SIR,

Having lately made the following experiments, I very chearfully

communicate them, in hopes of giving you some degree of pleasure,

and exciting you to further explore your favorite, but not quite

exhausted subject, _electricity_.

I placed myself on an electric stand, and, being well electrised,

threw my hat to an unelectrised person, at a considerable distance,

on another stand, and found that the hat carried some of the

electricity with it; for, upon going immediately to the person who

received it, and holding a flaxen thread near him, I perceived he was

electrised sufficiently to attract the thread.

I then suspended, by silk, a broad plate of metal, and electrised

some boiling water under it at about four feet distance, expecting

that the vapour, which ascended plentifully to the plate, would,

upon the principle of the foregoing experiment, carry up some of the

electricity with it; but was at length fully convinced, by several

repeated trials, that it left all its share thereof behind. This I

know not how to account for; but does it not seem to corroborate your

hypothesis, That the vapours of which the clouds are formed, leave

their share of electricity behind, in the common stock, and ascend in

the negative state?

I put boiling water into a coated Florence flask, and found that

the heat so enlarged the pores of the glass, that it could not

be charged. The electricity passed through as readily, to all

appearance, as through metal; the charge of a three-pint bottle

went freely through, without injuring the flask in the least. When

it became almost cold, I could charge it as usual. Would not this

experiment convince the Abbé Nollet of his egregious mistake? For

while the electricity went fairly through the glass, as he contends

it always does, the glass could not be charged at all.

I took a slender piece of cedar, about eighteen inches long, fixed

a brass cap in the middle, thrust a pin horizontally and at right

angles, through each end (the points in contrary directions) and hung

it, nicely balanced, like the needle of a compass, on a pin, about

six inches long, fixed in the centre of an electric stand. Then,

electrising the stand, I had the pleasure of seeing what I expected;

the wooden needle turned round, carrying the pins with their heads

foremost. I then electrised the stand negatively, expecting the

needle to turn the contrary way, but was extremely disappointed, for

it went still the same way as before. When the stand was electrised

positively, I suppose that the natural quantity of electricity in

the air being increased on one side, by what issued from the points,

the needle was attracted by the lesser quantity on the other side.

When electrised negatively, I suppose that the natural quantity of

electricity in the air was diminished near the points; in consequence

whereof, the equilibrium being destroyed, the needle was attracted by

the greater quantity on the opposite side.

The doctrine of repulsion, in electrised bodies, I begin to be

somewhat doubtful of. I think all the phenomena on which it is

founded, may be well enough accounted for without it. Will not cork

balls, electrised negatively, separate as far as when electrised

positively? And may not their separation in both cases be accounted

for upon the same principle, namely, the mutual attraction of the

natural quantity in the air, and that which is denser or rarer in the

cork balls? it being one of the established laws of this fluid, that

quantities of different densities shall mutually attract each other,

in order to restore the equilibrium.

I can see no reason to conclude that the air has not its share of

the common stock of electricity, as well as glass, and perhaps, all

other electrics _per se_. For though the air will admit bodies to

be electrised in it either positively or negatively, and will not

readily carry off the redundancy in the one case, or supply the

deficiency in the other, yet let a person in the negative state,

out of doors in the dark, when the air is dry, hold, with his arm

extended, a long sharp needle, pointing upwards, and he will soon

be convinced that electricity may be drawn out of the air; not

very plentifully, for, being a bad conductor, it seems loth to part

with it, but yet some will evidently be collected. The air near the

person's body, having less than its natural quantity, will have

none to spare; but, his arm being extended, as above, some will be

collected from the remoter air, and will appear luminous, as it

converges to the point of the needle.

Let a person electrised negatively present the point of a needle,

horizontally, to a cork ball, suspended by silk, and the ball will be

attracted towards the point, till it has parted with so much of its

natural quantity of electricity as to be in the negative state in the

same degree with the person who holds the needle; then it will recede

from the point, being, as I suppose, attracted the contrary way by

the electricity of greater density in the air behind it. But, as this

opinion seems to deviate from electrical orthodoxy, I should be glad

to see these phenomena better accounted for by your superior and more

penetrating genius.

