"American Method in Astronomical Observation"
date: label: Date made
content: ca 1850
name: label: maker
content: William Bond & Son
notes: label: Description
content: From its infancy, timekeeping has depended on astronomy. The motion of celestial bodies relative to the rotating Earth provided the most precise measure of time until the mid-twentieth century, when quartz and atomic clocks proved more constant. Until that time, mechanical observatory clocks were set and continuously corrected to agree with astronomical observations.
label: Description
content: The application of electricity to observatory timepieces in the late 1840s revolutionized the way American astronomers noted the exact movement of celestial events. U.S. Coast Survey teams devised a method to telegraph clock beats, both within an observatory and over long distances, and to record both the beats and the moment of observation simultaneously. British astronomers dubbed it the "American method of astronomical observation" and promptly adopted it themselves.
label: Description
content: Transmitting clock beats by telegraph not only provided astronomers with a means of recording the exact moment of astronomical observations but also gave surveyors a means of determining longitude. Because the Earth rotates on its axis every twenty-four hours, longitude and time are equivalent (fifteen degrees of longitude equals one hour).
label: Description
content: In 1849 William Cranch Bond, then director of the Harvard College Observatory, devised an important improvement for clocks employed in the "American method." He constructed several versions of break-circuit devices—electrical contracts and insulators attached to the mechanical clock movement—for telegraphing clock beats once a second. The Bond regulator shown here incorporates such a device. Bond's son Richard designed the accompanying drum chronograph, an instrument that touched a pen to a paper-wrapped cylinder to record both the beats of the clock and the instant of a celestial event, signaled when an observer pressed a telegraph key.
label: Location
content: Currently not on view
place: label: place made
content: United States: Massachusetts, Boston
setName: label: See more items in
content: Work and Industry: Mechanisms
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content: Science & Mathematics
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content: Measuring & Mapping
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1981.0322.01
label: accession number
content: 1981.0322
label: catalog number
content: 1981.0322.01
objectType: label: Object Name
content: clock
label: Other Terms
content: clock; Mechanical, Weight-Driven; Tall Case Clock
physicalDescription: label: Physical Description
content: "brass" (movement material)
label: Physical Description
content: wood (case material)
label: Physical Description
content: glass (pendulum bob, part of material)
label: Measurements
content: overall: clock: 78 in x 16 in x 8 1/2 in; 198.12 cm x 40.64 cm x 21.59 cm
label: Measurements
content: overall: crate: 89 in x 40 in x 29 in; 226.06 cm x 101.6 cm x 73.66 cm
label: Measurements
content: weight: 8 3/32 in x 1 3/4 in; 20.574 cm x 4.445 cm
label: Measurements
content: hood: 16 in x 15 1/2 in x 10 in; 40.64 cm x 39.37 cm x 25.4 cm
label: Measurements
content: case and movement: 75 in x 16 1/2 in x 10 in; 190.5 cm x 41.91 cm x 25.4 cm
label: Measurements
content: part: rating indicator: 13/16 in x 1/2 in x 5/32 in; 2.032 cm x 1.27 cm x .381 cm
label: Measurements
content: weight pulley: 2 3/4 in x 2 1/2 in x 13/16 in; 6.985 cm x 6.35 cm x 2.032 cm
label: Measurements
content: winding crank: 4 in x 3 1/2 in x 1 1/4 in; 10.16 cm x 8.89 cm x 3.175 cm
label: Measurements
content: case key: 1 3/4 in x 3/4 in x 3/16 in; 4.445 cm x 1.905 cm x .508 cm