On orders from King George III, the explorer, navigator, cartographer and naval officer Lieutenant James Cook (1728-1779) sailed out of Portsmouth harbour in England on 12th August 1768 on his way to the island of Tahiti in the South Pacific.
Lt. James Cook had been appointed to command the vessel Endeavour and he was given the responsibility of observing and recording an astronomically important event, the Transit of Venus.
This is when the planet Venus passes directly between the sun and the earth and becomes visible as a small black disc moving across the face of the Sun.
The transit is a rare phenomenon, which occurs only in a pattern that repeats itself every 243 years.
Transits are usually eight years apart and they can be separated by very long gaps of up to 121.5 years or 105.5 years.
On board the good ship Endeavour with Lieutenant James Cook was a Shelton Regulator, which is a particularly accurate long-case clock with a specialized dial.
It was to be used for timing observations of the event and was made by a brilliant clockmaker of the day, John Shelton of Shoe Lane, London.
Recording facts and events in writing is not always what makes history ‘tick’, sometimes it seems it could also be a clock.
John Shelton is known to have made five (5) examples of his so-called regulator clock. One of which went with Captain Cook on the recommendation of the Astronomer Royal, Fellow of the Royal Society and member of the Board of Longitude Dr. Nevil Maskelyne (1732-1811).
He had been part of the voyage to the island of St Helena in 1761 to measure the Transit of Venus of that year for himself and advised the Admiralty on the types of scientific instruments required for the transit Cook was sent to measure.
John Shelton’s Regulator Clocks were used in the 1760’s and 1770’s, and two clocks accompanied James Cook on his subsequent voyages to the South Seas. They were also used in the West Indies, Hudson Bay Canada, North Cape, Norway and Cornwall in England. Incredibly, they were still being used in 1955.
This highly important sister clock by John Shelton was put on view as part of the exciting landmark exhibition Mapping Our World, which will be held at National Library in Canberra in the summer of 2013-2014. Martyn Cook, Martyn Cook Antiques at Sydney arranged the loan on behalf of the current owner.
During the voyage the clock was cleaned regularly to keep it in perfect working order.
Enclosed in a plain but sturdy mahogany timber case, Shelton ensured the bolt and shutter mechanism of his clocks were always maintained in working order.
He used a special gridiron and brass pendulum that took full advantage of the different rates of the expansion of metals so that it would remain accurate.
This meant in practical terms, the length of the pendulum would remain constant, despite the temperature where the clock was set up to take measurements. It was particularly important because they were going to be in the tropics.
Astronomer Charles Green and botanist Joseph Banks went with Lieutenant James Cook on his amazing voyage to observe the transit in the Pacific Ocean. They were determining the Sun’s distance from the earth. Regulators were so very accurate that they could time the transit to the exact second.
Green had problems with his measurements, although they were deemed an improvement on those that had been made eight years earlier by Maskelyne himself. To ensure the clock remained steady it was braced for stability and placed in an enclosure under close guard by the Royal Marines.
In 1802, Matthew Flinders wrote to Nevil Maskelyne that ‘a great obstruction to our operation’ was that the small size of the portable observatory meant that the theodolite, a precision instrument that measures angles in vertical and horizontal planes, and the clock had to stand in different tents, while the tent’s canvas ‘was rotten and full of holes’, as a result of ‘the little room in the ship, which obliged us to take the parts out of the cases and stow them separately in different places’.
This in part explains why tents don’t survive, although in 1968 the National Maritime Museum did build a replica:
Maskelyne also provided the nautical tables that Green used to perform the mathematically complicated but effective method of calculating longitude, based on the lunar distances.
Captain Cook and Green both recorded what they saw, producing detailed diagrams to show the progress of the Transit of Venus from their own perspective.
These also illustrated the difficulties of their task because they found that discrepancies occurred when comparing their results.
This happened quite dramatically, even though they were in reality standing right next to each other at the time.
What both observers agreed upon was that the planet was surrounded by the “dusky shade” or atmosphere that made gaining accurate facts difficult.
Cook had sealed orders from the Navy to be opened after they had observed the Transit.
These instructed him to leave the island when the event was over and “search between Tahiti and New Zealand for a Continent or Land of great extent.”
In April 1770, they became the first Europeans to reach the east coast of Australia, making landfall on the shore of what is now known as Botany Bay.
There has always been confusion about where the five Shelton clocks all were at different times in history, and which ones were actually used for what astronomical events.
At the time cataloging instruments and recording their use by institutions was not yet standard practice. One of the lessons learned from Cook’s expeditions was that in order to have good results you needed your instruments recorded, in good working condition, and all aligned.
Four of the Five Shelton Regulators made for the Transit of Venus exhibition have had a chequered career. The four known have all had alterations of some type or another since they were first made.
One regulator clock is now in The Armagh Observatory Museum in Northern Ireland. Her Majesty Queen Victoria presented his Majesty King George III’s collection of scientific instruments, of which it was one, to the observatory.
Another is in the Library area of St John’s College, University of Cambridge in England.
The one used by Maskelyne to make his gravitational measurements at Schiehallion in Perthshire is known, and now in the National Museum of Scotland.
Another is in the National Maritime Museum, Greenwich, England.
It seems that no one is really sure where the fifth one might be?
This highly important clock by Shelton found its way to Australia came up for sale at Christie’s London on 5th May 1983: Lot number 113
In original condition, it was on loan for the Mapping Our World Exhibition at Canberra 2013-2014.
Because they are so infrequent, scientists today must still take advantage of knowing the dates of the Transit of Venus ahead of time.
They can then take the opportunity to keep up with the many events constantly happening in our universe.
The last transit of Venus was on 5th and 6th June, 2012. It was the most widely photographed and observed to date. The next transits won’t take place until 2117 and 2125.
Thomas Shelton, James Cook and Charles Green all did their bit for science. What they faced in their time, as they endeavoured to contribute to a further understanding of the Universe, compared to the technologically brilliant world we live in, was indeed difficult as they helped humans to find their place in the cosmos.
Carolyn McDowall, The Culture Concept Circle, 2013
Ref: MARTYN COOK ANTIQUES
Shelton Regulator Clock
John Shelton, London Regulator Clock, the movement housed in a plain mahogany case with raised panel to the plinth and moulded door. The 10” [25.4cm) square dial silvered and varnished, an outer minute ring numbered 5’s and dots with a well moulded blued steel hand. The seconds ring inside with emphasized 5-second divisions. In the lower part of the dial a curved slot showing the hours with roman numerals. The dial engraved John Shelton London; covered winding hole with shutter lever at 3 o’clock position.
The shaped plates separated by 6-latched pillars, the steady pinned dial feet also screwed to the front plate, the dial screwed to the 4-front pillars. A single end plate on the back plate covers the pivot holes. Vertically pivoted stop work to the train, of high count 4-spoked wheels and 6-spoked escape wheel of deadbeat type. Shelton’s own bolt and shutter mechanism with maintaining power active on the entre wheel on its upward path only (to prevent fouling) through spring action.
The pendulum suspended from the back plate consists of 5 steel and 3 brass rods and large brass faced bob. The movement held to the seat board with 4 securing brackets and 2 securing brackets to the backboard. Below the pendulum bob is a silvered beat scale attached to the backboard of the trunk. The front plate is stamped Shelton and inside the back cock twice stamped Shelton. The pendulum and the escapement in original condition without improvement due to wear.
Download Auction Pages Christies 5 May 1983