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Timestamp: 2019-04-22 14:22:53+00:00

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A less primitive way is to use a separate battery as the source of current; to connect to the positive plate by a wire the object to be plated, and a plate of copper, silver, nickel or other metal to the other pole of the battery. On immersing both object and plate (anode) in a bath of proper solution the object will become plated.
In general the anode is of the same material as the metal to be deposited, and dissolving keeps up the strength of the bath. There are a great many points of technicality involved which cannot be given here. The surface of the immersed object must be conductive. If not a fine wire network stretched over it will gradually fill up in the bath and give a matrix. More generally the surface is made conductive by being brushed over with plumbago. This may be followed by a dusting of iron dust, followed by immersion in solution ot copper sulphate. This has the effect of depositing metallic copper over the surface as a starter for the final coat.
Attention must be paid to the perfect cleanliness of the objects, to the condition of the bath, purity of anodes and current density.
Voltaic batteries are largely used for the current as well as special low resistance dynamos. Thermo-electric batteries are also used to some extent but not generally.
Electro-pneumatic Signals. Signals, such as railroad signals or semaphores, moved by compressed air, which is controlled by valves operated by electricity. The House telegraph, which was worked by air controlled by electricity, might come under this term, but it is always understood as applied to railroad signals, or their equivalent.
(a) Dissolve one pound of potassium bichromate in ten pounds of water, to which two and one-half pounds of concentrated sulphuric acid have been gradually added. The better way is to use powdered potassium bichromate, add it to the water first, and then gradually add the sulphuric acid with constant stirring.
(b) To three pints of water add five fluid ounces of concentrated sulphuric acid; add six ounces pulverized potassium bichromate.
(c) Mix one gallon concentrated sulphuric acid and three gallons of water. In a separate vessel dissolve six pounds potassium bichromate in two gallons of boiling water. Mix the two.
Electro-receptive. adj. A term applied to any device or apparatus designed to receive and absorb electric energy. A motor is an example of an electro-receptive mechanism.
Electroscope. An apparatus for indicating the presence of an electric charge, and also for determining the sign, or whether the charge is positive or negative. The simplest form consists of a thread doubled at its centre and hung therefrom. On being charged, or on being connected to a charged body the threads diverge. A pair of pith balls may be suspended in a similar way, or a couple of strips of gold leaf within a flask (the gold leaf electroscope). To use an electroscope to determine the sign of the charge it is first slightly charged. The body to be tested is then applied to the point of suspension, or other charging point. If at once further repelled the charge of the body is of the same sign as the slight charge first imparted to the electroscope leaves; the leaves as they become more excited will at once diverge more. If of different sign they will at first approach as their charge is neutralized and will afterwards diverge.
Electroscope, Bennett's. A gold-leaf electroscope, the suspended leaves of which are contained in a glass shade or vessel of dry air. On the inside of the glass shade are two strips of gold leaf, which rise from the lower edge a short distance, being pasted to the glass, and connected to the ground. These act by induction to increase the sensitiveness of the instruments.
Electroscope, Bohenberger's. A condensing electroscope (see Electroscope, Condensing) with a single strip of gold leaf suspended within the glass bell. This is at an equal distance from the opposite poles of two dry piles (see Zamboni's Dry Pile) standing on end, one on each side of it. As soon as the leaf is excited it moves toward one and away from the other pile, and the sign of its electrification is shown by the direction of its motion.
Electroscope, Condensing. A gold leaf electroscope, the glass bell of which is surmounted by an electrophorous or static condenser, to the lower plate of which the leaves of gold are suspended or connected.
In use the object to be tested is touched to the lower plate, and the upper plate at the same time is touched by the finger. The plates are now separated. This reduces the capacity of the lower plate greatly and its charge acquires sufficient potential to affect the leaves, although the simple touching may not have affected them at all.
Electroscope, Gold Leaf. An electroscope consisting of two leaves of gold leaf hung in contact with each other from the end of a conductor. When excited they diverge. The leaves are enclosed in a glass vessel.
Fig. 160. GOLD LEAF ELECTROSCOPE.
Electroscope, Pith Ball. Two pith balls suspended at opposite ends of a silk thread doubled in the middle. When charged with like electricity they repel each other. The extent of their repulsion indicates the potential of their charge.
Electrostatic Induction, Coefficient of. The coefficient expressing the ratio of the charge or change of charge developed in one body to the potential of the inducing body.
Electrostatic Lines of Force. Lines of force assumed to exist in an electrostatic field of force, and to constitute the same. In general they correspond in action and attributes with elcctro-magnetic lines of force. They involve in almost all cases either a continuous circuit, or a termination at both ends in oppositely charged surfaces.
Fig. 161. ELECTROSTATIC LINES OF FORCE BETWEEN NEAR SURFACES.
Fig. 162. ELECTROSTATIC LINKS OF FORCE BETWEEN DISTANT SURFACES.
The cut, Fig. 161, shows the general course taken by lines of force between two excited surfaces when near together. Here most of them are straight lines reaching straight across from surface to surface, while a few of them arch across from near the edges, tending to spread. If the bodies are drawn apart the spreading tendency increases and the condition of things shown in the next cut, Fig. 162, obtains. There is an axial line whose prolongations may be supposed to extend indefinitely, as occupying a position of unstable equilibrium. Here the existence of a straight and unterminated line of force may be assumed.
A direction is predicated to lines of force corresponding with the direction of an electric current. They are assumed to start from a positively charged and to go towards a negatively charged surface. A positively charged body placed in an electrostatic field of force will be repelled from the region of positive into or towards the region of negative potential following the direction of the lines of force, not moving transversely to them, and having no transverse component in its motion.
Electrostatics. The division of electric science treating of the phenomena of electric charge, or of electricity in repose, as contrasted with electro-dynamics or electricity in motion or in current form. Charges of like sign repel, and of unlike sign attract each other. The general inductive action is explained by the use of the electrostatic field of force and electrostatic lines of force, q. v. The force of attraction and repulsion of small bodies or virtual points, which are near enough to each other, vary as the square of the distance nearly, and with the product of the quantities of the charges of the two bodies.
Electrostatic Refraction. Dr. Kerr found that certain dielectrics exposed to electric strain by being placed between two oppositely excited poles of a Holtz machine or other source of very high tension possess double refracting powers, in other words can rotate a beam of polarized light, or can develop two complimentary beams from common light. Bisulphide of carbon shows the phenomenon well, acting as glass would if the glass were stretched in the direction of the electrostatic lines of force. To try it with glass, holes are drilled in a plate and wires from an influence machine are inserted therein. The discharge being maintained through the glass it polarizes light.
Electrostatic Series. A table of substances arranged in the order in which they are electrostatically charged by contact, generally by rubbing against each other. The following series is due to Faraday. The first members become positively excited when rubbed with any of the following members, and vice versa. The first elements correspond to the carbon plate in a galvanic battery, the succeeding elements to the zinc plate.
Cat, and Bear-skin—Flannel—Ivory—Feathers—Rock Crystal—Flint Glass—Cotton—Linen—Canvas—White Silk—the Hand—Wood—Shellac—the Metals (Iron-Copper-Brass-Tin-Silver-Platinum)—Sulphur. There are some irregularities. A feather lightly drawn over canvas is negatively electrified; if drawn through folds pressed against it it is positively excited. Many other exceptions exist, so that the table is of little value.
Electro-therapeutics or Therapy. The science treating of the effects of electricity upon the animal system in the treatment and diagnosis of disease.
Electrotonus. An altered condition of functional activity occurring in a nerve subjected to the passage of an electric current. If the activity is decreased, which occurs near the anode, the state is one of anelectrotonus, if the activity is increased which occurs near the kathode the condition is one of kathelectrotonus.
Electrotype. The reproduction of a form of type or of an engraving or of the like by electroplating, for printing purposes. The form of type is pressed upon a surface of wax contained in a shallow box. The wax is mixed with plumbago, and if necessary some more is dusted and brushed over its surface and some iron dust is sprinkled over it also. A matrix or impression of the type is thus obtained, on which copper is deposited by electroplating, q. v.
