Ocular refraction and the shadow test . optical centres ol a Itns. of the circle and with india ink and a fine hard wood point (a piece of jewelers peg wood makes the best point for this purpose) markcarefully at the periprery of the lens the four points A A B B, where the diameters meet the circumference; also mark across at O to indicate the centre, the lens will thus appear as shownby II, figure 47. The cross will thus mark the gfoiiicti-ical centre ofthe lens and also its optical centre, being the point upon its surface inthe principal axis. By figure 37 it is demonstrated that
Ocular refraction and the shadow test . optical centres ol a Itns. of the circle and with india ink and a fine hard wood point (a piece of jewelers peg wood makes the best point for this purpose) markcarefully at the periprery of the lens the four points A A B B, where the diameters meet the circumference; also mark across at O to indicate the centre, the lens will thus appear as shownby II, figure 47. The cross will thus mark the gfoiiicti-ical centre ofthe lens and also its optical centre, being the point upon its surface inthe principal axis. By figure 37 it is demonstrated that the ray traversing the princi-pal axis and therefore passing through the optical centre is not re-fracted. If we draw a vertical straight line, I, figure 48, upon apiece of paper and hold the lens so that in looking at the line S L throughit our line of vision follows the principal axis, the line will appearunbroken and passing through the points A and A as shown by II,figure 48. Move the lens to the rig/it in the same plane, and the. he appearance of appearance created will be illustrated by III, figure 48, the points Aand A will appear to the right of the line S L while the portion ofthe line, S L, seen through the lens will appear displaced to the Icf/.
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Keywords: ., bookcentury1900, bookdecade1900, bookidocularrefrac, bookyear1903
