with direct current; the effect with alternating current is very slight.
Emergency Lights.—Those lights arranged in theaters, 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 illumination. Emergency and exit lights are generally grouped together but must not be confused with each other.
Equivalent Focus.—The distance from the center of a set of lenses to the slide, when the picture on the slide is in focus on the screen.
Exit Lights.—The lights placed directly above exits; usually colored red.
Expansion Bolt.—A bolt adapted to be inserted into a socket which, expanded by the insertion, thus holds the bolt in place.
Face Plate.—The disc attached to the revolving spindle of a lathe to which the work is often fastened.
Feeders.—The main wires extending from the supply to the distributing center.
Field.—A term commonly used to designate the space traversed by the lines of the force of magnetism which is supposed to exist. The fields of a dynamo consist of the pole pieces around which the exciting current circulates.
Fire Trap.—The arrangement of rollers and their enclosure, usually placed on magazine or film tanks, through which the film is led, to prevent a flame from following the film in case of fire.
Flange.—A projecting edge or rim on a wheel or shaft by which it may be kept in place or fastened.
Flasher.—The term by which a contrivance for regularly, and at frequent intervals, turning lights on and off is described; used mostly in connection with electric signs.
Flicker.—The unsteady illumination of a motion picture; caused mostly by insufficient speed of film or too brilliant illumination.
Fly Floor.—A floor above the stage upon which the scene shifters, whose duty it is to raise and lower the curtains, work.
Footlights.—A row of lights placed at the stage level and directly in front of the actors.
Forging.—A piece of metal shaped by hammering; not a casting.
Framing Device.—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 screen.
Frequency.—The number of cycles per second; also spoken of as the periodicity. The most common frequencies are 25 and 60 cycles per second.
Gearing.—The parts by which motion given to one part of a machine is transmitted to other parts. In a narrower sense it refers only to cog wheels.
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 wheel.
A bevel gear is one in which the shafts of the two gears are not parallel.
A friction gear is one in which friction takes the place of the teeth.
A worm gear is one in which one of the members is in the form of a screw. The pitch of the screw may, or may not, be such as to prevent it from being turned by the other.
A herring-bone gear is one in which the teeth are cut across the face of the wheel at an angle. The teeth may be made to converge toward the center of the face or may be cut in a line across it. This gear is used where noiseless operation is required.
Generator.—A term frequently used to describe a dynamo-electric machine used in converting mechanical energy into electrical energy.
Geneva.—A form of intermittent movement first used in Geneva, Switzerland; hence the name. It is the form of intermittent mechanism most used.
Governor.—A contrivance used in connection with machinery to regulate the speed.
Grid, or Grid Floor.—This term refers to the topmost floor above the stage of a theater where the pulleys and the cables, by which scenery is raised and lowered, are placed. It is usually made up of iron bars with spaces between them; hence the name.
Ground.—-This term is used to describe any connection of an electrical conductor to any conducting medium, other than that to which it belongs, which may be common to other conductors or which may convey current to the opposite pole in a manner not desired.
Gudgeon.—The piece of iron in the end of a wooden shaft on which it turns in a collar or on a gudgeon block.
Heat Shield.—A part of a motion-picture machine which shields the film and adjacent parts from the heat of the light.
Helix.—See Solenoid.
Horsepower.—A unit or standard by which the capability of machinery is measured. Power sufficient to raise one pound 33,000 feet in one minute is called one horsepower. Electrically it is equal to 746 watts.
Hunting.—This term describes the regular and persistent changes in the speed of synchronous apparatus running in parallel, which are due to fluctuations in the load on the generators or in the speed of the prime mover; and causes cross currents. In theaters they would be noticeable only in connection with rotary converters which are sometimes used to convert a.c. into d.c. for arc lamps.
Idler.—A wheel placed between two other wheels to convey motion from one to the other without changing the direction of motion.
Impedance.—Impedance is to an alternating-current circuit what resistance is to a direct-current circuit. The e.m.f. divided by the impedance equals the current. The symbol for impedance is Z.
Impressed e.m.f.—The electromotive force brought to bear on any circuit to produce a current therein; the applied e.m.f.