Element, Chemical. The original forms of matter that cannot be separated into constituents by any known process. They are about seventy in number. Some of the rarer ones are being added to or cancelled with the progress of chemical discovery. For their electric relations see Electro-chemical Equivalents—Electro-chemical Series.
The elements in entering into combination satisfy chemical affinity and liberate energy, which may take the form of electric energy as in the galvanic battery, or of heat energy, as in the combustion of carbon or magnesium. Therefore an uncombined element is the seat of potential energy. (See Energy, Potential.) In combining the elements always combine in definite proportions. A series of numbers, one being proper to each element which denote the smallest common multipliers of these proportions, are called equivalents. Taking the theory of valency into consideration the product of the equivalents by the valencies gives the atomic weights.
Element, Mathematical. A very small part of anything, corresponding in a general way to a differential, as the element of a current.
Element of a Battery Cell. The plates in a galvanic couple are termed elements, as the carbon and zinc plates in a Bunsen cell. The plate unattacked by the solution, as the carbon plate in the above battery, is termed the negative plate or element; the one attacked, as the zinc plate, is termed the positive plate or element.
Elements, Electrical Classification of. This may refer to Electro-chemical Series, Electrostatic Series, or Thermo-electric Series, all of which may be referred to.
Embosser, Telegraph. A telegraphic receiver giving raised characters on a piece of paper. It generally refers to an apparatus of the old Morse receiver type, one using a dry point stylus, which pressing the paper into a groove in the roller above the paper, gave raised characters in dots and lines.
E. M. D. P. Abbreviation for "electro-motive difference of potential" or for electro-motive force producing a current as distinguished from mere inert potential difference.
E. M. F. Abbreviation for "electro-motive force."
End-on Method. A method of determining the magnetic moment of a magnet. The magnet under examination, N S, is placed at right angles to the magnetic meridian, M O R, and pointing directly at or "end on" to the centre of a compass needle, n s. From the deflection a of the latter the moment is calculated.
End Play. The power to move horizontally in its bearings sometimes given to armature shafts. This secures a more even wearing of the commutator faces. End play is not permissible in disc armatures, as the attraction of the field upon the face of the armature core would displace it endwise. For such armatures thrust-bearings preventing end play have to be provided.
Energy. The capacity for doing work. It is measured by work units which involve the exercise of force along a path of some length. A foot-pound, centimeter-gram, and centimeter-dyne are units of energy and work.
The dimensions of energy are force (M * L / T^2) * space (L) = M * (L^2 / T^2). Energy may be chemical (atomic or molecular), mechanical, electrical, thermal, physical, potential, kinetic, or actual, and other divisions could be formulated.
Energy, Chemical. A form of potential energy (see Energy, Potential) possessed by elements in virtue of their power of combining with liberation of energy, as in the combination of carbon with oxygen in a furnace; or by compounds in virtue of their power of entering into other combinations more satisfying to the affinities of their respective elements or to their own molecular affinity. Thus in a galvanic couple water is decomposed with absorption of energy, but its oxygen combines with zinc with evolution of greater amount of energy, so that in a voltaic couple the net result is the setting free of chemical energy, which is at once converted into electrical energy in current form, if the battery is on a closed circuit.
Energy, Conservation of. A doctrine accepted as true that the sum of energy in the universe is fixed and invariable. This precludes the possibility of perpetual motion. Energy may be unavailable to man, and in the universe the available energy is continually decreasing, but the total energy is the same and never changes.
Energy, Electric. The capacity for doing work possessed by electricity under proper conditions. Electric energy may be either kinetic or potential. As ordinary mechanical energy is a product of force and space, so electric energy is a product of potential difference and quantity. Thus a given number of coulombs of electricity in falling a given number of volts develop electric energy. The dimensions are found therefore by multiplying electric current intensity quantity ((M^.5) * (L^.5)), by electric potential ((M^.5)*(L^1.5) / (T^2)), giving (M * (L^2)/(T^2)), the dimensions of energy in general as it should be.
The absolute unit of electric energy in electro-magnetic measure is (1E-7) volt coulombs.
The practical unit is the volt-coulomb. As the volt is equal to 1E8 absolute units of potential and the coulomb to 0.1 absolute units of quantity, the volt-coulomb is equal to 1E7 absolute units of energy.
The volt-coulomb is very seldom used, and the unit of Electric Activity or Power (see Power, Electric), the volt-ampere, is universally used. This unit is sometimes called the Watt, q. v., and it indicates the rate of expenditure or of production of electric energy.
The storing up in a static accumulator or condenser of a given charge of electricity, available for use with a given change of potential represents potential electric energy.
The passing of a given quantity through a conductor with a given fall of potential represents kinetic electric energy.
In a secondary battery there is no storage of energy, but the charging current simply accumulates potential chemical energy in the battery, which chemical energy is converted into electric energy in the discharge or delivery of the battery.
Energy, Electric Transmission of. If an electric current passes through a conductor all its energy is expended in the full circuit. Part of the circuit may be an electrical generator that supplies energy as fast as expended. Part of the circuit may be a motor which absorbs part of the energy, the rest being expended in forcing a current through the connecting wires and through the generator. The electric energy in the generator and connecting wires is uselessly expended by conversion into heat. That in the motor in great part is utilized by conversion into mechanical energy which can do useful work. This represents the transmission of energy. Every electric current system represents this operation, but the term is usually restricted to the transmission of comparatively large quantities of energy.
A typical installation might be represented thus. At a waterfall a turbine water wheel is established which drives a dynamo. From the dynamo wires are carried to a distant factory, where a motor or several motors are established, which receive current from the dynamo and drive the machinery. The same current, if there is enough energy, may be used for running lamps or electroplating. As electric energy (see Energy, Electric,) is measured by the product of potential difference by quantity, a very small wire will suffice for the transmission of a small current at a high potential, giving a comparatively large quantity of energy. It is calculated that the energy of Niagara Falls could be transmitted through a circuit of iron telegraph wire a distance of over 1,000 miles, but a potential difference of 135,000,000 volts would be required, something quite impossible to obtain or manage.
Energy, Kinetic. Energy due to matter being actually in motion. It is sometimes called actual energy. The energy varies directly with the mass and with the square of the velocity. It is represented in formula by .5 *M * (v^2).
Synonyms—Actual Energy—Energy of Motion—Dynamic Energy.
Energy, Molar. The energy of masses of matter due to movements of or positions of matter in masses; such as the kinetic energy of a pound or of a ton in motion, or the potential energy of a pound at an elevation of one hundred feet.
Energy, Molecular. The potential energy due to the relations of molecules and set free by their change in the way of combination. It is potential for the same reason that applies to atomic and chemical energy, of which latter it is often a form, although it is often physical energy. The potential energy stored up in vaporization is physical and molecular energy; the potential energy stored up in uncombined potassium oxide and water, or calcium oxide (quicklime) and water is molecular, and when either two substances are brought together kinetic, thermal or heat energy is set free, as in slaking lime for mortar.
Energy of an Electrified Body. An electrified body implies the other two elements of a condenser. It is the seat of energy set free when discharged. (See Dielectric, Energy of.) The two oppositely charged bodies tend to approach. This tendency, together with the distances separating them, represents a potential energy.
Energy of Stress. Potential energy due to stress, as the stretching of a spring. This is hardly a form of potential energy. A stressed spring is merely in a position to do work at the expense of its own thermal or kinetic energy because it is cooled in doing work. If it possessed true potential energy of stress it would not be so cooled.
Energy, Physical. The potential energy stored up in physical position or set free in physical change. Thus a vapor or gas absorbs energy in its vaporization, which is potential energy, and appears as heat energy when the vapor liquefies.
