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Microscopy /29 : 6 



accurately measured only if the area of the object is large compared to 

 the square of the limit of resolution of the bright-field light microscope. 

 Knowing both the height and area allows one to compute a volume and 

 hence, a mass for subcellular structures. 



The interference-contrast microscope can be combined with a phase- 

 contrast microscope to give certain practical advantages in resolution 

 and contrast. Both of these types of microscopes and their numerous 

 variations have the end result of making visible unstained structures 

 which are almost transparent and which differ only slightly from their 

 surroundings. Another method of obtaining two interfering beams to 

 accomplish this same result is discussed in the next section. 



6. The Polarizing Microscope 



The polarizing microscope shown in Figure 9 consists of a bright-field 

 microscope with two (or three) added pieces. Below the specimen is the 



Electric 

 Vectors 



Eyepiece 



Analyzer <= 

 Compensator 



Objective 



Specimen 

 Condenser - 

 Polarizer 



Diaphragm 



(tj Past Analyzer 

 \/\ Further Rotated 



\*^j Rotated by Specime- 

 (~—y Past Polarizer 



I Unoriented 



Figure 9. The polarizing microscope. 



so-called "polarizer." It functions to pass light only if the electrical 

 vector is in a particular direction, for example, parallel to the plane of 

 the drawing. (The electrical vector will always be perpendicular to the 

 direction of propagation of the light beam. The direction of the light 

 beam and the direction of the electrical vector together define the plane 

 of polarization.) Above the objective is placed an analyzer which 



