_Martin Folkes_, Esq; LL.D.
President of the Royal Society.
_March 26, 1750._
When so great and unusual a _phenomenon_, as an earthquake, and that
repeated, happens among us; it will naturally excite a serious reflection
in everyone that is capable of thinking. And we cannot help considering
it, both in a philosophical and a religious view. Any mind will take the
alarm when we perceive a motion that affects the earth, that bears the
whole city of _London_, and some miles round it. And at the same time
while it gives us so sensible a shake, so gently sets us down again;
without damage to any buildings, and without a life lost.
'Tis hard to say, which is the greater wonder. But alas in the works
of nature, there are no degrees of great, and little; comparisons are
incompatible. We indeed are more affected with what seems great in our
own apprehensions: I would rather say, what is rare and unusual. An
omnipotent power admits of no distinctions. And when prodigious effects
are produc'd from causes imperceptible, it rightly claims our most serious
attention, as well as wonder. Nor need we lose sight of the theological
purpose of these amazing alarms; whilst we endeavor to find out the
philosophy of them.
Among all the appearances of nature, which are the subject of the
inquiries of the Royal Society, none more deserves the regard of a
contemplative mind. And among the very numerous accounts received there,
from all quarters, being only Observations upon the manner of it, and
its extent: I judg'd, it became us to inquire into the _cause_ of so
extraordinary a motion: of which we could not form a proper idea; had we
not repeatedly seen, and felt it.
The moderns have not improv'd upon the opinions of the ancients, in
this matter; any further than by the fancied analogy of some chymical
experiments. But these chymical experiments, and all sorts of explosions
by gun-powder, and the like, are to me a very unsatisfactory solution
they are merely artificial compositions, which can have nothing similar
in the bowels of the earth, and they produce their effects by violence,
by rending and tearing, by a _solutio continui_. This is indeed too
often the case of earthquakes, but _that_ is a partial degree, not
at all equivalent to the compass of the shock; and is very far from
being the constant concomitant of an earthquake. Quite the contrary.
Innumerable such happen, when there is no breach of the surface; and of
these three or four which we have now felt, nothing of it has appear'd.
But the immensity of the vibration of the earth which shook every house
in _London_, with impunity, and for twenty miles round, can never, in
my apprehension, be owing to so unbridled a cause, as any subterraneous
vapours, fermentations, rarefactions, and the like; the vulgar solution.
Nor does the kind of motion, which I discern in an earthquake, in any sort
agree with what we should expect from explosions.
In order then to proceed with some degree of certainty, in our inquiry
after the cause of earthquakes, it will be useful, in the first place,
to set in one view, the general appearances remarkable therein; the most
usual concomitants: As we can collect them from our own observation, or
from the relations and writings of others.
Circumstances.
I. That earthquakes always happen in calm seasons, in warm, dry, sultry
weather; or after a dry, frosty air.
II. That they are felt at sea, as well as land, even in the main ocean;
and at that time, the sea is calm.
III. That earthquakes differ very much in magnitude. Some shake a very
large tract of country, at the same instant of time; nay, sometime extend
to very many countries, separated by mountains, seas, lakes, the ocean.
IV. That earthquakes differ very much in the quantity, of their vibratory
motion: Whence in some, tho' largely extended, they are innocuous; in
others, both small and great, they lay all in ruin and destruction.
V. That a hollow, thundering, unusual noise accompanies them, or rather
seems to preceed the shock; which rolls in the air like the noise of
cannon.
VI. That they are felt more sensibly in the upper story of houses than in
the lower.
VII. That the shock is more violent upon more solid buildings, churches,
castles, and stone-houses, than upon those of slighter materials.
VIII. That many people find themselves sick at stomach, with headake, and
pains in their joints, and the like, which sometime lasts for the day
after, or longer.
IX. That earthquakes generally happen to great towns, and cities, and more
particularly to those that are situate on the sea.
X. That earthquakes do not cause any damage to springs and fountains; but
the water in wells becomes foul for a short time.