J. Zentmayer Philadelphia, Serial No. 330
The "Grand American" binocular model, c. 1867
Zentmayer's Grand American Microscope
Is eighteen inches high when arranged for use. The instrument is mounted on a broad tripod with revolving platform, beveled, silvered, and graduated in degrees for measuring the angular aperture of Achromatic Objectives. Upon this platform two pillars are planted, which carry the curved bell-metal bar to which the body of the instrument, the stage, the secondary body, and mirrors are attached. The bar supports almost the entire length of the body, giving great steadiness and freedom from tremor. The movement of the body it effected by rack and pinion, connected with two large milled heads, which form the coarse adjustment. It has a graduated draw-tube to receive the eye-piece, erector, and analyzer. A fine micrometer screw with graduated and silvered head, acting on a lever, forms the delicate fine adjustment.
Below the stage is the secondary body, a short tube, perfectly centrical to the main body, and moved by rack and pinion, to receive accessories.
The large plane and concave mirrors are so attached as to facilitate oblique illumination and to swing in one plane to the optical axis of the instrument. To ensure smoothness and durability in the movements, the touching parts are of different metals; one being always of hammered brass, the other of bell metal.
The stage is firm, broad, and steady, and only 3/16 inch thick, giving great facility for extreme oblique illumination. It has rectangular movements of one inch in both direction, operated by milled heads that work upon the same axis, with an additional one on the other side of the stage (not visible in the cut), by which diagonal movements are obtained. Upon the square stage a revolving object-carrier is placed. The beveled and silvered edge of the revolving plate is graduated into degrees, and serves as a goniometer, Graduation are also connected with the rectangular movements of the stage, to indicate the position of an object in view so that, when once recorded, it can be easily refound.
The mechanical stage on this example of the Grand American is not the usual stage supplied with this model microscope. The stage now on this microscope is of identical construction as those supplied with the R. & J. Beck, London "Large Best" model and it is possible that this is indeed a Beck stage. The Grand American was the top-of-the-line model produce by Zentmayer until 1876 when production of this model ceased and was replaced by the American Centennial model microscope. Elsewhere of this website is an earlier version of the monocular Grand American microscope. See the article written by Zentmayer entitled "What I Know About Late Improvements of the Microscope" published in the Journal of the Franklin Institute, LXXXIV, 1877.
Biographical Sketch of Joseph Zentmayer
See this article from: Proceedings of the American Microscopical Society. Vol. 14, No. 3, 1893.
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