I am interested to know more about the solfeggio scales - have gathered much information on internet already - my question about the ancient Gregorian chant method - the original hymn to St John the Baptist - Gloria in Excelsis Deo - is there a historical date when this was composed - if so by whom and when did the actual use of the 'In tonation' use of chant - change to the present use of the 12 Equal Temprament Method - has the actual 'sound' of the present Hymn be altered?