BAR, in physical geography, an underwater ridge of sand or silt crossing a river or harbour. It may be raised by wave action above sea-level. When a river enters a tidal sea its rate of flow is checked, and the material it carries in suspension is deposited in a shifting bar lying athwart the channel. Where the channel is only partly closed, and the bar is attached to the land on one side, the feature is called a spit ("Nehrung," in the Baltic area). A bar may be produced by tidal action alone in an estuary or narrow gulf (as at Port Adelaide) where the tides sweep the loose sand backward and forward, depositing it where the motion of the water is checked. Nahant Bay (Mass.) is bordered by a ridge which separates it from Lynn harbour, and ties Nahant settlement to the mainland; the bar has been formed in the above manner.
Bar in music, meant originally one of the short vertical lines which divide the stave at regular intervals and in this way mark off the several measures of a composition, but in mddern usage it has come to mean the measures themselves and is always used in this sense, the vertical dividing lines being now known as bar-lines. Bars serve not only to divide up a composition into convenient short sections which facilitate its performance but also to indicate its metre, the strongest accent falling always (unless intentionally and temporarily displaced) on the first beat of the bar, and the division is clearly marked.
The term bar is also used in meteorology (q.v.). Here it de notes the dynamical unit of atmospheric pressure. (See BA ROMETER : Units of Measurement of Pressure.)