CH. /.I MICROSCOPE AND ACCESSORIES. 23 



eye-lens toward the object and looking into the field-lens an image may be seen, 

 however. 



Special names have also been applied to oculars, depending upon the designer, 

 the construction, or the special use to which the ocular is to be applied. The fol- 

 lowing are most used.* 



* In works and catalogs concerning the microscope and microscopic apparatus, 

 and in articles upon the microscope in periodicals, various forms of oculars or eye- 

 pieces are so frequently mentioned, without explanation or definition, that it 

 seemed worth while to give a list, with the French and German equivalents, and a 

 brief statement of their character. 



Achromatic Ocular; Fr. Oculaire achromatique ; Ger. achromatisches Okular. 

 Oculars in which chromatic aberration is wholly or nearly eliminated. Aplanatic 

 Ocular ; Fr. Oculaire aplanatique ; Ger. aplanatisches Okular (see \ 19). Binocu- 

 lar, stereoscopic Ocular ; Fr. Oculaire binoculaire stereoscopique ; Ger. stereosko- 

 pisches Doppel-Okular. An ocular consisting of two oculars about as far apart as 

 the two eyes. These are connected with a single tube which fits a monocular mi- 

 croscope. By* an arrangement of prisms the image forming rays are divided, half 

 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. CampanVs Ocular (see Huygeniau Ocular). Com- 

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

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

 An ocular mounted in a tube of uniform diameter as in Fig. 31. 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 in. o. Cobweb m. o. 

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

 web micrometer ocular. Goniometer Ccular ; Fr. Oculaire a gouiometre ; Ger. 

 Goiiiometer-Okular. An ocular with goniometer for measuring the angles of mi- 

 nute crystals. High Ocul.ir, sometimes called a deep ocular. One that magnifies 

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

 Campaui's O., Airy's O. ; Fr. Oculaire d'Huygens, o. de Cauipani ; Ger. Ffuy- 

 gens'sches Okular, Canipaniches Okular, see \ 35. 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 satisfacto- 

 rily for micrometry. A'ellner's Ocular, see orthoscopic ocular. Low Ocular, also 

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

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

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

 Jackson m. o., see \, 38. Microscopic Ocular ; Fr. Oculaire microscopic ; Ger. mi- 

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

 Negative Ocular, see \ 33. Nelsoi'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 eve-lens and there 



