INTERVAL  , a space

left between the component parts of a continuous series, a pause in continuous action, a period of time intervening between two other points of time or chronological sequence of events . The Lat. intervallum, from which the English word has come through the French, originally meant a space between the palisades on a rampart (vallum), or between the rampart and the tents of the legionaries . In medical language " interval " is used of the intervening periods between attacks or paroxysms of a disease, particularly of the periods of a rational or normal condition of mind sometimes experienced by an insane person, a " lucid interval "; this phrase frequently occurs in legal documents from the 13th to the 15th centuries, non compos mentis sed gaudet lucidis intervallis . In music " interval " ex-presses the distance in pitch between two or more musical sounds (see Music) . Interval, or more commonly " intervale," is used, particularly in North America, as a geographical term for a low-lying tract of land along the banks of rivers, frequently overflowed by freshets, or more loosely for any low level land shut in by hills . This particular application, as also the form " intervale," is due to a confusion of the termination of the word with " vale," valley .