f T ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



585 



a slot and stopping the rotation at the right moment. On this frame 

 are four smaller round plates, the exchange plates, of 15 cm. diameter, 

 which rotate easily between the three rollers E (fig. 115) ; they are 

 rectangularly perforated at E, and bear the clips S for a slide. The knob 

 K serves for the proper adjustment of the exchange plate with its slide. 

 The security of the slide is provided for by the grooved clips S on the 

 long sides, and by a projecting fillet on the inner short side of the orifice ; 

 the other short side has a spring pin over which the slide is pushed, 

 which then immediately rises and holds the slide. The dimensions of 

 the orifice are 7 • 5 by 9 cm. 



Fig. 116. 



N\ 



The great advantage of the arrangement is that the operator has 

 thorough control over the insertion of the slides without leaning over 

 the instrumernt. 



Berber's Drawing Apparatus for Small Magnifications.* — This 

 apparatus is shown in fig. 116. On a cast-iron base-plate stands a strong 

 metal pillar M, on which slide two collars B x and B 2 . To Bj a frame- 

 shaped object-table is attached ; it can be swung aside by the pin K, 

 and replaced by an object placed on the base-plate. In the frame of the 



* Zeitachr. f. Instrumentenk., 1901, pp. 171-5 (3 figs.). 



