Explanation of the 3 Classes of Achromatic Microscopes, 

 Manufactured "by Smith and Beck. 



A Compound Achromatic Microscope consists, essentially, of an Ob- 

 ject-Glass, and an Eye-piece ; so called, because they are respectively 

 near the object and the eye when the Instrument is in use. The Object- 

 Glass screws, and the Eye-piece slides, into opposite ends of a tube 

 termed the Body, and upon the union of the two the Magnifying Power 

 depends. But some form of Stand is invariably employed to carry the 

 Magnifying Power, to hold, or to give traverse to the object, and to 

 receive various apparatus for Illumination. 



Under this general description the following Microscopes may be ar- 

 ranged in Three Classes : — 



In the First, the Magnifying Power, the Stand, and the Illumination 

 are carried to the greatest possible perfection. 



In the Second, the same Magnifying Power is combined with a 

 Stand, and apparatus for Illumination, less expensive but very efficient. 



In the Third, the capabilities of all the parts are limited, but yet 

 equal to the requirements of many, and of considerably less cost. 



Although the following Lists of Apparatus are complete in each Class, 

 any portion of them can be ordered, and the Stands are not required by 

 the makers for subsequent additions. 



