STANDARD ELECTRICAL DICTIONARY.Table of Declination or Variation at Paris.Year. Declination.1580 11º 30' E.1663 0°1700 8° 10' W.1780 19º 55' W.1785 22º 00' W.1805 22º 5' W.1814 22º 34' W.1825 22° 22' W.1830 22º 12' W.1835 22º 4' W.1850 20º 30' W.1855 19º 57' W.1860 19º 32' W.1865 18º 44' W.1875 17º 21' W.1878 17º 00' W.[Transcriber's note The value for 2008 is about 0° 48' W, changing by0° 7' E/year.]On scrutinizing these figures it will be seen that there is part of acycle represented and that the declination is slowly returning to thezero point after having reached its maximum western variation in 1814.Upwards of 300 years would be required for its completion on the basisof what is known. In other places, notably the coast of Newfoundland,the Gulf of the St. Lawrence and the rest of the North American seaboardand in the British Channel, the secular variations are much more rapidin progress. (b) Annual variations--These were first discovered in 1780by Cassini. They represent a cycle of annual change of small extent,from 15' to 18' only. In Paris and London the annual variation isgreatest about the vernal equinox, or March 21st, and diminishes for thenext three months, and slowly increases again during the nine followingmonths. It varies during different epochs. (c) Diurnal variations werediscovered in 1722 by Graham. A long needle has to be employed, or thereflection of a ray of light, as in the reflecting galvanometer, has tobe used to observe them. In England the north pole of the magneticneedle moves every day from east to west from sunrise until 1 or 2 P.M.; it then tends towards the east and recovers its original position by10 P. M. During the night the needle is almost stationary. As regardsrange the mean amplitude of diurnal variations at Paris is from April toSeptember 13' to 15'; for the other months from 8' to 10'. On some daysit amounts to 25' and sometimes is no more than 5'. The amplitude ofdiurnal variations decreases from the poles to the equator. Irregularvariations accompany earthquakes, the aurora borealis and volcaniceruptions. In Polar regions the auroral variations may be very great;even at 40° latitude they may be 1° or 2°. Simultaneous irregularitiessometimes extend over large areas. Such are attributed to magneticstorms. II. The Inclination is the angle which the magnetic needle makeswith the horizon, when the vertical plane in which the needle is assumedto be free to move coincides with the magnetic meridian. It is sometimescalled the dip of the needle. It varies as does the declination, asshown in the following table of inclinations of London.344 STANDARD ELECTRICAL DICTIONARY.Table of Inclination or Dip at LondonYear. Inclination.1576 71° 50'1600 72°1676 73° 30'1723 74° 42'1773 72° 19'1780 72° 8'1790 71° 33'1800 70° 35'1821 70° 31'1828 69° 47'1838 69° 17'1854 68° 31'1859 68° 21'1874 67° 43'1876 67° 39'1878 67° 36'1880 67° 35'1881 67° 35'III. Force or Intensity is the directive force of the earth. It varieswith the squares of the number of oscillations the magnetic needle willmake if caused to oscillate from a determined initial range. Theintensity is supposed to be subject to secular change. According toGauss the total magnetic intensity of the earth is equal to that whichwould be exerted if in each cubic yard there were eight bar magnets,each weighing one pound. This is, of course, a rough way of expressingthe degree of intensity. Intensity is least near the magnetic equatorand greatest near the magnetic poles; the places of maximum intensityare termed the magnetic foci. It varies with the time of day andpossibly with changes in altitude.Magnetic Elongation.The elongation a bar of iron or steel undergoes when magnetized. Bymagnetization it becomes a little longer and thinner, there being noperceptible change in volume. The change is accompanied by a slightsound--the magnetic tick. An exceedingly delicate adjustment ofapparatus is required for its observation.Magnetic Equator.A locus of the earth's surface where the magnet has no tendency to dip.It is, approximately speaking, a line equally distant from the magneticpoles, and is called also the aclinic line. It is not a great circle ofthe earth.345 STANDARD ELECTRICAL DICTIONARY.Magnetic Field of Force.The field of force established by a magnet pole. The attractions andrepulsions exercised by such a field follow the course of the electro-magnetic lines of force. (See also Field of Force.) Thus the tendency ofa polarized needle attracted or repelled is to follow, always keepingtangential to curved lines, the direction of the lines of force, howeversweeping they may be. The direction of magnetic lines of force isassumed to be the direction in which a positive pole is repelled or anegative one attracted; in other words, from the north pole of a magnetto its south pole in the outer circuit. The direction of lines of forceat any point, and the intensity or strength of the field at that point,express the conditions there. The intensity may bc expressed in terms ofthat which a unit pole at unit distance would produce. This intensity asunitary it has been proposed to term a Gauss. (See Weber.)The direction of the lines of force in a magnetic field are shown by thetime-honored experiment of sprinkling filings of iron upon a sheet ofpaper held over a magnet pole or poles. They arrange themselves, if thepaper is tapped, in more or less curved lines tending to reach from onepole of the magnet to the other. Many figures may be produced bydifferent conditions. Two near poles of like name produce lines of forcewhich repel each other. (See Magnetic Curves.)A magnetic and an electro-magnetic field are identical in all essentialrespects; the magnetic field may be regarded as a special form of theelectro-magnetic field, but only special as regards its production andits defined north and south polar regions.Synonyms--Magnetic Spin (not much used).Magnetic Field, Uniform.A field of identical strength in all parts, such as the earth's magneticfield. If artificially produced, which can only be approximately done,it implies large cross-section of magnet pole in proportion to thelength of the magnetic needle affected by it, which is used indetermining its uniformity.Magnetic Figures.The figures produced by iron filings upon paper or glass held nearmagnetic poles. By these figures the direction of lines of force isapproximately given, and a species of map of the field is shown. (SeeMagnetic Field of Force--Magnetic Curves.)Magnetic Filament.The successive rows of polarized molecules assumed to exist inmagnetized iron. Each molecule represents an infinitely small magnet,and its north pole points to the south pole of the next molecule. Such astring or row is a theoretical conception based on the idea that themolecules in a magnet are all swung in to parallelism in the magnetizingprocess. A magnetic filament may be termed the longitudinal element of amagnet. (See Magnetism, Hughes' Theory of.)[Transcriber's note: This description parallels the modernnotion of electron spin as the basis of magnetism in materials.]Magnetic Fluids.A two-fluid theory of magnetism has been evolved, analogous to thetwo-fluid theory of electricity. It assumes north fluid or "redmagnetism" and a south fluid or "blue magnetism." Each magnetism issupposed to predominate at its own pole and to attract its opposite.Before magnetization the fluids are supposed to neutralize each otherabout each molecule; magnetization is assumed to separate them,accumulating quantities of them at the poles.Magnetic Flux.Magnetic induction; the number of lines of force that pass through amagnetic circuit.Synonym--Magnetic Flow.346 STANDARD ELECTRICAL DICTIONARY.Magnetic Force.The forces of attraction and repulsion exercised by a magnet. ByAmpere's theory it is identical with the forces of attraction andrepulsion of electric currents.Magnetic Friction.The damping effect produced on the movements of a mass of metal byproximity to a magnet; the phenomenon illustrated in Arago's wheel, q.v. When a mass of metal moves in the vicinity of a magnet it cuts thelines of force emanating from its poles, thereby producing currents inits mass; as the production of these currents absorbs energy a dampingeffect is produced upon the movements of the mass.Magnetic Gear.Friction gear in which electro-magnetic adherence is employed to drawthe wheels together. (See Adherence, Electro-magnetic--Electro-magneticFriction Gear.)Magnetic Inclination.The inclination from the horizontal of a magnetic needle placed in themagnetic meridian. (See Magnetic Element--Inclination Map.)Synonym--Magnetic Dip.Magnetic Induction.The force of magnetization within an induced magnet. It is in part dueto the action of the surrounding particles of polarized material; inpart to the magnetic field. (See Magnetic Induction, Coefficient of.)In a more general way it is the action of a magnet upon bodies in itsfield of force. In some cases the magnetism induced causes the northpole of the induced magnet to place itself as far as possible from thenorth pole of the inducing magnet and the same for the south poles. Suchsubstances are called paramagnetic or ferromagnetic. They lie parallelor tangential to the lines of force. In other cases the bodies lie atright angles or normal to the lines of force. Such bodies are calleddiamagnetic.Some bodies are crystalline or not homogeneous in structure, and in themthe lines of magnetic induction may take irregular or eccentric paths.