GASSENDI (GASSEND), PIERRE (b. Champtercier, France, 22 January 1592; d. Paris, France, 24 October 1655), philosophy, astronomy, scholarship.

    illuminate it by making the earth revolve around the sun on the Copernican hypothesis.

Galileo explained his theological position in relation to science in 1615 in his letter to the grand duchess of Florence, Christine of Lorraine. The argument was immediately and widely disseminated, and Gassendi undoubtedly saw it at Aix. It was published in Latin in Strasbourg as early as 1635,6 although in response to the condemnation of 1633. Descartes's opposition also obliged Gassendi to take “precautions.” The word is Mersenne's, who, by publishing the Cinquièmes objections had provoked the dispute with Descartes. He spoke of precautions in praising Gassendi's works in a letter to Rivet (8 February 1642).7 That was precisely the date on which Gassendi undertook a new draft of his Epicurean works. Gassendi may probably have made these modifications in order to persevere in the same project, not to remove ambiguities or to modify it in some unexpected way. Mersenne gave his approbation to the earlier version, while expressing satisfaction with improvements in the new edition. Freethinkers were the only ones who judged differently and for their own reasons: they hoped that this physics would teach man to dispense with metaphysics.8

Was such a result what Gassendi wished? Not at all. In the seventeenth century it was possible to conceive of God's having created the universe in a single stroke, but after a model that permits the most convenient analysis. The “fable du monde,” which Descartes imagined to be separate from dogma without contradicting it, played a finalist role despite its author's intentions. The atomic model could be employed in the same fashion. An admirer of Gassendi, the physician Deschamps, asked whether, without impiety, one could say that.9

Gassendi's influence on epistemology may now be stated more precisely. Koyré summarized it by saying that Gassendi contributed to the new science “the ontology that it needed.”10 In order to eliminate “powers” and “acts,” “accidents” and “qualities,” whether occult or not, it was necessary to suppose fixed and measurable data in a medium that in no way influences what is observed. Such are the atoms, endowed with shape, solidity, impenetrability, and a natural tendency to motion, which is weight. Such is the void in which bodies move without interference and without any change occurring in their nature through mere endurance. Time does not “eat away” at things; rather their mechanical and spatial relations change in the course of time. Contrary to the Scholastic view, space and time are neither substance nor accident. They exist when their content disappears and when nothing is happening. They establish the general frame of any knowledge of reality—with atoms redividing in a homogeneous void and moving in the unalterable course of time. Gassendi was one of the first to state this universal, categorial law of space and time.

Despite his influence on the ontology of classical physics, Gassendi's scientific successes were not of the first rank. He owed what he achieved to his fidelity to the Democritean schema. Thus his study of Parhélies (1630) suggests a corpuscular explanation of light. His patient and thorough method made him a pioneer of observational astronomy, in which field Galileo had already set the example in 1610.11 But the observations, which almost fill the fourth volume of his Oeuvres, could serve only as a model for his contemporaries without leading him to any major discovery. For example, he corrected the geographical coordinates acknowledged for use in navigation in the Mediterranean, and he rejected the discovery of Jupiter's new satellites announced by de Rheita in 1643.

The observation of the transit of Mercury, in which he alone was successful and which confirmed Kepler and, indirectly, Copernicus, caused widespread discussion. Koyré, however, reproaches him for having disregarded the mathematical form that enabled Kepler to determine the elliptical orbits of the planets.12 Numerous sketches of various aspects of Saturn did not suggest to him the ring hypothesis, which Huygens proposed in 1659 without access to information that was much superior. Gassendi remained a prisoner of what the senses, even when fortified, are able to show. The Cours of 1644 at the Collège Royal (published in 1647) prudently presented Tycho Brahe together with Copernicus, while leaning sufficiently toward the latter to shock J.-B. Morin. In the De proportione qua gravia decidentia accelerantur of 1645, as in the De motu impresso, Gassendi defended—against the criticism of Le Cazre—the law of freely falling bodies, in which velocity is proportional to the square of the time elapsed and not to the distance traversed. But he never understood the importance of its having been deduced either from simple observations of motion on an inclined plane or in any other way.

In 1654 Gassendi joined to his other lives of astronomers the Life of Copernicus, in which the trial of Galileo, although not omitted, is barely mentioned. He thus insisted on the hypothetical and mathematical character of Copernicus' work, whereas in 1647 the Institutio astronomica had explained the condemnation of Galileo by considerations relating to Galileo himself, but presenting no objections to Copernicus' theories.13 It is further worth noting that Gassendi followed Galileo in the error of regarding