The Brazilian conceptual artist Cildo Meireles (Tate Modern until 11 January) is another creator with an ideological motivation. He came to prominence in 1970, with his country under a military dictatorship, when he silk-screened political messages -Who Killed Herzog? (a left-wing journalist) - on banknotes that then went back into circulation. Meireles has always been fascinated with scale and it is the pieces that play with accumulation that have the most impact - Babel 2001, a tower made from 800 radios, each tuned to a different channel; Fontes, a room where 6,000 rulers hang from the ceiling like icicles while 1,000 clocks line the walls and 500,000 vinyl numbers litter the floor; and Volatile, a dark space ankle-deep in talcum powder through which you walk shoeless towards a candle. As with so much conceptual art, the concepts themselves vary from the banal to the impenetrable and are not often strong enough to support the works. This is a show to visit for the sensations rather than the message.

If, however, time is truly pressing and you can get to see only one display in December then go to Edinburgh's National Gallery of Scotland. It is there that the Duke of Sutherland's for-sale Titians are on show while the clock runs down on the desperate attempt to raise the £50 million needed to save Diana and Actaeon for the nation. After January 1, the future of one of the world's great paintings is uncertain. Catch it while you can.