Precision Clock Gallery

The scientific community required a much higher level of precision in their laboratories and observatories than could be provided by a standard clock. In response to this demand, clockmakers worked to create even more precise clocks.

By the early 1700s, it was widely known that temperature affects clock metals, diminishing accuracy. George Graham performed research in 1715 on the thermal reactions of different metals, hoping to find two metals whose rates of expansion would “compensate,” or cancel one another out. He found such a relationship between steel and the viscous metal mercury, and went on to introduce a mercury-compensated pendulum in 1722.

As clockmakers coupled a growing understanding of metallurgy with new technological designs, timekeeping accuracy continued to improve.  By 1900, the Riefler Company of Germany was making timekeepers accurate to within 1/100th of a second per day. This performance was due not only to improved mechanics and materials,  but also to new case designs. To keep pressure, temperature, and humidity as constant as possible, manufacturers put precision clock movements in airtight cases called tanks. Precision clocks produced by W. H. Shortt in the 1920s were believed to keep time within two milliseconds (0.002 seconds) a day, but when tested in 1984, the clock kept time within 200 microseconds a day, or 10 times more accurately than previously believed.

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