ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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tion. The coarse adjustment is by rack-and-pinion, and the fine by micro- 

 meter screw. The circular rotating stage is fitted with centering screws. 

 The draw-tube is graduated. The instrument has an Abbe's illuminat- 

 ing apparatus and iris diaphragm, which can be focussed by means of a 

 screw-head under the stage. When the condenser is sufficiently screwed 

 down, further rotation puts it aside. Under the iris is a slotted ring 

 for receiving a coloured glass disc. 



Seibert's Preparation Microscope. — Tbis instrument (fig. 148) is 

 mainly intended for the preliminary inspection and sampling of large 

 objects. Tbe stage is of glass, 18 by 12 cm. The adjustment is by 



Fig. 14S. 



rack-and-pinion. By means of a three-jointed arm the loup can be 

 easily arranged for exploring every part of the object. The mirror is 

 movable, and can be pushed in all horizontal directions. 



Micrometer Screws and Fine Adjustments as applied to Modern 

 Stands.* — Prof. G. Marpmann introduces his article with some historical 

 remarks. He attributes the modern stand to Vincent Chevalier, further 

 developed by his son Charles and his nephew Arthur. These Chevalier 

 stands go back to 1824, and reach their highest perfection in Strauss' 

 grand Microscope of 1834, which has stage and substage, mirror, coarse 

 and fine adjustments, as in the instruments of to-day. The chief dif- 

 ference lies in the shape of the pillar, which in the old stands is half 

 round and with modern ones prismatic. In all the pillar is firmly 



* Zeitschr. angew. Mikr., vii. (1901) pp. 33-8 (2 figs.). 



