PIAZZI, GIUSEPPE, a celebrated astronomer, was b. at Ponte in the Valteline, July 16, 1746. He was received into the order of the Theatins at Milan in 1764; and studied in that city, and subsequently in the houses of the same order at Rome and Turin. Sum moned to the professorial chair of philosophy at Genoa, he so alarmed the Dominicans by the freedom and boldness of his opinions that he was removed to Malta, where, in 1770, he became professor of mathematics in the newly-founded' university. On the breaking up of this seminary, he returned to Italy, and after teaching philosophy in the nobles' college at Ravenna, he went to Rome, where lie became professor of dogmatic theology in the institution of San Andrea della Valle. He was transferred in 1780 to the chair of mathematics in Palermo, where, with the aid of government, he established an observatory, which was put in working order in 1789. The first results of his obser vations were the rectification of some errors in the estimation of the obliquity of the ecliptic, the aberration of light, the length of the tropical year, and the ,parallax of various heavenly bodies; these results were published in 1792. Piazzi had now attained a European reputation, which was further Neigh cued by his discovery, on the night of Jan. 1, 1801, of a new planet, the first known of the great group of planetoids between
Mars and Jupiter. Piazzi was only able to give a description of it to some of the German and Italian astronomers, when it disappeared; Gauss (q.v.), however, rendered certain the fact of its being a planet. Piazzi named it Ceres, after the ancient goddess of Sicily, to which country he was sincerely attached. In 1803 he published a map of the fixed stars, far superior to any before published, the result of ten years' observations: the work was crowned by the institute of France. In 1814 appeared a new and more com plete catalogue (containing .7,646 stars), for which he was again rewarded with a prize from Vie French institute. He also made researches into the nature of comets, and devoted the later years of his life to the improvement of public education in Sicily. He wrote a number of works, of which, besides the catalogues of stars above, mentioned,. the Lesioni Ielementari di Astronomia (Palermo, 181'7) is the chief. He also wrote mar. memoirs for the various scientific societies of Europe. Piazzi died July 22, 1826, iiet Naples.