Astronomer, b. at Achleuthen near Kremsmünster, Austria, in 1721; d. at Kremsmünster, Austria, 27 August, 1791. He received his early education at Salzburg, where he displayed a talent for mathematics. He joined the Benedictines at the age of sixteen and became distinguished for his broad scholarship. In 1756 he published a small treatise entitled "Reipublicæ sacræ origines divinæ". He intended to continue this work but the transit of Venus in 1761 again aroused his interest in mathematics. Though already forty years of age he resumed his old studies with ardour, and an opportunity soon presented itself for work in astronomy. He was appointed director of the observatory of Kremsmünster, which had been established by his uncle in 1748 while abbot. His first task was to improve the equipment and have new instruments constructed, and as soon as possible he determined the latitude and longitude of the observatory. He continued in charge of the observatory until his death and by his industry accumulated a number of observations of great variety and value. He did not, however, devote all his time to astronomy. For many years he was in charge of the college connected with the abbey and at the same time acted as professor of canon law. As such he was honoured with the dignity of notary Apostolic of the Roman Court. Fixlmillner is best known for his work in astronomy. He was one of the first to compute the orbit of Uranus after its discovery by Herschel. His numerous observations of Mercury were of much service to Lalande in constructing tables of that planet. Besides the treatise already mentioned he was the author of "Meridianus speculæ astronomicæ cremifanensis" (Steyer, 1765), which treats of his observations in connexion with the latitude and longitude of his observatory, and "Decennium astronomicum" (Steyer, 1776). After his death his successor P. Derfflinger published the "Acta cremifanensia a Placido Fixlmillner" (Steyer, 1791), which contain his observations from 1776 to 1791.
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