General Features—This instrument was designed and constructed primarily for the registration of vibrations from dynamite blasts, traffic, machinery, and general Industrial sources. For vibrations of a frequency of three cycles per second or more, it gives a record directly proportional to displacement. With a magnification factor of 25 over this range, it gives clear, full registration from about 0.0005 to 0,035 inch. The maximum on‐scale displacement which can be recorded usefully on any one of the components is 0.080 inch. Over a period of 15 years, experiments have shown that these constants are best adapted to the service for which this was desig