From Lucretius, Laertius, and _other ancient writers, he undertook to frame a consistent scheme of Epicurean doctrine, in which the phenomena of nature are immediately derived from the notion of primary atoms. But he was aware of the fundamental defect of this system, and added to it the important doctrine of a divine superintending mind, from whom he conceived the first motion and subse quent arrangement to have been derived, and whom he regarded as the wise gover nor of the world. He strenuously main tained the atomic doctrine, in opposition to the fictions of the Cartesian philoso phy, which were at that time obtaining great credit ; and particularly asserted, in opposition to Des Cartes, the doctrine of a vacuum. On the subject of morals, he explained the permanent pleasure or in dolence of Epicurus, in a manner per fectly consistent with the purest precepts of virtue. In the year 1628, Gassendi, for the sake of exte tiding his acquaintance with the learned, visited Holland, where his philosophical and literary merit soon procured him many admirers and friends. 'While he was in that country he wrote an elegant and judicious apology for his friend, the learned Mersenne, in reply to the censures of Robert Fludd, on the subject of the Mosaic philosophy. After his return to France, he continued his philosophical, and particularly his astro nomical studies, pursuing, with great care, a series of celestial observations, in order to complete his system of the hea vens. Being called by a law-suit to Pa ris, he there formed an acquaintance with the men most distinguished for science and learning in that capital, and by his agreeable manners, as well as reputation, secured the esteem of persons of high rank and quality, and in particular of Car dinal Richelieu, and of his brother the Cardinal of Lyons. Owing to the appli cation and interest of the latter, in the year 1645, Gassendi was appointed re gius-professor of the mathematics at Pa ris. This institution being chiefly in tended for astronomy, our author read lectures on that science to crowded audi tories, by which he acquired great popu larity, and rose to high expectations.— But the fatigues of that appointment were more than his strength, already re duced by too intense application, was able to bear ; and having caught a cold, which brought an inflammation upon his lungs, he was obliged, in the year 1647, to quit Paris, and to return to Digne for the be nefit of his native air. After having his health in some measure re-established by the intermission of his studies, in the year 1653 he returned again to Paris, where he published the lives of Tycho Brahe, Copernicus, Purbach, and Regiomonta nus ; and then resumed, with as much in tenseness as ever, his astronomical la bours. His feeble state of health, how ever, was now unequal to such exertions, which brought on a return of his disor der: under which, with the aid of too copious and numerous bleedings, he sunk in 1655, when in the sixty-third year of his age. A little before he expired, he desired his secretary to lay his hand upon the region of his heart ; which when he had done, and remarked on the feeble state of its pulsation, Gassendi said to him, " You see how frail is the life of man !" which were the last words he ut tered. He is ranked by Barrow among
the most eminent mathematicians of the age, and mentioned with Galileo, Gilbert, and Des Cartes.
His commentary upon the tenth book of Diogenes Laertius affords sufficient proof of his profound erudition, and his deep skill in the languages.
We have already mentioned his oppo sition to the philosophy of Des Cartes, by which he divided with that great man the philosophers of his time, almost all of whom were either Cartesians or Gas sendists. At one time a coolness took place between those two eminent charac ters, in consequence of irritating expres sions which had escaped from both their pens, during the course of their philoso phical warfare. The Abbe d'Estrees, af terwards Cardinal, with the design of bringing about a reconciliation between them, invited them both to dinner, in company with many of their common friends, among whom were father Mer Roberval, the Abbe de Marolles, &c. At the time fixed, all the expected guests made their appearance, excepting Gassendi, who, during the preceding night, had been attacked by a severe complaint, which prevented him from venturing abroad. As the cause of his absence was explained after dinner, the Abbe d'Estrees carried his whole com pany along with him to Gassendi's apart ments, where they had the pleasure of hearing the two philosophers make mu tual acknowledgments of their improper warmth and irritability, and generously declaring, that whatever difference in opinion might afterwards subsist between them, it should produce no unfavourable effect upon their friendship.
Gassendi was the first person who ob served the transit of Mercury over the sun. Kepler had predicted that it would take place on the 7th of November, 1631. Gassendi, who was then at Paris,made due preparations to observe it, and after hav ing for some time mistaken the appear ance of that planet for a solar spot, be came at length sensible of his error by the rapidity of its movement ; and took care to calculate the time of its egress from the sun's disk, as well as its distance from the sun's vertical point.
From Gassendi's letters, it appears that he was often consulted by the most celebrated astronomers of his time, as Kepler, Longomontanus, Snell, Hevelius, Galileo, Kircher, Bulliald, and others ; and his labours certainly entitle him to a high rank among the founders of the re formed philosophy. possessed a large and valuable library, to which he added an astronomical and philosophical apparatus, which, on account of their ac curacy and worth, were purchased by the Emperor Ferdinand III. and after wards deposited, with other choice collec. tions, in the Imperial Library at Vienna. The MSS. which he left behind him, and the treatises formerly published by him self; were printed together, accompanied by the author's life, and published by Sorbiere, in six volumes folio, 1655.— They consist of the philosophy of Epicu rus ; the author's own philosophy ; as tronomical works ; the lives of Periesc, Epicurus, Copernicus, Tycho Brahe, Purbeck, Regiomontanus, John Muller, &c. a refutation of the meditations of Des Cartes ; and epistles, and other treatises.