_Opinions and Conjectures, concerning the Properties and
Effects of the electrical Matter, and the Means of preserving
Buildings, Ships, &c. from Lightning, arising from Experiments and
Observations made at Philadelphia, 1749.--Golden Fish.--Extraction
of effluvial Virtues by Electricity impracticable._
§ 1. The electrical matter consists of particles extremely subtile
since 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
through the substance of bodies, or only over and along their
surfaces, a shock from an electrified large glass jar, taken through
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 though the particles of electrical matter do repel each other,
they are strongly attracted by all other matter[48].
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 hath 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. It is 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 portion 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 electric 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 entirely free from
electrical matter, and a single particle of the latter be brought
nigh, it will be attracted, and enter the body, and take place in the
centre, 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. It
is supposed they form triangles, whose sides shorten as their number
encreases; 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 cieling. 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, 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
electrified body, which will be attracted, and spread itself equally
on all sides, covering and concealing the body[49]. And this form it
takes, because it is attracted by all parts of the surface of the
body, though 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 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 before-mentioned;
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-needle 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 not sufficient 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 occurred to me, and while they first floated in my mind,
appeared perfectly satisfactory; but now I have written them, and
considered them more closely, 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 discovered, 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; it is enough if we know the laws
themselves. It is 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. It is 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 clothier's pasteboard, formed into a tube,
near ten feet long and a foot diameter. It is covered with Dutch
embossed-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 charged will strike, at near two inches distance, a pretty hard
stroke, so as to make ones 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 the 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 pack-thread
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 pack-thread. 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, though 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 lightning be the same,
as I have endeavoured to shew at large, in a former paper, this
pasteboard tube and these scales may represent electrified clouds.
If a tube of only ten 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 fixed 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 tried where it may be done conveniently. On the top of some high
tower or steeple, place a kind of centry-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 those 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, drooped 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 tried to kill, with the electrical
stroke, was a well-grown pullet.
23. Reading in the ingenious Dr. Miles'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 filletting 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[50]. 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 circuit, (the
ends of gold hanging out being of use to join with the other parts of
the circuit) 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_, or _aqua 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.
The pieces I send you were stained 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 six inches long; and placing leaf-gold between them, put them
between two smoothly-plained pieces of wood, and fixed 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 stained 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 mentioned, that gilding on a
book, though at first it communicated the shock perfectly well, yet
failed 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 filletting, 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 circuit,
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.
26. From the before-mentioned law of electricity, that points as
they are more or less acute, draw on and throw off the electrical
fluid with more or less power, and at greater or less distances, and
in larger or smaller quantities in the same time, we may see how
to account for the situation of the leaf of gold suspended between
two plates, the upper one continually electrified, the under one
in a person's hand standing on the floor. When the upper plate is
electrified, the leaf is attracted, and raised towards it, and
would fly to that plate, were it not for its own points. The corner
that happens to be uppermost when the leaf is rising, being a sharp
point, from the extreme thinness of the gold, draws and receives
at a distance a sufficient quantity of the electric fluid to give
itself an electric atmosphere, by which its progress to the upper
plate is stopped, and it begins to be repelled from that plate, and
would be driven back to the under plate, but that its lowest corner
is likewise a point, and throws off or discharges the overplus of
the leaf's atmosphere, as fast as the upper corner draws it on.
