jar, furnished with Mr. Lane’s electrometer. This instrument is made in
the following manner. From the wire extending beyond the mouth of the
jar, at about four inches from the upper extremity, let a piece of glass
or baked wood three inches long, project at right angles. At the outer
extremity of this stem let another piece of baked wood three inches
long, be fixed parallel to the rod of the jar; the upper end of the
parallel stem must be furnished with a brass socket, through which a
graduated wire may easily pass. This wire must be furnished with a knob
upon the end which is next the jar, and a hook or ring at its other
extremity, to which a chain connected with the outer coating of the jar
must be attached. From this construction it is readily perceived that
the force of the discharge or shock, will be proportioned to the
distance of the ball of the electrometer, and the usual ball of the jar;
i. e. when the shock is large it will pass from one knob to the other at
a larger distance, and when small at a smaller distance, and thus the
distance will be the measure of the shock.—The next thing to be provided
is a ball, either of metal, or of wood covered with tin foil; this must
have a metallic handle, which may be separated from the ball at
pleasure, having at one of its extremities a sharp point to receive a
stream of electric fire; small pointed pieces of wood made in a conical
shape, may be fixed on this point, when the patient requires a degree of
electricity between a spark and a stream.
The bottle director is the next instrument to be described. It is
exactly the same with the common Leyden phial, with the addition only of
a hook cemented to the bottom. To use this director (suppose for
instance you wished to pass a shock through the arm) let a communication
be made between its inner coating and the prime-conductor, by which
means it will be charged; then let a chain be fastened, by one end, to
the hook which is at the bottom; then by applying the other end of the
chain (which may be furnished with a ball) to one side of the arm, and
the knob of the jar to the other, a shock will be given.
These are the instruments for the electrical physician. We are now to
describe the manner in which electricity may be applied to the best
advantage.
1st. By simply placing the patient upon the electrical stool. While the
machine is in action the patient constantly emits the overplus of the
electric fluid that he receives, which continually passes off from every
part of his body, and produces a salutary effect. It may be suspected
that so gentle a treatment could have but little influence. It is
however upon good authority we assert, that nervous and sedentary
persons have derived considerable advantage from this mode of
application.
2d. By electric friction. Let the part affected be covered with a piece
of flannel or woollen cloth, and place the patient upon the insulated
chair, and connect him with the prime-conductor; then take a metallic
ball, communicating with the earth, and rub it over the flannel or
woollen cloth. Electricity thus applied has often removed violent
spasms, and many other afflicting complaints.
3d. By drawing sparks. Let the patient, as in the last instance, be
placed upon the insulated stool, and connected with the prime-conductor;
then bring the metallic ball, communicating with the ground, within
about half an inch of the part affected, and sparks will pass from it to
the ball. Cutaneous eruptions, scrophulous tumours and deafness, are
frequently benefitted, and sometimes removed, by this method of
application. Deafness, in particular, has been entirely cured by the
electric spark, when every other remedy has proved ineffectual. One of
these cases came under our own observation. A gentleman who was affected
with an almost total loss of hearing for more than six months, was
advised by his physician to make a trial of electricity as a remedy. He
applied to us, and was under our care about four or five weeks, when he
left us almost entirely recovered. This gentleman was treated in the
following manner.
We placed him on an insulated chair communicating with the
prime-conductor. Then, with a blunt pointed wire inserted into a glass
tube, we drew sparks from the _meatus auditorius_. This operation was
continued for eight or ten minutes, at every visit. He commonly attended
us twice or thrice a week. We were fully persuaded that the cure would
have been more speedy, if he had received the electricity more
frequently.
4th. By the stream. Place the patient as in the two last instances; then
bring the point, instead of the ball, near the part affected. When the
electrical stream is to be applied the wooden point is preferable to the
metallic one. Inflammations and other diseases of the eyes, and several
other disorders, have been thus removed.
