Chapter I: II (1)

Palladium, 60 to 75 parts 50 to 75 parts Copper, I5 to 25 " 20 to 30 " Iron. 1 to 5 " 5 to 20 "

401 STANDARD ELECTRICAL DICTIONARY.

The following are more complex: I. II. Palladium, 65 to 75 parts 45 to 50 parts Copper, 15 to 25 " 15 to 25 " Nickel, 1 to 5 " 2 to 5 " Silver, 3 to 10 " 20 to 25 " Gold, 1 to 2-1/2 " 2 to 5 " Platinum, 1/2 to 2 " 2 to 5 " Steel, 1 to 5 " 2 to 5 "

These alloys are used for balance springs, as well as for the balance wheels and escapement parts of watches. The elasticity of recently produced springs has been found to be very satisfactory.

Page Effect. The sounds produced by magnetizing and demagnetizing a bar of iron or steel; the magnetic tick. The sounds are strong enough to produce a telephonic effect. (See Magnetic Tick.)

Palladium. A metal of the platinum series. It has the highest power of occlusion, q.v., of all metals. It is the characteristic ingredient of non-magnetic watch alloys.

Palladium used as an electrode in the electrolysis of water will occlude 936 volumes of hydrogen, and the hydrogen-palladium alloy will exceed in size the original electrode.

Fig. 255. LUMINOUS PANE.

Pane, Luminous. A pane of glass, one side of which has pasted to it a long zigzag strip of tinfoil. A design is made by cutting through the strip. On discharging a Leyden jar or an electric machine through the strip sparks appear where the tinfoil is severed, thus producing the design in a luminous effect. Many variations can be employed in their construction.

402 STANDARD ELECTRICAL DICTIONARY.

Pantelegraphy. A system of telegraphy for transmitting designs, maps, drawing, and the like by telegraphy. (See Telegraphy, Facsimile.)

Paper Filaments. Filaments of carbon for incandescent lamps made from paper.

This is one of the earliest materials practically used. The paper is cut out of proper shape, and is carbonized in a close vessel, while embedded in powdered charcoal or some other form of carbon to absolutely cut off access of air. It is then placed in the lamp chamber and flashed or subjected to the regular treatment.

Parabola. A curve; one of the conic sections. It is approximately represented by a small arc of a circle, but if extended becomes rapidly deeper than a half circle.

If, from a point within called the focus, lines are drawn to the curve and then other lines are drawn from these points parallel to the axis, the angles of incidence will he equal to the angles of reflection as referred to tangents at the points where the lines touch the curve.

[Transcriber's note; The general equation of a parabola is A*x^2 + B*x*y + C*y^2 + D*x + E*y + F = 0 such that B^2 = 4*A*C, all of the coefficients are real, and A and C are not zero. A parabola positioned at the origin and symmetrical on the y axis is simplified to y = a*x^2 ]

Parabolic Reflector. A reflector for a light, a paraboloid or surface of revolution whose section is a parabola. A light placed at its focus has its rays reflected parallel to each other.

Examples of parabolic reflectors are seen in electric search lights and in locomotive head-lights. They are employed in electric search lights. The arc light must be of such construction as to maintain its ignited points always at the same point, the focus of the paraboloid.

Paraffine. v. To coat or saturate with paraffine wax. Paper may be paraffined by dipping in the wax, or by being sprinkled with fragments of wax, subsequently melted in with a hot iron or otherwise. The tops of battery carbons are often paraffined to prevent the acid from rising in the pores by capillary attraction and rusting the connections.

403 STANDARD ELECTRICAL DICTIONARY.

Paraffine Wax. A hydro-carbon composed principally of mixtures of the higher members of the paraffine series C n H2 n + 2. It is made from cannel coal, coal tar, or petroleum by distillation. It is an insulator. Its resistance at 46° C. (114.8° F.) per centimeter cube is 3.4E16 ohms, or about the highest resistance known.

Its specific inductive capacity (for milky wax) is 2.47 (Schiller). For
clear wax it is given as follows by different authorities:
1.92 Ayrton.
1.96 Wüllner.
1.977 Gibson & Barclay.
2.32 Baltzmann.

It is extensively used in condensers and other electric apparatus as a dielectric and insulator.

Paragrêles. Protectors against hail; lightning rods used to guard fields against hail; of little or no real utility.

Parallax. The apparent change in position of an object when looked at from two points of view. By looking at an object a few feet distant first with one eye and then with the other, the shifting in apparent position is seen.

In reading the position of an indicator or needle over a scale parallax introduces an error unless the eye is held vertically over the needle. By making the dial of looking- glass and holding the eye so that the reflection of its pupil is bisected by the needle this verticality is ensured.

Parallel. (a) In the nomenclature of electric circuits two or more conductors leading from one point to another, are said to be in parallel.

(b) When two or more conductors connect two main leads of comparatively large size and low resistance they are said to be in parallel or in multiple arc. This order is easiest pictured as the rungs of a ladder in parallel connecting its two sides representing the main leads.

It may be used as a noun as "arranged in parallel," or as an adjective as "a parallel circuit," the opposite of series, q. v.

Paramagnetic. adj. Possessing paramagnetic properties; tending to occupy a position with the longer axis parallel to the lines of force of a magnetic field; having magnetism; attracted by a magnet.

"If a homogeneous isotropic substance is placed in a magnetic field it becomes magnetized at every point in the direction of the magnetic intensity at that point, and with an intensity of magnetization proportional to the magnetic intensity. When the positive direction of the induced magnetization is the same as that of the magnetic intensity the substance is called Magnetic or Paramagnetic; when it is opposite, the substance is called Diamagnetic." (Emtage.)

