To the year 1648 belongs one of the dramatic experiments of the scientific revolution. F. Perier, brother-in-law of Blaise Pascal by whom the experiment had been proposed to him, climbed the Puy-de-Dôme in Auvergne bearing some glass tubes and a quantity of mercury. He found as he ascended the mountain that at each successive station the height of the mercury in his barometer was less, until at the summit it stood at only 23 inches. This was ocular testimony to the truth of the view that the column of mercury within the barometric tube was supported by the pressure of the atmosphere outside the tube: the column fell as it was carried higher in the ocean of air, so reducing that pressure. The phenomenon itself had been discovered in Italy; there was nothing very original in Pascal's prediction that the height of the mercury would decrease above sea-level; the experiment to test it was simple in the extreme. Yet it had not been made before, it was made in France, and it was widely publicised. It was characteristic of the time that it should be so, for this was the peak of one of the great creative periods in French science. The transformation of science had been first undertaken in Italy and in Germany; religious fanaticism had stultified the promising renaissance of the sciences in the Paris of the mid-sixteenth century and postponed to the reign of Louis XIII the development of anti-Aristotelian philosophy, the pursuit of the great Copernican debate, and the introduction of experimental inquiry. From this time, however, as in politics, manners and the arts of civilisation Paris became the arbiter of Europe, so in science France rose to a commanding position, to retire in turn before the challenge of English empiricism.