83 
Our Present Medical and Students' Microscopes. 
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. 
Glass , sliding ly hand. — Cannot be too highly commended for 
ordinary medical use. 
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. 
Plain. — Very desirable, and costs little. May be smaller. 
Diaphragm. 
Fitting should be removable, for oblique light. 
Disk with apertures. — Essential. Should be closed between dia- 
phragm and stage to prevent accidental oblique light. 
“ Graduating ” or “ Iris.” — Incomparably best, but unnecessarily 
expensive. 
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 use. Should always be negative. 
One-inch. — (Often named B or C, or No. 2 or 3.) X 10. Use for 
micrometry, occasionally for observations, and generally as achro- 
matic condenser. If willing to add j§5 or £>10, substitute Kellner’s 
orthoscopic, by European or American makers (superb field), or Tolies’ 
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 collar. — Best. 
Screw movement of outer tube. — Good for cheap lenses of small 
angles. 
* Magnifies, diameters. 
