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.