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They are the greatest and most formidable phenomena of nature. Aristotle and Pliny distinguish two kinds, with respect to the manner of the shake, viz., a tremour and a pulsation; the first being horizontal, in alternate vibrations, compared to the shaking of a person in an ague; the second perpendicular, up and down, their motion resembling that of boiling.

Agricola increases the number, and makes four kinds, which Albertus Magnus again reduces to three, viz., inclination, when the earth vibrates alternately from right to left, by which mountains have been sometimes brought to meet and clash against each other; pulsation, when it beats up and down, like an artery; and trembling, when it shakes and totters every way, like a flame.

The Philosophical Transactions furnish us with abundance of histories of earthquakes, particularly one at Oxford in 1665, by Dr. Wallis and Mr. Boyle. Another at the same place in 1683, by Mr. Pigot. Another in Sicily, in 1692-3, by Mr. Hartop, Father Alessandro Burgos, and Vin. Bonajutus, which last is one of the most terrible ones in all history.

It shook the whole island; and not only that, but Naples and Malta shared in the shock. It was of the second kind mentioned by Aristotle and Pliny, viz., a perpendicular pulsation or succussion. It was impossible, says the noble Bonajutus, for anybody in this country to keep on their legs on the dancing earth; nay, those that lay on the ground were tossed from side to side as on a rolling billow; high walls leaped from their foundations several paces.

The mischief it did is amazing; almost all the buildings in the countries were thrown down. Fifty-four cities and towns, besides an incredible number of villages, were either destroyed or greatly damaged. We shall only instance the fate of Catania, one of the most famous, ancient, and flourishing cities in the kingdom, the residence of several monarchs, and a university. "This once famous, now unhappy Catania," to use words of Father Burgos, "had the greatest share in the tragedy. Father Antonio Serovita, being on his way thither, and at the distance of a few miles, observed a black cloud, like night, hovering over the city, and there arose from the mouth of Mongibello great spires of flame, which spread all around. The sea, all of a sudden, began to roar and rise in billows, and there was a blow, as if all the artillery in the world had been at once discharged. The birds flew about astonished, the cattle in the fields ran crying, &c. His and his companion's horse stopped short, trembling; so that they were forced to alight. They were no sooner off but they were lifted from the ground above two palms. When, casting his eyes towards Catania, he with amazement saw nothing but a thick cloud of dust in the air. This was the scene of their calamity; for of the magnificent Catania there is not the least footstep to be seen." Bonajutus assures us, that of 18,914 inhabitants, 18,000 perished therein. The same author, from a computation of the inhabitants before and after the earthquake, in the several cities and towns, finds that near 60,000 perished out of 254,900.

Jamaica is remarkable for earthquakes. The inhabitants, Dr. Sloane informs us, expect one every year. The author gives the history of one in 1687; another horrible one, in 1692, is described by several anonymous authors. In two minutes' time it shook down and drowned nine tenths of the town of Port Royal. The houses sunk outright, thirty or forty fathoms deep. The earth, opening, swallowed up people, and they rose in other streets; some in the middle of the harbour, and yet were saved; though there were two thousand people lost, and one thousand acres of land sunk. All the houses were thrown down throughout the island. One Hopkins had his plantation removed half a mile from its place. Of all wells, from one fathom to six or seven, the water flew out at the top with a vehement motion. While the houses on the one side of the street were swallowed up, on the other they were thrown in heaps; and the sand in the street rose like waves in the sea, lifting up everybody that stood on it, and immediately dropping down into pits; and at the same instant, a flood of waters breaking in, rolled them over and over; some catching hold of beams and rafters, &c. Ships and sloops in the harbour were overset and lost; the Swan frigate particularly, by the motion of the sea and sinking of the wharf, was driven over the tops of many houses.

