Torsion balances of short period

Blau, Ludwig Wilhelm
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The torsion measures the variation of gravity in a horizontal plane. If the earth were a homogeneous sphere at rest, gravity would be the same everywhere over the surface of the earth and would vary only along the radius. On account of the rotation of the earth, centrifugal force tends to counteract slightly the earth's attraction. The effect is small but easily measurable; the acceleration of a body falling freely under the influence of gravity is greater by about five centimeters per second per second at the poles than at the equator. [...] It is the purpose of this paper to describe a general, short-period balance and two special cases, one a vertical, the other a horizontal instrument, both of short period, and to mention a method of preparing torsion wires so that they will show negligible twisting or untwisting with the changes in temperature ordinarily encountered in the laboratory or in the field