it can permeate common matter, even the densest metals, with such ease and
freedom, as not to receive any perceptible resistance.
2. If any one should doubt, whether the electrical matter passes thro' the
substance of bodies, or only over and along their surfaces, a shock from an
electrified large glass jar, taken thro' his own body, will probably
convince him.
3. Electrical matter differs from common matter in this, that the parts of
the latter mutually attract, those of the former mutually repel, each
other. Hence the appearing divergency in a stream of electrified effluvia.
4. But tho' the particles of electrical matter do repel each other, they
are strongly attracted by all other matter.[7]
5. From these three things, the extreme subtilty of the electrical matter,
the mutual repulsion of its parts, and the strong attraction between them
and other matter, arise this effect, that when a quantity of electrical
matter, is applied to a mass of common matter, of any bigness or length
within our observation (which has not already got its quantity) it is
immediately and equally diffused through the whole.
6. Thus common matter is a kind of spunge to the electrical fluid. And as a
spunge would receive no water, if the parts of water were not smaller than
the pores of the spunge; and even then but slowly, if there were not a
mutual attraction between those parts and the parts of the spunge; and
would still imbibe it faster, if the mutual attraction among the parts of
the water did not impede, some force being required to separate them; and
fastest, if, instead of attraction, there were a mutual repulsion among
those parts, which would act in conjunction with the attraction of the
spunge. So is the case between the electrical and common matter.
7. But in common matter there is (generally) as much of the electrical, as
it will contain within its substance. If more is added, it lies without
upon the surface, and forms what we call an electrical atmosphere: and then
the body is said to be electrified.
8. 'Tis supposed, that all kinds of common matter do not attract and retain
the electrical, with equal strength and force; for reasons to be given
hereafter. And that those called electrics _per se_, as glass, &c. attract
and retain it strongest, and contain the greatest quantity.
9. We know that the electrical fluid is _in_ common matter, because we can
pump it _out_ by the globe or tube. We know that common matter has near as
much as it can contain, because, when we add a little more to any protion
of it, the additional quantity does not enter, but forms an electrical
atmosphere. And we know that common matter has not (generally) more than it
can contain, otherwise all loose portions of it would repel each other, as
they constantly do when they have electric atmospheres.
10. The beneficial uses of this electrical fluid in the creation, we are
not yet well acquainted with, though doubtless such there are, and those
very considerable; but we may see some pernicious consequences, that would
attend a much greater proportion of it. For had this globe we live on as
much of it in proportion, as we can give to a globe of iron, wood, or the
like, the particles of dust and other light matters that get loose from it,
would, by virtue of their separate electrical atmospheres, not only repel
each other, but be repelled from the earth, and not easily be brought to
unite with it again; whence our air would continually be more and more
clogged with foreign matter, and grow unfit for respiration. This affords
another occasion of adoring that wisdom which has made all things by weight
and measure!
11. If a piece of common matter be supposed intirely free from electrical
matter, and a single particle of the latter be brought nigh, 'twill be
attracted and enter the body, and take place in the center, or where the
attraction is every way equal. If more particles enter, they take their
places where the balance is equal between the attraction of the common
matter and their own mutual repulsion. 'Tis supposed they form triangles,
whose sides shorten as their number increases; 'till the common matter has
drawn in so many, that its whole power of compressing those triangles by
attraction, is equal to their whole power of expanding themselves by
repulsion; and then will such piece of matter receive no more.
12. When part of this natural proportion of electrical fluid, is taken out
of a piece of common matter, the triangles formed by the remainder, are
supposed to widen by the mutual repulsion of the parts, until they occupy
the whole piece.
13. When the quantity of electrical fluid taken from a piece of common
matter is restored again, it enters, the expanded triangles being again
compressed till there is room for the whole.
