Yesterday we were enjoying a visit at the National Gallery in London. Covid has been a nightmare for museums, but it has offered us visitors the unprecedented possibility of wandering around in semi-deserted galleries, of being alone with a Leonardo da Vinci or a Caravaggio. Because this is the paradox of museums: the more successful they are, the worse your experience of them is, and the contrary is true. We stopped in front of one of the masterworks of the National Gallery,