Extracted from
HOW TO SEE WITH THE MICROSCOPE, J. EDWARDS
SMITH, 1885
THE NEW
NATIONAL MICROSCOPE.
The stand which is
fifteen inches in height, is constructed entirely
of brass, of the highest finish and best
workmanship, having a broad, heavy tripod base.
From the centre of this base rises a stout column,
to the top of which is attached, by a firm joint,
the Jackson model arm, carrying the compound body,
by which the inclination can be varied to any
degree, from vertical to horizontal, the whole
instrument being perfectly steady and free from
tremor in any position. The very highest powers may
be used with it, as the body, being supported by
the arm throughout its entire length, cannot have
any unsteadiness or motion of its own.
The quick adjustment
of focus is effected by means of rack and pinion,
with large milled heads, which works so smoothly
that there is no need to use the fine adjustment
for any power lower than one-quarter of an inch.
The latter adjustment is by means of a delicate
micrometer screw and lever attachment, working with
absolute freedom from all motion, and by which the
very highest powers may be focused with the
greatest exactness.
The stage is of
glass, with a complete rotation in the optic axis,
upon the top of which is a sliding object- holder,
very thin, and with a spring clip for holding the
object in place during rotation. This clip is
removable, in an instant, and the stage forceps can
be inserted in its place, thus allowing the latter
to be moved about with the object-carrier. Beneath
the stage is a tube carrying all the sub-stage
apparatus, as the achromatic condenser, Wenham's
parabola, polarizing apparatus, etc., etc. This is
securely attached to the stage by a bayonet- catch,
and can be instantly detached, leaving a very thin
and unobstructed stage for oblique illumination.
The shutter diaphragm is of novel construction,
with the various-sized openings almost in contact
with the underside of the object under examination,
a great improvement upon the old revolving disk
diaphragm. A double mirror concave and plane is
hung upon a swinging bar, and with every possible
motion for direct and oblique illumination.