The essential parts of a fax system are the transmitting devices that translate the graphic material into electrical impulses according to a set pattern, and a synchronized receiving device that retranslates these impulses and prints that. In a typical system, the fax scanner consists of a rotating cylinder, a source projecting a narrow beam of light and a photoelectric cell. The copy to be transmitted is wrapped around the cylinder and is scanned by the light beam, which moves along the cylinder as it revolves.
The output of the photoelectric cell is amplified and transmitted to the receiving end, where a similar cylinder, covered with specially impregnated paper, revolves in synchronism with the transmitting cylinder. A light of varying intensity moves along the rotation cylinder and darkens the paper by chemically reproducing the pattern of the original. When the fax is done, it pops out as a blue print of what the other person sent.
