The device known as a logarithm was invented in the late 1500s by a

Scottish baron named

John Napier as a tool to simplify

arithmetic. It was useful because it replaced

multiplication with

addition. This was accomplished by a property of logarithms:

ln *x**y* = ln *x* + ln *y*

You could multiply two positive numbers *x* and *y* by looking up their logarithms in a table, adding the logarithms, finding the sum in the body of the table, and reading the table backwards to find the product *x**y*.

Of course, you needed an actual table to do this, and Napier spent the last 20 years of his life working on a table he never finished. The table was later completed after Napier's death by his friend Henry Briggs.