The discovery leading to the possibility of mechanical television was an accident. While measuring the conductive capabilities of various metals for the first trans-Atlantic telgraph cables, it was discovered selenium conducted more electricity while lit than in darkness. The development of the neon tube in 1910 furthered mechanical television.
Television achieves the illusion of motion in a similar but unique fashion.
Rather than refresh the entire image at once, as film does with each cell that passes in front of the projector's light, television refreshes an image one line at a time in a scanning process. Within the cathode ray tube, an electron gun scans a single line of an image from one side to the other, then scans the line underneath it, until it has scanned an entire image. It consists of a disk that rotates on its axis. A series of evenly spaced, uniformly sized holes are cut into the disk, spiraling in toward the center. The rotation of the disk as seen through the viewing window provides scanning from side to side, and the spiral placement of the holes provides scanning from outermost to innermost scan line.