Shortt free-pendulum regulator, master clock no. 17
Date: circa 1929
Inventory Number: 1998-1-0187a
Classification: Clock
Subject:
Maker: William Hamilton Shortt (1881 - 1971)
Maker: Synchronome Company, Ltd (founded circa 1900)
User: Institute of Geographical Exploration (1929 - 1952)
Cultural Region:
Place of Origin:
City of Use:
Dimensions:
125 x 26 x 26 cm (49 3/16 x 10 1/4 x 10 1/4 in.)
DescriptionThis the the "free pendulum" of the Shortt-Synchronome clock system. The free pendulum is mounted in cylindrical copper chamber, which is wall mounted. The chamber is sealed at the top with heavy glass bell jar and at the bottom with a disc of heavy plate glass. The chamber is exhausted to an internal pressure of 20 mm Hg. A pressure gauge is attached to lower proper right of the chamber. There are two barometers inside the chamber--a mercury gauge and an oil gauge. The latter is more precise and able to detect the smallest leaks. Both are read through the glass bell jar at the top proper right of the chamber.
The Invar pendulum bob weighs 14 pounds. The rod is of fixed length to beat seconds (mean solar or sideral time) at the latitude at which the clock is meant to be used. It is fully compensated. Timing weights were included with the clock. These were set in a wood block with a forceps, and they ranged in weight from 10 mg to 10 grams.
The beat scale is at the bottom of the pendulum and read through a reflecting mirror or by means of a reflecting microscope fixed to the bottom of the exterior of the chamber.
An original jewel of the clock movement was broken in an earthquake.
To exhaust the chamber, a hand-operated, rotary, Geryk-type vacuum pump was used.
The free pendulum clock was used in conjuction with the Synchronome slave clock (1998-1-0187b) 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 Invar pendulum bob weighs 14 pounds. The rod is of fixed length to beat seconds (mean solar or sideral time) at the latitude at which the clock is meant to be used. It is fully compensated. Timing weights were included with the clock. These were set in a wood block with a forceps, and they ranged in weight from 10 mg to 10 grams.
The beat scale is at the bottom of the pendulum and read through a reflecting mirror or by means of a reflecting microscope fixed to the bottom of the exterior of the chamber.
An original jewel of the clock movement was broken in an earthquake.
To exhaust the chamber, a hand-operated, rotary, Geryk-type vacuum pump was used.
The free pendulum clock was used in conjuction with the Synchronome slave clock (1998-1-0187b) 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 label: SHORTT
on label: Designed by WM. HAMILTON SHORTT M. Inst. C.E. / in association with / THE SYNCHRONOME CO. LTD. / 32 & 34 CLERKENWELL Rd. / LONDON, E.C.
on label: Designed by WM. HAMILTON SHORTT M. Inst. C.E. / in association with / THE SYNCHRONOME CO. LTD. / 32 & 34 CLERKENWELL Rd. / LONDON, E.C.
Inscribedon label: CLOCK SHORTT NO. 17
on label: Designed by WM. HAMILTON SHORTT M. Inst. C.E. / in association with / THE SYNCHRONOME CO. LTD. / 32 & 34 CLERKENWELL Rd. / LONDON, E.C.
on label: Designed by WM. HAMILTON SHORTT M. Inst. C.E. / in association with / THE SYNCHRONOME CO. LTD. / 32 & 34 CLERKENWELL Rd. / LONDON, E.C.
FunctionIn the Shortt master-slave clock system, there are two separate pendulums. The master timekeeping pendulum is kept as free as possible by being enclosed in a sealed, constant low-pressure chamber. It was given an impulse only every 30 beats by means of a gravity arm that was electrically released by a slave pendulum in another clock.
The Shortt regulator system 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 system 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.
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.
