They race up and down in Spider-Man sneakers, flip-flops, and sparkly shoes like Dorothy’s from The Wizard of Oz. With each step, a different tone — maybe a flute, an oboe, or an animal call — rings out from a black Bose speaker suspended above the staircase. I’m at Boston’s Museum of Science watching children climb the famous musical stairs, a sound installation designed by artist Christopher Janney that has filled visitors’ ears since 1989. Each step — I counted 15 — has a sensor on one side that sends an invisible infrared-light beam to a reflector on the other side. When no one’s on the stairs, beams bounce off the reflectors and return to the sensors. But walking up and down the steps breaks the beams, sending signals to a computer to generate different tones. (They are programmed to be consonant but are otherwise randomized, so good luck trying to play “Call Me Maybe.”) Watching all the climbing and descending, I’m reminded of the many joys of discovery and of how empowering it can feel to turn silence into music.