her hand, she dragged it toward the desk, then beckoned Isaac to it.
It had been years since she last taught schoolchildren; the job as junior librarian at the Atheneum had offered far more than the $25 per annum she’d earned assisting Dr. Hall, not to mention the chance to read anything she wanted. But she missed her students’ hungry minds, powering their wonder with Truth. Her favorite lessons had explained how the Creator had puzzled their world together, the invisible, unbreakable connections among all living things.
She cleared her throat, then drew an old, dusty chronometer from the shelf and blew on it gently before wiping it off with her skirt. Then she put it down on the desk beside the Pearl ’s instrument.
“The chronometer,” she said, tapping it with her quill, “is a precision timekeeping instrument, built for seagoing vessels and used to determine longitude.” Turning the clock over, she unscrewed the small peg that kept it closed, then removed the entire back. Isaac winced, and she pretended not to notice. With sure hands, she removed the winding pin, the spindled gears, the escapement and balance wheel, pausing to admire the beauty of the spiral spring attached to it before laying it, light as a feather, in line beside the other parts.
“In order to keep time, a clock must measure out precise units with no aberration. It needs a source of power”—she paused and tapped the winding pin with her quill—“and it needs to store that power and use it up in small increments, so that it keeps going over a long spell at sea. That’s what these circular gears do.”
He was silent, but she went on, speaking slowly so that he might not miss anything.
“When these gears turn, they trigger this small lever—called the escapement—to move back and forth. This keeps the balance wheel moving, like a pendulum, and the motion of the balance wheel makes the gears rotate. The smaller one spins faster, to measure seconds, and the larger more slowly, to measure hours. The little hands on the clock that tell you the time are attached to these gears. Now, in a normal clock, the period of the balance wheel changes when the temperature changes, because metal expands and contracts with heat. In a chronom eter, this little spiral spring at the heart of the balance wheel is forged from a mix of different metals that expand and contract at different rates, so the balance wheel keeps a constant period, and thus the exact time, at sea. Even when the ship pitches and rolls about, and in any type of weather . ” In conclusion, she tapped her quill on the tabletop like a conductor.
“The time,” he stated, pointing at the chronometer, his eyes narrowed as if he suspected it of trickery.
“Why do you need the time ?”
He nodded, staring at the instrument.
“Well, to determine longitude, of course.” She paused before continuing. “Since the Earth rotates fifteen degrees each hour, one needs to know the time at the home port as well as one’s local time, in order to calculate the ship’s position.” When he didn’t answer, she sank into her own chair. His question hadn’t been about the function of the chronometer, after all; it had been about its purpose.
Hannah slowly replaced the panel on the chronometer and put it back down on the desk. Had he been testing her? Her cheeks burned and she tried to will them cool.
“I wish to learn,” Isaac said. “Can you? Is it possible?” He gestured to the sextant, the telescope, the books, then looked at her directly. “I can pay.”
“You want lessons in navigation? From me?” She repeated each word clearly, so there would be no mistake, waiting for his response before she allowed herself to consider it.
When he nodded, she wondered first where he’d gotten the ambition. Navigation was an officer’s duty, she supposed, and he was indeed now one of them. What came of it should be no matter. Yet she’d never known anyone of his color to advance