#OTD in 1822.
Charles Babbage proposes a difference engine in a paper to the Royal Astronomical Society.
The difference engine is based on the method of divided differences, a way to interpolate or tabulate functions by using a small set of polynomial co-efficients. Some of the most common mathematical functions are built from logarithmic & trigonometric functions, which can be approximated by polynomials, so a difference engine can compute many useful tables.