A SOBER brick building, unpretentious in scale and design, lies modestly low among lawns at the end of a road with playing fields on either side: the Dulwich Picture Gallery. It does not look as if it was designed by the architect of the Bank of England to house a mausoleum hung with most of the pictures assembled for the National Gallery of Poland. Its unusual history began when a rich Welshwoman from Glamorgan, Magaret Morris, married her French tutor, Noel Desenfans, just before ...