ZOOLOGY AND BOTANY. MICROSCOPY, ETC. 



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prong of the fork (in a horizontal projection Microscope the lower one) 

 takes the form of a straight bar ; the other prong is a strong steel spring 

 fitted with a metal roller. The object-slide is gripped firmly between 

 the bar and roller, which glide compactly over the stage. The bar is 

 bevelled inwards and the roller is slightly conical, so that slides of 

 various thicknesses are always firmly pressed upon the stage. The 

 apparatus has a vibratory movement about the attachment-point on the 



Fig. 21, 



stage-rim, which is clamped sufficiently tightly to prevent self-motion, 

 but not so tight as to prevent push-action. The roller spring instead of 

 being made of German silver is of good pliable steel, in order to adapt 

 itself to any possible change of size in the slide. The apparatus has 

 been designed in two forms, one for a strong circular stage (fig. 21), the 

 other for a photo-micrographic stage (fig. 22). The first has a metal strip 

 of same curvature as the stage, and carries at one end K a clamp fixed 

 from underneath by a screw not visible in figure. The other end of this 

 strip terminates in an arm above the stage and held fast to it by a screw 

 similar to that used for the ordinary spring slideholder. In the photo- 

 micrographic stage a different construction is necessary, because the stage 

 here consists of two parallel plates. The peripheral strip now takes the 



