 One source for Bacon’s methodology in an experimental science has been overlooked by the scholarship. It is clear to all that Bacon made much use of and privileged Ptolemy’s Optics. What has been missed is that Bacon was also influenced by Ptolemy’s methodology in the introductory chapter to the Almagest. The combination there of experience and geometrical reason is in some respects different and more detailed than in Aristotle’s scientific methodology. And so even as Bacon uses Aristotle’s texts, he is employing the methodological assumptions of Ptolemy. 