 Not less valuable are the contributions towards a knowledge of the ancient astronomical systems for which we have to thank him in his commentary on the books "de Caelo".We even find in his writings some traces of a disposition for the observation of nature.Although averse to Christianity he abstains from assailing Christian doctrines, even when he combats expressly the work of his contemporary, John Philoponus, directed against the Aristotelian doctrine of the eternity of the universe.