1. Galileo's pre-Paduan writings: years, sources, motivations;Drake;Studies in History and Philosophy of Science,1987
2. Galileo was composing commentaries on the Almagest, discussed below. He cited from De Revolutionibus a proposition deriving straight motion from two circular motions, which he used in refuting an opinion of Aristotle's that had nothing to do with astronomy. Galileo's acquaintance with the proposition implies his having read Copernicus with care.