In 1918 H. Nyquist began investigating ways to adapt
telephone circuits for picture transmission. By 1924 this
research bore fruit in "telephotography" - AT&T's fax machine.
The principles used in 1924 were the same as those used today, though the technology was comparatively crude. A photographic transparency was mounted on a spinning drum and scanned. This data, transformed into electrical signals that were proportional in intensity to the shades and tones of the image, were transmitted over phone lines and deposited onto a similarly spinning sheet of photographic negative film, which was then developed in a darkroom. The first fax images were 5x7 photographs sent to Manhattan from Cleveland and took seven minutes each to transmit.