It was attended with a hollow rumbling noise like that of thunder. In less than a minute three quarters of the houses, and the ground they stood on, with the inhabitants, were all sunk quite under water, and the little part left behind was no better than a heap of rubbish. The shake was so violent that it threw people down on their knees or their faces, as they were running about for shelter. The ground heaved and swelled like a rolling sea, and several houses, still standing, were shuffled and moved some yards out of their places. A whole street is said to be twice as broad now as before; and in many places the earth would crack, and open, and shut, quick and fast, of which openings two or three hundred might be seen at a time; in some whereof the people were swallowed up, others the closing earth caught by the middle and pressed to death, in others the heads only appeared. The larger openings swallowed up houses; and out of some would issue whole rivers of waters, spouted up a great height into the air, and threatening a deluge to that part the earthquake spared. The whole was attended with stenches and offensive smells, the noise of falling mountains at a distance, &c., and the sky in a minute's time was turned dull and reddish, like a glowing oven. Yet, as great a sufferer as Port Royal was, more houses were left standing therein than on the whole island besides. Scarce a planting-house or sugar-work was left standing in all Jamaica. A great part of them were swallowed up, houses, people, trees, and all at one gape; in lieu of which afterward appeared great pools of water, which, when dried up, left nothing but sand, without any mark that ever tree or plant had been thereon.

Above twelve miles from the sea the earth gaped and spouted out, with a prodigious force, vast quantities of water into the air, yet the greatest violences were among the mountains and rocks; and it is a general opinion, that the nearer the mountains, the greater the shake, and that the cause thereof lay there. Most of the rivers were stopped up for twenty-four hours by the falling of the mountains, till, swelling up, they found themselves new tracts and channels, tearing up in their passage trees, &c. After the great shake, those people who escaped got on board ships in the harbour, where many continued above two months; the shakes all that time being so violent, and coming so thick, sometimes two or three in an hour, accompanied with frightful noises, like a ruffling wind, or a hollow, rumbling thunder, with brimstone blasts, that they durst not come ashore. The consequence of the earthquake was a general sickness, from the noisome vapours belched forth, which swept away above three thousand persons.

After the detail of these horrible convulsions, the reader will have but little curiosity left for the less considerable phenomena of the earthquake at Lima in 1687, described by Father Alvarez de Toledo, wherein above five thousand persons were destroyed; this being of the vibratory kind, so that the bells in the church rung of themselves; or that at Batavia in 1699, by Witsen; that in the north of England in 1703, by Mr. Thoresby; or, lastly, those in New-England in 1663 and 1670, by Dr. Mather.

To David Rittenhouse

New and curious Theory of Light and Heat.– Read in the American Philosophical Society, November 20, 1788

Universal space, as far as we know of it, seems to be filled with a subtile fluid, whose motion or vibration is called light.

This fluid may possibly be the same with that which, being attracted by, and entering into other more solid matter, dilutes the substance by separating the constituent particles, and so rendering some solids fluid, and maintaining the fluidity of others; of which fluid, when our bodies are totally deprived, they are said to be frozen; when they have a proper quantity, they are in health, and fit to perform all their functions; it is then called natural heat; when too much, it is called fever; and when forced into the body in too great a quantity from without, it gives pain, by separating and destroying the flesh, and is then called burning, and the fluid so entering and acting is called fire.

While organized bodies, animal or vegetable, are augmenting in growth, or are supplying their continual waste, is not this done by attracting and consolidating this fluid called fire, so as to form of it a part of their substance? And is it not a separation of the parts of such substance, which, dissolving its solid state, sets that subtile fluid at liberty, when it again makes its appearance as fire?

For the power of man relative to matter seems limited to the separating or mixing the various kinds of it, or changing its form and appearance by different compositions of it; but does not extend to the making or creating new matter, or annihilating the old. Thus, if fire be an original element or kind of matter, its quantity is fixed and permanent in the universe. We cannot destroy any part of it, or make addition to it; we can only separate it from that which confines it, and so set it at liberty; as when we put wood in a situation to be burned, or transfer it from one solid to another, as when we make lime by burning stone, a part of the fire dislodged in the fuel being left in the stone. May not this fluid, when at liberty, be capable of penetrating and entering into all bodies, organized or not, quitting easily in totality those not organized, and quitting easily in part those which are; the part assumed and fixed remaining till the body is dissolved?

