Dactylomancy is a term covering the various forms of divination using rings. One form resembles the phenomenon of table-tapping found in Spiritualism. A round table is inscribed with the letters of the alphabet, and a ring is suspended above it.
The ring is believed to indicate certain letters that go to make up required messages. According to Ammianus Marcellinus this method was used to find Valen’s successor, and the name of Theodosius was correctly indicated. Solemn services of religious character accompanied this mode of divination.
Another form of dactylomancy, of which there is no detailed account, was the practiced with rings of gold, silver, copper, iron or lead, which were placed on the fingernails in certain conjunctions of the planets. A wedding ring is, however, most favorable for uses of this sort.
Another use is to suspend the ring within a glass tumbler, or just outside of it so, that the ring when swung may easily touch the glass. As with table-tapping, a code was devised, the glass being struck once for an affirmative answer, twice for a negative, and so on.
Suspended above a sovereign, the ring will indicate the person from whom head hair has been taken, or, if requested, any other member of the company. A.G.H.
Source: 81, 112.