SIR,

In considering the Abbé Nollet's Letters to Mr. Franklin, I am

obliged to pass by all the experiments which are made with, or in,

bottles hermetically sealed, or exhausted of air; because, not being

able to repeat the experiments, I could not second any thing which

occurs to me thereon, by experimental proof. Wherefore, the first

point wherein I can dare to give my opinion, is in the Abbé's 4th

letter, p. 66, where he undertakes to prove, that the electric matter

passes from one surface to another through the entire thickness

of the glass: he takes Mr. Franklin's experiment of the magical

picture, and writes thus of it. "When you electrise a pane of glass

coated on both sides with metal, it is evident that whatever is

placed on the side opposite to that which receives the electricity

from the conductor, receives also an evident electrical virtue."

Which Mr. Franklin says, is that equal quantity of electric matter,

driven out of this side, by what is received from the conductor on

the other side; and which will continue to give an electrical virtue

to any thing in contact with it, till it is entirely discharged of

its electrical fire. To which the Abbé thus objects; "Tell me (says

he), I pray you, how much time is necessary for this pretended

discharge? I can assure you, that after having maintained the

electrisation for hours, this surface, which ought, as it seems to

me, to be entirely discharged of its electrical matter, considering

either the vast number of sparks that were drawn from it, or the time

that this matter had been exposed to the action of the expulsive

cause; this surface, I say, appeared rather better electrised

thereby, and more proper to produce all the effects of an actual

electric body." _P._ 68.

The Abbé does not tell us what those effects were, all the effects

I could never observe, and those that are to be observed can easily

be accounted for, by supposing that side to be entirely destitute

of electric matter. The most sensible effect of a body charged with

electricity is, that when you present your finger to it, a spark will

issue from it to your finger: now when a phial, prepared for the

Leyden experiment, is hung to the gun-barrel or prime-conductor, and

you turn the globe in order to charge it; as soon as the electric

matter is excited, you can observe a spark to issue from the external

surface of the phial to your finger, which, Mr. Franklin says, is

the natural electric matter of the glass driven out by that received

by the inner surface from the conductor. If it be only drawn out by

sparks, a vast number of them may be drawn; but if you take hold of

the external surface with your hand, the phial will soon receive all

the electric matter it is capable of, and the outside will then be

entirely destitute of its electric matter, and no spark can be drawn

from it by the finger: here then is a want of that effect which all

bodies, charged with electricity, have. Some of the effects of an

electric body, which I suppose the Abbé has observed in the exterior

surface of a charged phial, are that all light bodies are attracted

by it. This is an effect which I have constantly observed, but do not

think that it proceeds from an attractive quality in the exterior

surface of the phial, but in those light bodies themselves, which

seem to be attracted by the phial. It is a constant observation,

that when one body has a greater charge of electric matter in it

than another (that is in proportion to the quantity they will hold)

this body will attract that which has less: now, I suppose, and it

is a part of Mr. Franklin's system, that all those light bodies

which appear to be attracted, have more electric matter in them than

the external surface of the phial has, wherefore they endeavour to

attract the phial to them, which is too heavy to be moved by the

small degree of force they exert, and yet being greater than their

own weight, moves them to the phial. The following experiment will

help the imagination in conceiving this. Suspend a cork ball, or a

feather, by a silk thread, and electrise it; then bring this ball

nigh to any fixed body, and it will appear to be attracted by that

body, for it will fly to it: now, by the consent of electricians, the

attractive cause is in the ball itself, and not in the fixed body to

which it flies: this is a similar case with the apparent attraction

of light bodies, to the external surface of a charged phial.

The Abbé says, _p._ 69, "that he can electrise a hundred men,

standing on wax, if they hold hands, and if one of them touch one

of these surfaces (the exterior) with the end of his finger:" this

I know he can, while the phial is charging, but after the phial is

charged I am as certain he cannot: that is, hang a phial, prepared

for the Leyden experiment, to the conductor, and let a man, standing

on the floor, touch the coating with his finger, while the globe is

turned, till the electric matter spews out of the hook of the phial,

or some part of the conductor, which I take to be the certainest sign

that the phial has received all the electric matter it can: after

this appears, let the man, who before stood on the floor, step on a

cake of wax, where he may stand for hours, and the globe all that

time turned; and yet have no appearance of being electrised. After

the electric matter was spewed out as above from the hook of the

phial prepared for the Leyden experiment, I hung another phial, in

like manner prepared, to a hook fixed in the coating of the first,

and held this other phial in my hand; now if there was any electric

matter transmitted through the glass of the first phial, the second

one would certainly receive and collect it; but having kept the

phials in this situation for a considerable time, during which the

globe was continually turned, I could not perceive that the second

phial was in the least charged, for when I touched the hook with

my finger, as in the Leyden experiment, I did not feel the least

commotion, nor perceive any spark to issue from the hook.

