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 gla.s.s-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 gla.s.s 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.
Ga.s.sing.
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.
Ga.s.siot"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. Sylva.n.u.s 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 pa.s.s 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 gla.s.s containing highly rarefied gases, and provided with platinum electrodes extending through the gla.s.s tightly sealed as they pa.s.s through it, and often extending a short distance beyond its interior surface.
On pa.s.sing through them the static discharge luminous effects are produced varying with the degree of exhaustion, the contents (gas), the gla.s.s 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 pa.s.s.
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.