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attract so much negative fluid, and those which are negative
so much positive fluid, as is sufficient to neutralize the forces
of their proper electricities, and then the atoms are unelectrized
and in their natural state.

When a body is charged with positive electricity, its atoms
act by induction upon the atoms of adjacent bodies, and these
upon the atoms next beyond them, and so on. The fluids in
the series of atoms through which the electricity is supposed to



PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 261

pass, assumes a polar arrangement such as that represented in
fig. 528.

123456789



Fig. 528.

The first atom of the series being surcharged with + electricity
acts by induction on the second, and decomposes its natural
electricity, the negative fluid being attracted to the side near
the first atom, and the positive repelled to the side near the
third atom. The same effect is produced by atom 2 on atom 3,
by atom 3 on atom 4, and so on. The surplus positive fluid on
1 then combines with and neutralizes the negative fluid on 2 ;
and, in like manner, the positive fluid on 2 combines with and
neutralizes the negative fluid on 3, and so on until the last
atom of the series is left surcharged with positive electricity.

Such is the hypothesis of decomposition and recomposition
which is at present in most general favour with the scientific
world.

The explanation which it affords of the electric spark and
other luminous electric effects, may be said to consist in trans-
ferring the phenomenon to be explained from the bodies them-
selves to their component atoms, rather than in affording an
explanation of the effect in question inasmuch as the produc-
tion of light between atom and atom by the alternate decompo-
sition and recomposition of the electricities stands in as much
need of explanation as the phenomenon proposed.

1827. Cracking noise attending electric spark. The sound
produced by the electric discharge is obviously explained by
the sudden displacement of the particles of the air, or other
medium through which the electric fluid passes.



CHAP. XII.

PHYSIOLOGICAL EFFECTS OF ELECTRICITY.

1828. Electric shock explained. The material substances
which enter into the composition of the bodies of animals are



262 ELECTRICITY.

generally imperfect conductors. When such a body, therefore,
is placed in proximity with a conductor charged with electricity,
its natural electricity is decomposed, the fluid of a like name
being repelled to the side more remote from, and the fluid of the
contrary name being attracted to the side nearest to, the elec-
trified body. If that body be very suddenly removed from or
brought near to the animal body, the fluids of the latter will
suddenly suffer a disturbance of their equilibrium, and will
either rush towards each other to recombine, or be drawn from
each other, being decomposed; and owing to the imperfection of
the conducting power of the fluids and solids composing the
body, the electricity in passing through it will produce a mo-
mentary derangement, as it does in passing through air, water,
paper, or any other imperfect conductor. If this derangement
do not exceed the power of the parts to recover their position
and organization, a convulsive sensation is felt, the violence of
which is greater or less according to the force of electricity
and the consequent derangement of the organs ; but if it exceed
this limit, a permanent injury, or even death, may ensue.

1829. Secondary shock. It will be apparent from this, that
the nervous effect called the electric shock does not require
that any electricity be actually imparted to, abstracted from, or
passed through the body. The momentary derangement of the
natural electricity is sufficient to produce the effect with any
degree of violence.

The shock produced thus by induction, without transmitting
electricity through the body, is sometimes called the secondary
shock.

The physiological effects of electricity are extremely various,
according to the quantity and intensity of the charge, and ac-
cording to the part of the body affected by it, and according to
the manner in which it is imparted.

1830. Effect produced on the skin by proximity to an electri-
fied body. When the back of the hand is brought near to the

glass cylinder of the machine, at the part where it passes from
under the silk flap, and when therefore it is strongly charged
with electricity, a peculiar sensation is felt on the skin, re-
sembling that which would be produced by the contact of a cob-
web. The hairs of the skin being negatively electrified by in-
duction, are attracted and drawn against their roots with a slight
force.



PHYSIOLOGICAL EFFECTS OF ELECTRICITY. 263

1831. Effect of the sparks taken on the knuckle. The effect
of the shock produced by a spark taken from the prime con-
ductor by the knuckle is confined to the hand ; but with a very
powerful machine, it will extend to the elbow.

