PAUL, a profound mathematician and astronomer, was born at Milan the 13th April 1728; his family had formerly emigrated from Strasbourg, and was established at Milan in an humble station of life.

At the age of fifteen he entered into the convent of the Barnabite friars, or of the congregation of St Paul, where his studies were at first confined to the attainment of some knowledge of geography from the contemplation of the old maps that were pasted on the walls of the galleries; he soon acquired, however, a taste for geometry, and made considerable progress in it without an instructor. He was sent to the university of Pavia to go through a course of divinity, and he did not neglect the opportunity of applying with increased diligence to the mathematics, with the assistance of Professor Olivettazzo. He was afterwards removed to Lodi, in order to give lectures there on philosophy; and he soon after distinguished himself by writing a most able essay on the Figure of the Earth, which, however, he had not the means of printing, as his brethren were unwilling to assist him, until he found a patron for his publication in the Count de Silva, who undertook to be at the expense of the impression. The credit which he acquired induced some other members of the society to follow his example, and the convent of the Barnabites at Milan soon began to be converted into a nursery of mathematics. His reputation procured him also, from the king of Sardinia, the appointment of professor of philosophy in the college of Casale. Here, however, he thought the conduct of his superiors unjust and tyrannical, and they were also dissatisfied with him on account of his great intimacy with Radicati, whose opinions were rather more liberal than they thought it prudent to tolerate. This friendship was, however, so far of advantage to Fristi, as it tended to improve his taste in modern literature; but it was the principal cause of his being removed to Novara, where he was obliged to undertake the duties of a preacher. In the mean time he was nominated a correspondent of the Parisian Academy of Sciences in 1753, and received similar honours from other scientific bodies. Soon after this he was recalled to Milan, and made professor of philosophy in the great Barnabite College of St Alexander in that city. His dissertation on the Figure of the Earth was very acrimoniously attacked by a young Jesuit, who accused him of being improperly led away by English and French innovations; but it was easy for him to repel so unfounded a charge. From this time he entertained much ill humour against the Jesuits in general, and had written a work to depreciate the order, but he was advised by his second brother to suppress it. He became, however, more and more connected with the enemies of the Jesuits, and, among them, with D'Alembert, Condorcet, and the other Encyclopédistes. He had before this time declared himself, in his lectures, an enemy to the popular opinions of the Italians respecting magic and witchcraft, though he felt himself in some danger of the animadversions of the Inquisition. He was much in the habit of frequenting the best societies in Milan, and even more than was thought consistent with his religious character; but he was in some measure emancipated from the restraints of his order, by his appointment, in 1756, to a professorship in the university of Pisa, for which he was indebted to the Grand Duke Leopold. This situation he retained for eight years, enjoying the highest degree of credit, and receiving marked attention from all travellers of distinction, and saving, at the same time, a considerable portion of his salary, to which he added the amount of some prizes which he obtained from Berlin and Petersburg in 1756, and from Paris in 1758. Notwithstanding his occupations as a professor of moral philosophy, he had always been in the habit of devoting the greater part of his attention to the mathematical sciences. In 1757 he was made an associate of the Imperial Academy of Petersburg, and a foreign member of the Royal Society of London; in 1758, a member of the Academy of Berlin; in 1766, of that of Stockholm; and in 1770, of the Academies of Copenhagen and of Berne. The Archduke Joseph had sent him, in 1759, a collar with a gold medal, and he received similar marks of distinction from the kings of Prussia and Denmark. He was also liberally rewarded by Pope Clement XIII. for his services in arranging a dispute between the people of Ferrara and of Bologna on the subject of rivers and torrents, which had been referred to him on the occasion of a tour that he made to Naples and to