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EXPERIMENTS
AND
OBSERVATIONS
ON
ELECTRICITY,
MADE AT
Philadelphia in
America,
BY
Mr. BENJAMIN
FRANKLIN,
AND
Communicated in several Letters to Mr. P. Collinson,
of London, F. R. S.
LONDON:
Printed and sold by E. Cave, at St. John's Gate.
(Price 2s. 6d.)
The PREFACE.
It may be necessary to acquaint the reader, that the following observations and experiments
were not drawn up with a view to their being made publick, but were communicated at different
times, and most of them in letters wrote on various topicks, as matters only of private
amusement.
But some persons to whom they were read, and who had themselves been conversant in
electrical disquisitions, were of opinion, they contain'd so many curious and interesting
particulars relative to this affair, that it would be doing a kind of injustice to the publick, to
confine them solely to the limits of a private acquaintance.
The Editor was therefore prevailed upon to commit such extracts of letters, and other
detach'd pieces as were in his hands to the press, without waiting for the ingenious author's
permission so to do; and this was done with the less hesitation, as it was apprehended the
author's engagements in other affairs, would scarce afford him leisure to give the publick his
reflections and experiments on the subject, finish'd with that care and precision, of which the
treatise before us shews he is alike studious and capable. He was only apprized of the step that
had been thus taken, while the first sheets were in the press, and time enough for him to transmit
some farther remarks, together with a few corrections and additions, which are placed at the end,
and may be consulted in the perusal.
The experiments which our author relates are most of them peculiar to himself; they are
conducted with judgment, and the inferences from them plain and conclusive; though sometimes
proposed under the terms of suppositions and conjectures.
And indeed the scene he opens, strikes us with a pleasing astonishment, whilst he conducts
us by a train of facts and judicious reflections, to a probable cause of those phænomena, which
are at once the most awful, and, hitherto, accounted for with the least verisimilitude.
He exhibits to our consideration, an invisible, subtile matter, disseminated through all
nature in various proportions, equally unobserved, and, whilst all those bodies to which it
peculiarly adheres are alike charged with it, inoffensive.
He shews, however, that if an unequal distribution is by any means brought about; if there
is a coacervation in one part of space, a less proportion, vacuity, or want, in another; by the
near approach of a body capable of conducting the coacervated part to the emptier space, it
becomes perhaps the most formidable and irresistible agent in the universe. Animals are in an
Instant struck breathless, bodies almost impervious by any force yet known, are perforated, and
metals fused by it, in a moment.
From the similar effects of lightening and electricity our author has been led to make some
propable conjectures on the cause of the former; and at the same time, to propose some rational
experiments in order to secure ourselves, and those things on which its force is often directed,
from its pernicious effects; a circumstance of no small importance to the publick, and therefore
worthy of the utmost attention.
It has, indeed, been of late the fashion to ascribe every grand or unusual operation of
nature, such as lightening and earthquakes, to electricity; not, as one would imagine, from the
manner of reasoning on these occasions, that the authors of these schemes have, discovered any
connection betwixt the cause and effect, or saw in what manner they were related; but, as it would
seem, merely because they were unacquainted with any other agent, of which it could not positively
be said the connection was impossible.
But of these, and many other interesting circumstances, the reader will be more
satisfactorily informed in the following letters, to which he is therefore referred by
The EDITOR.
{1}
LETTER I.
FROM
Mr Benj.
Franklin, in Philadelphia.
TO
Mr Peter
Collinson, F.R.S. London.
July 28, 1747.
SIR,
THE necessary trouble of copying long
letters, which perhaps when they come to your hands may contain nothing new, or worth your reading
(so quick is the progress made with you in Electricity) half discourages me from writing any more
on that subject. Yet I cannot forbear adding a few observations on M. Muschenbroek's
wonderful bottle.
{2}
The non-electric contain'd in the bottle differs when electrised from a non-electric
electrised out of the bottle, in this: that the electrical fire of the latter is accumulated on
its surface, and forms an electrical atmosphere round it of considerable extent: but the
electrical fire is crouded into the substance of the former, the glass confining it.
At the same time that the wire and top of the bottle, &c. is electrised
positively or plus, the bottom of the bottle is electrised negatively or
minus, in exact proportion: i. e. whatever quantity of electrical fire is thrown in
at top, an equal quantity goes out of the bottom. To understand this, suppose the common quantity
of Electricity in each part of the bottle, before the operation begins, is equal to 20; and at
every stroke of the tube, suppose a quantity equal to 1 is thrown in; then, after the first
stroke, the quantity contain'd in the wire and upper part of the bottle will be 21, in the bottom
After the second, the upper part will have 22, the lower 18, and so on 'till after 20 strokes,
the upper part will have a quantity of electrical fire equal to 40, the lower part none: and then
the operation ends: for no more can be thrown into the upper part, when no more can be driven out
of the lower part. If you attempt to throw more in, it is spued back thro' the wire, or flies out
in loud cracks thro' the sides of the bottle.
The equilibrium cannot be restored in the bottle by inward communication or contact
of the parts; but it must be done by a communication formed without the {3}bottle, between the top and bottom, by some non-electric,
touching both at the same time; in which case it is restored with a violence and quickness
inexpressible: or, touching each alternately, in which case the equilibrium is restored by
degrees.
