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Light is either transmitted or reflected. When 

 the former, it is used on transparent objects and 

 passes through the objects from below the stage 

 into the objective. In opaque objects this is 

 impossible and reflected light is required, when it 

 is directed onto the object from above and 

 illuminates its upper surface. In the following- 

 instructions it is assumed that transmitted light 

 is used unless otherwise stated. 



The concave mirror converges the light and 

 therefore has a focal point and it is evident that 

 if its focus is of such length that with parallel rays 

 (daylight) it will fall on the object, the focus will 

 be longer with the diverging rays (lamplight) and 

 when no provision is made in the instrument to 

 adjust the mirror to meet these two conditions, it 

 becomes difficult and sometimes impossible in 

 critical work to obtain the best result. For this 

 and other advantages an additional illuminating 

 apparatus, called a condenser, is now commonly 

 used. 



Before lighting an object make certain that the 

 mirror-bar is in exactly central position and set 

 the mirror at such an angle to the light, that it will 

 be directed upon the object, which can be done 

 most quickly at the outset by observing the object 

 direct, keeping the head at one side of the tube. 

 Now remove the eyepiece and observe the light 

 through the objective. It should be central and of 



