Article ID: CBB833174557

Gravitational conundrum: confusing clock-rate measurements on the 'First Fleet' from England to Australia (2022)

unapi

Voyages of exploration often included astronomers among their crew to aid with maritime navigation. William Dawes, a British Marine who had been trained in practical astronomy, was assigned to the 'First Fleet', a convoy of eleven ships that left England in May 1787 bound for Botany Bay (Sydney, Australia). Dawes was also expected to take measurements of the local gravitational acceleration, g, at any port of call by measuring the daily rate by which his Shelton pendulum clock differed from that at Greenwich, its calibration location. Although Dawes and Nevil Maskelyne, Britain's fifth Astronomer Royal, had planned to obtain clock-rate measurements in the Canary Islands, San Sebastian (Rio de Janeiro) and Table Bay, Captain Arthur Phillip, Commander of the First Fleet, only allowed Dawes to disembark the clock in Rio de Janeiro. Therefore, we have just one set of clock-rate measurements from the voyage, in addition to land-based measurements obtained in New South Wales. If gravity was the dominant factor affecting the clock's changing rate, Dawes' measurement of -48.067 sec per (sidereal) day obtained in Rio de Janeiro implies a local gravitational acceleration, g = 9.7946 m sec-2. On the other hand, if we adopt the modern value, g = 9.7878 m sec-2, the implied daily decay rate is almost exactly 30 sec greater than Dawes' clock-rate determination, a difference that is well in excess of the prevailing uncertainties. This suggests that the pendulum's regulator nut may have been offset by a full turn, thus implying that our assumptions regarding the pendulum length may have to be revisited.

...More
Citation URI
https://data.isiscb.org/isis/citation/CBB833174557/

Similar Citations

Article Richard de Grijs; Andrew P. Jacob; (2021)
William Dawes: practical astronomy on the ‘First Fleet’ from England to Australia (/isis/citation/CBB079817226/)

Article Morrison, Doug; Barko, Ivan; (2009)
Dagelet and Dawes: Their Meeting, Their Instruments and the First Scientific Experiments on Australian Soil (/isis/citation/CBB000932006/)

Article Richard de Grijs; Andrew P. Jacob; (2021)
Sydney’s scientific beginnings: William Dawes’ observatories in context (/isis/citation/CBB536441834/)

Chapter Dunn, Richard; (2014)
Heaving a Little Ballast: Seaborne Astronomy in the Late-Eighteenth Century (/isis/citation/CBB001420886/)

Chapter González González, Francisco José; (2011)
Astronomía y navegación en el Cádiz del siglo XVIII (/isis/citation/CBB001221492/)

Article Bronwen Douglas; (2013)
Philosophers, Naturalists, and Antipodean Encounters, 1748-1803 (/isis/citation/CBB254586561/)

Chapter Wayne Orchiston; (2016)
Astronomy on Cook’s Second Voyage: Dusky Sound and Queen Charlotte Sound, 1773–1774 (/isis/citation/CBB050292463/)

Book Ian Burnet; (2019)
The Tasman Map: The Biography of a Map (/isis/citation/CBB184792152/)

Book Starbuck, Nicole; (2013)
Baudin, Napoleon and the Exploration of Australia (/isis/citation/CBB001201503/)

Article Attenbrow, Valerie J.; Cartwright, Caroline R.; (2014)
An Aboriginal Shield Collected in 1770 at Kamay Botany Bay: An Indicator of Pre-Colonial Exchange Systems in South-Eastern Australia (/isis/citation/CBB001422060/)

Book Newton, Roger G.; (2004)
Galileo's Pendulum: From the Rhyme of Time to the Making of Matter (/isis/citation/CBB000470025/)

Book Baker, Gregory L.; (2011)
Seven Tales of the Pendulum (/isis/citation/CBB001022738/)

Article Carmody, John; (2013)
Medical History: Feeling No Pain (/isis/citation/CBB001320435/)

Article Barthélemy, Georges; (2004)
Newton découvreur du poids de toutes choses (/isis/citation/CBB000551130/)

Article P. Kenneth Seidelmann; (2019)
A history of Western astronomical almanacs (/isis/citation/CBB140947841/)

Book Clode, Danielle; (2007)
Voyages to the South Seas: In Search of Terres Australes (/isis/citation/CBB000850012/)

Authors & Contributors
Grijs, Richard de
Jacob, Andrew P.
Orchiston, Wayne
Morfouli, Meropi
Burnet, Ian
Cartwright, Caroline R.
Concepts
Travel; exploration
Nautical astronomy
Time measurement
Pendulums
Indigenous peoples; indigeneity
Instruments, astronomical
Time Periods
18th century
19th century
17th century
20th century, early
16th century
Places
Australia
France
Tasmania (Australia)
England
South America
Netherlands
Institutions
Great Britain. Board of Longitude
Comments

Be the first to comment!

{{ comment.created_by.username }} on {{ comment.created_on | date:'medium' }}

Log in or register to comment