228 HOW TO SEE WITH THE MICROSCOPE. 



advantage obtainable with the condenser is, that by a 

 careful manipulation of the apex of the small cone of 

 light we are often able to get just the right illumination 

 on certain details of our object, while the field generally 

 is kept in partial light only, " toned down" as it were. 

 This effect may be produced in two ways: First, by 

 raising or lowering the condenser; and, secondly, by 

 swinging the sub-stage laterally to a point but just 

 within the aperture of the objective employed. We 

 sometimes use the one plan and sometimes the other; 

 and then, again, we often use a mixture of both, and, 

 as a rule, the better illumination will be attained when 

 the condenser is somewhat within, or without the focal 

 point. 



Now let the novice understand that in thus employ- 

 ing the condenser there is no attempt to get " pretty dis- 

 plays" of the object. On the other hand, the primary 

 object is to obtain cool and reliable definition of struct- 

 ture. Those who thus use it will, I think, be pleased 

 with the results attained. It is somewhat more " bother " 

 than taking the light directly from the mirror, or with 

 the usual intervention of the diaphragm. Notwith- 

 standing this, one soon becomes accustomed and addicted 

 to its use. The swinging stage, too, is a valuable ad- 

 junct to the old diaphragm, and with this latter instru- 

 ment superior effects can be had working on the same 

 general plan as with the condenser, and using a small 

 aperture to the diaphragm. Should the light be too 

 weak it can be assisted by interposing the bull's eye, or 

 light can be shut off by depressing the diaphragm. 



