OCTAVE

, or 8th, in Music, is an interval of 8 sounds; every 8th note in the scale of the gamut being the same, as far as the compass of music requires.

Tones, or sounds, that are Octaves to each other, or at an Octave's distance, are alike, or the same nearly as the unison. In this case, the more acute of the two makes exactly two vibrations while the deeper or graver makes but one; whence, they coincide at every two vibrations of the acuter, which, being more frequent, makes this concord more perfect than any other, and as it were an unison. Hence also, it happens, that two chords or strings, of the same matter, thickness, and tension, but the one double the length of the other, produce th<*> Octave.

The Octave containing in it all the other simple concords, and the degrees being the differences of these concords; it is evident, that the division of the Octave comprehends the division of all the rest.

By joining therefore all the simple concords to a common fundamental, we have the following series: 1 : 5/6 : 4/5 : 3/4 : 2/3 : 5/8 : 3/5 : 1/2 Fund. 3dl, 3dg, 4th, 5th, 6thl, 6thg, 8ve.

Mr. Malcolm observes, that any wind instrument being over-blown, the sound will rise to an Octave, and no other concord; which he ascribes to the perfection of the Octave, and its being next to unison.

Des Cartes, from an observation of the like kind, viz, that the sound of a whistle, or organ pipe, will rise to an Octave, if forcibly blown, concludes, that no sound is heard, but its acute Octave seems some way to echo or resound in the ear.

OCTILE. See Octant.