Abstract
TWO electromagnetic microbarographs designed by H. Benioff to respond to pressure variations in the frequency range from five cycles per second to one cycle in thirty seconds approximately, and with sufficient sensitivity to record the natural unrest of the atmosphere, have been in operation at the Seismological Laboratory in Pasadena for approximately two years. These instruments were operated either at the same point with different characteristics, or at points separated by distances from several to more than 100 metres with identical characteristics. In the short-period galvanometer combination the response is approximately proportional to the rate of change of pressure. For periods of 1 second, the sensitivity is such that 1 mm. deflection of the galvanometer corresponds to a pressure change of 1 dyne per cm.2 approximately. The instruments respond to waves as well as to current variations. Discrimination between these two types of movements is made on the basis of their difference in velocity of propagation, the waves being propagated with the velocity of sound, while current variations are propagated with much smaller velocity.
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BENIOFF, H., GUTENBERG, B. Observations with Electromagnetic Microbarographs. Nature 144, 478 (1939). https://doi.org/10.1038/144478a0
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DOI: https://doi.org/10.1038/144478a0
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