A plaine and easie introduction to practicall musicke : set down in forme of a dialogue, deuided into three partes, the first teacheth to sing with all things necessary for the knowledge of pricktsong. The second treateth of descante and to sing two parts in one vpon a plainsong or ground, with other things necessary for a descanter. The third and last part entreateth of composition of three, foure, fiue or more parts with many profitable rules to that effect. With new songs of 2, 3, 4, and 5 parts