CH. /] MICROSCOPE AND ACCESSORIES 23 



being sent to each eye. The most satisfactory form was worked out by Tolles and 

 is constructed on true stereotomic principles, both fields being equally illuminated. 

 His ocular is also erecting. Campani^s Ocular (see Huygenian Ocular). Com- 

 pound Ocular ; Fr. Oculaire compose ; Ger. zusammengesetztes Okular. An ocu- 

 lar of two or more lenses, e. g., the Huygenian (see Fig. 30). Continental Ocular. 

 An ocular mounted in a tube of uniform diameter as in Fig. ^i.Deep Ocular, 

 see high ocular. Erecting Ocular ; Fr. Oculaire redresseur ; Ger. bildumkeh- 

 rendes Okular. An ocular with which an erecting prism is connected so that the 

 image is erect as with the simple microscope. Such oculars are most common on 

 dissecting microscopes. Filar micrometer Ocular; Screw m. o., Cobweb m. o., 

 Ger. Okular-Schraubenmikrometer. A modification of Ramsden's Telescopic Cob- 

 web micrometer ocular. Goniometer Ocular ; Fr. Oculaire a goniometre ; Ger. 

 Goniometer-Okular. An ocular with goniometer for measuring the angles of minute 

 crystals. High Ocular, sometimes called a deep ocular. One that magnifies 

 the real image considerably, i. e., 10 to 20 fold. Huygenian Ocular, Huygens' O., 

 Campani's O., Airy's O.; Fr. Oculaire d'Huygens, o. de Campani ; Ger. Huy- 

 gens'sches Okular, Campaniches Okular, see \ 38. Index Ocular ; Ger. Spitzen- 

 O. An ocular with a minute pointer or two pointers at the level of the real image. 

 The points are movable and serve for indicators and also, although not satisfac- 

 torily, for micrometry. Kellner's Ocular, see orthoscopic ocular Low ocular, 

 also called shallow ocular. An ocular which magnifies the real image only moder- 

 ately, i. e. , 2 to 8 fold. Micrometer or micrometric Ocular ; Fr. Oculaire microme- 

 trique ou a micrometre ; Ger. Mikrometer-Okular, Mess Okular, Beneches O., 

 Jackson m. o., see \ 41. Microscopic Ocular ; Fr. Oculaire microscopique ; Ger. mi- 

 kroskopisches Okular. An ocular for the microscope instead of one for a telescope. 

 Negative Ocular, see \ 36. Nelson's screw-micrometer ocular. A modification of 

 the Ramsden's screw or cob-web micrometer in which positive compensating ocu- 

 lars may be used. Orthoscopic Oculars; also called Kellner's Ocular ; Fr. Ocu- 

 laire orthoscopique ; Ger. Kellner'sches oder orthoskopisches Okular. An ocular 

 with an eye-lens like one of the combinations of an objective (Figs. 22, 23) and a 

 double convex field lens. The field-lens is in the focus of the eye-lens and there 

 is no diaphragm present. The field is large and flat. Par-focal Oculars, a series 

 of oculars so arranged that the microscope remains in focus when the oculars are 

 interchanged (Pennock, Micr. Bulletin, vol. iii, p. 9, 31). Periscopic Ocular ; Fr. 

 Oculaire periscopique ; Ger. periskopisches Okular. A positive ocular devised by 

 Gundlach. It consists of a double convex field-lens and a triplet eye-lens. It 

 gives a large, flat field. Positive Ocular, see \ 37. Projection Ocular ; Fr. Ocu- 

 laire de projection ; Ger. Projections-Okular, see \ 40. Ramsden's Ocular ; Fr. 

 Oculaire de Ramsden ; Ger. Ramsden'sches Okular. A positive ocular devised by 

 Ramsden. It consists of two plano-convex lenses placed close together with the 

 convex surfaces facing each other. Only the central part of the field is clear. 

 Searching Ocular ; Fr. Oculaire d'orientation ; Ger. Sucher-Okular, see 39, 

 Shallow Ocular, see low ocular. Solid Ocular, holosteric O. ; Fr. Oculaire holo- 

 stere ; Ger. holosterisches Okular, Vollglass-Okular. A negative eye-piece de- 

 vised by Tolles. It consists of a solid piece of glass with a moderate curvature at 

 one end for a field-lens, and the other end with a much greater curvature for an 

 eye-lens. For a diaphragm, a groove is cut at the proper level and filled with 

 black pigment. It is especially excellent where a high ocular is desired. Spectral 



