. Human physiology : designed for colleges and the higher classes in schools, and for general reading. om it strike the eye. 434. When light passes from one medium into another whichpresents a convex or concave surface, instead of a flat one, avery great change is produced in the direction of its suppose, as represented in Fig. 157, three diverging rayscoming from a point, a, through the air, enter a convex surfaceof glass, b, b. The central ray a, c enters the glass in a direc-tion perpendicular to its surface, and therefore does not bendfrom its course. But the ray a, d enters very
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. om it strike the eye. 434. When light passes from one medium into another whichpresents a convex or concave surface, instead of a flat one, avery great change is produced in the direction of its suppose, as represented in Fig. 157, three diverging rayscoming from a point, a, through the air, enter a convex surfaceof glass, b, b. The central ray a, c enters the glass in a direc-tion perpendicular to its surface, and therefore does not bendfrom its course. But the ray a, d enters very obliquely, and isbent towards the perpendicular at that point, e, and passes onin the direction /. So likewise the ray, a, g, is bent towardsthe perpendicular h, and passes on in the line i. These raysdiverging in the air have become converging in the glass, andthe point at which they meet is called the focus. To this pointall the other rays entering the convex glass converge also. 435. But if the surface of the glass be concave, as represented THE by convex and concave lenses. 289. in Fig. 158, the diverging rays which enter it will be made todiverge still more. The ray, a, c, being perpendicular to the sur-face is unchanged in its course; but the ray, a, d, is bent towardsthe perpendicular, e, into the line/, and the ray, a,j, is bent to-wards the perpendicular A into the line i. In the case of both FIG. 158.
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