A paramagnetic substance has high permeability or multiplying power for lines of force, hence in a magnetic field a bar of iron, etc., is in unstable equilibrium unless its longer axis is parallel with the lines of force in order to reduce as much as possible the reluctance of the circuit.

404 STANDARD ELECTRICAL DICTIONARY.

Iron is the most paramagnetic of all substances. Other paramagnetic metals are: Nickel, cobalt, manganese, platinum, cerium, osmium, palladium. Diamagnetic metals are bismuth, antimony, zinc, tin, mercury, lead, silver, copper, gold, arsenic. Bismuth is the most diamagnetic of all metals.

Of gases oxygen is most paramagnetic. Becquerel calculated that a cubic yard of oxygen condensed would act on a magnetic needle as powerfully as 5.5 grains of metallic iron. Liquefied oxygen will adhere to the poles of a magnet.

Changes of temperature and of other conditions may affect a body's magnetism. Thus hot oxygen is diamagnetic, and a substance paramagnetic in a vacuum may be diamagnetic in air.

Of liquids, solutions of iron or cobalt are paramagnetic; water, blood, milk, alcohol, ether, oil of turpentine and most saline solutions are diamagnetic.

Paramagnetism. (a) The science or study of paramagnetic substances and phenomena.

(b) The magnetic property of a paramagnetic substance; that of being attracted by a magnet, and of arranging itself with its longer axis parallel with the lines of force of a magnetic field.

Parchmentizing. If cellulose is treated with a mixture of two parts of sulphuric acid and one part of water perfectly cold, it becomes like parchment. It should at once be washed with water, and then with ammonia and water. The Swan incandescent light fibres are made of parchmentized cotton thread, which is afterward carbonized.

Partial Earth. A fault in a conductor caused by imperfect connection with the earth, where insulation from the earth is desired.

Passive State. A state of a substance in virtue of which it is unattacked by a solvent which ordinarily would dissolve or attack it. Iron in strong nitric acid is unattacked or assumes the passive state. This particular case is supposed to be due to a coating of magnetic oxide, so that there would be properly speaking no question of a passive state, but only one of superficial protection.

The existence of a true passive state of any substance is very doubtful.

P. D. Abbreviation for potential difference or difference of potential, or for electro-motive force.

405 STANDARD ELECTRICAL DICTIONARY.

Peltier Effect. The thermal effect produced by the passage of a current through the junction of two unlike conductors. Such junction is generally the seat of thermo-electric effects, and a current is generally produced by heating such a junction. If an independent current is passed in the same direction as that of the thermoelectric current, it cools the junction, and warms it if passed in the other direction. In general terms, referring to thermo-electric couples, if passed through them it tends to cool the hot and heat the cool junction. The phenomenon does not occur in zinc-copper junctions.

Peltier's Cross. A bar of bismuth and a bar of antimony soldered centre to centre at right angles, being notched or halved there to receive or to set into each other. It is used to demonstrate the Peltier effect, q. v. To one pair of ends are connected the terminals of a battery circuit; to the other pair are connected the terminals of a galvanometer.

The galvanometer by its deflections in one and then in the other direction indicates that the junction is heated when the current passes from antimony to bismuth and vice versa. It thus illustrates the heating and cooling of a thermo-electric junction by a current of electricity. The current from the battery by the Peltier effect either heats or cools the junction, as the case may be. This heating or cooling them produces a thermo-electric current in the galvanometer circuit. The battery has no direct influence on the galvanometer.

Pendant Cord. A double conductor or pair of conductors, insulated from each other and covered with a worsted, silk, or cotton covering and used to suspend incandescent lamps and at the same time to conduct the current to them. It is also used for other similar service, such as acting as conductors for small motors. Often each conductor is composed of a number of thin wires laid together. This gives flexibility to the cord.

Synonym--Flexible Cord.

Pendulum, Electric. (a) A pendulum operated by the intermittent action of an electro-magnet, whose circuit is opened and closed by the pendulum itself. A point at the lower end of the pendulum swinging through a globule of mercury may close and open the circuit. Various other methods of accomplishing the same end are employed ..

(b) A pith ball suspended by a thread from an insulating stand. It is used to show the attraction exercised by a piece of sealing wax or other substance excited by rubbing.

406 STANDARD ELECTRICAL DICTIONARY.

Pen, Electric. A stylus for producing a series of perforations in paper, so that the paper may act as a stencil for the reproduction of a great number of copies of the original matter. Various kinds of electric pens have been invented. One kind, invented by Edison, consists of a handle carrying an electric motor actuating a needle, which is driven in and out of the other end of the handle with high rapidity. It is used by being held vertically on the paper with the needle end downward, and is moved so as to describe perforated letters or designs. The paper is then used as a stencil with an ink roller to reproduce the writing or design ad libitum. A simpler kind dispenses with the motor and depends on the perforations produced by the electric spark. As shown in the cut the stylus is one terminal of an induction coil circuit. The support on which the paper rests is the other terminal and must be a conductor. In use the induction coil is started, and the stylus is moved over the paper; a series of sparks pass through the paper from stylus to the supporting tablet, perforating the paper and producing a stencil to be used for reproduction.

Fig. 256. ELECTRIC PEN.

Pentane Standard, Harcourt's. A standard of illuminating power; in it the combustible substance is a gas made by mixing one cubic foot of air with three cubic inches of liquid pentane, measured at 60° F. or, if measured as gases, 20 volumes of air to 7 of pentane. It is burned at the rate of 0.5 cubic foot per hour from a cylindrical tube one inch in diameter, closed at the top by a disc 0.5 inch thick with a hole 0.25 inch in diameter, through which the gas issues. It gives a flame 2.5 inches high.

The pentane used is the distillate of petroleum which boils at 50° C. (122° F.) ; it has a specific gravity at 15° C. (60° F.) of from 0.628 to 0.631. It is almost pure pentane (C5H12).