Index of Refraction.—The index of refraction, or the refraction index, is the ratio the sine of the angle of incidence bears to the sine of the angle of refraction. For glass the index of refraction is about 1.5.
Indirect Lighting.—A system of illumination in which all of the light is first thrown to the ceiling and reflected therefrom.
Inductance.—That property of an electric circuit which causes a current in it to create lines of force and thus generate a counter e.m.f. when the current changes in value.
Induction Motor.—A much used alternating-current motor in which there is no electrical connection between the primary and secondary or rotor and stator windings. It may be either single or polyphase.
Intermittent Movements.—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 machines. The other movements have mostly come into use in connection with cameras. The beater movement is one in which a certain length of film is pushed to one side at each movement. The claw movement is one in which claws reach up and pull down a fixed amount of film at each movement. Other intermittent movements are known as, the drunken screw; ratchet; pitman and grip. They have mostly only a historical interest.
Intrinsic Brilliancy.—This term refers to the candle power per unit area of a source of light. A light having a large candle power in proportion to its size is said to have a high intrinsic brilliancy. Lamps of high intrinsic brilliancy should never be placed in the line of vision.
Inverted Lighting.—Synonymous with indirect lighting.
Key.—A wedge-shaped piece of wood or metal used, to hold something in place; a cotter.
Key Seat.—A groove cut into a shaft to fit a similar groove in a wheel or flange, and into which a key may be fitted.
Key to Curtain.—A fictitious article, in quest of which novices employed in theaters are often sent; a hoax.
Kilowatt.—1000 watts.
Lagging Current.—A current, the maximum value of which occurs later than that of the e.m.f. producing it.
Laminated.—Made up of sheets. All iron parts subject to the influence of alternating fields must be laminated to reduce the losses due to Foucault or eddy currents.
Leading Current.—A current, the maximum value of which occurs earlier than that of the e.m.f. producing it. In connection with synchronous converters the current may be made either lagging or leading by adjusting the field excitation.
Lens.—A piece of glass, or other transparent substance, ground with two opposite regular surfaces. In practice the curved surfaces are generally spherical but sometimes they are made cylindrical.
Of spherical lenses there are six varieties: plano-concave; double-concave; plano-convex; double-convex; meniscus; and concave-convex. A double-convex lens, with one radius six times that of the other, is called a crossed lens.
A multiplying lens or glass is one consisting of a number of plane faces on one side and a convex surface on the other. The plane faces are inclined to one another and each presents a different picture; thus giving the appearance of the multiplication of images.
A polyzonal lens is one that is made up of a large number of pieces arranged in zones or rings. 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 piece.
Lime Light.—A light produced by means of a cylinder of lime which is subjected to a flame of gas or of oxygen and hydrogen.
Lines of Force.—Every magnetic field is supposed to be made up of imaginary lines called lines of force. The number of these lines per unit area perpendicular to the field is a measure of the strength of the field.
Lost Motion.—Refers to the loss or irregularity of motion caused by wear of machinery or poor adjustment.
Magic Pane.—This is a condenser formed of a sheet of glass, one side of which is covered by pieces of tin foil with spaces left between. 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 spaces.
Male Thread or Coupling.—In connection with piping, hose, etc., a coupling arranged to enter into another, is spoken of as “male”; that part which is entered into is known as “female.”
Mandrel.—A bar of metal inserted in the work to hold it, as in a lathe, during the process of manufacture. Also the spindle which carries the center chuck of a lathe, an arbor.
Matched Lenses.—The lenses in two stereopticon lamps to be used together must be matched to give the same size of picture.
Micrometer.—An instrument used for measuring very small diameters or thicknesses, the adjustments being made by a screw arranged to indicate very slight changes in the opening in which the object is inserted.
Mil.—The one-thousandth part of an inch. The circular-mil area of a circular area, such as the cross section of a wire, can be found by squaring the diameter.
Mirage.—An optical illusion due to an unequal refraction in the lower atmosphere which causes remote objects to be seen double and suspended in the air. A mirage can be arranged for by a prism or by a piece of beveled glass.
