The Standard Electrical Dictionary Part 96

Loop.

A portion of a circuit introduced in series into another circuit. The latter circuit is opened by a spring-jack, q. v. or other device, and the loop inserted. By loops any number of connections can be inserted into a circuit in series therewith, and in series or in parallel with one another.

Loop Break.

A double bracket or similar arrangement for holding on insulators the ends of a conductor which is cut between them, and to which are connected the ends of a loop. The s.p.a.ce between the insulators may be about a foot.

Luces.

This may be used as the plural of lux, q. v. It is the Latin plural.

Luminous Jar.

A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoil between which are very short intervals. When discharged, sparks appear all over the surface where the lozenges nearly join.

Lux.

A standard of illumination, q. v., as distinguished from illuminating power.

It is the light given by one candle at a distance of 12.7 inches--by a carcel, q. v., at a distance of one meter---or by 10,000 candles at 105.8 feet.

It was proposed by W. H. Preece. All the above valuations are identical.

M.

(a) Symbol of gaseous pressure equal to one-millionth of an atmosphere.

(b) The Greek m, ?, is used as the symbol of magnetic permeability.

333 STANDARD ELECTRICAL DICTIONARY.

Machine, Cylinder Electric.

A frictional electric machine whose rotating gla.s.s is in the shape of a cylinder instead of a disc as in the more recent machines.

Fig. 217. PLATE FRICTIONAL ELECTRIC MACHINE.

Machine, Frictional Electric.

An apparatus for development of high tension electricity by contact action, brought about by friction.

It consists of a plate or cylinder of gla.s.s mounted on insulating standards and provided with a handle for turning it. One or more cus.h.i.+ons of leather are held on an insulated support, so as to rub against the plate or cylinder as it is turned. A metal comb or combs are held on another insulating support so as to be nearly in contact with the surface of the gla.s.s plate at a point as far removed as possible from the rubbers. The combs are attached to a bra.s.s ball or round-ended cylinder, which is termed the prime conductor.

In use either the prime conductor or cus.h.i.+ons are connected by a chain or otherwise with the earth. a.s.sume it to be the cus.h.i.+ons. As the machine is worked by turning the plate, the gla.s.s and cus.h.i.+on being in contact develop opposite electricities. The gla.s.s is charged with positive electricity, and as it turns carries it off and as it reaches the prime conductor by induction and conduction robs it of its negative electricity. Meanwhile the cus.h.i.+ons negatively excited deliver their charge to the earth. The action thus goes on, the prime conductor being charged with positive electricity.

334 STANDARD ELECTRICAL DICTIONARY.

If the prime conductor is connected to the earth and the cus.h.i.+ons are left insulated, negative electricity can be collected from the cus.h.i.+ons.

In some machines both prime conductor and cus.h.i.+ons are kept insulated and without ground contact. Electrodes connecting with each are brought with their ends close enough to maintain a sparking discharge.

Machine Influence.

A static electric machine working by induction to build up charges of opposite nature on two separate prime conductors. In general they are based on the principle of the electrophorous. Work is done by the operator turning the handle. This rotates a disc and draws excited parts of it away from their bound charges. This represents a resistance to mechanical motion. The work absorbed in overcoming this mechanical resistance appears as electric energy. There are various types of influence machines, the Holtz, Toeppler-Holtz and Wimshurst being the most used. The electrophorous, q. v., is a type of influence machine.

Machine, Holtz Influence.

A static electric machine. It includes two plates, one of which is rapidly rotated in front of the other. Two armatures of paper are secured to the back of the stationary plate at opposite ends of a diameter. To start it one of these is charged with electricity. This charge by induction acts through the two thicknesses of gla.s.s upon a metal bar carrying combs, which lies in front of the further side of the movable plate. The points opposite the armature repel electrified air, which strikes the movable disc and charges it. A second rod with comb at the opposite end of the same diameter acts in the reverse way. Thus opposite sections of the disc are oppositely charged and the combs with them. By induction these portions of the disc react upon the two armatures. The opposite electricities escape from the armatures by paper tongues which are attached thereto and press against the back of the movable plate. As the plate rotates the opposite electricities on its face neutralize the electricity repelled from the combs. The charges on the back strengthen the charges of the armatures and bra.s.s combs. Thus the machine builds up, and eventually a discharge of sparks takes place from the poles of the bra.s.s combs.

335 STANDARD ELECTRICAL DICTIONARY.

Machine, Toeppler-Holtz.

A modification of the Holtz machine. The priming charge of the armatures is produced by friction of metallic brushes against metallic b.u.t.tons on the face of the rotating plate. (See Machine, Holtz.)

Machine, Wimshurst.

A form of static influence machine. It consists of two plates of gla.s.s, on which radial sectors of tinfoil are pasted. Both plates are rotated in opposite directions. The sectors of the two plates react one upon the other, and electric charges of opposite sign acc.u.mulate on the opposite sides of the plates and are collected therefrom by collecting combs.

Mack.

A name, derived from Maxwell, and suggested for the unit of inductance.

It is due to Oliver Heaviside, but has never been adopted. (See Henry.)

Magne-Crystallic Action.

The action of a supposed force of the same name, proposed by Faraday. It relates to the different action of a magnetic field upon crystalline bodies, according to the position of their axes of crystallization. A needle of tourmaline, normally paramagnetic, if poised with its axis horizontal, is diamagnetic. Bis.m.u.th ill.u.s.trates the same phenomenon. The subject is obscure. Faraday thought that he saw in it the action of a specific force.

Magnet.

A body which tends when suspended by its centre of gravity to lay itself in a definite direction, and to place a definite line within it, its magnetic axis, q. v., in a definite direction, which, roughly speaking, lies north and south. The same bodies have the power of attracting iron (Daniell), also nickel and cobalt.

Magnets are substances which possess the power of attracting iron.

(Ganot.)

[Transcriber's note: Edward Purcell and others have explained magnetic and electromagnetic phenomenon as relativistic effects related to electrostatic attraction. Magnetism is caused by Lorentz contraction of s.p.a.ce along the direction of a current. Electromagnetic waves are caused by charge acceleration and the resulting disturbance of the electrostatic field. (Electricity and Magnetism: Berkeley Physics Course Volume 2, 1960)]

Magnet, Anomalous.

A magnet possessing more than the normal number (two) of poles. If two straight magnets are placed end to end with their south poles in juxtaposition the compound bar will seem to possess three poles, one at each end and one in the middle. The apparent pole in the middle is really made up of two consequent poles, q. v. It sometimes happens that when a single long thin bar is magnetized consequent poles are produced, although such magnet is in one piece. This may be accidental, as in such case it is quite hard to avoid anomalous poles, or, as in the field magnets of some forms of dynamos, anomalous poles may be purposely produced.

Magnet, Artificial.