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Bulloch's Lithological Microscope

From The American Monthly Microscopical Journal, 1886

The general construction of this stand is similar to the Professional stand, except in the following details: There are two stages, one with a plain, sliding object carrier. Each stage is graduated to 15 minutes of arc, reading by a verier to 20 seconds, and can either be revolved by hand or by a tangent screw which also acts as a slow motion. The worm cut on the periphery of the stage has 360 teeth equal to single degrees, and the tangent screw head is devided into 60 parts, so that each division reads to one minute. The tangent screw can be thrown in or out of connection as required. This arrangement is common to both stages. The second stage is furnished with a sliding object carrier, and with micrometer screw movements in two directions for the direct movement of objects without reference to magnification. The screw threads are 1/2 millimeter, the head being graduated to 250, so that each division reads to two microns (.002 mm) which may be again subdivided by a vernier into tenths. At the side of the limb there is a scale reading to 1/2 millimeters, and the slow motion screw head is graduated to 300 divisions, reading to 1 micron. The polarizing prism below, fitting in the substage, has a graduated circle of degrees and a spring catch at each 90 degrees. The analysing prism at the lower end of the body tube has a revolving movement by a lever of 90 degrees, and can be removed by a slide similar to that of Wenham's binocular prism. There is also at the lower end of the tube a Klein quartz plate and a centering nosepiece. There is a gonometer eyepiece with crossed spider lines, a Nichol prism, and a calc-spar plate. The fitting is made adjustable, for if the calc-spar is not cut in the proper direction, the cross cannot be placed in the center of the field without slightly tilting the crystal. To change from polarized to ordinary illumination, the prism below the stage can be turned aside, leaving the wide angle condenser in position; or the whole substage can be turned aside, which movement is supplemetary to swinging on an axis with the object on the stage as a center. When the condenser is not required, there is a supplementary substage for the lower prism, so that the prism can be used close to the object, and no light admitted except that which has passed through the prism. Each stage has stops for a Maltwood finder, and also stops for the small lithological slides. Mr. Bulloch has already made several of these elaborate stands to order, which have given much satisfaction to their owners.

Walter H. Bulloch other microscope makers

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