34 HOW TO SEE WITH THE MICROSCOPE. 



siderable extent the same as that printed in Mr. Zent- 

 mayer's catalogue some portions being suppressed, 

 and the wording occasionally changed at the election of 

 the author.* 



ZENTMAYER'S AMERICAN CENTENNIAL STAND. 



Constructed especially for the Centennial Exhibition. 

 It is mounted on a tripod, with revolving graduated 

 platform ; the bar and trunnions are in one piece, and 

 swing between two pillars for inclining the instrument 

 to any angle. The coarse adjustment is accomplished 

 by rack and pinion. Thus far it is similar to the 

 " Grand American Stand" by the same maker. 



The swinging sub-stage, which carries the condenser 

 or other illuminating apparatus, including the mirror, 

 swings around a pivot, the axis ot which passes through 

 the object observed, so that this object is in every posi- 

 tion in the focus of illumination. The stage may be 

 detached with facility, and replaced by one constructed 

 for oblique illumination; the swinging illuminator 

 may then (i. e., with the last-named stage) be used for 

 illumination from above. 



The sub-stage is provided with a graduated circle for 

 indicating the degree of obliquity. 



An object placed on the stage being in a plane with 

 the axis of the trunnions, it is obvious that if the in- 

 strument is placed in a horizontal position, the object 



*In the several descriptions of stands, that of the respective makers will 

 be given as far as possible. The author will, however, at his election, sup- 

 nress certain portions or change the diction as to him may appear desirable. 



