George III's consuming interest in horology and science is attractively encompassed in this 4-sided astronomical clock. The central mechanism is a three train fusee driven movement. This houses the time, strike and chime trains. The clock has a jewelled dead beat escapement with an unusual off-set crutch arm which is necessary to get round the centre arbour that runs through to the front and back dials. The pendulum is at the back of the clock behind the back dial.

The complex and compact quarter-striking movement displays on the principal face the time of day on a 24-hour dial with hands for mean and solar time. The hour hand makes one revolution every 24 hours. The minute hand revolves once an hour with the equation hand in front or behind the minute hand depending on the date. In the centre a painted landscape with figures shows the passage of the sun across the sky and a small centre dial records the time at thirty locations around the world relative to mean time. This rises in the winter and lowers in the summer so that the sun always rises and sets at the correct time for that day of the year. A lunette at the top records the date and month.

All the motion work is controlled by gearing run off from the centre arbour sandwiched between sets of plates. The ting tang chimes and strike are counted on racks with gathering pallets between the main and first set of plates. Forward from the next plate the posts for the date mechanism, motion work and equation work are mounted. The equation and date wheels are mounted together on an arbour that comes out of the dial above the 12 midday. In front of those wheels are two further counter balanced wheels to lift and lower the landscape picture in the centre of the dial so that the sun rises & sets at the correct time for each day of the year.

The left side dial shows the date on a large revolving dial in the centre below three smaller dials. The top right dial indicates the day of the week. The top middle dial shows the month and the left hand dial regulates the motions. The motion work comes off a plate set at a 90 degree angle to the main plates. The transfer of time is run from the wheels driving the back dial with the moon and tides. The large wheel behind the date chapter ring revolves once every 73 days and 5 times a year. This wheel has pins set at regular distances to operate complicated levers to operate the day of the week dial and the month dial. The motions regulator works independently engaging with the motion work through its own independent train. As the large date wheel slowly moves round it operates a mechanism that slowly draws down the date indicator hand towards the centre during the year. At the end of the year the hand springs up to the 1st January at the top of the ring.

The right side dial shows the position of the planets in their orbits according to the system of Copernicus. This motion work is run off a plate at 90 degree angle to the main plates. The planets are powered and regulated by the central movement with the time being transferred in the same way as in the date train. Each planet has two wheels with the correct ratio of teeth in the gearing to move it at the right speed. Behind the gears for the planet is a wheel that revolves once a year and is fed its power by a worm gear. This is in the upper section of the motion work with a setting arbour in its centre above the chapters.

The back dial shows the age of the moon which is also represented by a globe in the arch. Also shown on this dial are 32 ports marked on a central disc. As high tide reaches each port a large silver wave goes by. All the motion work behind this dial is controlled by the gearing run off from the centre arbour that extends out of the back of the movement. The centre arbour revolves once an hour and from this all other gearing is calculated. This includes the disc with the ports, the silver wave that represents high tide, the hour and the age of the moon.

The Gentleman's Magazine for June 1765, which records that this clock had been installed at Buckingham House by Norton under the supervision of the King's clockmaker Christopher Pinchbeck, also notes that the calculations for the solar system were made by 'Dr. Bevis' and that the design for the dials and other calculations were made by 'Mr. Ferguson'. The latter was undoubtedly the natural philosopher and specialist in astronomical clocks James Ferguson (1713-85), who as a friend of Matthew Boulton advised on the movements of Boulton's celebrated 'Geographical' and 'Sidereal' clocks in the early 1770s.

This astronomical clock cost the King's Privy Purse the very large sum of £1,042. This payment probably included the charge for the exceptionally fine carved mahogany case, framed by palm-tree columns and mounted with silver plaques and lion and unicorn crestings. This is likely to have been made by John Bradburn, possibly using the specialist carver Sefferin Alken as a subcontractor. In the same year Bradburn supplied a glass cover for the clock to the King's direction costing £9 6s.

The following year, 1766, Bradburn delivered 'a very rich Antique carved & burnish'd gilt Bracket' with a sliding and revolving top section designed to show all four sides of the clock, supported on a 'Demi Lyon & Unicorn' at a cost of £38 15s. The existence of the designs for this bracket among Robert Adam's drawings in the Soane Museum implies that the clock case too may have been designed by Adam, whose involvement at Buckingham House is generally somewhat overshadowed by that of Sir William Chambers. His bracket, which no longer survives, was presumably dispensed with when the clock was moved, probably c.1770, from the King's Dressing Room to the Octagon Library to stand on the central desk, where it is recorded in Stephanoff's view of 1818.

Catalogue entry adapted from George III & Queen Charlotte: Patronage, Collecting and Court Taste, London, 2004