(See AEolotropic.)Synonym--Magnetic Influence.Magnetic Induction, Apparent Coefficient of.The apparent permeability of a paramagnetic body as affected by thepresence of Foucault currents in the material itself. These currents actexactly as do the currents in the coils surrounding the cores ofelectro-magnets. They produce lines of force which may exhaust thepermeability of the iron, or may, if in an opposite direction, add toits apparent permeability.Magnetic Induction, Coefficient of.The number, obtained by dividing the magnetization of a body, expressedin lines of force produced in it, by the magnetizing force which hasproduced such magnetization, expressed in lines of force producible bythe force in question in air. It always exceeds unity for iron, nickeland cobalt. It is also obtained by multiplying the coefficient ofinduced magnetization by 4 PI (4 * 3.14159) and adding 1. (See MagneticSusceptibility--Magnetization, Coefficient of Induced.)347 STANDARD ELECTRICAL DICTIONARY.The coefficient of magnetic induction varies with the material of theinduced mass, and varies with the intensity of the magnetizing force.This variation is due to the fact that as the induced magnetism in abody increases, the magnetizing force required to maintain suchinduction, increases in a more rapid ratio. The coefficient of magneticinduction is the same as magnetic permeability, and in a certain senseis the analogue of conductivity. It is also termed the multiplying powerof the body or core magnetized. It is the coefficient of inducedmagnetization (see Magnetization, Coefficient of Induced) referred to amass of matter. For diamagnetic bodies the coefficient has a negativesign; for paramagnetic bodies it has a positive sign.Synonyms--Permeability--Multiplying Power--Magnetic Inductive Capacity.Magnetic Induction, Dynamic.The induction produced by a magnetic field which moves with respect to abody, or where the body if moving moves at a different rate, or wherethe body moves and the field is stationary. In the case where both move,part of the induction may be dynamic and part static. (See MagneticInduction, Static.)Magnetic Induction, Static.Magnetic induction produced by a stationary field acting upon astationary body.Magnetic Induction, Tube of.An approximate cylinder or frustrum of a cone whose sides are formed oflines of magnetic induction. (See Magnetic Induction, Lines of.) Theterm tube is very curiously applied in this case, because the element orportion of a magnetic field thus designated is in no sense hollow ortubular.Magnetic Inertia.A sensible time is required to magnetize iron, or for it to part withits magnetism, however soft it may be. This is due to its magneticinertia and is termed the lag. Permanent or residual magnetism is aphase of it. It is analogous to self-induction of an electric circuit,or to the residual capacity of a dielectric.Magnetic Insulation.Only approximate insulation of magnetism is possible. There is noperfect insulator. The best ones are only 10,000 times less permeablethan iron. Hence lines of force find their way through air and all othersubstance, being simply crowded together more in paths of iron or otherparamagnetic substance.348 STANDARD ELECTRICAL DICTIONARY.Magnetic Intensity.The intensity of the magnetization of a body. It is measured by themagnetic lines of force passing through a unit area of the body, sucharea being at right angles to the direction of the lines of force.Magnetic Lag.In magnetism the tendency of hard iron or steel especially to take upmagnetism slowly, and to part with it slowly. (See Magnetic Inertia.)The lag affects the action of a dynamo, and is a minor cause of thosenecessitating the lead of the brushes.Synonym--Magnetic Retardation.Magnetic Latitude.Latitude referred to the magnetic equator and isoclinic lines.Magnetic Leakage.The lines of force in a field magnet which pass through the air and notthrough the armature are useless and represent a waste of field. Suchlines constitute magnetic leakage.Magnetic Limit.The temperature beyond which a paramagnetic metal cannot be magnetized.The magnetic limit of iron is from a red to a white heat; of cobalt, farbeyond a white heat; of chromium, below a red heat; of nickel at about350° C. (662°F.) of manganese, from 15° C. to 20° C. (59° to 68° F.)Magnetic Lines of Force.Lines of force indicating the distribution of magnetic force, which isdue presumably to whirls of the ether. A wire or conductor through whicha current is passing is surrounded by an electro-magnetic field offorce, q. v., whose lines of force form circles surrounding theconductor in question. A magnet marks the existence of a similarelectro-magnetic field of force whose lines form circuits comprisingpart of and in some places all of the body of the magnet, and which arecompleted through the air or any surrounding paramagnetic or diamagneticbody. They may be thought of as formed by the Ampérian sheet of current,and analogous to those just mentioned as surrounding a conductor.Fig. 223. MAGNETIC LINES OF FORCE, DIRECTION OF.A magnetic line of force may be thought of as a set of vortices orwhirls, parallel to each other, and strung along the line of force whichis the locus of their centres.If as many lines are drawn per square centimeter as there are dynes (perunit pole) of force at the point in question, each such line will be aunitary c. g. s. line of force.349 STANDARD ELECTRICAL DICTIONARY.Magnetic Mass.A term for a quantity of magnetism. Unit mass is the quantity which atunit distance exercises unit force.Magnetic Matter.Imaginary matter assumed as a cause of magnetism. Two kinds, onepositive and one negative, may be assumed as in the two fluid theory ofelectricity, or only one kind, as in the single fluid theory ofelectricity. Various theories of magnetic matter have been presentedwhose value is only in their convenience.[Transcriber's note: See "magnet" and Edward Purcell's explanation ofmagnetism using general relativity.]Magnetic Memory.The property of retaining magnetism; coercive force; magnetic inertia;residual magnetism.[Transcriber's note: Small ferrite magnetic donuts were used as computermain memory from 1950 to 1970.]Magnetic Meridian.A line formed on the earth's surface by the intersection therewith of aplane passing through the magnetic axis. It is a line determined by thedirection of the compass needle. The meridians constantly change indirection and correspond in a general way to the geographical meridians.Magnetic Moment.The statical couple with which a magnet would be acted on by a uniformmagnetic field of unit intensity if placed with its magnetic axis atright angles to the lines of force of the field. (Emtage.) A uniformlyand longitudinally magnetized bar has a magnetic moment equal to theproduct of its length by the strength of its positive pole.Magnetic Needle.A magnet with a cup or small depression at its centre and poised upon asharp pin so as to be free to rotate or oscillate in a horizontal plane.The cup is often made of agate. Left free to take any position, itplaces its magnetic axis in the magnetic meridian.Magnetic Parallels.Lines roughly parallel to the magnetic equator on all parts of each ofwhich the dip of the magnetic needle is the same; also called IsoclinicLines. These lines mark the places of the intersection of equipotentialsurfaces with the earth's surface. They are not true circles, and nearthe poles are irregular ellipses; the magnet there points toward theircentres of curvature. They correspond in a general way with theGeographical Parallels of Latitude.Magnetic Permeability.The specific susceptibility of any substance, existing in a mass, formagnetic induction. (See Magnetic Induction, Coefficient of, synonym forMagnetic Permeability and Magnetization, Coefficient of Induced.)Synonyms--Magnetic Inductive Capacity--Multiplying Power--Coefficient ofMagnetic Induction.350 STANDARD ELECTRICAL DICTIONARY.Magnetic Perturbations.Irregular disturbances of the terrestrial magnetism, as by the auroraand in electric storms.Magnetic Poles.The points where the equipotential surfaces of the terrestrial field offorce graze the earth's surface; the