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.
