BAR, in Music, a stroke drawn perpendicularly across the lines of a piece of music, including between each two a certain quantity or measure of time, which is various as the time of the music is either triple or common. In common time, between each two bars is included the measure of four crotchets; in triple, three. The principal use of bars is to regulate the beating of time in a concert. The use of bars is not to be traced higher than the time when the English translation of Adrian le Roy's book on the Tablature was published, viz. the year 1574; and it was some time after that before the use of bars became general. To come nearer to the point, Barnard's cathedral music, printed in 1641, is without bars; but bars are to be found throughout in the Ayres and Dialogues of Henry Lawes published in 1653; from whence it may be conjectured that we owe to Lawes this improvement.