Photograph "Opening of the picture telegraph between Berlin and Vienna"

August Karolus began working on a special photocell in 1923. The "Kerr-Karolus cell" reacted without inertia to changing brightness values, resulting in shorter transmission times and higher image quality on the receiving end. It was also no longer necessary to transfer the image to a slide: the reflection of direct light was enough to send the image. Developed jointly with the Reichspost, the "Siemens-Karolus-Telefunken system" was the foundation of modern image telegraphy in 1927.