Fig. 186. TORSION GALVANOMETER.
274 STANDARD ELECTRICAL DICTIONARY.
Galvanometer, Vertical.
A galvanometer whose needle is mounted on a horizontal axis and is
deflected in a vertical plane. One of the poles is weighted to keep it
normally vertical, representing the control. It is not used for accurate
work.
Synonym--Upright Galvanometer.
Fig. 187. VERTICAL GALVANOMETER.
Galvanometer, Volt- and Ampere-meter.
A galvanometer of Sir William Thomson's invention embodying the tangent
principle, and having its sensibility adjustable by moving the magnetic
needle horizontally along a scale (the "meter") towards or away from the
coil. A curved magnet is used to adjust the control. The leads are
twisted to prevent induction.
The instrument is made with a high resistance coil for voltage
determinations, and with a low resistance coil for amperage
determinations.
At one end of a long base board a vertical coil with its plane at right
angles to the axis of the board is mounted. A scale (the "meter" of the
name) runs down the centre of the board. A groove also runs down the
centre. The magnetic needle is contained in a quadrant-shaped
glass-covered box which slides up and down the groove. A number of short
parallel needles mounted together, with an aluminum pointer are used.
Fig. 188. SIR WILLIAM THOMSON'S
AMPERE-METER GALVANOMETER.
275 STANDARD ELECTRICAL DICTIONARY.
In the cut P is the base board, M is a glass covered case containing the
magnetic needle, and sliding along the base board, being guided by the
central groove, C, is the coil. Between the coil and the needle is the
arched or bent controlling magnet. The long twisted connecting wires are
seen on the right hand.
Galvano-plastics.
The deposition of metals by electrolysis, a disused term replaced
by electro-deposition, electroplating, and electro-metallurgy.
Galvano-puncture.
An operation in medical electricity. (See Electro-puncture.)
Galvanoscope.
An instrument, generally of the galvanometer type, used for ascertaining
whether a current is flowing or not. Any galvanoscope, when calibrated,
if susceptible thereof, becomes a galvanometer.
Gas, Electrolytic.
Gas produced by the decomposition, generally of water, by electrolysis.
It may be hydrogen or oxygen, or a mixture of the two, according to how
it is collected. (See Gases, Mixed.)
Gases, Mixed.
The mixture of approximately one volume of oxygen and two volumes of
hydrogen collected in the eudiometer of a gas voltameter or other
electrolytic apparatus.
Gassing.
The evolution of gas from the plates of a storage battery in the
charging process, due to too high voltage in the circuit of the charging
dynamo.
Gastroscope.
An apparatus for illuminating by an incandescent lamp the interior of
the stomach, and with prisms to refract the rays of light so that the
part can be seen. The stomach is inflated with air, if desirable, to
give a better view. An incandescent platinum spiral in a water jacket
has been employed for the illumination.
Gassiot's Cascade.
A goblet lined for half its interior surface with tinfoil. It is placed
in the receiver of an air pump from the top of whose bell a conductor
descends into it, not touching the foil. On producing a good
rarefaction, and discharging high tension electricity from between the
conductor just mentioned and the metal of the machine, a luminous effect
is produced, as if the electricity, pale blue in color, was overflowing
the goblet.
Gauss.
A name suggested for unit intensity of magnetic field. Sylvanus P.
Thomson proposed for its value the intensity of a field of 1E8 C. G. S.
electro-magnetic units. J. A. Fleming proposed the strength of field
which would develop one volt potential difference in a wire 1E6
centimeters long, moving through such field with a velocity of one
centimeter per second. This is one hundred times greater than Thomson's
standard. Sir William Thomson suggested the intensity of field produced
by a current of one ampere at a distance of one centimeter
The gauss is not used to any extent; practical calculations are based on
electro-magnetic lines of force.
276 STANDARD ELECTRICAL DICTIONARY.
Gauss' Principle.
An electric circuit acts upon a magnetic pole in such a way as to make
the number of lines of force that pass through the circuit a maximum.
Fig. 189. GAUSS' TANGENT POSITION.
Gauss, Tangent Positions of.
The "end on" and "broadside" methods of determining magnetization
involve positions which have been thus termed. (See Broadside Method and
End on Method.)
Gear, Magnetic Friction.
Friction gear in which the component wheels are pressed against each
other by electromagnetic action. In the cut, repeated from Adherence,
Electro-magnetic, the magnetizing coil makes the wheels, which are of
iron, press strongly together.
Fig. 190. MAGNETIC FRICTION GEAR.
277 STANDARD ELECTRICAL DICTIONARY.
Geissler Tubes.
Sealed tubes of glass containing highly rarefied gases, and provided
with platinum electrodes extending through the glass tightly sealed as
they pass through it, and often extending a short distance beyond its
interior surface.
On passing through them the static discharge luminous effects are
produced varying with the degree of exhaustion, the contents (gas), the
glass itself, or solutions surrounding it. The two latter conditions
involve fluorescence phenomena often of a very beautiful description.
The pressure of the gas is less than one-half of a millimeter of
mercury. If a complete vacuum is produced the discharge will not pass.
If too high rarefaction is produced radiant matter phenomena (see
Radiant State) occur.
Geissler tubes have been used for lighting purposes as in mines, or for
illuminating the interior cavities of the body in surgical or medical
operations.
Generating Plate.
The positive plate in a voltaic couple, or the plate which is dissolved;
generally a plate of zinc.
Synonyms--Positive Plate--Positive Element.
Generator, Current.
Any apparatus for maintaining an electric current. It may be as regards
the form of energy it converts into electrical energy, mechanical, as a
magneto or dynamo electric machine or generator; thermal, as a
thermo-electric battery; or chemical, as a voltaic battery; all of which
may be consulted.
Generator, Secondary.
A secondary or storage battery. (See Battery, Secondary.)
German Silver.
An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to
its high resistance and moderate cost and small variation in resistance
with change of temperature, it is much used for resistances. From Dr.
Mathiessen's experiment the following constants are deduced in legal
ohms:
Relative Resistance (Silver = 1), 13.92
Specific Resistance at 0° C. (32F.), 20.93 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 2.622 ohms.
1 foot long, 1/1000 inch thick, 125.91 "
1 meter long, weighing 1 gram, 1.830 "
1 meter long, 1 millimeter thick, 0.2666 "
Resistance of a 1 inch cube at 0°C. (32° F.), 8.240 microhms.
Approximate percentage increase of resistance per 1° C. (1.8° F.) at
about 20° C. (68° F.), 0.044 per cent.
Gilding, Electro-.
The deposition of gold by an electric current, or electrolytically in
the electroplating bath.
Gilding Metal.
A special kind of brass, with a high percentage of copper, used to make
objects which are to be gilded by electrolysis.
278 STANDARD ELECTRICAL DICTIONARY.
Gimbals.
A suspension used for ships' compasses and sometimes for other
apparatus. It consists of a ring held by two journals, so as to bc free
to swing in one plane. The compass is swung upon this ring, being placed
concentrically therewith. Its journals are at right angles to those of
the ring. This gives a universal joint by which the compass, weighted
below its line of support, is always kept horizontal.
