Notes on microscopical methods : For the use of laboratory students in the anatomical department of the Cornell university / by Simon H. Gage.

  • Gage, Simon Henry, 1851-1944.
Date:
1886-1887
Catalogue details

Licence: Public Domain Mark

Credit: Notes on microscopical methods : For the use of laboratory students in the anatomical department of the Cornell university / by Simon H. Gage. Source: Wellcome Collection.

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    — 5 — versely the shorter it is the higher is its magnification. So also the larger the eye lens the lower is the ocular and the smaller the eye (iT&S hig^er'* 3°> 42), (Ban. 34), (Beh. 35-38), (C. 27, 109), FOCUSING. (? 17) Focusing is arranging the object and the microscope in such a way that a clear image may be seen. With the simple microscope, either the object or the microscope may be moved ; but with the compound microscope the object more conveniently remains stationary on the stage and the body of the microscope is changed in position. In general, the higher the power of the microscope, the nearer together must the object and the microscope be brought. With the compound microscope, the higher the objective or ocular, f or the longer the body of the microscope, the nearer must the object- ive be brought to the object. ($ 18) Working distance.—By this is meant the space between the front of the objective and the object when the microscope is in focus. This distance is always less than the nominal focal length of the ob- jective. For example, the front or lower part of a 6 mm. or 1-4 inch objective would not be 6 mm. or 1-4 inch from an object when it was in focus, but considerably less than that. ($ T9) Focusing with low objectives.—Place a mounted fly’s wing under the microscope ($ 22); put the three-fourths objective in posi- tion ($ 11), and also the lowest ocular. Select the proper opening in the diaphragm (g 10), and light the object well with transmitted light (§9)- Hold the head at about the level of the stage, look toward the win- dow, and between the object and the front of the objective; with the coarse adjustment lower the body (Fig. 3), until the objective is within about half a cm. of the object. Then look into the microscope and slowly elevate the body with the coarse adjustment. The image will* appear dimly at first, but will become very distinct by turning the body still higher. If the body is raised too high the image will become indistinct, and finally disappear. It will again appear it the body is lowered the proper distance. ' When the instrument is well focused, change the position of the mirror and note the effect. Swing the mirror above the stage and *The student is referred to \ 46-54 for a consideration of magni- fying power or magnification. f Some microscope makers so arrange the oculars that they enter the tube of the microscope the proper distances, so that it is not nec-