Background
To a first order approximation the period depends on the pendulum length and the acceleration of gravity.
My interest in
Time & Frequency got me looking at precision
pendulum clocks. The accuracy of the clock is determined by the
pendulum.
In addition to clocks pendulums were used to measure gravity, which required a precision clock mechanism.
When
attempting to win the English prize for a way to find the
Longitude at sea, Harrison at first tried a clock based on a dual
pendulum, but gave up and switched to a balance wheel because pendulums
don't work well on ships. But they do work when fixed to a rigid
support.
Pendulums on this page are dynamic and make use of the period of
oscillation. Many pendulums that are used in a static way like a
plumb bob (gravity pendulum) or a weight at the end of a string.
The 3036465 patent by Dicke is an all quartz system which should be
better than those that use metal. But I've recently heard that
the quartz exhibits "jumps" in it's crystal lattice that causes the
length to change slightly, changing the rate.
Gravity Pendulum Patents
205808 Electric Gravity Escapement for Pendulums, J.F. Pratt, Jly 1878,
- the impuse is by gravity not electromagnet, not gravity meter
280463 Gravity Escapement for Clocks J.H. Gerry, Jly 1883
-
"
287181Gravity Escapement for Clocks, D. Shive, Oct 1883 - "
288027 Compensating Pendulum, A.S. Crane, Nov 1883 - tempereature compensation
301873 Escapement for Clocks, 1884 - "
383539 Pendulum for Clocks 1888
403999 Gravity Clock Escapement 1889
508530 Mercurial Compensation Pendulum, S. Riefler, Nov 1893, - temp comp
519421 Gravity Escapement for Clocks, H. Conant, May 8 1894, -
531935 Apparatus for Demonstrating Laws of Gravity and Mechanics, J.S. Hemenway, Jan 1895, -
625674 Gravity Machine, W.H. Hawkes, May 1899,
73/382R - measures distance of falling objects to determine gravity
626807 Gyrating-pendulum Escapement, F. Gundorph - clock
720426 Apparatus for Demonstrating Laws of Gravity and Mechanics, J.S. Hemenway,
739245Gravity Escapement for Clocks,
842130 Pendulum, A.W. Barnard, Jan 1907, - weighing scales
1097637 Gravity Escapement for Clocks,
1317072 Device for Measuring Accelerations, J. Carlier, Sep 1919, - spring & mass to some electrical change
1537395 Electric Clock, H.E. Warren, May 1925, - gravity escapement
1559192 Apparatus for Demonstrating Gravity Acceleration, B. David, Oct 1925,
1792013 Apparatus for Determining the force of Gravity at sea, February 10, 1931, 73/382R ; 250/230; 250/231.1; 250/235; 359/201
dual pendulum
1797044 Electric Clock, March 17, 1931, 368/166 ; 185/40A; 368/149; 968/454 - novel way to impulse the pendulum
1868769 Pendulum for Measuring Time, Max Schuler, July 26, 1932, 368/179 ; 968/306 -
radius of gyration P= SQRT(theta/m), theta = moment of inertia, m = mass
period = 2 * PI * SQRT( (2*P) / g)
uses helium or hydrogen to conduct heat instead of vacuum - lower termal gradients
1987786 Pendulum for Gravity Determination, January 15, 1935, 73/382R ; 368/182; 968/105
the use of screws located at key geometrical points so that if they turn it will not effect the period
"minimum pendulum" i.e. cg = (L of theoretical pendulum) / 2
1995305 - March 26, 1935, 73/382R ; 331/155; 331/156; 331/157; 340/870.3; 367/180; 73/514.29
a weighted wire vibrates at a ferquency up to 10 kHz depending on g
2077390 Frequency Comparing Device for Determining the Force of Gravity,
April 20, 1937, 73/382R ; 324/76.39; 324/76.41; 346/45; 346/7; 73/1.45; 968/770 - uses tuning fork & pendulum
2089745 Gravity Instrument, August 10, 1937, 73/382R - resilient suspension, isosynchronous movement?, temperature compensation
2097156 Gravity Pendulum, October 26, 1937, 73/382R - elastic pendulum
2732717 Gravity Meter, January 31, 1956, 73/382R - rotating and
swinging in the normal manner to determint the direction of anomoly
2794134 Mechanical Generators of Isosynchronous Oscillations, May 28, 1957, 310/39 ; 368/165; 968/472
2820338 Constant Periodic Motion Device, J. Rainbow, January 21, 1958, 368/134 ; 324/96; 368/166; 368/181; 73/652; 968/457
vacuum chamber surrounding pendulum is a second pendulum
3036465 Gravity Meter,
Robert H. Dicke, May 29, 1962, 73/382R ; 73/514.29 - >= 20 cps, Q >1,000,000
also invented the lock-in-amplifier and Dicke radiometer
optical pick up and electrostatic drive, mostly fused quartz parts
founder of Princeton Applied Research
3103819 Gravimeter, Blisagme, September 17, 1963, 73/382R ; 73/514.15 - inverted reed pendulum w/variable periods, rotated
3173297 Pendulum Apparatus for Relative Gravity Determination, March 16, 1965, 73/382R - dual anti-phase pendulums
3290874 Gravity Pendulum Clock Escapment, December 13, 1966, 368/134 ; 368/165; 368/170; 968/105; 968/435
electric motor driven spring wind & automatic correctoin for non plumb case
3242734 Pendulum for Gravity Determination, March 29, 1966, 73/382R ; 33/391 - 1/2 sec period, vacuum, temp control, small swing
3336806 Gravity Meter, August 22, 1967, 73/382R - rotating weights & strain gauge
3386327 Metronome, June 4, 1968, 84/484 ; 968/819
3424006 Superconduction Gravimeter, R.H. Dicke, January 28, 1969, 73/382R -
super conducting magnet and floating object. object moves up or down as gravity varies and is read out by interferometer
3429184 Gravity Meter, February 25, 1969, 73/382R ; 359/529; 359/577 - Falling retro reflector
3501958 Gravity Meter, March 24, 1970, 73/382R - 2 pendulums identical periods when static, but different when dynamic
3769710 Electronic Celestial Navigation Means,November 6, 1973, 33/320 ; 244/175; 250/203.6; 33/323; 33/355R; 701/220; 701/222
3960344 Precision mobile gravity survey and guidance system, June 1,
1976, 244/182 ; 244/177; 324/330; 368/136; 368/181; 700/303; 701/121;
702/144; 73/178R
4115996 Self actuating pendulum system, September 26, 1978, 368/181 ; 968/105; 968/453
4219940 Angular accelerometer stabilized pendulum, September 2, 1980, 33/366.24 ; 73/514.02
4295372 Gravity measurement apparatus for ships, October 20, 1981, 73/382G ; 73/178R
4445371 Gravity meter and method, May 1, 1984
4615022 Symmetrically-suspended vertical-swing long-period pendulum
means, September 30, 1986, 367/179 ; 181/122; 33/1HH; 33/391; 73/652
4628735 Vibrating beam accelerometer, December 16, 1986, 73/514.29
4649748 Accelerometer, March 17, 1987, 73/514.19 ; 73/514.23; 73/653
4723232 Pendulum indicator horological device, February 2, 1988, 368/76
; 368/179; 368/223; 40/426; 40/485; 968/214; 968/388; 968/395
5112126 Apparatuses and methods for making geophysical measurements
useful in determining the deflection of the vertical, May 12, 1992,
356/141.5 ; 33/283; 33/304; 33/306; 33/309; 356/148; 356/149; 356/250
5268881 Compensator for a mechanical pendulum clock, December 7, 1993, 368/134 ; 368/137
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