The Standard Electrical Dictionary Part 139

r.e.t.a.r.dation.

In telegraphy a r.e.t.a.r.dation of the rate of transmission of signals. It is due to several causes.

(a) The self-induction of the circuit, especially if it includes many electro-magnets, produces extra currents (see Currents, Extra.) These are opposed to the main current on closing it and hence r.e.t.a.r.d the action. They are in the same direction on opening it and hence again r.e.t.a.r.d the action.

(b) Every line has a certain static capacity. This is affected by the proximity of the lines to the earth. For each signal electricity has to be charged upon the line until the line is charged to its end with a certain proportion of the initial density. This charging takes time and hence introduces r.e.t.a.r.dation.

(c) The cores of the electro-magnets of the relays or sounders are not instantly magnetized and demagnetized. This magnetic lag, q. v., introduces r.e.t.a.r.dation.

471 STANDARD ELECTRICAL DICTIONARY.

r.e.t.a.r.dation of Phase.

The fractional lagging behind of waves or alternating currents; by lagging behind a portion of a wave length the corresponding phases, as of full amplitude, are kept back or r.e.t.a.r.ded. The phase of current intensity may be r.e.t.a.r.ded with reference to the electro-motive force by the introduction of transformers of high capacity with high resistance on open secondary circuits.

[Transcriber's note: Capacitors are used to correct current phase lag.]

Retentivity.

Coercitive or coercive force; by virtue of which steel retains its magnetism. It is the more modern name, "coercive force" as a term being rejected by many.

Synonyms--Coercive Force--Coercitive Force.

Retort Carbon.

Carbon deposited in coal gas retorts from decomposition of the hydrocarbons. It is a very hard, pure form, and is of graphitic modification. Owing to its great hardness it is little used for electrical purposes, the molded carbons being easier to make. The deposition occurs in the regular gas-making process, and is a disadvantage to the working.

Return.

A line or conductor which is supposed to carry current back to its starting point, after it has traversed a line. It may be a wire or the grounding of the ends of a line [or] may make the earth act as a return, termed ground- or earth-return. The best distinction of a return is to so term the portion of a circuit on which no apparatus is placed.

Reversibility.

The princ.i.p.al in virtue of which a device for producing a given form of energy can absorb the same and do work. The reversibility of the dynamo is its quality in virtue of which it can act as a current generator, thereby converting mechanical energy into electric energy, or if a current is pa.s.sed through it, it rotates, doing work, and thereby converting electric energy into mechanical energy. The knowledge of this principle can be traced back to Jacobi in 1850.

Reversible Bridge.

A form of Wheatstone's Bridge adapted for reversal of the positions or interchange of the proportionate arms, v., so that the accuracy of the coils can be tested.

Rheochord.

An apparatus by means of which variable quant.i.ties of wire are thrown into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)

Rheometer.

A galvanometer. (Obsolete.)

472 STANDARD ELECTRICAL DICTIONARY.

Rheomotor.

A source of current; a current generator; a producer of potential difference. (Obsolete.)

Rheoph.o.r.e.

The portion of an active circuit capable of deflecting a magnetic needle. This properly includes all of the metallic conductor of a circuit. (Obsolete.)

Rheoscope.

A galvanoscope; an instrument for qualitatively detecting potential difference, fall or rise. (See Galvanoscope.)

Rheostat.

An adjustable resistance; an apparatus for changing the resistance without opening the circuit. Its action may depend on the introduction of variable lengths of mercury column, of some other liquid, or of wire into a circuit. (See Rheostat, Wheatstone's.)

Rheostat Arm.

The third arm of known resistance in a Wheatstone bridge. (See Proportionate Arms.)

Rheostatic Machine.

An apparatus for increasing potential difference. It consists of a number of static condensers. They are charged in multiple arc or in parallel, and are discharged in series. Secondary batteries may be used for the charging; thus a static effect is produced from a galvanic battery.

Rheostat, Wheatstone's.

This apparatus consists of two cylinders, one, A, made of bra.s.s, the other, B, of wood, with a spiral groove. At its end is a copper ring a.

A fine bra.s.s wire has one end attached to this ring. Its other end is fastened at e, and it is wound as shown; n and o are binding screws connected, one with the cylinder-ring a, the other with the bra.s.s cylinder, A. The current entering at o, traverses the wire on B, as there the windings are insulated by the grooves, thence it pa.s.ses to m and by A, whose metal short circuits all the wire on it, to the binding-post n. The handle, d, is turned one way or the other to regulate the length of the wire through which the current must pa.s.s. On each cylinder there is a square head, one of which is shown at c, so that the handle can be shifted from one to the other as required; to A if the wire is to be wound on that cylinder, to B if the reverse is desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.

473 STANDARD ELECTRICAL DICTIONARY.

Rheotome.

An automatic circuit breaker, one which rapidly opens and closes a circuit, as in the case of the primary of an induction coil an interrupter. (Obsolete.)

Rheotrope.

A pole changer, current reverser, or commutator, g., such as the commutator of an induction coil. (Obsolete.)

Rhigolene.

A petroleum product; a hydrocarbon of low boiling point. Its vapor is used in flashing (q. v.) carbon filaments for incandescent lamps.