Miter Wheels.—A pair of bevel wheels of equal diameter working together, usually with their axes at right angles.
Motion Head.—By this term the whole of the motion-picture machine is usually designated.
Motor.—See dynamo.
Motor Generator.—A generator driven by a motor.
Multiple Series.—A system of wiring in which several lamps are connected in series and a number of such series combinations connected in multiple.
Neutral Wire.—The wire of a three-wire system which ordinarily carries no current. In a three-wire system it is usually run in the center.
Ohm.—The ohm is the unit of electrical resistance.
Ohmic Drop.—This is the loss of potential due to the resistance, as distinguished from that due to the reactance. It is always equal to the current multiplied by the resistance, the current being measured in amperes and the resistance in ohms.
Ohm’s Law.—This is a statement defining the relations existing between electrical pressure, current, and resistance.
The current is equal to the electrical pressure divided by the resistance.
The resistance is equal to the electrical pressure divided by the current.
p. d.—An abbreviation for difference of potential.
Pawl.—A short movable piece or bar connected at one end, by a joint, with some part of a machine; while the other end falls into notches or teeth on another part, in such a manner as to permit motion in one direction only.
Period.—The time required for one complete cycle.
Photometer.—An instrument used for comparing or measuring the candle power of illuminants.
Pinion.—A small wheel with leaves or teeth working into the teeth of a larger wheel or rack; especially such a wheel having its leaves formed of the substance of the arbor or spindle on which it turns; a toothed arbor.
Pitch.—The distance from center to center of any two adjacent teeth of gearing measured on the pitch line. The distance measured on a line parallel to the axis between two adjacent threads or convolutions of a screw.
Pitch Line.—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 it. The two circles must have a common velocity.
Plunger.—A part of machinery which is subject to a plunging motion.
Polarity.—A difference of polarity exists between any two wires, or points in one wire, where there is any tendency to produce a current. In practice, however, the term is used to designate wires pertaining to the two opposite poles of a system.
Polyphase.—Referring to more than one phase, multiphase.
Power.—This term designates the rate of doing work.
Power Factor.—This term expresses the ratio of the true power in an alternating-current circuit to the apparent power. It is always less than 1. The apparent power (product of volts and amperes measured by independent instruments) must be multiplied by the power factor to obtain the true power in alternating-current circuits.
Primary Battery.—A battery in which the p.d. is produced by primary action of the ingredients used, instead of by secondary action as in secondary batteries or accumulators.
Primary Coil.—That coil of a transformer, induction motor, or induction coil which is connected to the source of electrical energy.
Prism.—A transparent body usually having three rectangular faces and triangular ends. It is used in experiments on optics to show refraction and may also be made to produce total reflection.
Prismatic Colors.—The seven colors into which sunlight is resolved when passed through a prism.
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 color.
Pulley.—A broad-rimmed wheel used for transmitting power by means of a belt.
A narrow-rimmed wheel with a groove used for the same purpose is termed a sheave.
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 velocity.
A fast pulley is one which is rigidly attached to the shaft.
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 still.
Pulsating Current.—A current of electricity varying regularly in strength but not in direction.
Rack and Pinion.—A straight bar with teeth on its edge to work with the teeth of a pinion which is to drive or follow it.
Ratchet.—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 only. It may be used for preventing backward motion in machinery or for converting reciprocating motion into forward motion.
Ratchet Drill.—A drill attached to a ratchet.
Ratchet Wheel.—A wheel having teeth by which it may be moved forward as by a lever and catch, or by a pawl arranged to engage the teeth. The pawl may also be arranged to engage the teeth for the purpose of preventing backward motion.
Reactance Coil.—See Choke Coil.
Reactive Drop.—The drop in potential caused through the presence of reactance in the circuit, as distinguished from that caused by ohmic resistance which is known as the ohmic drop.
Rectifier.—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 direction.
Relay.—A device actuated by an electric current to open or close another circuit.
Rheostat.—An adjustable resistance.
Rock Shaft.—A shaft that vibrates or oscillates instead of making complete revolutions. Called also rocker or rocking shaft.
