The Riefler and Shortt Clocks

JägAir Institute of Time and Technology


New Acquisitions Aren't So New

Two new acquisitions for the Clockvault arrived recently, a Clemens Riefler Observatory Tank Regulator and a Shortt-Synchronome Astronomical Regulator. These clocks were acquired at the Sotheby's auction of "Masterpieces From The Time Museum" collection.

The Riefler Clock

Riefler, founded by Clemens Riefler in 1890, produced precision regulator clocks in Munich. His advances in clock design made Riefler Clocks the standard timekeepers in most national institutions and observatories. The clock is housed in a copper tank, which is partially evacuated to about 800 mm of mercury. This stabilizes the atmospheric pressure, which affects the rate of pendulum clocks.

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Fig. 1 - Riefler Clock, #394

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Fig. 2 - Riefler Clock, #394

This Riefler, number 394, came from the private observatory of Admiral C. A. Fountaine at Narford Hall, Norfolk, England. It was acquired in 1924 and used until the early 1930s.

The Shortt Clock

The Shortt Free Pendulum Clock considered the most accurate pendulum clock ever manufactured, changed the entire philosophy of time keeping. The Shortt clock invented by William Harrison Shortt and produced by the Synchronome Company was patented in September of 1921.

The master pendulum is enclosed in a copper tank and evacuated to approximately 25 mm of mercury. The vacuum reduces aerodynamic drag on the pendulum and eliminates variations on the clock's rate due to atmospheric pressure changes. The pendulum swings free of any mechanical attachments. The only disturbance to the free pendulum is a minimal impulse applied every 30 seconds to keep it running. The slave pendulum clock is housed in a wood case and is synchronized to the master (free) pendulum. The slave clock is a modified Synchronome clock that keeps track of the time and produces the electrical output impulses. The Shortt-Synchronome clock is accurate to within one second a year.

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Fig. 3 - Shortt Clock #6

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Fig. 4 - Shortt Clock #6

This Shortt Clock, serial number 6, was also purchased by Admiral Fountaine for his private observatory in 1924 and replaced his Riefler clock. The clock was installed in the Admiral's clockvault and its rate was carefully compared to astronomical observations. Admiral Fountaine's observations were so precise that they indicated small variations in the earth's rotation. Fountaine insisted that these irregularities were due to the earth not the clock. The Greenwich Observatory confirmed these nutations in 1927.

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Fig. 5 - Shortt Clock #6

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Fig. 6 - Shortt Clock #6

Shortt #6 was the first clock to show that the earth is a poor timekeeper. It started a revolution that would eventually lead to atomic clocks replacing astronomical observations as the standard of timekeeping.* Clocks had finally surpassed the earth's rotation in accuracy and stability.

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Fig. 7 - Shortt Clock #6

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Fig. 8 - Shortt Clock #6

Shortt Clocks became the principal timekeepers world wide until replaced by quartz clocks in the 1940s. They were used in many observatories, including the Greenwich Observatory from 1925 to 1945 and the United States Naval Observatory from 1930 to 1946.

*Note: Prior to the Shortt Clock, clocks were essentially used as "fly-wheels" to keep track of time between astronomical observations. On January 1, 1972 atomic clocks became the official timekeepers of the world, replacing the heavens as the source of time.

Click any thumbnail to see the full image.

Note: Clocks shown partially assembled.

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