. Animal physiology. Physiology, Comparative; Physiology, Comparative. REFRACTION BY CONVEX SURFACE. 399 528. The general law of refraction, then, is,—that all rays passing from a dense to a rare medium are refracted from the perpendicular, the degree of change being less as they are near the perpendicular, and greater as they depart from it. On the other hand, when rays pass from a rare medium into a dense one, they are bent towards the perpendicular; and this in a greater or less degree, according as their direction is more distant from the perpendicular, or nearer to it. Thus, in Fig. 194,
. Animal physiology. Physiology, Comparative; Physiology, Comparative. REFRACTION BY CONVEX SURFACE. 399 528. The general law of refraction, then, is,—that all rays passing from a dense to a rare medium are refracted from the perpendicular, the degree of change being less as they are near the perpendicular, and greater as they depart from it. On the other hand, when rays pass from a rare medium into a dense one, they are bent towards the perpendicular; and this in a greater or less degree, according as their direction is more distant from the perpendicular, or nearer to it. Thus, in Fig. 194, we will suppose the point a to be the position of the eye of a Fish ; and the end of the line a c (previously occupied by the eye of the observer) to be the position of an Insect in the air. Now this insect will not be seen by the fish in its true place ; for a ray passing from it to c would be so bent out of its course, as not to reach the point a. The direction in which it is really seen is a d; for the ray proceeding from the object to the surface of the water, there undergoes such a refraction, that it is bent downwards to a ; and, as we always judge of the place of an object by the direction in which the rays last come to the eye, the insect is seen by the fish at d, that is, considerably above its real place (§.476). 529. When the surface which separates the two media is not flat, but is convex or concave, (bulging or hollowed out,) a very important alteration is produced in the direction of the rays that fall upon it. Thus we shall suppose \ that three diverg- ing rays, issuing from a point, «, (Fig. 195), and traversing the air, strike upon a con- vex surface of glass, b V. The central ray a c falls upon the glass in a di- F[r m rection perpendi- cular to its surface at that point, and passes on unchanged in its F. F. 2. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appeara
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