ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



959 



white blotting-paper, between wbicli the covers are placed on edge. 

 This not only preserves them from breakage, and enables one to 

 readily pick them out when wanted for use, but also facilitates the 

 selection for special preparations of those of the most desirable thick- 

 ness; for, by holding the drawer or box between the eye and the 

 light, it is easy by comparison to select the thickest or thinnest cover, 

 and thus, for all practical purposes, to do away with the trouble of 

 measuring them. 



Sidle' s "Congress" Turntable. — This turntable (so called 

 from having been first exhibited at the " Congress of Microscopists " 

 at Indianapolis) is shown in Figs. 228 and 229. 



Fig. 228. 



Fig. 229. 



Into the upper surface of the rotating plate, and diametrically 

 opposite and equidistant from the centre, are set two circular plates or 

 disks, 1 inch in diameter, their surfaces flush with that of the large 

 plate. Pivots from the two disks project through the plate, and each 

 carries upon the lower side of the plate a toothed wheel. A hollow 

 sleeve rotating freely upon the stem of the table carries a third and 

 larger wheel, which gears into the two 

 others and thereby gives rotation to the 

 disks in the top of the plate. In Fig. 

 229 the turntable is inverted to show 

 the mechanism. 



Near the opposite edges of the two 

 disks, the angular jaws which hold oppo- 

 site corners of the slide are pivoted (as 

 in Cox's and other forms), so that by 

 giving rotation to the central wheel 

 under the plate, the jaws may be made 

 to approach or recede at pleasure. 



A coiled steel spring, concealed 

 within the hollow sleeve, serves to close 



the jaws, while a single motion of the milled head B, Fig, 229, upon 

 the sleeve, opens them to their full extent ; the lower milled edge A 

 serves to give rotation to the turntable. 



Although the jaws do not approach in a straight line, yet when 

 properly adjusted, a line joining the pivots of the jaws will cut the 