Rome in 1760. The senate of Venice also made him a proper acknowledgment for the assistance he gave to the commissioners whom they had appointed to control the ravages of the Brenta. The Empress Maria Theresa settled on him a pension of 100 sequins, or L50 a year. He was recalled to Milan in 1764, as professor of mathematics in the Palatine schools, with appointments equal to those which he had enjoyed at Pisa, and with the additional advantage of living near his family, and being enabled to promote their interests. He was at various times much engaged in the decision of controversies respecting canals and rivers, and obtained much credit for his skill and ingenuity; though the peculiarities of his temper tended somewhat to increase the number of enemies, which might possibly have been unavoidable. Among other controversies, he was engaged in a dispute respecting the propriety of adding a high pinnacle to the dome of the church at Milan, which has since been raised in opposition to his opinion. In 1766 he undertook a journey into France and England, and his celebrity everywhere procured him the most flattering attentions. At Paris a very liberal proposal was made to him to remove to Lisbon, but he preferred returning to his own country. In 1768 he went to Vienna, and he was consulted by the government there upon some important questions of ecclesiastical policy, in which his advice was adopted. He remained but little longer in the college of St Alexander, and Pope Pius VI. liberated him entirely from subjection to the superiors of his order, and allowed him to wear the habit of a secular priest. As one of the censors of the press, he had inadvertently been accessory to the publication of the Lanterna Curiosa, the work of a coffee-house club in Milan, which gave great offence to the government; and he afterwards still more imprudently undertook to defend it. This circumstance occasioned his removal from Milan for a time, but he was recalled in 1777, and was appointed director of a school of architecture. He was active in introducing the employment of conductors for security against lightning, and had one fixed for an example on the repository of the public archives. He was equally zealous on every other occasion, in the dissemination of useful novelties among his countrymen. In 1778 he made a tour into Switzerland, and his observations there gave rise to his speculations on subterraneous rivers. He enjoyed uninterrupted health until the age of forty-eight, when he was attacked by a haemorrhoidal affection, ending in an abscess, which, eight years afterwards, required the performance of an operation; this was unfortunately succeeded by a fatal mortification, and he died the 22nd November 1784, at the moment when he was about to be placed on the list of the eight foreign associates of the Parisian Academy; an honour which had been delayed by the preference of J. A. Euler, on the occasion of a former vacancy, to the no small mortification of his vanity. He had very lately obtained a prize from the Academy of Haarlem, for his memoir on the Inequality of the Satellites of Jupiter. He was buried in the church of St Alexander, and a medallion with his portrait was placed over his tomb by his brethren Barnabites. He had four brothers, Antony, a physician, botanist, and chemist; Antony Francis, an ecclesiastic, author of some antiquarian researches of merit; Louis, a canon of St Ambrose, a learned theologian and mechanician; and Phillip, a lawyer, author of a dissertation, De Imperio et Jurisdictione.

The works of Father Paul Frisi are, 1. Disquisitio mathematica in causam figure terrae, Milan, 1751; demonstrating, more completely than Newton had done, the spheroidal figure of the earth. 2. Estratto della storia litteraria d'Italia, Milan, 1753; an answer to a review. 3. Saggio della morale filosofia, Lugano, 1755. 4. Nova electricitatis theoria, Milan, 1755; seems to be the same with a dissertation De existentia et motu etheris, seu de theoria electricitatis ignis et lucis, printed with J. A. Euler's Disquisitio de causa physica electricitatis præmio coronata, 1755, 4to, Petersburg. This dissertation shows some ingenuity, but is by no means established on firm foundations. Among some other fanciful hypotheses, it suggests that light is probably an impulse transmitted by an elastic medium, but not of an undulatory nature. Both these essays seem to have been republished at Lucca, with another by Resaud, under the title of Dissertationes selectae qua ad I. P. academiam, anno 1755, missae sunt, 1757. 5. De motu diurno terrae, Pisa, 1758; a dissertation which obtained a prize from the Academy of Berlin in 1756. 