Adrian reached into his backpack, this time beneath the manila folder, and retrieved a small but heavy electronic device, about the size of a hardcover book. It had a screen on one side next to a panel of knobs and buttons. He had been careful during the six-mile ride from Medford not to hit any potholes or bumps that might damage the thing; Professor Vladimir Gregor, one of the heads of the electrical engineering department at Tufts, had assured him it was much more expensive than it looked.

Gregor had been surprisingly helpful when Adrian visited him in his engineering lab earlier that day, even though Adrian had done his best to hold back as much information as he could. Not because he didn’t trust Gregor, who was one of the few members of the faculty Adrian found serious enough to call a friend. But precisely because Gregor shared his sensibilities and might very well have laughed him right out of the engineering lab if he’d known the full, absurd-sounding truth.

Adrian had shown Gregor the engraving, which was unavoidable—and Gregor had only needed to look at the picture for a moment before he’d actually gotten excited. The wineglasses, he’d exclaimed, lined up like that in front of the bell—you see what they are, don’t you? And then he’d explained—the wineglasses were an ingenious if primitive version of the device that Adrian now held in his hands.

“What the hell is that?” Bevil asked. “You’re not going to damage the bell, are you? Because that’s gonna cost you way more than fifty bucks.”

“I’m not going to damage it. I’m just going to measure it. This is a spectrum analyzer. It measures sounds—tonal frequency, lengths of acoustic waves. Creates a pattern that can be understood mathematically.”

Adrian was saying words he barely understood himself. But Gregor had been sure. In the engraving, Paul Revere had set up the wineglasses to measure the waves of sound coming off the bell. Although when a bell was rung, the human ear translated the varying frequencies given off by the curvature of the metal as a single tone, the math behind what one was hearing was much more complex. Rising and falling sine curves representing the frequency of the sound waves.

In the engraving, Gregor had explained, the surface of the wine in the glasses would have rippled because of those waves. Where each wineglass was positioned, combined with how much liquid was in each one and the shape of the glasses themselves—would capture those waves differently, giving you a surprisingly precise measure of the length of the waves. The distance between each ripple could be calculated, and with that information, you could reconstruct the sound you were hearing mathematically. At least you could if you were brilliant at such things, like Gregor—or Paul Revere.