points toward which the north orsouth poles of the magnetic needle is attracted. Over a magnetic polethe magnetic needle tends to stand in a vertical position. There are twopoles, Arctic or negative, and Antarctic or positive. Magnetic needlessurrounding them do not necessarily point toward them, as they point tothe centres of curvature of their respective magnetic parallels. Thepoles constantly change in position. The line joining them does notcoincide with anything which may be termed the magnetic axis of theearth.Magnetic Poles, False.Poles on the earth's surface other than the two regular magnetic poles.There seem by observation to be several such poles, while analogy wouldlimit true magnetic poles to two in number.Magnetic Potential.The potential at any point of a magnetic field is the work which wouldbe done by the magnetic forces of the field upon a positive unit ofmagnetism as it moves from that point to an infinite distance. (Emtage.)Magnetic Proof Piece.A piece of iron used for testing magnets and the distribution ofmagnetism in bars, by suspending or supporting above or near the magnet,by detaching after adherence, and in other ways.Magnetic Proof Plane.An exploring coil used for testing the distribution of magnetism. It isconnected in circuit with a galvanometer, and exposed to alternation ofcurrent, or to other disturbing action produced by the magnet or fieldunder examination. This affects the galvanometer, and from its movementsthe current produced in the coil, and thence the magnetic induction towhich it was exposed, are calculated.Synonym--Exploring Coil.Magnetic Quantity.The magnetism possessed by a body; it is proportional to the action ofsimilar poles upon each other, or to the field produced by the pole inquestion. It is also called the strength of a pole.The force exercised by two similar poles upon each other varies withtheir product and inversely with the square of the distance separatingthem; or it may be expressed thus (m * m) / (L^2). This is a force, andthe dimensions of a force are ML/(T^2). Therefore, (m^2)/(L^2) =ML/(T^2) or m = (M^.5)*(L^1.5)/T.351 STANDARD ELECTRICAL DICTIONARY.Magnetic Reluctance.The reciprocal of permeance; magnetic resistance; the relativeresistance to the passage of lines of force offered by differentsubstances. The idea is derived from treating the magnetic circuit likean electric one, and basing its action on magneto-motive force actingthrough a circuit possessing magnetic reluctance.Magnetic Reluctivity.The reciprocal of magnetic permeability, q. v.Synonym--Magnetic Resistance.Magnetic Retentivity.The property of steel or hard iron by which it slowly takes up andslowly parts with a magnetic condition--traditionally (Daniell) calledcoercitive force.Magnetic Rotary Polarization.If a plane polarized beam of light is sent through a transparent mediumin a magnetic field its plane of polarization is rotated, and thisphenomenon is denoted as above. (Compare Refraction, Electric, and seeElectro-magnetic Stress.) This has been made the basis of a method formeasuring current. A field of force varies with the current; thepolarization produced by such field is therefore proportional to thecurrent. (Becquerel & Rayleigh.)A plane polarized beam of light passing through the transparent mediumin the magnetic field by the retardation or acceleration of one of itscircular components has its plane of polarization rotated as described.The direction of the lines of force and the nature of the mediumdetermine the sense of the rotation; the amount depends upon theintensity of the field resolved in the direction of the ray, and on thethickness and nature of the medium.Magnetic Saturation.The maximum magnetic force which can be permanently imparted to a steelbar. A bar may be magnetized beyond this point, but soon sinks to it.The magnetism produced in a bar is prevented from depolarization by theretentivity or coercive force of the bar. The higher the degree ofmagnetization the greater the tendency to depolarization.It is also defined as the maximum intensity of magnetism produced in aparamagnetic substance by a magnetic field as far as affected by thepermeability of the substance in question. The more lines of forcepassed through such a substance the lower is its residual permeability.It is assumed that this becomes zero after a certain point, and then thepoint of saturation is reached. After this point is reached the additionof any lines of force is referred entirely to the field and not at allto the permeability of the substance. But such a zero is only definableapproximately.Magnetic Screen.A box or case of soft iron, as thick as practicable, for protectingbodies within it from the action of a magnetic field. The lines of forceto a great extent keep within the metal of the box on account of itspermeability, and but a comparatively few of them cross the space withinit.Such screens are used to prevent watches from being magnetized, and area part of Sir William Thomson's Marine galvanometer.A magnetic screen may be a sphere, an infinite or very large plane, orof the shape of any equipotential surface.Synonym--Magnetic Shield.352 STANDARD ELECTRICAL DICTIONARY.Magnetic Self-induction.The cause of a magnet weakening is on account of this quality, which isdue to the direction of the lines of force within a magnet from thepositive towards the negative pole. "A magnet thus tends to repel itsown magnetism and to weaken itself by self-induction." (Daniell.)Magnetic Separator.An apparatus for separating magnetic substances from mixtures. Suchseparators depend on the action of electro-magnets. In one form thematerial falls upon an iron drum, magnetized by coils. Any magneticsubstance adheres to the drum and is thereby separated. They are used byporcelain makers for withdrawing iron particles from clay, by machiniststo separate iron filings and chips from brass, and for similar purposes.Fig. 224. MAGNETIC SEPARATOR.Magnetic Shell.A theoretical conception of a cause of a magnetic field or of adistribution of magnetism. If we imagine a quantity of very shortmagnets arranged in contact with their like poles all pointing in thesame direction so as to make a metal sheet, we have a magnetic shell.Its magnetic moment is equal to the sum of the magnetic moment of allits parts. If the shell is of uniform strength the magnetic moment of aunit area gives the strength of the shell; it is equal to the magneticquantity per unit of area, multiplied by the thickness of the shell.If its strength is uniform throughout a magnetic shell is called simple;if its strength varies it is termed complex.Emtage thus defines it: A magnetic shell is an indefinitely thin sheetmagnetized everywhere in the direction normal to itself.Magnetic Shell, Strength of.The magnetic quantity per unit of area of the shell multiplied by thethickness of the shell.353 STANDARD ELECTRICAL DICTIONARY.Magnetic Shield.In general a magnetic screen, q. v. Sometimes a strong local field ismade to act as a shield, by its predominance overcoming any local orterrestrial field to which the needle to be protected may be exposed.Magnetic Shunt.The conception of a magnetic circuit being formed, the shunt is acorollary of the theory. It is any piece of iron which connects pointsof a magnet differing in polarity, so as to divert part of the lines offorce from the armature or yoke. The shunt is especially applicable inthe case of horseshoe magnets. Thus a bar of iron placed across fromlimb to limb a short distance back from the poles would act as a shuntto the armature and would divert to itself part of the lines of forcewhich would otherwise go through the armature and would weaken theattraction of the magnet for the latter. In dynamos a bar of iron usedas a magnetic shunt has been used to diminish the lines of force goingthrough the armature and hence to weaken the field and diminish theelectro-motive force. By moving the shunt nearer or further from thepoles the dynamo is regulated.In the cut the projections between the yoke and poles of the magnetshown act as a shunt to the yoke, taking some lines of force therefrom.Fig. 225. MAGNETIC SHUNT.Magnetic Storms.Terrestrial magnetic disturbances sometimes covering very wide areas,and affecting the magnetic declination and inclination. One suchdisturbance was felt simultaneously at Toronto, Canada, the Cape of GoodHope, Prague and Van Diemen's Land. (Sabine.)354 STANDARD ELECTRICAL DICTIONARY.Magnetic Strain.The strain produced by magnetic lines of force in substances exposed totheir action. It is observed in substances placed between the poles of astrong electro-magnet, and evinces itself in the alteration of theoptical properties of transparent substances.Magnetic Stress.The stress produced by magnetic lines of force on substances throughwhich they pass, evidenced