An introduction to the skill of musick, [electronic resource] : in three books the first contains the grounds and rules of musick, acording to the gam-ut, and other principles thereof, the second, instructions and lessons both for the bass-viol and treble-violin, the third, The art of descant, or, Composing of musick in parts, in a more plain and easie method than any heretofore published / by John Playford