Acquired last year by the Science Museum, this rare Georgian clock records changes in air pressure and is one of only four of its type made by London clockmaker Alexander Cumming.

Dating from 1766, the clock (pictured) sits in a seven foot tall decorated case, believed to have been made by London cabinet-maker Thomas Chippendale. Inside is a barograph – comprised of two tubes of mercury in which a float rises and falls as atmospheric pressure changes and the data is recorded on the clock dial which rotates once a year.

Scottish-born Cumming, who constructed his first barograph clock on the orders of King George III a year before this one in 1765, designed this clock based on ideas first outlined by Royal Society founding member Robert Hooke.

Following Cumming’s death in 1814, the clock was purchased by meteorologist Luke Howard – known as the ‘father of scientific meteorology’ – who used it to observe atmospheric pressure at his homes in London and Ackworth. The data gathered was published in his book Barometrographia  in 1847.

While it has previously been loaned for display at the museum, it now forms part of the permanent collection.

WHERE: Science Museum, Exhibition Road, South Kensington (nearest Tube stations are South Kensington and Gloucester Road); WHEN: 10am to 6pm daily; COST: free; WEBSITE: www.sciencemuseum.org.uk. 

PICTURES: Courtesy of the Science Museum.