The analog television has been retired to make room for its digital sister in a large part of the world, but if we travel to a time that precedes the vacuum tubes and the cathode ray tubes, what do we find? The answer to that question is the mechanical television. In essence, a disk with holes spinning at high speed is responsible for reconstructing the received video signal, line by line.
The television was one of the most important technological developments of the twentieth century, but if we stop to study its history, we discover that the first developments even predate the vacuum tubes. So… how can there be a television without basic electronics? To answer that, we must call on an unexpected ally: the fax. In fact, the concept of mechanical television would not exist without the work of the Scottish inventor Alexander Bain, also known for creating the electric clock.
Mechanical Television
Bain developed an experimental fax machine in the middle of the nineteenth century, while the English physicist Frederick Bakewell optimized Bain's design and presented to the public his "telegraph of images" at the World's Fair. The first practical version capable of using the existing telegraph lines was the Pantelégrafo, invented by the Italian Giovanni Caselli, and so the roots of modern fax were established… but what does that have to do with the television?
Willoughby Smith discovered the photoconductivity of selenium, paving the way for the first photoelectric cells. With the remote and synchronized reproduction of static images already proven and a new sensor in the equation, basically what was needed was a device to "scan" moving images, and that is when the Nipkow disk appears, created by Paul Gottlieb Nipkow in the late nineteenth century.
The Nipkow disk is the fundamental piece of every mechanical television, and although it may seem unbelievable, it is only a perforated disk, with its holes following a spiral pattern. Even so, it was in the year 1925 that John Logie Baird discovered the possibility of focusing images on the Nipkow disk with a lens, obtaining an instantaneous reading of how dark or bright an image is (thanks to the cells), and the holes in the disk dividing it for transmission. On the other side, the "television" with a neon light and a second Nipkow disk synchronized with the first, is responsible for "decoding" the image, as large as a stamp.
Yes, I admit that the first video is quite difficult to follow, and this is because a mechanical television needs to be seen in action to be understood more precisely. For that reason, I included a second video, which shows a "homemade" mechanical television reproducing a person's face.
