The Standard Electrical Dictionary Part 140

Rhumbs.

In a mariners' compa.s.s, the thirty-two points, designated, north, north by east, north north east, etc. (See Compa.s.s Mariner's-Compa.s.s, Points of the.)

Rhumkorff Coil.

The induction coil, q. v.

Rigidity, Molecular.

The tendency of molecules to resist rotation or change of position; the a.s.sumed cause of magnetic coercive force, or retentivity.

Ring Contact.

A contact formed by a terminal clip in the shape of a ring, split or cut at one point so that its ends tend to spring together. The other terminal is a bar which pa.s.ses into the cut and is tightly pressed by the elastic ring.

Fig. 298. SWITCH WITH RING CONTACTS.

474 STANDARD ELECTRICAL DICTIONARY.

Ring, Faraday.

A closed ring of iron used as the core of a transformer or induction coil. The term is derived from Faraday's cla.s.sic experiment with such an apparatus when he produced a spark by induction in a secondary circuit.

Roaring.

A term applied to the noise sometimes produced in a voltaic arc, when the electrodes are close together and a heavy current is pa.s.sing.

Rocker.

In a dynamo the movable piece, mounted concentrically with the commutator, and carrying the rocker-arms and brush-holders. By moving it the brushes are adjusted for proper lead.

Rocker Arms.

The arms projecting from a rocker and each carrying one of the brush-holders.

Roget's Spiral.

An experimental apparatus for ill.u.s.trating the mutual attraction of currents going in like direction. A cylindrical helix or spiral of wire is suspended by one end. Its lower end just dips into a mercury cup. An active circuit is connected, one terminal to the upper end, the other terminal to the mercury cup, bringing the apparatus in series into the circuit. The current as it pa.s.ses causes the coil to shorten, each spiral attracting its neighbors. This breaks the circuit by drawing the lower end out of the mercury cup. The current being cut off the coils cease to attract each other, and the end dips into the mercury cup again. This closes the circuit, the coils again attract each other and the same sequence follows and is repeated over and over again. A bright spark is produced at each break of the mercury contact.

Rotation of Liquids, Electro-dynamic.

By pa.s.sing a current through a liquid, such as dilute sulphuric acid, it rotates if exposed to the induction of a current flowing at right angles to it. The condition resolves itself into a liquid traversed by horizontal currents from centre to circ.u.mference or vice versa, rotated by a current pa.s.sing through a circular conductor below it.

475 STANDARD ELECTRICAL DICTIONARY.

Rotation of Liquids, Electro-magnetic.

The rotation produced in a liquid carrying centripetal or centrifugal currents by an electromagnet. It is practically an intensification of electro-dynamic rotation. (See Rotation of Liquids, Electro-dynamic.)

Rubber.

In a frictional electric machine the cushion of leather which is pressed against the plate as it rotates.

S.

(a) Symbol for second.

(b) Symbol for s.p.a.ce, or length; L is preferable.

(c) Symbol for south-seeking pole of a magnet.

Saddle Bracket.

A bracket carried on the top of telegraph poles, carrying an insulator for the upper wire.

Safety Device.

(a) A device to prevent overheating of any portion of a circuit by excess of current. It generally consists of a slip of fusible metal which if the current attains too much strength melts and opens the circuit. To ensure its breaking a weight is sometimes suspended from the strip. In one form an insulated German silver wire is wrapped around the end of the fusible strip a number of times and its end is connected to it. The other end of the German silver wire connects with the main lead, so that all the current goes through both in series. If the German silver wire becomes heated from excess of current the coil wrapped tightly around the end of the fusible strip melts it and opens the circuit.

(b) Lightning arresters, q. v., may be cited under this heading.

Synonyms--Automatic Cut Out--Safety Fuse, Plug, or Strip.

Fig. 299. c.o.c.kBURN SAFETY FUSE.

Safety Fuse.

A strip of metal inserted so as to form part of a circuit and of such size that a smaller current [than] would heat the regular wire of the circuit dangerously, so as to cause a conflagration for instance, would melt the fuse and open the circuit. As it sometimes happens that a safety fuse melts without parting a weight is sometimes hung upon it, so as to break it as it softens.

Salt.

A salt is a chemical compound containing two atoms of two radicals,.

which saturate each other. One atom or radical is electro-positive referred to the other, which is electro-negative. By electrolysis salts are decomposed, the atoms or radicals separating and uniting to form new molecules.

476 STANDARD ELECTRICAL DICTIONARY.

Saturated. adj.

A liquid is saturated with a substance when it has dissolved all that it can, while an excess is present in the liquid. It is possible, by dissolving some salts in hot water and allowing the solution to cool without access of air, to obtain a supersaturated solution. On introduction of a crystal of the salt, or often on mere access of air, the solution forms crystals and the liquid left is saturated.

Saw, Electric.

A platinum coated steel wire mounted and connected to be raised to incandescence for cutting purposes.