Were these two points perfectly equal in acuteness, the leaf would
take place exactly in the middle space, for its weight is a trifle
compared to the power acting on it: but it is generally nearest
the unelectrified plate, because, when the leaf is offered to the
electrified plate, at a distance, the sharpest point is commonly
first affected and raised towards it; so _that_ point, from its
greater acuteness, receiving the fluid faster than its opposite can
discharge it at equal distances, it retires from the electrified
plate, and draws nearer to the unelectrified plate, till it comes to
a distance where the discharge can be exactly equal to the receipt,
the latter being lessened, and the former encreased; and there it
remains as long as the globe continues to supply fresh electrical
matter. This will appear plain, when the difference of acuteness in
the corners is made very great. Cut a piece of Dutch gold, (which
is fittest for these experiments on account of its great strength)
into the form of FIG. 10, the upper corner a right angle, the two
next obtuse angles, and the lowest a very acute one; and bring this
on your plate under the electrified plate, in such a manner as
that the right-angled part may be first raised (which is done by
covering the acute part with the hollow of your hand) and you will
see this leaf take place much nearer to the upper than the under
plate; because without being nearer, it cannot receive so fast at
its right-angled point, as it can discharge at its acute one. Turn
this leaf with the acute part uppermost, and then it takes place
nearest the unelectrified plate; because, otherwise, it receives
faster at its acute point, than it can discharge at its right-angled
one. Thus the difference of distance is always proportioned to the
difference of acuteness. Take care in cutting your leaf, to leave no
little ragged particles on the edges, which sometimes form points
where you would not have them. You may make this figure so acute
below, and blunt above, as to need no under plate, it discharging
fast enough into the air. When it is made narrower, as the figure
between the pricked lines, we call it the _golden fish_, from its
manner of acting. For if you take it by the tail, and hold it at a
foot or greater horizontal distance from the prime conductor, it
will, when let go, fly to it with a brisk but wavering motion, like
that of an eel through the water; it will then take place under the
prime conductor, at perhaps a quarter or half an inch distance, and
keep a continual shaking of its tail like a fish, so that it seems
animated. Turn its tail towards the prime conductor, and then it
flies to your finger, and seems to nibble it. And if you hold a plate
under it at six or eight inches distance, and cease turning the globe
when the electrical atmosphere of the conductor grows small, it will
descend to the plate and swim back again several times with the same
fish-like motion, greatly to the entertainment of spectators. By a
little practice in blunting or sharpening the heads or tails of these
figures, you may make them take place as desired, nearer or farther
from the electrified plate.
27. It is said in Section 8, of this paper, that all kinds of common
matter are supposed not to attract the electrical fluid with equal
strength; and that those called electrics _per se_, as glass, &c.
attract and retain it strongest, and contain the greatest quantity.
This latter position may seem a paradox to some, being contrary to
the hitherto received opinion; and therefore I shall now endeavour to
explain it.
28. In order to this, let it first be considered, _that we cannot
by any means we are yet acquainted with, force the electrical fluid
through glass_. I know it is commonly thought that it easily pervades
glass; and the experiment of a feather suspended by a thread, in
a bottle hermetically sealed, yet moved by bringing a rubbed tube
near the outside of the bottle, is alleged to prove it. But, if the
electrical fluid so easily pervades glass, how does the phial become
_charged_ (as we term it) when we hold it in our hands? Would not the
fire, thrown in by the wire, pass through to our hands, and so escape
into the floor? Would not the bottle in that case be left just as we
found it, uncharged, as we know a metal bottle so attempted to be
charged would be? Indeed, if there be the least crack, the minutest
solution of continuity in the glass, though it remains so tight that
nothing else we know of will pass, yet the extremely subtile electric
fluid flies through such a crack with the greatest freedom, and such
a bottle we know can never be charged: what then makes the difference
between such a bottle and one that is sound, but this, that the fluid
can pass through the one, and not through the other[51]?
29. It is true, there is an experiment that at first sight would
be apt to satisfy a slight observer, that the fire, thrown into
the bottle by the wire, does really pass through the glass. It is
this: place the bottle on a glass stand, under the prime conductor,
suspend a bullet by a chain from the prime conductor, till it comes
within a quarter of an inch right over the wire of the bottle; place
your knuckle on the glass stand, at just the same distance from
the coating of the bottle, as the bullet is from its wire. Now let
the globe be turned, and you see a spark strike from the bullet to
the wire of the bottle, and the same instant you see and feel an
exactly equal spark striking from the coating on your knuckle, and
so on, spark for spark. This looks as if the whole received by the
bottle was again discharged from it. And yet the bottle by this
means is charged[52]! And therefore the fire that thus leaves the
bottle, though the same in quantity, cannot be the very same fire
that entered at the wire, for if it were, the bottle would remain
uncharged.
30. If the fire that so leaves the bottle be not the same that is
thrown in through the wire, it must be fire that subsisted in the
bottle (that is, in the glass of the bottle) before the operation
began.
31. If so, there must be a great quantity in glass, because a great
quantity is thus discharged, even from very thin glass.
