A DOUBLE TRIANGLE is the haunting refrain that runs through "The Rising of a New Moon: A Century of Tabwa Art" at the Museum of African Art.

Like most symbols, it's deceptively simple, a double-helix of a sign that has embodied an entire world view and cosmology for the Tabwa people, who live in parts of Zaire and Zambia along Lake Tanganyika.

Two triangles, joined to form a diamond, signify the rising of the new moon or balamwezi. The balamwezi motif is repeated over and over again in wooden ancestor figures, jewelry, musical instruments, baskets and thrones. At one time, Tabwa men would even braid their long hair into this motif, and women's skin would be decorated with similar scarification.

Balamwezi stands for renewal. As described by guest curator Allen Roberts, i's the renewal one finds "after the two nights of total darkness prior to the new moon." During those dark nights, he says, the Tabwa assume that sorcerers and, quite rightly, lions, are going to jump out of the darkness at them.

"The moon has two faces of the same reality -- the moon you see and the moon you don't see," explains Roberts. "When you don't see it, it is denying its light, allowing men to be subjected to these dangers. When it shines, it allows people to see danger."

An anthropologist, Roberts lived with the Tabwa for four years and helped organize this show for the University of Michigan Museum of Art. The exhibit is said to be the first comprehensive study of Tabwa art.

For the Tabwa, the chief possesses a fearful symmetry of good and evil. The light of the moon is likened to the positive side of the chief; the darkness is his evil side, for he's the greatest of sorcerers.

The Tabwa belief in the duality of things has been expressed in the way they decoratively scarred their bodies down the middle. And in the way they still lay out a town on either side of a central avenue. And even in the way they see the sky: They look up and see the Milky Way splitting the universe in half.

During a period of political reorganization in the mid-18th century, Tabwa chiefs legitimized their growing power through the use of thrones and ancestor figures they commissioned to be carved. There are a number of such figures among the 80 items in the show, undeniably powerful male figures with axes and staffs, and carved headdresses that make them appear taller and fiercer.

But nature has done them an unspeakable indignity. Because the wooden figures were kept on low benches in shrines, insects were able to make their way up to the figures' feet. And the nibbling reduced their feet to stumps.

Untouched by insects, a chief's throne here is an artistic tour de force. On the high back of the low-slung chair twists a snake that stands for earth spirits that only the chief can contact. The snake is superimposed on a network of balamwezi, arranged in tilting rows that imply movement.

The chiefs' commissions stirred a flourish of Tabwa arts that continued until the 1920s, by which time European colonizers had imposed a new order. There was a change, says Roberts, from a collective community to a personal one. Old art traditions were no longer relevant to the individual trying to earn a living.

But Roberts dismisses as purely American the idea of mourning the loss of such art forms: "We shouldn't feel bad they are not made anymore. They're not useful anymore. It's not that creativity died. It's just that now the focus is on the individual.

"African art is like anybody else's art, it's always changing," says Roberts.

And he points to a modern basket here, an object central to a modern possession cult that focuses on the individual. Balamwesi, the rising of the new moon, persists as the artistic motif. But the basket looks like just another very well-made household article, when compared to the powerful ancestor figures. Despite their lack of footing.

THE RISING OF A NEW MOON: A CENTURY OF TABWA ART -- At the Museum of African Art through March 17.