THE use of crystals as oscillating elements and as light valves in electric circuits has given the mathematics of crystalline media an engineering importance. Soon after the first simple quartz oscillators were made it was noticed that some ways of cutting the block from the natural crystal gave lower temperature coefficients of frequency than did other ways. This led to studies of the change of elastic modulii with direction and temperature and finally to the discovery that there are directions in quartz for which the shear modulus does not change with temperature.
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W. L. Bond (1943) studied this question.