One of the decisive confirmations of the influence of atmospheric pressure was given by the so-called "void within a void" experiment, successively performed in 1648 in several variants by Gilles Personne de Roberval, Adrien Auzout, Blaise Pascal, the members of the Accademia del Cimento and Robert Boyle. They discovered that, if Torricelli's experiment was performed in a vacuum, the mercury would not remain in the vertical tube, but would descend completely into the basin. They also observed that, when air was allowed back in, the mercury rose back up the tube. To confirm Torricelli's experiment, Blaise Pascal devised a conclusive proof in 1648. He had a barometer carried to the top of the Puy de Dôme, in the Massif Central in France, where the level of the mercury column fell to a few inches lower than at normal ground level. Pascal correctly interpreted this variation as a result of the lowering of air pressure at higher altitudes.