Synchronome feedback clock, type B
Date: circa 1929
Inventory Number: 1998-1-0187b
Classification: Clock
Subject:
Maker: Synchronome Company, Ltd (founded circa 1900)
Maker: William Hamilton Shortt (1881 - 1971)
User: Institute of Geographical Exploration (1929 - 1952)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
Overall: 131 x 21 x 40.5 cm, 110.2 lb. (51 9/16 x 8 1/4 x 15 15/16 in., 50 kg)
Overall - Storage: 131 x 21 x 40.5 cm (51 9/16 x 8 1/4 x 15 15/16 in.)
DescriptionThis is a Type B Synchronome slave clock for use with the Shortt free pendulum clock. This mahogany-cased clock has three dials. The top dial is a typical, 24-hour astronomical regulator dial with a white matte finish. It gives readings to seconds, and was driven by a device on the slave pendulum that gave an audible signal every second (which astronomers found useful).
The pair of dials below the large dial are for the master and slave pendulums. They should always be in agreement. The master dial is labeled "Free P." for Free Pendulum. The other is labeled "Slave."
In the present situation, they have been marked with paper tape for other uses than intended. The large dial is labeled, "GREENWICH CIVIL TIME (G. C. T.)" and the smaller dial is labeled, "EASTERN STANDARD TIME (E. S. T.)."
So someone maintaining the clock would use the two lower dials to make sure the slave and master pendulums are in agreement. A scientist using the clock as a precision regulator would pay attention to the top dial.
Timing weights in a box with forceps were included with this clock.
The slave clock was used in conjuction with the free pendulum clock (1998-1-0187a) to regulate time in Harvard's Institute of Geographical Exploration.
For details on the parts and movement of this clock, please see the captions to the photographs.
The pair of dials below the large dial are for the master and slave pendulums. They should always be in agreement. The master dial is labeled "Free P." for Free Pendulum. The other is labeled "Slave."
In the present situation, they have been marked with paper tape for other uses than intended. The large dial is labeled, "GREENWICH CIVIL TIME (G. C. T.)" and the smaller dial is labeled, "EASTERN STANDARD TIME (E. S. T.)."
So someone maintaining the clock would use the two lower dials to make sure the slave and master pendulums are in agreement. A scientist using the clock as a precision regulator would pay attention to the top dial.
Timing weights in a box with forceps were included with this clock.
The slave clock was used in conjuction with the free pendulum clock (1998-1-0187a) to regulate time in Harvard's Institute of Geographical Exploration.
For details on the parts and movement of this clock, please see the captions to the photographs.
In Collection(s)
Signedon dial: SYNCHRONOME
Inscribedon dial: PATENT NO. 187814
FunctionIn the Shortt clock, there are two separate pendulums. The primary timekeeping pendulum is kept as free as possible by being enclosed in a sealed, constant pressure chamber. It was given impulses from a gravity arm that was electrically released by a secondary pendulum in another clock. Thus the two clocks gave feedback to each other.
The Shortt regulator was accurate to within a second in a year. It could detect slight seasonal variations in the rate of the earth's rotation.
The Shortt regulator was accurate to within a second in a year. It could detect slight seasonal variations in the rate of the earth's rotation.
Historical AttributesThis clock was set up in Harvard University's Institute of Geographical Exploration at 2 Divinity Avenue, Cambridge.
Curatorial RemarksTechnical description provided by Richard Ketchen, horologist, February 2008.
Historically, the two clocks in such a feedback system were called "master" and "slave." This terminology is no longer considered acceptable. We currently refer to them as the free-pendulum clock and the secondary or feedback pendulum clock.
Historically, the two clocks in such a feedback system were called "master" and "slave." This terminology is no longer considered acceptable. We currently refer to them as the free-pendulum clock and the secondary or feedback pendulum clock.
Primary SourcesSynchronome Company Ltd, copies of 9 patent drawings related to the clock movement, electrical circuitry, and more. In instrument file.
Synchronome Company, Ltd., "Instructions for the Erection of Free Pendulum, Master and Slave Clocks," circa 1959. Typescript in instrument file.
Synchronome Company, Ltd., "Memorandum on the Microscope and Special Beat Plate," circa 1959. Typescript in instrument file.
F. Hope-Jones, "The Free Pendulum," a lecture delivered before the British Horological Institute on April 19th, 1923 (London: The Synchronome Company, Ltd, [circa 1923]). Booklet in instrument file.
F. Hope-Jones, "The Free Pendulum," Journal of the Royal Society of Arts 72 (1924): 445-462. Offprint in instrument file.
Synchronome Company, Ltd, Astronomical Regulators and Observatory Time Installations, Together with a Brief Essay on the Free Pendulum and the General Principles of the Synchronome System on which It Is Based (Mount Pleasant, Alperton, Middlesex, UK: The Synchronome Company Ltd, [circa 1950]). Booklet in instrument file.
Synchronome Company, Ltd., "Instructions for the Erection of Free Pendulum, Master and Slave Clocks," circa 1959. Typescript in instrument file.
Synchronome Company, Ltd., "Memorandum on the Microscope and Special Beat Plate," circa 1959. Typescript in instrument file.
F. Hope-Jones, "The Free Pendulum," a lecture delivered before the British Horological Institute on April 19th, 1923 (London: The Synchronome Company, Ltd, [circa 1923]). Booklet in instrument file.
F. Hope-Jones, "The Free Pendulum," Journal of the Royal Society of Arts 72 (1924): 445-462. Offprint in instrument file.
Synchronome Company, Ltd, Astronomical Regulators and Observatory Time Installations, Together with a Brief Essay on the Free Pendulum and the General Principles of the Synchronome System on which It Is Based (Mount Pleasant, Alperton, Middlesex, UK: The Synchronome Company Ltd, [circa 1950]). Booklet in instrument file.
