Model of an Optical Telegraph. Model of an optical telegraph on a foot. It consists of two posts associated by an axle why an arm runs; The two ends of that arm are two narrow arms attached, one with a counterweight, the other without. The main arm is moved by a rope walking over two discs on one side of the posts; The outside arms are moved with hoists on a drum between the posts and topped on cleats against the posts. In the rectangular positions with respect to the main arm, the outside arms can be fixed with a spring. Scale 1:22 (Scale by model).