Blaise Pascal was unwell 350 years ago. We know this because he told us so, and also that it was for this reason that he was obliged to hand over to his brother-in-law, Florin Perrier, the honour of conducting one of the most significant scientific experiments of all time, ensuring for the latter a modest place in history.
But the underlying hypothesis - that atmospheric pressure decreases with increasing height - was Pascal's alone.
Pascal, of course, is well known in many other spheres. Much of his fame lies in his espousal of the Jansenist cause in 1654, when he retired to the monastery of Port Royal in Paris, adopted the ascetic mode of life, and began to rail against the Jesuits.
In the scientific field, however, he formulated one of the basic theorems of projective geometry, now known as Pascal's Theorem.
He also invented the first mechanical adding machine, and with the mathematician, Pierre de Fermat, he formulated the mathematical theory of probability. And he enunciated Pascal's Law, which states that fluids transmit pressure equally in all directions, and contributed to the development of the differential calculus.
But Pascal's contribution to meteorology rested on his extension of the work of Evangelista Torricelli, who in 1643 had invented the barometer. The instrument consisted of a glass bulb fitted with a neck some 40 inches long; the tube was filled with mercury and inverted into a dish containing more mercury, whereupon it was found that the mercury in the tube fell to a certain level - about 30 inches above the surface of the liquid in the dish - but no further.
Since the space above the mercury in the tube was a vacuum, the only force acting on the liquid must be the "weight" of the air outside, pressing down on the mercury in the dish. Moreover, close observation showed that the height of the column of mercury varied with changes in the weather
Pascal's major contribution to this theory was to infer that if air had "weight" in the way that Torricelli said, this weight should be less at the top of a high mountain than at the bottom, since in the former case less air existed overhead.
Thus it was that on September 19th, 1648, Pascal dispatched his agile relative to carry a mercury barometer up the 5000 ft Puy-deDome, the highest peak of the Massif Central in France.
The expected decrease in atmospheric pressure with height was amply demonstrated when Perrier confirmed that the mercury column was indeed much shorter at the top of the mountain than it had been at the base.