The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

[Transcriber's note: The image of the above paragraphs is included here.]
a and c or a and b can be combined giving M and H in C.G.S. measurement.
Magnetometer, Differential.
An apparatus, invented by Eickemeyer, for testing the magnetic qualities
of different samples of iron. It is very similar in construction and
principle to the magnetic bridge, q. v.
Magneto-motive Force.
The force producing a magnetic field or forcing lines of force around a
magnetic circuit. It is usually applied only to electro-magnets and is
expressible in turns of the wire winding multiplied by amperes of
current, or in ampere-turns.
Magnet Operation.
A term in surgery; the use of the electro-magnet or permanent magnet for
removing particles of iron from the eye.
Magnetoscope.
An apparatus for detecting the presence of magnetism, without measuring
its intensity. A simple magneto-scope consists of a magnetized bit of
watch-spring suspended in a vertical glass tube by a fine filament. A
bit of unmagnetized soft iron wire may be used in the same way. The
first has the advantage of indicating polarity; the latter merely shows
magnetic attraction. A cork may be used as base of the instrument.

Fig. 235. MAGNETOSCOPE.
366 STANDARD ELECTRICAL DICTIONARY.
Magnet, Permanent.
A bar of steel charged with residual magnetism. Steel possesses high
coercive force in virtue of which when once magnetized it retains part
of the magnetization.
Permanent magnets are generally straight bars or U shaped; they are
termed bar magnets, magnetic needles, horseshoe magnets, machine magnets
and otherwise, according to their shape or uses.
Magnet Pole.
The part of a magnet showing strongest polarity; the part which attracts
iron the most powerfully, and acts as the starting point for lines of
force.
Magnet Poles, Secondary.
Magnet poles are often not situated at the ends. Owing to inequality of
the material or other causes they may occupy intermediate positions on
the magnet. Such poles are called secondary poles.
Magnet Pole, Unit.
A unit magnet pole is one which exerts unit force on another unit pole
placed at unit distance from it. Unit force is the dyne; unit distance
is one centimeter.
Magnet, Portative Power of.
The power of sustaining a weight by attraction of its armature possessed
by a magnet. In general terms the adherence of the armature of a magnet
to the pole varies with the square of the number of lines of force which
pass through the point of contact. Hence an increased adherence of the
armature to a horseshoe electro-magnet is sometimes obtained by
diminishing the area of contact of one pole which concentrates the lines
of force. Steel magnets were frequently made with rounded ends to
increase the portative power.
Magnet, Simple.
A magnet made of one piece of metal, or at least magnetized as such; the
reverse of a compound magnet, which is magnetized piece by piece and
then fastened together.
Magnet, Solenoidal.
A magnet which is so uniformly magnetized and is so long in proportion
to its other dimensions that it virtually establishes two magnetic
poles, one at either end. It is a long thin bar so magnetized that all
its molecules would, considered as magnets, be absolutely equal.
(Daniell.) It acts like a solenoid, except that it is longer in
proportion than the solenoid generally is constructed.
Magnet, Sucking.
A magnet coil with movable or loose axial bar of soft iron.
The whole is usually mounted vertically. When a strong enough current is
passed the bar is drawn up into the coil as if by suction, whence the
name.
367 STANDARD ELECTRICAL DICTIONARY.
Magnet, Unipolar.
No such thing as a unipolar magnet is possible. The name is given to
poised or suspended magnets, one of whose poles lies in the axis of
suspension. It is obvious that such a magnet will act, as far as its
directive tendency and rotatory movements are concerned, as if it had
only one pole. As shown in the cut, the pole s in both magnets lies in
the axis of suspension or directly under the filament by which they are
suspended, while the other pole n is the active pole in causing rotation
or directive tendency; c c are counterweights or counterpoises.

