mVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 



1047 



Fig. 116. 



and grasping the limb by means of a screw, of wliicli the milled head 

 is seen at the right-hand side of the instrument. By loosening this 

 screw somewhat the curved limb is released ; the sectoral grooves 

 then permit it to slide between the jaws of the foot until the tube 

 reaches the desired position (vertical, horizontal, or an intermediate 

 position), when it may be clamped by tightening the screw. 



The fine adjustment moves the entire body by a lever in contact 

 with the screw (milled head) shown on the back of the limb, the 

 distance between the eye-piece and the objective not therefore 

 changing. 



The rotating stage-clips can be applied to hold the object on 

 either side of the stage, as described and figured in vol. ii. (1879), 

 p. 623, where this Microscope was briefly alluded to.* 



Seibert and Krafft's Fine Adjustment. — We referred on p. 883 

 to this fine adjustment (Figs. 99 to 101), citing an explanatory 

 passage from Niigeli and Schwcndener's ' Das Mikroskop.' The 

 accompanying figure (Fig. IIG ) from the same authors will enable the 

 reader to understand the mechanism, and the 

 description will correct a slight inaccuracy 

 (in the original) relative to the non-displace- 

 ment of the optic axis. 



The focussing - screw 8 acts upon the 

 funnel-shaped head of the pivot m, the upper 

 end of which acts in a similar manner upon 

 //, the solid bar attached to the optical body. 

 The ring r, which serves as a guide-piece, 

 lies loose in the hollow column, and as a 

 rule does not touch the pivot ; its function is 

 merely to prevent the point of the pivot from 

 slipping out of the notch in //. The cross- 

 bars h h (two on each side) are attached by 

 screws to the hollow column, and the optical 

 body is held between the points of four screws 

 near the front ends of the bars. The focus- 

 sing motion is communicated to the solid bar 

 //by the screw s acting against the pressure 

 of the spiral spring shown above by dotted 

 line, the friction being confined to the eight 

 screw-points of the four cross-bars. The 

 movement is similar to that of an ordinary 

 parallel ruler with connecting bars, the 

 hollow column being the stationary side. 



It is obvious from .an inspection of the 

 figure that the optical axis must suffer a 

 sliglit displacement. Any movement of the 

 focussing screw 8 upwards or downwards 

 from tlie normal position as shown, will 

 cause the cross-bars bh to assume a diagonal position ; the pivot m 

 will consequently incline from its base backwards, and the solid 



♦ See also Dr. Carpenter's obscrvntions on tliis Microscope, infra, p. lOSC. 



