William Kennedy Laurie Dickson, chief engineer with the Edison Laboratories, is credited with the invention of a practicable form of celluloid strip containing a sequence of images, the basis of a method of photographing and projecting moving images. Celluloid blocks were thinly sliced, the slice marks were then removed with heated pressure plates. After this, the celluloid strips were coated with a photosensitive gelatin emulsion. In 1893 at the Chicago World Fair Thomas Edison introduced to the public two pioneering inventions based on this innovation: the Kinetograph, the first practical moving picture camera, and the Kinetoscope. The latter was a cabinet in which a continuous loop of Dickson's celluloid film (powered by an electric motor) was backlit by an incandescent lamp and seen through a magnifying lens. The spectator neared an eye piece. Kinetoscope parlours were supplied with fifty-foot film snippets photographed by Dickson, in Edison's "Black Maria" studio. These sequences recorded mundane events (such as Fred Ott's Sneeze, 1894) as well as entertainment acts like acrobats, music hall performers and boxing demonstrations