Paper, 'Apparatus phono-campticus or what enquiries are principally to be made by such, who would attend to the certain knowledge of the nature of eccho's' by Walter Charleton Charleton writes on the velocity of a direct or original sound, the velocity of a reflex sound, and the super-reflexions of sounds or echoes. Subject: Acoustics Read to the Royal Society on 10 September 1662. [1662]