The horizontal movement
of the mechanical stage utilizes a worm gear while the
vertical movement is uses a fusee chain.
While the original wood
case did not survive with this microscope, the
accessory box did. Among the remaining accessories is a
Zentmayer objective with its canister marked 8/10, two
oculars, a camera lucida, a centerable achromatic
condenser, a substage polarizing prism in a rotating
mount, and the analyzing prism which mounts onto the
end of the draw-tube.
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.
He has written:
"In order to
make the investigation a thorough one, it will be
necessary for me to call your attention to the
so-called Grand American Stand, made for this academy
in October, 1859, and which now stands before you. The
novel points of this stand, which I claimed at that
time, were: 1st. The stage, with graduated revolving
plate to serve as goniometer. Although very firm, it is
only 3/16" thick, and is, even at the present date, the
thinnest mechanical stage made. 2d. The graduated
revolving base for measuring the angular apertures of
objectives. 3d. The hanging of the mirror to a joint as
near as possible to the plane of the stage
Early in 1860, I made
three stands (Nos. 13,14 and 15) precisely like the
Grand American, but somewhat lighter. No. 15 was made
for a gentleman who was not in favor of mechanical
stages, and who desired me to design for him a
revolving stage, the object to be moved by hand, and it
was for him that I constructed the first of my
graduated stages, giving a complete revolution in the
optical axis, in a large ring, which is adjustable
within another by three screws, in order to have the
axis of the stage coincident with the optical axis of
the instrument, exactly the same as the one before you,
which I made early in 1866. This stage has been for
years extensively copied, in France and in
England"
As suggested in the above
quote, No. 14 is among the first few Grand American
microscopes that were produced. This particular example
does not have graduations for the rotating stage plate,
which is a common feature found on most of the
instruments produced subsequently. The Grand American
microscope 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 on
this website is an example of a
binocular version of the Grand American
microscope and another one of later vintage.
Also in this collection is a Zentmayer microscope with serial No.1; this microscope is the first (or forerunner) Grand American.
Biographical Sketch of Joseph
Zentmayer
See this article from: Proceedings of the American Microscopical Society. Vol. 14, No. 3, 1893