Wind off the peaks had torn up the clouds and she saw stars, quickly covered again. The sphere of the heavens revolved from east to west, and so, seen from a motionless Earth, the stars rose in the east and set in the west. But maybe the heavens were at rest and it was the Earth which revolved from west to east, as the long-dead Arethousan astronomers Hipparchia and Aristachius had suggested. That would create the same effect, wouldn’t it? Or perhaps both heaven and Earth moved around the same axis, preserving their observable differences by rotating at differing speeds.
She picked up a rock and threw it into the air, put her hands over her head. It landed with a thunk beside her. Surely if the Earth were in motion, then if she threw a rock with enough force straight up into the air, the motion of the. Earth would carry her away from it before it fell to the ground?
Ai, God, she had to pee again. And by the time she had done with that, her mind had swung back to the most nagging question, the only one that clung to her all the time: Why didn’t she trust them?
Night was not a good time to work through such a complicated tangle of thoughts. And she was tired again; exhaustion always came on suddenly. But she had left a lantern burning and a book out, so she returned to the tower. All was peaceful there, just as she had left it, the lantern burning quietly and the book resting open on the table, a moment suspended in time that roped her thoughts back to where they had been. Certainly she couldn’t throw a rock with enough force to test the theory of the Earth’s rotation. Compared to the heavens, the Earth was tiny, but that didn’t mean that to a human walking its surface it could be quickly traversed. She had seen ships come up over the horizon, sails and masts emerging first; that suggested not only a spherical Earth but one of immense size compared to a single human stride. It seemed to her that she need only find a place where the summer solstice sun at noon cast no shadow when measured against a stick stuck vertically in the ground as a marker. Then she could walk north along that same longitude, measuring her path, and on the next summer solstice sun she need only measure the shadow cast by another vertical marker at a different location. If there was again no shadow, then the Earth wasn’t spherical; but if there was, then she ought to be able to calculate the circumference of the Earth by multiplying the degree of the angle with the distance in leagues between the two points. In The Book of Secrets Da had written of a town far to the south, in sun-raked Gyptos, where St. Peter the Geometer had dug a well so exactly situated that on the summer solstice the Sun’s rays touched its bottom. If she walked north from that point…
“Your thoughts are far from here.”
She jumped and gasped aloud, almost comically, and was relieved to see Sister Meriam standing just outside the threshold, walking stick in her right hand. Liath helped her over the threshold.
“I saw a light,” said Meriam. “You have not woken Brother Severus?”
Liath looked toward the ladder that led to a trapdoor set into the ceiling. “I have been quiet.”