A recording seismograph was assembled from commercially available components and by use of a 3/32 inches per second FM tape transport. The system was calibrated by three independent techniques, one of which included the Honeywell spectral analyzer which was used for data analysis. System linearity was checked by comparing the results of sine-wave and impulsive excitation.Microseism spectra were recorded at approximately 1:00 a.m. local time on July 18 and November 1, 1964. They represented on both occasions averages over a 1-hour period. The spectra were similar in shape but different in amplitude. In both spectra the peak ground amplitude per octave occurred at about 5.2 seconds period, and was 360 millimicrons per octave and 2.1 microns per octave for the two occasions, respectively.