COMPOUND MICROSCOPES 



11 



2. The Abbe condenser (Fig. 9) is a combination of two or 

 more lenses, arranged so as to concentrate the hght on the 

 specimen placed on the stage. The condenser is located in the 

 opening of the stage, and its uppermost 

 surface is circular and flat. 



3. Objectives (Figs. 10, 11, and 12). 

 There are low, medium, and high-power 

 objectives. The low-power objectives have 

 fewer and larger lenses, and they magnify 

 least, but they show more of the object than 

 do the high-power objectives. 



There are three chief types of objec- 

 tives: First, dry objectives; second, wet 

 objectives, of which there are the water-immersion objec- 

 tives; and third, the oil- immersion objectives. The dry 

 objectives are used for most histological and pharmacog- 

 nostical work. For studying smaller objects the water ob- 



FiG. 9. — Abbe 

 Condenser 



Fig. 10. 



Fig. II. 

 Objectives. 



Fig. 12. 



jective is sometimes desirable, but in bacteriological work the 

 oil-immersion objective is almost exclusively used. The globule 

 of water or oil, as the case may be, increases the amount of hght 

 entering the objective, because the oil and water bend many 

 rays into the objective which would otherwise escape. 



4. Eye-pieces (Figs. 13, 14, and 15) are of variable length, 

 but structurally they are somewhat similar. The eye-piece 

 consists of a metal tube with a blackened inner tube. In the 