As no more electrical fire can be thrown into the top of the bottle, when all is driven out
of the bottom, so in a bottle not yet electrised, none can be thrown into the top, when none
can get out at the bottom; which happens either when the bottom is too thick, or when the
bottle is placed on an electric per se. Again, when the bottle is electrised, but little of
the electrical fire can be drawn out from the top, by touching the wire, unless an equal
quantity can at the same time get in at the bottom. Thus, place an electrised bottle on
clean glass or dry wax, and you will not, by touching the wire, get out the fire from the top.
Place it on a non-electric, and touch the wire, you will get it out in a short time; but soonest
when you form a direct communication as above.
So wonderfully are these two states of Electricity, the plus and minus, combined
and balanced in this miraculous bottle! situated and related to each other in a manner that I can
by no means comprehend! If it were possible that a bottle should in one part contain a quantity of
air strongly comprest, and in another part a perfect vacuum, we know the equilibrium would be
instantly restored within. But here we have a bottle containing at the same time a
plenum of electrical fire, and a vacuum of the same fire; and yet {4}the equilibrium cannot be restored between them but by a
communication without! though the plenum presses violently to expand, and the hungry
vacuum seems to attract as violently in order to be filled.
Experiments confirming the
above.
EXPERIMENT I.
Place an electrised phial on wax; a small cork-ball suspended by a dry silk-thread held in your
hand, and brought near to the wire, will first be attracted, and then repelled: when in this state
of repellency, sink your hand, that the ball may be brought towards the bottom of {5}the bottle; it will there be instantly and strongly
attracted, 'till it has parted with its fire.
If the bottle had an electrical atmosphere, as well as the wire, an electrified
cork would be repelled from one as well as from the other.
EXPERIMENT II.
Fig. 1. From a bent wire (a)
sticking in the table, let a small linen thread (b) hang down within half an inch of the
electrised phial (c). Touch the wire of the phial repeatedly with your finger, and at every
touch you will see the thread instantly attracted by the bottle. (This is best done by a vinegar
cruet, or some such belly'd bottle). As soon as you draw any fire out from the upper part by
touching the wire, the lower part of the bottle draws an equal quantity in by the thread.
EXPERIMENT III.
Fig. 2. Fix a wire in the lead, with
which the bottom of the bottle is armed, (d) so as that bending upwards, its ring-end may
be level with the top or ring-end of the wire in the cork (e), and at three or four inches
distance. Then electricise the bottle, and place it on wax. If a cork suspended by a silk thread
(f) hang between these two wires, it will play incessantly from one to the other, 'till the
bottle is no longer electrised; that is, it fetches and carries fire from the top to the bottom of
the bottle, 'till the equilibrium is restored.
{6}
EXPERIMENT IV.
Fig. 3. Place an electricised phial
on wax; take a wire (g) in form of a C, the ends at such a distance when bent, as that the
upper may touch the wire of the bottle, when the lower touches the bottom: stick the outer part on
a stick of sealing wax (h) which will serve as a handle. Then apply the lower end to the
bottom of the bottle, and gradually bring the upper-end near the wire in the cork. The consequence
is, spark follows spark till the equilibrium is restored. Touch the top first, and on approaching
the bottom with the other end, you have a constant stream of fire, from the wire entering the
bottle. Touch the top and bottom together, and the equilibrium will soon be restored, but silently
and imperceptibly; the crooked wire forming the communication.
EXPERIMENT V.
Fig. 4. Let a ring of thin lead or
paper surround a bottle (i), even at some distance from or above the bottom. From that ring
let a wire proceed up, 'till it touch the wire of the cork (k). A bottle so fixt cannot by
any means be electrised: the equilibrium is never destroyed: for while the communication between
the upper and lower parts of the bottle is continued by the outside wire, the fire only
circulates: what is driven out at bottom, is constantly supply'd from the top. Hence a bottle
cannot be electrised that is foul or moist on the outside.
{7}
EXPERIMENT VI.
Place a man on a cake of wax, and present him the wire of the electrified phial to
touch, you standing on the floor, and holding it in your hand. As often as he touches it, he will
be electrified plus; and any one standing on the floor may draw a spark from him. The fire
in this experiment passes out of the wire into him; and at the same time out of your hand into the
bottom of the bottle.
EXPERIMENT VII.
Give him the electrified phial to hold; and do you touch the wire; as often you
touch it he will be electrified minus, and may draw a spark from any one standing on the
floor. The fire now passes from the wire to you, and from him into the bottom of the bottle.
EXPERIMENT VIII.
Lay two books on two glasses, back towards back, two or three Inches distant. Set
the electrified phial on one, and then touch the wire; that book will be electrified minus;
the electrical fire being drawn out of it by the bottom of the bottle. Take off the bottle, and
holding it in your hand, touch the other with the wire; that book will be electrised plus;
the fire passing into it from the wire, and the bottle at the same time supply'd from your hand. A
suspended small cork-ball will play between these books 'till the equilibrium is restored.
{8}
EXPERIMENT IX.
When a body is electrised plus it will repel an electrified feather or small
cork-ball. When minus (or when in the common state) it will attract them, but stronger when
minus than when in the common state, the difference being greater.
EXPERIMENT X.
