Mechanical device made up of two pendula moving both a biro and a flat surface on which a geometric figure such as an ellipse, spiral or other, is drawn. Although it was invented by mathematician Hugh Blackburn in the 19th century, similar devices were originally built in order to make visible vibratory movements produced by sound. Those experiments on the propagation of sound paved the way for research on mechanisms for recording and reproducing sounds that were later used in cinema. From the beginning of movie- making, attempts were made to incorporate sound to the images, first by accompanying the projection with live sounds and music, and later by adding certain sound recording formats that were played at the same time as the film. Then, in 1927 “The Jazz Singer” came out and is considered the first film with totally synchronized sound; the following year “Lights of New York” was the first movie with spoken dialogues – that is, talkies as we understand them today.