28 THE MICROSCOPE, ETC. 



original was found to be too thick for investigations 

 requiring very oblique light. 



A thin circular brass plate E covered with black- 

 ened glass, revolves on F in the optic axis of the 

 instrument, on its upper surface two thin brass clips 

 G are fastened, these hold the slide in position and 

 allow of its movement in every direction in the plane 

 of the stage. 



A brass tube H, lined with cloth, screws into the 

 centre of the stage, and holds the sub-stage appara- 

 tus, this can be removed when very oblique light is 

 required. 



A diaphragm I, attached to a short wide tube with 

 a thick rim R, slides up and down in H, the motion 

 being easily imparted to it on account of the cloth 

 lining. A line divided into sixteenths of an inch, is 

 cut on the side of the tube at right angles to the rim 

 E., this enables us to tell the distance between the 

 top of the condenser and the object by calculating 

 the number of divisions between the rim and edge 

 of the other tube H. 



This piece of apparatus, when made in the manner 