Energy, Potential, or Static Energy. The capacity for doing work in a system due to advantage of position or other cause, such as the stress of a spring. A pound weight supported ten feet above a plane has ten foot lbs. of potential energy of position referred to that plane. A given weight of an elementary substance represents potential chemical energy, which will be liberated as actual energy in its combination with some other element for which it has an affinity. Thus a ton of coal represents a quantity of potential chemical energy which appears in the kinetic form of thermal energy when the coal is burning in a furnace. A charged Leyden jar represents a source of potential electric energy, which becomes kinetic heat energy as the same is discharged.
Energy, Thermal. A form of kinetic molecular energy due to the molecular motion of bodies caused by heat.
Epinus' Condenser. Two circular brass plates, A and B, are mounted on insulating supports, and arranged to be moved towards or away from each other as desired. Between them is a plate of glass, C, or other dielectric. Pith balls may be suspended back of each brass plate as shown. The apparatus is charged by connecting one plate to an electric machine and the other to the earth. The capacity of the plate connected to the machine is increased by bringing near to it the grounded plate, by virtue of the principle of bound charges. This apparatus is used to illustrate the principles of the electric condenser. It was invented after the Leyden jar was invented.
E. P. S. Initials of Electrical Power Storage; applied to a type of secondary battery made by a company bearing that title.
Equalizer. In electro-magnetic mechanism an arrangement for converting the pull of the electro-magnet varying in intensity greatly over its range of action, into a pull of sensibly equal strength throughout. The use of a rocking lever acting as a cam, with leverage varying as the armature approaches or recedes from the magnet core is one method of effecting the result. Such is shown in the cut. E is an electro-magnet, with armature a. A and B are the equalizer cams. The pull on the short end of the cam B is sensibly equal for its whole length.
Many other methods have been devised, involving different shapes of pole pieces, armatures or mechanical devices other than the one just shown.
Equipotential. adj. Equal in potential; generally applied to surfaces. Thus every magnetic field is assumed to be made up of lines of force and intersecting those lines, surfaces, plane, or more or less curved in contour, can be determined, over all parts of each one of which the magnetic intensity will be identical. Each surface is the locus of equal intensity. The same type of surface can be constructed for any field of force, such as an electrostatic field, and is termed an equipotential surface.
Equipotential Surface, Electrostatic. A surface in an electrostatic field of force, which is the locus of all points of a given potential in such field; a surface cutting all the lines of force at a point of identical potential. Lines of force are cut perpendicularly by an equipotential surface, or are normal thereto.
Equipotential Surface, Magnetic and Electro-magnetic. A surface bearing the same relation to a magnetic or electro-magnetic field of force that an electrostatic equipotential surface (see Equipotential Surface, Electrostatic,) does to an electrostatic field of force.
Equivalent, Chemical. The quotient obtained by dividing the atomic weight of an element by its valency.
Equivalent, Electro-mechanical. The work or energy equivalent to unit quantities of electric energy, q. v.; or equivalent to a unit current in a conductor whose ends differ one unit of potential. The unit of electric energy taken is the watt-second or volt-coulomb. One volt-coulomb is equal to Ergs 1E7  Foot Pound .737337 Gram-degree C. .24068 Horse Power Second .0013406 Pound-degree F. .000955 One horse power is equal to 745.943 volt coulombs per second.
Equivalent, Thermo-chemical. The calories evolved by the combination of one gram of any substance with its equivalent of another substance being determined, the product obtained by multiplying this number by the equivalent (atomic or molecular weight / valency) of the first element or substance is the thermo-chemical equivalent. If expressed in kilogram calories, the product of the thermo-chemical equivalent by 0.43 gives the voltage required to effect such decomposition.
Equivolt. "The mechanical energy of one volt electro-motive force exerted under unit conditions through one equivalent of chemical action in grains." (J. T. Sprague.) This unit is not in general use as the unit of electric energy, the volt-coulomb and (for rate of electric energy) the volt-ampere being always used.
Erg. The absolute or fundamental C. G. S. unit of work or energy. The work done or energy expended in moving a body through one centimeter against a resistance of one dyne.
Erg-ten. Ten millions of ergs, or ten meg-ergs.
Escape. A term applied to leakage of current.
Etching, Electric. A process of producing an etched plate. The plate is coated with wax, and the design traced through as in common etching. It is then placed in a bath and is connected to the positive terminal from a generator, whose negative is immersed in the same bath, so that the metal is dissolved by electrolytic action. By attaching to the other terminal and using a plating bath, a rough relief plate may be secured, by deposition in the lines of metal by electroplating.
Ether. The ether is a hypothetical thing that was invented to explain the phenomena of light. Light is theoretically due to transverse vibrations of the ether. Since the days of Young the conception of the ether has extended, and now light, "radiant heat," and electricity are all treated as phenomena of the ether. Electrical attraction and repulsion are explained by considering them due to local stresses in the ether; magnetic phenomena as due to local whirlpools therein. The ether was originally called the luminiferous ether, but the adjective should now be dropped. Its density is put at 936E-21 that of water, or equal to that of the atmosphere at 210 miles above the earth's surface. Its rigidity is about 1E-9 that of steel (see Ten, Powers of); as a whole it is comparable to an all-pervading jelly, with almost perfect elasticity. The most complete vacuum is filled with ether.
All this is a hypothesis, for the ether has never been proved to exist. Whether gravitation will ever be explained by It remains to be seen.
Eudiometer. A graduated glass tube for measuring the volumes of gases. In its simplest form it is simply a cylindrical tube, with a scale etched or engraved upon it, closed at one end and open at the other. The gas to be measured is collected in it over a liquid, generally water, dilute sulphuric acid in the gas voltameter, or mercury. Many different shapes have been given them by Hoffmann, Ure, Bunsen and others.
Evaporation, Electric. The superficial sublimation or evaporation of a substance under the influence of negative electricity. It is one of the effects investigated by Crookes in his experiments with high vacua. He found that when a metal, even so infusible as platinum, was exposed to negative electrification in one of his high vacuum tubes, that it was volatilized perceptibly. A cadmium electrode heated and electrified negatively was found to give a strong coating of metal on the walls of the tube. Even in the open air the evaporation of water was found to be accelerated by negative electrification.
Exchange, Telephone. The office to which telephone wires lead in a general telephone system. In the office by a multiple switch board, or other means, the different telephones are interconnected by the office attendants, so that any customers who desire it may be put into communication with each other. The exchange is often termed the Central Office, although it may be only a branch office.
Excitability, Faradic. The action produced in nerve or muscle of the animal system by an alternating or intermitting high potential discharge from an induction coil.
Excitability, Galvanic. The same as Faradic excitability, except that it refers to the effects of the current from a galvanic battery.
Excitability of Animal System, Electric. The susceptibility of a nerve or muscle to electric current shown by the effect produced by its application.
Exciter. A generator used for exciting the field magnet of a dynamo. In alternating current dynamos, e. g., of the Westinghouse type, a special dynamo is used simply to excite the field magnet. In central station distribution the same is often done for direct current dynamos.
Expansion, Coefficient of. The number expressing the proportional increase in size, either length, area or volume, of a substance under the influence generally of heat. There are three sets of coefficients, (1) of linear expansion, (2) of superficial expansion, (3) of cubic expansion or expansion of volume. The first and third are the only ones much used. They vary for different substances, and for the same substance at different temperatures. They are usually expressed as decimals indicating the mixed number referred to the length or volume of the body at the freezing point as unity.
Expansion, Electric. (a) The increase in volume of a condenser, when charged electrostatically. A Leyden jar expands when charged, and contracts when discharged.
(b) The increase in length of a bar of iron when magnetized.
This is more properly called magnetic expansion or magnetic elongation.
Exploder. (a) A small magneto-generator for producing a current for heating the wire in an electric fuse of the Abel type (see Fuse, Electric), and thereby determining an explosion.
(b) The term may also be applied to a small frictional or influence machine for producing a spark for exploding a spark fuse.
Explorer. A coil, similar to a magnetizing coil (see Coil, Magnetizing), used for investigating the electro-magnetic circuit and for similar purposes. If placed around an electro-magnet and connected with a galvanometer, it will produce a deflection, owing to a momentary induced current, upon any change in the magnet, such as removing or replacing the armature. It is useful in determining the leakage of lines of force and for general investigations of that nature. It is often called an exploring coil. Hughes' Induction Balance (see Induction Balance, Hughes') is sometimes called a Magnetic Explorer. The exploring coil may be put in circuit with a galvanometer for quantitative measurements or with a telephone for qualitative ones.