Is it not this fluid which keeps asunder the particles of air, permitting them to approach, or separating them more in proportion as its quantity is diminished or augmented?

Is it not the greater gravity of the particles of air which forces the particles of this fluid to mount with the matters to which it is attached, as smoke or vapour?

Does it not seem to have a greater affinity with water, since it will quit a solid to unite with that fluid, and go off with it in vapour, leaving the solid cold to the touch, and the degree measurable by the thermometer?

The vapour rises attached to this fluid, but at a certain height they separate, and the vapour descends in rain, retaining but little of it, in snow or hail less. What becomes of that fluid? Does it rise above our atmosphere, and mix with the universal mass of the same kind?

Or does a spherical stratum of it, denser, as less mixed with air, attracted by this globe, and repelled or pushed up only to a certain height from its surface by the greater weight of air, remain there surrounding the globe, and proceeding with it round the sun?

In such case, as there may be a continuity of communication of this fluid through the air quite down to the earth, is it not by the vibrations given to it by the sun that light appears to us? And may it not be that every one of the infinitely small vibrations, striking common matter with a certain force, enters its substance, is held there by attraction, and augmented by succeeding vibrations till the matter has received as much as their force can drive into it?

Is it not thus that the surface of this globe is continually heated by such repeated vibrations in the day, and cooled by the escape of the heat when those vibrations are discontinued in the night, or intercepted and reflected by clouds?

Is it not thus that fire is amassed, and makes the greatest part of the substance of combustible bodies?

Perhaps, when this globe was first formed, and its original particles took their place at certain distances from the centre, in proportion to their greater or less gravity, the fluid fire, attracted towards that centre, might in great part be obliged, as lightest, to take place above the rest, and thus form the sphere of fire above supposed, which would afterward be continually diminishing by the substance it afforded to organized bodies, and the quantity restored to it again by the burning or other separating of the parts of those bodies?

Is not the natural heat of animals thus produced, by separating in digestion the parts of food, and setting their fire at liberty?

Is it not this sphere of fire which kindles the wandering globes that sometimes pass through it in our course round the sun, have their surface kindled by it, and burst when their included air is greatly rarefied by the heat on their burning surfaces?

May it not have been from such considerations that the ancient philosophers supposed a sphere of fire to exist above the air of our atmosphere?

B. Franklin.

Of Lightning; and the Methods now used in America for the securing Buildings and Persons from its mischievous Effects.

Experiments made in electricity first gave philosophers a suspicion that the matter of lightning was the same with the electric matter. Experiments afterward made on lightning obtained from the clouds by pointed rods, received into bottles, and subjected to every trial, have since proved this suspicion to be perfectly well founded; and that, whatever properties we find in electricity, are also the properties of lightning.

This matter of lightning or of electricity is an extreme subtile fluid, penetrating other bodies, and subsisting in them, equally diffused.

When, by any operation of art or nature, there happens to be a greater proportion of this fluid in one body than in another, the body which has most will communicate to that which has least, till the proportion becomes equal; provided the distance between them be not too great; or, if it is too great, till there be proper conductors to convey it from one to the other.

If the communication be through the air without any conductor, a bright light is seen between the bodies, and a sound is heard. In our small experiments we call this light and sound the electric spark and snap; but in the great operations of nature the light is what we call lightning, and the sound (produced at the same time, though generally arriving later at our ears than the light does to our eyes) is, with its echoes, called thunder.

If the communication of this fluid is by a conductor, it may be without either light or sound, the subtile fluid passing in the substance of the conductor.

If the conductor be good and of sufficient bigness, the fluid passes through it without hurting it. If otherwise, it is damaged or destroyed.

