Horizontal pendulum
The horizontal pendulum is a precision instrument for measuring the vertical direction fluctuations , which z. B. caused by the tides . It is installed underground - mostly in abandoned mines - and is used for geophysics and geodynamics, among other things, to determine the elasticity of the earth's body and plate tectonics .
The device was first specified by Lorenz Hengler in Munich in 1832 , but his invention was forgotten. Karl Friedrich Zöllner in Dresden reinvented it in 1869 and perfected the construction.
The instrument is a special type of pendulum that swings around an almost vertical axis of rotation in an almost horizontal plane . It corresponds in principle a frictionless bearing door , which like a door in the house a position of equilibrium occupies in a certain direction:
The more precisely the "door axis" coincides with the vertical, the perpendicular , the more sensitive the instrument is to horizontal forces. If the axis is exactly vertical, it is infinitely sensitive or indifferent. With a small incline , however, there is a defined position - that of the lowest center of gravity .
Thin metal strips or wires are used for all friction-free axes; the eccentrically suspended registration mirror is often sufficient as a mass . Of several possible designs , those according to Zöllner and Ernst von Rebeur-Paschwitz are the most important. The accuracy is a few 0.001 "but requires repeated calibration .
The Grotta Gigante horizontal pendulums in an Italian cave have an upper suspension length of 94 m and were installed in 1959.
A demonstration device with a rigid pendulum with an axis of rotation that can be adjusted from horizontally to vertically is called Mach's pendulum . An original from the time of Ernst Mach is at the Physics Institute of the University of Graz .
See also
literature
- A. Graf, Gravimetric Instruments and Measurement Methods. Handbook of Surveying Volume Va, JB Metzler, Stuttgart 1967, pp. 234–243.