When the Rays have found a Passage into the Pupil of the Eye, they fall upon a thin Membrane which is called the Retina, upon which Retina the exact Picture of the Object is represented, as may be seen by the Eye of an Ox, properly prepared and placed in the Hole of a Window-Shutter. This Retina is an Elongation from the Brain; and by this Means it is, that we receive those various agreeable or disagreeable Sensations with which we find ourselves affected, by the Sight of external Objects. So that we may observe, that it must be not only real Substance which must reflect Rays to the Eye, in order to cause Vision, but the Rays themselves, likewise, which come from that Object, are Substance. If this is the Case, the Apparition of a Person must be a Substance, which is reflected from a Substance, which belongs to the Body of him who is dead, or is going to die. With regard to him who is dead and buried, one would think, that he and his Substance are so safe under Ground, that no Part of him can reflect any Rays; but a Person who is above Ground, either dead or dying, may reflect Rays to the Eye of a Beholder, and if it happens to be a Friend or Relation, such Rays will make so strong an Impression upon the Retina, that they shall in such a Manner imprint themselves upon that pliable Spot, as will cause the Brain and Nerves of the Beholder to have the Sensation of seeing the dead or dying Person some Time after the real Action of seeing him. This will account for most of those positive Assertions, which we may hear in any Village, of the seeing the Apparitions of People after they are dead, or just before they die, 'tis all one. We very seldom hear of any such Thing in Town, which corresponds with what has been said; for in Town it is so common to have Deaths and Funerals, &c. that People are no more affected with the Sight of a dead Man than a living one. But the Case is quite different in Villages. A Village with fifty Houses in it, situated in a wholesome Country, shall not have above one Person die in a Year; this makes such a Stir, that all the old Women in the Town must have a Peep at the deceased, as he lies in his Coffin, with his Shroud on; which Alteration of Appearance in the dead Person, from what they remember him, a little while since, leaves such an Impression upon the Retinas of these old Women, that 'tis ten to one but some of them think they see him, as soon as the dark Hour comes on. And, very likely, a Person who thinks he sees an Apparition may not be altogether wrong; there may be some of the Picture of the dead Person still faintly remaining upon his Retina; and if so, it certainly will give the same Sensation as if he faintly saw the Person. If this is the Case, it is not the deceased come back again to bully us, as is generally imagined, if we do apprehend we see him; but the Remembrance of him strong in that Organ the Eye, by which we formed the Idea of him in our Minds, when we really did behold him.