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BELL SYSTEM TECHNICAL JOURNAL 



then be extinguished by the analyzer. If a = 90° the slow component 

 reduces to zero and the fast one goes through unchanged and again can be 

 extinguished by the analyzer. This effect can be used to check crystal 

 orientations. Such an instrument fitted with a divided circle used to meas- 

 ure a is called a stauroscope. The stauroscope often uses a special analyzer 

 capable of better determination of extinction setting. 



If a is not or 90° two components traverse the crystal and recombine at 

 the boundary. These two components are at right angles to each other; 

 they are of unequal intensities, and they differ in phase because they trav- 

 eled at different speeds. 



Fig. 2.23 — The intensity of the two components from Fig. 22 



Now Vs and V/ have the same frequency F so that in unit time each makes 

 F wave-lengths. This requires that the slow ray have F wave-lengths in a 

 distance Vs and hence that each wave have a length: 



Similarly 



X« — t; 





(2.3) 



(2.30 



In a distance t there are - fast waves and -- slow ones. Let us say that 



A/ As 



there are N more fast waves than slow ones in the distance /. Consequently 



iV = - — - which, from (2.3) and (2.3') may be written: 

 X/ Xg 



Vf Vs 



(2.4) 



All the data on light are given in terms of wave-lengths in a vacuum, not 

 in terms of frequency, so we will assume that in a vacuum the wave-length 



