XIV. The second reason assigned for distrusting the evidence of our
senses, is the experience we have of the alterations which are produced
on sensible species, either by the interposition of a medium, or the
different dispositions of our organs. The species, which by passing
through a uniform, or homogeneous medium, appears straight, by being
passed through a different one, will seem crooked, as may be evinced by
passing a straight wand from the air through water, which, by virtue
of the refraction of rays produced in its passage from one element to
the other, will make it appear crooked. To him who has a jaundice, every
thing he looks at seems yellow; and although it is true, that this is
the effect of a preternatural accident, we are not certain, whether
abstracted from all morbific dispositions, there are not in various
individuals, different temperaments and configuration of parts, which
are capable of producing different sensations with respect to the same
object; and it seems most probable, from all that is evident and manifest
to our observation and experience, that the thing is so, for we don’t
see any one individual, who is perfectly and exactly like another; and
we have known men, whose right eyes have represented objects, both with
respect to colour and magnitude, different from their left.