Extension Bell Call. A system of relay connection, q. v., by which a bell is made to continue ringing after the current has ceased coming over the main line. It is designed to prolong the alarm given by a magneto call bell, q. v., which latter only rings as long as the magneto handle is turned. A vibrating electric bell (see Bell, Electric,) is connected in circuit with a local battery and a switch normally open, but so constructed as to close the circuit when a current is passed and continue to do so indefinitely. The distant circuit is connected to this switch. When the magneto is worked it acts upon the switch, closes the local battery circuit and leaves it closed, while the bell goes on ringing until the battery is exhausted or the switch is opened by hand.
Eye, Electro-magnetic. An apparatus used in exploring a field of electro-magnetic radiations. It is a piece of copper wire 2 millimeters (.08 inch) in diameter, bent into an almost complete circle 70 millimeters (.28 inch) in diameter, with terminals separated by an air gap. This is moved about in the region under examination, and by the production of a spark indicates the locality of the loops or venters in systems of stationary waves.
Fahrenheit Scale. A thermometer scale in use in the United States and England. On this scale the temperature of melting ice is 32; that of condensing steam is 212; the degrees are all of equal length. Its use is indicated by the letter F., as 180 F. To convert its readings into centigrade, subtract 32 and multiply by 5/9. (b) To convert centigrade into F. multiply by 9/5 and add 32. Thus 180 F. = ((180-32) * 5/9) C. = 82.2 C. Again 180 C. = (180 * 9/5) + 32 = 324 F.
The additions and subtractions must be algebraic in all cases. Thus when the degrees are minus or below zero the rules for conversion might be put thus: To convert degrees F. below zero into centigrade to the number of degrees F. add 32, multiply by 5/9 and place a minus sign (-) before it. (b) To convert degrees centigrade below zero into Fahrenheit, multiply the number of degrees by 9/5, subtract from 32 if smaller; if greater than 32 subtract 32 therefrom, and prefix a minus sign, thus: -10 C. = 32 - (10 * 9/5) = 14. Again, -30C. = (30 * 9/5) - 32 = 22 = -22 F.
Farad. The practical unit of electric capacity; the capacity of a conductor which can retain one coulomb of electricity at a potential of one volt.
The quantity of electricity charged upon a conducting surface raises its potential; therefore a conductor of one farad capacity can hold two coulombs at two volts potential, and three coulombs at three volts, and so on. The electric capacity of a conductor, therefore, is relative compared to others as regards its charge, for the latter may be as great as compatible with absence of sparking and disruptive discharge. In other words, a one farad or two farad conductor may hold a great many coulombs. Charging a conductor with electricity is comparable to pumping air into a receiver. Such a vessel may hold one cubic foot of air at atmospheric pressure and two at two atmospheres, and yet be of one cubic foot capacity however much air is pumped into it.
The farad is equal to one fundamental electrostatic unit of capacity multiplied by 9E11 and to one electro-magnetic unit multiplied by 1E-9.
The farad although one of the practical units is far too large, so the micro-farad is used in its place. The capacity of a sphere the size of the earth is only .000636 of a farad.
Faraday's Cube. To determine the surface action of a charge, Faraday constructed a room, twelve feet cube, insulated, and lined with tinfoil. This room he charged to a high potential, but within it he could detect no excitement whatever. The reason was because the electricity induced in the bodies within the room was exactly equal to the charge of the room-surface, and was bound exactly by it. The room is termed Faraday's cube.
Faraday's Dark Space. A non-luminous space between the negative and positive glows, produced in an incompletely exhausted tube through which a static discharge, as from an induction coil, is produced. It is perceptible in a rarefaction of 6 millimeters (.24 inch) and upwards. If the exhaustion is very high a dark space appears between the negative electrode and its discharge. This is known as Crookes' dark space.
Faraday's Disc. A disc of any metal, mounted so as to be susceptible of rotation in a magnetic field of force, with its axis parallel to the general direction of the lines of force. A spring bears against its periphery and another spring against its axle. When rotated, if the springs are connected by a conductor, a current is established through the circuit including the disc and conductor. The radius of the disc between the spring contacts represents a conductor cutting lines of force and generating a potential difference, producing a current. If a current is sent through the motionless wheel from centre to periphery it rotates, illustrating the doctrine of reversibility. As a motor it is called Barlow's or Sturgeon's Wheel. If the disc without connections is rapidly rotated it produces Foucault currents, q. v., within its mass, which resist its rotation and heat the disc.
Faraday's Net. An apparatus for showing that the electric charge resides on the surface. It consists of a net, conical in shape and rather deep, to whose apex two threads, one on each side, are attached. Its mouth is fastened to a vertical ring and the whole is mounted on an insulating support.
It is pulled out to its full extent and is electrified. No charge can be detected inside it. By pulling one of the threads it is turned with the other side out. Now all the charge is found on the outside just as before, except that it is of course on the former inside surface of the bag. The interior shows no charge.
Faraday's Transformer. The first transformer. It was made by Michael Faraday. It was a ring of soft iron 7/8 inch thick, and 6 inches in external diameter. It was wound with bare wire, calico being used to prevent contact of the wire with the ring and of the layers of wire with each other, while twine was wound between the convolutions to prevent the wires from touching. Seventy-two feet of copper wire, 1/20 inch diameter, were wound in three superimposed coils, covering about one-half of the ring. On the other half sixty feet of copper wire were wound in two superimposed coils. Faraday connected his coils in different ways and used a galvanometer to measure the current produced by making and breaking one of the circuits used as a primary.
The coil is of historic interest.
Faradic. adj. Referring to induced currents, produced from induction coils. As Faraday was the original investigator of the phenomena of electro-magnetic induction, the secondary or induced electro-magnetic currents and their phenomena and apparatus are often qualified by the adjective Faradic, especially in electro-therapeutics. A series of alternating electrostatic discharges, as from an influence machine (Holtz), are sometimes called Franklinic currents. They are virtually Faradic, except as regards their production.
Faradic Brush. A brush for application of electricity to the person. It is connected as one of the electrodes of an induction coil or magneto generator. For bristles wire of nickel plated copper is generally employed.
Faradization. In medical electricity the analogue of galvanization; the effects due to secondary or induced currents; galvanization referring to currents from a galvanic battery; also the process of application of such currents.
Faults. Sources of loss of current or of increased resistance or other troubles in electric circuits.
Feeder. A lead in an electric central station distribution system, which lead runs from the station to some point in the district to supply current. It is not used for any side connections, but runs direct to the point where current is required, thus "feeding" the district directly. In the two wire system a feeder may be positive or negative; in the three wire system there is also a neutral feeder. Often the term feeder includes the group of two or of three parallel lines.
Feeder Equalizer. An adjustable resistance connected in circuit with a feeder at the central station. The object of the feeder being to maintain a definite potential difference at its termination, the resistance has to be varied according to the current it is called on to carry.
Feeder, Main or Standard. The main feeder of a district. The standard regulation of pressure (potential difference between leads) in the district is often determined by the pressure at the end of the feeder.
Feeder, Negative. The lead or wire in a set of feeders, which is connected to the negative terminal of the generator.
Feeder, Neutral. In the three wire system the neutral wire in a set of feeders. It is often made of less diameter than the positive and negative leads.
Feeder, Positive. The lead or wire in a set of feeders, which wire is connected to the positive terminal of the generator.
Ferranti Effect. An effect as yet not definitely explained, observed in the mains of the Deptford, Eng., alternating current plant. It is observed that the potential difference between the members of a pair of mains rises or increases with the distance the place of trial is from the station.
Ferro-magnetic. adj. Paramagnetic; possessing the magnetic polarity of iron.
