Gilles Personne de Roberval, a French mathematician, died Oct. 27, 1675, at the age of 73. Roberval is best known for his work in laying the foundation for calculus, with his “theory of indivisibles” (calculus itself would be discovered in the next generation, by Isaac Newton and Gottfried Leibniz). Roberval was also one of the original 7 members of the Royal Academy of Sciences in Paris, which was founded in 1666. And he played an important role in befriending and mentoring the young Blaise Pascal, when Pascal was introduced to the philosophic circle that met once a week in the convent of Marin Mersenne in Paris (others in the circle included René Descartes, Pierre Gassendi, and Pierre de Fermat). When Pascal and Roberval in 1646 heard about the new Italian barometric experiments of Torricelli, Pascal repeated the experiments by filling a glass tube with mercury and inverting it in a bowl of mercury, at which point the mercury fell in the tube to a level of 30″, leaving an empty space at the top. Pascal claimed this space was truly empty, a vacuum. Roberval responded with an ingenious experiment in which he placed a deflated fish bladder in the tube before adding the mercury. When the tube was inverted, the fish bladder swelled up like a balloon, suggesting there might be some kind of rarified air at the top of the tube. But Roberval did not object too much to Pascal’s proposed vacuum, because Descartes was adamant that there could be no void space in nature, and Roberval and Descartes did not get along at all.
We have two works of Roberval in the Library. The first is Aristarchi Samii De mundi systemate (1644), in which Roberval pretends to have found a lost work by Aristarchus, supporting the idea of a sun-centered solar system (third image). In fact, Roberval wrote the work himself, and, with the connivance of Mersenne, passed it off as an ancient treatise. No one was fooled, except perhaps the theological censors at the Sorbonne, where Copernicanism was still under the ban of the Catholic Church.
After the death of Roberval and various other Academicians, the Paris Academy published a number of their manuscripts in a folio volume with the title Divers ouvrages de mathematique de de physique (1693; third image). The table of contents shows the 6 short treatises and 3 letters by Roberval that were included (fourth image).
In 1675, an artist, Henri Testelin, recreated with his brush the moment when King Louis XIV was introduced to his Academy by his minister, Colbert (second image). It is said that the figure at left, behind the globe, is Roberval (detail, first image). We have never seen documentary evidence of this identification, but as a portrait of Roberval, it will do for now. The painting hangs in the palace at Versailles.
Dr. William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to email@example.com.