THE COMPOUND MICROSCOPE. 



69 



of being drawn out to the extent of jBve or six inches: this is 

 termed the draw-tube, into one end the eye-pieces fit, and 

 into the other an erecting-glass is made to screw. This 

 draw-tube has a scale of inches and parts engraved on its 

 outer side, as represented by fig. 42, where a is the eye- 

 piece, b the upper end of the com- 

 pound body, and c the draw-tube, 

 with the scale of inches and parts 

 on it. The many uses of this tube, 

 and of the erecting-glass also, will 

 be fully described hereafter. The 

 inner side of the tube carrying the 

 magnifiers is, in all cases, provided 

 with one or more stops or dia- 

 phragms for cutting off the extra- 

 neous pencils of light. 



The next part of the stand in 

 importance is the stage or appara- 

 tus on which the objects are to be 

 placed for examination ; this, in the 

 most complete microscopes, consists 

 of two or more plates of brass, one 

 of which, termed the stage-plate, is capable of being moved in 

 two directions, at right angles to each other, either by screws, 

 racks and pinions, by a combination of the two, or, more 

 simply, by a lever. Upon the stage-plate another plate is 

 adapted, termed the object-plate ; this last, for the more ready 

 adjustment of the object to be examined. Is made to slide up 

 and down upon the stage-plate, and is generally supplied with 

 a raised ledge at its lower part, against which the objects 

 themselves may rest when the stage is in an inclined position ; 

 and sometimes another piece of brass, termed a clip, with a 

 weak spring in its front part, is made to slide upon it, so that 

 any object, if necessary, may be firmly secured between the 

 clip and the raised ledge. The object-plate, besides the move- 

 ment up and down on the stage-plate, and that in two direc- 

 tions at right angles to each other, effected by the screws or 

 rack-work, has also a circular one in a horizontal plane, which 



Fig. 42. 



