But this arrangement was not comprehensive enough; for, as Burton adds, “no place was void, but all full of spirits, devils, or other inhabitants; not so much as an haire-breadth was empty in heaven, earth, or waters, above or under the earth; the earth was not so full of flies in summer as it was at all times of invisible devils.” Pneumatologists, therefore, made two grand distinctions of demons; there were celestial demons, who inhabited the regions higher than the moon; while those of an inferior rank, as the Manes or Lemures, were either nearer the earth, or grovelled on the ground. Psellus, however, “a great observer of the nature of devils,” seems to have thought, that such a classification destroyed all distinction between good and evil spirits: he, therefore, denied that the latter ever ascended the regions above the moon, and contending for this principle, founded a system of demonology, which had for its basis the natural history and habitations of all demons. He named his first class _fiery devils_. They wandered in the region near the moon, but were restrained from entering into that luminary; they displayed their power in blazing stars, in fire-drakes, in counterfeit suns and moons, and in the _euerpo santo_, or meteoric lights, which, in vessels at sea, flit from mast to mast, and forebode foul weather. It was supposed that these demons occasionally resided in the furnaces of Hecla, Etna, or Vesuvius. The second class consisted of aërial devils. They inhabited the atmosphere, causing tempests, thunder and lightning; rending asunder oaks, firing steeples and houses, smiting men and beasts, showering down from the skies, stones[64], wool, and even frogs; counterfeiting in the clouds the battles of armies, raising whirlwinds, fires, and corrupting the air, so as to induce plagues. The third class was _terrestrial devils_, such as lares, genii, fawns, satyrs, wood-nymphs, foliots, Robin good-fellows, or trulli. The fourth class were _aqueous devils_; as the various description of water-nymph, or mermen, or of merwomen. The fifth were _subterranean devils_, better known by the name dæmones itallici, metal-men, _Getuli_ or Cobals. They preserved treasure in the earth, and prevented it from being suddenly revealed; they were also the cause of horrible earthquakes. Psellus’s sixth class of devils were named lucifugi; they delighted in darkness; they entered into the bowels of men, and tormented those whom they possessed with phrenzy and the falling sickness. By this power they were distinguished from earthly and aërial devils; they could only enter into the human mind, which they either deceived or provoked with unlawful affections.