QUEKETTS DISSECTING MICROSCOPE. 



95 



four inches broad is attached by hinges on each side ; and the 

 two flaps are so shaped, that, when closed together, one lies 

 closely upon the other, as shown in Fig. 17, B. These flaps, 

 when opened, and kept asunder by a brass bar, as shown in Fig. 

 17, A, give a firm support to the stage at a convenient height ; 



FIG. 17. 



Quekett's Dissecting Microscope. 



and the bar also carries a socket, into which the stem of the 

 mirror-frame is inserted. At the back of the stage-plate is a 

 round hole, through which a tubular stem slides vertically, that 

 carries at its summit the horizontal arm for the magnifying pow- 

 ers ; this stem may or may not be furnished with a rack-and- 

 pinion movement ; but the author's experience leads him strongly 

 to recommend that it should be provided with this means of 

 making the focal adjustment ; since the sliding action, indepen- 

 dently of the greater trouble it always involves, is apt to become 

 uneven and difficult, especially if the surface of the stem should 

 have become roughened by the corrosion of sea-water, or by the 

 action of acids, salines, &c., used as reagents. The same frame 

 which carries the mirror, is also made to carry a lens which serves 

 as a condenser for opaque objects ; its stem being then fitted into 



