There is a spiral groove cut into the surface of the inner tube.
This meshes with a small protrusion inside the outer tube. As a consequence
of this, the microscope focuses smoothly just by twisting the inner tube
within the outer. The fine focus adjustment on this instrument is a knob
located under the stage that tilts the spring loaded upper stage plate up and down.
The stage has a built-in aperture wheel to moderate the light.
The microscope is
signed on the limb J. Grunow. New
York, but is without a serial
number. It dates from around 1880.
The Grunow brothers, Julius and William, emigrated
from Germany to New York around 1849. They started in
the scientific instrument business by first working
for the optician Benjamin Pike of that city. By
1854, they began their own operation in New Haven CT
where they concentrated on the production of
microscopes. By 1864, they were back in New York.
Some years later, the partnership ended. J. Grunow
continued on to produce microscopes up to around
1892. The total output of the Grunows was limited in
comparison to some other contemporary firms; on the
basis of the observed serial numbers, they
manufactured just over one thousand microscopes in
total.
