An influence machine for producing high potential or static electricity.

Two circular discs of thin glass are mounted on perforated hubs or
bosses of wood or ebonite. Each hub has a groove turned upon it to
receive a cord. Each disc is shellacked. They are mounted on a
horizontal steel spindle so as to face and to be within one-eighth of an
inch of each other. On the outside of each disc sixteen or eighteen
sectors of tinfoil or thin metal are cemented.

Two curved brass rods terminating in wire brushes curved into a
semi-ellipse just graze the outer surfaces of the plates with their
brushes. They lie in imaginary planes, passing through the axis of the
spindle and at right angles from each other.

Four collecting combs are arranged horizontally on insulating supports
to collect electricity from the horizontal diameters of the discs. These
lie at an angle of about 45° with the other equalizing rods. Discharging
rods connect with the collecting combs.

The principle of the machine is that one set of sector plates act as
inductors for the other set. Its action is not perfectly understood.

It works well in damp weather, far surpassing other influence machines
in this respect. On turning the handle a constant succession or stream
of sparks is produced between the terminals of the discharging rods.

(a) A conductor carrying an electric current is surrounded by circular
lines of force, which are sometimes termed an electric whirl.

(b) The Electric Flyer. (See Flyer, Electric.)

A system of connections applied to parallel circuits, including
resistance coils for the purpose of measuring an unknown resistance. A
single current is made to pass from A through two parallel connected
branches, joining together again at C. A cross connection B D has a
galvanometer or other current indicator in circuit. In any conductor
through which a current is passing, the fall of potential at given
points is proportional to the resistance between such points. Referring
to the diagram a given fall of potential exists between A and C. The
fall between A and B is to the fall between A and C as the resistance r
between A and B is to the resistance r + r’ between A and C. The same
applies to the other branch, with the substitution of the resistances s
and S’ and the point D for r r’ and B. Therefore, if this proportion
holds, r : r’ : : s : S’. No current will go through B D , and the
galvanometer will be unaffected. Assume s’ to be of unknown resistance,
the above proportion will give it, if r, r’ and s are known, or if the
ratio of r to r’ and the absolute value of s is known.

In use the resistances r, r’, and s are made to vary as desired. To
measure an unknown resistance it is introduced at S’, and one of the
other resistances is varied until the galvanometer is unaffected. Then
the resistance of S’ is determined by calculation as just explained. The
artificial resistances may be resistance coils, q. v., or it is enough
to have one unknown resistance at s. Then if the length of wire ABC is
accurately known, the point B can be shifted along it until the balance
is attained. The relative lengths A B, and B C, will then give the ratio
r : r’ needed for the calculation. This assumes the wire ABC to be of
absolutely uniform resistance. This is the principle of the meter-bridge
described below. The use of coils is the more common method and is
carried out by special resistance boxes, with the connections arranged
to carry out the exact principle as explained. The principle of
construction and use of a resistance box of the Wheatstone bridge type,
as shown in the cut, is described under Box Bridge, q. v.

The next cut shows the sliding form of bridge called the meter bridge,
if the slide wire is a meter long or a half- or a quarter-meter bridge,
etc., according to the length of this wire. It is described under Meter
Bridge, q. v. Many refinements in construction and in proper proportion
of resistances for given work apply to these constructions.

Synonyms–Electric Balance–Resistance Bridge–Wheatstone’s Balance.

The induction coil or transformer used in electric welding. For its
general principles of construction, see Welding, Electric.

Welding metals by heat produced by electricity. The heat may be produced
by a current passing through the point of junction (Elihu Thomson) or by
the voltaic arc. (Benardos & Olzewski.)

The current process is carried out by pressing together the objects to
be united, while holding them in conducting clamps. A heavy current is
turned on by way of the clamps and rapidly heats the metals at the
junction, which is of course the point of highest resistance. As the
metal softens, it is pressed together, one of the clamps being mounted
with feed motion, flux is dropped on if necessary, and the metal pieces
unite.

The most remarkable results are thus attained; almost all common metals
can be welded, and different metals can be welded together. Tubes and
other shapes can also be united. In many cases the weld is the strongest
part.

The alternating current is employed. A special dynamo is sometimes used
to produce it. This dynamo has two windings on the armature. One is of
fine wire and is in series with the field magnets and excites them. The
other is of copper bars, and connects with the welding apparatus, giving
a current of high intensity but actuated by low potential.

Where the special dynamo is not used, an induction coil or transformer
is used. The primary includes a large number of convolutions of
relatively fine wire; the secondary may only be one turn of a large
copper bar.

The cut shows in diagram an electric welding coil. P is the primary coil
of a number of turns of wire; S S is the secondary, a single copper bar
bent into an almost complete circle. It terminates in clamps D D for
holding the bars to be welded. B C, B’ C are the bars to be welded. They
are pressed together by the screw J. The large coil I of iron wire
surrounding the coils represents the iron core.

The real apparatus as at present constructed involves many
modifications. The diagram only illustrates the principle of the
apparatus.

In welding by the voltaic arc the place to be heated is made an
electrode of an arc by connection with one terminal of an electric
circuit. A carbon is connected to the other terminal. An arc is started
by touching and withdrawal of the carbon. The heat may be used for
welding, soldering, brazing, or even for perforating or dividing metal
sheets.

An ampere-meter or ammeter. The term is not used since the term “weber,”
indicating the ampere or coulomb, has been abandoned.

(a.) A name suggested by Clausius and Siemens to denote a magnet pole of
unit strength. This use is abandoned.

(b.) It has been used to designate the unit of quantity–the coulomb.
This use is abandoned.

(c.) It has been used to designate the unit of current strength the
ampere. This use is abandoned.

[Transcriber's note: Definition (a) is now used. One weber of magnetic
flux linked to a circuit of one turn produces an electromotive force of
1 volt if it is reduced to zero at a uniform rate in 1 second.]

Ether waves caused by electromagnetic disturbances affecting the
luminiferous ether. (See Discharge, Oscillatory–Maxwell’s Theory of
Light–Resonance. Electric.)

[Transcriber's note: The Michaelson-Morley experiment (1887) had already
called ether into question, but quantum theory and photons are decades
in the future.]

A unit of electric energy or work. One watt exerted or expended for one
second.

It is equivalent to
.24068     gram degree C. (calorie),
.000955    lb. degree F.,
.737337    foot lbs.,
.0013406   horse power second (English),
.0013592   horse power second (metric).

Synonym–Volt-coulomb.

The product in an alternating current dynamo of the virtual amperes by
the virtual volts. To give the true watts this product must be
multiplied by the cosine of the angle of lead or lag. (See Current,
Wattless.)

[Transcriber's note: This is now called a volt-amp. The usual usage is
KVA, or kilovolt-ampere.]