Tho', as in EXPER. VI. a man standing on wax may be electrised a number of times,
by repeatedly touching the wire of an electrised bottle (held in the hand of one standing on the
floor) he receiving the fire from the wire each time: yet holding it in his own hand, and touching
the wire, tho' he draws a strong spark, and is violently shock'd, no Electricity remains in him;
the fire only passing thro' him from the upper to the lower part of the bottle. Observe, before
the shock, to let some one on the floor touch him to restore the equilibrium in his body; for in
taking hold of the bottom of the bottle, he sometimes becomes a little electrised minus,
which will continue after the shock; as would also any plus Electricity, which he might
have given him before the shock. For, restoring the equilibrium in the bottle does not at all
affect the Electricity in the man thro' whom the fire passes; that Electricity is neither
increased nor diminish'd.
EXPERIMENT XI.
The passing of the electrical fire from the upper to the lower part of the bottle, to restore
the equilibrium is render'd strongly visible by the following pretty {9}experiment. Take a book whose cover is filletted with gold; bend a wire of
eight or ten inches long in the form of (m) Fig.
5, slip it on the end of the cover of the book over the gold line, so as that the shoulder of
it may press upon one end of the gold line, the ring up, but leaning towards the other end of the
book. Lay the book on a glass or wax; and on the other end of the gold lines, set the bottle
electrised: then bend the springing wire, by pressing it with a stick of wax till its ring
approaches the ring of the bottle wire; instantly there is a strong spark and stroke, and the
whole line of gold, which completes the communication between the top and bottom of the bottle,
will appear a vivid flame, like the sharpest lightning. The closer the contact between the
shoulder of the wire, and the gold at one end of the line, and between the bottom of the bottle
and the gold at the other end, the better the experiment succeeds. The room should be darkened. If
you would have the whole filletting round the cover appear in fire at once, let the bottle and
wire touch the gold in the diagonally opposite corners.
I am, &c.
B. FRANKLIN.
{10}
LETTER II.
FROM
Mr Benj.
Franklin, in Philadelphia.
TO
Mr Peter Collinson, F.R.S. London.
Sept. 1, 1747.
SIR,
In my last I informed you that, in pursuing our electrical enquiries, we had observed some
particular Phænomena, which we looked upon to be new, and of which I promised to give you some
account, tho' I apprehended they might possibly not be new to you, as so many hands are daily
employ'd in electrical experiments on your side the water, some or other of which would probably
hit on the same observations.
The first is the wonderful effect of pointed bodies, both in drawing off and throwing
off the electrical fire. For example:
Place an iron shot of three or four inches diameter, on the mouth of a clean dry glass bottle.
By a fine silken thread from the cieling, right over the mouth of the bottle, suspend a small
cork-ball, about the bigness of a marble; the {11}thread
of such a length, as that the cork-ball may rest against the side of the shot. Electrify the shot,
and the ball will be repelled to the distance of four or five inches, more or less, according to
the quantity of Electricity.—When in this state, if you present to the shot the point of a
long slender sharp bodkin, at six or eight inches distance, the repellency is instantly destroy'd,
and the cork flies to the shot. A blunt body must be brought within an inch, and draw a spark, to
produce the same effect. To prove that the electrical fire is drawn off by the point, if
you take the blade of the bodkin out of the wooden handle, and fix it in a stick of sealing wax,
and then present it at the distance aforesaid, or if you bring it very near, no such effect
follows; but sliding one finger along the wax till you touch the blade, and the ball flies to the
shot immediately.—If you present the point in the dark, you will see, sometimes at a foot
distance, and more, a light gather upon it like that of a fire-fly or glow-worm; the less sharp
the point, the nearer you must bring it to observe the light; and at whatever distance you see the
light, you may draw off the electrical fire, and destroy the repellency.—If a cork-ball so
suspended be repelled by the tube, and a point be presented quick to it, tho' at a considerable
distance, 'tis surprizing to see how suddenly it flies back to the tube. Points of wood will do as
well as those of iron, provided the wood is not dry; for perfectly dry wood will no more conduct
Electricity than sealing wax.
{12}
To shew that points will throw off as well as draw off the electrical fire; lay a
long sharp needle upon the shot, and you cannot electrise the shot, so as to make it repel the
cork-ball.—Or fix a needle to the end of a suspended gun-barrel, or iron rod, so as to point
beyond it like a little bayonet; and while it remains there, the gun-barrel, or rod, cannot by
applying the tube to the other end be electrised so as to give a spark, the fire continually
running out silently at the point. In the dark you may see it make the same appearance as it does
in the case beforementioned.
The repellency between the cork-ball and the shot is likewise destroy'd; 1. By sifting fine
sand on it; this does it gradually. 2. By breathing on it. 3. By making a smoke about it from
burning wood.[1] 4. By candle light, even tho' the
candle is at a foot distance: these do it suddenly.—The light of a bright coal from a wood
fire; and the light of red-hot iron do it likewise; but not at so great a distance. Smoke from dry
rosin dropt on hot iron, does not destroy the repellency; but is attracted by both shot and
cork-ball, forming proportionable atmospheres round them, making them look beautifully, somewhat
like some of the figures in Burnet's or Whiston's theory of the earth.
{13}
N. B. This experiment should be made in a closet where the air is very still.
The light of the sun thrown strongly on both cork and shot by a looking-glass for a long time
together, does not impair the repellency in the least. This difference between fire-light and
sun-light, is another thing that seems new and extraordinary to us.
