Definition of "diapason"

2 to 1, which is a duple ratio, forms the [symphony] diapason

1818, Iamblichus, translated by Thomas Taylor, Life of Pythagoras‎, page 328

The glories and the beauties of form, color, and sound unite in the Grand Canyon—forms unrivaled even by the mountains, colors that vie with sunsets, and sounds that span the diapason from tempest to tinkling raindrop, from cataract to bubbling fountain.

1895, J[ohn] W[esley] Powell, chapter XV, in Canyons of the Colorado, Meadville, PA: Flood & Vincent; republished as The Exploration of the Colorado River and Its Canyons, New York: Dover, 1961, page 397

the piano curving like a conch, corollas giving out diapasons of light […]

1934, Henry Miller, Tropic of Cancer, Grove Press, published 1961

he could hear nothing except the rattle of the crickets and the swelling diapason of the frogs […]

1961, Graham Greene, A Burnt-Out Case