* * * * *
CAUSES OF EARTHQUAKES.
The late earthquake felt here, and probably in all the neighbouring
provinces, having made many people desirous to know what may be the
natural cause of such violent concussions, we shall endeavour to gratify
their curiosity by giving them the various opinions of the learned on
that head.
Here naturalists are divided. Some ascribe them to water, others to
fire, and others to air, and all of them with some appearance of reason.
To conceive which, it is to be observed that the earth everywhere
abounds in huge subterraneous caverns, veins, and canals, particularly
about the roots of mountains; that of these cavities, veins, &c., some
are full of water, whence are composed gulfs, abysses, springs,
rivulets; and others full of exhalations; and that some parts of the
earth are replete with nitre, sulphur, bitumen, vitriol, &c. This
premised,
1. The earth itself may sometimes be the cause of its own shaking; when
the roots or basis of some large mass being dissolved, or worn away by a
fluid underneath, it sinks into the same, and, with its weight,
occasions a tremour of the adjacent parts, produces a noise, and
frequently an inundation of water.
2. The subterraneous waters may occasion earthquakes by their
overflowing, cutting out new courses, &c. Add that the water, being
heated and rarefied by the subterraneous fires, may emit fumes, blasts,
&c., which, by their action either on the water or immediately on the
earth itself, may occasion great succussions.
3. The air may be the cause of earthquakes; for the air being a
collection of fumes and vapours raised from the earth and water, if it
be pent up in too narrow viscera of the earth, the subterraneous or its
own native heat rarefying and expanding it, the force wherewith it
endeavours to escape may shake the earth; hence there arises divers
species of earthquakes, according to the different position, quantity,
&c., of the imprisoned _aura_.
Lastly, fire is a principal cause of earthquakes; both as it produces
the aforesaid subterraneous _aura_ or vapours, and as this _aura_ or
spirit, from the different matter and composition whereof arise sulphur,
bitumen, and other inflammable matters, takes fire, either from other
fire it meets withal, or from its collision against hard bodies, or its
intermixture with other fluids; by which means, bursting out into a
greater compass, the place becomes too narrow for it, so that, pressing
against it on all sides, the adjoining parts are shaken, till, having
made itself a passage, it spends itself in a volcano or burning
mountain.
But to come nearer to the point. Dr. Lister is of opinion that the
material cause of thunder, lightning, and earthquakes, is one and the
same, viz., the inflammable breath of the pyrites, which is a
substantial sulphur, and takes fire of itself.
The difference between these three terrible phenomena he takes only to
consist in this: that the sulphur in the former is fired in the air, and
in the latter under ground. Which is a notion Pliny had long before him:
"_Quid enim_," says he, "_aliud est in terrâ tremor, quam in nube
tonitru?_" For wherein does the trembling of the earth differ from that
occasioned by thunder in the clouds?
This he thinks abundantly indicated by the same sulphurous smell being
found in anything burned with lightning, and in the waters, &c., cast up
in earthquakes, and even in the air before and after them.
Add that they agree in the manner of the noise which is carried on, as
in a train fired; the one, rolling and rattling through the air, takes
fire as the vapours chance to drive; as the other, fired under ground in
like manner, moves with a desultory noise.
Thunder, which is the effect of the trembling of the air, caused by the
same vapours dispersed through it, has force enough to shake our houses;
and why there may not be thunder and lightning under ground, in some
vast repositories there, I see no reason; especially if we reflect that
the matter which composes the noisy vapour above us is in much larger
quantities under ground.
That the earth abounds in cavities everybody allows; and that these
subterraneous cavities are, at certain times and in certain seasons,
full of inflammable vapours, the damps in mines sufficiently witness,
which, fired, do everything as in an earthquake, save in a lesser
degree.
