MAGNETO-ELECTRICITY.
[Illustration: Fig. 234. Clarke's magneto-electrical machine.]
The correlation of the physical forces, heat, light, electricity,
magnetism, and motion, is one of the most interesting subjects for study
that can be suggested to the lover of science. The examination of the
precise meaning of the term correlation, so ably considered by Professor
Grove, indicates a necessary mutual or reciprocal dependence of one
force on the other. Thus, electricity will produce heat, and _vice
versâ_; motion, such as friction, produces electricity, and the latter,
by its attraction and repulsion, establishes itself as a source of
motion. Electricity produces light, also magnetism, and contrariwise
light is said to possess [Page 242] the power of magnetizing steel,
whilst magnetism again produces light and electricity. Such are the
intimate connexions that exist between these imponderable agents, and we
may trace cause and effect and its reversal amongst these forces, until
the mind is lost in the examination of the bewildering mazes, and is
content to return to the beaten track and work out experimentally the
practical truths. We have had occasion to notice in another part of this
playbook the fact that a current of electricity causes the evolution of
magnetism in its passage through various conducting media, and the truth
has been specially illustrated by the various experiments in the chapter
devoted to electro-magnetism. In commencing this portion of electrical
science, we have no new terms to coin for the title of the discourse, as
we merely reverse the other when we examine the nature and peculiarities
of
MAGNETO-ELECTRICITY.
The source of the power must necessarily be a bar or horse-shoe shaped
piece of steel permanently endowed with magnetism. If the former is
thrust into a cylinder of wood or pasteboard, around which coils of
covered copper wire have been carefully wound, so that the extremities
communicate with a galvanometer, an immediate deflection of the needle
occurs, which, however, quickly returns to its first position, but is
again deflected in the opposite direction on the withdrawal of the steel
magnet from the coil of copper wire. (Fig. 235.)
[Illustration: Fig. 235. A B. Coil of copper wire. C. Permanent bar
magnet placed inside the coil, when the galvanometer needle, D, is
deflected.]
The rapid entrance and exit of the steel magnet in the helix of copper
wire would be insufficient to produce any quantity of electricity, and
the ingenuity of man has been taxed to arrange a method by which a
magnet may be suddenly formed and destroyed inside a coil of insulated
copper wire. The difficulty, however, has been surmounted by several
ingenious contrivances, based on the principles first discovered by
Faraday; and the one especially to be noticed is the revolution of a
coil of copper wire enclosing a piece of soft iron, called the
_armature_, before the poles of a powerful magnet. The first machine was
invented [Page 243] by M. Hypolyte Pixii, of Paris, and in 1833, Mr.
Saxton improved upon this machine, and three years afterwards, Mr. E. M.
Clarke described a very ingenious modification of the electro-magnetic
machine, which is depicted at page 241 of this chapter. In this picture,
the letter A is the permanent fixed horse-shoe magnets, which are very
appropriately termed the _battery_ magnets, because they take the
position that would otherwise be occupied by a voltaic battery, and they
are indeed the prime source of the electrical power that is evoked. D is
the intensity _armature_ which screws into a brass mandril seated
between the poles of the magnets A, motion being communicated to it by
the multiplying wheel, E. This armature or _inductor_ has two coils of
fine insulated copper wire of 1500 yards in length, coiled on its
cylinders, the commencement of each coil being soldered to the bar D,
from which projects a brass stem, also soldered into D, carrying the
break-piece H, which is made fast in any position by a small
binding-screw in a hollow brass cylinder to which the other terminations
of the coils, F F, are soldered, these being insulated by a piece of
hard wood attached to the brass stem. O is an iron wire spring pressing
against one end of the hollow brass cylinder; P is a square brass
pillar; Q is a metal spring that rubs gently on the break-piece H; T is
a copper wire for connecting the brass pieces with the wood L between
them, and out of which P and O pass; R R are two handles of brass with
metallic wires, the end of one being inserted into either of the brass
pieces connected with P and O, and the other into the brass stem that
carries the break-piece H, delivers a most severe shock directly the
wheel is set in motion.