5th. By the director. Place the patient on a chair—insulation in this
case being unnecessary. Then lay the ball, which communicates with the
outside coating of the director, upon the affected part; after which,
bring the director, which must have been previously charged, near any
other part of the body, and the intended operation will be performed. It
is impossible to tell the precise quantity of electricity which ought to
be administered in every complaint, because persons who are affected
with the same disease will sometimes require very different degrees of
electrization, which must be judged of by the nature of their
constitution, their habits of body, and other circumstances. Small
sparks will sometimes have more effect upon a delicate and irritable
constitution, than pretty powerful shocks upon others. The Leyden phial,
with Mr. Lane’s electrometer, is the most convenient instrument for
sending shocks of different powers through particular parts of the
body.—To use this.—Let the wire of the electrometer be placed at the
proper distance for the required shock; connect a chain or wire,
communicating with this, with the part affected—and let a communication
be made between any other part of the body and the outside coating of
the phial. Now turn the cylinder, and the phial, when it has received
the proper charge, will discharge itself through the circuit formed by
the chains or wires, and the part of the patient which was to be
subjected to the shock.
CHAP. XIX.
_Directions concerning the use of the electrical apparatus, with some
practical rules for performing experiments with it to the best
advantage._
The machine described in Chapter IV, or one similar to it, is capable of
exhibiting the principal electrical phenomena, provided it be skilfully
managed; but without such management it will constantly disappoint the
electrician, and prove of little use. Let the following directions and
observations, then, be attentively regarded.
1. Keep all the instruments as free as possible from dust and moisture.
2. When the weather is clear, the air dry and a little cold, the
electric fire may be easily and copiously collected. But when the
weather is hot or damp, the electrical machine is much less powerful.
3. Before the machine is used, the cylinder should be wiped clean, with
a linen cloth that is soft, dry, and warm; after which a clean hot piece
of flannel, or old silk handkerchief, may be applied with
advantage.—This done, if the cylinder be turned pretty fast, when the
prime conductor and other instruments are removed, the electricity, upon
applying the knuckle or other conductor, will issue from the glass with
a crackling noise, accompanied with sparks; this indicates the machine
to be in good order, so that the electrician may proceed to perform his
experiments. But if, when the cylinder is turned and the knuckle
applied, no sparks be perceived, then the fault is most probably in the
rubber. If so, it must be removed and held to a fire, so that its silk
part may be dried. Then take a little tallow from a candle and just pass
it over the leather of the cushion, after which spread upon it, a little
amalgam, and force it as much as possible into the leather. Replace it,
and let the cylinder be again wiped; the machine is fit for use.
4. Sometimes the electric matter will not be well collected, because the
machine is not sufficiently supplied with it from the earth; which
happens, when the table upon which the electrical machine is placed and
to which the chain or wire of the rubber is connected, is very dry, and
consequently a bad conductor. In this case, the best method is to
connect the chain or wire of the rubber with some moist ground, or with
the iron-work of a water-pump, if convenient. Thus the rubber will be
supplied with as much of the electric fluid as is required.
5. When the cylinder is very hot (say above 110° of Fahrenheit’s
thermometer,) it will not collect the electric fluid well.
6. When a sufficient quantity of amalgam has been accumulated upon the
leather of the rubber, and the machine does not work well, then, instead
of putting more upon it, a small quantity of that which is already on
the leather must be taken off.
7. After the cylinder has been used for some time it will contract black
streaks, which continually increase, and greatly obstruct its electric
power.—These streaks must be taken off, and the glass frequently wiped
to prevent their being again formed.
8. Coated jars, before they are used, ought to be made a little warm. If
this be done, they will receive and retain the charge much better.
9. If one of the jars of a battery, as is sometimes the case, make a
spontaneous discharge prematurely, it will of course discharge the whole
battery; and in such case the faulty jar should be exchanged for one
which is free from this defect.
10. In making the discharge of an electrical battery, or of a single
jar, the electrician must be careful not to place the discharging-rod
upon the thinnest part of the glass, as that may cause the bursting of
the jar.