Add that the pyrites alone, of all the known minerals, yields this
inflammable vapour, is highly probable; for that no mineral or ore
whatsoever is sulphurous, but as it is wholly or in part a pyrites, and
that there is but one species of brimstone which the pyrites naturally
and only yields. The _sulphur vive_, or natural brimstone, which is
found in and about the burning mountains, is certainly the effects of
sublimation, and those great quantities of it said to be found about the
skirts of volcanoes is only an argument of the long duration and
vehemence of those fires. Possibly the pyrites of the volcanoes, or
burning mountains, may be more sulphurous than ours; and, indeed, it is
plain that some of ours in England are very lean, and hold but little
sulphur; others again very much, which may be some reason why England is
so little troubled with earthquakes, and Italy, and almost all round the
Mediterranean Sea, so much; though another reason is, the paucity of
pyrites in England.
Comparing our earthquakes, thunder, and lightning, with theirs, it is
observed that there it lightens almost daily, especially in summer-time,
here seldom; there thunder and lightning is of long duration, here it is
soon over; there the earthquakes are frequent, long, and terrible, with
many paroxysms in a day, and that for many days; here very short, a few
minutes, and scarce perceptible. To this purpose the subterraneous
caverns in England are small and few compared to the vast vaults in
those parts of the world; which is evident from the sudden disappearance
of whole mountains and islands.
Dr. Woodward gives us another theory of earthquakes. He endeavours to
show that the subterraneous heat or fire (which is continually elevating
water out of the abyss, to furnish the earth with rain, dew, springs,
and rivers), being stopped in any part of the earth, and so diverted
from its ordinary course by some accidental glut or obstruction in the
pores or passages through which it used to ascend to the surface,
becomes, by such means, preternaturally assembled in a greater quantity
than usual into one place, and therefore causeth a great rarefaction and
intumescence of the water of the abyss, putting it into great commotions
and disorders, and at the same time making the like effort on the earth,
which, being expanded upon the face of the abyss, occasions that
agitation and concussion we call an earthquake.
This effort in some earthquakes, he observes, is so vehement, that it
splits and tears the earth, making cracks and chasms in it some miles in
length, which open at the instant of the shock, and close again in the
intervals between them; nay, it is sometimes so violent that it forces
the superincumbent strata, breaks them all throughout, and thereby
perfectly undermines and ruins the foundation of them; so that, these
failing, the whole tract, as soon as the shock is over, sinks down into
the abyss, and is swallowed up by it, the water thereof immediately
rising up and forming a lake in the place where the said tract before
was. That this effort being made in all directions indifferently, the
fire, dilating and expanding on all hands, and endeavouring to get room
and make its way through all obstacles, falls as foul on the waters of
the abyss beneath as on the earth above, forcing it forth, which way
soever it can find vent or passage, as well through its ordinary exits,
wells, springs, and the outlets of rivers, as through the chasms then
newly opened, through the _camini_ or spiracles of Ætna, or other
neighbouring volcanoes, and those hiatuses at the bottom of the sea
whereby the abyss below opens into it and communicates with it. That as
the water resident in the abyss is, in all parts of it, stored with a
considerable quantity of heat, and more especially in those where those
extraordinary aggregations of this fire happen, so likewise is the water
which is thus forced out of it, insomuch that, when thrown forth and
mixed with the waters of wells, or springs of rivers and the sea, it
renders them very sensibly hot.
He adds, that though the abyss be liable to those commotions in all
parts, yet the effects are nowhere very remarkable except in those
countries which are mountainous, and, consequently, stony or cavernous
underneath; and especially where the disposition of the strata is such
that those caverns open the abyss, and so freely admit and entertain the
fire which, assembling therein, is the cause of the shock; it naturally
steering its course that way where it finds the readiest reception,
which is towards those caverns. Besides, that those parts of the earth
which abound with strata of stone or marble, making the strongest
opposition to this effort, are the most furiously shattered, and suffer
much more by it than those which consist of gravel, sand, and the like
laxer matter, which more easily give way, and make not so great
resistance. But, above all, those countries which yield great store of
sulphur and nitre are by far the most injured by earthquakes; those
minerals constituting in the earth a kind of natural gunpowder, which,
taking fire upon this assemblage and approach of it, occasions that
murmuring noise, that subterraneous thunder, which is heard rumbling in
the bowels of the earth during earthquakes, and by the assistance of its
explosive power renders the shock much greater, so as sometimes to make
miserable havoc and destruction.
