But what is most impressive is the frequent citation from Euclid and Aristotle, especially the latter. Not only the logical treatises are cited, but also the _History of Animals_[573] and the _Liber Coeli et Mundi_, while allusion is also made to Aristotle’s opinions concerning vision, motion, melancholy, waters, and various astronomical matters.[574] Such passages--as well as the fact that commentaries on Aristotle are ascribed to Neckam--suggest that Roger Bacon was mistaken in the much-quoted passage in which he states that the works of Aristotle on natural philosophy were first introduced to the medieval (Latin) learned world in Latin translations by Michael Scot about 1230. Neckam perhaps cites the _History of Animals_ indirectly: at any rate he makes little use of it; but his numerous mentions of Aristotle’s views on nature make it evident that “the truth of Aristotelian” doctrine is already known in the twelfth century. And he already regards “the most acute Aristotle” as the pre-eminent authority among all philosophers. After stating that “all philosophers generally seem to teach” that the planets move in a contrary direction to the firmament like flies walking on a rushing wheel, Neckam adds a number of objections to this view, and adds, “It therefore was the opinion of Aristotle, the most acute, that the planets moved only with the firmament.” He then expresses his amazement that the other philosophers should have dared to oppose Aristotle, should have presumed to set their opinions against so great a philosopher. It is as if a peacock spread its spotted tail in rivalry with the starry sky, or as if owls and bats should vie with the eagle’s unblinking eye in staring at the mid-day sun.[575] [Sidenote: Use of recent authors.] That Neckam had some acquaintance with Arabic and Jewish writers is indicated by his citing Alfraganus and Isaac. Of Christian writers of the century before him Neckam quotes from Hildebert, and four times from Bernard Silvester. He cites the _Pantegni_ or _Tegni_ of Constantinus Africanus more than once.[576] He does not mention Adelard of Bath by name but in discussing experiments with vacuums repeats the experiment of the water jar. In another chapter he states that, if the earth were perforated, an enormous weight of lead would fall only to the center. Neckam’s chapter on “Why in the same earth plants grow of contrary effects” is similar to the third chapter of the _Natural Questions_ of Adelard, and his chapter on “Why certain animals ruminate” is like Adelard’s seventh in the same work.[577] [Sidenote: Contemporary opinion of Neckam.]