Rotary Converter.—A rotating machine having a field excited by a direct current and an armature winding connected to a commutator and a set of collector rings. It is used to convert alternating current into direct, or vice versa; also called synchronous converter.
Rotor.—The moving part of an alternating-current generator or motor.
Secondary Battery.—A storage battery; an accumulator.
Secondary Coil.—The coil of a transformer or an induction coil into which currents are induced; the coil which is not connected to the source of energy.
Series Connection.—A connection in which a number of devices are joined so that the same current passes through all of them.
Series Multiple.—A system of wiring in which a number of devices are connected in multiple and several of such groups then connected in series. The same current must pass through each group.
Shaking Coil.—A coil used in connection with a mercury-arc rectifier for tilting or shaking the tube and starting the apparatus.
Shunt.—A by-pass. A wire which carries part or all of the current in a circuit around some other device connected in the circuit.
Single-Phase.—An alternating-current system using only two wires and only one e.m.f. It is sometimes termed uniphase or monophase.
Slip of Induction Motor.—The difference in the number of revolutions made by the revolving field and the rotor of the motor. It is usually expressed in per cent of the synchronous speed which is that of the revolving field.
Solenoid.—A round coil of wire generally used to control an iron core; an electromagnetic helix.
Spider.—A casting or part of a machine having projections or arms radiating from it so as somewhat to resemble a spider.
Spindle.—The revolving arbor of a machine tool; an axis.
Spiral Gear or Gearing.—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 axes. It is sometimes used in light machinery in place of bevel gearing.
Spiral Wheel.—A wheel having its teeth cut at an angle with its axis or so that they form small parts of screws or spirals.
Spline.—A rectangular piece fitting the key seats of a hub and shaft so that, while the one may slide endwise on the other, both must revolve together.
Spur Wheel.—A wheel in which the teeth are perpendicular to the axis and in the direction of the radii.
Static Electricity.—The name usually given to electricity generated by friction, as from belting in machine shops, etc.
Stator.—The stationary part of an alternating-current motor or generator.
Stay Bolt.—A bolt connecting opposite plates to keep them from bulging.
Stepdown Transformer.—A transformer used for reducing voltage.
Stepup Transformer.—A transformer used for increasing voltage.
Striking the Arc.—The act of bringing the carbons of an arc lamp together and immediately separating them and establishing the arc is called striking the arc.
Stud.—A projection of a bolt adapted to hold a lug or connection of some kind.
Stud Bolt.—A bolt with threads on both ends, to be screwed into a fixed part at one end and receive a nut upon the other.
Sustaining Coil.—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 anodes.
Swivel or Swivel Joint.—A joint, the two pieces of which can be turned around independently of each other.
Synchronism.—Being in time or occurring at the same time in regular order with some other event.
Synchronous Converter.—See rotary converter.
Tap Bolt.—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 nut.
Three-Phase.—Refers to a system of electrical distribution making use of three separate currents. These currents may be superimposed and generally only three wires are used in the transmission.
Thumb Screw.—A screw arranged so that it can be set up with the fingers. Similar to a wing nut.
Thumb Spot.—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 holder.
Travel Ghost.—The peculiar hazy appearance often seen in a motion picture; it is produced by the improper setting of the revolving shutter.
Trunnion.—Projection lugs on the sides of some piece of machinery upon which it is supported and upon which it can move.
Two-Phase.—This term refers to an a.c. system of electrical distribution making use of two currents of different phase. It may be arranged with three or four wires.
Unbalanced.—This term is used in connection with three-wire and three-phase systems.
The three-wire system is said to be unbalanced when one of the outside wires is carrying more current than the other.
The three-phase system is said to be unbalanced when the load is unevenly distributed over the three-phase wires.
Universal Joint.—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 angle.
Volt.—The unit of electromotive force.
Voltmeter.—An instrument used for measuring potential difference.
Water Rheostat.—A resistance in which water is used to carry the current. 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 increased.
Watt.—The unit of power.
Wattless Current.—That part of an alternating current which is either ahead of or behind the e. m. f. of the circuit.
Watt Meter.—An instrument used for measuring electrical energy.
Yoke.—A clamp resembling an ox yoke somewhat and adapted to join two pieces of a machine.