. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. In the foregoing we assumed a knowledge of the true formof some objects, and the direction of some lines or surfaces. Thisknowledge, indeed, is scarcely ever wanting. In a room we seesurfaces, which we may consider to be nearly horizontal or per-pendicular, and numerous objects which present to us vertical andhorizontal lines. Prom the angles which these surfaces and linesform on the perspective retinal images, we deduce our judg-ment. In nature the ground we walk upon, the horizo
. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. In the foregoing we assumed a knowledge of the true formof some objects, and the direction of some lines or surfaces. Thisknowledge, indeed, is scarcely ever wanting. In a room we seesurfaces, which we may consider to be nearly horizontal or per-pendicular, and numerous objects which present to us vertical andhorizontal lines. Prom the angles which these surfaces and linesform on the perspective retinal images, we deduce our judg-ment. In nature the ground we walk upon, the horizontal watersurface, ascending trees, houses with their frames and windows,lastly, man himself, are sufficient starting-points. Therefore also we 158 SPECTACLES AND THEIR ACTION IN GENERAL. judge tolerably correctly even what is seen only with one eye fromone point. Properly speaking our judgment can fail only through anintentional arrangement. For example, the table (Fig. 82 a) wouldhave produced the same retinal image, if the edge A B had had onlythe breadth a fi, but at the same time had been proportionallyr
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