ZOOLOaY AND BOTANY, MICROSOOPT, ETC. 



813 



Fig, 



Fig. 174 



Tlie mechanical stage (E',Fig. 173 andE, Fig. I72),wliicli is attached 

 at pleasure to the ordinary stage (shown in Fig. 1 74: E) when the clips 

 are removed, appears to be an anticipation in principle of those of Tolles 

 and Watson* recently introduced, the rect- 

 angular movements being controlled on the 

 surface by two milled heads acting entirely 

 within the circumference. B (Fig. 173;, and 

 the opposite symmetrical piece are attached 

 to the fixed bottom plate and have Y-shaped 

 grooves between which the movable plate A 

 slides. Eackwork is cut on the lower edge 

 of the latter, which is acted upon by a pinion 

 (milled head shown at B) giving about one 

 inch of motion. The plate A has in the same 

 way two opposite symmetrical pieces similarly 



grooved, and an upper movable plate slides between them by rack and 

 pinion motion (milled head shown on the left) acting at right angles 

 to the former motion. This upper plate is provided with an angle- 

 piece serving as a stop for the object, and a sprung " horse-shoe " clip 

 for holding the object in place. At A and B are graduations for use as 

 finders. The bevelled edge of the 

 rotating stage (Fig. 174) is graduated, 

 and a vernier is placed on a project- 

 ing angular piece for convenience of 

 reading the angle. The diaphragms 

 slide from beneath the stage into a 

 cylindrical tube, and can be used 

 flush with the surface of the stage. 



The mirror can ba raised or low- 

 ered, and swung laterally by the 

 arrangement shown in Fig. 172. 



The eyepiece-tube can be exactly 

 centered by the screws C and D 

 (Fig. 172), which is of advantage in 

 the determination of the polarizing 

 axis in minute crystals. 



When the instrument is required 

 for ordinary investigation the eye- 

 piece-tube is replaced by a draw-tube 

 of the usual construction. The me- 

 chanical stage is also removed, being 

 held in position by two pegs of brass simply fitting into corresponding 

 apertures in the ordinary stage E (Fig. 174; and the sprung stage-clips 

 are substituted. 



The Microscope is provided with a novel arrangement termed an 

 " extractor," for facilitating the rapid removal and change of objec- 

 tives at the nose-piece, shown in Figs. 172 and 174 G, and described 

 ante, p. 662, 



* See this .Jnumal, ante,'pp. 116 and 300. 



Ser. 2.— Vol. I. 



3 H 



