Froidmont's best known books are the two he wrote in answer to a defense of the Copernican position first by Philip Lansberg, then by his son. The _Ant-Aristarchus sive Orbis Terræ Immobilis, Liber unicus in quo decretum S. Congregationis S.R.E. Cardinal. an. 1616, adversus Pythagorico-Copernicanus editum, defenditur_, appeared in 1631 before Galileo's condemnation. The Jesuit Cavalieri wrote to Galileo in May about it thus:[311] "I have run it through, and verily it states the Copernican theory and the arguments in its favor with so much skill and efficacy that he seems to have understood it very well indeed. But he refutes them with so little force that he seems rather to be of an opinion contrary to that expressed in the title of his book. I have given it to M. César. If you wish it, I will have it sent to you. The arguments he brings against Copernicus are those you have so masterfully stated and answered in your _Dialogo_." Nearly a year later, Galileo wrote to Gassendi and Diodati that he had received this book a month before and, although he had been unable to read much of it on account of his eye trouble, it seemed to him that of all the opponents of Copernicus whom he had seen, Fromundus was the most sensible and efficient.[312] Again he wrote in January, 1633, regretting that he had not seen it till six months after he had published his dialogues, for he would have both praised it and commented upon certain points. "As for Fromundus (who however shows himself to be a man of great talent) I wish he had not fallen into what seems to me a truly serious error, although a rather common one, in order to refute the Copernican opinion, of beginning by poking scorn and ridicule at those who consider it true, and then (what seems to me still less becoming) of basing his attack chiefly on the authority of the Scriptures, and finally of deducing from this that in this respect it is an opinion little short of heretical. To argue in this way is clearly not praiseworthy;" for as Galileo goes on to show, if the Scriptures are the word of God, the heavens themselves are his handiwork. Why is the one less noble than the other?[313] [Footnote 311: Ibid: 94.] [Footnote 312: Galileo: _Opere_: XV, 25.] [Footnote 313: Ibid: XIV, 340-341.] Froidmont replied in 1633 to Lansberg's reply with his second attack, _Vesta, sive Ant-Aristarchi Vindex_, in which he laid even more emphasis upon the theological and scriptural objections. Yet, in ignorance of Galileo's condemnation, he considers the charge of heresy too strong. "The partisans of this system do not after all disdain the authority of the Scriptures, although they appear to interpret it in a way rather in their favor." He also, and rightly, denies the existence at that time of any conclusive proof.[314] [Footnote 314: Monchamp: 107-108.]