in alteration of the optical properties oftransparent bodies thus treated.Magnetic Susceptibility.The specific intrinsic susceptibility of any material for magneticinduction. It refers to the particle of matter, and not to the mass, asin the latter its own particles react on each other and bring about whatis termed permeability, q. v. (See also Magnetization, Coefficient ofInduced, and Magnetic Induction, Coefficient of.)Synonym--Coefficient of Induced Magnetization.Magnetic Tick.When a bar of iron is suddenly magnetized or demagnetized it emits aslight sound, called the Page sound, or the magnetic tick. This has beenutilized in a telephone by Reiss. The telephone will receive sound, butis very weak. It consists of a bar surrounded with a coil of insulatedwire. Variations in current produce sounds, which may be articulate ifthe currents are produced by a telephonic transmitter.Magnetic Twist.A bar of iron held in the magnetic meridian and pointing to the pole andtwisted becomes to some extent permanently magnetized. Conversely a barwhen magnetized seems to have a twist set up in it. The latter ismagnetic twist.Magnetic Variations.Changes in the value of magnetic declination or inclination. (SeeMagnetic Elements.)Magnetism, Ampére's Theory of.A theory accounting for magnetic phenomena by assuming the existence ofcurrents circulating around the molecules of permanent magnets. If suchcurrents so circulate and all in the same direction, the result is thesame as if the body of the magnet was enveloped in currents representingthose of an electro-magnet or solenoid. This is because in the interiorthe current around one molecule would counteract the current around itsneighboring ones in part, so that the only virtual currents left wouldbe represented by those on the outer surfaces of the outer shell ofmolecules, and these virtually resolve themselves into one generalcurrent sheet, surrounding the magnet and coinciding with its surface.The theory assumes that such currents permanently circulate around themolecules of paramagnetic substances. Under ordinary conditions there isno coincidence in their direction and no resultant current is produced.When magnetized or polarized the molecules are brought into order, sothat the direction of their current coincides and the body becomes amagnet.355 STANDARD ELECTRICAL DICTIONARY.Fig. 226. AMPÉRIAN CURRENTS IN MAGNETS.At the north pole of the magnet the direction of the Ampérian currentsis the reverse of that of a watch when the observer faces the pole; thereverse obtains for the south pole.The attraction of opposite and repulsion of similar poles is explainedby the actions of the Ampérian currents upon each other. If north andsouth pole are placed together these currents will coincide in directionand hence will attract each other. If two like poles are put togetherthe currents will have opposite directions and will repel each other.No energy is supposed to be required to maintain currents around or in asingle molecule.Fig. 227. NORTH AND SOUTH POLES OF A MAGNETSHOWING DIRECTION OF AMPÉRIAN CURRENTS.Magnetism, Blue.A term arising from the two fluid theory of magnetism; the magnetism ofthe south pole of a magnet. (See Magnetic Fluids.) The magnetism of thenorth pole is termed red magnetism. Both terms originated presumably inthe painting of magnets, and are little used.Synonym--South Magnetic Fluid.356 STANDARD ELECTRICAL DICTIONARY.Magnetism, Components of Earth's.The magnetic force of the earth acts in the plane of the magneticmeridian and in direction generally lies oblique to the plane of thehorizon. It can be resolved into two components, one vertical, which hasno directive effect upon the magnetic needle, the other horizontal,which represents the directive element for the usual compass needle. Forthe dipping needle, q. v., the vertical component is the only activeone. A magnetic needle mounted on a universal joint at its centre ofgravity would be acted on by both components.Magnetism, Creeping of.The gradual increase of magnetism when a magnetic force is applied withabsolute steadiness to a piece of iron. It is a form of magnetic lag. Itmay last for half an hour and involve an increase of several per cent.of the total magnetism.Synonym--Viscous Hysteresis.Magnet, Iron Clad.A magnet with a casing of iron connected at one end to the core. Theterm is generally applied to electromagnets of this form.Synonyms--Tubular Magnet--Jacketed Magnet.Magnetism, Decay of.The gradual loss of magnetism by permanent magnets, due to accidentalshocks, changes of temperature, slow spontaneous annealing of the ironand other similar causes.Magnetism, Discharge of.The loosing of magnetization. Thus in a shunt-wound dynamo there is acritical resistance for the outer circuit, below which the field ceasesto be magnetized, as enough current ceases to be shunted into it tomagnetize it. The machine is said to unbuild itself, and a discharge ofmagnetism occurs from the field magnet.Magnetism, Ewing's Theory of.Ewing found by a model consisting of a number of pivoted magneticneedles that the observed phenomena of magnetization could berepresented thereby. Thus there would be no need of assuming internalfrictional forces of Maxwell, nor the closed rings or chains of Hughes.The theory retains the notion, however, of paramagnetic matter,consisting of an assemblage of molecular magnets. The loss of energy byhysteresis is represented in the model by the energy lost by the needlesin beating against the air.357 STANDARD ELECTRICAL DICTIONARY.Magnetism, Free.The magnetism or magnetic field outside of a magnetic circuit. It is dueto escape of lines of force and to the magnetic leakage through the air.The lines of force are never, under the most favorable circumstances,confined to the metallic circuit of the magnet and armature. In a simplemagnet without armature all the lines of force have to follow an airpath, and the field is at its strongest. As the magnetism is strongestat the surface near the poles, the term is sometimes understood asapplying to the surface attraction. In such case it is defined as thedistribution, on a magnetized bar or mass, of magnetic lines of force asthey emerge from its surface.Synonym--Surface Magnetization.Magnetism, Hughes' Theory of.A theory accounting for magnetic phenomena by assuming that eachmolecule is a magnet, and that in a polarized or magnetized body theyare all arranged with their poles in the same direction, while in anunmagnetized body their poles, alternating in direction, neutralize eachother.Magnetization consists in a partial rotation of the molecules so as tomake them agree in position, thus, as a resultant developing north andsouth poles at the ends of the bar.The theory is in a certain sense simpler than Ampere's theory, but isnot so generally adopted.Magnetism, Lamellar Distribution of.The distribution of magnetism in thin and uniform or "simple magneticshells," q. v. A given distribution is termed lamellar if the substancein which it exists can be divided into simple magnetic shells, whicheither form closed surfaces, or have their edges in the surface of thesubstance. In lamellar distribution the polar area is very largecompared with the distance between opposite poles.Magnetism of Gases.Faraday experimented on this point by coloring gases with a little vaporof iodine or other colored gas, and letting them flow between the twopoles of a powerful electromagnet. In this way he found some arerepelled, some attracted, and in the case of oxygen, it is attracted atone temperature and repelled at another. At ordinary temperatures acubic yard of oxygen possesses the magnetism of 5.5 grains of iron andwhen liquefied it is strongly attracted.Magnetism or Magnetization, Temporary.When a mass of iron is magnetized by a current, when the current ceasesthe portion of its magnetism which disappears is the temporarymagnetism; the portion retained is the residual or permanent magnetism.Magnetism, Red.A term arising from the two fluid theory of magnetism; the magnetism ofthe north pole of a magnet. (See Magnetic Fluids.) The magnetism of thesouth pole is termed blue magnetism. Both terms originated in thepainting of magnets. They are but little used.Synonym--North Magnetic Fluid.358 STANDARD ELECTRICAL DICTIONARY.Magnetic Remanence.The residual magnetism left in a bar of steel or other paramagneticmaterial after the application of a powerful magnet. It is distinguishedfrom coercive force, as the latter is the amount of negative magnetizingor of demagnetizing force required to reduce the remanent magnetism tozero.Synonym--Remanence--Residual Magnetism.Magnetism, Solenoidal Distribution of.The distribution of magnetism in such a way that the poles are very farapart in proportion to their area. The magnetization of a long thin barof steel illustrates