Report on some experimental long-period seismographs

The unexpected usefulness in research of the Press-Ewing seismograph system (Press, Ewing and Lehner, 1958) has stimulated further efforts to obtain even higher seismograph sensitivity in the period range beyond 100 sec. A major difficulty has been in maintaining pendulum stability at long periods. This paper describes a stable long-period seismometer and gives results from several seismograph systems incorporating long-period pendulums and galvanometers.