Of these there are two kinds - simple and compound. The Simple Microscope is only a hand magnifying-glass or linen-tester, and consists of a double convex lens (or several mounted in juxtaposiFig. 469.

I Description of the Microscope 1096

Simple microscope (watchmaker's).

Fig. 470.

I Description of the Microscope 1097

Simple microscope (magnifier).

tion on a common axis), giving an extensive field of view and an erect image 5 - 30 times the size of the object. This instrument is valuable in field botanic work, crystallography, deciphering illegible prescriptions, recognizing various fabrics and other objects indistinctly visible by the naked eye.

The Compound Microscope is a more complex instrument, and consists of several lenses so separated at focal distances that each one

Fig. 471.

I Description of the Microscope 1098I Description of the Microscope 1099

Simple microscope. (Coddington.)

Fig. 472.

I Description of the Microscope 1100

Simple microscope (linen-tester).

serves to magnify the image transmitted by the preceding one. The higher the magnifying powers used, the smaller becomes the area of the object that is seen through the instrument, and the light being correspondingly diffused over a larger area in the image, the latter

Fig. 473.

I Description of the Microscope 1101

Tripod dissecting microscope.

Fig. 474.

Folding dissecting microscope.

Folding dissecting microscope.

appears less bright. The image is always inverted and magnified 10-4,000 times.

1. The Ocular Or Eye-Piece (G)

The Ocular Or Eye-Piece (G). This, in the line of vision, is the part nearest to the eye, and has several types - Huyghenian, Continentai, Kellner, Binocular, Solid (all negative), Rainsden, etc. (posi-tive). The first named* is used mostly, and consists of two planoconvex lenses (plane surfaces upward) mounted in a short metal tube: the one next to the eye - eye-lens; the one farthest - field-lens. Between these two a diaphragm is so placed as to cut off the blurred

Fig. 475.

I Description of the Microscope 1103

Compound microscope. A, base; B, pillar; C, pillar and arm; D, body; B, nose-piece; F, objective: G, ocular: H, draw-tube; I, collar; J, rack and pinion; K, coarse adjustment; L, fine adjustment; N, spring clips; O, mirror; P. mirror bar; Q, diaphragm and substage; R, substage screw; S, stage aperture; T, pillar hinge-joint.

edges of the image, thus giving a flat field and a sharp, round outline to the field of vision. The ocular magnifies the real image produced by the objective as though that image were itself the original object; its magnifying power is inversely proportional to the length - the longer the tube, the lower the power. Oculars are designated as follows: A-2 inch, B-1 1/2 inch, C-l inch, D-3/4 inch, E-1/2 inch - the first weakest, the last strongest.