Television as we now know it, an electronically scanned and reproduced image, was a development of the 1930s. I’ll spend more time discussing electronic TV at a later date. For now though, lets take a look at what came first, something called electro-mechanical TV.

Alexander Graham Bell invented the telephone in 1876. Despite the limited technology of the day, there were those who believed that if it was possible to send sound over wires, why not pictures. The photoconductive properties of the element selenium had been discovered in 1873. Selenium's electrical conductivity varies with the amount of light that it receives, making it ideal for converting varying amounts of light into an electrical signal.

In 1884 Paul Nipkow, a German college student, designed (on paper) and received a patent for an electromechanical television system. It is not known if he actually built a working model, but he is credited as being the first person to utilize a scanning principle which broke the image down into a series of individual lines. His patent application drawing depicted a rotating disc, perforated with holes in a spiral pattern, each hole focusing a single line of a scanned image on a selenium cell. At the receiving end, the intensity of a light source placed behind a similar rotating disc would vary due to the changing electrical current from the selenium cell. The resulting “sweep lines” would be focused on a screen, thus reproducing the image.

Nipkow’s design only produced 18 sweep lines, not much when compared to the 525 lines in a modern TV. At 18 lines, resolution would not have been very good. Long before radio, Mr Nipkow envisioned sending his images over wires. I’ll bet that you thought cable TV was a modern invention.

In a repeat of history, not long after sending audio over radio waves became popular, there were those who envisioned sending pictures over the airwaves. The nearly forgotten “Nipkow Wheel” was brought out of the closet. Reports of crude video images being transmitted by amateur radio operators were noted as early as 1923. By 1926 there were a variety of commercial scanning disk TVs available but sales were low due to the poor image and lack of programming. Another problem was lack of standardization. Each design used a different number of scan lines, different numbers of frames per second, and different methods of synchronizing the sending and receiving discs. Most were purchased by experimenters and amateur operators and few examples remain today. The electro mechanical scanning units were connected to conventional radio receivers via the speaker or headphone jack. The screens were small, often no larger than an inch. Some commercial units like the GE "Octagon" pictured here were equipped with a magnifying lens to make the screen appear to be about three inches wide. Experimentation and even some broadcast shows (a bit more popular in Great Britain) using Nipkow technology continued until the early 1930s. Most sets offered pictures with 60 lines or less, but near the end a few produced fairly viewable pictures with nearly 100 sweep lines. The mechanical television met its demise with the invention of the cathode ray camera and the picture tube. These devices evolved into television as we know it today.

Pictures of the mechanical TVs courtesy of The Early Television Museum of Hillard Ohio, used with permission.