. The Bell System technical journal . ockwise the rings of thepattern either expand or contract according to whether the crystal is right-hand quartz or left-hand quartz (IRE definition). A different kind of pattern is visible in the conoscope when viewed per-pendicular to z, a double set of hyperbolae as shown in Fig. This pat- SPECIFYING QUARTZ CRYSTAL ORIENTATION 255 tern has been used to check the orientation but much grief has ensued dueto not recognizing one of its properties. This property is that, if z does notlie parallel to the crystal boundary the center of the pattern is not
. The Bell System technical journal . ockwise the rings of thepattern either expand or contract according to whether the crystal is right-hand quartz or left-hand quartz (IRE definition). A different kind of pattern is visible in the conoscope when viewed per-pendicular to z, a double set of hyperbolae as shown in Fig. This pat- SPECIFYING QUARTZ CRYSTAL ORIENTATION 255 tern has been used to check the orientation but much grief has ensued dueto not recognizing one of its properties. This property is that, if z does notlie parallel to the crystal boundary the center of the pattern is not per-pendicular to the optic axis and a rather involved correction must be correction reduces the actual angle to about half the observed conoscope is an immersion instrument. The fluid is chosen to havean index of refraction to match the ordinary one for quartz. When thisis done light is not bent in passing between fluid and quartz. When thefluid does not match there is a bending and all readings are subject to a. Fig. —Crossed polarizers Fig. —Rotation of the plane of polarizer correction. For example if we measure the angle of an AT plate in a fluidthat is too low by .0048 (since «o for quartz in green mercury light is fluid has n = ), we will get a reading that is too high by a quar-ter degree (the 35° angle will then appear low). A temperature rise of 12° Cwill lower the relative refractive indices by this amount. Also the more perfectly the fluid matches, the more nearly will the roughquartz surface disappear and seem smooth and clear. This greatly en-hances the sharpness of the rings. The refractoscope (Fig. ) was designed by G. W. Willard to tell when the 256 BELL SYSTEM TECHNICAL JOURNAL match is good. It uses the elimination of the bending as a test for refractivematch. It also demonstrates the existence of two velocities in quartz, fortwo images are seen where a glass prism would cause but one. Also byviewing th
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