. Kirkes' handbook of physiology . istance of the retina from the lens re-quired for vision at all distances, supposing the cornea and lens to remainthe same, would not be more than about one line. Beer has shown that thesecond method is indeed the type of accommodative apparatus in in man and the higher animals accommodation occurs by the firstmethod, , by changing the convexity of the refracting surface. The accommodation of the human eve for objects at different distances isprimarily due to a varying shape of the lens, its front surface becoming moreor less convex, according
. Kirkes' handbook of physiology . istance of the retina from the lens re-quired for vision at all distances, supposing the cornea and lens to remainthe same, would not be more than about one line. Beer has shown that thesecond method is indeed the type of accommodative apparatus in in man and the higher animals accommodation occurs by the firstmethod, , by changing the convexity of the refracting surface. The accommodation of the human eve for objects at different distances isprimarily due to a varying shape of the lens, its front surface becoming moreor less convex, according as the distance of the object looked at is near orfar. The nearer the object, the more convex the front surface of the lens,up to a certain limit, and vice versa; the back surface takes little or no sharein accommodation. The following simple experiment illustrates this point:If a lighted candle be held a little to one side of a persons eye, an observerlooking at the eye from the other side sees three distinct images of the flame,. 644 THE SENSES figure 457. The first and brightest is, i, a small erect image formed by theanterior convex surface of the cornea; the second, 2, is also erect, but largerand less distinct than the preceding, and is formed at the anterior convexsurface of the lens; the third, 3, is smaller, inverted, and indistinct; it isformed at the posterior surface of the lens, which is concave forward, and
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