24 



MICROSCOPE AND ACCESSORIES. 



[CH. I. 



\ 35. Huygenian Ocular. — A negative ocular designed by Huygens for the tele- 

 scope, but adapted also to the microscope. It is the one now most commonly em- 

 ployed. It consists of a field-lens or collective (Fig. 30), aiding the objective in 

 forming the real image, and an eye-lens which magnifies the real image. While 



Ocular Ho 2 



Fig. 31. Compensating Oculars of Zeiss, with section removed to show the con- 

 struction. The line A- A is at the level of the upper end of the tube of the micro- 

 scope while B-B represents the lower focal points. It ivill be seen that the mount- 

 ing is so arranged that the lower focal points in all are in the same plane and 

 therefore the microscope remains in focus upon changing oculars. ( The oculars are 

 par-focal). The loiver oculars, 2, 4 and 6 are negative, and the higher ones, 8, 12 

 iS, are positive. The numbers 2, 4, 6. S, 12, 1S, indicate the magnification of the 

 ocular. {From Zeiss' Catalog Ao. 30). 



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

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

 interchanged (Peunock, 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 \ 34. Projection Ocular ; Fr. Ocu- 

 laire de projection ; Ger. Projections-Okular, see \ 37. 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 purt of the field is clear. 

 Searching Ocular ; Fr. Oculaire d'orientatiou ; Ger. Sucher-Okular, see \ 36. 

 Shalloxv 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 or 

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

 crospectroscope, Ch. VI. Stauroscopic Ocular ; Fr. Oculaire Stauroscopique. 

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

 ical purposes. Working Ocular; Fr. Oculaire de travail; Ger. Arbeits Okular, 

 see I 36. 