We had for some time been of opinion, that the electrical fire was not created by friction, but
collected, being really an element diffus'd among, and attracted by other matter, particularly by
water and metals. We had even discovered and demonstrated its afflux to the electrical sphere, as
well as its efflux, by means of little light windmill wheels made of stiff paper vanes, fixed
obliquely and turning freely on fine wire axes. Also by little wheels of the same matter, but
formed like water wheels. Of the disposition and application of which wheels, and the various
phænomena resulting, I could, if I had time, fill you a sheet. The impossibility of electrising
one's self (tho' standing on wax) by rubbing the tube and drawing the fire from it; and the manner
of doing it by passing the tube near a person or thing standing on the floor, &c. had also
occurred to us some months before Mr Watson's ingenious Sequel came to hand, and
these were some of the new things I intended to have communicated to you.—But now I need
only mention some particulars not hinted in that piece, with our reasonings thereupon; though
perhaps the latter might well enough be spared.
{14}
A person standing on wax, and rubbing the tube, and another person on wax drawing the fire;
they will both of them, (provided they do not stand so as to touch one another) appear to be
electrised, to a person standing on the floor; that is, he will perceive a spark on approaching
each of them with his knuckle.
But if the persons on wax touch one another during the exciting of the tube, neither of them
will appear to be electrised.
If they touch one another after exciting the tube, and drawing the fire as aforesaid, there
will be a stronger spark between them, than was between either of them and the person on the
floor.
After such strong spark, neither of them discover any electricity.
These appearances we attempt to account for thus. We suppose as aforesaid, that electrical fire
is a common element, of which every one of the three persons abovementioned has his equal share,
before any operation is begun with the Tube. A, who stands on wax and rubs the tube
collects the electrical fire from himself into the glass; and his communication with the common
stock being cut off by the wax, his body is not again immediately supply'd. B, (who stands
on wax likewise) passing his knuckle along near the tube, receives the fire which was collected by
the glass from A; and his communication with the common stock being likewise cut off, he
retains the additional quantity received.—To C, standing on the floor, both appear to
{15}be electrised: for he having only the middle quantity
of electrical fire, receives a spark upon approaching B, who has an over quantity; but
gives one to A, who has an under quantity. If A and B approach to touch each
other, the spark is stronger, because the difference between them is greater; after such touch
there is no spark between either of them and C, because the electrical fire in all is
reduced to the original equality. If they touch while electrising, the equality is never
destroy'd, the fire only circulating. Hence have arisen some new terms among us: we say, B,
(and bodies like circumstanced) is electrised positively; A, negatively. Or
rather, B is electrised plus; A, minus. And we daily in our
experiments electrise bodies plus or minus as we think proper.—To electrise
plus or minus, no more needs to be known than this, that the parts of the tube or
sphere that are rubbed, do, in the instant of the friction attract the electrical fire, and
therefore take it from the thing rubbing: the same parts immediately, as the friction upon them
ceases, are disposed to give the fire they have received, to any body that has less. Thus you may
circulate it, as Mr Watson has shewn; you may also accumulate or substract it upon or from
any body, as you connect that body with the rubber or with the receiver, the communication with
the common stock being cut off. We think that ingenious gentleman was deceived, when he imagined
(in his Sequel) that the electrical fire came down the wire from the cieling to the
gun-barrel, thence to the sphere, and so electrised the machine {16}and the man turning the wheel, &c. We suppose it was driven
off, and not brought on thro' that wire; and that the machine and man, &c. were
electrised minus; i. e. had less electrical fire in them than things in common.
As the vessel is just upon sailing, I cannot give you so large an account of American
Electricity as I intended: I shall only mention a few particulars more.—We find granulated
lead better to fill the phial with, than water, being easily warmed, and keeping warm and dry in
damp air.—We fire spirits with the wire of the phial.—We light candles, just blown
out, by drawing a spark among the smoke between the wire and snuffers.—We represent
lightning, by passing the wire in the dark over a china plate that has gilt flowers, or applying
it to gilt frames of looking-glasses, &c.—We electrise a person twenty or more
times running, with a touch of the finger on the wire, thus: He stands on wax. Give him the
electrised bottle in his hand. Touch the wire with your finger, and then touch his hand or face;
there are sparks every time.—We encrease the force of the electrical kiss vastly, thus: Let
A and B stand on wax; give one of them the electrised phial in hand; let the other
take hold of the wire; there will be a small spark; but when their lips approach, they will be
struck and shock'd. The same if another gentleman and lady, C and D, standing also
on wax, and joining hands with A and B, salute, or shake hands.—We suspend by
fine silk thread a counterfeit spider, made of a small piece of burnt cork, with legs of {17}linnen thread, and a grain or two of lead stuck in him to
give him more weight. Upon the table, over which he hangs, we stick a wire upright as high as the
phial and wire, two or three inches from the spider; then we animate him by setting the
electrified phial at the same distance on the other side of him; he will immediately fly to the
wire of the phial, bend his legs in touching it, then spring off, and fly to the wire in the
table; thence again to the wire of the phial, playing with his legs against both in a very
entertaining manner, appearing perfectly alive to persons unacquainted. He will continue this
motion an hour or more in dry weather.—We electrify, upon wax in the dark, a book that has a
double line of gold round upon the covers, and then apply a knuckle to the gilding; the fire
appears every where upon the gold like a flash of lightning: not upon the leather, nor, if you
touch the leather instead of the gold. We rub our tubes with buckskin, and observe always to keep
the same side to the tube, and never to sully the tube by handling; thus they work readily and
easily, without the least fatigue; especially if kept in tight pastboard cases, lined with
flannel, and fitting closeto the tube.[2]—This I
mention because the European papers, on Electricity, frequently speak of rubbing the tube,
as a fatiguing exercise. Our spheres are fixed on iron axes, which pass through them. At one end
of the {18}axis there is a small handle, with which we
turn the sphere like a common grindstone. This we find very commodious, as the machine takes up
but little room, is portable, and may be enclosed in a tight box, when not in use. 'Tis true, the
sphere does not turn so swift, as when the great wheel is used: but swiftness we think of little
importance, since a few turns will charge the phial, &c. sufficiently.