As long as the rate of consumption is between 0.48 and 0.52 cubic foot per hour the flame gives practically the same light.

407 STANDARD ELECTRICAL DICTIONARY.

Perforator. An apparatus used in automatic high speed telegraphy for perforating strips of paper. These are then used by drawing between a roller and contact spring for making and breaking the telegraphic circuit for the production of a record, such as the Morse record, at the distant receiving station.

The perforated strip has different classes of holes punched in it to represent dots or dashes. It is fed by machinery very rapidly, so that the message is transmitted with the highest speed. Several operators may simultaneously prepare the paper strips, and thus in conjunction with its rapid feeding in the transmitter, far surpass the time of ordinary direct transmission.

Fig. 257. PERFORATOR FOR WHEATSTONE'S AUTOMATIC TELEGRAPH.

Perforators may be entirely mechanical but are sometimes pneumatic, compressed air being used to operate them. The holes they make are on different levels of the paper strip, as shown in the cut.

Period. The time required for the completion of one complete element of periodic motion. This may be a complete alternation (See Alternation, Complete) of an alternating current, or of an oscillatory discharge.

Periodicity. The rate of succession of alternations or of other fixed phases; the rate of recurrence of phenomena.

408 STANDARD ELECTRICAL DICTIONARY.

Permanency. In electric current conductors the property of possessing conductivity unaffected by lapse of time. Generally the permanency of conductors is very high. In some cases a slow annealing takes place which causes a gradual change with the lapse of time. Annealed German silver wire has been found to increase in conductivity at about .02 per cent. in a year. (Matthiessen.) Wire, whether annealed or not, is left in a strained condition after the drawing operations, and such a change is consonant with this fact. The figure only applies to the samples tested by Matthiessen.

Permanent State. In a telegraph line or other current conductor, the condition when a uniform current strength obtains over the whole line. When a current is started it advances through the line with a sort of wave front gradually increasing in strength. At the further end some time may elapse before it attains its full intensity. When its does the permanent state prevails. Until then the variable state, q. v., exists in the line.

Permeameter. An apparatus for determining the permeability of samples of iron. It consists of a large slotted block of iron. A coil is placed within the slot. A hole is drilled through one end, and a rod of the iron to be tested is passed through this hole and through the coil to the bottom of the slot. The lower end of the rod must be accurately faced off. The current is turned on, upon which the rod adheres to the bottom of the slot. The force required to detach it is determined with a spring balance. The permeation through its face is proportional to the square of the force required.

Fig. 258. PERMEAMETER.

Permeance. The multiplying or the conducting power for magnetic lines of force possessed by a given mass of material. It varies with the shape and size of the substance as well as with the inducing force. It is distinguished from permeability, as the latter is a specific quality proper to the material, and expressed as such; the permeance is the permeability as affected by size and shape of the object as well as by its material.

409 STANDARD ELECTRICAL DICTIONARY.

Pflüger's Law. A law of electro-therapeutics. It states that stimulation of a nerve is only produced by successive appearance of the kathelectrotonic state, and disappearance of the anelectrotonic state.

Phantom Wires. The extra transmission circuits obtained in multiplex telegraph systems. A single line arranged for four separate simultaneous transmissions by quadruplex apparatus is said to establish three phantom wires.

Phase. In wave motion, oscillating motion, simple harmonic motion, or similar periodic phenomena, the interval of time passed from the time the moving particle moved through the middle point of its course to the instant when the phase is to be stated.

Pherope. An apparatus for the electric transmission of pictures. (See Telephote.)

[Transcriber's note: Precursor of the contemporary Fax and scanner.]

Philosopher's Egg. An ellipsoidal vessel mounted with its long axis vertical and with two vertical electrodes, the upper one sliding, and arranged to be attached to an air pump. A discharge through it when the air is exhausted takes the general shape of an egg.

Phonautograph. An apparatus for registering the vibrations of a stylus, which is mounted on a diaphragm and is acted on by sound waves.

It is virtually a resonating chamber, over one of whose ends a parchment diaphragm is stretched. To the centre of the parchment a needle or stylus is attached. A cylinder covered with soot is rotated in contact with the point of the stylus. As the chamber is spoken into the diaphragm and stylus vibrate and the vibrations are marked on the cylinder. It is of some electric interest in connection with telephony.

Phone. Colloquial abbreviation for telephone.

Phonic Wheel. A form of small motor of very simple construction. It consists of a toothed wheel of soft iron. A bar electro-magnet is fixed with one pole facing the teeth of the wheel. By a tuning fork make and break a succession of impulses of rapid frequency and short duration are sent through the magnet. The teeth act as armatures and are successively attracted by the magnet. The regulated speed is one tooth for each impulse, but it may rotate at one-half the speed, giving two teeth for each impulse, or at certain other sub-multiples of its regular speed. It is the invention of Paul Lecour.

410 STANDARD ELECTRICAL DICTIONARY.

Phonograph. An apparatus for reproducing articulate speech. It is not electric, except as it may be driven by electricity.

It consists of a cylinder of wax-like material which is rotated and moved slowly, longitudinally, screw fashion, at an even speed. A glass diaphragm carrying a needle point is supported with the point barely touching the wax. If the diaphragm is agitated, as by being spoken against, the needle is driven back and forwards cutting a broken line or groove following the direction of the thread of a screw in the wax, the depth of which line or groove continually varies.

This imprints the message. If the needle is set back and the cylinder is rotated so as to carry the needle point over the line thus impressed, the varying depth throws the needle and diaphragm into motion and the sound is reproduced.

The cylinder is rotated often by an electric motor, with a centrifugal governor.

