French mathematician, philosopher, and religious figure. He studied the region above the mercury in a barometer, maintaining that it was a vacuum. In his investigations of the barometer, he found that the height to which the mercury rose was the same regardless of shape. Based on his double vacuum experiment, he formulated Pascal's principle, which states that the pressure is constant throughout a static fluid. He performed an experiment in which he convinced his brother-in-law to climb the Puy-de-Dôme Mountain in France. He found the height of the mercury dropped with altitude, indicating pressure decreases with altitude.

Pascal also designed and built mechanical adding machines, and incorporated a company in 1649 to produce and market them. Unfortunately, the machines were rather highly priced and had reliability problems. Only seven of Pascal's devices survive today.

Pascal suffered from serious health problems, and spent most of his final years writing on religious philosophy.

Additional biographies: MacTutor (St. Andrews), Dublin Trinity College, Bonn