. The microscope; an introduction to microscopic methods and to histology. Microscopes. 46 LIGHTING WITH THE MICROSCOPE [ reflected light is but little used; but in the study of opaque objects, like whole insects, etc., it is used a great deal. For a simple micro- scope and low powers of the compound microscope, ordinary day- Hght that naturally falls upon the object, or is reflected or condensed , upon it with a mirror or condensing lens, answers very well (fig. 21 A, 34). For high powers and for special pur- poses, special illuminating apparatus has* been devised (fig. 50). § 85. Transm
. The microscope; an introduction to microscopic methods and to histology. Microscopes. 46 LIGHTING WITH THE MICROSCOPE [ reflected light is but little used; but in the study of opaque objects, like whole insects, etc., it is used a great deal. For a simple micro- scope and low powers of the compound microscope, ordinary day- Hght that naturally falls upon the object, or is reflected or condensed , upon it with a mirror or condensing lens, answers very well (fig. 21 A, 34). For high powers and for special pur- poses, special illuminating apparatus has* been devised (fig. 50). § 85. Transmitted light. — By this is meant light which passes through an object from the opposite side (fig. 21 B, 3s). The details of a photo- graphic negative are in many cases only seen or best seen by transmitted light, while the print made from it is best seen by reflected hght (fig. 21 A, 34). Almost all objects studied in ani- mal and vegetable Histology are Ughted by transmitted light, and they are in some way rendered trans- parent or semi-transparent. The hght traversing and serving to illu- minate the object in working with a compound microscope is usually reflected from a plane or concave mirror, or from a mirror to a con- denser, and thence transmitted to the object from below (fig. 20, 41). § 86. Axial or central light. — By this is meant hght reaching the object in such a way that it is sym- metrically arranged around the optic axis of the microscope, then the object will be equally illuminated from all sides. If bundles of paral- lel rays are reflected upon the object from the mirror, they must be so disposed that the object will receive an equal quantity of light Fig. 34. Low-power Objec- tive Showing Working Dis- tance AND Reflected Light. Axis The principal optic axis of the objective extended. SI The glass slide on which the object is mounted. 0 Object. c Cover-glass over the object. W The working distance be- tween the cover and the objective. Mirror The mirror
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