US NAVAL OBSERVATORY / SCIENCE PHOTO LIBRARY US NAVAL OBSERVATORY / SCIENCE PHOTO LIBRARY
Time Service at US Naval Observatory, 1915. The Time Service department here consists of master clocks (including a chronograph and a transmitting clock) used for all official time signals used in astronomical and navigational calculations. These clocks were built by the Self-Winding Clock Company. Photographed in around 1915, at the US Naval Observatory, Washington DC, USA.
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