THE NEW NATIONAL MICROSCOPE. 83 



ported by the arm throughout its entire length, cannot 

 have any unsteadiness or motion of its own. 



The quick adjustment of focus is effected by means of 

 rack and pinion, with large milled heads, which works 

 so smoothly that there is no need to use the fine adjust- 

 ment for any power lower than one-quarter of an inch. 

 The latter adjustment is by means of a delicate micro- 

 meter screw and lever attachment, working with abso- 

 lute freedom from all motion, and by which the very 

 highest powers may be focused with the greatest exact- 

 ness. 



The stage is of glass, with a complete rotation in the 

 optic axis, upon the top of which is a sliding object- 

 holder, very thin, and with a spring clip for holding the 

 object in place during rotation. This clip is removable, 

 in an instant, and the stage forceps can be inserted in its 

 place, thus allowing the latter to be moved about with 

 the object-carrier. Beneath the stage is a tube carrying 

 all the sub-stage apparatus, as the achromatic conden- 

 ser, Wenham's parabola, polarizing apparatus, etc., etc. 

 This is securely attached to the stage by a bayonet- 

 catch, and can be instantly detached, leaving a very 

 thin and unobstructed stage for oblique illumination. 

 The shutter diaphragm is of novel construction, with the 

 various-sized openings almost in contact with the 

 underside of the object under examination, a great 

 improvement upon the old revolving disk diaphragm. 

 A double mirror concave and plane is hung upon a 

 swinging bar, and with every possible motion for di- 

 rect and oblique illumination. 



