A semaphore apparatus invented by R. L. Edgeworth (1744–1817), English educational writer and engineer.
The device consisted of a small number of posts (typically four) placed side by side, each carrying a large black pointer, readily visible from a distance, which could be turned to different angular positions to represent different digits. Different combinations of digits denoted different words according to a prearranged code.
Late 18th century. Alteration of telegraph after ancient Greek λόγος word.