Oil a Microscope with Geometric Slides. By Keith Lucas, 273 



(E, figs. 49, 52), which passes up inside the limb, and has two 

 guides at the level of the stage, and two, consisting of adjustable 

 screws (F, figs. 49, 52, 53), at a higher level. 



The detailed arrangement of the body tubes and focussing 

 mechanism is shown in fig. 51, which is a vertical section passing 

 through the limb and tubes. The long coarse-adjustment tube (D) 

 passes right through the shorter and wider fine-adjustment tube (B). 

 At each end of the latter there is a ring (C, C), which carries the 

 guides of the coarse-adjustment tube. Between the two tubes 

 there lies a long leaf-spring (G), whose middle point presses back- 



Fig. 49. — Side Elevation of Microscope. 



A, limb; B, rine-adjustnieut tube; D, coarse-adjustment tube; E, guide- 

 tube of substage ; F, aligning screws of substage ; L, ring carrying bear- 

 ings of coarse-adjustment barrel ; O, nut retaining fine-adjustment 

 tube against guides ; S, substage bracket ; T, focussing screw of sub- 

 stage ; W, spring retaining substage ring against centring screws. 



wards upon the coarse-adjustment tube, holding it firmly against 

 its four guides. A piece of smaller tube (H), fixed parallel to the 

 back of the coarse-adjustment tube, and passing through a slot in 

 the upper bearing-ring, prevents the tube from rotating about its 



long a 



The next point for consideration is the means adopted for 

 moving the coarse-adjustment tube to obtain focus. This is effected 

 by means of a wire and barrel (J and K, fig. 51). The two ends of 

 the wire are anchored to the extreme ends of the coarse-adjustment 



