Michael McConnell, age 9, of Louisville, Kentucky, for his question:

Who invented the slide rule?     

It seems that all our handy gadgets were invented in easy stages. The granddaddy of our neat modern slide rule was invented way back in 1617. People called it Napier's bones because it was made by John Napier and it looked somewhat like a row of flat movable bones, marked with black figures. The so called bones were wooden rulers marked with figures. People could slide them and read the matching numbers and do multiplication sums in a hurry.     

John Napier lived in Merchiston, England, and he was a great one for figuring. In 1614, he invented the table of logarithms. We use this on our modern slide rules to do complicated multiplication and division    by adding and subtracting. But strange to say, Napier did not use his logarithms when he made his so called bones, three years later. Through the 1700s and 1800s, many inventors added improvements to our modern logarithm slide rule.