. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 858 PHYSIOLOGY OP THE DOMESTIC ANIMALS. posterior portion of the eyeball the image of external objects in a strong light may be seen upon the retina inverted and reduced in size (Figs. 380 and 381). The principal surfaces by which rays of light passing through the eye are refracted are the cornea and the anterior and posterior surfaces of the lens. Since rays of light passing from the atmosphere to the cornea pass from a rarer to a denser mediu
. The physiology of the domestic animals; a text-book for veterinary and medical students and practitioners. Physiology, Comparative; Domestic animals. 858 PHYSIOLOGY OP THE DOMESTIC ANIMALS. posterior portion of the eyeball the image of external objects in a strong light may be seen upon the retina inverted and reduced in size (Figs. 380 and 381). The principal surfaces by which rays of light passing through the eye are refracted are the cornea and the anterior and posterior surfaces of the lens. Since rays of light passing from the atmosphere to the cornea pass from a rarer to a denser medium, the rays of light will be bent toward the perpendicular. The degree of refraction at this point will be more marked than in passing from the cornea to the aqueous humor, both of which possess- the same refractive power. On the other hand, the refraction will be still greater in the lens, so that the rays will be still more strongly deflected inward. It has been seen that rays of light passing through the central point of the optical centre of a convex lens do not undergo refraction, and in a double convex lens of equal curvature the optical centre will coincide with the. Fig. 380.—Formation of an Image in the Eye. (Landois.) By following the rays from the object, A E, it may be seen that they are brought to a focus on the retina, where a small inverted image is formed. geometrical centre. In such a compound, system of refracting media as in the eye the optical centre is less readily determined. It has been determined that in the eye the optical centre lies, not exactly in the centre of the crystalline lens, but between that point and the posterior surface of the lens; consequently, the rays passing through this point will practically undergo no refraction. It has been stated that a screen may be so arranged in relation to a convex lens that a distinct image of the object will fall upon it. This relation is attained when the screen is in the exact focus of the lens. If appr
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