Encyclopaedia Britannica > Volume 8, DIA-England

ELECTRICITY.
592
Phenome- mity of which supports upon a pivot another ball E,
na. and which represents the earth, having a wire passing through
Lau-s. jt? an[| carrying at one end a small ball M, representing
the moon, avhile the other end is bent into a sharp point m.
A sharp point H is also fixed to the arm EF. If these
balls are electrified as in the last experiment, by a chain A
connecting them with the prime conductor, the discharge
of electricity from the point H will give a rotatory motion
to the arm CE and the earth E, while the electrical dis¬
charge from the point m will give a rotatory motion to
the moon M round the earth E. In this manner the
moon revolves round the earth, while the earth and moon
are together carried round the sun.
Electrical Exp. 3. By the same principle a chime of bells may be
bells. rung in a more elegant manner than that which is exhibit¬
ed in fig. 4, Plate CCIX. Five cross arms of wire are made
to revolve upon the pivot A of an insulated stand AB, as
Fig. 11. shown in fig. 11, and each wire has its extremity pointed
and turned in the same direction. To one of these arms C,
which is purposely made longer than the rest, is suspend¬
ed a glass ball or clapper 6, by a silk thread ab, and im¬
mediately behind it a rod CD. Eight bells are placed
upon the stand, and if a chain connects the point A with
the prime conductor, the discharge of the electricity from
the points will move the cross arms round, and cause the
clapper b to ring the bells during its revolutions.
Electrical Exp. 4. The electrical inclined plane, shown in fig. 12,
inclined acts upon the same principle. Two straight parallel wires,
plane.^ MO, NP, are stretched upon the insulating stands M, N, O,
j ig- — p? fixed on a base of wood. Across these wires is placed
a wire ab, having another wire cd at right angles to
it, terminated by two bent points lying in a plane pass¬
ing through cd, and at right angles to ab. When the ap¬
paratus is electrified by a chain, the electricity is dis¬
charged at the points Z> in a vertical plane, the wires re¬
volve, and the wire cd rolls up the inclined plane, in op¬
position to the force of gravity.
Electrical In order to explain the phenomena of attraction and re-
atti action pulsion which have been already described, we must avail
sion PUl" ourse^ves °f several principles which have been either
previously deduced from experiment, or which may be
readily proved.
1. The electric fluid has a tendency to escape from all
electrified bodies, whether conductors or non-conductors,
in consequence of the mutual repulsion of its particles.
2. The electric fluid is prevented from escaping from
bodies so rapidly as it would otherwise do, by the pres¬
sure of the air with which they are surrounded, and which
is itself a bad conductor of electricity.
3. If the pressure of the air is increased, the escape of
the electricity is diminished ; and if the pressure of the
air is diminished, the escape of the electricity is increased.
4. In conductors the electric fluid passes with the ut¬
most facility and rapidity among the material particles, and
does not seem to be in any way acted upon by them.
5. In non-conductors the electric fluid escapes from them,
and moves among their material particles with difficulty;
so that there is some force by which the electric fluid ad¬
heres to or is detained by the material particles of non¬
conducting bodies.
With the aid of these principles, we are now able to ex¬
plain the three different cases of electrical attraction and
repulsion.
PI. CCXI. !• When the two bodies are non-conductors. Let A be a
Fig. 13. fixed electrified non-conducting body, and B another of
the same kind capable of moving. The particles of the Pheno
electric fluid in A will repel each other; but this repul- "a ai
sive force cannot produce any motion on the centre of ■*-,aw
gravity of the ball, as their united tendency is to produce
rest. The same is true of the repulsive force of the
electric fluid in B. Let us suppose that A and B are both
electrified positively, or both negatively, then the repul¬
sion between the electric fluid in A, and that in B, will
cause B to recede from A, because the electric fluid in
B adhering as it were to the particles of B, cannot recede
from A without taking the body along with it. In like
manner, if A is positive and B negative, or vice versa, the
attraction of the positive electric fluid for the negative
electric fluid will cause the electric fluid in the move-
able body B to approach to that in A, and, by its bring¬
ing the material particles along with it, will produce the
phenomena of attraction.
Hence it follows that the attractions and repulsions of
non-conducting bodies are produced by the attractions and
repulsions of the electric fluid, which, from its adhesion
to their matter, causes them to partake in its motion.
2. When the one body is a non-conductor, and the other a Fig. l-
conductor. Let A, fig. 14 and 15, be a fixed and non-con- lo-
ducting body, and B a moveable and conducting body.
When these two spheres are separate, the electric fluid
is distributed on the surface of each in a stratum or thin
shell of equal thickness ; but when they are brought near
each other, the fluid is distributed as in fig. 14, when A
and B are oppositely electrified, and as in fig. 15, when
they are similarly electrified ; the space between the dark-
circles and the i otted outlines representing the section of
the stratum of electrified fluid upon each sphere. The
arrangement of the fluid in fig. 14 is produced by the at¬
traction of the fluid in A for the fluid in B, and vice versa,
producing an accumulation of it on each sphere on the
sides nearest one another; and the arrangement of the
fluid in fig. 15 is produced by the repulsion of the two
opposite fluids, producing an abstraction of the fluid from
the sides nearest one another, and an accumulation of it
on the sides farthest from each other. But since the non¬
conducting sphere A is fixed, the adhesion of its fluid to
its material particles cannot produce any motion; and
since there is no adhesion between the fluid in the con¬
ductor B and its material particles, these particles, or the
body which they compose, cannot move along with the
fluid. The accumulated fluid, however, at the points
O, O, fig. 14 and 15, tends to escape from the spheres in
virtue of the mutual repulsion of its own particles ; but it
is restrained by the pressure of the air, which re-acts upon
it. But the pressure of the air is an uniform force on
every part of the sphere ; and as the force with which the
electric fluid resists this uniform pressure is greatest at
the sides O, O, the ball B, in fig. 14, will recede in virtue
of this force from A; and the ball B, in fig. 15, will from
the same cause approach to A. The attraction, therefore,
of the two opposite fluids in fig. 14 produces, through the
agency of the atmosphere, a repulsion of the moveable
sphere ; and the repulsion of the similar electric fluids in
fig. 15 produces, through the same agency, an attraction
of,the moveable to the fixed sphere.
Hence it follows that the attractions and repulsions of
two bodies, one a conductor and the other a non-conduc¬
tor, are merely apparent, and are produced solely through
the agency of the atmosphere.
3. When the two bodies are conductors. In this case the
phenomena will be nearly.the same as in the last; for, by
making A a conductor, we have only removed the adhe¬
sion between its fluid and the particles of which the body
is composed, a force which was not brought into play in
case 2, owing to A being fixed.
Sec r. XL—Explanation of the Phenomena of Electrical
Attraction and Repulsion.