ommission for a sale of an El Greco he recommended to them in 1905; occasionally he assisted in the smuggling of works to America. In 1906 Berenson hired Geoffrey Scott, a young classics student from Oxford to be his secretary/librarian; his wife, Mary, fell deeply in love with him. In retaliation to Mary for this affair, he started his own tryst with the librarian hired by J. Pierpont Morgan (1837-1913) for his collection, Belle da Costa Greene (1883-1950). North Italian Painters of the Renaissance, the final book of the quartet on Italian painters, appeared in 1907, in many ways his least successful book because these painters resisted Berenson's stylistic analysis. Berenson, who had previously been taking percentages from dealers for sales to those he advised, such as Isabella Stewart Gardner and others, first accepted a confidential retainer fee from Agnew Galleries. That same year, 1907, after introducing Mrs Gardner to the aggressive and unscrupulous art dealer Joseph Duveen (1869-1939), he sealed a secret deal with Duveen. Though Berenson had advised Duveen since 1906, the new agreement cut him in an unconventional 25 percent of the total Duveen sale. Duveen used Berenson's authority to sell pictures to the wealthiest collectors in the United States (and former Berenson confidents) Morgan and Joseph E. Widener (1871-1943). Berenson published a volume on Stefano di Giovanni Sassetta in 1909. He wrote the catalog of the Widener's collections in 1913, which he himself helped assembled, and again for Johnson in 1916. He was one of the original six contributors to the first issue of Art in America in 1913, which Duveen bankrolled in order to educate American collectors. Berenson published the first and second of his four major works, Venetian Painting in America, and the third series of The Study and Criticism of Italian Art in 1916. His war duty for World War I consisted of translating and negotiating in Italy, duties recommended by his friend, the author and art writer Edith Wharton. The third book of his quartet, Essays in the Study of Sienese Painting was published in 1918. An affair in Paris with Baroness Gabrielle La Caze, a French art collector, ensured. The following year, Berenson hired Elisabetta "Nicky" Mariano (1887-1968) to be his librarian and secretary. In 1925 the young Japanese scholar of Botticelli, YukioYashiro began to assist Berenson with a new edition of Drawings of the Florentine Painters. Berenson, apparently somewhat prejudiced against Japanese fell out with Yashiro, replacing Yashiro with a young Renaissance scholar from Oxford, Kenneth Clark, introduced Berenson by then Keeper of the Art Department of the Ashmolean Museum, Oxford, Charles F. Bell. Clark, still a student, assisted Berenson in the revision the Florentine drawings book for over two years. Berenson issued the final of his four major publications, Studies in Medieval Painting, and a combined volume of his regional Renaissance art books, Italian Painters of the Renaissance, both in 1930. He severed his ties with Duveen permanently in 1937. The art historian Fern Rusk Shapley assisted him at I Tatti with the second edition of his Drawings of the Florentine Painters, published with her own funds in 1938. As his wife's health declined, Mariano, became Berenson's lover as well. During World War II, he found himself a virtual prisoner in I Tatti, despised as an American by the Mussolini government, but admired by the locals and protected. Berenson and Mariano hid at a friend's house, fearful his Jewish heritage would make him a target. Mary Berenson died away from him at I Tatti in 1944. His war diary was published in 1952 as Rumour and Reflection, 1941-1944 and the notes on his reading for those years of enforced solitude as A Year's One Year's Reading for Fun, 1942 (1960). In 1948 Berenson wrote Aesthetics and History in the Visual Arts which expanded his concepts of "ideated sensations" and the notion of life-enhancing qualities of art. He continued to consult for the dealer Georges Wildenstein. His postwar writing included articles 