GALVANISM.
GALVANI’S DISCOVERY—THE FROGS ELECTRIFIED—EXPERIMENTS—VOLTA’S PILE—THE
TEST—ITS USEFULNESS—FARADAY’S “RESEARCHES.”
Galvanism owes its origin to the researches of Galvani, the celebrated
professor of Bologna, and we are indebted to what was a mere “accident”
for our knowledge of this science.
Before Galvani’s time there had been many instances adduced of animal
electricity. The Rev. F. Lunn, in his article upon Electricity,[15]
mentions the fact that fire streamed from the head of Servius Tullius
when about seven years of age, and Virgil we know refers to flame
emitted by the hair of Ascanius—
“Lambere flamma comas, et circum tempora pasci”;
and if any one will comb his or her hair with an ebonite comb in the
dark, with what is sometimes called an “india-rubber comb,” the hair
will give out sufficient light to enable the operator to see himself
in a looking-glass. In olden days it is related that a lady when
touched with a linen cloth emitted sparks, and the same phenomenon
was observable when a bookseller at Pisa removed his under-garment
or vest (De Castro). We are all aware of the electricity of the cat
and of certain fishes (_see_ Electricity of Animals in sequel), and
“torpedos.” Galvani had of course a knowledge of this property, and had
occupied himself for some time making experiments upon the electricity
in animals. He was not in his laboratory that day when the great
discovery was made by means of the edible frog.
Galvani’s wife was just then in a very delicate state of health,
and in accordance with usage had been ordered soup made from frogs.
It is related that some of these animals, ready skinned, were lying
upon the laboratory table, for the Professor had been just previously
investigating the question of what he opined was “animal” electricity;
that is, he fancied that muscular motion depended upon that subtle
force.
The electric machine was in action, and one of the attendants happening
to approach or touch one of the frogs, the man as well as Madame
Galvani observed that the limbs were violently agitated. Galvani was
at once informed of this, and he made repeated experiments, which
showed him that the convulsive movements only took place when a spark
was drawn from the prime conductor of the electric machine, and while
the nerve was touched by a conductor. Galvani then suspended a number
of frogs to a railing by metal hooks, with a view to experiment upon
them with atmospherical electricity. But the frogs’ limbs were again
agitated when no electricity was apparent, and Galvani after some
consideration came to the conclusion that the movement was owing to the
position the animals assumed with reference to the metallic bodies.
Thus when muscle and nerve were in contact with metallic bodies and
connected by metal, the movements of the limbs were observable, and
the greater the surface contact the greater was the convulsion. The
philosopher next tried various metals, and discovered that the most
powerful combination was zinc and silver.
Galvani, in 1791, published his discovery and his theory that the body
acted as a Leyden jar, different parts being in a different state of
electricity. No sooner were his deductions published than all Europe
was in a ferment, and philosophers of all nations were discussing
it. Fowler, Valli, Robison, Wells, Humboldt, etc., all were deeply
interested, but none of them appear to have arrived at so correct
conclusions as did Volta, the physician of Pavia. “Wherever frogs were
to be found,” says Du Bois Reymond, “and where two different kinds of
metal could be procured, everybody was anxious to see the mangled limbs
of frogs brought to life in this wonderful way. Physiologists believed
that at length they should realize their visions of a vital power, and
physicians thought no cure was impossible.”
But notwithstanding the popular theory, Volta, in his letters to
Carallo, while giving a full and clear account of the discovery made
by Galvani and his own experiments, attacked and finally defeated the
Professor. Volta quite upset Galvani’s Leyden-jar theory; Volta says
that it was by accident that Mr. Galvani discovered the phenomenon, and
by which he was more astonished than he ought to have been. Volta’s
letters will be found in the _Philosophical Transactions_ of the Royal
Society (in French), and he attributes the effect to the metals which
produced a small amount of electricity. He found that the nerve was
acted upon on even parts of a muscle laid upon two different metals,
and if those were united, a contraction took place.
“Many experiments were made in all parts of Europe,” says Doctor Roget,
and “an opinion had been very prevalent that the real source of the
power developed existed in the muscle and nerve which formed part of
the circuit, and that the metals which composed the other part acted
merely as the conductors by which that agency was transferred from the
one to the other of these animal structures. But the discoveries of
Volta dispelled the error, by proving that the sources of power were
derived from the galvanic properties of the metals themselves when
combined with certain fluids,” and decided that this principle was
electricity. From this the “general fact” was deduced—viz., “that when
a certain portion of a nerve which is distributed to any muscle is made
part of a galvanic circuit, convulsions, generally of a violent and
convulsive kind, are produced in that muscle.”
Volta at length made the discovery that when two metals were brought
together electricity was developed, and by uniting a disc of copper
and one of zinc, and subjecting them to the test of an Electroscope,
he found positive and negative electricity developed in the zinc and
copper respectively; so Volta came to the conclusion that each metal
parted with electricity, and one became all “positive” and the other
all “negative.” But when he came further to consider the possibility
of building up a “pile” of these metal discs sufficiently strong to
produce electric effects, he found that if his theory were correct he
would lose from one side of the metal all he would gain from the other,
and therefore he could never obtain more than the slight effect he had
originally produced.
This was at first a difficulty apparently impossible to remove. It
was so self-evident that the discs of metal, if placed in a pile in a
series of pairs, would continually exercise like effects to the first
pair of discs, that Volta was puzzled, and for some time he could
not arrive at any reasonable solution. At last it struck him that
if he placed between the discs some slow-conducting substance, the
electricity would not pass from disc to disc, and the force developed
or set in motion would be more powerful.
He made the experiment. The result was the Voltaic pile made in 1800,
of which we give an illustration (fig. 219). A communication on the
subject of Electricity by contact, written by M. Volta, is to be found
in the _Philosophical Proceedings_ for the year 1800.
Volta constructed the pile which bears his name, on the assumption
that “every two heterogeneous bodies form a galvanic circle or arc in
which electricity is generated.” The “pile” consisted of a number of
discs of zinc and copper separated by discs of card soaked in water.
This combination of metals separated by a bad conductor, developed
considerable electricity, the “positive” going to the zinc at the top,
and the “negative” turning to the opposite end. By touching the zinc
and copper extremities simultaneously with wetted fingers we shall
experience a shock. “I don’t need your frog,” Volta said, when he had
proved his theory; “give me two metals and a moist rag, and I will
produce your animal electricity. Your frog is nothing but a moist
conductor, and in this respect it is inferior to my wet rag!”
[Illustration: Fig. 219.—Voltaic Pile.]
After this discovery the theory of animal electricity died away for
many years, till in 1825, Nobili, and afterwards Matteucci, proved the
existence of galvanic currents in muscles.
After Volta had succeeded in obtaining a shock from his “pile,”
he proceeded to the construction of another instrument, or rather
apparatus, which he denominated “Couronne des tasses” (fig. 220). It
consisted of a series of small glasses containing water or a saline
solution. He then procured a number of “metallic arcs,” partly composed
of zinc and partly of copper; these were inserted into the glasses, so
that every glass contained the zinc of one and the copper of another
arc, not in contact, but one at the right hand the other at the left.
The electro motion, supposed to be the primary cause of the galvanic
action, was thus produced as well as from the “pile.” The principle was
just the same in both apparatus, the metals being divided by the water
in one case, and by a wet card or cloth in the other.
Volta, in 1800, addressed to the Royal Society his celebrated letter
upon electricity excited by contact of conducting substances, and then
the English philosophers proceeded to make further experiments. It
was Fabroni of Florence who had just before suggested that chemical
action was really the cause of the phenomena exhibited. Sir Humphrey
Davy warmly advocated this theory, and made numerous experiments with
the view to establish it. Nicholson, Carlisle, and Cruickshank also
paid great attention to the subject. Volta, although he had laid the
foundation, did not venture to build upon it. Messrs. Nicholson and
Carlisle found the two kinds of electricity in the pile, the zinc
being positive and the silver negative. They also found that the
water was decomposed both in the circuit and in the body of the pile.
Subsequently Cruickshank confirmed Nicholson’s observations, and made
use of what is termed the “trough” apparatus. He found that hydrogen
was emitted from the silver or upper end, and oxygen from the other.
[Illustration: Fig. 220.—Volta’s couronne des tasses.]
These discoveries opened up a wide field. “The power of the pile
in decomposing chemical substances was now established.” Dr. Henry
employed galvanism for analysis, and Sir Humphrey Davy invented new
combinations of substances. He formed a pile of charcoal and zinc,
and found out that a pile could consist of only one metal, different
fluids being applied to the opposite surfaces separated by water, and
one fluid “capable of oxidating the metal, the other of preventing the
effect of oxidation.” Soon after a pile was made of charcoal.
