means of a transparent (colorless) cement in such a 

 perfect manner that to the unpracticed eye they appear 

 as one piece of glass. An achromatic objective may 

 consist of a simple system having two or three lenses, 

 or it may have two, three or four and even five systems 



d 

 h 



Fig. 33. 



with as many as eight or ten lenses in all. The 

 systems are called in their order : anterior or front, 

 middle, and posterior. When a system consists of two 

 lenses it is called a doublet, when of three lenses, a 

 triplet. 



Thus in Fig. jj, a is the anterior, m the middle, 

 and p the posterior system : thus also, h is a single, 

 d a double, t a triple, and q a quadruple system. 



While all the work connected with the microscope 

 must be extremely accurate, that involved in the produc- 

 tion of an objective is of the highest degree of accuracy; 

 in fact there is no production of the human hand which 



66 



