Of the Seismological Society of America Blasts

Seismographic registration of vibratory earth motion was begun with an experimental torsion seismometer assembly at the laboratories of the Mount Wilson Observatory in Pasadena, California, in January, 1923. Not long af terward a second assembly was put into experimental operation at the Norman Bridge Labora to ry of Physics at the California Institute of Technology at Pasadena. Wi th many small, expe r imen ta l changes in design and adjustment, which led to change in constants and necessitated some interruptions, recording on an experimental basis continued for more than four years. However , in October, 1926, recording was begun with equipment of more permanent fo rm at Riverside and, af ter a short time, at the Seismological Labora to ry at Pasadena in March, 1927, and at Santa Barbara and at La Jolla in May, 1927. Af t e r the occupation of the Seismological Laboratory, the experimental recording at the laboratories of the Mount Wilson Observatory and at the Norman Bridge Labora tory of Physics was brought to a close in the course of a few months. In April, 1928', recording was begun at the Observatory on Mount Wilson ; and in September, 1929, at Tinemaha, and at Haiwee, in the Owens Valley, Inyo County, California. stations, and the heights above sea-level, are