On the morning we started work, I was surprised to see that Sam’s equipment consisted of a tape measure and a fishing line with a lead sinker hanging from the end of it.
“Where’s your hook?” I asked, wondering if he had decided to have a day’s fishing on the near-by river.
He gave me a long-suffering look. “This is a plumb bob,” he explained. “It is attached to what is called a plumb line.” He spoke slowly and clearly as if to a child. “As the bottom of many of the big balls are underground, and it would take too long to dig them out, we will use the plumb bob to measure their diameters to find out if the balls are perfectly round. See?”
“Of course,” I said at once, although I didn’t see at all.
I still don’t see, although for many days I watched Sam performing incredible gyrations with plumb line dangling from one hand and tape measure clutched in the other, while I ran around blindly jotting down figures.
The first site we tackled contained three enormous stone balls, and after several hours of mysterious computations, Sam pronounced all three to be six feet in diameter and practically perfect spheres.
“Good,” I said with relief, as the temperature had reached 94 degrees and my head ached. “Let’s go home and have a cold drink.”
“Not at all,” said Sam. “As long as the diameters don’t show any variation, we’d better take the circumferences.”
“Why?” I asked, which is the word I use most frequently on archaeological trips.
Sam sighed. “Because anything that is six feet in diameter must be almost twenty feet in circumference, and errors will therefore be more easily detected.”
This time I swallowed the “why” because I recognized that no explanation would make a mathematician of me. So we enlisted the aid of two workmen to help hold the tape.