Joseph Williamson, A Solar Time Longcase Clock in Associated Walnut Case, London, circa 1730

12-inch dial with mask and leaf spandrels, matted center with seconds dial, calendar aperture, and signed Josephus Williamson, Londini Inv. & Fecit on a banner around the motto Horae Indicantur Apparentes Involutis Aequationibus, an annual calendar in the arch with sun pointer flanked by dolphin spandrels, five-pillar rack and bell striking movement, the calendar arbor extending to the rear of the movement where it carries an irregularly shaped disc which, by means of a pivoted lever, causes the effective length of the pendulum to increase and decrease throughout the year, thereby causing the clock to indicate true solar time, the associated case with domed caddy cresting and brass finials above a frieze fret, brass capped fluted hood pillars, broken-arch trunk door and plain plinth with stepped base.

Time Museum Inventory No. 1209

Lloyd, H. Alan.  The Collector’s Dictionary of Clocks.  New York, 1964, pp. 200-201
Jagger, Cedric.  Royal Clocks.  Robert Hale, 1983, pp. 49-50
von Bertele, Hans.  "Equation Clock Inventions of Joseph Williamson."  Antiquarian Horology.  (December 1955), pp. 123-127
Roberts, Derek.  British Longcase Clocks.  Pennsylvania, 1990, pp. 108-109
Robinson, Tom.  The Longcase Clock. Antique Collectors’ Club, 1981, pp. 180-184

Little seems to have been recorded about the early life of Joseph Williamson but it is thought that he was apprenticed in 1683. He appears to have worked for Daniel Quare but did not enter the Clockmakers’ Company until later when he set up in business on his own account. He was Junior Warden in 1721 and became Master in 1724 but died in office in June 1725. His surviving clocks demonstrate that he must have been a gifted mathematician with a good knowledge of astronomy. He was appointed watchmaker to King Charles II of Spain.

This clock shows solar time in accordance with that indicated by a sundial and not Greenwich Mean Time as it is known today. The Latin inscription on the dial translates approximately to mean that the clock shows apparent (sundial) time by means of complicated equation work. This feat is achieved by the use of a cam which controls the effective length of the pendulum throughout the year.  Joseph Williamson claimed to have invented this device in a letter which was published in Philosophical Transactions towards the end of 1719. Some of Daniel Quare’s longcase clocks incorporate this feature and it is thought that Williamson made this part of the clock for him.