solenoidal distribution.Magnetism Sub-permanent.The magnetism of a paramagnetic substance which presents a considerabledegree of permanency, but which gradually disappears, leaving thepermanent magnetism present. It is noticeable in iron or steel shipswhose magnetism gradually reduced in quantity, eventually becomes fullypermanent.Magnetism, Weber's Theory of.The molecules of a magnetizable material by this theory are supposed tobe magnets with their poles lying in every direction, and henceneutralizing each other. By magnetization these are supposed to beturned with their similar poles in the same direction, and their axisparallel, hence acting like a group of magnets. It is practicallyidentical with Hughes' theory.Magnetism, Terrestrial.The magnetism of the earth. (See Magnetic Elements.)Fig. 228. MAGNETIZATION BY DOUBLE TOUCH.Magnetization by Double Touch.The process of magnetizing a steel bar by simultaneously stroking itwith two poles of a horseshoe magnet or with two opposite poles of twobar magnets. The poles must be close but not touching. A block of woodmay be placed between the ends if single magnets are used. The poles areplaced on the middle of the bar and carried back and forth to one end,then to the other, and so on, ending at the middle of the bar in suchdirection as to give each end the same number of strokes. The poles mustbe close together or consequent poles will be produced. If bar magnetsare used they may be held inclined at an angle of 15º to 20º with thehorizontal bar to be magnetized. The ends of the latter may rest onpoles of two other magnets, each end on a pole of the same name as thatof the magnetizing magnet on its side. (See Magnetization, Hoffer'sMethod.)359 STANDARD ELECTRICAL DICTIONARY.Magnetization by Separate Touch.A method of magnetization. Two magnets are used. Held in an inclinedposition two opposite poles are touched to the bar near its centre, andare drawn off to the two ends. They are returned through the air and theprocess is repeated.Magnetization by Single Touch.A method of polarizing or magnetizing steel bars, by stroking themalways in one direction with one pole of a magnet, returning it throughthe air. The stroking is best done on both sides. The stroking may beginat one end and end at the other, or it may be commenced in the center ofthe bar and be carried to one end with one pole, and the same done forthe other half with the other pole.Magnetization by the Earth.The earth imparts magnetism to iron masses. If a rod of steel is heldparallel to the inclination and in the magnetic meridian it exhibitspolarity, which by jarring or hammering, can be made to some extentpermanent. A piece of soft iron held vertically, or still better in theline of the dip as above, and which is twisted when in that position,becomes magnetized with some degree of permanence. Many other instancesare cited, such as fire-irons, lamp-posts, iron gates, lathe turnings,all of which often exhibit polarity, having been magnetized by theearth's field.[Transcriber's note: The earth's magnetic field is believed to originateit electric currents in the moving molten core.]Magnetization, Coefficient of Induced.The coefficient (q. v.) expressing the relation between the specificintensity of magnetization of a particle and the magnetizing force. Themagnetizing force is measured by the lines of force it can produce in afield of air. The coefficient of induced magnetization is the factor bywhich the intensity of a magnetizing field must be multiplied to producethe magnetization imparted by it to a particle of any substance. Thiscoefficient varies for different substances, and is also called magneticsusceptibility. It is distinguished from permeability as referring onlyto a particle isolated from influence of a mass of surrounding particlesof its own kind. It is definable as the intensity of the magnetizationassumed by an exceedingly long and exceedingly thin bar placed in a unitfield. If a mass of metal were placed in such a field all its particleswould become affected and within the mass no unit field could exist.Hence magnetic susceptibility (another name for this coefficient) doesnot apply to the case of large cores of electro-magnets anddynamo-armatures, but is really a theoretical rather than a practicalfigure.The sign of the coefficient of diamagnetic bodies is negative; ofparamagnetic bodies is positive.Synonym--Magnetic Susceptibility. \360 STANDARD ELECTRICAL DICTIONARY.Magnetization, Cycle of.A cycle of positive or of positive and negative magnetization representsthe application of a magnetizing force beginning at a fixed value,generally zero, rising to a maximum, or to a value of maximum distancefrom the initial and then returning to the original basis. It isvirtually a full wave of magnetization and may extend on both sides of azero line giving positive and negative values.Cycles of magnetization apply especially to transformers and otherapparatus of that character used with the alternating current system.Magnetization, Hoffer's Method.For horseshoe bars an armature is placed against the poles of the magnetbar to be treated. The poles of a strong horseshoe magnet are strokedover it from poles to bend and returned through the air, or vice versa.In the first case the poles will be the same as those of the inducingmagnet; in the second case they will be opposite. A maximum effect isproduced in ten strokes. The stroking should be applied to both sides.An electro-magnet may be used as inducer as shown, but an armatureshould be used; in the cut it is omitted.Fig. 229. MAGNETIZING A HORSESHOE MAGNET.Magnetization, Intensity of.The amount of magnetism induced in or present in a body. It is expressedin Magnetic Lines of Force, q. v., per cross-sectional area.Magnetization, Isthmus Method of.A method used by Ewing in a research on the magnetization of iron invery strong fields. He used samples of iron turned down in the centre toa narrow neck, and thus concentrated the lines of force greatly.Magnetization, Elias' Method.The bar to be magnetized is surrounded by a magnetizing coil, q. v. Astrong current is passed through it, and the coil is moved back andforth a few times.Magnetization, Jacobi's Method.For horseshoe bars. The bar is placed with its poles against those of ahorseshoe magnet. A bar of soft iron, long enough to reach from outsideto outside of the legs, is laid across near the junction and is drawnalong towards the bend of the new bar and away from it. This is repeateda few times on both sides.361 STANDARD ELECTRICAL DICTIONARY.Magnetization, Limit of.As the induction of magnetizing force increases, magnetization ofparamagnetic metals tends towards a limit, the increase in magnetizationbeing continually less and less as the metal becomes more highlymagnetized. In diamagnetic substances no limit is discernible.Synonym--Maximum Magnetization.Magnetization, Specific.The magnetic moment per gram of a substance.Magnet-keeper.A bar of iron connecting the two poles of a permanent magnet. Often thesame bar serves as armature and keeper.Magnet, Lamination of.It is advantageous to make magnets of laminated construction, or of thinplates of steel. The thin metal can be better tempered or hardened thanthick metal. A slight separation of the plates is advantageous from somepoints of view. If in actual contact there is some danger that theweaker members will have their polarity reversed by the stronger ones.This is counteracted to some extent by separation.Magnet, Long Coil.A high resistance electro-magnet; one whose coil is of thin wire ofconsiderable length.Magnet, Natural.The lodestone, q. v.; a variety of magnetite or magnetic oxide of iron,exhibiting permanent magnetism, attracting iron, and possessing northand south poles.Magnet, Neutral Line of.A line at right angles to the magnetic axis of a magnet, q.v., andnearly or quite at the centre, so situated with reference to the poleson either end that it marks the locus of no polarity. It has been calledthe equator of the magnet. It is defined by the intersection of theplane of no magnetism with the surface of the bar.Synonym--Magnetic Equator.Magnet, Normal.A bar or compound bar magnet, magnetized to such an extent that thecurves of the lines of force run into each other in the middle, is thustermed by Jamin.Magneto.Abbreviation for Magneto-electric Generator. (See Magneto-electricGenerator.)Magneto Call Bell.A call operated by current from a magneto-electric generator. It is verygenerally used in telephone systems.362 STANDARD ELECTRICAL DICTIONARY.Magneto-electric. adj.Relating to induced electric effects due to the cutting of true magneticlines of force by, or equivalent action of or upon a conductor. Theseeffects are identical with electro-magnetic effects and are onlydistinguished from them by the field being