Our Liotard exhibition has arrived from Edinburgh.   It looks wonderful in the Sackler galleries with their good height and generous proportions, enhanced by clever but low-key design by Eric Pearson with minimal red banding in the first gallery to give a sense that they are works for private rather than public space.   The exhibition gives a particularly good view of the aristocracy in the late 1730s, grand tourists in Rome and Constantinople, cultivated and louche, members of the Society of Dilettanti (Viscount Duncannon was a founder member) and of the Hellfire Club (Simon Luttrell founded the Dublin Hellfire Club).   Viscount Mountstuart stayed in Geneva with the Pictet family, whose bank are sponsoring the exhibition.