In 1806, Sir H. Davy gave the results of his researches to the world
upon the electro-chemical action of bodies. In the course of his
experiments he found out the chemical constituents of the alkalies, and
a surprising number of new things were brought to light, and chemical
science received a most astonishing ally. Sir W. S. Harris says: “A
series of new substances were speedily discovered, the existence of
which had never before been imagined. Oxygen, chlorine, and acids
were all dragged, as it were, to the positive pole, while metals,
inflammable bodies, alkalies, and earths became determined to the
negative pole of the (galvanic) battery. When wires connected with each
extremity of the new battery were tipped with prepared and well-pointed
charcoal, and the points brought near each other, then a most intense
and pure evolution of light followed, which on separating the points
extended to a gorgeous arc.” So the elements of all bodies were
separated and the composition of their compounds closely investigated.
Michael Faraday threw himself _con amore_ into the question. He
set about to classify the pile phenomena, and arranged them with
appropriate terms, and in a series of papers, between the years 1830
and 1840 (_see_ his “Experimental Researches”), he explained the
chemical effects of voltaic electricity and electro-magnetic induction.
He showed that the electricities obtainable from the voltaic pile and
the electrical machine are essentially the same in their action. He
proved that the theory held respecting the necessity for the presence
of water in electro-chemical composition was erroneous, and that
many other fluids and compounds were equally effective. We have not
space at our disposal to include a digest of his various lectures and
papers. He calculated that as much electricity is employed in holding
the gases oxygen and hydrogen together in a grain of water, “as is
present in a discharge of lightning.” When water is decomposed by
the electric current, the force which determines the oxygen and acid
matter held in solution to the positive, while the hydrogen passes to
the negative pole, is not in the poles, but in the body decomposed, he
says. “The poles,” writes Faraday, “are merely the surfaces or doors
by which the electricity enters into or passes out of the decomposing
substance. They limit the extent of that substance in the course of the
electric current, being its termination in that direction. Hence the
elements evolved passed so far and no farther.” Faraday named the poles
“electrodes”—the way (in or out) of electricity.
A very simple voltaic pile may be constructed with “gold-leaf” paper.
Take two sheets of the gold paper and paste them back to back,
and two of silver paper; cut them into discs about the size of a
five-shilling-piece (or even of half-a-crown), and place them one on
the top of the other, so as the gold and silver may be alternate; press
the discs together slightly when a good many layers have been piled up,
and introduce them into a glass tube; close the ends of the tubes with
corks through which wires are passed from the discs top and bottom. It
will be found that the ends are charged with opposite electricities.
This is the _Zamboni_ pile, or the dry pile, which was constructed of
hundreds of paper discs “tinned on one side, and covered with binoxide
of manganese on the other,” put into a tube, and closed with brass
stoppers. The electricity will last a long time in a dry pile.
[Illustration: Fig. 221.—The Galvanic Pile.]
In the accompanying illustration of the Galvanic Pile a disc of copper
is at the bottom and a disc of zinc at the top. The latter, P,
is the positive pole; the former, N, the negative. When the
wires are united the current is closed, and no sign of disturbance can
be detected, although the action, of course, is proceeding within the
pile. The opposite kinds of electricity neutralize each other, and if a
continuous supply were not kept up the electricity would disappear; but
as it is, a powerful current is obtained, and if the wire be divided a
spark will be observed.
[Illustration: Fig. 222.—Bunsen Battery.]
There are many forms of galvanic batteries. The Trough Battery or
Cruickshank has been mentioned. There is Wollaston’s Pile, Bunsen’s
Battery, Grove’s Battery, and Daniell’s, called the “Constant” Battery.
In this last a porous earthenware cell is placed within a cylinder
of copper; in the cell a rod of zinc is inserted, the cell being
filled with diluted sulphuric acid,—one part of acid to ten parts of
water,—and in the outer cylinder is a solution of sulphate of copper.
[Illustration: Fig. 223.—Daniell’s Battery.]
[Illustration: Fig. 224.—Grove’s Battery.]
The cut above illustrates Daniell’s Battery (fig. 223) with connectors.
In _Bunsen’s Battery_ (or the Zinc-Carbon Battery), which is very like
the “Daniell” arrangement, as will be seen from the plates (figs. 222,
223), the porous cell has a prism of carbon immersed in it, and is
apparently a modification of the powerful “Grove” Battery (fig. 224).
This consists of slips of platinum, _h_, placed in porous cells, _g_,
each cell being surrounded by a glass cylinder. The outer (glass) cells
are filled, or nearly filled, with diluted sulphuric acid; nitric
acid is used in the porous cells, and a platinum plate inserted. The
chemical action of the Grove cell is thus explained by Professor
Stewart: “The zinc dissolves in the dilute sulphuric acid, and during
this process hydrogen gas is given off. But this hydrogen does not
rise up in the shape of bubbles; it finds its way into the porous
vessel which contains the strong nitric acid. It there decomposes the
acid, taking some oxygen to itself, so as to become water (hydrogen
and oxygen forming water), and thereby turning the nitric into nitrous
acid, which shows its presence by strong orange-coloured fumes.” By
this decomposition of the nitric acid the polarization of the platinum
(due to hydrogen) is avoided. The porous cell, while keeping the
liquids apart, does not interfere with the chemical action.
A great number of cells are used in the Grove Battery; perhaps even a
hundred may be employed.
_Smee’s Battery_ consists of a plate of platinized silver, S, with a
bar of wood to prevent contact with the zinc on each side, Z. These are
immersed in a glass jar, A, which contains dilute sulphuric acid. The
current is obtained by metallic communication with the binding-screws
on the top. This battery has much the same general arrangement as
Wollaston’s—the position of the plates being, however, reversed; in the
latter there are two negative plates to one positive. In Smee’s Battery
there are two positive (zinc) plates to one negative plate.
[Illustration: Fig. 225.—Smee’s Cell.]
[Illustration: Fig. 226.—Smee’s Battery.]
It will now be understood how an electric current is produced; the
electricity passing through the cells, etc., to wires, confers certain
properties upon the wires, and we can ascertain the effect of the
current by means of a _Galvanometer_, an instrument used to detect the
strength and direction of electric currents. The current will evolve
heat and light; it will excite muscular action, and will decompose
substances into their constituent elements. The deflection of the
magnetic needle by the electric current is considered the best evidence
of its power; it is on this that the Galvanometer is based.
We can perform a few simple experiments with the current. Suppose, for
instance, that a piece of fine wire be fixed between the pole wires of
the battery; it will be heated “white hot.” Or if two carbon points
be approached in a glass of water, as in the illustration (fig. 227),
they will emit a brilliant light in the fluid from the _voltaic arc_
which has given us the electric light. The current is the passage of
electricity along the wire, and continues until the working power or
“potential” of one conductor is equal to that of the other. When they
become equal of course the action ceases, as there is equilibrium. But
when an apparatus like the galvanic battery is brought to bear so that
the force of electricity from one conductor is made always greater than
that of the other conductor, we have a continuous flow while the action
of the battery goes on. One view of the principle is thus expressed by
Professor Gordon:[16]
“If two metals be placed near together, but not in contact, in a liquid
which acts chemically more upon one than upon the other, the metals
become charged, so that the one least acted on is of higher potential
than the one most acted on. The difference of potential produced
depends only upon the nature of the metals and of the liquid, and not
on the size or position of the plates. As soon as the difference of
potential has reached its constant value the chemical action ceases.
[Illustration: Fig. 227.—The Voltaic arc.]
“If now the metals are connected by a wire outside the liquid the
difference of potential begins to diminish, and an electric current
flows through the wire. As soon as the difference of potential becomes
less than the maximum for the metals and liquid, chemical action
recommences and brings it up to the maximum; and thus if no disturbing
cause interferes the current will continue until the metal most acted
on is entirely dissolved.”
The metal most acted on is considered the “generating plate,” and is
“positive.” The other attacked less is “negative,” and is known as
the “collecting plate,” and the zinc is the positive plate. Sir W.
Thomson has shown that the electrical movement in the galvanic circuit
is entirely due to the electrical difference produced at the surfaces
of contact of the dissimilar metals. The electro-motive force obtained
is not the same with all metals. We have mentioned that some are
electro-positive and some electro-negative, and it is with reference
to each other that the metals are considered to be endowed with these
properties respectively. It all depends how the metals are arranged or
coupled. With reference to their behaviour in this respect scientists
have arranged them in a series, as follows:—
1. Zinc.
2. Cadmium.
3. Tin.
4. Lead.
5. Iron.
6. Nickel.
7. Bismuth.
8. Antimony.
9. Copper.
10. Silver.
11. Gold.
12. Platinum.
13. Graphite.
Each metal in the list is arranged so that it is electro-positive to
any one below, and electro-negative to any one above it.
There is another curious fact which should be mentioned. In associating
these metals it has been found that when two are brought into contact
the electro-motive force becomes greater the more distant they are in
the series given above; in other words, the force between any two is
equal to the sum of the forces between those intervening between those
two. So when zinc is used with copper its force is not so great as when
used with platinum.