14. To explain this: take two apples, or two balls of wood or other matter,
each having its own natural quantity of the electrical fluid. Suspend them
by silk lines from the ceiling. Apply the wire of a well-charged vial, held
in your hand, to one of them (A) Fig. 7. and it will receive from the wire
a quantity of the electrical fluid; but will not imbibe it, being already
full. The fluid therefore will flow round its surface, and form an
electrical atmosphere. Bring A into contact with B, and half the electrical
fluid is communicated, so that each has now an electrical atmosphere, and
therefore they repel each other. Take away these atmospheres by touching
the balls, and leave them in their natural state: then, having fixed a
stick of sealing wax to the middle of the vial to hold it by, apply the
wire to A, at the same time the coating touches B. Thus will a quantity of
the electrical fluid be drawn out of B, and thrown on A. So that A will
have a redundance of this fluid, which forms an atmosphere round it, and B
an exactly equal deficiency. Now bring these balls again into contact, and
the electrical atmosphere will not be divided between A and B, into two
smaller atmospheres as before; for B will drink up the whole atmosphere of
A, and both will be found again in their natural state.
15. The form of the electrical atmosphere is that of the body it surrounds.
This shape may be rendered visible in a still air, by raising a smoke from
dry rosin, dropt into a hot tea-spoon under the electrised body, which will
be attracted and spread itself equaly on all sides, covering and concealing
the body. And this form it takes, because it is attracted by all parts of
the surface of the body, tho' it cannot enter the substance already
replete. Without this attraction it would not remain round the body, but
dissipate in the air.
16. The atmosphere of electrical particles surrounding an electrified
sphere, is not more disposed to leave it or more easily drawn off from any
one part of the sphere than from another, because it is equally attracted
by every part. But that is not the case with bodies of any other figure.
From a cube it is more easily drawn at the corners than at the plane sides,
and so from the angles of a body of any other form, and still most easily
from the angle that is most acute. Thus if a body shaped as A, B, C, D, E,
in Fig. 8, be electrified, or have an electrical atmosphere communicated to
it, and we consider every side as a base on which the particles rest and by
which they are attracted, one may see, by imagining a line from A to F, and
another from E to G, that the portion of the atmosphere included in F, A,
E, G, has the line A, E, for its basis. So the portion of atmosphere
included in H, A, B, I, has the line A, B, for its basis. And likewise the
portion included in K, B, C, L, has B, C, to rest on; and so on the other
side of the figure. Now if you would draw off this atmosphere with any
blunt smooth body, and approach the middle of the side A, B, you must come
very near before the force of your attracter exceeds the force or power
with which that side holds its atmosphere. But there is a small portion
between I, B, K, that has less of the surface to rest on, and to be
attracted by, than the neighbouring portions, while at the same time there
is a mutual repulsion between its particles and the particles of those
portions, therefore here you can get it with more ease or at a greater
distance. Between F, A, H, there is a larger portion that has yet a less
surface to rest on and to attract it; here therefore you can get it away
still more easily. But easiest of all between L, C, M, where the quantity
is largest, and the surface to attract and keep it back the least. When you
have drawn away one of these angular portions of the fluid, another
succeeds in its place, from the nature of fluidity and the mutual repulsion
beforementioned; and so the atmosphere continues flowing off at such angle,
like a stream, till no more is remaining. The extremities of the portions
of atmosphere over these angular parts are likewise at a greater distance
from the electrified body, as may be seen by the inspection of the above
figure; the point of the atmosphere of the angle C, being much farther from
C, than any other part of the atmosphere over the lines C, B, or B, A: And
besides the distance arising from the nature of the figure, where the
attraction is less, the particles will naturally expand to a greater
distance by their mutual repulsion. On these accounts we suppose
electrified bodies discharge their atmospheres upon unelectrified bodies
more easily and at a greater distance from their angles and points than
from their smooth sides.--Those points will also discharge into the air,
when the body has too great an electrical atmosphere, without bringing any
non-electric near, to receive what is thrown off: For the air, though an
electric _per se_, yet has always more or less water and other non-electric
matters mixed with it; and these attract and receive what is so discharged.
