Well-Tempered Clavier

From Conservapedia

The Well-Tempered Clavier (German Das Wohltemperierte Klavier) refers to two volumes of preludes and fugues by Johann Sebastian Bach. Each volume contains a prelude and a fugue in every major and minor key, adding up to 24 pairs total. The order of keys begins from C Major, followed by C Minor, then proceeds up by half-step until the 24th in B Minor.

Bach compiled the first part in 1722, followed by the second in 1742, intending them for the study of keybard playing. They were not published until the 19th century, but after Bach's death they were well-known by some influential Leipzig-based keyboardists such as C. G. Neefe, who taught Beethoven in Bonn. They were also known by Mozart, and both Frederic Chopin and Sergei Rachmaninoff claimed to have played a prelude and fugue from it every morning.