Posting the size of these slides would help determine if they are magic lantern slides for home use or movie theater slides. Some info
http://www.learnaboutmovieposters.com/newsite/index/articles/glassslides.aspSomething else to ponder ...
http://en.wikipedia.org/wiki/History_of_filmIn the silent era of film, marrying the image with synchronous sound was not possible for inventors and producers, since no practical method was devised until 1923. Thus, for the first thirty years of their history, films were silent, although accompanied by live musicians and sometimes sound effects and even commentary spoken by the showman or projectionist.
Illustrated songs were a notable exception to this trend that began in 1894 in vaudeville houses and persisted as late as the late 1930s in film theaters.[7]
In this early precursor to the music video, live performance or sound recordings were paired with hand-colored glass slides projected through stereopticons and similar devices. In this way, song narrative was illustrated through a series of slides whose changes were simultaneous with the narrative development. The main purpose of illustrated songs was to encourage sheet music sales, and they were highly successful with sales reaching into the millions for a single song. Later, with the birth of film, illustrated songs were used as filler material preceding films and during reel changes.[8]
In most countries the need for spoken accompaniment quickly faded, with dialogue and narration presented in intertitles, but in Japanese cinema it remained popular throughout the silent era.