due to a permanent magnetinstead of an electromagnet.Magneto-electric Brake.A device for bringing to rest an oscillating galvanometer needle. Itconsists essentially of a coil in circuit with a key and with thegalvanometer. On opening the circuit an inverse current is establishedby induction, tending to bring the needle to rest.Magneto-electric Generator.A current generator operating by maintaining a potential difference atits terminals, by reactions in a field of force, which field isestablished by a permanent magnet.The cut, Fig. 230, shows the general principle of construction of adirect current generator. The armature is rotated between the poles of apermanent magnet. Any of the regular types of dynamo armature can beused. From its commutator the current is taken by brushes.Fig. 230. MAGNETO-ELECTRIC GENERATOR.Fig. 231. MAGNETO-ELECTRIC GENERATOR.363 STANDARD ELECTRICAL DICTIONARY.The cut, Fig. 231, shows an alternating current machine. In it a pair ofbobbins, wound in series, and both either right-handed or left-handed,are rotated between permanent magnet poles. The current may be taken offby two brushes bearing on two collecting rings on the axis of thebobbins, the ends of the wire being connected thereto. Or if a shockingcurrent is desired, one of the brushes or springs may strike a series ofpins forming virtually a broken or interrupted collecting ring. Thisgives a current for medical purposes.Synonyms--Magneto-dynamo--Magneto-electric Machine.Magnetograph.An apparatus for recording variations in magnetic elements. One typeincludes a magnetic needle to which a concave mirror is attached. Thelight ray from the mirror is reflected upon sensitized paper where itsmovements are photographically reproduced. The movements of the spot aredue to the movements of the needle and act as the record of the same.Magneto-Inductor.An instrument for use with a ballistic galvanometer to reproduce adefinite current impulse. Two magnets are fastened together in onestraight line, the north poles almost touching. This is mounted at theend of a rod like a pendulum, the axis of the magnets transverse to therod. The magnets are carried by a frame and oscillate at the end of therod, back and forth within a fixed coil, which is one-half the lengthof the double magnet. A bob is attached to the bottom of the frame bywhich the whole can be swung. As the magnets are of fixed value, theirtime of oscillation constant, and the coil fixed in size, the apparatusprovides a means of getting a definite instantaneous current ofidentical value whenever needed.Fig. 232. MAGNETO-INDUCTOR.364 STANDARD ELECTRICAL DICTIONARY.Magnetometer.(a) A reflecting galvanometer, with heavy magnetic needle, dampened by acopper frame. It was devised by Weber.(b) An apparatus for measuring the intensity of magnetic force. It mayconsist of a magnet suspended by bifilar or by torsion suspension. Areflecting mirror and scale as in the reflecting galvanometer may beused to act as indicator of its motions. It is used in investigations ofthe intensity of the earth's field.If the motions of the spot of light are received on a moving strip ofsensitized paper and are thereby reproduced photographically, theinstrument is self-recording. Such an apparatus is used in the KewObservatory, Eng., for recording the terrestrial magnetic elements.Magnetometry.The determination of the magnetic moment of a magnet.It involves the determination by experiment of--( a) the product of themagnetic moment, M, of the magnet by the horizontal component, H, of theearth's magnetism; (b) the quotient of M divided by H. Knowing these twoquantities, M is given by the formula M = SquareRoot( )M * H) * (M/H) )and if desired H is given by the formula H = SquareRoot( (M*H) / (M/H)).M*H is determined by the method of vibrations. A very long, thin magnetsuspended by a torsion filament is caused to oscillate, and its periodis determined. Calling such period T and the moment of inertia of themagnet I, we have the formula T= 2* PI * SquareRoot( I / (H*M) ) (a),whence H*M is calculated, I of course being known or separatelydetermined.Fig. 233 END-ON METHOD.Fig. 234. BROADSIDE METHOD.M/H is determined by the End-on deflection method, or the Broadsidedeflection method. In both cases the deflection of a compass needle bythe magnet in question is the basis of the work.In the end-on method AB is the magnet under examination; DE the compassneedle; a the angle of deflection; d the distance between C and themiddle of AB, which should be considerable compared with the length ofDE; 2l, the length of AB. We then have the formulatan a = (M/H) * (2d / (d^2 - l^2)^2),which if 2l is small compared to d reduces totan a = M/Hd 3(b), which gives M/H, a and d being known.365 STANDARD ELECTRICAL DICTIONARY.In the broadside method the line d is the magnetic meridian, and thediagram shows the relative positions. We then have the formulatan a = (M/H) / (d2 + l2)^1.5;which if 1 is relatively small reduces totan a = M/(H * d3 )(C.)[Transcriber's note: The image of the above paragraphs is included here.]a and c or a and b can be combined giving M and H in C.G.S. measurement.Magnetometer, Differential.An apparatus, invented by Eickemeyer, for testing the magnetic qualitiesof different samples of iron. It is very similar in construction andprinciple to the magnetic bridge, q. v.Magneto-motive Force.The force producing a magnetic field or forcing lines of force around amagnetic circuit. It is usually applied only to electro-magnets and isexpressible in turns of the wire winding multiplied by amperes ofcurrent, or in ampere-turns.Magnet Operation.A term in surgery; the use of the electro-magnet or permanent magnet forremoving particles of iron from the eye.Magnetoscope.An apparatus for detecting the presence of magnetism, without measuringits intensity. A simple magneto-scope consists of a magnetized bit ofwatch-spring suspended in a vertical glass tube by a fine filament. Abit of unmagnetized soft iron wire may be used in the same way. Thefirst has the advantage of indicating polarity; the latter merely showsmagnetic attraction. A cork may be used as base of the instrument.Fig. 235. MAGNETOSCOPE.366 STANDARD ELECTRICAL DICTIONARY.Magnet, Permanent.A bar of steel charged with residual magnetism. Steel possesses highcoercive force in virtue of which when once magnetized it retains partof the magnetization.Permanent magnets are generally straight bars or U shaped; they aretermed bar magnets, magnetic needles, horseshoe magnets, machine magnetsand otherwise, according to their shape or uses.Magnet Pole.The part of a magnet showing strongest polarity; the part which attractsiron the most powerfully, and acts as the starting point for lines offorce.Magnet Poles, Secondary.Magnet poles are often not situated at the ends. Owing to inequality ofthe material or other causes they may occupy intermediate positions onthe magnet. Such poles are called secondary poles.Magnet Pole, Unit.A unit magnet pole is one which exerts unit force on another unit poleplaced at unit distance from it. Unit force is the dyne; unit distanceis one centimeter.Magnet, Portative Power of.The power of sustaining a weight by attraction of its armature possessedby a magnet. In general terms the adherence of the armature of a magnetto the pole varies with the square of the number of lines of force whichpass through the point of contact. Hence an increased adherence of thearmature to a horseshoe electro-magnet is sometimes obtained bydiminishing the area of contact of one pole which concentrates the linesof force. Steel magnets were frequently made with rounded ends toincrease the portative power.Magnet, Simple.A magnet made of one piece of metal, or at least magnetized as such; thereverse of a compound magnet, which is magnetized piece by piece andthen fastened together.Magnet, Solenoidal.A magnet which is so uniformly magnetized and is so long in proportionto its other dimensions that it virtually establishes two magneticpoles, one at either end. It is a long thin bar so magnetized that allits molecules would, considered as magnets, be absolutely equal.