The spinning wheel drives a cord that is attached to the flyer (the U-shape shown in the lower left corner of this picture).
Grace carefully feeds the raw wool to the bobbin inside the flyer. As the flyer spins, it twists the wool, turning it into a single-ply yard that is gathered up and wound around the bobbin inside the flyer.
While Grace spins, she talks, her voice a gentle, quiet cadence in rhythm with the treadle, wheel and flyer. "The spinning wheel was invented around the time of da Vinci," she says. "He drew a flyer." But, she explained, "The Egyptians used a drop spindle, on which they made finer linen than we can create today."
Later in the day, Grace demonstrated a drop spindle. It's essentially little more than a stick that spins downward, using gravity, while it twists the fiber.