Riefler Tank Clock
This clock was purchased from Riefler company in Munich, Germany in 1910. The original price, including installation, was $988.10. The clock was used in the regulation of the timekeeping service provided by the Goodsell observatory from the time of the clock was acquired until the service was discontinued in December of 1931.
The "tank" in the clock's description refers to the glass jar that hung below the clock and enclosed the pendulum. In operation, there was also a bell jar over the movement creating an airtight chamber. This chamber was partially evacuated and held at a constant pressure providing a constant pressure environment for the pendulum.
Overall the clock is very well preserved and is in good condition. The one exception is the glass tank which was broken in an unfortunate construction accident in the 1990's.
This model of clock is generally regarded as the most precise purely mechanical clock ever made with a claimed mean variation of 0.010 seconds/day.