11. In large batteries, some of the jars frequently burst in the
discharge. To remedy this inconvenience, Mr. Nairne says that the
discharging-rod should never be made of a good conducting substance,
except the circuit be at least five feet long. But here it may be
remarked, that the length of the circuit weakens the force of the shock
proportionably; the highest degree of which is in many instances
required. When a coated phial is cracked, either by a spontaneous
discharge or otherwise, the outside coating must be removed from the
fractured part; then make it moderately hot by holding it near the fire;
in this situation apply burning sealing-wax to the part, so as to cover
the fracture completely, taking care that the thickness of the wax be
rather more than the thickness of the glass; lastly, cover all the
sealing-wax, and part of the glass beyond it, with a composition made of
four parts of bee’s-wax, one of rosin, one of turpentine, and a little
oil of olives: which composition must be spread upon a piece of oiled
silk, and applied in the form of a plaister. In this manner jars which
have been broken may be repaired effectually.
12. When a jar, and especially a battery, has been discharged, the wires
ought not to be touched with the hand before the discharging-rod has
been applied a second, and even a third time; as there generally remains
a residuum of the charge, which is sometimes very powerful. This
residuum is in a great measure occasioned by the electricity, which,
when the jar is charging, spreads itself over the uncoated part of the
glass, and which is not discharged at first, but gradually returns to
the coating after the first discharge is made.
13. When an experiment is to be performed which requires only a small
part of the apparatus, the remaining part should be removed from the
table.—Candles should never be placed near the prime-conductor; for the
effluvia of their flames carry off much of the electric matter.
14. One or two inches of the lower part of a Leyden phial should be
coated with some thick paint, in order to prevent the amalgam, which is
often scattered upon the table, from corroding the tin-foil, and thereby
diminishing the charge.
15. When a prime-conductor is used, those sparks are strongest which are
taken from the extremity farthest from the cylinder.
16. The longest sparks are drawn from any conductor along an electric
substance. Thus, if the conductor be supported by pillars of glass or
baked wood, the longest sparks may be taken close to the pillar. If the
conductor be bent a little inward, so as to make the surface concave, a
particularly large and undivided spark may be drawn from that place: but
where the surface is convex, the spark is more apt to be divided and
weakened.
17. It sometimes happens that cylindric or globe machines do not work
well, owing to the air within them being too much rarefied by the heat
of the cement, when the caps are fixed on. To remedy this, a small hole
may be bored through one of the caps, so as to admit air into the
cylinder or globe.
18. If the electric by any means become scratched, the working of the
machine will be greatly impeded, if not altogether prevented. This is
accounted for upon the principle that smooth and rough glass electrify
differently when excited by the same rubber, and the two different
states destroy one another. This may be remedied by filling up the
scratches with a little tallow.
EPITOME
OF
ELECTRICITY.
DIVISION II.
CHAP. I.
_Entertaining Experiments, made by electrical Attraction and Repulsion._
Electric attraction and repulsion, observed in excited amber, was, as we
have already had occasion to remark, the first phenomenon which was
noticed in the science of which we treat. We have also hinted that, to
the present time, no explanation of this attraction and repulsion which
is entirely satisfactory, has been given. Facts, however, are known in
abundance; and certain principles, relative to this part of our subject,
are clearly ascertained. To exhibit and illustrate these has been our
object in selecting the following experiments; some of which may be
considered as intended chiefly for amusement, but all of which, if
thoroughly comprehended, will serve to fix the principles of the science
more deeply in the mind of a learner.
EXPERIMENTS.
