Vernet relates, that he was once employed to paint a landscape, with a cave, and St. Jerome in it; he accordingly painted the landscape, with St. Jerome at the entrance of the cave. When he delivered the picture, the purchaser, who understood nothing of perspective, said, ‘the landscape and the cave are well made, but St. Jerome is not in the cave.’ ‘I understand you, Sir,’ replied Vernet, ‘I will alter it.’ He therefore took the painting and made the shade darker, so that the saint seemed to sit farther in. The gentleman took the painting; but it again appeared to him that the saint was not in the cave. Vernet then wiped out the figure, and gave it to the gentleman, who seemed perfectly satisfied. Whenever he saw strangers to whom he shewed the picture, he said, ‘Here you see a picture by Vernet, with St. Jerome in the cave.’ ‘But we cannot see the saint,’ replied the visitors. ‘Excuse me, gentlemen,’ answered the possessor, ‘he is there; for I have seen him standing at the entrance, and afterwards farther back; and am therefore quite sure that he is in it.’

— Thomas Byerley and Joseph Clinton Robertson, The Percy Anecdotes, 1821