Magic is hardly mentioned in the _De naturis rerum_. In a passage, however, telling how Aristotle ordered some of his subtlest works to be buried with him, Neckam adds that he so guarded the neighborhood of his sepulcher “by some mysterious force of nature or power of art, not to say feat of the magic art, that no one in those days could enter it.”[606] But Neckam is a believer in occult virtues and to a certain extent in astrology. He would also seem to believe in the force of incantations from his assertion that “in words and herbs and stones diligent investigators of nature have discovered great virtue. Most certain experience, moreover, makes our statement trustworthy.”[607] He mentions a much smaller number of stones than Marbod, but ascribes the same occult virtues to those which he does name. In the preface to his first book he says that some gems have greater virtue when set in silver than when set in gold. A tooth separated from the jaw of a wild boar remains sharp only as long as the animal remains alive, an interesting bit of sympathetic magic.[608] The occult property of taming wild bulls possessed by the fig-tree which we have already seen noted by various authors is also remarked by Neckam.[609] A moonbeam shining through a narrow aperture in the wall of a stable fell directly on a sore on a horse’s back and caused the death of a groom standing nearby. Out-of-doors the effect would not have been fatal, since the force of the moon’s rays would not have been so concentrated upon one spot and the humidity would have had a better chance to diffuse through space.[610] [Sidenote: Fascination.] After telling of the fatal glances of the basilisk and wolf, Neckam says that fascination is explained as due to evil rays from someone who looks at you. He adds that nurses lick the face of a child who has been fascinated.[611] [Sidenote: His limited belief in astrology.]