And it is for this reason that Italy, Sicily, Anatolia, and some parts
of Greece, have been so long and often alarmed and harassed by
earthquakes; these countries being all mountainous and cavernous,
abounding with stone and marble, and affording sulphur and nitre in
great plenty.
Farther, that Ætna, Vesuvius, Hecla, and the other volcanoes, are only
so many spiracles, serving for the discharge of this subterraneous fire,
when it is thus preternaturally assembled. That where there happens to
be such a structure and conformation of the interior part of the earth,
as that the fire may pass freely, and without impediment, from the
caverns wherein it assembles unto those spiracles, it then readily gets
out, from time to time, without shaking or disturbing the earth; but
where such communication is wanting, or passage not sufficiently large
and open, so that it cannot come at the spiracles, it heaves up and
shocks the earth with greater or lesser impetuosity, according to the
quantity of fire thus assembled, till it has made its way to the mouth
of the volcano. That, therefore, there are scarce any countries much
annoyed by earthquakes but have one of these fiery vents, which are
constantly in flames when any earthquake happens, as disgorging that
fire which, while underneath, was the cause of the disaster. Lastly,
that were it not for these _diverticula_, it would rage in the bowels of
the earth much more furiously, and make greater havoc than it doth.
We have seen what fire and water may do, and that either of them are
sufficient for all the phenomena of earthquakes; if they should both
fail, we have a third agent scarce inferior to either of them; the
reader must not be surprised when we tell him it is air.
Monsieur Amontons, in his _Mémoires de l'Académie des Sciences, An.
1703_, has an express discourse to prove, that on the foot of the new
experiments of the weight and spring of the air, a moderate degree of
heat may bring the air into a condition capable of causing earthquakes.
It is shown that at the depth of 43,528 fathoms below the surface of the
earth, air is only one fourth less heavy than mercury. Now this depth of
43,528 fathoms is only a seventy-fourth part of the semi-diameter of the
earth. And the vast sphere beyond this depth, in diameter 6,451,538
fathoms, may probably be only filled with air, which will be here
greatly condensed, and much heavier than the heaviest bodies we know in
nature. But it is found by experiment that, the more air is compressed,
the more does the same degree of heat increase its spring, and the more
capable does it render it of a violent effect; and that, for instance,
the degree of heat of boiling water increases the spring of the air
above what it has in its natural state, in our climate, by a quantity
equal to a third of the weight wherewith it is pressed. Whence we may
conclude that a degree of heat, which on the surface of the earth will
only have a moderate effect, may be capable of a very violent one below.
And as we are assured that there are in nature degrees of heat much more
considerable than boiling water, it is very possible there may be some
whose violence, farther assisted by the exceeding weight of the air, may
be more than sufficient to break and overturn this solid orb of 43,528
fathoms, whose weight, compared to that of the included air, would be
but a trifle.
Chymistry furnishes us a method of making artificial earthquakes which
shall have all the great effects of natural ones; which, as it may
illustrate the process of nature in the production of these terrible
phenomena under ground, we shall here add.
To twenty pounds of iron filings add as many of sulphur; mix, work, and
temper the whole together with a little water, so as to form a mass half
wet and half dry. This being buried three or four feet under ground, in
six or seven hours time will have a prodigious effect; the earth will
begin to tremble, crack, and smoke, and fire and flame burst through.
Such is the effect even of the two cold bodies in cold ground; there
only wants a sufficient quantity of this mixture to produce a true Ætna.
If it were supposed to burst out under the sea, it would produce a
spout; and if it were in the clouds, the effect would be thunder and
lightning.
An earthquake is defined to be a vehement shake or agitation of some
considerable place, or part of the earth, from natural causes, attended
with a huge noise like thunder, and frequently with an eruption of
water, or fire, or smoke, or winds, &c.
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?