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 lo. 2 



Fjg. 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 will be seen that the mount- 

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

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

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

 jS, are positive. The numbers 2, 4, 6, S, 12, 18, indicate the magnification of the 

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



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 \ 34. Projection Ocular ; Fr. Ocu- 

 laire de projection ; Ger. Projectious-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 part of the field is clear. 

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

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

 st£re ; 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 eve- 

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

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

 see I 36. 



