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Powers make a great part of our complex Ideas of Substances.       §10. Powers therefore, justly make a great part of our complex Ideas
of Substances. He, that will examine his complex Idea of Gold, will
find several of its Ideas, that make it up, to be only Powers, as the
Power of being melted, but of not spending it self in the Fire; of
being dissolved in Aqua Regia, are Ideas, as necessary to make up our
complex Idea of Gold, as its Colour and Weight: which if duly
considered, are also nothing but different Powers. For to speak
truly, Yellowness is not actually in Gold; but is a Power in Gold, to
produce that Idea in us by our Eyes, when placed in a due Light:
and the Heat, which we cannot leave out of our Idea of the Sun, is
no more really in the Sun, than the white Colour it introduces into
Wax. These are both equally Powers in the Sun, operating, by the
Motion and Figure of its insensible Parts, so on a Man, as to make
him have the Idea of Heat; and so on Wax, as to make it capable to
produce in a Man the Idea of White.
Locke Hum II, 23, §10, p. 301