Source : Webster's Revised Unabridged Dictionary (1913)

Napier's bones \Na"pi*er's bones`\, Napier's rods \Na"pi*er's
rods`\
   A set of rods, made of bone or other material, each divided
   into nine spaces, and containing the numbers of a column of
   the multiplication table; -- a contrivance of Baron Napier,
   the inventor of logarithms, for facilitating the operations
   of multiplication and division.

Source : WordNet®

Napier's bones
     n : a set of graduated rods formerly used to do multiplication
         and division by a method invented by John Napier [syn: {Napier's
         rods}]