  Bacon's speculative system is a hybrid based on different sources which provided him with seminal ideas: e.g., atomism, Aristotelianism, Arabic astronomy, Copernican theory, Galileo's discoveries, the works of Paracelsus, and Gilbert. In his theory he combines astronomy, referring to Alpetragius (see Dijksterhuis 1956, 237–43; Rees and Upton 1984, 26; Gaukroger, 2001, 172–5; and see Grant 1994, 533–66, for discussion of the cosmology of Alpetragius), and chemistry (Rees 1975a, 84–5): 