1832. Methods of limiting and regulating the shock by ajar,
The effects of the discharge of a Leyden jar extend through
the whole body. The shock may, however, be limited to any
desired part or member by placing two metallic plates con-
nected with the two coatings of the jar on opposite sides of the
part through which it is desired to transmit the shock.

1833. Effect of discharges of various force. The violence
of the shock depends on the magnitude of the charge, and may
be so intense as to produce permanent injury. The discharge
of a single jar is sufficient to kill birds, and other smaller
species of animals. The discharge of a moderate-sized battery
will kill rabbits, and a battery of a dozen square feet of coated
surface will kill a large animal, especially if the shock be trans-
mitted through the head.

1834. Phenomena observed in the autopsis after death by the
shock. When death ensues in such cases, no organic lesion or
other injury or derangement has been discovered by the autopsis ;
nevertheless, the violence of the convulsions which are mani-
fested when the charge is too feeble to destroy life, indicates a
nervous derangement as the cause of death.

1835. Effects of a long succession of moderate discharges.
A succession of electric discharges of moderate intensity, trans-
mitted through certain parts of the body, produce alternate
contraction and relaxation of the nervous and muscular organs,
by which the action of the vascular system is stimulated and
the sources of animal heat excited.

1836. Effects upon a succession of patients receiving the
same discharge. The electric discharge of a Leyden jar may
be transmitted through a succession of persons placed hand in
hand, the first communicating with the internal, and the last
with the external coating of the jar.

In this case, the persons placed at the middle of the series
sustain a shock less intense than those placed near either ex-
tremity, another phenomenon which favours the hypothesis of
two fluids.

1837. Remarkable experiments of Nollet, Dr. Watson, and
others. A shock has in this manner been sent through a



264 ELECTRICITY.

regiment of soldiers. At an early period in the progress of
electrical discovery, M. Nollet transmitted a discharge through
a series of 180 men ; and at the convent of Carthusians a chain
of men being formed extending to the length of 5400 feet, by
means of metallic wires extended between every two persons
composing it, the whole series of persons was affected by the
shock at the same instant.

Experiments on the transmission of the shock were made in
London by Dr. Watson, in the presence of the Council of the
Royal Society, when a circuit was formed by a wire carried from
one side of the Thames to the other over Westminster Bridge.
One extremity of this wire communicated with the interior of a
charged jar, the other was held by a person on the opposite bank
of the river. This person held in his other hand an iron rod,
which he dipped in the river. On the other side near the jar
stood another person, holding in one hand a wire communicating
with the exterior coating of the jar, and in the other hand an
iron rod. This rod he dipped into the river, when instantly
the shock was received by both persons, the electric fluid
having passed over the bridge, through the body of the person
on the other side, through the water across the river, through
the rod held by the other person, and through his body to the
exterior coating of the jar. Familiar as such a fact may now
appear, it is impossible to convey an adequate idea of the
amazement bordering on incredulity with which it was at that
time witnessed.



CHAP. XIII.

CHEMICAL AND MAGNETIC EFFECTS OF ELECTRICITY.

1838. Phenomena which supply the basis of the electro-chemical
theory. If an electric charge be transmitted through certain
compound bodies they will be resolved into their constituents,
one component always going in the direction of the positive,
and the other of the negative fluids. This class of phenomena
has supplied the basis of the electro-chemical hypothesis already
briefly noticed (1826). The constituent which goes to the posi-



CHEMICAL EFFECTS OF ELECTRICITY. 265

tive fluid is assumed to consist of atoms which are electrically
negative, and that which goes to the negative fluid, as con-
sisting of atoms electrically positive.

1839. Faraday's experimental illustration of this. This
class of phenomena is more prominently developed by voltaic
electricity, and will be more fully explained in the following
Book. For the present it will therefore be suflicient to indicate
an example of this species of decomposition by the electricity of
the ordinary machine. The following experiment is due to
Professor Faraday.

Lay two pieces of tinfoil T T',Jig. 528. a, on a glass plate, one
being connected with the prime conductor of the machine, and




Fig. 528 a.

the other with the ground. Let two pieces of platinum wire
PP', resting on the tinfoil, be placed with their points on a drop
of the solution of the sulphate of copper c, or on a piece of
bibulous paper wetted with sulphate of indigo in muriatic acid,
or iodide of potassium in starch, or litmus paper wetted with a
solution of common salt or of sulphate of soda, or upon tur-
meric paper containing sulphate of soda.

