Nipkow, Paul Gottlieb

Nipkow, Paul Gottlieb (1860-1940), German inventor, who devised a mechanical apparatus for scanning images that was used in prototypes of television.

Nipkow was born in Lauenburg, Germany. While still a student, he built a mechanical device to scan objects—that is, to break the surfaces of the objects into small areas of light and dark. The device, which he named the Nipkow disc, consisted of a round, flat disc perforated with square holes in a spiral pattern. In its simplest implementation, the disc is placed between the viewer and the object to be viewed. When spun with an electric motor, the small holes pass between the viewer and the object in such a way that only a small portion of the object is visible at any one time. Because the holes sweep through overlapping paths, if the disc is spun fast enough, the eye can reconstruct an image of the object.

Nipkow devised a method for transmitting images over a distance using electricity and his disc. A selenium cell, placed where a viewer would normally watch the disc, was the key to the process. The amount of electric current passed through the cell and the cell’s electrical resistance were dependent on the intensity of light falling on it. Nipkow connected the selenium cell to a power source and a light bulb some distance away. The brightness of the bulb varied according to the intensity of light falling on the selenium cell, which in turn depended on whether the hole in the Nipkow disc was passing over a light or dark area of the object. Nipkow then set up a second Nipkow disc near the light bulb and synchronized its rotation to the rotation of the disc near the object. When the light bulb was viewed through the second disc, a blurry image of the object could be seen.

Owing to the limitations of the selenium cell, Nipkow was unable to develop the apparatus to the point that it could transmit moving images. In 1923, however, the Scottish engineer John Logie Baird replaced the selenium cell with a photoelectric cell that had not been available to Nipkow; Baird was soon able to transmit moving images. By the late 1920s the British Broadcasting Company (BBC) was using Baird’s adaptation of Nipkow’s apparatus to transmit images across the Atlantic—the first commercial television broadcasts.

Baird and Nipkow’s photo-mechanical method of image transmission was soon replaced by all-electric methods. However, a highly refined version of Nipkow’s disc is still used in an advanced modern microscope known as the tandem-scanning reflected-light microscope. This instrument offers high-resolution stereoscopic images of very thin slices of specimens.