The phonautograph is the earliest known device for recording sound. Previously, tracings had been obtained of the sound-producing vibratory motions of tuning forks and other objects by physical contact with them, but not of actual sound waves as they propagated through air or other mediums. Invented by Frenchman Édouard-Léon Scott de Martinville, it was patented on March 25, 1857. It transcribed sound waves as undulations or other deviations in a line traced on smoke-blackened paper or glass. Scott believed that future technology would allow the traces to be deciphered as a kind of "natural stenography". Intended as a laboratory instrument for the study of acoustics, it was used to visually study and measure the amplitude envelopes and waveforms of speech and other sounds or to determine the frequency of a given musical pitch by comparison with a simultaneously recorded reference frequency.