CHAPTER IV 



THE COMPOUND MICROSCOPE 



IN our chapters, dealing with the history of 

 the Microscope, we attempted to trace the 

 gradual development of the compound instru- 

 ment from the simple lens ; we stated that the latter, 

 in a crude form, had been known and used from very 

 early times and that the former developed side by 

 ^Y^ ^ side with the telescope. We have also said a few 

 'Sy' words in Chapter III. concerning light for the reason 

 that the microscope can be better understood and 

 used more efficiently when we are acquainted with 

 the phenomena due to light. The simple lens, sold 

 under the name of pocket magnifier, in its cheapest 

 form consists of a double convex lens, that is to say, 

 a lens with two outwardly curved surfaces. Better 

 quality pocket magnifiers consist of two or more 

 lenses, which may be either double convex; plano- 

 convex, i.e., with one surface perfectly flat and the 

 other outwardly curved, or they may be constructed 

 of a combination of double convex and plane 

 -^ concave lenses, such as were described on p. x 

 syT *J^(The object of both the simple and compound 



