Pole, Positive.

(a) In a magnet the north pole; the pole from which lines of force are a.s.sumed to emerge into the air.

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

Poles.

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

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

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

426 STANDARD ELECTRICAL DICTIONARY.

Pole, Salient.

In dynamo and motor field magnets, salient poles are those projecting from the base or main body of the field magnet, as distinguished from consequent poles formed by coils wound on the main body itself.

Fig. 268. SALIENT POLES OF FIELD MAGNET.

Poles, Compensating.

A device for avoiding the cross-magnetizing effect on the commutator core due to the lead of the brushes. It consists in maintaining a small bar electro-magnet perpendicularly between the pole pieces. This compensates the cross-magnetizing effect.

Poles of Intensity.

The locus of highest magnetic force on the earth's surface. One such pole is in Siberia, another is about lat. 52? N., long. 92? W.

[Transcriber's note: 52? N., long. 92? W is about 250 miles Northeast of Winnipeg.]

Poles of Verticity.

The magnetic poles of the earth. (See Magnetic Poles.)

Pole Tips.

The extreme ends of the expanded poles of a field magnet. In some machines some of the pole tips are made of cast iron, to alter the distribution of the lines of force and resulting magnetic pull upon the armatures. This is done to take off the weight of the armature from its bearings.

Pole, Traveling.

A term applied to the poles produced in the action of a rotatory field, whose poles constantly rotate around the circle of the field. (See Field, Rotatory.)

417 STANDARD ELECTRICAL DICTIONARY.

Porous Cup.

A cup of pipe clay, unglazed earthenware or other equivalent material used in voltaic cells to keep two liquids separate and yet to permit electrolysis and electrolytic conduction.

They are necessarily only an expedient, as their porous nature permits considerable diffusion, and were they not porous electrolytic action would be impossible.

Synonym--Porous Cell.

Porret's Phenomenon.

In electro-physiology, an increase in the diameter of a nerve produced by the positive pole of a voltaic circuit, when placed in contact with the tissue and near to the nerve in question, the other pole being connected to a more or less remote part of the body.

Portelectric Railroad.

A railroad worked by solenoidal attraction, the car forming the core of the solenoids. It includes a series of solenoids or hollow coils of copper wire distributed all along the road and inclosing within themselves the track. On this a cylindrical car with pointed ends moves on wheels. Current is supplied to the solenoid in advance of the car, and attracts it. As it advances it breaks the contacts of the attracting solenoid and turns the current into the one next in advance. This operation is repeated as the car advances.

The solenoids are placed close together, each including in the trial track 630 turns of No. 14 copper wire. The car was of wrought iron, 12 feet long, 10 inches in diameter and weighing 500 lbs. It was proposed to employ the system for transportation of mail matter and similar uses.

Position Finder.

An instrument for determining the position of objects which are to be fired at from forts. It is designed for use from forts situated on the water.

Fiske's position finder may be thus generally described. On a chart the channel is divided into squares, and the position finder determines the square in which a vessel lies. For each square the direction and elevation of the guns is calculated beforehand. The enemy can therefore be continuously located and fired at, although from smoke or other cause the object may be quite invisible to the gunner.

It comprises two telescopes situated at distant extremities of as long a base line as is obtainable. These telescopes are kept directed upon the object by two observers simultaneously. The observers are in constant telephonic communication. As each telescope moves, it carries a contact over an arc of conducting material. Below each telescope is an arm also moving over an arc of conducting material. These arcs enter into a Wheatstone bridge and are so connected that when the arm and the distant telescope are at the same angle or parallel a balance is obtained. Thus each observer has the power of establishing a balance. A chart is provided for each of them, and over it the arm connected with the distant telescope and an arm or indicator attached to the telescope at that station move so that as long as both telescopes point at the object and each observer maintains the electric balance, the intersection of the arms shows the position on the chart.

The Position Finder is a simplification and amplification of the Range Finder, q. v. In practice the observers may be placed far from the forts, and may telephone their observations thereto. It has been found accurate within one-third of one per cent.

428 STANDARD ELECTRICAL DICTIONARY.

Positive Direction.

The direction which lines of force are a.s.sumed to take in the air or outer circuit from a positive to a negative region. It applies to electrostatic, to magnetic and to electro-magnetic lines of force.

Positive Electricity.

The kind of electricity with which a piece of gla.s.s is charged when rubbed with silk; vitreous electricity.

In a galvanic cell the surface of the copper or carbon plate is charged with positive electricity. (See Electrostatic Series.)

According to the single fluid theory positive electrification consists in a surplus of electricity.

[Transcriber's note: "Positive electricity" is a deficiency of electrons.]

Post Office. adj.

Many pieces of electric apparatus of English manufacture are thus qualified, indicating that they are of the pattern of the apparatus used by the British Post Office in its telegraph department.

Potential.

Potential in general may be treated as an attribute of a point in s.p.a.ce, and may express the potential energy which a unit ma.s.s would have if placed at that point.

This conception of potential is that of a property attributable to a point in s.p.a.ce, such that if a unit ma.s.s were placed there the forces acting upon it would supply the force factor of energy, while the body would supply the ma.s.s factor. This property is expressible in units, which produce, if the supposed ma.s.s is a unit ma.s.s, units of work or energy, but potential itself is neither.