X-RAYS AND ORIENTATION OF QUARTZ CRYSTALS 



309 



such a plate is being rotated about the V axis as in Fig. 3.11 the normal 

 to the atomic plane lies in the plane of the instrument. We can also use 



.25 



.75 



1.00 



.50 



F"ig. 3.12 — Variation of intensity of reflected ray with entering angle ge and the 



Bragg angle, 6 



u) 



Case (b) 



Fig. 3.13 — Position of quartz plate relative to vertical a.xis of instrument in case (b) 

 and case (c). (Stippled face is reference bevel, normal to Z axis.) In the absence of a 

 reference licvel the X direction can be determined with polarized light. (See Chajjter II, 

 p. 246.) 



the same atomic plane to correct the orientation of this i)late about the 

 axis WW normal to the X axis (Fig. 3.13 and Fig. 3.14). Here, since the 



