On a Microscope with Geometric Slides. By Keith Lucas. 275 



that the upper part of the tube shall be firmly held against its 

 guides, and, secondly, it pulls the whole tube downwards against 

 the end of the lever by which it is moved. 



Fig. 51.— Section through Limb and Body Tubes. 



C C, rings carrying guides of coarse-adjustment tubes ; G, leaf spring retain- 

 ing coarse-adjustment tube against guides; H, small tube which pre- 

 vents tube D from rotating ; J, wire of coarse-adjustment ; K, barrel ; 

 L, ring carrying bearings of K ; M, rod, and N, spring retaining lube B 

 against its guides ; P, spring forcing tube B downwards against tbe 

 fine-adjustment lever; Q, fine-adjustment lever. Other letters as in 

 figs. 49, 50. 



This lever (Q, figs. 51, 52), which transmits the motion of the 

 fine-adjustment screw to the body-tube, is of the bell-crank type, 

 with its axis of rotation running from back to front of the limb. 

 It is moved by a fine-threaded screw (E, figs. 52, 53), which passes 

 through the left-hand side of the limb, a short distance above 

 the stage. The arrangement of the lever is partially seen in fig. 51 

 and partially in fig. 52, which is a section passing through the back 

 part of the limb, viewed from the front. 



The essential parts of the substage are : a long tube (E, fig. 52), 

 sliding in geometric guides inside the limb, and a bracket (S, fig. 52) 

 attached to this tube, extended laterally to encounter the focussing- 

 screw (T, figs. 52, 53), and forwards to carry the centring ring, into 

 which the condenser is fitted. The lateral extension also carries 

 a rod (U, fig. 52), mounted parallel to the tube, and preventing 

 rotation about the long axis of the latter. The whole substage is 

 forced upwards, against its focussing screw, by a long spiral spring 

 (V, fig. 52), anchored to the limb at its upper end, and passing down 



