Clermont-Ferrand

A town in the volcanic Auvergne of central France, dominated by the dark lava-stone of its cathedral, and the birthplace of Blaise Pascal in 1623. It was on the Puy de Dôme above the town that Pascal's brother-in-law, following his instructions, carried a barometer up the mountain and proved the weight of the air, the experiment that made the vacuum respectable.

Clermont sits in the Auvergne beneath a line of extinct volcanoes, and its cathedral is built from the black lava of them. Pascal was born there in 1623 and taught at home by a father who kept mathematics away from him until he worked out geometry on his own. In 1648 he had his brother-in-law carry a barometer up the Puy de Dome above the town and record the mercury falling with every stage of the climb, which settled a question philosophers had argued for two thousand years.