This watercolour by Hubert Airy, son of the Astronomer Royal George Airy, shows the Royal Observatory's time ball in the courtyard, having fallen from the roof of Flamsteed House. It bears the inscription, "The ball fell on Dec 6 1855. Drawn on the spot by Hubert Airy". The time ball, with the attached weather vane, had been blown down by the wind, although the exact dates of the event or the sketch are unclear. An inscription on the reverse reads "1857 May 10. The Catastrophe occurred 1855 Dec 27". The original ball, made of wood and canvass was evidently damaged and required repair before being re-erected.

The time ball (ZBA2245) , dropped at 1pm every day, was mounted in 1833 as a time signal for mariners within sight on the Thames. It could be used to check the rates of on-board chronometers. The first time ball, the invention of Captain Wauchope, had been installed at Portsmouth in 1829.

Hubert Airy (1838-1903) was the fifth child of George and Richarda Airy. Educated at Blackheath Proprietary
School in Kent, he entered Trinity College, Cambridge, and became a physician. In 1870, in Philosophical Transactionsof the Royal Society, he published one of the clinically definitive papers on migraine, based on his and his father's experiences of visual aura: ‘On a distinct form of transient hemiopsia’. He was later author of a number of reports to the English Local Government Board on issues of public health, and in the journal 'Nature' on natural history.