17. But points have a property, by which they _draw on_ as well as _throw
off_ the electrical fluid, at greater distances than blunt bodies can. That
is, as the pointed part of an electrified body will discharge the
atmosphere of that body, or communicate it farthest to another body, so the
point of an unelectrified body, will draw off the electrical atmosphere
from an electrified body, farther than a blunter part of the same
unelectrified body will do. Thus a pin held by the head, and the point
presented to an electrified body, will draw off its atmosphere at a foot
distance; where if the head were presented instead of the point, no such
effect would follow. To understand this, we may consider, that if a person
standing on the floor would draw off the electrical atmosphere from an
electrified body, an iron crow and a blunt knitting kneedle held
alternately in his hand and presented for that purpose, do not draw with
different forces in proportion to their different masses. For the man, and
what he holds in his hand, be it large or small, are connected with the
common mass of unelectrified matter; and the force with which he draws is
the same in both cases, it consisting in the different proportion of
electricity in the electrified body and that common mass. But the force
with which the electrified body retains its atmosphere by attracting it, is
proportioned to the surface over which the particles are placed; i.e. four
square inches of that surface retain their atmosphere with four times the
force that one square inch retains its atmosphere. And as in plucking the
hairs from the horse's tail, a degree of strength insufficient to pull away
a handful at once, could yet easily strip it hair by hair; so a blunt body
presented cannot draw off a number of particles at once, but a pointed one,
with no greater force, takes them away easily, particle by particle.
18. These explanations of the power and operation of points, when they
first occurr'd to me, and while they first floated in my mind, appeared
perfectly satisfactory; but now I have wrote them, and consider'd them more
closely in black and white, I must own I have some doubts about them: yet
as I have at present nothing better to offer in their stead, I do not cross
them out: for even a bad solution read, and its faults discover'd, has
often given rise to a good one in the mind of an ingenious reader.
19. Nor is it of much importance to us, to know the manner in which nature
executes her laws; 'tis enough if we know the laws themselves. 'Tis of real
use to know, that china left in the air unsupported will fall and break;
but _how_ it comes to fall, and _why_ it breaks, are matters of
speculation. 'Tis a pleasure indeed to know them, but we can preserve our
china without it.
20. Thus in the present case, to know this power of points, may possibly be
of some use to mankind, though we should never be able to explain it. The
following experiments, as well as those in my first paper, show this power.
I have a large prime conductor made of several thin sheets of Fuller's
pasteboard form'd into a tube, near 10 feet long and a foot diameter. It is
cover'd with _Dutch_ emboss'd paper, almost totally gilt. This large
metallic surface supports a much greater electrical atmosphere than a rod
of iron of 50 times the weight would do. It is suspended by silk lines, and
when charg'd will strike at near two inches distance, a pretty hard stroke
so as to make one's knuckle ach. Let a person standing on the floor present
the point of a needle at 12 or more inches distance from it, and while the
needle is so presented, the conductor cannot be charged, the point drawing
off the fire as fast as it is thrown on by the electrical globe. Let it be
charged, and then present the point at the same distance, and it will
suddenly be discharged. In the dark you may see a light on the point, when
the experiment is made. And if the person holding the point stands upon
wax, he will be electrified by receiving the fire at that distance. Attempt
to draw off the electricity with a blunt body, as a bolt of iron round at
the end and smooth (a silversmith's iron punch, inch-thick, is what I use)
and you must bring it within the distance of three inches before you can do
it, and then it is done with a stroke and crack. As the pasteboard tube
hangs loose on silk lines, when you approach it with the punch iron, it
likewise will move towards the punch, being attracted while it is charged;
but if at the same instant a point be presented as before, it retires
again, for the point discharges it. Take a pair of large brass scales, of
two or more feet beam, the cords of the scales being silk. Suspend the beam
by a packthread from the cieling, so that the bottom of the scales may be
about a foot from the floor: The scales will move round in a circle by the
untwisting of the packthread. Set the iron punch on the end upon the floor,
in such a place as that the scales may pass over it in making their circle:
Then electrify one scale by applying the wire of a charged phial to it. As
they move round, you see that scale draw nigher to the floor, and dip more
when it comes over the punch; and if that be placed at a proper distance,
the scale will snap and discharge its fire into it. But if a needle be
stuck on the end of the punch, its point upwards, the scale, instead of
drawing nigh to the punch and snapping, discharges its fire silently
through the point, and rises higher from the punch. Nay, even if the needle
be placed upon the floor near the punch, its point upwards, the end of the
punch, tho' so much higher than the needle, will not attract the scale and
receive its fire, for the needle will get it and convey it away, before it
comes nigh enough for the punch to act. And this is constantly observable
in these experiments, that the greater quantity of electricity on the
pasteboard tube, the farther it strikes or discharges its fire, and the
point likewise will draw it off at a still greater distance.
