READING GLASSES
Reading glasses (Fig. 4) are large simple magnifiers, often six inches in diameter. The lens is encircled with a metal band and provided with a handle.
Fig. 5.—Steinheil Aplanatic Lens
STEINHEIL APLANATIC LENSES
Steinheil aplanatic lenses (Fig. 5) consist of three or four lenses cemented together. The combination is such that the field is large, flat, and achromatic. These lenses are suitable for field, dissecting, and pocket use. When such lenses are placed in simple holders, they make good dissecting microscopes.
Fig. 6.—Dissecting microscope
DISSECTING MICROSCOPE
The dissecting microscope (Fig. 6) consists of a Steinheil lens and an elaborate stand, a firm base, a pillar, a rack and pinion, a glass stage, beneath which there is a groove for holding a metal plate with one black and one white surface. The nature of the object under observation determines whether a plate is used. When the plate is used and when the object is studied by reflected light it is sometimes desirable to use the black and sometimes the white surface. The mirror, which has a concave and a plain surface, is used to reflect the light on the glass stage when the object is studied by transmitted light. The dissecting microscope magnifies objects up to twenty diameters, or twenty times their real size.