26 



MICROSCOPE AND ACCESSORIES 



\_CH.I 



I 43. Positive Oculars are those in which the real, inverted image of the 

 object is formed outside the ocular, and the entire system of ocular lenses 

 magnifies the real image like a simple microscope (Fig. 16). 



Positive and negative oculars may be readily distinguished, as the dia- 

 phragm is below the ocular lenses with the positive ocular and between the 

 lenses in the negative ocular (Figs. 36-37). 



Fig. 36. Sectional view of a Huygenian ocular to 

 show the formation of the Eye-Point. 



Axis. Optic axis of the ocular. D. Diaphragm 

 of the ocular. E. L. Eye-Lens. F. L. Field-Lens. 



E. P. Eye-Point. As seen in section, it appears 

 something like an hour-glass. When seen as looking 

 into the ocular, i. e. , in transection, it appears as a cir- 

 cle of light. It is at the point where the most rays cross. 



TABLE OF OCULARS 



\ 44. 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 seems worth while to give a list, with the French and Ger- 

 man equivalents, and a brief statement of their character. 



Achromatic Ocular; Fr. Oculaireachromatique; Ger. achromatisches Oku- 

 lar. Oculars in which chromatic aberation is wholly or nearly eliminated. — 

 Aplanatic Ocular; Fr. Oculaire aplanatique; Ger. aplanatisches Okular (see 

 (S 24) . — Binocular, stereoscopic Ocular; Fr. Oculaire binoculaire stereoscopique; 

 Ger. stereoskopisches 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 microscope. By an arrangement of pri9tns 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 princi- 

 ples, both fields, being equally illuminated. His ocular is also erecting-. — 

 Campani 1 s Ocular (see Huygenian Ocular). — Compound Ocular; Fr. Oculaire 

 compost; Ger. zusammengesetztes Okular. An ocular of two or more lenses, 

 e. g., the Huygenian (see Fig. 36). — Continental Ocular. An ocular mounted 

 in a tube of uniform diameter as in Fig. 37. — Deep Ocular, see high ocular. — 

 Erecting Ocular; Fr. Oculaire redresseur; Ger. bildumkehrendes 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 3, goniometre; Ger. 



