last natural drop has separated from it and apply the 

 remainder, or less than a drop, to the front of the 

 objective. 



Attach the objective and lower it until the fluid 

 comes in contact with the cover, observe this by lower- 

 ing the 'head to the level of the stage. Focus as with 

 dry objectives. The use of immersion fluid in itself 

 involves a certain amount of inconvenience, but the 

 observance of fixed rules will materially help to over- 

 come some of the . disagreeable features. Extreme 

 cleanliness should be observed with it. After the 

 work has been completed the objective should be 

 removed from the stand and its front as well as the 

 slide should invariably be cleaned. The fluid may be 

 removed by a moist piece of soft linen and the front 

 then cleaned with a dry piece or with lens paper. 

 Chamois skin is not suitable, as it does not absorb 

 the fluid. 



Immersion Objectives on Test Plate. Oil 



immersion objectives are not so sensitive to variations 

 in thickness of cover, although many of the most expert 

 manipulators prefer adjustable mountings in order to 

 obtain the highest results. 



To determine the highest capacity on test objects, 

 ordinary daylight is not sufficient ; a flat-wick oil lamp 

 is best suited. If the right hand is used on micro- 

 meter screw, place the lamp at the right side of the 



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