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. (Lat. intervallum, space between the palisades on a rampart [vallum], or between the rampart and the tents of the legionaries.) In military language "interval" is the lateral space between men or bodies of troops, measured from the flank of one body to the flank of the next. It is used in contradistinction to "distance," the space from front to rear.
In medical language "interval" is used of the intervening periods between attacks of a disease, particularly of the periods of a normal condition of mind sometimes experienced by an in sane person, a "lucid interval." In music, an interval is the distance separating one note from another in respect of pitch. It is named according to the number of degrees of the scale, otherwise the number of alphabetical notes, included by the two notes which contribute it. Thus E
to F, E to F sharp and E to F double sharp are all seconds because there are in each case two degrees of the scale included. Similarly E to G, E to G sharp and E sharp to G are all thirds because there are three alphabetical notes included in each case. It is obvious, however, that the actual intervals are not the same in these cases and additional qualifying terms are therefore em ployed. Thus E to F, E to F sharp and E to F double sharp are minor, major and augmented second respectively; while E sharp to G, E to G and E to G sharp are similarly diminished, minor and major thirds.
Intervals beyond the 9th are regarded as repetitions and classed as compound. (See Music.)