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bility of these different metals, silver and copper being among
the best, and lead and tin being among the worst metallic con-
ductors of electricity.

If two pointed pencils of thick platinum wire, being connected
with the poles of the battery, be presented point to point, so
that the current may pass between them, they will be fused at
the points and united, as though they were soldered together.
This effect will equally be produced under water.

2138. Substances ignited and exploded by the current.
Combustible or explosive substances, whether solid or liquid,
may be ignited by the heat developed in transmitting a current
through them. Ether, alcohol, phosphorus, and gunpowder
present examples of this.

2139. Application of this in civil and military engineering.

This property has been applied with great advantage in

engineering operations, for the purpose of springing mines, an
operation which may thus be effected with equal facility under
water. Experiments made by the Russian military engineers
at St. Petersburg, and by the English at Chatham, have de-
monstrated the advantage of this agency in military operations,
more especially in the springing of subaqueous mines.

In the course of the construction of the South Eastern Rail-
way it was required to detach enormous masses of the cliff near
Dover, which, by the direct application of human labour, could
not have been accomplished, save at an impracticable cost.
Nine tons of gunpowder, deposited in three charges, at from
fifty to seventy feet from the face of the cliff, were fired by a
conducting wire, connected with a powerful battery, placed at
u 5



442 VOLTAIC ELECTRICITY.

1000 feet from the mine. The explosion detached 600,000 tons
weight of chalk from the cliff. It was proved that this might
have been equally effected at the distance of 3000 feet.

2140. Jacob fs experiments on conduction by water. Jacob!
instituted a series of experiments with a view to ascertain how
far water might be substituted for a metallic conductor for tele-
graphic purposes. He first established (as Peschel states) a
conduction of this nature between Oranienbaum and an arm of
the Gulph of Finland, a distance of 5600 feet, one half through
water, and the other through an insulated copper wire, three-
fourths of a line in diameter, which was carried over a dam, so
that the entire length of the connexion was 1 1,200 feet. The
electric current was excited by a Grove's battery of twenty-
four pairs, and a common voltaic pile of 150 six-inch plates.
A zinc plate of five square feet was sunk in the sea from one
pole of the battery, and at the opposite end of the connecting
wire a similar plate was sunk in a canal joining the sea. Char-
coal points were used for completing the circuit of the Grove's
battery ; these, and also a fine platinum wire, were made red-
hot, and these phenomena appeared to be more intense than
when copper wires were used as conductors. In a later experi-
ment he employed a similar conduction, the distance in this
case being 9030 feet, namely, from the winter palace of the
emperor to the Fontanka, near the Obuchowski bridge. One of
the conductors was a copper wire carried under ground, the
other was the Neva itself, in which a zinc plate five square feet
was sunk beneath the surface of the river. At the other ex-
tremity a similar zinc plate was immersed in a small pond,
whose level was five or six feet above the Fontanka, from which
it was separated by a flood-gate. The battery consisted of
twenty-five small Daniell's constant batteries, by means of
which, notwithstanding the great extent of water, all the gal-
vanic and magnetic phenomena were produced. At Lenz's sug-
gestion, a different species of conduction was tried between the
same stations. A connexion was established with a point of the
iron roof of the winter palace, which was connected with the
ground by means of conducting rods, and the current was
carried equally well along the moist earth.

2141. Combustion of the metals. If thin strips of metal
or common metallic leaf be placed in connexion with the poles
of a battery, it will undergo combustion, the colour of the



EFFECTS OF THE VOLTAIC CURRENT. 443

flame varying with the metal, and in all cases displaying very
striking and brilliant effects. Gold thus burned gives a bluish-
white light, and produces a dark brown oxyde. Silver burns
with a bright sea-green flame, and copper with a bluish-green
flame, mingled with red sparks, and emits a green smoke.
Zinc burns with a dazzling white light, tin with red sparks,
and lead with a purple flame. These phenomena are produced
with increased splendour, if the metal to be burned attached to
one pole be brought into contact with mercury connected with
the other pole.

2142. Spark produced by the voltaic current. Bring nearly
together the amalgamated ends of the polar wires, while the
battery is in a state of activity ; a small, white, starlike spark
will be seen accompanied by a crackling noise like that which
attends the emission of a feeble electrical spark.

