Witelo, in book 10 of his Optics, gives another such example of a close acquaintance who, after going without sleep for three or four nights, saw someone riding beside him along a riverbank and making all the same gestures. When more light appeared, the figure vanished. Hermits and anchorites frequently have such absurd visions and revelations because of much fasting and poor diet. Many are deceived by sleight of hand, as Scot has well shown in his Discovery of Witchcraft, and Cardan in On Subtlety, book 18.

Fumigating substances, perfumes, smoke, compound candles, optical glasses and such natural causes make people look as though dead, or as though they had horses’ heads, bulls’ horns and similar animal forms; or make the room seem full of snakes and adders, dark, light, green, red, of every colour, as you may read in Baptista Porta, Alexis, Albertus and others. Glow-worms, fiery apparitions, meteors and the will-o’-the-wisp, which Pliny, book 2, chapter 37, calls Castor and Pollux, and many such things appear on marshy ground, around churchyards, in damp valleys or where battles have been fought; read their causes in Goclenius, Velcurius, Finkius and others. Such scares are often contrived to frighten children with squibs, rotten wood and so on, or to make people look dead, “larger than usual,” bigger, smaller, fairer or uglier: “to make those standing nearby appear headless, entirely on fire, or in the form of demons, take the hairs of a black dog,” and so on, says Albertus.

And so strange, unfamiliar sights are commonly seen through catoptrics. Who does not know that if light is admitted into a dark room through a single small hole, with paper or glass placed over it, the shining sun will project onto the opposite wall all the objects illuminated by its rays? With concave and cylindrical mirrors we can reflect whatever shapes of people, devils or grotesques we please, as magicians commonly do to trick a gullible spectator in a dark room, and make them seem suspended in the air; when there is nothing but a frightening image, such as Agrippa describes, placed in another room.

Roger Bacon is said to have used this art long ago to make his own image appear to walk in the air, although nothing of the kind appears in his writings on optics. But for the most part, what deceives them is in the brain; although I cannot deny that the devil often deludes them, taking his opportunity to suggest and present unreal objects to melancholy people and those who are ill.

To these you may add the roguish impostures of conjurors, exorcists, mass priests and quacks, of whom Roger Bacon speaks in On the Wonders of Nature and Art, chapter 1. They can imitate the voices of almost all birds and brute beasts, and every human tone and tune, speaking within their throats as though from far away. They make their listeners believe they hear spirits, leaving them astonished and terrified. There are also artificial devices for overhearing their confessions, like the whispering place at Gloucester here in England, or the duke’s place at Mantua in Italy, where a concave wall reflects sound. Blancanus explains and mathematically demonstrates the cause in his Echometria.

Hearing, then, is deceived as often as sight, and by almost the same causes: someone listening to bells will make them sound whatever he pleases. “As the fool thinks, so the bell clinks.” Theophilus, in Galen, thought he heard music because vapours made his ears ring. Some are deceived by echoes, some by the roar of water, or by cavities and the reverberation of air in the ground, hollow places and walls. At Cadurcum in Aquitaine, a remarkable echo repeats words and sentences in full, or whatever you play on a musical instrument, more distinctly and loudly than they were first uttered.

Some echoes repeat something spoken seven times, as at Olympus in Macedonia, according to Pliny, book 36, chapter 15; some twelve times, as at Charenton, a village near Paris in France. At Delphi in Greece there was formerly a marvellous echo, and likewise in many other places. Cardan, On Subtlety, book 18, has remarkable stories of people deceived by these echoes. The Jesuit Blancanus, in his Echometry, has various examples and fully explains all such sounds to his reader by demonstration. At Barry, an island in the mouth of the Severn, people seem to hear a smith’s forge; likewise at Lipari and those sulphurous islands, and at many similar places mentioned by Olaus in the mainland of Scandinavia and those northern countries. Cardan, On the Variety of Things, book 15, chapter 84, mentions a woman, a painter’s wife in Milan, who constantly supposed she heard the devil calling and speaking to her; and many similar illusions and voices, which arise mostly from a disordered imagination.

I have briefly touched on how they come to prophesy, speak various languages, and discuss astronomy and other sciences unknown to them, of which they have always been ignorant. Here I will add only this: Arculanus, Bodin in his Demonomania, book 3, chapter 6, and some others regard it as a clear sign that such people are possessed by the devil. So do Hercules de Saxonia and Aponensis, and they consider them fit to be cured only by a priest.

But Guianerius, Montaltus, Pomponazzi of Padua, and Lemnius, book 2, chapter 2, ascribe it wholly to the disordered condition of the humour, citing Aristotle’s Problems 30.1, because such symptoms are cured by purging. Just as striking flint forces out fire, so violent movements of the spirits “draw forth unheard utterances”: they compel strange speeches to be spoken. Another argument he takes from “Plato’s recollection,” which is every bit as plausible as what Marsilio Ficino says of his friend Pierleone: by a kind of divine infusion he understood the secrets of nature and the doctrines of Greek and non-Greek philosophers before he had ever heard of, seen or read their works. But in this I would rather agree with Avicenna and his associates that such symptoms proceed from evil spirits, which take every opportunity afforded by corrupted humours, or otherwise, to pervert the human soul. Besides, the humour itself is “the devil’s bath”—the devil’s bath—and, as Agrippa proves, entices him to seize upon them.