It was Herr G. S. Ohm who laid down the law that the strength of
the electric current is equal to the electro-motive force divided
by the resistance, for he proved that the “resistance was inversely
proportional to the strength of a current.”
There are two other laws respecting currents; viz.,—
(1.) Parallel currents in the same direction attract each other.
(2.) Parallel currents in opposite directions repel each other.
[Illustration: Fig. 228. Chemical action of electricity. Fig. 229.]
Upon these two hang all the varied phenomena of electro-dynamics. That
chemical action develops electricity we can perceive with the aid of
the two cuts (figs. 228 and 229). If the wires be attached to the
collecting-plate of a condenser of electricity and the metal plate of a
cell, as shown in the figure (fig. 228), the electricity on the plate
will be negative. If the operation be reversed, and the plate be put in
connection with the acid, and the metal with the earth, the instrument
will be charged with positive electricity. In the other case, when two
cups are used, united by a magnet so that the solutions (one acid and
the other alkaline) can by capillary attraction unite upon the binding
of the magnet, and we place the wires as in fig. 229, the charge on
the plate will be positive if it be in connection with the acid, and
negative if in communication with the alkaline solution. Every time
there is chemical action between two bodies in contact electricity
is produced—positive on one negative on the other, and that is the
fundamental principle of the voltaic pile.
The decomposition of water can also be effected by means of the
electric current. If two tubes or vessels be placed in a vase of water,
and the wires from the battery be inserted in them respectively, the
oxygen will go to the platinum or positive pole wire, and the hydrogen
to the zinc or negative pole. This decomposition or “splitting up” of
components was termed ELECTROLYSIS by Faraday, who gave a
series of names to the action and the actors in these phenomena (fig.
230).
Any liquid body, such as the water we have just decomposed for
instance, Faraday termed an _electrolyte_; the surfaces where the
current enters or leaves the body were called _electrodes_—the “ways,”
from _odos_, a “way”; the entry is the _anode_; the leaving point
the _katode_, from _ana_, “up,” and _kata_, “down.” The electrolyte
is divided into two portions, “ions” (“movers”), which move towards
the electrodes, which are positive and negative. In the case of the
decomposition of water the hydrogen goes to the negative electrode, the
oxygen to the positive.
[Illustration: Fig. 230.—Decomposition of water.]
There are a few observations to be made respecting electrolysis. One
rule is, that it “never takes place unless the electrolyte is in a
liquid state.” The liquid state is essential. It is also observed
that the components go to the different electrodes; such elements as
go to the negative electrode are termed electro-positive, the others
electro-negative; or, as Faraday termed them, “anions” or “kations:”
The chemical power or electrolytic action of the current is the same at
all parts of the circuit; the quantity of the substance decomposed is
in exact proportion to the strength of the current. Faraday measured
the strength of the electric current, and invented for the purpose an
instrument called the Voltameter. We have mentioned the Galvanometer
more than once, and will proceed to describe it. There are several
forms of this instrument: the Tangent, the Marine, and the Reflecting
Galvanometers, and the Astatic, or “Multiplier.” In the first-named the
direction of the current is determined by Ampère’s rule, which is as
follows:—
“Imagine an observer placed in the wire so that the current shall pass
through him from his feet to his head; let him turn his face to the
needle: its north pole is always deflected to his left side.”
The _“Tangent” Galvanometer_ consists of a vertical circle like an
upright ring, across which is a support in the centre holding a
copper wire, through which the electric current passes. On this point
(where the wire is) a needle is very lightly supported, and when the
instrument is to be used it is placed so that the plane of the circle
is parallel to the line in which the needle points. The current passes,
and the needle is deviated. By noting which side the north end of the
needle goes the _direction_ of the current is ascertained, and the
length of the needle being small in comparison with the diameter of the
circle through which the current passes, the _strength_ of the current
in the vertical circle is in proportion to the _tangent_ of the angle
through which the needle turns. Hence the term “Tangent” Galvanometer.
The “Reflecting” instrument is the invention of Sir William Thomson, in
which a mirror is attached to the needle, and reflects a small focus of
light upon a scale. The movements, however minute, are easily read. Sir
W. Thomson’s Galvanometers are extremely sensitive. We need not mention
any other varieties, as full descriptions can easily be obtained. We
only need to indicate the mode of working.
[Illustration: Fig. 231.—Galvanometer.]
The accompanying illustration (fig. 231) shows an Astatic Galvanometer
which may be used in two ways—either to measure strength of current,
or to find out a current; in the latter case it would be termed a
Galvanoscope. It is a compound needle instrument, and consists of two
needles placed in parallel directions with opposite poles above each
other in a coil. The wire coil is wound round a bobbin, and the astatic
needle is placed therein and suspended freely, as in the illustration,
by a cocoon thread. The upper needle moves upon a scale, O
O, and the instrument is enclosed in a glass shade. The screw,
V, communicates with the upper needle, and fixes it at zero
point when ready for use. The wires are fastened to the binding-screws,
and the current is then sent. The needle is deflected accordingly, and
the number of degrees on the scale can be read off.
The uses of the galvanic current are many. Amongst them Electroplating
is perhaps the most generally useful, though Electrotyping is also a
very important process in art. A visitor to Birmingham may view the
process carried on there by some enterprising firms, who have succeeded
wonderfully in producing electro-plate. The principle is very simple
and easy to understand, but the greatest care and watchfulness are
required on the part of the men employed. The principle, as we have
said, is simple, and consists in the fact that if a plate of metal be
suspended and attached to the positive pole of a galvanic battery and
immersed in a solution of the same metal, the conducting substance hung
opposite at the negative pole becomes coated with the metal immersed in
the solution.
[Illustration: Fig. 232.—Trough for electro-deposition.]
[Illustration: Fig. 233.—Plates immersed.]
Suppose we take a plate of silver, and immerse it in cyanide of
silver dissolved in cyanide of potassium; a coating of silver will
be deposited upon the nickel spoon or other article suspended at the
other pole. But to make the coating adhere the spoons, forks, etc.,
are prepared for the bath by cleansing in caustic potash to remove
grease, and washed in nitric acid to remove all traces of oxide, then
are scoured with sand. Next, a thin coating of mercury is put on by
immersion in solution of nitrate of mercury. Finally, they are hung
in the bath. A metal rod is hung across the bath (fig. 232), and the
plate is immersed. If the rod to which the articles are suspended be
attached to the zinc or negative pole, and the plate of silver to the
positive pole of the battery, decomposition begins, and the silver
begins to attach itself to the suspended objects. If it be desirable
to give the plated articles a thick coating, they are retained for a
long time in the bath, which is of some non-conducting material. The
dull appearance is easily removed by brushing and burnishing, and then
the “Electro-plate” is ready for the warehouse. The gilding process is
performed in the same manner, a gold plate being substituted for the
silver.
[Illustration: Fig. 234.—Medico-galvanic Battery.]
[Illustration: Fig. 235.—Battery in case.]
ELECTROTYPING may be briefly explained as follows:—Take two vessels, A
and B, and in one, A, put some dilute sulphuric acid and two plates,
one of zinc, Z, the other of copper, D, but be sure they are not
touching each other; each of these plates must have a piece of wire
fastened, by soldering to their upper parts. In the vessel, B, put some
solution of sulphate of copper and a small quantity of dilute sulphuric
acid, and attach another copper plate to the wire which comes from the
copper plate in the acid; this second copper plate is to be immersed in
the solution of sulphate of copper, and to the wire from the zinc plate
is to be fixed the object to be coated. If a medallion or other object
in plaster, it should be soaked in very hot wax and then brushed over
with blacklead until the surface is perfectly blackened and bright;
the wire should be bound all round the margin and soldered (as it
were) with melted wax to the medallion, taking care that this wax also
is well coated with blacklead. If the object be now immersed in the
sulphate of copper solution and kept at a short distance from the plate
(it must not touch it), a coating of copper will soon cover the surface
and form a perfect cast, which, when of sufficient thickness, may be
removed by filing the edge all round. If instead of the plaster cast
a copper coin or other copper object be used, the blackleading is not
required, but the surface must be first made clean and bright.
Many uses are made of the galvanic current by medical men. If the
circuit of the pile is closed and we take a wire in each hand and
break contact, a concussion will be felt in the joints of the arm and
fingers, and a certain contraction of the muscles. The currents of
electricity cause the shocks, and by a peculiar arrangement by which
the circuit can be closed or broken at pleasure, a series of shocks can
be sent through the body when it forms the connection between the poles
of the battery. We give illustrations of a medico-galvanic machine.
