Abstract
THE Revue générate des Sciences of January 30 contains a full abstract of a very interesting paper by D. Korda in Archives des Sc. Phys. et Nat. (Geneva) of November 15 last. It appears that Baron Eotvos, in examining the records of gravitation made at sea, found certain anomalies which he traced to the speed and course of the ship. The weight of a thing on the surface of the earth is less than that due to the attraction of the earth by an amount equal to the centrifugal force, which at the equator amounts to g/288, and which, resolved in a vertical direction, varies as the square of the cosine of the latitude. Any variation in the centrifugal force therefore affeots the weight to this reduced extent. The velocity at the surface of the earth may be 46,500 cm./sec., while that of a ship in the water may be jooo cm./sec, so that the motion of the ship round the axis of the earth may vary between 47,500 and 45,500 cm./sec. at the equator. Centrifugal force varies as the square of the velocity, so, calling V and v the velocities of the earth's surface and of the ship in the water, the centrifugal force on a body in the ship may vary between (V—v)2 and (V + v)2—that is, through a range of 4Vv depending on the course. While v may be relatively small, the large factor V may, and does, at times make the product so great as to introduce an error in the apparent gravity as determined on board ship. For example, in the case supposed, which corresponds with a speed of 19–4 knots and at the equator, the difference in weight as shown by a spring balance going east with the earth and west against the earth would be as much as 1/3355, or more than two grains per pound—quite a serious amount in a gravitational survey.
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BOYS, C. The Rotation of the Earth . Nature 101, 53–54 (1918). https://doi.org/10.1038/101053a0
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DOI: https://doi.org/10.1038/101053a0