6. Dissertationes variae, 2 vols. 4to, Lucca, 1759, 1761; the first volume containing a geometrical solution of the problem of Precession and Nutation; a Dissertation on the Atmospheres of the Heavenly Bodies, which obtained the prize at Paris in 1758; an Essay on the Nature and Motion of the Ether; the second, a Treatise on the Inequality of the Motion of the Planets, being an enlargement of a prize dissertation which obtained the second premium at Paris in 1760; a Dissertation on the geometrical method of Fluxions, and some Metaphysical Meditations. 8. Piano de lavori per liberare dalle acque, Lucca, 1761; for the use of the provinces of Bologna, Ferrara, and Ravenna. 9. Del modo di regolare i fiumi e torrenti, Lucca, 1762, 1760; Flor. 1770; French, Paris, 1774; especially of the Bolognian and Roman territories, making great use of Guglielmini's works. At the end there is an Elogio di Gabriele Manfredi. 10. Prae- tectio habita Mediolani; 1764. 11. Saggio sopra l'architettura Gotica, Leghorn, 1766. 12. Lettere a M. d'Alembert, Par. 1767. 13. Elogio del Galileo, Leghorn and Milan, 1775; French by Floncel, 12mo, Par. 1767; an elegant specimen of biography. 14. On the supposed Inequalities in the Rotation of the Earth and Moon, Inst. Bologn. vol. v. Op. p. 11 (1787). The same volume contains a prospectus of the work on the Laws of Gravity, p. 514. 15. De gravitate universale libri tres, 4to, Milan, 1768; a work considered as a model of elegance, simplicity, and facility; leaving, however, the fact of the moon's acceleration still unexplained, and even stating doubts of its existence. 16. Della maniera di preservare gli edifici dal fulmine, Milan, 1768; by conductors. 17. De inaequitate motus planetarum, a dissertation which obtained the second premium at Paris in 1768. 18. Melandri et Frisi de theoria lune commentarii, Parma, 1769. 19. Cosmographia physica et mathematica, 2 vols. 4to, Milan, 1774, 1775; this is Frisi's principal work; it contains the substance of the three books on the laws of gravity, with additional matter. It is only superseded by the Mécanique Céleste in point of practical utility, but still retains the advantage of more satisfactory geometrical representation, and less unnecessary complication in the modes of reasoning employed. 20. Dell architectura statica e idraulica, Milan, 1777. 21. A Letter to Meander on the transit of Venus, Atti di Sienna, vol. iv. p. 21 (1771); with some illustrations of the lunar perturbations. 22. Geometrical problems, ib. vol. v. p. 27 (1772); relating to intersections and circles. 23. Elogi di Galileo e di Cavalieri; Milan, 1778; Pisa, 1779. 24. Elogio del Cav. I. Newton, 8vo, Milan, 1778. 25. Elogio del Conte D. Silva, Milan, 1779; anonymous. 26. Elogio di Tito Pomponio Attico, Milan, 1780; a compliment to the Count de Firmian. 27. Opuscoli filosofici, Milan, 1781; denying the fancied influence of the moon on the weather, which Toaldo very unsuccessfully attempted to assert in answer; with dissertations on Conductors, on the effect of Oil on Water, on the Heat of the Earth, and on Subterraneous Rivers. 28. On isoperimetricum maxima et minima, Atti di Sienna, vol. vi. p. 121 (1781); intended as a simpler mode of obtaining the results than that of Euler. 29. A Collection of his Works, in 3 volumes, was begun in 1782, and remained unfinished at the time of his death. The first volume contained Algebra and Geometry; the second, Mechanics and Hydraulics; the third, the Cosmography. 30. Elogio di Maria Teresa, Pisa, 1783; anonymous. 31. Lettera intorno agli studi del Sign. T. Perelli, Pisa, 1784. 33. Elogio di D'Alembert, Milan, 1788; posthumous. 32. An Essay on Arches and Domes, Atti della Società Patriottica di Milano, vol. i. 1783; correcting some statements of Couplet and Belidor.

He left several unpublished works in the hands of his two brothers: 1. On the mediocrity of the Jesuits. 2. Elements of the Cartesian Algebra. 3. Institutions of Mechanics. 4. Of the restoration of the navigation between Milan and Pavia. 5. Institutiones Hydrometriae. 6. Elements of Hydrodynamics. 7. Elements of Hydraulics. 8. Memoirs of his travels in France and England. 9. Lectures delivered at Pisa. 10. Prelectiones de malis spiritibus. 11. Several miscellaneous dissertations.

(Verri Memorie del S. D. P. Frisi, 4, Milan, 1787; Fabbrobi Elogi d'illustri Italiani, Atti di Milano, vol. ii.; Chalmers's Biographical Dictionary, vol. xiv. 8, London, 1814; Aikin's General Biography, vol. x. 4, London, 1815; Guillon in Biographie Universelle, vol. xvii. 8, Paris, 1816.)