. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . B Pigs. 81-82.—Determination of the Position of an Entoptie Object. (After Brewster.) parallel; likewise dcx and opx are parallel. Hence from the trianglesdccx and oppx we have the ratio PPi OP ccx de Two circles of diffusion are seen which partly overlap. We measurethe distance pp\ between the two shadows of the same object and thediameter, DE, of the free part of one of the diffusion circles as inFig. 82. The ratio between these measurements is equal to the ratio 164 PHYSIOLOGICAL OPTICS betwe
. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . B Pigs. 81-82.—Determination of the Position of an Entoptie Object. (After Brewster.) parallel; likewise dcx and opx are parallel. Hence from the trianglesdccx and oppx we have the ratio PPi OP ccx de Two circles of diffusion are seen which partly overlap. We measurethe distance pp\ between the two shadows of the same object and thediameter, DE, of the free part of one of the diffusion circles as inFig. 82. The ratio between these measurements is equal to the ratio 164 PHYSIOLOGICAL OPTICS between the distances of the object from the retina and that of theretina from the pupil. Fig. 82 shows that cct = DE = R -f- a, if R isthe radius of the circle of diffusion. One has, therefore, only toproject the mutual distance of the two centers, i. e., the breadth ofthe uncovered part of the circles and that of the double shadows ofany object in order to obtain the experimental data necessary to solvethe equality of ratios given above and determine op, the distance ofthe particle from the reti
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