Traitez de l'eqvilibre des liqvevrs, et de la pesantevr de la masse de l'air
Blaise Pascal(1623-1662)
 Pascal’s fame is far greater in the discipline of philosophy because of his work “pensees sur la Religion”, one of the most profound reflections on humanity in the history of thought. Pascal, however, also made great contributions to natural science in the first half of his short life time. As a child genius, he wrote an excellent treatise on the conic theory of Apollonius Pergaeus. It was said that Descartes did not believe the author of this treatise was only a sixteen-year-old boy. Pascal later studied the theory of probability and invented a kind of calculator, the predecessor of the modern mechanical calculator.
 This book, which dealt with pneumatics and hydromechanics was Pascal’s decisive contribution to physics. Pascal learned of Torricelli’s barometer experiment in 1646, and retried this experiment under various height conditions from the top to the bottom of a church tower for two years. In 1648, Pascal, too week to do the experiment himself, had his brother-in-law climb Mt. Puy-de-dome with a barometer to observe the change in mercury column height at different levels. Pascal confirmed that column height and atmospheric pressure decreased in accordance with an increase in height from the foot of the mountain. He also described for the first time how the reading of a barometer was related to changes in weather. These pneumatic studies were recorded in the second half of this book.
 In the first half of this book what is now known as the hydrostatic principle was described as “Pascal’s law”. In this law the pressure applied to fluid in an enclosed vessel pressed with equal pressure on each unit area at right angles regardless of the shape of the vessel. Between two pistons connected through their pipe arrangement, applied pressure and transmitted pressure are in proportion to each sectional area of the piston and the moving distance of the pistons is in inverse proportion. That is the product of pressure times distance is in equal in both pistons. Since then all hydraulically operated machines have been devised on the basis of this law. Pascal established the foundation of modern hydrostatics succeeding Galileo in this study. Following the completion of this study in 1653, Pascal experienced a strong mystic experience and conversion in 1654, after which he devoted the rest of his life to religious thinking.