Whether the electricity in the air, in clear dry weather, be of the

same density at the height of two or three hundred yards, as near

the surface of the earth, may be satisfactorily determined by your

old experiment of the kite. The twine should have throughout a very

small wire in it, and the ends of the wire, where the several lengths

are united, ought to be tied down with a waxed thread, to prevent

their acting in the manner of points. I have tried the experiment

twice, when the air was as dry as we ever have it, and so clear that

not a cloud could be seen, and found the twine each time in a small

degree electrised positively. The kite had three metalline points

fixed to it: one on the top, and one on each side. That the twine

was electrised, appeared by the separating of two small cork balls,

suspended on the twine by fine flaxen threads, just above where the

silk was tied to it, and sheltered from the wind. That the twine

was electrised positively, was proved, by applying to it the wire

of a charged bottle, which caused the balls to separate further,

without first coming nearer together. This experiment showed, that

the electricity in the air, at those times, was denser above than

below. But that cannot be always the case; for you know we have

frequently found the thunder-clouds in the negative state, attracting

electricity from the earth; which state, it is probable, they are

always in when first formed, and till they have received a sufficient

supply. How they come afterwards, towards the latter end of the

gust, to be in the positive state, which is sometimes the case, is a

subject for further enquiry.

After the above experiments with the wooden needle, I formed a cross,

of two pieces of wood, of equal length, intersecting each other at

right angles in the middle, hung it horizontally upon a central

pin, and set a light horse with his rider, upon each extremity;

whereupon, the whole being nicely balanced, and each courser urged on

by an electrised point of a pair of spurs, I was entertained with an

electrical horse-race.

I have contrived an electrical air thermometer, and made several

experiments with it, that have afforded me much satisfaction and

pleasure. It is extremely sensible of any alteration in the state

of the included air, and fully determines that controverted point,

Whether there be any heat in the electric fire? By the enclosed

draught, and the following description, you will readily apprehend

the construction of it. (See Plate II.)

A B is a glass tube, about eleven inches long, and one inch diameter

in the bore. It has a brass ferrule cemented on each end, with a top

and bottom part, C and D, to be screwed on, air-tight, and taken off

at pleasure. In the centre of the bottom part D, is a male screw,

which goes into a brass nut, in the mahogany pedestal E. The wires

F and G are for the electric fire to pass through, darting from one

to the other. The wire G extends through the pedestal to H, and may

be raised and lowered by means of a male screw on it. The wire F may

be taken out, and the hook I be screwed into its place. K is a glass

tube, with a small bore, open at both ends, cemented in the brass

tube L which screws into the top part C. The lower end of the tube

K is immersed in water, coloured with cochineal, at the bottom of

the tube A B. (I used, at first, coloured spirits of wine, but in

one experiment I made, it took fire.) On the top of the tube K is

cemented, for ornament, a brass ferrule, with a head screwed on it,

which has a small air-hole through its side, at _a_. The wire _b_,

is a small round spring, that embraces the tube K, so as to stay

wherever it is placed. The weight M is to keep strait whatever may be

suspended in the tube A B, on the hook I. Air must be blown through

the tube K, into the tube A B, till enough is intruded to raise, by

its elastic force, a column of the coloured water in the tube K, up

to _c_, or thereabouts; and then, the gage-wire _b_, being slipt down

to the top of the column, the thermometer is ready for use.

[Illustration: (of the experiment below)

_Plate II._ _Vol. I. page 336._

_Published as the Act directs, April 1, 1806, by Longman, Hurst, Rees

& Orme, Paternoster Row._]

I set the thermometer on an electric stand, with the chain N fixed

to the prime conductor, and kept it well electrised a considerable

time; but this produced no sensible effect; which shews, that the

electric fire, when in a state of rest, has no more heat than the

air, and other matter wherein it resides.

