Orazio Grassi, S.J. (b. Savona 1 May 1583 – d. Rome 23 July 1654), was an Italian Jesuit priest, who is best noted as a mathematician, astronomer and architect. He was one of the authors in controversy with Galileo Galilei on the nature of comets. His writings against Galileo were published under the pseudonym Sarsi. Early life Grassi was born in Savona, then part of the Republic of Genoa. He entered the novitiate of the Society of Jesus at the Church of Sant'Andrea al Quirinale in Rome in 1600. Following his profession of his first religious vows in 1603, he began studies at the Roman College, there taking courses in philosophy, theology and mathematics. Among his professors were the noted German Jesuit mathematicians, Christopher Clavius, Christoph Grienberger and Odo Van Maelcote. He continued his studies there until 1610. In 1614 Grassi was assigned to serve as Jesuit college in Genoa in the capacity of assistant Master of novices. He served in that position for two years, before being named as to the faculty of the Roman College as a professor of mathematics. During that period, his research focused on pure mathematics, as well as on optics and architecture. In 1617 he published a series of lectures he had given on the eye, , under the pseudonym of Galeazzo Mariscotto, as well as the . He pronounced solemn vows in the Society in 1618, at which time he received Holy Orders as a priest, following which he was given the chair in mathematics. He held this position until 1628. Dispute with Galileo Early in 1619, under the title "", Grassi published a lecture he had given to the Collegio Romano about three comets which had appeared in the autumn of 1618. He argued that the absence of parallax meant that the comets must be very distant from the Earth, and he suggested that they existed beyond the moon. Galileo received a copy of Grassi's lecture and was very angered by it. The notes he scribbled in the margin of his copy are full of insults— ('piece of utter stupidity'), ('buffoon'), ('wicked idiot'), ('bumbling idiot'). Galileo responded with his Discourse on Comets, which was a rebuttal of many of the arguments, advanced by Grassi, but originally made by Tycho Brahe. It suggested that the absence of parallax with comets was due not to their great distance from the Earth, but to their