_The self-moving Wheel._
This machine was invented by Dr. Franklin. It is made of a thin round
plate of window-glass, 17 inches in diameter, covered on both sides with
tin-foil, except about two inches next the edge. Two small hemispheres
of wood are cemented to the two sides centrally opposite, and in each of
these a strong thick wire eight or ten inches long is placed; and these
form the hub and axis of the wheel. It turns horizontally on a point at
the lower end of its axis, which must be insulated. The upper end of the
axis, passes through a hole in a thin plate of brass, cemented to a
strong piece of glass or baked wood, which keeps it six or eight inches
distant from any non-electric, and is furnished with a ball of wax or
metal on the top, to keep in the fire. In a circle on the table which
supports the wheel, are fixed twelve small pillars of glass about four
inches apart, with a thimble or metallic ball on the top of each. On the
edge of the wheel is a small metallic bullet, communicating by a wire
with the upper coating of the wheel; and about six inches from it, is
another bullet communicating, in like manner, with the lower coating.
When the wheel is to be charged by the upper coating, a communication
must be made from the under one to the table. When it is well charged it
begins to move; the bullet nearest to a pillar is attracted by the
thimble or bullet on that pillar and passing by, electrifies it, and is
immediately repelled from it; the succeeding bullet, which communicates
with the other coating of the glass, more strongly attracts that
thimble, on account of its being previously electrified by the other
bullet; and thus the wheel increases its motion, till its velocity is
regulated by the resistance of the atmosphere.—The wheel will turn half
an hour, and make, one minute with another, 20 turns in a minute, which
is 600 turns in the whole; the bullet of the upper coating giving, in
each turn, 12 sparks to the thimbles or balls, which make 7200 sparks;
and the bullet of the under coating receiving as many from the thimbles;
those bullets moving in the time near 2500 feet. The thimbles are well
fixed, and in so exact a circle, that the bullets may pass within a very
small distance of each of them. If, instead of two bullets, there be
eight, four communicating with the upper, and four with the under
coating, placed alternately, the motion will be considerably increased,
but then it will not continue so long. These wheels may be applied to
the ringing of chimes, and the moving of light-made orreries.
_The electrical Dance._
Suspend from the prime-conductor, by means of a hook, a metallic plate,
six inches in diameter. About three or four inches from this, and
directly under it, place another plate of the same kind, communicating
with the earth. Upon the lower plate, throw small painted figures of men
and women, cut in paper, or made of the pith of elder. Now, if the
cylinder be turned, the figures will begin to move between the plates,
leaping from one to the other, with surprising velocity, exhibiting many
curious and ludicrous attitudes and motions.
_The electrified Bells._
The phenomena of attraction and repulsion may be very satisfactorily
shown with the electrified bells. In order to make this experiment,
provide yourself with a piece of wire, furnished with a hook equidistant
from both ends, and by which it may be suspended from the
prime-conductor. At each end of this wire suspend a small bell by a
chain or wire; and from the middle point between these two bells,
suspend a third, by a silk thread; let a clapper be hung between each of
the bells, also by silk threads. From the concave or under side of the
middle bell let a chain proceed, communicating with the table, and
having a silk thread at its extremity. Now if the cylinder of the
machine be turned, the clappers will fly from bell to bell with a very
quick motion, and the bells will ring as long as the electrization
continues.
The two outer bells, being suspended by chains or wires, are electrified
first; hence they attract the clappers; and having communicated to them
part of their electricity, repel them. The middle bell, which is in its
natural state, now attracts them, and deprives them of their acquired
electricity; after which they are again attracted by the outer bells,
and again repelled. If, by holding the silk thread, the chain of the
middle bell be raised from the table, the bells, after ringing a short
time, will stop; because the middle one, being insulated, will soon
become as strongly electrified as the other two; in which case, the
clappers being equally attracted by both bells, must discontinue their
motion towards either.
If the experiment be made in a darkened room, a spark will be seen
between the clapper and bells, at every stroke.
This experiment will have a better effect, if, instead of keeping the
machine in motion, a charged jar be placed in contact with the
prime-conductor; and when joined with the preceding experiment, the
whole will have the appearance of an _electrical ball_.
_The inflammable air Balloons._
The following experiment may serve to illustrate some of the phenomena
observed in thunder storms.
