out that historians will never know the real story behind the khipus. When the Spanish
conquered the Inca Empire starting in 1532, they destroyed most of the strings, believ-
ing they might be idolatrous items containing accounts of Incan history and religion.
What are Napier’s Bones?
A tool called Napier’s Bones (also called Napier’s Rods) was invented by Scottish math-
ematician John Napier (1550–1617). These were multiplication tables inscribed on
strips (also called rods) of bone (not Napier’s, but animal bone), ivory, or wood. He
published the idea in his book Rabdologia,which contained a description of the rods
that aided in multiplication, division, and the extraction of square roots. (For more
about Napier, see “Algebra.”)
Each bone is a multiplication table for a single digit, with the digit appearing at
the top of its bone. As seen below, consecutive, non-zero products of this digit are
carved in the rod, with each product occupying a single cell. For example, to multiply
63 by 6, the two bones or rods corresponding to 6 and 3 would be put alongside each
other and would look like the illustration below.
The first number would be the number in the diagonal at the sixth position (3);
then the product (or solution) is evaluated diagonally, or by adding the two numbers 351
MATH IN COMPUTING
The people of the ancient Inca civilization of South America used knotted strings called khipus to make mathe-
matical calculations. The Image Bank/Getty Images.