"I was staggered when I saw the works ... A new sense came upon me, a new heaven and a new Earth stood before me." So wrote William Hazlitt in 1798 when he saw the collection of old master paintings bought in France by the 3rd Duke of Bridgewater.
Among them were two Titian masterpieces whose net worth 210 years on may now reach £300m - which would make them easily the most valuable paintings ever sold. Yesterday the national galleries in London and Scotland announced they are uniting in an attempt to buy them for the nation.
The artist Lucian Freud described them as the most beautiful pictures in the world. Remarkably, they have been on public display almost since Hazlitt first saw them, for more than a century in London and since 1945 on loan at the National Gallery of Scotland in Edinburgh. But now their current owner, the 7th Duke of Sutherland, has announced he wants to sell them.
John Leighton, the director general of the National Galleries of Scotland, said: "It is the most important old master paintings loan to any public museum in the world and is of supreme importance to Scotland and the rest of the UK."
The Titians, Diana and Actaeon and Diana and Callisto, are part of a series of six mythological paintings by the Venetian master, painted between 1556 and 1559 for Philip II of Spain. The duke, with estates in Scotland and East Anglia, has most of his wealth contained in the collection and has decided to sell to diversify his assets.
He has told the galleries he wishes the paintings, which have never been separated, to be bought for the nation at a knockdown price of £100m, and they have until the end of the year to indicate whether they can raise the money. If not, the paintings - or a number of others from the Bridgewater collection, which also includes three Raphaels, a Rembrandt and eight Poussins - will go to public auction next year.
"They could be one of the greatest acquisitions we could ever make. These are among the four or five pictures which would come to mind if one thought of what Titian stood for as an artist," said National Gallery director Nicholas Penny. It is the first time the two galleries have collaborated in such a way. If the paintings are bought, they will go on show for five years at a time in each gallery.
The immediate need is to raise £50m for Diana and Actaeon, or at least show the money is obtainable by the end of the year, though it would be paid in instalments over three years, with a similar deal to follow for the second painting from 2013.
The galleries are approaching the Scottish and British governments to underwrite some of the cost as well as art funds and wealthy sponsors, though they have not ruled out making a public appeal.
Both acknowledge that it is scarcely a propitious time to be asking for money, but Penny said: "It is really important to realise that art is not there just for the country in its moments of affluence. It is a major solace for times of difficulty. Most major acquisitions have been made against a background of economic distress."
Terence Fane-Saunders, the duke's spokesman, said: "Obviously his strongly preferred option is to sell them to the national galleries. The price represents a huge discount. I know the duke is extremely fond of these paintings. They mean a lot to him."