ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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attached by a pinion to the circular base-plate (milled on the edge) 

 and carries a toothed wheel that moves both plates in the vertical by 

 a side-rack shown in the slot opening ; whilst the other one acts on a 

 rack, under the bar in the hollow horizontal track that forms part of 

 the upper plate, and causes this plate only to traverse. The two 

 moving plates are of German silver, each about 3^0 inch in thickness ; 



Fig. 9. 



the lower one is held on the circular stage by three short pins with 

 spring washers that travel in corresponding slots cut through the 

 stage and forming a triangular support ; the upper one lies nearly flat 

 on the lower one, touching merely round the outer edge. The total 

 thickness of this mechanical stage may be better appreciated by a 

 glance at Fig. 10 (actual size), in which the ring, graduated on the edge, 

 is the main stage ring, attached at right angles to the vertical disk 

 (shown in part) having within it another one that carries either of the 

 two moving stages figured, and which can be exactly centered to rotate 

 on the optic axis by the three steel screw studs (two of which are seen 

 on the edge). From the upper surface of the moving plates, where 

 the object is placed, the perpendicular thickness is slightly less than 

 half an inch — probably the thinnest mechanical stage ever made to a 

 first-class stand. As no portions of the stage project beyond the 

 circular edge in any position of motion, the complete rotation can be 

 made. The absence of projecting pinions or milled heads is of some 

 advantage in connection with the full radial swing of the substage. 



When the Microscope is placed horizontal, the object on the stage 

 is in a perpendicular axis, passing through the centre of the rotating 

 foot ; if then a lamp flame be adjusted in a line with the optic axis the 

 rotation of the Microscope on the foot will provide a practically 

 perfect range of oblique illumination on either side. The hemi- 