All metals and water are good conductors. Other bodies may become conductors by having some quantity of water in them, as wood and other materials used in building; but, not having much water in them, they are not good conductors, and, therefore, are often damaged in the operation.

Glass, wax, silk, wool, hair, feathers, and even wood, perfectly dry, are non-conductors: that is, they resist instead of facilitating the passage of this subtile fluid.

When this fluid has an opportunity of passing through two conductors, one good and sufficient, as of metal, the other not so good, it passes in the best, and will follow it in any direction.

The distance at which a body charged with this fluid will discharge itself suddenly, striking through the air into another body that is not charged or not so highly charged, is different according to the quantity of the fluid, the dimensions and form of the bodies themselves, and the state of the air between them. This distance, whatever it happens to be, between any two bodies, is called the striking distance, as, till they come within that distance of each other, no stroke will be made.

The clouds have often more of this fluid, in proportion, than the earth; in which case, as soon as they come near enough (that is, within the striking distance) or meet with a conductor, the fluid quits them and strikes into the earth. A cloud fully charged with this fluid, if so high as to be beyond the striking distance from the earth, passes quietly without making noise or giving light, unless it meets with other clouds that have less.

Tall trees and lofty buildings, as the towers and spires of churches, become sometimes conductors between the clouds and the earth; but, not being good ones, that is, not conveying the fluid freely, they are often damaged.

Buildings that have their roofs covered with lead or other metal, the spouts of metal continued from the roof into the ground to carry off the water, are never hurt by lightning as, whenever it falls on such a building, it passes in the metals and not in the walls.

When other buildings happen to be within the striking distance from such clouds, the fluid passes in the walls, whether of wood, brick, or stone, quitting the walls only when it can find better conductors near them, as metal rods, bolts, and hinges of windows or doors, gilding on wainscot or frames of pictures, the silvering on the backs of looking-glasses, the wires for bells, and the bodies of animals, as containing watery fluids. And, in passing through the house, it follows the direction of these conductors, taking as many in its way as can assist it in its passage, whether in a straight or crooked line, leaping from one to the other, if not far distant from each other, only rending the wall in the spaces where these partial good conductors are too distant from each other.

An iron rod being placed on the outside of a building, from the highest part continued down into the moist earth in any direction, straight or crooked, following the form of the roof or parts of the building, will receive the lightning at the upper end, attracting it so as to prevent its striking any other part, and affording it a good conveyance into the earth, will prevent its damaging any part of the building.

A small quantity of metal is found able to conduct a great quantity of this fluid. A wire no bigger than a goosequill has been known to conduct (with safety to the building as far as the wire was continued) a quantity of lightning that did prodigious damage both above and below it; and probably larger rods are not necessary, though it is common in America to make them of half an inch, some of three quarters or an inch diameter.

The rod may be fastened to the wall, chimney &c., with staples of iron. The lightning will not leave the rod (a good conductor) through those staples. It would rather, if any were in the walls, pass out of it into the rod, to get more readily by that conductor into the earth.

If the building be very large and extensive, two or more rods may be placed at different parts, for greater security.

Small ragged parts of clouds, suspended in the air between the great body of clouds and the earth (like leaf gold in electrical experiments) often serve as partial conductors for the lightning, which proceeds from one of them to another, and by their help comes within the striking distance to the earth or a building. It therefore strikes through those conductors a building that would otherwise be out of the striking distance.

Long sharp points communicating with the earth, and presented to such parts of clouds, drawing silently from them the fluid they are charged with, they are then attracted to the cloud, and may leave the distance so great as to be beyond the reach of striking.

It is therefore that we elevate the upper end of the rod six or eight feet above the highest part of the building, tapering it gradually to a fine sharp point, which is gilt to prevent its rusting.

Thus the pointed rod either prevents the stroke from the cloud, or, if a stroke is made, conducts it to the earth with safety to the building.

