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 stage on the example shown on this page differs from the usual mechanical stage mentioned in the
above catalog description. In this case, there is a round stage which can be centered and
is calibrated with a silvered scale. It is capable of a full
360° rotation. The stage supports a gliding slide holder which is held down by an
ivory-tipped screw allowing a smooth hand movement of the holder in any direction.
This type of stage was first introduced by Zentmayer in early 1860. 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 where he stated:
"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"
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 with serial number 14 and
a binocular version with serial number 330 having a Beck-type mechanical stage.
Also represented in this collection is the first (or forerunner)
Grand American with serial number 1.
This microscope was purchased from a descendant of the original
owner, George Edward Smith (1840-1917). George Edward Smith
was born in Rutland, MA and died in Brookline, MA. He was
apparently a wealthy man of many interests. He was
particularly interested in precious stones having a valuable
collection and in investments in other natural resources and real estate.
Accompanying this microscope is a quantity of wooden collection
boxes containing unmounted specimens, mostly insects
and insect parts. There is the possibility that these specimens
were collected by either by Louis Agassiz
or his son Alexander.
Sometime after the death of Louis Agassiz, the family of G. E. Smith acquired the Agassiz summer house in Nahant MA where
Louis Agassiz maintained a laboratory in a part of the laundry room.
Family members recall seeing specimen jars at that location and
they believe that these boxes were included among the Agassiz specimens.
The Nahant house has since been destroyed by a fire.
Biographical Sketch of Joseph
Zentmayer
See this
article from: Proceedings of the American
Microscopical Society. Vol. 14, No. 3,
1893