80 



MICROSCOPIC ILLUSTRATIONS. 



explanation of the different terms used in this and other 

 works respecting - the microscope, omitting Aplanatic ; 

 Achromatic ; Chromatic Aberration, or Dispersion ; 

 Spherical Aberration ; Engiscope and Microscope, as 

 being explained already in the u Cabinet," p. 102. 



Fie. 8. 



4*- 



Fig. 9. 



First, then, we will commence with the optical part 

 of a compound microscope, or engiscope, the external 

 appearance of which let fig. 8 represent. This is gene- 

 rally called the body of the microscope, and is either 

 composed of a conical or a parallel tube, as here shewn. 

 The interior of the body should be as black and as sombre 

 as possible, and furnished with diaphragms or stops (as 

 at e), to prevent any false light entering the eye: of 

 course these stops must be so arranged, and of such 

 apertures, at not to cut off or impede any portion of the 

 rays passing through the various lenses. 



The larger end of the body, a, is called the eye-end, into 

 which the eye-pieces fit, either by a screw or simply 

 by sliding them within it. The latter plan is the better, 