Plunge the end of one of the wires into a small vessel of
mercury, and bring the other near the surface of the metal. A
similar spark is emitted just before the point touches the mer-
cury, on which a small black speck may be seen where the
spark struck it.

The spark obtained from an amalgamated point is visible
under water or in the flame of a candle.

Fasten a fine sewing-needle to the end of one of the wires,
and touch the other pole with the free end of the needle ; a
starlike red spark will be emitted. A continued stream of
these sparks may be obtained by connecting a small round or
triangular file with one pole, and presenting to it and removing
from it with great rapidity the point of a copper wire attached
to the other pole.

Coat the ends of the connecting wires with soot, by holding
them in the flame of an oil lamp, and the sparks will be both
larger and brighter ; they will be obtained of the greatest in-
tensity by holding the points of the wires in the flame opposite
to each other.

Nobili says, that, in performing experiments of this kind he
obtained the brightest sparks by connecting the two ends of the
battery with a long spiral copper wire, or with a wire insulated
by being wound round with silk.

2143. The electric light. Of all the luminous effects pro-
duced by the agency of electricity, by far the most splendid is
the light produced by the passage of the current proceeding



444 VOLTAIC ELECTRICITY.

from a powerful battery between two pencils of hard charcoal
presented point to point. The charcoal
being an imperfect conductor is rendered
incandescent by the current, and being in-
fusible at any temperature hitherto at-
tained, the degree of splendour of which
its incandescence is susceptible has no
other practical limit except the power of
the battery.

The charcoal best adapted for this experi-
ment is that which is obtained from the re-
siduum of the coke in retorts of gas works.
This is hardened and formed into pencil-
shaped pointed cylinders, from two to four




Fig. 665.




inches in length, and mounted as represented ir\fig. 665., where
p and r, the two metallic pencil-holders, are in metallic con-
nexion with the poles of the pile, and so mounted that the char-
coal pencils fixed in them can at pleasure be made to approach
each other until their points come into contact, or to recede from
each other to any necessary distance. When they are brought
into contact, the current will pass between them,
and the charcoal will become intensely luminous.
When separated to a short distance, a splendid
flame will pass between them of the form repre-
sented in jig. 666. It will be observed that the
form of the flame is not symmetrical with rela-
tion to the two poles, the part next the positive
point having the greatest diameter, and the diame-
ter becoming gradually less in approaching the negative point.
2144. Action of a magnet on the, electric flame. If the
pole of a bar magnet be presented to this flame it will imme-
diately affect it as it would affect a moveable current, and will,
even at a considerable distance, throw it into the
curved form represented in Jig. 667., the curva-
ture being turned to the one side or the other
according as the austral or boreal pole is pre-
sented to the flame. The action of the magnet
may, in such cases, be so intense as to extinguish
the flame altogether, just as a blast of air would
extinguish the flame of a candle.



Fig. 666.




Pig. 667.



This fact renders it probable, if not certain, that the earth's



EFFECTS OF THE VOLTAIC CURRENT. 445

magnetism exerts a similar influence on a larger scale upon the
electrical phenomena of the atmosphere, especially on those
which are manifested in its more elevated regions, and which,
because of the more rarefied state of the air, have more diffusion.

2145. Incandescence of charcoal by the current not combus-
tion. It would be a great error to ascribe the light produced
in charcoal pencils to the combustion of that substance. None
of the consequences or effects of combustion attend the phe-
nomena, no carbonic acid is produced, nor does the charcoal
undergo any diminution of weight save a small amount due to
mere mechanical causes. On the contrary, at the points where
the calorific action is most intense, it becomes more hard and
dense. But what negatives still more clearly the supposition
of combustion is, that the incandescence is still more intense
in a vacuum, or in any of the gases that do not support com-
bustion, than in the ordinary atmosphere.

Peschel states that, instead of two charcoal pencils, he has
laid a piece of charcoal, or well burnt coke, upon the surface of
mercury, connected with one pole of the battery, while he has
touched it with a piece of platinum connected with the other
pole. In this manner he obtained a light whose splendour was
intolerable to the eye.

