An inexpenseive, horizontal motion, torsion seismometer, of the Wood-Anderson type, was built and tested. It used photovoltaic cells to sense motion of the inertial mass, and electronic amplification in the recording system, rather than a strictly photographic recording system. It was anticipated that this instrument and a duplicate of it would be able to give a two-axis record of sufficient linearity to allow determination of earthquake magnitifude. However, test results show that significant improvements in machining precision and in photovoltaic cell matching and linearity are necessary.
