Chrysippus affirms, these four are different one from another. Imagination is that passion raised in the soul which discovers itself and that which was the efficient of it; to use example, after the eye hath looked upon a thing that is white, the sight of which produceth in the mind a certain impression, this gives us reason to conclude that the object of this impression is white, which affecteth us. So with touching and smelling Phantasy or imagination is denominated from [Greek omitted] which denotes light; for as light discovers itself and all other things which it illuminates, so this imagination discovers itself and that which is the cause of it. The imaginable is the efficient cause of imagination; as anything that is white, or anything that is cold, or everything that may make an impression upon the imagination. Fancy is a vain impulse upon the mind of man, proceeding from nothing which is really conceivable; this is experienced in those that whirl about their idle hand and fight with shadows; for to the imagination there is always some real imaginable thing presented, which is the efficient cause of it; but to the fancy nothing. A phantom is that to which we are brought by such a fanciful and vain attraction; this is to be seen in melancholy and distracted persons. Of this sort was Orestes in the tragedy, pronouncing these words: Mother, these maids with horror me affright; Oh bring them not, I pray, into my sight! They're smeared with blood, and cruel, dragon-like, Skipping about with deadly fury strike. These rave as frantic persons, they see nothing, and yet imagine they see. Thence Electra thus returns to him: O wretched man, securely sleep in bed; Nothing thou seest, thy fancy's vainly led. (Euripides, "Orestes", 255.) After the same manner Theoclymenus in Homer. CHAPTER XIII. OF OUR SIGHT, AND BY WHAT MEANS WE SEE. Democritus and Epicurus suppose that sight is caused by the insertion of little images into the visive organ, and by the reception of certain rays which return to the eye after meeting the object. Empedocles supposes that images are mixed with the rays of the eye; these he styles the rays of images. Hipparchus, that the visual rays extend from both the eyes to the superficies of bodies, and give to the sight the apprehension of those same bodies, after the same manner in which the hand touching the extremity of bodies gives the sense of feeling. Plato, that the sight is the splendor of united rays; there is a light which reaches some distance from the eyes into a cognate air, and there is likewise a light shed from bodies, which meets and joins with the fiery visual light in the intermediate air (which is liquid and mutable); and the union of these rays gives the sense of seeing. This is Plato's corradiancy, or splendor of united rays. CHAPTER XIV. OF THOSE IMAGES WHICH ARE PRESENTED TO OUR EYES IN MIRRORS.