. Elements of applied microscopy. A text-book for beginners. Microscopy. MANIPULATION OF THE MICROSCOPE. 35 ter IV. The resolving power by which fine structures are made visible varies directly with the numerical aperture, as has been already explained. This power is ordinarily tested by examining the wing-scales of certain Lepidop- tera or the shells- of diatoms which possess very fine markings. For example, the shell of Pleurosigma shows three systems of striations when examined under a mag- nification of 250 diameters with a numerical aperture of over .80, while two of them disappear with l
. Elements of applied microscopy. A text-book for beginners. Microscopy. MANIPULATION OF THE MICROSCOPE. 35 ter IV. The resolving power by which fine structures are made visible varies directly with the numerical aperture, as has been already explained. This power is ordinarily tested by examining the wing-scales of certain Lepidop- tera or the shells- of diatoms which possess very fine markings. For example, the shell of Pleurosigma shows three systems of striations when examined under a mag- nification of 250 diameters with a numerical aperture of over .80, while two of them disappear with lesser aper- ture. Penetration, or the power to see clearly different planes of the object at the same time, varies inversely with the numerical aperture and directly with the square of the equivalent focus of the lens. Illuminating power • varies with the square of the numerical aperture, and with the square of the equivalent focus. Two common faults should be looked for in a micro- scope, curvature of the field and imperfect correction of chromatic and spherical aberration. If a stage microme- ter, marked with lines at right angles, be examined, the image should resemble a, Fig. 23. If it has the appear-. a b 0 Fio. 23.—Cttrvature of the Field. (After Hager-Mez.) ance of 6 or c the lenses are so ground that the magnifica- tion is greater or less at the periphery than at 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 Winslow, C. -E. A. (Charles-Edward Amory), 1877-1957. New York, J. Wiley; London, Chapman & Hall
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