THE MICROSCOPE 



35 



OPTICAL PARTS OP THE COMPOUND MICROSCOPE 



The optical parts of a compound microscope 

 include the objectives and oculars, together with the 

 condensing lens and the mirror. 



Objectives. Microscope objectives consist of one 

 or more combinations of convex and plano-convex 

 lenses. The lower-power objectives consist of one 

 or two such combinations, while those used for higher 

 magnifications consist of three or four combinations 

 (Fig. 19). The degree of magnification produced by 



FIG. 19. Sectional Views of Objectives. 

 (Bausch & Lomb.) 



different objectives is usually indicated by certain 

 markings upon the mounting. The systems employed 

 in the marking of objectives and oculars are the Con- 

 tinental, the English and the metric. The Conti- 

 nental system of marking objectives is entirely empirical 

 and consists of a series of numerals beginning with 

 No. 1, the lowest power, and continuing up to No. 9, 

 which is the highest of the series. In the English 

 system, the relative powers are indicated in inches 

 or fractions of an inch, usually beginning with the 



