Glass, sliding by hand. nary medical use. Cannot be too highly commended for ordi Brass.-Sliding by hand (cloth-lined, or otherwise). A good and cheap substitute. Plain. Saves expense. Should have removable spring clips. Could have glass or brass sliding-stage added. MIRROR. Must have lateral, vertical and two rotary movements. Lateral movement by cranked arm: not common in students' microscopes. Lateral movement by mirror swinging partly around the bar which carries it. Lateral movement by hinge joint at top of bar which carries mirror: obliquity entirely independent of distance of mirror from object. Concave. Indispensable. Should be nearly two inches wide. DIAPHRAGM. Fitting should be removable, for oblique light. Disc with apertures.- Essential. Should be closed between diaphragm and stage to prevent accidental oblique light. sive. Graduating" or "Iris."-Incomparably best, but unnecessarily expen OCULARS (eye-pieces). Negative (Huyghens') always meant, unless otherwise stated. Quality (and performance) varies greatly, though seldom suspected. Two-inch. (The A or No. 1 of most makers.) X* 5. Best for general Should always be negative. use. One-inch. (Often named B or C, or No. 2 or 3.) X 10. Use for Micrometry, occasionally for observations, and generally as achromatic condenser. If willing to add $5.00 or $10.00, substitute Kellner's orthoscopic, by European or American makers (superb field), or Tolles' orthoscopic, by Boston Optical Works (field narrower, but peculiarly clear). OBJECTIVES. (If extravagant anywhere, put it here.) All above 50° angular aperture, should have adjustment for cover glass. All above about 75° must have the same. Screw movement of outer tube.-Good for cheap lenses of small angles. Sliding movement of outer tube, with oblique slot.-Good for cheap lenses of small angles. One-inch. - X 10 (with lowest ocular, X about 50). Should be about 25° angular aperture. One-fourth or one-fifth inch. -X 40 or 50 (with low ocular, X about 200 or 250). May be 75° to 85°. One-sixth to one-eighth inch. - X 60 to 80. (With low ocular, X about 300 to 400.) Should be 120° to 140°. Best added after a few years' experience with the others. *Magnifies, diameters. MAGNIFYING POWERS. Quality more than quantity. Theoretical. One inch X 10. Oculars and objectives as above, X 50, 100, 200, 400, 800. Practical. Should approximate to this. ACCESSORIES. Essential, and should be furnished free. A few glass slides and covers; stage-plates with ledge; pipettes ; pliers; and needles mounted in handles. Desirable, for medical and general use. Compressorium, or animalcule cage. Curved scissors (sideways). Camera lucida, for drawing and micrometry.* Stage micrometer. Graduated Draw-tube. Cylindrical fitting, below stage, to use ocular for achromatic condenser. Reagents. (In twelve one or two ounce vials.) Turn table, and mounting materials. Desirable, more for general than medical use. Condensing lens, on separate stand, for opaque objects, and for parallel light, etc.; or condensing lens to limb or stage of instrument, for opaque objects; or mirror on curved arm, to swing above stage, for opaque objects; or mirror removable to stage or separate stand for opaque objects. Spotted lens, or glass paraboloid, for translucent objects. Stage forceps. Maltwood finder. PRICE. Including walnut or mahogany case, $50 to $100. Varies with quantity. and quality of work and reputation of maker. Less, at present, unsatisfactory. More, unnecessary. About double, by substituting binocular stand. * For occasional measurements the camera is entirely satisfactory. Where large numbers of measurements are to be made, this method is not sufficiently rapid and convenient. Dr. White's micrometer, a semicircle of thin glass, graduated at the straight edge, and lying upon the diaphragm in focus of the eye lens, is most used by the writer for this purpose. With low powers the object is easily brought up obliquely to the required position; for high powers the Jackson adjusting screw must be used, unless the stand have a mechanical stage. The simplest ocular micrometer, and best for general students' use, is a circular disc cut, to fit, from the centre of a rather thin stage-micrometer graduated to hundredths or to two-hundredths of an inch, and lying, only when used, upon the diaphragm in the ocular like Dr. White's form. This rather thick circle is more durable, more easily obtained and handled, and capable of giving unexpectedly good results. It should cost $2 or $3. Wm. Y. McAllister, 728 (No. 5374.) Transverse 13 43 16 bar. Wm. Y. McAllister, 728 (No. 5374.) Transverse 13 43 1 bar. † Arm expands to fill whole space between uprights, and gives, with conical steel pin, a very simple Trunnion joint. Screw to Plain, with Concave, 13 in.. 1 in. 1 in. & 75 to in. 300. Screw with Plain, with Plane and con-1 in. 1 in. & 475 to Mirror to sep 100.80., extra lever to fitting for cave, 1 in., in. for binocular eyepiece. 450. arate stand ill., draw tube & cam Screw to Plain, with Concave, with A & B 1 in. 16° 37 to Mirror to stage 60. 100. stage. spring hinge move clips. ment. Screw with Plain, with Concave, 1 in.. A & B 1 in. 16° 37 to Stage plates & 80. 100. lever to spring with side Diaphragm, sunk into upper surface of stage, so as to be close to the object slide. |