Other gems suggest stories of Alexander. Near the frontier of India in a valley guarded by deadly serpents whose mere glance was fatal were many precious gems. Alexander disposed of the serpents by erecting mirrors in which they might stare themselves to death, and he then secured the gems by employing the carcasses of sheep in the manner which we have already heard described by Epiphanius.[822] A somewhat similar tale is told of Socrates by Albertus Magnus in his commentary on the pseudo-Aristotelian work on the properties of the elements and planets.[823] In the reign of Philip of Macedon, who is himself described as a philosopher and astronomer, the road between two mountains in Armenia became so poisoned that no one could pass. Philip vainly inquired the cause from his sages until Socrates came to the rescue and, by erecting a tower as high as the mountains with a steel mirror on top of it, saw two dragons polluting the air. The mere glance of these dragons was apparently not deadly, for men in air-tight armor went in and killed them. The same story is told by William of St. Cloud, who composed astronomical tables based upon his own observations from about 1285 to 1321, in which he detected errors in the earlier tables of Thebit, Toulouse, and Toledo.[824] In Peter of Abano’s treatise on poisons,[825] however, although he too cites the Pseudo-Aristotle _On the causes of the elements_, the mirror has become a glass cave in which Socrates ensconces himself to observe the serpents. A _Lapidary_ dedicated to King Wenzel II of Bohemia tells of Socrates’ killing a dragon by use of quicksilver.[826] That Socrates also shared the medieval reputation of Aristotle and Plato for astrology and divination we have already seen from the _Prenostica Socratis Basilei_. [Sidenote: Alexander’s submarine.] Similar to Abano’s tale of Socrates in the glass cave is the story told a century earlier by Alexander Neckam of Alexander himself. So sedulous an investigator of nature was the Macedonian, says Neckam, that he went down in a glass vessel to observe the natures and customs of the fishes. He would seem to have remained submerged for some time, since Neckam informs us that he took a cock with him in order to tell when it was dawn by the bird’s crowing. This primitive submarine had at least a suggestion of war about it, since Neckam goes on to say that Alexander learned how to lay ambushes against the foe by observing one army of fishes attack another. Unfortunately, however, Alexander failed to commit to writing his observations, whether military or scientific, of deep-sea life; and Neckam grieves that very few data on the natures of fishes have come to his attention.[827] We shall hear Roger Bacon tell of Alexander’s descending to see the secrets of the deep on the authority of Ethicus.[828] [Sidenote: Arabian tales of Alexander.]