<P> In 1687, Isaac Newton published Philosophiæ Naturalis Principia Mathematica, which provided an explanation for Kepler's laws in terms of universal gravitation and what came to be known as Newton's laws of motion . This placed Heliocentrism on a firm theoretical foundation, although Newton's Heliocentrism was of a somewhat modern kind . Already in the mid-1680s he recognized the "deviation of the Sun" from the centre of gravity of the solar system . For Newton it was not precisely the centre of the Sun or any other body that could be considered at rest, but "the common centre of gravity of the Earth, the Sun and all the Planets is to be esteem'd the Centre of the World", and this centre of gravity "either is at rest or moves uniformly forward in a right line". Newton adopted the "at rest" alternative in view of common consent that the centre, wherever it was, was at rest . </P> <P> Meanwhile, the Church remained opposed to Heliocentrism as a literal description, but this did not by any means imply opposition to all astronomy; indeed, it needed observational data to maintain its calendar . In support of this effort it allowed the cathedrals themselves to be used as solar observatories called meridiane; i.e., they were turned into "reverse sundials", or gigantic pinhole cameras, where the Sun's image was projected from a hole in a window in the cathedral's lantern onto a meridian line . </P> <P> In 1664, Pope Alexander VII published his Index Librorum Prohibitorum Alexandri VII Pontificis Maximi jussu editus (Index of Prohibited Books, published by order of Alexander VII, P.M.) which included all previous condemnations of heliocentric books . </P> <P> In the mid-eighteenth century the Church's opposition began to fade . An annotated copy of Newton's Principia was published in 1742 by Fathers le Seur and Jacquier of the Franciscan Minims, two Catholic mathematicians, with a preface stating that the author's work assumed Heliocentrism and could not be explained without the theory . In 1758 the Catholic Church dropped the general prohibition of books advocating Heliocentrism from the Index of Forbidden Books . The Observatory of the Roman College was established by Pope Clement XIV in 1774 (nationalized in 1878, but re-founded by Pope Leo XIII as the Vatican Observatory in 1891). In spite of dropping its active resistance to Heliocentrism, the Catholic Church did not lift the prohibition of uncensored versions of Copernicus's De Revolutionibus or Galileo's Dialogue . The affair was revived in 1820, when the Master of the Sacred Palace (the Church's chief censor), Filippo Anfossi, refused to license a book by a Catholic canon, Giuseppe Settele, because it openly treated heliocentrism as a physical fact . Settele appealed to pope Pius VII . After the matter had been reconsidered by the Congregation of the Index and the Holy Office, Anfossi's decision was overturned . Pius VII approved a decree in 1822 by the Sacred Congregation of the Inquisition to allow the printing of heliocentric books in Rome . Copernicus's De Revolutionibus and Galileo's Dialogue were then subsequently omitted from the next edition of the Index when it appeared in 1835 . </P>

Who was not a proponent of the heliocentric model of the solar system