[time-nuts] Pendulums & Atomic Clocks & Gravity

Brooke Clarke brooke at pacific.net
Sat May 26 22:23:46 EDT 2007


Hi Mike:

Yes, it has an invar rod pendulum.  I haven't taken it apart but expect there 
are compensating metals being used.  I've heard a well tuned version of this 
clock lost 15 seconds in 70 days.  But in use the USNO supplied a synchronizing 
pulse on the hour so they really only needed to run for an hour.  See:
C:\Webdocs_Hosted\I\SWCC.shtml for the self winding clock and
http://tycho.usno.navy.mil/history.html for some USNO history.

The clock above has just minute and hour hands but the movement is designed to 
also support a second hand.  I have another clock coming that has the second 
hand.  The Self Winding design is still being used in the London underground.

These are not what's a called precision clock, but rather are what I'd call 
functional commercial clocks.  In-between consumer clocks and precision clocks.

As far as I can tell the Russion Fedchenko observatory clock was the ultimate. 
    About 2 milliseconds per day.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com



Mike S wrote:
> At 07:49 PM 5/26/2007, Brooke Clarke wrote...
> 
>>Back in the 1800s clock makers found ways to temperature compensate 
>>the
>>pendulum such as putting a Mercury thermometer at the bottom, using 
>>metals with
>>dissimilar expansion coefficients (Harrison used steel and bronze (no 
>>zinc
>>then)) or materials with almost zero COE like Invar.
>>
>>The Dent clock at Greenwich in 1885 had an arenoid type compensator to 
>>remove
>>barometric pressure effects, later clocks were run in vacuum.
> 
> 
> Does your clock (you only stated you were adjusting the bob on a 
> pendulum clock) have either feature? The vast majority, I would hazard 
> to say, don't. 
> 
> 
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