BULL'S-EYE CONDENSER. 



6l 



microscope, and should be purchased by all who can afford 

 it, when much work has to be done ; but on no account 

 should the beginner purchase one of those made to hold 

 three or four objectives they are too heavy, and often 

 nullify completely the action of the fine adjustment. 



Some years ago Mr. Swift introduced a centering nose- 

 piece, which is shown in Fig. 35. In this accessory the 

 objective can be accurately centred after it has been 

 screwed into the nose-piece, which latter screws into the 

 lower end of the 

 body of the micro- 

 scope. The center- 

 ing screws are similar 

 to and act in the 

 same manner as those 

 connected with the 

 achromatic condenser. 

 Centering nose-pieces 

 are not very common ; 

 the author has seen 

 but one in use, and 

 that with high powers 

 only. 



The student will 

 find the bull's-eye 

 condenser (Fig. 36), 

 or stand condenser, 

 as it is sometimes 

 called, a necessary ad- 

 junct, an instrument 

 which may be used 

 in a variety of ways ; but its proper use, and the methods of 

 illumination generally, can only be completely understood 

 by consulting a few diagrams of mirrors and lenses which 



PIG. 36. 