Now if the fire of electricity and that of lightening be the same, as I
have endeavour'd to show at large in a former paper, this pasteboard tube
and these scales may represent electrified clouds. If a tube of only 10
feet long will strike and discharge its fire on the punch at two or three
inches distance, an electrified cloud of perhaps 10,000 acres, may strike
and discharge on the earth at a proportionably greater distance. The
horizontal motion of the scales over the floor, may represent the motion of
the clouds over the earth; and the erect iron punch, a hill or high
building; and then we see how electrified clouds passing over hills or high
buildings at too great a height to strike, may be attracted lower till
within their striking distance. And lastly, if a needle fix'd on the punch
with its point upright, or even on the floor below the punch, will draw the
fire from the scale silently at a much greater than the striking distance,
and so prevent its descending towards the punch; or if in its course it
would have come nigh enough to strike, yet being first deprived of its fire
it cannot, and the punch is thereby secured from the stroke. I say, if
these things are so, may not the knowledge of this power of points be of
use to mankind, in preserving houses, churches, ships, &c. from the stroke
of lightning, by directing us to fix on the highest parts of those
edifices, upright rods of iron made sharp as a needle, and gilt to prevent
rusting, and from the foot of those rods a wire down the outside of the
building into the ground, or down round one of the shrouds of a ship, and
down her side till it reaches the water? Would not these pointed rods
probably draw the electrical fire silently out of a cloud before it came
nigh enough to strike, and thereby secure us from that most sudden and
terrible mischief?
21. To determine the question, whether the clouds that contain lightning
are electrified or not, I would propose an experiment to be try'd where it
may be done conveniently. On the top of some high tower or steeple, place a
kind of sentry-box, (as in FIG. 9.) big enough to contain a man and an
electrical stand. From the middle of the stand, let an iron rod rise and
pass bending out of the door, and then upright 20 or 30 feet, pointed very
sharp at the end. If the electrical stand be kept clean and dry, a man
standing on it when such clouds are passing low, might be electrified and
afford sparks, the rod drawing fire to him from a cloud. If any danger to
the man should be apprehended (though I think there would be none) let him
stand on the floor of his box, and now and then bring near to the rod, the
loop of a wire that has one end fastened to the leads, he holding it by a
wax handle; so the sparks, if the rod is electrified, will strike from the
rod to the wire, and not affect him.
22. Before I leave this subject of lightning, I may mention some other
similarities between the effects of that, and these of electricity.
Lightning has often been known to strike people blind. A pigeon that we
struck dead to appearance by the electrical shock, recovering life, droop'd
about the yard several days, eat nothing though crumbs were thrown to it,
but declined and died. We did not think of its being deprived of sight; but
afterwards a pullet struck dead in like manner, being recovered by
repeatedly blowing into its lungs, when set down on the floor, ran headlong
against the wall, and on examination appeared perfectly blind. Hence we
concluded that the pigeon also had been absolutely blinded by the shock.
