The first issue of The Geophysical Directory was published in 1946. It consisted of twopages which listed seismograph, gravity meter, torsion balance and magnetometer contractors only.
A listing of instrument makers was not included until 1947 (the second issue), even though a number of such companies had by then existed for some years. Those companies listed in the 1947 issue which I would classifyas the pioneers in the manufacture and sale of complete seismic systems were Century Geophysical Corporation, Electro-Technical Labs (ETL), Engineering Laboratories, Inc. (ELI), Heiland Research Corporation, Houston Technical Laboratory (HTL), Southwestern Industrial Electronic Company (SIE) and Technical Instrument Company (TICO).
Coleman Instrument Company, Hale Instrument Company, Hathaway Instrument Company, Ruska Instrument Company and S.A. Scherbatskoywere early suppliers of various individual components.
A number of early geophysical contractors – such as Petty, Western and Seismic Exploration, Inc. – maintained in-house instrument laboratories which designed and built proprietary equipment that was not offered for sale to others.
Seismograph Service Company (SSC), Century Geophysical, United Geophysical, and later National Geophysical and Midwestern Geophysical started out by building complete seismic systems for their own use but then later offered these systems for sale to the industry with varying degrees of success.
So many other companies have made contributions to the evolution of seismic instrumentation that it would be an impossible task to even list (much less detail the histories) of all. Consequently, I have chosen only a few of the above for more complete treatment. Selection was made either because of close personal association or because