prepared in a common porter bottle, by mixing a handful of iron filings
with two wine-glassfuls of water, and an ounce of sulphuric acid,
commonly called _oil of vitriol_. The air when thus made should be kept
in a bottle closely stopped.
To use the instrument, have ready a cork, fitted to the mouth of the
cannon,—uncork the bottle containing the air, and immediately apply the
cannon to the mouth of the bottle; a sufficient quantity of the gas will
rise into the cannon, in the course of a few seconds, when both the
cannon and bottle must be corked. Now, if the knob of the wire passing
through the tube be applied to the prime-conductor, so that a spark may
pass through it to the inner surface of the cannon, the gas will be
inflamed with a loud report, and the cork will be forced out with
considerable violence.
_Curious Figures made upon Glass, Paper, and other Substances, by means
of Electricity._
Professor Lichtenburg first observed some curious figures made with
pulverized rosin, on a large electrophorus; but since this original
discovery, a variety of other methods have been contrived, for making
them upon glass, paper, resinous substances and many others. The
ingenious electrician may derive considerable information from these
figures; their various appearances, in many instances, showing him the
direction and quality of the electric fluid.
The principal method of making these impressions is to electrify a
perfect or imperfect electric, and then to throw certain powders upon
the electrified substance, which will be arranged in different forms.
The most convenient method of projecting these powders is to put them
into a small bottle of India-rubber, and then fasten a tube of glass or
metal to the neck of the bottle; the orifice of this tube must be
covered with a piece of flannel when used.
As to the nature of the powders, almost every substance which can be
pulverized will do.—Thus chalk, rosin, sulphur, rose-pink, dragon’s
blood, gum-arabic, lake, and evaporated decoctions of colouring woods,
may be used with advantage, either singly or mixed.
Take a clean pane of glass, fourteen or fifteen inches square, and after
drying it thoroughly, hold it by one corner, and pass over its surface
the knob of a jar, moderately charged with positive electricity—then,
keeping it suspended, project upon it, by means of the bottle above
described, a mixed powder of dragon’s blood and gum-arabic, in equal
parts. If you examine the glass, you will find that the two powders will
be separated upon it, the red powder of dragon’s blood falling on
certain places, and the white powder of gum-arabic falling upon certain
other places, so as to form a track upon the parts which were touched
with the charged jar, consisting of two colours disposed in a thousand
different ways.
If, instead of drawing the knob of the jar over the surface of the
glass, you only touch it here and there with it, and then throw on the
mixed powders as before, separate star-shaped figures will be formed
about these places. The stars will be better defined when a single
powder is used; their rays are sometimes few and strong; at others, many
and slight, and frequently they do not go entirely round the parts which
have been touched by the phial. These different effects depend chiefly
upon the quantity of the charge in the jar.
If the jar be charged negatively, the appearances will be very
different, from those occasioned by positive electricity. Very few rays
will now be observed, the powders for the most part disposing themselves
in round figures, and generally a central spot of one powder will be
surrounded by another of a different colour.
Some powders adhere but slightly to the glass, so as not to bear being
touched; but if a piece of paper be laid upon the painted side, without
disturbing the figures, and the edge of it be fastened all round to the
edge of the glass, the figure may be preserved without injury. But a
better method is to lay another pane of glass over the one with the
figures upon it, and then to fasten them together with sealing-wax, or a
piece of paper pasted over the edges.
If the powders of such colours as are used for enamel-painting be
projected upon glass or porcelain, and these substances be afterwards
exposed to a proper degree of heat, as that of an enameller’s furnace,
the figures will be rendered indelible.
Take a piece of common writing paper, and hold it near the fire, so as
to make it quite dry and very hot—lay it upon a dry table and pass the
knob of a charged jar over it—then take up the paper by one corner, and
holding it suspended, throw upon it a mixed powder of dragon’s blood and
gum-arabic, in the way above mentioned.—The figures in this instance
will be very beautiful, and may be made in various shapes, as letters,
stars, or stripes. If the paper thus painted be held near the fire for a
few seconds, the powder of dragon’s blood, being a resinous substance,
will be melted and fastened to the paper, after which the gum-arabic may
be taken off.