32. That this electrical fluid or fire is strongly attracted by
glass, we know from the quickness and violence with which it is
resumed by the part that had been deprived of it, when there is an
opportunity. And by this, that we cannot from a mass of glass, draw a
quantity of electric fire, or electrify the whole mass _minus_, as we
can a mass of metal. We cannot lessen or increase its whole quantity,
for the quantity it has it holds; and it has as much as it can hold.
Its pores are filled with it as full as the mutual repellency of the
particles will admit; and what is already in, refuses, or strongly
repels, any additional quantity. Nor have we any way of moving the
electrical fluid in glass, but one; that is, by covering part of the
two surfaces of thin glass with non-electrics, and then throwing an
additional quantity of this fluid on one surface, which spreading in
the non-electric, and being bound by it to that surface, acts by its
repelling force on the particles of the electrical fluid contained
in the other surface, and drives them out of the glass into the
non-electric on that side from whence they are discharged, and then
those added on the charged side can enter. But when this is done,
there is no more in the glass, nor less than before, just as much
having left it on one side as it received on the other.
33. I feel a want of terms here, and doubt much whether I shall be
able to make this part intelligible. By the word _surface_, in this
case, I do not mean mere length and breadth without thickness; but
when I speak of the upper or under surface of a piece of glass, the
outer or inner surface of the phial, I mean length, breadth, and
half the thickness, and beg the favour of being so understood. Now
I suppose, that glass in its first principles, and in the furnace,
has no more of this electrical fluid than other common matter: that
when it is blown, as it cools, and the particles of common fire leave
it, its pores become a vacuum: that the component parts of glass are
extremely small and fine, I guess from its never showing a rough
face when it breaks, but always a polish; and from the smallness of
its particles I suppose the pores between them must be exceedingly
small, which is the reason that aqua-fortis, nor any other menstruum
we have, can enter to separate them and dissolve the substance; nor
is any fluid we know of, fine enough to enter, except common fire,
and the electric fluid. Now the departing fire, leaving a vacuum, as
aforesaid, between these pores, which air nor water are fine enough
to enter and fill, the electric fluid (which is every where ready
in what we call the non-electrics, and in the non-electric mixtures
that are in the air) is attracted in; yet does not become fixed with
the substance of the glass, but subsists there as water in a porous
stone, retained only by the attraction of the fixed parts, itself
still loose and a fluid. But I suppose farther, that in the cooling
of the glass, its texture becomes closest in the middle, and forms
a kind of partition, in which the pores are so narrow, that the
particles of the electrical fluid, which enter both surfaces at the
same time, cannot go through, or pass and repass from one surface to
the other, and so mix together; yet, though the particles of electric
fluid, imbibed by each surface, cannot themselves pass through to
those of the other, their repellency can, and by this means they
act on one another. The particles of the electric fluid have a
mutual repellency, but by the power of attraction in the glass they
are condensed or forced nearer to each other. When the glass has
received, and, by its attraction, forced closer together so much of
this electric fluid, as that the power of attracting and condensing
in the one, is equal to the power of expansion in the other, it can
imbibe no more, and that remains its constant whole quantity; but
each surface would receive more, if the repellency of what is in
the opposite surface did not resist its entrance. The quantities of
this fluid in each surface being equal, their repelling action on
each other is equal; and therefore those of one surface cannot drive
out those of the other; but, if a greater quantity is forced into
one surface than the glass would naturally draw in, this increases
the repelling power on that side, and overpowering the attraction
on the other, drives out part of the fluid that had been imbibed by
that surface, if there be any non-electric ready to receive it: such
there is in all cases where glass is electrified to give a shock.
The surface that has been thus emptied, by having its electrical
fluid driven out, resumes again an equal quantity with violence, as
soon as the glass has an opportunity to discharge that over quantity
more than it could retain by attraction in its other surface, by the
additional repellency of which the vacuum had been occasioned. For
experiments favouring (if I may not say confirming) this hypothesis,
I must, to avoid repetition, beg leave to refer you back to what is
said of the electrical phial in my former papers.
