The microscope; an introduction to microscopic methods and to histology . y as described for air bubbles (§ 136), and addat one edge a little of the mixture of oil and mucilage(§ J39) ! cover and examine. The sub-stage need not be used in this experiment. Search thepreparation until an air bubble and an oil globule, each appearingabout 1 mm. in diameter, are found in the same field of view. Lightfirst with central light, and note that, in focusing up, the air bubblecomes into focus first and that the central spot is smaller than that ofthe oil globule. Then, of course, the black ring will be w
The microscope; an introduction to microscopic methods and to histology . y as described for air bubbles (§ 136), and addat one edge a little of the mixture of oil and mucilage(§ J39) ! cover and examine. The sub-stage need not be used in this experiment. Search thepreparation until an air bubble and an oil globule, each appearingabout 1 mm. in diameter, are found in the same field of view. Lightfirst with central light, and note that, in focusing up, the air bubblecomes into focus first and that the central spot is smaller than that ofthe oil globule. Then, of course, the black ring will be wider in theair bubble than in the oil globule. Make the light oblique. Thebright spot in the air bubble will move away from the mirror whilethat in the oil globule will move toward it. See Fig. 91.* § 143. Air and Oil by Reflected Light.—Cover the diaphragmor mirror so that no transmitted light (§ 64) can reach the preparation,using the same preparation as in § 142. The oil and air will appearlike globules of silver on a dark ground. The part that was darkest in. *It should be remembered that the image in the compound microscope isinverted (Fig. 21), hence the bright spot realty moves toward the mirror for air,and away from it for oil. 96 INTERPRETATION OF APPEARANCES [CH. Ill each will be lightest, and the bright central spot will be somewhatdark.* § 144. Distinctness of Outline.—In refraction images thisdepends on the difference between the refractive power of a body andthat of the medium which surrounds it. The oil and air were verydistinct in outline as both differ greatly in refractive power from themedium which surrounds them, the oil being more refractive than themucilage and the air less. (Figs. 54-56.) Place a fragment of a cover-glass on a clean slide, and cover it(see under mounting). The outline will be distinct with the unaidedeye. Use it as object and employ the 16 mm. (Jfi in.) objective andhigh ocular. Light with central light. The fragment will be out
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