Napier’s Bones

Halloween is almost here, hope you enjoyed my last post about Witch of Agnesi. Starting to feel the Halloween mood more this time with Napier’s Bones.


Napier’s Bones is in fact a calculator, a manually-operated one used for calculations of products and quotients of numbers. In general, the technique used is called Rabdology. With this calculator, John Napier published his own rabdology version in 1617 in Edinburgh, Scotland. Here is a small description of the machine:

The complete device usually includes a base board with a rim; the user places Napier’s rods inside the rim to conduct multiplication or division. The board’s left edge is divided into 9 squares, holding the numbers 1 to 9. The Napier’s rods consist of strips of wood, metal or heavy cardboard. Napier’s bones are three-dimensional, square in cross section, with four different rods engraved on each one. A set of suchbones might be enclosed in a convenient carrying case.

A rod’s surface comprises 9 squares, and each square, except for the top one, comprises two halves divided by a diagonal line. The first square of each rod holds a single digit, and the other squares hold this number’s double, triple, quadruple, quintuple, and so on until the last square contains nine times the number in the top square. The digits of each product are written one to each side of the diagonal; numbers less than 10 occupy the lower triangle, with a zero in the top half. A set consists of 10 rods corresponding to digits 0 to 9. The rod 0, although it may look unnecessary, is needed for multipliers or multiplicands having 0 in them.

napier's bones

I got quite excited by the method and it gets quite interesting. Bellow you have 2 videos which explain how the calculator was used. I find it quite ingenious.

Hope you liked this small post. Thank you for your help and support. You can find me on Facebook,  Tumblr,  Google+,  Twitter,Instagram and Lettrs, I will try to post there as often as possible. Don’t forget that maths is everywhere! Enjoy! 


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