Powders of different colours may be projected upon the paper after the
same manner, but unless they be of a resinous nature, so as to be easily
melted by heat, it is very difficult to fasten them to the paper.
A little experience will enable the operator to make them in a neat and
handsome manner. It will however be necessary to observe a few
precautions.—The charge of the jar should not be too great or too small;
for in the former case the figures will be confused and irregular; and
in the latter they will be too faint.—These experiments should be
performed as quickly as possible, for if the paper be suffered to cool
too much, or the communicated electricity be dissipated, the desired
effect will not be produced.
_The Electrified Capillary Syphon._
Let a small bucket of metal be suspended from the prime-conductor, and
put into it a syphon of glass or metal, so narrow at the outer extremity
that the water may just drop from it.—Now, if the cylinder be turned,
the water, which when not electrified came over only in drops, will run
in a stream, or even be subdivided into a number of smaller ones.—If the
experiment be made in the dark, the streams appear luminous.
The same phenomenon may be exhibited by a small bucket, with a jet pipe
fixed in the bottom. This must be hung on the prime-conductor, as in the
last experiment: or the experiment may be agreeably varied, by hanging
one bucket from a positively, and another from a negatively electrified
conductor: so that the two jets may be about three inches from each
other.—The stream issuing from the one will be attracted by that issuing
from the other, and both will unite into one: but, though both are
luminous in the dark, before meeting, after this has taken place they
will not be so, unless one of them was more powerfully electrified than
the other.
_The Lateral Explosion._
If a jar be discharged with a rod which has no electric handle, the hand
which holds the rod, on making the discharge, frequently feels something
similar to a shock, especially when the charge is considerable.—This
shock, or lateral explosion, as it has been called, may be rendered
visible in the following manner.—Connect a chain with the outside
coating of a charged jar—then discharge the jar through another circuit;
for instance, a discharging rod—The chain which is connected with the
outside coating, but which forms no part of the circuit, will appear
lucid in the dark; that is, sparks will be seen at every link. This
chain will also appear lucid, if it be only put close to the jar,
without touching it; and on making the discharge a spark will be seen
between the coating and the end of the chain. This luminous appearance
is what has been denominated the _Lateral explosion_.
_To represent the Constellations._
Provide yourself with a piece of paste-board, of the size you intend the
figure of the constellation, (four or five inches square will be found
convenient) and cover one side with tin-foil or silvered paper. Let
needles, or any other small metallic points, project from the other side
of the paste-board, from the places where you intend stars to appear,
taking care to form a communication between each of the points, or
needles, and the tin-foil on the other side. If the instrument thus
prepared be fixed upon the prime-conductor, negatively electrified, all
the points will be illuminated at once.—The experiment may be performed
with the prime-conductor positively electrified; but in this case, the
light at the points, being in the shape of a divergent cone, does not
appear so proper to represent stars, as the round globular lights, which
are characteristic of points negatively electrified.—It is scarcely
necessary to remark that this experiment should be performed in a
darkened room.
_The Electrical Snake._
Cut a circular piece of silvered paper into a spiral form. The outer end
must be shaped like a serpent’s head, with the mouth open and the tongue
protruded. Then provide an upright shaft of wood or metal, terminating
upward in a point, and having the lower extremity fastened in a foot or
bottom-board. The snake, being put spirally round the shaft, with its
tail on the point, and then placed under a metallic point suspended from
the prime-conductor, will turn round, and in a darkened room will appear
to spit fire.
_The luminous Shower._
Electrify a common tumbler, by passing a chain, communicating with the
prime-conductor, over its inner surface. Place a small heap of steel or
brass-filings on an uninsulated conductor, and invert the electrified
tumbler over it: the filings will be attracted up the sides of the
tumbler, and then thrown off. This, at night, forms a very beautiful
experiment, as the filings become luminous, and appear like a shower of
fire.
