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BELL SYSTEM TECHNICAL JOURNAL 



relatively small volume that the reflection does not noticeably darken the 

 photographic film in five seconds. Successive ten-minute exposures are then 

 taken with the crystal plate turned at successively greater angles from the 

 zero position. At any given angle the disturbed quartz that has thus been 

 brought into the proper position to reflect the characteristic radiation does so, 

 producing a center line on the film whose intensity is roughly proportional to 



-6° 



-5° 30' 



-5° 



-4° 30' 



-4° 



-3° 30' 



-3° 



-2°30' 



+2° 



-l°30' 



ROCKING 



ZERO 



Fig. vS. — Spectrometer photograph of BT quartz plate lapped with 3()-H emery 



the volume of quartz misoriented to this angle. \'arious wave-lengths of 

 the white radiation will satisfy the Bragg equations for various atomic planes 

 of the main plate at each angular position and will be reflected to other posi- 

 tions on the film. Although the incident white radiation is relatively weak 

 the reflected beams are strong enough to darken the film in ten minutes be- 

 cause rays reflected from the main plate are reflected by a much greater 