[Transcriber's note; Due to T. A. Edison, 1877, fifteen years before this book.]

Phonozenograph. An apparatus for indicating the direction of the point where a sound is produced. It operates by a microphone and telephone in conjunction with a Wheatstone bridge to determine the locality.

Phosphorescence. The emission of light rays by a substance not heated, but whose luminosity is due to the persistence of luminous vibration after light has fallen upon it.

A phosphorescent body, after exposure to light, is luminous itself. Phosphorescence may be induced by rubbing or friction, by heat, by molecular bombardment, as in Crookes' tubes, and by static discharge of electricity, as well as by simple exposure to light.

Another form of phosphorescence may be due to slow chemical combustion. This is the cause of the luminosity of phosphorous.

Phosphorous, Electrical Reduction of. Phosphorous is reduced from bone phosphate by the heat of the electric arc. The phosphate mixed with charcoal is exposed to the heat of the voltaic are, and reduction of the phosphorous with its volatilization at once ensues. The phosphorous as it volatilizes is condensed and collected.

Photo-electricity. The development of electrical properties by exposure to light. Crystals of fluor spar are electrified not only by heat (see Pyro-electricity) but also by exposure to sunlight or to the light of the voltaic arc.

[Transcribers note: Although first observed in 1839 by Becquerel, it was not explained until 1905 by Albert Einstein with the introduction of photons.]

Photo-electric Microscope. A projection, solar or magic-lantern microscope worked by the electric light.

Photo-electro-motive Force. Electro-motive force produced in a substance by the action of light.

411 STANDARD ELECTRICAL DICTIONARY.

Photometer. An apparatus for measuring the intensity of light emitted by a given lamp or other source of illuminating power. They may be classified into several types.

Calorimetric or Heat Photometers act by measuring relatively the heat produced by the ether waves (so-called radiant heat) emitted by the source. The accuracy of the instrument is increased by passing the rays through an alum solution. A thermopile, or an air thermometer, may be used to receive the rays.

Chemical Photometers. In these the light falls upon sensitized photographic paper. The depth of coloration is used as the index of illuminating power.

Direct Visual Photometers. These include Rumford's Shadow Photometer, Bunsen's Bar Photometer, and Wheatstone's Bead Photometer, in which the light is estimated by direct visual comparison of its effects.

Optical Photometers. These include Polarization Photometers, in which the light is polarized; Dispersion Photometers, in which a diverging lens is placed in the path of the rays of light so as to reduce the illuminating power in more rapid ratio than that of the square of the distance.

Selenium Photometers, in which the variations in resistance of selenium as light of varying intensity falls upon it is used as the indicator of the intensity of the light.

Jet Photometers, for gas only, in which the height of a flame under given conditions, or the conditions requisite to maintain a flame of given height, is used to indicate the illuminating power.

The subject of photometers has acquired more importance than ever in view of the extensive introduction of the electric light. (See Candle, Standard--Carcel--Violé's Standard--and Photometers of various kinds.)

Photometer, Actinic. A photometer whose registrations are produced by the action of the light being tested upon sensitized paper or plates, such as used in photography. Some efforts at self-registering photometers have been based on actinic registration of the height of a flame of the gas to be tested.

Photometer, Bar. A photometer in which the two lights to be compared are fixed at or opposite to the ends of a bar or scale of known length, generally 60 or 100 inches. The bar is divided by the rule of the inverse square of the distances, so that if a screen is placed on any part of the bar where it receives an equal amount of light from both sources, the figure on the bar will indicate the relative illuminating power of the larger lamp or light in terms of the smaller. The divisions of the bar are laid out on the principle that the illuminating power of the two sources of light will vary inversely with the square of their distance from the screen.

412 STANDARD ELECTRICAL DICTIONARY.

The screen used is sometimes the Bunsen disc. This is a disc of paper with a spot of paraffine wax in the centre melted thoroughly into the paper or with a ring of paraffine wax surrounding the untouched centre. When this disc is equally illuminated on both sides the spot is nearly invisible. Inequality of illumination brings it out more visibly. Sometimes a Leeson disc is used. This consists of three pieces of paper, two thin ones between which a thicker piece, out of which a star is cut, is laid. When equally illuminated on both sides the star appears equally bright on both sides.

The bar photometer is the standard form. A candle or pair of candles may be burned at one end and an incandescent lamp at the other, or a gas flame may first be rated by candles and used as a standard.

Synonyms--Bunsen's Photometer--Translucent Disc Photometer.

Fig. 259. BAR PHOTOMETER.

Photometer. Calorimetric. A photometer in which the radiant energy, so called radiant heat, is used as the measurer of the light.

In one type a differential air thermometer is used, one of whose bulbs is blackened. On exposing this bulb to a source of light it will become heated, and if lights of the same character are used the heating will be in proportion to their illuminating power quite closely. The heating is shown by the movements of the index. By careful calibration the instrument may be made quite reliable.

Photometer, Dispersion. A photometer in which the rays from one of the lights under comparison are made more divergent by a concave lens. In this way a strong light, such as all arc lamp can be photometered more readily than where only the natural divergence of the beam exists. The law of the variation of the intensity of light with the square of the distance is abrogated for a law of more rapid variation by the use of a concave lens.

The diagram, Fig. 260, illustrates the principle. E represents a powerful light, an arc light, to be tested. Its distance from the screen is e. Its light goes through the concave lens L and is dispersed as shown over an area A1, instead of the much smaller area A, which the same rays would otherwise cover. Calling l the distance of the lens from the screen, f its focus, and c the distance of the standard candle from the screen when the shadows are of equal intensity, we have the proportion.

