— 142 —
Secondary Qualities two-fold; First, Immediately perceivable; Secondly, Mediately perceivable.       §26. To conclude, beside those before mentioned primary
Qualities in Bodies, viz. Bulk, Figure, Extension, Number, and
— 143 —
Motion of their solid Parts; all the rest, whereby we take notice of
Bodies, and distinguish them one from another, are nothing else,
but several Powers in them, depending on those primary Qualities;
whereby they are fitted, either by immediately operating on our
Bodies, to produce several different Ideas in us; or else by operating
on other Bodies, so to change their primary Qualities, as to render
them capable of producing Ideas in us, different from what before
they did. The former of these, I think, may be called Secondary
Qualities, immediately perceivable: The latter, Secondary Qualities,
mediately perceivable.
Locke Hum II, 8, §26, pp. 142-143