For nine months a year the average art collector cannot be separated from his collection. But in summer vacation time the art turns into a burden, vulnerable to theft and damage. "Most collectors send their paintings to their favorite dealers or store them in a warehouse, or sometimes leave them locked up at home," says Manhattan's Metropolitan Museum of Art Director James Rorimer. "We'd rather have them on our walls."
In 1949 Theodore Rousseau Jr., the Met's curator of European paintings, deciding to hang them there, launched a campaign to persuade collectors to...