It was always a bit of a puzzle what the people clustered on the sands, or peering down from the dunes, were actually looking at on a bleak stretch of windswept Dutch beach. The startling truth has just been revealed, after the conservator Shan Kuang took a delicate scalpel to a painting which has been in the collection of the Fitzwilliam Museum in Cambridge for the past 140 years.

She first uncovered a baffling figure of man apparently standing in mid air, and then gradually revealed that he was standing on the great hillock of a beached whale, washed up on the shallows.