In photometry, the Bunsen Disc is a piece of paper upon whose centre a spot is saturated with melted paraffin, or a ring of paraffined surface surrounds an untouched central spot. If placed in such a position that it receives an equal illumination on each side, the spot almost disappears. It is used on the bar photometer. (See Photometer, Bar.)

Synonym--Grease Spot.

93 STANDARD ELECTRICAL DICTIONARY.

Buoy, Electric.

A buoy for use to indicate channels or dangers in harbors and elsewhere, which carries an electric light, whose current is supplied by cable from sh.o.r.e. It has been proposed to use gla.s.s tubes exhausted of air and containing mercury, which, as moved by the waves, would produce a luminous effect. A fifty-candle power incandescent lamp is an approved source of light.

Burner, Electric Gas.

A gas burner arranged for the flame to be lighted by electricity. It takes a great variety of forms. In some cases a pair of terminals are arranged near the flame or a single terminal is placed near the metal tip, the latter forming one of the terminals. The spark is generally produced by an induction coil, or a spark coil. The gas may first be turned on and the spark then pa.s.sed. Sometimes the turning of the gas c.o.c.k of an individual burner makes and breaks a contact as it turns, and thereby produces simultaneously with the turning on of the gas a spark which lights it.

Another form is wholly automatic. A pair of electro-magnets are attached below the base of the burner, one of which, when excited, turns on the gas, and the other one when it is excited turns it off. At the same time a spark is produced with the turning on of the gas so that it is lighted. Thus, by use of a automatic burner, a distant gas burner can be lighted by turning an electric switch. An out-door lamp may be lighted from within a house.

The increasing use of electric incandescent lamps, lighted by the turning of a switch, tends to displace electric gas burners. The latter have been cla.s.sified into a number of types depending on their construction.

Burners are sometimes connected in series with leads from an induction coil. Then the gas is turned on all at once, and a succession of sparks pa.s.sed until the gas is all lighted. The ignition is practically instantaneous.

b.u.t.ton, Push.

A species of switch which is actuated by the pressure of a b.u.t.ton. In its normal position the b.u.t.ton is pressed outwards by a spring, and the circuit is open. When pressed inwards, it closes the circuit. When released it springs backward and opens the circuit again.

They are princ.i.p.ally used for ringing bells. If the latter are of the automatic type, they ring as long as the b.u.t.ton is pressed.

For door-bells and room-bells, the b.u.t.ton often occupies the center of a rosette of wood or bronze or other ornamental piece. Sometimes, as shown in the cut, they are constructed for use on floors to be pressed by the foot. The general principle of their construction is shown, although the method of making the contact varies.

Synonym--Press b.u.t.ton.

Fig. 71. FLOOR PUSH b.u.t.tON.

94 STANDARD ELECTRICAL DICTIONARY.

Burning.

(a) In a dynamo, the production of shifting and temporary arcs between the commutator and brushes, which arcs produce heat enough to injure the parts in question.

(b) In electro-plating, a defect due to too strong a current in proportion to the strength of solution and area of electrodes. This gives a black or badly-colored deposit.

Bus Rod.

A copper conductor used in electric lighting or power stations, to receive the current from all the dynamos. The distributing leads are connected to the bus wires.

In the three-wire system there are three; in the two-wire system there are two bus wires.

The name is undoubtedly derived from "omnibus."

The bus wires may be divided into positive, negative, and, in the three-wire system, neutral bus wires.

Synonyms--Omnibus Rod, Wire, or Bar--Bus Bar, or Wire.

Buzzer.

An electric alarm or call produced by a rapid vibration of electric make and break mechanism, which is often magnified by enclosure in a resonating chamber, resembling a bell, but which is not struck or touched by the vibrating parts. Sometimes a square wooden box is used as resonator.

Fig. 72. BUZZER.

95 STANDARD ELECTRICAL DICTIONARY.

B. W. G.

Abbreviation for Birmingham Wire Gauge. (See Wire Gauge, Birmingham.)

C.

(a) Abbreviation for Centigrade, as 100 C., meaning 100 Centigrade. (See Centigrade Scale.)

(b) A symbol of current or of current strength. Thus in the expression of Ohm's law C = E/R. C indicates current strength or intensity, not in any fixed unit, but only in a unit of the same order in which E and R are expressed; E Indicating electro-motive force and R resistance.

Cable.

(a) Abbreviation for Cablegram, q. v.

(b) v. It is also used as a verb, meaning to transmit a message by submarine cable.

(c). An insulated electric conductor, of large diameter. It often is protected by armor or metallic sheathing and may be designed for use as an aerial, submarine, subterranean or conduit cable. A cable often contains a large number of separately insulated conductors, so as to supply a large number of circuits.

Cable, Aerial.

A cable usually containing a large number of separately insulated wires, and itself insulated. It is suspended in the air. As its weight is sometimes so great that it could not well sustain it, a suspending wire is in such cases carried along with it, to which it is suspended by cable hangers, q. v.

Cable Box.

A box for receiving underground cable ends and connecting the separate wires of the cable to air-line wires. It is often mounted on a pole, which forms the starting point of the air-line portion of the system.

Cable, Bunched.

A cable containing a number of separate and individual conductors. In some forms it consists virtually of two or more small cables laid tangent to each other and there secured. Thus each in section represents two or more tangent circles with the interstice solidly filled with the metal sheathing.

Cable, Capacity of.

The electrostatic capacity of a cable. A cable represents a Leyden jar or static condenser. The outer sheathing or armor, or even the more or less moist coating, if it is unarmored, represents one coating. The wire conductors represent the other coating, and the insulator is the dielectric.

The capacity of a cable interferes with its efficiency as a conductor of broken or interrupted currents, such as are used in telegraphy or telephoning. As each impulse or momentary current is sent into the line, it has to charge the cable to at least a certain extent before the effects of the current are perceptible at the other end. Then the cable has to discharge itself. All this creates a drag or r.e.t.a.r.dation.