The Standard Electrical Dictionary Part 95

330 STANDARD ELECTRICAL DICTIONARY.

Lightning, Ascending.

Lightning is sometimes observed which seems to ascend. It is thought that this may be due to positive electrification of the earth and negative electrification of the clouds.

Lightning, Globe or Globular.

A very unusual form of lightning discharge, in which the flashes appear as globes or b.a.l.l.s of light. They are sometimes visible for ten seconds, moving so slowly that the eye can follow them. They often rebound on striking the ground, and sometimes explode with a noise like a cannon.

They have never been satisfactorily explained. Sometimes the phenomenon is probably subjective and due to persistence of vision.

Lightning Jar.

A Leyden jar whose coatings are of metallic filings dusted on to the surface while sh.e.l.lacked, and before the varnish has had time to dry. In its discharge a scintillation of sparks appears all over the surface.

Line of Contact.

The line joining the points of contact of the commutator brushes in a dynamo or motor.

Synonym--Diameter of Commutation.

Lines of Force.

Imaginary lines denoting the direction of repulsion or attraction in a field of force, q. v. They may also be so distributed as to indicate the relative intensity of all different parts of the field. They are normal to equipotential surfaces. (See Electro-magnetic Lines of Force--Electrostatic Lines of Force--Magnetic Lines of Force.)

Lines of Induction.

Imaginary lines within a body marking the direction taken within it by magnetic induction. These are not necessarily parallel to lines of force, but may, in bodies of uniform agglomeration, or in crystalline bodies, take various directions.

Synonym--Lines of Magnetic Induction.

Lines of Slope.

Lines in a field of force which mark the directions in which the intensity of force in the field most rapidly falls away.

Links, Fuse.

Links made of more or less easily fusible metal, for use as safety fuses.

Listening Cam.

In a telephone exchange a cam or species of switch used to connect the operator's telephone with a subscriber's line.

331 STANDARD ELECTRICAL DICTIONARY.

Lithanode.

A block of compressed lead binoxide, with platinum connecting foils for use as an electrode in a storage battery. It has considerable capacity, over 5 ampere-hours per pound of plates, but has not met with any extended adoption.

Load.

In a dynamo the amperes of current delivered by it under any given conditions.

Local Action.

(a) In its most usual sense the electric currents within a battery, due to impurities in the zinc, which currents may circulate in exceedingly minute circuits, and which waste zinc and chemicals and contribute nothing to the regular current of the battery. Amalgamated or chemically pure zinc develops no local action.

(b) The term is sometimes applied to currents set up within the armature core or pole pieces of a dynamo. (See Currents, Foucault.)

Local Battery.

A battery supplying a local circuit (q. v.); in telegraphy, where it is princ.i.p.ally used, the battery is thrown in and out of action by a relay, and its current does the work of actuating the sounder and any other local or station instruments. (See Relay.)

Local Circuit.

A short circuit on which are placed local apparatus or instruments. Such circuit is of low resistance and its current is supplied by a local battery, q. v. Its action is determined by the current from the main line throwing its battery in and out of circuit by a relay, q. v., or some equivalent.

Local Currents.

Currents within the metal parts of a dynamo. (See Currents, Foucault.) In a galvanic battery. where there is local action, q. v., there are also local currents, though they are not often referred to.

Localization.

Determining the position of anything, such as a break in a cable, or a grounding in a telegraph line. In ocean cables two typical cases are the localization of a break in the conductor and of a defect in the insulation admitting water. The first is done by determining the static capacity of the portion of the line which includes the unbroken portion of the conductor; the other by determining the resistance of the line on a grounded circuit.

Locus.

A place. The word is used to designate the locality or position of, or series of positions of definite conditions and the like. Thus an isogonic line is the locus of equal declinations of the magnetic needle; it is a line pa.s.sing through all places on the earth's surface where the condition of a given declination is found to exist.

332 STANDARD ELECTRICAL DICTIONARY.

Lodestone.

Magnetic magnet.i.te; magnet.i.te is an ore of iron, Fe3 04 which is attracted by the magnet. Some samples possess polarity and attract iron.

The latter are lodestones.

Synonym--Hercules Stone

Logarithm.

The exponent of the power to which it is necessary to raise a fixed number to produce a given number. The fixed number is the base of the system. There are two systems; one, called the ordinary system, has 10 for its base, the other, called the Naperian system, has 2.71828 for its base. The latter are also termed hyperbolic logarithms, and are only used in special calculations.

Log, Electric.

An apparatus for measuring the speed of a ship. A rotating helical vane of known pitch is dragged behind the vessel. As the helix rotates its movements may actuate electric machinery for registering its rotations.

The number of these in a given time, multiplied by the pitch of the vane, gives the distance traversed in such time.