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.
28. 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 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 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_.
_April 29,
1749._
[Illustration]
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.
2. Electrical fire loves water, is strongly attracted by it, and they can
subsist together.
3. Air is an electric _per se_, and when dry will not conduct the
electrical fire; it will neither receive it, nor give 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.
4. 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.
5. 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.
6. 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.
7. 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 least motion, particles are continually pushed into the
situation represented by FIG. 6.
8. Friction between a non-electric and an electric _per se_, will produce
electrical fire; not by _creating_, but _collecting_ it: for it is equally
diffused in our walls, floors, earth, and the whole mass of common matter.
Thus the whirling glass globe, during its friction against the cushion,
draws fire from the cushion, the cushion is supplied from the frame of the
machine, that from the floor on which it stands. Cut off the communication
by thick glass or wax placed under the cushion, and no fire can be
_produced_, because it cannot be _collected_.
9. The Ocean is a compound of water, a non-electric, and salt an electric
_per se_.
10. When there is a friction among the parts near its surface, the
electrical fire is collected from the parts below. It is then plainly
visible in the night; it appears at the stern and in the wake of every
sailing vessel; every dash of an oar shows it, and every surff and spray:
in storms the whole sea seems on fire.--The detach'd particles of water
then repelled from the electrified surface, continually carry off the fire
as it is collected; they rise, and form clouds, and those clouds are highly
electrified, and retain the fire 'till they have an opportunity of
communicating it.
11. The particles of water rising in vapours, attach themselves to
particles of air.
12. The particles of air are said to be hard, round, separate and distant
from each other; every particle strongly repelling every other particle,
whereby they recede from each other, as far as common gravity will permit.
13. The space between any three particles equally repelling each other,
will be an equilateral triangle.
14. In air compressed, these triangles are smaller; in rarified Air they
are larger.
15. Common fire joined with air, increases the repulsion, enlarges the
triangles, and thereby makes the air specifically lighter. Such Air among
denser air, will rise.
16. Common fire, as well as electrical fire gives repulsion to the
particles of water, and destroys their attraction of cohesion; hence common
fire, as well as electrical fire, assists in raising vapours.
17. Particles of water, having no fire in them, mutually attract each
other. Three particles of water then being attached to the three particles
of a triangle of air, would by their mutual attraction operating against
the air's repulsion, shorten the sides and lessen the triangle, whereby
that portion of air being made denser, would sink to the earth with its
water, and not rise to contribute to the formation of a cloud.
18. But if every particle of water attaching itself to air, brings with it
a particle of common fire, the repulsion of the air being assisted and
strengthened by the fire, more than obstructed by the mutual attraction of
the particles of water, the triangle dilates, and that portion of air
becoming rarer and specifically lighter rises.
19. If the particles of water bring electrical fire when they attach
themselves to air, the repulsion between the particles of water
electrified, joins with the natural repulsion of the air, to force its
particles to a greater distance, whereby the triangles are dilated, and the
air rises, carrying up with it the water.
20. If the particles of water bring with them portions of _both sorts_ of
fire, the repulsions of the particles of air is still more strengthened and
increased, and the triangles farther enlarged.
21. One particle of air may be surrounded by twelve particles of water of
equal size with itself, all in contact with it; and by more added to those.
22. Particles of air thus loaded would be drawn nearer together by the
mutual attraction of the particles of water, did not the fire, common or
electrical, assist their repulsion.
23. If air thus loaded be compressed by adverse winds, or by being driven
against mountains, &c. or condensed by taking away the fire that assisted
it in expanding; the triangles contract, the air with its water will
descend as a dew; or, if the water surrounding one particle of air comes in
contact with the water surrounding another, they coalesce and form a drop,
and we have rain.
24. The sun supplies (or seems to supply) common fire to all vapours,
whether raised from earth or sea.
25. Those vapours which have both common and electrical fire in them, are
better supported, than those which have only common fire in them. For when
vapours rise into the coldest region above the earth, the cold will not
diminish the electrical fire, if it doth the common.
