Only sporadic work was done on the Kinetoscope for much of 1890 as Dickson concentrated on Edison's unsuccessful venture into ore milling—between May and November, no expenses at all were billed to the lab's Kinetoscope account. By early 1891, however, Dickson, his new chief assistant, William Heise, and another lab employee, Charles Kayser, had succeeded in devising a functional strip-based film viewing system. In the new design, whose mechanics were housed in a wooden cabinet, a loop of horizontally configured 19 mm (3/4 inch) film ran around a series of spindles. The film, with a single row of perforations engaged by an electrically powered sprocket wheel, was drawn continuously beneath a magnifying lens. An electric lamp shone up from beneath the film, casting its circular-format images onto the lens and thence through a peephole atop the cabinet. As described by Robinson, a rapidly spinning shutter "permitted a flash of light so brief that frame appeared to be frozen. This rapid series of apparently still frames appeared, thanks to the persistence of vision phenomenon, as a moving image." The lab also developed a motor-powered camera, the Kinetograph, capable of shooting with the new sprocketed film. To govern the intermittent movement of the film in the camera, allowing the strip to stop long enough so each frame could be fully exposed and then advancing it quickly (in about 1/460 of a second) to the next frame, the sprocket wheel that engaged the strip was driven by an escapement disc mechanism—the first practical system for the high-speed stop-and-go film movement that would be the foundation for the next century of cinematography.