Over two nights at Carnegie Hall, the Boston Symphony Orchestra presented the New York premieres of works by Thierry Escaich and Thomas Adès.When orchestras come to Carnegie Hall, their programs typically tell you two things: who they are and what they can do.That was true earlier this season when the Vienna Philharmonic and Christian Thielemann offered authoritative Strauss and Bruckner. Or when the Berlin Philharmonic and Kirill Petrenko opened up the complex worlds of Mahler’s Seventh with coordinated virtuosity. Or when the Los Angeles Philharmonic and Gustavo Dudamel found irrepressible dynamism in blazing scores by Gabriela Ortiz.And over two nights at Carnegie this week, the Boston Symphony Orchestra and its music director, Andris Nelsons, told their story gradually, one piece at a time, in canonical works by Ravel, Rachmaninoff, Sibelius and Mozart. It was only when they unveiled two New York premieres — Thierry Escaich’s “Les Chants de l’Aube,” with the cellist Gautier Capuçon, and Thomas Adès’s “Air,” with the violinist Anne-Sophie Mutter — that they tapped into something special all at once.Among American orchestras, the Boston Symphony’s sound is enviably rich. That opulence was readily apparent in the ceaseless flow of cantabile melodies in Rachmaninoff’s Second Symphony. You could hear it too in the briefest articulations, such as the resonant pizzicatos of Ravel’s cheeky “Alborada del Gracioso,” which on Monday opened the first concert, or the sonorous orchestral stabs on the last page of Sibelius’s Fifth Symphony, which on Tuesday closed the second.The Rachmaninoff often felt like an hourlong showcase for the spacious, burnished tone of the orchestra’s violin section. Nelsons coaxed gorgeous, heart-in-your-throat playing from them in one long-breathed line after another. As if to balance that, the Sibelius symphony was rife with woodwind and brass chorales; the strings don’t even enter until the 18th measure. The ensemble’s new principal horn, Richard Sebring — a longtime Boston Symphony player who recently won the chair after an international search — anchored his section with a glowing, edgeless sound.Nelsons seemed to celebrate one section at a time without employing his full forces — or full imagination — in the standard repertory pieces. Occasionally, an overwhelming plushness traded the vulnerability of Rachmaninoff’s music for invincible solidity. In the final movement, the players relaxed into the piece’s complexity, its romance caught in a swirl of vexed intent. Nelsons took the second movement of the Sibelius, built on a deceptively simple rhythmic unit, at face value, without the pluck, personality or sly contentment others have mined in it. In a piece as graceful and zesty as the Ravel, the slowly accumulating strength of the orchestra could be taken for turgidity.The violinist Anne-Sophie Mutter, left, was the soloist in the New York premiere of Thomas Adès’s “Air.”Fadi KheirIn the two New York premieres, though, Nelsons unleashed the ensemble’s astonishing range of colors to enliven the particular atmosphere of each work.In a program note, Escaich compared his cello concerto “Les Chants de l’Aube” to a stained-glass window. The metaphor isn’t readily apparent; the music doesn’t bring to mind a mosaic of translucent, jeweled tones. If anything, its palette feels cool, foreboding.Escaich might be embodying spiritual forces both good and evil. With a glinting, coppery tone, Capuçon gave the opening phrase — a Baroque homage that nods to Bach’s Invention No. 13 — a cunning flicker of darkness and light. The violins played long notes on high, not unlike the angelic overture to Wagner’s “Lohengrin,” as the horns droned down below. Flutes dipped like swallows, and brasses popped out like goblins. Tubular bells tolled ritualistically. Within this frame, both beatific and ominous, Capuçon’s cello maneuvered: warm, bodily, determined.In that sense, the cello, in both design and execution, was very much the piece’s animating force, passing through light and shadow, and knowing something of both. Escaich wrote cadenzas to link the three movements into a continuous form, and Capuçon emphasized their atmospheric expressivity as opposed to their show-pony virtuosity. The orchestra navigated the shifting meters and watery textures of the second movement with conviction, and Nelsons masterfully plotted the way in which the final movement’s heavenly motif for celesta and harp melted away into a dangerous dance. Jazzy dalliances and an abrupt ending didn’t ultimately detract from the concerto’s absorbing sound world.Adès’s “Air,” by contrast, devotes itself to a single idea — one of fragile beauty — for its 15-minute duration. The way Adès pitches the violin writing high up, almost daring the soloist to sustain it, recalls the extreme tessitura for the soprano role of Ariel in his opera “The Tempest.” This time, though, the effect is serene instead of unnervingly otherworldly.Mutter, who gave the world premiere of “Air” at the Lucerne Festival last year, played at Carnegie with a platinum tone, densely concentrated. The orchestra drew mesmeric circles around her, conjuring a world of glass, as Mutter’s sound irradiated a childlike innocence full of whispered awe.With the sensitivity of an opera conductor who loves his singers, Nelsons consistently scaled the orchestra’s sound to his soloists’ resources. If his rendition of Sibelius’s “Luonnotar” — a tone poem about the mythic creation of the earth and firmament — lacked a cosmic spatial sense, then at least its quiet intensity was of a piece with the soprano Golda Schultz’s rosy tone and haloed high notes; these performers were very much describing, rather than dramatizing, the piece’s world-shattering dimensions. Nelsons cushioned Mutter’s elegantly assured playing with spirited, swift touches in Mozart’s First Violin Concerto, and he matched Capuçon’s dazzling, consuming focus and mercurial coloring. Each collaboration felt natural, intuitive.At times during the Boston Symphony’s performances, the parts were greater than the whole. A textbook reading can be exemplary but also plain. But when this orchestra had a new story to tell, it was full of surprises. More