Fibre and Spring Suspension. A suspension of the galvanometer needle used in marine galvanometers. The needle is supported at its centre of gravity by a vertically stretched fibre attached at both its ends, but with a spring intercalated between the needle and one section of the fibre.
This suspension, while the most delicate and reliable known, is very subject to disturbance and exacts accurate levelling of the instrument.
Fibre suspension is always characterized by a restitutive force. Pivot suspension, q. v., on the other hand, has no such force.
Field, Air. A field the lines of force of which pass through air; the position of a field comprised within a volume of air.
Field, Alternating. Polarity or direction being attributed to lines of force, if such polarity is rapidly reversed, an alternating field results. Such field may be of any kind, electro-magnetic or electrostatic. In one instance the latter is of interest. It is supposed to be produced by high frequency discharges of the secondary of an induction coil, existing in the vicinity of the discharging terminals.
Field Density. Field density or density of field is expressed in lines of force per unit area of cross-section perpendicular to the lines of force.
Field, Distortion of. The lines of force reaching from pole to pole of an excited field magnet of a dynamo are normally symmetrical with respect to some axis and often with respect to several. They go across from pole to pole, sometimes bent out of their course by the armature core, but still symmetrical. The presence of a mass of iron in the space between the pole pieces concentrates the lines of force, but does not destroy the symmetry of the field.
When the armature of the dynamo is rotated the field becomes distorted, and the lines of force are bent out of their natural shape. The new directions of the lines of force are a resultant of the lines of force of the armature proper and of the field magnet. For when the dynamo is started the armature itself becomes a magnet, and plays its part in forming the field. Owing to the lead of the brushes the polarity of the armature is not symmetrical with that of the field magnets. Hence the compound field shows distortion. In the cut is shown diagrammatically the distortion of field in a dynamo with a ring armature. The arrow denotes the direction of rotation, and n n * * * and s s * * * indicate points of north and south polarity respectively.
The distorted lines must be regarded as resultants of the two induced polarities of the armature, one polarity due to the induction of the field, the other to the induction from its own windings. The positions of the brushes have much to do with determining the amount and degree of distortion. In the case of the ring armature it will be seen that some of the lines of force within the armature persist in their polarity and direction, almost as induced by the armature windings alone, and leak across without contributing their quota to the field. Two such lines are shown in dotted lines.
In motors there is a similar but a reversed distortion.
Fig. 169. DISTORTION OF FIELD IN A RING ARMATURE OF AN ACTIVE DYNAMO.
Fig. 170. DISTORTION OF FIELD IN A RING ARMATURE OF AN ACTIVE MOTOR.
Field, Drag of. When a conductor is moved through a field so that a current is generated in it, the field due to that current blends with the other field and with its lines of force, distorting the field, thereby producing a drag upon its own motion, because lines of force always tend to straighten themselves, and the straightening would represent cessation of motion in the conductor. This tendency to straightening therefore resists the motion of the conductor and acts a drag upon it.
Field of Force of a Current. A current establishes a field of force around itself, whose lines of force form circles with their centres on the axis of the current. The cut, Fig. 172, shows the relation of lines of force to current.
Fig. 171. EXPERIMENT SHOWING LINES OF FORCE SURROUNDING AN ACTIVE CONDUCTOR.
Fig. 172. DIAGRAM OF FIELD OF FORCE SURROUNDING AN ACTIVE CONDUCTOR.
Fig. 173. LINK OF FORCE INDUCED BY A CURRENT SHOWING THE MAGNETIC WHIRLS.
The existence of the field is easily shown by passing a conductor vertically through a horizontal card. On causing a current to go through the wire the field is formed, and iron filings dropped upon the card, tend, when the latter is gently tapped, to take the form of circles. The experiment gives a version of the well-known magnetic figures, q. v. See Fig. 171.
Field, Pulsatory. A field produced by pulsatory currents. By induction such field can produce an alternating current.
Field, Rotating. In a dynamo the field magnets are sometimes rotated instead of the armature, the latter being stationary. In Mordey's alternator the armature, nearly cylindrical, surrounds the field, and the latter rotates within it, the arrangement being nearly the exact reverse of the ordinary one. This produces a rotating field.
Field, Rotatory. A magnetic field whose virtual poles keep rotating around its centre of figure. If two alternating currents differing one quarter period in phase are carried around four magnetizing coils placed and connected in sets of two on the same diameter and at right angles to each other, the polarity of the system will be a resultant of the combination of their polarity, and the resultant poles will travel round and round in a circle. In such a field, owing to eddy currents, masses of metal, journaled like an armature, will rotate, with the speed of rotation of the field.
Field, Stray. The portion of a field of force outside of the regular circuit; especially applied to the magnetic field of force of dynamos expressing the portion which contributes nothing to the current generation.
Figure of Merit. In the case of a galvanometer, a coefficient expressing its delicacy. It is the reciprocal of the current required to deflect the needle through one degree. By using the reciprocal the smaller the current required the larger is the figure of merit. The same term may be applied to other instruments.
It is often defined as the resistance of a circuit through which one Daniell's element will produce a deflection of one degree on the scale of the instrument. The circuit includes a Daniell's cell of resistance r, a rheostat R, galvanometer G and shunt S. Assume that with the shunt in parallel a deflection of a divisions is obtained. The resistance of the shunted galvanometer is (GS/G+S ; the multiplying power m of the shunt is S+G/S; the formula or figure of merit is m d (r+R +G S/G+S).
The figure of merit is larger as the instrument is more sensitive. Synonym—Formula of Merit.
Fire Alarm Telegraph System. A system of telegraphic lines for communicating the approximate location of a fire to a central station and thence to the separate fire-engine houses in a city or district. It includes alarm boxes, distributed at frequent intervals, locked, with the place where the key is kept designated, or in some systems left unlocked. On opening the door of the box and pulling the handle or otherwise operating the alarm, a designated signal is sent to the central station. From this it is telegraphed by apparatus worked by the central station operator to the engine houses. The engines respond according to the discipline of the service.
Fire Cleansing. Freeing the surface of an article to be plated from grease by heating.
Fire Extinguisher, Electric, Automatic. A modification of the electric fire alarm (see Fire Alarm, Electric, Automatic), in which the thermostats completing the circuits turn on water which, escaping through the building, is supposed to reach and extinguish a fire.
Flashing in a Dynamo or Magneto-electric Generator. Bad adjustment of the brushes at the commutator, or other fault of construction causes the production of voltaic arcs at the commutator of a generator, to which the term flashing is applied.
Flashing of Incandescent Lamp Carbons. A process of treatment for the filaments of incandescent lamps. The chamber before sealing up is filled with a hydro-carbon vapor or gas, such as the vapor of a very light naphtha (rhigolene). A current is then passed through the filament heating it to redness. The more attenuated parts or those of highest resistance are heated the highest, and decompose most rapidly the hydro-carbon vapor, graphitic carbon being deposited upon these parts, while hydrogen is set free. This goes on until the filament is of uniform resistance throughout. It gives also a way of making the resistance of the filament equal to any desired number of ohms, provided it is originally of high enough resistance. The process increases the conductivity of the filament.
After flashing the chambers are pumped out and sealed up.
Flashing Over. A phenomenon observed in high potential dynamos. On a sudden alteration of the resistance of the circuit a long blue spark will be drawn out around the surface of the commutator from brush to brush. The spark is somewhat of the nature of an arc, and may seriously injure commutators whose sections are only separated by mica, or other thin insulation. In the case of commutators whose sections are separated by air spaces it is not so injurious.
Flats. In a commutator of a dynamo, the burning or wearing away of a commutator segment to a lower level than the rest. Sometimes two adjacent bars will be thus affected, causing a flat place on the commutator. It is not always easy to account for the formation of flats. They may have their origin in periodic vibrations due to bad mounting, or to sparking at the particular point.
Floor Push. A press or push button constructed to be set into the floor to be operated by pressing with the foot. It is used to ring an alarm bell, sound a buzzer or for similar service.
