[Transcriber's note: Yet to be discovered: electron--1897 (5 years), proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69 years).]

Atomic Attraction.

The attraction of atoms for each other, in virtue of which they combine into molecules; chemical affinity, q. v., treats princ.i.p.ally of this, although molecular attraction also plays a part in it.

Atomic Heat.

The product of the atomic weight of a substance by its specific heat.

This product is approximately the same, 6.4; this approximation is so close that it is of use in determining the valency and atomic weights of substances. The atomic weight of a substance therefore represents the approximate number of gram-calories required to raise one gram-atom, q.

v., of such substance through 1? C. (1.8? F.)

Atomicity.

The quantivalence or valency of the atoms; the number of combination bonds, or bonds of affinity, possessed by the atoms of any substance.

Thus two atoms of hydrogen combine with one atom of oxygen, and three of oxygen with one of sulphur, forming saturated compounds. Therefore, taking hydrogen as of single atomicity or a monad, oxygen is of double atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad.

The elements are thus cla.s.sified into seven orders of atomicities, thus:

1, Monads or Univalent elements, Hydrogen, etc.

2, Dyads or Bivalent " Oxygen, etc.

3, Triads or Trivalent " Nitrogen, etc.

4, Tetrads or Quadrivalent " Lead, etc.

5, Pentads or Quinquivalent " Phosphorous, etc.

6, Hexads or s.e.xivalent " Chromium, etc.

7, Heptads or Septivalent " Chromium, etc.

The same element often possesses several atomicities. Barium is generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad, triad, tetrad and pentad. The familiar electrolysis of water, giving two volumes of hydrogen to one of oxygen, is one of the ill.u.s.trations of the theory indicating that two atoms of hydrogen are combined with one of oxygen.

53 STANDARD ELECTRICAL DICTIONARY.

Atomic Weight.

The number expressing the relative weight of the atom of any substance, that of hydrogen being generally taken as unity. This is the universal system, although any other element might be taken as the basis of the system. The whole theory of atomic weights is based on the indivisibility of the atom and on the theory of atomicity, q. v. (See Equivalents.)

[Transcriber's note: The standard is now the isotope carbon-12 as exactly 12.]

Attraction.

The tendency to approach and adhere or cohere, shown by all forms of matter. It includes gravitation, cohesion, adhesion, chemical affinity and other forms, and is opposed by repulsion, and is sometimes overcome by it, although it may be a.s.sumed to be always present. See the different kinds of attractions under their t.i.tles: Atomic Attraction, Electro-magnetic Attraction and Repulsion, Electro Static Attraction and Repulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attraction and Repulsion; Molar Attraction.

Audiometer.

An apparatus for obtaining a balance of induction from two coils acting upon a third. The third is placed between the other two and is free to move towards either. A scale is provided to show the extent of its movement. A varying or interrupted current being pa.s.sed through the two outer coils, the preponderating current will produce the most induction if the central coil is equidistant. It can always be moved to such a point that there will be no inductive effect, one counteracting the other. Thus its position measures the relative induction. A telephone is in circuit with the intermediate coil and is used to determine when its position is such that no current is induced in it. It is sometimes used as a direct test of hearing. (See Hughes' Induction Balance.)

Synonym--Acoutemeter.

Aura, Electrical.

The blast of air produced at highly electrified points.

Aurora.

A luminous display seen in the northern heavens in the northern hemisphere, where it is the Aurora Borealis, and seen in the southern heavens in the southern hemisphere, where it is called Aurora Australis, or indifferently for either, the Aurora Polaris. It takes the form of pale luminous bands, rays and curtains varying in color. Near the poles they are very numerous. A French commission observed 150 auroras in 200 days. Their height is variously estimated at from 90 to 460 miles; they are most frequent at the equinoxes and least so at the solstices. There is a secular variation also, they attain a maximum of occurrence every 11 years together with sun spots, with a minimum 5 or 6 years after the maximum. There is also a period of 60 years, coincident with disturbances in the earth's magnetism. Various attempts have been made to account for them. They have a constant direction of arc with reference to the magnetic meridian (q. v.) and act upon the magnetic needle; in high lat.i.tudes they affect telegraph circuits violently.

There is a strong probability that they represent electric currents or discharges. De la Rive considers them due to electric discharges between the earth and atmosphere, which electricities are separated by the action of the sun in equatorial regions. According to Balfour Stewart, auroras and earth currents.(q. v.) may be regarded as secondary currents due to small but rapid changes in the earth's magnetism. The subject is very obscure. Stewart treats the earth as representing the magnetic core of an induction coil, the lower air is the dielectric, and the upper rarefied and therefore conducting atmosphere is the secondary coil. This makes the aurora a phenomenon of induced currents. Then the sun may be regarded as the instigator of the primary changes in the earth's lines of force representing the primary of an induction coil.

[Transcriber's note: Solar wind, streams of electrons and protons, interacting with the earth's magnetic field causes aurora. Neither electrons (1897) nor protons (1920) were known in 1892. The Soviet satellite Luna first measured the solar wind in 1959. Even today increased understanding of solar and auroral phenomenon continues.]

54 STANDARD ELECTRICAL DICTIONARY.

Austral Pole.

The north pole of the magnet is thus called sometimes in France; the austral pole of a magnet is the one which points towards the north polar regions As unlike magnetic poles attract each other, it is but rational to call the north-seeking pole of the magnet the south or Austral Pole.

In the same nomenclature the south pole of a magnet, or the south-seeking pole, is called the Boreal Pole.

A. W. G.

Abbreviation for American Wire Gauge, q. v.

Axis, Electric.

The electric axis of a pyroelectric crystal, such as a tourmaline crystal; the line connecting the points of greatest pyroelectric excitability.

Axis of Abscissa.

In a system of rectilinear, or right angle co-ordinates, the horizontal axis. (See Co-ordinates.)

Synonym--Axis of X.

Axis of Ordinates.

In a system of rectilinear right angle co-ordinates, the vertical axis.

(See Co-ordinates.)

Synonym--Axis of Y.

Azimuth.

The angle between the plane of the meridian and the plane of an azimuth circle, q. v.

Azimuth Circle.

A great circle, whose plane pa.s.ses through the zenith or point of the heavens directly overhead; any great circle in whose plane the vertical at the point of observation is included.

Each celestial body has or determines an azimuth circle.

55 STANDARD ELECTRICAL DICTIONARY.