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 vial, 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 exceeding 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 electrical 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
electrical 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 electrical fluid, imbibed by each surface,
cannot themselves {74}pass through to those of the other,
their repellency can, and by this means they act on one another. The particles of the electrical
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 electrified 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 {75}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.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 supply'd from the
common stock. But the instant the parts of the glass so open'd and fill'd have pass'd 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.[10] But if
the inside of the globe be lined with a non-electric, the {76}additional repellency of the electrical fluid, thus collected by friction
on the rubb'd 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 rubb'd 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 charg'd 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.So if a tube lined with a [11]non-electric, be
rubb'd, 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 {77}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 so be charged. But thus it
may: after every stroke, before you pass your hand up to make another, let the 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 overcharg'd pores in the outer surface discharge
that overplus; the equilibrium being restored through your body, which could not be restored
through the glass.[12] 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 {78}the inner
surface, without a non-electric conductor: but air resists its 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 mix'd with
it: it rather keeps such an atmosphere confin'd, 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 concern'd, are, I think, explain'd
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.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 electrical fluid it contains. You {79}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 contain'd 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 electrical 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 further end, where the overplus is
discharg'd; 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 entring one of its surfaces to pass thro' to the other.Hence we see the impossibility of success, in the experiments propos'd, to draw out the
effluvial virtues of a non-electric, as cinnamon for instance, and mixing them with the electrical
fluid, to convey them with that into {80}the body, by
including it in the globe, and then applying friction, etc. For though the effluvia of cinnamon,
and the electrical 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 electrical fluid itself cannot
come through; and the prime conductor is always supply'd from the cushion, and that from the
floor. And besides, when the globe is filled with cinnamon, or other non-electric, no electrical
fluid can be obtain'd from its outer surface, for the reason before-mentioned. I have try'd
another way, which I thought more likely to obtain a mixture of the electrical 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 touch'd no part of the frame of the
machine. Another chain was fix'd to the prime conductor, and held in the hand of a person to be
electrised. 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 turn'd, 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 {81}chains whose ends
were dipt 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 electrical 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 electrical 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 electrical matter, and
adheres to the knuckle receiving the sparks, and to other {82}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 electrical 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 electrical fluid, and relate the variety of
little experiments we have try'd. I have already made this paper too long, for which I must crave
pardon, not having now time to make it shorter. I shall only add, that as it has been observed
here that spirits will fire by the electrical 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.
{83}
ADDITIONAL EXPERIMENT, proving that the Leyden Bottle has no more
electrical Fire in it when charged, than before; nor less when discharged: That in discharging,
the Fire does not issue from the Wire and the Coating at the same Time, as some have thought,
but that the Coating always receives what is discharged by the Wire, or an equal Quantity; the
outer Surface being always in a negative State of Electricity, when the inner Surface is in a
positive State.
Place a thick plate of glass under the rubbing cushion, to cut off the communication of
electrical fire from the floor to the cushion; then, if there be no fine points or hairy threads
sticking out from the cushion, or from the parts of the machine opposite to the cushion, (of which
you must be careful) you can get but a few sparks from the prime conductor, which are all the
cushion will part with.
Hang a phial then on the prime conductor, and it will not charge, tho' you hold it by the
coating.——But
Form a communication by a chain from the coating to the cushion, and the phial will charge.
For the globe then draws the electrical fire out of the outside surface of the phial, and
forces it, through the prime conductor and wire of the phial, into the inside surface.
{84}
Thus the bottle is charged with its own fire, no other being to be had while the glass plate is
under the cushion.
Hang two cork balls by flaxen threads to the prime conductor; then touch the coating of the
bottle, and they will be electrified and recede from each other.
For just as much fire as you give the coating, so much is discharged through the wire upon the
prime conductor, whence the cork balls receive an electrical atmosphere. But
Take a wire bent in the form of a C, with a stick of wax fixed to the outside of the curve, to
hold it by; and apply one end of this wire to the coating, and the other at the same time to the
prime conductor, the phial will be discharged; and if the balls are not electrified before the
discharge, neither will they appear to be so after the discharge, for they will not repel each
other.
Now if the fire discharged from the inside surface of the bottle through its wire, remained on
the prime conductor, the balls would be electrified and recede from each other.
If the phial really exploded at both ends, and discharged fire from both coating and wire, the
balls would be more electrified and recede farther: for none of the fire can escape,
the wax handle preventing.
But if the fire, with which the inside surface is surcharged, be so much precisely as is wanted
by the outside surface, it will pass round through the wire fixed to the wax {85}handle, restore the equilibrium in the glass, and make no alteration in the
state of the prime conductor.
Accordingly we find, that if the prime conductor be electrified, and the cork balls
in a state of repellency before the bottle is charged, they continue so afterwards. If not, they
are not electrified by that discharge.
CORRECTIONS and ADDITIONS
to the Preceding Papers.
Page 2, Sect. 1. We since find, that the fire in the bottle is not
contained in the non-electric, but in the glass. All that is after said of the top
and bottom of the bottle, is true of the inside and outside surfaces, and
should have been so expressed. See Sect. 16, p. 16.
Page 6, Line 13. The equilibrium will soon be restored but
silently, etc. This must have been a mistake. When the bottle is full charged, the crooked
wire cannot well be brought to touch the top and bottom so quick, but that there will be a loud
spark; unless the points be sharp, without loops.
Ibid. line ult. Outside: add, such moisture continuing up to the cork or wire.
Page 12, line 14. By candle-light etc. From some observations
since made, I am inclined to think, that it is not the light, but the smoke or non-electric
effluvia from {86}the candle, coal, and red-hot iron,
that carry off the electrical fire, being first attracted and then repelled.
Page 13, line 15. Windmil wheels, &c. We afterwards
discovered, that the afflux or efflux of the electrical fire, was not the cause of the motions of
those wheels, but various circumstances of attraction and repulsion.
Page 16, line 21. Let A and B stand on wax, &c.
We soon found that it was only necessary for one of them to stand on wax.
Page 19. in the title r. on.
Page 24, line 12. r. contact, line 24. confined.
Page 25, line 10. for stand r. hand.
Page 28, line 2. The consequence might perhaps be fatal, &c.
We have found it fatal to small animals, but 'tis not strong enough to kill large ones. The
biggest we have killed is a hen.
Page 31, line 20. Ringing of chimes, &c. This is since
done.
Page 33, line 22. Fails after ten or twelve experiments. This was
by a small bottle. And since found to fail after with a large glass.
Page 40, sect. 50, 51. Spirits must be heated before we
can fire them, &c. We have since fired spirits without heating, when the weather is
warm.
FINIS.
{87}
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RE: Experiments and Observations on Electricity [Part 1/4]