  Périer arranged for two similar barometric tubes to be filled with mercury, on 19 September 1648. He left one at the bottom of the mountain, and charged a local friar to keep watch during the day and note any changes in the height of the mercury. Together with other witnesses, Périer climbed the mountain and took readings of the height of the mercury on the mountain top, and subsequently at two intermediate places on their return journey down the mountainside. As expected, the height of the mercury column varied inversely with the height (above sea-level) at which the measurements were taken. When the experimenters rejoined the friar at the bottom of the mountain and compared the measurements on both tubes, they concurred exactly. The friar reported that, throughout the day, there had been no variation in the height of the mercury column that he observed, “despite the fact that the weather was very changeable, sometimes calm, sometimes rainy, sometimes very foggy and sometimes windy” (I, 433). The results of this experiment were published as Récit de la grande expérience de l'équilibre des liqueurs (1648). Pascal concluded, mistakenly, that the experiment guaranteed his interpretation of its results [see below, Section 4].