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30 THREEDI can when the object is only a few feet away. It Is apparent that If the Inside parts of the eye were ri«*icHv fixed the Image in one case would be much more "indistinct than in the other. In using binoculars we know that we must refocus the lenses when we change from a nearby object to one a mile away. Is he retina of the eye a movable screen or lens.' When we change our gaze from the nearby object to one a mile or so away, do we unconsciously shift the position of the retina toward the lens in the eye? The images In each case are perfectly distinct,, but it seeing ex ceedingly unlikely that this distinctness is obtained by a shifting of the retina, for we know that the eye ball is filled with, a jellylike substance. It Is equally absurd to suppose* that the lens of the eye is bodily shifted. The true answer is that the lens of the eye alters its form by making its front surface more or less convex, and by this means a perfect Image Is pro duced on the retina, whether the object gazed at be far off or near. In other words, the eye Is focused by this procedure. This change in the crystalline lens seems to be effected by means of a peculiar ring-shaped muscle., concentric "with the Iris. The outer edge ot this ciliary muscle is attached to the same portion of the cornea as the Inner margin of the iris. Whenever we look at a very near object, we contract this muscle, and this acts upon the attachments of the lens of the eye as to allow It to become more convex on its front surface; Instantly the glance is transferred to a distant object, the ciliary muscle ceases to contract,, and the eye lens Is now pulled by its attachments into a flatter form. This device enables us, without being aware of it, to bring pictures of objects, whether near or far off, perfectly on the retina with the retinal membrane