PLACIDUS,** an eminent astronomer, was born at Achleiten near Linz, in Austria, on the 28th of May, 1720. He received the rudiments of his education in the monastery of Kremsmünster, of which his uncle Alexander was abbot. Here he studied during five years, and delighted so much in drawing straight and curve-line figures, that his mother called him the *almanack-maker*. He went afterward to Salzburg, where he studied a regular course of philosophy, and particularly turned his attention to mathematics under a professor Stuard, whose method of teaching that science was truly extraordinary, as he never made use of any figures, and yet conveyed such a clear idea of every proposition as made it perfectly easy. He was admitted as a novice into Kremsmünster in 1737, and the next year he took the solemn vow in presence of his uncle. After being two years in this monastery, during which time he devoted every leisure hour to the study of mathematics and philosophy, he went to Fixmillner, Salzburg to finish his studies in divinity and jurisprudence, acquiring at that time a competent knowledge of oriental and modern languages, history and antiquities. In the year 1745, he obtained the degree of L.D., after which he received priest's orders in his own monastery, and was created professor of ecclesiastical law, which office he held for 40 years, discharging the duties belonging to it till within a few days of his death. He was also chosen dean of the higher schools, and regent of the young nobility, which he retained during life.

He wrote a commentary on the *Jus Canonicum*, notwithstanding his extensive epistolary correspondence, and the management of the whole business of the monastery; but this work was never published. He was, by the intrigues of his friends, induced to publish his *Reipublicae sacrae origines divinae, seu Ecclesiae Chrifti exterorior junctura, imperium, et hierarchia, ex primigenia ejus institutione eruta et demonstrata*. His commendable diligence procured him universal esteem, but it was his knowledge of astronomy which rendered him illustrious. His uncle Alexander fitted up an apartment for containing the instruments necessary for the dissemination of mathematical knowledge, and he also erected an observatory, which was begun in 1748, and completed in 1758, under the direction of Anfelm Dering of Emdorf, a celebrated architect. While the observatory was building, Fixmillner led a life of retirement and severe study, his favourite subject during these ten years being astronomy. When it was finished, one Dobler, a celebrated mathematician, was appointed first astronomer; but the successors of Fixmillner's uncle having discovered his extensive mathematical knowledge, made him an offer of the astronomical department, and the sole direction of the observatory. This place he accepted in the year 1762, still retaining his chair as professor of ecclesiastical law. He was not yet master of the learning which practical astronomy requires, to remedy which defect he attentively perused Lalande's *Exposition du Calcul Astronomique*, soon after which he obtained the large astronomical work of the same great man, and in 1766 he published his *Meridianus Speculæ Astronomicæ Cremsenensis*, by which he acquired considerable reputation. Ten years after this period he gave the world his *Decennium Astronomicum*, containing many curious and important particulars respecting the theory and practice of astronomy. His *Acta Astronomicæ Cremsenensis*, which did not appear till after his decease, still farther increased his astronomical reputation; and he was a large contributor to many periodical publications in different countries.

He made and collected a number of observations of the planet Mercury, which were at that period both scarce and difficult, the importance of which was publicly acknowledged by Lalande, as they greatly assisted him in constructing his tables of that planet. Fixmillner was one of the first astronomers who calculated the orbit of the new planet Uranus (Georgium Sidus), and his tables respecting it may be seen in the Berlin almanack for 1789. He also proved the truth of what was formerly conjectured, that the 34th star of Taurus, which Flamsteed observed in 1690, was the new planet. It may be said of most philosophers, that they observe a great Fixmilliner great deal, and calculate little, but the conduct of Fixmilliner was exactly the reverse. He turned his attention to the observation of the solar spots more than any of his predecessors, which he noticed in the years 1767, 1776, 1777, 1778, and 1782, from which he deduced important inferences respecting the revolution of the sun on his axis.

He had a genius uncommonly adapted to the study of mechanics, by which he was enabled to invent a new micrometer, and a machine for grinding concentric circles. As an additional proof of his profound inventive genius, he resided in the country, by which means he was in a great measure deprived of literary assistance, yet to the very close of life he was a singular instance of the most indefatigable zeal, diligence, and perseverance. He was little subject to the influence of the turbulent passions;—perhaps less so than most other men. Like the laws of nature, which it was his chief delight to study, he was simple, uniform, and constant; and such were the mildness and integrity of his character, that he could not fail to acquire the love and esteem of mankind. His high reputation never inspired him with vanity, and he rather wished to conceal than to propagate what was written in his praise. It gave general joy to his monastic brethren to celebrate the anniversary of the fiftieth year of his residence in it, which he did not long survive. His health was very much impaired by his intense application, and he finished his career on the 27th of August 1791, in the 71st year of his age.