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BELL SYSTEM TECHNICAL JOURNAL 



for the inspection of quartz in various stages of processing, and for other 

 transparent materials than quartz. 



By means of a polarized light optical system the stones are examined 

 for optical (but not electrical) twinning. By this same means the direction 

 of the optic axis through the stone is also determined. By means of con- 

 centrated high-power illumination the stones are inspected for cracks, color 

 and inclusions. By both means the stones are illuminated and inspected 

 while immersed in an immersion fluid of matching index of refraction. 



PROJECTION LAMP 

 AND HOUSE 



MERCURY LAMP 



AND HOUSE 



Fig. 4.3 — The raw quartz INSPECTOSCOPE, top and front views. The stones are 

 held in the immersion tank and viewed from above. Polarized light from the mercury 

 lamp is used for locating the direction of the optic axis and for detecting optical twinning. 

 Concentrated light from the projection lamp is used for detecting other interior defects. 

 See also Fig. 4.5. 



Without such immersion it is difficult or impossible to illuminate the interior 

 properly, or to see into the interior, of oddly shaped or rough surfaced stones. 

 Such immersion eliminates refraction (bending of light rays) at the surface. 

 The interior of stones with ground, fractured, or other surfaces, are as easily 

 examined as a piece of plate glass. 



The important design features, maintenance and operation procedures 

 are given below. Figure 4.3 is a diagram of the instrument, and Fig. 4.5 

 shows an early model utilizing many of the features described below. Three 

 plate glass windows W are cemented into apertures in the open-top, steel 



