64. Another phenomenon of frequent occurrence, according to the nature of the
medium, is the production of raps that seem to be made in the tissue of the wood,
without the table's moving at all; these raps, sometimes very faint and gentle, at others,
extremely loud, are also often heard in the other furniture of the room, in the doors,
walls, or floor: a phenomenon to which we shall presently recur. When these raps occur
in the table, they produce a very perceptible vibration, which is felt distinctly by the
finger, and is equally apparent to the ear, on placing one's head upon the table.