In fig. 235 there are two batteries, A and B, with cells, C D. Each
battery consists of a central plate of platinized silver separated
from the zinc plates by a piece of wood, E and F; the binding-screws
are fastened to the silver plates, and G H retain the zinc plates; I
is a copper band connecting the zinc plate of one battery with the
silver plate of the other. At Z and opposite are wires leading to the
coil machine. The quantity and intensity of the current are regulated
respectively by the indicator, O, and the wires, Q. There is a point, R
S, for the breaking of the contact; P N are screws retaining the wires
which lead to the handles, U V, grasped by the patients.
[Illustration: Fig. 236. Fig. 237. Fig. 238.
Horse-shoe magnets.]
The electric current is employed in many diseases, and is of great use
in some cases, but the further consideration of it with reference to
its medical applications does not fall within the scope of our present
work. We will now pass on to one of the most useful applications of the
electric force, the Telegraph, and in dealing with it we must make a
few remarks upon magnetism. First, let us make an experiment or two,
and see the reciprocal action between electricity and magnetism.
(1.) If we take a piece of iron of the form of a horse-shoe (fig. 236),
and wind around it copper wire, and pass through the wire an electric
current from our battery, the iron will exhibit strong magnetic
properties, which it will lose when the current is interrupted. The
conducting wires are insulated with silk, and the current will then
travel in one direction.
(2.) If we cover the ends of a non-magnetic piece of iron with coils
of wire, and rotate the magnet, A B, so as to cause the poles to
approach each end of the iron alternately, an electric current will be
established in the wire.
(3.) Referring to the first experiment, if we bring a needle in contact
with the iron horse-shoe, while the current is passing through the wire
we shall find that the needle has become a magnet; _i.e._, that it will
point due north and south when suspended.
We will now see what a Magnet is, and why it has obtained this name.
[Illustration: Fig. 239.—Magnetic attraction.]
In Magnesia, in Lydia, in olden times was found a stone of peculiar
attributes, which had the property of attracting small portions of
iron. The Chinese were acquainted with it, and nowadays it is found in
many places. In our childhood we have all read of it in the story of
“Sinbad the Sailor.” Popularly it is known as the loadstone; chemists
call it magnetic oxide of iron (F_{2}O_{3}). This stone is a _natural
magnet_. In Sweden it exists in great quantities as “magnetic iron,”
for it has a great affinity for that metal.
If we rub a piece of steel upon the loadstone we convert the former
into a magnet—an artificial magnet as it is called, and the _magnetic
needle_ so useful to us in our compasses and in the working of one form
of the electric telegraph is thus obtained. Let us see how this needle
acts.
[Illustration: Fig. 240.—Simple touch.]
[Illustration: Fig. 241.—Double touch.]
Take a magnetic needle and dust upon it some iron filings. You will
observe that the filings will be attracted to both ends of the magnet,
but the centre will remain uncovered. The ends of a magnet are termed
“poles,” the centre the equator. So one end is north and the other
south, and we might perhaps imagine that the same characteristics would
abide in the bar when it is cut in two. But we find that as when a worm
is divided, each portion gets a new head or tail, and makes a perfect
worm, so in the magnet each divided half becomes a perfect magnet with
separate poles, one of which always points to the north.
The poles of the magnet display the same phenomena as regards
attraction and repulsion, as do the opposite kinds of electricity. If
we suspend a magnet and bring the north pole of another to the north
pole of the suspended magnet, the latter will turn away; but if we
apply the north pole of one to the south pole of the other they will be
attracted just as opposite electricities attract each other.
MAGNETIZATION is the term applied to the making of artificial
magnets, which act is accomplished by bringing the needle in contact
with other magnets, or sometimes by means of the electric current. If
we carefully stroke the needle with the magnet, always in the same
direction, lifting the magnet and beginning afresh every time, we shall
magnetize the needle, but with a different polarity from the pole it
was rubbed with. A magnet rubbing its _north_ pole against a needle
will make the latter’s point _south_, and _vice versâ_.
Now that we have seen how the “magnetic needle” is arrived at, we
can proceed to explain the electric telegraph. The term telegraph is
derived from the Greek words _tele_, “far,” and _graphein_, “to write,”
and now includes all modes of signalling. Signalling, or telegraphing,
is of very ancient origin; the Roman generals spelt words by fire.
The beacons fired on the hills, the “Fiery Cross,” and other ancient
modes are well known. The semaphore and flags have long been and are
still used as modes of signalling, while the flashing of the heliograph
“telegraphs” to a distant camp.
The Semaphore was invented by Chappé, and was really the first
practical system of telegraphy. It was adopted in 1794, but before
this, in 1753, a letter appeared in the _Scots Magazine_, by Charles
Marshall, suggesting that signals should be given by means of electric
wires, equal in number to the letters of the alphabet. Soon afterwards
Lesage, of Geneva, made an electric telegraph to be worked by
frictional electricity, and many ingenious attempts were subsequently
made to utilize electricity for signalling purposes, but without any
permanent success; indeed, the British government were quite content
with their semaphores, for they wrote that “telegraphs of any kind are
now wholly unnecessary, and no other than the one now in use will be
adopted”!
The _Electric Telegraph_ has had considerable antiquity claimed for
it, but it is pretty certain that the discovery made by Doctor Watson,
in 1747, that electricity would pass through wires, and that the earth
would complete the circuit, gave the first impetus to the Electric
Telegraph. Doctor Watson was enabled to transmit shocks across the
Thames, and made experiments at Shooters Hill. Franklin did likewise
across the Schuykill in 1748, and De Luc performed the same experiments
on the Lake of Geneva. Both Lesage and Lomond caused pith balls to
diverge at distant points, and in 1794 Reizen made use of the electric
spark for transmitting signals, and made strips of foil show out
certain letters when the spark passed. He had a wire and a return wire
for each letter of the alphabet.
These were all slow advances, and subsequently many learned men in
Europe sought to improve upon the ideas then promulgated. We read
of telegraphs constructed at Madrid by Salvá and Betancourt in 1797
and 1798, one extending for more than twenty miles. The first-named
gentleman finally proposed to substitute the Voltaic pile for the usual
machine, and Ronalds and Dyar in England and New York respectively
employed frictional electricity with some success. The latter sent
charges of frictional electricity through a wire, and they were
recorded by being made to pass through litmus paper. The distances
between the discharges were intended to indicate the letters of the
alphabet, but even if the experiment was fairly tried it failed, for
little was heard of the result.
After the invention of Volta’s pile, which Salvá wished to adopt,
Sömmering began his experiments. He used thirty-five wires, set up
vertically at the bottom of a glass reservoir of water, and terminating
in gold points. These wires ended in the opposite direction in brass
plates attached to a bar of wood. At one end the points and at the
other the plates bore the same letters respectively; hydrogen at one
gold point, and oxygen at another, and two different letters were
indicated when the current was sent through any two plates. This
arrangement was afterwards improved upon, and only two wires retained.
It was not until electro-magnetism had been developed, however, that
Œrstead found out the power of electricity to deflect the magnetised
needle, and in 1820, Scheweigger added a “multiplier.” Then came
Arago into the field with his discovery, that a “wire carrying a
current could magnetise a steel rod.” Ampère substituted a helix for
a straight wire, and Sturgeon used soft iron for steel, and developed
the electro-magnet. Daniell’s battery, and Faraday’s discoveries of
magneto-electricity and the induction coil were the means of putting
a constant supply of electricity at the service of the telegraph and
so on, till 1830 brought out a more practical method introduced by
Schilling.
In that year Baron Schilling made a telegraph, and exhibited it in 1832
at Bonn. This invention, with five vertical needles, was shown to Mr.
Cooke in 1836. But in 1834, Gauss and Weber had succeeded in sending
signals by means of a voltaic current acting upon a magnetised needle,
and this apparatus was really the first practical electric telegraph
in use, and it was much improved by Professor Steinheil of Munich.
They employed a magnetic-electro machine, and caused a bar to move in
certain directions to indicate certain letters of the alphabet. This
was really of value, but Steinheil, the pupil of Gauss, assisted by his
government, employed only a single wire, and made the earth complete
the circuit for him instead of having a return wire as his predecessors
had. This telegraph was perfected by a series of bells, which gave
different tones for different letters, and he also caused the needle to
make certain tracings as it moved upon a paper slip, something like the
Morse pattern, which was completed in 1837.
Professor Morse, in 1832, conceived the idea of an electric telegraph
but his claim was disputed by a Doctor Jackson, who was on the same
vessel when the subject was discussed. We need not enter into the
details of the controversy. Mr. Morse won the day, and patented his
invention.
“It was once a popular fallacy in England and elsewhere that Messrs.
Cooke and Wheatstone were the original inventors of the electric
telegraph. The electric telegraph had, properly speaking, no
inventor.... Messrs. Cooke and Wheatstone were, however, the first who
established a telegraph for practical purposes comparatively on a large
scale, and in which the public were more nearly concerned.... Therefore
it was that the names of these enterprising and talented inventors
came to the public ear, while those of Ampère and Steinheil remained
comparatively unknown.[17] The telegraph, as used in Great Britain, was
the result of the co-operation of Professors Cooke and Wheatstone.
