XLI. The evidence of our senses alone, then, is not sufficient to enable
us to derive just conclusions from experiments; for caution, reflection,
judgement, and reason, are always necessary; and sometimes in so great
a degree, that all the exertion of human talents and ingenuity, is not
equal to an adequate examination of the phenomena. Sir Isaac Newton, an
Englishman, who was a genius of the first rate, and a member of the Royal
Society of London, in the beginning of the present century, published
various tracts upon optics, in which, he displayed a great novelty to
the philosophers and mathematicians; that is, that all colours exist
and are contained, actually and formally, in the rays of light; which
are constituted of heterogeneous particles, of unequal refrangibility.
He proved this singular opinion, with many experiments of exquisite
invention, contrived and considered, with no less exquisite delicacy, and
in fact, made more than a few converts to his opinion in many parts, but
more especially among the English mathematicians; and a Mr. Gauger who
was one of these, enforced the Newtonian doctrine, with a great number
of additional experiments; but in a short time, one Senor Rizetti, wrote
against this new system, and stated many experiments in favour of the
old opinion, and even pretended, that those which had been quoted by
Gauger, militated against the Newtonian sentiment. Gauger replied to
this, and paid Rizetti in his own coin; that is, he not only defended
the consequences which he deduced from his own experiments, but turned
those derived from the experiments of Rizetti against the doctrine of the
Italian. It is certain that experience, as applied to many objects, opens
a most extensive and fertile field for exercising the ingenuity of man,
and that nature, even to him who seeks to know her in that way, is in
various instances impenetrable and inaccessible.
XLII. But we should acknowledge that in general, the difficulties are not
so invincible, as not to be surmounted by reason and industry, and that
the deceptions which sometimes result from experiments, proceed either
from the want of proper diligence and attention in making them, or from
the want of adequate ingenuity, to judge of, and decide upon them.
XLIII. This is very frequently the case with respect to medicinal
observations; and from hence springs that enormous disagreement, with
respect to the opinions that are alledged to be founded upon them.
One says, that he has experienced the efficacy and salutary fruits,
of such a medicine, in such a disease; and another insists, that he
has administered the same medicine, in the same disease, and under the
same circumstances, and found it to be pernicious. One of the two must
be mistaken, and I believe it is not very uncommon for both of them
to be so; for it might possibly happen, that the medicine neither did
good nor harm, and that the administration of it, was a mere matter of
indifference, and the thing itself what we call a chip in porridge.
But from what could this difference of sentiment and assertion arise?
Why from one of them seeing that his patient, after administering the
medicine to him grew better, and from the other perceiving, that his
after taking it grew worse; although it might possibly happen, that
neither the one grew better, nor the other grew worse in consequence
of taking the medicine, but from a very different cause. The diseases
of the two patients, from their different constitutions, or internal
temperaments, (which is for the most part, a thing impenetrable to
physicians) might be in such a state, that the one was disposed to
abate, and the other to increase.
XLIV. And although the patients may be numerous, with respect to whom
this experience is alledged; and admitting that they neither all die,
nor all recover, every one according to his pre-occupation, will impute
to the remedy, either the happiness of those who did well, or the
misfortune of those who perished; and unless they shall resolve, to make
a computation of the good or bad success of the practice of those who use
that medicine, with that of those who never administer it, and compare
them carefully together, this doubt will probably never be cleared up.