Charles Babbage's "Difference Engine"

Laura Sydell,"A 19th-Century Mathematician Finally Proves Himself," NPR's"Morning Edition," 10 December, reviews the story of Charles Babbage's 'Difference Engine.' It was conceived in the late 18th and early 19th centuries and built in the late 20th century.

The Difference Engine was an automatic, mechanical calculator designed to tabulate polynomial functions. Both logarithmic and trigonometric functions can be approximated by polynomials, so a difference engine can compute many useful sets of numbers.

Here, its modern builder explains how the Difference Engine works.