When the wires F and G are in contact, a large charge of electricity

sent through them, even that of my case of five and thirty bottles,

containing above thirty square feet of coated glass, will produce no

rarefaction of the air included in the tube A B; which shows that the

wires are not heated by the fire's passing through them.

When the wires are about two inches apart, the charge of a three

pint bottle, darting from one to the other, rarefies the air very

evidently; which shows, I think, that the electric fire must produce

heat in itself, as well as in the air, by its rapid motion.

The charge of one of my glass jars (which will contain about five

gallons and a half, wine measure) darting from wire to wire, will,

by the disturbance it gives the air, repelling it in all directions,

raise the column in the tube K, up to _d_, or thereabouts; and

the charge of the above-mentioned case of bottles will raise it

to the top of the tube. Upon the air's coalescing, the column, by

its gravity, instantly subsides, till it is in equilibrio with the

rarefied air; it then gradually descends as the air cools, and

settles where it stood before. By carefully observing at what height

above the gage-wire _b_, the descending column first stops, the

degree of rarefaction is discovered, which, in great explosions, is

very considerable.

I hung in the thermometer, successively, a strip of wet writing

paper, a wet flaxen and woollen thread, a blade of green grass, a

filament of green wood, a fine silver thread, a very small brass

wire, and a strip of gilt paper; and found that the charge of the

above-mentioned glass jar, passing through each of these, especially

the last, produced heat enough to rarefy the air very perceptibly.

I then suspended, out of the thermometer, a piece of small

harpsichord wire, about twenty-four inches long, with a pound

weight at the lower end, and sent the charge of the case of five

and thirty bottles through it, whereby I discovered a new method of

wire-drawing. The wire was red hot the whole length, well annealed,

and above an inch longer than before. A second charge melted it;

it parted near the middle, and measured, when the ends were put

together, four inches longer than at first. This experiment, I

remember, you proposed to me before you left Philadelphia; but I

never tried it till now. That I might have no doubt of the wire's

being _hot_ as well as red, I repeated the experiment on another

piece of the same wire, encompassed with a goose-quill, filled with

loose grains of gun-powder; which took fire as readily as if it had

been touched with a red hot poker. Also tinder, tied to another piece

of the wire, kindled by it. I tried a wire about three times as big,

but could produce no such effects with that.

Hence it appears that the electric fire, though it has no sensible

heat when in a state of rest, will, by its violent motion, and the

resistance it meets with, produce heat in other bodies when passing

through them, provided they be small enough. A large quantity will

pass through a large wire, without producing any sensible heat;

when the same quantity passing through a very small one, being

there confined to a narrower passage, the particles crowding closer

together, and meeting with greater resistance, will make it red hot,

and even melt it.

Hence lightning does not melt metal by a cold fusion, as we formerly

supposed; but, when it passes through the blade of a sword, if the

quantity be not very great, it may heat the point so as to melt it,

while the broadest and thickest part may not be sensibly warmer than

before.

And when trees or houses are set on fire by the dreadful quantity

which a cloud, or the earth, sometimes discharges, must not the heat,

by which the wood is first kindled, be generated by the lightning's

violent motion, through the resisting combustible matter?

If lightning, by its rapid motion, produces heat in _itself_; as

well as in other bodies (and that it does I think is evident from

some of the foregoing experiments made with the thermometer) then

its sometimes singeing the hair of animals killed by it, may easily

be accounted for. And the reason of its not always doing so, may,

perhaps, be this: The quantity, though sufficient to kill a large

animal, may sometimes not be great enough, or not have met with

resistance enough, to become, by its motion, burning hot.

We find that dwelling-houses, struck with lightning, are seldom set

on fire by it; but when it passes through barns, with hay or straw in

them, or store-houses, containing large quantities of hemp, or such

like matter, they seldom, if ever, escape a conflagration; which may,

perhaps, be owing to such combustibles being apt to kindle with a

less degree of heat than is necessary to kindle wood.