Illuminating power of lamps: ditto of standard candle:: (l (e-l) + fe)2 : (c f)2

413 STANDARD ELECTRICAL DICTIONARY.

Fig. 260. DIAGRAM OF PRINCIPLE OF THE DISPERSION PHOTOMETER.

The cut, Fig. 261, gives a perspective view of Ayrton's Dispersion Photometer. C is the standard candle, L the concave lens, R the rod for producing the two shadows on the screen S.

Fig. 261. AYRTON'S DISPERSION PHOTOMETER.

The mirror M is fixed at an angle of 45° with the stem on which it rotates. The light of the arc lamp is received by the mirror and is reflected through the lens. The candle holder slides along a graduated bar C, and at D is an index plate to show the angle at which the spindle carrying the mirror is set.

414 STANDARD ELECTRICAL DICTIONARY.

Dr. J. Hopkinson in his dispersion photometer uses a double convex lens. This gives a focal image of the arc-lamp between the lens and screen, whence the rays diverge very rapidly, thus giving the desired dispersion effect.

It is principally for arc lamps that dispersion photometers are used.

Photometer, Shadow. A photometer in which the relative intensity of the two lights is estimated by the intensity or strength of shadows of the same object which they respectively cast.

Fig. 262. RUMFORD'S SHADOW PHOTOMETER.

Fig. 263. RUMFORD'S SHADOW PHOTOMETER ARRANGED FOR TESTING INCANDESCENT LAMPS.

415 STANDARD ELECTRICAL DICTIONARY.

A rod is supported in a vertical position. Back of it is a screen of white paper. The two lights to be compared are arranged in front of the rod and at a little distance from each other. They are shifted about until the two shadows appear of equal darkness. The relative intensity of the lights varies inversely with the square of their distances from the shadows cast respectively by them on the screen.

The cut, Fig. 262, shows the simplest type of the shadow photometer. In the cut, Fig. 263, a shadow photometer for testing incandescent lamps is shown. In it E is the lamp under trial supported by a clamp H. A is an ampere meter in circuit with the lamp, and V is a voltmeter. A candle C can be moved along a graduated scale G G. R is the vertical rod, and S is the screen on which the shadows fall.

Photophore. An instrument for medical examination of the cavities of the body. It includes an incandescent lamp mounted in a tube with a concave mirror and convex lens.

Photo-voltaic Effect. The change in resistance of some substances effected by light. Selenium, of all substances, is most susceptible to this effect. (See Selenium.)

Piano, Electric. A piano whose manual or key-board operates to close electric circuits, whereby electro-magnets are caused to operate to drive the hammers against the strings.

Pickle. An acid solution for cleaning metal surfaces before electro-plating, galvanizing or other deposition of metal upon them.

Picture, Electric. A picture produced by passing a strong discharge through a piece of gold leaf clamped or firmly pressed upon a sheet of paper. The gold leaf is cut out of the desired shape, or else a stencil of paper overlays it. The discharge dissipates the gold, and produces a purple colored reproduction of the design upon the paper. The design is due to the deposition of an exceedingly thin film of metallic gold.

Synonym--Electric Portrait.

Pile. A galvanic or voltaic battery. It is sometimes restricted to a number of voltaic couples connected. It should be only applied to batteries with superimposed plates and no containing vessel such as the Dry Pile, q. v., or Volta's Pile, q. v.

Pilot Transformer. In alternating current distribution a small transformer placed at any part of the system and connected to a voltmeter in the central station, to indicate the potential difference of the leads.

Pilot Wires. Wires brought from distant parts of electric light or power mains, and leading to voltmeters at the central station, so that the potential of distant parts of the system can be watched. The wires can be very small, as they have but little current to transmit.

416 STANDARD ELECTRICAL DICTIONARY.

Pistol, Electric. An experimental apparatus for exhibiting the power of electric incandescence or of the electric spark. A tube is mounted with a handle like a pistol. A plug is provided to screw in and out of its side. The plug carries two wires connected on its inner side by a fine platinum wire, or else disconnected but with their ends brought near together to act as terminals for the production of a spark. To use it the tube is filled with a mixture of air and gas, the latter either hydrogen, hydro-carbon or other combustible gas. The tube when full is corked. The wire is heated to incandescence by a current, or a spark is passed from a Leyden jar or other source of electrostatic excitation. The mixture, if properly proportioned, explodes and expels the cork violently.

Fig. 264. ELECTRIC PISTOL.

Pith. A light and soft cellular tissue forming the central core of exogenous trees and plants. In the older parts of the tree the woody tissue often encroaches in and partly obliterates it.

For electrical pith-balls, the pith of the elder, of corn, or, best of all, of sun-flower stems is used.

Pith-balls. Ball made of pith. They are used in the construction of electroscopes and for other experiments in static electricity.

They are cut out with a sharp knife and their shape may be improved by gentle rolling in the hand or between the fingers.

Pivot Suspension. Suspension poising or supporting of an object on a sharp pivot. This is used for the needle in the ordinary compass. A cavity or inverted cup, which may be made of agate, is attached to the middle of the needle which has a hole for its reception. The centre of gravity of the needle comes below the bottom of the cup.

Pivot suspension is not perfect, as it has considerable friction. There is no restitution force, as with torsion filaments.

417 STANDARD ELECTRICAL DICTIONARY.

Plant. The apparatus for commercial manufacturing or technical works. An electric lighting plant includes the boilers, engines and dynamos for producing the current, and the electric mains and subsidiary apparatus.

Plant Electricity. Electricity manifested by plant life. By means of a galvanometer potential differences are found to exist in different parts of trees or fruits. The roots and interior portions are negative, and the flowers, smaller branches and fruit are positive.

In some cases a contraction of the tissue of plants can be produced by an electric current. The sensitive plant and others exhibit this phenomenon, exactly analogous to the action of muscular tissue.