34. Let us now see how it will account for several other
appearances.--Glass, a body extremely elastic, (and perhaps its
elasticity may be owing in some degree to the subsisting of so great
a quantity of this repelling fluid in its pores) must, when rubbed,
have its rubbed surface somewhat stretched, or its solid parts
drawn a little farther asunder, so that the vacancies in which the
electrical fluid resides, become larger, affording room for more of
that fluid, which is immediately attracted into it from the cushion
or hand rubbing, they being supplied from the common stock. But the
instant the parts of the glass so opened and filled, have passed the
friction, they close again, and force the additional quantity out
upon the surface, where it must rest till that part comes round to
the cushion again, unless some non-electric (as the prime conductor,
first presents to receive it[53]). But if the inside of the globe
be lined with a non-electric, the additional repellency of the
electrical fluid, thus collected by friction on the rubbed part
of the globe's outer surface, drives an equal quantity out of the
inner surface into that non-electric lining, which receiving it, and
carrying it away from the rubbed part into the common mass, through
the axis of the globe, and frame of the machine, the new collected
electrical fluid can enter and remain in the outer surface, and none
of it (or a very little) will be received by the prime conductor. As
this charged part of the globe comes round to the cushion again,
the outer surface delivers its overplus fire into the cushion, the
opposite inner surface receiving at the same time an equal quantity
from the floor. Every electrician knows that a globe wet within
will afford little or no fire, but the reason has not before been
attempted to be given, that I know of.
34. So if a tube lined with a non-electric be rubbed[54], little or
no fire is obtained from it; what is collected from the hand, in the
downward rubbing stroke, entering the pores of the glass, and driving
an equal quantity out of the inner surface into the non-electric
lining: and the hand in passing up to take a second stroke, takes out
again what had been thrown into the outer surface, and then the inner
surface receives back again what it had given to the non-electric
lining. Thus the particles of electrical fluid belonging to the
inside surface go in and out of their pores every stroke given to the
tube. Put a wire into the tube, the inward end in contact with the
non-electric lining, so it will represent the Leyden bottle. Let a
second person touch the wire while you rub, and the fire driven out
of the inward surface when you give the stroke, will pass through him
into the common mass, and return through him when the inner surface
resumes its quantity, and therefore this new kind of Leyden bottle
cannot be so charged. But thus it may: after every stroke, before
you pass your hand up to make another, let a second person apply his
finger to the wire, take the spark, and then withdraw his finger;
and so on till he has drawn a number of sparks; thus will the inner
surface be exhausted, and the outer surface charged; then wrap a
sheet of gilt paper close round the outer surface, and grasping it
in your hand you may receive a shock by applying the finger of the
other hand to the wire: for now the vacant pores in the inner surface
resume their quantity, and the overcharged pores in the outer surface
discharge that overplus; the equilibrium being restored through your
body, which could not be restored through the glass[55]. If the tube
be exhausted of air, a non-electric lining, in contact with the
wire, is not necessary; for _in vacuo_ the electrical fire will fly
freely from the inner surface, without a non-electric conductor: but
air resists in motion; for being itself an electric _per se_, it
does not attract it, having already its quantity. So the air never
draws off an electric atmosphere from any body, but in proportion to
the non-electrics mixed with it: it rather keeps such an atmosphere
confined, which, from the mutual repulsion of its particles, tends to
dissipation, and would immediately dissipate _in vacuo_.--And thus
the experiment of the feather inclosed in a glass vessel hermetically
sealed, but moving on the approach of the rubbed tube, is explained.
When an additional quantity of the electrical fluid is applied to
the side of the vessel by the atmosphere of the tube, a quantity
is repelled and driven out of the inner surface of that side into
the vessel, and there affects the feather, returning again into its
pores, when the tube with its atmosphere is withdrawn; not that the
particles of that atmosphere did themselves pass through the glass to
the feather. And every other appearance I have yet seen, in which
glass and electricity are concerned, are, I think, explained with
equal ease by the same hypothesis. Yet, perhaps, it may not be a true
one, and I shall be obliged to him that affords me a better.