The lower end of the rod should enter the earth so deep as to come at the moist part, perhaps two or three feet; and if bent when under the surface so as to go in a horizontal line six or eight feet from the wall, and then bent again downward three or four feet, it will prevent damage to any of the stones of the foundation.

A person apprehensive of danger from lightning, happening during the time of thunder to be in a house not so secured, will do well to avoid sitting near the chimney, near a looking-glass, or any gilt pictures or wainscot; the safest place is the middle of the room (so it be not under a metal lustre suspended by a chain), sitting on one chair and laying the feet up in another. It is still safer to bring two or three mattresses or beds into the middle of the room, and, folding them up double, place the chair upon them; for they not being so good conductors as the walls, the lightning will not choose an interrupted course through the air of the room and the bedding, when it can go through a continued better conductor, the wall. But where it can be had, a hammock or swinging bed, suspended by silk cords equally distant from the walls on every side, and from the ceiling and floor above and below, affords the safest situation a person can have in any room whatever; and what, indeed, may be deemed quite free from danger of any stroke by lightning.

B. Franklin.

Paris, September, 1767.

To Peter Collinson, London

ELECTRICAL KITE

Philadelphia, October 16, 1752.

As frequent mention is made in public papers from Europe of the success of the Philadelphia experiment for drawing the electric fire from clouds by means of pointed rods of iron erected on high buildings, &c., it may be agreeable to the curious to be informed that the same experiment has succeeded in Philadelphia, though made in a different and more easy manner, which is as follows:

Make a small cross of two light strips of cedar, the arms so long as to reach to the four corners of a large thin silk handkerchief when extended; tie the corners of the handkerchief to the extremities of the cross, so you have the body of a kite, which, being properly accommodated with a tail, loop, and string, will rise in the air like those made of paper; but this, being of silk, is fitter to bear the wet and wind of a thunder-gust without tearing. To the top of the upright stick of the cross is to be fixed a very sharp-pointed wire, rising a foot or more above the wood. To the end of the twine next the hand is to be tied a silk riband, and where the silk and twine join, a key may be fastened. This kite is to be raised when a thunder-gust appears to be coming on, and the person who holds the string must stand within a door or window, or under some cover, so that the silk riband may not be wet; and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder-clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified, and the loose filaments of the twine will stand out every way, and be attracted by an approaching finger. And when the rain has wetted the kite and twine, so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle. At this key the vial may be charged; and from electric fire thus obtained, spirits may be kindled, and all the other electric experiments be performed, which are usually done by the help of a rubbed glass globe or tube, and thereby the sameness of the electric matter with that of lightning completely demonstrated.

B. Franklin.

Physical and Meteorological Observations, Conjectures, and Suppositions.– Read at the Royal Society, June 3, 1756.

The particles of air are kept at a distance from each other by their mutual repulsion * * *

Whatever particles of other matter (not endued with that repellancy) are supported in air, must adhere to the particles of air, and be supported by them; for in the vacancies there is nothing they can rest on.

Air and water mutually attract each other. Hence water will dissolve in air, as salt in water.

The specific gravity of matter is not altered by dividing the matter, though the superfices be increased. Sixteen leaden bullets, of an ounce each, weigh as much in water as one of a pound, whose superfices is less.

Therefore the supporting of salt in water is not owing to its superfices being increased.

A lump of salt, though laid at rest at the bottom of a vessel of water, will dissolve therein, and its parts move every way, till equally diffused in the water; therefore there is a mutual attraction between water and salt. Every particle of water assumes as many of salt as can adhere to it; when more is added, it precipitates, and will not remain suspended.

Water, in the same manner, will dissolve in air, every particle of air assuming one or more particles of water. When too much is added, it precipitates in rain.

But there not being the same contiguity between the particles of air as of water, the solution of water in air is not carried on without a motion of the air so as to cause a fresh accession of dry particles.

