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BELL SYSTEM TECHNICAL JOURNAL 



mark a long line approximately parallel to the optic axis and a short line in- 

 dicatmg, in the case shown, the approximate direction and the sense of cut 

 of a BT-plate. It is to be noted, here, that neither handedness nor elec- 

 trical sense need be individually determined or considered, as such, for the 

 sense of cut is directly obtained. 



The size of an etch-tigure depends upon the thickness of the section being 

 examined, as explained in Section 5.43. For the etch-figures here presented 

 the size of the figure relative to the thickness of the section, may be estimated 



Fig. 5.18— The BASIC PIX-HOLE ORIASCOPE with matching and marking arms 

 for use on X-cut sections. Twinning, and the direction of the Z axis, and the direction and 

 sense of cut may be determined and marked on the section. 



from a knowledge of the ratio, A', of the total diameter of the view to the 

 thickness of the section giving that view. For Fig. 5.17A and B, N = 1.3; 

 for Fig. 5.19A and B, .V = 2.7; for Fig. 5.20, N = 1.7; for Fig. 5.21, T = 

 2.5. 



The pin-hole oriascope may be used in a variety of other wa}-s for exam- 

 ining any cr}-stal cut with at least one etched surface. When used with 

 sections as described above the bottom flat surface may be very small, just 

 large enough to cover the pin-hole. However, this restricts the inspection 



