The science of communicating with spirits by means of raps,
various codes being arranged for the purpose. The sitters may
read the alphabet aloud, or slowly pass a pencil down a printed
alphabet, and the rappings will indicate letters that form a message
or an answer to some question. One rap may be made to
mean ‘‘yes,’’ two ‘‘no,’’ and so on. Some relationship seems to
exist between such rapping and the use of the divining rod and
pendulum in dowsing