2146. Electric lamps of Messrs. Foucault, Deleuil, and
Dubosc-Soleil. M. Foucault first applied the electric light
produced by charcoal pencils as a substitute for the lime light
in the gas microscope. Further improvements in these arrange-
ments have been made more recently by M. Deleuil and M.
Dubosc-Soleil, the eminent philosophical instrument makers of
Paris. The effect of these improvements is to supply a self-
acting adjustment by which the current passing between the
charcoal pencils, and consequently the splendour of the light, is
rendered uniform, or nearly so. This is accomplished by the
agency of electro-magnets, which are so affected by the current,
that they act upon a mechanism which regulates the distance of
the charcoal points so as to maintain the uniformity of the
current.

2147. Method of applying the heat of charcoal to the fusion
of refractory bodies and the decomposition of the alkalis. This
is accomplished by substituting for the charcoal pencil, p,fig*
665., a piece of charcoal in the form of a small cup, as re-
presented in fig. 668.




446 VOLTAIC ELECTRICITY.

A small piece of the substance to be acted on is placed in the
charcoal cup s, and the electric flame is made to
play upon it by bringing it into proximity with the
pencil above it. In this way gold or platinum may
be fused, or even burned. If a small piece of soda
or potash be placed in the cup s, its decomposition
will be effected by the flame, and small globules

PJ 66g of sodium or potassium will be produced in the cup,
which will launch themselves towards the point of
the pencil, undergoing at the same time combustion, and thus
reproducing the alkali.

2148. Physiological effects of the cur rent. This class of effects
is found to consist of three successive phases : first, when the
current first commences to pass through the members affected
by it ; secondly, during its continuance ; and, thirdly, at the
moment of its cessation. A sharp convulsive shock attends the
first and last ; and the intermediate period is marked by a con-
tinued series of lesser shocks rapidly succeeding each other.
The shock of a voltaic battery has been said to be distinguished
from that produced by a Leyden jar, inasmuch as the latter is
felt less deeply, affecting only our external organs, and being
only instantaneous in its duration ; while the latter pervades
the system, propagating itself through the whole course of the
nerves which extend between its points of admission and
departure.

It appears that the physiological effect of the current depends
altogether on its intensity, and little or not at all upon its
quantity. This is proved by the fact, that the effect of a
battery of small plates is as great as one consisting of the same
number of large plates. A single pair, however extensive be
its surface, produces no sensible shock. To produce any sen-
sible effect, from ten to fifteen pairs are necessary. A battery
of 50 to 100 pairs gives a pretty strong convulsive shock. If
the hands, previously wetted with salted water, grasp two
handles, like those represented at p and N, fig. 624., connected
with such a battery, violent shuddering of the fingers, arms, and
chest will be produced ; and if there be any sore or tender parts
of the skin, a pricking or burning sensation will be produced
there.

The voltaic shock may be transmitted through a chain of
persons in the same manner as the electric shock, if their hands



EFFECTS OF THE VOLTAIC CURRENT. 447

which are joined be well moistened with salted or acidulated
water, to increase the conducting power of the skin.

As the strongest phases of the shock are the moments of the
commencement and cessation of the current, any expedient
which produces a rapid intermission of the current will augment
its physiological effect. This may be accomplished by various
simple mechanical expedients, by which the contact of the con-
ductors connecting the poles may be made and broken in rapid
succession ; but no means are so simple and effectual for the at-
tainment of this object, as the contrivances for the production
of the magneto-electro current described in (1981), which, in
fact, is exactly the rapidly intermitting current here required.

2149. Medical application of the voltaic shock The influ-
ence of the galvanic shock on the nervous system in certain
classes of malady has been tried with more or less success, and
apparatus have been contrived for its convenient application,
both generally and locally, to the system. The most convenient
form of apparatus for this purpose is the magneto- electric
machine, represented in fig. 624. This has been recently im-
proved by certain medical practitioners in Paris, where it is
extensively used. Expedients are applied to it by which the
operator can measure and regulate the force of the shock with
the greatest certainty and precision. This is accomplished by
surrounding the arms of the electro-magnet with loose cylinders
or gloves of thin copper, which may be moved so as to uncoil
the arms to a greater or less extent, and thus increase or diminish
the force of the induced current.

