John Napier (1550-1617) was a respected theologian and one of the foremost mathematicians of his period. He is best remembered as the first inventor of logarithms to publish his theories (if not the first inventor, if one accepts Bürgi's priority), as a populariser of decimal notation used with the decimal point, and as the inventor of his famous calculating rods, or "bones". The bones were first described in Napier's Rabdologia, (Edinburgh, 1617), and quickly became an essential mathematical aid, making complex calculations of division, multiplication, square and cube roots simple and quick. Such was their popularity that they remained in use for the next two centuries, undergoing various modifications and improvements. In Rabdologia, Napier says: "Some are accustomed to make arithmetic frightening through very love of the subject. This instrument provides a readily understood explanation.". His success may be judged by Jonas Moore's comment of 1660, "I commend ... certain rods invented by the L, Nepair, called Nepair's bones of such expedition and ease that to any one who knows how to adde and subtract, I dare affirm that in 2 hours time to shew them how to multiply and divide and extract the square and cube roots".
cf. D.J. Bryden, Napier's Bones. A History and Instruction Manual (London, 1992)
Dictionary of Scientific Biography (New York, 1970)