I am, &c.
B. FRANKLIN.
{19}
LETTER III.
FROM
Mr Benj.
Franklin, in Philadelphia.
TO
Mr Peter Collinson, F.R.S. London.
Farther Experiments and Observations in ELECTRICITY.
SIR,
§ 1. There will be the same explosion and shock, if the electrified phial is held in one hand
by the hook, and the coating touch'd with the other, as when held by the coating, and touch'd at
the hook.
To take the charg'd phial safely by the hook, and not at the same time diminish its force,
it must first be set down on an electric per se.
The phial will be electrified as strongly, if held by the hook, and the coating apply'd to
the globe or tube; as when held by the coating, and the hook apply'd.
{20}
But the direction of the electrical fire being different in the charging, will also
be different in the explosion. The bottle charged thro' the hook, will be discharged thro' the
hook; the bottle charged thro' the coating, will be discharged thro' the coating, and not other
ways: for the fire must come out the same way it went in.
To prove this; take two bottles that were equally charged thro' the hooks, one in each hand;
bring their hooks near each other, and no spark or shock will follow; because each hook is
disposed to give fire, and neither to receive it. Set one of the bottles down on glass, take it up
by the hook, and apply its coating to the hook of the other; then there will be an explosion and
shock, and both bottles will be discharged.
Vary the experiment, by charging two phials equally, one thro' the hook, the other thro' the
coating: hold that by the coating which was charged thro' the hook; and that by the hook which was
charg'd thro' the coating: apply the hook of the first to the coating of the other, and there will
be no shock or spark. Set that down on glass which you held by the hook, take it up by the
coating, and bring the two hooks together: a spark and shock will follow, and both phials be
discharged.
In this experiment the bottles are totally discharged, or the equilibrium within them restored.
The abounding of fire in one of the hooks (or rather in the internal surface of one bottle)
being exactly equal to the wanting of the other: and therefore, as each bottle has in
itself the abounding as {21}well as the
wanting, the wanting and abounding must be equal in each bottle. See §. 8, 9, 10, 11. But
if a man holds in his hands two bottles, one fully electrify'd, the other not at all, and brings
their hooks together, he has but half a shock, and the bottles will both remain half electrified,
the one being half discharged, and the other half charged.
Place two phials equally charged on a table at five or six inches distance. Let a cork-ball,
suspended by a silk thread, hang between them. If the phials were both charged through their
hooks, the cork, when it has been attracted and repell'd by the one, will not be attracted, but
equally repelled by the other. But if the phials were charged, the one through the hook, and the
other[3] through the coating, the ball, when it is
repelled from one hook, will be as strongly attracted by the other, and play vigorously between
them, 'till both phials are nearly discharged.
When we use the terms of charging and discharging the phial, 'tis in
compliance with custom, and for want of others more suitable. Since we are of opinion, that there
is really no more electrical fire in the phial after what is called its charging, than
before, nor less after its discharging; excepting only the small spark that might be given
to, and taken from, the non-electric matter, if separated from {22}the bottle, which spark may not be equal to a five hundredth part of what
is called the explosion.
For if, on the explosion, the electrical fire came out of the bottle by one part, and did not
enter in again by another; then, if a man standing on wax, and holding the bottle in one hand,
takes the spark by touching the wire hook with the other, the bottle being thereby
discharged, the man would be charged; or whatever fire was lost by one, would be
found in the other, since there is no way for its escape: But the contrary is true.
Besides the phial will not suffer what is called a charging, unless as much fire can
go out of it one way, as is thrown in by another. A phial cannot be charged standing on wax or
glass, or hanging on the prime conductor, unless a communication be form'd between its coating and
the floor.
But suspend two or more phials on the prime conductor, one hanging to the tail of the
other; and a wire from the last to the floor, an equal number of turns of the wheel shall charge
them all equally, and every one as much as one alone would have been. What is driven out at the
tail of the first, serving to charge the second; what is driven out of the second charging the
third; and so on. By this means a great number of bottles might be charged with the same labour,
and equally high, with one alone, were it not that every bottle receives new fire, and loses its
old with some reluctance, or rather gives some small resistance to the charging, which in a number
of bottles {23}becomes more equal to the charging power,
and so repels the fire back again on the globe, sooner than a single bottle would do.
When a bottle is charged in the common way, its inside and outside surfaces
stand ready, the one to give fire by the hook, the other to receive it by the coating; the one is
full, and ready to throw out, the other empty and extremely hungry; yet as the first will not
give out, unless the other can at the same instant receive in; so neither will the
latter receive in, unless the first can at the same instant give out. When both can be done at
once, 'tis done with inconceivable quickness and violence.
So a strait spring (tho' the comparison does not agree in every particular) when forcibly
bent, must, to restore itself, contract that side which in the bending was extended, and extend
that which was contracted; if either of these two operations be hindered, the other cannot be
done. But the spring is not said to be charg'd with elasticity when bent, and discharg'd
when unbent; its quantity of elasticity is always the same.