Mr. Cooke, in 1836, having seen the needle telegraph when in
Heidelberg, made certain designs, and soon entered into partnership
with Professor Wheatstone for the application of electric telegraphs
to railways. Their apparatus with five needles and five wires was put
up on the London and North-Western (then London and Birmingham) and
Great Western lines, but proved too expensive. The instrument was
subsequently modified, and is used on the English railways still.
[Illustration: Fig. 242.—Cell.]
We may now proceed to look at the Wheatstone needle telegraph and see
the method of working it. We know already that when a pair of metallic
plates are immersed in a fluid which acts chemically more rapidly on
the one than the other, and a wire connects the upper parts of these
plates, this wonderful agency is set in motion, and circulates from
the one plate to the other (fig. 242). This arrangement may be best
shown by using one plate of zinc and the other of copper, and a dilute
solution of sulphuric acid for the liquid; this, however, produces by
far too little of the agent to be used on a telegraphic line, there are
therefore combinations of such pairs of plates, so arranged that the
power of one pair shall be added to the next in such a way that at the
end of the series (called a “battery”) there shall be a great increase
of the power accumulated; this arrangement is shown in fig. 244. Now
(if the power be sufficient) it does not signify what length of wire
there may be between the two ends of this arrangement or “battery”;
whether they be connected by a few feet or many hundred miles, the
electricity passes instantaneously from one end to the other; and
furthermore, it has been found in practice, that this electrical
influence can be transmitted through the earth in one direction if
sent by a wire in the other; for instance, if a wire from one end of
the battery be carried on from London to Liverpool, instead of having
another from Liverpool to London, to connect the two ends of the
battery, it is found to answer the same purpose if the end of the wire
at Liverpool be fastened to a plate of metal buried beneath the surface
of the earth, and the other end of the battery at London furnished with
a similar plate, also buried. In this arrangement, the electricity
will pass beneath the surface of the earth from Liverpool to London,
and through the wire from London to Liverpool, thus completing
the circuit. The end from which the electricity passes is called
the “positive electrode,” that to which it returns, the “negative
electrode.” Fig. 245 will show this arrangement.
[Illustration: Fig. 243.—The Needle Telegraph.]
[Illustration: Fig. 244.—The Battery.]
[Illustration: Fig. 245.—The circuit.]
[Illustration: Fig. 246. Fig. 247. Fig. 248.
Magnetic needles.]
If a bar-magnet be suspended on a pivot so that it may turn freely,
it will (as is well known) turn with one end to the north, which is
owing to a current of natural electricity passing round the earth in
the direction of east and west, the magnet crossing the current at
a right angle; and if a coil of wire coated with silk (to keep one
part of the coil from another) be placed round, above, and below the
long axis of a bar of steel, as shown at fig. 246, and a current of
electricity passed through the wire, the steel becomes a magnet, and
will take a direction similar to the natural magnet, more or less, at
right angles to this coil, as in fig. 247, according to the intensity
of the current; and the instant this electrical current is stopped, it
will resume its former direction. This fact has been made use of to
form the principal feature of all English telegraphs; such a needle is
mounted in an upright position, and instead of its tendency to turn
to the north, a tendency to maintain the upright position is given
to it by having one of the arms of the magnet a little heavier than
the other; such a magnet having a coil of wire surrounding it. When
the electric current passes through the coil, it will turn out of the
upright position to either one side or the other, according to the
direction of the current, from its tendency to assume a position at
an angle thereto (fig. 248); if the current be stopped even for an
instant, then the needle, or magnet, will again assume its upright
position. The pivot of this magnet is brought forward, and has on its
front part another needle, which turns with it; this is visible on the
outside of the apparatus, and is looked at to ascertain the movement of
the one within. There is also an arrangement called a “commutator,” so
contrived, that by moving a handle to the right or left, a connection
shall be made with either end of the battery, and thereby cause the
direction of the current and needle to be changed at pleasure; also
by moving the handle into an upright position the current shall be
stopped; and finally, by a third movement, a bell shall be rung. Now,
as has already been explained, when the current goes in one direction,
the magnetic needle is deflected in that direction; and when the
current is reversed the position of the needle is also reversed, and
when the current is cut off the needle will resume its perpendicular
position. If two such needles and two such handles be at each station,
when the handles at one station are moved, the needles at the other
station will take on a similar movement; and when the handles at that
station are moved, the needles at the first station will be moved to
correspond. This constitutes the system of communication kept up by
the electric telegraphs in England; but it remains to be shown how all
the letters of the alphabet and numerals can be represented by the
movements of the two handles. These handles can be placed in eight
positions (besides the upright one) by a single movement of each hand,
as may be seen in fig. 249; and these eight signals if repeated, or
made twice in rapid succession will make eight more, and by being
repeated three times will constitute a third eight, making twenty-four;
finally, by a rapid motion right and left, they may be caused to
signify a fourth eight, or thirty-two signals, which are found to be
sufficient for every purpose, and by practice may be both produced and
read off with facility. Before a message is about to be delivered the
commutator is so placed as to ring a bell, which is done by the same
arrangement as in a common alarm-clock, but the action is set in motion
by a peculiar contrivance, which depends upon the property a bar of
soft iron has of becoming magnetic when a wire is wound round it and a
current of electricity passed through this wire; this magnetic property
exists only as long as the current passes, and stops the instant it is
cut off. The catch of the alarm is disengaged by the movement of a bar
of iron being drawn to the magnet while the current passes, and forced
back again by a spring when it is stopped, thus setting in action the
mechanism of the alarm; or in some cases there is a simple contrivance
for causing a rapid flow and stoppage of the electricity, so that the
bar is alternately attracted by the magnet and released by the spring,
and this motion rings the bell as long as it is continued. The bell
is always rung to give notice that a message is about to be sent, and
at the station where it rings, the bell at the former station is rung
in return, to show that they are prepared to receive the message:
which is then spelt, letter after letter, by moving the handles into
the proper positions, and as it is being sent, the eye is kept on
the dials, certain single signs are made and recognised, which will
communicate any reply from the station to which the message is being
sent, such as “repeat,” or “not understood.” The wires which convey
the electricity are made of galvanised iron (iron coated with zinc),
and as they must be kept from all communication with the earth by some
substance incapable of conducting it, they are therefore stretched
between wooden poles (fig. 250), and rest upon sockets or supports of
glass or glazed earthenware, which are both substances incapable of
conducting the electricity to the earth (fig. 251), and in order that
these may be quite dry, an inverted cup of metal, glass, or earthenware
is placed over it, or the whole is blown or moulded in one piece. If
the support for the wires were not kept from the rain, the wet would
form a conducting surface, and allow the electricity to escape into the
earth.
[Illustration: Fig. 249.—Handles and needles of telegraph.]
[Illustration: Fig. 250.—Telegraph wires.]
[Illustration: Fig. 251.—Insulator.]
The Telegraph Alphabet, in the two-needle instrument, now not generally
used in England, is given below.
TWO-NEEDLE ALPHABET.
Movements of | |
First Needle. | Of Second Needle. |Of both Needles
| | together.
| |
A is signified by moving| |
needle once to right| |
B “ “ “ once to left| |
C |By moving needle |
| once to right|
D | “ “ once to left|
E | |Moving to right.
F | |Moving to left.
G twice to right| |
H “ to left| |
I (or J) | Twice to right|
K | “ left|
L | |Twice to right.
M | |Twice to left.
N One to right, | |
one to left | |
O One to left, | |
one to right | |
P |One to right, |
| one to left |
O |One to left, |
| one to right |
R | |One to right,
| | one to left.
S | |One to left,
| | one to right.
T Two to right, | |
one to left | |
U One to right, | |
two to left | |
V |Two to right, |
| one to left |
W X |One to right, |
| two to left |
Y | |Two to right,
| | one to left.
Z | |One to right,
| | two to left.
In the single needle instrument the letters are indicated by right and
left vibrations, from A one right, to B one right and left, and so on,
increasing to Z. This mode is now generally used.
The manner in which the current passes is shown by the following
illustrations (figs. 252, 253).
[Illustration: Fig 252.—Passage of the current (1).]
[Illustration: Fig. 253.—Passage of the current (2).]
For the sake of clearness, the diagram has been drawn with simple
lines only. In the real needle-machine the construction is much more
complicated; perspective drawings of it may be seen in Lardner’s
“Electric Telegraph,” and numerous other works. In fig. 1, B is a
single cell of a battery containing a plate of copper, C, and a plate
of zinc, Z, immersed in sulphuric acid and water. H is the handle of
the instrument, turning from left to right, and _vice versâ_, like the
handle of a door, consisting of two pieces of brass insulated from
each other by being inserted in an axis of ivory. To the ends of the
two pieces of brass are fixed the wires, CW and ZW, leading from the
copper and zinc ends of the cell respectively. Fixed on each side of
the handle are two plates of metal, which may be called LP, the left
plate, and RP, the right plate. They are connected with the needle
wire, NW, which passes before and behind the magnetized needle, N,
suspended perpendicularly on its axis, with its north pole upwards.