Part of a fluid, having more of what it dissolves, will communicate to other parts that have less. Thus very salt water, coming in contact with fresh, communicates its saltness till all is equal, and the sooner if there is a little motion of the water. * * *

Air, suffering continual changes in the degrees of its heat, from various causes and circumstances, and, consequently, changes in its specific gravity, must therefore be in continual motion.

A small quantity of fire mixed with water (or degree of heat therein) so weakens the cohesion of its particles, that those on the surface easily quit it and adhere to the particles of air.

Air moderately heated will support a greater quantity of water invisibly than cold air; for its particles being by heat repelled to a greater distance from each other, thereby more easily keep the particles of water that are annexed to them from running into cohesions that would obstruct, refract, or reflect the light.

Hence, when we breathe in warm air, though the same quantity of moisture may be taken up from the lungs as when we breathe in cold air, yet that moisture is not so visible.

Water being extremely heated, i. e., to the degree of boiling, its particles, in quitting it, so repel each other as to take up vastly more space than before and by that repellancy support themselves, expelling the air from the space they occupy. That degree of heat being lessened, they again mutually attract, and having no air particles mixed to adhere to, by which they might be supported and kept at a distance, they instantly fall, coalesce, and become water again.

The water commonly diffused in our atmosphere never receives such a degree of heat from the sun or other cause as water has when boiling; it is not, therefore, supported by such heat, but by adhering to air. * * *

A particle of air loaded with adhering water or any other matter, is heavier than before, and would descend.

The atmosphere supposed at rest, a loaded descending particle must act with a force on the particles it passes between or meets with sufficient to overcome, in some degree, their mutual repellancy, and push them nearer to each other. * * *

Every particle of air, therefore, will bear any load inferior to the force of these repulsions.

Hence the support of fogs, mists, clouds.

Very warm air, clear, though supporting a very great quantity of moisture, will grow turbid and cloudy on the mixture of colder air, as foggy, turbid air will grow clear by warming.

Thus the sun, shining on a morning fog, dissipates it; clouds are seen to waste in a sunshiny day.

But cold condenses and renders visible the vapour: a tankard or decanter filled with cold water will condense the moisture of warm, clear air on its outside, where it becomes visible as dew, coalesces into drops, descends in little streams.

The sun heats the air of our atmosphere most near the surface of the earth; for there, besides the direct rays, there are many reflections. Moreover, the earth itself, being heated, communicates of its heat to the neighbouring air.

The higher regions, having only the direct rays of the sun passing through them, are comparatively very cold. Hence the cold air on the tops of mountains, and snow on some of them all the year, even in the torrid zone. Hence hail in summer.

If the atmosphere were, all of it (both above and below), always of the same temper as to cold or heat, then the upper air would always be rarer than the lower, because the pressure on it is less; consequently lighter, and, therefore, would keep its place.

But the upper air may be more condensed by cold than the lower air by pressure; the lower more expanded by heat than the upper for want of pressure. In such case the upper air will become the heavier, the lower the lighter.

The lower region of air being heated and expanded, heaves up and supports for some time the colder, heavier air above, and will continue to support it while the equilibrium is kept. Thus water is supported in an inverted open glass, while the equilibrium is maintained by the equal pressure upward of the air below; but the equilibrium by any means breaking, the water descends on the heavier side, and the air rises into its place.

The lifted heavy cold air over a heated country becoming by any means unequally supported or unequal in its weight, the heaviest part descends first, and the rest follows impetuously. Hence gusts after heats, and hurricanes in hot climates. Hence the air of gusts and hurricanes is cold, though in hot climates and seasons; it coming from above.

The cold air descending from above, as it penetrates our warm region full of watery particles, condenses them, renders them visible, forms a cloud thick and dark, overcasting sometimes, at once, large and extensive; sometimes, when seen at a distance, small at first, gradually increasing; the cold edge or surface of the cloud condensing the vapours next it, which form smaller clouds that join it, increase its bulk, it descends with the wind and its acquired weight, draws nearer the earth, grows denser with continual additions of water, and discharges heavy showers.