Glass, in like manner, has, within its substance, always the same quantity of electrical
fire, and that a very great quantity in proportion to the mass of glass, as shall be shewn
hereafter.
This quantity, proportioned to the glass, it strongly and obstinately retains, and will
have neither more nor less, though it will suffer a change to be made in its parts and situation;
i. e. we may take away part of it from one {24}of
the sides, provided we throw an equal quantity into the other.
Yet when the situation of the electrical fire is thus altered in the glass; when some has
been taken from one side, and some added to the other, it will not be at rest or in its natural
state, till 'tis restored to its original equality.—And this restitution cannot be made
through the substance of the glass, but must be done by a non-electric communication formed
without, from surface to surface.
Thus, the whole force of the bottle, and power of giving a shock, is in the GLASS ITSELF; the non-electrics in contact with the two surfaces, serving
only to give and receive to and from the several parts of the glass; that is, to
give on one side, and take away from the other.
This was discovered here in the following manner. Purposing to analyse the electrified
bottle, in order to find wherein its strength lay, we placed it on glass, and drew out the cork
and wire which for that purpose had been loosely put in. Then taking the bottle in one hand, and
bringing a finger of the other near its mouth, a strong spark came from the water, and the shock
was as violent as if the wire had remained in it, which shewed that the force did not lie in the
wire. Then to find if it resided in the water, being crouded into and condensed in it, as connfi'd
by the glass, which had been our former opinion, we electrify'd the bottle again, and placing it
on glass, drew out the wire and cork as before; then taking up the bottle we decanted all its
water into an empty bottle, which likewise stood on {25}glass; and taking up that other bottle, we expected if the force resided in
the water, to find a shock from it; but there was none. We judged then, that it must either be
lost in decanting, or remain in the first bottle. The latter we found to be true: for that bottle
on trial gave the shock, though filled up as it stood with fresh unelectrified water from a
tea-pot.—To find then, whether glass had this property merely as glass, or whether the form
contributed any thing to it; we took a pane of sash-glass, and laying it on the stand, placed a
plate of lead on its upper surface; then electrify'd that plate, and bringing a finger to it,
there was a spark and shock. We then took two plates of lead of equal dimensions, but less than
the glass by two inches every way, and electrified the glass between them, by electrifying the
uppermost lead; then separated the glass from the lead, in doing which, what little fire might be
in the lead was taken out and the glass being touched in the electrified parts with a finger,
afforded only very small pricking sparks, but a great number of them might be taken from different
places. Then dexterously placing it again between the leaden plates, and compleating a circle
between the two surfaces, a violent shock ensued.—Which demonstrated the power to reside in
glass as glass, and that the non-electrics in contact served only, like the armature of a
loadstone, to unite the force of the several parts, and bring them at once to any point desired:
it being a property of a non-electric, that {26}the whole
body instantly receives or gives what electrical fire is given to or taken from any one of its
parts.
Upon this, we made what we call'd an electrical-battery, consisting of eleven panes
of large sash-glass, arm'd with thin leaden plates pasted on each side, placed vertically, and
supported at two inches distance on silk cords, with thick hooks of leaden wire, one from each
side, standing upright, distant from each other, and convenient communications of wire and chain,
from the giving side of one pane, to the receiving side of the other; that so the whole might be
charged together, and with the same labour as one single pane; and another contrivance to bring
the giving sides, after charging, in contact with one long wire, and the receivers with another,
which two long wires would give the force of all the plates of glass at once through the body of
any animal forming the circle with them. The plates may also be discharged separately, or any
number together that is required. But this machine is not much used, as not perfectly answering
our intention with regard to the ease of charging, for the reason given § 10. We made also of
large glass panes, magical pictures, and self-moving animated wheels, presently to be
described.
I perceive by the ingenious Mr Watson's last book, lately received, that Dr
Bevis had used, before we had, panes of glass to give a shock; though, till that book came
to hand, I thought to have communicated it to you as a novelty. The excuse for mentioning it here,
is, that we {27}tried the experiment differently, drew
different consequences from it, (for Mr Watson still seems to think the fire accumulated
on the non-electric that is in contact with the glass, page 72) and, as far as we hitherto
know, have carried it farther.
The magical picture is made thus. Having a large metzotinto with a frame and glass, suppose
of the King, (God preserve him) take out the print, and cut a pannel out
of it, near two inches distant from the frame all round. If the cut is through the picture 'tis
not the worse. With thin paste or gum-water, fix the border that is cut off on the inside of the
glass, pressing it smooth and close; then fill up the vacancy by gilding the glass well with leaf
gold or brass. Gild likewise the inner edge of the back of the frame all round except the top
part, and form a communication between that gilding and the gilding behind the glass: then put in
the board, and that side is finished. Turn up the glass, and gild the fore side exactly over the
back gilding, and when it is dry, cover it by pasting on the pannel of the picture that had been
cut out, observing to bring the corresponding parts of the border and picture together, by which
the picture will appear of a piece as at first, only part is behind the glass, and part
before.—Hold the picture horizontally by the top, and place a little moveable gilt crown on
the king's-head. If now the picture be moderately electrified, and another person take hold of the
frame with one hand, so that his fingers touch its inside gilding, and with the other hand
endeavour to take {28}off the crown, he will receive a
terrible blow, and fail in the attempt. If the picture were highly charged, the consequence might
perhaps be as fatal as that of high-treason; for when the spark is taken through a quire of paper
laid on the picture, by means of a wire communication, it makes a fair hole through every sheet,
that is, through 48 leaves, (though a quire of paper is thought good armour against the push of a
sword or even against a pistol bullet) and the crack is exceeding loud. The operator, who holds
the picture by the upper-end, where the inside of the frame is not gilt, to prevent its falling,
feels nothing of the shock, and may touch the face of the picture without danger, which he
pretends is a test of his loyalty.—If a ring of persons take the shock among them, the
experiment is called, The Conspirators.
