in those of the other, it will increase the
motion of the one hand and lessen it in the other; and so cause the
different sensations of heat and cold that depend thereon.

22. An excursion into natural philosophy.

I have in what just goes before been engaged in physical inquiries a
little further than perhaps I intended. But, it being necessary to make
the nature of sensation a little understood; and to make the difference
between the QUALITIES in bodies, and the IDEAS produced by them in the
mind, to be distinctly conceived, without which it were impossible to
discourse intelligibly of them;--I hope I shall be pardoned this little
excursion into natural philosophy; it being necessary in our present
inquiry to distinguish the PRIMARY and REAL qualities of bodies, which
are always in them (viz. solidity, extension, figure, number, and
motion, or rest, and are sometimes perceived by us, viz. when the bodies
they are in are big enough singly to be discerned), from those SECONDARY
and IMPUTED qualities, which are but the powers of several combinations
of those primary ones, when they operate without being distinctly
discerned;--whereby we may also come to know what ideas are, and what
are not, resemblances of something really existing in the bodies we
denominate from them.

23. Three Sorts of Qualities on Bodies.

The qualities, then, that are in bodies, rightly considered are of three
sorts:--

FIRST, The bulk, figure, number, situation, and motion or rest of their
solid parts. Those are in them, whether we perceive them or not; and
when they are of that size that we can discover them, we have by these
an idea of the thing as it is in itself; as is plain in artificial
things. These I call PRIMARY QUALITIES.

SECONDLY, The power that is in any body, by reason of its insensible
primary qualities, to operate after a peculiar manner on any of our
senses, and thereby produce in US the different ideas of several
colours, sounds, smells, tastes, &c. These are usually called SENSIBLE
QUALITIES.

THIRDLY, The power that is in any body, by reason of the particular
constitution of its primary qualities, to make such a change in the
bulk, figure, texture, and motion of ANOTHER BODY, as to make it operate
on our senses differently from what it did before. Thus the sun has a
power to make wax white, and fire to make lead fluid.

The first of these, as has been said, I think may be properly called
real, original, or primar