26. Hence clouds formed by vapours raised from fresh waters within land,
from growing vegetables, moist earth, &c. more speedily and easily deposite
their water, having but little electrical fire to repel and keep the
particles separate. So that the greatest part of the water raised from the
land is let fall on the land again; and winds blowing from the land to the
sea are dry; there being little use for rain on the sea, and to rob the
land of its moisture, in order to rain on the sea, would not appear
reasonable.
27. But clouds formed by vapours raised from the sea, having both fires,
and particularly a great quantity of the electrical, support their water
strongly, raise it high, and being moved by winds may bring it over the
middle of the broadest continent from the middle of the widest ocean.
28. How these ocean clouds, so strongly supporting their water, are made to
deposite it on the land where 'tis wanted, is next to be considered.
29. If they are driven by winds against mountains, those mountains being
less electrified attract them, and on contact take away their electrical
fire (and being cold, the common fire also;) hence the particles close
towards the mountains and towards each other. If the air was not much
loaded, it only falls in dews on the mountain tops and sides, forms
springs, and descends to the vales in rivulets, which united make larger
streams and rivers. If much loaded, the electrical fire is at once taken
from the whole cloud; and, in leaving it, flashes brightly and cracks
loudly; the particles instantly coalescing for want of that fire, and
falling in a heavy shower.
30. When a ridge of mountains thus dams the clouds, and draws the
electrical fire from the cloud first approaching it; that which next
follows, when it comes near the first cloud, now deprived of its fire,
flashes into it, and begins to deposite its own water; the first cloud
again flashing into the mountains; the third approaching cloud, and all the
succeeding ones, acting in the same manner as far back as they extend,
which may be over many hundred miles of country.
31. Hence the continual storms of rain, thunder, and lightning on the
east-side of the _Andes_, which running north and south, and being vastly
high, intercept all the clouds brought against them from the _Atlantic_
ocean by the trade winds, and oblige them to deposite their waters, by
which the vast rivers _Amazons_, _La Plata_, and _Oroonoko_ are formed,
which return the water into the same sea, after having fertilized a country
of very great extent.
32. If a country be plain, having no mountains to intercept the electrified
clouds, yet is it not without means to make them deposite their water. For
if an electrified cloud coming from the sea, meets in the air a cloud
raised from the land, and therefore not electrified; the first will flash
its fire into the latter, and thereby both clouds shall be made suddenly to
deposite water.
33. The electrified particles of the first cloud close when they lose their
fire; the particles of the other cloud close in receiving it: in both, they
have thereby an opportunity of coalescing into drops.--The concussion or
jerk given to the air, contributes also to shake down the water, not only
from those two clouds but from others near them. Hence the sudden fall of
rain immediately after flashes of lightning.
34. To shew this by an easy experiment. Take two round pieces of pasteboard
two inches diameter; from the center and circumference of each of them
suspend by fine silk threads eighteen inches long, seven small balls of
wood, or seven peas equal in bigness; so will the balls appending to each
pasteboard, form equal equilateral triangles, one ball being in the center,
and six at equal distances from that, and from each other; and thus they
represent particles of air. Dip both sets in water, and some cohering to
each ball they will represent air loaded. Dexterously electrify one set,
and its balls will repel each other to a greater distance, enlarging the
triangles. Could the water supported by the seven balls come into contact,
it would form a drop or drops so heavy as to break the cohesion it had with
the balls, and so fall.--Let the two sets then represent two clouds, the
one a sea cloud electrified, the other a land cloud. Bring them within the
sphere of attraction, and they will draw towards each other, and you will
see the separated balls close thus; the first electrified ball that comes
near an unelectrified ball by attraction joins it, and gives it fire;
instantly they separate, and each flies to another ball of its own party,
one to give, the other to receive fire; and so it proceeds through both
sets, but so quick as to be in a manner instantaneous. In the collision
they shake off and drop their water, which represents rain.
35. Thus when sea and land clouds would pass at too great a distance for
the flash, they are attracted towards each other till within that distance;
for the sphere of electrical attraction is far beyond the distance of
flashing.
