B.

(a) Abbreviation for Baum?, a hydrometer scale. (See Baum?.) Thus 10? B.

means "ten degrees Baum?."

(b) Symbol for the coefficient of induced magnetization, or the number of lines per square centimeter induced in a magnetic circuit or in any specified part of it.

B. A.

Abbreviation for British a.s.sociation. It is prefixed to standards fixed by the committee of the British a.s.sociation for the Advancement of Science. Thus the B. A. ohm means the British a.s.sociation ohm, a measure of resistance which is equal to the resistance of a column of mercury 104.9 centimeters long and one square millimeter area of cross-section.

(See Ohm.)

Back Induction.

A demagnetizing force produced in a dynamo armature when a lead is given the brushes. The windings by such setting of the brushes are virtually divided into two sets, one a direct magnetizing set, the other a cross magnetizing set. The latter have a component due to the obliqueness of the neutral line, which component is demagnetizing in its action.

Back Shock or Stroke of Lightning.

A lightning stroke received after the main discharge of the lightning, and caused by a charge induced in neighboring surfaces by the main discharge. The discharge affects the evenness of distribution of surrounding surfaces so that a species of secondary discharge is required to make even the distribution, or to supply charge where needed to bind an opposite one. The effects are much lese severe as a rule than those of the main charge, although the back stroke has caused death. The back stroke is sometimes felt a considerable distance from the place of the original lightning stroke.

Synonym--Return Stroke.

Back Stroke.

(a) In telegraphy the return stroke of the lever in a telegraph sounder, striking the end of the regulating screw with a sound distinct from that which it produces on the forward stroke as it approaches the magnet poles. It is an important factor in receiving by ear or sound reading.

(b) See Back Shock or Stroke of Lightning.

Balance.

(a) Wheatstone's Bridge, q. v., is sometimes termed the Electric Balance.

(b) A suspension or torsion balance is one which includes a filament or pair of filaments to whose lower end or ends are attached a horizontal indicator often called a needle, or a magnetic needle. (See Torsion Balance.)

(c) See Induction Balance, Hughes'.

(d) For Thermic Balance, see Bolometer.

(e) See Balance, Ampere.

56 STANDARD ELECTRICAL DICTIONARY.

Balance, Ampere.

A cla.s.s of electrical measuring instruments due to Sir William Thomson may be grouped under this head.

The instrument is a true balance or scales such as used for weighing. It is supported by a torsional wire support in place of knife edges. At each end it carries a circle of wire through which the current to be tested is pa.s.sed. The torsional wire support enables the current to be carried to these wire rings. Above and below each of these rings are two similar rings, also connected so as to receive the current. They are so connected that the current shall go through them in opposite senses.

When a current pa.s.ses, therefore, one of these rings repels and one attracts the balanced ring.

The extent of this action measures the intensity of the current. A sliding weight moving along a graduated scale on the balance is used to bring the balance beam into equilibrium when the current is pa.s.sing. The degree of displacement of this weight gives the strength of the current in amperes.

These balances are made for different currents. Thus there is a centi-ampere balance, deka-ampere balance and others, as well as an ampere balance.

Balata.

A gum used as an insulating material. It is the insp.i.s.sated juice of a sapotaceous tree, the bullet tree, Mimusops globosa, of tropical America, from the Antilles to Guiana. It is intermediate in character between caoutchouc and gutta percha. It is superior to gutta percha in some respects, being very slightly acted on by light.

Synonym--Chicle.

B. & S.. W. G.

Abbreviation for Brown & Sharpe Wire Gauge; the regular American Wire Gauge. (See Wire Gauge, American.)

Barad.

An absolute or fundamental unit of pressure, equal to one dyne per square centimeter.

Barometer.

An apparatus for measuring the pressure exerted by the atmosphere. It consists, in the mercurial form, of a gla.s.s tube, over 31 inches long, closed at one end, filled with mercury and inverted, with its open end immersed in a cistern of mercury. The column falls to a height proportional to the pressure of the atmosphere from 30 to 31 inches at the sea level. The "standard barometer" is a height of the mercury or of the "barometric column" of 30 inches or 760 centimeters, measured from the surface of the mercury in the cistern.

The column of mercury is termed the barometric column. Above it in the tube is the Torricellian vacuum.

[Transcriber's note: More accurately, 29.92 inches of mercury or 14.696 PSI.]

Bars of Commutators.

The metal segments of a commutator of a dynamo or motor. They are made of bars of copper, bra.s.s or bronze insulated from one another. (See Commutator.)

Synonyms--Segments, Commutator Segments, Commutator Bars.

57 STANDARD ELECTRICAL DICTIONARY.

Bath.

(a) In electro-plating the solution used for depositing metal as contained in a vat or tank; as a silver, copper, or nickel bath used for plating articles with silver, copper, or nickel respectively.

(b) In electro-therapeutics a bath with suitable arrangements, electrodes and connections for treating patients with electricity. It is termed an electric bath or electro-therapeutic bath.

Bath, Bipolar Electric.

In electro-therapeutics a bath in which the electrodes are both immersed in the water. The patient placed between them receives part of the discharge. The electrodes are large copper plates, termed shovel electrodes.

Bath, Electric Shower.

An electro-medical shower bath. The patient is placed on a metallic stove or support connected to one of the electric terminals. Water slightly alkaline is showered upon him. The other electrode is in connection with the water. The rain of drops and streamlets is the conductor of the current or discharge.