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THE

AMERICAN NATURALIST.

Vol. VI.-JUNE, 1872.-No. 6.
STUDENTS' MICROSCOPES.*

BY R. n. WARD, M. D.

Those who use the microscope as an elegant and costly luxury will, of course, be guided in so doing by their general ideas of taste, economy, etc.; the few who use the instrument as medical experts, or original investigators in science, will, at the same time, by years of practice, grow into the use and the possession of an instrument suited to their wants; but a larger class are those who use the instrument as an incidental though frequent aid in their daily work in various sciences or professions, who reasonably desire the simplest instruments consistent with real usefulness, and who, however eminent in other specialties, are often unfamiliar with the styles and prices of the various makers, and at a loss to know what available resources would best supply their wants. The following tables are designed to be of use to buyers of microscopes, of the latter class, and to persons who desire information in a concise and convenient form, in regard to the progress thus far made in this department of microscopy. "While the styles and prices will be subject to endless variation, the statements made will be sufficiently accurate to form a basis for selection aud correspondence for a considerable time.

For the convenience of persons who desire to compare our styles with those of European makers, the table of American Students' Microscopes has been rearranged so as to correspond in form with Dr. J. F. Payne's recently published table of European instru

•From a paper on Medical Microscopes, read at the Medical Society of the State of New York, Feb. 7,1872.

Entered according to the Act of Congress, in the year 1872, hy the Fjsadody Academy Of Science, In the Office of the Librarian of Congress, at Washington.

AMER. NATURALIST, VOL. VI. 21 (321)

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SYNOPSIS OF STUDENTS' MICROSCOPES.

MODEL.

Must have joint to incline at various angles from horizontal to perpendicular.

Curved Bar. — " Jackson" (but not prolonged beneath stage); steadiest form for equal weights.

Transverse Bar. — Most convenient In some respects.

WEIGHT.

Four to ten pounds. —A question of convenience vs firmness.

Height. (12 to 16 inches.)

Tall. — Much room below stage. Standard length of tube gives usual powers. Looks well, and is most convenient when Inclined.

Short. — Easiest for vertical use. Short tube works lenses at too low power. Should be lengthened by draw-tube when inclined.

. DIAMETER OF TUBE. (1 tO 1 3-8 in.)

Small. — Looks best and is steadiest on small instruments.
Large. — Gives wider field with low power oculars.

MATERIAL.

All Brass. — Looks best.

Iron Base. — Saves expense. Wears well unless broken by falling.

COARSE ADJUSTMENT.

liaek and Pinion. — Easiest; preferable but costly. Friction Pinion. — Said to be very delicate. Chain Movement. — Fine motion. Easily repaired if necessary. Sliding Tube, by hand. — Saves expense. Most delicate, but awkward. Wants expert hands, and often two of them.

Fine Adjustment. Essential.

Screw and lever moving nose-piece. —Best. Costly.

Screw and lever moving compound body. —Good for moderate powers.

Screw moving compound body. — Less delicate.

Screw against shoulder, moving nose-piece. — Less delicate.

Screw on nose-piece. — Little used.

Screw moving stage. — Cheapest in use in this country. Bad in theory and history; but quite satisfactory in use, as made at present.

Bar moving pinioti of rack. — Not in this country. Good for low powers. May be added to instruments having no other fine adjustment.

STAGE.

Mechanical. —Not required. Lever. — Plausible, but not successful. Magnetic. —Plausible, but not successful. (Insecure.) Hand movement. (In two rectangular directions.) —Best substitute for mechanical, for high powers, and with Maltwood Finder. Glass, concentric. — Best for Binocular.

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