How to Enter the British Library Reading Rooms

"For nine days before the ritual, the operator must be free of pollution in mind and body, abstain from food and drink and hateful or immoderate words.  Each day he must attend mass and place the book of experiments on the altar, then take it home, sprinkle it with holy water, wrap a priestly cincture and stole around it in the form of a cross, kneel facing east and say various prayers (The Seven Penitential Psalms, the Litany of the Saints, and other prayers specifically for the occasion), then open the book with humble devotion, "so that Almighty God in his mercy and goodness may sanctify and bless and consecrate this book dedicated to his most holy names."  In the prayers written for this ritual, the magician professes his own unworthiness and begs God's pardon for his sins... One of the prayers recites a long litany of divine names, and then proceeds:

'By these most holy names, and by others which it is not lawful to name, I humbly beseech thee, that thous mayest bestow power and strength upon the prayers, consecrations, and invocations contained in this book, by the divine power, for the consecration of all experiments and invocations of demons, so that wheresoever the malign spirits are summoned and exorcised by the power of thy names, they may come at once from every quarter and fulfill the will of the exorcist, without inflicting any harm or terror, but rather showing themselves obedient.' "

from "The holy and the unholy: sainthood, witchcraft and magic in late medieval Europe" by  Richard Kieckhefer in Christendom and Its Discontents, ed. Scott L. Waugh and Peter. D Diehl (Cambridge: Cambridge University Press, 1996) 310-337

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Ok so maybe this is how to summon a demon from a book of spells possessed by a medieval magician. For what really happened, read here.