A companion to the United States pharmacopia; . e, or ocular, the first ofwhich is the magnifying lens, and isattached to the lower end of the body,while the other is a small tube slidinginto the upper part of the draw-tubeand carrying a combination of lensesfor enlarging or amplifying the imagemade by the objective. The relation of the optical parts toeach other are shown in Fig. 550. The objective should be correctedfor chromatic and spherical aberration,which is done by combining a double-convex lens of crown-glass and a plano-concave lens of flint-glass (doublet).In the better class of obj
A companion to the United States pharmacopia; . e, or ocular, the first ofwhich is the magnifying lens, and isattached to the lower end of the body,while the other is a small tube slidinginto the upper part of the draw-tubeand carrying a combination of lensesfor enlarging or amplifying the imagemade by the objective. The relation of the optical parts toeach other are shown in Fig. 550. The objective should be correctedfor chromatic and spherical aberration,which is done by combining a double-convex lens of crown-glass and a plano-concave lens of flint-glass (doublet).In the better class of objectives the correction is obtained by a combi-nation of three lenses (triplet), and often one objective contains severaltriplets and doublets combined, so as to act as one lens. Objectives are designated by their focal distance, thus : 1 inch, \ inch, etc. This is the distance at which a. single lens with thesame magnifying power would have to be placed from the object toform the distinct image, but the actual distance of the front lens of the. eye-lens. diaphragm. . objective. Fig. 550.—Construction of Optical partof Compound Microscope. 1038 A COMPANION TO THE combination from the object is much less when in focus. The magni-fying power increases as the focal distance decreases. The eye-piece has two lenses, the lower and larger being called thefield-lens, the upper, which is next to the eye, being the eye-lens. By looking into a microscope provided with the above parts we per-ceive an illuminated surface when the light is reflected upward throughthe objective. This illuminated disk is called the field. But while thecentral portion will be bright, the edges are dim and gradually fadeinto darkness toward the circumference. If we place a large, flat,transparent object on the stage, reflect the light upward through it,and brins; the lenses into focus, we see the enlarged imas:e clear andsharp in the central part of the field, but diffuse and indistinct to
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishernewyo, bookyear1884
