The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 chap, xxiv.] FORMATION OF IMAGES BY MIRRORS. 307 rays; the image of a is therefore formed at A, and b at B. AB would thus become the image. If, then, the object be between the centre of curvature and the principal focus, the image is real, and in- verted, but larger than the object; and the nearer the object ap- proaches to the princi- pal focus, the larger will Fig. 132.—F
The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 chap, xxiv.] FORMATION OF IMAGES BY MIRRORS. 307 rays; the image of a is therefore formed at A, and b at B. AB would thus become the image. If, then, the object be between the centre of curvature and the principal focus, the image is real, and in- verted, but larger than the object; and the nearer the object ap- proaches to the princi- pal focus, the larger will Fig. 132.—Formation of a real Image be the image. Should, b>T a Concave Mirror. however, the object be at the principal focus, the incident rays are reflected in a direction parallel to one another (page 303). No conjugate focus is formed, and hence no image. Finally, suppose the object to be nearer to the mirror than the principal focus, then, as already noted (page 305), the reflected rays are divergent. They do not meet in front of the mirror, and no real image is formed. If the reflected Fig. 183.—Virtual Image of Concave raVS be prolonged back- wards, however, they will meet behind the mirror and so form a virtual image. Thus, let MN (Fig. 133) be a concave mirror, xQx' its principal axis, c its centre of curvature, and F its principal focus. Within F place an arrow AB. Let AG AE be incident rays from A. They are reflected in the directions p and R. Rays BH BL from B are reflected in the directions s and T. Prolonged backwards, the former met at a and the latter at b. Thus ab becomes the image of AB. It is behind the mirror, virtual; is ERECT, and larger than the object. The nearer the object is to the principal focus, without coinciding with it, the larger is the virtual image, the nearer the object is to the surface of the mirror, the smaller is the image.
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