On the principle, in § 7, that hooks of bottles, differently charged, will attract and
repel differently, is made, an electrical wheel, that turns with considerable strength. A small
upright shaft of wood passes at right angles through a thin round board, of about twelve inches
diameter, and turns on a sharp point of iron fixed in the lower end, while a strong wire in the
upper-end passing thro' a small hole in a thin brass plate, keeps the shaft truly vertical. About
thirty radii of equal length, made of sash glass cut in narrow strips, issue horizontally
from the circumference of the board, the ends most distant from the center being about four inches
apart. On the end of every one, a brass thimble is fixed. If now the wire of a bottle electrified
in the {29}common way, be brought near the circumference
of this wheel, it will attract the nearest thimble, and so put the wheel in motion; that thimble,
in passing by, receives a spark, and thereby being electrified is repelled and so driven forwards;
while a second being attracted, approaches the wire, receives a spark, and is driven after the
first, and so on till the wheel has gone once round, when the thimbles before electrified
approaching the wire, instead of being attracted as they were at first, are repelled, and the
motion presently ceases.—But if another bottle which had been charged through the coating be
placed near the same wheel, its wire will attract the thimble repelled by the first, and thereby
double the force that carries the wheel round; and not only taking out the fire that had been
communicated to the thimbles by the first bottle, but even robbing them of their natural quantity,
instead of being repelled when they come again towards the first bottle, they are more strongly
attracted, so that the wheel mends its pace, till it goes with great rapidity twelve or fifteen
rounds in a minute, and with such strength, as that the weight of one hundred Spanish
dollars with which we once loaded it, did not seem in the least to retard its motion.—This
is called an electrical jack; and if a large fowl were spitted on the upright shaft, it would be
carried round before a fire with a motion fit for roasting.
But this wheel, like those driven by wind, water, or weights, moves by a foreign force, to
wit, that of the bottles. The self-moving wheel, though constructed on the {30}same principles, appears more surprising. 'Tis made of a thin round plate
of window-glass, seventeen inches diameter, well gilt on both sides, all but two inches next the
edge. Two small hemispheres of wood are then fixed with cement to the middle of the upper and
under sides, centrally opposite, and in each of them a thick strong wire eight or ten inches long,
which together make the axis of the wheel. It turns horizontally on a point at the lower end of
its Axis, which rests on a bit of brass cemented within a glass salt-celler. The upper end of its
axis passes thro' a hole in a thin brass plate cemented to a long strong piece of glass, which
keeps it six or eight inches distant from any non-electric, and has a small ball of wax or metal
on its top to keep in the fire. In a circle on the table which supports the wheel, are fixed
twelve small pillars of glass, at about four inches distance, with a thimble on the top of each.
On the edge of the wheel is a small leaden bullet communicating by a wire with the gilding of the
upper surface of the wheel; and about six inches from it is another bullet communicating in
like manner with the under surface. When the wheel is to be charged by the upper surface, a
communication must be made from the under surface to the table. When it is well charg'd it begins
to move; the bullet nearest to a pillar moves towards the thimble on that pillar, and passing by
electrifies it and then pushes itself from it; the succeeding bullet, which communicates with the
other surface of the glass, more strongly attracts that thimble on account of its being {31}before electrified by the other bullet; and thus the wheel
encreases its motion till it comes to such a height as that the resistance of the air regulates
it. It will go half an hour, and make one minute with another twenty turns in a minute, which is
six hundred turns in the whole; the bullet of the upper surface giving in each turn twelve sparks,
to the thimbles, which make seven thousand two hundred sparks; and the bullet of the under surface
receiving as many from the thimbles; those bullets moving in the time near two thousand five
hundred feet.—The thimbles are well fixed, and in so exact a circle, that the bullets may
pass within a very small distance of each of them.—If instead of two bullets you put eight,
four communicating with the upper surface, and four with the under surface, placed alternately;
which eight, at about six inches distance, compleats the circumference, the force and swiftness
will be greatly increased, the wheel making fifty turns in a minute; but then it will not continue
moving so long.—These wheels may be applied, perhaps, to the ringing of chimes, and moving
of light-made Orreries.
A small wire bent circularly with a loop at each end; let one end rest against the under
surface of the wheel, and bring the other end near the upper surface, it will give a terrible
crack, and the force will be discharged.
Every spark in that manner drawn from the surface of the wheel, makes a round hole in the
gilding, tearing off a part of it in coming out; which shews that the fire {32}is not accumulated on the gilding, but is in the glass itself.
The gilding being varnish'd over with turpentine varnish, the varnish tho' dry and hard, is
burnt by the spark drawn thro' it, and gives a strong smell and visible smoke. And when the spark
is drawn through paper, all round the hole made by it, the paper will be blacked by the smoke,
which sometimes penetrates several of the leaves. Part of the gilding torn off, is also found
forcibly driven into the hole made in the paper by the stroke.