In all these cases the solutions are decomposed : in the first,
the copper goes to the positive wire ; in the second the indigo is
bleached by the chlorine discharged at the same wire ; in the
third the iodine is liberated at the same wire ; in the fourth
the litmus paper is reddened by the acid evolved at the positive
wire, and when muriatic is used, it is bleached by the chlorine
evolved at the same wire ; and, in fine, in the fifth case, the
turmeric paper is reddened by the alkali evolved at the negative
wire.

1840. Effect of an electric discharge on a magnetic needle.
When a stream of electricity passes over a steel needle or
bar of iron, it produces a certain modification in its magnetic
state. If the needle be in its natural state it is rendered mag-
netic. If it be already magnetic its magnetism is modified,

II. N



266 ELECTRICITY.

being augmented or diminished in intensity, according to
certain conditions depending on the direction of the current
and the position of the magnetic axis of the needle ; or it may
have its magnetism destroyed, or even its polarity reversed.

This class of phenomena, like the chemical effects just men-
tioned, are, however, much more fully developed by voltaic
electricity ; and we shall therefore reserve them to be explained
in the following Book. Meanwhile, however, the following
experiments will show how common electricity may develop
them.

1841. Experimental illustration of this. Place a narrow
strip of copper, about two inches in length, on the stage of the
universal discharger, and over it place a leaf of any insulating
material, upon which place a sewing needle transversely to the
strip of copper. Transmit several strong charges of electricity
through the copper. The needle will then be found to be mag-
netized, the end lying on the right of the current of electricity
being its north pole.

If the same experiment be repeated, reversing the position of
the needle, it will be demagnetized. But by repeating the
electric discharges a greater number of times, it will be mag-
netized with the poles reversed.



67



BOOK THE FOURTH.

VOLTAIC ELECTRICITY.
CHAP. I.

SIMPLE VOLTAIC COMBINATION.

1842. Discovery of galvanism. In tracing the progress of
physical science, the greatest discoveries are frequently found
to originate, not in the sagacity of observers, but in circum-
stances altogether fortuitous. One of the most remarkable
examples of this is presented by Voltaic Electricity. Speaking
of the voltaic pile, Arago, in his Eloge de Volta, says, that
" this immortal discovery arose in the most immediate and
direct manner, from an indisposition with which a Bolognese
lady was affected in 1790, for which her medical adviser
prescribed frog-broth."

Galvani, the husband of the lady, was Professor of Anatomy
in the University of Bologna. It happened that several frogs,
prepared for cooking, lay upon the table of his laboratory, near
to which his assistant was occupied with an electrical machine.
On taking sparks from time to time from the conductor, the
limbs of the frogs were affected with convulsive movements
resembling vital action.

This was the effect of the inductive action of the electricity
of the conductor upon the highly electroscopic organs of the
frogs ; but Galvani was not sufficiently conversant with this
branch of physics to comprehend it, and consequently regarded
it as a new phenomenon. He proceeded to submit the limbs of
frogs to a course of experiments, with the view to ascertain the
cause of what appeared to him so strange. For this purpose,
he dissected several frogs, separating the legs, thighs, and
lower part of the spinal column from the remainder, so as to lay
bare the lumbar nerves. He then passed copper hooks through
that part of the dorsal column which remained above the
junction of the thighs, without any scientific object, but merely



268 VOLTAIC ELECTRICITY.

for the convenience of suspending them until required for
experiment. It chanced, also, that he suspended these copper
hooks upon the iron bar of the balcony of his window, when,
to his inexpressible astonishment, he found that whenever the
wind or any other accidental cause brought the muscles of the
leg into contact with the iron bar, the limbs were affected by
convulsive movements similar to those produced by the sparks
taken from the conductor of the electric machine.

