PASCAL Blaise Traitez de l’équilibre des liqueurs et de la pesanteur de la masse de l’air.

Dibner 143; DSB X, 330; Norman 1650; Sparrow Milestones of Science 157; Tchemerzine V, p. 59; Waller 12161.

Posthumous first edition of the treatise recounting Pascal’s discovery of atmospheric pressure, thereby laying the foundations of modern hydrostatics.

Pascal’s research into the weight of air and the vacuum built on Torricelli’s experiments. In 1643, the Italian physicist had discovered that a column of mercury could remain standing in an inverted tube, leaving an empty space above it. Pascal took up these experiments and published his initial observations in 1647 in Les Expériences nouvelles touchant le vide, in which he challenged the traditional explanation of the phenomena as being due to the ‘abhorrence of a vacuum’.

He then sought to establish experimentally that the height of the mercury column varied with atmospheric pressure. On 19 September 1648, at his request, his brother-in-law Florin Périer carried out the famous Puy-de-Dôme experiment: the mercury column, measured at different altitudes, proved to be lower the higher the altitude. The experiment thus provided decisive proof of the role of the weight of air in the equilibrium of mercury and constituted an experimental refutation of this ‘abhorrence of a vacuum’.

Pascal continued his experiments and generalised the results in the two treatises brought together here. Written around 1653, they set out the fundamental principles of the equilibrium of liquids and atmospheric pressure. In particular, Pascal develops what would become Pascal’s principle, the foundation of modern hydrostatics.

However, the work was not published until after Pascal’s death on 19 August 1662. Florin Périer and the scholar’s close associates ensured the publication of his manuscripts by Guillaume Desprez in 1663, making this edition the first printed version of these major research findings.

The significance of this work would extend far beyond the field of hydrostatics: it would help lay the foundations of modern physics relating to pressure, with the pascal (Pa) becoming, nearly three centuries later, the international unit in the International System of Units.

The edition is illustrated with two large fold-out plates depicting the apparatus and experiments described by Pascal.

A fine copy.

Provenance: Chebrou de Lespinats [?] handwritten bookplate on the title page – André Chrétien (bookplate) pasted in.