A sketch of Waterloo Bridge by John Constable sold for £2.3m as auction this week.

The canvas, confirmed as the first prototype for “The Opening of Waterloo Bridge”, the celebrated work by one of Britain’s greatest landscape artists that hangs in Tate Britain. was discovered hanging in the hallway of a private home.

It is an excellent example of how Constable managed to harness the realistic detail of skies of the period, a detail that was overlooked by artists before him.

Sketched shortly after his 41st birthday on June 18th 1817, the scene depicts a pleasant summer afternoon, echoing that day’s meteorological observations in Luke Howard’s Climate of London: a high of 26C with light SE’ly winds, the start of a fine spell of weather.

It is thought that Constable, who in 1817 moved from his native Suffolk to London, had been greatly influenced by Howard’s work on naming the clouds a decade or so earlier. It was the same year that Howard gave his Seven Lectures In Meteorology, the subject matter of which was later published as the first meteorological textbook in 1837.

The sketch, which shows ceremonial barges leaving the shore at Whitehall to celebrate the opening of the new bridge, with St Paul’s Cathedral and the spires of Wren’s City churches visible beyond, fetched £2,289,000, far the figure it was expected to receive, between £1m and £1.5m, at Sotheby’s, on Wednesday.