\_CH.I MICROSCOPE AND ACCESSORIES 27 



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 Cam- 

 pani; Ger. Huygens'sches Okular, Campanisches Okular, see \ 45. — 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 satisfactorily, for micrometry. — Kellner's Ocular, see 

 orthoscopic ocular — Low ocular, also called shallow ocular. An ocular 

 which magnifies the real image only moderately, i. e., 2 to 8 fold. — 

 Micrometer or micrometric Ocular; Fr. Oculaire micrometrique ou & 

 micrometre; Ger. Mikrometer-Okular, Mess Okular Benches O, Jack- 

 son m. o., see $48. — Microscopic Ocular; Fr. Oculaire microscopique ; 

 Ger. mikroskopisches Okular. An ocular for the microscope instead 

 of one for a telescope. — Negative Ocular, see \ 42. — Nelson's screw- 

 micrometer ocular. A modification of the Ramsden's screw or cob-web 

 micrometer in which positive compensating oculars may be used. — Orthoscopic 

 Oculars; also called Kellner's Ocular; Fr. Oculaire orthoscopique; Ger. Kel- 

 ner'sches oder orthoskopisches Okular. An ocular with an eye-lens like one 

 of the combinations of an objective (Figs. 27, 29) 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 inter- 

 changed (Pennock, Micr. Bulletin, vol. iii, p. 9. 3r, 1886). — 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 \ 43. — Projection 

 Ocular ; Fr. Oculaire de projection ; Ger. Projections-Okular, see \ 47. — 

 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'orienta- 

 tion ; Ger. Sucher-Okular, see $46. Shallow Ocular, see low ocular. — Solid 

 Ocular, holosteric O.; Fr. Oculaire holost£re ; Ger. holosterisches Okular, 

 Vollglass-Okular. A negative eye-piece devised 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 dia- 

 phram, a groove is cut at a proper level and filled with black pigment. It is 

 especially excellent where a high ocular is desired. — Spectral or spectroscopic 

 Ocular ; Fr. Oculaire spectroscopique ; Ger. Spectral-Okular, see Microspec- 

 troscope, Ch. VI. — Stauroscopic Ocular ; Fr. Oculaire Stauroscopique ; Ger. 

 Stauroskop-Okular. An ocular with a Bertrand's quartz plate for mineralog- 

 cal purposes — Working Ocular ; Fr. Oculaire de travail ; Ger. Arbeits- 

 Okular, see \ 46. 



\ 45. Huygenian Ocular. — A negative ocular designed by Huygens for 

 the telescope, but adapted also to the microscope. It is the one now most 

 commonly employed. It consists of a field-lens or collective (Fig. 36. ), aid- 