If a tumbler, electrified in this way, be inverted over pith balls,
instead of brass-filings, the balls will leap with surprising velocity
up the sides of it.
_The luminous Discharging-rod._
Provide a glass tube in the shape of a common discharging-rod, about ten
inches in length, and let the bore of the tube be nearly the eighth of
an inch in diameter; upon one end fasten with cement, or otherwise, a
brass knob, so as to be perfectly air tight. Now expel the air from the
tube, by heat or the air pump, and then fix another knob upon the open
end, in a way similar to the former.
If the instrument be used as the common discharging-rod, it will be
found to answer its purposes equally well; while at the same time all
the inner surface of the tube, during the discharge of a jar with it, is
beautifully luminous.
Mr. Nairne also contrived a luminous discharging-rod. It consisted of an
arched glass tube, with a metallic ball at each end, and a communication
from one ball to the other was made by a brass chain, which passed
through the bore of the tube.—In the discharge of a jar with it, small
sparks are seen between the links of the chain within the tube.—Both
these dischargers should have handles fastened to them.
_To decompose Water by Electricity._
Let a glass tube, having a small bore, be filled with water; then close
each end of the tube with a piece of cork, and let two wires pass
through the corks, so that their extremities may come pretty near each
other within the tube.
If sparks of electricity be made to pass between the ends of the wires,
within the tube, the water will be converted into oxygen and hydrogen
gases.
If this process be continued till the extremities of the wires become
immersed in the two gases, they will explode and again form water.
_The Electrified Fountain._
Insulate a small fountain made of metal, (one on the construction of
_Hiero’s_ will be found most convenient,) and connect it with the
prime-conductor—put it in operation—the jet will be undivided, except at
the top—now turn the cylinder, and you will immediately perceive the jet
divided much lower than at first; the drops, which before fell nearly
perpendicularly, will now be thrown off in elliptical lines, and
attracted by any conductor brought near them. A small Leyden phial may
be charged at the top of the jet, which will present the curious
spectacle of fire coming out of water.
EPITOME
OF
ELECTRICITY.
DIVISION III.
CHAP. I.
_Introductory Observations to the theory of Electricity._
There is scarcely any thing to which an inquisitive mind, such as a
philosopher possesses, submits with more reluctance, than to the
inability of assigning the causes of the most interesting appearances or
phenomena of nature. That every effect has a cause, is a first or self
evident principle, and the mind is not easily brought to acquiesce in
its utter ignorance of the cause, when the effect is visible and
striking.—From this circumstance proceeded the numerous wild, fanciful,
and delusive systems of natural philosophy, which existed before the
time of the great Lord Bacon.—His penetrating and discriminating mind
saw that nothing solid could ever be achieved in that noble science,
unless such a procedure were relinquished;—unless men would consent to
confess their ignorance of causes which were actually unknown;—unless
they would cease to rely on hypotheses, however plausible, until they
were verified by experiment;—consent to take facts as they are found,
and by experiments alone endeavour to ascend to their causes. On this
immoveable base the Newtonian philosophy is founded, and it will of
course prove as durable as nature herself.
Two things, however, in regard to this subject, are of some importance
to be remarked.—The first is, that experiments may sometimes be supposed
to ascertain causes which will afterwards be found not to exist, or to
be wrongly assigned; because the experiments had not been accurately or
extensively made.
The second remark is, that though hypotheses are not to be taken for
philosophy, till they have stood the test of experiment; yet in the
process of the mind in making discoveries, hypothesis is perhaps always
used, where the discovery is not merely accidental. No man can
rationally make experiments till he has conceived a notion, supposition,
or hypothesis in his mind, which he imagines experiment may serve to
verify.—It is this which prompts him to his researches and guides him in
conducting them.
In regard to electricity, it is remarked by Dr. Priestley, that “no
other part of the whole compass of philosophy affords so fine a scene
for ingenious speculation. Here the imagination may have full play, in
conceiving of the manner in which an invisible agent produces an almost
infinite variety of visible effects. As the agent is invisible every
philosopher is at liberty to make it whatever he pleases, and ascribe to
it such properties and powers as are convenient for his purpose. And,
indeed, if he can frame his theory so as really to suit all the facts,
it has all the evidence of truth, that the nature of things can admit.”
