An introduction to the skill of musick [electronic resource] : in two books. The first: the grounds and rules of musick, according to the gam-ut, and other principles thereof. The second: instructions & lessons for the bass-viol: and instructions & lessons for the treble-violin. By John Playford. To which is added, The art of descant, or Composing musick in parts. by Dr. Tho. Campion. With annotations thereon, by Mr. Chr. Simpson