Slave Dial to Tower Clock

Slave Dial to Tower Clock

Usage conditions apply
In places that required many clocks—factories, office and public buildings, or schools—time was often distributed by a system of "master" and "slave" clocks. In such a system, a central timekeeper, the master clock, sent periodic impulses, usually electric or pneumatic, to any number of secondary or slave clocks. These slave clocks could be located anywhere, without regard for convenience of winding, because they needed none. The master clock could also drive other time signals like classroom bells, factory whistles, or time stamps. More economical to install and more convenient to maintain than an equal number of independent clocks, the system also ensured that all dials within the system agreed.
The museum collection contains such a timekeeping system. The system's master clock (Cat. 310,569), built by E. Howard and Company of Boston, is a mechanical tower clock movement equipped with electrical contacts. Once a minute the escapement, through a pair of rotary switches, closes an electrical circuit and sends an impulse to the slave dial (Cat. 310,570), where electromagnets advance the hands. Batteries at the base of the master clock supply current.
This clock and dial were components of a system that served the Smithsonian between about 1881 and 1932. First housed in the north tower of the Arts and Industries Building, the clock movement distributed impulses to eighteen dials in that building and the Castle, the Smithsonian's earliest building. Tunnels under the floors carried the wiring. The clock room also housed a telephone switchboard, a watchman's clock, a central burglar alarm, and call bells—all of which, like the time distribution system, relied on the newly harnessed power of electricity. "Indeed," boasted the Smithsonian's annual report for 1881, "it is believed that in no building in the world, with the exception of the Grand Opera House in Paris, is there so perfect and complete an application of electricity to practical services."
Object Name
slave dial
Other Terms
slave dial; Mechanical, Weight-Driven; Tower Clock
Date made
overall: 17 in x 4 in x 2 in; 43.18 cm x 10.16 cm x 5.08 cm
ID Number
catalog number
accession number
See more items in
Work and Industry: Mechanisms
Engineering, Building, and Architecture
Exhibition Location
National Museum of American History
Data Source
National Museum of American History
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