Complex sentence: In 1918 he published his first work on music theory (a tone-color theory based on Goethe's), and in August 1919 discovered his "law of the twelve tones", requiring that all twelve chromatic notes be sounded before any is repeated.
Split into simpler sentences: In 1918 he published his first work on music theory (a tone-color theory based on Goethe's). In August 1919 he published his "law of the twelve tones", requiring that all twelve chromatic notes sound before any is repeated.