36. When a great number of clouds from the sea meet a number of clouds
raised from the land, the electrical flashes appear to strike in different
parts; and as the clouds are jostled and mixed by the winds, or brought
near by the electrical attraction, they continue to give and receive flash
after flash, till the electrical fire is equally diffused.
37. When the gun-barrel (in electrical experiments) has but little
electrical fire in it, you must approach it very near with your knuckle,
before you can draw a spark. Give it more fire, and it will give a spark at
a greater distance. Two gun-barrels united, and as highly electrified, will
give a spark at a still greater distance. But if two gun-barrels
electrified will strike at two inches distance, and make a loud snap, to
what a great distance may 10,000 acres of electrified cloud strike and give
its fire, and how loud must be that crack!
38. It is a common thing to see clouds at different heights passing
different ways, which shews different currents of air, one under the other.
As the air between the tropics is rarified by the sun, it rises, the denser
northern and southern air pressing into its place. The air so rarified and
forced up, passes northward and southward, and must descend in the polar
regions, if it has no opportunity before, that the circulation may be
carried on.
39. As currents of air, with the clouds therein, pass different ways, 'tis
easy to conceive how the clouds, passing over each other, may attract each
other, and so come near enough for the electrical stroke. And also how
electrical clouds may be carried within land very far from the sea, before
they have an opportunity to strike.
40. When the air, with its vapours raised from the ocean between the
tropics, comes to descend in the polar regions, and to be in contact with
the vapours arising there, the electrical fire they brought begins to be
communicated, and is seen in clear nights, being first visible where 'tis
first in motion, that is, where the contact begins, or in the most northern
part; from thence the streams of light seem to shoot southerly, even up to
the zenith of northern countries. But tho' the light seems to shoot from
the north southerly, the progress of the fire is really from the south
northerly, its motion beginning in the north being the reason that 'tis
there first seen.
For the electrical fire is never visible but when in motion, and leaping
from body to body, or from particle to particle thro' the air. When it
passes thro' dense bodies 'tis unseen. When a wire makes part of the
circle, in the explosion of the electrical phial, the fire, though in great
quantity, passes in the wire invisibly: but in passing along a chain, it
becomes visible as it leaps from link to link. In passing along
leaf-gilding 'tis visible: for the leaf-gold is full of pores; hold a leaf
to the light and it appears like a net; and the fire is seen in its leaping
over the vacancies.--And as when a long canal filled with still water is
opened at one end, in order to be discharged, the motion of the water
begins first near the opened end, and proceeds towards the close end, tho'
the water itself moves from the close towards the opened end: so the
electrical fire discharged into the polar regions, perhaps from a thousand
leagues length of vaporiz'd air, appears first where 'tis first in motion,
_i. e._ in the most northern part, and the appearance proceeds southward,
tho' the fire really moves northward. This is supposed to account for the
_Aurora Borealis_.
41. When there is great heat on the land, in a particular region (the sun
having shone on it perhaps several days, while the surrounding countries
have been screen'd by clouds) the lower air is rarified and rises, the
cooler denser air above descends; the clouds in that air meet from all
sides, and join over the heated place; and if some are electrified, others
not, lightning and thunder succeed, and showers fall. Hence thunder-gusts
after heats, and cool air after gusts; the water and the clouds that bring
it, coming from a higher and therefore a cooler region.
42. An electrical spark, drawn from an irregular body at some distance is
scarce ever strait, but shows crooked and waving in the air. So do the
flashes of lightning; the clouds being very irregular bodies.
43. As electrified clouds pass over a country, high hills and high trees,
lofty towers, spires, masts of ships, chimneys, _&c._ as so many
prominencies and points, draw the electrical fire, and the whole cloud
discharges there.
44. Dangerous, therefore, is it to take shelter under a tree during a
thunder-gust. It has been fatal to many, both men and beasts.
45. It is safer to be in the open field for another reason. When the
clothes are wet, if a flash in its way to the ground should strike your
head, it will run in the water over the surface of your body; whereas, if
your clothes were dry, it would go thro' the body.
