Clock vaults

“Owing to the courtesy of Prof. Upton, the laboratory has now the advantage of a set of time signals.”

―Carl Barus, Report of the Professor of Physics. Annual Report of the President to the Corporation of Brown University, June 18, 1896.

The masonry pier that supports the Ladd Observatory’s main telescope contains two clock vaults. These are very small rooms (4 by 4 feet square inside) that contain precision pendulum timepieces called regulators. The purpose of a clock vault is to provide a vibration-free and temperature-stable environment for exact timekeeping. The main clock vault is located in the entrance foyer on the first floor of the Observatory. The basement level vault has not been used in many years. Professor Winslow Upton calibrated the regulators using observations of stars starting in the 1890s.

clock vault
A regulator made by Robert Molyneux in London during the 1850s can be seen inside the main vault on the first floor.

The double doors to the vault seal out drafts and have windows through which the regulators can be observed without disturbing the environment inside. The brick walls are two feet thick which provides insulation to prevent fluctuating temperatures which could cause inaccuracy. There are  telegraph wires to send time signals from the regulators to other locations around Rhode Island. Starting September 12, 1893 and continuing until as late as 1973 the Observatory also transmitted time signals to City of Providence fire stations. Every day at noon and 8:30 p.m. signals sounded on the fire-alarm bells allowing residents and businesses to set their clocks to the correct time. Public time signaling was a common practice during this era.

constant temperature vault
The constant temperature vault beneath the entrance to Wilson Hall. Credit: Gould and Angell Architects, c 1890.

These constant temperature vaults were commonly constructed in observatories and scientific laboratories. Today the United States Naval Observatory still uses 20 temperature controlled clock vaults for the most precise atomic clocks. Another vault constructed on the Brown University campus at the same time that Ladd’s was built was located in the Physical Laboratory at Wilson Hall which opened in 1891. This vault in the basement beneath the front entrance likely would have been used for temperature sensitive physics experiments.

physical laboratory
The Physical Laboratory at Wilson Hall. A regulator used for physics experiments  can be seen on the far wall. Credit: Brown University, An Illustrated Historical Souvenir. E.A. Locke, 1897

Time signals from Ladd Observatory were also sent to locations on the Brown campus including the Physical Laboratory. They were used for accurate timing of experiments. Another signal was sent to University Hall where it was used to ring the bell announcing the start of classes. Operating the regulators in a clock vault was critical to achieving the 1/100th of a second accuracy of the time signals.

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