Astronomer, mathematician, b. at Florence, Italy, 20 March, 1816; d. at Frederick, Maryland, 17 Jan., 1890. He entered the Society of Jesus at Rome on 30 Oct., 1836, and studied at the Roman College where he followed the courses of Father Caraffa, the distinguished professor of mathematics; endowed with mathematical ability, supplemented by keen sight and skill as a draughtsman, he was appointed assistant to Father De Vico, director of the Roman Observatory. He was ordained in 1844, and filled the chair of higher mathematics at the Roman College, when the Revolution of 1848 caused his precipitate flight from Rome; coming to America he lived at Georgetown College, except for a few years, until 1869. He was stationed at Woodstock, Maryland, at the opening of the scholasticate, and remained there until 1884. On account of failing health, he was transferred in 1885 to the novitiate, Frederick, Maryland, where paralysis terminated his career. In astronomy, his principal work is his "Catalogue of Star-Colors", published in his "Memoirs of the Roman College", 1845 and 1847. The second memoir includes the first, and forms the entire catalogue, except the twelve celestial charts that accompanied the first. The Revolution broke out at Rome when the second memoir was in the printer's hands, and prevented the completion of the work. The colour catalogue is important for two reasons: it is the first general review of the heavens for star-colours, embodying the entire B. A. C. catalogue, from the North Pole to 30 degrees south of the Equator; then, as the observations are now about seventy years old (having been made from 1844 to 1846), the "Catalogue" will be invaluable for deciding the question whether there are stars variable in colour. For these reasons it has been republished, with notes, at the Vatican Observatory, as No. III Publications, 1911. It is remarkable how few are the errors of identification, in view of the then existing difficulties, and how closely Sestini's general scale of colours agrees with that of the Potsdam catalogue.

At Georgetown Observatory, in 1850, Sestini made a series of sunspot drawings, which were engraved and published (44 plates) as "Appendix A" of the Naval Observatory volume for 1847, printed in 1853. His last scientific work as an astronomer was the observation of the total eclipse of 29 July, 1878, at Denver, Colorado. A sketch of the corona as it appeared to him was published in the "Catholic Quarterly Review". From his arrival at Georgetown (1848) until his retirement from Woodstock (1884) he had been almost constantly engaged in teaching mathematics to the Jesuit scholastics, and he published a series of textbooks on algebra, geometry and trigonometry, analytical geometry, infinitesimal analysis. These were works of sterling merit, but they never became popular with students or teachers; their severe analytic method was repellent to practical American taste; he had no sympathy with commercial mathematics, and furthermore the make-up of the books was not as attractive as the ordinary high-school and college textbooks. He wrote treatises on natural science for the use of his pupils; some of these were lithographed and others were privately printed at Woodstock: "Theoretical Mechanics" in 1873; "Animal Physics" in 1874; "Principles of Cosmography" in 1878. He founded the American "Messenger of the Sacred Heart" in 1866, and retained editorial control of it until 1885; during these years he was also head director of the Apostleship of Prayer in the United States. He was an indefatigable worker and had many difficulties to contend with in launching and sustaining the "Messenger", and in directing the League of the Sacred Heart, but he was supported in this labour of love by his cheerful disposition and ardent zeal for the glory of God. It was pleasantly said of him that he had two passions---one for pure mathematics, and the other for the pure Catholic religion.

SOMMERVOGEL, Bibliothèque de la C. de J., VII, 1159; Woodstock Letters, XIX, 259; XXX, 99; Messenger of the Sacred Heart, new series, V (1890), 161, 343, 435, 486.

E. I. Devitt.