35. Thus I take the difference between non-electrics, and glass, an
electric _per se_, to consist in these two particulars. 1st, That a
non-electric easily suffers a change in the quantity of the electric
fluid it contains. You may lessen its whole quantity, by drawing
out a part, which the whole body will again resume; but of glass
you can only lessen the quantity contained in one of its surfaces;
and not that, but by supplying an equal quantity at the same time
to the other surface: so that the whole glass may always have the
same quantity in the two surfaces, their two different quantities
being added together. And this can only be done in glass that is
thin; beyond a certain thickness we have yet no power that can make
this change. And, 2dly, that the electric fire freely removes from
place to place, in and through the substance of a non-electric, but
not so through the substance of glass. If you offer a quantity to
one end of a long rod of metal, it receives it, and when it enters,
every particle that was before in the rod pushes its neighbour quite
to the farther end, where the overplus is discharged; and this
instantaneously where the rod is part of the circle in the experiment
of the shock. But glass, from the smallness of its pores, or stronger
attraction of what it contains, refuses to admit so free a motion:
a glass rod will not conduct a shock, nor will the thinnest glass
suffer any particle entering one of its surfaces to pass through to
the other.
36. Hence we see the impossibility of success in the experiments
proposed, to draw out the effluvial virtues of a non-electric, as
cinnamon, for instance, and mixing them with the electric fluid, to
convey them with that into the body, by including it in the globe,
and then applying friction, &c. For though the effluvia of cinnamon,
and the electric fluid should mix within the globe, they would never
come out together through the pores of the glass, and so go to the
prime conductor; for the electric fluid itself cannot come through;
and the prime conductor is always supplied from the cushion, and that
from the floor. And besides, when the globe is filled with cinnamon,
or other non-electric, no electric fluid can be obtained from its
outer surface, for the reason before-mentioned. I have tried another
way, which I thought more likely to obtain a mixture of the electric
and other effluvia together, if such a mixture had been possible. I
placed a glass plate under my cushion, to cut off the communication
between the cushion and floor; then brought a small chain from the
cushion into a glass of oil of turpentine, and carried another chain
from the oil of turpentine to the floor, taking care that the chain
from the cushion to the glass, touched no part of the frame of the
machine. Another chain was fixed to the prime conductor, and held in
the hand of a person to be electrified. The ends of the two chains
in the glass were near an inch distant from each other, the oil of
turpentine between. Now the globe being turned could draw no fire
from the floor through the machine, the communication that way being
cut off by the thick glass plate under the cushion: it must then
draw it through the chains whose ends were dipped in the oil of
turpentine. And as the oil of turpentine, being an electric _per
se_, would not conduct, what came up from the floor was obliged to
jump from the end of one chain to the end of the other, through the
substance of that oil, which we could see in large sparks, and so
it had a fair opportunity of seizing some of the finest particles
of the oil in its passage, and carrying them off with it: but no
such effect followed, nor could I perceive the least difference in
the smell of the electric effluvia thus collected, from what it has
when collected otherwise, nor does it otherwise affect the body
of a person electrised. I likewise put into a phial, instead of
water, a strong purgative liquid, and then charged the phial, and
took repeated shocks from it, in which case every particle of the
electrical fluid must, before it went through my body, have first
gone through the liquid when the phial is charging, and returned
through it when discharging, yet no other effect followed than if
it had been charged with water. I have also smelt the electric fire
when drawn through gold, silver, copper, lead, iron, wood, and the
human body, and could perceive no difference: the odour is always the
same, where the spark does not burn what it strikes; and therefore I
imagine it does not take that smell from any quality of the bodies
it passes through. And indeed, as that smell so readily leaves the
electric matter, and adheres to the knuckle receiving the sparks, and
to other things; I suspect that it never was connected with it, but
arises instantaneously from something in the air acted upon by it.
For if it was fine enough to come with the electric fluid through the
body of one person, why should it stop on the skin of another?
But I shall never have done, if I tell you all my conjectures,
thoughts, and imaginations on the nature and operations of this
electric fluid, and relate the variety of little experiments we
have tried. I have already made this paper too long, for which I
must crave pardon, not having now time to abridge it. I shall only
add, that as it has been observed here that spirits will fire by
the electric spark in the summer time, without heating them, when
Fahrenheit's thermometer is above 70; so when colder, if the operator
puts a small flat bottle of spirits in his bosom, or a close pocket,
with the spoon, some little time before he uses them, the heat of his
body will communicate warmth more than sufficient for the purpose.