I likewise made the following experiment: having charged two phials

(prepared for the Leyden experiment) through their hooks; two persons

took each one of these phials in their hand; one held his phial by

the coating, the other by the hook, which he could do by removing

the communication from the bottom before he took hold of the hook.

These persons placed themselves one on each side of me, while I stood

on a cake of wax, and took hold of the hook of that phial which was

held by its coating (upon which a spark issued, but the phial was not

discharged, as I stood on wax) keeping hold of the hook, I touched

the coating of the phial that was held by its hook with my other

hand, upon which there was a large spark to be seen between my finger

and the coating, and both phials were instantly discharged. If the

Abbé's opinion be right, that the exterior surface, communicating

with the coating, is charged, as well as the interior, communicating

with the hook; how can I, who stand on wax, discharge both these

phials, when it is well known I could not discharge one of them

singly? Nay, suppose I have drawn the electric matter from both of

them, what becomes of it? For I appear to have no additional quantity

in me when the experiment is over, and I have not stirred off the

wax: wherefore this experiment fully convinces me, that the exterior

surface is not charged; and not only so, but that it wants as much

electric matter as the inner has of excess: for by this supposition,

which is a part of Mr. Franklin's system, the above experiment is

easily accounted for, as follows:

When I stand on wax, my body is not capable of receiving all the

electric matter from the hook of one phial, which it is ready to

give; neither can it give as much to the coating of the other phial

as it is ready to take, when one is only applied to me: but when both

are applied, the coating takes from me what the hook gives: thus I

receive the fire from the first phial at B, the exterior surface of

which is supplied from the hand at A: I give the fire to the second

phial at C, whose interior surface is discharged by the hand at D.

This discharge at D may be made evident by receiving that fire into

the hook of a third phial, which is done thus: In place of taking

the hook of the second phial in your hand, run the wire of a third

phial, prepared as for the Leyden experiment, through it, and hold

this third phial in your hand, the second one hanging to it, by

the ends of the hooks run through each other: when the experiment

is performed, this third phial receives the fire at D, and will be

charged.

[Illustration: (of the experiment above)]

When this experiment is considered, I think, it must fully prove

that the exterior surface of a charged phial wants electric matter,

while the inner surface has an excess of it. One thing more worthy

of notice in this experiment is, that I feel no commotion or shock in

my arms, though so great a quantity of electric matter passes them

instantaneously: I only feel a pricking in the ends of my fingers.

This makes me think the Abbé has mistook, when he says, that there

is no difference between the shock felt in performing the Leyden

experiment, and the pricking felt on drawing simple sparks, except

that of greater to less. In the last experiment, as much electric

matter went through my arms, as would have given me a very sensible

shock, had there been an immediate communication, by my arms, from

the hook to the coating of the same phial; because when it was taken

into a third phial, and that phial discharged singly through my arms,

it gave me a sensible shock. If these experiments prove that the

electric matter does not pass through the entire thickness of the

glass, it is a necessary consequence that it must always come out

where it entered.

The next thing I meet with is in the Abbé's fifth letter, _p._

88, where he differs from Mr. Franklin, who thinks that the whole

power of giving a shock is in the glass itself, and not in the

non-electrics in contact with it. The experiments which Mr. Franklin

gave to prove this opinion, in his _Observations on the Leyden

Bottle_, p. 179, convinced me that he was in the right; and what the

Abbé has asserted, in contradiction thereto, has not made me think

otherwise. The Abbé, perceiving, as I suppose, that the experiments,

as Mr. Franklin had performed them, must prove his assertion, alters

them without giving any reason for it, and makes them in a manner

that proves nothing. Why will he have the phial, into which the,

water is to be decanted from a charged phial, held in a man's hand?

If the power of giving a shock is in the water contained in the

phial, it should remain there though decanted into another phial,

since no non-electric body touched it to take that power off. The

phial being placed on wax is no objection, for it cannot take the

power from the water, if it had any, but it is a necessary means to

try the fact; whereas, that phial's being charged when held in a

man's hand, only proves that water will conduct the electric matter.

The Abbé owns, _p._ 94, that he had heard this remarked, but says,

Why is not a conductor of electricity an electric subject? This is

not the question; Mr. Franklin never said that water was not an

electric subject; he said, that the power of giving a shock was in

the glass, and not in the water; and this, his experiments fully

prove; so fully, that it may appear impertinent to offer any more:

yet as I do not know that the following has been taken notice of by

any body before, my inserting of it in this place may be excused.

