The Nuttall Encyclopedia
The theory that light is due to vibrations or undulations in the ether as the medium through which it is transmitted from its source in a luminous body.
Wood, James, ed. Entry for 'Undulatory Theory'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/u/undulatory-theory.html. Frederick Warne & Co Ltd. London. 1900.