Fluorescence. The property of converting ether waves of one length, sometimes of invisible length, into waves of another length (visible). AEsculin, quinine salts, uranium glass and other substances exhibit this phenomenon. The phenomenon is utilized in the production of Geissler tubes.
Flush Boxes. A heavy iron box covered with a heavy hand plate and laid flush (whence the name), or even with the surface of a roadway. Into it conductors of an underground system lead, and it is used to make connections therewith and for examining the leakage of the conductors and for similar purposes. It is a "man-hole" (q. v.) in miniature.
Fluviograph. An electric registering tide gauge or water level gauge.
Fly or Flyer, Electric. A little wheel, ordinarily poised on a point, like a compass needle. It carries several tangentially directed points, all pointing in the same sense. When connected with a source of electricity of high potential it revolves by reaction. The tension of its charge is highest at the points, the air there is highly electrified and repelled, the reaction pushing the wheel around like a Barker's mill or Hero's steam engine. Sometimes the flyer is mounted with its axis horizontal and across the rails on a railroad along which it travels.
Foci Magnetic. The two points on the earth's surface where the magnetic intensity is greatest. They nearly coincide in position with the magnetic poles.
Fog, Electric. Fogs occurring when the atmosphere is at unusually high potential and accompanied by frequent change of such polarity.
Following Horns. In dynamo-electric machines the projecting ends of the pole pieces towards which the outer uncovered perimeter of the armature turns in its regular operations. The leading horns are those away from which the armature rotates. In considering rotation the exposed portion of the superficies of the armature is considered. The definition would have to be reversed if the part facing the pole pieces were considered.
Foot-candle. A unit of illuminating power; the light given by one standard candle at a distance of one foot. The ordinary units of illuminating power are entirely relative; this is definite. It is due to Carl Herring.
Foot-pound. A practical unit of work or energy. The quantity of work required to raise a pound one foot, or one hundred pounds one-hundredth of a foot, and so on; or the potential energy represented by a weight at an elevation under these conditions.
Foot-step. In a dynamo with armature at the lower end of its field magnets, the plate generally of zinc, interposed between it and the iron base plate to prevent the leakage of lines of force outside of the circuit. Any diamagnetic material which is mechanically suitable may be used.
Force. Force may be variously defined. (a) Any cause of change of the condition of matter with respect to motion or rest.
(b) A measurable action upon a body under which the state of rest of that body, or its state of uniform motion in a straight line, suffers change.
(d) as the rate at which work is done per unit of space traversed.
Force is measured by the acceleration or change of motion it can impart to a body of unit mass in a unit of time, or, calling force, F, mass, m acceleration per second a we have F = m a.
The dimensions of force are mass (M) * acceleration (L/(T^2)) = (M*L)/(T^2).
Force de Cheval. Horse power (French). It is the French or metric horse power. It is equal to: 542.496 Foot lbs. per second. .9864 English Horse Power. 75.0 Kilogram-meters per second.
Force, Electro-magnetic. The mechanical force of attraction or repulsion acting on the electro-magnetic unit of quantity. Its intensity varies with the square of the distance. It may also be defined as electric force in the electro-magnetic system.
Its dimensions are equal to mechanical force ((M*L)/(T^2)) divided by quantity ((M^.5)*(L^.5)) = ((M^.5)*(L^.5))/(T^2).
Force, Electrostatic. The force by which electric matter or electrified surfaces attract or repel each other. It is also termed electric force (not good) and electro-motive intensity. It is the mechanical force acting upon a unit quantity of electricity. Its intensity varies with the square of the distance.
Its dimensions are therefore equal to (quantity * unity / (square of distance) Q. * 1 / (L^2) = ((M^.5) * (L^1.5) )/ T*1 / (L^2) = ((M^.5) * (L^.5)) / T These dimensions are also those of potential difference.
The objection to the term electric force is that it may be applied also to electro-magnetic force, and hence be a source of confusion.
Forces, Parallelogram of. The usual method of composing forces or resolving a force. The sides of a parallelogram of forces represent component forces and the diagonal represents the resultant. See Component—Resultant—Forces, Composition of—Forces, Resolution of.
Forces, Composition of. When several forces act in a different direction upon a point they may be drawn or graphically represented as arrows or lines emanating from the point in the proper direction and of lengths proportional to the force they exercise. Any two can be treated as contiguous sides of a parallelogram and the parallelogram can be completed. Then its diagonal, called the resultant, will represent the combined action of the two forces, both as regards direction and intensity. This is the composition of two forces.
If more than two forces act upon the given point the resultant can be composed with any of the others and a new force developed. The new resultant can be combined with another force, and the process kept up, eliminating the components one by one until a final resultant of all is obtained. This will give the exact direction and intensity of the forces, however many or varied.
Force, Tubes of. Aggregations of lines of force, either electrostatic or magnetic. They generally have a truncated, conical or pyramidal shape and are not hollow. Every cross-section contains the same number of lines. The name it will seem is not very expressive.
Force, Unit of. The fundamental or C. G. S. unit or force is the dyne, q. v.
The British unit of force is the poundal (the force which will produce an acceleration of one foot per second in a mass of one pound). It is equal to about 10/322 pound. A force cannot be expressed accurately in weight units, because weight varies with the latitude.
Foundation Ring. In a dynamo armature the ring-shaped core on which Gramme ring armatures and other ring armatures are wound.
Fourth State of Matter. Gas so rarefied that its molecules do not collide, or rarely do so; radiant matter, q. v.
Frame. In a dynamo the bed-piece is sometimes called the frame.
Franklin's Experiment. Franklin proved the identity of lightning and electricity by flying a kite in a thunder storm. The kite was of silk so as to endure the wetting. When the string became wet sparks could be taken from a key attached to its end. The main string was of hemp; at the lower end was a length of silk to insulate it. The key was attached near the end of and to the hemp string.
Franklin's Plate. A simple form of condenser. It consists of a plate of glass coated on each side with tinfoil with a margin of about an inch of clear glass. One coating may be grounded as indicated in the cut, and the plate charged like a Leyden jar. Or one side may be connected with one terminal, and the other with the other terminal of an influence machine and the pane will be thus charged.
Franklin's Theory. The single fluid theory, q. v., of electricity.
Frequency. The number of double reversals or complete alternations per second in an alternating current.
Frictional Electricity. Electricity produced by friction of dissimilar substances. (See Electrostatic Series.) The contact theory holds that friction plays only a secondary rle in this process; that it increases the thoroughness of contact, and tends to dry the rubbing surfaces, but that the charges induced are due to contact of dissimilar substances, not to friction of one against the other.
Frictional Heating. The heating of a conductor by the passage of a current; the Joule effect, q. v.
Fringe. The outlying edge of a magnetic field.
Frog, Galvani's Experiment With. A classic experiment in electricity, leading to the discovery of current or dynamic electricity. If a pair of legs of a recently killed frog are prepared with the lumbar nerves exposed near the base of the spinal column, and if a metallic conductor, one half-length zinc and the other half-length copper, is held, one end between the lumbar nerves and the spine, and the other end against one of the muscles of the thigh or lower legs, the moment contact occurs and the circuit is completed through the animal substance the muscles contract and the leg is violently drawn upwards. Galvani, in 1786, first performed, by accident, this famous experiment, it is said, with a scalpel with which he was dissecting the animal. He gave his attention to the nerves and muscles. Volta, more happily, gave his attention to the metals and invented the voltaic battery, described by him in a letter to Sir Joseph Banks, dated 1800.
Frog, Rheoscopic. If the nerve or living muscle of a frog is suddenly dropped upon another living muscle so as to come in contact with its longitudinal and transverse sections, the first muscle will contract on account of the stimulation of its nerve due to the passage of a current derived from the second muscle (Ganot). The experiment goes under the above title.
Fulgurite. An irregular and tubular mass of vitrified quartz, believed to be formed by melting under the lightning stroke.
Furnace, Electric. A furnace in which the heat is produced by the electric current. It has hitherto been practically used only in the extraction of aluminum and silicium from their ores. The general principle involves the formation of an arc between carbon electrodes. The substances to be treated are exposed to the heat thus produced. Sometimes the substances in the arc form imperfect conductors, and incandescence takes a part in the action. Sometimes the substances are merely dropped through the arc.
