Napier's bones, also called Napier's rods, are numbered rods which can be used to perform
multiplication of any number by a number
2-9. By placing "bones" corresponding to the
multiplier
on the left side and the bones corresponding to the digits of the
multiplicand
next to it to the right, and product can be read off simply by adding pairs of numbers
(with appropriate carries as needed) in the row determined by the
multiplier.
This process was published by Napier in 1617 an a book titled
Rabdologia,
so the process is also called rabdology.
There are ten bones corresponding to the digits 0-9, and a special eleventh bone that is used the represent the
multiplier. The multiplier
bone is simply a list of the digits 1-9 arranged vertically downward. The remainder
of the bones each have a digit written in the top square, with the multiplication
table for that digits written downward, with the digits split by a diagonal line
going from the lower left to the upper right. In practice, multiple sets of bones
were needed for multiplication of numbers containing repeated digits.
