Again and again I accompanied Barbour to King’s College, leaving the Laboratory at four o’clock, walking beside my loose-limbed companion through Cannon Street, down Ludgate Hill, up Fleet Street to the Strand, stopping at an A.B.C. for a cup of tea and a bun, and sometimes breaking the journey to spend ten minutes in St. Paul’s where evensong was in progress, and the sexless soprano voices of the choir-boys rose, disembodiments of the semi-transparent figures from the paintings of Fra Angelico.