. The microscope and its revelations. fixed in a variety of positionssuitable for dissecting and for other manipulations. It consists inits best form of a circular foot, wherein is screwed a short tubularpillar (lig. 202), provided with a rack and-pinion movement, andcarrying a jointed arm movable in manv directions by ball-and-orkft and other joints. />, c, e, but capable of being clamped bythumb screws or milled heads. <i, b, e ; one end of this arm carries . to which is attached a ring for holding the lenses. Bylengthening or shortening the pillar, by varying the angle which1


. The microscope and its revelations. fixed in a variety of positionssuitable for dissecting and for other manipulations. It consists inits best form of a circular foot, wherein is screwed a short tubularpillar (lig. 202), provided with a rack and-pinion movement, andcarrying a jointed arm movable in manv directions by ball-and-orkft and other joints. />, c, e, but capable of being clamped bythumb screws or milled heads. <i, b, e ; one end of this arm carries . to which is attached a ring for holding the lenses. Bylengthening or shortening the pillar, by varying the angle which1 lie arm makes with its summit, and by using the various joints,aliiiM any position and elevation may be given to the lens that can required for the purposes to which it may lie most usefully:pplid. care being taken in all instances that. 1 lie ring which carries LENS-HOLDERS 249 the lens should (by means of its joint) be placed horizontally. Thelenses now most suitable for such a holder are those constructed &. FIG. 200.—Stephensons binocular by Swift (1887). upon the Steinheil formula, composed of three cemented lensesforming a system which gives relatively long working distanceswith large flat field. As made by Zeiss they magnify 6, 12, 20, and 250 THE HISTORY AND DEVELOPMENT OF THE MICEOSCOPE 30 times, .-mil. employed in such ;i stand ;is fig. 202, they are ad-miral ily adapted for picking out minute shells or for other similarmanipulations, the sand or dredgings to be examined being spreadupon a piece of black paper, and raised upon a book, a box, or someother Mipport to such a height that when the lens is adjustedthereto, the eve may be applied to it continuously without unneces-sary fatigue. It will be found advantageous that the foot of themicroscope should not stand upon the paper over which the objectsare spread, as it is desirable to shake this from time to time in orderto bring a fresh portion of the matters to be examined into view ;


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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901