LESS A THEME AND MORE A MOOD, the saturnine was the tragic muse of the second installment of the Turin Triennial, curated by Daniel Birnbaum. Subtitled “50 Moons of Saturn”—one for each artist included—and spread across three sites, this triennial was symptomatic of a spate of recent exhibitions that seem to have developed feelings in place of concepts. Last year’s group exhibition at Stockholm’s Moderna Museet, “Eclipse: Art in a Dark Age,” and Massimiliano Gioni’s “After Nature” at the New Museum in New York were similarly despondent and dejected, while at the other end of the emotional