For ourselves we are by no means satisfied that there is yet any theory
of electricity which will “suit _all_ the facts;” and therefore if this
be requisite to entitle a theory _philosophy_, as contra-distinguished
from _hypothesis_, we must think that the best theory of electricity is
yet hypothesis, and not philosophy. We believe that the Franklinian
theory accounts for _more_ facts, and is far more plausible, than any
other. But, as we have already had occasion to remark in a former
chapter, it does not appear to us fully and satisfactorily to account
for all the phenomena of electric attraction and repulsion. Dr. Franklin
always spoke with great diffidence of his own theory, and always
denominated it an hypothesis.
“Every appearance, says he, which I have seen, in which glass and
electricity are concerned, are, I think explained with ease by this
_hypothesis_. Yet, perhaps, it may not be a true one, and I shall be
obliged to him who affords me a better.” In like manner Æpinus, who
adopted the theory of Franklin, and who has illustrated its leading
principles in a far more masterly and scientific manner than any other
writer, still denominates the theory which he maintains an _hypothesis_.
Why should pupils affect to go farther than their masters? We think that
the theory of electricity is still an hypothesis. We are however clearly
of opinion that the hypothesis of Franklin is preferable to every other.
We have therefore adopted it in the whole of our system, and mean to
close this division of our subject by giving it, somewhat in detail,
with the leading facts and considerations by which its claim to
superiority appears to us to be supported. In the mean time, as every
student of electricity may wish to know, and ought to know, what other
theories have been adopted, we shall fill the following chapter with a
brief and compendious recital of some of the principal of them.—It would
be endless to recite them all. We shall, however, enter into no
extensive argument to prove their fallacy, as this would be inconsistent
with our plan, as well as unprofitable in itself. We shall afterwards
say what we can to confirm the theory of Franklin, and if we succeed,
every thing opposed to it, must, of course, appear to be unsupported.
CHAP. II.
_Theories of Electricity, exclusive of that of Franklin._
The first electricians supposed that the attraction of electric
substances, was caused by certain unctuous _effluvia_, emitted from
these substances when they were excited. Such effluvia were supposed to
fasten upon all bodies which fell in their way, and if not too heavy, to
carry them back to the emitting substances. For at that time, all
effluvia were supposed to return to the bodies whence they had been
emitted; because they could not otherwise account for the fact, that
such substances were not sensibly wasted by emitting effluvia. But when
the subtilty of light was demonstrated by Newton, and that of the
effluvia of many bodies was better understood, philosophers gave up the
doctrine of the return of effluvia, both with regard to electricity and
other subjects.
2. They applied to electricity the general, but unknown _principles of
attraction and repulsion_—properties which they supposed to be
immediately communicated by the Creator to certain bodies. But the laws
of this attraction and repulsion, in regard to electricity, we do not
know that they attempted to explain.
3. Mr. Du Faye discovered the two opposite species of electricity, which
he termed the _vitreous_ and the _resinous_, because one was found in
glass and the other in rosin, sealing-wax, &c. He immediately adopted
the theory of _two distinct electric fluids_, repulsive with respect to
themselves, and attractive of one another. But he did not know at this
time, that both these species were concerned in every electrical
operation, and that glass or rosin alone always produces both of them.
When he found that electric appearances took place at an insulated
rubber, and it was demonstrated that the action of the rubber did not
produce, but only collect the electric fluid, he perceived that both
electricities, as they had heretofore been called, were produced at the
same time, by one and the same electric; and with a candour that does
him honour, he gave up his theory, and embraced that of Franklin, which
was first suggested about this time.