Fig. 236. UNIPOLAR MAGNETS.
Magnetophone.
An apparatus for producing a loud sound, involving the principles of the
telephone. A rapidly alternating or make and break current being
produced by any means and being transmitted through the telephone gives
a loud note of pitch dependent on the current producing it. Sometimes a
perforated metallic disc is rotated in a magnetic field, and produces
the requisite type of current.
Magnus' Law.
A law of thermo-electricity. In a homogeneous circuit, however, the
temperature varies from point to point; there is no current.
Whatever potential differences may be established by the variations in
temperature it is evident that they must counteract each other and
reduce to zero.
Mains, Electric.
The larger conductors in a system of electric light or power
distribution.
Make. v.
To complete a circuit, as by closing a switch.
Make and Break Current.
A current which is continually broken or interrupted and started again.
It is applied only where the "makes" and "breaks" succeed each other
with great rapidity, as in the action of an induction coil or pole
changer, etc. It has had considerable importance in litigation affecting
the Bell telephone patents, the courts holding that the original Bell
patent (No. 174,465, of 1876,) covered the undulating current, for the
transmission of speech. Many efforts have been made by litigants to
prove that specific telephones have transmitted articulate speech by the
make and break current, but without success. If this could have been
proved the assumption is that the courts would have sustained the use of
such device as not infringing upon the claims of the Bell patent.
Malapterurus.
A fish, sometimes called the thunder fish, an inhabitant of African
rivers, occurring in the Nile and Senegal. It possesses considerable
electric power, similar to that of the gymnotus and torpedo, although
inferior in amount.
368 STANDARD ELECTRICAL DICTIONARY.

Fig. 237. MALAPTERURUS.
Man-hole.
The cistern-like depression in the ground for giving access to the ends
of tubes in electric conduits. (See Conduit, Electric Subway.)
Marked End or Pole.
The north pole or north seeking pole of a magnet, so called because it
is usually marked with a notch or scratch by the maker. The south pole
is called the unmarked end.
Mass.
The quantity of matter in a body. The C. G. S. unit of mass is the
quantity of matter in a gram. While weight varies with latitude and
other circumstances, mass is invariable.
The unit of mass is also defined as the quantity of matter which in a
balance will counterpoise a standard mass, the gram or pound. As the
gram is intended to be the mass of one cubic centimeter of water at
3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.
As a primary unit its dimensions are indicated by M.
Mass, Electric.
A term for quantity of electricity. The unit mass is such a quantity as
at unit distance will act with unit force.
Matter, Electric.
The imaginary substance constituting electricity; a conception used
purely as a matter of convenience.
[Transcriber's note: The electron was discovered five years after this
publication.]
Matter, Radiant.
Matter in the ultra-gaseous or so-called fourth state. In the gaseous
state the molecules of a gas are in perpetual kinetic motion, colliding
actually or virtually with each other, rebounding from such approach,
and striking also the walls of the containing vessel. But except for
these deflections, which are of enormous frequency, the paths of the
molecules would be perfectly straight.
In the radiant state matter exists in so high a vacuum that collisions
of the molecules rarely occur, and the molecules simply beat back and
forth in straight lines from side to side of the containing vessel.
A layer of gas in this condition is termed a Crookes' layer, from Prof.
William Crookes, who discovered and investigated these phenomena.
369 STANDARD ELECTRICAL DICTIONARY.
Luminous streams of the molecules are produced by electric high
potential discharges between electrodes. The course of the discharge is
normal, in general terms, to the surfaces of the electrodes, and reaches
from one to the other in a curve or straight line, as the case may be.
These luminous streams are deflected by a magnetic field; if brought to
a focus can heat refractory material in that focus to a full white heat,
and can develop phosphorescence. The latter is termed electric
phosphorescence. A great variety of experiments have been devised to
illustrate the phenomena of radiant matter. The vacuum is generally
produced in a hermetically sealed glass vessel into which the electrodes
are sealed, and which contain the phosphorescent substances or other
essentials for the experiments. The vessels are termed Crookes' Tubes.
[Transcriber's note: Crookes reported on "radiant matter" in 1879. It is
actually electrons, but he failed to distinguish them from ordinary
atoms. Thompson properly described electrons in 1897.]
Matteueci's Experiment.
An experiment for showing the inductive effect of the discharge of a
Leyden jar. Two glass plates are supported on standards in a vertical
position. Flat coils of wire are wound or coiled and secured to one
surface of each plate. One plate has much finer and longer wire than the
other. Metal handles are connected to the ends of the coarser wire coil.
The plates are placed with their coils facing each other. A Leyden jar
is discharged through the coarser coil, while the handles are grasped by
a person. The shock of the discharge is felt by him.
Matting, Electric Floor.
Matting or floor covering underlaid with burglar alarm contacts, so
arranged as to be closed by anyone walking on the matting. The contacts
are connected to a burglar alarm system. The object is to provide an
alarm if a burglar enters a house, in case he should enter a door or
window without sounding the bell. The latter can be done by cutting out
the window or part of the door instead of opening it.
Maxwell's Theory of Light.
A theory of light. It is due to J. Clerk Maxwell.
It supposes the phenomena of electric induction to be due to the ether,
q. v. It supposes the condition of the ether when conveying light to be
the same as if exposed to the induction of rapidly alternating currents
or discharges (in this case synonymous). It therefore is an
electro-magnetic effect if the theory is correct.
An electric stress such as one due to the induction of an
electrostatically charged body is not a wave-creating element or factor,
but is a simple stress. But let this stress be stopped and renewed and
at once it appears as a wave-forming agency.
This stoppage and renewal represents evidently a discharge succeeded by
a charge, or if repeated is equivalent to an intermittent current or an
alternating one.
370 STANDARD ELECTRICAL DICTIONARY.
Again the electrostatic stress kept constant may by being carried
through space carry with it a wave, just as a moving projectile carries
a wave of air in advance of itself.
Admitting this much the following consequences follow:
Since in non-conductors the displacement produces a restitution force,
which varies as the displacement which is requisite or is a criterion
for the propagation of waves, while in conductors no such force is
manifested and the electric energy appears as heat, it follows that
light vibrations are not possible in conductors, because
electro-magnetic waves do not exist in them when they are in circuit,
and conductors should be opaque, while the reverse is true for
non-conductors. (Daniell.)
This is carried out often enough to make a striking evidence in favor of
Maxwell's theory.
The velocity of propagation of an electro-magnetic disturbance in a
non-conductor should be equal to that of light. This constant is proved
by mathematical considerations, to be approximately the same as the
ratio of the electrostatic to the electromagnetic unit of intensity or
quantity. This ratio is 3E10 (30,000,000,000), which is almost exactly
the velocity of light.
It also follows from what has been said that if an electrostatically
charged body were whirled around a galvanometer needle at the rate of
3E10 revolutions per second it should affect it like a circulating
current. This rate of rotation cannot be attained, but Rowland has made
manifest the effect of a rotating statically charged body upon a
magnetic needle.
The above is the merest outline of Maxwell's theory. The full
development must be studied in his own and succeeding works.
Mayer's Floating Magnets.
An experiment due to Prof. Mayer. A number of sewing needles are
magnetized and thrust into bits of cork, almost all the way through,
with their like poles projecting. They are floated in a basin of water
and take, under the effects of attraction and repulsion, when approached
by a magnet pole, regular geometric positions, marking out the positions
of angles of polygons.
Measurements.
The determination of the value of quantities; determination of the
factor by which the unitary value must be multiplied to produce the
quantity under examination. Such are the measurement of the voltage of a
galvanic battery, or of the ohms of resistance of a conductor.
Electricity has been termed the science of measurement.
Meg or Mega.
A prefix, meaning one million times. A megohm is one million ohms; a
megerg is one million ergs; a megadyne is one million dynes.
371 STANDARD ELECTRICAL DICTIONARY.

