. The microscope : an introduction to microscopic methods and to histology. Microscopes. 52 LIGHTING AND FOCUSING \_CH. II turned wholly aside. A transparent specimen like the fly's wing is put under the microscope and focused. The condenser is then turned up and down until the image of the flame is apparently on the specimen. If this cannot be Accomplished the relative position of the lamp and condenser is not correct and should be so changed that the image of the edge of the flame is sharply defined. This image must also be centered. This is easily accomplished by manip- ulation of the mirro
. The microscope : an introduction to microscopic methods and to histology. Microscopes. 52 LIGHTING AND FOCUSING \_CH. II turned wholly aside. A transparent specimen like the fly's wing is put under the microscope and focused. The condenser is then turned up and down until the image of the flame is apparently on the specimen. If this cannot be Accomplished the relative position of the lamp and condenser is not correct and should be so changed that the image of the edge of the flame is sharply defined. This image must also be centered. This is easily accomplished by manip- ulation of the mirror or, if a lamp is used, by changing the position of the lamp or of the bull's eye (Fig. 60). § 94. Proper Numerical Aperture of the Condenser.—As stated above, the aperture of the condenser should have a range by means of properly selected diaphragms to meet the requirements of all objectives from the lowest to those of the highest aperture. It is found in practice that for diatoms, etc., the best images are obtained when the object is lighted with a cone which fills about three-fourths of the diameter of the back lens of the objective with light, but for histological and other preparations of lower refractive power only one-half or one-third the aperture often gives the most satisfactory images (§ 40). Fig. 50. Shows the image of the flame {Fl.) in the center (C) of the field of the microscope and illuminating the object. Fig. 51. Shows the image of the flame {Fl.) at one side of the center {Exc.) and not properly il- luminating the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gage, Simon Henry, 1851-1944. Ithaca, N. Y. : Comstock Publishing Company
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