The construction and use of the simple microscope (magnifiers) undoubtedly date back to very early times. There is sufficient evidence to prove that spheres of glass were used as burning spheres and as magnifiers by people antedating the Greeks and Romans.

The simple microscopes of to-day have a very wide range of application and a corresponding variation in structure and in appearance.

Simple microscopes are used daily in classifying and studying crude drugs, testing linen and other cloth, repairing watches, in reading, and identifying insects. The more complex simple microscopes are used in the dissection and classification of flowers.

The watchmaker's loupe, the linen tester, the reading glass, the engraver's lens, and the simplest folding magnifiers consist of a double convex lens. Such a lens produces an erect, enlarged image of the object viewed when the lens is placed so that the object is within its focal distance. The focal distance of a lens varies according to the curvature of the lens. The greater the curvature, the shorter the focal distance and the greater the magnification.

The more complicated simple microscope consists of two or more lenses. The double and triple magnifiers consist of two and three lenses respectively.

When an object is viewed through three lenses, the magnification is greater than when viewed through one or two lenses, but a smaller part of the object is magnified.

Forms Of Simple Microscopes. Tripod Magnifier

The tripod magnifier (Fig. 1) is a simple lens mounted on a mechanical stand. The tripod is placed over the object and the focus is obtained by means of a screw which raises or lowers the lens, according to the degree it is magnified.

Watchmaker's Loupe

The watchmaker's loupe (Fig. 2) is a one-lens magnifier mounted on an ebony or metallic tapering rim, which can be placed over the eye and held in position by frowning or contracting the eyelid.

Tripod Magnifier.

Fig. 1. Tripod Magnifier.

Watchmaker's Loupe.

Fig. 2. Watchmaker's Loupe.

Folding Magnifier

The folding magnifier (Fig. 3) of one or more lenses is mounted in such a way that, when not in use, the lenses fold up like the blade of a knife, and when so folded are effectively protected from abrasion by the upper and lower surfaces of the folder.

Folding Magnifier.

Fig. 3. Folding Magnifier.

Reading Glass.

Fig. 4. Reading Glass.

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.

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.

Steinheil Aplanatic Lens.

Fig. 5. Steinheil Aplanatic Lens.

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.

Dissecting Microscope.

Fig. 6. Dissecting Microscope.