It is this: Hang a phial, prepared for the Leyden experiment, to

the conductor, by its hook, and charge it, which done, remove the

communication from the bottom of the phial. Now the conductor shews

evident signs of being electrised; for if a thread be tied round it,

and its ends left about two inches long, they will extend themselves

out like a pair of horns; but if you touch the conductor, a spark

will issue from it, and the threads will fall, nor does the conductor

shew the least sign of being electrised after this is done. I think

that by this touch, I have taken out all the charge of electric

matter that was in the conductor, the hook of the phial, and water

or filings of iron contained in it; which is no more than we see all

non-electric bodies will receive: yet the glass of the phial retains

its power of giving a shock, as any one will find that pleases to

try. This experiment fully evidences, that the water in the phial

contains no more electric matter than it would do in an open bason,

and has not any of that great quantity which produces the shock, and

is only retained by the glass. If after the spark is drawn from the

conductor, you touch the coating of the phial (which all this while

is supposed to hang in the air, free from any non-electric body)

the threads on the conductor will instantly start up, and shew that

the conductor is electrised. It receives this electrisation from

the inner surface of the phial, which, when the outer surface can

receive what it wants from the hand applied to it, will give as much

as the bodies in contact with it can receive, or if they be large

enough, all that it has of excess. It is diverting to see how the

threads will rise and fall by touching the coating and conductor of

the phial alternately. May it not be that the difference between

the charged side of the glass, and the outer or emptied side, being

lessened by touching the hook or the conductor; the outer side can

receive from the hand which touched it, and by its receiving, the

inner side cannot retain so much; and for that reason so much as it

cannot contain electrises the water, or filings and conductor: for

it seems to be a rule, that the one side must be emptied in the same

proportion that the other is filled: though this from experiment

appears evident, yet it is still a mystery not to be accounted for.

I am in many places of the Abbé's book surprised to find that

experiments have succeeded so differently at Paris, from what they

did with Mr. Franklin, and as I have always observed them to do. The

Abbé, in making experiments to find the difference between the two

surfaces of a charged glass, will not have the phial placed on wax:

for, says he, don't you know that being placed on a body originally

electric, it quickly loses its virtue? I cannot imagine what should

have made the Abbé think so; it certainly is contradictory to the

notions commonly received of electrics _per se_; and by experiment I

find it entirely otherwise: for having several times left a charged

phial, for that purpose, standing on wax for hours, I found it to

retain as much of its charge as another that stood at the same time

on a table. I left one standing on wax from ten o'clock at night

till eight the next morning, when I found it to retain a sufficient

quantity of its charge, to give me a sensible commotion in my arms,

though the room in which the phial stood had been swept in that time,

which must have raised much dust to facilitate the discharge of the

phial.

I find that a cork-ball suspended between two bottles, the one fully

and the other but little charged, will not play between them, but is

driven into a situation that makes a triangle with the hooks of the

phials: though the Abbé has asserted the contrary of this, p. 101,

in order to account for the playing of a cork-ball between the wire

thrust into the phial, and one that rises up from its coating. The

phial which is least charged must have more electric matter given to

it, in proportion to its bulk, than the cork-ball receives from the

hook of the full phial.

The Abbé says, p. 103, "That a piece of metal leaf hung to a silk

thread and electrised, will be repelled by the bottom of a charged

phial held by its hook in the air:" this I find constantly otherwise,

it is with me always first attracted and then repelled: it is

necessary in charging the leaf to be careful, that it does not fly

off to some non-electric body, and so discharge itself when you think

it is charged; it is difficult to keep it from flying to your own

wrist, or to some part of your body.

The Abbé, p. 108, says, "that it is not impossible, as Mr. Franklin

says it is, to charge a phial while there is a communication formed

between its coating and its hook." I have always found it impossible

to charge such a phial so as to give a shock: indeed, if it hang on

the conductor without a communication from it, you may draw a spark

from it as you may from any body that hangs there, but this is very

different from being charged in such a manner as to give a shock. The

Abbé, in order to account for the little quantity of electric matter

that is to be found in the phial, says, "that it rather follows the

metal than the glass, and that it is spewed out into the air from

the coating of the phial." I wonder how it comes not to do so too,

when it sifts through the glass, and charges the exterior surface,

according to the Abbé's system!

The Abbé's objections against Mr. Franklin's two last experiments, I

think, have little weight in them: he seems, indeed, much at a loss

what to say, wherefore he taxes Mr. Franklin with having concealed a

material part of the experiment; a thing too mean for any gentleman

to be charged with, who has not shown as great a partiality in

relating experiments, as the Abbé has done.