(Daniell.) It acts like a solenoid, except that it is longer inproportion than the solenoid generally is constructed.Magnet, Sucking.A magnet coil with movable or loose axial bar of soft iron.The whole is usually mounted vertically. When a strong enough current ispassed the bar is drawn up into the coil as if by suction, whence thename.367 STANDARD ELECTRICAL DICTIONARY.Magnet, Unipolar.No such thing as a unipolar magnet is possible. The name is given topoised or suspended magnets, one of whose poles lies in the axis ofsuspension. It is obvious that such a magnet will act, as far as itsdirective tendency and rotatory movements are concerned, as if it hadonly one pole. As shown in the cut, the pole s in both magnets lies inthe axis of suspension or directly under the filament by which they aresuspended, while the other pole n is the active pole in causing rotationor directive tendency; c c are counterweights or counterpoises.Fig. 236. UNIPOLAR MAGNETS.Magnetophone.An apparatus for producing a loud sound, involving the principles of thetelephone. A rapidly alternating or make and break current beingproduced by any means and being transmitted through the telephone givesa loud note of pitch dependent on the current producing it. Sometimes aperforated metallic disc is rotated in a magnetic field, and producesthe requisite type of current.Magnus' Law.A law of thermo-electricity. In a homogeneous circuit, however, thetemperature varies from point to point; there is no current.Whatever potential differences may be established by the variations intemperature it is evident that they must counteract each other andreduce to zero.Mains, Electric.The larger conductors in a system of electric light or powerdistribution.Make. v.To complete a circuit, as by closing a switch.Make and Break Current.A current which is continually broken or interrupted and started again.It is applied only where the "makes" and "breaks" succeed each otherwith great rapidity, as in the action of an induction coil or polechanger, etc. It has had considerable importance in litigation affectingthe Bell telephone patents, the courts holding that the original Bellpatent (No. 174,465, of 1876,) covered the undulating current, for thetransmission of speech. Many efforts have been made by litigants toprove that specific telephones have transmitted articulate speech by themake and break current, but without success. If this could have beenproved the assumption is that the courts would have sustained the use ofsuch device as not infringing upon the claims of the Bell patent.Malapterurus.A fish, sometimes called the thunder fish, an inhabitant of Africanrivers, occurring in the Nile and Senegal. It possesses considerableelectric power, similar to that of the gymnotus and torpedo, althoughinferior in amount.368 STANDARD ELECTRICAL DICTIONARY.Fig. 237. MALAPTERURUS.Man-hole.The cistern-like depression in the ground for giving access to the endsof tubes in electric conduits. (See Conduit, Electric Subway.)Marked End or Pole.The north pole or north seeking pole of a magnet, so called because itis usually marked with a notch or scratch by the maker. The south poleis called the unmarked end.Mass.The quantity of matter in a body. The C. G. S. unit of mass is thequantity of matter in a gram. While weight varies with latitude andother circumstances, mass is invariable.The unit of mass is also defined as the quantity of matter which in abalance will counterpoise a standard mass, the gram or pound. As thegram is intended to be the mass of one cubic centimeter of water at3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.As a primary unit its dimensions are indicated by M.Mass, Electric.A term for quantity of electricity. The unit mass is such a quantity asat unit distance will act with unit force.Matter, Electric.The imaginary substance constituting electricity; a conception usedpurely as a matter of convenience.[Transcriber's note: The electron was discovered five years after thispublication.]Matter, Radiant.Matter in the ultra-gaseous or so-called fourth state. In the gaseousstate the molecules of a gas are in perpetual kinetic motion, collidingactually or virtually with each other, rebounding from such approach,and striking also the walls of the containing vessel. But except forthese deflections, which are of enormous frequency, the paths of themolecules would be perfectly straight.In the radiant state matter exists in so high a vacuum that collisionsof the molecules rarely occur, and the molecules simply beat back andforth in straight lines from side to side of the containing vessel.A layer of gas in this condition is termed a Crookes' layer, from Prof.William Crookes, who discovered and investigated these phenomena.369 STANDARD ELECTRICAL DICTIONARY.Luminous streams of the molecules are produced by electric highpotential discharges between electrodes. The course of the discharge isnormal, in general terms, to the surfaces of the electrodes, and reachesfrom one to the other in a curve or straight line, as the case may be.These luminous streams are deflected by a magnetic field; if brought toa focus can heat refractory material in that focus to a full white heat,and can develop phosphorescence. The latter is termed electricphosphorescence. A great variety of experiments have been devised toillustrate the phenomena of radiant matter. The vacuum is generallyproduced in a hermetically sealed glass vessel into which the electrodesare sealed, and which contain the phosphorescent substances or otheressentials for the experiments. The vessels are termed Crookes' Tubes.[Transcriber's note: Crookes reported on "radiant matter" in 1879. It isactually electrons, but he failed to distinguish them from ordinaryatoms. Thompson properly described electrons in 1897.]Matteueci's Experiment.An experiment for showing the inductive effect of the discharge of aLeyden jar. Two glass plates are supported on standards in a verticalposition. Flat coils of wire are wound or coiled and secured to onesurface of each plate. One plate has much finer and longer wire than theother. Metal handles are connected to the ends of the coarser wire coil.The plates are placed with their coils facing each other. A Leyden jaris discharged through the coarser coil, while the handles are grasped bya person. The shock of the discharge is felt by him.Matting, Electric Floor.Matting or floor covering underlaid with burglar alarm contacts, soarranged as to be closed by anyone walking on the matting. The contactsare connected to a burglar alarm system. The object is to provide analarm if a burglar enters a house, in case he should enter a door orwindow without sounding the bell. The latter can be done by cutting outthe window or part of the door instead of opening it.Maxwell's Theory of Light.A theory of light. It is due to J. Clerk Maxwell.It supposes the phenomena of electric induction to be due to the ether,q. v. It supposes the condition of the ether when conveying light to bethe same as if exposed to the induction of rapidly alternating currentsor discharges (in this case synonymous). It therefore is anelectro-magnetic effect if the theory is correct.An electric stress such as one due to the induction of anelectrostatically charged body is not a wave-creating element or factor,but is a simple stress. But let this stress be stopped and renewed andat once it appears as a wave-forming agency.This stoppage and renewal represents evidently a discharge succeeded bya charge, or if repeated is equivalent to an intermittent current or analternating one.370 STANDARD ELECTRICAL DICTIONARY.Again the electrostatic stress kept constant may by being carriedthrough space carry with it a wave, just as a moving projectile carriesa wave of air in advance of itself.Admitting this much the following consequences follow:Since in non-conductors the displacement produces a restitution force,which varies as the displacement which is requisite or is a criterionfor the propagation of waves, while in conductors no such force ismanifested and the electric energy appears as heat, it follows thatlight vibrations are not possible in conductors, becauseelectro-magnetic waves do not exist in them when they are in circuit,and conductors should be opaque, while the reverse is true fornon-conductors. (Daniell.)This is carried out often enough to make a striking evidence in favor ofMaxwell's theory.The velocity of propagation of an electro-magnetic disturbance in anon-conductor should be equal to that of light. This constant is provedby mathematical considerations, to be approximately the same as theratio of the electrostatic to the electromagnetic unit of intensity orquantity. This ratio is 3E10 (30,000,000,000), which is almost exactlythe velocity of light.It also follows from what has been said that if an electrostaticallycharged body were whirled around a galvanometer needle at the rate of3E10 revolutions per second it should affect it like a circulatingcurrent. This rate of rotation cannot be attained, but Rowland has mademanifest the effect of a rotating statically charged body upon amagnetic needle.The above is the merest outline of Maxwell's theory. The fulldevelopment must be studied in his own and succeeding works.Mayer's Floating Magnets.An experiment due to Prof. Mayer. A number of sewing needles aremagnetized and thrust into bits of cork, almost all the way through,with their like poles projecting. They are floated in a basin of waterand take, under the effects of attraction and repulsion, when approachedby a magnet pole, regular geometric positions, marking out the positionsof angles of polygons.Measurements.The determination of the value of quantities; determination of thefactor by which the unitary value must be multiplied to produce thequantity under examination. Such are the measurement of the voltage of agalvanic battery, or of the ohms of resistance of a conductor.Electricity has been termed the science of measurement.Meg or Mega.A prefix, meaning one million times. A megohm is one million ohms; amegerg is one million ergs; a megadyne is one million dynes.371 STANDARD ELECTRICAL DICTIONARY.Fig. 238. MAYER'S FLOATING MAGNETS.Mercury.A metal; one of the elements; symbol, Hg; atomic weight, 200 ;equivalent, 200 or 100; valency, 1 and 2.It is a conductor of electricity.The following data are 0º C. (32º F.)Relative Resistance, 62.73Specific Resistance, 94.32 microhms.Resistance of a wire,(a) 1 foot long, weighing 1 grain, 18.51 ohms.