2150. Effect on bodies recently deprived of life. This class
of phenomena is well known, and, indeed, was the origin of the
discovery of galvanism. Galvani's original experiment on the
limbs of a frog, already noticed (1842), has often been repeated.
Bailey substituted for the legs of the frog those of the grass-
hopper, and obtained the same results.

Experiments made on the bodies of men and inferior animals
recently deprived of life have afforded remarkable results.
Aldini gave violent action in this way to the various members
of a dead body. The legs and feet were moved rapidly, the
eyes opened and closed, and the mouth, cheeks, and all the
features of the face were agitated by distortions. Dr. Ure
connected one of the poles of a battery with the supraorbital
nerve of a man cut down after hanging for an hour, and con-



448 VOLTAIC ELECTRICITY.

nected the other pole with the nerves of the heel. On com-
pleting the circuit the muscles are described to have been
moved with a fearful activity, so that rage, anguish, and de-
spair, with horrid smiles, were successively expressed by the
countenance.

This agency has been used occasionally with success as an
expedient for restoring suspended animation.

The bodies and members of inferior animals recently killed
are susceptible of the same influence, though in a less degree.
The current sent through the claw of a lobster recently torn
from the body, will cause its instant contraction.

Effect of the shock upon a leech. If a half-crown piece
be laid upon a sheet of amalgamated zinc, a leech placed upon
the coin will betray no sense of a shock, until, by moving, some
part of it comes into contact with the zinc. The connexion
being thus established, the leech will receive a shock, as will be
rendered manifest by the sudden recoil of the part which first
touches the zinc.

2151. Excitation of the nerves of taste. If a metallic plate,
connected with one pole of the battery, be applied to the end of
the tongue, and another wetted with salted water, and connected
with the other pole, be applied to any part of the face, the metal
on the tongue will excite a peculiar taste, acid or alkaline, ac-
cording as it is connected with the positive or negative pole.
This is explained by the decomposition of the saliva by the
current.

2152. Excitation of the nerves of sight. If a metallic plate,
wetted with salted or acidulated water, be applied at or near the
eyelids, and another be applied at any other part of the person,
a peculiar flash or luminous appearance will be perceived the
moment the plates are put into connexion with the poles of a
battery. The sensation will be reproduced, but with less in-
tensity, the moment the connexion is broken. A like effect,
but less intense, is produced, when the current is transmitted
through the cheek and gums.

2153. Excitation of the nerves of hearing. If the wires
connected with the poles of a battery be placed in contact with
the interior of the two ears, a slight shock will be felt in the
head at the moment when the connexion is made or broken,
and a roaring sound will be heard so long as the connexion is
maintained.



EFFECTS OF THE VOLTAIC CURRENT. 449

2154. Supposed sources of electricity in the animal organis-
ation. Although Galvani's theory of animal electricity did
not survive its author, the supposition that there exists in the
organisation of animals a source of electrical action has never
been abandoned. Humboldt and Pfaff discovered traces of
electrical development in connecting the nerve and muscle of
a frog. Reoscopic tests have indicated the presence of a
current, when two remote portions of a nerve, or of the muscle
belonging to it, are brought into connexion. Dr. Donne of
Paris thinks that there is a source of electrical excitement be-
tween the inner and outer skins. He placed the inner and
outer skins of the mouth in .connexion by a platinum wire,
upon which the presence of a feeble current was detected by a
reoscope. Dr. Wilson Philip showed that in certain cases
a voltaic current might perform the functions of the nerves.
Having destroyed the action of some of the nerves leading to
the stomach of a dog, he restored their suspended action by
connecting the severed ends with a voltaic current.

2155. Electrical fishes. The most conspicuous example of
the development of electricity in the animal organization is pre-
sented by certain species of fish. Of these ELECTRICAL FISHES
there are seven genera :

1. Torpedo narke risso. 5. Silurus electricus.

2. unimaculata. 6. Tetraodon electricus.

3. mannorata. 7. Gymnotus electricus.

4. galvanii.

