A Hydraulic Stage: An Aid in Counting Mineral Grains

D. W. Humphries
1964 Mineralogical magazine  
A hydraulically operated microscope stage is described and con-s~ructional details are given. The stage is foot-operated, which leaves both hands free for continuous focusing of the microscope and the operation of a mechanical counting device. A further advantage of the hydraulic stage is that unmounted grains (or small fossils) can be moved smoothly and without relative movement between individual grains. The rate at which grains (or small fossils) can be counted is thus greatly increased. T
more » ... atly increased. T HE counting of mineral grains (or small fossils) under the microscope involves three separate processes: the focusing of the microscope on the object, the identification and tabulation of the grain, and the movement of the specimen holder to bring the next grain into the centre of the field of view. The whole cycle is then repeated. For rapid counting of large numbers of grains, it is highly desirable that one hand is continuously used for focusing the microscope, while the other operates a mechanical or electro-mechanical counting device. When the grains are mounted, the electro-mechanical stage of the 'point-counter' type, operated directly from the counting device, is suitable for the movement of the slide. Where the grains are unmounted, however, the jerky movement of this type of stage rapidly piles the grains in a heap. The hydraulic stage provides a means of moving loose grains across the field of view smoothly and without relative movement between individual grains. Being foot-operated, it leaves the hands free for counting and focusing. The principle of operation is the transference of oil from the master cylinder in the foot-operated control unit to a slave cylinder in the stage unit and back. The two milts are connected by a wire-wound flexible plastic tube. The apparatus is shown in fig. 1 and the details of construction in figs. 2, 3, and 4. The control unit ( fig. 2) . A brass cylinder (a) closed at its lower end and attached centrally to a steel base plate (b) is closed by a piston (c)
doi:10.1180/minmag.1964.033.265.08 fatcat:ht7py4ivdzch7ngbzjb6ponh24