Bars and Bar-Lines ::Composers and performers find it helpful to 'parcel up' groups of notes into bars, although this did not become prevalent until the seventeenth century. In the United States a bar is called by it's old English name, measure. Each bar contains a particular number of notes of a specified denomination and, all other things being equal, successive bars each have the same temporal duration. The number of notes of a particular denomination that make up one bar is indicated by the time signature. We will examine time signatures further in the lesson 4.
The end of each bar is marked usually with a single vertical line drawn from the top line to the bottom line of the staff or stave. This line is called a bar-line.
As well as the single bar-line, you may also meet two other kinds of bar-line.
The thin double bar-line (two thin lines) is used to mark sections within a piece of music. Sometimes, when the double bar-line is used to mark the beginning of a new section in the score, a letter or number may be placed above it.
The double bar-line (a thin line followed by a thick line), is used to mark the very end of a piece of music or of a particular movement within it.
In music scored for keyboard instruments, where the music lies across two staves, the upper indicating the notes to be played by the right hand, the lower indicating the notes to be played by the left hand, bar-lines are commonly drawn from the top of the upper line on the upper staff to the bottom line on the lower staff. This is illustrated below.
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