An English 17th-century double portrait holds many clues to its meaning

This is a big book about a minor painting — a double portrait of John Bankes, aged about 16 (the son of the Chief Justice of the Common Pleas, Sir John Bankes), and his tutor, Dr Maurice Williams. It was done in Oxford in 1643-4 by Francis Cleyn, a court painter. At the time, Oxford was the headquarters of the royalist army, and painters were busy recording for their loved ones Cavaliers who would soon be dead. In the left corner of the painting there is a copy of Galileo’s Dialogues Concerning the Two Chief World Systems, in its Latin translation, open at the frontispiece, along with a globe and a telescope. Young John holds out a drawing compass into the centre of the image, and looks out into empty space.

J.L. Heilbron devotes 500 pages to trying to make sense of this painting, but makes surprisingly little progress. What does he get wrong? First, let’s ask who the painting is for.