But the movement wasn't doing any harm to the glass, nor to the structural integrity of the building. What it was doing was making life very uneasy for people on the upper floors. The tower, in ordinary wind conditions, was accelerating too fast for comfort. It was doing a sort of cobra's dance, swaying a few inches forward and back and, at the same time, twisting. The two motions were reinforcing each other.
All problems have solutions.
Perhaps the Hancock could have been braced with guy wires, like a ship's mast. But instead a knight arrived on the scene in the person of William LeMessurier, a famous Cambridge engineer. LeMessurier slowed the Hancock's dance by installing something called a Tuned Mass Damper, which he'd just invented for the Citicorp Tower in New York. Here's how the damper works. Two 300-ton weights sit at opposite ends of the 58th floor of the Hancock.