This fact, reproduced and generalized, supplied the founda-
tion of the theory of animal electricity propounded by Galvani,
and for a considerable time universally accepted. In this
theory it was assumed, that in the animal economy there exists
a specific source of electricity; that at the junction of the
nerves and muscles this electricity is decomposed, the positive
fluid passing to the nerve, and the negative to the muscle ; and
that, consequently, the nerve and muscle are in a state of
relative electrical tension, analogous to that of the internal and
external coatings of a charged Leyden jar. When, under these
circumstances, rods of metal z c, fig. 529., are applied, one to
the nerve, and the other to the muscle, the opposite electricities
rush towards each other along the conducting rods ; a dis-
charge of the nerve and muscle takes
place, like that of the Leyden jar ;
and this momentary derangement of
the electrical condition of the organ
produces the convulsive movement.
1843. Yalta's correction of Gal-
vanfs theory. Volta, then Professor
of Natural Philosophy at Como, and
afterwards at Pavia, repeating the
Fig. 529. experiments of Galvani, overturned

his theory by various ingenious experimental tests, one of which
consisted in showing that the effects of the electric shock
were equally produced when both metallic rods were applied
to the muscle, neither touching the nerve. He contended that
Galvani, in taking the nerve and muscle to represent the coat-
ings of the Leyden jar, and the metallic rods the discharging
conductor, had precisely inverted the truth, for that the rods
represented the jar, and the nerve and muscle the conductor.

If the rods, as Galvani supposed, played the part of the
metallic conductor, communicating between the opposite elec-




SIMPLE VOLTAIC COMBINATION. 269

tricities imputed to the nerve and muscle, a single rod of one
uniform metal would serve this purpose, not only as well, but
better than two rods of different metals ; whereas, the presence
of two different metals in contact, was essential to the develop-
ment of the phenomenon.

In fine, Volta maintained, and ultimately proved, that the
electricity decomposed, was not that of the nerve and muscle,
but that of the metallic rods ; that the seat of the decomposition
was not the junction of the nerve and muscle, but the junction
of the two metals ; that the positive and negative fluids passed,
not upon the nerve and muscle, but upon the iron and copper
forming the rods flowing in opposite directions from their point
of junction; and that, in fine, the nerve and muscle, or the latter
alone, served merely as the conductor by which the opposite
electricities developed on the metals were recomposed, exactly
as they would if placed between the internal and external coat-
ings of a charged Leyden jar.

1844. Theory of animal electricity exploded. After a con-
flict of some years' duration, the animal electricity of Galvani
fell before the irresistible force of the reasoning and experiments
of Volta, whose theory obtained general acceptation. This form
of electric agency has since been denominated indifferently,

GALVANISM Or VOLTAIC ELECTRICITY.

1845. Contact hypothesis of Volta. According to the hy-
pothesis of Volta, now known as the CONTACT THEORY, any two
different metals, or, more generally, any two different bodies
which are conductors of electricity, being placed in contact, a
spontaneous decomposition of their natural electricity will be
effected at their surface of contact, the positive fluid moving
from such surface and diffusing itself over the one, and the ne-
gative moving in the contrary direction and diffusing itself over
the other, the surface of contact constituting a neutral line
separating the two fluids.

1846. Electro-motive force. This power of electric decom-
position was called by Volta, ELECTRO-MOTIVE FORCE.

Different bodies placed in contact manifest different electro-
motive forces, the energy of the electro-motive force being
measured by the quantity of electricity decomposed.

Its direction and intensity. The electro- motive force acts
on the two fluids in opposite directions, but it will be convenient
to designate its direction by that of the positive fluid.

3



270



VOLTAIC ELECTRICITY.



To indicate, therefore, the electro-motive force developed when
any two conductors are placed in contact, it is necessary to
assign the energy and direction of such force, which is done by
showing the intensity of the electricity developed, and the
conductor towards which the positive fluid is directed.

1847. Classification of bodies according to their electro-
motive property . Although the results of experimental research
are not in strict accordance on these points, the electric tensions
produced by the mere contact of heterogeneous conductors
being in general so feeble as to elude the usual electroscopic
tests, it has nevertheless been found, that bodies may be arranged
so that any one placed in contact with another holding a lower
place in the series, will receive the positive fluid, the lower
receiving the negative fluid, and so that the electro-motive force
of any two shall be greater the more distant they are from each
other in the series. How far the results of experimental re-
searches are in accordance on these points, will be seen by com-
paring the following series of electromoters given by Volta,
Pfaff, Henrici, and Peclet :



Volta.