Plate, Arrester. In a lightning arrester the plate connected to the circuit. Sometimes both plates are designated arrester plates.

Plate Condenser. A static condenser having a flat plate of glass for dielectric. (See Epinus' Condenser.)

Plate Electrical Machine. A frictional electric machine, in which a circular plate of glass is excited by friction with the cushions. It is the most recent type of frictional machine and has superseded the old cylinder machines. In its turn it is superseded by influence machines, really plate machines, but not so termed in practice.

Plate, Ground. In a lightning arrester, the plate connected to the earth.

Plate, Negative. In a voltaic battery, either primary or secondary, the plate which is unattacked by the oxygen or negative radical or element of the fluid. It corresponds to the carbon plate in the ordinary voltaic battery, and is the one charged with positive electricity.

Plate, Positive. In a voltaic battery, either primary or secondary, the plate which is dissolved or attacked by the oxygen or negative radical or element of the fluid. It is the plate corresponding to the zinc plate in the ordinary voltaic battery, and is the one charged with negative electricity.

Plating Balance. A balance or scales to which articles in an electroplater's bath are suspended. A weight exceeding by a known amount that of the article as immersed overbalances the article. When the plating is being deposited as soon as it exceeds the excess of weight of the counterpoise the balance tips, the article descends a little, the electric circuit is broken and the plating ceases. Thus the plating is automatically stopped when a predetermined amount of metal is deposited.

418 STANDARD ELECTRICAL DICTIONARY.

Plating Bath. A vessel of solution for the deposition of metal by electrolysis as used in electro-plating.

Plating, Electro-. The deposition of metal by electrolysis so as to coat the conducting surface of objects therewith. The full details of the many processes are very lengthy and cannot be given here.

The general principle includes a battery or source of electric current. The object to be plated is connected to the negative terminal and is immersed in the solution. Thus with a battery the object is in electrical connection with the zinc plate. To the other terminal a metallic plate is connected. The object and the plate termed the anode being introduced into a suitable bath, the metal whose solution is in the bath is deposited upon the surface of the object.

The bath is a solution of the metal in some form that will lend itself to the electrolytic action. The anode is often a plate of the metal of the bath, so that it dissolves as fast as metal is deposited on the object, thus keeping up the strength of the solution.

The objects to be plated must be scrupulously clean, and great care must be taken to keep the bath uncontaminated.

When the object has a non-conducting surface, it is made conducting by being brushed over with plumbago q.v. In addition iron dust is sometimes dusted over it. This acts by precipitating the metal of the bath directly and thus giving a conducting basis for the metal to deposit on. To avoid getting iron in a bath the object may be dipped in copper sulphate solution. This precipitates copper in place of the iron and leaves the article in good shape for silver or other plating.

Electro-plating, if made thick enough, gives a reverse of the article when separated therefrom. A direct copy can be got by a second plating, on the first plating after separation, or a wax impression can be employed.

Under the different metals, formulae for the baths will be found. (See also Quicking-- Steeling--Plating Balance.)

Platinoid. An alloy of copper, nickel, zinc in the proportions of German silver with 1 or 2 per cent of tungsten. It is used for resistances. It has a specific resistance (or resistance per centimeter cube) of about 34 microhms. Its percentage variation in resistance per degree C. (1.8° F.) is only about .021 per cent., or less than half that of German silver. This is its most valuable feature.

419 STANDARD ELECTRICAL DICTIONARY.

Platinum.
A metal; one of the elements; symbol, Pt; atomic weight, 197.4;
equivalent, 49.35; valency, 4; specific gravity, 21.5.
It is a conductor of electricity.
The following data refer to the annealed metal at 0° C. (32° F.)
Relative Resistance (Silver annealed = 1), 6.022
Specific Resistance, 9.057 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 2.779 ohms.
(b) 1 foot long, 1/1000 inch thick, 54.49 "
(c) 1 meter long, weighing 1 gram, 1.938 "
(d) 1 meter long, 1 millimeter thick, .1153 "
Resistance of a 1 inch cube, 3.565
Electro-chemical equivalent (Hydrogen = .0105), 0.5181.

The coefficient of expansion by heat is almost the same as that of glass. It can be passed through holes in glass and the latter can be melted about it so as to hermetically seal its place of passage through the glass. It is used in incandescent lamps for leading-in wires and other similar uses.

Platinum Black. Finely divided platinum. It is made by boiling a solution of platinic chloride with excess of sodium carbonate and a quantity of sugar, until the precipitate is perfectly black and the supernatant liquid is colorless. It seems to possess a great power of occluding oxygen gas. When heated to redness it becomes spongy platinum. The negative plates of a Smee battery are coated with platinum black.

Platinum-silver Alloy. An alloy of 1 part platinum and 2 parts silver, used for resistance coils.

Relative Resistance (silver annealed = 1 ), 16.21 microhms.
Specific Resistance at 0°C. (32° F.), 24.39
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 4.197 ohms.
(b) 1 foot long, 1/1000 inch diameter, 146.70 "
(c) 1 meter long weighing 1 gram, 2.924 "
(d) 1 meter long, 1 millimeter diameter, 0.3106 "
Resistance of a 1 inch cube, 9.603 microhms.
Percentage Variation per degree C. (1.8° F.)
at about 20° C. (68° F.), 0.031 per cent.

Synonym--Platinum Alloy.

Platinum Sponge. Finely divided platinum obtained by igniting platinum black, q.v., and also by igniting salts of platinum. It has considerable power of condensing or occluding oxygen. It will, if in good condition, set fire to a jet of hydrogen impinging upon it.

Plow. Contact arms projecting downwards from the motors, trucks, or bodies of electric street cars, which enter the underground conduit through the slot and carry contact pieces or brushes, to take the current for driving the motors from the leads within the conduit.

