. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] GRAVITY AT SEA the average value of which, over a 5-min interval, is 141 X\ K{d—a)—p{h—ho)i—mgl kV K (4) the same as for a deflection in the absence of the wave motion. In practice one computes the gravity value from the dial setting of the instrument and adds to it the correction read from the axial position of the record. The 5-min averaging time is imposed by the time constant of the com- plete mechanical-electrical system. Graf (1958) gives more details about the construction and testing of the instrument. The
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] GRAVITY AT SEA the average value of which, over a 5-min interval, is 141 X\ K{d—a)—p{h—ho)i—mgl kV K (4) the same as for a deflection in the absence of the wave motion. In practice one computes the gravity value from the dial setting of the instrument and adds to it the correction read from the axial position of the record. The 5-min averaging time is imposed by the time constant of the com- plete mechanical-electrical system. Graf (1958) gives more details about the construction and testing of the instrument. The first tests of the Graf Sea Gravimeter were made in August, 1955, on Lake Starnberg (Graf, 1956) using a gimbal mounting. Later tests were made DlfFEKEMCE BETWEEN METERS 104 & 102 0.\ RUN 7 980150 ^80050-. Dl STANCE 150 Fig. 4. Comparison of observed gravity on eight rvms over as nearly the same course as possible and the differences observed by two meters on the same stable platform on the same run. in the Adriatic Sea in May, 1956 (Graf, 1957). Comparisons were made with the Vening Meinesz pendulum apparatus on board Becuna in August, 1956 (Worzel and Graf, 1957). Of the 59 observations 3 had large discrepancies, 17 fell within the range of 3-9 mgal and 39 within the range 0-3 mgal, showing a close approach to a statistical distribution. The first successful surface-ship gravity observations were made with this instrument mounted on a gyro- stabilized platform on an cruise on Compass Island in November, 1957 { Bull., 1958). More complete comparisons, as well as a number of continuous profiles, were reported by Worzel (1959). Seven continuous profiles, 150 nautical miles long, agreed with themselves and with previous submarine gravity measurements within a spread of 20 mgal (Fig. 4). The spread is partially caused by navigation errors, and partially by the inability to recover the same course and jDositions. At three other crossings of f
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