4. With some, and particularly Mr. Wilson, the chief agent in all
electrical operations is _Sir Isaac Newton’s ether_; which is supposed
to be more or less dense in all bodies, in proportion to the smallness
of their pores, except that it is much denser in sulphureous and
unctuous bodies. To this ether are ascribed the principal phenomena of
attraction and repulsion. “On this theory, (says Dr. Priestley) I shall
make no particular remarks, because I cannot say that I clearly
comprehend it.”
5. The ingenious Abbè Nollet, whose theory has been more the subject of
debate than all the others, before Dr. Franklin’s, supposes that in all
electrical operations the fluid, (of which he admits there is but one)
is thrown into two opposite motions; that the _affluence_ of this matter
drives all light bodies before it, by impulse, upon the electrified
body; and that its _effluence_ carries them back again. But he seems
very much embarrassed in accounting for facts where both these currents
must be considered as taking place at the same time, and in finding out
expedients to prevent their impeding and interrupting the effects of
each other. To obviate this great difficulty, he supposes that every
excited electric, and likewise every body to which electricity is
communicated, has two orders or kinds of pores, one for the emission of
the effluvia, and the other for the reception of them.
The Abbè maintained this hypothesis with a zeal and ingenuity worthy of
a better cause. For it is manifest at once, that the existence of such
kinds of different pores in bodies, is a mere gratuitous assumption. Our
senses do not inform us of the existence of any such pores, nor have we
evidence of any kind that they even exist at all, unless we consider it
as evidence of their existence, that they are necessary to account for
the appearances on which the Abbè grounds his theory.
Yet this theory, with some modification, has been strenuously
maintained, and has its advocates to the present day. They say that “in
bodies positively electrified, there is a flux of electric matter, from
their surface all round; that is, the fluid contained in their pores
pushes out on every side, and communicates a similar motion to the
electric fluid contained in the adjacent atmosphere. This must of
necessity very soon exhaust the body of its electric matter altogether,
if it was not instantaneously supplied after every emission. But this
supply is immediately procured from the surrounding atmosphere. The
quantity sent off is instantaneously returned from the air, and a
_vibratory motion or struggle between the air and electric fluid_,
immediately takes place. The positive electricity therefore consists in
a vibratory motion in the air and electric fluid; and the force of the
vibration is directed _outwards_ from the electrified body. In bodies
negatively electrified, the fluid contained in the neighbouring
atmosphere is directed _towards_ the body so electrified. But it is
certain, that this motion inwards cannot be continued unless there is
also a motion of the fluid outwards from the body. In this case also,
there is a vibratory motion, but the force of it is directed _inwards_,
and as the source of it lies not in the body, but in the surrounding
atmosphere, it manifests itself somewhat less vigorously.” We have taken
this account of the modification of the Abbè Nollet’s theory from one
who firmly believed it. But we cannot pretend to controvert it, because,
(as Dr. Priestley says,) “we cannot say that we clearly comprehend it.”
6. There are some who explain the phenomena of electricity upon
_chemical_ principles. They also believe in the existence of two
distinct and positive fluids; but instead of a _mechanical_ operation,
they consider all their sensible effects as arising from _chemical_
affinity and union. The following may serve as a specimen of chemical
electricity. It is said—
(1.) “There are two kinds of electric ether, which exist either
separately or in combination. That which is accumulated on the surface
of smooth glass, when rubbed with a cushion, is here termed _vitreous_
ether; and that which is accumulated on the surface of resin, or
sealing-wax, when rubbed in like manner, is here termed _resinous_
ether; and a combination of them, as in their usual state, may be termed
_neutral_ electric ethers.
(2.) Atmospheres of vitreous, or of resinous, or of neutral electricity,
surround all separate bodies, are attracted by them and permeate those
which are called conductors, as metallic, aqueous, and carbonic
substances; but will not permeate those which are called non-conductors,
as air, glass, silk, resin, sulphur.
(3.) The particles of vitreous ether, strongly repel each other, but
attract the particles of resinous ether and _vice versa_. When the two
electric ethers unite, a chemical explosion occurs, in some respects
like that of gun-powder, light and heat are liberated, and rend or fuse
the bodies which they occupy.