In Saxton's electro-magnetic machine, the permanent steel magnets are
placed horizontally instead of perpendicularly, and are composed of six
or more horse-shoe-shaped pieces of steel. The armatures, or inductors,
or electro-magnets (for they consist of pieces of soft round iron with
wire wound round them), are two in number, and are adapted to exhibit
either _quantity_ or _intensity_ effects. The quantity armature is
constructed of stout iron, and covered with thick insulating wire. The
intensity armature is made of slighter iron, and covered with from one
thousand to two thousand yards of fine copper wire coated with silk. The
_quantity_ armature is intended for the exhibition of results similar to
those which are procurable from a voltaic battery, such as the magnetic
spark, inducing magnetism in soft iron, heating platinum wire. The
intensity armature is employed for the chemical decomposition of water
and other bodies, and likewise for the administration of those terrible
blows to the nervous system which cause strong men of the mildest
deportment to become painfully excited, and to make those ejaculations
which are so peculiar to the genus John Bull.
EXPERIMENTS WITH THE MAGNETO-ELECTRIC MACHINE.
_First Experiment._
The decomposition of water by the passage of electricity from one
platinum plate to another, has already been illustrated at page 198.
The [Page 244] same fact may likewise be displayed by the following
arrangement of the machine. (Fig. 236.)
[Illustration: Fig. 236. A. Apparatus for decomposing water and
collecting the gases separately. B B. Wires proceeding from the machine
at M, N. Q, works on the single break, H.]
_Second Experiment._
The electric light obtained by the passage of the electricity from the
battery through the charcoal points, is also an effect that can be
produced by magneto-electric machines, the wires leading from the points
A B being insulated by glass handles, and placed in the holes M N. (Fig.
237.)
[Illustration: Fig. 237. The electric light obtained from the magneto
machine.]
[Page 245]
_Third Experiment._
The scintillation of iron wire is one of the most pleasing experiments
with this apparatus, and is performed by pressing gently one end of a
piece of thin iron wire (attached by means of a binding-screw to the
upright bar A) against the armature, D. (Fig. 238.)
[Illustration: Fig. 238. Deflagration of iron wire.]
_Fourth Experiment._
The combustion of ether or other inflammable spirit may also be
demonstrated with the aid of this powerful apparatus, and the
arrangement, in common with the others employed by Mr. Clarke, is shown
in Fig. 239.
[Illustration: Fig. 239. The break is removed, and the double blades, B,
fixed in its place. The brass cup, A, containing mercury is so adjusted
that the points will leave the surface of the mercury when the armature
is vertical. Ether or alcohol poured on the surface is quickly inflamed
by the electric spark.]
With the assistance of the magneto-electric machine, telegraphic
communication may be conducted without the assistance of a battery. It
has also been applied to the art of electro-plating by Mr. J. P.
Woolrich, of Birmingham; and whilst visiting that place, the author had
the opportunity of witnessing the arrangement employed.
It consists of a very powerful magneto-electric machine turned by a
steam-engine, and connected with the large troughs containing the
silvering solution. If it is required to deposit a thin coating of
silver on the article, a short period suffices for the action of the
machine, whilst a thick deposit of the precious metal is only obtained
by the constant operation of the magnets for several hours. At Mr.
Woolrich's factory, the goods which were being coated with silver were
all kept in motion, moving slowly backwards and forwards in the trough
by means of an eccentric connected [Page 246] with the same
steam-engine that worked the electro-magnetic machine. (Fig. 240.)
[Illustration: Fig. 240. Silvering and plating by the magneto machine,
turned by a steam-engine.]
The magneto-electric telegraph patented by Mr. Henley in 1848, offers
another example of the application of the electric current induced in
electro-magnetic coils, when they rotate in close proximity to the poles
of a powerful steel magnet. This telegraph is now in constant use by the
English and Irish Magnetic Telegraph Company, through a distance of more
than 2100 miles. The whole length of wires in use amounts to the
astonishing quantity of 13,900 miles, of which 6350 miles are hidden
underground, and 7500 conducted above.
This telegraph is considered to be one of the simplest and most
economical yet brought into practical working.
[Page 247]