mediately after Edison introduced the phonograph in 1877), and some early experiments had the projectionist manually adjusting the frame rate to fit the sound, but because of the technical challenges involved, the introduction of synchronized dialogue became practical only in the late 1920s with the perfection of the Audion amplifier tube and the advent of the Vitaphone system. Within a decade, the widespread production of silent films for popular entertainment had ceased, and the industry had moved fully into the sound era, in which movies were accompanied by synchronized sound recordings of spoken dialogue, music and sound effects. Most early motion pictures are considered lost owing to their physical decay, as the nitrate filmstock used in that era was extremely unstable and flammable. Many films were destroyed, because they had negligible remaining financial value in that era. It has often been claimed that around 75 percent of silent films produced in the US have been lost, though these estimates' accuracy cannot be determined due to a lack of numerical data. Elements and beginnings (1833–1894) Main article: Precursors of film Main article: History of film technology Animation of 11 frames of Eadweard Muybridge's 1878 cabinet card of running horse "Sallie Gardner" from the series The Horse in Motion Roundhay Garden Scene, which has a running time of just over two seconds, was filmed in 1888. It is believed to be the world's earliest surviving motion-picture film. The elderly lady in black is Sarah Whitley, the mother-in-law of filmmaker Louis Le Prince; she died ten days after this scene was filmed. Film projection mostly evolved from magic lantern shows, in which images from handpainted glass slides were projected onto a wall or screen. After the advent of photo