Provide two balloons, made of the allantoides of a calf, containing
about two cubic feet, and fill them with inflammable air. To each of
these attach, by a silk thread about eight feet long, a weight
sufficient to prevent their rising higher than the above distance in the
air. Then connect one of them with the positive, and the other with the
negative conductor, or insulated rubber of the machine, by very thin
wires, thirty feet long: keep them a considerable distance asunder, and
as far from the machine as the wires will admit. On being electrified,
the balloons will rise as high in the air as the silk thread will allow
them, then attract each other, and uniting as it were in one cloud, will
gradually descend.
The rising of these balloons is attributed to the expansion of the air
contained in them, in consequence of the repulsive power communicated to
its particles by the action of the electric matter upon them.—When in
contact, their opposite electrical powers destroy one another, and they
descend in consequence of the condensation of the internal air.
_Dr. Franklin’s Experiment for illustrating his Theory of Thunder
Storms._
Take two round pieces of paste-board, two inches in diameter; from the
centre and circumference of each of them suspend, by fine silk threads
eighteen inches long, seven small balls of wood, or seven peas, equal in
size, so that the balls appended to each paste-board will form
equilateral triangles, one ball being in the centre and six at equal
distances from that, and from each other, around the circumference. Thus
they represent particles of air. Dip both setts in water; and some of it
adhering to each ball, they will represent air loaded with moisture.
Electrify one sett, and its balls will repel each other to a greater
distance, enlarging the triangles. Could the water, supported by the
seven balls, come in contact, it would form a drop or drops, so heavy as
to break the cohesion it had with the other balls, and so fall. Let the
two setts then represent two clouds, the one a sea-cloud electrified,
and the other a land-cloud. Bring them within the sphere of attraction,
and they will instantly draw towards each other. Now you will see the
separated clouds close thus—the first electrified ball that comes near
an unelectrified one, by attraction joins it, and gives it fire;
instantly they separate, and each flies to another of its own party, one
to give and the other to receive fire; and so they proceed through both
setts, but so quick as to be in a manner instantaneous. In the collision
they shake off and drop their water, which represents rain.
CHAP. II.
_Experiments with electric Light._
These experiments should be made in a darkened room, for though the
electric light is visible frequently in day light, yet the appearance of
it is very often confused, so that a distinct idea of it cannot be
formed.
Before we proceed to describe the experiments under this head, it will
be necessary to inform the reader that by the term _vacuum_ which he
will frequently meet with in this chapter, we mean such an one as is
formed by the action of an air pump, which is a good conductor of
electricity.
EXPERIMENTS.
_The Aurora Borealis._
Take a phial nearly of the shape and size of a Florence flask; fix a
stopcock or valve to its neck, and exhaust it of air.—If this phial be
rubbed in the usual way to excite electrics, it will appear luminous
within, being full of a flashing light, very much resembling the
northern lights or aurora borealis. This phial may also be made luminous
by presenting one end of it to the prime-conductor, while the other is
held in the hand. In this case, the whole cavity of the glass will
instantly appear full of a flashing light, which remains in it for some
time after the glass has been removed from the prime-conductor.
A glass tube exhausted of air in the same manner, and hermetically
sealed, may be used instead of this phial, and perhaps with more
advantage.
The most remarkable circumstance attending this experiment is, that
after the phial or tube has been removed from the prime-conductor, and
even several hours after the flashing light has ceased, strong flashes
will be again visible upon applying the hand.
The causes of this phenomenon are two; first, the conducting nature of
the vacuum; and second, the charging of the glass; for when one side of
the phial is touched with the prime-conductor, the electric fluid
communicated to that part on the outside, occasions the natural fluid of
the inside surface, to leave its place and pass to the opposite side of
the phial, which does not communicate with the electrified conductor;
this passing of the fluid through the vacuum occasions the light within,
which is more or less subdivided as the vacuum is more or less perfect.