We had four houses in this city, and a vessel at one of the wharfs,

struck and damaged by lightning last summer. One of the houses was

struck twice in the same storm. But I have the pleasure to inform

you, that your method of preventing such terrible disasters, has, by

a fact which had like to have escaped our knowledge, given a very

convincing proof of its great utility; and is now in higher repute

with us than ever.

Hearing, a few days ago, that Mr. William West, merchant in this

city, suspected that the lightning in one of the thunder-storms last

summer had passed through the iron conductor, which he had provided

for the security of his house; I waited on him, to enquire what

ground he might have for such suspicion. Mr. West informed me, that

his family and neighbours were all stunned with a very terrible

explosion, and that the flash and crack were seen and heard at the

same instant. Whence he concluded, that the lightning must have been

very near, and, as no house in the neighbourhood had suffered by it,

that it must have passed through his conductor. Mr. White, his clerk,

told me that he was sitting, at the time, by a window, about two

feet distant from the conductor, leaning against the brick wall with

which it was in contact; and that he felt a smart sensation, like an

electric shock, in that part of his body which touched the wall. Mr.

West further informed me, that a person of undoubted veracity assured

him, that, being in the door of an opposite house, on the other side

of Water-street (which you know is but narrow) he saw the lightning

diffused over the pavement, which was then very wet with rain, to

the distance of two or three yards from the foot of the conductor;

and that another person of very good credit told him, that he being

a few doors off on the other side of the street, saw the lightning

above, darting in such direction that it appeared to him to be

directly over that pointed rod.

Upon receiving this information, and being desirous of further

satisfaction, there being no traces of the lightning to be discovered

in the conductor, as far as we could examine it below, I proposed to

Mr. West our going to the top of the house, to examine the pointed

rod, assuring him, that if the lightning had passed through it, the

point must have been melted; and, to our great satisfaction, we found

it so. This iron rod extended in height about nine feet and a half

above a stack of chimneys to which it was fixed (though I suppose

three or four feet would have been sufficient.) It was somewhat more

than half an inch diameter in the thickest part, and tapering to the

upper end. The conductor, from the lower end of it to the earth,

consisted of square iron nail-rods, not much above a quarter of an

inch thick, connected together by interlinking joints. It extended

down the cedar roof to the eaves, and from thence down the wall of

the house, four story and a half, to the pavement in Water-street,

being fastened to the wall, in several places, by small iron hooks.

The lower end was fixed to a ring, in the top of an iron stake that

was drove about four or five feet into the ground.

The above-mentioned iron rod had a hole in the top of it, about two

inches deep, wherein was inserted a brass wire, about two lines

thick, and, when first put there, about ten inches long, terminating

in a very acute point; but now its whole length was no more than

seven inches and a half, and the top very blunt. Some of the metal

appears to be missing, the slenderest part of the wire being, as I

suspect, consumed into smoke. But some of it, where the wire was a

little thicker, being only melted by the lightning, sunk down, while

in a fluid state, and formed a rough irregular cap, lower on one side

than the other, round the upper end of what remained, and became

intimately united therewith.

This was all the damage that Mr. West sustained by a terrible stroke

of lightning;--a most convincing proof of the great utility of this

method of preventing its dreadful effects. Surely it will now be

thought as expedient to provide conductors for the lightning, as for

the rain.

Mr. West was so good as to make me a present of the melted wire,

which I keep as a great curiosity, and long for the pleasure of

shewing it to you. In the mean time, I beg your acceptance of the

best representation I can give of it, which you will find by the side

of the thermometer, drawn in its full dimensions as it now appears.

The dotted lines above are intended to shew the form of the wire

before the lightning melted it.

And now, Sir, I most heartily congratulate you on the pleasure you

must have in finding your great and well-grounded expectations so far

fulfilled. May this method of security from the destructive violence

of one of the most awful powers of nature, meet with such further

success, as to induce every good and grateful heart to bless God for

the important discovery! May the benefit thereof be diffused over the

whole globe! May it extend to the latest posterity of mankind, and

make the name of FRANKLIN, like that of NEWTON, _immortal_.