As long as the wires, CW and ZW, remain insulated from each other,
no current passes from the cell; but as soon as the handle, H, is
turned, so that the copper end touches the left plate (fig. 2), and
the zinc end touches the right, communication is established between
the plates of the cell, and the current commencing at the copper
passes along CW, the top half of H, into LP, along N W, travelling
_up before_ and _down behind_ the needle, causing it to deflect to
the observer’s left, according to the rule given above. Reaching RP,
it passes downwards to the cell to Z, and so on to C, continuing its
travels and keeping the needle deflected as long as the handle remains
in contact with the plates. If it is required to deflect the needle to
the right, the handle is turned to the right, bringing its copper end
in contact with the right plate, causing the current to travel in the
opposite direction. By following the current from the copper to the
zinc, as indicated by the arrows in fig. 3, it will be seen that it now
travels _up behind_ and _down before_ the needle, deflecting it to the
observer’s right. Thus, by causing a current of voltaic electricity to
pass alternately _up before_ and _down behind_, and _up behind_ and
_down before_, the needle is moved to the left or the right at will.
The way in which the current is made to act on a distant needle is now
simple. The following figure (fig. 253) shows the arrangement. The
left portion of the figure represents an instrument at London, that
on the right an instrument at York. The needle-wire, instead of being
continued directly to the zinc plate of the battery, passes away from
the needle over poles to York, where it joins an instrument similar in
all respects to that at London. It passes similarly before and behind a
magnetized needle, joining the right plate of the instrument. As long
as the two plates are unconnected, no current can pass. The current is
therefore completed by a contrivance which may be represented by the
semicircular piece of metal, K. In practice the two plates or springs,
which, when not in use, are always pressed against the connector, K,
which is a cross-piece on the top of the handle, keeping the London
needle in circuit with the York battery, and _vice versâ_. As soon
as London uses his handle, it presses the spring-plate, and puts
his needle out of the York circuit, the current he sets up sending
York needle to the right or left, as the case maybe. The second wire
connecting the left York plate with the right London plate is, it will
be seen, not carried along like the first wire. Use is made in this
case of the conducting power of the earth itself, plates from the wires
being buried many feet below the surface at London and York. When
London wishes to speak to York, he first signifies his intention of so
doing by ringing York’s alarum. This he effects by sending a current
through an electro-magnet placed above York’s instrument. The armature
is attracted, and frees the detent of the alarum, setting it ringing
until York signals ready. London then stops the bell, and commences his
message. By following the direction of the current, when the handle is
turned to the left, as in fig. 4 [within fig. 253], it will be
readily seen how this is effected: commencing with London’s copper, LC,
it passes up before and down behind London’s needle, flowing along the
wire between the two cities to York’s needle, up before and down behind
which it travels, sending it also to the left. It then passes to York’s
right plate, through the connector to the left plate, and so on to
earth at York, coming to the surface again at London, passing through
London’s right plate and through the lower part of the handle to the
zinc of the battery. The reverse current may be easily followed. Any
number of instruments with similar needles may be interposed along the
course of the wire. When the operator wishes to speak to any particular
one, he rings all the bells for attention, and then signals Derby or
Nottingham, as the case may be. They all then throw their instruments
out of current except the one required. The mode by which the needle
movements are converted into language is simple. A is signalled by
causing the needle to vibrate once to the right, B once right and once
left, C once right and twice left; and so on, as arranged.
The following is the alphabet (with numbers) once in use on the
South-Eastern Railway for the double-needle instrument. The table is
taken from Mr. Walker’s translation of De la Rive’s work on Electricity
and Magnetism.
A is signified by two movements of left needle to left.
B ” by three ” ” ”
C (and fig. 1) by two ” ” right first, then left.
D (and fig. 2) by two ” ” left first, then right.
E (and fig. 3) by one ” ” to the right.
F by two ” ” ”
G by three ” ” ”
H (and fig. 4) by one ” right needle to the left.
I by two ” ” ”
J (same as G).
K by three ” ” ”
L (and fig. 5) by two ” ” right and left.
M (and fig. 6) by two ” ” left and right.
N (and fig. 7) by one ” ” to the right.
O by two ” ” ”
P by three ” ” ”
Q (same as K).
R (and fig. 8) by one parallel movement of lower points, both needles
to the left.
S by two ” ” ”
T by three ” ” ”
U (and fig. 9) by two ” ” first right, then left.
V (and fig. 0) by two ” ” first left, then right.
W by one movement of both needles (lower points) to right.
X by two ” ” ” ”
Y by three ” ” ” ”
Z (same as S) or specially.
The Morse system of telegraphy was first brought out in 1844, and was
worked by means of a Voltaic battery, an electro-magnet being used at
the receiving station. This magnet attracted an “armature,” and by
it dots or lines are marked on a moving paper band by a point at the
other end of the wire, on the register in which the paper is carried
by rollers which move out by clockwork. The lever being “tapped” down
in fast or slow pressures will give a corresponding series of dots or
lines (according as the pressure is long or short) upon the moving
strip of paper at the receiving station. Three taps will give C, one
tap and a pause will make A. The dots are “taps” on the key, the lines
brief “rests” on it, as will be seen from the alphabet below, which is
given as a specimen.
MORSE ALPHABET.
A .-
B -...
C .. .
D -..
E .
F .-.
G --.
H ....
I ..
J -.-.
K -.-
L -
M --
N -.
O . .
P .....
Q ..-.
R . ..
S ...
T -
U ..-
V ...-
W .--
X .-..
Y .. ..
Z ... .
NUMBERS.
1 .--.
2 ..-..
3 ...-.
4 ....-
5 ---
6 ......
7 --..
8 -....
9 -..-
0 ___
The various stops are also indicated in the same manner by combinations
of dots and lines.
The Atlantic telegraph cables and similar enclosed wires between other
countries are too well known to need detailed description. There
is a great variety of telegraphic instruments. The dial, and other
arrangements, are very common, and the Wheatstone Key instrument is
supplied to private firms as being the most handy. It requires but
a very short apprenticeship, and any person who is handy can easily
learn to work it in a few minutes. The apparatus consists of a dial
upon which the letters of the alphabet are printed, each letter being
supplied with a key or stop. A pointer is placed in the centre, as in
the wheel barometer, and there is a handle beneath. In front, upon a
sloping board, is another dial plate and pointer; thus we have the
receiver and transmitter before us in a very small space.
[Illustration: Fig. 254.—Receiver. Dial Telegraph. Fig.
255.—Manipulator.]
When it is necessary to work the instrument a bell is rung by turning
the handle rapidly. To speak by the instrument it is necessary to keep
turning the handle with the right hand while the fingers of the left
are employed in pressing down in as rapid succession as practice will
permit the keys corresponding to the letters on the dial while the
handle is kept turning. When a word is completed the operator must stop
at the + at the top, and then begin again, stopping after each word.
When all is said, a couple of rapid turns of the dial will signify that
you have ended.
There are many other systems of telegraph, but all are dependent upon
the same principles. The accompanying illustrations (figs. 254, 255)
show a dial telegraph of a simple kind, which almost explains itself.
The first figure is the receiver, on which is a pointer fixed to a
dial-plate having the letters of the alphabet inscribed around it.
When the manipulator is being worked the dart points to the letters
in succession of the words used, and they are separately spelt. The
manipulator (fig. 255), by closing and opening the circuit, works the
needle.
In the manipulator we have a wheel with an index point fixed above
it. In this wheel are thirteen teeth, with the openings between them
filled with ivory. The axis of the wheel is in contact with the wire
from the positive pole, _p_, and a spring attached to the wire or by
the binding-screw, _t_, presses against the circumference of the wheel,
and completes the circuit. When the wheel is placed so that the arrow
point is above the +, the needle of the receiver is also at +. By
turning the wheel to bring the needle to A, the spring on the
circumference is passed from an ivory “tooth” to a “metal” one; the
circuit is closed, the point of the receiver also turns to A,
and so on through the word by successive closing and breaking of the
circuit.
As there are a great many other applications of electricity of
which we have to treat,—the Electric Light, and Mr. Edison’s other
inventions,—our space will not permit a much more detailed account of
the telegraph, but there are some incidents connected with its progress
which it would be as well to mention.
[Illustration: Fig. 256.—Electric cable.]
[Illustration: Fig. 257.—Ocean cable.]
Alexander Bain, about 1840, attempted to produce a printing telegraph,
and in 1846 he actually accomplished a registering apparatus, which was
an application of the principles of Dyar and Davy. But although Bain’s
system was good, Morse had the advantage of possession in the United
States, where it was tried, and Bain went out of fashion. Bain’s system
was, in fact, the present chemical “automatic” telegraph, which has
been perfected for rapid transmission.
