The page on the left, the verso of the title page, is part of the front matter of the Astronomia Nova. The page contains a defense of Copernican heliocentrism, beginning with a quote from the French humanist Petrus Ramus, who, clearly misled by the ambiguity of the preface of the De Revolutionibus, accuses Copernicus of trying to demonstrate natural phenomena through false causes. Kepler replies that, through the application of physics, the Astronomia Nova will prove that Copernicus demonstrated the veracity of his hypotheses. In the last paragraph, Kepler reveals the identity of the author of De Revolutionibus’ Preface: Andreas Osiander.
The page was partially expurgated for two main reasons. First, it contains the name of an author, [Petrus] Ramus, who had been condemned by the Church: in 1561 Petrus Ramus converted to Protestantism and, after years of persecution, he was murdered two days after the outbreak of the Massacre of St. Bartholomew’s Day in 1572. Secondly, the censor must have agreed with the tone of the preface: he expurgated the lines whereby Kepler criticized the role played by Andreas Osiander in undermining the truthfulness of Copernicus’ hypotheses.