Pfaff.


Henrici.


Peclet.


Zinc.


Zinc.


Zinc.


Zinc.


Lead.


Lead.'


Lead.


Lead.


Tin.


Cadmium.


Tin.


Tin.


Iron.


Tin.


Antimony.


Bismuth.






Bismuth.


Antimony.




Bismuth.






Graphite.
Charcoal.


Cobalt.
Arsenic.


Brass.
Copper.


Copper.
Silver.


Crystallized Amber.


Copper.


Silver.
Mercury.


Gold.
Platinum.




Platinum.'


Gold.






Gold.


Platinum.






Mercury.








Silver.








Charcoal.







To which Pfaff adds the following mineral substances in the
order here given : Argentum vitreum (vitreous silver ore), sul-
phurous pyrites, cuprum mineralisatum pyritaceum (yellow
copper ore), galena, crystallized tin, niccolum sulphuratum arse-
nicum pyritaceum (arsenical mundick), molydena, protoxyde of
uranium, oxyde of titanium, graphite, wolfram (tungstate of iron
and manganese), gypsum stillatium, crystallized amber, peroxyde
of lead (?).

It is to be understood, that, according to the results of the
experimental researches of the observers above named, the



SIMPLE VOLTAIC COMBINATION. 271

electro-motive force produced by the contact of any two of the
bodies in the preceding series will be directed from that which
holds the lower to that which holds the higher place, and that
the energy of such electro-motive force will be greater the more
remote the one body is from the other in the series.

1848. Relation of electro-motive force to susceptibility of oxy-
dation. The mere inspection of these several series will
suggest the general conclusion, that the electro-motive force is
directed from the less to the more oxydable body, and that the
more the one exceeds the other in its susceptibility of oxyda-
tion, the more energetic will be the electro-motive force. Thus,
a combination of zinc with platinum produces more electro-
motive energy than a combination of zinc with any of the more
oxydable metals.

If several electromotors of the series be placed in contact in
any order, the total electro-motive force developed is found to
be the same as if the first were immediately in contact with the
last. The intermediate elements are therefore in this case
inefficient.

1849. Analogy of electro-motive action to induction. It
appears, therefore, that when two pieces of different metals
taken from the series of electromoters, such as zinc and copper
for example, are brought into contact, an electric state is pro-
duced in their combined mass similar to that which would be
produced by placing an insulated conductor charged with
positive electricity near the copper side of the combination.
The inductive action of such a conductor would decompose
the natural electricity of the combined mass, attracting the
negative fluid to the side near the conductor, that is, to the
copper element, and repelling the positive fluid to the opposite
side, that is, to the zinc element. But this is precisely the
effect of the electro-motive force of the two metals as already
described.

Let z and c, Jig. 530., be cylinders of zinc and copper placed
end to end. The former will, by the contact, be charged with
positive, and the latter with negative
electricity. Let the two cylinders,
being insulated, be separated, and the
one will be positively, and the other
negatively electrified ; but in this case
Fig. 530. t ] ie intensity of the electricity deve-



272 VOLTAIC ELECTRICITY.

loped upon them will be so feeble, that it cannot be rendered
manifest by any of the ordinary electroscopic tests. Let it,
however, be imparted to the collecting plate of a powerful con-
densing electroscope, and, after the two cylinders z and c are
discharged, let them be again placed in contact. They will be
again charged by their electro-motive action, and their charges
may, as before, be imparted to the collecting plates of the
electroscopes ; and this process may be repeated until the
electricities of each kind accumulated in the plates of the
electroscopes becomes sensible.

1850. Electro-motive action of gases and liquids. Several
German philosophers have recently instituted elaborate experi-
mental researches to determine the electro-motive action of
liquids, and even of gases, on solids and on each other. The
labours of Pfaff have been especially directed to this inquiry,
and have enabled him to arrive at the following general con-
clusions respecting the electro-motive force developed by the
contact of solid with liquid conductors.



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