— 555 —
Because of their Minuteness.
      §25. If a great, nay far the greatest part of the several ranks of
Bodies in the Universe, scape our notice by their remoteness, there
are others that are no less concealed from us by their Minuteness.
These insensible Corpuscles, being the active parts of Matter, and
— 556 —
the great Instruments of Nature, on which depend not only all
their secondary Qualities, but also most of their natural Operations,
our want of precise distinct Ideas of their primary Qualities, keeps
us in an uncurable Ignorance of what we desire to know about them.
I doubt not but if we could discover the Figure, Size, Texture, and
Motion of the minute Constituent parts of any two Bodies, we
should know without Trial several of their Operations one upon
another, as we do now the Properties of a Square, or a Triangle.
Did we know the Mechanical affections of the Particles of Rhubarb,
Hemlock, Opium, and a Man, as a Watchmaker does those of a
Watch, whereby it performs its Operations, and of a File which by
rubbing on them will alter the Figure of any of the Wheels, we
should be able to tell before Hand, that Rhubarb will purge, Hemlock
kill, and Opium make a Man sleep; as well as a Watch-maker can,
that a little piece of Paper laid on the Balance, will keep the Watch
from going, till it be removed; or that some small part of it, being
rubb’d by a File, the Machin would quite lose its Motion, and the
Watch go no more. The dissolving of Silver in aqua fortis, and Gold
in aqua Regia, and not vice versa, would be then, perhaps, no more
difficult to know, than it is to a Smith to understand, why the turn-
ing of one Key will open a Lock, and not the turning of another.
But whilst we are destitute of Senses acute enough, to discover the
minute Particles of Bodies, and to give us Ideas of their mechanical
Affections, we must be content to be ignorant of their properties and
ways of Operation; nor can we be assured about them any farther,
than some few Trials we make, are able to reach. But whether they
will succeed again another time, we cannot be certain. This
hinders our certain Knowledge of universal Truths concerning
natural Bodies: and our Reason carries us herein very little beyond
particular matter of Fact.
Locke Hum IV, 3, §25, pp. 555-556