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BELL SYSTEM TECHNICAL JOURNAL 



will be shifted to the left and the value of c^' can be measured by means of 

 a specially graduated scale. See Fig. 3.24. (Scale used is of Lucite and 



Fig. 3.24 — Back reflection Lauc photograph of a BT plate 



Fig. 3.25 — Relation of displacement directions on the film to the (-( and iv-w axes 



calibrated to 10 minutes.) Similarly, if the crystal is misoriented about U 

 by amount e( the spot pattern will shift along w'w' and e(' can be measured 

 by the same scale used on ew> . To compensate for film expansion due to 



