Progress Report, Seismological Laboratory, California Institute of Technology, 1950

In addition to the papers published during 1950 (list, at end), the following research activities have been carried forward. Instrument development under Benioff has involved further modification of the capacity‐transducer seismometer mentioned in our previous report. In its present form the mechanical moving member is positioned between two fixed capacitor plates so that motion of the member produces capacity increments of opposite sign in the two condensers formed between the fixed and moving members. The two condensers are shunted by inductances of equal size so mounted as to have low mutual coupling. The two tuned circuits thus formed have the same resonant frequency—approximately 10.75 mc. The two inductors are coupled to the output circuit of an electron‐coupled frequency doubling crystal oscillator operating at 5.35 mc fundamental frequency.