TRIANGULATION.(Norman Foster, architect)

Norman Foster is the Mozart of modernism. He is nimble and prolific, and his buildings are marked by lightness and grace. He works very hard, but his designs don't show the effort. He brings an air of unnerving aplomb to everything he creates--from skyscrapers to airports, research laboratories to art galleries, chairs to doorknobs. His ability to produce surprising work that doesn't feel labored must drive his competitors crazy.

Foster, who is English and lives in London, is an artist with the savvy of a corporate consultant. He knows how to convince chief executives that the avant-garde is in their interest. In the nineteen-eighties, he persuaded H.S.B.C., the international bank, to spend nearly a billion dollars to build a tower in Hong Kong; the novel structure, in which five enormous steel modules were stacked on top of one another, was the most innovative skyscraper since the Seagram Building. In 2000, he secured a commission from the Hearst Corporation, the publishing firm, to design its new headquarters, in Manhattan. The gorgeous, gemlike tower, which will officially open in a few months, is Foster's first big project in America.

In the nineteen-twenties, William Randolph Hearst commissioned Joseph Urban to design his company's first headquarters: six stories of megalomaniacal pomp on Eighth Avenue between Fifty-sixth and Fifty-seventh Streets. Despite its low height, everything about the yellowish stone structure suggests grandiosity, especially the monumental fluted columns that stretch higher than the building itself, giving it the look of a base for a much taller structure. (Hearst and Urban had planned to add a tower, but they never did.) The Hearst Corporation long ago outgrew this zany palazzo, dispatching most of its employees to rented space nearby. When the company decided to gather its operations under one roof, its executives smartly concluded that Urban's building was too much fun to give up. Hearst hired Foster to build something on top of it, and in October, 2001, he unveiled a scheme to add forty stories to the original headquarters. It was the first major construction project to be announced in New York after September 11th.

As with all Foster designs, the Hearst tower is sleek, refined, and filled with new technology. It looks nothing like the Jazz Age confection on which it sits. The addition is sheathed in glass and stainless steel--a shiny missile shooting out of Urban's stone launching pad. The tower's most prominent feature is the brash geometric pattern of its glass and steel, which the architect calls a "diagrid": a diagonal grid of supporting trusses, covering the facade with a series of four-story-high triangles. These make up much of the building's supporting structure, and they do it with impressive economy: the pattern uses twenty per cent less steel than a conventional skyscraper frame would require.

Foster's brilliance can be seen in the way that he exploits this engineering trick for aesthetic pleasure. The triangles are the playful opposites of the dark Xs that slash the facade of the John Hancock Center, in Chicago. They give the building a jubilantly jagged shape. Foster started with a box, then sliced off the corners and ran triangles up and down the sides, pulling them in and out--a gargantuan exercise in nip and tuck. The result resembles a many-faceted diamond. The corners of the shaft slant in and out as the tower rises, and the whole form shimmers.

Such a scheme could have become a pretentious exercise in structural exhibitionism, but in Foster's hands it presents the perfect foil for Urban's building. The design avoids the two most obvious approaches: imitating the style of the base or erecting a neutral glass box. Joseph Urban's goal in the original Hearst Building was to create a respectable form of flamboyance, and Foster has figured out how to do the same thing with his tower, but in unquestionably modern terms, and without compromising his commitment to structural innovation. Foster is at his best when solving puzzles like this one; unlike most elite architects, he isn't obsessed with creating his own pure forms. His gift for building a meaningful conversation between new and old architecture became apparent six years ago, with the unveiling of the ...