ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 



61& 



fig. 07. It has a range of 80 and 45 mm. in both directions, which 

 can be read on three scales with verniers. 



Fig. 97. 



i2i Eye-pieces and Objectives. 



Siedentopf s Microscope Ocular with Quartzwedge Compensator.* 

 This ocular with push-action quartz wedges resembles that described by 

 J. Amaun.f It has the shape of the ocular screw-micrometer if except 

 that the lateral measuring dnim is omitted and in lieu thereof an 

 opening is contrived into which the quartz wedges can be pushed. 

 Fig. 98 shows the ocular with the wedge, aud fig. 99 shows the wedge by 

 itself. The whole arrangement is dropped into the Microscope tube, 

 thus replacing the usual ocular, and clamped. The ocular is a Ramsden, 

 and the wedge operates in its focal plane. The optical axis of the 

 wedge is parallel to its long sharp angle, and the wedge is adjustable in 

 direction of its length. On its upper face is a graduation which gives in 

 thousandths of a millimetre the retardation difference experienced by 

 the ordinary and extraordinary rays in their respective cross-sections as 

 they pass through the wedge. When the polarising planes of the 

 polariser and of the analyser (inserted on the ocular) are crossed and 

 inclined at 45° to the principal plane of the quartz wedge, and so placed 

 on the preparation under examination that the polarising plane of the 

 quicker wave lies perpendicularly to the optic axis of the quartz wedge, 



* Extract from Centralbl. f. Min. etc., 1906, No. 23; published by Carl 

 Zeiss, Jena. 



+ Zeitschr. wiss. Mikrosk., xi. (1894) p. 440-54. See also this Journal, 1895, 

 pp. 237-40. X Zeiss' Catalogue, Mikroskope, 1906, p. .33. 