Bakewell’s instrument, which has been improved upon by later
electricians, is termed the fac-simile telegraph. The message to be
sent is written with a pen which has been dipped in varnish (for ink),
and the characters are inscribed upon prepared tinfoil. The message is
then put upon a cylinder covered with prepared paper, and has a pointer
attached. There is a precisely similar cylinder at the receiving
station. When the cylinders are simultaneously set going, the point at
one will trace a spiral line as the first (transmitting) point passes
round its cylinder. However, as the latter “stylus” meets the varnish
letters a break occurs, and these spaces are exactly reproduced as
blanks at the other end, and the form of the letters can be seen.
Coselli, in his adaptation, caused dark letters to be registered on
a white ground, and thus simplified matters. Since then we have had
printing telegraphs, and dials, and writing machines, one of which will
be described presently.
Submarine telegraphs were, it is said, first suggested by Salvá in
1797, and Wheatstone, in 1840, declared that it was quite possible to
connect England and France by wire. Morse and Calt experimented with
submarine cables in America, and Lieutenant Siemens first applied
gutta-percha to the wires as an insulator in the Prussian line of
telegraph across the Rhine. The English laid a wire between Dover and
Calais, which was broken, but successfully relaid. And so on, till in
1857 the great project of the Atlantic cable was broached. We give
illustrations of the cables; the circumstances connected with the
laying of which, and the enthusiasm over the successful accomplishment
of the task, must be in the memory of all. The readings of the messages
were shown by delicate galvanometers, the beam of light being reflected
from a mirror. This cable was lost, and in 1862 Mr. Field came over to
urge the importance of the submarine cable between this country and
America. The cable was shipped on the _Great Eastern_ in 1865, and
was 2,186 miles long. It consisted of seven copper wires twisted, and
covered with gutta-percha. The outside coating consists of ten iron
wires surrounded by manilla yarn. But this cable broke, and a third was
made and laid in 1866. The old cable was then recovered and spliced.
There are some two hundred cables now in existence, the last being the
Cape cable, laid when the Boer War was engaging our attention. The
transmitting apparatus of Mr. Varley and Sir W. Thomson has greatly
accelerated the rapidity of messages, and Thomson’s syphon recorder
farther increased the speed.
The following description of a new system is from _Scribner’s Magazine_
for 1880:—
“NEW TELEGRAPHIC SYSTEM.
“A new system of sending and receiving electrical impulses over an
insulated wire has recently been brought into successful operation,
that seems to promise not only a radical change in the present methods
of telegraphing, but a material gain in the speed and cost of sending
messages by wire. It is founded on a union of the so-called “automatic”
and “chemical” systems of telegraphy. The first of these employs a
strip of paper having, by some mechanical means, a series of small
holes punched in it, the design being to pass the perforated strip
under a needle, or stylus, in electrical connection with the line. This
stylus, on passing over the paper, opens the circuit, but in passing
one of the holes, drops through and closes it,—this alternate making
and breaking of the circuit transmitting the message. The chemical
telegraph records any electrical impulses sent over a line by staining
a strip of prepared paper passing under it. This is founded on the fact
that electricity has the power of decomposing certain chemicals, and
if paper is soaked in these chemicals and submitted to the action of
electricity, it will be discoloured wherever the current passes. While
both of these systems have been used, neither has been able to compete
with the more simple Morse key and sounder, and it has remained for
the new system to bring them to a position where they may come into
general use. The new system is a modification and combination of the
automatic and chemical systems, the transmitting being performed by
means of a perforated strip of paper, and the receiving of the message
being recorded by the discolouration of chemically prepared paper. The
process is entirely mechanical and chemical, the telegraph operator
having no direct control over the message, either by sight, sound, or
touch. The written message is sent to the operating-room, and given
to the person using the perforating machine. This consists of a small
key-board, with black and white keys, each marked with a letter or
sign, and an ingenious system of levers, operated by the keys, for
punching small holes in a ribbon of paper moving past the side of the
machine. The machine stands upon a small table, and under it is a
treadle for giving motion to the feeding apparatus for supplying the
paper to the machine. The operator moves the treadle with his feet, and
at the same time touches each key to spell out the message. In a very
few seconds the message is imprinted on the ribbon in the form of a
double row of small perforations, each group of two holes representing
a dash, and each single hole a dot, as in the Morse alphabet. Each
letter is separated from the next by a longer dash, and each word by a
still longer dash, and each sentence by a dash of indefinite length.
This spacing of the letters is performed automatically, the spacing of
words and sentences is performed by the operator. The perforated slip
containing the message is then sent to the transmitting machine. This
consists essentially of a metallic wheel, divided into two sections by
means of a thin insulation of hard rubber. One section of the wheel is
connected with the positive pole of the battery, and the other section
with the negative pole. A pair of fine metallic brushes, both of which
are connected directly with the line, are suspended above the wheel,
and are arranged so as to press lightly upon the latter, when desired.
When resting on the wheel the circuit is closed, and when raised above
it the circuit is broken. The perforated strip is, by a simple piece
of mechanism, made to pass over the face of this wheel and under the
brushes. While the paper is passing, both brushes are raised from the
wheel, and slide over the paper, and the circuit is broken. On passing
a hole, one of the brushes drops through and closes the circuit for
an instant. On passing two or more holes, arranged in a series close
together, the brush closes the circuit for a shorter or longer time,
according to the number of holes, and as the perforations on the
paper are arranged in two rows, alternating from one to the other,
the brushes are used alternately, and the polarity of the current is
continually changed with every impulse sent over the line. No special
skill is required in sending a message, as the operator has only to put
the perforated strip in the machine and turn a hand-crank, to cause it
to pass rapidly under the brushes, and with a little practice, a young
girl can send messages at the rate of one thousand words a minute, with
absolute precision. The receiving apparatus consists essentially of a
simple piece of mechanism for causing a strip of chemically prepared
paper to pass rapidly under two small needles that are connected with
the line. As the paper passes the needles, the electricity sent over
the line from the transmitting machine seeks the earth through the wet
paper and the machine, and in passing discolours the paper, each stain
representing a dot or dash, and the message is printed on the paper in
a double row of marks at the same speed with which it was dispatched.
In practice, a Morse key and sounder is placed at each end of the
line, and on sending a message the transmitting operator calls the
receiving station, and when the operator at the distant end replies,
both turn the cranks in their machine swiftly, and the message is
sent and received at an average speed of one thousand words a minute.
The message received is given to a person using a type-writer, and
at once translated into print and sent out by the messenger boy. It
is found in practice that two operators, one at each end of a single
wire of indefinite length, can keep fifteen operators fully employed
in preparing the messages, and fifteen girls busy in translating and
printing the messages for delivery. The system is of American origin.”
Of the hundred and one uses to which electric wires are now
appropriated—of the alarms, fire-calls, clocks, etc.—we need not speak.
We must pass on to the Writing Machine (fig. 258) before we make
mention of Mr. Edison’s inventions.
The Writing Machine is as remarkable for the simplicity of its
mechanism as for the facility and ease with which it can be used. It
was invented by Remington, the American, whose name is so universally
known in connection with a repeating rifle. He makes these writing
machines in his own factory, where he associates them with rifles and
sewing machines—implements for war and peace.
The appearance of the Writing Machine may be easily perceived from the
illustration (fig. 258), which is drawn to scale one-fourth of the
actual size. It comprises a key-board, upon which there are forty-four
keys or stops, including numbers from 2 to 9, the _i_ and _o_ of the
alphabet serving for numbers 1 and 0, and all the letters of the
alphabet arranged in the manner most convenient for manipulation. There
are also the various accents and stops, with note of interrogation,
etc. The flat ruler at the base of the key-board is struck when it is
necessary to separate one word from another.
In the interior of the apparatus every letter is attached to a small
hammer, and corresponds to the pressure bestowed upon the notes, which
are disposed in a circle. If A, for example, be touched upon the
key-board, the hammer will bring A to the centre of the circle, and so
every letter of the word will be, by such action, brought to the centre
of the circle in succession. The paper upon which the letter is printed
is wound upon a cylinder mounted upon a slide, as seen in the upper
portion of the illustration.
When the letter is pressed down on the key-board the corresponding
hammer strikes against the cylinder, between which and the hammer is
a ribbon prepared with a special ink. The letter being in relief like
ordinary type is impressed upon the paper. The slide upon which the
paper is mounted is so arranged as to move from right to left exactly
a letter-breadth after each impression. Thus as every hammer strikes
at the same spot a regular succession of letters are printed off, the
paper moving with regularity. When the line is filled—that is, when
the paper has moved across the cylinder—a bell rings, and a handle is
moved by the operator who is thus warned. The lever moved brings the
slide back again, and a new plain surface is ready to commence upon the
cylinder moving upwards at the same time, and displaying the printed
line.
