BOOK I PART II
sures, and their different degrees of exactness,
have given as an obscure and implicit notion
of a perfect and entire equality. The case is the
same in many other subjects. A musician find-
ing his ear becoming every day more delicate,
and correcting himself by reflection and atten-
tion, proceeds with the same act of the mind,
even when the subject fails him, and entertains
a notion of a compleattierceoroctave, without
being able to tell whence he derives his stan-
dard. A painter forms the same fiction with re-
gard to colours. A mechanic with regard to mo-
tion. To the one light and shade; to the other
swift and slow are imagined to be capable of
an exact comparison and equality beyond the
judgments of the senses.
We may apply the same reasoning tocurve
andrightlines. Nothing is more apparent to the