420 STANDARD ELECTRICAL DICTIONARY.

Plücker Tubes. A special form of Geissler tube designed for the production of stratification and for observing the effects produced in the space surrounding the negative electrode.

Plug. (a) A piece of metal with a handle and a somewhat tapered end, used to make connections by insertions between two plates or blocks of metal slightly separated and with grooves to receive it.

(b) A plug or wedge with two metallic faces, insulated from each other with a separate wire connected to each one. It is used in spring-jacks q. v., to introduce a loop in a circuit.

Synonym--Wedge.

Plug. v. To connect by inserting a plug, as in a resistance box.

Fig. 265. PLUGS FOR RESISTANCE COIL BOX.

Fig. 266. PLUG SWITCH.

Plug, Double. A spring-jack plug or wedge with two pairs of insulated faces, one behind the other, so as to simultaneously introduce two loops into a circuit.

Plug, Grid. A piece or mass of lead oxide, inserted into the holes in the lead plates of storage batteries. The holes are often dovetailed or of uneven section to better retain the plugs.

Plug Infinity. In a box-bridge or resistance box, a plug whose removal from between two disconnected discs opens the circuit. All the other discs are connected by resistance coils of various resistance.

Plug Switch. A switch composed of two contact blocks, not touching each other and brought into electrical connection by the insertion of a metallic plug. The latter is usually provided with an insulating handle, and a seat is reamed out for it in the two faces of the contact blocks.

421 STANDARD ELECTRICAL DICTIONARY.

Plumbago. Soft lustrous graphite, a native form of carbon; sometimes chemically purified. It is used in electro-plating to give a conducting surface to non-conducting objects, such as wax moulds. The surface, after coating with plumbago, is sometimes dusted over with iron dust, which precipitates the metal of the bath and starts the plating. It is sometimes plated with copper, silver or gold, and is then termed coppered, silvered, or gilt plumbago. It is gilded by moistening with etherial solution of gold chloride and exposing to the air, and drying and igniting.

Plunger. A movable core which is used in connection with a so-called solenoid coil, to be drawn in when the coil is excited. (See Coil and Plunger.)

Fig. 267 COIL AND PLUNGER WITH SCALES TO SHOW ATTRACTION.

P. O. Abbreviation for Post Office, q.v.

Poggendorf's Solution. An acid depolarizing and exciting fluid for zinc-carbon batteries. The following is its formula: Water, 100 parts; potassium bichromate, 12 parts; concentrated sulphuric acid, 25 parts. All parts by weight. Use cold.

Point, Neutral. (a) On a commutator of a dynamo the points at the ends of the diameter of commutation, or where the brushes rest upon the surface of the commutator, are termed neutral points. At these points there is no generation of potential, they marking the union of currents of opposite direction flowing from the two sides of the armature into the brushes.

(b) In electro-therapeutics, a place in the intra-polar region of a nerve so situated with reference to the kathode and electrode as applied in treatment, that its condition is unaffected.

Synonym--Indifferent Point.

(c) In a magnet the point of no attraction, situated between the two poles, at about an equal distance from each, so as to mark the centre of a magnet of even distribution of polarity.

(d) In thermo-electricity the point of temperature where the thermo-electric powers of two metals are zero; in a diagram the point where the lines representing their thermo-electric relations cross each other; if the metals are arranged in a thermo-electric couple, one end at a temperature a given amount above, the other at a temperature the same amount below the neutral point, no current or potential difference will be produced.

422 STANDARD ELECTRICAL DICTIONARY.

Point, Null. A nodal point in electrical resonators; a point where in a system of waves or oscillations, there is rest, the zero of motion being the resultant of oppositely directed and equal forces. In electrical resonators it is to be sought for in a point symmetrically situated, with reference to the spark gap, or in a pair of points, which pair is symmetrically placed.

The null point in resonators is found by connecting a lead from one of the secondary terminals of an induction coil to different parts of the resonator. The null point is one where the connection does not give rise to any sparks between the micrometer knobs or spark gap, or where the sparks are of diminished size.

The whole is exactly comparable to loops and nodes in a vibrating string or in a Chladni plate as described in treatises on sound and acoustics. (See Resonance, Electrical--Resonator, Electrical.)

Synonym--Nodal Point.

Point Poles. Magnet poles that are virtually points, or of no magnitude. A long thin magnet with little leakage except close to the ends may be supposed to have point poles within itself a short distance back from the ends.

Points, Consequent. In a magnet with consequent poles, the points where such poles are situated.

Points, Corresponding. In bound electrostatic charges the points of equal charges of opposite potentials; the points at opposite extremities of electrostatic lines of force. This definition implies that the bound charges shall be on equal facing areas of conductors, as otherwise the spread or concentration of the lines of force would necessitate the use of areas of size proportionate to the spreading or concentrating of the lines of force. At the same time it may figuratively be applied to these cases, the penetration of the surface by a single line of force including the area fixed by its relation to the surrounding lines.

Points, Isoelectric. In electro-therapeutics, points of equal potential in a circuit.

423 STANDARD ELECTRICAL DICTIONARY.

Points of Derivation. The point where a single conductor branches into two or more conductors, operating or acting in parallel with each other.

Polar Angle. The angle subtended by one of the faces of the pole pieces of the field- magnet of a dynamo or motor. The centre of the circle of the angle lies in the axis of the armature.

Synonym--Angle of Polar Span.

Polar Extension. An addition made of iron to the poles of magnets. Various forms have been experimented with. The pole pieces of dynamo field magnets are polar extensions.

Synonyms--Pole Piece--Polar Tips.

