MICROSCOPIC ILLUSTRATIONS. 



the wheel of diaphragms ; it has a bayonet-catch to fix 

 the box securely, independent of its gravity. 



Figure 29 is a frame and slip of glass for crystal- 

 lizations of salts. 



Such is the description of an instrument which will be 

 found a regular working tool, either for amusement or 

 scientific investigation. It is not pretended (be it always 

 remembered) that it is a perfect or standard instrument, 

 but Dr. G, hopes it will be found an approximation to one. 



A. P. 



March 1829. 



Most of the apparatus described in Chapter VI. as appli- 

 cable to my microscope can be applied to this. In the 

 instruments of this kind manufactured by me I have 

 made the socket at h to extend an inch or more above 

 the surface of the stage : this increases the steadiness of 

 the triangular gun-metal bar, b, which in practice is not 

 required to be depressed much lower than represented 

 in the engraving. The milled head, s, of the pinion is 

 made of much larger diameter than represented ; it 

 works against the posterior angle of the triangular bar, 

 and is placed at h. The fine) adjustment for the focus, as 

 also the moveable stage described at page 105, can be at- 

 tached to this stage, y, and the foot of the stand made of a 

 solid tripod. 



A. P. 



May 183P. 



