Dr Otfried Lieberknecht has posted on the Medieval Religion discussion group some more about medieval divination which readers may find interesting following on from my post Onychomancy:
For those who, like myself, had not yet been familiar with this practice: Onychomancy is a variant or subtype of "Scrying", i.e. of divination by means of a mirror (catoptromancy) or other object with a reflecting surface. Attested in ancient times by Pausanias (VII, xxi, 12) for an oracle in Patrai where the mirror was immersed into the water of a sacred fountain and supposed to reveal whether a sick person would convalesce or die. A boy used as a diviner or medium subject for catoptromancy (as in Reynes' description) is mentioned in the Historia Augusta (Aelius Spartianus, IX, vii, 10) as one of the "madnesses"(amentia) of Didius Julianus: the boy's eyes were blindfolded and charms were spoken upon his head before he had to look into the mirror ("et ea, quae ad speculum ducunt fieri, in quo
respicere dicuntur, Iulianus fecit").
John of Salisbury (late 1110s-1180) himself in his childhood was used, or, in his opinion, abused in a similar way by a priest who was supposed to teach him the Psalms (i.e. Latin), see his Polycraticus II, 28:
"Dum enim puer ut psalmos addiscerem sacerdoti traditus essem qui forte speculariam magicam exercebat, contigit ut me et paulo grandiusculum puerum praemissis quibusdam maleficiis pro pedibus suis sedentes ad speculariae sacrilegium applicaret, ut in unguibus sacro nescio
"During my boyhood I was placed under the direction of a priest, to teach me psalms. As he practiced the art of crystal gazing, it chanced that he after preliminary magical rites made use of me and a boy somewhat older, as we sat at his feet, for his sacrilegious art, in order that what he was seeking by means of finger nails moistened with some sort of sacred oil or crism, or of the smooth polished surface of a basin, might be made manifest to him by information imparted by us. And so after pronouncing names which by the horror they inspired seemed to me, child though I was, to belong to demons, and after administering oaths of which, at God's instance, I know nothing, my companion asserted that he saw certain misty figures, but dimly, while I was so blind to all this that nothing appeared to me except the nails or basin and the other objects I had seen there before. As a consequence I was adjudged useless for such purposes, and, as though I impeded the sacrilegious practices, I was condemned to have nothing to do with such things, and as often as they decided to practice their art I was banished as if an obstacle to the whole procedure. So propitious was God to me even at that early age. But as I grew older more and more did I abominate this wickedness, and my horror of it was strengthened because, though at the time I made the acquaintance of many practitioners of the art, all of them before they died were, either as the result of physical defect or by the hand of God, not to mention other miseries with which in my plain view they were afflicted. There were two exceptions - the priest whom I have mentioned and a certain deacon; for they, seeing the affliction of the crystal gazers, fled (the one to the bosom of the collegiate church - the other to the refuge of the monastery of Cluny) and adopted holy garb. None the less I am sorry to say that even they, in comparison to others in their congregations, suffered many afflictions afterward." (tr. by J. B. Pike, Frivolities of courtiers, 1938,p.147)
A child, boy or girl, was required because the incorrupt (virgin) flesh of a child was supposed to have stronger spritiual insights, as Gervasius of Tilbury states ("caro enim incorrupta magis spiritualiter habet intuitus, unde asserunt nigromantici in experimentis gladii, vel speculi, vel unguis solos oculos virgineos praevalere", Otia Imperialia I, 17).
Petrus Garsias (García), who wrote is Determinationes magistrales against Pico della Mirandola by the end of the 15th century, reports and discusses a more or less developed framework of Platonic theory which seems to have served for explaining the the way how scryning works:
"The first manner is by gazing at luminous bodies and instruments. The principle here is that the acies of the human mind in one who gazes on such instruments reflects back upon itself, for the luminosity of the instrument prevents direction or concentration of the mind on exterior things, and repels it, and turns it back upon itself, so that it is forced to gaze upon itself. Thus, according to the philosophy of Plato, if it is purged and cleansed of defilements, which come from the body and cling to the soul, they see as in a clear and clean mirror, and when they inquire about all hidden things, or some portion of them, or some particular hidden thing, it is no surprise that the
soul, turned back into itself, should see such hidden things, for according to Plato the human soul is created fully inscribed with the forms of all knowable things, in respect of its intellectual power..." (quoted from Richard Kieckhefer, Forbidden rites, 1998, p.99)
I am not suggesting anyone takes up scrying or onychmancy - not something to practise (or practice) at home - but it is an interesting insight into the medieval mindset.