Fuse Board. A tablet on which a number of safety fuses are mounted. Slate is excellent material for the tablet, as it is incombustible, and is easily drilled and worked.
Fuse Box. A box containing a safety fuse. Porcelain is an excellent material for its base. No combustible material should enter into its composition.
Fuse, Cockburn. A safety fuse or cut off which consists of a wire of pure tin running from terminal to terminal, to whose centre a leaden ball is secured by being cast into position. The connection with the terminals is made by rings at the ends of the wire through which the terminal screws are passed and screwed home. When the tin softens under too heavy a current the weight of the shot pulls it apart.
Fig. 176 COCKBURN SAFETY FUSE.
Fuse, Electric. A fuse for igniting an explosive by electricity. There are two kinds. In one a thin wire unites the ends of the two conducting wires as they enter the case of the fuse. The larger wires are secured to the case, so that no strain comes on the fine wire. On passing a current of sufficient strength the small wire is heated. In use the fuse is bedded in powder, which again may be surrounded by fulminating powder, all contained in a copper or other metallic case. Such a detonator is used for exploding guncotton and other high explosives.
The other kind of fuse is similar, but has no thin connecting wire. The ends of the conductors are brought nearer together without touching. In use a static discharge is produced across from end to end of the conductors, igniting a proper explosive placed there as in the other case.
The first kind of fuse is generally operated by a battery or small mechanical generator—the latter by a spark coil, frictional or influence machine or by a Leyden jar.
Galvanic Element. A galvanic couple with exciting fluid and adjuncts; a galvanic cell. The word element is sometimes applied to the electrodes of a cell, as the carbon element or zinc element.
Galvanism. The science of voltaic or current electricity.
Galvanization. (a) Electroplating or depositing a metal over the surface of another by electrolysis.
(b) In medical electricity the effects produced on any part of the system by the current of voltaic battery. Various descriptive qualifications are prefixed, such as "general" galvanization, indicating its application as applied to the whole body, "local" for the reverse case, and so on.
Galvanization, Labile. Application of the galvanic current in electro-therapeutics where one sponge electrode is employed which is rubbed or moved over the body, the other being in constant contact with the body.
Galvanized Iron. Iron coated with zinc by cleaning and immersion in melted zinc. The iron is prevented from rusting by galvanic action. It forms the negative element in a couple of which the zinc is the positive element. From this electric protective action the name is derived.
Galvano-cautery, Chemical. Electro-therapeutic treatment with sharp electrodes, one of which is inserted in the tissue and a current passed by completing the circuit through the tissue so as to electrolyze or decompose the fluids of the tissue. It is applied in the removal of hair or extirpation of the follicle. The process is not one of heating, and is improperly named cautery.
Galvano-faradization. In medical electricity the application of the voltaic and induced or secondary current simultaneously to any part of the system.
Galvanometer. An instrument for measuring current strength and sometimes for measuring inferentially potential difference, depending on the action of a magnetic field established by the current, such action being exerted on a magnetic needle or its equivalent.
A current passing through a conductor establishes circular lines of force. A magnetic needle placed in their field is acted on and tends to place itself parallel with the lines, in accordance with the principles of current induction. (See Induction, Electro-magnetic.) A common compass held near a conductor through which a current is passing tends to place itself at right angles to such conductor. For a maximum effect the conductor or the part nearest the needle should lie in the magnetic meridian. If at right angles thereto its action will only strengthen the directive force of the earth's induction or magnetic field, as the needle naturally points north and south. Such combination is virtually a galvanometer.
A typical galvanometer comprises a flat coil of wire placed horizontally within which a magnetic needle is delicately poised, so as to be free to rotate with the least possible friction. The needle may be supported on a sharp point like a compass needle, or may be suspended by a long fine filament. It should be covered by a glass plate and box, or by a glass shade. Finally a graduated disc may be arranged to show the amount of deflection of the needle.
In use the apparatus is turned about until the needle, as acted on by the earth's magnetic field, lies parallel to the direction of the coils of wire. On passing a current through the coil the needle is deflected, more or less, according to its strength.
By using exceedingly fine wire, long enough to give high resistance, the instrument can be used for very high potentials, or is in condition for use in determining voltage. By using a coil of large wire and low resistance it can be employed in determining amperage. In either case the deflection is produced by the current.
The needle is often placed above or below the coil so as only to receive a portion of its effect, enough for all practical purposes in the commoner class of instruments.
The galvanometer was invented by Schweigger a short time after Oersted's discovery, q. v.
Galvanometer, Absolute. A galvanometer giving absolute readings; properly one whose law of calibration can be deduced from its construction. Thus the diameter of the coil, and the constants and position of a magnetic needle suspended in its field being known, the current intensity required to deflect the needle a given number of degrees could be calculated.
Galvanometer, Aperiodic. A galvanometer whose needle is damped (see Damping) as, for instance, by the proximity of a plate of metal, by an air vane or otherwise, so that it reaches its reading with hardly any oscillation. A very light needle and a strong magnetic field also conduce to vibrations of short period dying out very quickly. Such galvanometers are termed "dead-beat." No instrument is absolutely dead-beat, only relatively so.
Galvanometer, Astatic. A galvanometer with a pair of magnetic needles connected astatically, or parallel with their poles in opposition. (See Astatic Needle.) Each needle has its own coil, the coils being wound in opposite directions so as to unite in producing deflections in the same sense. As there should be some directive tendency this is obtained by one of the magnets being slightly stronger than the other or by the proximity of a fixed and adjustable controlling magnet, placed nearer one needle than the other.
For small deflections the currents producing them are proportional to their extent.
Galvanometer, Ballistic. A galvanometer whose deflected element has considerable moment of inertia; the exact opposite of an aperiodic or dead beat galvanometer. (See Galvanometer, Aperiodic.) All damping by air vanes or otherwise must be carefully done away with.
Fig. 179. SIEMENS & HALSKE'S GALVANOMETER.
Siemens & Halske's galvanometer is of the reflecting or mirror type (see Galvanometer, Reflecting) with suspended, bell-shaped magnet, in place of the ordinary magnetic needle, or astatic combination of the lightest possible weight in the regular instrument. A copper ball drilled out to admit the magnet is used as damper in the ordinary use of the instrument. To convert it into a ballistic galvanometer the copper ball is removed. The heavy suspended magnet then by its inertia introduces the desired element into the instrument.
Referring to the cut, Fig. 179, M is the suspended magnet, with north and south poles n and s; S is the reflecting mirror; r is the tube containing the suspending thread; R is the damper removed for ballistic work.
Galvanometer Constant. Assume a galvanometer with a very short needle and so placed with respect to its coils that the magnetic field produced by a current circulating in them is sensibly uniform in the neighborhood of the needle, with its lines of force at right angles thereto. The field is proportional to the current i, so that it may be denoted by G i. Then G is the galvanometer constant. If now the angle of deflection of the needle is ? against the earth's field H, M being the magnetic moment of the needle we have G i M cos ? = H M sin ? or i = (H/G)* tan ?. H/G is the reduction factor; variable as H varies for different places.
For a tangent galvanometer the constant G is equal to 2*PI*(n/a), in which n denotes the number of turns of wire, and a denotes the radius of the circle.
Galvanometer, Differential. A galvanometer in which the needle is acted on by two coils wound in opposition, each of equal deflecting action and of equal resistance. If a current is divided between two branches or parallel conductors, each including one of the coils, when the needle points to zero the resistances of the two branches will bc equal. In the cut, C C' represent the coils, and A and B the two leads into which the circuit, P Q, is divided.
Fig. 180. THEORY OF DIFFERENTIAL GALVANOMETER.
Galvanometer, Direct Reading. A calibrated galvanometer, whose scale is graduated by volts or amperes, instead of degrees.
Galvanometer, Potential. A galvanometer wound with fine German silver wire to secure high resistance used for determination of potential difference.