The biggest animal we have yet killed or try'd to kill with the electrical
stroke, was a well-grown pullet.
23. Reading in the ingenious Dr. _Hales_'s account of the thunder storm at
_Stretham_, the effect of the lightning in stripping off all the paint that
had covered a gilt moulding of a pannel of wainscot, without hurting the
rest of the paint, I had a mind to lay a coat of paint over the filleting
of gold on the cover of a book, and try the effect of a strong electrical
flash sent through that gold from a charged sheet of glass. But having no
paint at hand, I pasted a narrow strip of paper over it; and when dry, sent
the flash through the gilding; by which the paper was torn off from end to
end, with such force, that it was broke in several places, and in others
brought away part of the grain of the Turky-leather in which it was bound;
and convinced me, that had it been painted, the paint would have been
stript off in the same manner with that on the wainscot at _Stretham_.
24. Lightning melts metals, and I hinted in my paper on that subject, that
I suspected it to be a cold fusion; I do not mean a fusion by force of
cold, but a fusion without heat. We have also melted gold, silver, and
copper, in small quantities, by the electrical flash. The manner is this:
Take leaf gold, leaf silver, or leaf gilt copper, commonly called leaf
brass or _Dutch_ gold: cut off from the leaf long narrow strips the breadth
of a straw. Place one of these strips between two strips of smooth glass
that are about the width of your finger. If one strip of gold, the length
of the leaf, be not long enough for the glass, add another to the end of
it, so that you may have a little part hanging out loose at each end of the
glass. Bind the pieces of glass together from end to end with strong silk
thread; then place it so as to be part of an electrical circle, (the ends
of gold hanging out being of use to join with the other parts of the
circle) and send the flash through it, from a large electrified jar or
sheet of glass. Then if your strips of glass remain whole, you will see
that the gold is missing in several places, and instead of it a metallic
stain on both the glasses; the stains on the upper and under glass exactly
similar in the minutest stroke, as may be seen by holding them to the
light; the metal appeared to have been not only melted, but even vitrified,
or otherwise so driven into the pores of the glass, as to be protected by
it from the action of the strongest _Aqua Fortis_ and _Ag: Regia_. I send
you enclosed two little pieces of glass with these metallic stains upon
them, which cannot be removed without taking part of the glass with them.
Sometimes the stain spreads a little wider than the breadth of the leaf,
and looks brighter at the edge, as by inspecting closely you may observe in
these. Sometimes the glass breaks to pieces: once the upper glass broke
into a thousand pieces, looking like coarse salt. These pieces I send you,
were stain'd with _Dutch_ gold. True gold makes a darker stain, somewhat
reddish; silver, a greenish stain. We once took two pieces of thick
looking-glass, as broad as a Gunter's scale, and 6 inches long; and placing
leaf gold between them, put them betwixt two smoothly plain'd pieces of
wood, and fix'd them tight in a book-binder's small press; yet though they
were so closely confined, the force of the electrical shock shivered the
glass into many pieces. The gold was melted and stain'd into the glass as
usual. The circumstances of the breaking of the glass differ much in making
the experiment, and sometimes it does not break at all: but this is
constant, that the stains in the upper and under pieces are exact
counterparts of each other. And though I have taken up the pieces of glass
between my fingers immediately after this melting, I never could perceive
the least warmth in them.
25. In one of my former papers, I mention'd, that gilding on a book, though
at first it communicated the shock perfectly well, yet fail'd after a few
experiments, which we could not account for. We have since found, that one
strong shock breaks the continuity of the gold in the filleting, and makes
it look rather like dust of gold, abundance of its parts being broken and
driven off; and it will seldom conduct above one strong shock. Perhaps this
may be the reason; when there is not a perfect continuity in the circle,
the fire must leap over the vacancies; there is a certain distance which it
is able to leap over according to its strength; if a number of small
vacancies, though each be very minute, taken together exceed that distance,
it cannot leap over them, and so the shock is prevented.