SPECIFYING QUARTZ CRYSTAL ORIENTATION 



261 



For a given value of d, we can plot the values of e as a function of 8 as given 

 by (2.12). This plot is a chart of corrections to be added to the readings R 

 to find the true angle 5. 



Examination of Equation (2.12) shows us that the correction e is indepen- 

 dent of the thickness t' and even of the birefringence; hence, the chart 

 could serve for all uniaxial crystals. Equation (2.12) can be given an ap- 

 proximate solution: 



e = 1820 tan2 d tan R minutes 

 e = 30.3 tan- d tan R degrees 



(2.13) 



Fig. 2.42 — Refraction at a surface 



For R not more than 60 degrees and d not more than 15 degrees the error 

 in e is not more than 5 minutes. Figure 2.33 is a chart of these corrections 

 computed from the more exact equation (2.12). 



Annulling the Ring Eccentricity Correction by Means of the 

 Refraction Correction 



The difference in quartz index and liquid index is 



H ^ Ng- Nc 

 and by the law of refraction: 



NfsinR = iV, sin (R-^-e) 