[Illustration: Fig. 258.—Remington’s Writing Machine.]
In operating both hands may be employed, but between each word care
should be taken to press down the flat board at the base of the
key-board, which has the effect of leaving a space upon the paper.
Immediately the sound of the warning bell is heard the lever at the
right-hand side must be lowered. The word can be finished in the line
following if it be not concluded, the hyphen button being pressed to
indicate the continuation.
The paper used must not exceed the width of the cylinder, but it may
be of any less width, and a post-card or any small sheet of paper
may be substituted. If the width be thus limited the length may be
indefinite, and a very long line of paper may be used if desirable.
The cylinder being made of gutta-percha offers a soft surface to the
impression of the hammer, and causes the letter to assume greater
distinctness.
The inked ribbon which passes underneath the paper is so arranged that
no two successive letters strike it on the same place. It moves from
an ink reservoir on the right to another on the opposite side, and it
can be made to return beneath the paper, thus keeping up the supply.
The impression being made in copying ink, the message or letter when
finished can easily be reproduced in an ordinary press. The characters
are all “capitals.”
At first it may be found a slow means of writing, and the manipulator
may imagine he can do better without it. But if the author be certain
of what he intends to say, after a little practice at the instrument,
and when he becomes accustomed to the positions of the various letters,
etc., the rate at which words can be printed off will far exceed that
at which even rapid writers can work. A young English lady after some
days’ practice was able to write as many as ninety words a minute
with this machine—a rate more than double the average writing rate of
penmanship. When such a rate or an approximation to it can be attained,
those who are quick in their ideas will find the machine a great saving
of time, and for any one afflicted with “writer’s cramp” the gain must
be enormous. We need not insist upon the advantages the adaptation of
the apparatus would confer upon editors and readers of MSS. too often
badly written, and to compositors the invention is a great boon.
Finally, the working of the machine could be entrusted to the blind,
and by teaching them the form of letters which could be raised upon
the key-board, those so sadly afflicted could write with facility.
Some methods for teaching the blind to manipulate and to read from the
impressions of the hammers on the paper have already been tried with
success.
The Electric Pen, an invention of the fertile brain of Mr. Edison, is
shown in fig. 259. The “writing” consists of a series of little holes
close together, made by a fine steel point like a put-crayon. This
point is thrust in and out with great rapidity, and passes quickly over
the paper. If the characters cannot be formed so quickly as with an
ordinary pen, the writing is very distinct.
The alternative movement is given to the pen by an electric motor at
once simple and ingenious, which is placed on the top of the penholder.
The general appearance of the apparatus will be understood from the cut
on next page.
The point is the termination of a wire which traverses the penholder,
and the upper extremity of which catches on the motor by an eccentric.
This eccentric has three teeth or cogs, and it makes sixty revolutions
a second, thus producing one hundred and eighty beats in that time.
The axle carries a plate of soft iron, which acts like the armature
of an electro-magnet, before which it turns with great rapidity, the
current being interrupted twice in every revolution by the commutator.
The current which moves this little apparatus is furnished by a pile
of two elements in bichromate of potash, according to Mr. Edison’s
arrangement, which is considered very successful. Carbon and zinc are
employed, and when ready for action the battery assumes the appearance
of the cells in the illustration. When the operator wishes to
discontinue writing, he simply raises the stem which has the electrodes
attached to it, and the elements are thus preserved for a future time.
Under these circumstances the battery could be made to last several
days without any renewal of the liquid, and the plates will last for
weeks. Thus a very simple arrangement is at our disposal. Let us see
what use can be made of it.
[Illustration: Fig. 259.—Edison’s Electric Pen.]
When we use the electric pen we obtain a great number of small holes
close to each other. Such hand-writing is not easy to decipher by mere
inspection like ordinary writing. By holding it up to the light it is
more easy to read, but in both instances reading is not easy, nor does
it come by nature as Dogberry declares. But if we consider the paper as
a “negative,” we may obtain a number of positive proofs or copies of
the writing. To obtain these successfully we must use a press, as shown
in the accompanying illustration (fig. 260).
The writing, or negative, is placed upon the cover to the left, where
it is firmly fastened. Upon the body of the press a sheet of white
paper is placed, and when the lid is shut down the negative comes
in contact with the paper. By means of a roller, represented in the
box, the writing is blackened,—the ink penetrates into all the holes
which are upon the paper,—and after the manner of a stencil plate the
impression will be found upon the paper when the cover is removed.
The writing will have a curious effect, but practice will speedily
remove all deficiencies. The same negative will serve for a great many
impressions, quite a thousand having been taken from one. By people
accustomed to such work as many as six proofs a minute may be obtained.
Of course a little practice will be necessary in this, as in every
other case, before a correct or rapid result can be obtained, but there
is no difficulty in the practice.
There are two or three other applications of electricity which we must
refer to; such as the electric stamp, of which we give an illustration,
and a curious method of stopping a horse by electricity. The electric
stamp might be very advantageously employed in our post offices to
obliterate the “Queen’s Head.” The description, with illustration of
this apparatus, is annexed. (_See_ fig. 261.)
[Illustration: Fig. 260.—Duplicating press.]
At the lower end of the apparatus is a thin platinum wire, so arranged
as to form either a design or an initial; by this the postage stamp
can be defaced. The stamp being put in communication with the pile,
the circuit is closed by the pressure of the finger, as shown in the
illustration. The platinum grows heated and carbonises the paper, and
thus proves itself an ineffaceable stamp.
This apparatus may easily be used, not only by the post office
authorities, but by every one who is obliged to deface a certain
number of stamps every day, and wishes to do so rapidly and without
possibility of error.
An ingenious, if scarcely necessary arrangement for conquering
restive horses, and frightening them into submission, is shown in
the illustration (fig. 262). Many means have been tried to stop or
conquer a restive horse, but the most efficacious has been designed by
M. Defoy; and the director of the Paris General Omnibus Company has
experimented successfully, as we are informed, with the arrangement we
are about to describe. A small magneto-electric machine is contained
in a box beside the driver, within easy and convenient reach of his
hand. The reins contain a wire, one end of which terminates in the
horse’s bit, and the other in the electro-magnetic apparatus. When
the electro-magnet is put in action an electric current is generated,
which gives the horse a shock in the mouth, and so astonishes him that
he suddenly stops in his course. If the operator have the humanity
and good sense to unite kindness to the abrupt application of the
electricity,—which in our opinion should be only used as a last
resource,—no doubt some excellent results may be obtained even with
vicious animals.
[Illustration: Fig. 261.—The electric stamp.]
M. Bella, the Director of the Omnibus Company, has reported that the
apparatus was tried in his presence and found very successful, and
quite easy of application; and that even the most unruly animals have
been subjected by it. On one occasion a most restive animal was thus
treated on the way to the forge. He had a tremendous objection to be
shod, and made no secret of his dislike. But a gentle application of
the electric current put quite an opposite complexion upon the matter,
and after a few minutes the animal permitted himself to be patted and
caressed, and even allowed the smith to feel his legs and inspect his
feet without making any objection whatever. His shoes were taken off,
and the horse was re-shod without any of the dangerous demonstrations
hitherto indulged in by the animal.
We may quote another instance of the efficacy of this method, which is
reported from Paris by M. Camille.
[Illustration: Fig. 262.—Electric apparatus for checking vicious
horses.]
“Many experiments have been made upon horses which had been most
difficult to shoe, and in each case we have succeeded when the electric
apparatus has been put in requisition. One horse, in particular,
nothing could subdue. He kicked and bit and jumped about in such
a manner as to render all approach impossible. We had recourse at
length to M. Defoy’s apparatus, and after the first application, and
without any great difficulty, we were able to raise the animal’s feet;
but after a second lesson we were permitted to shoe him without his
offering the slightest resistance. He was completely subdued.”
M. Defoy recently made the experiment with a very dangerous animal,
which he stopped instantaneously in full gallop (_see_ fig. 262).
It may be remarked that the application of the current is not
sufficiently strong to stop the horse too suddenly. It merely causes
a very unpleasant sensation—he is not stupefied nor galvanized by
the electricity. The narrator has felt the shock applied without
inconvenience, and the conclusion arrived at is, that this method
of employing electricity is far superior to the violent and inhuman
treatment so often employed to break horses, which renders them
subsequently sulky and vindictive.
M. Defoy has completed an electric bit and an _electric stick_ quite
as ingenious as the electric rein. The _modus operandi_ is simple and
effective, the wires being insulated by leather, and terminating at the
extremities of the stick. The current is induced, as before, by a small
magneto-electric machine.
[Illustration: Electric Time Ball.]
FOOTNOTES:
[15] _Encly. Metrop._
[16] “Treatise on Electricity and Magnetism.”
[17] Sabine: “The Electric Telegraph.”