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. SECT. V. XV. The third ground for the said distrust, is derived from the erroneous representation of things made by the imaginary faculty, which fancies external sensations of objects that do not exist. Such, for example, as the imagination of him who has had a leg cut off, representing to him a pain in the leg or foot that has been amputated; or that of an hypocondriac person, who fancies himself to be glass, earthen ware, a wolf, or a dog, whose imagination represents those strange forms, as evidently and manifestly palpable to his senses; so that he who fancies himself glass, will swear with invincible firmness, that he perceives in his own person the transparency, and feels on his own skin the smooth surface, which is proper and peculiar to that artificial composition.