For now, Altaeros is concentrating fully on the turbine in Somerville, the one whose fin has finally finished inflating before me. By now, most of the employees have drifted back to their cubicles in the rear of Greentown Labs. The company helped found this incubator in 2011 for start-ups with a focus on green technology, and it's grown to include 45 of them--many of which have carved out space in the building's cavernous fabrication area. Glass tells me to try lifting the fin, which now bisects the room. It takes one hand and almost no effort--a feat that's to his credit, not mine. "It's light, isn't it?" he asks, beaming with that special sort of pride only inventors can get away with. He picks up the other end, and the future of wind energy, it would seem, floats in our fingertips.