Polarity, Diamagnetic. The induced polarity of diamagnetic substances; it is the reverse of paramagnetic polarity, or of the polarity of iron. A bar of diamagnetic material held parallel with the lines of force in a magnetic field has a like pole induced in the end nearest a given pole of the field magnet, and vice versa. This theory accounts for the repulsion by a magnet of a diamagnetic substance. The existence of this polarity is rather an assumption. It originated with Faraday.

Polarity, Paramagnetic. The induced polarity of paramagnetic substances, such as iron, nickel, or cobalt.

When such a substance is brought into a magnetic field the part nearest a specific pole of a magnet acquires polarity opposite to that of such pole and is thereby attracted.

Another way of expressing it, in which the existence of a pole in or near to the field is not implied, is founded on the conventional direction of lines of force. Where these enter the substance a south pole is formed and where they emerge a north pole is formed.

Such polarity tends always to be established in the direction of greatest length, if the body is free to rotate.

424 STANDARD ELECTRICAL DICTIONARY.

Polarization. (a) The depriving of a voltaic cell of its proper electro-motive force. Polarization may be due to various causes. The solution may become exhausted, as in a Smee battery, when the acid is saturated with zinc and thus a species of polarization follows. But the best definition of polarization restricts it to the development of counter-electro-motive force in the battery by the accumulation of hydrogen on the negative (carbon or copper) plate. To overcome this difficulty many methods are employed. Oxidizing solutions or solids are used, such as solution of chromic acid or powdered manganese dioxide, as in the Bunsen and Leclanché batteries respectively; a roughened surface of platinum black is used, as in the Smee battery; air is blown through the solution to carry off the hydrogen, or the plates themselves are moved about in the solution.

(b) Imparting magnetization to a bar of iron or steel, thus making a permanent magnet, is the polarization of the steel of which it is made. Polarization may be permanent, as in steel, or only temporary, as in soft iron.

(c) The strain upon a dielectric when it separates two oppositely charged surfaces. The secondary discharge of a Leyden jar, and its alteration in volume testify to the strain put upon it by charging.

(d) The alteration of arrangement of the molecules of an electrolyte by a decomposing current. All the molecules are supposed to be arranged with like ends pointing in the same direction, positive ends facing the positively-charged plate and negative ends the negatively-charged one.

(e) The production of counter-electro-motive force in a secondary battery, or in any combination capable of acting as the seat of such counter-electro-motive force. (See Battery, Secondary--Battery, Gas.) The same can be found often in organized cellular tissue such as that of muscles, nerves, or of plants. If a current is passed through this in one direction, it often establishes a polarization or potential difference that is susceptible of giving a return current in the opposite direction when the charging battery is replaced by a conductor.

Polarization Capacity. A voltaic cell in use becomes polarized by its negative plate accumulating hydrogen, or other cause. This gradually gives the plate a positive value, or goes to set up a counter-electro-motive force. The quantity of electricity required to produce the polarization of a battery is termed its Polarization Capacity or Capacity of Polarization.

Polarization of the Medium. The dielectric polarization, q. v., of a dielectric, implying the arrangement of its molecules in chains or filaments; a term due to Faraday. He illustrated it by placing filaments of silk in spirits of turpentine, and introduced into the liquid two conductors. On electrifying one and grounding (or connecting to earth) the other one, the silk filaments arranged themselves in a chain or string connecting the points of the conductors.

Polar Region. That part of the surface of a magnet whence the internal magnetic lines emerge into the air. (S. P. Thompson.) As such lines may emerge from virtually all parts of its surface, the polar regions are indefinite areas, and are properly restricted to the parts whence the lines emerge in greatest quantity.

Polar Span. A proportion of the circle which represents the transverse section of the armature space between the pole pieces of the field magnet in a dynamo or motor; it is the proportion which is filled by the faces of the pole pieces.

425 STANDARD ELECTRICAL DICTIONARY.

Pole, Analogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end when heated become positively electrified. On reduction of temperature the reverse effect obtains.

Pole, Antilogous. The end of a crystal of a pyroelectric substance, such as tourmaline, which end, while increasing in temperature, becomes negatively electrified. During reduction of its temperature the reverse effect obtains.

Pole Changer. (a) An automatic oscillating or vibrating switch or contact-breaker which in each movement reverses the direction of a current from a battery or other source of current of fixed direction, as such current goes through a conductor.

(b) A switch moved by hand which for each movement effects the above result.

Pole, Negative. (a) In a magnet the south pole; the pole into which the lines of force are assumed to enter from the air or outer circuit.

(b) In a current generator the pole or terminal into which the current is assumed to flow from the external circuit. It is the negatively charged terminal and in the ordinary voltaic battery is the terminal connected to the zinc or positive plate.

Pole Pieces. The terminations of the cores of field or other electro-magnets, or of permanent magnets. These terminations are variously shaped, sometimes being quite large compared to the core proper of the magnet.

They are calculated so as to produce a proper distribution of and direction of the lines of force from pole to pole. As a general rule the active field should be of uniform strength and the pole pieces may be of contour calculated to attain this end.

Pole, Positive. (a) In a magnet the north pole; the pole from which lines of force are assumed to emerge into the air.

(b) In a current generator the pole or terminal whence the current is assumed to issue into the outer circuit. It is the positively charged terminal, and in the ordinary voltaic battery is the terminal connected to the copper or carbon plate, termed the negative plate.

Poles. (a) The terminals of an open electric circuit, at which there necessarily exists a potential difference, produced by the generator or source of electro-motive force in the circuit.

(b) The terminals of an open magnetic circuit; the ends of a magnetized mass of steel, iron or other paramagnetic substance.

(c) The ends in general of any body or mass which show electric or magnetic properties more developed than those of the central sections of the body.

426 STANDARD ELECTRICAL DICTIONARY.