Abstract
Basilar membrane displacements in response to sound at threshold intensities are in the fractional Ångström range. Visual measurements, as used by Bé-késy in his pioneering studies, are by definition limited to values above 10 000 Å. The present paper discusses a number of modern techniques capable of taking measurements at lower Ångström levels: One-point methods (capacitive probe, Mössbauer effect, laser interferometry, and optical heterodyne spectroscopy) and pattern-assessing methods (time-averaged and real-time holography). Advantages and disadvantages of these methods are being discussed.

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