On the Change in Gravity When Bodies Move Along the Earth’s Surface to the East and West

(Roland Eötvös, Experimenteller Nachweis der Schwereänderung, die ein auf normal geformter Erdoberfläche in östlicher oder westlicher Richtung bewegter Körper durch diese Bewegung erleidet. Ann. d. Phys. 59, p. 743—1919).

When moving over the surface of the rotating Earth, every body must experience changes in gravity, since the measured force of gravity is composed of its true magnitude, from which the normal component of the centrifugal force is subtracted.

Since, when a body moves over the Earth’s surface to the east and to the west, the velocity of the body’s motion in one case is added to the velocity of the Earth’s motion, while in the other it is subtracted, it is clear that the centrifugal force will be different in the two cases, and the measured gravity of the body will also be different.

Attempts at determination were made, as R. Eötvös indicates, as early as the beginning of the 1900s by Heckerl on ships in the Atlantic Ocean, the Indian Ocean, and the Great Ocean; and Eötvös describes an instrument that makes it possible to measure the effect in the laboratory. In doing so, Eötvös gives the following calculation: an object (for example, a person) of 100 kilograms weight, at a speed of motion of 1 meter to the east and to the west, should show a difference in weight of 2 grams. The phenomenon is thus so great that it is easy to detect, especially if the resonance method is applied.

Eötvös’s instrument consists of a balance beam, whose column can be set into uniform rotation by a clockwork mechanism. Heavy loads of equal weight are suspended from the two sides of the beam.

If both loads rotate together with the column, then at the moments when the loads move in the direction of the meridian their gravity is the same. When, during circular motion, their motion coincides with the direction of the parallel and one load moves eastward and the other westward, the beam receives an impulse. Upon a turn through 180°, the beam receives an impulse in the other direction, and thus periodic forces begin to act on the rotating system, bringing the system into oscillation. Eötvös observes these oscillations by means of a very sensitive mirror method.

P. Lazarev.