Fig. 238. MAYER'S FLOATING MAGNETS.
Mercury.
A metal; one of the elements; symbol, Hg; atomic weight, 200 ;
equivalent, 200 or 100; valency, 1 and 2.
It is a conductor of electricity.
The following data are 0º C. (32º F.)
Relative Resistance, 62.73
Specific Resistance, 94.32 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 18.51 ohms.
(b) 1 foot long, 1/1000 inch thick, 572.3 "
(c) 1 meter long, weighing 1 gram, 12.91 "
(d) I meter long, 1 millimeter thick 1.211 "
Resistance of a 1 inch cube, 37.15 microhms.
Percentage increase of resistance per degree C. 1.8° F.
at about 20° C. (68° F.), .72 per cent.
Electro-chemical equivalent (Hydrogen = .0105), 2.10 mgs.
1.05 "
372 STANDARD ELECTRICAL DICTIONARY.
Mercury Cup.
A cup of iron, wood or some material that does not amalgamate or is
unattacked by mercury, which is filled with mercury and made an
electrode of a circuit. By dipping the other terminal of the circuit
into the mercury a very good contact is obtained. It is well to cover
the mercury with alcohol. The cup may be filled so that the mercury
rises in a meniscus or semi-globule above its edges.
For some purposes this form is useful, as for contacts with the end of a
swinging wire or pendulum, because in such cases the contact can be made
without the contact point entering the cup. The point swings through the
projecting meniscus without touching the edges of the cup. A mercury cup
and contact constitute a mercury break.
Meridian, Astronomical.
The great circle passing through the north and south poles of the
celestial sphere. It lies in a plane with the corresponding geographical
or terrestrial meridian.
Meridian, Geographic.
The true north and south meridian; the approximate great circle formed
by the intersection of a plane passing through north and south poles of
the earth with the earth's surface.
373 STANDARD ELECTRICAL DICTIONARY.