XXIII. If even in those consequences, which to all human appearance, we
deduce immediately from the truths which nature herself presents to our
senses, we are sometimes liable to be mistaken; what dependance can we
place in those, that are founded on principles, which without consulting
nature, are established by our fancy? What consequence to all appearance
could seem better inferred, than that of the repugnance of nature to a
vacuum, founded on the palpable experiment of the water rising in the
pump? But by the light of innumerable other experiments, the mistake was
discovered; and it was found out, that the true cause of that, and all
such-like phænomena, was the weight of the air.
XXIV. We see with our eyes, whether we explain the cause of it as
proceeding from an intrinsic quality, or from attraction, or from
impulse, that gravity precipitates bodies with a swift movement towards
the earth. It seems most natural to suppose, by reasoning from the
famous axiom, _sicut se habet simpliciter ad simpliciter, ita magis ad
magis_, that to a duplicate gravity, there would correspond a duplicate
acceleration of motion. But the fact differs widely from this proportion.
XXV. It is plain, that air is much more subtle and thin than water. Who
from hence, would not infer as an unavoidable consequence, that air must
penetrate all bodies which water penetrates? Notwithstanding this, we
see that water penetrates paper, which air does not penetrate, or it
penetrates it in so small a degree, or so slowly, that we look upon it as
next to no penetration at all.
XXVI. Who judging by general or common principles, would not conclude,
that wet hay was much less liable to take fire than dry? But experience
teaches us, that by putting together quantities of hay too moist, it will
take fire of itself, which could never have happened, if the hay had been
put together sufficiently dry, or more thoroughly made.
XXVII. What maxim is better established, or more generally assented
to among the naturalists, than that a vivifying heat of the blood, is
indispensably necessary for the preservation of life? But with all this,
Father Plumier, a learned priest of the order of Minimus, in a voyage in
the Pacific ocean, for want of water, found himself under a necessity of
drinking the blood of turtles, and declares, he found it as cold as the
common water in Europe. (Mem. de Trevoux, an. 1704, tom. 1. page 175.)
Who, agreeable to the laws of ratiocination, can say otherwise, than that
the third quality, resulting from the mixing three or four fœtid things
together, must be fœtid also? But experience manifests to us, that this
consequence is not infallible. Mr. Lemeri bought a certain quantity of
the gums galbanum, sagapenum, and opopanax, and also some bitumen of
Judæa, which he put all together into a retort, and found that there
resulted from the mixtures, a strongly scented oil, greatly resembling
musk; now the bitumen in smell, does not in the least resemble musk, and
the other three drugs are absolutely fœtid. (Hist. de l’Academ. Royal,
ann. 1706.)
XXVIII. If a philosopher, destitute of all other information, except that
which he had acquired in the schools, should be told that two liquids,
which to the touch appear cold, should upon being mixed together, not
only heat and boil, but also emit a flame; he would be in a terrible
agitation, and armed with his infallible conclusive principle, _that
nothing can communicate a quality which it does not possess_, would
exclaim against the proposition. But let him exclaim as much as he will,
it is a certain fact, that from mixing a pure acid, with the essential
oil of an aromatic plant, there will result that commotion.
XXIX. We know that water, is much heavier than air; and we also know,
that the vapours which arise from the earth, are nothing else but
particles of water, very minutely divided, and consequently, that they
must be much heavier than particles of air of the same size. We know
also, that a liquid cannot ascend above another, when they are put
together, except when it’s particles of equal size are lighter than those
of the other. From these premises, it should follow as an infallible
consequence, that these vapours cannot rise superior to the air we
breathe. But let this consequence appear ever so infallible, experience
convinces us that the fact is otherwise.
XXX. Nobody is ignorant, that the aromatic species, such as the clove,
the pimienta, and the cinnamon, are hot or heating, and that the regions
nearest the poles are cold, and those nearest the equinoctial hot. From
these premises, what naturalist would not infer, that the use of these
species would be less pernicious to the inhabitants of the cold regions,
than to those of the hot? But experience is ever demonstrating to us the
contrary. For a scruple of clove is more offensive to, and has a greater
effect on the first, than a drachm has on the last.
XXXI. And similar to this, has been the experience of the Hollanders, in
some of their voyages to the East Indies. It happened once, that upon
passing the line, the greatest part of the people belonging to a ship
were taken sick, and that more than half of them died, and that those
only recovered, to whom in their sickness they gave great quantities of
brandy. The medical men found great difficulty in believing, that these
people could owe the preservation of their lives to drinking to excess
of a liquor, which if not taken sparingly and with moderation, is found
to be very pernicious to health. But in the end, they found themselves
obliged to yield to experience; and admit of the liberal use of brandy,
which afterwards delivered with equal success, all the afflicted from
their illness.
XXXII. It is then absolutely necessary to submit to experience, and if we
are not disposed to abandon the real road of truth, to seek for nature in
herself, and not in the deceitful image which our fancy forms of her.