Hence a wet rat cannot be killed by the exploding electrical bottle, when a
dry rat may.
46. Common fire is in all bodies, more or less, as well as electrical fire.
Perhaps they may be different modifications of the same element; or they
may be different elements. The latter is by some suspected.
47. If they are different things, yet they may and do subsist together in
the same body.
48. When electrical fire strikes thro' a body, it acts upon the common fire
contained in it, and puts that fire in motion; and if there be a sufficient
quantity of each kind of fire, the body will be inflamed.
49. When the quantity of common fire in the body is small, the quantity of
the electrical fire (or the electrical stroke) should be greater: if the
quantity of common fire be great, less electrical fire suffices to produce
the effect.
50. Thus spirits must be heated before we can fire them by the electrical
spark. If they are much heated a small spark will do; if not, the spark
must be greater.
51. Till lately we could only fire warm vapours; but now we can burn hard
dry rosin. And when we can procure greater electrical sparks, we may be
able to fire not only unwarm'd spirits, as lightning does, but even wood,
by giving sufficient agitation to the common fire contained in it, as
friction we know will do.
52. Sulphureous and inflammable vapours arising from the earth, are easily
kindled by lightning. Besides what arise from the earth, such vapours are
sent out by stacks of moist hay, corn, or other vegetables, which heat and
reek. Wood rotting in old trees or buildings does the same. Such are
therefore easily and often fired.
53. Metals are often melted by lightning, tho' perhaps not from heat in the
lightning, nor altogether from agitated fire in the metals.--For as
whatever body can insinuate itself between the particles of metal, and
overcome the attraction by which they cohere (as sundry menstrua can) will
make the solid become a fluid, as well as fire, yet without heating it: so
the electrical fire, or lightning, creating a violent repulsion between the
particles of the metal it passes thro', the metal is fused.
54. If you would, by a violent fire, melt off the end of a nail, which is
half driven into a door, the heat given the whole nail before a part would
melt, must burn the board it sticks in. And the melted part would burn the
floor it dropp'd on. But if a sword can be melted in the scabbard, and
money in a man's pocket, by lightning, without burning either, it must be a
cold fusion.
55. Lightning rends some bodies. The electrical spark will strike a hole
thro' a quire of strong paper.
56. If the source of lightning, assigned in this paper, be the true one,
there should be little thunder heard at sea far from land. And accordingly
some old sea-captains, of whom enquiry has been made, do affirm, that the
fact agrees perfectly with the hypothesis; for that, in crossing the great
ocean, they seldom meet with thunder till they come into soundings; and
that the islands far from the continent have very little of it. And a
curious observer, who lived 13 years at _Bermudas_, says, there was less
thunder there in that whole time than he has sometimes heard in a month at
_Carolina_.
ADDITIONAL PAPERS.
TO
Mr. PETER COLLINSON, F.R.S. _London_.
PHILADELPHIA, _July 29, 1750_
_SIR_,
As you first put us on electrical experiments, by sending to our library
company a tube, with directions how to use it; and as our honourable
proprietary enabled us to carry those experiments to a greater height, by
his generous present of a compleat electrical apparatus; 'tis fit that both
should know from time to time what progress we make. It was in this view I
wrote and sent you my former papers on this subject, desiring, that as I
had not the honour of a direct correspondence with that bountiful
benefactor to our library, they might be communicated to him through your
hands. In the same view I write, and send you this additional paper. If it
happens to bring you nothing new (which may well be, considering the number
of ingenious men in _Europe_, continually engaged in the same researches)
at least it will show, that the instruments, put into our hands, are not
neglected; and, that if no valuable discoveries are made by us, whatever
the cause may be, it is not want of industry and application.
_I am, Sir,
Your much obliged
Humble Servant_,
B. FRANKLIN.
OPINIONS and CONJECTURES,
_Concerning the Properties and Effects of the electrical Matter, arising
from Experiments and Observations, made in_ Philadelphia, 1749.