. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, flected to the principal focus do not inter-sect in front of the mirror, but if projected, will meet at aand ;- behind the mirror, forming a magnified image ofA R. If the mirror is withdrawn from the object, theerect magnified imag-e would increase in size, but at theprincipal focus no image would be formed, as the rayswould be reflected parallel. i6 REFRACTION AND HOW TO REFRACT. Figure 6 shows a real inverted image of A R at ^ r;A R situated beyond the principal focus
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, flected to the principal focus do not inter-sect in front of the mirror, but if projected, will meet at aand ;- behind the mirror, forming a magnified image ofA R. If the mirror is withdrawn from the object, theerect magnified imag-e would increase in size, but at theprincipal focus no image would be formed, as the rayswould be reflected parallel. i6 REFRACTION AND HOW TO REFRACT. Figure 6 shows a real inverted image of A R at ^ r;A R situated beyond the principal focus. Lines drawnfrom A and R through are secondary axes. Parallelrays from A and R converge and cross at the principalfocus (). Where D P and F E intersect the secondary axes, the in-verted image a r of A R is situated. When the object, asin this instance, is situated beyond the center of curvature,the image is smaller than the object. As the image andobject are conjugate to each other, they are interchange-able, and in such a case the image would be larger thanthe object and inverted. This is always true when the. Fig. 6. object is situated between the center of curvature and theprincipal focus. When an object is situated at the centerof curvature, its image is equally distant and of the samesize, but inverted. Tilting a concave mirror gives an object placed inside ofits principal focus the appearance of moving as the mirroris tilted ; but if the object is situated beyond the principalfocus, the object appears to move in the opposite direction. Reflection from a Convex Mirror.—All rays are re-flected divergently from a convex mirror, and parallel ra)\sdiverge as if they came from the principal focus situatedbehind the mirror at a distance equal to one-halt its radius OPTICS. 17 of curvature. The principal focus of a convex mirror istherefore negative. The foci of convex mirrors are virtual. Images Formed by a Convex Mirror.—These arealways virtual, erect, and smaller
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