They were blinded by powerful bluish light. The Schloß’s galleries—which served not only as connecting passages, but also as a sort of perimeter defense against the climate—ran around its exterior wall, and had plenty of windows. The low light of the heavy winter sun ricocheted off the ice-crusted snow that covered the dead gardens, filling these corridors with chilly brilliance. An indignant servant slammed the doors behind them to keep the heat in. Leibniz and Fatio began to match each other’s pace down the length of the gallery, moving just short of a sprint. The cold seemed to have dissolved their stockings. It was imperative to keep the knees and calves working.