No observations sufficiently exact and extensive have yet
supplied the data necessary to determine the source of the vast
quantities of electricity which these creatures are capable of
developing at will. There is nothing in the phenomena ob-
served which countenances the supposition that the electricity
is the result either of mechanical, thermal, or chemical causes
analogous to those which have been already explained. When
it is therefore stated to arise from a physiological action pecu-
liar to the organization of the animal, a name is merely given
to an unknown agency. In the absence, therefore, of any rea-
sonable theory, we are compelled to limit ourselves to a mere
statement of the phenomena.

2156. Properties of the torpedo ; observations of Walsh. >
According to the observations of Walsh, who first submitted
this animal to exact inquiry, the following are its effects :



450 VOLTAIC ELECTRICITY.

If the finger or the palm of the hand be applied to any part
of the body of the animal out of the water, a shock will be felt
similar to that produced by a voltaic pile.

If, instead of applying the hand directly, a good conductor,
such as a rod of metal several feet in length, be interposed, the
shock will still be felt.

If non-conductors be interposed, the shock is not felt.

If the continuity of the interposed conductor be anywhere
broken, the shock is not felt.

The shock may be transmitted along a chain of several per-
sons with joined hands, but in this case the force of the shock
is rapidly diminished as the number of persons is increased.
In this case the first person of the chain should touch the
torpedo on the belly, and the last on the back.

When the animal is in the water, the shocks are less intense
than in the air.

It is evident that the development of electricity is produced
by a voluntary action of the animal. It often happens that in
touching it no shock is felt. But when the observer irritates
the animal, shocks of increasing intensity are produced in very
rapid succession. "Walsh counted as many as fifty electrical
discharges produced in this way in a minute.

2157. Observations of Becquerel and Breschet. In a series
of observations and experiments made on the torpedos of
Chioggia near Venice by MM. Becquerel and Breschet, it
was ascertained that when the back and belly were connected
by the wires of a sensitive reoscope, a current was indicated as
passing from the back to the belly. They also found that the
animal could at will transmit the current between any two
points of its body.

2158. Observations of Matteucci. In a series of experiments
made on the torpedos of the Adriatic, M. Matteucci confirmed
the results obtained by MM. Becquerel and Breschet, and also
succeeded in obtaining the spark from the current passing
between the back and belly.

2159. The electric organ. In the several species of fish
endowed with this quality, the structure of the organ in which
the electric fluids are developed is alike, differing only in its
form, magnitude, and position. In the torpedo, which has been
submitted to the most rigorous examination, it consists of two
parts symmetrically arranged at each side of the head and



EFFECTS OF THE VOLTAIC CURRENT. 451

resting against the gills. They fill all the thickness which
separates the two coats of the skin. On dissection it is proved
to consist of an extremely open cellular tissue, having the form
of a cylinder, or, more exactly, that of a five or six-sided prism.
It has been compared to the cellular structure of the honeycomb,
only that the partitions, instead of being thin membranes, are
fibres separated and extended in different directions.

Four or five hundred of these prisms are commonly counted
in each organ. Hunter in one case found 1182. They are
nearly at right angles to the surface of the skin, to which they
are strongly attached at the ends. When the structure of each
of these prisms is examined, they are found to consist of a
multitude of thin plates whose planes are perpendicular to the
axis of the prism, separated from each other by strata of mucous
matter, and forming a combination resembling the original
galvanic pile.

Four bundles of nerves of considerable volume are distributed
in the organ, and, according to Matteucci, the seat of the elec-
trical power is at their origin.



INDEX.



ABSORPTION of heat, 121.

Agonic lines, 172. ; American, 172. ; Asiatic,
172.

Air, rarefied, a conductor of electricity, 198.

Alcohol, congelation of, 81.

Alloys, liquefaction of, 73.

Ampere, method to reverse galvanic current,
301.; apparatus for supporting moveable
currents, 304. ; method of exhibiting revo-
lution of galvanic current round a magnet,
318. ; electro-magnetic rectangle, 362.

Animal heat, 138.

Animals, wool and fur of, their uses, 111.

Anion, 394.

Annealing, use of, 85.



Online LibraryDionysius LardnerHand-book of natural philosophy and astronomy (Volume 2) → online text (page 43 of 45)