*dactylology*

n. [ Gr. da`ktylos finger + -logy. ] The art of communicating ideas by certain movements and positions of the fingers; a form of sign language, especially the manual alphabets used by the deaf and dumb. [ 1913 Webster +PJC ]

☞ There are two different manual alphabets, the one-hand alphabet (which was perfected by Abbé de l'Epée, who died in 1789), and the two-hand alphabet. The latter was probably based on the manual alphabet published by George Dalgarus of Aberdeen, in 1680. See Illustration in Appendix. [ 1913 Webster ]