# Seigneur Dieu ta pitié

The remarkable *chanson*, *Seigneur Dieu ta pitié* by Guillaume Costeley, was written with instructions that it was to be performed so that the tone was exactly divided into three equal parts, which entails the diatonic semitone must be exactly twice as large as the chromatic semitone. This leads to an exact division of the octave into 19 equal parts, 19edo. This piece, dating from 1558, therefore represents the first time in history that 19 equal was specified as the desired tuning. The organist and music theorist Francisco de Salinas effectively defined the same system by way of 1/3-comma meantone, which has exactly pure minor thirds, but it is not clear he intended the circulating character of that temperament when played or performed on a gamut of 19 notes, which Costeley clearly did. In any case his book *De musica libri septem* did not appear until 1577. Costeley, like Nicola Vicentino who served as his inspiration, was a true pioneer, well ahead of his time and perhaps ours as well.