Astronomical Regulator

This is a precision clock associated with Andrew Ellicott. Ellicott became Surveyor General of the United States in 1792 and completed critical national astronomical surveys—most notably the boundaries for the District of Columbia in 1791-92 and the border between the United States and Spanish Florida in 1800.
The clock’s original case and seat board for the movement have not survived. The square iron dial is marked “Ellicott/Baltimore.” It was originally painted white, with added painted floral spandrels. It has Roman hour numerals, Arabic minute numerals and separate seconds in Arabic numerals under 12. Andrew Ellicott or his father Joseph Ellicott made the brass time-only, weight-driven movement sometime before about 1790. The younger Ellicott made and attached the gridiron temperature-compensating pendulum, which he described as the first ever made in the United States, in a letter to Thomas Jefferson on 6 March 1803.
Astronomers and surveyors used precision clocks like this one to observe the time that specific "clock stars" passed overhead. With a transit, a special kind telescope for observing stars, they noted the instant the star passed the local line of longitude.
Reference: Robert S. Edwards, “Andrew Ellicott’s Field Regulator,” NAWCC Bulletin (October 1990): 419-427.
Currently not on view
Object Name
clock movement in wooden case
date made
ca 1790
overall: 158.1404 cm x 45.4152 cm x 27.305 cm; 62 1/4 in x 17 7/8 in x 10 3/4 in
overall - key: 3 in x 3 1/2 in x 1 1/2 in; 7.62 cm x 8.89 cm x 3.81 cm
place made
United States
ID Number
catalog number
accession number
Measuring & Mapping
See more items in
Work and Industry: Mechanisms
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Henry Ellicott Magill
Additional Media

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