(b) 1 foot long, 1/1000 inch thick, 572.3 "(c) 1 meter long, weighing 1 gram, 12.91 "(d) I meter long, 1 millimeter thick 1.211 "Resistance of a 1 inch cube, 37.15 microhms.Percentage increase of resistance per degree C. 1.8° F.at about 20° C. (68° F.), .72 per cent.Electro-chemical equivalent (Hydrogen = .0105), 2.10 mgs.1.05 "372 STANDARD ELECTRICAL DICTIONARY.Mercury Cup.A cup of iron, wood or some material that does not amalgamate or isunattacked by mercury, which is filled with mercury and made anelectrode of a circuit. By dipping the other terminal of the circuitinto the mercury a very good contact is obtained. It is well to coverthe mercury with alcohol. The cup may be filled so that the mercuryrises in a meniscus or semi-globule above its edges.For some purposes this form is useful, as for contacts with the end of aswinging wire or pendulum, because in such cases the contact can be madewithout the contact point entering the cup. The point swings through theprojecting meniscus without touching the edges of the cup. A mercury cupand contact constitute a mercury break.Meridian, Astronomical.The great circle passing through the north and south poles of thecelestial sphere. It lies in a plane with the corresponding geographicalor terrestrial meridian.Meridian, Geographic.The true north and south meridian; the approximate great circle formedby the intersection of a plane passing through north and south poles ofthe earth with the earth's surface.373 STANDARD ELECTRICAL DICTIONARY.Fig. 239. SCHALLENBERG'S ALTERNATING CURRENT METER.Meter, Alternating Current.A meter for measuring alternating current, as supplied to consumers,from an alternating current system. Like most commercial meters its onlyfunction is the measurement of quantity; the potential difference ismaintained at a constant figure by the generating plant.The cut shows the Schallenberg meter. It is simply an alternatingcurrent motor (see Motor, Alternating Current), with air vanes mountedon its spindle. A main coil passes all the current. Within this is asecond coil complete in itself, and not touching or connecting with theother. The latter is built up of copper rings. Within the two coils, andconcentric with both is a disc of copper carried by a vertical spindle.The same spindle carries air vanes, and is free to rotate. As it does soit moves the indicating machinery.The current in the outer coil induces one in the inner coil. Owing tolag, the current in the inner one differs in phase from that in theouter one, and a rotatory field is produced. The copper disc acquiresinduced polarity, and rotates with speed which normally would be inproportion to the square of the current. But the object of the meter isto register the current only. The air vanes effect this. The resistanceof the air to their motion causes the rate of rotation to vary directlyas the speed.Meter Bridge.A form of Wheatstone's bridge in which one lateral pair of arms isrepresented by a straight wire. The other pair comprise a knownresistance, and the resistance to be determined. The galvanometer isconnected on one side between the known and unknown resistance. On theother side its connection is moved back and forth along the straightwire until the balance is secured and the galvanometer reads zero.The relative lengths of wire intercepted between the two ends thereofand the movable galvanometer connection are proportional to theresistance of these parts and give the necessary data with the one knownresistance for determining the unknown resistance.374 STANDARD ELECTRICAL DICTIONARY.In the original meter bridge the wire was one meter long, whence itsname, and was stretched straight. In more recent examples the wirevaries in length and in one form is bent into a circle or spiral, so asto make the instrument more compact.The contact is not a sliding one, but is adjusted by trial. The contactpiece is slid along, but not touching the wire, and from time to time ispressed down against the wire. This prevents wear of the wire. The wiremay be made of platinum or of platinum-iridium alloy. The latter isvery hard and not easily worn out.Sometimes, as shown in the cut, three parallel wires are stretched alongthe baseboard of the instrument, and arranged so that a single wire, twowires or three wires in series can be used for the proportional sides ofthe bridge, thus making it a two-meter or three-meter bridge as desired.On the other hand some are made of restricted length, as a half orquarter meter only.Fig. 240. METER BRIDGE.In the cut J K is the wire, traversed by the contact key. By moving thecontact C back and forth in the slot it can be brought over any of thethree divisions of the wire. H is the handle for depressing the key. Sis a flat spring, carrying the contact piece and holding it up from thewires, except when pressed downwards. As shown in the cut, it is in usefor calibrating a voltmeter V, by Poggendorff's method, G being thegalvanometer and r1 and r2 being resistances.Synonyms--Slide Bridge--Slide Balance.Meter Candle.A unit of illuminating power; the light given by one standard candle ata distance of one meter. The ordinary units of illuminating power arealtogether relative; this one is definite.375 STANDARD ELECTRICAL DICTIONARY.Meter, Chemical Electric.A current meter in which the current is determined by the amount ofchemical decomposition which it can effect. In the Edison meter thesolution is one of zinc sulphate. Two electrodes of zinc are immersed init, and a fractional part of the current is passed through it. The gainin weight of one electrode and the loss in the other are proportional tothe current. Both electrodes are weighed periodically, one acting ascheck upon the other.Meter, Current.An instrument for measuring the quantity of electricity in current formsupplied to consumers. It may be of various types. The general principleinvolved is that in commercial installations for incandescent light andpower supply a fixed potential is usually maintained, the multiple arcsystem being employed. Hence all that is requisite is to measure thecoulombs or the ampere-hours to know what quantity of energy has beensupplied.Meter, Electro-magnetic.A current meter in which the current is measured by its electro-magneticeffects.Meter-millimeter.A unit of resistance. (See Resistance, Meter-millimeter.)Meter, Thermal Electric.A current meter in which the current is measured by the heat it impartsto a conductor. In one meter a very light helix of mica is poisedhorizontally over a conductor, and the whole is enclosed in a case. Asthe wire is heated it causes an ascending current of air which rotatesthe vane, and the latter moves delicate clockwork which moves indicatinghands. The hotter the wire the more rapidly the air ascends, andconsequently the speed of the vane is proportional to the current,because the heat of the conductor is proportional thereto.Meter, Time Electric.An electric meter which measures the length of time during which currentis used. It assumes a constant current and potential. It is virtually aclock, which is turned on when the current passes, and is turned offwith the current.Meter, Watt.A combined current and potential meter. It is constructed on the generallines of a Siemens' Electro Dynamometer. If in it one coil is made ofcoarse wire and is placed in series with the current conductor, and ifthe other is wound with fine wire and is connected as a shunt from pointto point whose potential difference is to be determined, the instrumentbecomes a watt meter.Synonym--Energy Meter.Methven Standard or Screen.A standard of illuminating power. It is the light emitted by athree-inch Argand gas flame through a rectangular aperture in a silverplate carried by a screen. The aperture is of such size and so fardistant from the flame as to permit the passage of exactly two candlesilluminating power.