Galvanometer, Proportional. A galvanometer so constructed that the deflections of its index are proportional to the current passing. It is made by causing the deflecting force to increase as the needle is deflected, more and more, or by causing the restitutive force to diminish under like conditions, or by both. The condition is obtained in some cases by the shape and position of the deflecting coils.
Galvanometer, Quantity. A galvanometer for determining quantities of electricity, by the deflections produced by discharging the quantities through their coils. It is a ballistic galvanometer with very little or no damping.
Fig. 182. PRINCIPLE OF REFLECTING GALVANOMETER.
Galvanometer, Reflecting. A galvanometer the deflections of whose needle are read by an image projected by light reflected from a mirror attached to the needle or to a vertical wire carrying the needle. A lamp is placed in front of the instrument facing the mirror. The light of the lamp is reflected by the mirror upon a horizontal scale above the lamp. An image of a slit or of a wire may be caused thus to fall upon the scale, the mirror being slightly convex, or a lens being used to produce the projection.
If the mirror swings through a horizontal arc, the reflected image will move, in virtue of a simple geometrical principle, through an arc of twice as many degrees. The scale can be placed far from the mirror, so that the ray of light will represent a weightless index of very great length, and minute deflections of the needle will be shown distinctly upon the scale.
In the cut, Fig. 182, the ray of light from the lamp passes through the aperture, m m, and is made parallel by the lens, L. At s is the mirror attached to the needle and moving with it. A scale placed at t receives the reflection from the mirror. The cut, Fig. 183, shows one form of the instrument set up for use.
Galvanometer, Sine. A galvanometer whose measurements depend upon the sine of the angle of deflection produced when the coil and needle lie in the same vertical plane.
The needle, which may be a long one, is surrounded by a coil, which can be rotated about a vertical axis passing through the point of suspension of the needle. Starting with the needle at rest in the plane of the coil, a current is passed through the coil deflecting the needle, the coil is swung around deflecting the needle still more, until the needle lies in the plane of the coil; the intensity of the current will then be in proportion to the sine of the angle through which the coil and needle move.
In the galvanometer M is a circle carrying the coil, N is a scale over which the needles, m and n, move, the former being a magnetic needle, the latter an index at right angles and attached thereto; a and b are wires carrying the current to be measured. The circles, M and N, are carried by a base, O, around which they rotate. H is a fixed horizontal graduated circle. In use the circle, M, is placed in the magnetic meridian, the current is passed through the coil, M; the needle is deflected; M is turned until its plane coincides with the direction of the needle, m. The current strength is proportional to the sine of the angle of deflection. This angle is measured by the vernier, C, on the circle, H. The knob, A, is used to turn the circle, M.
Galvanometer, Tangent. A galvanometer in which the tangents of the angles of deflection are proportional to the currents producing such deflections.
(4) the magnetic axis of the needle must lie in the plane of the coil when no current is passing.
If a single current strength is to be measured the best results will be attained when the deflection is 45; in comparing two currents the best results will be attained when the deflections as nearly as possible are at equal distances on both sides of 45.
The needle should not exceed in length one-tenth the diameter of the coil.
For very small deflections any galvanometer follows the law of tangential deflection.
As for very small deflections the tangents are practically equal to the arcs subtended, for such deflections the currents are proportional to the deflections they produce.
The sensibility is directly proportional to the number of convolutions of wire and inversely proportional to their diameter.
The tangent law is most accurately fulfilled when the depth of the coil in the radial direction is to the breadth in the axial direction as squareRoot(3):squareRoot(2), or about as 11:9.
Galvanometer, Torsion. A galvanometer whose needle is suspended by a long filament or by a thread and spiral spring against whose force of torsion the movements of the needle are produced. The current strength is determined by bringing the needle back to its position of rest by turning a hand-button or other arrangement. The angle through which this is turned gives the angle of torsion. From this the current strength is calculated on the general basis that it is proportional to the angle of torsion.
Galvanometer, Vertical. A galvanometer whose needle is mounted on a horizontal axis and is deflected in a vertical plane. One of the poles is weighted to keep it normally vertical, representing the control. It is not used for accurate work.
Galvanometer, Volt- and Ampere-meter. A galvanometer of Sir William Thomson's invention embodying the tangent principle, and having its sensibility adjustable by moving the magnetic needle horizontally along a scale (the "meter") towards or away from the coil. A curved magnet is used to adjust the control. The leads are twisted to prevent induction.
The instrument is made with a high resistance coil for voltage determinations, and with a low resistance coil for amperage determinations.
At one end of a long base board a vertical coil with its plane at right angles to the axis of the board is mounted. A scale (the "meter" of the name) runs down the centre of the board. A groove also runs down the centre. The magnetic needle is contained in a quadrant-shaped glass-covered box which slides up and down the groove. A number of short parallel needles mounted together, with an aluminum pointer are used.
Fig. 188. SIR WILLIAM THOMSON'S AMPERE-METER GALVANOMETER.
In the cut P is the base board, M is a glass covered case containing the magnetic needle, and sliding along the base board, being guided by the central groove, C, is the coil. Between the coil and the needle is the arched or bent controlling magnet. The long twisted connecting wires are seen on the right hand.
Galvano-plastics. The deposition of metals by electrolysis, a disused term replaced by electro-deposition, electroplating, and electro-metallurgy.
Galvanoscope. An instrument, generally of the galvanometer type, used for ascertaining whether a current is flowing or not. Any galvanoscope, when calibrated, if susceptible thereof, becomes a galvanometer.
Gases, Mixed. The mixture of approximately one volume of oxygen and two volumes of hydrogen collected in the eudiometer of a gas voltameter or other electrolytic apparatus.
Gassing. The evolution of gas from the plates of a storage battery in the charging process, due to too high voltage in the circuit of the charging dynamo.
Gastroscope. An apparatus for illuminating by an incandescent lamp the interior of the stomach, and with prisms to refract the rays of light so that the part can be seen. The stomach is inflated with air, if desirable, to give a better view. An incandescent platinum spiral in a water jacket has been employed for the illumination.
Gassiot's Cascade. A goblet lined for half its interior surface with tinfoil. It is placed in the receiver of an air pump from the top of whose bell a conductor descends into it, not touching the foil. On producing a good rarefaction, and discharging high tension electricity from between the conductor just mentioned and the metal of the machine, a luminous effect is produced, as if the electricity, pale blue in color, was overflowing the goblet.
The gauss is not used to any extent; practical calculations are based on electro-magnetic lines of force.
Gauss' Principle. An electric circuit acts upon a magnetic pole in such a way as to make the number of lines of force that pass through the circuit a maximum.
Fig. 189. GAUSS' TANGENT POSITION.
Gear, Magnetic Friction. Friction gear in which the component wheels are pressed against each other by electromagnetic action. In the cut, repeated from Adherence, Electro-magnetic, the magnetizing coil makes the wheels, which are of iron, press strongly together.
Fig. 190. MAGNETIC FRICTION GEAR.
Geissler Tubes. Sealed tubes of glass containing highly rarefied gases, and provided with platinum electrodes extending through the glass tightly sealed as they pass through it, and often extending a short distance beyond its interior surface.
On passing through them the static discharge luminous effects are produced varying with the degree of exhaustion, the contents (gas), the glass itself, or solutions surrounding it. The two latter conditions involve fluorescence phenomena often of a very beautiful description.
The pressure of the gas is less than one-half of a millimeter of mercury. If a complete vacuum is produced the discharge will not pass. If too high rarefaction is produced radiant matter phenomena (see Radiant State) occur.
Geissler tubes have been used for lighting purposes as in mines, or for illuminating the interior cavities of the body in surgical or medical operations.
Generating Plate. The positive plate in a voltaic couple, or the plate which is dissolved; generally a plate of zinc.
Generator, Current. Any apparatus for maintaining an electric current. It may be as regards the form of energy it converts into electrical energy, mechanical, as a magneto or dynamo electric machine or generator; thermal, as a thermo-electric battery; or chemical, as a voltaic battery; all of which may be consulted.

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