Blaise Pascal was born in Clermont in Auvergne, the son of a government official who was also an enthusiast for the new mathematical learning. With his family, he moved to Paris in 1631, and stayed there until 1638, when his father was forced to flee because of his public opposition to an aspect of Richelieu’s fiscal policy. Blaise was educated privately by his father, who wanted him to be fully conversant with Greek and Latin before introducing him to mathematics: but his prodigy son worked out for himself the principles of geometry as far as the thirty-second proposition of Book I of Euclid at the age of twelve. It was also during this Parisian period that he was able to attend the mathematical academy of Father Marin Mersenne who was actively engaged both in European scientific and philosophical circles and in the religious controversy surrounding the new scientific ideas, as Pascal himself was also to become engaged.

After his father had been pardoned by Cardinal de Richelieu for his dissent and given the office of royal tax commissioner for the province of Haute Normandie, Pascal went with him to Rouen in 1640; in the same year his first mathematical publication, the Essai pour les Coniques (Essay on conical sections), appeared. Two years later he invented a calculating machine, which he had originally conceived to help his father with his tax work; this remarkable achievement was far in advance of the industrial skills required to produce it, although various versions were made and demonstrated to scientific colleagues, prominent politicians and members of the aristocracy.

2 The debate over the vacuum

Between 1646 and 1648, Pascal became embroiled in the fierce European debate concerning the existence of the vacuum. Torricelli’s experiment with a barometer, which involved placing a tube of mercury upside down in a bowl of mercury, had been made public in France by Mersenne in 1644, and had given rise to many competing interpretations. Nearly all of these had recourse to the notion of atmospheric pressure as an explanation, and there was general agreement that the space at the top of the tube contained some kind of rarefied and invisible matter, which was consistent with the Aristotelian adage natura abhorret vacuum.

In 1647, Pascal published his Expériences nouvelles touchant le vide (Experiments on the vacuum); this was the summary of a series of experiments he conducted with Pierre Petit, using variously sized and shaped tubes and different liquids. Through them he was able to determine the quantity of water and mercury that could be supported by air pressure and the size a siphon had to be in order to function. He also set out in this summary the reasons why there was no rarefied and invisible matter occupying the space above the column of liquid supported in the barometer, but did not feel able yet to affirm the existence of a vacuum.

He was challenged in his conclusions by Father Étienne Noel, the Jesuit Rector of the Collège de Clermont in Paris and a proponent of traditional Aristotelian physics; Pascal set out in his reply what are now taken to be the basic principles governing the application of scientific judgment and method. At the same time, he wrote to his brother-in-law Florin Périer to ask him to undertake the experiment of carrying a barometer up a mountain (the Puy-de-Dôme), the results of which showed that the level in the column of mercury varied with height. Pascal confirmed this himself on a church tower in Paris, and published the findings in 1648 in his Récit de la grande expérience de l’équilibre des liqueurs (Account of the great experiment on equilibrium in liquids); he concluded that experiment, not authority, governed physics, that his experiments had shown that nature has no horror of a vacuum, and that air pressure accounts for all the effects associated with said imaginary horror. These experimental writings played an important role in discrediting Aristotelian and scholastic scientific ideas

3 Pascal and Jansenism