'Tis amazing to observe in how small a portion of glass a great electrical force may lie. A
thin glass bubble, about an inch diameter, weighing only six grains, being half-filled with water,
partly gilt on the outside, and furnish'd with a wire hook, gives, when electrified, as great a
shock as a man can well bear. As the glass is thickest near the orifice, I suppose the lower half,
which being gilt was electrified, and gave the shock, did not exceed two grains; for it appeared,
when broke, much thinner than the upper half.—If one of these thin bottles be electrified by
the coating, and the spark taken out thro' the gilding, it will break the glass inwards at the
same time that it breaks the gilding outwards.
And allowing (for the reasons before given, § 8, 9, 10,) that there is no more electrical
fire in a bottle after charging, than before, how great must be the quantity in this small portion
of glass! It seems as if it were of its very substance and essence. Perhaps if that due quantity
of {33}electrical fire so obstinately retained by glass,
could be separated from it, it would no longer be glass; it might lose its transparency, or its
brittleness, or its elasticity.—Experiments may possibly be invented hereafter, to discover
this.
We are surprized at the account given in Mr Watson's book, of a shock communicated
through a great space of dry ground, and suspect there must be some metaline quality in the gravel
of that ground; having found that simple dry earth, rammed in a glass tube, open at both ends, and
a wire hook inserted in the earth at each end, the earth and wires making part of a circle, would
not conduct the least perceptible shock, and indeed when one wire was electrify'd, the other
hardly showed any signs of its being in connection with it.—Even a thoroughly wet
pack-thread sometimes fails of conducting a shock, tho' it otherwise conducts electricity very
well. A dry cake of ice, or an icicle held between two in a circle, likewise prevents the shock;
which one would not expect, as water conducts it so perfectly well.—Gilding on a new book,
though at first it conducts the shock extremely well, yet fails after ten or a dozen experiments,
though it appears otherwise in all respects the same, which we cannot account for.
There is one experiment more which surprizes us, and is not hitherto satisfactorily
accounted for; it is this. Place an iron shot on a glass stand, and let a ball of damp cork,
suspended by a silk thread, hang in contact with the {34}shot. Take a bottle in each hand, one that is electrify'd through the hook,
the other through the coating: Apply the giving wire to the shot, which will electrify it
positively, and the cork shall be repelled: Then apply the requiring wire, which will take
out the spark given by the other; when the cork will return to the shot: Apply the same again, and
take out another spark, so will the shot be electrify'd negatively; and the cork in that
case shall be repelled equally as before. Then apply the giving wire to the shot, and give the
spark it wanted, so will the cork return: Give it another, which will be an addition to its
natural quantity, so will the cork be repelled again: And so may the experiment be repeated as
long as there is any charge in the bottles. Which shews that bodies having less than the common
quantity of Electricity, repel each other, as well as those that have more.
Chagrined a little that we have hitherto been able to produce nothing in this way of use to
mankind; and the hot weather coming on, when electrical experiments are not so agreeable, 'tis
proposed to put an end to them for this season, somewhat humorously, in a party of pleasure, on
the banks of Skuylkill.[4] Spirits, at the same
time, are to be fired by a spark sent from side to side through the river, without any other
conductor than the water; an experiment which we some time since performed, to the {35}amazement of many. A turkey is to be killed for our dinner
by the electrical shock, and roasted by the electrical jack, before a fire kindled
by the electrified bottle; when the healths of all the famous electricians in
England, Holland, France, and Germany, are to be drank in [5]electrified bumpers, under the discharge of guns
from the electrical battery.
{36}
LETTER IV.
CONTAINING
OBSERVATIONS and SUPPOSITIONS, towards forming a new Hypothesis, for explaining the several Phænomena of Thunder-Gusts.[6]
SIR,
§. 1. Non-electric bodies, that have electric fire thrown into them, will retain it 'till other
non-electrics, that have less, approach; and then 'tis communicated by a snap, and becomes equally
divided.
Electrical fire loves water, is strongly attracted by it, and they can subsist together.
Air is an electric per se, and when dry will not conduct the electrical fire; it will
neither receive it, nor give {37}it to other bodies;
otherwise no body surrounded by air could be electrified positively and negatively: for should it
be attempted positively, the air would immediately take away the overplus; or negatively, the air
would supply what was wanting.
Water being electrified, the vapours arising from it will be equally electrified; and
floating in the air, in the form of clouds, or otherwise, will retain that quantity of electrical
fire, till they meet with other clouds or bodies not so much electrified, and then will
communicate as beforementioned.
Every particle of matter electrified is repelled by every other particle equally
electrified. Thus the stream of a fountain, naturally dense and continual, when electrified, will
separate and spread in the form of a brush, every drop endeavouring to recede from every other
drop. But on taking out the electrical fire, they close again.
Water being strongly electrified (as well as when heated by common fire) rises in vapours
more copiously; the attraction of cohesion among its particles being greatly weakened, by the
opposite power of repulsion introduced with the electrical fire; and when any particle is by any
means disengaged, 'tis immediately repelled, and so flies into the air.
Particles happening to be situated as A and B, are more easily disengaged than
C and D, as each is held by contact with three only, whereas C and D
are each in contact with nine. When the surface of water has the {38}least motion, particles are continually pushed into the situation
represented by Fig. 6.