In order to determine the way in which mechanical analysis of frequency occurs in the cochlea, a technique was developed for preparing anatomical specimens. This technique made it possible to measure the amplitude of vibrations along the cochlear partition when the stapes was driven with pure tones. It made it possible, further, to determine how the amplitude of vibration at any given place on the cochlear partition varies with the frequency. The relation of amplitude of vibration at a given place to frequency gives a curve very similar to a resonance curve. We can then calculate the logarithmic decrement characterizing the vibrations of the cochlear partition. This log decrement is almost independent of frequency and has a value ofd= 1.3. The decay time of the vibrations of the cochlear partition was observed directly with a microscope, and the values obtained in this way agreed with those derived from the resonance curves. All the measurements have been made on preparations of the human ear.